THE ANATOMY AND PHYSIOLOGY OF THE HUMAN BODY. BY JOHN AND CHARLES BELL. THE WHOLE MORE PERFECTLY SYSTEMATIZED AND CORRECTED By CHARLES BELL, Professor of Anatomy and Surgery to the Royal College of Surgeons of London, Sfc. <$t. IN TWO VOLUMES. jFtftij Emertcan IS&ttton; (REPRINTED FROM THE SIXTH LONDON EDITION OF 18?6.) THE TEXT REVISED, WITH VARIOUS IMPORTANT ADDITIONS, FROM THE WRITINGS OF SOEMMERING, BICHAT, BECLARD, MECKEL, SPURZHEIM, WISTAR, &c. BY JOHN D. GODMAN, M.D. Professor of Anatomy and Physiology in Rutger's Medical College, N. Y. VOL. II. NEW-YORK: PUBLISHED BY COLLINS & CO. 1827. Southern District of New- Forfc, m. Be it remembered, that on the 4th day of October, A. D. 1827, in the 52nd year of the Independence of the United States of America, Collins & Co., of the said District, have deposited in this office the title of a book, the right whereof they claim as proprietors, in the words following, to wit: “ The Anatomy and Physiology of the human body ; by John and Charles Bell. The whole more perfectly systematized and corrected by Charles Bell, Professor of Anatomy and Surgery to the Royal College of Surgeons of London, &ic. Sic. In Two Volumes. The Fifth American edition: reprinted from the Sixth London edition of 1826. The text revised, with various important additions from the •writings of Soemmering, Bichat, Beclard, Meckel, Spurzheim, Wistar, &c. By John D. Godman, M. D. Professor of Anatomy and Physiology in Rutger’s Medi- cal College, New-York.” In conformity to the Act of Congress of the United States, entitled “An Act for the encouragement of Learning, by securing the copies of Maps, Charts, and Books, to the authors and proprietors of such copies, during the time therein mentioned.” And also to an Act, entitled “An Act, supplementary to an Act, entitled an Act for the encouragement of Learning, by securing the copies of Maps, Charts, and Books, to the authors and proprietors of such copies, during the times therein mentioned, and extending the benefits thereof to the art3 of de- signing, engraving, and etching historical and other prints.” FRED. J. BETTS, Clerk of the Southern District of New-York. W. E. Dean, Printer, 70 Frankfort-Street. OF THE BRAIN AND NERVES. OF THE NERVOUS SYSTEM. * The nervous system embraces the brain, the nerves, and the 'organs of sense. The brain is defined to be that soft mass contained within the crani- um, from which the nerves are propagated.* The nerves are those white cords visible every where in the parts of the body, having sensation or motion. The organs of the senses are the expanded extremities of certain nerves, within a structure capable of conveying the external im- pressions to them. The capacity of receiving impressions, the endow- ment of thought and feeling, and the power of putting the muscular ma- chine into action, are the great attributes of the nervous system. That sensibility is seated in the nerves, there can be no doubt. Is there, any ground for supposing that a different part of the animal com- pound possesses the same property 1 It were unphilosophical to sup- pose so. Where similar qualities or endowments reside, we discover a resemblance in the matter of animal bodies ; and it would be foreign to all analogy if two different kinds of matter possessed the same proper- ties. For these reasons I hold, that the susceptibility of receiving im- pressions, which is the grand distinction of living matter, and the origin of all that is peculiar in the intestinal changes which animals undergo, re- sults from the presence of nervous matter. If sensibility, in its broadest meaning, result from the presence of nervous matter, then it must be, as anatomy in part proves, and many celebrated men have concluded—the matter of nerve must be extensive- ly distributed, and extend where nervous cords cannot be traced. We have proof of sensibility, that is, of impressions received, and actions thereby excited, where no nerves are visible: and we know that ani- mals, without possessing nervous cords, are susceptible of the impres- sions and of the re-actions necessary to their existence. Matter similar to what we see accumulated in masses and in the nerves is expanded every where; and the susceptibility which distin- guishes living matter is inherent in it; and through it, therefore, is the most essential endowment of animal bodies bestowed. Every part having its proportion of nervous matter, and possess. ▼ * The statement that the nerves are “ propagated’’ from the. brain, should be understood as merely expressive of their connexion, or continuity with that organ; not that they are produc- tions or elongations thereof. Researches, to which we shall have occasion hereafter to refer, relative to the development of the nervous system, show that the order of formation is directly inverse to that commonly stated ; and these researches are confirmed by observations made in comparative anatomy relative to the successive additions to the nervous system in ascend- ing from the lowest to the highest classes. In acephalous human fetuses, we find the nerves of the trunk and extremities perfect, although no brain exists; and we have within a few days dissected a fetus in which bolh brain and spinal marrow were deficient without any imperfec- tion of the nerves, J. D. G. 4 OF THE BRAIN AND NERVES. properties through it, what uses are we to attribute to the nervous cords which we see extended through the body, and the nervous masses con- nected with them? STRUCTURE OF A NERVE. The nerves are firm white cords, which are dispersed through the body, and extend to every part which enjoys that sensibility which gives rise to perception, and to having a concatenated action with another. Nerves differ in form ; but this appears to be a result arising from their place and relations, rather than connected with any peculiarity of function. They vary in firmness and density also; but this, like their form, de- pends upon their places: where they lie protected from injuries, they are soft; when exposed, they are provided with a harder covering. The matter of a nerve is all that is peculiar in it; for the manner in which that matter is bound up does not differ from the structure of a bone or a muscle. As the phosphate of lime is bound up in cellular membrane, as the muscular fibre is surrounded with cellular membrane, so is the peculiar matter of the nerves bound up and supported by the cellular textures. Wherever we discover the matter of the nerves, it has certain quali- ties which distinguish it, whether in masses, as in the brain, or in the organs of the senses, or in the nerves themselves. It is a soft pulpy matter which drops from the probe, being betwixt fluid and solid. When putrid, it acquires a green colour; when dried, it is transparent: cor- rosive sublimate and muriate of soda harden it; alkalis dissolve it. The matter of nerve in health, and in the full exercise of its influ- ence, is of an opaque white; by want of use, the matter is either not secreted in due proportion, or it changes its appearance, for the nerve then acquires a degree of transparency. The coats of a nerve are forms of the cellular texture, and are three in number. They resemble the 'coats of the brain in structure and in use, and are, as anatomists speak, derived from them, that is to say, they are continuous.* Some have supposed it possible to inject the nerves. From the na- ture of the proper matter of the nerve, this is obviously a thing impos- sible. In these clumsy experiments they have done no more than to force the mercury into the delicate sheaths of cellular texture in which the tracts of nervous matter are contained and supported. * The neuriiema is formed of a layer of condensed cellular substanee, of argentine lustre, Solid and difficult to tear, having its external surface more or less blended with the adjacent cellular tissue ; its internal surface is furnished with a vast number of folds or prolongations, which.extend into the substance of the nerve. A number of blood-vessels enter this coat, which divide at right angles into two branches, the one direct and the other retrograde, frequently anartomosing. From the internal surface of this tunic serosity is secreted, and almost always oily matter also. Within this external membrane we find a delicate membrane resembling the pia mater on which the vessels are expanded, before they penetrate the nervous substance. When the nervous matter is removed by means of an alcaline solution, the little canals formed by the neuriiema, may be seen, or the neuriiema may be removed by acids, which at the same time harden the nervous matter, so as to render the most delicate fibre visible. Vide Reil de Structura Nervorum, p. 3- 17. F. Meckel, vol. 1. p. 251. Beclard Anat. Gen. p- 587. J. D.G. OF THE BRAIN AN1> NERVES. 5 Inattention to the structure of nerves has led to another mistake, that they have a power of contraction. They are in truth formed with a particular guard against the injury or disturbance of the proper nervous matter by the motions of the frame. Each tube of cellular membrane, or, as it is improperly termed, each fibril of the nerve, is convoluted, run- ning not in a straight line, but zigzag. I cannot better illustrate this than by a very humble comparison with the thread drawn from a worsted stocking, which has by its form acquired an elasticity which it would not otherwise possess; or with a brass wire which has been wound round a rod, and thereby acquired a spring and elusStcity. I am at a loss to conceive what three celebrated men of our country* aim at, when they would persuade us that nerves are irritable and con- tractile. For to suppose them capable of contractions or vibrations, is to suppose them sensible to the impression which causes them to con- tract ; and is it not the nature of this sensibility into which they are en- quiring ? To suppose the nerves to have the property of muscular fibres, does not, I apprehend, tend much to the progress of physiological know- ledge. The mind becomes familiarized to an idea which, if it were true, would not aid us in our farther progress of understanding, and as it is in- correct, leads us astray. There is an idea prevails that some fluid or spirit is contained in the nerves, for which purpose they are supposed to be tubes. This notion has originally been derived from contemplating the brain as a great secreting organ, and a proof of it is, that it requires five times more blood than any other part; and then they ask, why should it have so much blood if it were not a secreting organ 1 It is wonderful how general this desire has been of interposing some visible agent to explain effects ; yet for my part I am equally at a loss to conceive, how a nervous fluid, more than the vibration of a nerve, should serve to explain the phenomena of a liv- ing body. Fluids, spirits, aether, galvanism, have at different times been supposed to be contained in the nervous tubes, which tubes, be it remembered, were equally matter of conjecture; and many men great in their department of philosophy have been inclined to favour the indea of galvanism being the material of life, because the body of a man after execution can be made to gape and stare, by the application of this penetrating stimulus ! How are the oscillations, or tremors, or vibrations of a solid, or the undulations of a fluid, to explain the varieties evinced in the nervous in- fluences ? Even if it were to be concluded that galvanism was the means employed in the animal system to stimulate the muscles, it would not follow that the sensibilities of the muscles wrere also owing to gal- vanism. Other and greater difficulties would be encountered, on the supposition of galvanism being the agent, than those we have now to con- tend with. Some, like Loewenhoeck, have cut the nerves across, and examining them with microscopes, have thought that they discovered minute hol- low vessels ; and as it were to prove that we are destined to run ever in a circle, Sir E verard Home, in our Royal Society Transactions, has employ- ed somebody to discover globules in the nerves through the microscope.! * Darwin, Home, and Abernethy. f Dellatorre, Prochaska, J. & Ch. Wenzell, Barba, Home, Bauer, and Milne Edwards. 6 OF THE BRAIN AND NERVES. One of the most important considerations regarding the nerves is their supply of blood-vessels : their arteries and veins are numerous, and their dependence on the supply of blood immediate. If a limb be de- prived of blood, the nerves are deprived of their powers, and sensibility is lost. If a nerve be partially compressed, so as to interrupt the free entrance of blood into it, both the power over the muscles and the re- ception of sensation through it are interrupted ; and when the blood is admitted again, painful tingling accompanies the change. A similar and universal painful tingling accompanies the returning sensibility, and the returning force of circulation after submersion. How much vain theory has been suggested from the simple experi- ment of loss of power in consequence of trying a nerve ; and yet it was not the compression of the tubes of the nerve, but the obstruction of blood-vessels, which produced the effect. The brain, the nerve of the eye, the ear, the nerves of sense and of motion, are all affected by the change of circulation; and each organ, according to its natural function, is variously influenced by the same cause—the rushing of blood into it, or the privation of its proper quan- tity. SENSIBILITY OF NERVES. It may appear strange to question the sensibility of nerves; for has not the common testimony of mankind determined that there is no- thing so exquisitely sensible as an exposed nerve. But these universal principles of belief are the very circumstances which impede the progress of knowledge on very many occasions. There remains not the slight- est doubt in my mind, that there are nerves as perfectly and delicately constituted as those which give sensibility to the eye or ear, which pos- sess no sensibility whatever. That sensibility, therefore, which conveys the impression to the sensorium, and is followed by perception or by pain, is only one out of many functions performed by the nervous sys- tem ; and I cannot resist stating, that, on the morning I wrote this, I have had my finger deep in the anterior lobes of the brain, when the pa- tient, being at the time acutely sensible, and capable of expressing himself, complained only of the integument.* When the very seat of perception is found not to be sensible, it leads us to consider on what the varieties of sensation depend. We see that sensibility is not an accidental nor a necessary consequence of the struc- ture of a nerve, or the presence of nervous matter, nor even the com- munication of that nerve with the brain. It is obvious that the sensibi- lity results from the particular part of the brain which is affected by the nerve. have all, at different times, made observations on the globules of the nervous matter. Ac- cording to the observations of Edwards, the most recent examiner, these globules composing the brain, medulla spinalis, and nerves of the four classes of vertebral animals, are 1 300th of a millimetre in diameter, united together so as to form primitive fibres of a considerable length. Beclard has verified this statement, and considers it of much importance, since all the other animal tissues are composed of similar globules somewhat differently arranged. J. D. G. * A pistol-ball had passed through the head, and having ascertained that it had penetrated the dura mater, by forcing my finger into the wound, I trepanned on the opposite side of the. head and extracted the ball.' OP THE BRAIN AND NERVES. 7 It' the eye-ball is pressed, the outward integuments feel pain; butjthe retina gives no pain, only rings of light or fire appear before the eye. In the operation of couching the cataract, the needle must pierce the retina: the effect, however, is not pain, but to produce, as it were, a spark of fire. So an impression on the ear, the papillae of taste, orjan organ of sense, does not produce pain; nor does the sensation excit- ed relate to the body which makes the impression, but to the nerve, or rather, as I have said, to the part of the brain to which the nerve is re- lated at its root. Ideas of sense are excited according to the part of the brain brought into operation by the touch of the outward nerve. But the nerve may have no relation to outward impression. It may be a nerve purely for governing the muscular frame ; and if it be consti- tuted for conveying the mandate of the will, it will not stand related to an organ of sense in the brain, and no sensibility and no pain will be produced by that nerve. It may be a nerve of exquisite feeling in one sense, that is, it may be a cord which unites two organs in intimate sym- pathies, so as to cause them to act in unison; and yet being bruised or injured, it will give rise to no perception of any kind, because it does not stand related to a part of the brain, whose office it is to produce either the general impression of pain, or heat, or cold, or vision, or hearing: It is not the office of that part of the brain to produce perception at all. These are very interesting facts, and it is obvious enough, I think, that if physiologists had known or considered the various offices of the nerves, the variety of functions performed by nerves of the same struc- ture, and the various sensibilities of the brain, an accumulated mass of the same material, they would not have thought it a satisfactory improve- ment to have established vibrations and vibratiuncles, nor to have consi- dered the whole difficulty of nervous influence explained, on the idea of a galvanic fluid being contained in tubes. OF GANGLIONS. The ganglions are small reddish tumours seated in the conflux of the nervous filaments. They are laid in a regular succession in the whole length of the body, and in the vertebral animals form a regular series down each side of the spinal marrow; the nerve of communication among them is the great sympathetic nerve. But besides the spinal ganglions, there are others seated in the head, neck, and cavities of the chest and belly, which are very irregular in their situation and form. Of the latter, the most important from situation and connection is the semilunar ganglion, which with its fellow forms the grand centre of connection to the nerves of the abdominal viscera. All the ganglions are in the recesses of the body, and placed like parts of importance protected from injury. Around the ganglion there is a firm, minute tissue of cellular membrane : or we may describe it as a firm dense network of fibres so interwoven as to cover the proper sub- stance of the ganglion, at the same time that it enters intimately into its composition; the ganglion has, therefore, a firmness independent of its proper matter, and indeed foreign to the general character of nervous matter. • No fat is deposited in the membranes of the ganglions or of the nerves. The colour of the ganglion differs from that of the nerves; 8 NATURAL SYSTEM OF THE it is redder, which is owing to the greater number of blood-vessels: when blanched of the blood the ganglions are greyish, and when putrid they are of the green colour of putrid brain. I conceive that these bodies consist of the same matter with the brain, and that all the difference observable by boiling, macerating, and apply- ing chemical agents, is merely owing to the firmer texture of the mem- branes which surround them, the intention of which is evidently to pro- tect the proper matter of the ganglion. Dr. Monro conceived that there was cineritious matter in the ganglions, and so undoubtedly there is. Scarpa thinks they do not differ from plexuses, being only very minute subdivisions uf the nervous filaments. An appearance which countenances this opinion may undoubtedly be given to them by maceration and dissection ; but during this process we see that a softer composition peculiar to the ganglion is washed away and lost, and Scarpa admits such a substance betwixt the filaments. Bichat errs on the other side, by affirming that there is nothing fibrous in their appearance, and that they are uniform and homogeneous. This complicated and beautiful structure of nervous matter, protected by situation and by the support of peculiar membranous texture supplied bountifully with blood-vessels, and consisting of white and cineritious coloured nervous matter, has been supposed to be only a means of cut- ting off the course of sensation to the brain along those nerves which pos- sess such knots or ganglions. But they are undoubtedly organs of im- portance ; and how great their importance may be to the system, will be better gathered from the following comparative view of the system of the brain and nerves. AN EXPOSITION OF THE NATURAL SYSTEM OF THE NERVES, AC- CORDING TO THE DISCOVERIES OF THE AUTHOR. The nerves of the human body are, beside the nerves of vision, smell, and hearing, four systems combined into a whole. Nerves en- tirely different in function extend through the frame; those of sensation; those of voluntary motion; those of respiratory motion ; and, lastly, nerves which from their being deficient in the qualities that distinguish the three others, seem to unite the body into a whole, in the performance of the functions of nutrition, growth, and decay, and whatever is direct- ly necessary to animal existence. These nerves are sometimes separate; sometimes bound together; but they do not, in any case, interfere with or partake of each other’s influence. If we take up a nerve to examine it, we find that it consists of dis- tinct filaments : but there is nothing in these filaments to distinguish them from each other, or to declare their offices. One filament may be for the purpose of sensation; another for muscular motion: a third for combining the muscles when in the act of respiration. But the subser- viency of any of all these filaments to its proper office must be disco- vered by following it out, and observing its relations, and especially its origin in the brain and spinal marrow. In their substance there is no- thing particular. They all seem equally to contain a soft pulpy matter enveloped in cellular membrane, and so surrounded with a tube of this NERVES OF THE HUMAN BODY. 9 membrane as to present a continuous tract of pulpy nervous matter, from the nearest extremity in the tyain to the extremity which ends in a mus- cle or in the skin. The figure represents a nerve, consisting of distinct filaments. A. the nerve ; B. one of the threads dissected out. Previous to the observations which I have made, such a nerve as I have described was supposed to have all it threads alike; they were sup- posed to be branches from the same root, and all capable of exciting a muscle, or conveying a sensation. The key to the system will be found in the simple proposition, that each filament or tract of nervous matter has its peculiar endowment, inde- pendently of the others which are bound up along with it; and that it continues to have the same endowment throughout its whole length. If we select a filament of a nerve, (for example, one of those in the com- pound nerve represented above,) and if its office be to convey sensation, that power shall belong to it in all its course wherever it can be traced : and wherever, in the whole course of that filament, whether it be in the foot, leg, thigh, spine, or brain, it may be bruised, or pricked, or injured in any way, sensation and not motion will result; and the perception ari- sing from the impression will be referred to that part of the skin where the remote extremity of the filament is distributed. As the matter of the nerve is every where the same, and the apparent difference is only in the manner in which the fine cellular membrane forms the envelope, (it being soft where the nerve is protected, hard and cordlike where it is exposed or subject to pressure ;) I have been de- sirous of having some term or terms which might be applicable to the same tract of matter through its different stages, whether traced in one direction or the other. Where certain whitish streaks of nervous matter are discoverable in the substance of the brain, we may still use the term Tractus, as being already an anatomical term. Where, in any part, the line of a nerve is not merely discoverable by its colour, or the direction of its texture, but when it is raised, and exhi- bits an external convexity in form of a cord, the term Column or Rod may be used. Where they emerge in distinct threads, Funiculi has seemed to me a proper term : and where these funiculi are projected in combination, I use the word Fascis. Although we must keep the term Nerve, yet it is, as we may say, an abused term. Let us only distinguish betwixt a simple and a compound nerve. A simple nerve is where the threads or funiculi which form its roots arise in a line or sequence from the brain or spinal marrow. A compound nerve is where the threads forming the 10 CAUSE OF THE COMPLEXITY OK NERVES. roots arise in double rows, and each row from a different column or tract of nervous matter; for example, the Ninth Nerve is simple; a Spinal Nerve is compound. A Nerve, then, is a cord composed of nervous matter and cellular sub- stance ; the nervous matter is in distinct funiculi, and these funiculi are bound together in their course to the point of distribution, and may pos- sess properties quite dissimilar. If we were successfully to trace a nervous cord, (we shall suppose from a muscle of the fore-arm,) it would be found a simple filament, thread, or funiculus. We should then trace it into a compound nerve ; perhaps the ulnar nerve ; which we call compound, because there are in it fila- ments of motion and filaments of sensation bound together. At the root of the axillary nerve we should trace it into the composition of a fascis, where it forms the anterior root of a spinal nerve. Being further traced, it would merge in the anterior column of the spinal marrow; and traced into the base of the brain, it might be followed as a tractus, a streak of matter distinguishable from the surrounding substance, until it was seen to disperse and lose itself in the cineritious matter of the cerebrum. In all this extent, however combined or bound up, it con- stitutes one organ, and ministers to one function the direction of the ac- tivity of a muscle of the hand or finger. Even in this respect is its operation perfectly simple, for while it excites the muscle to change its state, which we call its state of contraction or of relaxation, does it also convey to the sensorium a sense of the condition of that muscle 1 * So if we trace other fasciculi or, rather filaments, whether they be for the purpose of sensation or of motion, each retains its office from one extremity to the other; nor is there any communication betwixt them, or any interchange of powers, further than that a minute filament may be found combined with filaments of a different kind, affording a new property to the nerve thus constituted, that is to say, it accompa- nies it, and gives an additional power to the part where it is ultimately distributed. THE CAUSE OF THE COMPLEXITY OF UERVES. It was the chief purpose of my papers in the Philosophical Transac- tions, to explain the cause of the seeming intricacy of the nerves of the face, neck, and thorax : but independently of the complexity arising from the causes afterwards to be explained, there are these :—It will be rea- dily understood that some degree of irregularity in the distribution of nerves, must arise from their being compound nerves ; but the principal cause is the necessity of arranging and combining a great many mus- cles in their different offices. Wherever we trace nerves of motion, we find, that, before entering the muscles, they interchange branches, and form an intricate mass of nerves, or what is termed a plexus. This plexus is intricate in proportion to the number of the muscles to be sup- plied, and the variety of combinations into which the muscles enter, while the filaments of nerves which go to the skin regularly diverge to * This, it would be easy to prove, is a very important consideration in studying the organs of the senses. OF THK SPIJfAL MARROW. 11 their destination. The nerves on the face, and those on the side of the neck, form plexus ; but the grand plexus are near the origins of the nerves of the upper and lower extremity: and from the fin of a fish to the arm of a man the plexus increases in complexity in proportion to the variety or extent of motions to be performed in the extremity. The explanation of a plexus which I have offered, is founded on these facts ; viz. that by the interchange of filaments, the combination among the muscles is formed; not only are the classes of extensors and flex- ors constituted in the plexus, but all the varieties of combinations are there formed, and the curious relations established which exist between opposing muscles, or rather between the contraction of one class and the relaxation of the other. THE SPINAL MARROW.* In this view of the nerves the internal and radical distinctions are more insisted upon, than that enumeration of their origin and description of their devious course through the body which have hitherto served only to confound the enquirer. We must, there- fore, begin the description of the system with that of the spinal marrow. It is by a right arrangement of matters which are familiar, and by attention to a few remarka- ble and prominent facts, that the ground- work of this system will be best under- stood. The spinal marrow is peculiar to the ver- tebral animals. It will suffice for superfi- cial observers to say, that it must be so, because the spine is necessary to conceal and protect the marrow : but there is much more than this in the established relation- ship ; the spine formed by the vertebras is necessary to such a constitution of the thorax as shall be capable of the motion of respiration ; and the spinal marrow is equally necessary to that form and distribution of the nervous system which is required for associating and combining the muscles of respiration. Without the machinery of the spine and ribs, the thorax and abdomen could not rise and fall in re- spiration ; and without the spinal marrow that arrangement of nerves would be wanting, which is necessary to regulate the motions of the trunk in respiration. Thus the spinal marrow, the spine and ribs, and the muscles of respiration, are essential to each other; as constituting the several parts of a grand design subservient to respiration. Different columns of nervous matter combine to form the spinal mar- row. Each lateral portion of the spinal marrow consists of three tracts * I have represented above, in a general way, the columnar appearance of the spinal mar- row at its upper part; that superior extremity, which, being traced out of the base of the brain, is called medulla oblongata. 12 OF THE SPINAL MARROW. or columns ; one for voluntary motion, one for sensation, and one for the act of respiration. So that the spinal marrow comprehends in all six rods, intimately bound together, but distinct in office ; and the capi- tal of this compound column is the medulla oblongata. These six columns of the spinal marrow are discoverable on looking to the fore part of that body; but no doubt these grander columns contain within them subdivisions. Thus, if we lift up the medulla spinalis from the cerebellum, and look to it on the back part, we shall see more nume- rous cords, the offices of which will one day be discovered. The medulla oblongata raised by a thread, so as to expose the posterior sur- face. This view of the constitution of the spinal marrow led me to institute experiments, which were followed by the discovery of the distinct func- tions performed by the several roots of the spinal nerves ; but without stating these experiments or their results, we shall proceed with the ge- neral view. The anterior column of each lateral division of the spinal marrow is for motion; the posterior column is for sensation; and the middle one is for respiration. The two former extend up into the brain, and are dis- persed or lost in it: for their functions stand related to the sensorium : but the latter stops short in the medulla oblongata, being in function inde- pendent of reason, and capable of its office independent of the brain, or when separated from it. It is the introduction of the middle column of the three, viz. that for respiration, which constitutes the spinal marrow, as distinct from the long central nerve of the animals without vertebrae, and which is attend- ed with the necessity for that form of the trunk which admits of the res- piratory motions. In animals which do not breathe by a uniform and general motion of their bodies, there is no spinal marrow, but only a long compound and gan- OF THE NERVES, &C. 13 glionic nerve, extending through the body for the purpose of sensation and motion. This cord in those creatures does not actuate the animal ma- chine with alternate dilatation and contraction. There may be a motion of some part which admits and expels air from a cavity, or agitates the water, and which motion is subservient to oxygenation of the blood ; and there may be a nerve supplied to that apparatus with sensibility and pow- er suited to the function thus to be performed, and resembling our par vagum in office ; but there is no regular and corresponding distribution of a respiratory system of nerves to both sides of the body, and no ar- rangement of bones and muscles, for a general and regular motion of the frame like that which takes place in vertebral animals, and which is ne- cessary to their mode of existence. OF THE NERVES WHICH ARISE FROM THE SPINAL MARROW. COMPARISON WITH THE NERVES OF THE ENCEPHALON. The first conception which I entertained of the true arrangement of the nerves, arose from a comparison of the nerves which take their ori- gin from the brain, with those which arise from the spinal marrow. The perfect regularity of the latter, contrasted with the very great irre- gularity of the former, naturally led to an inquiry into the cause of this difference. I said, if the endowment of a nerve depend on the relation of its roots to the columns of the spinal marrow and base of the brain, then must the observation of their roots indicate to us their true distinc- tions and their different uses. AB the spinal marrow seen late- rally ; C the posterior roots of a spi- nal nerve ; D the anterior roots of the same nerve pinned out. The spinal nerves are perfectly regular in origin and distribution, and are thirty on each side.'* Each nerve has two distinct series of roots coming out in packets or fasces, one from the posterior column, and one from the anterior column, of the spinal marrow. The posterior fascis is formed of funiculi, which come out with re- markable abruptness from the column; and their roots form a very regu- lar row or series along the sides of the spinal marrow. They seem at * The tenth nerve of the head, as enumerated by Willis, and called suboccipital from its situation, is in constitution a spinal nerve, i. e. it has a double root, a ganglion on its poste- rior root, and its distribution is similar to the spinal nerves, quite unlike those of the ence- phalon. 14 OF THE NERVES WHICH ARISE once to burst out from the confinement of the arachnoid coat. These funiculi, converging towards the foramen of the sheath of the spinal marrow, and being collected together, form a ganglion. This ganglion is not seen within the sheath of the spinal marrow; its seat is in the part where the fascis is surrounded and united to the sheath, and just before this root of the nerve joins the anterior one to constitute a spinal A the spinal marrow seen in front; B a spinal nerve; C the anterior root of the spinal nerve ; D the ganglion on the posterior root. The funiculi of the anterior roots of these nerves gather their minute origins with more irregularity than the posterior ; and from a wider sur- face. The thirty nerves thus formed of two distinct fasciculi, are suited to perform all the offices of the trunk and limbs. Is it, then, by that com- bination of properties which they acquire through their double roots, that they are capable of performing their offices ? And is this the cause of their simplicity of arrangement in their course through the body, as con- trasted with the nerves of the head 1 Again, what cerebral nerves, in their distribution to the head and face, correspond in office with the spi- nal nerves 1 On the solution of these questions will depend our know- ledge of the whole nervous system. It was necessary to know, in the first place, whether the phenomena exhibited on injuring the separate roots of the spinal nerves correspond- ed with what was suggested by their anatomy. After delaying long on account of the unpleasant nature of the operation, I opened the spinal canal of a rabbit, and cut the posterior roots of the nerves of the lower extremity; the creature crawled, but I was deterred from repeating the experiment by the protracted cruelty of the dissection. I reflected, that an experiment would be satisfactory, if done on an animal recently knocked down and insensible ; that whilst I experimented on a living animal, there might be a trembling or action exerted in the muscles by touching a sensitive nerve, which motion it would be difficult to distin- guish from that produced more immediately through the influence of the motor nerves. I therefore struck a rabbit behind the ear, so as to de- prive it of sensibility by the concussion, and then exposed the spinal marrow. On irritating the posterior roots of the nerve, I could perceive no motion consequent, on any part of the muscular frame ; but on irri- FROM THE SPIX4L MARROW. 15 tating the anterior roots of the nerve, at each touch of the forceps there was a corresponding motion of the muscles to which the nerve was dis- tributed. These experiments satisfied me that the different roots and different columns from whence those roots arose, were devoted to dis- tinct offices, and that the notions drawn from the anatomy were correct. The anterior roots of the spinal nerves, and the anterior column of the spinal marrow, being thus shown to have a power over the muscular sys- tem, the next step of the enquiry was distinctly indicated. If I pursue the track of the anterior column of the spinal marrow up into the brain, shall I find the nerves which arise from it to be muscular nerves ? An anatomist will at once answer, that only muscular nerves arise in this line. We see here the anterior root of the spinal nerve, arising from the co- lumn at A. We trace the column up into the corpus pyramidale, and find there the origin of the ninth nerve B. We see that this nerve has only one series of roots, corresponding with the anterior roots of the spinal nerves, and that these roots come from the tractus motorius, and we cannot for- get that this nerve is entirely devoted to the muscles of the tongue ; that it is the motor of the tongue. Following up the corpus pyramid- ale, we find issuing from it the sixth nerve, a muscular nerve of the eye. Still following up the tractus motorius through the pons varolii, we come to the roots of the third nerve, the mo- tor nerve of the eye. Thus all the nerves arising in one line from the crus cerebri to the cauda equina are muscular nerves ; and no nerves of a different kind arise in all this line. On finding this confirmation of the opinion, that the anterior column of the marrow, and the anterior roots of the spinal nerves were for motion, the conclusion presented itself that the posterior column and posterior roots were for sensibility. But here a difficulty arose. An opinion has pre- vailed that ganglia were intended to cut off' sensation ; while every one of the nerves, which I supposed were the instruments of sensation, had ganglia on their roots. Some very decided experiment was necessary to overturn this dog- ma. I selected two nerves of the encephalon : the fifth, which had a ganglion, and the seventh, which had no ganglion. On cutting across the nerve of the fifth pair on the |ace of an ass, it was found that the sensjbility of the parts to which it was distributed was entirely destroyed. 16 OF THE NERVES WHICH ARISE On cutting across the nerve of the seventh pair on the side of the face of an ass, the sensibility was not in the slightest degree diminished. By pursuing the enquiry, it was found that a ganglionic nerve is the sole organ of sensation in the head and face : and thus my opinion confirmed, that the ganglionic roots of the spinal nerves, were the fasces or funiculi for sensation. It now became obvious why the third, sixth, and ninth nerves of the encephalon were single nerves in their roots, as contrasted with the spi- nal nerves; for if the fifth nerve bestowed sensibility universally on the head and face and all the parts contained, there was no necessity, so to speak, for the third, sixth, and ninth, having the posterior or ganglionic root. Pursuing the subject and still directed by the anatomy, the next mat- ter of enquiry was to ascertain how far the fifth nerve of the encephalon corresponded with the spinal nerves. It was discovered that the fifth nerve bestowed sensibility on all the cavities and surfaces of the head and face. It was also observed, that where the sensibility of the integu- ments remained after the division of the fifth nerve, it was only to the extent of surface supplied by the nerves of the spine. Where certain fibrils of the spinal nerve extend upon the integuments of the side of the jaw, these are equivalent in office to those of the fifth nerve. In short, in regard to their property of bestowing sensibility, the fifth and the spi- nal nerves were identified. We have an exact drawing of the 5th nerve, and one of the spinal nerves. A the 5th nerve; E a spi- nal nerve; C the pons Varo- lii; D the Corpus Pyramidale ; a that origin of the 5th which has no ganglion ; b the root of the 5th which has a ganglion ; c the ganglion ; d the anterior origin of the spinal nerve having no ganglion; e the posterior ganglionic root of the same nerve; f the ganglion. FROM THE SPINAL MARROW. 17 But was the fifth nerve in other essential circumstances similar to the spinal nerves 1 On recurring to the anatomy, and comparing the fifth nerve of the encephalon with a spinal nerve, the resemblance, both in man and brutes, was very remarkable. In this sketch we recognize cor- responding parts. In both nerves we seet the double roots ; the ante- rior root passing the ganglion, and the posterior root falling into it or forming it. On following back the anterior root, we may perceive that it comes out betwixt the ftines of the Pon3 Yarolii, and, in fact, from the crus of the cerebrum. Observing that there was a portion of the fifth nerve, which did not enter the ganglion of that nerve, and being assured of this fact by the concurring testimony of anatomists, I conceived that the fifth nerve was in fact the uppermost nerve of the spine ; that is to say, the uppermost or most anterior of those nerves which order the motion, and bestow sensibility, in its extended sense, on the frame of the body. A Crus Cerebri ; B Pons Varo- lii; C Medulla Oblongata; D two ropes or funes of the pons, which part to give origin to the anterior root of the 5th nerve ; E a fasci • cuius from the Crus Cerebri, giving origin to the anterior root of the 5th nerve, To confirm this opinion by experiment, the nerve of the fifth pair was exposed at its root, in an ass, the moment the animal was killed ; and on irritating the nerve, the muscles of the jaw acted, and the jaw was closed with a snap. On dividing the root of the nerve in a living ani- mal, the jaw fell relaxed. Thus its functions were no longer matter of doubt: it was at once a muscular nerve and a nerve of sensibility: and thus the opinion was confirmed, that the fifth nerve was to the head, what the spinal nerves were to the other parts of the body. One circumstance I may notice in passing ; the origin of the fifth nerve being above or anterior to the termination of the column of the spinal marrow for respiration, it can receive no roots from it. How then are the features to be moved in sympathy wjjh the lungs, and with 18 EXPLANATIONS. OP PLANS. the respiratory actions of the breast, neck, and throat ? We shall fine presently that this is effected through the portio dura of the seventh. I have now only to add, that these opinions and experiments have been followed up to the satisfaction of all Europe. It has been acknow- ledged that the anterior roots of the spinal nerves bestow the power of muscular motion ; and the posterior roots sensibility. Wrhen the ante- rior roots of the nerves of the leg are cut in experiment, the animal loses all power over the leg, although the limb still continues sensible. But if, on the other hand, the posterior roots are cut, the power of motion continues, although the sensibility is destroyed. When the posterior co- lumn of the spinal marrow is irritated, the animal evinces sensibility to pain ; but no apparent effect is produced when the anterior column is touched. I shall now proceed, by reference to the plate, to explain the symme- trical system of nerves. We see thirty-one nerves similar in origin and constitution, ranging with perfect order, and going forth to the head, body, and limbs in regular succession ; and in their essential attributes, common to every class of animals, from the creeping thing tip to man.* EXPLANATION OF PLANS. When we contemplate the dissection which we have made of the nerves of the face, neck, and chest, and are lost in the confusion of the YHth, VIHth, and IXth, of the branches of the Cervical Nerves, and of the Sympathetic—of the Diaphragmatic, Spinal Accessory, and Infe- rior External Respiratory Nerves—we shall be prepared to see the ad- vantages of the plans which are annexed. The reader will soon disco- ver that the system, of which the plans may give him some idea, is not only a remarkable improvement in the knowledge of the structure and functions of animal bodies, but is of the greatest use in practical anato- my in facilitating the comprehension of the nerves. The arrangement is this :—There is an obvious division of the me- dulla spinalis corresponding to the cerebrum and cerebellum : every re- gular nerve has two roots, one from the anterior of these columns, the other from the posterior : such are the Vth pair; the Suboccipital ; the seven Cervical; the twelve Dorsal; the five Lumbar ; and the five or six Sacral ; viz., thirty-one pairs of perfect, regular, or double nerves in the human body. These are laid down in the first plan. They are common to all animals, from the worm up to the man ; and are for the purposes of common sensation and motion, or acts of volition ; they run out laterally to the regular divisions of the body, and never take a course longitudinal to the body.f * This will be condemned as a term not systematic, but it is strictly correct. It is the ne- cessity of a correspondence in the motions of the body and feet which, if we may so express it, calls for symmetry in the distribution of the nervous system. When a creature has no feet, or substitute for them, there is no symmetrical system of nerves. If we were to consi- der the necessity of correspondence in the motions of the hands and feet, as well as in the four quarters of brutes, that each foot does not move by itself, but on the contrary, that there is a combination of motion betwixt the limbs in walking, ambling, trotting, galloping, &c. we should sec that the muscular system must be united by a longitudinal cord, and uniformity. of branches going out laterally. f “ Crustaceous animals and insects are the only inverlc-bra) animals which have a sort of spinal marrow • it. is formed of a double medullary cord, united from space to snare by I.'ittl.irc£ Petidlr, toii.Boston PLATE 1. EXPLANATION OF PLANS. 19 For the sake of arrangement, the remaining nerves are called irregu- lar nerves. These are distinguished by a single fasciculus, or single root; that is, a root from one column. These are simple in their origin ; irregular in their distribution ; and deficient in that symmetry which characterizes the first class. They are superadded to the original class, and correspond to the number and complication of the superadded or- gans. Of these there are—the IHd, I Vth, and YIth to the eye ; the Yllth to the face ; the IXth to the tongue ; the Glosso Pharyngeal to the pharynx; the Nervus Vagus to the larynx, heart, lungs, and sto- mach ; the Phrenic to the diaphragm ; the Spinal Accessory to the mus- cles of the shoulder ; the External Respiratory to the outside of the chest. If we enquire into the seeming confusion in the second class, or irre- gular nerves, we shall perceive that it is owing to the complication of the superadded apparatus of respiration, and the variety of offices which this apparatus has to perform in the higher animals. To explain this the second plan is given. It presents in one view the nerves destined to move the muscles in all the varieties of respiration, speech, and expression. We may now see how confounding is the numbering of the nerves, according to the system of Willis ; and how impossible it is to make a natural arrangement while the nerves are so numbered. EXPLANATION OF PLATE I. A A Cerebum.—B B Cerebellum.—C C Crura Cerebri.—D D Crura Cere- bell!.—E E E Spinal marrow. 1 X Branches of the Vth pair, or Trigeminus, which are seen toarise from the union of the crura cerebri anil crura cerebelli: one root coming from the crus cere- bri, and another from the crus cerebelli; anil on the last a ganglion is seen, like the ganglion of the spinal nerves. The branches (he Vth nerve are universally distributed to the head and face. 2 2 Branches of the Suboccipital Nerves, which have double origins and gan- glions. 3 3 The branches of the four inferior Cervical Nerves and of the first Dorsal, forming the Axillary Plexus : the origins of these nerves are similar to those of the Vth and the Suboccipital. 4 4 4 4 Branches of the Dorsal Nerves, which also arise in the same manner. 5 5 The Lumbar Nerves. 6 6 The Sacral Nerves. OF THE NERVOUS CIRCLE WHICH CONNECTS THE VOLUNTARY MUSCLES WITH THE BRAIN. I have been slow to make my particular opinions part of this general system, and I have not included my papers in these volumes, until the conclusions in them have received something like a general approbation. I shall, however, shortly notice the subject of a paper which I gave in lately to the Royal Society. The muscles have two nerves, which fact has not hitherto been no- ganglions ; we might rather consider it as a great sympathetic nerve.” Cuvier Lccons d’ Anatomie Comparee, tom. 2. p. 100. There can be no question but that inverjebral animals may have nerves for “ sensation and motion, or acts of volition,” but in such as have neither cerebellum nor medulla spinalis, it is unnecessary and inexact to extend the analogy so positively to them. J. D. G. 20 ticed, because they are commonly bound up together. But whenever the nerves, as about the head, go in a separate course, we find that there is a sensitive nerve and a motor nerve distributed to the muscular fibre, and we have reason to conclude that those branches of the spinal nerves which go to the muscles, consist of a motor and a sensitive filament. It has been supposed hitherto, that the office of a muscular nerve is only to carry out the mandate of the will, and to excite the muscle to action; but this betrays a very inaccurate knowledge of the action of the muscular system; for before the muscular system can be controlled under the influence of the will, there must be a consciousness or know- ledge of the condition of the muscle. When we admit that the various conditions of the muscle must be es- timated or perceived in order to be under the due control of the will, the natural question arises, is that nerve which carries out the mandate of the will capable of conveying, at the same moment, an impression retrograde to the course of that influence which is going from the brain towards the muscle 1 If we had no facts of anatomy to proceed upon, still reason would declare to us that the same filament of a nerve could not convey a motion, of whatever nature that motion may be, whether vibration, or motion of spirits in opposite directions, at the same moment of time. I find that to the full operation of the muscular power, two distinct filaments of nerves are necessary, and that a circle is established be- tween the sensorium and the muscle ; that one filament or simple nerve carries the influence of the will towards the muscle, which nerve has no power to convey an impression backwards to the brain, and that another nervo connects the muscle with the brain, and acting as a sentient nerve conveys the impression of the condition of the muscle to the mind, but has no operation in a direction outward from the brain towards the mus- cle, and docs not, therefore, excite the muscle, however irritated. OF THE SYSTEM OF NERVES The observation of the frame of man or of brute, and especially the review of it in a state of high activity, or under the influence of passion, will convince us that the motions dependent on respiration extend almost over the whole body, while they more directly affect the trunk, neck, and face. We may perceive, also, that during the involuntary action of res- piration the same muscles are in operation as in the voluntary actions. This is evident not only in breathing, but also in coughing, sneezing, crying, laughing, speaking, swallowing, and vomiting; for all these are states or conditions of the respiratory nerves and muscles. In every effort but that of simple voluntary motion, the respiratory organs become the agents ; and even in violent voluntary efforts, or the long continu- ance of exercise, the instinctive motions chime in with the voluntary motions, and the activity of the frame becomes general. Under the class of respiratory motions we have to distinguish two kinds : first, the involuntary, or instinctive ; secondly, those which ac- company an act of volition. We are unconscious of that state of al- ternation of activity and rest which characterises the instinctive act of breathing in sleep ; and this condition of activity of the respiratory or- gans we know, by experiment is independent of the brain. But, on the OF THE SYSTEM OF NERVES CALLED RESPIRATORY. CALLED RESPIRATORY. 21 other hand, we see that the act of respiration is sometimes an act of voli- tion, intended to accomplish some other operation, as that of smelling or speaking. I apprehend that it is this compound operation of the organs of breathing which introduces a certain degree of complexity into the system of respiratory nerves. A concurrence of the nerves of distinct systems will be found necessary to actions which at first sight appear to be very simple. To make this evident, before proceeding further, I shall give an ex- ample of the necessity of this combination of different powers. Let us observe, in the act of eating and swallowing, the necessary combination of three powers of sensation, voluntary muscular activity, and the act of the respiratory muscles. If we cut the division of the fifth nerve which goes to the lips of an ass, we deprive the lips of sensibility : so when the animal presses the lip3 to the ground, and against the oats lying there, it does not feel them ; and consequently there is no effort made to gather them. If, on the other hand, we cut the seventh nerve where it goes to the lips, the ani- mal feels the oats, but it can make no effort to gather them, the power of muscular motion being cut off by the division of the nerve. Thus we perceive that in feeding, just as in gathering any thing with the hand, the feeling directs the effort; and two properties of the nervous system are necessary to a very simple action. In drinking, the fluid is sucked in by the breath, and when the mouth is full we swallow. The water is felt; the lips are moulded into the right form by volition, and the muscles of inspiration combine to draw in the fluid. In the act of swallowing, the liquid would descend into the windpipe were there not a combination of the muscles of respiration with the apparatus of deglutition to prevent it; nor could the fluid or the solid morsel pass the diaphragm without a similar coincidence of activity and relaxation betwixt parts animated by different systems of nerves. In speaking, it is still more obvious that the act of respiration must be- come voluntary, in order to push out the breath, in combination with the contractions of the larynx, and tongue and lips, for producing sound, and more especially articulate language. The respiratory system must be exercised under an instinctive and in- volutary impulse, as in breathing during sleep, and insensibility. But it must, at certain times, be associated into voluntary actions. By fore- seeing this difficulty we shall avoid the danger of pushing the investi- gation of the anatomy too far; or of throwing a doubt over important discoveries by attempting too much. After the investigation of the regular system of nerves of sensation and voluntary motion, the question that had so long occupied me, viz. —what is the explanation of the excessive intricacy of the nerves of the face, jaws, throat, and breast? became of easy solution. These nerves are agents of distinct powers ; and they combine the muscles in subserviency to different functions. As far as regards mption and sensation, the original and symmetrical nerves appeared sufficient to the concatenation of the muscles. By them creatures feel pain, and move and withdraw themselves from injury. But these nerves are not capable of (that is to say, were not designed for) the vital act of respiration, far less from smelling, speaking, singing, 22 OP THE SYSTEM OF NERVES laughing, in which several acts the respiratory system is brought into activity. As animals rise in the scale of beings, new organs are bestowed upon them : and as new organs and new functions are super-added to the original constitution of the frame, new nerves are given also, and new sensibilities, and new powers of activity. In tire act of respiration we sec a succession of regular motions ex- tending to a great part of the animal machinery; we perceive, at one glance, that this is a new species of activity, and that this new energy must be derived from a source different from locomotive powers. Look- ing to the simultaneous motions of the abdomen, thorax, neck, throat, lips, and nostrils, in breathing, it is obvious, in the first place, that they must be animated by nerves partaking of similar powers ; and that these nerves must have a centre somewhere, so that they may be simultane- ously and equally excited, and give a uniform impulse to the muscles of respiration. A the Pons Varolii; B Corpus Pyramidale ; C Corpus Olivare ; D the Spinal Accessory nerve ; E Par Vaguin; F Glosso-Pharyngeal nerve; G Portio Dura of the seventh ; H Fourth Nerve. A11 these are respiratory nerves, arising in a line from the same column. CALLED RESflUATORY. 23 The reader will now understand the course of my reflections, when I observed that there were certain nerves arising from a distinct column of the spinal marrow, not only different from the spinal nerves, W un- like either of the roots of the spinal nerves; and that they had \heir roots in a row or regular series. After the course of the enquiry which I have described, it was natural to suppose that these nerves must have a distinct function, and what so probable as that pointed out by their course and distribution ? viz.—that they were connected with the offices of respiration. Observing that the Spinal Accessory nerve, the Par Vagum, the Glosso-Pharyngeal nerve, the Portio Dura of the seventh or respiratory nerve of the face, and the Fourth Nerve, arose in a dis- tinct tract and in sequences, I conceived that they offered themselves as fair subjects of experiment; and that by an experiment the question would be determined, viz.—whether or not these five nerves connected the remote parts to which they were distributed in the act of respiration. The consideration of the course of the Par Vagum (E) gave counte- nance to this idea, and the comparative anatomy of the nerve confirmed it. On comparing the experiments that had been made from time to time on this nerve, all conspired to shew that its use was to combine the proper organs of respiration; while the other nerves (as D F G H) were intended to draw the exterior apparatus of muscles into sympathy W’ith the heart and lungs. Experiments fully confirmed these opinions. In this course of enquiry it was natural to ask why the Spinal Accesso- ry of authors (D) arose from the spinal marrow in the neck? why it ascended into the head, to join itself with the Par Vagum, instead of fol- lowing the direct and short route to its destination on the muscles of the neck and shoulder, like the spinal nerves ? I divided ita branches in the living animal, and by that means cut off certain muscles from partaking in the act of breathing, while they retained their office under the other nerves; that is, they remained under the direction of the will when they had ceased to be influenced by the lungs. Directed in the next place to the Portio Dura (G), I wished to an- swer the question, Why does the nerve which supplies the muscles of the face take an origin and a course different from the Fifth Nerve destined to the same parts ? By experiment I proved that this was the respiratory nerve of the face : and by inference I concluded, that it had the origin we see, and took it course with the respiratory nerves ; be- cause it was necessary to the association of the muscles of the nostrils, cheek, and lips, with the other muscles used in breathing, speaking, &c. For this reason it was associated with the roots of the Eighth Pair instead of the Fifth. The course of enquiry into the functions of the branches of the Por- tio Dura which go to the eyelids, led me to make observations on the motions of the eyeball; and finally directed me to the Fourth Nerve (H) to account for the sympathetic motions of the eyeball in combina- tion with the other parts moved in the excited state of respiration. I may here observe, that on thrusting a pin or the probe into the sub- stance of the medulla oblongata near the root of the Portio Dura (G), and then turning to the other side, we shall find that we have thrust he- I twist the roots of the Fourth Nerve.* * I have indicated the course of the Fourth hjerve bv a dotted line, 24 OP THJK. SVSTKM OF NERVES. This intricate subject is discussed in the last of the series of papers given to the Royal Society, and republished in this volume. Nothing can better prove the importance of the principles laid down in the beginning of this exposition than the explanation which it offers of the seeming intricacy of the nerves of the orbit and of the whole head and face; and the variety of curious facts which it brings to light. These, as I have said, are detailed in the last of these papers. It appears, then, that there are four nerves coming out of a tract or column of the spinal marrow, froip which neither the nerves of sensation, nor of common voluntary motion, take their departure. Experiment further proves, that these nerves excite motions dependent on the act of respiration. There can be no hesitation or doubt that as far as the neck, throat, face, and eyes depend on, or are related to the actions of respiration, it is through these nerves that they are so associated. I have been always desirous of stating, that the absolute proofs stop here, and that the rest is hypothesis. I imagine that the same column or track which gives origin to the fourth, seventh, glosso-pharyngeai, par vagum, and spinal accessory nerves, is continued downward along the lateral part of the spinal marrow, and that it affords roots to the spinal nerves, constituting them respiratory nerves, as well as nerves of mo- tion and sensation ; and that it especially supplies the roots of the dia- phragmatic nerve, and the external respiratory nerve. The spinal nerves are adequate to the gentle and uniform motions of respiration, but not to the associated actions of respiration. Thus, when a creature cries, or a man speaks or sings, the muscular effort is not in the muscles of the thorax only, and directed by the intercostal nerves ; but the shoulders are raised and the thorax expanded by the in- fluence of the spinal accessory nerve, and the external respiratory nerves. The larynx is excited by the branches of the par vagum called laryngeal. The cheeks, lips, and nostrils, are directed by the Portio Du- ra and the Fourth Nerves. It is remarkable that in the investigation of this subject every nerve and twig of nerve is accounted for, and its office explained, with the ex- ception of certain divisions of the sixth nerve of the brain. EXPLANATION OF PLATE II. A Cerebrum.—B Cerebellum.—CC Spinal Marrow.—D Tongue.—E Larynx. —F Bronchia.—G Heart.—H Stomach.—1 Diaphragm. Ill Par Vagum, arising by a single set of roots and passing to the larynx, the lungs, heart, and stomach. 2 2 Superior laryngeal branches of the par vagum. 3 Recurrent or inferior laryngeal of the par vagum. 4 Pulmonic plexus of the par vagum. 5 Cardiac plexus of the par vagum. 6 Gastric plexus or corda ventriculi of the par vagum. 7 Fourth nerve a branch of this system to the trochlearis muscle. 8 Respiratory nerve or portio dura to the muscles of the face, arising by a series of single roots. 9 Branches of the glosso-pharyngeai. 10 Origins of the superior external respiratory or spinal accessory nerve. 11 Branches of the last nerve to the muscles of the shoulder. 12 12 12 Internal respiratory, or the phrenic to the diaphragm. The origins of this nerve may be seen to pass much higher up than they are generally describee* 13 Inferior external respiratory to the serrntus magau?. PLATW II. on of //,, Vt'/f-ex of Ffexpirah.0}?. ANATOM* OF THE lift AIN. 25 It was said that we understand the use of all the intricate nerves of the body, with the exception of the sixth. The sixth nerve stands con- nected with another system of nerves altogether ; I mean the system hi- therto called the sympathetic, or sometimes the ganglionic system of nerves ; and of this system we know so little, that it cannot be mat- ter of surprise if we reason ignorantly of the connection of the sixth with it. On reviewing the whole nerves of the human body, the sensitive, motor, and respiratory systems combined, surely these views come strongly recommended. They present a series of facts unexampled for their number and importance. Such, for instance, as the distinct func- tions of the nerves of the face ; the fact that all sensibility in the head and face depends solely on the fifth nerve ; the singular circumstance, that the common sensibility of the whole frame results from a series of ganglionic nerves extending from the head to the sole of the foot ; that the act of respiration in the face, nostrils, throat, &c. results from a se- ries of nerves differing from the common nerves ; and last of all, it will not be said that I have left the question unresolved with which I set out, viz., the cause of the intricacy of the nerves of the face, neck, and chest. I have shown that the same part, as for example the tongue, has different nerves suited to its different functions ; and that the intricacy arises from the interweaving of the branches of different systems. But all this has an easy explanation when v/e know the properties of the co- lumns from which they proceed. If there were no facts to give proof of the truth of the view which I have presented, it would surely be enough to recommend it, that a sub- ject which has been hitherto difficult, and intricate, and forbidding, has., by means of it, become interesting, simple, and satisfactory. INTRODUCTORY VIEW OF THE ANATOMY OF THE BRAIN. The brain is a mass of soft matter, in part of a white colour, and gene- rally striated; in part of a grey or cineritious colour, which has no fibrous appearance. It has grand divisions and subdivisions : and as the forms ex- ist before the solid bone incloses the brain: and as the distinctions of parts are equally observable in animals whose brain is surrounded with fluid, they evidently are not accidental, but are a consequence of internal struc- ture. On examining the grand divisions of the brain we are forced to admit that there are four brains. For the brain is divided longitudinally by a deep fissure; and the line of distinction can even be traced where the sides are united in substance. Whatever, we observe on one side has a corres- ponding part on the other ; and an exact resemblance and symmetry is preserved in all the lateral divisions of the brain. And so, if we take the proof of anatomy, we must admit that as the nerves are double, and the organs of sense double, so is the brain double ; and every sensation conveyed to the brain is conveyed to the two lateral parts, and the opera- tions performed must be done in both lateral portions at the ment. 26 INTRODUCTORV VIEW OF THE i speak of the lateral divisions of the brain being distinct brains com- bined in function, in order the more strongly to mark the distinction be- twixt the anterior and posterior grand divisions. Betwixt the lateral parts there is a strict resemblance in form and substance : each principal part is united by transverse tracts of medullary matter ; and there is every provision for their acting with perfect sympathy. After observing the great divisions of the brain, the distinctions observ- able in its substance demand our attention. All the outer surface of the cerebrum and cerebellum is of a grey or cineritious colour. Certaincen- tral spots of the cerebrum and cerebellum present the same appearance. The ganglions have also cineritious coloured matter in their composi- tion ; it is found in the spinal marrow and in some of the nerves. Encompassed by the grey cortical matter, there is a large central por- tion of white matter, commonly called the medullary substance of the brain. This white substance is striated, and the stria? have a regular order. First grand order of striae.—The strise which first attract atten- tion are those which run across from side to side of the brain : they form the media of communication betwixt the two lateral divisions. In the cerebrum, we find these stria? converging from the circumfer- ence towards the centre, and accumulated in the centre to form the great commissure. In the cerebellum, the same convergence takes place, and the commissure formed, is what is called the pons varolii. Second grand order of stride.—From the inner surface of the cineritious or cortical matter, strite of medullary matter descend towards the base of the brain. They converge as they descend; and the striated structure becoming more distinct and more resembling the nerves, they at last appear extricated from the covering of the cineritious matter, and are what we call the crura cerebri and crura cerebelli. As the crura cerebri are formed by the descending strise of the cere- brum, so are the crura cerebelli formed by the descending and converg- ing fibres of the medullary matter of the cerebellum. Certain cineriti- ous masses (insulated from the great cortical mass of the same colour) are observable in the course of these medullary stria?: these masses have hitherto received the names, corpora striata, thalami nervo- rum OPTICORUM, CORPORA DENTICULATA, CORPUS NIGRUM, &C. If we continue to trace the crura of the cerebrum we shall find them still converging and assuming a smaller diameter and passing under the commissure of the cerebellum (or pons varolii), and joining to the crura cerebelli they are prolonged into the portion called medulla oblonga- ta, and this last portion contracting again is continued into the spinal marrow or medulla spinalis. The medulla spinalis has a central division, and also a distinction into anterior and posterior fasciculi, cor- responding with the anterior and posterior portions of the brain. Fur- ther, we can trace down the crura of the cerebrum into the anterior fas- ciculus of the spinal marrow, and the crura of the cerebellum into the posterior fasciculus. Since the time of Galen down to Cuvier, anatomists have been in the use of describing the medullary matter as descending and passing out to form the medulla oblongata. But there are some authors in the present day who choose to consider the matter as entirely the reverse ; the spi- ANATOMY OF THE BRAIN. 27 nal marrow they would describe as the trunk from which the brain ex- pands, and they trace the different divisions of the brain from the seve- ral cords or columns of the spinal marrow. What is there in the spi- nal marrow that it should constitute that root from which the brain is formed. The spinal marrow consists of the nervous centre which orders the actions of respiration, and besides this, it is nothing but the cord of nerve leading to the inferior parts of the body. There is nothing here then, which should in an especial manner be connected with the ence- phalon or organ of the mind. On the other hand, philosophers say truly that the powers of the mind are developed through the organs of the senses, and if we consider how closely related the operations of the mind are to the impressions received through the nerves of sense, we must be inclined to trace these nerves into the base of the brain, and look for the principal organ of the brain by following the tracts of these nerves into its substance. Comparative anatomy will exhibit the nerves of the senses with the organs of the senses at their further extremities, and the ganglia at their nearer extremities : and when these ganglia run. together, they constitute the brain. We ought to enquire what parts of the brain continue to enlarge as the organs of the senses expand, and what parts of the brain bear no correspondence with the change of the organs of the senses. Surely that part of the brain, the developement of which corresponds with the nerves of sense, must be directly con- nected with them. But if there be portions of the brain which are evolved, and increase, and finally assume the form and size of the ce- rebrum and cerebellum of the human head ; and if these bear no rela- tion at all to the developement of these organs of sense, whilst they bear an intimate correspondence with the developement of the powers of the mind; the natural conclusion is, that they constitute the higher and more important parts of the brain.* OF THE CINERITIOUS MATTER OF THE BRAIN. Physiologists have been mistaken in supposing it necessary to prove sensibility in those parts of the brain which they are to suppose the seat of the intellectual operations. We are not to expect the same pheno- mena to result from the cutting or tearing of the brain as from the inju- ry to the nerves. The function of the one is to transmit sensation ; the other has a higher operation. The powers of the organs of sense are different; the sensibilities of the parts of the body are very various. If the needle piercing the retina during the operation of couching give no remarkable pain, except in touching the common coats of the eye, ought we to imagine that the part which is the seat of the higher operations of the mind should, when injured, exhibit sensibility, when the nerve of vision does not 1 So far therefore from thinking the parts of the brain which are insensible, to be parts inferior (as every part has its use,) I should even from this be led to imagine that they had a higher office. * The relative importance of parts of the brain has nothing to do with the question as to its mode of developement, or as to the best method of investigating the structure. The growth of the brain from the superior part of the spinal marrow is incontestibly proved by the obser- vations made in comparative anatomy, as well as by the recent researches of Tiedemann concerning the growth of the foetal brain. In another place a sketch 'of these proofs of the developement of this important organ will be given. J. D. G. 28 INTRODUCTORY VIEW OF THE And if there be certain parts of the brain which are insensible, and other parts which being injured shake the animal with convulsions, exhibiting phenomena similar to those of a wounded nerve, it seems to follow that the latter parts which are endowed with sensibility like the nerves, are similar to them in function and use ; while the parts of the brain which possess no such sensibility are different in function and organization from the nerves, and have a distinct and probably higher operation to per- form. If in examining the structure of the brain, we find a part consisting of white medullary striie, and fasciculated like a nerve, we should conclude, that as the use of a nerve is to transmit sensation, not to perform any more peculiar function, such tracts of matter are media of communica- tion, connecting the parts of the brain ; rather than the brain itself, and the seat of mind. On the other hand, if masses are found in the brain unlike the matter of the nerve, and which yet occupy a place guarded as organs of importance, and holding evidently important relations, we may presume that such parts have uses different from that of merely convey- ing sensation ; we may rather look upon such parts as the seat of the higher powers. Again, if those parts of the brain which are directly connected with the nerves, and which resemble them in structure, give pain when injur- ed, and occasion convulsion to the animal as the nerves do when they are injured ; and if on the contrary such parts as are more remote from the nerves, and of a different structure, produce no such effect when in- jured, we may conclude, that the office of the latter parts is more allied to the intellectual operations, less to mere sensation. When we compare the structure of the brain in different animals we find that in certain lower classes there are no convolutions, the surface of the cineritious matter is uniform. As we ascend in the scale of be- ings we find the extent of the cineritious matter increased. To admit of this, it is convoluted ; the depth of the sulci are the consequence of the extension of the cineritious mass ; and in man above all other animals, are the convolutions numerous and the sulci deep, and consequently, the cineritious mass great, and its extension of surface far beyond that of all other creatures. Another circumstance which points out the importance of the cineri- tions matter of the brain is, that every portion has a fibre of medullary matter which runs across and forms a commissure with the correspond- ing portion of the opposite side. Unless the cineritious masses were important organs, why should there be commissures or nerves forming a distinct system arising and terminating in nothing 1 But if we take them as commissures, i. e. bonds of union betwixt the corresponding sides of the great organ of the mind, we at once perceive how careful nature is to unite the two lateral organs together, and out of two organs to make one more perfect. If we grant that this cineritious matter of the brain is an organ or or- gans of importance, then we may also acknowledge that the portions or masses of cineritious coloured matter which we discover in remote parts of the nervous system, minister to some similar important office. The ganglia have all cineritious matter in their composition; and there are portions of cineritious matter found in the crura or processes of the brain, and in the spinal marrow. ANATOMY OF THE BRAIN. 29 I have found at different times all the .internal parts of the brain dis- eased without loss of sense; but I have never seen disease general on the surfaces of the hemispheres without derangement or oppression of the mind during the patient’s life. In the case of derangement of mind, falling into lethargy and stupidity, I have constantly found the surface of the hemispheres dry and preternaturally firm, the membrane separat- ing from it with unusual facility. From these considerations I must conclude, that the cineritious mat- ter of the brain is the seat of intellect, and the medullary of the subser- vient parts.* At first it is difficult to comprehend, how the part to which every sen- sation is referred, and by means of which we become acquainted with the various sensations, can itself be insensible ; but the consideration of the wide difference of function betwixt a part destined to receive impres- sions, and a part which is the seat of intellect, reconciles us to the phe- nomenon. It would be rather strange to find, that there was no distinc- tion exhibited in experiments on parts evidently so different in function as the organs of the senses, the nerves, and the brain. Whether there be a difference in the matter of the nervous system, or a distinction in organization, is of little importance to our enquiries, when it is proved that their essential properties are different, though their union and co- operation be necessary to the completion of their function, viz. the deve- lopement of the faculties by impulse from external matter. OF THE CEREBELLUM. Although the cerebellum be composed of the same nervous matter with the cerebrum, and although there be here also the distinction of ci- neritious and medullary matter, yet in form and in internal arrangement it is quite unlike the cerebrum. Betwixt the lateral portions of the cerebrum there is a strict resem- blance, and an intimate connection is preserved by the commissures; that is to say, every part is united by transverse tracts of medullary mat- ter, and there is every provision for their acting with perfect sympathy. On the contrary, the cerebrum, which is the anterior grand division of the brain, and the cerebellum the posterior grand division, have slight and indirect connection. In form and division of parts, and in the arrange- ment of white and grey matter, there is no resemblance betwixt them ; therefore there is nothing of that symmetry which is so remarkable in com- paring the sides of the brain. There cannot therefore be a correspon- dence in their functions.t We have already explained that the cerebrum has connection with the * We cannot believe that this conclusion of our author is founded upon sufficiently exten- sive observation, because a great number of instances are on record in which the intellectual operations were apparently uninjured, notwithstanding the cineritious substance of both he- mispheres was very considerably diseased, and even removed by ulceration. See Haller’s Opera Minora, &c. J. D. G. t The cerebellum, though not so strikingly symmetrical as the cerebrum, is nevertheless actually as regular. The right and left portions of the cerebellum are perfectly correspond- ent, and the one portion is fully adequate to perform the functions of the other, in case of any accidental impairment. By the expressions of the author, nothing more is meant than that the cerebrum and cerebellum are very different in construction and office. The symme- try, or correspondence of parts, is perfect in both organs. J. D. G. 30 INTRODUCTORY VIEW OF THE anterior columns of the spinal marrow, and the cerebellum with the poste- rior columns. No one has given reason to doubt the correctness of the statement that I have made, that the anterior column is for motion, and the posterior for sensibility. If we were to indulge in opinions which we could not bring to the test of experiment, we should say that the cerebrum had power over the motions of the body, and the cerebellum over its sensibility. This only I know for certain, that the destruction of the hemisphere of the cerebrum destroys the motion of the corresponding part of the body; but I have seen no decided proof that the injury of the cerebellum destroys the sensibility of the corresponding part of the body. I have no doubt that we shall find out the functions of these different parts of the encephalon, although the experiments made hitherto have been rude and unsatisfactory. OF THE MEDULLA OBLONGATA. Although the medulla oblongata is in our systematic works always termed one of the three great divisions of the brain, it is in truth no more than themedullary matter which we trace from the cerebrum and cerebel- lum into the spinal marrow. If we speak of the spinal marrow as a co- lumn of nervous matter, the medulla oblongata resembles the ornament- ed capital of that column. Looking to future improvement, the great desideratum in the investiga- tion of the brain, is to ascertain which are the essential and fundamen- tal parts, and which are the superadded parts ; and in the next place to determine what is the difference produced on the arrangement of these parts in consequence of the animal possessing a spinal marrow. The formation of the spinal marrow requires an entire change in the arrangement of the nervous system, both brain and nerves. When there is a spinal marrow there is a cerebellum, but none without it. From the cerebrum and cerebellum go down processes, to form the spinal mar- row. When a spinal marrow is given, there is a regular series of nerves, arising from it by double origins. To what then is owing this remark- able change in the arrangement of the nerves? To the possession of a regular apparatus for respiration ; the respiration by ribs, abdominal muscles, and diaphragm, requires that distribution of nerves which is bestowed through the spinal marrow, and thus influences the arrange- ment of the whole nervous system. In the lower animals, in insects, worms, and snails, there is a nervous thread extending from one ganglion to another, in all their length. There is nothing which, by its magnitude, would indicate a brain; for the ganglion in the head is smaller than the ganglions in the body. Lin- naeus said, insects have no brain. But wherever there is a concatenated motion, there is a brain, as in the nervous system of the caterpillar, the worm, or the slug. If we cut off the anterior ganglion, it will be found that the direction of motion is lost. If a worm be divided, it will have abundant motion in the posterior division ; but the anterior division is possessed of the power of combining, which enables it to remove itself from the injury : the anterior portion will move away, while the posterior twists itself in the same spot. The nervous system of insects is full of interest, as we see an exact adaptation of the nerves to the organs and muscles, and a dependence of the brain upon the arrangement of the nerves. It is interesting to see, in the change from the larva to the ANATOMY OF THE BRAIN. 31 winged state, how the brain, ganglions, and nerves accompany these changes of the organs of motion. Notwithstanding that the brain in the lower creatures is distinguished as the source of volition, in them it is not of the same value to life as in the higher animals. In man it is not only beyond calculation great in its appropriate energies, but, as a vital part, it is of the first class, and second only to the stomach. * OF THE MEMBRANES OF THE BRAIN, AND OF THE SUBSTANCE AND TEXTURE OF THE BRAIN ITSELF. OF THE DURA MATER. Many authors, while they describe the cranium as containing the brain, conceive that it also gives it shape. But the brain is formed be- fore the bones which invest it. The first thing that we observe in the embryo is the disproportionate size of the brain to the diminutive body. The ossification of the bones of the skull is a gradual process. The brain, already formed, is invested with the strong membranes ; and be- twixt the laminse of the outer membrane the points of ossification com- mence, and are not completed until the ninth year. The bony matter, which is deposited betwixt the layers of this membrane, retains a firm connection and interchange of vessels with the now apparently distinct membranes on its inner and outer surfaces. The outer layer, which is so strong in children newly born, becomes the delicate pericranium, whilst the inner layer is the dura mater. Thus we find that the bones of the head are moulded to the brain, and the peculiar shapes of the bones of the head are determined by the original peculiarity in the shape of the brain. This view corrects an error into which many have fallen, that the dura mater and the vessels ramifying upon it impress their form upon the so- lid bones, and wear channels upon their surface by their incessant pulsa- tion. The membranes and vessels precede the formation of the bone, and the osseous matter is depoited so as to be moulded round the ves- sels. * Thus the dura mater may be considered as the internal pericranium, f The dura mater f is a firm opaque membrane of considerable thick- ness.—When the skull-cap is torn of, and it is cleaned from the blood which escapes from the ruptured vessels, it is seen marbled with azure and rosy colours. Its outer surface is rough, from the adhesions to the * Albini Acad. Anat. “ Quomodo cranium crescendo accomraodat se eis quae continet.” Fischer, dissertatio de modo, quo, ossa se vicinis accommodant partibus. f Some regard only its external lamina as the internal pericranium. Haller, t. iv. p. 92. Fallopius first viewed the dura mater in this light, and he is followed by the best anatomists. | The membranes of the brain have the name of mater, because they defend the brain, and protect its tender substance; or, according to some anatomists of the Arabian school, because the other membranes of the body are produced from them. Before Galen, the term meninx was common to all the membranes of the body, afterwards it was appropriated to those of the brain. 32 OF THE MEMBRANES OF THE BRAIN. bone being torn up: but on the surface lying in contact with the brain* it is smooth, shining, and of a pearl colour. Although the dura mater is really the strongest membrane of the body, it is yet divisible into laminae ; these are firmly connected by the inter- texture of strong fibres. Most anatomists describe it as composed of two laminae. * Some, however, describe three laminae : the outer lami- nae, or squamosa; the middle, or filamentosa; and the internal (being smooth and uniform,) the lamina membranosa. f But to separate the dura mater into such laminae, it will, I believe, be necessary to dry it and tear it into shreds. N o doubt it may be possible thus to tear it, as some have done, into four, six, seven, or even eight laminae or squamae. It is to be regretted that anatomists should have been proud of such dissections. The dura mater is insensible, as we prove by the operation of trepan ; it has, in the way of experiment, been pricked and injured by every pos- sible contrivance, by mechanical and by chemical stimulants ; yet the animals, the subjects of such cruel experiments, have given no sign of pain. J Before the fact of the insensibility of the dura mater was thus es- tablished, physicians regarded this membrane as the seat and origin of ma- ny diseases. § Formerly the natural connection of the skull and dura mater was so resolutely denied, so hotly contested among the various parties in anato- my and surgery, that we might, by reading their disputes, almost doubt one of the plainest and most obvious facts, were not the closeness of this connection sufficiently proved by the manner of the original forma- tion of the cranium, and by the bleeding surface of the dura mater when the bone is raised; or, if further proof be required, we may macerate these bones and their membranes in acids, when the laminae of the dura mater will be seen intimately connected with the bone, while the pericra- nium and outer laminae of the dura mater are seen to be continued into each other, || by the intermediate cellular texture in which the earth of the bones was lodged. IT The dura matter adheres more firmly to the bone in young subjects, because the bone is yet imperfect, and its surface spongy and rough ; and for the same reason, it is more firmly attached to the skull in the chronic hydrocephalus, because the ossification is imperfect. It frequently ad- heres so firmly to the skull-cap, as to leave its outer lamina adhering to the skull when it is raised. * Scemmerring Corp. Hum. Fabrica, t. iv. p. 26. Haller, t. iv. f Malacarne, p. 22. It is described as partly tendinous, partly ligamentous; that is to say, of a nature resembling these, yet not altogether the same. Vicq d’ Azyr found it separat- ed by purulent matter into two laminae, the fibres of which had a different direction. Acad, des Sciences, An. 1781, p. 497.—Bartholin Sp. Histor. Anatomise. | Zinn. Esper. circa corpus callosum, cerebellum, duram meningem.—M6m. par. HallSr sur les Parties sensibles et irritables.—Blegny, Journal de M6d. An. 1. p. 16. 5 See Hoffman. Med. Ration, part 2. sec. ii. c. 1. § 2. and Boneti Sepulch. Anat. lib. i. sec. i. [| Vicq. d’Azyr, M6m. de l’Acad. Roy. 1781, p. 497, and Malacarne (Aderenze della D. M. alle pareti interne del cranio), p. 24. Taking a portion of the dura mater betwixt the finger and thumb, we can move the two laminae upon each other, owing to a slight degree of laxity in the connecting cellular substance. This cellular texture is demonstrated by Malacarne, by forcibly injecting quicksilver betwixt the layers of the nembrane. OF THE MEMBRANES OF THE BRAIN. 33 GLANDS OF THE DURA MATER. Upon the external surface of the dura mater there are little holes, from which emerge fleshy-coloured papilla?, and which, upon examining the skull-cap, will be found to have corresponding fovese. These are the glandulae Pacchioni. * They are in number from ten to fifteen j on each side, and are seen chiefly lateral to the course of the longitudinal sinus. These bodies were supposed by Pacchioni to be glands. When press- ed, they gave out a fluid; J but in this they do not differ from the loose common cellular membrane. As they are chiefly seen along the line of the great sinus, and are not scattered over the whole dura mater, their supposed use of moistening the surface of the membrane § is quite im- probable ; and, indeed, this is a part of that unfounded hypothesis which supposed an interstice betwixt the dura mater and skull, and ascribed independent motion to this membrane. The surfaces of the dura and pia mater, where they are in contact, being of the nature of the se- creting surfaces of the investing membranes of the other viscera, re- quire no such further aid in moistening them, or preventing their adhe- sion. Many glands are described by authors in the substance, and upon both surfaces of the membrane. Of the bodies which adhere to the surface of the pia mater, and of those also which are to be seen in the sinuses, we shall speak afterwards, when considering the veins which enter the longitudinal sinus. ARTERIES OF THE DURA MATER. This membrane must necessarily be supplied with vessels for its own nourishment, for that of the contiguous bone, and for the perpetual ex- udation of the fluid which moistens or bedews its internal surface. We may divide the arteries of the dura mater into anterior, middle, and pos- terior. The first proceeding from the ophthalmic and ethmoidal branches of the internal carotid; the second from the internal maxil- lary and superior pharyngeal; the posterior from the occipital and ver- tebral arteries and posterior auris. || The principal artery of the dura mater, named, by way of distinction, the great artery of the dura mater, is derived from the internal maxillary artery, a branch of the external carotid. It is called the spinalis, or spheno-spinalis, from its passing into the head through the spinous hole of the sphenoid bone ; or meningea media, from its relative situation, as it rises in the great middle fossa of the skull. This artery, though it sometimes enters the skull in two branches, H usually enters in one con- * See M. Littre Acad. Roy. des Sciences, 1704. Hist. p. 32 art. 19. f Haller, El. Pbys. p. 106. M6ra. par M. Vicq. d’Azyr. Mem. de i’Acad. Roy. 1781, p. 497. f Malacame. $ Viz. the opinion of Fantonius. || Soemmerring, C. H. Fabric. A. Murray, Descrip. Arteriarum, in tab. redact. IT Soemmerring de Corp. Hum. Fab. tom. v. p. 142. This is not the sole artery sent to the dura mater from the internal maxillary: a twig also rises from that branch which goes to the pterygoid muscles and parts about the Eustachian tube—it enters the skull, and is distri- buted to the fifth pair of nerves, and to the dura mater and cavernous sinus; another enters with the inferior maxillary nerve by the foramen ovale, and rises upon the dura mater. 34 OF THE MEMBRANES OP THE BRAIN. siderable branch, and divides soon after it reaches the dura mater into three or four branches, of which the anterior is the largest; and these spread their ramifications beautifully upon the dura mater, over all that part which is opposite to the anterior, middle, and posterior lobes of the brain. Its larger trunks run tipon the internal surface of the parietal, bone, and are sometimes, for a considerable space, buried in its sub- stance. The extreme branches of this artery extend so as to inoscu- late with the anterior and posterior arteries of the dura mater, and through the bones (chiefly the parietal and temporal bones) they inos- culate with the temporal and occipital arteries.* The meningeal artery has been known to become aneurismal and dis- tended at intervals; it has formed an aneurism, destroying the bones, and causing epilepsy, t THE SKULL-CAP, WITH THE DURA MATER ADHERING, (a) Falx—(b) Tentorium—(c) Longitudinal sinus—(d d)Great lateral sinuses— («) Fourth sinus—(/) Artery of the dura muter. OP THE SEPTA WHICH INTERSECT THE BRAIN. Those septa, or, as they are called, processes of the dura mater, be- ing extended across from the internal surface of the cranium, support the brain in the sudden motions of the body, and prevent the gravitation of its parts; but I believe they are chiefly useful in retaining the sinuses in their triangular form. * Malacarne.—»Soemmerring, tom. v. p. 142. ■jf Malacarne, p. 1. sec. 105, OF THE MEMBRANES OF THE BRAIN. 35 These partitions are formed by the reflection of the internal laminae of the dura mater. The falx is the largest of the partitions; it is attached to the cranium in the line of the sagittal suture, and reaching from the crista galli of the ethmoid bone to the middle of the tentorium, or to the crucial ridge of the occipital bone, it passes deep into the middle of the cerebrum, and divides it into its two hemispheres. It is in shape like a scythe, for an- teriorly it does not pass so deep into the substance of the brain ; but it gradually becomes broader, or descends deeper betwixt the hemispheres, as we follow it backwards, which, with the curve it necessarily takes from the shape of the cranium, has obtained it the name of falx: it is also called septum sagittale, verticale, or mediastinum cerebri.* The tentorium separates the cerebrum and cerebellum. It stretches horizontally over the cerebellum, and sustains the posterior lobes of the cerebrum. It is formed ny tne inner lamina of the dura mater, reflect- ed off from the os occipitis along the whole lengtn of the grooves of the lateral sinuses, and the edge or angle of the temporal bones. This sep- tum, thus running round the cavity of the cranium, divides it into two de- partments ; the upper one for the lodgment of the cerebrum, and the lower for the cerebellum. But to allow the union of these two great divisions of the encephalon, a circular opening is left upon the anterior part of the tentorium, which is called the notch of the tentorium. There is a little process of the dura mater, which may be called the falx of the cerebellum. It runs down upon the internal spine of the occipital bone from the tentorium, gradually contracting until it termi- nates on the margin of the great occipital foramen. It serves as a kind of ligament strengthening the tentorium, while it divides the cerebellum. It enters, however, but a little way betwixt the lobes. The falx and tentorium being connected and continued into each other at their broadest part, they mutually support each other, and are quite tense. This tenseness depends on their mutual support, for when one of them is cut the other falls loose, t The lateral extremities of the tentorium are continued forward into acute lines, formed by the duplicature of the dura mater coming off from the edges of the pars petrosa of the temporal bones, and take firm hold on the posterior clinoid processes. From these two points a fold of the membrane stretches forward on each side to the anterior clynoid process, forming thus a hollow or cell for the lodgment of the pituitary gland. Another fold or duplicature of the dura mater, runs onwards a little way from the edge of the little wing of Ingrassias. These are the sphenoi- dal FOLDS. Where the internal lamina of the dura mater forsakes the external to form the falx and tentorium, it leaves a channel or triangular canal; the basis of which triangle is the lamina of the membrane investing the cranium, while the tension of the partitions carries the apex out into an acute point. This forms a channel for receiving all the blood of the veins, and this tension and triangular shape gives a degree of incompres- sibility to the canals. These are the sinuses which receive the veins of the encephalon, and guard them from compression:— * The falx has not been found in some subjects. Garengeot Splancbtiologie. Mr, Car!is?$, Medical Transactions, 1795 + Monro. 36 OF THE MEMBRANES OF THE BRAIN. SECTION OF THE LONGITUDINAL SINUS. (a.) The skull. (6.) The dura mater. (e.) The extremities of the ar- tery of the dura mater passing into the bone. (c.) The falx. (d.) The sinus. (/) A branch of the temporal artery passing into the dura mater. Upon the surfaces of the dura matei* thovo nm many lacerti, or slips of fibres, which are interwoven with the membrane, so as to strengthen it. These fibres aro peculiarly strong in the angles, where the duplicatures pass inwards, giving firmness to the sinuses, while they allow the veins to insinuate their trunks betwixt them ; these fasciculi or slips of fibres, on the sides of the sinuses, are the cordas Willisianse. They were con- sidered by Baglivi and Pacchioni * as the tendons of the muscles of the dura mater, Pacchioni conceiving that this membrane was muscular. Vicq d’ Azyr observes, that in inflammation of the dura mater he has seen it red, and of a fleshy appearance; and that such a circumstance might have deceived Pacchioni, and made him believe that there were muscular bellies, t These physicians conceived that the contraction of the falx and dura mater raised the tentorium; they even conceived that the action of the heart depended upon this motion of the dura mater. J They were de- ceived by the pulsation in the arteries of the brain, communicated to the dura mater, after the operation of trepan, or iu their experiments on liv- ing animals. § The motion communicated to the dura mater, those Italian anatomists conceived to depend on the rising of the tentorium. This motion, which is occasioned by the beating of the arteries of the brain, had been long before observed ||: some conceived it to be a motion on the brain itself, others believed it to depend on the sinuses. The motion caused by respiration was likewise observed. ** M. de Lamure’s conclusion was that the motion of the brain was caused by the reflux of the blood towards it from the vena cava in expiration, tt He un- dertook to demonstrate this ; and he conceived his proof to be good, when, by pressing the ribs of a subject, he saw the refluent blood swelling the jugular and abdominal cava. Haller observed the jugular veins * These were Italian anatomists. Pacchioni was physician to Clement the Xlth. ■I M£m. de l’Acad. Roy. 1781. 1 Duveraey. $ There is a distinction in the movement of the dura mater to be observed upon opening the skull; one depending upon the pulsation of the arteries of the brain ; the other caused by an obstruction to the exit of blood from the cranium, depending upon the lungs. See Etper. 78. M&n. ii. par Haller sur le Mov. du Cerv. Exper. 79. s. chat. || By Coiterus, Riolanus, Bartholin. IT Diemerbroek. f * M. Schlichting Mgm. des Savans Etrangers, 1774. Larry, Mem. present, * l’Acai. des Scien. par divers Savans Etrangers. t'!' M. de Lamirre; vide l’Acad, des Sciences, 1744. OF THE MEMBRANES OF THE BRAIN, 37 swell, and become turgid, during expiration; and be concluded, that the motion of the brain was occasioned by the refluent blood distending the sinuses of the brain. But he did not believe, as Lamure did, that this motion took place before the opening of the cranium, as well as it. When the skull is opened by a wound, the dura mater still protects tho brain, resisting inflammation, and giving the necessary and uniform sup- port to the more delicate substance and vascular membrane of the brain ; but when the dura mater is lacerated by the trepan, or punctured, or worn by the pulsation against the edge of the bone, there may be sudden hernia of part of the brain from coughing, or a rapid and diseased growth from the pia mater forming a fungus tumour. This fungus is occasioned by the taking away of that compression which the resistance of the dura mater gives when entire ;* for by this yielding at a point, the whole force of the circulating blood is directed to it. OF THE TUNICA ARACHNOIDEA. While the dura mater is closely connected with the cranium, and in contact with the surface of the brain, but still unconnected with it, (ex-* cept by means of veins entering the sinuses, and that only in the course of the sinuses) the pia mater is closely attached to the brain, and passes into its inmost recesses. While the dura mater is firm and opaque, and not prone to inflammation, the pia mater is delicate, transparent, extremely vascular, and most peculiar in being easily inflamed, f Like the dura mater it is not endowed with sensibility ; { it is of great strength, consi- dering its apparent delicacy. § The pia mater, which was formerly considered as a simple mem- brane, consists, in reality, of two membranes, the tunica arachnoidea, or meninx media, and the proper pia mater, or tunica vasculosa.|| The tunica arachnoidea was discovered and commented upon by a society formed by Blasius, Sladus, Quina, Swammerdam.T They call- ed it Arachnoides, because of its extreme tenuity, comparing it to a spi- der’s web. It was called also Membrana Cellulosa, from the appearance it took when they insinuated a blow-pipe under it, and blew it up, sepa- rating it from the pia mater.** This membrane is without the pia mater; and while the pia mater sinks down into the sulci of the brain, this covers the surface uniformly, without passing into the interstices of the convolutions, or into the ven- tricles, ft This membrane is so extremely thin, that it cannot by dissection be se- parated for any considerable space from the pia mater, and, least of all, * I have seen in one day seven wounds of the head with fracture; of these, three had the bones thrust through the dura mater, and they died with fungus cerebri; the four others did well. f Mr. Hunter on the blood. | Haller. Oper. Minor, de Part. Corpor. Humani sent. & irrit. 5 Sir C. Wintringharn, Exper. Essays. Taken comparatively it is stronger than the aorta. f| There are many, however, who with Lieutaud consider the arachnoid coat as the exter- nal lamella of the pia mater. H This was in 1665. I am, perhaps, not correct in saying they discovered it) for Varolius describes it plainly, covering the medulla oblongata. ** RuyschTab. 10. Epist. Anat. Prob. viii. ft Haller Elem, Phys, tom. iv. sec. viii. p. 7. 38 OF THE MEMBRANES OF THE BRAIN. over the middle hemisphere of the brain. By the blow-pipe, indeed, we may raise it into ceils, but it immediately subsides again; on the posterior part of the cerebellum, on the spinal marrow and base of the brain, it separates spontaneously, and is very easily demonstrated.* It does aot pass deep into the sulci of the brain, but unites them by an ex- tremely delicate cellular texture. OF THE PROPER PIA MATER, OR TUNICA VASCULOSA. The pia mater is a simple membrane without either tendinous, apo- neurotic, or muscular fibres. It is extremely vascular, but it is transpa- rent in the interstices of its vessels ; it is the membrane which immedi- ately invests and connects itself with the substance of the brain; and although delicate, it forms the support and strength of the cineritious and medullary substance. All vessels distributed in the body, however minute, are conveyed in membranes ; the pia mater, therefore, follows, or rather conveys the vessels not only into the cavities of the brain, but to every part of its substance, it being intimately blended with it.t We see it more distinctly descending in strong plicae into the interstices of the convolutions ; nor is it into them only that it enters, but into every pore which conveys a vessel, j The pia mater, as it passes into the sub- stance of the brain, divides and subdivides into partitions and cells, and every capillary vessel, and every molecule of the substance of the brain, is invested and supported by its subdivisions. The pia mater is to the brain what the cellular membrane is to the other viscera and parts of the body ; for it is the peculiar matter lying in the interstitious cellular membrane 'As in muscles, bones, &c.) that gives the peculiarity of cha- racter to the parts ;§ the cellular membrane itself is nearly alike in all; therefore, in my judgment, the pia mater is properly enough considered by anatomists as a cellular substance.|| Malacarne says, I atn much inclined to consider it with the illustrious Haller, as being composed of laminae like common adipose membrane, and that the extreme arteries ramify through its cells, for, with a blow- pipe, we can raise it into cells like the common membrane ; and if this be carefully done, the air may be made to pass from cell to cell, following the arteries in their course betwixt the lobuli, and in the substance of the brain.IT We can follow the pia mater into the ventricles, by tracing it betwixt the posterior lobe of the cerebrum, and the cerebellum, where it forms the velum interpositum of Haller, and passes under the fornix. * F Ruyschw Responsio ad A. os Goelecke Epistol. ix. See Bidloo, table 10; but the membrane is sodelit ate that it can be but very imperfectly represented by engraving. See also Sandifort Thesaur. vol. ti. p 291. f Columbus the assistant of Vesalius, and afterwards professor in Rome, explained this intimate intertexture ol the pia mater with the proper substance of the brain, so far back as 1559 { When we tear off the pia mater from the brain (for it cannot be called dissection, it does not adhere merely at the sulci, but to the whole surface of the convolutions; and every where small vessels enter, and with these vessels descends also the lamina of the pia mater. { See Leeuwenhoek, Epist. Phys. xxxiv. || Bergen. Program, de Pia Mater. See Haller Anat. IT See Albinus Ann. Acad. vol. i. lib. i. cap. xii. and the beautiful plate iii. See Ruysch. tab 8. Epist. Anat. vii. & tab. 15. Such is the profusion of vessels distributed to inconceiva- ble minuteness, that it has been considered as entirely composed of vessels; it has received the name of chorion, from the membrane of the secundines. Galen de Usu Part. I. viii. cap. 8 Malacarne, part. i. sec. 2i3. OF THE MEMBRANES OF THE BRAIN. 39 We can follow it also into the posterior horn of the lateral ventricles from the base of the brain, where the branches of the middle artery of the cerebrum pass into the lower part of the choroid plexus ; we trace it also into the bottom of the fourth ventricle. The pia mater lining the ventricles, is more delicate, and less vascular than that seen upon the surface, and betwixt the convolutions of the brain. It has been said that the ventricles of the encephalon served to in- crease the surface of the pia mater, and that whatever purposes are served by that membrane and its vessels on the arface of the brain, we must suppose the same performed by it within the ventricles.* This seems more like a satisfactory conclusion than it really is. As the tunica arachnoidea is of a peculiar nature, and has few, if any, vessels, and as it covers the external surface of the brain only, it seems to me probable that this membrane is the cause why effusions in the ventricles are so common, and why fluids are so seldom found betwixt the surface of the brain and the dura mater. When by the diseased ac- tion of the vessels of the pia mater on the surface of the brain, an effu- sion is thrown out, it very seldom lies unconfinerl upon the surface; but frequently fluids are contained in s»*»a of the arachnoid coat, betwixt the convolutions of the brain, or raised pellucid vesicles upon the surface. The want of a tunioa ai-achnoidea upon the pia mater of the ventricles, may be a cause of the fluids being so much more readily secreted into these cavities. The raising of the arachnoidea into vesicles by the action of the ves- sels of the pia mater, is rather an argument for the distinct nature of these membranes. The tunica arachnoidea is raised by the action of the vessels of the pia mater, as the cuticle is raised into blisters by the inflammatory action of the vessels of the cutis, while no other membranes of the body present such an appearance in their disease. They inflame, indeed; they thicken ; their laminae become more distinct, or their cel- lular substance fills with water, or hydatids are formed in them; but this appearance of water secreted under the tunica arachnoidea is peculiar to the surface of the brain. OF THE SUBSTANCE OF THE BRAIN. The cerebrum and cerebellum consist, as we have said, of two sub- stances very different in colour, viz. the cineritious and medullary matter, first described by Picolomini. The cineritious, or ash-coloured matter, forms the superficial or outer part of the encephalon, and is therefore called also the cortical part. This cortical matter is of a reddish grey colour, and semitransparent, but varies considerably in the crura cere- bri it is very dark ; in the pons varolii it is redder ; in the coi pora oliva- ria J it is yellower. The consistency of this matter also varies consi- derably in different parts: it is soft in the base of the brain, betwixt the optic nerves and anterior commissure, and in the third ventricle. The medullary matter is chiefly in the internal part of ttie brain, forming a * Dr. Monro’s Nervous System, chap. vi. t Cuvier describes it black in some places. j Vicq. d’Azyr. Soemmerring Hum. Corp. Fab. vol. iv. p. 41. Albinas; Annot. Academ. vol. h. c. 12, 40 OF THE MEMBRANES OF THE RRAfN. kind of nucleus or white central part; but in many parts of the brain, there is a mixture of these which form striae ;* and in some of the emi- nences, the internal part is cineritious, while the external part, or what we might here call the cortical part, is medullary. The cortical or cineritious substance does not blend gradually with the white medullary matter, but on the contray, their line of distinction is abrupt: and even an intervening substance has been observed. In inflammation of the brain, particularly, it has been said, that this third substance has been found. This may be merely the effect of light upon the union of the two substances. VVe, however, often observe an ap- pearance of successive coloured circles upon the edge of the medullary matter of the arbor vitae, in the cerebellum. It has been asserted by M. Ludwig t that the masses and striae of the cineritious substance, dispersed through the internal parts of the brain, have a communication with each other. This, however, is denied, by Vicq d’ Azyr. J He conceives, that the cineritious substances of the pons varolii, or of the corpora olivaria, have no communication with the cineritious substance in any other part of the brain; and that in several parts of the brain the cineritious substance is surrounded and isolated by the medullary matter. Its great importance (which should never have been doubted) has been deduced from its being so generally found to- wards the origin of the nerves. § The cineritious substance seems to have a greater proportion of blood circulating in it than the medullary substance. Its vessels come by two distinct routes, partly from the extremities of those arteries which appear in large branches upon the surface of the brain, and partly by vessels which penetrate through the medullary substance from the base of the brain. Ruysch and Albinus have made the most minute injections of this part of the brain. The former conceived it to consist entirely of vessels; but Vicq d’Azyr and Albinus found always, in their experi- ments, that a great proportion of it remained colourless after the most minute injection. It is, indeed, very improbable, that so soft a body should be entirely composed of vessels. How, for example, can we suppose the commissura mollis, or cineritious matter on the sides and bottom of the third ventricle, or almost transparent laminae, which we find in some parts, to be composed of vessels ? || The white medullary substance is a pulpy mass. We observe no peculiarity of structure in it towards the surface of the brain, where it is contiguous to the cortical matter; but towards the origin of the nerves it takes a more fibrous and striated appearance. The medullary matter, be- ing chiefly internal, has every where through the brain a communication as from the fore to the back part, from the upper part to the base.H * Thus the cinerltious substance is mixed with the medullary matter in the corpus callo- Bum, in the corpora striata, the thalami nervorum opticorum, in the tubercula quodrigemina, the eminentia mamillaria ; in the crura cerebri; in the pons Varolii; in the corpora olivaria, and medulla spinalis. f De Cineria Cerebri Substantia. Leipsia;. j Hist, de l’Acad. Roy. an. 1781, p. 507. § See M6m. de l’Acad. Scien. an. 1781, p. 507. (1 The centrical and cortical substance of white blooded animals present no difference of colour. Cuvier. tT Meckel found, upon comparing the brains of an European and of a Negro, that the me- dullary matter differed very much in colour. In tbe Negro, instead of the whiteness of tho Eu- OF THE MEMBRANES OF THE BRAIN. 41 OF THE MINUTE STRUCTURE OF THE BRAIN. The opinions regarding the structure of the brain have had a depend- ence on the general doctrines of the structure of the secreting organs, and it is, of course, connected with the disputations of Malpighi and Ruysch. The doctrine of the glandular nature of the brain, and the be- lief of the nervous fluid, being a secretion, has, in all ages, formed the basis of the most favourite theories. * Malpighi found, on throwing in black and fluid injection, that there re- mained always particles colourless, and to which the injection did not penetrate. He conceived these to be glandular folicules, and that the cineritous substance of the brain consisted of this lolicular or glandular structure, while the medullary matter of the brain was merely the fibril- 1® of the excretory duct. This opinion was founded on conjecture, with but a very poor show of experiments. By boiling the substance of the brain in oil, he found it take a granulated appearance, as if formed of small grains, or little glands, as he presumed.! Such was the received opinion until Ruysch, with a despotic authority, swayed the opinions of physiologists; he alleged, in proof, only his own experiments and preparations, in which other anatomists could not follow nor refute him, and therefore, perhaps, they acquiesced. His most un- answerable and most insulting argument was “ veni et vide.” J According to Ruysch, the cortical substance of the brain is entirely vas- cular, and has no appearance of a glandular or folicular structure ; nay, he conceived it to be entirely composed of arteries. § This opinion Al- binus confuted, and Malacarne observes, though we suppose the extre- mities of the arteries of the cineritious substance to be more minute than those which are distributed to the microscopal corpusculi of the smallest visible insect, there must still remain some part, which is not composed of vessels ; and in regard to the veins of the cineritious sub- stance we may appeal to Albinus, who, from the substance of the brain, finds many veins connected with the arteries of the cineritious substance when he carefully lifts the pia mater. But there is this peculiarity in the distribution of the blood-vessels of the brain, that though the cineritious substance be the most vascular, yet, in the medullary matter, we see the vessels with large open mouths, and more distinct than in the cineritious substance. In following the blood-vessels from the base of the brain into the medullary substance, we see them distinct, and of considerable mag- nitude ; but when they are about to enter the cineritious substance, they ropean, the medullary matter was of a yellow colour, and nearly like the cineritious matter; he observed, also, that this very peculiar distinction of colour was only to be observed when the section was recently made, and that the darker colour of the medullary matter became fainter when exposed to the air. * Indeed this doctrine of the glandular nature of the brain has descended from Hippo- crates—“ Caput quoque ipsum glandulas habet cerebrum, enim est ut glandula album est et friabile,” &c. + Ruysch. Thes. An. x. No. xxxii. t “ Milites quando hostium adventum audiunt, clament ad arma! ad arma '■ sic ego dico “ ad hie visum ad visum !” Responsioad J. Ch. Bohlium. } Vieussens was latterly of the same opinion, and is accused of plagiarism by Ruysch Accordingly, we find, that in some parts of his works he describes the glands and ducts of Malpighi. OF THE MEMBRANES OF THE BRAIN. disperse into minute branches. * In the same manner those arteries, which are carried into the sulci of the surface by the pia mater, branch into extreme minuteness before they finally penetrate the cineritious sub- stance. f Leeuwenhoeck J observed, in the cortical substance of the brain, a pellucid, crystalline, and, to appearance, oily matter ; he calls this, there- fore the substantia pellucida et vitrea. When he had put a small portion of this under his glass, he saw a fluid, which he at first conceived might have escaped from the globules that were necessarily cut by the knife. This fluid also he found to consist of very minute globules, thirty-six times less than those of the blood. § These small globules he con- ceived to have probably constituted a fluid, which, during the life of the animal, was moveable, in vessels, though now in death congealed and fixed. || The colour of the cortical substance he found to depend upon the minute ramification of the vessels which were of a dark brown colour, while, in the medullary part, they were clearer and more trans- parent. Independently of this distinction of vessels, he could observe little difference in the medullary and cineritious substance; the refraction of the rays of light amongst the transparent globules being the cause of the whiteness of the former. R. Della Torre,IT in his microscopical observations, describes globuli in the brain ; he says, that he saw them floating in a pellucid viscous fluid. But Prochaska** thinks Della Torre must be mistaken in this, for when he took a small portion of the brain, he saw it consisting of innumerable globules, which continued to adhere to each other, even after three months’ maceration in water; and thence he concludes, that it could not be as R. Della Torre conceived, that these spherical bodies moved from the brain on towards the extremities of the nerves; nor do these bodies lie imbedded in a glutinous fluid (he continues,) but they are connected by the extremely minute and pellucid sepimentae of the pia mater, and by the vessels which pervade both the cortical and medullary matter, and which nourish as well as support and connect these corpus- culi. Fontanatt, on submitting a portion of the medullary matter to the mi- croscope, thought he discovered it to consist of small winding tubes * Leeuvvenhoeck saw, in the substance of the brain, but especially in the cortical substance, red blood-vessels, but so delicate that he could not comprehend how the globules of red blood, could pass along them; and what appeared more particular, they were of a deeper colour than the red particles themselves; for when seen singly, they appeared to have very little colour. This he explained by an experiment made upon a louse. After it had sucked blood very plentifully, he observed that the blood was broken down by digestion, and conveyed through the limbs here and horns of the creature, so as to make it universally red. So here he conceives that the globules of the blood may be broken down and altered in their shape to enter the minute vessels of the brain. •}■ Malacarne, Part ii. sect. 18. | He was born in Delft in Holland, 1632, and died 1723. He is celebrated for his miscro- scopical discoveries; his papers are chiefly in the Transactions of the Royal Society of Lon- don, about the year 1674. } Anatomica Conteinplatio, 30. Ridley, Anat. Cerebri, cap. xi. || Among these globules of which the brain is composed, he saw also the globules of the blood, which it was easy to distinguish by their roundness. These red globules he supposes had escaped in consequence of the minute vessels having been cut by the knife. 11 Nuove Oservaziono Microscopiche, Napoli, 1776. ** Tract. Anatom, de Struct. Nervorum. it Fontana’s Treatise on Poison, and on the Primitive Structure of Animals, translated. OP THE VENTRICLES OF THE BRAIN. 43 filled with a transparent gelatinous humour. This he chose to call tire intestinal substance of the brain. Prochaska* cannot, from his own observations, determine whether the globular bodies of Della Torre be convoluted vessels, or what they are. R. Della Torre had observed, that they were largest in the cortical part, less in the medullary substance, still diminishing in the medulla oblon- gata, and least of all in the nerves ; but succeeding observations did not support this assertion.! Malacame expresses himself to be nearly of the same opinion in regard to the vesicular structure of the cortical sub- stance of the brain. The minute processes of the pia mater, says he, embrace and support the medullary substance, which is surrounded with a matter of a darker colour, and less distinctly fibrous, but not less es- sential, and which is composed of corpuscules, that, in figure and ar- rangement, resemble the vesicles of the pulp of a lemon. Many authors endeavour to support their conjectures regarding this vesicular structure of the brain by morbid dissection. But in this edi- tion I have thrown out the detail of their opinions, as well as all refer- ence to their authority. I have given more place to these observations on the minute struc- ture of the brain than in my judgment they deserved, rather to prevent the repetition of the folly by such as might conclude they were pursu- ing an unexplored path, than from any hope of the subject proving use- ful. When the brain is examined in the foetus of the early months, al- though the substance of the brain is extremely soft, and even of a fluid consistence, the membranes and vessels are fully formed, exquisitely minute, and perfect in all their processes, so that they give form and firmness to the brain. As the brain is perfected, and as it is covered by a firmer bone, it acquires more consistence and firmness. With this firmness it does not acquire strength, for the brain of a child will suffer more injury without destruction of organization, than the brain of an adult. The substance of a child’s brain is soft and yielding, while the bones of the cranium are loose and yielding, and for the same purpose, to admit the compression of the head at birth. OF THE EXTERNAL DIVISIONS OF THE BRAIN, AND OF THE PARTS SEEN WITHIN IT ON DISSECTION. It has been usual to disengage the brain from the skull, and to exa- mine it in its different aspects; and looking upon it thus to divide it, first into the cerebrum the greater and anterior brain, and the cerebellum the lesser and posterior brain, and into a third part which appeared ob- viously the part common to both, viz. the medulla oblongata. The me- * Professor of Anatomy at Prague. f This was certainly a theoretical deception ; it is like the accurate observation ofFra- cassati, who could distinguish a difference of taste in the medullary and cineritious substance of the brain- 44 OF THE VENTRICLES OF THE BRAIN. dullary masses of both cerebrum and cerebellum being visible, as it were descending in form of crura, they seem, and have always been described as combined in the nodus cerebri, to form this prolongation in- to the third grand division, the medulla oblongata ; and this last portion, though much less than the other grand divisions, has always been held important from its manner of formation or its connections. After this first division into cerebrum, cerebellum, and medulla ob- longata, anatomists have made a further subdivision of the cerebrum into hemispheres, viz. those two grand lateral divisions visible on the upper surface: and hemispheres up so as to exhibit the irregula- rities on their lower surfaces, they have made the further divisions into anterior, middle, and posterior lobes of the cerebrum. The cerebellum is describedi n the same manner; first we distinguish a central part, sometimes called corpus vermiforme, and two great lobes or hemispheres, which, indeed, constitute the longer portion of the body in the human subject; but which are, notwithstanding, parts superadded to the original and fundamental part, as seen in the lower animals. The medulla oblongata is very obviously divided by a rapha on the fore and back part into two lateral portions. Having noticed these divisions, we proceed to inspect the interior of the brain. To explain the connections of the several parts of which the brain consists, there have always been two methods; the one commencing with the base of the brain, splitting and turning up the crura, and prose- cuting them in this course inwards; the other by sections commencing on the upper part of the cerebrum, and dividing its substance to inspect the cavities.* OF THE CAVITIES OF THE BRAIN IN GENERAL. Before giving the demonstration of the ventricles, I must affirm, that there are no cavities in the brain, and no surfaces which can correctly be called internal. 4The walls of the ventricles lie in contact: there is no space betwixt them, and therefore, in correctness of language, no cavity. But I have another meaning in saying that there are no internal surfaces. To comprehend the proper structure and relation of the parts of the brain, it is necessary to recollect that these cavities can be laid open with- out making a breach into the proper substance of the brain, and, there- fore, that they are, in fact, the surfaces continued from the exterior convolutions of the brain, and the ventricles, therefore, are formed by the portions of the brain rolled up and adhering at certain parts by the pia mater. There are within the brain many tubercles and irregular surfaces, of which it is infinitely more difficult to convey an idea by description than of the external parts. The surface of the cavities or ventricles of the brain is naturally bedewed with a fluid or halitus, which flows from the general surface of the ventricle, and from the plexus choroides. This moisture preserves those surfaces from adhesion: during life and health * These two methods were followed by Mr. John Bell, in his lectures, and have always been followed by me, since I gave public lectures; and they have been followed by the old anatomists, and must be followed while the object of this study is acknowledged to be, first, to understand the connection, and, secondly, to understand the morbid anatomy of the brain. OF THE VENTRICLES OF THE BRAIN. 45 it is not accumulated so as to form a fluid; but in many diseases, and after death, it is effused or collected into a fluid. The external convo- lutions of the brain we have seen to be cineritious on the surfaces ; the internal surface of the brain may be considered also as forming convo- lutions ; but they are chiefly medullary, and are more irregular, or rather have a greater variety of shape, than those of the outer surface. In regard to the use of the ventricles of the brain, since the hypothe- ses of the older physicians have been tacitly rejected, no opinion has been offered, except this, that “ they seem to be made of a necessary consequence, and towards the greater use and distinction of parts or, as we have already had occasion to mention, that the ventricles serve to increase the surface of the pia mater, and that whatever may be the purposes which are served by that membrane on the surface of the brain, we must suppose the same to be performed by it within the ven- tricles. But this is a conclusion which may not be altogether satisfacto- ry to an inquisitive mind. It is necessary to take into consideration the general peculiarities of the brain : we find that within the skull there is no adipose substance, though it pervades every other part of the body. We at once see a rea- son for this. It is evident that as the fat is incessantly undergoing changes (being alternately absorbed and deposited); as at one time it is deposited in greater quantities, and at another absorbed; as it is in perpetual variation according to the prevailing habits of the body, the proportion of exercise taken, or the state of the health; its continual changes would have the very worst consequence upon such a part as the brain; that if accumulated, it would oppress the circulating vessels ; if rapidly absorbed, it would be followed by accumulation or surcharge of the vessels ; for the skull does not allow of distention, nor is it pos- sible that the cavity of the cranium can admit of depletion. The ventricles of the brain are in their natural state merely surfaces in contact. The forms of these internal surfaces are resulting from the internal conformation of the substance, as the great external convexities are, and as the superficial convolutions are ; I have just said, that we can arrive at these interior surfaces by splitting up the divisions of the brain without tearing the substance of it. The next enquiry is, Why this evident difference of surface within and without the brain ? The cavities, as we shall continue to call them, have no arachnoid coat, they have, therefore, secreting surfaces. Here is the real distinction of the external and internal surfaces of the brain. It has long appeared to me that these cavities and the provision for se- cretion into them had a very particular influence, in preserving the due relation of the parts of the brain, which would otherwise be deranged or unequally pressed. A collection of water in the ventricles of the brain is, perhaps, the most frequent of all diseased appearances, and when within the ventricles it is much less injurious than in the external sur- face ; when collected on the surface, under the tunica arachnoidea, it is ever attended with oppression of the faculties. It is not to be supposed that the ancients, so fertile in their hypo- theses, and so easy in their proofs, could neglect the evident importance of the ventricles of the brain. We accordingly find that the spirits were manufactured in these cavities; that they were the “ spirituum ani- malium officina,” whence the spirits were conveyed over all the nervous 46 OF THE VENTRICLES OF THE BRAIN* system.* They were again degraded from this higher office, and be- came the mere receptacles of the excrementitious matter of the brain (meras cloacas esse asseruerintt); and Willis seems inclined still fur- ther to degrade the importance of the ventricles, by considering them merely as of secondary importance; or rather as resulting solely from the accidental conformation of the brain. Again, we find it a prevalent opinion that the ventricles contained air; that the air supported the soft medullary substance of the brain; and that it gave motion to the whole mass, so as to circulate the spirits in the substance of the brain. J; OF THE CORPUS CALLOSUM AND CENTRUM OVALE OF VIEUSSENS. The corpus callosum is a medullary body which is a centre of com- munication ; or, it is the great commissure § passing betwixt the hemi- spheres of the cerebrum: it is seen without incision by merely separat- ing those hemispheres with the fingers. It is a white body, firmer than the rest of the medullary substance. It is but slightly convexed upon its upper part, but turns convex downwards upon the fore and back part. As the corpus callosum is the continuation of the internal medullary sub- stance of the brain, it is superfluous to say that it is continued down, anteriorly, into the medullary matter betwixt the corpora striata, termi- nating in its pedunculi; or backwards, that it is continued with the fornix and cornua ammoms and the surface of the posterior prolongation of the lateral ventricle. We see upon the surface of the corpus callosum two medullary lines considerably raised, running parallel to each other || in the length of the body. Betwixt these salient lines there is of course a kind of rut, called sometimes the rapha, or suture, which may be considered as dividing this body into two equal parts, and which, in truth, forms the accurate divi- sion of the two sides of the whole brain. IT Other lines less elevated from the surface, are to be observed running across these, as if passing from one hemisphere to the other. If the corpus callosum be cut horizontally, and the section be continued into the sub- stance of the hemispheres, we still can perceive those transverse lines, and observe them to be lost in the medullary matter of the hemispheres.** * Lately, by chemical aids, (which make the cineritious substance black, or dark brown, while the matter remains white or takes a slight greenish tinge,) the origin of ma- ny of the nerves have been traced into the substance of the brain even t» the surface of the ventricles, which has given occasion to the revival of similar ideas of the use of the ven- tricles. f Willis Cereb. Anat. p. 32. j Malpighi. ? Commissure is a term applied to those tracts generally of medullary matter, which pass- ing through the brain are supposed to be media of communication. || They are not strictly parallel in all their length; we find them often separated both upon the fore and back part; but generally more separated upon the back part, and even sometimes they are curved. 1i In which conceit Duverney calls this “ clef du cerveau,” from its being the centre of communication. Tom. i. p. 39. ** The necessity of explaining paralysis and convulsive motions of that side of the body opposite to the side of the brain injured, have made anatomists attend to those transverse lines, in the hopes of finding such a decussation of these lines as would account for it. Sabba- tier says, they have brought themselves to believe that there was a decussation, but after careful investigation he could find no such thing. See Winslow. Ludwig (de Cinerea Cere- bri, sub. p. 5.) observed striae of cineritious substance in the corpus callosum. See also Gunz, and Haller. OP the ventricles op the brain. 47 This body is properly called the great commissure (commissura mag- •na,) for it is the great part of medullary matter which formed by trans- verse striae incorporates and unites into one whole the two lateral divi- sions of the cerebrum. CENTRUM OVALE OF VIEUSSENS. The centrum ovale is merely the appearance which the white and internal part of the cerebrum takes when the brain is cut horizontally on the level of the corpus callosum ; for then the corpus callosum is the centre of the great medullary mass of the cerebrum, and the cineritious matter being on the external edges only, forms the central white mass into an irregular oval. The two lateral ventricles lie under the corpus callosum and medullary centre ; they are divided by a partition, which descends from the lower surface of the corpus callosum, and rests upon the fornix. This septum of the ventricles is transparent, and consists of two laminae, and each of these consists of medullary and cineritious matter. * Betwixt these la- minae is the cavity of the septum lucidum. t The size and shape of this cavity differs in a variety of subjects. It is of a triangular shape, and from eighteen to twenty lines in length, f It has a fluid exhaling into it like the ventricles, and is by some counted as a fifth ventricle: according to Santorini it opens in the base of the brain, opposite to the union of the optic nerves. Vieussens describes it communicating with the third ven- tricle. § Winslow also has seen it reaching a great way backwards, and conceives it to open into the third ventricle. Soemmerring describes it as large in the middle, contracted backwards, and having no communication; but he asserts that it is shut in on every side. || In the base of the brain we find a narrow longitudinal sulcus betwixt the pedunculi of the corpus callosum. In the bottom of this cavity there is a medullary lamina, which Vicq d’Azyr calls “ Cloison d la cavite du septum lucidum.” And the sulcus he calls “ Fosse tite la base, du septum lucidum.” By a careful section of this medullary substance, we lay open the cavity of the septum lucidum. THE SEPTUM LUCIDUM. LATERAL VENTRICLES. Under the corpus callosum and medullary centre, and on each side of the septum just described, are the lateral ventricles. They are dis- tinguished into right and left. They are of a very irregular shape, stretch- ing into three prolongations or cornua, whence they have the name of tricornes. They are the great ventricles of the brain; the third and fourth being comparatively very small. What may be considered as the principal chambers of these ventricles are formed betwixt the corpus * Vicq d’Azyr. f It was discovered by Silvius. See also Santorini- 1 Sabbatier. 5 “In qua pellucidam non raro reperimus aquamque haud dubie in tertium illabitam ven- “ triculum.” Vieussens de Cerebro, p. 59. !} He Corporis Hurnaui Fabrica, tom. iv. p. 55. 48 OF THE VENTRICLES OF THE BRAIN. callosum, the medullary substance forming the centrum ovale, and the convexity of the corpora striata and thalami nervorum opticorum. Fol- lowing the cavity forwards, we find what is called its anterior horn or sinus; it is formed betwixt the more acute convexity of the corpus stria- tum and the anterior part of the corpus callosum: the posterior horn stretches into the posterior lobe of the cerebrum, which rests upon the tentorium. It makes a curve outwards, and at the same time inclines a little downward. The inferior or descending horn is like the continued cavity of the ventricle : it takes a curve backwards and outwards, and then turning forwards and downwards, it descends into the middle lobe of the brain. The lateral ventricles do not terminate in the others by any of those prolongations; but they communicate, upon a very high level, with the third ventricle and with each other, by a wide opening, formed under the fore part of the arch of the fornix. This communication we easily find by following the choroid plexus forward and under the fornix: it is a space betwixt the most anterior part of the convexity of the optic thalami and the anterior crura of the fornix. OF THE PARTS SEEN IN THE LATERAL VENTRICLES. The fornix is a medullary body, flat, and of a triangular shape: its lower surface is towards the third ventricle : its lateral margins are in the lateral ventricle. On its upper surface it supports the septum lucidum, or partition of the two lateral ventricles, and under its most anterior part is the communication betwixt the lateral ventricles and the third ventri- cle. * One of the angles is forward, and the other two towards the back part: it rests chiefly upon the thalami nervorum opticorum, but it is separated from them by a vascular membrane, which is continued from the external pia mater, and which stretches into the brain betwixt the posterior part of the corpus callosum and tubercula quadrigemina. This membrane connects the plexus of the lateral ventricle. The fornix leaves betwixt it and the convex faces of the anterior parts of the corpo- ra striata, a triangular space, which is in part occupied by the septum lucidum. O The extremities of this body are called crura. The posterior crura coalescing with the corpus callosum, (which is continued downwards posteriorly,) are prolonged upon the edges of the hippocampi, and the anterior crura, forming the anterior angle, being close together, bend downwards before the anterior commissure, and are connected with it: they then bend round the thalami, and may be traced into the crura cere- bri ; or, according to others, they form the corpora albicantia. f Those pillars or crura of the fornix are fibrous in some slight degree like a nerve. This is to be observed by cutting them either across or in their length.]; Upon the lower surface of the fornix there are lines like those of the corpus callosum, and which are erroneously conceived by many to be the impression of the vessels of the velum. It is this lower surface of * Of this communication see farther in the Anatomy of the Brain, illustrated by engravings. I Two white bodies seen on the base of the brain behind the infundibulum. [The crura of the fornix very unequivocally commence within these processes.] J. D. G. 1 Vicq d’ Azyr, Acad. Scien. 1781, p. 517. OF THE VENTRICLES OF THE BRAIN. 49 the fornix which is called lyra, corpus psalloides, it being compared to a stringed instrument. OF THE HIPPOCAMPI, OR CORNUA AMMONIS, AND OF THE TENIA HIPPOCAMPI. These are parts to be seen by following the posterior crura of the fornix. They are covered by a soft vascular substance, the plexus choroides. We have observed, that upon the back part, the fornix ad- heres to, or is continuous with, the corpus callosum. We shall find also that its posterior crus on each side divides into two laminae of medullary matter: the one of these is continued into the cornu ammonis, and the other (being the anterior of these portions) forms the tenia hippocampi. The hippocampus is narrow at its commencement in the posterior crus of the fornix ;* but is enlarged as it descends, following the course of the inferior prolongation of the lateral ventricle towards the base of the brain. It is, indeed, merely a relief or particular convexity of the floor of this lower horn of the ventricle, like a pad. The inferior extremities of the hippocampi on each side turn inwards, pointing to the crura cere- bri, and taking thus a curve like a ram’s horn, f In it whole extent the hippocampus consists of internal cineritious substance, and a superficial layer of white medullary matter. The tenia hippocampi, or corpus fimbriatum, is the prolonged margin of the fornix: it is merely the thin edge of the hippocampus, which follows in the whole of its circuit, and terminates in an acute point near its bulbous extremity in the inferior horn of the lateral ven- tricle. The lesser hippocampus or colliculus, is a relief or convexity in the floor of the posterior horn of the ventricles, which may be traced backwards from the crura of the fornix. It has the same relation to the fornix which the greater hippocampus has, and lies in the posteri- or horn or prolongation of the ventricle into the posterior lobe of the brain, in the same way in which the great hippocampus lies in the inferior horn or prolongation of the ventricle into the middle lobe of the brain. The velum and plexus require to be taken away before we can fully understand the situation of the third ventricle, or of those tubercles which are but partially seen in the lateral ventricles. The velum vasculosum lies in the centre of the brain, and extends from the surface inward betwixt the posterior lobes of the cerebrum and the cerebellum, then betwixt the corpus callosum and nates and testes, and then under the fornix. It forms thus a great communication be- twixt the external and internal membranes of the brain. As it lies under the fornix, that medullary lamina adheres to it, while the velum again adheres to the thalami nervorum opticorum, which are beneath it. Its * la speaking of the origin of the hippocampus as from the fornix, I mean simply that the student having gained the knowledge ot the one part of the brain may trace the others front their relation to it, and that, understanding the situation and relation of the fornix, he traces its crura until he finds them terminating in the hippocampus. We might fully as well say that the hippocampi are formed from the posterior part of the corpus callosum, for they are the same medullary matter continued. f Betwixt the extreme point of the hippocampi and the crura cerebri (when the base of the brain is turned up) we can insinuate the probe into the inferior horn of the ventricle, with- out piercing the substance of the brain, but merely tearing the pia mater. 50 OP THE ventricles of the brain. margin seems to be terminated laterally by the choroid plexus (when we view it after raising the fornix); but it is not strictly so, for the choroid plexus is continued with the membrane of the ventricles, and has no where a termination. For the vascularity of this membrane, turn to what has already been said in speaking of the internal veins of the brain. Seeing how the plexus choroides are formed and connected, they can- not be strictly said to have either beginning or termination \ they are the connected folds and plicae of the internal membrane of the ventricles loaded with vessels ; but to describe them intelligibly we must, notwith- standing, trace them in this manner. The plexus of the lateral ventricles rise from the bottom of the inferior horns of these ventri- cles (called the digital cavity), betwixt the pedunculi or crura cerebri and the termination of the hippocampi; they lie like fleshy bodies in that lower horn. As they rise into the superior level, they are at their great- est size (there they have often a diseased appearance, being hard, and -as if schirrous or full of little vesicles or hydatids) ; they then pass for- wards and inwards, diminishing in thickness, and approaching gradually until they coalesce under the fornix, immediately behind the communi- cation betwixt the ventricles. The plexus of the third ventricle, formed by the union of those of the lateral ventricles, turns back upon the lower surface of the velum, and is comparatively very small. If my reader has any difficulty in comprehending the relation and place of the velum interpositum, he has only to notice the place of the choroid plexus, lying the one in the left and the other in the right lateral ven- tricle ; then he is to lift the fornix and he will discover a vascular mem- brane passing betwixt the plexus of the right and left sides. This is the velum or diaphragma. The corpora striata are smooth, cineritious convexities in the fore part of the lateral ventricle. They are somewhat of the shape of a pear ; they are obtuse forwards ; they approach each other towards the fore part with a regular convexity, and they are narrow as they pass backwards, separating at the same time ; their posterior extremity being as it were pushed out by the thalami nervorum opticorum. These last lie more under the back part of the fornix, and are more concealed when the lateral ventricle only is laid open. The corpora striata are so called from the intermixture of the medullary matter in their substance, which gives the appearance of striae when they are cut. They descend down to the base, and are intimately connected with the crura cerebri. The striae of medullary matter pass from above downwards, they therefore appear in the horizontal sections of this body like white points. A su- perficial horizontal section of the corpora striata shows those striae con- nected with the medullary matter of the middle and posterior lobe. A deeper incision brings into view a mass of cineritious substance betwixt those striae and the medullary matter of the middle lobe. Another in- cision shows the course of the striae altered, and brings into view the connexion betwixt the corpora striata of each side, by means of the an- terior commissure. The commissura anterior is a cylindrical medullary cord, which unites the fore and lower part of the corpora striata, and which spreads its connexions for a full inch and a half into the middle lobe of the brain upon each side. We see it stretched transversely immediately under the anterior crura of the fornix. It is in figure like a bow ; its extremi- OF THE VENTRICLES OE THE BRA Iff. 51 ties stretching (with a convexity forward) into the middle portion of the brain towards the extremity of the fossa Silvii, where it terminates in the medullary matter of the middle lobe of the brain. The thalami nervorum opticorum are hid by the posterior angles of the fornix, and the plexus choroides : we do not see them fully until we have lifted the fornix, and the velum or membrane which stretches under the fornix. They are somewhat of an irregular oval shape ; they are whiter than the corpora striata, their surface being chiefly of medul- lary matter. Internally they are cineritious ; and the medullary and ci- neritious matter is blended in striae like the anterior tubercles of the ven- tricles or corpora striata. The thalami nervorum opticorum, having their convex surface towards each other, unite under the fornix by what is called the commissura mollis, in opposition to the commissura magna, which is the corpus cal- losum ; the commissura anterior, which unites the fore part of the cor- pora striata; and the commissura posterior, which is yet to be described. This soft commissure of the brain, or the union of the optic thalami, is so soft that the slightest force will tear it, or in dissection, the parts being unequally supported, the thalami will be separated and this con- nection lost.* After such separation of the tubercles, there remains ve- ry little appearance of their having been united. Sabbatier, after the most careful dissection, says expressly that he could never observe this union; and he conceives, that in the smoothness of the contiguous sur- faces he has a proof of there never being such a union ; but he goes on to say, “ The fruits of my research were, that I constantly found a soft “ cord of a cineritious colour, and about a line, or a line and a half in “ diameter passing betwixt them.” I have seen, when the ventricles were distended in hydrocephalus, and the communication betwixt the three ventricles enlarged to a square ca- vity of nearly an inch in diameter,+ that this union was drawn out to some length, but still was above half an inch in diameter. The com- missura mollis is exceedingly soft, of a cineritious colour, and vessels are sometimes seen to cross upon its surface. It seems to be the con- tinuation of the grey or cineritious substance which covers the internal surface of the optic thalami. J Towards the fore part of the thalami we have to observe a peculiar eminence or convexity, viz. the anterior tubercles of the optic tha- lami. In making a horizontal section of the thalami, we find that we cut across a medullary streak or cord which descends from this tubercle to the mamillary processes, or corpora albicantia, in the base of the brain. § Its course is deep in the substance of the brain, and somewhat oblique. The limits of the thalami externally are contiguous to the corpus stria- tum, but betwixt them there intervenes a white medullary tract, which is contiguous to the medullary striae, and which, as it marks the li- mits of the two great tubercles of the lateral ventricles, takes a course inwards towards the anterior pillars or crura of the fornix and mid- dle of the anterior commissure. The surface of this tract, as seen in * Morgagni and Vicq d’Azyr say (hey have seen (his commissure double, + In quadrupeds the adhesion is more extensive. | Mais il n’y a point de continuity, propreineat dite, entre la substance intime de cep couches et la commissure molle dont ill s’agit. Vicq d’Azyr, Plane, de Cerv. p. 23. See Vicq d’Azyr, plate xii. de 1’Acad Royale. 1781, p. 528. and plate 2 fig. 5. 52 OF THE VENTRICLES OF THE BRAIN. the lateral ventricle, is the tenia semicircularis geminum, which we shall presently more particularly describe. To understand the further connexions and importance of the optic thalami, we must dissect the base of the brain. There we find that it is through the corpora striata, and the thalami nervorum opticorum, that the crura cerebri establish their extensive connexion with the internal mass of the brain; particularly we find that the crura shoot up into the back and lower part of the thalami. Here on the lower part also we may observe the tractus opticus, which we may trace backwards from the optic nerves. They surround the crura cerebri with a semicircular sweep, swelling out at the same time, and terminating in three considerable tuberosities: they are finally confounded with the lower part of the optic thalami; at the same time there runs up a division into the nates. The tenia semicircular geminum is visible on the upper part of these convexities in prosecuting the dissection from above; it is the tract of the medullary matter, which is betwixt the two great tubercles of the lateral ventricle, the corpus striatum and thalamus nervi optici. To- wards the fore part of this tract its surface is covered with a layer of a semi-transparent greyish matter, through which we see the veins which pass from the surface of the corpora striata to join the vena Galeni. Sab- batier makes the anterior extremity of this medullary body join the ante- rior pillar of the fornix. Haller makes it join the anterior commissure; and Yicq d’Azyr says they separate again, where they seem to unite forwards and lose themselves on the corpora striata. Their posterior extremities are lost in the hippocampi; they thus form a kind of longitu- dinal commissure which establishes a communication betwixt the fore and back part of the cerebrum. OF THE THIRD VENTRICLE. The third ventricle does not at all answer to the conception we form of the ventricles from the lateral ones. It is a mere sulcus, lying betwixt the thalami nervorum opticorum, and betwixt the crura cerebri, which are continued down from these tubercles. It is a longitudinal slit, rima, or gutter-like cavity, which is made irregular, and is divided by the union of the optic thalami : and finally, it is canopied by the fornix and vascular velum which stretches over the thalami. * The third ventricle opens forward and upwards into the two lateral ventricles, and under the common communication it opens into the in- fundibulum. Backwards it is continued by a canal which passes under the tubercula quadrigemina, or nates and testes, into the fourth ventricle. The bottom of the third ventricle is closed by a small stratum of cineri- tious matter, cloison pulpeuse du troisieme ventricule; this fills up the space betwixt the junction of the optic nerves and the anterior commis- sure. We see it when dissecting the base of the brain. Lifting the optic nerves, we shall find it strengthened by the pia mater, and consisting of striae which pass obliquely backwards and downwards, and some of which, while they adhere to the optic nerves, pass into them. * “ Hanccaveam ventriculum tertium vulgo vocantj quae et ipsa cum plena sint omnia nib;' w est nisi contiguorum tbalanrorum limes.” Haller. OF THE VENTRICLES OF THE BRAIN. 53 As we have found that the pia mater could be traced into the lateral ventricles, and as by tearing with the probe the connections of those membranes, we could penetrate into the lateral ventricle without piercing the substance of the brain ; so here we can penetrate into the third ven- tricle, which is deepest of all; and also into the fourth, without lacerat- ing the substance of the brain. Thus after raising the vascular mem- brane of the base, we can pass a probe under the corpus callosum back- wards into the third ventricle, and by raising the cerebellum from the medulla oblongata, and separating the adhesions of the pia mater, we get access to the fourth ventricle. We conclude, then, that the ven- tricles are not formed, as we should at first conceive, in the substance of the brain, but that they are formed by the replication and foldings of the convolutions of the brain. OF THE JNFUNDIBUEUM. As I have explained in my tables of the brain, there is much confusion regarding the terms vulva and anus. Vulva is the space by which the three ventricles communicate, as seen when the fornix is lifted, in pro- secuting the dissection from above downwards, viz. betwixt the thalami nervorum opticorum and before the commissura mollis. The anus is be- hind this commissure, and near the nates and testes; both these are mentioned as communications betwixt the ventricles ; but we know that the union of the plexus choroides, of the two lateral ventricles, and of the termination of the velum under the anterior part of the fornix, leaves the vulva free. But the velum spreading over the thalami, and under the posterior part of the fornix, covers the anus; and it appears as a communication similar to the other only when the velum is torn up. If we pass a probe gently downwards and forwards from the vulva or foramen commune anterius, or communication betwixt the ventricles, we pass it into the infundibulum. The infundibulum is a funnel of a soft cineritious matter, which leads from the bottom and fore part of the third ventricle towards the glandula pituitaria, which is seated in the sella turcica of the sphenoid bone. The infundibulum is formed of cineritious matter, which is continued from the bottom of the third ventricle, and which adheres to the back part of the optic nerves ; or, according to Wharton, of an external mem- brane with cineritious matter internally. Its cavity becomes contracted before it reaches the glandula pituitaria. Whether it be really capable of conveying the fluids of the ventricles, or whether it be actually per- vious, is likely to remain a disputed point. Tarin, and M. Adolphus Murray, and Haller, believe with the oldest writers that it is pervious. Soemmerring and Vicq d’Azyr have in their experiments found it shut.* But to the opinion that the infundibulum conveyed the superfluous mois- ture from the ventricles, it did not seem necessary to Vieussens that we should find it to have a cavity in all its length. He conceived that where the apparent cavity terminated, less visible pores were continued towards the gland. * “ Sed non ad apicem usque pervium.” Soemmerring 54 OF THE VENTRICLES OF THE BRAIN. INFUNDIBULUM AND PITUITARY GLAND. What is called pituitary gland is a reddish body of a gland-like appearance, which is seated in the sella Turcica of the sphenoid bone. It is plain upon its upper surface, or rather perhaps a little hollowed, of a globular shape below, and having a division into two lobes. The in- fundibulum terminates in it, piercing the dura mater, a thin lamina of which spreads over the gland. The gland lies surrounded with the cir- cular sinus, and has the cavernous sinus upon the sides, into these last, vessels have been seen to pass from the gland,* which, as Soemmer- ring observes, were probably veins. A distinction of substance has been observed in this gland, and it is by some considered as a part of the brain, or being like the cineritious substance, it has been supposed that it gave nerves to the fifth or sixth pair. It was conceived that this body receiving the superfluous moisture of the brain, conveyed it into the nose; or into the neighbouring sinuses.t To countenance this opinion, there was no want of cases proving the accumulation of the fluids of the ventricles, in consequence of the schir- rus of this gland, while in truth dissection has shown no connexion betwixt the diseases of the ventricles and pituitary gland. M. Littre gave both a vascular structure and muscular fibres to this body, and con- ceived that its operations brought down the water and air from the ven- tricles of the brain.! THE TUBERCULA QUADRIGEMINA. The tubercula quadrigemina, or nates and testes, are seen when we continue to lift back the posterior part of the fornix and corpus callo- sum, and when we have lifted back the velum with the vena Galeni. We find, in doing this, that the velum is connected with the pineal gland, which is seated upon these tubercules. The tubercula quadrigemina are not in the cavities or ventricles of the brain, but are seen upon lifting and turning forward the posterior lobes of the cerebrum from the cerebellum. These four tubercules are behind the third ventricle, and above the fourth. As they are immediately in the centre of the brain, they form a kind of commissure, and they both communicate with the tubercles, from which the tractus opticus emerges. The uppermost two are the nates, the lower are the tf.stes ; the former are less white than the lat- ter. A little under the inferior tubercle we find a small tract of medul- lary matter which extends to the thalami nervorum opticorum, and the crura cerebri. And from the lower part of the testes there projects backwards, connecting itself with the crura cerebelli, a thin medullary lamina, which is the valvula Yieussenii, processus a cerebello ad testes, or velum interjectum. Behind the posterior tubercle, or from this medullary lamina itself, the fourth pair of nerves take their ori- * Adolph. Murray de Infundib. Lower, Tract de Corde. » SeeLittre, Mem. del’Acad. des Sciences, 1707 OF THE VENTRICLES OF THE BRAIN. 55 gin. Sometimes those four tubercles are of the same size ; sometimes the posterior, sometimes the anterior tubercles, are the larger : a per- pendicular section of them shows a mutual communication of strioe of medullary and cineritious matter, but those are seen faintly. THE PINEAL GLAND. Peduncule of the pineal gland. Third ventricle Posterior commissure Pineal gland. Tubercula quadrigemina. The pineal gland is a little glandular-like body, seated above the tu- bercula quadrigemina, and behind the thalami nervorum opticorum : it is fixed, says Winslow, like a button. It consists of cineritious matter co- vered with the pia mater ; its base is surrounded with medullary mat- ter ; it adheres firmly to the velum vasculosum, and is apt to be displac- ed or torn from its pedunculi in lifting that membrane. It is a small soft greyish body, irregularly round, or of the figure of a pine-apple ; or, of all things, likest the heart of a frog.* Its pedunculi, or footstalks, pass out from a transverse medullary base, which unites it to the posterior commissure. Those pedunculi pass on each side to the thalami nervo- rum opticorum (leaving a passage under and betwixt them to the fourth ventricle). Their extremities pass forward upon the internal surface of the thalami nervorum opticorum, and are united to the anterior crura of the fornix. Vicq d’Azyr remarks, that although the ideas of Galen and Descartes and a crowd of others, are remembered only with ridicule, there are still some peculiarities in the situation and connexion of this body, which mark its importance. It is composed of cineritious substance ; it is in fact, a pro- longation of the substance of the brain, and by its pedunculi, which are like two nerves, it is connected with the thalami nervorum opticorum, with the fornix, and consequently with the corpus callosum, the hypocampus and corpora albicantia, which are themselves the centre of union to seve- ral medullary cords : therefore he concludes that the pineal gland must be an important organ. + The pineal gland has often in it little peculiar grains and calculi, re- sembling bone in its constituent parts. \ It has a great variety of form * Ruysch considered the substance of this gland as different from that of the cerebrum or cerebellum, and different, also, from all other glands. [It is entirely ridiculous to call it “ a gland ” at all.] J. D. G. fM6m.de l’Acad. Royal, An. 1781, p. 533. See Observ. par M. Meckel sur le Gland pineal, sur la cloison transparente, et sur l’origine du nerf de la septieme paire. L’Acad. Berlin, 1765. t Malacarne, part ii. p. 81. Acervulus: Meckel, M6m. de l’Acad. des Sciences a Berlin, 1755. fig. 1. b. b. Vicq d’Azyr, tab. xxvii. Soemmerring, p. 63. 56 op the ventricles of the brain. and size; sometimes hollow, and there is also a sinus found in it. I have found it surrounded with pus in an idiot boy, who was accustomed to wander about the Leith glass-houses. He died with symptoms of hy- drocephalus, and in his ventricles, accordingly, there was found much fluid. Malacarne gives a case of its having degenerated into hyda- tids, like a cluster of grapes; I have also seen this appearance. ■ In some cases it has not been found upon dissection. The base of the pineal gland is connected with the posterior commis- sure of the brain. This commissure is seen like a cord, or like the an- terior commissure, towards the back part of the third ventricle, before the tubercula quadrigemina, and above the iter and quartum ventriculum. Betwixt this commissure and the base of the pineal gland, we have to observe two or three medullary filaments, not passing from the gland, but lying parallel to the commissure. But this part of the brain, which ap- pears like a cord, does not deserve the name of commissure ; it does not pass on each side into the substance of the brain, as the anterior one does ; it is lost in the neighbouring border of the medullary matter, and is merely this matter reflected, so as to present a rounded edge. POSTERIOR COMMISSURE. CEREBELLUM. The cerebellum is one of the grand divisions of the brain. It weighs about a sixth or seventh part of the whole brain ; it lodges in that part of the base of the cranium which belongs to the occipital bone, and has the tentorium stretched over it; it is divided into a central or middle part, and two great lateral portions or lobes. The central, or middle part, is anterior to the lobes, and betwixt them and the cerebrum; this is the part very commonly called, from its appear- ance, the vermiform process; and upon the sides we have two por- tions, sometimes called lateral vermiform processes. The term process here, is certainly improper : for it implies that those parts are extended from the lobes ; whereas the processus vermiformis is the part we see in all creatures which have a spinal marrow ; while the lateral lobes or hemispheres are the superadded parts, and bestowed upon the higher animals. The cineritious matter of the cerebellum is external, like that of the great mass of the cerebrum ; but the medullary internal matter presents an appearance somewhat different, for on a section being made, it ap- pears branching like a tree, and has been called arbor vitw. The concentration of the medullary matter, from the two sides of the cerebellum, towards the nodus cerebri, forms what are called the crura cerebelli. One portion of this medullary matter forms the pons or no- dus, and constitutes the commissure uniting the lateral divisions of the cerebellum; the other division of the crus is the corpus restiforrne, which runs into the medulla oblongata. In dividing these crura we find in each of them the stain,of yellow- ish matter, which is called corpus rhomboideum, or corpus denta- tum. OF THE VENTRICLES OF THE BRAIN. 57 OF THE FOURTH VENTRICLE. The fourth ventricle is the ventricle of the cerebellum; it descends perpendicularly before the cerebellum ; it is inclosed on the upper part by the valvula Vieussenii ; on the sides by the crura cerebelli; behind, by the pars media ; below, by the medulla spinalis, and is closed there by the pia mater. When, from the third ventricle ; we pass our probe obliquely back- wards and downwards under the posterior commissure, it passes into the ITER AD QUANTUM VENTRICULUM, Or AQUEDUCT of SlLVIUS. This passage to the fourth ventricle, goes before the tubercula quadrigemina. The valvula Vieussenii, it was supposed, prevented the falling down of the moisture of the other cavities into the fourth ventricle * : it is more properly called the processus cerebelli ad testes, being a me- dullary lamina spread over the ventricle and betwixt, the crura cerebelli, as they rise from the internal medullary part of the cerebellum. From the aqueduct there is continued down upon the fore part of the fourth ventricle a kind of fissure, which Vesalius, conceiving it to have some resemblance to a writing quill, called calamus scriptorius. The same fissure or furrow is continued down some way upon the spi- nal marrow. There pass up obliquely outwards, on each side of the calamus scrip- torius, medullary lines, three or four in number, but sometimes seven are observed.! In the fourth ventricle, as in the others, are some convolutions of the plexus choroides; these are on each side at the termination of the ver- mis ; they are continued out upon the base of the brain, and are seen exposed betwixt the seventh and eighth pair of nerves. OF THE BASE OF THE BRAIN AND ORIGIN OF THE NERVES. We have anticipated much that might have fallen to be treated of in this division of our subject; but my intention here is to give a connected view of the parts, as seen when we have raised the brain from the skull, and when, having the base presented to us, we are about to enumerate the origins of the nerves. The first appearance which strikes us, is the great proportion of the medullary matter in the base of the brain; the whole surface of the brain seen from above, was cineritious, but below, the central medullary part of the brain is seen emerging from the covering of the cineritious matter, and, gathering together from the several internal medullary processes of the brain. Those great medullary prolongations of the cerebrum and cerebellum are the crura, and from them the principal nerves arise. Shall we here yield to the fascination of new doctrines, and derange the demonstration according to the method of Dr. Spurzheim? For the whole question amounts to this . shall we describe these crura of the cerebellum coming down from the brain, or going up and expanding into it ? It is obvious, I think, that these are only modes of speaking ; for we have no authority in nature for following the nerves, and processes * Alveus Silvii. * Haller, Physiol, tom. iv. p. 78 58 OF THE VENTRICLES OF THE BRAIN.' of nervous matter, in one direction, more than another.* If, therefore, I continue to say, that the crus cerebri “ comes down,” I mean only that from the internal parts of the brain, which, from previous description, my reader may be supposed to know is connected or continuous with the part I am now describing. The crura cerebri are composed of a white fibrous medullary mat- ter, in which also there is a mixture of cineritious substance. They are formed from the whole central medullary part of the cerebrum; or more immediately from the inferior and lateral part of the corpora striata, and from the superior and internal part of the thalami nevorum opticorum : and from the conflux of medullary matter, from the anterior and posterior lobes of the cerebrum. They are, in short, formed by the converging strim of the cerebrum. From all these various parts, the medullary matter may be traced downwards and backwards, and concentrating into a smaller space, to form the crura. The crura, contracting their diame- ters, unite together at an acute angle, and are united to the pons Varolii, or nodus cerebri, they pass on, under the pons Yarolii, to form the ante- rior columns of the medulla oblongata, and, as they unite with it, they raise it into the eminences, called corpora pyramidalia. In those pro- cesses of the cerebrum, the cineritious and medullary substances mingle with some degree of confusion; so that when we make a section of the crura cerebri near to their union with the pons Varolii, we observe a sub- * We cannot avoid attributing this observation to the force of the author’s prejudice. The best of all reasons can be given for studying the brain and nerves as Spurzheim does, because it is according to the inode in which the formation of these parts originally takes place. .T, d. g. op the ventricles of the brain. 59 stance of a dark-brown colour. The locus niger crurum cerebri of Yicq d’Azyr. Behind the union of the optic nerves, and nearer these crura, we per- ceive two white bodies, called the corpora albicantia. Anterior to these is the infundibulum.—The tuber cinereus. In the angle of the union of the crura cerebri, behind the corpora albicantia, and before the protuberance of the pons Varolii, we observe a matter less perfectly white than the surrounding medullary substance, which forms a floor to the third ventricle. This part is perforated with a great many holes, for the transmission of blood-vessels, and is the soustance perforee of Yicq d’Azyr.* CRURA CEREBELLI. The crura cerebelli are more exposed than those of the cerebrum. A medullary mass is seen to come out of the lateral portion of the cere- bellum, and join itself to the posterior part of the medulla oblongata. This has been called corpus restiformf., or processus cerebelli ad medui lam oblongatam. That is, they have described this portion like a cord of connexion, or like a prolongation of the cerebellum, to which as a mode of expression, I say again, there is as little rational objection as to the mode of Spurzheim. It is, I believe, quite impossible to avoid the language of metaphor here. If I use the words divide or split, I am tracing, as it were, in a course for which, I again acknowledge, I have no authority in the thing itself. These crura, then, are formed by the union of the internal medullary part of the cerebellum, or the arbor vitae, and also by a medullary prolongation from the processus vermiformis. They are composed of medullary matter, except near the pons Yarolii, where we observe a mixture of coloured striae : and on dividing one of the crura longitudinally, as it comes out of the cerebellum, we find a mass of cineritious coloured matter. This is the corpus dentatum, or rhom- boideum of authors.t PONS VAROLII. The pons varolii, tuber annulare, or nodus cerebri, is form- ed by the union of the crura cerebri and cerebelli; those names are almost descriptive of its shape and relation to the other parts. Va- rolius, looking upon those parts inverted, compares the crura cerebri to a river passing under a bridge, and thetice named it Pons. The nodus cerebri, again is a name well applied, since this medullary eminence has much the appearance of a knot cast upon the medullary processes of the cerebrum. On the surface of this medullary protuberance there are many trans- verse fibres, which, uniting in the middle, form a kind of raphe, which, upon a superficial section, shows a longitudinal medullary line. The fibres upon the surface of this body are uniform and parallel to each * Vicqd’Azyr makes three divisions of this soustance pcrjorte—1st. At the roots of the tubercles, from whence the first pair of nerves emerge betwixt the roots of those nerves, and near the origin of the optic nerves. 2d. Those I mention betwixt the crura cerebri. 3rd. On the outer contour of the optic thalami. f Sive serratum of Vieussens: Le corps ou dentele of Vicq d’Azyr. 60 OF THE VENTRICLES OF THE BRAIN. other in the most projecting part; but upon the sides, they disperse to give place to the fifth pair of nerves.* A deep incision of the pons Varolii, while it shows the union of the crura cerebri, cerebelli, and pons Varolii, also shows the white medul- lary tracts which extend from the crura cerebri through the pons Varolii, to the corpora pyramidalia; a little higher up, part of these strise pass through the locus niger crurum cerebri. We see also the transverse fibres of the medullary and cineritious substance, which make a right angle with those longitudinal tracts. On the whole, though the pons Varolii differs in form and place from the commissura magna cerebri, yet I am of opinion, that it stands in the same relation to the lateral portions of the cerebellum, that the corpus callosum does to the cerebrum. That it is the great commissure of the cerebellum, uniting its lateral parts, and associating the two organs. Anatomists have sought to explain a very curious phenomenon, by sup- posing that there is a decussation of the nervous filaments in the nodus or pons. It has often happened that an injury to the one side of the brain, an ulcer or tumour on one side, caused a loss of power in the op- posite side of the body t, and the latest authority we havej proves that a tumour on the one side of the pons Varolii, will produce an effect on the other side of the body. But no decussation can be observed ; fibres, as I have said, run across like commissures, but the tract of matter is is direct and parallel, not oblique. I am tempted to think there must remain much obscurity on this subject of the decussation of the fibres of the brain, or origin of nerves. I have found that the effect is not constant. An ulcer in the hemisphere of the cerebrum produced weakness in the same side ; and in one well marked case of hydrocephalus, when the brain on dissection was equally affected on both sides, the one side of the body was convuls- ed and drawn up, and the other side motionless. This is not a singular occurrence ; I have seen the eyes, face, and tongue in perpetual motion; but the action entirely on one side, the paralysis on the other, while both lateral ventricles were full of water, and the disorder of the brain, as seen on dissection, equally affecting both sides of the organ. MEDULLA OBLONGATA. The medulla oblongata is the prolongation of the substance of the crura cerebri and cerebelli, frorn the pons Varolii ; it is consequently the continuation of the after giving off the nerves that pass through the foramina of the skull, enters the canal of the spine to supply the spinal nerves. The medulla oblongata is marked at its upper end by a deep sulcus dividing it from the pons Varolii: but towards the spinal cavity it decreases in thickness, and there is no natural distinction * Some have divided the surface of the pons Varolii, into three divisions or bands: 1. The su- perior band, which winds round to embrace the ( rura cerebri ; ‘2. the middle band, and 3d the inferior band, the fibres of which intermingle with those of the crura cerebolli. They likewise subdivide the crura cerebelli; and that part which we have called corpus restiforme, has been named pedoncule inferieure of the crura cerebelli. But these are unmeaning minutiae, the attention to which has of late retarded the improvement of useful knowledge. f The observation has descended from Hippocrates, and the explanation that it depends on a decussation of the roots of the nerves is from Aretans. | The Medico-Chirur. Transactions, VII. OF THE VENTRICLES OF THE BRAIN. 61 or sulcus to mark the point where the medulla oblongata ends, and the medulla spinalis begins ; nor perhaps is the medulla oblongata to be considered in any other light than as the beginning of the spinal marrow. * When it passes the foramen magnum, it ceases to be called the medulla oblongata, and is more properly medulla spinalis. We have to observe certain eminences upon the fore part of the me- dulla oblongata, viz. two corpora pyramidalia, and two corpora olivaria. The corpora pyramidalia, so called from their shape, are those in the middle. There is formed betwixt them and the pons Varolii (being three tubercles placed together) a little sulcus, which some have called the foramen CjEcrm. Betwixt these eminences called pyramidalia, there is a longitudinal fissure, in the bottom of which there may be observed transverse little cords, which are like commissures connecting the two sides of the medulla oblongata; and the corpora pyramidalia which are prolonged downwards, twist, and form a decussation. The corpora oli var,ia lie upon the outside of the corpora pyrami- dalia. They are distinct oval cohvexities rising from the fore and lateral parts of the medulla oblongata. They are of a very peculiar structure, for anatomists had observed a mixture of a yellow or cineritious-colour- ed matter in them ; but Vicq d’Azyr has described a regular oval medul- lary substance, or body surrounded with cineritious-coloured matter, like a miniature representation of the cerebrum itself; he calls it corpus DENTATUM EMINENT!.® OLIVARIS. The corpora restiformia are the projections or cords behind the corpora olivaria, which come down from the crura cerebelli. (Betwixt this column of nervous substance, and the corpus olivare, there is a cord or column which gives origin to the nerves of respiration.) The corpus restiforrne, as it is called, if by that is meant the posterior portion of nervous matter, which goes down from the cerebellum to the medulla spinalis, is double, or forms two columns distinct on the posterior surface of the medulla oblongata. MEDULLA SPINALIS. The medulla spinalis is certainly, in part at least, an elongation of the brain. Its name implies its situation, that it is contained within the tube of the spine. Though chiefly composed of medullary matter, it is not entirely so ; for there is an irregular, central, cineritious substance, through its whole extent, having something of a crucial form when a section is made of it.* There are continued down from the calamus scriptorius behind, and the rima, formed by the corpora pyramidalia, be- fore, two fissures which divide the spinal marrow into lateral portions. On the back part, however, the fissure is less distinguishable. Into the anterior one the little vessels penetrate to supply the cineritious matter with blood. The two lateral portions are divided into an anterior and posterior portion, so that this prolongation has four distinct portions very distinctly seen ; but that there are other columns of different functions in the composition of the spinal marrow, I have given reasons to believe in the introduction. * The surface of the spinal marrow has also been observed to be of a darker colour, and ;n large animals cineritious. (Dr. Monro’s Nervous System.) 62 SUPPLEMENTARY OBSERVATIONS. The tube of the vertebrae is connected by a strong ligamentous sheath, which runs down the whole length within the tube. The dura mater, af- ter lining the internal surface of the cranium, goes out by the great fo- ramen, and forms a kind of funnel; at the occipital foramen it is united firmly to the ligaments. Further down, however, it forms a separate tube. The tunica arachnoidea again adheres loosely to the medullary matter of the spinal marrow, having a kind of secretion within it, while the pia mater closely embraces, and is intimately united to it. Through the whole length of the spinal marrow the arachnoid mem- brane forms a ligamentous connexion betwixt the medullary matter and the sheath or theca A firm slip passes betwixt the roots of the nerves, and being tucked in the form of acute processes at distinct intervals to the sheath, it assumes the form of the teeth of a saw. It is from this pointed appearance that it is called the Ligamentum Denticulatum, or Dentatum. Laying aside authorities, and only contemplating the dissection of the medulla oblongata and medulla spinalis, I would describe them as a great column continued from the brain, and lying embraced and protected by a sort of continued skull, the spinal tube. This column consists of les- ser columns, so that it resembles a Gothic pillar. These different co- lumns, as I have already expressed my opinion, are distinct organs, and give rise to nerves, which are possessed of powers which correspond with the origin or connexion of their roots. SUPPLEMENTARY OBSERVATIONS ON THE DEVELOPEMENT OF THE CENTRAL PARTS OF THE NERVOUS SYSTEM. [The volume of the central portion of the nervous system is general • ly greater in proportion to that of the body, according to the youth of the organism. Until the third month of pregnancy, the spinal marrow occu- pies the whole length of the vertebral canal. It is true, that from this period it begins to gather up, but it is not until the eighth month of in- tra-uterine life, that it assumes the proportions which are subsequently preserved. It is also thicker during the first periods of life than it is af- terwards. The encephalon, excepting the cerebellum, has also a proportionably greater extent. However it must not be thought, especially in relation to this viscus, that greater extent is perfectly synonymous with more voluminous mass; because the parietes of the brain are proportionally thinner than they are at a more advanced age. Until the period of full developement, the encephalon continues to be larger in proportion to the body than it is afterwards ; for between six and seven years, according to Wenzel, and ever after the third year according to Soemmering, it has already acquired the volume and weight it is to preserve during the rest of life. The very imperfect developement of the posterior part of the vertebral column, leaves the spinal marrow and encephalon much more free and disengaged during the first periods of existence. The caliber of the spinal marrow is the more uniform according to the youth of the embryon. The enlargements corresponding to the nerves [From Rieckel ] SUPPLEMENTARY OBSERVATIONS. 63 of the extremities are only developed in proportion as the extremities themselves are formed. The spinal marrow which is entirely solid not only in adult subjects, but from a few months after birth, has at first a canal extending through its whole length which is continuous with the cerebral fissure, and is lar- gest in those places where the spinal chord is enlarged. This canal is not round at first, but elongated from before backwards, and with the exception of the thin lamellae bounding it anteriorly, traverses the entire thickness of the spinal marrow. It thence results that the in- ternal and external surfaces of the spinal marrow are continuous original- ly, that the whole canal is much larger during the first periods of life than at a more advanced age, and that then it is less like a canal, properly speaking, than a fissure which separates almost totally the two lateral halves of the spinal chord. By degrees this canal is closed and con- tracts at the posterior part from without inwards. Subsequently, the spi- nal marrow is folded longitudinally as much before as behind ; hence arise the anterior and posterior longitudinal grooves, which never com- municate with the central canal, as the brain and even the summit of the spinal cord have during life, not only two longitudinal fissures, one supe- rior and the other inferior, but also central cavities, which are separated from these fissures by medullary matter throughout a great part of their extent at least, and by the pia mater throughout their whole course. However, the longitudinal grooves of the spinal marrow are larger dur- ing the first periods of life, and it is not uncommon for the posterior to disappear entirely as the subject advances in years. Although the spinal marrow is at first very much larger in proportion to the whole body than it is in the adult, nevertheless, we readily per- ceive an inverse ratio to be established between it and the encephalon, both on account of the developement acquired by the latter, and the di- minution of the spinal cord. Thus I have found that the proportion of the spinal marrow to the brain was still as 1 to 107, and even 1 to 112 in the foetus at birth and a child of five months ; for the brain of the foetus weighed nine ounces and four drachms, that of the child of five months 21 ounces ; the spinal marrow of the foetus weighed two scruples, five grains, that of the child a drachm and a half. On the contrary in a foe- tus of five months the proportion was as 1 to 63, since the brain weighed six drachms one scruple and eight grains, and the spinal marrow six grains. It was as 1 to 18 in a foetus of three months whose brain weighed thirty six grains and the spinal marrow two. In the adult it is as 1 to 40. These calculations will serve to rectify the estimates which some ana- tomists have given of the difference observed at different periods of life in the respective proportions of the spinal marrow and encephalic mass. The younger the embryon is, the larger is the spinal marrow in pro- portion to the encephalic mass. It is manifestly more voluminous and weighty in proportion to the latter even in the human embryon of three months, both on account of its more considerable size and the smallness of the encephalon ; but the latter soon transcends it more than in the adult, both because it increases very much, and because the spinal mar- row itself diminishes. The younger the embryon is, the more distinct is the medulla oblon- gata from the medulla spinalis, and the open angle between them is more 64 SUPPLEMENTARY OBSERVATIONS. of a right angle. The medulla oblongata is proportionally more deve- loped during the early periods of life, than at a more advanced age ; this may especially be stated of its inferior and anterior part, which concurs in the formation of the brain. The medulla oblongata is still more dis- tinct in the foetus at full time and in the young infant than in the adult, and all its parts, principally the eminences on its inferior surface, the py- ramidal and olivary bodies, are more salient at the same time and separat- ed by more precise limits. This circumstance seems in direct relation with the more considerable developement of the brain. The calamus scriptnrius is much larger in the first periods of exist- ence, because its parietes are thinner, and there is greater distance be- tween them from behind forward. The transverse cord which closes it superiorly, does not exist in the beginning, but it is much more conside- rable during the latter part of intra-uterine life, than in the adult. The white lines which are seen on the floor of the calamus, do not become apparent until some months after birth, while the grey eminences, situat- ed in front of thefn, are visible in a foetus of three months old. The olivary bodies are perceptible from the third month of uterine life ; but at the time the foetus is matured they are only externally formed of cineritious substance. At the third and even at the fifth month of preg- nancy, a small ramified cavity may be discovered within them, which al- together disappears by the sixth month. After they become solid the ci- neritious substance at first ramifies in them in a more simple manner than it does at subsequent periods. The pyramidal bodies are obvious much sooner than the olivary, and are equally in proportion larger in the early state than in the adult. The annular protuberance, or pons Yarolii, does not appear until the third month. It is at first thin and short; its proportional volume to the spinal bulb is still less considerable. The longitudinal groove of the in- ferior surface is shallower in the full formed foetus than in the adult. The cerebellum is developed sooner than the brain in respect to its composition. Depressions are already visible on the middle of its sur- face towards the end of the fourth month of uterine life ; thus the most considerable depressions, which divide the organ into lobes, appear before the small ones, and they are more superficial and simple at first than they are subsequently. Notwithstanding all the researches hitherto made, the manner in which the central mass of the nervous system is formed has not yet been per- fectly demonstrated. Two characters which it offers at all times of life are especially developed during the early periods, the ventricles, and the distinction into two corresponding lateral portions. We may then con- jecture that the central portion of the nervous system is formed in the midst of a fluid, and at its expense; that it assumes the figure of a hollow canal, or that it is developed by plates or cords more or less se- parated by a median line, where they reunite to form a cavity. Accord- ing to the latter hypothesis, the number of degrees of developement which the spinal marrow and brain undergo are greater than in the first, which does not admit the primitive form of simple plates. But there are actually facts which support this view, and although it renders the forma- tion of the central mass of the nervous system more complicated, they must not be set aside for the sake of admiring at all hazards the simpli- city of the operations of nature. The facts alluded to are the almost SUPPLEMENTARY OBSERVATIONS. 65 total] division of the spinal marrow into two lateral portions ; the pos- sibility of separating entirely the anterior cords from each other, and thus to change the spinal marrow into two lateral cords ; the con- siderable breadth and thinness of the medulla oblongata ; and final- ly the total separation of the two lateral halves ef the cerebellum; probably also of the quadrigeminal tubercles, and very certainly of the optic thalami. Thus, the central mass of the nervous system is developed from be- low upwards, without its being determinable whether it is effected by two plates or a single one ; these plates growing from before backward, are curved inwards to meet each other, and blend together at the median line, giving origin in this manner to a semi-canal, and afterwards of a complete canal. This theory is supported not only by the facts which are furnished by the history of the embryon, but also by the develope- ment of the nervous system in the series of animals. The dorsal me- dulla and brain of worms and insects correspond sensibly to the inferior or anterior cords of the same parts in the superior classes of animals, and we may without much difficulty carry these organs to a much high- er degree of organization ; on one hand by mentally adding the superior cords, and on the other by supposing them united together posteriorly ; conditions sufficient to convert the plates or cords which first exist into a canal. The ulterior developement of the central portion of the nervous sys- tem is produced by the growth of the mass which augments the thick- ness of the walls of the ventricles, and contracts the latter themselves. A period then arrives at which the mass, which was originally smooth and even, becomes very unequal, and acquires at the same time a much greater extent. Still later, differences are established in the nervous substance, which is divided into grey and white, a phenomenon which terminates the developement of the intimate structure. In general these different characters are pronounced in parts, according to their order of appear- ance. The spinal marrow is the part which first arrives at perfection in all respects. The quadrigeminal tubercles change little after birth. The cerebellum seems to be an exception to the rule, because, although formed later, it arrives at perfection in respect to configuration and tex- ture a long time before the brain, and even before the annular protube- rance.*] SCHEME AND GENERAL DESCRIPTION OF THE ORIGIN OF THE NERVES OF THE ENCEPHALON AND SPINE. In enumerating the nerves which pass from the cranium, I must now keep to the old way of Willis, counting only nine nerves of the ence- phalon. Because this is a natural method, and can never be entirely exploded. When we open the cranium and look to the nerves, we see them coming off, and taking their course exactly as Willis described them. His enumeration serves the purposes of dissection, therefore I shall first present them according to his arrangement, only reminding my reader, that nerves of very distinct offices are, in this arrangement, bound toge- ther, and take their course through the same foramina. * For the observations of Tiedemann, Spurzheimi &c. See Appendix) A. 66 THE ORIGIN OF THE NERVES. From the olfactory nerve to that which passes out betwixt the cranium and first vertebra, there are nine nerves. 'Carunculcs mamillares Math, de Grad. Processus ad nares. Gonth d’Andernac. Sum par Spigel. 1st pair of Willis. 1st pair. —Olfactory nerves. Nervus visivus seu visorius. Carpi, lm par anti- quorum. 2d pair of Willis. 2d~pair.—Optic nerves. 2um par Fallop. et Vesal. Nerfs moteurs communs des yeux. Winslow. 3d pair of Willis. 3d pair.—-Motores oculorum ' Minor prop ago 3“ Paris, id est 5* recentiorum, Fal- lop. Gracilior radix 3‘i Paris, id est 5 recentiorum. Ve- sal. Nervus qui prope nates oritur.—Eustach. gum par Cortes: et Columb. 4th pair ; or, pathetic nerves of Willis. 4th pair—Trochleares. 5th pair.—Trigemini,Symme- trical nerve of the head, an- swering to the spinal nerves. Nervus anonymus trigeminus mullorum. 3um par Fallop. et Vesal. 5th pair of Willis. Trijumeaux of Winslow. 4Hm par Fallop. Radix gracilior 5* Paris, id est 7i recentiorum Vesal. Par oculis prospiciens Sum par Casp. Bauhini. 6th pair of Willis. Nerfs oculo-musculaires, ou moteurs externes de Winslow. 6th pair.—Abductores. oum par Alexand. Benedict. | 4“m par Carol. Stephan. { 5um par Vesal. et aliorum. | 6um par V. Horne. I Portio mollis, of the Moderns. 'Auditory nerves. | Nervus communi- | cans faciei. Mus- cular, or motor nerve of the face. Respiratory nerve of the face. Distinctus a molli nervus. Fallop. Porlio ut prcecedens 5‘ Paris id est 7i recentiorum. Vesal. Portio dura, of the Moderns. Le petit sympathique, of Winslow. Facial nerve. 7th pair. Glosso-pharyuge- us. j Par vagum. «j Spinal accessory nerve. Qm' ad musculos linguce et faucium tendet. Fallop. Le rameau liDgual de la 8« paire of Winslow. 8th pair d’Andersch. Superior fasciculus of the 8th pair of Willis. Glosso-Pharyngeus. Haller. 8th pair. Grand re- spiratory nerve. Nervus sextus Galeni et aliorum. 5a conjugatio Carol. Stephen. 7um par Alex. Benedict. 6um par Casp. Bauhini. gum par Bidloo et Andersch. 8th pair of Willis. Le moyen sympathique of Winslow. The spinal nerve. 7um par Fallop. Vesal. et aliorum. llum par Bidloo- 10um par Andersch. Par linguale medium, vel nervus Ungualis medium. —Haller. Soemmerring et aliorum. The hypoglossal sub-lingual, or gustatorv. The 9th pair ofWillis. 9th pair.—Lingual. THE ORIGIN OP THE NERVES. 67 10th pair—Symmetrical and 1st spinal nerve. Sub-occipi- tal nerve. 10th pair of Willis. 1st spinal, or cervical nerve of Haller. I count this the first cervical nerve. FIRST PAIR ; OR, OLFACTORY NERVES. The olfactory nerve is soft and pulpy, and soon resolved by putrefac- tion ; therefore, we should not be surprised that it was neglected by the ancients. * It adheres firmly to the lower surface of the anterior lobe of the brain, but it does not take its origin here. It is of a triangular shape, as if moulded to the sulcus in which it lies ; by being sometimes sunk into the sulcus more or less on one side than the other, it has the appearance of being larger on one side than the other. It takes its ori- gin by three medullary tracts 1st, From the corpus striatum ; 2d, From the medullary matter of the anterior lobe ; 3d, From the fore and under part of the corpus callosum. J When a section is made of it, we observe in it a cineritious portion. Towards the fore part, this nerve expands into a bulbous oval lobe, which consists of a semi-transparent cineritious substance. This lies upon the cribriform plate, and from it are sent down the nerves which expand upon the membrane of the nose, and compose the organ of smelling. § SECOND PAIR ; OR OPTIC NERVES. || The optic nerves arise from the posterior part of the optic thalami, and from the tubercula quadrigemina or nates. When we trace the optic nerves backwards into the tractus opticus, we find them adhering to the tuber cinereus, or layer of grey matter, then taking a circle round the crura cerebri, then enlarging, each forms a tubercle towards the back part of the thalamus opticus, and afterwards unites with the posterior tu- bercle of the thalamus opticus; at the same time a division stretches further backwards to the testes, while betwixt the posterior tubercle of the thalamus opticus and the nates, there is also a communication. When those tubercles are fairly exposed by separating the middle lobes of the brain, and dissecting away the tunica arachnoides and pia mater, they are seen smooth, and formed of medullary matter : which is uniformly continued from the one to the other, following their gentle convexities with an uninterrupted surface. Within those tubercles is a mixture of * The olfactory nerve is in brutes a large prolongation of the substance of the brain, and is the proper mamillary processes. Their olfactory nerves have a cavity or ventricle in them, and .it was natural for the ancients to imagine that the pituita of the brain was from this strained through the cribriform plate into the nose. t Or we say that the external root generally splits, having two fasciculi. See Prochaska, lab. 1. Scarpa Annot. Anat. p. 106. | Vicq d’Azyr, M. de I’Acad. Roy. 1781.—“ Breviores fibrae medullares cum longioribus “ exterioribus connex* nonnunquam cineream particulam excipiunt.” Soemmerring, 5 Duverney has shown us, that those nerves passing through the cribriform plate become firm nerves, like those in the other parts of the body. They are to be seen by tearing the membrane of the nose from the bone. |j The optic nerves were the first pair of Galen and many of the older anatomists, they being ignorant of the olfactory nerves. 68 THE ORIGIN OF THE NERVES. cineritious and medullary matter, and especially, there is a distinct streak which passes from the tractus opticus to the nates. * Tracing the optic nerves from their origin in the brain towards their exit from the skull, we find them approaching gradually, and uniting just before the corpora albicantia and the infundibulum. Since the days of Galen, it has been a disputed point, whether there is a union simply of the nerves or a decussation. Fishes have the nerve arising from one side of the brain, passing to the eye of the other side: they cross, but they do not unite. Birds have but one optic nerve arising from the brain, which splits and forms the right and left optic nerves. Vesalius dissected a young man at Padua, who had lost his eye a year before: at the same time he dissected a woman, whose eye had been lost a long while. In the latter he found the nerve of that side smaller, firm- er, and of a reddish colour, through all its extent. In the young man he observed no effect upon the nerve. He also gives a plate descriptive of an instance in which he found the optic nerves pass on to the eyes of the same side from which they take their origin, without adhering at all. Valverda, a physician of Spain, who travelled into Italy, and studied the works of Yesalius and human dissection, says, that at Venice, he had frequent opportunities of assuring himself that there was no decus- sation ; for robbers were punished for the first offence by losing one of their eyes ; and for the second by death. Riolanus, Rolefinkius, and Santorini, give observations of the nerve of the injured eye being small and shrivelled, and of their having traced them past their union to the same side of the brain with the eye to which they belonged. Yicq d’ Azyr, who, of all authors, I conceive to be the best authority upon such subjects, is decidedly of opinion that there is no decussation. Zinn also agrees with the opinion of Galen, that there is an adhesion and inti- mate union of substance, but no crossing of the nerves. Soemmerring deems it sufficient to point out the authoritie-pmn both sides of the ques- tion, while he has no decided opinion whether there be a perfect decus- sation or not. f Porterfield, while he allows the intimate union of the optic nerves, has several observations, proving that they have no inter- section or decussation. Sabbatier, encouraged by the authority of Morgagni, says, that he could trace the affection of the nerve of the injured eye no farther than to the union. He discredits the accounts of their having been traced to the same side of the brain, and believes the assertions to be the conse- quence of previous opinion and prejudice.—There are certain observa- tions of Valsalva, Cheselden, and Petit, which seem to prove, that where the brain is injured, it is the eye of the opposite side that is affect- ed. After their union the optic nerves are much contracted in diameter; still the optic nerve is the largest of the head excepting the fifth pair. It is the firmest of all the nerves of the senses, but softer than the other nerves. 1 What remains to be said of the optic nerves, falls more naturally to be treated of when speaking of the organ of vision. * Santorini tab. Scarpa Anatom. Annotat. p. 106. f “ Ergo utrum omnes nervorum librae, an quaedam tantum mutuo se secent, certe statui nequit.” I Soemmerring. They seem to come from the angle betwixt the crura cerebri and pons Varolii. They are flat near their origin, but become round and firm. THE ORIGIN OF THE NERVES. 69 THIRD PAIR OF NERVES ; MOTORES OCULORUM. The third pair of nerves arise from the internal margin of the crura cerebri, and the perforated medullary matter which is betwixt the crura. The delicate filaments of this nerve cannot be traced far into the sub- stance of the brain, but still we may observe them spreading their fila- ments, and traversing the dark-coloured spot which we have already mentioned to be visible in the crura cerebri. Some anatomists have said, that the third pair of nerves had an origin also from the nates and testes. Ridley describes them as rising from the pons Varolii. Mala- carne describes an accessary filament to this third pair from the crura cerebelli.* In relation to the arteries, those nerves are betwixt the posterior arte- ry of the cerebrum, arising from the division of the basilar artery and the anterior artery of the cerebellum. They diverge from each other as they proceed forwards, and each penetrates under the anterior point of the tentorium by the side of the cavemus sinus, and passes through the foramen lacerum. In the general description it is sufficient to say, that they are distributed in common to all the muscles of the eye. THE FOURTH PAIR OF NERVES. The fourth pair of nerves, pathetici, or trochleares, are the smallest nerves of the encephalon, being not much larger than a sewing thread. This nerve comes out from betwixt the cerebrum and cerebellum, passes by the side of the pons Varolii, and after a long course pierces the dura mater behind the clynoid process, runs along for some way in a canal or sheath, formed by the dura mater ; it then passes above the cavernous sinus, continues its course onwards through the foramen lacerum to the orbit, and is finally appropriated to the superior oblique muscle of the eye. The origin of the fourth pair, if we take the descriptions of authors, seems to have a much greater variety than any of the other nerves; so that it is common to say, the fourth pair of nerves arises about the region of the nates and testes, f It is affirmed that the trochlearis arises some- times by two filaments, but more commonly by one undivided root.J This root, according to Vicq d’Azyr, is seen to emerge from a point be- twixt the medullary lamina of the cerebellum, or valvula Yieussenii, and the lower part of the tubercula quadrigemina.§ My opinion is, as I have elsewhere expressed, that it comes from the upper part of the spinal * See Desmoulins, Anatomie des Systernes IJerveux des Animaux & Atlas, p], xiii. fig. 1. and 3. z. f Soemmerring, vol. iv. p. 209. } Santorini says, they have three roots or little fasciculi. Wrisberg, following Vieussens, says, the fourth pair arises from the valvula cerebri. Vicq d’Azyr. See Haller, fas. vii. tab. 3. “ Origo alius simplex est, alius duplex ; quando simplex est, a processu a cerebello ad “ testes exterius prodit, quam est transversa stria, quae eos processus conjungit.” Haller, Phys. vol. iv. p. 208. § “ Et souvent ils se confondent avec un tractus medullaire plac£ transversalement au-des- sus de la valvule du cerveau.” Vicq d’ Azyr. This nerve, says he, cannot be followed into the anterior part of the brain from its extreme delicacy, and because it is formed from tlie medullary substance itself, without the admixture of filaments to give it strength. He quotes these words of Soemmerring : “ Continua medulla oritur.” 70 THE ORIGIN OF THE NERVES. marrow, and that the reason of this nerve taking a course different from the other nerves of the encephalon, is, because it is connected with that column of the spinal marrow which orders the actions of respiration. FIFTH PAIR OF NERVES ; GRAND SENSITIVE NERVE OF THE HEAD AND FACE. The fifth nerve of the brain arises from the fore and lowest part of the crura cerebelli, where they unite with the pons Yarolii. The origin of this nerve may be divided into two portions ; an anterior is small, and somewhat elevated above the other. The posterior part of this origin takes its rise a little lower than the anterior part, and is broader and flat- ter. These two origins of the nerve are connected by a cellular mem- brane, and have betwixt them a little groove, in which not unfrequently an artery creeps.* According to Santorini the anterior of these divi- sions is formed by the transverse fibres of the pons Varolii, and the posterior by the crura cerebelli.| Yicq d’Azyr could never, except in one dissection, perceive that any of its fibres arose from the pons Yaro- lii. J The nerve of the right side has been observed sometimes larger than that of the left. This fifth nerve, the largest of the skull, passing forwards and down- wards, slips in betwixt the lamina of the dura mater, opposite to the point of the pars petrosa of the temporal bone. It is here firmly attached to the dura mater, and forms a flat irregular ganglion. This ganglion§ is formed entirely by the posterior portion of the nerve ; the anterior por- tion passes the ganglion, and enters the foramen ovale. From this great nerve there pass out three branches, hence the term trigeminus is given to the fifth :—1st, One to the socket of the eye and forehead, through the foramen lacerum ; 2d, One to the upper jaw and face, through the foramen rotundum ; and 3d, One to the lower jaw and tongue, passing through the foramen ovale. As I have explained in the introduction to the nerves, this fifth nerve of Willis is the upper or anterior of the re- gular system of nerves. It is to the head what the spinal nerves are to the body. It is a double nerve, bestowing sensibility on the head and face, and supplying muscular branches to the muscles of the jaw. SIXTH PAIR OF NERVES ; OR, ABDUCENTE3.|| The sixth nerve of the skull seems to arise from betwixt the pons Va- rolii and medulla oblongata. In the origin of its fibres it has, however, much variety ; and authors differ very much in this point of the descrip- tion. 1T We may say, however, that the sixth pair of nerves arise from the corpora pyramidalia.—Sometimes the nerve rises in two branches, * Vicq d’Azyr distinguished the roots into “ la portion filamenteusej et la portion arondie “ qui a la consistence d’un gros nerf.” f See two wood-engravings at pp. 16 and 17, which exhibit the exact origins of the 5th pair. Santorinus. Wrisberg de quinto p. Nervor. Scarpa Anat. Annotat. p. 107. t “ Oritur e nodo cerebri, prope cerebellum duabus partibus, &c.” Soemmerring. { Viz. the Gasserian ganglion. II Or, motores externi. IT Simple as the anatomy of the nerve is, Vieussens, Morgagni, Lieutaud, Winslow, Sab- batier—all differ in their account of the origin of this nerve in some little circumstance ; and Vicq d’Azyr gives six varieties of it. THE ORIGIN OF THE NERVES. 71 which do not unite until they are entering into the cavernous sinus.* The sixth nerve is in size somewhat betwixt the third and fourth: it passes forward under the pons Varolii, until near the lateral and lower part of the body of the sphenoid bone: it thence continues its route for- wards and downwards by the side of the carotid artery, through the ca- vernous sinus : here it seems increased in size. It gives off that small twig which anatomists account the beginning of the great sympathetic nerve. This communication often consists of two nerves ; and there is seated on the carotid artery a small square ganglion, which sends branch- es to the sixth, fifth, and sympathetic. The sixth nerve, after giving off this communication, passes on through the foramen lacerum to the ab- ductor muscle of the eye. SEVENTH PAIR OP NERVES ; OR, AUDITORY. The seventh nerve arises from the posterior and lateral part of the pons Yarolii, at the point where it is joined by the crura cerebelli. But this seventh pair of Willis consists of two parts ; the facial nerve or portio dura, and the auditory or portio mollis; the last is the larger and posterior portion, f The portio dura comes out from the fossa formed betwixt the pons Varolii, corpus olivare, and corpus restiforme ; 1 and upon a more care- ful examination we find it rising distinctly from the superior point of that column of the spinal marrow, which gives origin to the par vagum, spi- nal accessory, or glosso-pharyngeal nerves. The origin of the portio mollis, of the seventh pair, is to be traced from the fore part of the fourth ventricle. We observe passing obliquely upwards from the calamus scriptorius several medullary striae, which vary in number from two to seven, and are sometimes very indistinct. || To these are added certain fibres arising from the pons Varolii, which alto- gether constitute the portio mollis. The whole of this portio mollis is larger than the third nerve, firmer than the first, but less so than the se- cond pair. It forms a kind of groove which receives the portio dura. They are divided by a small artery which comes off from the basilar to supply the ear. The portio mollis and portio dura entering the mea- tus auditorius internus of the petrous bone, the former is divided into four portions which pass to the several parts of the internal ear, while the latter traverses the petrous portion, and comes out by the stylo-mas- toid foramen behind the ear, spreads upon the cheek, and forms the prin- cipal nerve of the face : that nerve which commands the muscles of the face. * Sabbatier. Scarpa loc. cit. f And we may add a third portion; the portio media of Wrisberg. i “ Fosse de 1’eminence olivare,” of Vicq d’Azyr. $ Prochaska, tab. iii. f. f. Scarp, loc- cit. || It is a curious circumstance, should future observation confirm it, which has been men- tioned by Santorini, that those origins of the auditory nerve have been observed particularly strong in a blind man, whose hearing had been very acute. 72 THE ORIGIN OF THE NERVES. EIGHTH PAIR OF NERVES. To understand a very intricate demonstration, it is necessary to recol- lect that the eighth pair of nerves, as they have a relation to the brain, consist of three distinct nerves.—These are, 1st, The glosso-pharyn- geal nerve ; 2d, The par vagum ; 3d, The spinal accessory.—Taken altogether, they arise from the superior and lateral part of the medulla oblongata, from that part which I consider the respiratory column of the spinal marrow. The glosso-piiaryngeal nerve is only distinguished within the skull as a larger filament of the eighth pair ; it is, however, distinct in its course from the origin of the point where it pierces the dura mater ; it is the up- permost of the fibres of this pair of nerves. Sometimes there is a very delicate filament running parallel with its lower edge, which belongs to it. It has the same origin with the fibres of the par vagum.* The par vagum is composed of ten or twelve very small filaments, which are sometimes united into three or four fasciculi. These filaments arise from the outer border of the corpus olivare, or from the lateral part of the medulla oblongata, f A few fibres are to be traced from the side of the calamus scriptorius of the fourth ventricle. The spinal accessory nerve comes up from the spine to join the par vagum; it begins by small twigs from the middle column of the spinal marrow below the roots of the fourth, fifth, sixth, and even the seventh Cervical nerves. In the size, length, and origin of those little slips, there is much variety. As the nerve ascends to the top of the spine, it connects itself with the sub-occipital nerve: it then passes behind the trunk of the vertebral artery, approaches the par vagum, and receives some filaments from the medulla oblongata.—Those three nerves, the glosso-phrayngeal, par vagum, and accessory nerves, in their passage out of the skull are connected in a very intricate way. They then sepa- rate from each other. The anterior branch, the glosso-pharyngeal nerve, goes to the tongue and pharynx; the middle nerve, the par vagum, has an extensive course through the body, and finally terminates in the sto- mach ; the lowest nerve, the accessory, passing into the neck, perforates the mastoid muscle, and distributes its branches amongst the muscles of the shoulder. NINTH PAIR OF nerves; OR, LINGUAL ; THE MUSCULAR NERVE OF THE TONGUE. The ninth nerve of the skull originates from betwixt the corpora pyra- midalia, and olivaria; from that column which gives off all the motor nerves. It is composed of several little filaments; those unite into a fasciculus of a pyramidal shape: still those filaments do not form a nerve before perforating the dura mater, but pierce it severally J ; they * Soemmerring. f Some filaments, according to Vieussens, Santorini, and Soemmerring, are derived from the side of the 4th ventricle. t The ninth pair of nerves often differ very much in one side from the other, in regard to the origin and number of those fasciculi. OP THE VEINS OP THE BRAIN. 73 then unite and pass out of the skull by the condyloid foramen of the oc- cipital bone; they are then connected with the eighth pair and ganglion of the sympathetic nerve. The final distribution of the nerve, is to the muscles of the tongue. THE TENTH ; OH, SUB-OCCIPITAL NERVE. From its origin, its manner of passing betwixt the skull and first ver- tebra, and its distribution, it must be classed with the nerves of the spine. It is of the class of symmetrical nerves, being double in its roots, and performing the double office of giving sensibility and motion. The nerves of the spine are divided into the eight cervical, twelve dorsal, five lumbar, five, and sometimes six or seven, sacral nerves.* Each of those thirty nerves arise in two fasciculi, one from the fore, and the other from the back part of the spinal marrow. They are to be traced a great way in the length of the spinal marrow before they pass the membranes. The posterior and anterior fasciculi penetrate the dura mater separately, and afterwards unite. The posterior fasci- culi, before they unite with the other, swell into a little ganglion. The posterior fasciculi of the cervical nerves communicate with each other by intermediate filaments : these considerations carry us back to the view delivered in the introduction. OF THE VEINS AND SINUSES OF THE BRAIN. In proportion to the intensity with which the function of a part is performed is its supply of blood. The brain is very profusely supplied with blood, in so much, that it is estimated that four times more blood circulates here than in any proportionate weight of the body. This is the most moderate circulation, and it has been formed from a compari- son of the quantity of blood circulating in the head, with that which circulates in the arm. Boerhaave and Kiel, comparing the area of the arteries of the cerebrum with that of the ascending aorta, made a most erroneous calculation of the proportion of blood circulating in the brain, compared with that of the rest of the body. Had they compared the quantity of blood within the head with that of the lungs, of the liver, of the spleen, or of the kidney, the difference would have been less striking. Wherever there is great arterial vascularity, we are sure to find also peculiarities in the venous system of the part; wherever we find an ac- cumulation of tortuous arteries passing to a gland, we shall also find the veins tortuous and large. The following appear on the first view to be the most striking peculia- rities in the veins of the brain; their sise; the little connection they seem to have with surrounding cellular membrane, and the inconsidera- ble support which they appear to receive from it; their having no valves; their being in their course distinct from the arteries ; and lastly, * “ Plerumque quinque sunt, nonnunquam sex, raro tres vel quatuor.” Soemmerring. 74 OF THE VEINS OF THE BRAIN. their not being gathered into great trunks, but emptying themselves into the sinuses of the dura mater. It is not easy to conceive how the veins of the brain should have been so much overlooked by the older anatomists; but from the dis- sections of Albinus, and the microscopical observations of Lieeuwen- hoeck, we have authority for what is, perhaps, in itself sufficiently evi- dent, that the veins of the surface of the brain are derived from minute ramifications conveyed in the delicate pia mater; and that these, as in the other parts of the body, proceed from the extremities of the arteries, without any apparent peculiarity in the connexion betwixt the extremi- ties of the arteries and the veins of the brain.* I divide the veins of the brain into the external and internal, or those which emerge from its substance, and are seen upon the surface; and those which, coming chiefly from the sides of the ventricles, are convo- luted in the plexus choroides, and terminate in the fourth sinus. OF THE VEINS WHICH ARE SEEN UPON THE SURFACE OF THE BRAIN. Vicq d’Azyr has been minute in his attention to the veins of the sur- face of the brain. He confirmed the observation, that almost all the veins which pass into the longitudinal sinus, open in a direction contrary to the stream of blood .in the sinus. These superficial veins of the sur- face of the hemispheres, are in number generally from ten to fifteen on each side. They really do not seem to be worthy of the minute atten- tion which Vicq d’Azyr has bestowed upon them : he has most carefully described each individual branch, and that not in general terms, but first those of the right, and then those of the left side. Now, although these veins do not enter the sinus opposed to each other, nor in pairs, still the irregularity is trifling, and, were it important, does not admit of descrip- tion. Those veins do not lie in the sulci of the brain, but pass occa- sionally along the interstices, or over the convolutions of the brain ; they take in general a course from before backwards, but previous to their en- tering the sinus, are turned forwards. We have already observed, that the pia mater and dura mater have no connexion, but at the place where those veins enter the lamina of the dura mater ; and here their connex- ion is somewhat peculiar. It is not a simple adhesion of the pia mater and dura mater; but a white spongy substance seems to connect and strengthen them, and, when torn asunder, it leaves a soft fatty kind of roughness upon the pia mater. These appear to me to be the same bodies which Ruysch so frequently mentions as little particles of fat, and which others have taken to be the glands of the pia mater, f Vicq d’A- zyr, in his xxxiiid plate, fig. 14. has confounded them under the name of the glandulae Pacchioni. Of these veins lying upon the surface of the brain, there is one, or very often there are two large veins on each side, and which enter generally pretty far back in the sinus, and are somewhat peculiar from their greater size, and their semicircular course. These, from their state of dilatation, and the colour and fluidity of their blood, will be found in morbid dissection, to mark sufficiently, in many instances, the character of the venous system of the brain. There is * See Ridley, cap. vi. de Cerebri Motu, ejusque Simrbus. * Thesaurus Anal. is. N. xlii, Epist. is. p. 8. Thes. vi. No. 1. OP THE VEINS OF THE BRAIN.- 75 again another vein somewhat peculiar in its course; whilst those take a superficial course, and are upon the level of the longitudinal sinus, it gathers its branches upon the internal flat surface of the left hemisphere, and rises so as to insinuate itself into the inferior part of the sinus. * All these veins of the surface of the cerebrum have very free inoscula- tions with each other. I cannot any where better observe the negligence of authors, in re- gard to the glandulm Pacchioni, than when speaking of the mouths of those veins which open into the great longitudinal sinus. I cannot help thinking, that many of our best authors have overlooked entirely the importance of the glandulse Pacchioni; and many also have been entirely ignorant of them. We have already mentioned, that a few small bodies, by no means constant or regular, were to be seen upon the external surface of the dura mater, in the course of the longitudinal sinus, or at no great distance from it. We have mentioned also those fatty-like adhesions of the roots of the veins, as they enter the sinus, and which rather belong to the pia mater. Both these are called the glandulae Pacchioni improperly. The bodies which engaged Pacchioni and Fauto- nus in such violent disputes, are seen on the inside of the longitudinal si- nus, and are connected with the openings of the veins they appear of a fleshy colour, projecting like papillae, or like the granulations of a sore. Pacchioni says, “ Ovorum instar bombycinorum apparent,” which de- scribes their conglobate appearance ; but they are of a pale fleshy colour, which Pacchioni says is owing to their being surrounded with muscular fibres. The preparation from which Pacchioni had taken his plate, was previously macerated in vinegar. These bodies being soft and vascular, have allowed the minute injection to transude in some of the experi- ments of anatomists, which has given rise to the opinion of the actual communication of the arteries of the dura mater with the sinuses. As to their use,J I am in considerable doubt. Joan. Fautonus (in his let- ters to Pacchioni) conceives that they give out a fluid into the sinus, to dilute the venous blood.§ Pacchioni describes ducts passing from them to the pia mater, (which are those connexions that we have already re- marked,) and conceives that they lubricate the surface, or communicate with the substance of the brain ; and that they are pressed, and their se- cretion promoted by the motion of the chordae Willisianae, and the action of the dura mater. j| I should rather conceive that they had a valvular action of the mouths of the veins ; they project from the mouths of the veins in the sinus, and the blood passing from the veins must filter through them, and be check- ed in its retrogade course. This check we know to be very necessary, since the blood flows backwards through the sinuses with a powerful im- petus. As these bodies differ very much in the variety of subjects, they must sometimes impede the free egress of the blood from the veins of the cerebrum into the longitudinal sinus, and cause disease, especially as they are softer and larger in old men. IT At all events, they are too much overlooked in morbid dissection. * Vicq d’Azyr. f Vide Pacchioni, p. 126. Ruyseh. Thes. vii. No. xxxiv. i It is curious that these bodies are confined to the longitudinal sinus. Pacchioni, p. 127. § Fautonus Epist. D. A. Pacch. Oper. Pacch. 177. || “ Ex iis autem in minimum quidem vasculum lymphaticum prodire conspicere potui.” Ruyseh. V Pacchioni Oper. p. 126,127. - 76 OF THE VEINS OF THE BRAIN. The veins which answer to the arteria corporis callosi, and which are seen lying upon the corpus callosum in a very fine cellular membrane, rise and pass into the inferior longitudinal sinus, that sinus which is form- ed in the laminae of the inferior edge of the falx. OP THE INTERNAL VEINS OF THE BRAIN AND OF THE CHOROID PLEXUS. Under this title of the internal veins of the brain, the choroid plexus comes naturally to be considered. The most remarkable thing in the ventricles of the brain is, the choroid plexus. The lining membrane of these cavities is extremely thin and smooth, insomuch, that some ana- tomists have denied its existence ; but through the whole ventricle there run certain folds or plaits of this membrane, which are so loaded with vessels as to resemble a fleshy substance, and thus lose their resemblance of the lining membrane. The plaits, before they are unravelled, look like masses of tortuous vessels, lying loose and unconnected in the bot- tom of the ventricles. The largest portion of each choroid plexus comes up from the inferior horn of the lateral ventricle, and runs forward in a direction to the ante- rior horn. It lies in the groove, betwixt the thalamus nervi optici and corpus striatum : and covers the tenia semicircularis geminum. The two plexus of the lateral ventricles unite under the anterior crus of the fornix, and form a small plexus which is continued upon the inferior sur- face of the velum interpositum, and even into the third ventricle. Again, there is another plexus which lies in the fourth ventricle. Yicq d’Azyr describes, as occasionally occurring, little insulated plexuses attached to the veins, branching on the corpora striata. * Very often we find the portion of the plexus, which is ascending from the lateral ventricle, thicker and firmer than natural, and sometimes it has in it small bodies like glands, which, however, are of the nature of hydatids or vesicles, and are a production of disease or over excite- ment. j A foolish notion prevailed, that the blood accumulated in these convoluted vessels, occasioned such a gentle continued heat as favoured the circulation of the spirits through the cavities of the brain, and preserved the fluidity of the water of the ventricle. J Great variety of opinions have prevailed regarding the structure of those bodies. We see them consisting of knots of convoluted vessels ; chiefly veins; or these at least are most evident from their size, and the colour of their blood. It is these convolutions of vessels, which are by many good anatomists described as glands. Varolius, Syl- vius, Wharton, Willis, Santorini, and Lieutaud consider them as such.§ Three sets of arteries pass up to the plexus choroides, from the base betwixt the crura of the brain ; they come, 1st, from the * Yicq d’Azyn Memoir. I’Acad. Roy. 1781, p. 540. f The supposed glands of the plexus choroides were conceived to secrete the fluid of the ventricles. Where the plexus lies upon the posterior crura of the fornix, it is often diseased, having knots like glands, or, being raised into vesicles, like hydatids. Haller, tom. iv. 48. t See Duverney, tom. i. p. 55. Willis Cerebri Anat. p. 47. $ Galen gives a good description of the choroid plexus ; he describes the innumerable veins of which it is composed, and their joining the fourth sinus by the vein which retains his name. Some have confused themselves with a passage of Ruysch. Thes. iii. No. Ixv. &c. m which he is speaking of the choroid plexus, where it appears in the base of the skull from the bottom of the fourth ventricle. They have understood him to say, that the plexus was covered not with the pia mater, but with the tunica arachnoides, first described by Morgagni, OF THE VEINS OF THE BRAIN. 77 curve of the internal carotid artery; 2d, from the communication betwixt the basilar and carotid artery ; 3d, from the basilar artery and posterior part of the branch of communication. These arteries, which are small, are convoluted in their course, and run into great minuteness * in the membrane, and their blood is returned by veins, which taking a very tor- tuous course, seem to entangle their branches, and form a confused mesh. I conceive the use of these loose and vascular membranes, is to secrete the fluid of the cavities. They are undoubtedly the parts of the brain the most excitable, for if but a temporary change takes place in the cir- culation of the blood in the brain, it will upon dissection be manifested in the state of fulness of these veins, in the vesicles which are formed in their folds, and in the accumulation of fluid in the ventricles themselves. The blood of the two plexuses of the lateral ventricles, and that of the third, is conveyed into the velum interpositum, or that membrane which stretches under the fornix, and over the third ventricle. The branches of veins also which extend themselves upon the sides of the lateral ventricles, and into the processus digitalis, being gathered together upon this membrane, open into the vena Galeni, or rather form it. The most remarkable branches of veins in the lateral ventricle are these : a considerable vessel is seen to collect its branches upon the an- terior part of the ventricle, and in the anterior sinus, or horn of the ven- tricle. This vein runs back towards the anterior crus of the fornix, and dips under it, just above the communication of the ventricles ; and joins the veins in the velum of Haller. Other small veins are seen collecting their branches upon the corpora striata ; and, passing under the centrum semi-circulare geminum, connect themselves with the plexus. Again several branches of veins are extended in the posterior part of the ven- tricle. These are from the medullary substance of the posterior lobe of the cerebrum. They pass under the posterior crus of the fornix and join the vena Galeni. Lastly, a vein remarkably tortuous, frequently full of blood, passes forward, and is seen at intervals in the plexus choroides. This vein, taking an acute turn, joins its fellow under the anterior crura of the fornix, and is reflected backwards and under the fornix, so as to form the beginning of the vena Galeni. The vena galeni then is the great central vein of the brain. It stretches from the extremity of the fourth sinus into the internal part of the brain, to receive the blood from the membrane lining the ventricles, —from the substance of the brain,—from the plexus choroides,—and from the velum interpositum. j" It lies under the posterior part of the corpus callosum, under the fornix and above the nates and testes. It is entangled in the velum itself. It consists of two great branches which lie parallel to each other, and which sometimes have the appearance of being twisted, and these unite before they enter the fourth or straight sinus. and whose authority we may consult for much of this part of anatomy. Adversar. Anat. vi. Animad. 1. et sequent. * “ Huncce plexum nil esse nisi arteriolas, ad visam succosas, a naturali constitutionearte- “ riosanon nihil recedentes, mirumque in modum contortas, serpentinoque modo reptantes, “ glandulasque representantes.” Ruysch, Thes. v. Asser. quartus, No. lxviii. Not. 2. 1 The velum lying upon the nates and testes, and adhering to them and the pineal gland ; the vena Galeni receives here also veins from those bodies, and from the upper part of the cerebellum. 78 OP THE VEINS OP THE BRAIN. In the basis of the brain the veins are not remarkable, nor do they require any description distinct from the sinuses into which they open. They are small, having little way to run ; and before they become large trunks, they empty themselves into the numerous lesser sinuses betwixt the dura mater and the base of the skull. This is perhaps a provision against the pressure of the brain. In passing into those si- nuses, the veins take a long oblique course betwixt the lamellae of the dura mater ; which has given occasion to anatomists to describe many intricate lesser sinuses. OF THE PARTICULAR SINUSES. (a) The great longitudinal sinus, (A) superficial veins : (c) the inferior longitu- dinal nus; (d) the vena Galeni; (fi) the fourth sinus; (/) the right lateral sinus ; (g) the left lateral sinus ; (A) the cavernous sinus ; (i) the circular sinus; (A) the petrous sinus ; (/) the jugular veins. By the term sinus we are to understand the great veins of the brain, where they are received into the triangular canals of the dura mater. SUPERIOR LONGITUDINAL SINUS. This is a triangular channel running into the falx from the crista'galli of the ethmoid bone to the crucial ridge of the occipital bone. It is not OF THE VEINS OF THE BRAIN. 79 constant in its origin. Sometimes it begins from a blind foramen before the crista galli. * Sometimes from the orbital sinus, t In some sub- jects it begins only opposite to the fontanelle, or even further back, and then at once swells out to a large size. As the sinus passes backwards it is gradually enlarging for the recep- tion of the veins from the surface of the cerebrum. The course of the sinus corresponding with the form of the skull is a curve answering to the sulcus, which runs in all the length of the cranium, from the aeth- moid bone to the crucial ridge of the occipital bone. The angle formed by the splitting of the internal layers of the dura mater, to form this sinus, is strengthened by strong slips of fibres, sometimes called cord® Willisianae, which upon the inside of the sinus have the effect of making the canal irregular, so that it has the appearance of cells, into some of which the probe enters, and leads to the veins on the surface of the brain ; others are blind, or lead to lesser sinuses, which not unfrequently run parallel for some length to the great sinus; or the probe passes from one of these cells to another. Sometimes the sinus has no such irregula- rities, but is straight and smooth through its whole length. J This sinus has in some rare instances been found of a square shape ; its lower surface serving as a roof for another sinus of a triangular form, which, for some way, ran parallel with the great sinus, and which was of course also included in the lamina of the falx—these Malacarne calls seni subalterni. Irregular lesser sinuses are by no means uncommon, and they form, sometimes, communications through a great extent of the longitudinal sinus; or again it will be found that the longitudinal sinus deviates considerably in some subjects, from the straight line, tak- ing a curve or circle, generally behind the fontanelle ; or it sends off branches, which again unite with it; or it is fairly divided. In all these cases the chords or fasciculi of the dura mater stretch out over the si- nuses, and protect them from compression. Instead of reaching backwards to the crucial line upon the occipital bone, the longitudinal sinus has been found to divide at the beginning of the lambdoidal sutures, and to follow them in a direction towards the pe- trous bone, § while the lateral sinuses, running in the duplicature of the tentorium, were reduced to a very narrow compass. From the strength of the connexions of the sinuses, and from the languid course of the blood through them, I cannot believe that the sinus has ever suffered the distention which Malacarne says he has observed. I should rather suppose that what he mentions had been natural and con- genital enlargements; especially considering that the sinuses, like the other veins of the body, are frequently irregular. LATERAL SINUSES, OR THE FIRST AND SECOND OF THE ANCIENTS. The lateral sinuses are formed by the splitting of the laminae of the tentorium, as the longitudinal sinus is formed by the falx. They are * Malacarne, Haller, Gautier. f These sinuses as frequently are continued into the inferior longitudinal sinus, or into the circular or elliptical sinus; they are like azure streaks under the dura mater covering the orbital process. t The internal membrane of the sinus is perfectly smooth, and is continued into the coats of the internal jugular veins; it is of the same nature with the internal coat of the vein. 4 Malcarne, parti. 148. 80 OF THE VEINS OF THE BRAIN. continuations of the longitudinal or first sinus. From the crucial ridge of the occipital bone they stretch nearly horizontally, going off right and left, following the connexions of the tentorium in a direction toward the petrous bone ; then they take a curve downwards and forwards, to ter- minate in the internal jugular vein; passing through the foramen lace- rum betwixt the temporal and occipital bones. Very frequently the one lateral sinus is larger than the other—gene- rally the right is the larger, and sometimes the left is entirely wanting.* They diverge from the termination of the superior longitudinal sinus at the crucial point of the occipital bone; but sometimes they are irre- gular, diverging higher, and even passing round in the circle of the poste- rior part of the cranium, at some distance from the tentorium, f The right lateral sinus for the most part begins higher than the left. It is generally longer, and may be considered as the continuation of the longitudinal sinus. Nay, in some subjects, the right or left lateral sinus begins from the longitudinal one, while that of the other side is continu- ed from the fourth, and then the lateral sinuses are separated at their ori- gin by a membranous isthmus. If one of the lateral sinuses receives the superior longitudinal one, it will be found to be four times the size of the other. J I have seen a more remarkable variety of the lateral sinuses. The blood which should flow from all those parts of the brain from which the superior and inferior longitudinal sinus, and the vena Galeni, and fourth sinus are derived, instead of passing by the root of the tentorium, for- sook these channels, and consequently the lateral sinuses were left di- minutive ; and the blood took a course in the tract of the posterior occi- pital sinuses, and after encircling the foramen magnum, they gained their usual outlet. § The angles of the lateral sinuses are strengthened by membranous fas- ciculi ; betwixt these the veins enter as in the longitudinal sinus ; where the sinus descends from the level of the tentorium in the angle formed by the occipital and petrous bones, there are many strong irregular fasciculi of fibres : under this point, being no longer protected from compression, by their triangular shape and the tension of the tentorium, the sinuses are irregular; they are now sunk in the sulci of the bones, and the dura mater its sheath over them. The great irregular cavity, || in which the extremities of the lateral sinuses lie,1T and the foramen lacerum have much variety, and their straightness seems to affect the size of the sinus in its whole length.** OF THE INFERIOR LONGITUDINAL SINUS. The inferior longitudinal sinus, or the lesser, or inferior sinus of the falx, runs in that edge of the falx which penetrates betwixt the hemi- * Lieutand, Anat. Hist. f Malacarne. $ See Morgagni Adversaria VI. tab, 1. fig. 1. } There are instances of the lateral sinuses opening into the external jugular vein. |i Lower conceives that the size of the jugular fossa was the effect of the reflux of the blood; and that the greater size of the sinus of the right side was to be traced to the practice of nurses laying their children chiefly on the right side! See also Morgagni Adversaria Anat. H See Willis Anatom. Cereb. Hum. p. 29. and the plate. ** Some very large veins open into the lateral sinus; they are derived from the posterior lobes of the cerebrum and the cerebellum. These insinuating irregularly betwixt the la- minae of the tentorium, and running for some way, have been considered as additional sinuses. See Haller, tom. iv. p. 149. OF THE VEINS OF THE BRAIN, 81 Spheres of the cerebrum. It is extremely small towards the fore part of the falx; but, as it passes backwards, it goes on increasing by the acces- sion of veins which come from the hemispheres, and corpus callosum, and from the falx itself. It is formed betwixt the laminae of the falx. Sometimes it runs in its very edge, but as frequently a little way removed from it; sometimes it is found beginning very far back in the falx. The fore part of it is more like a vein running in the falx than a sinus. It is in general to be seen more superficial, and in every respect like a vein, (there being no provision for preserving it from compression,) upon one side of the falx. It very often takes a waving course upon the falx ; while it receives the veins which branch in the substance of the falx, and form communications betwixt it and the superior longitudinal sinus. It opens into the straight or internal sinus, called also the fourth, near the edge of the tentorium. OF THE INTERNAL, STRAIGHT, OR FOURTH SINUS.* I would call this the internal sinus, from its situation, but more par- ticularly from its receiving the veins from the internal part of the brain. This sinus is formed chiefly by the vena Galeni; which, coming out from betwixt the corpus callosum and tubercula quadrigernina, enters betwixt the laminae of the middle part of the tentorium, where it is united to the falx ; so that by the tension of these two partitions, this sinus is drawn into a triangular form, and is as incompressible as those sinuses which run connected with the bone. It opens, for the most part, by an oval mouth, formed by strong pillars of fibres into the left lateral sinus, rather than directly in the middle of the communication of the three great sinuses. We shall find this like the other sinuses, suffering considerable variety ; or irregular smaller si- nuses will often be found running betwixt the laminae of the tentorium. POSTERIOR OCCIPITAL SINUSES. These are so called in opposition to some irregular and small sinuses, which run upon the occipital bone before the great foramen. The pos- terior occipital sinus lies in the little falx of the cerebellum : it rises upwards, and opens into the common union of the longitudinal and la- teral sinuses ; it commonly, however, lies rather to the left, and empties itself into the left lateral sinus. It is by no means constant; like the other lesser sinuses, it is subject to great variety ; and before it rises into the tentorium, or empties itself into the larger sinuses, it has a com- munication or emissaria, by which part of the blood may pass into the external veins, through a foramen in the centre of the occipital bone.t * Sinusquarlus, Perpendicularis. Haller.—The fourth sinus; the two lateral being the first and second, and the longitudinal being the third sinus. f Malacarne.—This sinus is sometimes double; or it has two branches encircling the terior margin of the occipital hole; or, as I have already observed, it takes the office of the great superior lateral sinuses, and empties it into the foramen lacerum; or it communicates with the vertebral veins. See Observations surune dilatation singultere des sinus occipitaux, Mem. de l’Acad. Roy. Anno 1781, p. 596. 82 OF THE VEINS OF THE BRAIN. THE INFERIOR LATERAL SINUSES. The inferior lateral sinuses are still more rarely to be found than the last, in so much that Yicq d’Azyr says he never has seen them. They run in the laminae, or under the dura mater of the posterior fossa of the base of the skull; that is, the hollow of the occipital bone, which is under the tentorium. They are so irregular that they frequently occur in one eide only. They communicate with the posterior part of the foramen lacerum; with the posterior petrous sinus or vertebral veins; or lastly, they occur as an irregular collection of channels running in the several neighbouring sinuosities.* We see, then, that there is a point of union for all these sinuses, which we have not as yet described : we see that the superior longitudinal sinus, the two lateral sinuses, the fourth (and consequently the inferior longitudinal sinus), and the posterior occipital sinus, unite at the crucial spine of the occipital bone. This is the torcular hierophili t, tor- CULAR, LACUNA, PLATE A, TF.RTIA VENA, PALMENTUM, PELVIS, LAGUN- cula. It was natural that the attention of the ancients should be drawn to this part; for, upon opening this union of the sinuses, we find a large irregular cavity, which seems to be particularly strengthened by these strong fasciculi of fibres, which indeed are the support of the sinuses.| Ignorant of the circulation, imagining that the blood as- cended by the great jugular veins to the lateral sinus, and seeing that the lateral sinuses opened into this central cavity, they conceived that the blood destined for the brain underwent an operation there, and was thence sent through every part of the brain. § OF THE LESSER SINUSES IN THE BASE OF THE SKULL. Besides those larger sinuses which we have described, and which convey back the great proportion of blood circulating in the brain, there is a set of lesser sinuses which lurk betwixt the dura mater and the anterior part of the base of the skull. These last are fully more intricate than the others; they lie upon the irregular surface of the sphenoid, temporal, and occipital bones; and tend backwards to the great outlet formed by the irregular hole in the temporal and occipital bones. THE SPHENOIDAL SINUSES. The superior sphenoidal sinuses are seated in a fold of the dura mater, on the internal margin of the wing of Ingrassias, and before the great wing of the sphenoid bone ; they receive the blood in part from the orbit and from the dura mater; they open into the cavernous sinus, or perhaps into the ophthalmic sinus, which of course, for the most part, conveys the blood into the superior or inferior longitudinal sinus. The inferior sphenoidal sinus is very irregular and inconstant. * Malacarnc, p. 113, 114. f Hierophilus was a Greek physician, a disciple of Praxagoras, and coteraporary with Erasistratus. | Lib. Nonus de Cerebri,'&c. Dissectione. \ Galen, cap. vi. de torculare. Et quo pacto venae intro cerebrum distribuantur. or THE VEINS or THE BRAIN. 83 It is m the dura mater, covering the great wing of the sphenoidal bone : the blood of this sinus is emptied into the cavernous sinus, or escapes by emissarise into the trunk of the temporal veins. The clinoid sinus.—The posterior clinoid sinus, or elliptic sinus, and the circular sinus, are one and the same ; the difference consists only in the manner of describing them ; the circular sinus lies with- in the clinoid processes of the sphenoid bone, and surrounds the glan- dula pituitaria. As this circular sinus opens upon each side into the cavernous sinus, it is not unaptly divided into two ; the anterior half of the circle, being the anterior clinoid sinus of some authors ; the posterior half (which is in general wider), the elliptical or posterior clinoid sinus, or semi- lunar. This sinus, like most of the lesser sinuses, is irregular in its shape, its size, its communications, and its origin,* Its natural communica- tion is with the cavernous sinus, which in fact encroaches upon its side; it will be found to communicate also with the sphenoidal sinuses, and the oblique or petrous sinuses f : at one time the anterior half of the circle is wanting; at another the posterior. THE CAVERNOUS SINUS. The cavernous sinus is a great irregular centre of communication with the lesser sinuses in the base of the skull. This sinus is sunk up- on each side of the sella turcica, and is formed in the irregular split- ting of the lamellae of the dura mater: it is of a triangular shape; it extends from the sides of the sella turcica, to the foramen spinale. The pointed extremity of the tentorium, which extends forwards from the an- gle of the petrous bone to the posterior clinoid process, covers and protects it. The cavernous sinus is different from all the others ; it is irregular, having fibrous cords traversing it, which give it a kind of cel- lular appearance. It is like a diseased part into which the blood has been driven, till the cellular texture has been distended and partly des- troyed. After a minute injection, small arteries are seen to ramify among these fibres ; the internal carotid artery rises through it, and the sixth pair of nerves is involved in it, in their passage from the skull. This sinus is the centre of the little sinuses and veins of the anterior part of the base of the brain and cranium : four or five veins pour their blood into it, from the anterior lobes of the brain and the fossa Silvii; some- times, even the ophthalmic veins open into this receptacle. J The superior and inferior petrous sinuses, and the basilar sinus, open into it behind; the circular before ; the sphenoidal sinuses and veins of the dura mater upon the side ; while the right and left sinuses often communicate by means of the transverse sinus. Besides these, the petrous sinuses have several communications, or emissarise as they are called, viz. into the orbit, by the funnel of the carotid artery, through which descends a vein (the vena so- dalis arteriae carotidis), which terminates in the pterygoid plexus of veins; again veins pass out by the sphenoidal fissure. The transverse or posterior clinoid sinus, runs across from one * Malacarne, p. 123. t Haller, tom. iv. p. 154. t Soemmerring;, vol. v. p. 354. 84 OF THE VEINS OF THE BRAIN. lateral basilar sinus to another behind the posterior elinoid processes.* In its form it is not peculiar, nor is it very regular. Petrous sinuses.—These are three small sinuses which maybe call- ed petrous, from lying betwixt the dura mater and petrous bone: one runs near the angle formed by the pars squamosa and pars petrosa of the temporal bone ; another occupies the groove on the salient angle of the bone ; and the third is rather belonging to the cuneiform process of the occipital bone. The anterior petrous sinus runs upon the anterior face of the pe- trous bone; from near the spinal hole;| whence making a semicircular curve in the angle of the petrous and squamous portions of the temporal bone, it terminates in the lateral sinus. The posterior petrous sinus J lies in that pointed extremity of the tentorium, which stretches forward, connected with the acute angle of the petrous bone. It is narrow ; and a sulcus or groove on the angle of the bone gives a partial lodgment to it; it passes from the cavernous si- nus to the great lateral sinus, The lateral basilar sinus, or inferior petrous sinus, is shorter and larger than the last; and it makes an oblique curve from the caver- nous sinus under the pointed extremity of the tentorium, which is con- tinued by the side of the sella turcica, to the termination of the lateral sinus, or rather into the beginning of the jugular vein by a channel, sepa- rated by a bony lamina from the termination of the lateral sinus ; or it is continued into a vein in the base of the cranium, which afterwards joins the great jugular vein. The middle basilar sinus.—This scarcely deserves the name of si- nus. It consists, in general, of a few cellular-like communications, formed in strong fibres of the dura mater, which here partakes of the nature of a ligament. These open into the last-mentioned sinus, or sometimes into the vertebral vein. The vertebral sinuses are veins included in the lamellae of the du- ra mater ; and, divided into right and left, they descend into the tube of the vertebrae, on its fore part, and pass down even to the sacrum. They are connected in all their length with the vertebral, dorsal, and lumbar veins. These sinuses or veins, at each vertebra, are joined by a trans- verse branch ; they are connected at the top of the spine with the ba- silar or anterior occipital sinuses. EMISSARY SANTORINI. “ Vena: emissarije ” is but another term for those lesser veins which form communications between the sinuses within the head, and the ex- ternal veins in the base of the cranium. These, then, are chiefly the ophthalamic,§ mastOidean, and vertebral veins. But the vena sodalis ar- teriae carotidis, the small vein which penetrates the parietal bone by the side of the sagittal suture, even the venae arteriae meningese sodales, and * The superior and inferior, or oblique sinus, the cavernous and the transverse, meet near- ly at a point. + And here it has a transverse branch of communication with the cavernous sinus, which runs under tbs extended point of the tentorium. | Or superior petrous sinus. Vicq d’Azyr. v Vicq d’Azyr, Acad, Royale, 1781, p. 504. OF THE VEINS OF THE BRAIN. 85 the little veins which pass with some of the nerves, or through the fis- sures of the bone, are also brought into account. To these a much greater importance has been attached than they merit; particularly in apo- plectic affections of the head, they have been supposed to be eminently useful in emptying the surcharged sinuses and veins of the brain into the external veins. But those lesser passages for the blood, supposing us to be assured that the blood flowed through them, from the sinus to the external veins, are insignificant, when compared with the great outlet of the internal jugular vein ; to which we have seen all the sinuses tend. But the accumulation of blood in the vessels of the brain is seldom mechanically produced : it is a diseased action of the system of the brain, to which we become more and more liable as we advance in years ; and perhaps it is owing to the same gradual change which is operating on the venous system from infancy to old age. The importance of the sinuses in the circulation of the blood in the brain, does not appear to be perfectly understood, at least judging from the expressions of authors. We find it said, that the sinuses support the blood against compression, and protect its free circulation. This may be one use of the structure which is peculiar to these veins, but sure- ly not the principal one. Another conception of the use of the sinuses is nearer the truth ; viz. to prevent the sudden and violent action of the muscles of respiration, or of the muscles of the head and neck, from injuring the smaller veins of the brain; that the sinuses prevent that impulse from being commu- nicated to the blood in the smaller and tender veins of the brain, which might endanger a rupture of them.* Yet this is not exactly the manner in which the sinuses preserve the lesser veins ; they do not suffocate nor take oft' the force of the impulse from the regurgitating blood, so much as they would do if they were, like the trunks of veins in other parts, distensible ; because, being incapable of distention, they throw the undulation of the blood (when it is thus checked in its exit,) backwards upon the extremities of the veins. But then the effect is, that no par- ticular vein or trunk receives the shock; all suffer in a lesser degree, and equally, which is their safety. All the veins in the base of the brain, which would be liable to rupture, or distention, from receiving, in their sudden turns, the shock of the blood, are preserved by being inclosed in sinuses, and covered by the strong lamellae of the dura mater. The less- er vessels again are removed from the shock : its force is spent because it has spread among many branches; and it has become a general im- pulse upon the brain, which the brain resists, because it is incompres- sible. That the brain does receive such an impulse in violent coughing and straining, is sufficiently evident from the rising of its surface seen on these occasions, when it is accidently laid open by fracture, or the tre- pan. t * Monro, Nervous system, p. 4. f The older physicians, observing the connection betwixt the motion of respiration and of the brain, conceived that the air was drawn through the nose and cribriform bone into the brain, so as to distend it. Upon this hypothesis followed many wonderful cases. We have already mentioned the hypothesis which supposed compression and relaxation of the cerebrum and cerebellum alternately, by the action of the falx and tentorium. 86 OF THE PARTICULAR NERVES. We ought not to confound the idea of incompressibility of the bram with that of a solid substance, which would allow no motion in the ves- sels within the cranium, and would require us to invent some specious means to account for the circulation of the blood in the brain, different from that of the other viscera of the body. Were the brain thus incom- pressible, or rather solid, so as to prevent a free action of the vessels within the cranium, then, as the blood enters with an evident pulsation, it must necessarily have returned by the veins with a distinct pulsation. We accordingly observe that whenever the surface of the brain is ex- posed it is seen beating. When pus or blood is forcing its way from under the cranium, we can see that a pulsation is communicated to it, and in the oozing out of blood from the longitudinal sinus, I have per- ceived the same pulsation. When the blood is sent into the arteries of the brain, by the stroke of the heart, they dilate ; and this dilatation the pliability of the brain allows, by throwing a comparative degree of pres- sure upon the veins. Again, when the arteries (during the dilatation of the heart) are in action, and contract, their blood enters the veins, so as to give to them a degree of dilatation equivalent to their former com- pression, and which now allows the freedom of contraction in return to the arteries ; without any compression, therefore, of the brain into a lesser space, there is an activity allowed in the vessels. This motion, communicated through the brain, is very little, nor does it affect the function of the brain ; as we see, when the skull is laid open by wounds, or when the motion is allowed by the fontanelle not being closed. The circulation of the blood in the brain may be obstructed, or it may be accelerated, and by either of these the function of the brain may be affected : or too much blood may be accumulated within the cra- nium : but during this accumulation of the blood there must be a pro- portional space, freed by the absorption of the brain itself, or the partial accumulation in one part of the vascular system of the brain, must be accompanied by a deficiency in the other. OF THE PARTICULAR NERVES. THE FIRST PAIR OF NERVES ; OR, OLFACTORY NERVES. We have described the three roots of this pair of nerves : their trian- gular form, their bulbous extremities, and their manner of perforating the cribriform plate of the mthmoid bone. Where the soft and pulpy-like mass of the olfactory nerves perforate the sethmoid bone, the dura mater involves them, and gives them firm coats. There are two sets of nerves thus formed. First, those which pass through the holes in the cribriform plate, nearest the crista galli, run down upon the septum of the nose, under the Schneiderian mem- brane, and betwixt it and the periosteum ; they become extremely minute as they descend : and they, finally, pass into the soft substance of the membrane. The second class of filaments are those which pass down by the outer set of holes of the sethmoid plate, and which are distributed to the membrane investing the spongy bones. Both of these sets of OF THE PARTICULAR NERVES. 87 nerves form a considerable net-work or plexus before they are very mi- nutely distributed. * Although branches of the ophthalmic, pterygoid, palatine, and sub- orbital nerves pass to the membrane of the nose, they have no power of conveying the impression of odours. These nerves are necessary that the membrane may possess the common sensibility bestowed through the fifth nerve. Before my discovery that the sensibility of the head and face depend- ed on the fifth nerve, there was much controversy whether or not these additional nerves increased the sensibility of the membrane of the nose to odours. We find that there pass to the other organs of sense subor- dinate nerves ; and we know that a nerve may be modified to much va- riety of functions ; and this is evident from the nerve of taste being a branch of the fifth pair. But it is doubtful how far a nerve may be ca- pable of receiving at one instant various impressions. Far from consi- dering distinct nerves sent to the same organ as affording an argument for these nerves receiving one uniform impression, and conveying one simple sensation, it would seem more rational to infer, that one individual nerve cannot perform two functions, and that two functions are often re- quired in the organs of sense. The olfactory nerve is incapable of bes- towing common sensation on the membrane of the nose ; the other nerves which ramify on that membrane, do, on the other hand, contribute nothing to the sense of smell ; we find that the inflammation of the pi- tuitary membrane, which raises the sensibility of the branches of the fifth pair of nerves, does in no degree make those of the olfactory nerve more acute. The membrane is painfully inflamed, but the sense of smell is deadened. SECOND PAIR ; OR, OPTIC NERVES. In this part of the work there is no occasion to deliver any thing further concerning the optic nerves, than has been already said of their origin, and final expansion in the retina of the eye. They are uniform in their shape and course, and give off no branches, implying that they are ap- propriate to a distinct office from the other nerves. THIRD PAIR OP NERVES ; OR, MOTORES OCULORUM. These nerves have the name of motores oculorum, because they are distributed to the muscles which move the eye-balls. They pass up- wards from their origin ; and then diverging, they penetrate the dura mater under the extreme point of the tentorium : they descend again by the side of the cavernous sinus, and pass out of the cranium by the fo- ramen lacerum of the sphenoid bone. When this nerve has entered the orbit by the foramen lacerum, it gives out at the lower and outer part of the optic nerve, a lesser superior branch which crosses the optic nerve to supply the superior rectus muscle of the eye, and from which a branch, having perforated that muscle, goes to the levator palpebrse. The trunk of the third continues its course under the optic nerve, and nearly at * Duverney first observed this course and firmness of the olfactory nerves. John Hunter. Animal Economy, p. 265. Monro, tab. xxiv. 88 OF THE PARTICULAR NERVES. the same place it sends out three branches lying close together. 1. To the inferior rectus, or depressor oculi. 2. To the inferior oblique mus- cle. 3. And to the internal rectus. Or sometimes, varying somewhat, it gives off the first branch to the internal rectus or adductor, another large branch to the depressor, and the continued trunk terminates in the inferior oblique muscle. In tracing the branch which goes to the inferior oblique, we come upon a division of this nerve, which forms the princi- pal root of the ophthalmic, or ciliary, or lenticular ganglion. Haller is of opinion that the ganglion is formed by the third nerve alone, but there is no doubt that a branch of the fifth, viz. of the nasal branch of the ophthalmic division, enters into its composition. Besides the small ciliary nerves coming from the ganglion, other deli- cate nerves, both from the third and fifth, pierce the sclerotic coat of the eye. We may more especially notice a twig from the nasal branch of the fifth which goes to the inner part of the eye. FOURTH PAIR OF NERVES ; TROCHLEARES, OR PATHETICI. These nerves are very small. Their origin, from the superior part of the spinal marrow, and their long course under the base of the brain, have been already described; after proceeding a considerable way, in- cased in the duplicature of the dura mater, where it forms the extreme point of the tentorium, they pass amongst the lamellae of the dura mater, where it forms the cavernus sinus. They pass by the outside of the third pair of nerves ; turn round so as to be above them, and make their egress through the foramen lacerum of the sphenoid bone. They pass forward in the orbit, undiminished by the giving off of branches ; and are each finally distributed to the superior oblique muscle or trochlearis. Sometimes, however, in their course over the cavernous sinus to the orbit, they send branches to unite with the ophthalmic division of the fifth pair; but this is by some anatomists described as only a close ad- hesion to the dura mater. My pupils have traced these connections be- twixt the fourth and fifth nerves. In the part of these volumes which treats of the motions of the eyeball, a reason will be assigned why the origin of the fourth nerve is near the por- tio dura of the seventh pair, and consequently remote from that of the third. THE FIFTH PAIR ; OR, TRIGEMINI, OR, GRAND SENSITIVE NERVE OF THE HEAD. The tracing of the branches of the fifth pair, by dissection, is a diffi- cult task; for those branches are distributed among the bones of the face, to the eyes, nose, mouth, tongue, and throat. From this extensive distribution, the fifth nerve is necessarily the largest of those that pass out of the cranium. It is of a flattened form ; * it penetrates the dura mater at the anterior point of the petrous bone, and spreads flat under it. Here, under the dura mater, it is matted into one irregular ganglion ; viz. the semilunar, or Gasserian ganglion. This ganglion lies on the anterior point of the temporal, and on the sphenoidal bone. In their passage from the brain, the * So it is said, by Meckel, to resemble the flat worm, or tenia OP THE PARTICULAR NERVES. 89 filaments composing the fifth nerve are loose, or easily separated; at this place, they are found so subdivided and entangled as to resist fur- ther division. The nerve here swells out into a greater size ; it seems to be incorporated with the dense fibres of the dura mater ; it becomes of a dark red, or mixed colour, having a semilunar mass of matter of the same appearance as ganglion, stretching across it; all which circum- stances have, by no means, been unobserved by anatomists. Vieussens supposed, that the use of this ganglion of the fifth pair, before it perfo- rates the cranium, was to strengthen the nerve, and enable it to withstand the motion of the jaws ! Others have said it was a ganglion connecting in sympathy all those parts to which the nerve is finally distributed ; and that it was the source of the sympathy which we observe among the muscles of the face.* The connection of the Gasserian ganglion with the dura mater, is so firm, that it yet remains undecided, whether there are sent off here any nerves to that membrane; but I conceive that there are none, and that the connection of the ganglion with the fibrous membrane, or sheath which covers it, has been mistaken for nerves passing from the ganglion to the dura mater. From the semilunar or Gasserian ganglion, the fifth nerve divides into three great branches ; whence the name of trigeminus : 1st, The ophthalmic branch of Willis, which passes through the foramen lacerum into the orbit. 2d, The superior maxillary nerve, which passes through the fo- ramen rotundum. 3d, The inferior maxillary nerve, which passes to the lower jaw, through the foramen ovale. Such was the description of this nerve, until I found a necessity of examining it more minutely. I then found that Soemmerring, and others, had observed, that this nerve had two roots, and that one of these roots did not go into the ganglion. Afterwards, upon comparing it with the spinal nerves, I found its correct correspondence to them ; and, as I have stated in the introductory view, that it was the superior spinal nerve, corresponding in function and bestowing upon the head the powers of sensibility and motion, which were given to the body through the spinal nerves. The ophthalmic and superior maxillary nerves go off from the gan- glion of this nerve, and so does a part of the third division. The root or fasciculus, which passes the Gasserian ganglion, joins the thiid divi- sion, and goes out with it through the foramen ovale f * “ Et affectum animi indicia in faciei partibus depingere adjuvet.” Hirsch. Sand- Thes Diserta. p. 491. , f Ope horuin vasorum communis nervi truncus in duo fasciculorum strata separaoatur an- terius nempe et posterius. Posteriori nunc strato parva portio adhaerebat, perpendiculariter in caveam descendebat et absque omni curn iutumescentia semilunari facta coirimistione in ra- mum tertium seu maxillarem inferiorem inserebatur. Wrisberg. tom. i. p. 267. Ludwig. Wrisberg has also a drawing which shows the roots forming the 5th pair ; he distinguish- es them thus: P. s. portio ejusdem, (Quinti Paris,) superior et anterior; p. i. portio inferior posterior major. _ Soemmerring makes particular mention of the distinction of the two roots forming the nith pair. “ Suinme autem memorabile videtur secundam vel minorem quinti portionem omnino non immisceri subrubello plexui gangliforftii, in quem portio major dissolvitur, sed fere inte- grant) ad ramum tertium abire.”(l) (1) Primus et solus hoc in tabujis expressit celeb. Prochaska libro; sec. 3. citato tab. 2. tig. 4, 5, 6. Soemmerring de Basi encephali, etc., sec- Ixi. tom. ii. Ludwig. 90 OP THE PARTICULAR NERVES. THE OPHTHALMIC BRANCH OF THE FIFTH PAIR. This nerve enters the orbit in three divisions; these are, the frontal, the nasal, and the lachrymal nerves. Before its division, the trunk of this nerve communicates by a small branch with the third nerve.* 1st, The first of these runs under the periosteum of the upper part of the orbit, and above the levator palpebrae superioris. Upon entering the orbit it gives off a small branch, which passes to the frontal sinus ; the nerve then divides into the super-trochlearis, and the proper frontal nerve. The first of these passes to the inner part of the orbicularis occuli and frontal muscle. The other, the outermost, and the proper frontal nerve, passes through the hole, or notch, in the margin of the orbit, and mounts upon the muscles and integuments of the forehead. These superficial branches communicate with the extreme branches of the portio dura, or nervus communicans faciei; a circumstance which we have proved to be of the highest interest, since the division of the branches of the fifth de- prive the parts of sensibility; whilst the division of the branches of the portio dura deprive the muscles of motion. Cases are on record, of wounds of the frontal nerve occasioning a great variety of nervous symptoms, and especially loss of sight; and it cer- tainly marks a very particular connection and sympathy betwixt this branch and the common nerves which pass to the eye-ball and iris, and the retina, that blindness is actually occasioned by the pricking of the frontal nerve. Morgagni supposes this to be occasioned by the spasmo- dic action of the recti muscles pressing the globe of the eye down against the optic nerve. 2d, The nasal branch of the ophthalmic nerve sends off a slip or twig to form with a branch of the third pair, the lenticular, or, oph- thalmic ganglion ;f while the trunk of the nerve passes obliquely forwards, under the atollens palpebrae, and levator oculi, it gives some filaments to these muscles. While pursuing its course along the inside of the optic nerve, it gives oft’ one or two extremely small twigs, which join the fasciculi of ciliary nerves coming off from the ganglion. The nasal branch then continues its course betwixt the superior oblique and adductor muscles; before piercing the orbital plate, its sends forward a branch, which, passing under the pulley of the superior oblique muscle, joins that division of the frontal nerve which passes over the pulley. This branch supplies the caruncula lachrymalis, and sends a twig down to the lachrymal sac and duct. It emerges from the orbit superficial to the tendon of the orbicularis oculi, and unites with the branches of the por- tio dura, and of the infra-orbital branch of the fifth. The proper nasal nerve passes through the foramen orbitarium anterius, enters the skull again, and lies on the cribriform plate of the aethmoid bone under the dura mater. It passes through one of the anterior holes of the cribri- form plate, and gives branches to the frontal sinuses. After having con- tinued its course in a groove on the nasal process of the frontal bone, it runs forward and downward in a similar groove on the inside of the os nasi; from thence, getting on the outside of the cavity of the nose, it * See Meckel’s Disertation on the fifth pair. f Vieussens describes delicate twigs which are distributed on the inferior rectus and the abducens muscles before this lenticular branch is given off. Fig. xxii. let. g. h. i. i. OF THE PARTICULAR NERVES. 91 runs along the cartilaginous part of the ala, and near the extremity of the nose mounts upon the tip of the ala, and then, dipping down between the two alae, is lost on the anterior extremity of the cartilaginous septum. In its course it sends several small filaments into the aloe. It bestows common sensibility to the membrane of the nose, while the sensibility to odours belongs to the first nerve.* We observe such a connection of the nerves of the eye and nose, and of those distributed to the inner angle of the eye, and muscles of the eye-lids, as sufficiently accounts for the sympathy existing among those parts. We see the necessity of this connection, since the excitement of the glands which secrete the tears, the action of the muscles, and the absorption of the tears into the nose, must constitute one action; never- theless this motion of the muscles, when the surfaces are excited, results from the connection of the nerves (the fifth and seventh,) in the brain, as might be easily shown. Willis describes a nerve going off from the nasal branch to the retractor oculi in brutes. The lenticular, or, ophthalmic ganguon, comes again to be considered under this division of the fifth pair. It is formed by a twig from the nasal branch of the fifth pair, and a division of the third pair of nerves. The ganglion is of a square form, and is situated upon the out- side of the optic nerve. The ciliary nerves pass out from this ganglion in two fasciculi; they are ten or twelve in number ; they are joined by branches of the continued nasal nerve. The ciliary nerves run forward amongst the fat of the orbit, to the sclerotic coat of the eye, and pierce it very obliquely in conjunction with the ciliary arteries. The ciliary nerves and arteries then pass forward betwixt the sclerotic and choroid coats of the eye to the iris. The iris is considered as the part the most plentifully supplied with nerves (as it certainly is also with arteries) of any part in the body. It follows, indeed, from what we formerly said, that a profuse circulation of blood is necessary to an accumulated nervous pow- er. The fine sensibility and mobility enjoyed by the iris is owing to those nerves : the fifth nerve giving sensibility, and the third mobility. From the connection of these ciliary nerves with those passing to the nose. Soemmerring accounts for sneezing being the consequence of a strong light upon the eye. This may perhaps be true ; but, certainly, the temporary loss of sight from sneezing does not depend upon this connection of the nerves, but upon the immediate affection of the optic nerve and retina, from the concussion and interruption to the circulation, or from the accumulation of blood in the eye. The lachrymal nerve is the least of the three divisions of the ophthalmic nerve ; it divides into several branches before and after it has entered the gland, j- Several of these branches pass on to the tunica conjunctiva, being joined by a twig of the first branch ot the superior maxillary nerve. Others connect themselves with the extremities of the portio dura of the seventh pair, and with the superior maxillary nerves. By these the flow of the tears is commanded by the degree of irritation of the surface of the eye, so that the tears flowing, wash away the of- * See John Hunter, Animal Economy. Munro, tab. xxiv. f Vieussens, Haller, and Meckel take notice of small delicate nerves which are the continu- ation of the nerves of the lachrymal gland, and can be traced to the tunica adnata. Although they observe some anatomists have considered these to be the ducts of the lachrymal gland. 92 OP THE PARTICULAR NERVES. fending matter. I have had several cases communicated to mo of total insensibility of the surface of the eye, while the motion and sensibility to light remained entire. In all these instances I had reason to attribute the defect to the injury of the fifth nerve. THE SECOND BRANCH OF THE FIFTH PAIR ; VIZ. THE SUPERIOR MAXILLARY NERVE.* The superior maxillary nerve, the middle one of the three divisions of the fifth, having passed the foramen rotundum, emerges behind the an- trum Highmorianum, at the back part of the orbit, and near the root of the pterygoid process of the sphenoid bone. The infra-orbital canal lies directly opposite, and ready to receive one branch, while the spheno- maxillary opening is ready to receive another. Here several small branches go off, the Rami molles medullares, and render the dissection difficult, f The chief part or trunk, of the nerve may be said to be seat- ed, and to give out its divisions in the pterygo-palatine fossa. Through the spheno-maxillary fissure, a branch of the superior nerve is sent into the socket of the eye. This twig unites with branches of the lachry- mal nerve, and in general supplies the periosteum of the orbit. It then sends, through the foramen in the os malse, a branch which is distribut- ed to the orbicularis muscle of the eye-lid, and to the skin of the cheek, vix. subcutaneus males. Another branch of this division passes upward from the zygomatic fossa, in a groove of the wing of the sphenoid bone, to the temporal muscle, and getting superficial, it accompanies the branches of the temporal artery. Here it becomes superficial, forming the subcutaneus temporalis. The superior maxillary nerve, after sending off these branches, di- vides into four branches : 1. Vi dianus. 2. Palatinus. 3. Alveolaris; whilst the continued nerve is, 4. Infra-orbitalis. The Vidian nerve sends off branches which enter the nares, and ex- tend betwixt the mucous membrane and periosteum to the ethmoid and spongy bones. These are divided into the nasales superiores anteriores et posteriores. Where the Yidian nerve parts from the trunk, the spheno- palatine ganglion is formed, J and having sent these nasal branches off, it enters the foramen pterygoideum and runs backwards. Here it splits ; one branch, after a long retrograde course, enters the Yidian hole of the petrous part of the temporal bone, and forms a connection with the portio dura §, while the other, in the carotid canal, forms a connection with the great sympathetic nerve, by joining the branches of the fifth and sixth pair, which pass down with the carotid artery. In the manner of joining of the sixth, the Yidian and the sympathetic in the carotid canal, and around the carotid artery, a considerable variety occurs. It is, in fact, a union of the fifth, sixth, and seventh with the ascending vis- ceral nerve. * According to Winslow. f Meckel de 5lo pare, lviii. | Meckel de Ganglio Secundi Rami Quinti Paris nuper detecto Histoire de l’Acad. Roy. des Sciences, Ann6e 1749, & Berlin 1751, p. 84. § In the foetus, the foramen innominatum or vidian hole is so short, that the union of the vidian nerve and portio dura may be seen. In the adult it is seldom necessary to cut more than the tenth of an inch to expose clearly the union of the nerves. See John Hunter. Ani- mal Economy, p. 260. OF THE PARTICULAR NERVES. 93 The superior posterior nerves of the nose come off from the Vidian just when it has entered within its canal. The Palatine nerve is the largest of the branches sent out from the spheno-palatine ganglion. Before it descends it gives off small nerves called anterior superior internal, which ascend to the superior spongy bone, and join with the posterior branches of the olfactory nerves. The palatine nerve next gives off the naso-palatine described by John Hunter and Scarpa. This nerve bending upon the superior part of the vomer, and coursing in an oblique manner towards the anterior and lower part of the vomer, pierces the foramen incisivum, and is lost in the gum, behind the incisor tooth, and on the membrane of the roof of the mouth at that part. We have to recollect that there are two canals in the palatine bone, conveying nerves to the palate ; one the anterior and larger, another run- ning nearly parallel to it, which is smaller. The division of the pala- tine nerve, descending at first along the spheno-palatine canal, which leads to the palatine foramen, gives off the inferior internal nerves of the nose, which are distributed principally on the upper and lower turbi- nated bones. Continuing its course along the canal, it sends off a branch to the tonsils, which descends before the pterygoid processes and betwixt the maxillary and palatine bones, and is called the palatinus minimus ex- terior. A small nerve descends through that foramen, which is imme- diately anterior to the pterygoid process, to supply the circumflexus, levator palati, and azygos uvulae. * While the larger branch descends through the greater and more anterior foramen, and divides into three branches, which supply the soft parts lining the palatine bone, and the palatine plate of the maxillary bone ; also the arches of the palate. A groove in the bone points out the course of this nerve forwards. The superior maxillary nerve, after sending off the branches which form the spheno-palatine ganglion, passes obliquely downward to the infra-orbital canal. In this course it gives off the posterior nerve to the teeth of the upper jaw ; and this again gives off a twig, which takes a course on the outside of the maxillary bone, and supplies the gums and alveoli, and buccinator muscle. Before entering the canal it sends off the alveolar branch, which supplies the molares, through the foramina, on the posterior surface of the maxillary bone, and then follow the alveolar branches of the inter- nal maxillary artery; a branch from this division enters the buccinator muscle. W'hile passing in its canal, the infra-orbital nerve gives off the an- terior nerves to the teeth; and when it emerges from the infra-orbital foramen, it spreads widely, and forming a plexus, enters the muscles of the lip and nose, goes on to the integuments ; and here it is of course joind by the appropriate division of the portio dura, connecting itself with the extremities of the portio dura of the seventh pair or nervous communicans facialis. The “ tic doloureux,” and the “ tic convulsif,” of the French authors, are diseases attributed to the affection of this nerve. The seat of the tic doloureux is the side of the face, the nostril, the cheek-bone, and * I am of opinion that these muscular nerves may in part be ramifications of the portio 'lura, coming along the virlean foramen. 94 of the! particular nerves* root of the alveoli. Sauvage calls it the trismus dolorificus, or maxiila- ris. But it is a disease not absolutely fixed to this point of the cheek- bone ; but on the contrary, from the universal connection betwixt the nerves of the face, it takes, sometimes, a wide range ; however I attri- bute it to the influence of the sympathetic nerve, and conceive that this is the reason that the disease is so often seated in this superior max- illary nerve, which has the most direct connections with the sympathetic. It is a disease attended with extreme pain, which forces the patient to cry out in great agony. i he patient has described it to me as like a flash of lightning through the head, so sudden is it in its attack. And as to its violence, it is sufficient to say, that it throws the same patient into the most violent contortions of pain, who will sit unmoved and suf- fer the ne rve to be deliberately cut across. The pain is felt deep rooted in the bones of the face, and seems to spread upon the expanding ex- tremities of the nerve; it is sudden, violent, and reiterated in its attack, and it varies in the length and repetition of its accession. This disease is apt to be confounded with the affection of the antrum Highmorianum, the toothach, rheumatism, and clavis hystericus, or even with venereal pains. In hemicrania, the affection of the three branches of the fifth nerve is such as to mark their distributions. There is swelling and pain of the face, pain in the upper maxillary bone, pains in the ear and in the teeth, difficulty of swallowing, and lastly, stiffness in moving the lower jaw, in consequence of the affection of those branches which pass up to the temporal muscle. There are cases spoken of by Sabbatier, where this infra-orbital nerve being wounded, unusual nervous affections, and even death, were the consequence: but it would rather appear, that, independently, alto- gether of the affection of the nerves of the face, inflammation spread- ing from the wound to the brain, had, in the examples which he gives, been the occasion of the unusual symptoms, and of the death of the patients. THIRD BRANCH OF THE FIFTH PAIR: OR, LOWER MAXILLARY NERVE. This, the last of the three great divisions of the fifth pair of nerves, the largest but the shortest branch within the skull, passes out by the foramen ovale.* It is distributed to the muscles of the lower jaw, tongue, the glands, and skin. On instituting the comparison betwixt the spinal nerves and the fifth, I observed that a fasciculus passed the Gasseraan ganglion and joined the third division, and passed with it through the foramen ovale. Hav- ing followed it thus far, I put my pupils on the further prosecution of this branch to determine whether the peculiarity of this division was owing to its being the gustatory, or a muscular branch. I could, upon their authority, show that this was the motor portion of the fifth nerve, and that it went to the muscles of the jaw and cheek. But at the same time I consulted books, and I found the most perfect description of * The lower maxillary nerve of Winslow, gustatory of Meckel. Ramus major posterior nervi quinti paris, Vieussenii. OF THE PARTICULAR NERVES. 95 the nerve, and so entirely unbiassed by a mere dissector, that I shall prefer stating what Palletta affirms.* Having observed this free division of the fifth nerve, he chooses to consider it as a newly discovered nerve ; traces it from its origin along the inside of the proper fifth, and past the ganglion, and into the foramen ovale. While they are passing together through the bone, a few filaments from that portion of the nerve which has a ganglion, unite with the nerves proceeding from the newly-discovered trunk. I may just observe that if we were to admit this to be a new nerve, we might so distinguish the anterior roots of all the spinal nerves, since this division is to the fifth what the anterior division is to the proper spinal nerves. Observing this (anterior) division of the fifth narrowly, he finds it consisting of two nerves: 1. Fasciculus primus seu nervus crotaphiticus 2. Fasciculus sccundus, seu nervus buccinatorius. Tracing them on their course through the foramen ovale he finds them passing as their names imply, into the temporal and buccinator muscles. The First of these gives off the nervus massetericus. The ramus massetericus passing betwixt the external pterygoid and temporal muscles, and over the semi-lunar notch of the lower maxillary bone, and behind the tendon of the temporal mus- cle, sinks into the masseter. Hence, a branch passes out of the integu- ments of the cheek, viz. the nervus temporalis superjtcialis seu auricula- ris which emerges from the parotid gland near the root of the jugum.f This nerve also gives off the two temporal nerves, which are named temporalis profundus exterior and temporalis profundus interior. J The Second of these, or the buccinatorius, supplies the pterygoideus exter- nus, and gives some twigs to the temporal muscle. It then supplies the buccinator muscle, the glandulae buccales, and a few delicate nerves upon the cheek, unite with the branches of the portio dura. The nervus buc- cinatorius gives off the ramus pterygoideus, which is a small branch going to the pterygoideus internus, and circumflexus palati. In short, tracing this division of the maxillary nerve, in all its course, he finds it exclusively given to the muscles of the jaw and cheek. § But a cir- cumstance occurs here not without interest: before entering the mus- cles these branches are joined by branches of the ganglionic portion of the nerve, (which he persists in calling the maxillary nerve, in contradis- tinction to his supposed discovery of the new nerve.) When we compare the distribution of the nerves to the muscles of the jaws and cheek, with the distribution of the seventh pair and the fifth pair, to the external muscles of the face, and when we take into considera- * J. B. Palletta de nervis Crotaphitico et Buccinatorio, 1784. Mediolani. Ludwig, tom. iii. p. 63. f Winslow describes this cutaneous branch, joining with the portio dura. Meckel has not observed it. $ A branch of the temporalis profundus enters the orbit and joins the lachrymal nerve. § Meckel, in his description of the third division of the fifth pair, follows Eustachius and Al- binus in subdividing this nerve into two distinct sets of branches. When it has passed through the foramen ovale it is divided into two portions, which Albinus distinguishes as the Anterior and Posterior branches. Meckel describes them under the names of Superior and Inferior. The former splitting at once into many separate branches, while the latter is the larger nerve, and forms the continued descending portion of this third division. He enumerates as be- longing to the Superior Ramus, 1. The Massetericus. 2. Temporalis profundus exterior. 3. Temporalis profundus interior. 4. Buccinatorius. 5. Pterygoideus. The Inferior Ramus, after giving off some small branches to join those of the Superior, is composed of three prin- cipal branches: 1. Maxillaris inferior. 2. Lingualis seu gustatorius. 3. Temporalis su- perficialis. See Meckel, de quinto pare nervorum. Sect. v. tom. 1. Ludwig. 96 OF THE PARTICULAR NERVES. tion that the division of the seventh nerve cuts off all power of moving the muscles of the face, a question may very naturally occur. If divid- ing the muscular nerves is attended with loss of motion in the muscle, what is the use of the sensitive nerves which are given to these same muscles, seeing they confer no power of motion ?* We now attend more particularly to the two greater divisions of this nerve, the proper maxillary nerve which passes into the lower jaw, and the gustatory or lingual nerve, after the nerve has passed the pterygoid mus- cles. The gustatory nerve is the division which descends to the tongue. Immediately after its separation from the nerve of the lower jaw, it is joined by the chorda tympani; or, perhaps, we should rather say, a branch of this nerve, by traversing the petrous portion of the temporal bone in a retrograde direction, unites itself with the portio dura of the seventh pair, as it is passing through the ear. This nerve being seen passing across the tympanum is the reason that it is called chorda tym- pani. It is comonly described as going along the Eustachian tube; we ought rather to say in the groove of the bone under that passage. Arriv- ing in the cavity of the tympanum, it runs across and joins the portio dura before its exit by the stylo-mastoid foramen. The gustatory nerve, pro- ceeding obliquely downward, sends off twigs to the salivary glands and muscles, situated betwixt the jaw-bone and tongue. Where it is passing by the side of the sublingual gland, it gives out some filaments which form a small ganglion, from which branches penetrate the submaxillary and sublingual glands. The trunk then proceeds onward betwixt the sub-lingual gland and the musculus hyo-glossus ; several twigs are sent off, which form a kind of plexus amongst the muscles and salivary glands ;t and communicating with the ninth pair of nerves, are distribu- ted, finally, to the gums and membrane of the mouth. The gustatory nerve terminates in a lash of nerves, which sink deep into the substance of the tongue, betwixt the insertion of the stylo and genio-glossal muscles. These pass to the papillae on the tip and edges of the tongue. The sense of taste, the impression of which is received upon this nerve, is seated in the edge and anterior part of the tongue. The proper lower maxillary nerve, which enters into the lower jaw-bone, sometimes called mandibulo labralis, passes downward in an oblique di- rection to the groove of the lower jaw-bone. Before this nerve enters the canal of the bone, it gives off branches to the mylo-hyoideus and digastricus, to the sub-maxillary glands, and to the fat. The nerve then entering the bone, runs its course all the length of the lower jaw within the bone, and comes out at the mental hole. In this course it gives branches which enter the roots of the teeth, and accompany the branches of the arteries. When this lower maxillary nerve has escaped from the mental hole, it divides into two branches upon the chin ; one of these is distributed to the orbicularis and depressor anguli oris, and to the skin and glands of the lips ; the other to the depressor labii inferioris and integuments, and forms a kind of plexus, which surrounds the lips. These nerves are also connected with the wide spreading branches of * This is the first idea which suggested the paper in the Transactions of the Royal Society entitled “On the Nervous Circle which connects the Voluntary Muscles with the Brain.” f Plexus gangliformis. Scarpa. OF THE PARTICULAR NERVES; 97 the portio dura of the seventh pair; and they are the lowest branches of the facial nerves, and the last enumerated of the intricate branches of the fifth pair. In recapitulating the branches of the fifth nerve, it is only necessary to say that it goes every where to the head and face, externally and inter- nally ; that it is then universally the nerve of common sensibility; that it possesses also some peculiar sensibilities, as on the surface of the eye. Finally, that it is the nerve of the muscles of the jaw. On exciting the root of the fifth pair of an ass recently killed, the jaws were made to snap violently. And on dividing the fifth in another ass, the jaw fell down, the muscles being incapable of closing the jaw. On attempting to excite the muscles of the eye by galvanism sent through the fifth pair, the muscles of the jaw were affected. Professor Boch of Leipsic, and M. Cloquet of Paris, in prosecuting the minute anatomy of the sympathetic nerve, have described a small ganglion lying on the carotid artery, where it has just entered within the skull. This my pupils have frequently shown to me, and we find it des- cribed by Willis. * From the dissection of those nerves, in the larger animals, it appears quite an error to suppose that the principal connec- tion between the nerves of the head and the sympathetic is through the sixth pair. For this small ganglion is a centre from which nerves can be traced to the ophthalmic division of the fifth, the sixth, and the sym- pathetic. f THE SIXTH PAIR OF NERVES; ABDUCENTES, OR MOTORES EXTERNI. The sixth pair of nerves, as we have seen, arises betwixt the tuber an- nulare and the corpus pyranaidale. Advancing forwards and upwards, sometimes above and sometimes beneath the branches of the basilar ar- tery, it penetrates the dura mater by the side of the basilar sinuses. It then passes by the side of the carotid artery, and through the cavernous sinus. Here it gives off filaments, which, clinging to the carotid arte- ry, descend with it until they are joined by a branch of the Fifth Pair. These together form what was formerly considered the origin of the great sympathetic nerve. It has been disputed whether a branch is given out from, or received into, the sixth nerve ; and in the description of the sixth pair, we might say, with reason, that as it passes the carotid artery, it receives one or more nerves which come up through the carotid hole, and encircle the artery. The sixth nerve enters the orbit by the foramen lacerum, with the third and fourth nerves and first branch of the fifth. It * Alter superior idemque major Paris quinti ramus, sub dura matre juxta sell® turcicae latus aliquanto spatio recta incedit: atque 6 regione Glandul* pituitari* carotidis trunco propagines qua9dam elargitur dein nei vo sexti Paris inosculatur : et exinde surculum, modo unum, modo duos remittit, qui cum surculo altero, a nervo sexti Paris reflexo, uuiti, nervi in- tcrcostalis radicem, sive caudicem prinium constituunt. Willisii Opera Omnia, cap. xxii. tig. 1., litt. A. 6. b. f It was a subject of very warm discussion amongst Haller’s pupils, whether there were any twigs connecting the 5th pair to the sympathetic within the skull. Meckel, in his treatise on the 5th pair, inveighs most vehemently against all persons who pretend that the 5th pair has any connection with the sympathetic, besides that which it has through the Vidian nerve. He appeals to the characters of Eustachius, Haller, Albinus, and Morgagni, to support him in the denial of such branches existing. He affirms that no other nerve than the sixth gives origin to the sympathetic. See Winslow translated by Douglas, pp. 80, 121, vol. ii. for a true description of the connections of these nerves. 98 OF TH,E PARTICULAR NERVES. pierces the abductor muscle of the eye before it is finally distributed to its substance. It is with particular pleasure that I have here to refer again to our celebrated countryman, Willis, whose minute knowledge of anatomy cannot be sufficiently admired. He describes a branch of this sixth nerve going to the retractor oculi of brutes. When we consider the office of the retractor oculi to be the protrusion of the haw, it suggests to us a reason why the sixth nerve should go to the external rectus : for the direction of that muscle is such, that in its action it must draw the eye-ball towards the os planum, and assist the retractor oculi in thrusting out the haw. If it be said, what then is its use in the human eye 1 we may allege that it is for the same purpose, that is, to draw the eye when painfully excited towards the os planum, and so thrust out the semilunar fold and carun-- cula lacrymalis. In matter of fact, the caruncula and membrane are thrust out, however we may explain it ; for if the eye-lids be kept for- cibly apart, and an attempt be made to wink, as if a mote were in the eye, the membrana semilunaris and caruncula lacrymalis are brought for- ward over the eye so as to make no bad representation of the haw. It is curious that Soemmerring describes the sixth arising in two roots, an external and an internal portion. Yicq d’Azyr, and Scarpa describe an external larger and internal smaller portion constituting the roots of this nerve. It has been presumed that the sixth nerve does not give off the sym- pathetic nerve, but receives those branches from it, because the sixth nerve is larger betwixt this point and its distribution in the orbit, than be- twixt the same point and its origin from the brain. But I conceive, that this enlargement of the sixth pair is not owing to such a junction ; but that, on the contrary, the nerve naturally swells out when it enters the sinus, not from being soaked in the blood of the sinus, but from its hav- ing additional investing coats, or from the coats being strengthened in or- der to prepare the nerve for its passage through the sinus. Again, that the sympathetic nerve sends up those branches to join the sixth, has been presumed from the effects of experiments on brutes in which the sympathetic nerve has been cut or bruised. Inflammation and heaviness of the eye has been observed to result from these experi- ments. We shall probably cease to dispute this point, when we consider the relations and use of the sympathetic nerve. The sympathetic nerve may be defined, a tract of medullary matter, passing through and connecting the head and neck, the viscera of the thorax, abdomen, and pelvis, into one whole. * The sympathetic nerve is singular in this, that it takes no particular origin, but has innumerable ori- gins, and a universal connection with the other nerves through all the trunk of the body. Many of the viscera to which it is distributed are entirely independent of the will, and have functions to perform too es- sential to life to be left under the influence of the will. The sympathe- tic nerve is thus, as it were, a system within itself, having operations to perform of which the mind is not conscious ; whilst the extent of its connections occasion, both in health and disease, sympathetic affections not easily traced. It is impossible seriously to consider the sixth nerve as giving the ori- gin to the sympathetic in any other light, than as such an expression may OF THE PARTICULAR NERVES. 99 be subservient to arrangement, description, and general enumeration of the nerves ;—a thing most necessary in so intricate a piece of anatomy. The character of the sympathetic nerve (or, I believe I should say, sympathetic system of nerves,) is that of having ganglions formed upon it ;—and thus the ganglions in the sockets of the eyes, in the fossae of the jaws, and every where, whether within or without the head, are to me proofs of the sympathetic nerve extending its connections to such parts. OF THE SEVENTH PAIR OF NERVES. The nerves of the seventh pair consist each of two fasciculi which arise together, and pass into the foramen auditorium internum.* But these portions do not pass through the bone in union ; for the anterior and lesser fasciculus, is a muscular nerve, which passes through to the face, and is invested, like the common nerves of the body, with strong coats. It is therefore called the portio DURA.f The more posterior fasciculus is the auditory nerve, and is distributed to the organ within the pars petrosa of the temporal bone ; and in distinction it is called the PORTIO MOLLIS. The PORTIO DURA, OR NERVUS COMMUNICANS FACIALIS, OR RESPIRA- TORY nerve of the face. This is the grand motor and respiratory nerve of the face. When divided all motions but those of the jaws cease, and more especially all consent of the muscles of the face with the actions of respiration are cut off by the loss of this nerve. The portio dura in passing from the brain to the internal auditory foramen is lodged in the fore part of the auditory nerve, as in a groove. When it leaves the auditory nerve, it passes on through the bone, and emerges on the side of the face through the stylo-mastoid foramen at the root of the styloid process, so as to come out betwixt the lower jaw and the ear, co- vered, of course, by the parotid gland. The portio dura, while passing through the canal of the temporal bone (which is the aqueduct of Fallo- pius), gives off a branch which unites with the Yidian nerve of the fifth pair : or rather, we may conclude with the best authors, that it receives a branch which comes retrograde from the vidian nerve, passing through the small hole on the anterior surface of the petrous part of the tempo- ral bone. The portio dura, when it has proceeded onwards by the side of the tympanum, gives off one or more very minute branches to the muscles within the tympanum, which give motion to the small bones of the ear. A little further on, this nerve gives off a more remarka- ble branch, which passing across the tympanum, is called chorda tym- pani. This is the branch, which, as we formerly mentioned, joins the gustatory branch of the lower maxillary nerve. The chorda tym- pani passes into the tympanum by the hole in the pyramid : it takes its course on the membrane betwixt the long process of the incus and the handle of the malleus ; it is then received into a groove of the bone, it passes by the side of the Eustachian tube, and after enlarging consi- derably, it is united with the gustatory nerve as described. * The intermediate filaments of Wrisberg, which are betwixt these two portions of the seventh nerve, is afterwards united to the portio dura, and must be considered as one of its roots. t Galen divided all the nerves of the brain into those two classes, mollis and dura ; of which the first were those of the senses, the latter the motores corporis. 100 OF THE PARTICULAR NERVES. When the portio dura, has escaped from the stylo-mastoid foramen, but is yet behind the condyle of the lower jaw, and under the parotid gland, it gives off, 1st, The posterior auris. This has connection with the first cervical nerve, and passing up behind the ear, it is connected with the occipital branches of the third cervical nerve. 2d, The nervus stylo-hyoideus to the styloid muscles, and here it unites with the sympa- thetic. 3d, A branch which supplies the deep muscles, and joins the laryngeal branch of the eighth pair. The portio dura, rising through the parotid gland, spreads out in three great divisions, and where it divides, the membranes connecting the di- visions are like webs betwixt them, and this has acquired for this division, the name pes anserinus. Here indeed, a sort of plexus is formed. 1. An ascending branch, which divides into three temporal or jugal nerves; so called, because they ascend upon the jugum, or zygomatic process, to the occipito-frontalis muscle. Two orbitary nerves, which passing up to the orbicularis muscle, branch upon it and inosculate with the extremities of the fifth pair. These branches of the portio dura to the muscles of the eye-lids are the sole movers of the muscles here, and if they be destroyed by tumor, abscess, or the knife, the eye-lids remain open and the eye-ball exposed. 2d. The superior facial branch passes out from the upper part of the parotid gland, across the face to the cheek and orbicularis muscle of the eye. The middle facial nerve passes from under the risorius Santo- rini ; it goes under the zygomatic muscle, and encircles the facial vein ; it sends branches forward to the lips, and upwards to the eye-lids, and to unite with the infra-orbital nerve. There is an inferior facial nerve, which comes out from the lower part of the parotid gland, passes over the angle of the jaw, and is distributed to those fibres of the platysma my- oides which stretch up upon the face, and to the risorius Santorini: it passes on to the angle of the lips, and is distributed to their depressor muscle. Betwixt those facial nerves there are frequent communications, while they are at they same time united with the extremities of several branches of the fifth pair before piercing the substance of the muscles. 3. The descending branches pass along the margin of the jaw, down upon the neck, and backward upon the occiput. Thus we see that the portio dura is well named the communicating nerve of the face. It is distributed to the side of the face, head, and upper part of the neck: it unites its extreme branches with those of the three great divisions of the fifth pair, with the eighth and ninth, with the accessory of the eighth pair, with the second and third cervical nerves, and with the sympathetic. From those various connections the portio dura has also been called the lesser sympathetic. The connection of the nerves of the face, throat, and neck, with the nerves of respiration, affords one of the most curious subjects of inquiry as connected with expression.* (The portio mollis of the seventh pair of nerves is the acoustic or auditory nerve; which shall be considered in a more particular manner when we describe the organ of hearing.) * This opinion I beg leave to let remain as in former editions, as implying my conviction of the importance of those nerves which I have since proved. OF THE PARTICULAR NERVES. 101 [further illustration of the functions of the nerves of the FACE AND HEAD. I shall add here some familiar instances and cases to show the importance of the knowledge of the nerves of the face in the investigation of disease. The reader has only to take with him these facts ; 1. The branches of the fifth nerve bestow sensibility to the head and face: 2. The same nerve supplies the muscles of the jaws for mastication: 3. The portio dura is the muscular nerve of the face, it combines the muscles with the acts of respiration, and is the source of all expres- sion in the face. “ J. Richardson, October, 1820.—On first looking at this man, there does not appear to be any thing unusual in the state of his face ; but the moment he speaks or smiles, the mouth is drawn to the left side. When he laughs, the distortion is increased ; and when he sneezes, the difference between the two sides is quite ex- traordinary. “ On holding ammonia to his nose, it was observed that he could not inhale freely with the right nostril; and, on examining the state of the muscles, when the act of sneezing was excited by the ammonia snuffed up by the left nostril, it was found, that not only those of the right side of the nose and mouth, but also of the eyelids, were passive, while all the muscles of the left side were in full action. When he blew, or attempted to whistle, the air escaped by the right angle of the mouth, the right buccinator not at all corresponding in action with the muscle of the left side, nor with that of the muscles of the chest and neck, by which the air was expelled. The sensibility of the paralyzed cheek was equal to that of the other side, and he could close his jaws with equal force on both sides.” The early history of the case, according to the account given by the patient’3 friends was this:— “He was seized with a severe pain under the ear, and in a short time became so delirious, and his face so distorted, that the people in whose house he lodged, sup- posing him to be mad from brain fever, carried him to the parish work-house. There he lay until his friends discovered him, and brought him into the hospital, It was then found, that the phrensy which had led the people of the lodging-house to suppose that he was mad, was only a high state of delirium, in consequence of a severe attack of cynanche parotidea ; indeed, the inflammation had run so high, that an abscess formed and burst under the ear. When the swelling sub- sided the degree of paralysis was very observable. The delirium and the paralysis of the face naturally led the medical gentlemen, who first saw this patient, to suppose that the symptoms were caused by an affec- tion of the brain. Luckily, the treatment generally followed in cases of phre- nitis, was best adapted for the particular affection which had caused both the de- lirium and the paralysis. The portio dura being engaged in the inflammation un- der the ear, was the true cause of the paralysis.” For the next case I am indebted to a physician in Worcester:— Worcester, July 25, 1824.—“Dear Sir:—My acquaintance with the nature of your late researches upon the functions of the nerves induces me to send you the following case: — “ A young gentleman, aged 14, residing in the village of Kempsey, in this coun- ty, was observed by his family to have the expression of his countenance much altered. As long as the features were quiet nothing unusual was observable in the countenance ; but as soon as any passion was excited the expression of the face was so different to what was natural to him, that his brothers and others of the family complained of his ‘ making faces at them.’ He, in fact, only smiled, laugh- ed, or frowned upon the left side of his face, the muscles of the right side remain- ing inactive; and, as they passively yielded to the contraction of the muscles of the left side, the countenance, of course, was much distorted whenever these were called into action. He lost the power of whistling, and, for the same reason, of blowing, and was unable to close his right eye. The sensibility of the right side was as perfect as that of the left. He was quite unconscious of any change in himself, and was not at all aware of the distortion of his countenance when he smiled, &c. This affection did not occur suddenly, but seemed gradually to in- crease, and became so evident in the course of a week, as to induce the father of 102 Or THE PARTICULAR NERVES. the young man to send for his apothecary, Mr. Bick, of Kempsey. When Mr. B. saw him he found the symptoms as above stated; but upon examining the right side of the face more minutely he discovered a fulness immediately beneath the right ear, produced by a hard, fixed, and ipdoieut tumour, lying between the ra- mus of the lower jaw and the mastoid process of the temporal bone. “He ordered him some aperient medicine, and directed the tumour to be rub- bed with camphorated oil. In a fortnight the tumour disappeared, and with it, gradually, the paralysis of the muscles of that side of the face. It is a fortnight since Mr. Bick first saw him, and he has now recovered every power, excepting that of blowing or whistling I saw him several times during the progress of his cure. It appears to me that the portio dura of the seventh pair wa3, in this case, injured by the pressure of an enlarged gland soon after its emergence from the stylo-mastoid foramen, and that upon the removal of the pressure its functions were restored. “ I remain, dear sir, your obedient servant, “ Jonas Malden, M. D.” The danger to which the eye is exposed by paralysis of the portio dura, or by any operation on the face, in which its functions are not attended to, is well illus- trated by the following case :— “ This poor man, about nineteen years ago, was attacked by a severe pain ac- companied with discharge from the right ear. After a paroxysm severer than usual, he found, on getting up one morning, that the right side of his face was pa- ralytic. His present condition, and the description which he gives of the pro- gress of the symptoms, prove that the same results followed this paralysis, as in the instances already related. But what this poor fellow particularly laments is, that since the day he was first attacked, he has not been able to close his right eye; and well he may regret this, for the constant exposure of the eye to the light and dust has been the cause of many attacks of inflammation, and, conse- quently, of opacity of the cornea, so that the vision is now entirely lost. This, I fear, will often occur in similar cases, for I have observed that the eye has always become inflamed in those animals in which the portio dura has been cut. It is wor- thy of remark, that the inflammation has been more severe in the dog and in the ass than in the monkey. One great source of the increase of the inflammation is the purulent secretion from the conjunctiva; this the monkey wiped away with his hand; but it lodged between the eyelids of the dog and of the ass, so as to form an additional source of irritation.” The ultimate effects of the loss of power over the muscles of the face, in con- sequence of an affection of the portio dura, are shown in the following extract: — “ A most remarkable appearance in the face of Garrity is the wasting of all those muscles of the face which are subservient to respiration and expression. His cheek is so thin that when he speaks it flaps about as if it were only skin, and the corrugator supercilii and occipito-frontalis, which are principally muscles of ex- pression, are so wasted, that we might, at first sight, suppose they had been remov- ed by operation, and that now the bones were only covered by skin. There can be little doubt that the wasting of these muscles has been in consequence of their long inactivity ; since the masseter and temporalis muscles of the same side, which retain their office, are not at all diminished in size, being as large as those of the opposite side.” A curious example of a contrary effect produced on the growth of the muscles of respiration and expression, by an injury of the portio dura, was afforded in an ex- periment made upon a young dog. After the nerve was cut he was taught to snarl whenever a stick was held out to him ; this being often repeated, the muscles of the side upon which the nerve was entire, became very strong, while those on the paralysed side rather diminished than increased as the dog grew older. In a few months the one side of the face was much larger than the other. Every day we see similar results following palsy of the muscles of the limbs. Many instances will now occur to my reader of cases where the paralysis of the face, consequent on a local affection of the portio dura, has been mistaken for an attack of apoplexy, and the patient treated accordingly. In one case the patient, after having undergone the discipline of bleeding, purging, and starving, and after having had his head shaved and blistered, was suddenly cured by the bursting of an abscess in his ear. In another case, the disease commenced with a violent pain below the ear, and OF THE PARTICULAR NERVES. 103 in a short time one side of his face became paralysed. For this paralytic affection he consulted many eminent men. The first plan of treatment was bleeding* blister- ing, and starving, the disease being supposed to have its origin in the brain ; but as he got rather worse than better under this treatment, he was put upon a course of mercury, which was carried to such an extent, that he lost several of his teeth. After he recovered from the bad effects of the mercury, he was recommended to at- tend only to the state of his digestive organs. But the blue pill had no effect upon the distortion. The last advice which this gentleman received was to wear an is- sue in his neck ; with this, however, he has not complied, as he feared it would, like some of the other remedies, have the effect of rendering him more uncomfort- able. A great many cases, sowewhat similar, have been presented to me by my pupils. The first regards a patient who had suffered an attack of common apoplexy ; it may be offered in example of that train of symptoms which is consequent on an affection of the original or symmetrical system of nerves, and as distinguishable from those which follow an affection of the superadded class. The second is of a man, in whom both the portio dura and the fifth had been injured by a blow ; and the third is of a patient in whom both these nerves seem to have been affected by a disease within the skull. J. Cooper—This man’s general appearance is completely that of an old pa- ralytic* but the distortion of his face is more remarkable than usual, in consequence of the right or paralyzed side being marked with a red blotch. The arm and leg of the same side are nearly powerless, his intellect is much im- paired, and his memory gone. The history of his case was given very clearly by his wife ; according to her account, her husband was, for the first time, attacked with apoplexy about seven years ago; from this attack he gradually recovered, but at the end of twelve months he was a second time seized, and, since that pe- riod, he has had two distinct attacks every year ; for the last two or three years he has been nearly in the same condition as at present. State of the cheeks and mouth.—When he is made to laugh, the right cheek rises in the same degree with the left; when he blows (he always bursts into a laugh when asked to whistle), the buccinator of the right cheek is in as much action as on the other side. When his nose is irritated by snuffing ammonia, the actions of the muscles, preparatory to sneezing, are equal on both sides of the face. These phenomena prove that the muscles of both cheeks are perfect in their actions as far as they are regulated by the respiratory nerve ; they stand in contrast with the state of the same muscles in the cases related* when the act of sneezing was ex- cited. The next inquiry related to the influence of the branches of the fifth pair of nerves. The right cheek, and the right side of the mouth, fall lower than the left. When a piece of bread was put between the teeth and right cheek, the patient could not push it from its place, but was obliged to pick it out with his tongue. The saliva constantly flows from the right side of his mouth, and when drinking, part of the fluid escapes from the same side. The loss of* the sensibility of the orbicularis oris was farther shown by the inability to hold a pencil or a tobacco-pipe in the right side of his mouth. The comparative degree of sensibility in the two cheeks was next examined ; when he was pricked on the right cheek with a needle he seemed perfectly insen- sible, even though I drew blood, but on giving the least prick to the left side, he immediately started ; the same difference in the degree of sensibility was observa- ble in pulling a hair from each whisker (the sensibility of the right and left limb corresponded with that of the cheeks). On putting hartshorn to the right nostril he inhaled it as well as with the left, and immediately all the symptoms observable in a person about to sneeze were pre- sented. * As the nose was turned up, and the alae nasi of both sides were equally in action, this was a sufficient proof of the state of the paralyzed side being here very different from the condition described in the foregoing cases. The influence of the fifth pair within the nose was tried : by tickling the inside of the right nos- * The apparent sensibility of the nostril over which the fifth had lost its influence may be explained, by supposing that the fumes of the ammonia passed by the posterior nares to the other nostril, and thus caused sneezing. 104 OF THE PARTICULAR NERVES. tril no effect was produced ; but on tickling the left nostril the symptoms of sneez- ing were evident. The motion of the eye was perfect. He could close the eyelid of the paralyzed side as well as the other ; and when his nose was irritated by the hartshorn, or when he laughed, the orbicularis oculi and corrugator supercilii were in complete action, so that there was not here that heaviness in the expression of the upper part of the face, which is so remarkable in paralytic persons. Here, then, was proof that those actions of the eyebrows which we find to be deficient, when the portio dura is affected, are, in a case of common palsy, left entire ; indeed, we may have daily opportunities, while walk- ing in the streets, of observing that patients with palsy of one side of the body, have no difficulty in closing the eyelids. In the next Case, both systems of nerves seem to have beeu affected. Phipps, a bricklayer, on the 1st of September, 1821, fell from a scaffold thirty feet high. His right clavicle was broken, his right loin and hip were much bruised, and he received a severe contusion on the head, the marks of which were particu- larly observable in a puffiness behind ihe right ear, and in bleeding from the same ear and from the nose. He was in a state of stupor when brought into the hospital, but from this he recovered in the course of the day. For the two or three first days he appeared to suffer only from the effects of concussion, never having any of those symptoms which are generally attributed to compression. On the fourth day it was observed, that the angle of the mouth was drawn rather to one side, and there was also a de- gree of inequality in the contraction of the pupils. On the sixth day it was Vemarked, that while he was asleep, the right eye was more than half open, while the left was closed. The notes of the case are very full up to the 24th of September, and show that the patient had, during the interval, gone through the common series of symptoms which accompany that slight inflammation of the brain which is often the conse- quence of concussion. On the 1st of October, he was made an out-patient, his face being, at this time, very much distorted. The general appearance of his face at this time was that of a man who has suf- fered paralysis from apoplexy. But it was further remarkable, that when he spoke or laughed, the distortion was much increased, the mouth being pulled more to the left side than I ever saw in any other patient. The following are the notes that were taken at this time. There appears to be total paralysis of the muscles of the right side of the face. When he smiles or laughs they are passive, while those of the left are regularly in action. If he at- tempts to whistle, he cannot close his lips sufficiently; when he blows, the right cheek is dilated, but passive, like a distended bladder ; he can smoke by putting the pipe into the left side of his mouth ; he throws the smoke out of the right side, but in doing this, the action is evidently confined to the muscles of the left cheek. The cheek and mouth hang down, as in the common case of hemiplegia—he cannot by a voluntary act move his-cheeks; when a piece of bread is put between the cheek and teeth of the right side, he cannot push it out with the buccinator but picks it out with his tongue. He cannot hold his pips or my pencil with the right side of his lips. These may be considered as sufficient proofs of the total paralysis of the muscles of the face. The difference of the sensibility in the two cheeks was very distinct. Wheu a hair of the right whisker was pulled, he was not conscious of pain ; but he started immediately on pulling one from the left. When his cheeks were pricked with a needle, his expression was—“ I feel you push against the right side, but in the left you prick me.” When he brought his jaws forcibly together, he said he was not conscious of striking his teeth on the right side though he felt them most dis- tinctly on the left. On examining the state of the nose, we found that it was im- possible to excite the muscles of the right nostril to any action. The state of the right eyelids and eyebrow corresponded with those of pati- ents who have paralysis of the portio dura, for both the orbicularis oculi and cor- rugator supercilii were so completely paralytic, that he could neither close his eye, nor knit his brow on the right side. On examining how far the branch of the fifth, which passes to the eye and eye- lids, was affected, we found that the symptoms did not exactly correspond with those OP THE PARTfCUliAR NERlTEa.r 105 observed in the parts regulated by the other divisions of the fifth pair, and particu- larly in the degree of sensibility; for when a hair was palled from each temple, or from the eyebrows, the pain felt in the two sides was nearly the same; neither the temporalis, nor masseter muscles of this side were paralyzed. The motions of the eye-ball were so far perfect, that he could follow an object carried before him, but he could not direct both eyes truly, he saw double. The contraction and dilatation of the pupil of the right eye, were much the same as in the other eye. He can put out the tongue, and move it in every direction with the greatest ease : the motions are all apparently correct and natural; he can throw a morsel from one side of the mouth to the other, and towards the throat, and he can pick it out from between his cheek and teeth. These observations led us to conclude, that not only the motor linguae, or ninth, nerve, but also the glosso-pharyngaeal were perfect. This case differs from the common examples of partial paralysis of the face, not only in there being evident marks of paralysis while the muscles of the face are at rest, but in the sensibility of the skin of the same side being in a great measure destroyed. It differs also from the case of hemiplegia. The first difference which we observe in it, from the case of common hemiple- gia, is, that the paralysis is confined to the face. Secondly, that the paralysis is on, the same side with that on which the head is injured. Thirdly, that the palsy i3 more evident when the patient is made to sneeze or laugh. From these circum- stances, we may conclude that there was here an injury of the skull affecting both the fifth and the seventh nerve, i. e. in their course, not in the brain. “James Gulland, aetat. 26.—Was admitted into the Middlesex hospital, April, 15, 1823. His mouth and left cheek are twisted towards the right side: the whole surface of the left side of his face is insensible: he has not the power of moving the eye of that side, and it was lately become inflamed; he complains of a deep pain in the temple of the same side. “ His trade has been so profitable as to enable him to live in a most dissipated manner during the last five years. He has frequently strolled about the streets at night in a state of drunkenness, and has for three weeks never thrown off his clothes, and has been seldom in bed. He has been twice affected with syphilis; he was confined by his first attack for eighteen months, during which time he was under the influence of mercury. After regaining his health, he frequently expe- rienced a pricking pain in his left eye and temple, so severe as to prevent his read- ing, especially by candle-light. About twelve months ago he was knocked down : he fell on the back of his head, and wounded the occipital artery; he thinks that he has never been quite well since that time. On the 13th of October, la3t year, one of his comrades noticed to him that his mouth was drawn to one side, this induced him for the first time to observe in a looking-glass the condition of hi3 face. He tried to spit, and observed that his saliva, instead of passing through the centre, was squirted out of the right corner of his mouth, which was contracted. Hi3 lips were in other respects perfectly natural, being possessed of sensibility and the power of motion. He could then likewise close the eyelids of the left eye, but to do this he required to shut the other eye also. “ On the following moruing he was conscious of a peculiar numbness above the left eye. This numbness imperceptibly and gradually spread over the left cheek, and at the same time affected the external and internal surfaces of almost all that side of his head. He lost the sense of taste on the left side of his longue, and in little more than a fortnight he became deaf in the left ear. Now he complains principally of the inflamed condition of the left eye, (which commenced about ten days ago,) and of the pain in his left temple. “ The above circumstances he himself could relate distinctly ; the following is an account of his present condition, April 20. “ The left side of his face is drawn towards the right, and is slightly cedematoue. The left nostril is collapsed, and does not expand during breathing. The mouth is distorted towards the right side. When he speaks, the two sides of hi3 face are distinctly marked by aline of division; the action of the muscles of the mouth and nostrils, on the right side, being quite distinct, while those of the left are motion- less. He has lost all power over the left eye-lids; until lately, he could elevate his upper eye-lid, although, since the time of his first attack, he has always expe- rienced a certain difficulty in closing it. At present the eye-iid haqgs down flaccid and shut; he is unable to press the eye-lids together. 106 OF THE PARTICULAR NERVES. “ The sensibility to touch is gone on the greater part of the left side of his head and face, and this insensibility extends to the vertex of the head. The surfaces of the conjunctiva and eye-lids are also completely insensible, yet the eye is in- flamed and ulcerated; the left side of the nose, the cheek, the upper and lower lips, are all equally insensible ; but he is sensible when touched upon the left side, below the under jaw, and even over the lower jaw itself, as high as the inferior part of the lower lip. The external ear, and likewise the back part of his head, nearly as high up as the vertex, retain their natural sensibility. “ The internal surfaces of the left nostril, and of the mouth and gums on the same side, are insensible to touch; and he has neither the sense of taste or common feeliug in this side of the tongue; inconsequence of this, portions of food have sometimes lodged within the left side of his mouth, without his being aware of their presence, until they became actually putrid. “ The power of moving his tongue is quite perfect: if at rest, it lies in its natu- ral position within the mouth; nor is it dragged towards either side when he is told to move it. Being tickled with a probe on the left side of the root of his tongue, the sensation of nausea and the effort of retching are produced as on the opposite side. He can open and close his jaws; yet it can be observed, when he is made to clench his teeth, or to bite forcibly, that the masseter and temporal muscles of the right side are hard, rigid, and strongly in action, while the same muscles belonging to the opposite side are totally different in that respect, for they feel soft and flaccid. . “■ With regard to his left eye, it has been already noted, that it is deprived of common sensibility, and that he has no power of shutting or raising his eyelid. Besides these, he possesses no command over the eye-ball: his eye remains fixed and motionless, and directed straight forwards when he attempts to turn it towards objects. No motion exists in the pupil when a light is presented to the eye. He has the power of vision, although he sees dimly ; this is, probably, on account of the eye being inflamed and the cornea ulcerated and opaque. When both his eyes are closed, he is sensible of a red light in the left eye, while nothing is visible in the right one. “ He was questioned as to the period when he observed that he had lost the power of directing the left eye to objects, but he was unable to inform us, because he imagined always that that eye was as much in motion as the other. “ August, 1824.—This man is still alive, several of the symptoms of paralysis both of the portio dura and of the fifth are become more indistinct; he has re- gained a little power over the motions of the ej’e-lids, and of some of the mus- cles of the face, and the surfaces are endowed with a slight degree of sensibili- ty.” In this case we may '•observe, that the symptoms show the affection to be li- mited to the seventh and fifth nerves of the left side, and they best correspond with the supposition, that a disease of the bone, or membranes, has affected these nerves in their course, and is gradually extending forward to the nerves of the orbit. I shall close the narration of these cases by the statement of a circumstance which occurred to me a few years ago :— A gentleman, in the vigour of life, came into my room to consult me, having the most remarkable distortion of countenance I had ever seen. He proceeded to state to me what he conceived to be the cause of this paralytic affection of one side of his face: he had been knocked down by a blow upon the ear, and had re- mained a whole night insensible, with bleeding from the ear, from which time his features had been thus drawn to the opposite side. I thought I should give him comfort by stating to him that this was a paralysis attributable to the injury of the bone, and that, as it had not proceeded from an apoplectic tendency, there was no danger of a future attack or of increase of the paralysis. But this was not what he expected from me ; he had consulted my brother, then at Rome, and he had proposed to cure him by an operation. I was quite at a loss to conceive what operation his ingenuity had contrived to relieve so remarkable a deformity. This gentleman mentioned that it had been intended to make three small incisions on different parts of his face, so as to res- tore the balance of his features: and he was obviously disappointed in finding me less intelligent, or less able than he had expected, and we parted. OF THE PARTICULAR NERVES. 107 On reflecting on the conversation of this gentleman, it occurred to me, that my brother, believing that the paralysis had arisen from an injury of the fifth nerve, had proposed to restore the features to an equilibrium by dividing the branches of the same nerve on the opposite side ; trusting, no doubt, to the fea- tures being still auimated by the seventh pair of nerves. A singular consequence would have resulted from such an operation. The features would have re- mained drawn to the same side as before, and he would have been deprived of all sensibility of that side! If it was designed to have cntth e portio dura of the side contracted, a more unhappy consequence would have resulted ; for he could never afterwards have spoken, or even have kept his lips to his teeth, or retained the saliva. The features of both sides would have fallen in relaxation, and the eye would have remained uncovered, and he would have lost his sight by the in- flammation and opacity consequent on its continual exposure! It must, indeed, appear a singular circumstance now, that so many surgeons were cutting the blanches of the fifth pair of nerves for the tic doloureux, with- out being led to enquire more particularly into the functions of the several nerves of the face. We see how near my brother’s ingenuity was leading him wrong, from having often cut the fifth pair without producing horrible distortion. And I believe that the very same mistake led an honourable baronet to say that I had not cut the frontal branch of the fifth pair of nerves on the face of a nobleman, when I had only cut that branch without interfering with the branches of the portio dura, and consequently without producing the slightest effect on the mus- cles of the eyebrow. All these circumstances, 1 hope, tend to enforce the impor- tance of anatomy. At this stage of the description of the nervous system we experience some dif- ficulty ; for if we follow, undeviatingly, the manner of Willis, we shall certainly fall into the same mistakes. Instead of following the nerves of the brain and spi- nal marrow according to their regular succession, it will be necessary to class them according to their functions. This will oblige us to throw together some of the nerves of the brain, and some of the spinal marrow.] OF THE RESPIRATORY NERVES, MORE PARTICULARLY, VIZ. THE GLOSSO-PHARYNGEAL NERVE, PAR VAGUM, SPINAL ACCESSORY, DIAPHRAGMATIC NERY’E, AND EXTERNAL RESPIRATORY NERVE. ORIGINS OF THE RESPIRATORY NERVES. The nerves on which the associated actions of respiration depend, and which have been proved to belong to this system by direct experiment and the induction from anatomy, arise very nearly together. Their ori- gins are not in a bundle, or fasciculus, but in a line or series, and from a distinct column of the spinal marrow. Behind the corpus olivare, and anterior to that process which descends from the cerebellum, the corpus restiforrne, a convex strip of medullary matter, may be observed ; and this convexity, or fasciculus, or virga, may be traced down the spinal mar- row, betwixt the sulci, which give rise to the anterior and posterior roots of the spinal nerves. This portion of medullary matter is narrow above where the pons Va- rolii overhangs it. It expands as it descends ; opposite to the lower part of the corpus olivare it has reached its utmost convexity, after which it contracts a little, and is continued down the lateral part of the spinal marrow. From this tract of medullary matter on the side of the medulla ob- longata, arise in succession, from above downwards, the fourth nerve; the portio dura of the seventh nerve; the glosso pharyngeal nerve ; the nerve of the par vagum; the nervus ad par vagum accessorius : the phrenic, and the external respiratory nerves. 108 OF THE PARTICULAR NERVES. It is probable that the branches of the intercostal and lumbar nerves, which influence the intercostal muscles and the muscles of the abdomen in the act of respiration, are derived from the continuation of the same cord or slip of medullary matter. Nor will it escape observation, that the nerves called phrenic and external respiratory, though coming out with the cervical nerves, do, in all probability, take their origin from the same portion of the medulla spinalis with the accessory nerve. The intercostal nerves, by their relations with the medulla oblongata, are equal to the performance of respiration, as it regards the office of the lungs ; but they are not adequate to those additional functions which are, in a manner, imposed upon the respiratory apparatus, when they are brought to combine in other offices. OF THE MUSCLES OF THE TRUNK, WHICH ARE BROUGHT IN AID OF THE COMMON RESPIRATORY MUSCLES. If we look upon the frame of the body for the purpose of determining which are the muscles best calculated to assist the motions of the chest, when there is an increased or excited action, we shall have little difficulty in distinguishing them, and we shall have as little hesitation in assigning a use to the nerves which supply these muscles exclusively. For these nerves have the same origin : they take an intricate course, threading and passing betwixt other nerves and other muscles, to be entirely given to the muscles which heave the chest. In this enquiry it is necessary to observe, that the life of animals is protected by a particular sense which gives rise to an instinctive motion of drawing the breath, and by which the chest is suddenly and power- fully expanded on exertion or alarm. The start, on sudden alarm, is ac- companied with a rapid expansion and rising of the chest, and the voice, at such a moment, is produced by suddenly inhaling, and not by expira- tion ; and this expansion of the chest combines with the preparation for flight or defence, since the extension of the muscles lying on the breast and back is produced by this motion, and since they are thereby ren- dered more powerful in their influence upon the arms or anterior extremi- ties. It cannot escape observation, that oppression and difficulty of breathing is exhibited in gasping and forcible inspiration, in drawing the breath, not in throwing it out. Accordingly, when we examine the trunk of the human body, we have no difficulty in distinguishing the muscles most capable of raising the chest; and these, in effect, we see powerfully influenced in deep inspi- ration, whether the action be voluntary, as in speech, or involuntary, as in the last efforts of life, when sense is lost. They are the mastoid mus- cle, the trapezius, the serratus magnus, and the diaphragm. 1. Sterno-cleido-mastoideus.—This muscle, by its attachment to the sternum or breast-bone, raises or heaves the chest; and the opera- tion of this muscle is very evident in all excited states of respiration, in speaking, and still more in singing, coughing, and sneezing. But there is something necessary to the full effect of this muscle on the chest, for otherwise it will be a muscle of the head, and not of the chest. 2. The trapezius must fix the head or pull it backwards before the mastoideus can act as a respiratory muscle, and how they are combined we shall presently see. The position of the head of the asthmatic* dui- OF THE PARTICULAR NERVES. 109 mg the tit, as well as the posture of the wounded or the dying, prove the influence of the upper part of the trapezius in excited respiration. The trapezius has a still more powerful and important influence in respiration when the action rises above the ordinary condition, and that is by drawing back the scapula, to give the necessary effect to the action of the serrratus magnus. 3. The serratus magnus anticus being extended over the whole side of the chest, and attached in all the extent from the second to the ninth rib, is very powerful in raising the ribs ; but it cannot exert this power, independently of the trapezius, since, without this combination, its force would be exerted in moving the scapula, and not the ribs ; un- less the scapula be fixed, or pulled back by the trapezius, the serratus is not a muscle of respiration. In this manner do these three powerful muscles hang together in their action, combining with the diaphragm to enlarge the cavity of the chest in all its diameters. The course of our enquiry leads us to ask, Are these muscles privi- leged above others by any peculiarity of nerves 1 And the answer is plain : To these muscles alone, are the nerves, which I am about to call respiratory nerves of the chest, distributed. ANATOMY OF THE RESPIRATORY NERVES OF THE PAR VAGUM. The par vagum, or as we are to describe it, nervus vagus, is one of three nerves which Willis describes as the eighth pair of nerves, viz. nervus vagus, glosso-pharyngeus, and spinal accessory. These go out through the foramen lacerum, formed betwixt the occipital and temporal bone. THE GEOSSO-PHARYNGEAL NERVE Is the first to be described. This nerve, parting from its connection with the par vagum and accessory nerve, perforates the dura mater sepa- rately from them, and in many subjects, passes through an osseous canal altogether distinct. When it escapes from the cranium, it lies deep un- der the angle of the jaw, and passes across the internal carotid artery upon its outer side. It ;s to be seen by lifting the styloid muscles, at which point it sends small branches to the styloid and digastric muscles, and to join the par vagum. It sends also some very small twigs down upon the internal carotid artery ; some of which join that pharyngeal branch * which is formed from the par vagum and accessory nerve. Several branches communicate with the ganglion and plexus, (expansio plexuosa,) of the pharyngeal nerve, and are distributed in the superior constrictor and the stylo-pharyngeal muscles. The trunk of the glosso-pharyngeal nerve, after giving off the nerves which pass in the direction of the internal carotid artery, continues its course attached to the stylo-glossal and stylo-pharyngeal muscles, to which it gives more branches, and also to the upper division of the con- * This is a branch to the pharynx which is formed by the par vagum and the spinal ac- cessory of Willis. After this nerve is formed, it again forms connection with the par vagum. —Pain in the throat having been observed by Galen to extend to the back, Scarpa explaius it on the ground of this connection with the spinal accessory nerve. 110 OF THE PARTICULAR NERVES. strictor pharyngis. A division of the extreme branches of this nerve terminates in the tongue, under the denomination of rami linguales PROFUNDI, RAMI LINGUALES LATERALS8, NERVI GLOSSO-PHARYNGEI. * Amongst the branches of the pharyngeal nerve is to be enumerated, that which turns back to join the ninth pair in its distribution to the tongue, j' The remaining branches of the glosso-pharyngeal nerve are distributed in innumerable filaments upon the pharynx ; they are joined by branches from the ganglion of the sympathetic nerve. A remarkable branch of this nerve goes to the papillee, on the surface of the posterior part of the tongue ; and it is probably on the excitement of this, that the pharynx and tongue are brought into activity in swallowing. I consider the glosso-pharyngeal to be the nerve of deglutition. I have elsewhere explained, that the act of deglutition is necessarily joined with that of respiration. PAR VAGUM. The nervus vagus is the grand division : the middle fasciculus of the three nerves composing the eighth pair. It arises in filaments from that column of the lateral part of the spinal marrow which reaches up behind the corpus olivare. In its exit from the cranium, it is divided from the jugular vein by a small partition of bone. These filaments, indeed, sometimes pass out separately, and join to form the trunk of the nerve when out of the skull. Deep under the lower jaw, and the mastoid process of the temporal bone, the glosso-pharyngeal nerve, the par vagum, the spinal accessory, the sympathetic nerve, the portio dura of the seventh, and the upper cervical nerves, are entangled in a way which will fatigue the dissector. The par vagum, lying behind the internal carotid artery, and as it were escaping from the confusion of the ninth, accessory and glosso-pharyngeal nerves, descends and swells out into a kind of ganglion. J We now observe three branches to be sent off: The first and second pharyngeal nerves, which pass to the constrictor pharyngis muscle, and the superior laryngeal nerve. This last- mentioned nerve is even larger than the glosso-pharyngeal nerve. It is behind the carotid artery, and passes obliquely downward and forward. In its progress the principal branch passes under the hyo-thyroideus muscle, and betwixt the os hyoides and the thyroid cartilage ; while others, more superficial, pass down, and are connected with the exter- nal laryngeal, or phari ngo-laryngeus ; which is a nerve formed by the sympathetic and par vagum conjointly. The principal branch of the internal laryngeal nerve runs under the hyo-thyroideus, and is distributed to the small muscles moving the cartilages. The minute extremities of this nerve pass also to the apex of the epiglottis, and the glandular membrane covering the glottis. We have, at the same time, to remark, a very particular communicating nerve betwixt this internal laryngeal nerve and the recurrent branch of the par vagum. This branch * Scarpa. There is then a plexus formed, which is called the Circulus Tonsillaris Am derschii. It lies on the side and nearly on the dorsum of the tongue, and sends out sour very delicate twigs to the tonsils, t Sabbatier. \ Truncus gangliformis octavi, tumidulum, corpus olivare Fallopii ; but it is suspects that in this he meant the ganglion of the sympathetic nerve. OF THE PARTICULAR NERVES. 111 is described by Galen. The par vagum continues its uninterrupted course betwixt the carotid artery and jugular vein ; it is involved in the same sheath with these vessels, but lies rather behind them. In this course down the neck, it sometimes sends back a twig which unites with the ninth pair, and when near the lower part of the neck, it sends for- ward twigs to unite with those from the sympathetic nerve, which pass down to the great vessels of the heart, to form the superior cardiac plexus. On the right side, those nerves to the great vessels are in ge- neral given off by the recurrent nerve. The nervus vagus now penetrates into the thorax by passing before the subclavian artery ; it then splits into two. The main nerve passes on by the side of the trachea, and behind the root of the- lungs ; while the branch, on the right side, turns round under the arteria innominata, and on the left, under the arch of the aorta, and ascends behind the trachea to the larynx. This ascending branch of the par vagum is the recurrent nerve. On the right side it is sometimes double. It ascends behind the carotid artery, and sometimes is thrown round the root of the thyroid artery. On the left side, this nerve, from its turning round the arch of the aorta, is much lower than on the right, it gives off filaments which go to the lower cardiac plexus, after having united with the branches of the sympa- thetic. Under the subclavian of the right side, also, there are sent branches from the recurrent to the cardiac plexus; and on both sides there pass branches of communication betwixt the sympathetic nerve and the recurrent. When the recurrent nerve has turned round the artery, it ascends in a direction to get behind the trachea, and here it lies betwixt the trachea and oesophagus. It now sends off many branches to the back and membranous part of the trachea which pierce this posterior part, to supply the internal membrane. It gives also branches to the oesopha- gus and thyroid gland. The final distribution of this nerve is to the larynx. It pierces betwixt the thyroid and cricoid cartilages, and sepa- rates into many filaments, which terminate in the crico-arytenoideus, late- ralis, and posticus, and thyreo-arytenoideus, and in the membrane of the larynx. We have already mentioned the branch of communication be- twixt the recurrent and internal laryngeal nerves, and Sabbatier describes a branch of the recurrent, which sometimes ascends and joins the sympa- thetic high in the neck. Two cases, mentioned by Galen, of scrophulous tumours in the neck opened, where the consequence was loss of voice, have tempted many anatomists to institute experiments on the recurrent and internal laryn- geal nerves.* Notwithstanding the deep situation of those recurrent nerves, Galen says, they were cut in these cases, and he believed that the branch of communication betwixt the laryngeal and recurrent restored the voice after some time had elapsed. Both the internal laryngeal and recurrent nerves are necessary to the formation of the voice. Experi- ments have been made upon them in dogs, and the result is curious; although the lesser changes of the strength, acuteness, and modulation of the voice could not be well observed in the lower animals. When the laryngeal nerve is cut, the voice is feeble, but acute; when the re- * Martin, in the Edinburgh Essay, Professor Sue of Paris, Dr. Haighton, in the memoirs of the Medical Society of Loudon, Cruikshanks, Professor Scarpa, Arnemann, Majendie, &c. 112 OF THE PARTICULAR NERVES. current nerve is cut, there is a relaxation of those muscles moving the arytenoid cartilages which command the opening of the glottis, and in consequence the voice is flatter or graver, or more raucous. The par vagum, after sending off the recurrent nerve, descends by the side of the trachea. Before it passes behind the vessels and branch of the trachea going to the lungs, it sends minute branches which form the anterior pulmonic plexus. This plexus is entangled in the con- nections of the pericardium, and is dissected with difficulty. The branch- es of this plexus throw themselves round the pulmonic arteries and veins, and follow them into the lungs. The par vagum, passing on behind the root of the lungs, forms the posterior pulmonic plexus. From this also the nerves proceed into the lungs, by attaching themselves to the pulmonic arteries and veins, and bronchial arteries, and the branches of the trachea.* The trunks of the nerve, continuing their course upon each side of the oesophagus, unite and split into branches, and again unite so as to form a netting upon the oesophagus; these are the anterior and posterior plexus gula:, or cesophageal plexus. The par vagum, thus attached to the oesophagus, pierces the diaphragm with it, the anterior plexus unites again into a considerable trunk, and is attached to the lesser arch of the stomach. It stretches even to the pylorus, and sends its branches to the upper side of the stomach, and to the lesser omentum; at the same time it unites with the left hepatic plexus, some of its branches terminate in the solar plexus which surrounds the root of the cceliac ar- tery. The posterior oesophageal plexus, likewise uniting again into a considerable cord when it has come into the abdomen, sends branches to encircle the cardiac orifice of the stomach; it branches also to the infe- rior side and great arch of the stomach; it sends also branches to the splenic plexus and solar plexus. Thus we see that the par vagum has a most appropriate name, and that it is nearly as extensive in its connections as the sympathetic itself. It is distributed “ to the oesophagus, pharynx, and larynx ; to the thy- roid gland, vessels of the neck and heart, to the lungs, liver, and spleen, stomach, and duodenum, and sometimes to the diaphragm.” The re- collection of this distribution will explain to us many sympathies ; for example, the irritability of the larynx in exciting laughing ; the hysteri- cal affection of the throat when the stomach is distended with flatus ; the exciting of vomiting by tickling the throat; the effect which vomiting has * Nerves of the Lungs.—Galen, Vesalius, and others, conceived that there were very few nerves sent to the lungs, and that those which were, went only to the membranes, and not to the substance of the lungs. They believed also that the discharge of blood from the lungs and the existence of vomicae without pain, while there was great pain in peri-pneumony, was a confirmation of this opinion. Fallopius corrected this idea, and shewed that the bronchi* were also atttended through their course with nerves. There often exjst vomicae and effusions of blood in the lungs; and Haller says, the lungs can be lanced without the animal feeling pain, but still the bronchi* are extremely sensible.—Water accumulated in the interlobular cellular membrane, or the infraction of blood into it, gives no acute pain, but only a sense of weight and difficulty of breathing. It is an oppression in a great measure depending upon the return of the blood from the lungs, unchanged in consequence of the com- pression of the cells. In these observations they have not sufficiently distinguished betwixt common sensibility and the appropriate sensibility of the'organ. Are not the stomach and intestines sensible ? and yet they are not to handling. The connection betwixt the stomach and bronchi*, through the medium of the par vagum and pulmonia plexus, is evident from those asthmatic attacks which depend upon foulness in the stomach. OP THE PARTICULAR NERVES.' 113 xn diminishing the sense of suffocation ; the relations betwixt the heart and lungs ; the lungs and stomach, and the stomach and heart. The nerves which give rise to the extraordinary intricacy of this sys- tem on the side of the neck, are the spinal accessory nerve, the phrenic nerve, and the external thoracic nerve. The phrenic nerve has its great root or origin from the fourth cervical nerve ; and there joins this root, a more slender branch from the third cervical nerve. But, besides these roots, it has connections, which of themselves would mark the re- lations of the nerve ; high in the neck, it is connected with the nervus va- gus and with the lingualis medius, while, at the same time, a branch is given off to the muscles of the larynx. The trunk of the nerve descends into the cavity of the thorax, and gives no branches, until, arriving at the diaphragm, it sends out numerous diverging branches, which are lost in the substance of that muscle. It has been long known that irritation of this nerve convulses the dia- phragm, and that cutting it across paralyses that muscle. These facts, with the consideration of its course, prove it to be a respiratory nerve, and such has been the universal opinion. But to what purpose should a distinct nerve be sent to the diaphragm, if the other muscles, seated externally, and which are associated in ac- tion with the diaphragm, and as important to respiration, were left with- out a similar tie to unite them with each other, and with the organs of the voice ? The inferior external respiratory nerve of the thorax (fig. 13. PI. II.) is a counterpart of the internal or phrenic nerve. It comes out from the fourth and fifth cervical nerves, and often it is connected with the phre- nic. It diverges somewhat from that nerve, because, instead of de- scending within the chest, it falls over the ribs, and descends in a distinct flat trunk upon the outside of the chest, to be distributed entirely to the serratus magnus anticus. This muscle has other nerves coming from the spinal marrow, because it has to combine the motions of the frame in loco-motion. But the long descending nerve is a respiratory nerve; which we may know from its origin, course, and destination; in its origin and course it is like the diaphragmatic nerve, and in its destination also, since it is given to a muscle necessary to full inspiration. I come now to the spinal accessory nerve (fig. 11. Plate II.)* It is called here the superior respiratory nerve of the trunk. Experiments may take a colour from the preconceived idea, but the accurate inves- tigation of the structure will not deceive us. The author, therefoi-e, en- treats attention to the anatomy of this nerve, as leading in the most con- clusive manner to a knowledge of its functions. It arises from the cervical portion of the spinal marrow ; but instead of collecting its branches to go out by the side of the vertebne, like the internal and external respiratory nerves, it shoots upwards through the theca of the spinal marrow, enters the skull, and joins the eighth pair of nerves ; from which it has its term of accessory. We see the roots of this nerve as far down as the fourth cervical nerve, t These roots arise neither from the posterior nor the anterior column of the spinal mar- row, but betwixt the posterior roots of the cervical nerves and the liga- * JYervus ad par vagurn accessorius. f Iu the ass, its roots are seen to extend much lower down. 114 OF THE PARTfCULAR NERVES. mentum denticulatum, and from the column of medullary matter above described. The origins of this nerve come off in one line, and that line is in the direction of the roots of the eighth pair, and of that nerve which has been proved to be the respiratory nerve of the face, the por- tio dura. In its ascent the accessory nerve is attached to the posterior root of the first cervical nerve. The nerve having ascended through the J or amen magnum, passes out from the skull associated with the nerves constituting the eighth pair, and in the same sheath with them ; they all go out through the foramen lacerum, and by the side of the jugular vein. In this course the acces- sory nerve divides into two. One of these divisions joins filaments of the par vagum ; and these again send nerves to the glossc-pharyngeal nerve ; and sometimes a branch may be seen going to the lir.gualis me- dius. The more exterior division of the accessory nerve descends be- hind the jugular vein, and comes forward and perforates the mastoid mus- cle. In its passage through the muscle it sends off branches which course through its substance; and if, as sometimes happens, though rarely, the nerve does not pass through the muscle, these branches are, notwithstanding, invariably given to it. When the nerve has escaped from the back part of the mastoid mus- cle, it forms a communication with that branch of the third cervical nerve that ascends behind the muscle ; and nearly at the same time it is joined by a branch from the second cervical nerve. The superior respiratory nerve now descends upon the neck, and begins to disperse its branches in regular order to the edge of the trapezius muscle ; four or five branches take their course to that muscle, separate into minute subdivisions, and are lost in its substance. One more considerable division, being the lowest of these, is joined by a long descending branch of the second cervical nerve. Increased by this addition, it descends under the trape- zius and behind the clavicle. Following this descending branch, it will be found exclusively attached to the trapezius. Behind the scapula it is again joined by branches from the spinal nerves ; and here a sort of im- perfect plexus is formed, from which divisions of the nerve, still de- scending, follow the lower edge of the muscle, and are finally dispersed among its fibres. < This nerve arises from the same column with the respiratory nerves ; it takes a most intricate and circuitous passage to form a junction with nerves which we know to belong to that class ; it sends branches to join the nerves of the tongue and pharynx; it sends branches to the larynx in company with the branches of the par vagum; it then crosses the great nerves of the neck, passes under the spinal nerves, goes to no other muscles in its course, but lavishes all its branches on the mastoid and trapezius muscles. To an anatomist it is as plainly set forth as if it were written in our mother tongue, this is the superior respiratory nerve of the trunk.* * Lobstein, in a dissertation on this nerve, finding the difficulty of accounting for the ner- vous Jiuid coming by a double passage to the muscle, concludes, veniet forsan tempus quo ista q-uae nunc latent, dies extrnkat et longioriscevi diligentia. OF THE PARTICULAR NERVES, 115 COMPARATIVE VIEW OF THESE NERVES. If we examine the par vagum, the pnrtio dura of the face, the exter- nal thoracic, the diaphragmatic, and the spinal accessory nerves, by com- parative anatomy, we shall conclude that they are all respiratory nerves, by their accommodating themselves to the form and play of tho organs of respiration. In fishes, the respiratory nerve * goes out from the back part of the medulla oblongata. When it escapes from the skull it be- comes remarkably enlarged, and then disperses its branches to the bran- chiae and the stomach. But from the same nerve go off branches to the muscles moving the gills and operculum, whilst a division of the nerve is prolonged under the lateral line of the body to the tail. It is said, this division sends off no branches, but this is not correct: it gives branches in regular succession to the muscles from the shoulder to the tail. Ex- periments have been made upon these nerves, but their detail would lead us too far. It is scarcely necessary to add, that there are neither phre- nic nor spinal accessory, nor external thoracic nerves in fishes, the order of their muscular system not requiring them. In birds, the structure of the wing, and the absence of the mastoid muscle, render the spinal ac- cessory nerve unnecessary ; it is wanting, for the same reason, that in the absence of the diaphragm there is no phrenic nerve. Quadrupeds have the three respiratory nerves of the trunk ; but even in them there are variations in the muscular frame, which illustrate the appropriation of the nerves. The construction of the neck of the camel is like that of birds ; there is a succession of short muscles along the side of the neck, and attached to the vertebrae ; but there is no long muscle, like the ster- no-cleido-mastoideus, contributing to the motion of respiration. There is, accordingly, no spinal accessory nerve in the neck of this animal. We have a remarkable example of the manner in which these nerves vary in their course of distribution, and yet retain their appropriate func- tions, in the nerves of the neck of birds. In them, the bill precludes the necessity of the portio dura going forward to the nostrils and li/>s ; the nerve turns backwards, and is given to the neck and throat/ and it is particularly worthy of remark, that the action of raising tbs feathers of the neck, as when the game-cock is facing his opponent is taken away by the division of this nerve. If we compare the anatomy of the facial respiratory nerve, in the various classes of birds, we shall find its distri- bution to be analogous to that of the same nerve in the different tribes of quadrupeds. In the game-cock, a few branches of the nerves pass to the loose skin under the jaw, which is dilated in crowing, the greater number being dis- tributed on the muscles of the neck, which causes the elevation of the feathers when he puts himself in an attitude for fighting. But in the duck, which, when enraged, has little or no power of expression, the same nerve is not larger than a cambric thread, and passes only to the skin under the jaw.f * The nerve which by its subdivision supplies the heart, lungs, and stomach, and the mus- cles of the gills. f These respiratory nerves of the thorax, the diaphragmatic, the superior, and the external thoracic nerve, are all nerves of inspiration. The act of inspiration is provided for in a morte especial manner than the act of expiration. It requires more muscular effort, and is more es- sential to life. Inspiration is the first act of resuscitated life, the last of exhausted nature, and 116 OP THE PARTICULAR NERVES. [the functions of these nerves farther illustrated. Before having recourse to experiments on brutes, we may observe what takes place in our own bodies. By placing the hand upon the neck, we may be sensi- ble that the mastoid muscle has two motions. The lower extremity of the muscle is fixed when we move the head ; but when we use the muscle in inspiration, the head, and consequently the upper extremity of the muscle, are fixed. Now, if we endeavour to raise the sternum through the operation of this muscle, we shall find that other muscles are, insensibly to us, brought into action, which have no- thing to do with this raising of the sternum. For example, if we strain to raise the lower extremity of the muscle, we shall unavoidably prpduce an action of the muscles of the nostrils; by which association of actions, we shall discover, that we are using the mastoideus as a respiratory muscle. It we reverse the action, and move the upper extremity of the muscle, other muscles will be drawn into co-operation, but they will be such as assist in the motion given to the head. Or we may vary the operation in another way. In snuffing or smelling, if we place the fingers on the portions of the mastoid muscles which are attached to the ster- num, we shall find every little motion of the nostrils accompanied with corres- ponding actions of the sternal portions of the muscles in the neck. When a man suffers fracture of the spine at the sixth cervical vertebrae, and the marrow is crushed, he continues to breathe by the influence of the three nerves which arise above the injured portion. He inspires with force; but he cannot perform expiration by muscular effort, it is only by the elasticity and gravitation of the parts. He can yawn, for that is an action of drawing the breath ; but he cannot sneeze, for that is an action of expelling the breath. Bat this is a subject so curious in itself, and which has hitherto been considered so carelessly, that I shall reserve it for a distinct dissertation. * A man having a complete hemiplegia, the side of his face relaxed, the arm hang- ing down powerless, and the leg dragged in walking, we were curious to know if the influence pervaded all the nerves of the side, or only the regular or voluntary nerves. Some trouble was taken to make him heave up the shoulder of the de- bilitated side, but to no purpose. He could only do it by bending the spine to the other side, and as it were weighing up the paralytic shoulder. But on setting him fairly in front, and asking him to make a full inspiration, both shoulders were elevated at the same time that both the nostrils were in motion. The respiratory nerve of the face, and the superior respiratory nerve, were entire in their office; and, »lthough the regular system of nerves refused acting, the sterno-masloideus and the trapezius partook of their share in the act of respiration. Seeing that the mastoid muscle has two sets of nerves, that one of these is of the class of volun- tary nerves, and the other of respiratory nerves, are we not borne out in conclud- ing, that whe« the head is moved, being a voluntary act strictly, it is performed through the com-aion class of voluntary nerves ? that when the chest is raised, it is an act of respiration, and is effected through those nerves which controul the mus- cles in respiration? This conclusion is confirmed by the following experiment. In the ass, there are two muscles which take the office of the mastoid muscle; one is inserted into the jaw, which we may call aterno-maxUlaris, and the other into the vertebra, viz. sterno-vertebralis. To these the superior respiratory nerve (or spinal accessory) is distributed in its passage to the trapezius. These muscles are at the same time supplied with numerous nerves directly from the spinal marrow. If we expose the superior respiratory nerve, and then induce excited respiration, so as to bring these muscles into powerful action in combination with the other muscles of res- piration, and if, while this action is performed, we divide the nerve, the motion ceases, and the muscle remains relaxed until the animal brings it into action as a voluntary muscle. An ass being thrown, its phrenic nerves were divided, on which a remarkable for this reason the muscles of inspiration are large and powerful, and the nerves in a double order; for not only do the lateral branches of the spinal marrow influence the act of inspira- tion, but these additional respiratory nerves descend from the upper part of the spinal marrow to the chest, as an additional and especial provision, guarding life. * See the observations, p. 118. OF THE PARTICULAR NERVES* 117 heaving of the chest took place. It rose higher, and the margins of the chest were more expanded at each inspiration. There was no particular excitement of the muscles of the neck, shoulder, or throat, at this time; so that to excite the actions of these muscles it was necessary to compress the nostrils. When they began to act with more violence, keeping time with the actions of the other muscles of respira- tion, the superior respiratory nerve was divided ; immediately the action ceased in the muscles attached to the sternum of the side where the nerve was divided, while the corresponding muscles of the other side continued their actions. After dividing the spinal marrow between the vertebrae of the neck and those of the back, respiration is continued by the diaphragm; which experiment, as it is often mentioned by physiologists, the author has not thought it necessary to repeat, but only to institute the following experiment on an ass. The phrenic nerves being first divided, and then the spinal marrow cut across at the bottom of the cervical vertebrae, respiration was stopped in the chest; but there continued a catching and strong action at regular intervals in the muscles of the nostrils, face, and side of the neck. The main part of the apparatus of respiration was stopped, but these acces- sory muscles remained animated, and making ineffectual endeavours to perform the respiration. When apparent death had taken place, the ass was re-animated by artificial breathing, and then these muscles on the face and neck were restored to activity, and became subject to regular and successive contractions, as in excited respiration, whilst the chest remained at rest. These actions continued for a short time, and then ceased ; but upon artificial respiration being again produced, the same results followed. This was repeated several times, the animal remaining in- sensible during these experiments. Upon stimulating the nerves after the death of this animal, it was observed, that the class of respiratory nerves retained their power of exciting their respective muscles into action, long after the other nerves had ceased to exert any power; they were evidently of that class which retain their life the longest. It is a duty to avoid the unnecessary repetition of experiments, and I have now to make a short statement of facts, resting on the highest authorities ; experiments made without reference to the conclusions which I am now to draw. The division of the recurrent branch of the par vagum destroys the voice.* The division of the larynapeal branch of the par vagum stops the consent of mo- tion between the muscles of the glottis and the muscles of the chest.t The injury or compression of the par vagum produces difficulty of breathing.\ By the assistance of these well-known facts, we complete the knowledge of the circle of actions which result from the respiratory nerves. The medulla oblongata and spinalis are composed of columns of nervous matter, and from the different powers of the nerves, as they arise from the one or other of these columns, it is proved that they possess distinct properties. In animals that breathe by ribs and a numerous class of muscles, and which animals have a spinal marrow, we see that a column of nervous matter i3 embraced between the ante- rior and posterior virgce of that body, and that this portion may be traced down- wards between the roots of the spinal nerves. From the upper part of this co- lumn, where it begins in the medulla oblongata, the several nerves proceed which have formed the subject of these papers, and on the influence of which, it has been proved, the motions of respiration principally depend. It is not an extrava- gant conclusion to say farther, that the power of the regular succession of inter- costal and lumbar nerves, as far as they regulate the respiratory actions, proceeds from the connections of the roots of these nerves with this column, which is con- tinued downwards, and which can throughout be distinguished from the rest of the spinal marrow. We are now enabled to distinguish the influence of the spinal marrow, and its regular succession of nerves, from those which have been traced in these papers. The first are essential to the act of respiration ; without them the others are un- equal to the task. But on the other hand, although the regular succession of spinal nerves be equal to the raising and depressing the thorax, they are not equal to the full heaving of the chest in animated exertion of the voice. They are not compe- * Sectis ambobus nervis recurrentibus vox perit: Arnemann, Soemmerring, Morgagni, f Le Gallois. t Vinculo compressis nervis vagis oriuntur in bestiis spirandi difficultas, surditas, vomitus. corruptiociborum in ventriculo. Soemmerring, Haller, Brun deligaturis nervorum. 118 OF THE PARTICULAR NERVES. tent to the performance of the motions of the glottis, pharynx, lips, and nostrils, which several parts are necessarily influenced in excited respiration, as well as in the acts of smelling, coughing, sneezing, and speaking : for these, the co-operation of the whole extended class of respiratory nerves is required. Surveying the complicated machinery which in man is prepared for these various offices, we may reap the benefit of these fatiguing details, in the contemplation of the most interesting phenomena in nature. The relations of the subject may be presented under the heads of Pathology, and Expression. ON THE ACTIONS OF RESPIRATION IN THOSE WHO HAVE SUFFERED FRAC- TURE OF THE SPINE AT THE LOWER CERVICAL VERTEBRA. When the spinal marrow is crushed at the upper part of the spine, the man dies instantly ; but if the spinal marrow be crushed opposite to the lower part of the neck, although the injury be such as to deprive him of all sense and all voluntary motion of the parts below, he continues to breathe. It has been stated by our first authorities, that a man in these circumstances breathes by his diaphragm, in consequence of the phreaic nerve, which supplies that muscle, takingits origin from the spinal marrow above the part injured. But the observations have been inaccurately made which have led to this opinion. I shall first show how untenable such a supposition is, and then detail the pheno- mena which attend the fracture of the spine at this part; and, finally, show that other nerves, besides the phrenic, descend from the same source to supply the ex- terior muscles of the chest, and that it is through their influence the act of respira- tion is continued. The diaphragm is that muscular septum which divides the thorax and abdomen, and by the descent of which the depth of the cavities of the chest is increased in inspira- tion. When it has acted and descended, and the air is admitted into the lungs, that air is again expelled by the re-action of the abdominal muscles. These muscles compress the viscera, and by pushing them up, raise the relaxed diaphragm, pre- paring it for another effort of inspiration. Is it not obvious, that if the power of the diaphragm remains entire, and the power of the •abdominal muscles be lost, that the respiration must stop ? It would be so, were it not that there are other muscles and other nerves no less important than the diaphragm and the phrenic nerves, and which physiologists have not contemplated. In the first part of this paper it is shown that the sterno-cleido-mastoideus, the trapezius, and the serratus magnus, are muscles calculated, by their combined ope- ration, to raise the chest with great force, and to perform inspiration. It is also shown that the nerves there described as the superior and the external respiratory nerves, take their course exclusively to those muscles which act upon the chest, and that what the phrenic nerves are to the diaphragm, these are to the three great exterior muscles. It is further shown by what has preceded, that as all these nerves take their origins from the same part of the spinal marrow, they are consequently in the same circumstances as to fracture of the spinal tube. When the spine is fractured at the lower cervical vertebrae, these nerves escape injury, and continue to animate the muscles exterior to the ribs as well as the diaphragm. The great importance of these exterior nerves and muscles to the continuance of life will be proved by the following cases. I have purposely omitted all the detail of practice, and have taken the symptoms purely in a physiological view, and as if it were an experiment instead of a most afflicting accident to a fellow-creature. Within the space of one month these three instances of fracture of the vertebra* of the neck have occurred in my practice. In one instance, the bones were broken at the lower part of the neck, and the patient lived some days. In the second in- stance, the vertebrae of the neck were fractured in the middle of the neck, and the man lived half an hour. In the last instance, the uppermost vertebra was fractur- ed, and the death was immediate. Case I.—Percy Ward, 29th May.—Charles Osborne, aetat. 26.—On Saturday evening this man was putting pulleys into a window-sash, when the small steps on which he stood slipped from under him, and he was precipitated through the window into the area, a height of 13 feet. He thinks he fell upon his back ; but he is uncertain, as he lay for some time senseless. He lies now in bed, supine and powerless, but describes the part injured to be the spine betwixt the scapulae. As OF THE PARTICULAR NERVES. 119 we desired to have only the essential feature of this case, it is better to say at once, that this was a deception, that he felt the pain of the injury at a point considerably lower than the fracture, and that on his death it was discovered that the arches and bodies of the sixth and seventh cervical vertebrae were broken. The lower extremities are motionless and insensible. He can raise his shoulders and bend his arm, but over the motion of the hands he has no power. Another report adds,—his expression is singular ; he says he can move his arm by the strength of his shoulders, which is exactly true, for by moving the shoulder he can give a certain rotatory motion to the humerus, and, consequently, move the fore arm when it is bent at the elbow. The skin of the arms, however, retains its sensibility to the point of a pin. The abdominal muscles are relaxed, and the viscera feel flaccid. He can make no effort to expel the urine ; his urine is drawn off by the catheter, and his faeces pass involuntarily : there is priapism. When I induce him to attempt an effort and to strain, no change on the abdominal muscles can be felt; there is no firmness or rigidity in them. The integuments of the abdomen and of the chest, as high as the nipples, are insensible. His breathing is frequent, and at each inspiration the chest is heaved with a short and quick movement; at each expiration the abdomen is protruded with a sudden shock and undulation. The belly, during this effort of breathing, is uni- formly soft and full, and when drawn in it is by the elevation of the ribs, and when the chest falls it is protruded. He has been observed to yawn naturally. Query. Can he cough ? An examination has been made to-day to answer this query. When he is asked to cough, he pulls up the rib3 and extends the chest, and lets them fall: he coughs, but not strongly : it is obviously by his power of raising the chest and giving elasticity to the ribs, and by the weight of the parts falling, that he is enabled to expel the breath. He cannot divide the expiration into two coughs, nor give two impulses to the air; but each time he coughs the elevation of the chest must precede it. On spreading the hands and fingers on the side of his chest the action of the ser- ratus muscle could be felt, and also the lower margin of the trapezius muscle was felt to become firm during the act of inspiration, as when he prepared to speak. Being asked if he had sneezed by any chance, his answer was—■“ No> sir ; I can- not blow my nose.” This was not that he could not raise his hand to his head: he was conscious of wanting the power of forcibly expelling the air. Mr. B., ta- king a handkerchief from a nurse, and holding the patient’s nose as a woman does a child’s, the patient could not blow the nose ; he could not give that sudden im- pulse of expiration which is necessary, In one of the reports of this case it was stated that the patient was disturbed by horrible dreams. This is very likely from the respiration being in part obstructed; but I omitted to verify that observation during the patient’s life. It is remarkable in this case, that on feeling his stomach he, of his own accord, marks the difference of sensibility, internal and external. He says he feels inter, nally, but he does not feel on his skin. He feels me when I press the stomach, and has complained of the griping from his medicines. Another instance proving that the par vagum is a compound nerve. U This man died in the night of the seventh day from the accident. The night nurse gave no particular description of the manner of his death, further than that he seemed to desire to speak and could not: he made attempts to articulate, but could not. Case II.—James Saunders, setat. 45, J une 30.—This man fell only four feet, but he fell backwards, and struck his neck against an iron railing. The transverse processes of the fifth and sixth cervical vertebrae were found fractured; and there was diastasis of the articulations between these vertebrae. The body of the sixth vertebra was fractured. The spmous processes, also, of the fourth and fifth ver- tebrae were found fractured at their bases. The house surgeon reports of this man, that when he was brought into the hos- pital he was perfectly sensible; that his face indicated great alarm and anxiety. Every time he drew his breath it was attended with an effort to raise the should- ers, and a contraction of the muscles of the throat: every time he breathed his head appeared to sink beneath his shoulders. On putting his hand on the pit of his sto- mach no motion of the viscera of the abdomen could be perceived. He had no feeling even iD the upper part of his chest: he had feeling on his face and neck, and indistinctly near the collar bone. He had a motion of his hands, a sort of rolling 120 OF THE PARTICULAR NERVES. motion, which may have proceeded from the shoulders. When he spoke it was in a tremulous voice, like a man frightened: his voice was weak, but he did not speak in a whisper; the sound of his voice was more like sighing than common breathing. Pulse was felt at his wrist. In teu minutes after he was brought in, half an hour from the time of the accident, he died. Case III.—On the following day a man was brought into the hospital dead. He had fallen fifty feet, and had lighted on the ground upon both his shoulders. By the accounts of the men who carried him to the hospital, he appears to have been instantaneously killed. The dissection sufficiently proved that he was killed sud- denly. For besides extensive fracture and injury to the lower part of the spine, the atlas and dentata were found likewise fractured. The tooth-like process of the ver- tebra dentata was broken through just at its base. It was separated completely, and was found embraced by the transverse ligament in its natural situation upon the atlas. The arch of the atlas was partially fractured on each side, and a portion of its body, where the process of the dentata rolls upon it, xyas also fractured and detached.* In the above narratives we have the account of those symptoms which accom- pany fracture of the cervical vertebrae, and which have hitherto been negligently considered, from an entire want of interest in the subject. It appeared to me very distinctly, that, in the case first described, the man had the power of drawing his breath by muscular elcertion ; but that the expulsion of the breath was not a mus- cular effort, but occasioned entirely by the elasticity of the ribs, and the gravitation of the parts forcibly raised by the action of the muscles. This was evident in the total want of the power to exert the abdominal muscles, or to compress or depress the chest above its condition of rest; in the necessity of raising the chest at the ut- terance of each word ; in the perfect power of yawning, which is a gradual and powerful act of inspiration : in the want of the power of sneezing or blowing the nose, which is a sudden call of the muscles of expiration into action. The strongest reason of all for this view of the use of these nerves, which I have called respiratory, is, that respiration and the activity of the muscles of the chest did actually continue after the f unctions of the spinal marrow were destroyed by violence done to the tube, and that there is no other explanation of the fact than this, that thAee nerves which take their origin from the medulla oblongata and up- per part of the spinal marrow, aud which descend upon the neck and chest, did continue to animate the sterno-cleido mastoideus and the trapezius, and the muscles of the throat, iu the act of inspiration. We have only further to recollect, that it was not the forcible, occasional, and voluntary motions of respiration that were thus preserved, but that by the same means, viz. the superior, the external, and the phrenic nerves, the play of the chest in respiration during sleep was continued. In the second case, it is clearly proved, both by the symptoms and the dissection of the bones, that the fracture must have affected the roots of the phrenic nerves and we are at liberty to conclude, that the difference of symptoms, in comparing it with the first case, as well as the shorter period of his sufferings, was owing to this cause. The manner of breathing was very different, and is described by our house * A young man was brought into the Middlesex Hospital, who had fallen upon his head. He soon recovered, and lay for some time in the hospital without exhibiting a symptom to raise alarm. He had given thanks to the assembled governors of the hospital, and had re- turned into the ward for his bundle, when, on turning round to bid adieu to the other patients, he fell, and in the instant expired. Upon examining his head, it was found that the margins of the occipital hole had been broken; no doubt it had happened that, in turning his head the pieces were displaced, and dosed aud crushed the medulla oblongata, as it passes from the skull. A man was trundling a wheel-barrow in Goodge-street, which is immediately adjoining the Middlesex Hospital: in going from the carriage-way to the flag-stones he met the impedi- ment of the curb stone. He made several efforts to overcome it, and at length drawing back the wheel-barrow he made a push, aud succeeded ; but the wheel running forward, he fell, and remained motionless. He was taken into the hospital, but he was found to be quite dead. The tooth like process of the second vertebra of the neck had burst from the transverse liga- ment of the first. Tire impulse given to the head had done this violence, and had at the same time carried forward the spinal marrow against the process, and on which it was crushed. These cases occurred before my time, but I have had two instances of sudden death from the dislocation of the atlas from the second vertebra of the neck. In short, the fact is perfect- ly well ascertained. OF THE PARTICULAR NERVES. 121 surgeon * in a manner to produce conviction. His breathing was like sighing; and at each inspiration his head was drawn betwixt his shoulders. That is to say, that by the loss of the action of the diaphragm the action was thrown on the muscles exercised through the spinal accessory nerve, and this is confirmed by what is said of the want of motion in the viscera of the abdomen ; for, as it was proved in the first case, at each contraction of the diaphragm the viscera of the abdomen are propelled outward.. The want or defect of action in the diaphragm, and the action of breathing be- ing circumscribed to the muscle* of the neck and shoulders, were undoubtedly the cause of the patient sinking so soon. In the last case, it appears, the spinal marrow being injured so high up as to destroy the roots of all the respiratory nerves, the death was sudden, as in pithiu®- an animal. When we have ascertained these facts, certain queries arc naturally suggested. Why should these respiratory nerves, which descend from above upon the thorax, go o ily to muscles which assist in raising and expanding the chest? Why should the act of inspiration be secured by a double provision of nerves, viz. those which come out from the sides of the spine, and those which descend from the neck, when the act of expiration is provided for solely through the former? I would offer these reasons:— First. The act of drawing the breath is the more difficult, and requires the more force; the act of expiration is comparatively easy, being assisted by the weight of the parts incumbent on the ribs, as well as the resiliency or elasticity of the ribs themselves. Second. The act of inspiration is the active state; the condition of expiration is a state of rest. Third. The inspiration is necessary to life, and must be guarded with more care, and performed with more force than the expiration. In oue suffocating, the agony is in elevating the chest and drawing the breath. On the approach of death, the inspiration becomes more laboured, that is, the exterior muscles are in violent action ; but the act of expiration is on interval of rest. Fourth. These nerves, which govern the muscles of inspiration, are linked more intimately by sympathy with the state of circulation and respiration ; for we see in disease, as in experiments on animals, that when the powers of life have run low, the sympathy is still exerted with such sudden catching of the muscles of inspiration, and with an effort so powerful and unexpected as to startle, while the expiration is soft and without effort. We perceive the same sympathy causing the same sudden and powerful inspirations, and marking the presence of life, when a person is recovering from fainting, or from suspended animation, from whatever cause; as drowning, haemorrhage, &c. The sudden inspiration is al- ways the first of the renewed actions of life, as it i3 the last in exhausted nature. This corresponds with the experiments made on animals. When the sensibili- ty is exhausted in the common spinal nerves, from the ebbing of life, the respira- tory nerves on the neck and side of the chest are still capable of exciting the mus- cles to renewed vibrations ; they are the last to die. These considerations exhibit the importance of the act of inspiration over that of expiration, and prove the necessity for these exterior nerves of respiration. We have seen by experiments, that the respiratory nerves are distinguished from the other nerves by retaining their power longer: that they are alive to im- pression, and can be made to produce convulsions in the muscles they supply, af- ter the other nerves are dead to the application of stimuli. In disease, during the oppression of the mental faculties, and on the approach of death, we witness these nerves, and the muscles put into operation by them, continuing their functions, when in other respects the body is dead. This circumstance, so familiar to the medical observer, might have led to the conclusion to which we have arrived, more laboriously, through anatomical investigations; that there are a great many muscles extended over the body, and which perform the common offices under the will, which are occasionally drawn into combination with the muscles of respira- tion, and are held in relation to the- vital functions by a distinct system of nerves, and that these nerves have a centre and a source of power, different from that of the voluntary nerves. * Mr. Turner. 122 OP THE PARTICULAR NERVES. SOME FURTHER REMARKS ON THE PATHOLOGY OF THE RESPIRATORY SYSTEM OF NERVES. When we surrey the full extent of the respiratory system of nerves, we are prepared to comprehend its importance to the continuance of life. The infant born without a brain can breathe if the origins of these nerves be entire. Deep wounds of the brain, though eventually fatal, are not necessarily, or instantly so. The man wounded in the spine, below the of the nerves which we have traced, drags on existence for a few days; but a bruise on the part of the medulla oblongata, from which these nerves take their departure, is death in the instant; a breath is not drawn again. In describing the effects of violence on the medulla oblongata, authors have at- tributed the sudden death to injury of the roots of the nerves of the par vagum ; and yet we have a statement from the same authority, that an animal will survive the division of both nerves of the par vagum. Now that we find that many re- spiratory nerves depart from the same centre, and go out to all the parts of the muscular frame, which move in respiration, we can better comprehend, how injury of the medulla ohlongata suppresses at once the act of respiration in the nostrils, throat, and windpipe, as well as the action of the muscles both without and within the chest; even the expression of the agony of dying is, by the injury of the roots of all these nerves, suddenly interrupted, and actual death follows quickly, owing to the cessation of the respiratory functions. The first thing that strikes us is the vital character of these nerves, called re- spiratory ; that as they form a system belonging to the heart, lungs, stomach, la- rynx, throat, and the whole exterior association of muscles of respiration, they must be essential to life, and influenced in all mortal affections ; and that, in fact, death cannot take place whilst this division of the nervous system is unchanged or unaf- fected. On the contrary, the injury of their function is attended with immediate death, and the change takes place with appalling suddenness ; not a breath is drawn, nor a word uttered, nor a struggle to indicate pain, nor a feature discomposed. On the contrary, if other parts of the body are injured by disease or accident, death comes slowly from the rising of inflammation, or the extension of the influ- ence slowly over the system ; at length the respiratory system partakes of the influ- ence, the chest rises higher and more frequently, an alarming symptom, when there is reason to fear approaching dissolution; the throat is then affected ; the whole apparatus of respiration is violently agitated; the chest, neck, lips, and cheeks, and eyeballs are wrought with terrible convulsions; the breathing is about to stop; the action returns with sudden and startling effort, and then ceases, the patient dying in the stale of expiration, the muscles of inspiration being incapable of renewing their effort. If it he important to know the approach of danger, and to distinguish betwixt nervous agitation from the formidable symptoms of approaching dissolution, it is necessary to know the causes of these symptoms, otherwise the physician is no bet- ter than the nurse. It must happen that the derangement of one part of this class of important or- gans must affect the other. The stomach, for example, as the most abused in its office, is daily exhibiting the effect of its close alliance with this system of nerves; and what we learn from this anatomy of the respiratory system, is, that the stomach Etands in close connection with the respiratory nerves, and that an irritation on the stomach will have all the effects of an injury immediate upon the lungs. The stomach, heart, and lungs are undoubtedly the seat of that affection which is attended with sudden death ; when there are no tokens or symptoms in the agi- tations of the respiratory organs, the source from which danger is to be most ap- prehended is the stomach ; and founding on the fact expressed above, l have to suggest, that it is the duty of the patient to struggle against the increasing influence of the stomach on the condition of the respiratory organs: that the physician has not merely to regulate the stomach as the organs of digestion, but that the patient has to study to preserve his freedom of respiration against the prevailing influence of the stomach. One of our athletse out of training is pursy, breathless, and cannot bear the buf- fets, shocks, and falls to which he is liable in a bruising bout. But by spare and healthful diet, regular severe exercise, mimic combats, in which his breast, belly, OF THE PARTICULAR NERVES* 123 ami head are repeatedly buffeted, he is at length capable of standing under shocks that would be fatal to a man of equal strength and better constitution, but other- wise unprepared for what he is to undergo. Whether it be an effort of the body, or of the constitutional strength; whether it be an exertion of the head, or hands, or feet, we must come to the full exercise gradually and by slow degrees. Thus I argue the matter with a man whose palpitations are excessive and painful, on every accelerated step; he must not altogether avoid the occasion which gives him un- easiness, but by encountering them repeatedly, and by slow degrees, familiarize himself with the exertion. As these nerves belong to a distinct system, and have a different origin from the nerves of sensibility and common muscular motion, so it is fair to presume that they will occasionally be affected by disease, when the others are left in a natural and healthy condition. But if the natural distinctions of the nerves be negligently considered, the affection of the respiratory nerves must remain obscured. 1 have already had occasion to remark, that the portio dura, or respiratory nerve of the face, is very subject to derangement, producing partial paralysis, or frequent and spasmodic twitchings of the face. The most frequent defect proceeding from this cause is a rapid and twinkling motion of the eyelid on one side. Sometimes we find the whole of one side of the face subject to contractions, by which the features are drawn towards the ear. This condition of nerves, and consequent spasmodic muscular contractions, sometimes extends to the neck ; then we see the head sud- denly twitched sideways, at the same moment that the mouth is drawn aside. This i3 a great deformity; for while the individual is animated and speaking with ex- ertion, he gives those sudden startling motions, opening his mouth and turning it to his shoulder, as if he were catching flies. The neck is twisted, the head bent down, and the mouth turned laterally and opened. These motions must now be attributed to the influence of the respiratory nerves of the face and neck. But the same class of nerves, in their distribution to the chest, are subject to the same arrangement. It is not very uncommon to find the shoulder of a young per- son falling low, and the appearance of distortion produced by a paralysis of that part of the trapezius muscle which supports the shoulder, and which is supplied by the spinal accessory nerve. This affection forms a parallel with the paralysis of the eyelid and the cheek ; and there are not wanting examples of spasmodic af- fection of the thorax resembling those which I have just noticed on the side of the face and neck. We perceive that these nerves of respiration, so peculiar in relation and func- tion, are differently influenced by disease from the other division of the nervous system. We know that their functions are left entire when the voluntary nerves have ceased to act, and they are sometimes strangely disordered, while the mind is entire in all its offices, and the voluntary operations perfect. In tetanus the volun- tary nerves are under influence, and the voluntary motions locked up in convul- sions ; in hydrophobia, on the contrary, the respiratory system is affected; and hence the convulsions of the throat, the paroxysms of suffocation, the speechless agony, and th6 excess of expression in the whole frame, while the voluntary mo- tions are free. The confusion between vital and voluntary nerves, the combining the par vagum and sympathetic nerves together, and the exclusion of the portio dura of the seventh nerve, the spinal accessory nerve, and the external thoracic nerve, from their na- tural classification with the diaphragmatic or phrenic, has given rise to very vague theories, and occasioned very inaccurate statements of pathological facts. The frequency of sudden death, where no corresponding appearance are exhi- bited in the brain or heart, leads us to consider more attentively the only part of the system through which life can be directly extinguished. In angina pectoris, we witness the agony of suffering in this system when the patient survives ; and when he dies suddenly, we can imagine it to proceed from an influence extending over these nerves, and interrupting the vital operations. We have seen that a branch of this system may suddenly cease to operate on the corresponding muscles, and that in this way the side of the fuce may be deprived of all participation in the act of respiration, and all expression be lost. What would result from a more universal defect in the actions of this class of nerves, but sudden death ? The stomach, supplied with the great central nerve of this system, exhibits the most powerful influence on these extended nerves ; a blow on the stomach” double* up” the bruiser, and occasions that gasping and crowing which sufficiently indicates 124 OF THE PARTICULAR NERVES. the course of the injury: a little more severe, and the blow is instantly fatal. A man broken on the wheel suffers dreadful blows, and his bones are broken, but life endures ; the coup de grace is the blow on the stomach. The position of the asthmatic shows how this system is affected ; whether di- rectly or indirectly, it is not our present business to enquire. He stands stooping forward, resting his arms so as to throw the muscles of the chest into operation upon the ribs. The position of the head and the rigidity of the muscles of the neck, the action of the mastoid muscle, and of the cutaneous muscle, visible in the retraction of the cheeks and mouth, and the inflation of the nostrils, carry us back in review of the nerves and muscles of respiration. It will now, perhaps, be acknowledged, that the methods of physiologists, in account- ing for the combination of parts in the actions of respiration, were very imperfect, or rather altogether erroneous. To account for the convulsion of the diaphragm in sneezing, they were constrained to go a far way about: first, connecting the roots of the phrenic with the sympathetic nerve : bestowing sensibility on the latter, which it does not possess: then, following a remote connection between it and the nerves of the nose ; then again, counting the relations between the facial nerve and the third of the neck : they satisfied themselves that they had explained the manner in which the diaphragm became convulsed upon irritating the membrane of the nose. Another misconception was engrafted on the first; they spoke of these actions as convulsive and irregular, which are amongst the most admirable provi- sions for the protection of life. As to the act of sneezing, like coughing, it is a con- sequence of an irritation of the extremity of one of the respiratory nerves, whence the whole muscles of respiration are brought into action. That there is nothing accidental, nor of the nature of convulsion, is shown by the admirable adjustment of the muscles to the object. A body irritating the glottis will call into simulta- neous action the muscles of respiration, so as to throw out the air with a force ca- pable of removing ihe offending body. But if the irritation be on the membrane of the nose, the stream of air is directed differently, and, by the action of sneezing, the irritating particles are removed from these surfaces. By the consideration of bow many little muscles require adjustment to produce this change in the direction of the stream of air, we may know, that the action is instinctive, ordered with the utmost accuracy, and very different from convulsion. OF SMELLING, AS INFLUENCED BY THE PORTIO DURA OF THE SEVENTH NERVE. It will, I hope, be acknowledged that I have studied the functions of the parts to which the nerves are before I made my experiments or drew my conclusions. Even in the exercise of the sense of smelling, parts are employed, which do not, at first, seem necessary. For the highest enjoyment or exercise of the sense of smell- ing, it is necessary that the stream of air inhaled through the nostrils should change its direction, and be increased in force. In breathing through the nose, the air is carried directly backward. If the nostrils are expanded in anxious or hurried res- piration, the passage is enlarged, and made more direct. But, perhaps, my reader is not aware that in each nostril there are two circular openings, the innermost something more than half an inch within the other. This interior circle expands, and becomes lower when the breath is forcibly drawn into the lungs; but in the act of smelling it is much diminished and elevated. The change in the form and relation of the exterior and internal nostril is performed by the action of the mus- cles on the cartilages ; and the elfect of the change is to increase the force of the stream of air, and to direct it up towards the seat of the sense of smelling. In common breathing some part of the effluvia afloat in the atmosphere reaches the seat of the sense; but fully to exercise the sense, it is necessary to concentrate and direct the stream of air, as 1 have described. It will now be comprehended how the destruction of the portio dura, or respira- tory nerve of the face, affects the organ of smelling; for if by the injury of that nerve the motion of the muscles of the nostrils be lost, the breath may be drawn into the lungs through the relaxed passage, but it Will not be drawn forcibly up OF THE PARTICULAR NERVES. 125 towards the seat of the olfactory nerve, nor will the air brush over the surface on which the proper nerve of sense is expanded. A man being paralytic on one side of the face by the loss of power in the portio dura, he was made to smell ammonia : it did not affect the paralytic side, because it was forcibly inhaled into the cells of the nose only on the side where the nostril was moveable. On trying the experiment on a dog, in whom the portio dura of one side had been cut, the same thing was manifested ; he snuffed it up with the sound side, and showed the natural consequence of the irritation of the membrane ; while he was not similarly affected when the bottle was put to the paralytic nostril. Unless I had attended to the structure and function of the part, on witnessing these phenomena, I might have conceived that the seventh nerve was the nerve of smelling, like a noted French physiologist, who concluded too hastily, that he had discovered the nerve of vision and of smelling in the fifth nerve. I allude to certain experiments lately performed in London by a distinguished visitor, which afford a proof of the utter impossibility of reasoning correctly on these subjects without the knowledge of the anatomy. The olfactory nerve was destroyed, and ammonia put to the nostrils of the animal, and when the creature sneezed it was a coup de thialrti then the gentlemen congratulated themselves that it was discovered that the first pair of nerves was of no use! ! The common irri- tability of the schneiderian membrane results from the fifth nerve: why does the membrane possess this sensibility, and why is the sensibility joined to the actions of the respiratory system ? because these passages must be guarded as the larynx is guarded. When any thing offensive is lodged there, it must be removed, and the means nature employs is to drive the air by an instinctive action of the respi- ratory organs, violently and suddenly, through the nostrils. But what has this to do with smelling ? As well might we destroy the olfactory nerve, and wonder that the creature experimented on still coughed when the larynx was tickled. We have some observations on this subject in Mr. Shaw’s paper already quoted, “ The effect upon the nostril is the most obvious symptom, when the nerve is cut in the a3S. If after having cut the right nerve (portio dura,) we hold the nostril for a short time, so as to prevent the animal from breathing, he will, when freed, begin to snort, but with the left nostril only. If we hold carbonate of ammonia to the paralysed nostril he will not be affected ; but if it be held to the other, he will snuff it up, and then curl the nostril, and have an expression in the whole of that side of the face, as if he were going to sneeze, while the right side will remain quite un- moved.” The rationale of this is worth attention; by the neglect of it some physiologists and experimenters have appeared to much disadvantage. The act of smelling is not simply the act of drawing the breath; but while the breath is drawn there is a conformity in the motion of the nostrils, by which the air, loaded with the effluvia, is directed to the seat of the olfactory nerve ; that is to say, is made to circulate in the higher parts of the cavities of the nose, instead of streaming directly backwards into the posterior nostrils. This was the reason why, on putting the ammonia to the nostril which was still, the creature was not excited, although there had been nothing done to injure the sensibility of that side of the nose. If a man were simply to draw his breath in taking snuff, the powder would be drawn into his fauces and lungs; but to snuff, the point of the nose is drawn down, and the nostrils contracted, and then when the air is inhaled, the snuff rises to the superior cells, and stimulates all the interior of the nostrils. Al- though by this stimulus he sneezes, the olfactory nerve has nothing to do with it. The luxury is in the stimulus of the respiratory system through the excitement of the membrane, not in the odour as enjoyed by the olfactory nerve. The sensitive branches of the fifth are first excited, then the respiratory system is in a secondary manner affected; and to ascertain whether the mode of communication between the fifth and the respiratory nerves be affected at their roots in the brain, or at their extremities, is a fair question to be determined by experiment or reasoning. THESE RESPIRATORY NERVES ARE ORGANS OP EXPRESSION. We may notice another office of these respiratory nerves; in smiling, laughing, and weeping, the influence is solely propagated through them. The face, we have 126 OF THE PARTICULAR NERVES. seen, is dead to all changes of the kind when the nerve of this class which goes to it is destroyed, whether it be by division of the nerve, or from its being surrounded with inflammation or suppuration. When we consider that all the respiratory nerves depart from the same source, and participate in the same functions ; and more especially when we see the respiratory organs so very distinctly affected in the conditions of the mind, which give rise to these affections, it is not too much to suppose, that what is proved in regard to one of these nerves, is true of the whole class, and that they alone are influenced in laughter. Physiologists who have not investigated the cause, are yet agreed in describing laughter to be a condition of the respiratory muscles, where the air is drawn in rapidly, and thrown out in short spasmodic motions of these muscles; that crying is nearly the reverse, the inspi- ration being cut by spasmodic actions of the muscles of inspiration. By these con- siderations are explained the subrisus which arises from abdominal irritation, and the sardonic retraction of the muscles of the face produced by wounds of vital parts, and particularly of the diaphragm. It explaius also the successive convulsive lift- ing of the shoulders in wounds of the diaphragm. That a system of nerves so intimately combined as this is with the other parts of the general system, should suffer in hysterical disorders, cannot surprise us; and admitting that irritation reaches to the respiratory system, we may perceive how rapidly the change may be produced, from the convulsions of laughte r to those of crying; and where, if there be a corresponding condition of the mind, it rather follows than precedes the expression of the frame. It would have been extraordinary if we had arrived at any satisfactory theory of expression, before it was known through what instruments the mind influenced the body, during emotion or passion. But since we know that the division of the respiratory nerve of the face, deprives an animal of all expression ; and that the expressive smile of the human face is lost by an injury of this nerve : since it is equally apparent, that the convulsions of laughter arise from an influence extend- ed over this class of nerves, it comes to be in some sort a duty, in pursuing this matter, to examine farther into the subject of expression. We may be at the same time assured of this, that whatever serves to explain the constant and natu- ral operations of the frame, will also exhibit to us the symptoms of disease with more precision. In terror, we can readily conceive, why a man stands with eyes intently fixed on the object of his fears, the eyebrows elevated, and the eyeballs largely uncover- ed ; or why, with hesitating and bewildered steps, his eyes are rapidly and wildly in search of something. In this we only perceive the intent application of hi? mind to the objects of his apprehensions, and its direct influence on the outward organs. But when we observe him farther, there is a spasm on his breast: he cannot breathe freely: the chest remains elevated, and his respiration is short and rapid ; there is a gasping and convulsive motion of his lips : a tremor on his hollow cheeks: a gulping and catching of his throat: his heart knocks at his ribs, while yet there is no force in the circulation, the lips and cheeks being ashy pale. It is obvious, that there is here a reflected influence in operation. The lan- guage and sentiments of every people have pointed to the heart, as the seat of passion, and every individual must have felt its truth. For though the heart be not in the proper sense the seat of passion, it is influenced by the condition of the mind, and from thence its influence is extended through the respiratory organs, so a3 to mount to the throat, and lips, and cheeks, and account for every movement in passion, which is not explained by the direct influence of the mind upon the features. So we shall find, if we attend to the expression of grief, that the same pheno- mena are presented; and we may catalogue them, as it were, anatomically. Imagine the overwhelming influence of grief—the object in the mind has absorb- ed the powers of the frame; the body is no more regarded, the spirits have left it; it reclines, and the limbs gravitate, the whole body is nerveless and relaxed, and the person scarcely breathes; so far there is no difficulty in comprehending the effect in the cause. But why, at intervals, is there a long drawn sigh, why are the neck and throat convulsed, and whence the quivering and swelling of the lip, why the deadly paleness, and the surface earthy cold; or why does convulsion spread over the frame like a paroxysm of suffocation ? OF THE PARTICULAR NERVES. 127 To those I address, it is unnecessary to go farther, than to indicate that the nerves treated of in these papers are the instruments of expression, from the smile upon the infant’s cheek to the last agony of life. It is when the strong man is sub- dued by this mysterious influence of soul on body, and when the passions may be truly said to tear the breast, that we have the most afflicting picture of human frailty; and the most unequivocal proof, that it is the order of functions which we have been considering that is then affected. In the first struggles of the infant to draw breath, in the man recovering from a state of suffocation,and in the agony of passion, when the breast labours from the influence at the heart, the same sys- tem of parts is affected, the same nerves, the same muscles, and the symptoms or characters have a strict resemblance. Having examined the system of nerves and muscles, which are the agents in respiration, in their fullest extent and in all their bearings: having looked at •them in their highest state of complication in the human body, and having traced them upwards, from the animals of simple structure, and then by experiment, and in a mannner analytically as well as synthetically, their relations become obvious. Instead of one respiratory nerve, the par vagum, the nerve so called, is found to be the central one of a system of nerves of great extent. Instead of the relations of the vital organs of circulation and respiration depending on some supposed influence of the sympathetic nerve, they are found to have an appropriate sys- tem. This system of nerves, extricated from the seeming confusion in which it lay hitherto encumbered, is found to be superadded to that of mere feeling and agen- cy, attributes common to all animals : through it we see, engrafted as it were, and superadded to the original nature, higher powers of agency, corresponding to our condition of mental superiority : these are not the organs of breathing merely, but of natural and articulate language also, and adapted to the expression of senti- ment, in the workings of the countenance and of the breast, that is, by signs, as well as by words. So that the breast becomes the organ of the passions, and bears the same relation to the developement of sentiments, as the organs of the senses do to the ideas of sense.] OF THE NINTH PAIR5 LINGUALIS, OR HYPO-GLOSSUS. This nerve arises by a number of filaments coming off in regular succession from the medulla oblongata, and from the side of the corpus pyramidale, and betwixt that body and the corpus olivare. These fila- ments collecting in the direction of the condyle of the occipital bone, pass out from the skull by the anterior condyloid foramen ; when it has made its exit, this nerve adheres to the eighth pair, by cellular fila- ments*, and from that part of the eighth nerve where it gives off the laryngeal branch, there comes off a communication to the ninth nerve. It receives also branches from the first cervical nerve, or from the branch of union of the first and second cervical nerves. Here it is also joined by a twig from the sympathetic nerve. When dissecting in the neck, we find the ninth nerve lying by the side of the internal jugu- lar vein under the stylo-hyoideus muscle, and under the sub-maxillary gland, and near the horn of the os hyoides. The nerve making a curve to ascend again to the tongue, gives off' that branch which is called the descendens noni. The continued trunk of the nerve passes before the external carotid artery, and forwards un- der the larger branches of veins. It lies parallel to the lingual artery, * Some affirm that there is a connection by filaments of nerves at this junction of the 8th and 9th:—“ etiam interdum tradita acceptave fibrilla nervea.” Scarpa, Tab. I. so Asch. Fallopius. 128 OP THE PARTICULAR NERVES. but not so deep, and on a higher level. Here it turns upwards under the stylo-hyoideus and digastricus muscles, and betwixt the stylo-glossus and hyo-glossus. Where the nerve is near the os hyoides, and passing under the hyo-glossus muscle, it sends down a twig which passes to the thyreo-hyoideus muscle. The continued nerve goes under the mylo-hyoideus and is liberally distributed to the muscles of the tongue, but not before these branches have formed a sort of plexus. It terminates by numerous filaments, which form a net-work amongst the muscles of the tongue ; to which is united part of that branch of the fifth pair which goes to the tongue.* The ramus descendens noni comes off from the lower edge of the ninth nerve, (the origin is covered by the internal jugular vein, and by the occipital artery.) This branch, near its origin, is connected with the par vagum ; it then passes downward, obliquely over the sheath of the caro- tid artery, and under the thyroid vein. In the superficial dissection of the muscles of the neck, two slender twigs of nerves will be seen to come from the side of the neck, and crossing the jugular vein, unite to this descending branch of the ninth. Those twigs come from the second and third cervical nerves, (in some instances those twigs are found to be derived from the first origin of the phrenic nerve) ; and a plexus is form- ed by their union with the descendens noni, viz. the superficial cervical plexus. From this centre are sent out many delicate and superficial nerves to the omo-hyoideus, sterno-thyroideus, and sterno-hyoideus mus- cles; and a branch of the descendens noni takes a course along the cen- tral tendon of the omo-hyoideus, to supply the lower division of this muscle. There is a branch of some interest, although small and deep, among so many greater nerves ; it comes from the par vagum, and the descending branch of the ninth, and joins this cervical plexus, where it may be traced piercing the scalenus muscle. Thus we find that the ninth nerve has connections with the eighth pair of nerves, with the spinal accessory, the sympathetic, the cervical, and phrenic nerves. When this nerve is injured, the motion of the tongue is lost, but the sense of taste remains unimpaired. On the contrary, when the branch of the fifth nerve going to the tongue is hurt, the sense of taste is lost, while the mobility of the tongue remains. | Columbus knew a man who had no sense of taste, and who ate indifferently every thing presented to him. When he died, Columbus was curious to know the cause of this, and he found that he altogether wanted the gustatory nerve or lingual branch of the inferior maxillary nerve. Cases detailed by Pro- fessor Scarpa still further illustrate this fact. A woman subject to epip- lectic attacks in an early age, was seized in her pregnancy with an hemi- plegia and loss of speech. From this attack, by the use of medicines, she recovered ; but in a future labour the disease recurred. Now the cure was less complete : for, though she regained the use of her arms, she never recovered the faculty of speech, or was only capable of articu- lating with great dissonance the monosyllables, affirming or denying.— Upon making her exert herself to speak, they observed no motion in the tongue; and, upon applying the hand under the jaw, they could feel no motion in the muscles of the tongue ; yet she relished her food and drink, * This has been called plexus cerato-basio-stylo-glossus ! f Soemmerrinar de Cerebro et Nerris. OF THE PARTICULAR NERVES. 129 and had an acute sense of taste, and could swallow easily. He mentions another case, where the patient was attacked with a sense of weight at the root of the tongue, a difficulty of speaking, and copious flow of sali- va. In a short time he entirely lost the power of articulating, but retained acutely the sense of taste.* OF THE CERVICAL NERVES* We have now done with the more irregular nerves of the head, and now we come to the spinal nerves, which all agree in structure and func- tion, being double at their roots; and having one root given to bestow sensibility, and the other root to bestow motion. First cervical nerve. Tenth pair of the skull. Sub-occipi- tal nerve.—This is the least of all the nerves of the spine ; it arises by two roots from the medulla spinalis. Some difference has been observed in the manner in which those roots collect their filaments ; and only the anterior root or fasciculus is described by some authors. The posterior fasciculus is, indeed, the larger, and comes in a direction different from the general direction of the roots of the other cervical nerves. The roots of the sub-occipital nerve are connected with the spinal accessory nerve, so as to give rise to some difference of opinion, and sometimes they form a union with the posterior roots of the second cervical nerve. The fibres of the sub-occipital nerve passing transversely, and a little obliquely up- wards, go out under the vertebral artery, and betwixt it and the first verte- bra of the neck. The little trunk of the sub-occipital nerve, thus formed, swells into a kind of ganglion, and having escaped from the spine, it rises for a little way upwards, and then divides into two branches. The anterior of these branches is the smaller. It passes down upon the inside of the vertebral artery; its filaments unite with the hypo-glos- sal nerve, or ninth pair, and with the superior cervical ganglion of the sympathetic, and with the first branch of the second cervical nerve.f The larger and posterior branch divides into eight twigs, which are chief- ly distributed to the muscles moving the head—to the obliquus superior and inferior, the recti postici and laterales, complexus, and splenius, Some of those muscular branches unite with that branch of the second cervical nerve which ascends upon the occiput. Second cervical nerve.—This nerve, arising by a double origin from the spinal marrow, like the other nerves of the spine, passes be- twixt the first and second vertebrae. It is larger than the last, and di- vides into two branches. The superior branch sends up a considerable division behind the projection of the transverse process of the first vertebra, to be united to the sub-occipital or first cervical nerve. Several twigs pass forward to unite with the superior cervical ganglion of the sympathetic nerve, and with some of the more anterior branches of the third cervical nerve, and with the ninth and spinal accessory nerves. Besides these intricate connections, irregular branches of this nerve proceed to the small mus- * Tabulae Neurologicae, Auctore Anton. Scarpa. It has long been the authpr’s intention to prosecute the subject of the nerves of the tongue, and he hopes in the succeeding season to accomplish it. + A very small nerve is described by'some authors as passing from the anterior division of this nerve, into the canal of the vertebra! artery 130 OK THE PARTICULAR NERVES. cles, moving the head, and lying on the fore part of the spine. The pos- terior branch of the second pair of cervical nerves is chiefly a muscular nerve. It rises up by the side of the complexus, gives branches to that muscle and to the splenius, and communicates with the branches of the first cervical. Its branches are also distributed to the upper part of the trapezius muscle, from which they extend along the integuments, covering the occiput even to the summit of the head. The third cervical nerve, in the first place, communicates with the second and fourth cervical nerves, then forwards with the sympathetic and lingual nerves. It sends down a twig to unite with the origin of the phrenic nerve from the fourth cervical nerve. From the anterior divi- sion of the third cervical nerve, branches pass to the splenius and com- plexus, and trapezius, and upwards to the ear. We may observe also a cutaneous nerve which accompanies the external jugular vein, viz. ner- vous superficialis colli ; the distribution of which is chiefly to the angle and margin of the lower jaw, while some of its branches enter the parotid gland, and unite with the extremities of the portio dura and other facial nerves.* The small posterior division of the nerve passes to the complexus, spinalis cervicis, and multifidus spinae, while at the same time it unites to the branches of the second cervical nerve. The fourth cervical nerve, coming out from betwixt the third and fourth cervical vertebrae, divides into its anterior and posterior branches like the other cervical nerves. The first goes to form, with the third and fifth cervical nerves, the phrenic nerve. It sends also for- ward a branch to the sympathetic, and also to the integuments of the neck and shoulder, and to the supra and infra spinatus muscles. These are called by Soemmerring superclaviciit.ares anteriores, medii, and posteriores ; to these are attributed the false pains when the diaphragm is irritated. These too in all probability cause the convulsions of the shoul- der when the diaphragm is wounded. The great posterior division of the fourth cervical nerve passes to the muscles of the spine and shoulder, in conjunction with the branches of the third cervical nerve. Fifth cervical n_rve.—This nerve comes of course from betwixt the fourth and fifth vertebrae, and from betwixt the scaleni muscles. It divides also into two branches. The superior of these passes backwards to the muscles of the back and shoulder; and a branch formed by it, and the sixth passes down under the scapula and serratus major. This last is the nerve I have described under the term external re- spiratory nerve. It has the same source with the phrenic nerve : it is connected with that internal nerve ; at its origin it is separated from the phrenic by a very small portion of the scalenus. Its course is through the axilla, passing deep under the nerves of the arm, and uncon- nected with the axillary plexus ; it is distributed to the muscles on the side of the chest, and combines them into a class with the internal respi- ratory muscles. The superior division of the nerve sends up also two small twigs of communication with the fourth cervical nerve. The inferior division of the fifth cervical nerve sends down upon * This nerve continues to give sensibility to the lower part of the face, after the branches of the 5 th are cut. OF THE PARTICULAR NERVES. 131 the side of the neck a considerable branch to the formation of the phre- nic nerve. It communicates with the root of the sixth nerve, and sends muscular branches backward. The sixth cervical nerve.—The muscular branches of this nerve are large, and extensive in their course. They pass into the levator scapulae, extend under the trapezius, and unite with the extreme branches of the spinal accessory nerve. They are prolonged to the latissimus dorsi and serratus magnus. Branches also extend down behind the clavicle, and under the pectoral muscle. Besides these branches, this nerve communicates with the fifth, and gives out an origin to the phrenic nerve; and lastly, uniting to the seventh, it passes into the axillary plexus. The seventh cervical nerve.—This nerve goes almost entirely to form the axillary plexus. There is a communicating nerve from the last of this, and from that communicating branch generally there passes off a filament to the phrenic nerve; and from the very root of the nerve there passes off a branch to the lower cervical ganglion of the sympa- thetic.* Irregular twigs also descend from this nerve under the clavicle to the pectoralis minor and major. The eighth cervical nerve.—The greater part of this nerve passes to the axillary plexus. It sends small branches to the lower cervical ganglion of the sympathetic, and to the muscles of the breast ; which last descend behind the clavicle. RECAPITULATION OF THE DISTRIBUTION OF THE CERVICAL NERVES. Upon reviewing the description of these nerves, we find that the ge- neral tendency of their branches is backwards over the side of the neck, to the muscles moving the head and shoulders. We find also that they are connected in a very intricate manner with the most important nerves of the cranium. High in the neck and under the jaw, they are connect- ed with the portio dura, with the fifth pair, with the eighth and ninth pairs, and with the sympathetic. Towards the middle of the neck they are still throwing their connecting branches to the descendens noni, and sympathetic, and eighth pair. The lower cervical nerves again are still supplying the connections with the lower ganglion of the sympathetic. Further, we find that the phrenic nerve is derived principally from the the third and fourth, and branch of communication betwixt the fourth and fifth. The inferior external respiratory nerve is derived principally from the fifth cervical nerve, and also has communicating branches with the fourth and sixth. The axillary plexus is formed by the fifth, sixth, seventh, and eighth cervical nerves, and first of the back. OF THE DORSAL NERVES. There are twelve dorsal nerves. These, like all the other spinal nerves, are formed by two fasciculi of fibres ; one from the fore, and the other from the back part of the spinal marrow. These filaments run for some way superficially in the length of the spinal marrow before they * These communications betwixt the cervical nerves, and the sympathetic nerve, are, I be- lieve, branches of the sympathetic running down upon the arms. 132 or THE PARTICULAR NERVES. pierce the dura mater. They pierce it separately; the posterior root first forms a ganglion, and then the two fasciculi are united. They are now betwixt the heads of the ribs. We must here recollect, that the trunk of the sympathetic nerve, which passes along the thorax, runs down behind the pleura, and before the heads of the ribs through all the length of the back. It receives, as it passes, the interstices of the se- veral ribs, at each interval a communicating nerve from the spinal mar- row, that is, an additional root is afforded by each nerve as it passes ; it is in a manner thus made up of roots, from the intercostal nerves, hence the sympathetic is sometimes called intercostal. The intercostal nerve, properly so called, sends its greater branch forwards betwixt the ribs ; some lesser branches pierce backwards to the muscles of the back ; opposite to this there goes out from each nerve the first branch of union with the sympathetic, and on this union a gan- glion is formed. Sometimes there run out in this direction two short branches from the spinal nerve, to unite with the ganglion of the sym- pathetic ; but more commonly there passes in a retrograde direction from the intercostal nerve, where it is about to take its course between the ribs, another branch of communication which joins the sympathetic. The intercostal nerves pass on betwixt the ribs, and under the protec- tion of the groove on the lower edge of the rib, in company with the in- tercostal arteries, and reach even to the sternum. In this course they supply the intercostal muscles and triangularis sterni, while they are at the same time sending- out branches, which, piercing the intercostal muscles and fascia of the thorax, are distributed to the muscles on the outside of the chest.—Those branches which we mentioned as passing betwixt the heads of the ribs, and which are sent oft' immediately upon -the trunk escaping from the vertebral opening, supply the multifidus spinae and levatores costarum, and other extensor muscles of the spine. Slips proceeding from the second, third, fourth, and fifth intercostal nerves, send branches to the pectoral muscles, the serratus anticus, and serratus posticus superior, trapezius, and rhomboideus. The sixth, and all the lower nerves of the back, send branches from betwixt the ribs to the latissimus dorsi, serratus inferior, and abdominal muscles. The eleventh and twelfth are distributed to the diaphragm, quadratus lumborum, psoas mugnus, and iliacus internus. LUMBAR NERVES. The lumbar nerves are five in number. They arise like the other spinal nerves. The first comes out under the first lumbar vertebra, and the others in succession. Their trunks are covered by the psoas mag- nus. They pass very obliquely downward, and the three lowest are of remarkable size. In the general distribution, we may first remark the posterior branches, which go backwards to the muscles which support and extend the spine. Again, the anterior branches ; which give, 1st, additional branches to the sympathetic nerve as it passes over the vertebrae of the loins, and by which it is supported and reinforced till it terminates in the pelvis ; 2dly, they have frequent connexion with each other, and with the last nerve of the back, and first of the sacrum ; 3dly, they send out branches, de- licate but of great extent, to the muscles of the Joins and back, and to OP THE PARTICULAR NERVES. 133 the abdominal muscles and integuments of the groin and scrotum; 4thly, the principal anterior branches of the lumbar nerves pass down to form (along with the great nerves of the sacrum) the anterior crural nerve, the obturator, and the great ischiatic nerve. SACRAL NERVES. The nerves which come out from the extremity of the medulla spinalis, or cauda equina, through the sacrum, are in general five in number. Sometimes there is one more or less. The first division of each sacral nerve is into those branches which pass out by the posterior fora- mina of the sacrum, and those which, by the anterior foramina, come into the pelvis. The posterior branches are very small, and pass to the muscles supporting the spine ; while the anterior ones are particularly large, especially the first and second, which, with the lowest of the loins, go to form the largest nerve of the body, the ischiatic nerve. It is difficult to recollect the distribution of the several branches of the lumbar and sacral nerves, when taken thus together; but when we de- liver the description of the nerves of the thigh and leg, we count them, and remember them with comparative ease. At present we are best pre- pared to follow the sympathetic nerve in its course. OP THE GREAT GANGLIONIC NERVE ; OH, INTERCOSTAL NERVE. This nerve, called sympathetic, is, in fact, an entire system of nerves, which distributed most evidently to the viscera of the thorax, abdomen, and pelvis, does in fact extend universally, by joining the other nerves of the head and extremities. But in this extended distribution it is lost by joining other nerves. While in the abdomen and thorax it is particularly distinct and demonstrable. The old method of describing the sympa- thetic nerve is to consider it as derived from the sixth and fifth, for they had no idea of a nerve but as a tube coming from the brain; for the sake of clearness we shall still describe it as thus descending. The sympathetic nerve is in general considered as originally derived from the sixth pair ; it also takes its origin from the first or ophthalmic division of the fifth pair, and from the Vidian branch of the fifth pair. It appears without the skull, sometimes behind and sometimes before the carotid artery, and sometimes it is double in its exit from the base of the skull. Almost immediately after it has escaped from the skull, it forms its first ganglion; which is very large and remarkable, and has the name of the superior cervical ganglion of the sympathetic nerve. It is of a soft consistence and reddish colour, and it extends from the skull to the transverse process of the third vertebrae. It gradually tapers downwards until it becomes a very slender nerve. This ganglion has much variety of shape in different subjects, and may be said in general to receive twigs of nerves upon the back part; whilst it gives them out upon the fore part. The superior cervical ganglion of the sympathetic nerve receives nerves from the second, third, and fourth cervical nerves, and even sometimes from the root of the phrenic nerve. It has also connections with the hypo-glossal, par vagum, and glosso-pharyngeal nerves. It sends out branches to unite with the glosso-pharyngeal, and which follow that 134 or THE PARTICULAR NERVES. nerve in its distribution to the tongue and pharynx. Many of its branches surrounding the carotid artery form connexions with the internal and ex- ternal laryngeal nerves and proceed in meshes, or form plexus along with the branches of the artery. These may be followed to great minuteness. To be more particular in the description of these anterior branches of the sympathetic nerve, they are called the nervi molles, or nervi va- sorum. They are nerves peculiarly soft, with a greater proportion of cellular membrane; they spread in net-works along the arteries, and form frequent connexions by little knots like small ganglions. Classed with these nervi vasorum, are branches which pass forward from the up- per ganglion of the sympathetic, to unite with filaments from the internal laryngeal nerve of the par vagum, and which form the external laryngeal nerve. It is remarked, that none of these branches of the sympathetic nerve are distributed to the larynx and pharynx without being mingled and associated with the glosso-pharyngeal nerve, or with the pharyngeal branch of the par vagum.* Of the nervi molles some form a plexus upon the internal carotid artery. These are extremely soft and pulpy, and are united with branches which descend from the glosso-pharyngeal nerve.* A net-work is also formed, which covers the beginning of the ex- ternal carotid artery. From this, as from a centre, branches are sent out with the arteries to the neck, and face, and glands under the jaw ; and these last, with a mesh which passes up upon the temporal artery, unite with the portio dura of the seventh pair. It has been often observed, that the branches of the carotid artery have a peculiar provision of nerves, and that these nerves are more nu- merous and minutely distributed than in any other part of the body. There are indeed no nerves in any part of the body which have so ex- tensive and intricate connections with important vital nerves as the cuta- neous nerves of the face and neck. This distribution of the nerves has been considered a provision for that power possessed by the imagination, or rather that uncontrolable con- nexion which exists betwixt the feelings and the action of the vessels in blushing, and in the expression of the passions. But I have proved this to be altogether false, since by cutting the portio dura of the seventh I have taken all expression from the face. The emotions visible in the countenance are, therefore, not attributable to the sympathetic nerve, and its nervi molles. The lowest of the nervi vasorum or molles, sent off from the superior ganglion of the sympathetic nerve, descends in the course of the trunk of the nerve, and forms, with other branches, the superior cardiac nerve. This nerve, generally called nervus cordis superficialis, passing down in the direction of the trunk of the sympathetic nerve, and near the longus colli muscle, is for some length a very slender branch ; but in its course it receives two, three, or four additional twigs from the sym- pathetic, and branches which come under the carotid artery from the pharyngeal nerves. When this superior cardiac nerve is within an inch or two of the subclavian artery, branches of union pass betwixt it and the recurrent nerve of the par vagum; and branches of the nerves passing to the heart from the lower cervical ganglion, also join it. It then, at- taching itself to the investing membranes and sheaths of the carotid and * Scarpa. OF THE PARTICULAR NERVES. 135 subclavian arteries, forms with1 others, a plexus of nerves, which run along the great vessels to the heart. The continued trunk of the sympathetic, where it emerges from the superior cervical ganglion, is extremely small. It descends behind the carotid artery, and lies near to the spine.* When opposite to the fifth and sixth cervical vertebrae, the inferior cervical ganglion of the sympa- thetic is formed. In this course, twigs of communication pass betwixt it and the cervical nerves, or join it with the beginning of the phrenic nerve. But not unfrequently on the left side, there are three cervical ganglions formed by the sympathetic nerve; the superior, middle, and inferior ganglions : or it happens that we find the sympathetic nerve split into two branches in the neck ; one of which forms the middle, and the other the lower ganglion. There are received by the middle cervical ganglion, or thyroid ganglion, branches of nerves, from the third, fourth, fifth, and sixth cervical nerves, and also sometimes from the phrenic nerve. The gan- glion is by no means constantly found, and it is irregular in its size and shape. When large, and in what may be considered as its more perfect state, it gives off some considerable branches. Of these, part unite with the superior cardiac nerve already mentioned; others form the great or deep cardiac nerve, while lesser ones play round the subclavian artery, and unite with the lower cervical ganglion, or the upper thoracic ganglion. The deeper cardiac branch of the sympathetic, splitting and again unit- ing so as to form rings, runs outwards, attached to the arteria innominata and arch of the aorta, to the heart. In this course, while it passes before the trachea, it forms connections with the recurrent branch and trunk of the par vagum. Under the arch of the aorta, we find this branch con- centrated to form the ganglion cardiacum of Wrisberg, or ganglion molle et pellucidum of Scarpa. This ganglion is like a mere en- largement or swelling of the nerve. From this, four or five branches may be enumerated; 1st, A branch passing behind the pulmonary artery to the back of the heart, and following the left coronary artery; 2dly, A small division to the anterior pulmonary plexus of the par vagum ; 3dly, A pretty considerable branch which, passing behind the aorta, and betwixt it and the pulmonary artery, is distributed with the right coronary artery to the anterior part of the heart. On the left side of the neck, the sympathetic, receiving on the one side branches from the cervical nerves, and on the other giving off branches, which descend behind the carotid artery to the heart, (viz. the superior cardiac,) often splits before it forms the middle or thyroid ganglion, and sometimes throws its branches over the thyroid artery, and the ganglion lies upon that artery. Again, from the ganglion there descend two series of numerous lesser filaments, which form meshes upon the thyroid and subclavian arteries to the heart. Others proceed downward behind the arteries to the lower cervical gan- glion. Those branches which descend upon the arteries, intangle the roots of the thyroid, transversalis colli, and internal mammary arteries, in their plexus ; these uniting, follow the subclavian artery, and form again ' It is to be observed, that in the horse and the ass, the sympathetic and the par vagum are incorporated in one sheath. In the neck of the bird, the sympathetic is lodged within the canal for the vertebral artery, 136 OF THE PARTICULAR NERVES. a plexus upon the arch of the aorta. This is joined by branches from the par vagum and recurrent The principal branches of this plexus terminate in the cardiac ganglion under the arch of the aorta. The lower cervical ganglion of the sympathetic nerve is placed upon the limits betwixt the neck and thorax upon the head of the first rib, and by the side of the musculus longus colli; and it is in part co- vered by the root of the vertebral artery. The ganglion is of an irre- gular cushion-like shape. It lies close to the cervical nerves which go to the brachial plexus, and it receives branches from them : and even it receives branches sometimes from the fifth and sixth, more rarely the seventh and eighth, from the first and second of the back: and lastly, from the phrenic nerve. Branches also pass from this ganglion to the par vagum and recurrent, and also pass on to the cardiac and pulmonic plexus. That nerve, which must be considered as the continued sympa- thetic,* throws a ring round the root of the vertebral artery, and sending out branches upon the subclavian, terminates in the first dorsal or tho- racic ganglion."}" THE SUPERIOR THORACIC GANGLION. This ganglion surpasses the other thoracic ganglions in size. It is, indeed, frequently composed of many branches of the nerve in the neck, coming both before and behind the subclavian artery. It receives also nerves from the three or four lowest cervical nerves, and first dor- sal nerve. It is of a very irregular figure, or rather it varies exceeding- ly in its shape ; so that by various anatomists it is described as round, oval, triangular, quadrangular, cylindrical !—Filaments proceed from this ganglion into the canal of the vertebral artery, which communicate with the sixth and seventh cervical nerves, and sometimes with the the fourth, by a long descending filament. J This first dorsal ganglion communicates likewise with the first dorsal pair of nerves ; and gives branches to the cellular coat of the subclavian artery, and to the car- diac plexus, and also to the pulmonic plexus; or to supply the posterior surface of the lungs. SYMPATHETIC NERVE IN THE THORAX. The sympathetic nerve (as we have explained in describing the dor- sal nerves), through all its course in the thorax, has additional branches from the dorsal or intercostal nerves. It forms also, while it is lying on the side of the vertebrae, a division in the thorax, which it will be im- portant to recollect. One nerve is sent more forwards upon the body of the vertebrae, and passes into the abdomen betwixt the crura of the diaphragm; while the trunk of the sympathetic continues its course by the heads of the ribs, passes over the ligamentum arcuatum, and down- wards upon the lumbar vertebrae. * The name applied to this part of the nervous system is manifestly erroneous, and tends so immediately to mislead the student that it should be entirely relinquished for that of gan- glionic nerve, or ganglionic system ; terms which refer to no theory of the functions performed by the structure. J. D. G. f See note B in the Appendix. t In brutes I have traced a considerable division of this nerve along the canal of the verte- feral artery. OF THE l'ARTICULAK NERVES. 137 The splanchnic nerve, then, is this anterior branch of the sympa- thetic in the thorax. It is the great nerve of the viscera of the abdo- men. It generally has two or four roots from the trunk of the sympa- thetic nerve, where it is opposite to the sixth, seventh, and eighth in- tercostal nerves. It is seen lying under the pleura, and passing ob- liquely over the bodies of the dorsal vertebrae, from the seventh to the tenth. It then passes through the crura of the diaphragm, enters the abdomen, and forms the great semilunar ganglion. One or more branches are sent forward from the sympathetic, com- monly from the ganglions, opposite to the interstice betwixt the ninth and tenth, or tenth and eleventh ribs. These also pass the diaphragm, and unite with the semilunar ganglion. There is, however, a conside- rable variety to be observed both in the origins of the splanchnic nerve, and in the number of these subsidiary branches. A larger branch, going off betwixt the tenth and elevdhth ribs, is so common, that it has the name of splanchnicus minor, or accessorius. This nerve as frequently terminates in the renal plexus, as in the semilunar ganglion ; or sometimes it sends branches to both. SEMILUNAR GANGLION AND CffiLIAC PLEXUS. The ganglion which is called the semilunar ganglion, has no regular shape—and least of all when it is fully dissected. It is formed by the splanchnic nerve, and by branches which come from the lumbar nerves. It lies by the side of the coeliac artery and consists of many lesser gan- glions, (sometimes to the number of eleven or twelve,) matted together into a glandular-like shape. The semilunar ganglions of the splanchnic nerves lie on each side of the root of the cosliac artery ; their connection with each other is fre- quent and intricate ; so that they throw a mesh of nerves round the root and branches of this artery, which is the great source of vessels to the stomach, liver, and spleen.—This plexus, formed by the semilunar gan- glions round the coeliac artery, is the solar or coeliac plexus. CCELIAC PLEXUS. The coeliac plexus is the great source of nerves to the higher viscera of the abdomen. The splanchnic nerves are the principal, not the only nerves which form this plexus. The par vagum sends branches down from the stomach which join it; and even the phrenic nerve, which is the nerve of the diaphragm, sends down twigs to unite to the branches of the splanchnic and par vagum. We shall find also small nerves which come from the seat of the kidney, and which are derived from the supe- rior lumbar nerves.—These pass across the crura of the diaphragm, and enter into the coeliac plexus.—In pursuing the nerves of the viscera fur- ther, we have it no longer in our power to follow individual branches, but must rather mark the course, and enumerate the various sources of the plexus, and net-work of nerves which follow the great vessels. From the coeliac plexus, there pass out, 1. Nerves which accompany the phrenic arteries upon the lower surface of the diaphragm. 2. Nerves to the liver-.—and of these there are two plexuses, the right and left he- patic plexus ; one passes along the vena portae, biliary ducts, and right 138 OF THE PARTICULAR NERVES. hepatic artery, to the right side of the liver, the gall bladder and ducts ; this of course is the right hepatic plexus : the left hepatic plex- us passes along the left hepatic artery; and this has connexion with the nerves of the stomach, branches of the par vagum. 3. That plexus, which runs upon the lesser curve of the stomach, while it is formed in a great measure by the par vagum, has also connexion with the solar or cceliac plexus. 4. The plexus of nerves which pass to the lower ori- fice of the stomach and duodenum is chiefly a division of the right he- patic plexus. These nerves, to the liver, stomach, and duodenum, are attached to the branches of the cceliac artery. Along the great splenic artery, which is also derived from the cceliac artery, there passes out a plexus of nerves to the spleen. From this splenic plexus there pass nerves to the great omentum ; and they even unite with those passing out upon the duodenum, and which attach themselves to the right epi- ploic artery, and take a course upon the great curvature of the stomach. Thus the solar or cceliac plexus is a great central net-work of nerves, which pass out in divisions to the liver, spleen, pancreas, stomach, duo- denum, and omentum. SUPERIOR MESENTERIC PLEXUS. The place and connexions of the superior mesenteric plexus is at once known, when it is considered that it is formed upon the root of the supe- rior mesenteric artery.—It is formed by a division of the cceliac plexus continued down upon the aorta so as to involve the root of the mesenteric artery, and by nerves coming over the side of the vertebrae of the loins from the lumbar nerves. This plexus spreads betwixt the membranes of the mesentery, and extends upon the branches of the artery, and is dis- tributed to the small intestines and part of the colon. It consequently supplies the mesenteric glands, and it sends nerves also to the pancreas, that join those which it receives from the splenic plexus. INFERIOR MESENTERIC PLEXUS. The same mesh of nerves, being continued down upon the face of the aorta, surround the lower mesenteric artery, and follow its branches. This is the lower mesenteric plexus, or mesocolic plexus; and it is formed in a great measure from the branches of the continued trunk of the sympathetic nerve. As this plexus spreads upon the branches of the lower mesenteric artery, it passes to the left side of the colon, and rectum. While the lower mesenteric plexus is continued from the upper one, on the side of the lumbar vertebrae, it is continuous with the renal and spermatic plexus; and towards the pelvis, with the hypogastric plexus. Before considering the other lesser plexus of nerves in the abdomen, it is necessary to follow the continued trunk of the sympathetic nerve, which we had described as following closely the lateral part of the dorsal and lumbar vertebrae, whilst the splanchnic nerves pass obliquely over them to the viscera of the upper part of the belly. The continued trunk of the sympathetic nerve, after it has given off the splanchnic nerve in the thorax, sends several small nerves forward over the vertebrae to the mediastinum and sheath of the aorta. It then OF THE PARTICULAR NERVES. 139 passes the diaphragm, keeping close to the transverse processes of the vertebra. When, however, it comes lower upon the lumbar vertebra, it lies more upon the side of their bodies, and the connexions with the lum- bar nerves are by small and numerous twigs which stretch over the side of the vertebra. In this course, it is giving off upon the fore part numerous irregular twigs to the several plexuses which have been described.— Where it lies under the vessels which pass to the kidney, it sends up some branches to the renal plexus. The renal plexus, however, is not entirely formed of these branches of the continued sympathetic, but is rather a continuation from the coeliac and superior mesenteric plexus; while the lesser splanchnic nerve, which was sent off in the thorax, also terminates in it. This plexus is thrown over the vessels of the kidney, and forms several little ganglions. From the renal plexus descends the spermatic plexus, with the ves- sels to the testicle. This plexus of nerves in woman follows the sper- matic artery in its distribution to the ovaria and uterus. In passing down upon the loins, the sympathetic nerve forms five or six ganglions with the branches from the lumbar nerves. These are ob- long, angular, stellated, —irregular in their form, and in their number, situation, and size, as the twigs which, by their union with the sympathetic, form them. Betwixt these ganglions or connexions with the lumbar nerves, the sympathetic is not always one nerve, but is sometimes split into several smaller nerves, which unite again. From the sympathetic nerves of both sides we have to observe frequent interchange of branches, which sometimes attach themselves to the lumbar nerves, sometimes creep under the aorta, or unite to the plexus covering the face of the aorta. There are several little ganglions formed by these nerves upon the face of the lumbar vertebra : they have the name of ganglia acces- sory. Before the sympathetic nerve descends into the pelvis, it has become extremely delicate. In many subjects it seems to terminate in the last lumbar, or first sacral nerve; but upon more minute dissection, lesser branches will be found to descend amongst the loose cellular substance of the pelvis. When regular, or perhaps we may say with truth when regularly and fully dissected, the sympathetic nerves of each side are seen to descend upon the fore part of the sacrum, and form connections with the sacral nerves similar to those with the dorsal nerves. As they descend, they of course approach, and finally unite in an acute point on the os coccygis. At the points of union of these extreme branches of the sympathetic nerves with the branches of the sacral nerves, small ganglions are formed; and there pass out branches from them, which cover the intermediate surface of the sacrum with an extensive plexus. The ultimate ganglion, formed by the union of the two sympathetic nerves, is the coccygeal ganglion, or ganglion sine pare, and from it there pass three or four nerves to the extremity of the rectum. HYPOGASTRIC PLEXUS. This is a plexus which lies on the side of the pelvis, and involves the hypogastric artery. It consists of the nerves passing to the parts con- tained in the pelvis; which do not, however, pass in distinct branches, but like those of the abdomen, are formed into a minute interwoven net- 140 or THE PARTICULAR NERVES. work. The hypogastric plexus takes no determinate origin, but is con- tinuous with, or formed by, the extreme branches of the sympathetic nerve, the extremity of the spermatic plexus, the sacral nerves, (and particularly the third sacral nerve,) and by the branches of the accesso- ry ganglions on the sacrum. The opinion, borrowed from the continental writers, and more particu- larly from Bichat, has been entertained, that the sympathetic nerve of the human body was the same with the nervous cord found running down the centre of the vermes. This is paying too much respect to a name— too little attention to nature. Then again, it has been said that this part of the nervous system should be called (with Bichat,) the ganglionic sys- tem! True, there are ganglions universally distributed wherever we find the branches of the sympathetic nerve ; but what a perversion it is when we know that the posterior root of every spinal nerve has a gan- glion, to call this the ganglionic system, as if it alone had ganglions, and as if it were true that ganglions cut off sensation. The nerves of the lower animals, though they, in form, resemble the sympathetic system, possess both power over the voluntary muscles, and bestow sensibility on the parts they are distributed to. We neither ob- serve that the sympathetic nerve possesses voluntary power over the muscles, nor that it bestows sensibility. Surely this is enough to distin- guish it from the system of the lower creatures. The ganglions on the sympathetic nerve do not cut off sensation. There is no reason for continuing in that antiquated hypothesis, since I have shown that all the spinal roots which possess sensibility have gan- glions. In short, we only know what the sympathetic nerve is not; and by that means we are left to conjecture what really are its functions. It posses- ses no power over the features ; it is not the nerve of emotion ; it does not controul any voluntary motion : it has no sensibility. But, indepen- dent of these functions, we have to consider that the parts of the frame are united into a whole ; it may be by the sympathetic nerve, which is universally distributed. The nutrition and growth of the body, — the cir- culation and secretion, —the deposition and absorption of the fluids and solids of the body require some controlling influence, and there is every probability that the sympathetic nerve performs these offices, ministering :to the vital and constitutional powers. FUNCTION OF THE SYMPATHETIC NERVE. NERVES OF THE ARM ; AXILLARY, OR BRACHIAL PLEXUS. The nerves which proceed from the spine, and go to supply the arm, are formed into an intricate plexus before they divide into the several nerves of the arm. This brachial, or axillary plexus, is formed of five of the spinal nerves : viz. the fifth, sixth, seventh, and eighth cervical nerves, * and the first dorsal nerve. The highest of these nerves proceeds from betwixt the fourth and fifth cervical vertebrae ; the last from betwixt the first and * This is of course counting the sub-occipital as the first cervical nerve. OF THE PARTICULAR NERVES. 141 second dorsal vertebrae. They pass out betwixt the middle and anterior divisions of the scaleni muscles ; and even while covered by this muscle, and before they have proceeded far from their foramina, the last nerve of the neck and first of the back unite. *—The plexus extends from above the clavicle to the edge of the tendon of the latissimus dorsi. It allows of no natural division, t The axillary artery passes for some way close under it, and then perforates betwixt the divisions which form the radial nerve. In the plexus of the axilla, the nerves of the arm make that interchange of branches which combines the muscles of the arm into classes, and which consequently orders the action of the muscles in the several mo- tions of the arm and hand. Before describing the plexus, I should notice the nervi a rill ares inter- costales. These nerves do not belong to the axillary plexus. They come from the intercostal nerves, and, perforating the intercostal spaces, two or three nerves cross the axilla and go to the glands and integuments. —We may now arrange the nerves of the axillary plexus thus:— 1. The thoracic nerves.—Although the nerves which supply the muscles of the chest are derived from the intercostal nerves, as we have seen, yet there also pass otf branches from the axillary plexus to the great and little pectoral muscles, to the latissimus dorsi, to the skin and mam- mae. These thoracic branches proceed from the upper division of the plexus, or that which gives out the external cutaneous, and from one of the roots of the radial nerve. 2. The supra and infra-scapular nerves. 3. The circumflex, or articular nerve. 4. The perforans Casserii, or external cutaneous nerve. 5. The radial nerve (better named median). 6. The ulnar nerve. 7. The muscular spiral nerve. 8. The internal cutaneous nerve. 9- The nerve of Wrisberg. Which may be arranged thus :— ’ I. Nerve of Wrisberg. * 2. Internal cutaneous nerve. 3. External cutaneous nerve, or perforans Casserii. I. Cutaneous nerves. II. Nerves to the shoul- der-joint. ]. Supra-scapular nerve. 2. Infra-scapular nerve. 3. Circumflex nerve. III. To the muscles of the arm and to the fingers. 1. Radial nerve. 2. Ulnar nerve. 1 3. Muscular spiral nerve. * Before the nerves which form the plexus intermix their filaments, or are connected to- gether, they send off small branches to the scaleni muscles, to the muscles of the spine, and to the levator scapulae.'—The branches which they give to the sympathetic nerve we have al- ready noticed. f I mean that it admits of no division useful in the arrangement of the demonstration, see Monro’s Nervous System, and the Latin work of Anton. Scarpa. Scarpa describes the con- nection of filaments betwixt the ulnar and radial nerves at their separation from the great plexusj Plexus brachialis minor. Vide tab. ii. fig. ii. h. 142 01’ THE PARTICULAR NERVES. The supra-scapular nerve comes off from the upper edge of the plexus, and is the highest of the branches. It runs towards the root of the coracoid process, it passes through the notch of the scapula, and goes to supply the supra and infra spinatus muscles, the teres minor, and the sub-scapularis. The sub-scapular nerves come out from the posterior part of the plexus along with the articular nerve. They are attached to the sub- scapular muscle; they turn round the fleshy edge of the muscle, and insinuate their branches betwixt the tendon of the latissimus dorsi and the teres major. The circumflex, or articular nerve, or axillaris, lies very deep. It comes from the back part of the plexus, passes behind the neck of the humerus, accompanied by the posterior circumflex artery, and above the tendon of the latissimus dorsi, and teres major. One of its branches we trace into the teres major, while another passes round the bone, and is distributed to the under surface of the deltoid muscle, the joint, and the cellular membrane. The internal cutaneous nerve.—This nerve is derived from the ulnar at its root, or comes off from the plexus along with it; passes down the arm, giving off no considerable branches; accompanies the basilic vein, and twists its branches over it; divides into four branches upon the fascia of the fore-arm; and running betwixt the fascia and veins of the fore-arm, it is finally distributed to the cellular membrane and integuments, while one of its branches reaches to the ligaments of the wrist. The cutaneous nerve of Wrisberg comes sometimes from the axillary plexus, as a distinct nerve; sometimes it is a branch of the great internal cutaneous nerve; sometimes it is derived, or a nerve which takes its place is derived, from the intercostal nerves. This nerve of Wrisberg is distributed to the integuments of the arm, and ter- minates near the internal condyle. Perforans Casserii, or the external cutaneous nerve.—This nerve passes through the coraco-brachialis muscle before the os hume- ri, to gain the outside of the arm. From its perforating this muscle, and being described by Casserius, it is called the nervus perforans Cas- serii. Before passing through the coraco-brachialis muscle, it sends a nerve into the substance of that muscle. Here it also sends down a branch of communication with the radial nerve; and in many subjects it will be found to be like a branch from one of the origins of the radi- al nerve. Where the nervus perforans lies betwixt the brachialis in- ternus muscle and biceps, (and, of course, after it has perforated the coraco-brachialis muscle,) a branch or two are sent up to the heads of the biceps muscle ; another branch turns inward to the belly of that muscle ; another is given to the brachialis internus ; and, finally, twigs pass inwards to the cellular membrane, which involves the brachial ar- tery. The continued nerve passes obliquely across the arm, and under the biceps. When approaching the outside of the arm, it divides into three small branches; one to the integuments which are upon the supinator longus, another to the integuments on the inside of the fore-arm, and a third, which continues its course along the edge of the supinator longus to the wrist. Of this prolonged branch of the perforans Casserii, a mi- OF THE PARTICULAR NERVES. 143 nute twig is lost on the ligament of the wrist, another passes to the ball of the thumb, and a third goes round to the integuments of the back of the thumb. The radial or median nerve.—This nerve is formed by those di- visions of the plexus which surround the brachial artery, and sometimes by a division from the perforans Casserii. It takes its course in the up- per part of the arm by the outer side of the brachial artery. In the middle of the arm it crosses the artery superficially, and continues to lie on its ulnar side, separated from it by some thin cellular membrane, as far as to the bend of the arm. It gives off no branches until it has sunk under the aponeurotic expansion of the biceps muscle. When the median nerve has come to the bend of the arm it gives off three branches. The first belongs to the pronator teres, flexor radialis, palmaris longus, and flexor digitorum; a second passes to the pronator teres ; a third to the deep muscles of the fore-arm, to the flexors of the thumb particularly ; and from this a fine branch attaches itself to the in- terosseous membrane, and, taking its course with the anterior interosse- ous artery, is distributed to the pronator quadratus muscle. The median nerve perforates the pronator teres, and then, continuing its course down the fore-arm betwixt the flexor sublimis and profundus digitorum, sends off branches to those muscles ; and in this part of its course we see why the name median is more applicable than radial. Before passing under the ligament of the wrist, it gives out a branch which emerges from the tendons, and passes to the integuments, short flexor, and abductor mus- cles of the thumb. The trunk of the median nerve passes with the tendons of the flexor muscles of the fingers under the ligament of the wrist. In the palm of the hand it divides into five branches :—the first passes to the abductor and flexor pollicis brevis; a second goes to the adductor pollicis, and side of the thumb next the fore-finger; the third passes to the fore-finger, and to the lumbricalis muscle ; the fourth to the side of the fore and mid- dle fingers ; and tta fifth to the sides of the middle and ring finger. All these nerves, while in the palm of the hand, send off branches to the lum- bricales muscles. The ulnar nerve comes off from the lower part of the plexus, in union with the internal cutaneous nerve. It descends upon the inside of thq arm, accompanied by the inferior profunda artery, and is tied down by the firm intermuscular fascia, and then passes behind the internal con- dyle of the humerus. While above the bend of' the arm, it gives off a superficial branch to the integuments on the inside of the arm, and the ulnar side of the fore-arm ; at the same time it sends a muscular branch through the triceps muscle, along with the arteria profunda inferior. Im- mediately above the elbow-joint, twigs are sent off, some of which ac- company the ramus anastamoticus major of the brachial artery. After passing the condyle of the humerus, it sends a branch to the flexor car- pi ulnaris, and to the head of the flexor digitorum profundus. It then sinks deeper betwixt the flexor ulnaris and flexor digitorum sublimis ; it is here connected with the ulnar artery, and descends along with it to the wrist, lying on its ulnar side ; when it approaches to the annular liga- ment, it is rather posterior to the artery. In this course, along the fore- arm, the ulnar nerve gives branches to the flexor digitorum sublimis. Of- ten it sends a branch of communication to the median nerve, while some 144 OF THE PARTICULAR NERVES. few lesser muscular nerves are sent off, and accompany the brunches of the ulnar artery. When arrived near the wrist, the ulnar nerve divides into two branch- es. The continued trunk passes on under the protection of the tendon of the flexor ulnaris, and then under the annular ligament into the palm of the hand ; while a branch, the ramus posticus, takes a turn under the flexor ulnaris, and over the edge of the flexor digitorum profundus ;— it passes then over the lower end of the ulna to the back of the hand ; on the back of the hand it is found branching over the expanded tendons and under the veins, and is finally distributed to the back of the little and ring fingers. The continued ulnar nerve passes under the palmaris brevis muscle and palmar aponeurosis, and above the flexor brevis and adductor mini- mi digiti. Here it divides into two, viz. the sublimis and profundus of Camper. The superficial branch passes by the side of the adductor mi- nimi digiti to the integuments on the ulnar edge of the hand, and adduc- tor minimi digiti,—to the outer edge of the little finger,—to the side of the little and ring fingers, and a branch communicates with the median nerve. Albinus, Monro, and Camper differ in their description of the nerves to the lumbricales muscles, which only proves that the twigs passing to those little muscles are irregular. They come from the deep branch of the ulnar nerve. The deep branch (profundus) forms a deep palmar arch, and is sent to the lumbricales, to the adductor and flexor pollicis. The muscular spiral nerve.—We find the external cutaneous nerve, or perforans Casserii, passing before the arm-bone. The muscu- lar spiral nerve, on the contrary, passes behind the bone, and takes a spiral turn under it to get to the outside of the arm. It perforates the flesh of the arm betwixt the middle and the short head of the triceps muscle. Before it perforates the triceps muscle, the muscular spiral sends off branches which pass over the tendon of the ladssimus dorsi; and before it enters the triceps muscle, it may be observed to divide into several branches. Three of these may be mentioned; a branch to the middle head, and one to the short head of the triceps muscle; and a third and larger nerve, which pierces betwixt the muscles, along with the trunk of the nerve. This last nerve does not follow the trunk of the nerve in its course; but perforating the triceps more directly across, it comes out behind the supinator longus, where it takes its origin from the os humeri. This is a cutaneous branch, and might be considered as the external cutaneous nerve with as much propriety as the perforans Casserii. Often we shall find some lesser branches of the muscular spiral nerve piercing the fibres of the triceps muscle, and terminating in the skin. The great division of the nerve, after piercing the triceps muscle, lies betwixt the brachialis internus and the inner edge of the supinator longus ; and here it sends a branch upon the bend of the arm, and on the edge of the triceps muscle. Where it is near the elbow-joint it divides into the nervus profundus and superjicialis : the profundus gives branches to the extensor carpi radialis; then perforates the supinator radii brevis ; twists round the radius ; and here divides amongst the extensor muscles, send- ing branches to the extensor carpi ulnaris, to the extensor pollicis, and primus, secundus pollicis; the extended nerve keeping still under the ex- OF THE PARTICULAR NERVES; 145 tensor tendons, passes to the back of the wrist, and is lost under the inser- tions of the extensores radiales. But the great superficial division of the muscular spiral nerve comes out betwixt the head of the supinator longus muscle and the joint. This branch then lies betwixt the supinator longus and pronator teres. Con- tinuing its course by the side of the supinator longus and flexor radialis, on the outer side of the radial artery, it passes under the tendon of the former, it then becomes superficial, on the radial edge of the wrist, and is distributed to the integuments of the back of the hand, back of the thumb, fore, middle, and ring fingers. This branch is sometimes called radial. NERVES OF THE THIGH, LEG, AND FOOT. In tracing the nerves of the lower extremity, we find no difficulty in the arrangement, for they fall into a very simple and natural order. They are all derived from the lumbar and sacral nerves. They are three in num- ber. 1. One passes out under Poupart’s ligament to the extensor mus- cles of the leg, viz. those which lie on the forepart of the thigh. This of course is called the anterior crural nerve. 2. The second nerve is the obturator nerve, so called because it passes out from the pelvis by the obturator hole. This nerve passes out in the middle of the pelvis, lies amongst the deep muscles of the thigh, and distributes its branches chiefly to the adductor muscles. 3. The third nerve is the greatest nerve of the body. We may call it the posterior crural nerve, its proper name however is the ischiatic nerve. It passes out from the back part of the pelvis, through the sacro-sciatic notch, and takes it course down the back of the thigh into the ham. In this course it supplies the muscles lying on the back of the thigh, but its chief destination is to the leg and foot. But before we attend to these three principal nerves of the lower ex- tremity, we must notice the lesser nerves, which pass out from the pel- vis, and which, indeed, are not without interest. LESSER NERVES WHICH PASS OUT FROM THE PELVIS, The cutaneous branches of nerves which have their source internal, are always important, because the internal affection, as in the present in- stance of the kidney, the intestine, the uterus, are attended with external pains, or pains felt as if they were external, and these will often guide us to the real source of the disease. There arc three divisions of nerves which deserve attention for this reason ; iirst, those cutaneous nerves which, coming off from the lumbar nerves, drop over the spine of the ilium upon the integuments of the hip and thigh. Secondly, there are nerves which course from the loins round in the spermatic passage, and go to the scrotum and membranes of the testicle, and turning up from the groin pass to the integuments of the pubes. In the third class are those nerves which go down upon the integuments of the thigh. These cutaneous nerves of the thigh come from the lumbar nerves, or more immediately from the anterior crural nerve. They pierce the ten- don of the oblique muscle of the abdomen, or pass under Poupart’s liga- ment, and are distributed to the groin, scrotum, and betwixt the fascia and 146 OF THE PARTICULAR NERVES. integuments of the fore part of the thigh. There may be described four cutaneous nerves on the fore part of the thigh, viz. the external cutaneous, the middle cutaneous, the anterior cutaneous, the internal cutaneous, be- sides those of the groin and scrotum. The external cutaneous nerve is that which comes out from the belly near the superior spinous process of the ilium. It is derived from the third lumbar nerve. It divides almost immediately into two great branches, and in the front view of the thigh the anterior branch alone is to be seen. It takes a course above the fascia in the direction of the line which divides the vastus externus from the rectus femoris, and termi- nates near the knee; while the posterior branch passes over the tensor va- ginae femoris, and down upon the outside and back of the thigh. The middle cutaneous nerve is seen amongst the integuments of the groin, and emerges from under the fascia near the upper edge of the Sartorius muscle. It passes down upon the rectus muscle, and is distri- buted to the integuments in three or four divisions. The anterior cutaneous nerve comes out to the integuments very high up, in the middle of the groin, betwixt the pubes and spine of the os ilii. It passes down the thigh along the surfaces of the Sartorius and vastus internus muscles. This, like all the other cutaneous nerves, runs above the fascia, and immediately under the skin. The internal cutaneous nerve is the least regular. It does not pierce the fascia in one trunk, but sends three, four, or five branches through the fascia which are distributed to the integuments on the inside of the thigh. Some of these, after running a considerable way under the fascia, emerge and encircle the inside of the knee. We must not dismiss the consideration of those nerves without put- ting the knowledge of their distribution to some use. Suppose that a nerve of the spine divides into two, and that one branch goes internal to the viscera, and the , other external to the integuments ; it will come to pass that all internal morbid irritations will produce sensations attribu- table to the part to which the external or cutaneous nerve is distributed. These pains will not be easily described, and the terms the patient uses, too frequently, appear, therefore, fanciful. Is this a sufficient explanation of the pain actually seated in the throat, affecting the back of the neck ? The disorder actually seated in the heart, affecting the mammoe and arms ? The disease of the lungs pro- ducing pain, referable to the back, betwixt the scapula; ? The inflamma- tion of the liver, and the irritation of the diaphragm, pain in the shoulder ? Disorders actually seated in the stomach, produce an extensive class of sympathetic pains. But the disorder of the duodenum is distinctly refer- able to the lower part of the hack, as the distention of the colon, or the lodgment of matter there, produces pain in the loins and region of the kidney. When we come to the contemplation of these nerves of the loins, the subject does not diminish in interest or usefulness. 1. Disordered function of the womb, conception, quickening, delivery, after-pains, menstruation, &c. produce pain in the lower part of the back and loins. 2. The disease of the testicle produces similar pain in the loins. 3. Disorder of the bladder often produces pains in the groin and pe- ri me um OP THE PARTICULAR NERVES. 147 4. Disorder in the rectum, or irritation of faeces there, produces pains in the perinaeum, &c. 5. Lastly, diseases in the kidney and ureter, produce pain down the fore part of the thigh, and retraction and pain in the testicle. THR PUDIC NERVE. The pudic nerve comes off from the third, fourth, and fifth of the«sa- crum, holding connexion with the roots of the great ischiatic nerve. It runs towards the outlet of the pelvis, and to the side of the tuber ischii. In the female it sends branches to the anus, vulva, and clitoris. In the male it accompanies the common pudic artery in its course, and it con- sequently runs to the muscles of the anus, and of the perinaeum, to the caput gallinaginis, to the penis, and to the glans, in many branches : and here it is the organ of a peculiar sense. Besides being the organ of ve- nereal sensation, it bestows the sensation which orders the contraction of the bladder, not only furnishing us with these sensations in addition to the common sensibilities, but under the influence of these sensations it controls the various necessary actions of the muscles. NERVES OF THE LOWER EXTREMITY. ANTERIOR CRURAL NERVE.* This nerve arises from the union of the second, third, and fourth of the lumbar nerves, or the second and third lumbar nerves uniting into one trunk, are afterwards joined by a division of the fourth,| or the anterior crural, is formed by the anterior branch of the third and the first branch of the second lumbar nerve,J or by the four first lumbar nerves .; and the first sacral nerve. At its origin, it lies under the psoas magnus, and, as it descends, it holds its course between the psoas magnus and iliacus internus. It then descends towards the thigh, and passes out under Pou- part’s ligament; and in its course along the brim of the pelvis, it is quite removed from the external iliac artery. Here, while within the pelvis, it gives off several small nerves, which pass into the iliacus internus, and to the psoas magnus muscles. These form a kind of small plexus. As the anterior crural nerve passes under Poupart’s ligament, it is im- bedded between the iliac and psoas muscles, and lies about half an inch to the iliac side of the femoral artery. It here splits into its numerous branches which supply the muscles and integuments on the fore part of the thigh. From the fore part of the nerve there is sent out a muscu- lo-cutaneous branch, which, while it descends and supplies several mus- cles of the thigh, gives out the middle cutaneous nerve. The anterior cutaneous nerve is sent off lower down. But almost immediately af- ter it has passed under Poupart’s ligament, the internal cutaneous nerve is sent off from some of those branches which run under the internal ar- ticular artery. The last of the cutaneous branches of the anterior crural nerve, and the most important, is the nervus saphenus, or cutaneus longus. * Crural nerve, truncus lumborum, femoralis magnus. t Fischer.—Walter. t Sabbatier and Haller. 148 OF THE PARTICULAR NERVES. This is the chief cutaneous nerve of the leg ; but it is to be distinguish- ed as a particular nerve, so high as under the external articular or cir- cumflex artery, being a division of what is called the nervus longus. This nerve is joined by a branch of the obturator nerve ; and about the same place muscular branches are given off to the vastus internus. When we are dissecting in the course of the femoral artery, we have to observe two nerves running parallel to and connected with the sheath of the artery. That which is on the inside is the largest, the course ol which we shall prosecute. It follows the artery, lying along its outer side, and rather before it, as far as the tendon of the triceps muscle; it is here enclosed in a firm fascia, but it does not descend into the ham with the popliteal artery. It passes along the tendon with the perforat- ing branches of the popliteal artery, or with the upper and internal arti- cular artery. It then becomes a superficial nerve, having passed be- tween the tendons of the gracilis and Sartorious muscles, and descends upon the inside of the leg with the saphena vein, to the inner ancle and foot. This nerve, which lies near the femoral artery in the middle of the thigh, I have seen taken up with the extremity of the artery in amputation. This occasions twitching in the stump, and a good deal of distress. Where the continued nerve descends upon the inside of the leg, it sends out many twigs to the integuments, and is entangled with the saphena vein. It has been pricked in bleeding in the ancle. — Sabba- tier gives us an instance of this. The patient had been previously subject to nervous affections. She felt in the instant of the operation an acute pain, which was succeeded by convulsive motions, first of the limb, and then of the whole body. These attacks returned from time to time, she lost her health, and for many years was in great suffering. He relates to us another instance of the injury of this nerve accompa- nying the saphena vein, in the case of a young man who received a wound with the small sword in the inside of the knee. There came on much fever and swelling of the part, with great pain of the limb. This subsiding, there followed slight trembling of the limb, which gradually in- creased to an extreme degree. The caustic was proposed, but the pa- tient had not resolution to let it be applied. After long suffering, with exhausted strength, he was at last relieved by nature, and his health gradually returned. Wlien the nerve passes over the tibia, it is subject to be bruised, and I have seen tetanus proceed from such an injury. These branches we have mentioned are only the cutaneous or super- ficial branches of the anterior crural nerve. The larger and more nu- merous set of branches are those to the muscles lying on the fore part of the thigh. These diverge suddenly in many twigs, and are entangled with the branches of the arteries, and follow them in their distribution. There can be no excuse for bestowing particular names on these branches ;—to say that one is the branch to the pectinalis, another the branch to the Sartorius, another tofthe rectus, &c. is sufficient. OBTURATOR NERVE. This nerve arises in common with the anterior crural, from the third and fourth lumbar nerves, or we say it arises by fasciculi from the second and third lumbar nerves, and sometimes by a small twig from the fourth. or THE PARTICULAR NERVES. 149 It iies under the internal border of the psoas magnus. It descends into the pelvis, and goes obliquely downwards to pass through the ligamentous membrane which fills up the thyroid hole. The obturator nerve, before it escapes from the pelvis, sends off a branch which, accompanying the parent nerve, is given to the external obturator muscle. When it has escaped from the pelvis, this nerve lies in the middle of the flesh of the thigh; here it divides into a deeper and more superficial branch; the more superficial lies betwixt the adductor longus and brevis, and divides into three branches. These divisions pass to the adductor longus, ad- ductor brevis, and the gracilis. The branch which passes to the adductor longus, sends a small nerve under the inner edge of that muscle, and down through the tendon of the triceps to the inside of the vastus inter- nus, and there it unites with the nervus saphenus, and then passes be- twixt the adductor longus and brevis. The posterior division of the ob- turator goes down betwixt the adductor magnus and brevis, sends branches to the obturator externus and adductor brevis, and continues its course downward before the great fleshy partition of the adductor muscles, and parallel with the crural vessels, to the fat above the inner condyle of the femur, and to the skin. THE ORIGIN OF THE ISCHIATIC NERVE. The ischiatic nerve is formed by the two last nerves of the loins, and the three first of the sacrum ; or we may describe its origin more par- ticularly thus; the anterior branch of the fourth lumbar nerve and the trunk of the fifth uniting, form a strong cord of about two inches in length: this root is joined to another nearly as large, formed by the first and second sacral nerves ; and again, a third division joins it from the inferior branch of the second sacral nerve and from the third.* The ischiatic nerve is thus formed of three great roots matted together into a kind of plexus. It is flat to escape from pressure ; it passes back- wards betwixt the pyriformis muscle and the gemini, and thus escapes from the back part of the pelvis by the great ischiatic notch. But before following this great nerve into the thigh, we must take no- tice of some lesser nerves sent out from the sacral nerves, and from the trunk of the ischiatic nerve. These nerves pass to the muscles and in- teguments of the nates and back of the thigh to the perinaeum and pri- vate parts. There pass off one or two very small nerves from the body of the ischiatic nerve, while yet within the pelvis, or from the middle divisions of its origins, which go to the pyriformis and glutseus medius muscles. Just where the great nerve passes over the posterior ligaments of the pelvis, there goes off* a twig to the obturator externus, gemini, and quad- ratus femoris. While these branches are sent off upon the anterior face of the nerve, there goes backward a large fasciculus of nerves to the glutasi muscles, and to the integuments of the nates.| * This third and lowest origin, before uniting with the others to form the ischiatic nerve, gives out many small branches to the hypogastric plexus and viscera of the pelvis, to the perinaeum and private parts. + The 'posterior cutaneous nerve arises within the pelvis from the sacral nerves, and con- necting itself with the sciatic as it escapes, it afterwards descends upon the integuments on the back of the thigh; it sends branches also to the skin about the anus, and to the back part of the scrotum: pains are felt in the course of this nerve from disorder in the rectum. 150 OF THE PARTICULAR NERVES. When the integuments are dissected off from the nates and back of the thigh, we see two sources of the cutaneous nerves ; first, from the lumbar nerves come many small nerves which pass over the spine of the os ilii; and, secondly, from under the lower margin of the great glutaeus muscle, there come many extensive cutaneous nerves, of which that last described is the principal. A little further down, the ischiatic nerve gives off small nerves to the muscles surrounding the hip-joint; and, whilst the sciatic nerve is pass- ing over the quadratus femoris, the inferior and internal cutaneous nerve is given off. This nerve runs down even to the inside of the calf of the leg.—The external and posterior cutaneous nerve is a branch sent off from the ischiatic nerve, after it has descended from under the glutseus maximus. and just before its division into two fasci- culi, viz. the tibial and peromeal nerves. This external and posterior cutaneous nerve passes down upon the integuments of the back part and outside of the leg. OP THE TRUNK OF THE ISCHIATIC NERVE IN THE THIGH. But we must not allow these lesser branches to distract our attention from the general course of the great nerve, which passes over the ge- mini muscles, betwixt the tuberosity of the ischium and the trochanter then runs deep under the bellies of the hamstring muscles, and is lodged immediately in the great cavity behind the knee-joint, in com- pany with the popliteal artery and vein. In this course the sacro-sciatic gives off branches to the quadratus femoris, the biceps cruris, semiten- dinosus, and semimembranosus and triceps. A little below the middle of the thigh, the great ischiatic nerve di- vides into the internal and greater, and the lesser and external popliteal nerves. But as this is really the division into the two great nerves of the leg, they take the more determinate names of tibial and fibular nerves. TIBIAL NERVE. The greater and more internal of these divisions of the popliteal nerve is the tibial nerve Whilst it is yet in the hollow behind the joint formed by the hamstring tendons, it gives off a nerve which comes out from the ham, and descends superficially on the back of the leg. This has been called ramus communicans tibialis. When this nerve has arrived op- posite to the beginning of the tendo Achillis, it turns a little to the outer side, passing upon the outer margin of the Achilles tendon, over the outer side of the heel-bone, and is finally distributed on the outside and fore- part of the foot. Upon the back of the leg, this nerve unites with a branch descending from the fibular nerve, nearly in the same course, and with the same destination. ' After giving off this superficial branch, the tibial nerve sends branches to the back of the knee-joint, and popliteus muscle, to the plantaris mus- cle, and to both heads of the gastrocnemius. It then descends behind the articulation, and behind the head of the tibia. It then passes under the origins of the solseus, and betwixt the solseus and flexor longus di- gitorum pedis, and tibialis posticus, and descends to the inner ankle, braced down by a very dense fascia. In this course it furnishes many OF THE PARTICULAR NERVES. 151 branches to the lower part of the popliteal muscle, to the tibialis posticus, to the flexor communis digitorum, and to the flexor pollicis longus, and many of these branches end in cutaneous twigs. We have also to ob- serve a particular branch which the tibial nerve detaches, which passes betwixt the heads of the tibia and fibula, and goes to supply the muscles arising from the fore-part of the interosseous ligament. Further down, two or more small branches of the nerve also perforate the interosseous ligament, to supply the muscles lying on the outside of the tibia. The tibial nerve, in its course amongst those posterior muscles, accompanies the posterior tibial artery, lying on its outer or fibular side. When it has arrived behind the inner ankle, it sends off a branch to the integu- ments of the inside of the foot, and to the abductor muscle of the great toe. Continuing its course by the side of the heel-bone, and under the ligament, it begins to split into those branches which are naturally called the plantar nerves, because of their lying in the sole of the foot. THE PLANTAR NERVES. The internal plantar nerve passes over the abductor muscle of the great toe, and by the inside of the short flexor to the first metacarpal bone; and in this course it gives out several twigs to the muscles of the sole of the foot. It now divides into three branches. These are distributed to the great toe, to the second, the third, and one side of the fourth toes; and these nerves in their course give branches to the lum- bricales and interossei muscles. The external plantar nerve is the lesser of the two. It gives branches to the short flexor and adductor of the little toe, and to the massa carnea Jacobi Silvii. It gives also a deep branch to the third and fourth inter- osseous muscle and adductor muscle of the toe. Another of its branches makes the arch with the internal plantar nerve, while its extreme dis- tribution is to the little toe, and ,to one side of the fourth toe. These nerves of the sole of the foot are connected with the internal and ex- ternal plantar arteries, and are protected like them by the plantar apo- neurosis. THE FiBULAR NERVE. The fibular nerve is the more external division of the popliteal nerve. It separates from the tibial branch about four inches above the knee- joint ; it does not pass down under the gastrocnemius, like the tibial nerve, but turns towards the outside of the joint, and passes round the head of the fibula, and under the origin of the peronseus longus.—Be- fore the fibular nerve passes from behind the joint, it gives off several branches. There are sent down two branches to the integuments. One of these branches unites with the communicans tibialis, and de- scends with it to the outer ankle. Sometimes this anastomosis is form- ed high in the leg upon the heads of the gastrocnemius. More gene- rally there is a double communication formed by these nerves, about the termination of the belly of the gastrocnemius muscle in the Achil- les tendon. This prolonged branch of the fibular nerve terminates up- on the side and upper part of the foot, and upon the little toe. There 152 OF THE PARTICULAR NERVES. are also some nerves sent off from the fibular, which are distributed about the back and sides of the knee-joint. When the fibular nerve has turned over the head of the fibula, it divides into two great branches. The deeper seated of these branches, though it is not the largest of them, may be considered as the continu- ed trunk. It passes deep amongst the muscles, lying betwixt the tibia and fibula, and supplies the tibialis anticus, the extensor communis di- gitorum, extensor longus pollicis, and the peronaeus brevis. Thus the deeper division of the fibular nerve, taking its course between the ti- bialis anticus, and the peronaeus longus muscles, and lower down betwixt the tibialis and extensor pollicis longus, continues giving oft' branches in rapid succession, and when it arrives at the annular ligament it is much diminished. Here it divides into the ramus dorsalis pedis pro- fundus, and superjicialis.—This division is made after the nerve has crossed under the tendon of the tibialis anticus muscle, and while it lies betwixt the lower heads of the tibia and fibula.—Although they are distinguished by the name of deep and superficial branches, they are both deep compared with the extremities of the great and outer division of the peronseal nerve. The branch which lies most towards the out- side of the foot passes under the extensor digitorum brevis muscle, and on the outside of the tarsus. It distributes its branches to the extensor digitorum brevis, and interossei muscles. That branch which is more towards the inside of the foot, although distinguished by the term su- perficialis, goes forward not only under flie fascia which covers the foot, but also under the tendons; and after dividing and again uniting, and after sending off some small branches, it comes out betwixt the great toe and the second toe, and sends numerous branches to their contigu- ous surfaces. The great superficial division of the fibular nerve is some- times double, or immediately splits into two. Its first branches are to the peronaeus longus, extensor longus digitorum, and to the peronaeus brevis and tertius. The trunk or principal division runs down under the head of the peronaeus longus, and then coming out from under it, con- tinues its course beneath the strong aponeurosis, which covers the mus- cles on the fore-part of the leg. It then pierces the aponeurosis and becomes cutaneous, and runs obliquely down to the convexity of the foot, giving off in its course a nerve which passes over the outer ankle. .THE METATARSAL NERVES. When the superficial branch of the peronaeal nerve descends before the ankle-joint, it divides into the metatarsal nerves, or the rami dorsales pedis. The external of those branches passes above the tendons, and above the tendinous expansion on the dorsum pedis ; is united to the extreme branches of the ramus communicans tibialis, and is finally distributed to the outside of the third toe, to the fourth, and to the in- side of the little toe.—The internal branch is again subdivided : one branch extends over the middle of the foot to the second and third toes, while the other passes straight along the metatarsal bone of the great toe (above the tendons); sends many branches over the inside of the foot, and terminates on the inside and dorsum of the great toe. OF THE PARTICULAR NERVES. 153 The nerves of the lower extremity have the same connexion with the visceral nerves, or the system of the sympathetic, that the nerves of the arm have, and this connexion is further proved by various sympathies; the influence of cold feet on the bowels, the effect of cold water dashed on the legs to promote a purgative, the spasms of the legs in cholera, pains in the knee preceding a fit of the bile. OF THE ORGANS OF THE SENSES. OF THE SENSES. INTRODUCTION. The brain is the seat of the mind; and certain mental changes are called perceptions. Those changes proceed, in the first place, from the operation of the organs of sense. The organs of the senses are so con- stituted as to admit the influence of things external to the body, while through the connexions of their nerves and the brain, they excite the mind to a condition corresponding with the external impressions. It is in this manner, that through the organs of sense we receive those simple sensations which are the first elements of our thoughts, and the means of developing all the powers of the understanding. We never think of attending to the first simple intimations of the senses : before we are capable of reflecting on the nature of the perceptions which the several senses convey, they are so complicated and distorted by habits and association, that observation comes too late for us to ascertain the simple progress of nature. To one who looks upon nature as a philosopher, there is a conviction that such researches may be carried too far. To whatever he directs his attention, to the changes of the globe itself, or to the structure of the human body, to the physiology of vegetables, or to the phenomena of chemical science: whether he endeavours to comprehend the great sys- tem of the universe, or pores over the minutiae of natural science, he finds every where a limit placed to his enquiries ; a line which no indus- try or ingenuity can enable him to pass. We may please ourselves with conjecture beyond this limit, but we find our opinions nothing better than a dream of something allied to the impressions of our gross senses. The agency of external matter on the senses, the influence of the or- gans of the senses on the mind, and the influence of the will over the body, are mysterious, and, probably, inexplicable phenomena; yet we scruple not to explain them precisely and mechanically ; we reduce them to the level of our own capacity in the same manner as mankind have formed the idea of a Divinity by the combination of all human perfec- tions. Yet, when we imagine that we have discovered the secret of these mysteries, it is mortifying to find ourselves without any sign or language by which to communicate those great truths to the companions of our studies ! We struggle for expression ; and, as all our ideas upon such abstract subjects are derived from analogy, we express our opinions OF THE SENSES. 155 respecting the powers of the mind, or the manner in which we perceive the objects of the senses, in the same language, and by reference to the same notions, which belong to the sensations themselves. From this scantiness and inaccuracy of language, it unavoidably happens, that very different ideas of the operation of the senses are expressed by several men in the same terms ; and in attempting to convey our ideas in lan- guage more precise and definite, we are insensibly led to materialize the faculties of the mind, and to make the operations of the senses merely mechanical. What other explanation can we give of theories, which suppose the nerves to be tubes carrying animal spirits, or containing'an elastic ether; or which represent them as vibrating cords, and reduce all the variety of sensation to the difference of tension and tone ? These are, indeed, what Dr. Reid calls them, “ unhandy engines for carrying images.” Nothing has been undertaken in philosophy but entire systems, fa- thoming at once the greatest depths of nature. The custom has been to frame hardy conjectures, and if, upon comparing them with things, there appeared some agreement, however remote, to hold that as fully sufficient. What chimeras this method of philosophising has brought forth, it would be more invidious than difficult to specify. The principles of philosophising have been laid down on this basis, that on no account are conjectures to be indulged concerning the powers and laws of nature; but we are to make it our endeavour, with all dili- gence, to search out by experiment the true laws by which the constitu- tion of things is regulated. In the subject now before us we have a very remarkable proof of the superiority of investigation by experiment over the lazy indulgence of conjecture ; and I hope the whole tenor of the following account of the senses may serve among other instances to strengthen the conviction of the student, that it is only by assiduous stu- dy, and patient observation of nature, that he is to look for the attain- ment of knowledge in the medical profession. The office of the brain and nerves is to receive the impressions of ex- ternal bodies, by which corresponding changes and representations are made in the mind. We know nothing further than that, by the opera- tion of the senses, new thoughts are excited in the mind. Betwixt the sensation excited in the organ of the external sense, and the idea excited in the brain, there is an indissoluble, though inexplicable, connexion; the brain is not sensible, nor does the eye perceive, but both together give us the knowledge of outwards things. But when the sensation is once received and communicated to the brain, it is treasured there, and may afterwards be excited independent of the external organ: hence comes the term internal senses : for by the act of the will a retrograde impression may be made on the organs of the outward senses, they may be excited by imagination, which is an effort internal, as well as by an impulse from without. It is very agreeable to reflect, that the soul is no more bound to the things around us, than is necessary to our present existence. It has powers independent of sensations, and the perceptions outlive the original cause of them in the influence of the organs of sense and the material impulse which excites them. We are not creatures depending on external sensations merely; the impulse on our nerves is not the sole cause of our sensibilities; the conditions of the body 156 OF THE SENSES. itself furnish occasions of change to the mind; while many of its powers are possessed and brought into activity independent of the material impulse on the organs of sense. Perception first arises from external impulse; memory is the power of recalling these perceptions, and imagination the power of combining them, and there ultimately arises a wide field for the internal affections, without dependence on the system of material things. These powers of the mind are weak in infancy, for then the perceptions are feeble and transitory ; but by exercise and experience they acquire strength, the memory becomes vigorous, the store of ideas is increased, but still we are in a remarkable manner tied down to the ideas received from the external senses. At the same time, I would not have it supposed that this connexion betwixt the state of the mind, and the external senses, is a necessary de- pendence of the former on the latter. Wherever it is necessary to the safety of the individual, to the production of the species, to the formation of societies, to the relation of man with his Creator; faculties are be- stowed, and perceptions and sentiments arise in the mind independent altogether of the operations of the external organs of sense. It is in the combination and reciprocal effects of the mental powers, and of the impression on the external senses, that we are to find an ex- planation of the operation of attention. When the mental powers are led to the contemplation of an idea which assimilates easily with the sen- sation about to be presented by the external organ, the perception is quick and vivid ; but when the mind is strongly impressed and occupied with the contemplation of past ideas, the present operation of the sense is neglected and overlooked. Thus the vividness of the perception or idea, is always proportionate to the degree of undistracted attentidh which the mind is able to bestow on the object of sensation or of memory. In solitude and darkness, the strength of the memory in the contemplation of past events is increased, because there is no intrusion in the objects of the outward senses ; and the deaf or blind receive some compensation for their loss in the increased powers which are acquired by a more fre- quent and undisturbed use of the organs which remain, and a keener at- tention to the sensations which they present. On the other hand, when we are under the enchantments of a waking dream or reverie, our atten- tion is wholly detached from the present objects of the senses. This ab- sence, in a certain degree, is common, natural, and by no means unplea- sant ; it is the exercise of a faculty of the mind. But it may become disease ; for health of mind consists in the due correspondence betwixt the excitement on the outward sense and the operation of the mind rous- ed by the external sense. The mind (united to the body) suffers in the diseases of the body. In the debility of the body, in fever, in spasms, and pain, the faculties of the mind languish, or are roused to unequal strength or morbid acute- ness. Sometimes the phantasms and internal sensations of things once received by the outward senses, become so strong in the mind, as to be independent of the outward organ, and mistaken for objects actually pre- sent. Such phrenzy or delirium arises from a disordered and acutely sensible state of the internal senses. These impressions being great in degree, hurry and bustle is in the countenance of the patient, and un- common strength and violence in his actions, just as passion gives great excitement to one in health, causing a disregard or forgetfulness of all OF THE SENSES. 157 besides. In health, during the exercise of imagination, there is a con- viction that the ideas are not realities, and the operation of the external senses preponderates in recalling the attention to what exists around us. But the internal perceptions may become so strong as to be mistaken for realities, and the effect attributed to real existences. Sleep is another state of the animal system, fitting it for its condition. It is a state of comparative repose and recovery. The child in the ute- rus sleeps always ; the new born infant sleeps a great deal; but at length, the change of watchfulness and sleep, appears to correspond with the revolution of our planet. Those at least, will believe so, who perceive a correspondence in the weight of the body and the power of the mus- cles, to the size and consequent attraction of the earth, and the condition of our fluids and circulation to the pressure of the atmosphere. During health, there are vicissitudes of consciousness and insensibility. This is true, however, only comparatively, and by a gross reference to de- gree ; for even during natural sleep there is not a total oblivion of past perceptions, nor is there always a total unconsciousness of the present, as the senses are in part awake ; some one train of ideas may be present to the mind, and the lapse of time may be observed. Even these per- ceptions are sometimes so strong, as to be followed by voluntary exer- tion, and yet the person remains asleep. Whatever conduces to take the excitement from the mind, or lessen the vivacity of its impressions, conduces to sleep. Thus, rest, stillness, and darkness, by excluding the most lively impressions conveyed by the senses ; and haemorrhage and evacuations, by lessening the velocity of the circulation; and cold, by lessening the sensibility, induce sleep. Again, compression of the returning blood from the head, by giving it a slow languid motion, and by depriving the vessels of their freedom of ac- tion, also conduces to sleep ; because, as formerly remarked, the powers and faculties of the brain must be renovated through the means of the circulation ; and by the diminished circulation there is a diminished sen- sibility, and therefore a weakness of impression on the external senses. By long watching, muscular exertion, and fatigue, the body is brought nearly to a feverish condition. By sleep, rest is given to the voluntary muscles, and an abatement of the vital motions ensues; the quiescent state of the muscles permits the blood to return to the heart, with a slow, re- gular, and calm progress ; the heart is restored to its equable pulsation ; the breathing becomes more gentle, and the wasted strength of the system is recruited. We may define sleep to be a state in which the sensations are dull, the voluntary muscles inert, and the vital motions calm and regular. In dreaming, the sensations are dull and obscure, but the imagination active. The vital actions, which are calm, slow, and equable, during na- tural sleep, become oppressed in soporific diseases ; and the sensibility, which is gradually diminished upon the approach of sleep, but always capa- ble of being roused by the senses, becomes quite oppressed ; the voluntary muscles are relaxed, as in sleep, but sometimes convulsed by irregular mo- tions. In apoplexy, the faculties of the mind, and those powers of the nervous system which are placed under the guidance of the will, are sus- pended, while the vital operations proceed ; and life continues until the derangement reaches the latter, which sooner or later happens, for the body is a whole, and cannot exist in part. Somewhat opposed to the state of apoplexy, is that condition where 158 OF THE SENSES. the imagination is oppressed by some sensation, as in the night-mare the powers of motion are locked up. If natural sleep is not profound, the imagination is awake; but there may be false perceptions, false judgment and associations, and dispro- portioned emotions ; and if sensations are perceived, they do not pro- duce the ordinary associations. If such a state of the intellectual func- tions occurs during the waking state, it becomes delirium. That this de- lirium is analogous to the perturbed state of the imagination during sleep, appears from the delirium in fevers uniformly showing its approach in the patient’s slumbers only. It is a disposition to form false images and as- sociations, which, in the beginning, the excitement of the outward senses has power to counteract, insomuch that a patient can be roused from de- lirium as he can be roused from sleep; but, by and by, the external senses lose their superiority, and their excitement is attended with unusual as- sociations ; they no longer convey impressions to the intellect, but be- come subservient to and modified by it, and the judgment, which depends on the due balance of memory and imagination, is lost. In fever, the delirium is transitory; in low fevers, it is combined with a comatose state. In melancholy, the delirium runs upon one object chiefly, or trains of ideas, which refer to the patient’s health and corporeal feelings. In madness the variety is infinite; but chiefly consisting in a vitiated ima- gination and perverted judgment, with fierceness and increased power of corporeal exertion. There are five organs peculiarly adapted to convey sensations to the mind; or, as I am more inclined to say, to rouse the faculties of the mind by exercising the internal organs of the senses in the brain ; these may be considered as forming a medium of communication betwixt the external creation and the sentient principle within us ; and in some mea- sure the bond of union betwixt sentient beings. These organs are called the external senses ; viz. the sense of seeing, the sense of hearing, the sense of smelling, the sense of tasting, and the sense of touch. If I were willing to break in upon received opinions in an elementary book, I would say that there is a sixth sense, the most important of all, the sense of motion ; for it is by a sense of motion that we know many of the qualities of outward things, as their distance, shape, resistance, and weight. Individually, these organs convey little information to the mind ; but by comparison and combination, the simple and original affection or feelings received from them are associated and combined to infinity, and administer to all the powers of the understanding, to the memory and imagination, to taste, reasoning, and moral perception, the passions and affections, and every active power of the soul. X.et us not deceive ourselves into the belief, that by attention to this subject we shall be enabled to comprehend the nature of sensation ; the impression is made directly on the nerves of touch, taste, and smelling. We, perhaps, understand something of the body impressed ; and we see the naked nerve on which the impression is made, and yet the effect is incomprehensible. In truth, when engaged in the study of the senses, we learn only how the strength of impression is increased, e. g. how the eye is calculated to transmit, and to accumulate, and to strengthen the im- pression on the nerve: or how the organization of the ear increases the vibrations of sound ; but of the nature of sensation we learn nothing. OF THE ORGANS OF THE SENSES. 159 OF THE EYE. INTRODUCTORY VIEW OF THE PRINCIPLES OF OPTICS. The organ of vision is a subject of general interest, every man of edu- cation studies it; and for a medical man to be ignorant of it, implies a dulness of apprehension. That my reader may have a proper interest in it, we shall begin the investigation by an inquiry into the properties of light. The grand source of light is the sun, but we may add, that light is a matter thrown out from ignited, or reflected from shining surfaces ; which, entering the eye, and impressed on the nerve of that organ gives the sensation of sight. The minuteness and inconceivable velocity of light, the facility with which it penetrates bodies of the greatest density and closest texture, without a change of its original properties, make it the source of the most wonderful phenomena in the physical world.* The smallest stream of light which propagates itself through a minute hole, we may consider to be a ray ; and, as rays of light pass through a uniform medium in a straight course, they are represented in our diagrams by lines. But a ray is not simple ; light is not uniform in respect of colour; every part of a ray is not capable of exciting the same idea. White light is composed of different kinds of rays, which individually give a different sensation : one of red, another of orange, a third of yellow, a fourth ,of green, a fifth of light blue, a sixth of indigo, and a seventh of a violet or purple.f These are named the prismatic colours; because, in the spectrum produced by making a ray of light to pass through a prism, these several colours are seen in the succession in which they are above enumerated. Each of these rays individually impresses the eye with its own colour ; but when they all impress the eye at once, the sensa- tion upon the organ of sight is a compound effect; no individual colour is presented, but that mixed light which is called whiteness. Dr. Wool- aston limits the prismatic colours to four—four primary divisions of the prismatic spectrum. These colours are red, yellowish-green, blue, and violet. * This is the Newtonian doctrine; but there are great names, as Hook, Huygens, Euler, and Dr. Young, who support an opinion, that light results from the undulations of an ethereal medium pervading matter. On the truth of this I cannot decide, but the opinions.of New- ton form a much more simple introduction to optics and the structure of the eye. As to mak- ing the impression on the eye analogous to the impression on the ear, I would be inclined to turn the proof the other way, and say, that the senses are each of them endowed with a pro- perty of receiving distinct impressions from the qualities of matter which are totally dissimilar. f There is a fact not a little extraordinary regarding the emanation of rays from the sun, and which has been discovered in the present day, viz. that there are invisible rays, giving heat, but no light, which are less refrangible than the coloured rays; and that all rays, in proportion to their refrangibility, have less power of producing heat. See Herschell on the invisible rays of light. Phys. Trans. 1800, part ii. p. 284. 160 OF THE EYE. It is the nature of most bodies to attract these rays of light differently, and consequently to produce different colours. A body absorbs some of these rays of light, and reflects others from its surface ; the colours of bodies depend upon the particular rays which are reflected from them, or upon the combination of such rays as are reflected from them; and therefore they appear of that colour of which the light coming from them is chiefly composed. When a ray of light passes from a rarer to a denser medium, or from a denser into a rarer (as A into B), it alters its course, if there be any ob- liquity in the original direction; but if it strikes from one medium into another perpendicularly to the surfaces (as C), its original direction is not changed. If the ray passing from the air enter obliquely into glass or water, or any denser medium, it turns more towards the perpendicular; but if it pass through the glass and emerges again into the air, it resumes its original direction, diverging from the perpendicular. This effect of different mediums upon the ray of light, is called refraction; when a ray of light impinging upon a surface does not enter, it rises again accord- ing to the angle of its incidence; and this is reflection. The prism is a piece of glass of a triangular form, of which we have here a section at A ; the inclined surfaces of which, when placed in the course of the ray of light B, refract, and separate the several parts of the heterogeneous ray, and show its compound nature, C. If the sun be permitted to shine into a dark room through a small hole in the window- shutter, and the beam of light be made to fall upon a glass prism, it is, in passing through the glass, separated into its constituent parts; be- cause the several coloured rays have different degrees of refrangibility, in the order in which I have already enumerated them. If the rays, af- OF THE EYE. 161 ter passing through the prism, be made to pass also through a convex glass, they are brought again to a point in the focus of that glass; and the effect of the whole colours, thus re-united, is perfect whiteness. We might suspect that the beams of light were homogenous, and that the degree of refraction gave different colours to the rays, were it not proved, that how much soever any of the coloured rays is further refracted, it does not change its nature ; nor will rays suffer any change by reflec- tion from bodies of different colours, for red lead will appear yellow, green, blue, &c. according to the colour of the ray of light directed upon it. It is found, that the coloured rays have not all the same power of illuminating objects; the orange ray possesses this property more than the red ; the yellow more than the orange, &c.; and the maximum of illumination lies in the brightest yellow or palest green : nor do the several rays equally affect the thermometer.* As the impression of light remains some time upon the nerve of the eye, it gave Sir Isaac Newton the opportunity of examining whether each coloured ray makes a distinct impression on the eye, or whether they so affect each other as to impress the sense of whiteness on the eye. When a burning coal is whirled in a circle, the eye perceives an entire circle of fire, because the impression made by the coal in any point of the circle, remains until the coal returns again to the same place, and renews the sensation. When all the varieties of colours are paint- ed in a circle, and turned in the same way with the burning coal, they must each make their separate impression upon the optic nerve ; but the general sensation is whiteness ; or when the teeth of a comb are drawn across the stream of light issuing from a prism, the different colours arc intercepted in such quick succession, that a perfect whiteness is the re- sult of the mixture of impressions. There are many experiments which show that the inequalities of the refraction of light are not casual; that they do not depend upon any irregularity of the glass : on the contrary, it is proved that every ray of the sun has its own peculiar degree of re- frangibility, according to which it is more or less refracted in passing through pellucid substances, and, that the rays are not split and multi- plied by the prism ; but that rays originally constituted distinct, are se- parated by this instrument. 1^.1. * This curious fact we owe to Herschell. He found not only that the prismatic rays had different powers, both of heating and illuminating objects, but that there were invisible rays beyond the red margin of the spectrum, which had no power of illumination, but only a power of heating ! Other rays, invisible, but possessed of a chemical influence, have since been discovered, beyond the violet extremity of the prismatic spectrum. Light moves with inconceivable velocity; 195,000 miles in a second. How minute, then, to make no impression but on the appropriate nerve of the sense. See Herschell’s Exp. Phys. Trans. 1800, p. ii. p. 255. 162 OF THIS EYE. When a ray of light falls upon the surface of a glass obliquely, it in- clines to a line drawn (through the point of incidence) perpendicular to the surface. Thus the ray A, proceeding from the object, is refracted upon entering the mass of glass in the direction of the line B, having a tendency to- wards the perpendicular line. By this means if a number of rays pro- ceeding from any one point, fall on a convex or spherical surface of glass, they will be inflected so as to ga- ther about the perpendicular line A A, in the centre of the glass; which perpendicular line is the axis of the glass. If the rays of light proceeding from an object be made to strike into a mass of glass with a concave surface, the obliquity with which they impinge upon the surface, being the reverse of the convex surface, they are not made to converge upon the central line, but diverge from it. Farther, the rays of the sun when passing from a medium of glass into the air, are turned, by refraction, farther off from the central line to which they were drawn in entering the convex surface of glass. But if the rays, in passing through the glass A, were in a direction converging to the perpendicular line, they will be made to converge still farther, as is seen here in the figure. Fig. 2. Fig. 3. Fig. 4. If, however, the rays be made to pass from the glass b into the air, and the surface of the glass be concave, the rays will be made to have a less degree of convergence, so as to remove the image * farther from the surface of the glass. But if the rays passing through the medium of glass have no convergence, but pass in parallel lines, they will diverge as the lines A A do, when they emerge from the concave surface of the glass. OF THE EYE. 163 VY e see, then, the operation of a dou- ble convex glass, in forming the im- age of a luminous body upon a surface. If, for example, such a glass be held be- tween a candle and a piece of white pa- per, (the distances being properly ad- justed,) the image of the candle will appear very distinctly upon the opposed surface, but inverted ; because the rays coming from the point a converge at c, and those from the point b at d. Before proceeding farther in this short exposition of the principles of optics, it will be necessary to take a very slight view of the structure of the eye. Let us apply these facts in explana- tion of the structure of the eye. Fig. 5. INTRODUCTORY VIEW OF THE STRUCTURE OF THE EYE. The function of the eye is not simply to transmit the rays of light to the expanded optic nerve ; it collects the rays and presents them in a small the image being strong from the concentration of the rays. It is the first principle of the constitution of the eye, that the rays of Kght must be so concentrated as to impinge strongly on the expanded nerve or retina in the bottom of the eye. Now, as we have seen that a lens (which is a double convex glass) is necessary to concentrate the rays of light proceeding from an object, so as to form a small and lively image of it (as in the marginal plate,) in the same manner, an essential part of the eye is the lens, which brings the rays of light to a focus ; and that the lens may make the rays proceeding from an object converge into an accurate focus, so as to form a distinct image on the eye, the vi- treous humour is interposed betwixt the lens and the surface of the re- tina. Again, it is necessary to the constitution of the eye, that, in order to increase the sphere of vision, the anterior part of it shall project and form a large segment of a small circle, so as to take a greater circum- ference into the sphere of vision than could have been done, had the larger sphere of the eye-ball been continued on the fore part* Another necessary part of the apparatus of the eye is the iris, which is a curtain in the anterior chamber of the eye, perforated with a hole, which is ca- pable of being enlarged or diminished so as to admit a larger or smaller stream of light according to the intensity of the light. In this provision, we see the necessity of the anterior humour of the eye being different from the others. It is a perfect fluid, a mere aqueous secretion, while the others possess a degree of firmness : thus the iris or curtain of the eye is permitted to move with perfect freedom in it. The humours of the eye, therefore, are three: the aqueous, crystalline, and vitreous humours ; and they stand in this relation:— 164 OF THE EYE. 1. The AQUEOUS HU- MOUR is the anterior hu- mour of the eye. It dis- tends the anterior and pel- lucid part of the eye, so as to increase the sphere of vision. It is perfectly fluid, and of a watery con- sistence, that it may allow free motion to the iris. 2. The lens or crys- talline humour is plac- ed immediately behind the perforation in the iris ; which perforation is called the pupil. The lens collects the rays of light like a double convex glass, so as to concentrate them, and make a more forcible image on the bottom of the eye. 3. The vitreous humour is behind the lens. It distends the great ball of the eye into a regular sphere, that it may move easily in the orbit; and its diameter in the axis of the eye is so proportioned to the focal dis- tance of the lens (affected also in some degree by the other humours) that the image of an object is formed accurately on the surface of the retina; accordingly, when the coats are cut from the back of the eye, the picture of a luminous object held before the pupil is seen exquisitely minute and distinct on the bottom of the eye. While these humours have each its distinct character, they possess in proportion to their density, different powers of refracting the rays of light. This has the still farther happy effect of correcting the disper- sive powers of the humours, and giving the truest colours, as well as the most correct image of the object presented to the eye. It was not till the present day that the method was invented of correcting the false colours which form around the image of an object seen through power- ful magnifying glasses ; at last, Dolland invented the achromatic tele- scope, by compounding the lenses of two different kinds of glass. It is almost superfluous to add, that the eye possesses this power, and in it the true colours only of an object are represented on the nerve of the eye. (See of the Lens.) If the lucid anterior part of the eye be formed too prominent, or if the lens of the eye have too great a degree of convexity, or, lastly, if the size of the ball of the eye, and consequently the diameter of the vitreous humour in the axis of the eye, be unusually great, then the person does not see distinctly ; because the powers of the humours, in concentrating the rays of light, are too great, and the image of the object is not formed accurately on fhe retina, but before it. Thus the convexity of the cor- nea, the lucid anterior part of the eye, or the focal powers of the lens, being too great for the distance intervening betwixt the lens and retina, the image is formed at a before the rays reach the surface of the retina ; and after coming accurately to the point, they again begin to diverge ; which diverging rays, striking the surface of the retina, give the indis- tinct vision of a near-sighted person. But as this indistinctness of vi- sion proceeds from no opacity, but only the disproportion of the con- vexity of the eye to the diameter, the defect is corrected by the concave Fig.C. Atpieous Tiumm'- ■ Iris ,Lcns Vitreous humor - OF THE EYE. 165 glass, a ; for, the effect of this glass being the reverse of the convex lens, it causes the rays to fall correctly upon the surface of the retina ; that is, it corrects the too great conver- gence caused by the convexity of the humours. But, when a near-sighted person has brought the object near enough to the eye to see it distinctly, he sees more minutely, and, conse- quently, more clearly ; because he sees the object larger, just as a per- son does when assisted with a magni- fymg glass or lens. The near-sighted person sees dis- tant objects indistinctly ; and as the eye, in consequence, rests with less accuracy upon the surrounding ob- jects, the steady piercing look of the eye is diminished. Again, the near- sighted person knits his eye-brows, and half closes his eye-lids : this he does to change the direction of the rays, and to correct the inaccuracy of the image, in a manner which may be understood by the following analogy. If we make a card approach a stream of light passing through the window, it will so attract the rays of light, as to extend the margin of the figure of the circular spot of light upon the wall. In the same way when a stream of light, proceeding from an object towards the eye, is made to pass through a small hole, the circular margin of the hole so attracts the rays, as to produce an effect similar to the concave glass ; as if they proceeded from a nearer object, the image is carried farther back from the lens ; and when a near-sighted person peers through his eye-lids, it makes the rays impinge more accurately upon the retina, and he sees more distinctly. The effect of old age, is gradually to reduce the eye to a less promi- nent state, and, consequently, to bring it to the reverse condition of the near-sighted eye ; near-sightedness, therefore, diminishes with extreme old age. From the decrease of the humours, and the lessened convexity of the cornea, the image of objects is not formed soon enough to impinge ac- curately on the retina, the rays tend to form the image behind the retina, or they meet the retina before they have arrived at what is termed their focus. In this figure, we have the effect of old age on the humours repre- sented : without the intervention of the glass a, the rays have a direction which would form the image at some distance beyond the retina, as at b. But by the convex glass a (which is of the nature of the common spectacles for old people) the direction of the rays of light is so corrected, that the image falls accurately on the bottom of the eye. We understand, then, whence these opposite defects of sight arise ; that in old people, objects cannot be seen distinctly when near, and, in short-sighted people, they cannot be seen distinctly when at a distance, %-7 Bg.S. 166 OF THE EYE. We see, also, why old age corrects short-sight- edness by gradually reducing the convexity of the eye, enabling the person to see objects far- ther removed, until, by degrees, he comes to see perfectly at the distance most convenient for the common affairs of life. It has been, by some, thought extremely diffi- cult to account for the image appearing to us, as it is in reality, erect, since it is actually figur- ed on the bottom of the eye in an inverted po- sition ; but the terms above and below have no relation to the image in the bottom of the eye, but to the position of our bodies and the surround- ing things. When I look to a tall man’s face, I direct my eyes upwards ; I observe his situa- tion, as it relates to the area before my eye, or to a space in the sphere of vision. I know, after long experience, that I direct my eye ; and it is the effort of direction, combined with the sensation of the retina, that gives the compound idea of the place of the object. Motion of the eye, (if not produced by the voluntary effort of the proper muscles of the eye,) conveys no idea ; the image does not appear to move. When an object approaches towards the eye, the diameter of the pic- ture on the retina increases in the same proportion as the distance be- tween the eye and the object of decreases; and, consequently, it de- creases in the same proportion as the distance increases. But the de- gree of brightness of the picture of an object on the retina continues the same at all distances, between the eye and the object, unless some of the rays of light are interrupted in their progress ; for, as the advancing object becomes bright, it increases doubly in length and breadth, or qua- druply in surface. The faint appearance of remote objects is occa- sioned by the imperfect transparency of the atmosphere. There is nothing more astonishing in the structure of the eye, than the sensibility of the expanded nerve, as proved by the extent of the changes or degrees of light which illuminate visible objects, and of which the eye is sen- sible ; or the great degree of light which the eye can bear, and the low de- gree of light at which objects are visible. Thus, the proportion betwixt the degrees of light illuminating an object by the sun, and by the moon, at any equal altitudes, is calculated at 90,000 to 1.* Again, by M. de la Hire’s calculation, we see the sail of a wind-mill, six feet in diameter, at the distance of four thousand toises. The eye being supposed to be an inch in diameter, the picture of this sail, at the bottom of the eye, will be ¥«Vo °f an inch, which is the 666th part of a line, and is about the 66th part of a common hair. This conveys to us an idea of the great sensi- bility of the nerve in accommodating itself to such varieties in the de- gree of illumination ; it also proves to us that the expanded nerve must have a surface mathematically correct, on which the image is represented; for how else could the image of an object be distinct, if the picture of that object in the bottom of the eye be only the 66th part of a hair in di- ameter ? It is evident that some guard to the eye must be furnished, in >F&9. * See Smith’s Optics, vol. i. p. 29. OF THE EYE. 167 order that the organ may accommodate itself to this surprising vari- ety in the intensity of impression. The pupil of the eye is the central perforation in the iris or curtain, which hangs before the lens. This membrane is moveable ; it dilates or contracts the hole or pupil which transmits the rays, so as to adapt the diameter of the stream of light, darting into the eye, to the intensity or degree of light. If a body is illuminated but faintly, the pupil is (insensibly to us) enlarged, and a greater quantity of the rays are allowed to be transmitted to the retina. As the convexity of the pellucid part of the eye. and the concentrating powers of the lens, remain the same, the size of the image is not altered by this dilatation of the pupil, but only the strength of the image or pic- ture in the bottom of the eye increased. We have understood that the rays of light are refracted, when they pass out of one transparent medium into another of different density.— For example, the rays of light are refracted towards the perpendicular line, when they enter the cornea of the human eye; but they will be re- fracted in a very small degree in entering the cornea of fishes, because the aqueous humour is of the same density with the fluid from which the rays of light are transmitted; accordingly, the cornea of fishes is not prominent; it would be of no use. On the other hand, this would limit their sphere of vision, were not the deficient convexity of the cornea counterbalanced by the prominence of the whole eye, and the more an- terior situation of the crystalline lens in the eye: a large pupil and long diameter of the lens we shall afterwards find to be necessary to the dis- tinct vision of fishes.* It is natural on the present occasion, to inquire into the effects of the several humours of the eye, in producing in those who are short-sighted the obscurity arising from the double appearance of small and shining points. This is prettily explained by Jurin, upon Sir Isaac Newton’s principle, concerning the fits of easy refraction and reflection of light. The horns of the new moon, or the top of a distant spire, or the lines upon the face of a clock, appear doubled or tripled, and sometimes much more multiplied, to a short-sighted person. The same appearance will be given when an object is held too near the eye for perfect vision. If the light is seen through a narrow slit in a board, and the board is brought nearer to the eye than the point of distinct vision, the aperture will ap- pear double, or as two luminous lines, with a dark line between them; and as the distance is varied, two, three, four, or five dark and luminous lines will be observed. There are many such deceptions in viewing lu- minous bodies; all of them proceed from the same cause, which is this : —Before Sir Isaac Newton’s philosophy was acknowledged, it was the received opinion, that light was reflected from the surface of bodies by its impinging against their solid parts, and rebounding from them like a ten- nis-ball when struck against a hard and resisting surface : further, as they saw that part of the rays of light were in glass reflected, and the rest transmitted, they conceived that part entered the pores of the glass, * Neither fish out of water, nor other animals within water, can see any object distinctly. Di- vers see objects as an old man would do, through a very concave glass put near to the eye; and it has been found, that the convexity of spectacles for divers in the sea must be that of a double convex glass, equal on both sides to the convexity of the cornea. The necessity of this is plain; the aqueous humour of the eye being of the same density with the water, there is no refraction of the rays in passing from the water into the eye, and this deficiency must be supplied. 168 OF THE EYE. and partjimpinged upon its solid parts. But this does not account for the refractions which take place when the rays have passed the glass, and are about to be transmitted into the air; they cannot find solid parts to strike against in entering the air, for the refraction of the light is greater in passing from the glass into the air, than from the air into the glass; and if water be placed behind the glass, the refraction of rays passing out from the glass is not increased but diminished by this sub- stitute for the rarer medium of the air. Again, when two glasses touch each other, no refraction is made in rays passing from the one into the other. To explain this, Sir Isaac Newton taught, that in the progress of rays of light, there is an alternation of fits of easy transition or reflec- tion : or, in other words, that there is a change of disposition in the rays, to be either transmitted by refraction, or to be reflected by the surface of a transparent medium. Jurin illustrates this opinion, and its application to our present purpose, in this manner. Suppose that a b d, and b d f, are media of different density, and that their surfaces are intersected by the line b n ; again, let a be a pencil of rays, which issuing from this point, falls upon b a d, as the refracting sur- face b a d is convex, and no two points of it, from a to d, are equally distant from the source of the rays a ; and, as the rays of light in their pro- gress, alter alternately from the fit of refraction to the fit of reflection, they must be in part refracted to the focus F, and reflected in the direction of the dotted lines c e. Thus, if the ray a a happens to be in disposition to pass through the medium b d f, it will psss on towards the point f. If the next ray a b should be in no fit to be transmitted, because, being in a degree farther advanced from its source a, it lias changed to the fit of reflection, then it will not be refracted towards the focus f, but reflected off towards c ; but, again, the ray a d being ad- vanced farther from its source, it will impinge upon the surface b d, during its disposition to refraction, and will concentrate its beams at f ; and so with all the others, alternately reflect- ed and refracted. The consequence of this obstruction to the equal refraction of light, is, that the image formed at f is feeble ; but still it is distinct and per- fect ; because the transmitted rays are regularly concentrated, and form the proper focus. But if the converging rays should be received upon a plane before they arrive at the focus f, the reflected rays of light will have left spaces dark where they would have fallen by refraction, and. Fig.10. OF THE ( OATS OF THE EYE. 169 consequently, distinct luminous circles will be thrown on the plane; again, if the plain surface be opposed to the rays, after they have formed their focus, and are again dispersing after having crossed, the same un- equal effect of light and dark circles will be thrown on it; though now, the rays of the right side of the pencil bdf, will form the left of the pencil f g h. The effects of the alternate disposition of the rays for transmission and reflection would not be perceptible, did the coverging powers of the cornea and lens bring the focus of the rays exactly to the surface of the retina, as in the perfect eye. But in the near-sighted person the focus is formed at a point before the retina, the rays decussate and spread out again before they form the image upon the bottom of the eye. Instead, therefore, of forming an accurate image, they are spread out into con- centric circles ; or in a lesser degree, the person experiences a confused outline of the object, which becomes surrounded with several rings or false outlines.* OF THE COATS OF THE EYE. The coats of they eye are divided into three classes. 1. The anterior and external coats, viz. The conjunctiva and the ALBUGINEA. 2. The proper coats, viz. The sclerotica, the choroides, the RETINA. 3. The transparent tunics of the eye. As the first class belongs to the external apparatus of the eye, we shall begin with the proper coats. Speaking generally, and without considering the minuter divisions of anatomists, we may say, that there are three proper coats of the eye, viz. the sclerotic coat, giving strength ; the choroid coat, being the vehicle of the chief vascular structure of the eye ; and the retina, or expanded nerve, being the organ itself. These are the proper coats of the eye. Although these coats may be capable of being divided by the art of the anatomist, either by the knife, by injections, which form extravasa- tion between their layers, by maceration, or by the chemical action of fluids; yet it is better, in a general enumeration, to take a natural divi- sion, than to enumerate all their subdivisions. OF THE SCLEROTIC COAT. The sclerotic coat is so called from its hardness, t The sclerotica and cornea are often considered as one continued coat investing the eye; hence they say, the opaque and the lucid cornea. But, although these parts are actually in union, yet as they are really of so very different a * By fits of easy transition, it was not meant by Sir Isaac Newton that the rays must necessarily be transmitted through every pellucid medium, and at any obliquity of incidence, but only that the ray was more easily transmitted, and more difficultly reflected; nor was it meant that, during its Jit of easy reflection, it was absolutely incapable of being transmitted, but only more readily reflected than transmitted, t Dura seu sclerotica : Vesaliusi Rusvch, &c, 170 OP THE COATS OP THE EYE. nature, we must consider them apart, and treat at present only of the opaque white sclerotic coat. The sclerotic coat is a strong, firm, and white membrane, consisting of lamellae firmly attached and interwoven, and not capable of being regularly separated by maceration; it has the denseness of tanned leather. In firmness, whiteness, opacity, and the little appearance of vascularity, it more resembles the dura mater than any other membrane of the body. In adults, the sclerotic coat is stronger and firmer, comparatively, than in the foetus; the cornea less so. On the outer surface, it has (towards the orbit) a loose cellular membrane attached to it, which allows the mo- tion of the eye-ball. Upon the fore part it is invested by the tunica al- buginea or tendinea. Upon its inner surface, it has a loose and soft membrane which connects it with the choroid coat. In birds, and the tortoise, the posterior part of the sclerotic coat is thin; the fore part of it is split into laminae, betwixt which there are in- terposed thin plates of bone*, while in fishes it is in part cartilagi- nous t, but thin and transparent, so that there appears a very beautiful spotted coat beneath it. There are also seen in the sclerotic of fishes little white granules like glands. The vagina of the optic nerve can be separated into two laminae J; the outer one is observed to unite intimately with the outer part of the sclerotic coat, while the inner lamina of the vagina is contiguous with its inner surface. The pia mater, too, says Zinn, when it has pierced the foramen in the sclerotic coat, along with the substance of the nerve, expands upon the inner surface of this coat, and extends even to the cornea, and forms one of its intimate laminae. This must be only that part of the pia mater which invests the optic nerve, or, more strictly speaking, that membrane which stands in the same relation to the nerve that the arachnoid coat does to the brain; for the membrane, which sinks into intimate union with the nerve, accompanies it even in forming the retina. § The sclerotic coat is the great support of the globular figure of the eye ; it defends the more delicate internal structure from slighter injuries, by its strength; and from the progress of inflammation, by being of a structure but little vascular, and not prone to disease. That inflamma- tion which we see to be so frequent in the eye, is not in the sclerotica, but in the adventitious coat, the conjunctiva. But in proportion as the scle- * Cuvier, vol. i. p. 387. f Morgagni Epist. An. xvi. 40. Cuvier, 388. { Rusych. Zinn. • } It rnay be well in this place, to mention the opinions of the chief supporter of that scheme of the coats of the eye, which derives them all from the investing membranes of the brain and optic nerve. M. le Cat, in his Traits desSens, describes them thus:—When the optic nerve has entered the orbit, the dura mater which surrounds it splits into two laminae : the external one attaches to the orbit, and forms the periosteum, the other forms the vagina of the nerve. In the angle formed by these, the muscles of the eye arise. This continued sheath of the nerve (he continues) expands into the globe of the eye, as the mas9 of glass is blown into a bottle. The dura mater of the nerve is expanded into the cornea (viz. sclero- tica). The second envelope, or pia mater, forms two lamina:; the one is applied to the scle- rotic coat, and the other forms the choroid coat. The choroid coat divides anteriorly, and forms the iris and ciliary processes. The internal medullary part of the optic nerve forms the retina. Finally, “ L’ceil est tr&s evidernment [’extremity nerveuse epanouie boursoufUe en bouton creux et plein de liqueurs,” p. 158. See also Bonn Sandifort Thesaur. de Continua- fi'one Membranrv-. OF THE COATS OF THE EYE. 171 rotic coat resists pressure and the progress of disease from without, it re- sists the swelling of the parts within when they become diseased, and gives the greatest torture. Of what importance the entireness of the coats, and the uniform re- sistance of the humours of the eye is to the healthy state of the organ, will be afterwards examined. OF THE CORNEA. The cornea is so called, from being firm, transparent, and composed of laminae.* It is the pellucid circle on the fore part of the eye, which seems variegated with colours ; though this is a deception, owing to its perfect transparency. The circle of the cornea is, however, far from being regular; its margin is flat towards the nose. The cornea, being a segment of a smaller sphere than the eye-ball, enlarges the field of vision. The field or sphere of vision is further extended by the motion of the eye. The motion of the eye has a range of 55 degrees in every direction ; so that there is altogether a range of 110 degrees.| The cornea consists of laminae; betwixt which there is interposed a cellular substance, filled with a perfectly pellucid fluid.J These cells seem, like the common cellular membrane of the body, to have a free communication with each other, so that the fluid freely exudes, and as quickly is imbibed by maceration. The fulness ol' the cornea, with the perfect transparency of the fluid, gives a brilliancy to the eye, and is a sign of health ; the reverse dims the eye, and with the fallen features accompanies ill health. Steno observed, and Petit confirmed, the fact,§ that the pores on the surface of the cornea exuded the fluid which fills the cells of the cornea; and that, after the surface was carefully dried by pressure, the moisture might be seen to form in drops upon the surface. The moisture can be thus forced out from the pores of either surface of the cornea. || This moisture becomes dull and clammy on the ap- proach of death, and forms sometimes a pellicle over the cornea. The laxity with which the laminae of the cornea are connected, may be, in some measure, demonstrated, by taking it betwixt the finger and the thumb ; we shall then find, that the layers can be made to glide very freely on each other. In the foetus, and in young children, the cornea is of great thickness, and resists the point of the lancet or scissars. This resistance in the foetus proceeds from a great degree of toughness, while, in the adult, the surface of the cornea is so hard, that I have often seen the point of the knife, in extracting the cataract, bend upon it. This turning of the elastic point of the knife is very apt to give a wrong direction to the incision; and, indeed, this occurred to me in my first operation. There is a pellicle, or exceedingly thin coat, which, by maceration, can be taken off from the surface of the cornea. This is the conjunc- tiva continued over it. The membrane in fishes, analogous to the adnata, lies loose over the cornea; and, in serpents, it is thrown off from the cornea, with the * “ Cornu modo, dura, et cornu instar in laminas dividareque potest.” Vesalius. ■f Dr. Young, Phil. Trans. Nov. 27, 1800. t Substantia spongiosa Valsalvae. j See also Hovius, p. 82. || Zinn. 172 OF THE COATS OF THE EYE. scales of the body, and remains attached to the cast skin of the head ; and in the foetus calf, I have forced the blood in the vessels of the con- junctiva into the vessels passing over the surface of the cornea. By maceration, I have found, raised in the fluid, a very delicate and transparent membrane from the inner surface of the cornea * ; and, after long continued soaking, the whole cornea can be taken out of the scle- rotic coat, like an optician’s glass from its frame. The cornea possesses great sensibility ; although much of the pain, from hard bodies flying into the eye, is to be attributed to the motion of the eye-lids, and the great sensibility with which they are endued. When a splinter of glass or metal strikes and sticks in the cornea, inflammation is excited: in consequence of this, vessels carrying red blood strike into it, or shoot over its surface in a new film of membrane.t Petit thought he observed first in a negro, and afterwards in a variety of instances, red lines in the cornea, which he conceived to be the anastomosing of vessels. There are, besides, says he, many circumstances which argue that there are blood-vessels in the cornea. When the eye receives a stroke, there is often blood effused in its substance ; ab scesses, also are found within it, and phlyctaense are seen on its surface ; and in great in- flammation of the eye, the cornea appears red ; which, he supposed, must be produced by the same cause which makes the albuginea red, viz. the enlargement of its vessels, and the circulation of red blood. But we must not imagine, he continues, that in the natural state, red bood circulates in the cornea; for the vessels are not to be seen with the microscope; nor are they penetrated by injection ; nor do they appear in the foetus ; nor, when little abscesses are formed in the cornea ; but only when violence has been done by a stroke upon the eye. In an eye in which the tunica conjunctiva was most minutely injected, as well as the internal vessels of the eye, I had resolved carefully to examine the struc- ture of the cornea; and after a long maceration, in which it had greatly swelled, I observed a set of vessels totally distinct from the extremities of the minute blood-vessels. The minute blood-vessels which were injected, stopt abruptly on the margin of the cornea. But these I now mention are particular; they are in great profusion, large, and perfectly pellucid ; they are large towards the middle of the cornea, and diminish towards the margin. Their free communication formed a net-work deep in the thickened substance of the cornea. The size, perfect pellucidness, and intimate connexion of these vessels, might perhaps incline one to call this a cellular structure. Vessels attach themselves both to the inner and to the outer surface of the cornea ; and when it becomes spongy and vascular in this way, little can be explained of its natural structure. Thus, the pannus and ptery- gium are membranes which stretch across and adhere to the cornea, while the iris frequently attaches to its inside. In this case, the cornea be- comes spongy, thick, and vascular; and, when cut, there is red blood in * This, within these few years, has been claimed as a discovery. I fear that this must be considered as the capsule of the aqueous humour long since described. I have found the spark from iron in blacksmiths and masons, buried in the cornea for se- veral days (some authors say months), without exciting pain or much inconvenience. I have also more than once picked a little black slough from the cornea, mistaking it for a piece ot iron, when it was only the consequence of the injury. OP THE COATS OP THE EYE. 173 it * ; and in the iris is generally attached to the cornea. I have a preparation in which the form and character of the iris are en- tirely lost: it is extended into a reticulated membrane which lines the surface of the extended cornea. OP THE CHOROID COAT. The choroid is the vascular tunic of the eye ; it is so called from its resemblance to one of the membranes of the secundines. It is the mid- dle coat of the eye, lying betwixt the sclerotic coat and retina. Injections show it to consist of two layers or membranes ; and it has upon its inner surface a pigment, which being sometimes firm, might be taken for a membrane. It was Ruysch who observed this division of the choroid coat into two laminae ; and the inner one his son called the tunica Ruy- schiana : but of these hereafter. Those anatomists who supposed the sclerotic coat to be the produc- tion of the dura mater, naturally concluded, that the choroid coat was derived from the pia mater : and as Ruysch found it to be divisible into two laminae, so Sladius found the pia mater to consist of two membranes. It followed that the one lamina of the choroid coat was the continuation of the tunica arachnoides, and the other of the pia mater : but this ac- count of these membranes has no support from observation. Betwixt the pia mater and choroid coat there is no resemblance ; the lattqr we shall find loaded with vessels: but these vessels are peculiar, and mi- nister to a secreting surface. The pia mater in the brain, and optic nerve, is in strict union with the substance of the brain, and supports and nourishes it; but the choroid coat has no connexion with the retina or expanded nerve. There can be no better mark of distinction between membranes than their degree of vascularity, and particularly in the manner of the distri- bution of their vessels. The choroid coat is most particular in the dis- tribution of its arteries and veins. The great arterial vascularity of the choroid coat is to be seen only after a very minute injection, and the ve- nous vascularity after artificial or accidental infarction of the blood, or by a successful injection from the superior cava ; J although the very great vascularity of this coat was known to our oldest writers, yet the appear- ance of these vessels, when empty, has deceived many. Morgagni§ and Maitre-jean have described fibres which they affirm to be distinct from the vessels, but which prove to be, in fact, the appearance presented by the collapsed vessels. The great peculiarity of the choroid coat, is its being a secreting mem- brane ; by which I mean that the pigmentum nigrum which is applied to the fine external membrane of the retina, being a secretion, the cho- roid coat has necessarily that peculiar structure of vessels which belongs to the secreting membranes. This structure has enabled anatomists to * Pterygium, is a disease of the conjunctiva, but which resembles a membrane extended over the cornea from (he canthus. Pannus, is a disease of the same kind, but covering the cornea as with a white opaque membrane. f Staphyloma, uvea, viz. a protrusion and opacity of the cornea; which, from the loss of transparency and the general appearance of the tumour, is supposed to resemble a grape. jAn observation of Walter, j Morgagni Epist. Anat. xvii. 2. 174 OF THE COATS OF THE EYE. tear it into laminae. For that part of the choroid coat next the sclerotic is merely a vehicle of vessels and nerves, and is a tissue of them con- nected by very fine cellular membrane. The internal part, again, is or- ganized into a secreting surface, and is the tunica Ruyschiana.* I con- ceive, that the division into the choroid coat, and tunica Ruyschiana, is warranted from the nature of the membrane, as the divisions of the coats of the intestines are.f Morgagni says, that from his earliest youth, he had many proofs that the choroid coat was not single in brutes ; he asserts, also, thatFran- ciscus Sylvius and Guenellonius had demonstrated the double laminae of this membrane before Ruysch.J Certain it is, that Ruysch was not so fortunate in ascribing a use to this tunica Ruyschiana. He supposed that it gave strength to the choroid coat, and, by bringing a greater af- flux of arterial blood, supplied the necessary heat to the otherwise cold humours. § Tapetum.—The internal surface of the choroid coat has been long called tapetum, from its villous or fleecy appearance, when seen through the microscope. This surface in the adult is of a brown colour: in very young subjects it is red and bloody ; and, when minutely injected, it is like scarlet cloth. It is by this vascular surface or tapetum that the black pigment, which is laid under the expanded retina in the human eye, is secreted. The pigmentum nigrum.—The pigmentum nigrum is the black or deep brown mucous substance which lies between the choroid coat and retina. It is of a nature to be washed away with a little water and a soft pencil. || This brown taint pervades the whole texture of the choroid coat. It is in immediate contact with the exterior membrane of the optic nerve. Its use is apparently to stifle the rays of light after they have impinged on the sensible surface of the retina; for we know that blackness is owing to the absorption of the light, as whiteness and colour is the reflection of it from the surface of bodies. The dark colour of the secreted pigment of the choroid coat is, in some measure, peculiar to those animals which see in the brightest light of day; but is wanting, or of a bright reflecting green or silvery whiteness, in such as prowl by night. The natural con- clusion, therefore, is, that the pigmentum nigrum subdues the intensity of the impression, while the reflecting colours of the surface in animals which see during the night, strengthen the effect of the light on the sur- face of the retina, by repelling it. As fishes have the other provisions for seeing in an obscure light, they have also this of the reflecting surface of * Ruysch. Epist. Anat. xiii. j- Albini Annot. Acad. lib. vii. cap. iv. | Morgagni Epist. Ariat. xvii. 3. 5 Quod ad usum tunicas Ruyschianae attinet crediderim banc tunicam inter Caeteros usus esse destinatam, non solum ad robur choroid*, verum etiam ut a sanguinis arteriosi majori copia requisitus calor tribus humoribus natura frigidis conciliaretur. Ruys. Repons, ad Christ. Wedelium, p. 14. || I cannot conceive how this matter should be confounded with the tapetum or tapis, which, as the name implies, is the villous surface of the choroid coat. Tapetum is. properly, cloth wrought with various colours ; and the analogy was first used by the French Academicians, in the account of their dissection of a lioness. “ The membrane which is put into the bottom “ of the eye, and laid on the choroides, which we call the tapetum, was of an Isabella colour, “intermixed with a greenish blue. It was easily separable from the choroides, which re- “ mained entire, with its ordinary thickness, after that we had taken away the membrane “ which forms the tapetum.” The explanation of this, I suppose, will be found in Morg. Epist. An. xvii. 3. OP THE COATS OP THE EYE. 175 the tapetum : as it is a secretion of the villous surface of the choroid, we see why it becomes somewhat deficient in old men, and sometimes want- ing in the degenerate varieties of animals; when entirely deficient, the blood circulating in the vessels of the choroid coat gives a lurid redness to the reflections from the bottom of the eye.* Finally, in regard to the choroid coat, we have to understand that it consists of two laminae: the outer, and that which is next to the sclerot u coat, being the proper choroid ; the internal lamina, the tunica Ruyschi- ana; that on the surface of the tunica Ruyschiana, there is a pile or fleece, which is called tapetum: and lastly, that the secretion of this in- ner surface is a pigment, which, in the human eye, has the appropriate name of pigmentum nigrum; but, in many animals, it is of a silver, golden, or Isabella colour; though, in my apprehension, the colour, in all these varieties, depends still upon a peculiar secreted matter. ANNULUS LIGAMENTOSUS. When we take away the sclerotic coat from the choroides, we see at the termination of the choroides forward in the iris, a white ring; this should be called the ciliary ligament: it is the bond of union betwixt the choroid coat, the iris, and corona ciliaris. Soemmering calls this the annulus gangliformis tunicse choroideae. OF THE CILIARY PROCESSES, OR CORONA CILIARIS. The ciliary processes are formed of the anterior margin of the cho- roid coat; they give the appearance as if the choroid coat, at the an- terior part, were folded inward to the margin of the crystalline lens; and, as if, to accommodate it to this sudden inflection, it had been plaited, and not regularly contracted; at least, this is much the appearance of the circle of ciliary processes, when, after cutting across the eye, we look from behind upon the lens in its natural situation. In this view, we And the pigmentum nigrum of the choroid coat continued over the ciliary processes, which gives to them the appearance of the regular plicae of the choroid coat, converging to the edge of the lens, and form- ing altogether a disk round it. When the black paint on the ciliary processes is a little washed away, and when we attentively examine this part, we find the ciliary processes to be actually little oblong plicae, which gradually arise from the cho- roid coat at the angle of its inflection, and terminate abruptly, approx- imating, but not attached, to the margin of the lens. When the paint is washed entirely away, the whole circle of these processes appears evi- dently to be the continued choroid coat. When not injected, the ciliary processes are pale and loose ; but when minutely injected, they take a perfect scarlet colour : they resem- ble, in their uninjected state, the valvular-like doublings of the villous coat of the stomach and intestines. Before the choroid coat is inflect- ed towards the lens, in the form of ciliary processes, it forms a firm ad- * As the pigmentum nigrum is a secretion, we shall not be surprised to find it become de- ficient in the commencement of some diseases of the eye. This is known by the possibility of seeing to the bottom of the eye : that is, the choroid coat becomes a reflecting surface, and throws out the beams like a cat’s eye. See Med. Obser. and Enquiries, vol. iii- p. 124. 176 OF THE COATS OF THE EVE. hesion to the sclerotic coat near the circular margin of the cornea, and at the same time is united firmly to the root of the iris forming the an- nulus ligamentosus. From this, the processes tend inward, and a little backwards ; and are, at their external extremities, detached from the iris; nor are they attached to the margin of the lens, but are loose and floating. When the vitreous humour and lens fall out from the anterior segment of the eye, we find that the plicae or ciliary processes have left their impression on the anterior surface of the vitreous humour, and also on the intermediate expansion of the retina which extends before the mem- brane of the vitreous humour. This circular impression of the ciliary processes is called by Haller, striae retinae subjectae ligamento ciliari.* I have called this impression halo signatus, because it is formed of a circle of radiations, formed by the impression of the ciliary processes, and is not peculiar to the retina, for the retina again makes its impression on the membrane of the vitreous humour. The furrows and doublings of the anterior part of the retina, formed by the impression of the cilia- ry processes, l)r. Monro has called the ciliary processes of the retina; but, for my part, I think this a term likely to confound and mislead a student; and we might as well speak of the ciliary processes of the vi- treous humour, or of the membrane of the vitreous humour, since they also take the impression of the ciliary processes.| When the vitreous humour and lens are taken out of the coats, we see also that the ciliary processes have left the stain of the fuliginous paint.| This it is necessary to remark, since I have seen students con- found this mark with the ciliary processes themselves. The ciliary pro- cesses are of a most elegant vascular structure. Their contorted arte- ries are beautifully represented in Zinn’s figure. He traces them from the extreme branches of the choroid coat; but, of their veins, he says nothing further than that they are continued from the branches of the vasa vorticosa, or veins of the choroid coat. The points of the ciliary processes are not attached to the lens, but float loose in the posterior chamber of the aqueous humour§ ; but at a little distance from their points they adhere to the retina, where it is continued over the anterior part of the vitreous humour. Through this attachment only are they connected with the lens ; for, as we shall find presently, the retina (as a membrane, but not as the sensible retina) is continued over the crystal- line lens. j| Soemmering [/co?ies oculi humani~\ describes the retina as spontane- ously falling off and separating from the exterior circle of the corona ci- liaris. But he also has mistaken the nervous matter which stops here for the whole retina. The transparent tunica vasculosa retinae t.;oceeds to the lens. * Fasq. vii. icon. ocul. f Winslow uses the term sulci ciliares, for the impression on the vitreous humour. Zinn calls this corona ciliarisi after Camper : he describes them well, p. 75. J See Morgagni Epist. Auat. xvii. n. 13-and Rusych also, Nonnulli proprocessu ciliari agnoscunt pullas pigmenti nigri reliquias, membranula; tenuissimae humoris crystallini et vitrei, et quasi fibres mentientes,oeulo sc. aperto, humoribusque exemptis; life autern nil sunt nisi avulsae particulae pigmenti nigri.” Rusych. Thes. An. ii. Ass. 1. No. xv. i) This was demonstrated in a particular manner by Ruysch and Morgagni. || Zinn and other later writers have entertained the idea, that the adhesion of the ciliary processes to the membranes covering the vitreous humour is by a kind of gluing, rather than a union by cellular membrane. See Zinn, p. 75. OF THE IliiS. 177 The ciliary processes, collectively, form a circle round the lens, which I call corona ciliaris. This circle forms a perfectly opaque partition, which stifles all rays that might otherwise be transmitted by the side of the lens. The corona ciliaris, or ciliary circle, no doubt, serves at the same time as a connexion between the outer and strong coats of the eye and the transparent coats and humours ; for, it is to be observed, that, excepting the connexions which naturally exist between the optic nerve and retina, this slender hold which the ciliary processes take of the expanded retina, is the only attachment betwixt the humours of the eye and the proper coats. In regard to the names appropriated to this part of the eye, there is more confusion than it is possible to believe. It is necessary to attend to this ambiguous use of terms, else we shall be in danger of misunder- standing our best authors. Vesalius considers the whole as a septum betwixt the vitreous and posterior chamber of the aqueous humour ; but he seems to find much difficulty in giving it an appropriate name.* Fal- lopius and Morgagnif use the term corpus ciliare for the whole cir- cle of the processes, and in the same sense that I have ventured to use corona ciliaris. It is a name which conveys the idea neither of the shape nor of the substance of the thing meant. Ruysch makes great con- fusion by his use of terms ; the corona ciliaris, or ciliary body, he calls the ligamentum ciliare ; and the the back surface of the iris, he calls processus ciliaris musculosus; or rather, he means by this, the straight fibres of the iris. J Duverney, with Ruysch and Winslow, fol- lowing Fallopius, calls the corona ciliaris also ligamentum ciliare. But the ciliary ligament is used by others in a widely different sense, viz. for the circular root of the ciliary body and iris, the annulum album cellulo- sum, or the frenula membranosa of Zinn. By Hovius, what I have called halo signatus is called ligamentum ciliare. In Haller’s fifth figure of the eye, this circular root of the ciliary processes is called orbiculus ciliaris. Maitre-jean, Haller, and others, call the whole body, or corona, the ciliary circle. M. Ferrein, “l’anneau de la choroide,” and M. Lieu- taud denominated the ciliary processes “ rayons ciliares,” and the root of the corona ciliaris and iris, “ plexus ciliaris.” OF THE IRIS. The ins is the coloured circle which surrounds the pupil, and which we see through the transparent cornea of the eye. It is a membrane hung before the crystalline lens.§ It is perforated in the middle ; and this * “ Neque mihi ullurn occurit nomen quod ipsi aptius indam quam tunicas : aut si voles, interstitii vel septi inter vitreum humorum et eum quem albugineum nuncupamus repositi.” Vesal. vol. i. p. 558. t Epist. Anat. xvii. 11. X Ruysch has this expression: “Ligamentum ciliare neutiquam esse considerandum tan- quarn musculum ad pupiilie et humoris crystallini motum destinatum, totumque Hoc nego- tium perfici a processu ciliavi ut et a circulo musculari posterius in confinio pupilla* si to.” Thes. Anat. ii. xv. See also the explanation of fig. iv. of this Thesaurus, where wo have “ Iris enim est facies exterior, processus lig. ciliaris facies interior. § Winslow and Haller, and most of the old anatomists, call this uvea ; by which they mean to imply that it is a part of the choroides. See Ophthalmograpbia, Authore G. Briggs, Cantab. 1676: but most of the modem anatomists follow Zinn and Lieutaud in calling-it 178 OF THE IRIS. h )\e in the middle of the iris is the pupil; and through the pupil only can the rays be transmitted to the bottom of the eye. When we hear of the dilatation and contraction of the pupil, it is an inaccuracy of lan- guage ; we have to understand the action of the iris, which, by possess- ing the power of contracting and relaxing, diminishes or enlarges the pupil, and so holds a controui over the quantity of light transmitted to the bottom of the eye. For by the extension of this membrane, the di- ameter of the pupil is diminished, and by contraction of the membrane it is enlarged. This motion of the iris, and, consequently, the size of the pupil, is connected with the sensation of the retina ; by which means, in disease of internal parts of the eye, it is often an index to us of the state of the nerve, and of the possibility of giving relief by ope- ration. The iris and corona ciliaris, or ciliary processes, are, in general, con- sidered, as being the two laminee of the choroid coat, continued forward and split; the internal lamina of the choroid forming the corona ciliaris, and the outer one forming the iris. The former I was willing to con- sider as the anterior margin of the choroid coat, because it has no dis- tinction in its structure from that coat; but the iris I cannot consider as the continued choroid coat; in the first place, because I have found it fall out a perfect circle by maceration; secondly, because it has no resemblance in structure to the choroid coat; and, chiefly, as by its power of contracting, it shows quite a dilferent character from any of the other membranes of the eye. The outer surface of this circular membrane gives the colour to the eye during life; and from its beautiful and variegated colours, it has gained to the whole membrane the name of iris. Haller and Zinn, nearly at the same time, explained the cause of this colour of the iris, which had been, till then, supposed to be occasioned by the refraction of the light amongst its stride and fibres. When this membrane is put in water, and examined with a microscope, its anterior surface is seen to be covered with minute villi. The splendid colouring of the iris pro- ceeds from the villi; but by beginning putrefaction, the splendid reflection fades, as the brilliant surface of the choroid of brutes is lost by keeping. For this reason, I imagine the colour and brilliancy of the iris to depend on the secretion of tiiese villi. But the colour of the iris depends, a great measure, on the black paint upon its posterior surface shining through it; and the black and hazel-coloured eye is owing to the great- er degree of transparency of the iris, which allows the dark uvea to shine through it. The iris is acknowledged to be the most acutely sensible part in the body. We have, then, to expect in its composition, muscular fibres, and to account for its acute irritability and sympathy, by a profusion of nerves : again, as the power of the muscular fibre, and the sensibility of the nerve, are both, in some measure, indebted to the circulation of the blood, we may expect to find also a profusion of vessels in the iris. In all these respects we shall find the iris to be an object of admiration. iris; though Lieutaud and others called the anterior surface only iris, while they still conti- nued to call this perforated membrane choroides, or uvea. See Lieut, p. 117. Again, others call the posterior surface of the iris uvea, from its likeness to the dark colour of a raisin ; and the word ins is borrowed, I suppose, from the varied colours of the rainbow on its ante- rior surface. OF THE IRIS. 179 OF THE MUSCULAR FIBRES OF THE IRIS. It is evident from a note, under the head corona ciliaris, that Ruysch had observed two sets of muscular fibres in the iris; for, under the name of ciliary ligament, he describes a set of radiated fibres which go from the ciliary processes towards the circular margin of the pupil: he ob- served, also, the circular or orbicular fibres which run round the margin of the pupil. Winslow says, that between the two laminse of the uvea (viz. iris) we find two thin planes of fibres, which appear to be fleshy: the fibres of one plane orbicular, and lying round the circumference of the pupil, and those of the other being radiated; one extremity of it being fixed to the orbicular plane, the other to the great edge of the uvea. Zinn describes, with much minuteness, radiated fibres (on the anterior surface of the iris), but does not consider these as muscular fibres; and he confesses, that he could not observe the orbicular mus- cle which Maitrejean and Ruysch had painted. Even in owls and other creatures having a strong iris, he could not discover an orbicular mus- cle ; nor were Haller and Morgagni more successful in this investiga- tion.* Wrisberg also affirms, that no muscular fibres could be seen in the iris of the ox. Dr. Monro, on the other hand, adheres to the opi- nion of the muscularity of the iris : he describes minutely both the radi- ated and sphincter fibres. Wrisberg and others have thought they found sufficient proof against the muscularity of the iris, in the fact of its not contracting when the light falls upon its surface. To this Dr. Monro answers, that the colour or paint upon the iris must, like a cuticle, prevent the light from irritating the iris. I cannot think that this circumstance should prevent the excitement of the iris. The reti- na is in a peculiar manner susceptible of the impression of light; but we cannot wonder that light should not stimulate a muscle to contrac- tion, when we have every proof that it has no effect on the most delicate expanded nerve of the other senses. That the iris is to be affected only through the sensation of the retina, communicated to the sensorium, we have sufficient proof. I have, in couching, repeatedly rubbed the side of the needle against the iris with- out exciting any motion in it: I have seen it pricked slightly by the nee- dle without its showing any sign of being irritated; nay, what was too a convincing proof, I have seen it cut by falling before the knife in ex- tracting the cataract. In this last instance, far from being stimulated to contraction, it hung relaxed.f It is evident, then, that no common stimulus, immediately applied to the iris, has any sensible effect in exciting it to contraction ; and that it is subject to be influenced, in a secondary way, by the degree of inten- sity of light admitted to the retina. The movement of the iris is in ge- neral involuntary; but terror and sudden fright affect it. In some ani- * See Zinn, p. 89. and 90. Morgagni Epist. Anat. xvii. { 4. Haller and Ferrein attribute the motion of the iris to an afflux of humours in its vessels. f This fact destroys the hypothesis of M. Mery, of the Royal Acad, of Sciences, that the straight fibres of the iris are little cavernous bodies, and that the action of the light upon the retina swelled and elongated them so as to cause the diminution of the size of the pupil: for by this cut, they must have fallen from their erected state, and contracted so as to hate dilat- ed the pupil. See Acad. Roy. de Sc. 1704, Mem. p. 261. 180 of the iris. mals, particularly in the parrot, it is a voluntary muscle.* As an ob- ject, upon which we look, approaches the eye, the pupil contracts, which is an effect of the increasing intensity of the light reflected from the ob- ject ; for, as the object advances, it fills a greater space in the sphere of vision, and of course more rays flow from it into the eye. Nerves of the ihis. —The iris is supplied with nerves in great pro- fusion. They are derived from the long ciliary nerves which run for- ward betwixt the cornea and choroid coat towards the common root of the corona ciliaris and the iris. They there divide, and are seen to pass in numerous branches into the substance of the iris. In the substance of the iris, the branches of the nerves, from their extreme minuteness, are soon lost amongst its pale fibres. Blood-vessels of the iris. — I have had preparations which showed so great a degree of vascularity in the iris, that I was ready to believe its action to be produced entirely by a vascular structure ; but when, on other occasions, my admiration was excited by the profusion of nerves, and I was led to observe that in the former instances they had been ob- scured by the injection, I could not but allow that the muscular fibres might have been obscured as the nerves were. There are four arteries sent to the iris : two long ciliary arteries which take a long course on the outside of the choroid coat, and two lesser and anterior arteries which pierce the ligamentum ciliare from without. These arteries approach the root of the iris at four opposite points, and branching widely form a vascular circle round tho root of the iris, viz. the larger circle of the iris. From this circle branches pass otF, which run with a serpentine course, converging to the edge of the iris : here they again throw out inosculating branches, which form a circle sur- rounding the pupil, but at some little distance from the edge of the iris —this is the lesser circle of the iris. From this lesser circle there again proceed minute branches towards the edge of the iris, t The vein's, which intermingle their branches with these arteries, pass some of them into the vasa vorticosa of the choroid coat, and others take a long course betwixt the choroid and sclerotic coat, accompany- ing the ciliary nerves, whilst some branches pierce the sclerotic coat at the root of the iris, and become superficial upon the fore part of the eye. It was at one time believed, on the authority of many excellent ana- tomists, that the vessels of the iris were colourless, and did not circulate red blood ; after what has been said, it is scarcely necessary to notice the fallacy of this opinion. \ I have seen the iris cut and bleeding, though not profusely as I expected ; the small quantity of blood soon coagulated into a dark speck, while I expected it should have been effus- ed in the aqueous humour. ■* 'When a cat'is revised to attention, as by the scratching of a mouse, it dilates the pupil, Which allows a stronger impression on the bottom of the eye; nay, whenever puss struggles violently to get loose, the pupil dilates, which may sufficiently account for M- Mery’s cat hav- ing her pupil dilated, when he plunged her under the water. See Acad. Hoy. des Sc. 1704, 361 • f See Ruysch. Epist. Anat. Prob. xiii. p. 31. 4 Dr, Monro, in treating of this subject, mentions his having seen a net-work of vessels co- iVts'ii with paint darker than that of the iris, and extended from the iris upon the surface of ’Jibelens; and, in another instance, a net-work of filaments passing quite across the pupil, feis Dissertations, p. 108 OF THE RETINA. 181 OF THE RETINA, AND DIGRESSION CONCERNING THE SEAT OF VISION. The term retina has, in a modern publication, been objected to, as improperly applied to the inner coat of the eye. Such a term, it has been said, may well be applied to the nerve expanded on the lamina spi- ralis of the cochlea, because it is there formed into an intricate plexus by innumerable joinings and separations of its component parts ; but used for the expanded nerve of the eye, the term retina is thought improper.* We must look for the resemblance, however, which justifies this term, not in the medullary matter of the nerve, but in its vessels. “ Hanc “ figuram egregie reprsesentat dicta tunica retina cum arteriolae ceracea “ materia sunt repletae.” f The retina is the expansion of the optic nerve ; the immediate seat of sensation, and the most internal of those membranes which are called the coats of the eye. It has been already observed, that there is a dis- tinction betwixt a nerve in its course from the brain to the organ of sense, and where it is actually expanded and adapted to the reception of the external impression. Before the optic nerve has perforated the scle- rotic coat of the eye, it is surrounded with a firm sheath ; and its sub- stance is evidently composed of bundles of fibres, though not so coarse, yet like those of the nerves in the other parts of the body. The opaci- ty of the nerve makes it have little the appearance of vascularity, but when the body of the nerve is made transparent, it becomes like a red cord ; so necessary is it that the medullary substance of the nerve be supplied with blood. The stronger sheath which surrounds the body of the optic nerve is loose, and may be separated into lamellae. There is a more delicate membrane which immediately adheres to the surface of the nerve ; and its substance is formed into the minute fasciculi which give it the fibrous appearance by a still firmer intertexture of membrane. This interwo- ven membrane proceeds, with the retina, into the eye ; the other sheaths are reflected off, and unite with the sclerotic coat. Some little way from the back part of the eye, the arteria centralis retinae pierces the sheath of the nerve, plunges into the centre, and passes into the eye along with it. If the optic nerve be cut near to the eye, the open mouth of this small artery may be seen ; but if we make our section some way re- moved from the back of the eye, it will, of course, not be seen. The space left by the artery contracting in the centre of the nerve when thus cut, (or perhaps it was the open mouth of the artery itself,) was observed by the ancients, and by them called the porus opticus ; they were ignorant of this central artery of the retina. J Where the optic nerve is about to enter into the ball of the eye, it is * Dr. Monro’s 4(0. Treatises. t Ruysch. Epist. Anat. xiii. p. 14. Quamobrem servare adhuc retinue, appeilationern si non ex fibrarum ul eerie ex vasorutn implicatione, &c. Morgagni Epist. Anat. xvii. { 43. | Porum opticurn Hierophilus et omnis at> ea antiquitas dixit, foramen nempe quod in dis- secto nervo tie vacua arteria superest. Hall. Arter. Ocul. Hist. p. 42. De Vasis Nervi Op- tiei vide Ruysch. Epist. Anat. xiii. tab. xvL Albinus Acad. Anat. lib. vii. c. vii. 182 OF THE RETINA. much diminished in diameter ; it is contracted and condensed, and, at the same time, lays aside the strong coats. The proper nerve then per- forates a cribriform lamina in the sclerotic coat. Within the eye, the filaments seen in the nerve are no longer distinguishable ; but from the extremity of the nerve the fine web of the retina is produced. The lamina cribrosa, and the delicate fasciculi of the optic nerve, are shown in this manner : after making a section of the eye, wash away the retina from the extremity of the optic nerve, and also the cho- roid coat; then press the optic nerve betwixt the finger and thumb, when the pulp of the nerve will be seen to protrude through the forami- na in the sclerotic coat like white points. It is observed by Zinn, that, in doing this, there is a central foramen which remains unfilled up by the compression of the nerve. This is the hole perforated by the arteria centralis retime. * Where the threads of nerves are accumulated af- ter passing these foramina, and before they are finally expanded into the retina, they necessarily form a small cone or papilla. This conical form of the extremity of the optic nerve is much more evident in some ani- mals than in others ; but in a section of the human optic nerve we may also observe it. "j* The retina is a membrane of the most delicate texture of any in the animal body : it is transparent in the recent state, and so soft, that it will tear with its own weight. In spirits and weak acids, it becomes opaque and firmer. It lies expanded over the vitreous humour, and con- tiguous, but not adhering to the choroid coat, or its pigment. The re- tina does not consist merely of the expanded nervous matter, but has in its composition two very fine membranes, and many minute vessels. This part of my subject brings me to the beautiful discovery of Dr. Ja- cob of Dublin, of a new membrane or layer of this coat of the eye. If the sclerotic and choroid coats of the eye be dissected off a recent eye, and the retina disclosed, and especially if this be done under water, a fine film may be seen to rise and float from the outer surface of the retina. The pulp or proper nervous matter of the retina is retained be- tween the two membranes, the tunica vasculosa retinae on the inside, and the newly discovered membrane on the outer surface. Zinn, it may be perceived from the note below, had no idea of such a separation being- possible. When the retina is macerated for a considerable time, the pulp of the nerve can be washed away, and there remains only the re- ticulated and delicate membrane which supports the vessels that nourish it. But though the pulp of the nerve may be dissolved, it cannot, by dissection, be freed from the membranes which support it oil the inside. J I have a preparation which more resembles some of Ruysch’s plates than any I have seen; in it, the nerve being washed away, we may see * Zinn de oculo humano, p. 106. Coin. Reg. Soc. Sclent. Gotting. loc. cit. About thirty foramina have been observed in the lamina cribrosa. See Haller Fasc. de Arter. Oculi, p. 42. f Zinn. “ At the place which answers to the insertion of the optic nerve, we observe a small depression, in which lies a sort of medullary button terminating in a point.” Wins- low, p. 78. | “ Posse vere medullarem retinae laminam removeri ut vasculosum rete membranae figu- ram retineat, alterainque ab altera integram detrahi ultra hominum artem positum esse vide- tur nec ulli unquam contigisse legere me memini, etsi, deleta macerendo medulla, rete vas- culosum laminam peculiarem referre videatur. Ex quibus omnibus elicio retinam esse tu- nicam simplicem, ex cellulosa conflatam: que vascula et substantiam medullarem sustinet etsi duas diversas ostendat facies alteram vasculosam interiorem, alteram medullarem ex- teriorem.” Zinn, p. 112. OF THE RETINA. 183 distinctly the whole course of the arteria centralis retinae. Of this pre- paration I have given an engraving, to show how plentifully this organ is supplied with red blood ; from which circumstance we may learn the strict dependence of its function on the circulation, and sometimes we may deduce the derangement of the powers of vision as a consequence of the disordered action of these vessels. The outer membrane of the retina is transparent, but the proper mat- ter of the nerve is opaque in the dead subject, and the opacity of the nervous matter prevents the vessels of this coat being seen when we look upon the outer surface * for the vessels of the retina run upon the surface contiguous to the vitreous humour.! The arteria centralis reti- nae is derived from the ophthalmic artery. It pierces the optic nerve, as we have already observed, and enters the eye through the porus opti- cus, to supply the retina. But the arteries of the retina do not always enter into the eye in one trunk; on the contrary, sometimes two or three branches pierce the lamina cribrosa,J and afterwards, two, three, or four principal branches, spread out on the circumference of the retina; from these, the ramifications are so numerous, that Ruysch describes them as constituting the membrane. § Corresponding with the arteria centralis retinae in the adult, there are veins, the minute extremities of which, after forming connexions with the veins of the corona ciliaris, run back- wards on the inner surface of the retina in three or four distinct branches. These uniting into a trunk, perforate the lamina cribrosa, and become the sociae arteriae centralis. Many have been led to believe, that the retina terminates forward on the roots of the ciliary processes ; others have conceived it to be con- tinued over the fore part of the vitreous humour, and over the surface of the lens.|| The most prevalent opinion is, that it terminates on the mar- gin of the lens. Correctly speaking, there is no termination to a proper membrane : I know no instance of it. That the retina, considered as the organ of sense, extends over the back of the lens, and receives there the impression of light, is very improbable; but that the membrane which supports the nervous matter, is continued over the lens, is demon- strable. I have said above, that the retina consists of two distinct parts, viz. the medulla of the nerve, and pellucid membranes supporting it. It * “ C’est sur-tout dans les poissons qu’il est facile do distinguer et meme de separer ces deux lames.” Cuvier, tom. ii. p. 419. The opacity of the outer surface of the retina prevents the vascularity from being appa- rent. Albinus, after a very minute injection, observed that when he lifted up the choroid coat, the vascularity of the retina was not seen: “ Autem de ea aliquid acuto scalpello subtilliter levissirneque deradens, mox conspicio vasa iinpleta tnulta qu;e sub medulla cujus nirnirum portionem deraseram latuerant.” Aibin. An. Acad. lib. iii. cap xiv. + Dr. Monro has these vvords, expressive of an opposite opinion : ‘ The whole appears to be composed of an uniform pulpy matter, on the outer side of which chiefly vessels arc dispersed, supported, I suppose, by a membrane the same or analogous to the pia mater.” 4to. Treatises on the Eye, Ear, Sic. } Haller loc. cit. Morgagni Ep. Anat. xvii. n. 44., nor do they always pierce the centre of the nerve exactly. Morgagni. } “ Iteratis perscrutiniis reperio oculis arraatis arteriolarum extrema tarn esse numerosa et tarn arete sibi invicem et intricate annexa ut peculiarem representent membranulam ex arteriolarum extremis constitutam, cui connectetur dicta medullosa substantia.” Ruysch. Epist. Anat. xiii. p. 15. || Many anatomists, Winslow, Cassobohm, Ferrein, Lieutaud, and Haller, have taught that the retina extends over the great convexity of the lens, or that it is inserted into it. Galen believed it to extend over the lens. For an impartial history of opinions, see Morgagni Epist. Anat. xvii. 47. and Zinn, 114. 184 Ul’ THE RETINA. is by most anatomists believed, that the retina passes forward betwixt the vitreous humour and corona ciliaris, and adheres to the margin of the lens. Now, as this adhesion is not a gluing together of parts, but a union or intermixture of membranous filaments, the interchange and mingling of fibres, wc may safely say, that the membsane of the retina is continu- ed over the lens, and forms part of its capsule. The opacity of the re- tina is diminished at the root of the ciliary processes, and disappears al- together at the margin of the lens; and here it is not only changed by becoming perfectly transparent and allied to the membranes of the hu- mours, but it becomes also distinguishable from the opaque retina by a greater toughness and strengtii. The continuity of the retina with the capsule of the lens is more apparent, when both membranes have be- come opaque by being immersed in spirits or vinegar, but more particu- larly when that opacity is produced by disease. In disease, I have found the veins of the retina runn.ng over the margin of the lens, and branching on its posterior convexity. THE FORAMEN OF SOEMMERRING. When a student in Edinburgh, I found, on dissecting a recent human eye, a yellow spot on the retina of an irregular figure- I noticed that it was opposite the pupil, and conceived it to be a disease of this part of the nerve. I preserved the preparation carefully. When the discovery of Soemmerring was made known to me I found my mistake, and that this curious spot was a natural appearance.* Soemmerring describes the appearance as a foramen, surrounded with a yellow edge. But it is not a foramen: the pellucid membranes are not perforated; the ap- pearance is a consequence of the imperfect opacity of a point in the centre of the yellow spot. He describes, too, a fold, which hangs over the hole, and tends to conceal it. In my preparations, the foramen is on the prominence of this fold. The existence of this fold in the liv- ing eye has been disputed. Blumenbach thinks he has a use for this hole. He supposes that it expands and contracts; but how this is “ to prevent the inconvenience of too intense a light,” I cannot, as yet, com- prehend. I Where the retina lies betwixt the vitreous humour and the ciliary pro- cesses, it is plaited, and descends into the interstices of these processes. When we take oft' the sclerotic and choroid coats of the eye, by dis- secting them round the insertion of the optic nerve, and fold them back, carefully preserving the retina ; and when we have taken away the cilia- ry processes from their adhesion to the fore part of the retina, we find * Soemmerring De foramine ceutrali limbo luteo cincto retiuae humane;.—Comment. Soc. Reg. Scien. Gotting. f The foramen of Soemmerring, or foramen centrale retina:, was discovered by Baron Soemmerring in the human e\e about the } ear 1795. He described at the same time a yel- lowish margin, partly surrounding it, and a fold of the retina close to it. The structure was at first supposed peculiar to man, but was soon after shewn by Cuvier and Michaelis to be present in the Quadrumana: it has since been discovered by Dr. Knox to be present in the Cameleon, and in certain species of the lizard, as the Lacerta superciiiosa, &c. The fora- men is larger in the Cameleon than in man; it occupies the same relative situation with re- gard to the entrance of the optic nerve, and is exactly in the line of vision. The margin is not yellow. Dr. K. affirms, that the fold generally described in the human retina is a post mortem appearance. See his papers in the Transactions of the Royal Society of Dublin, and of the Wernerian Society of Edinburgh, and the preparations which he has added to my Mu- seum. OF THE RETINA. 185 the retina to form a sac surrounding the vitreous humour, and attached to the lens. In all this surface, the membrane is smooth and uninter- rupted, and up to the margin of the lens all this sac is opaque ; because the nervous matter contained betwixt the membranes is opaque, but the coats of the lens are transparent, yet continuous with the arachnoid por- tion of the retina. When these parts of the eye are thus dissected, they hang all together by the optic nerve ; viz. the lens, the vitreous hu- mour, and the expanded matter of the nerve, and the organ is divested only of its outer apparatus ; we still retain within this sac the more es- sential and important parts. There is here a natural division ; and I am willing to pause upon this, knowing well with how much difficulty the student gains a knowledge of the minute structure of the eye. All within the connexions of the reti- na I shall call the internal globe of the eye, as distinguishing it from the outward coats of the eye and parts subservient to them. A view of the little vascular system of these internal parts, thus classed, will show how strictly they are connected together, and how much insulated from the other parts. But this is a subject upon which we cannot enter until we have consi- dered the nature and relative situation of the humours of the eye. DIGRESSION ON THE SEAT OF VISION. M. 1’ Abbe Marriotte discovered the curious fact, that when the rays fall upon the centre of the optic nerve, they give no sensation. He de- scribes his experiment in this manner :— “ Having often observed, in dissections of men as well as of brutes, that the optic nerve does never answer just to the middle of the bottom of the eye ; that is, to the place where the picture of the object we look directly upon is made ; and that in man, it is somewhat higher, and on the side towards the nose ; to make, therefore, the rays of an object to fall upon the optic nerve of my eye, and to find the consequence thereof, I made this experiment. I fastened on an obscure wall, about the height of my eye, a small round paper, to serve me for a fixed point of vision ; I fastened such another on the side thereof towards my right hand, at the distance of about two feet, but somewhat lower than the first, to the end that I might strike the optic nerve of my right eye while I kept my left shut. Then I placed myself over against the first paper, and drew back by little and little, keeping my right eye fixed and very steady upon the same, and being about ten feet distant, the second paper totally disappeared.” * This defect in the vision of the one eye is corrected by that of the other ; for the insertion of the optic nerves being towards the side next the nose, no part of an image can ever fall on the optic nerve of both eyes at once; the defect of vision, therefore, is observed only in very careful experiments. Experiments were, however, made by M. Picard, Marriotte, and Le Cat, to render this effect produced by the image falling on the centre of the optic nerve evident, when looking with both eyes. Marriotte’s second experiment was this ; Place two round pieces of paper at the height of your eyes, three feet from one another, then place your- self opposite to them at the distance of 12 or 13 feet, and hold your thumb * Vide Phil, Trans. No. 35. Smith’s Optics, Remarks on art, 87. 186 OF THE RETlkA. before your eyes at the distance of about eight inches, so that it may conceal from the right eye the paper that is to the left hand, and from the left eye the paper to the right hand. If now, you look at your thumb steadily with both eyes, you will lose sight of both the papers.* The novelty of such a discovery was likely, as frequently is the case, to carry men’s minds beyond the true point. It requires time for such facts to descend to their level, in the scale of importance, with other less novel observations. Marriotte, upon this fact, formed a new hypothesis relat- ing to the seat of vision. We have observed, that the choroid coat and pigmentum nigrum are deficient, where the optic nerve enters the eye, and is about to expand into the retina. He fixed upon the most unac- countable supposition, that the retina does not receive the impression of the rays, but that the choroid coat is the seat of the sense. In support of this theory, he soon found other arguments than those arising from the deficiency of the choroid coat at the entrance of the nerve. He saw that the pupil dilated in the shade, and contracted in a more intense light: now, says he, as the iris is a continuation of the choroid coat, this is a proof of the great sensibility of that coat: again, the dark colour of the choroid coat he supposed to be well calculated for the action of the rays of light, which are not reflected from it or transmitted, but absorbed ; while, on the other hand, the retina is transparent. If vision were per- formed in the retina, says Marriotte, it seems that it should be found wherever the retina is ; and since the retina covers the whole nerve as well as the rest of the bottom of the eye, there appears no reason why there should be no vision in the place of the optic nerve. M. Picquet ar- gued in opposition to Marriotte. He observed in regard to the fitness of the black colour of the choroides for the action of the rays of light, that the choroid is not universally black; that there are many shades of dif- ference in the human eye; and that it is black, blue, green, yellow, or of a metallic shining surface, in a variety of animals. He conceived that the defect of vision at the insertion of the nerve is occasioned by the blood-vessels of the retina, t He observed, also, that the opacity of the retina is such, as necessarily to obstruct the transmission of the rays of light to the choroid coat. M. de la Hire took part in this controversy. He considered the retina as the organ of sight, although a particular point of it is not susceptible of immediate impressions from outward ob- jects ; for, says he, we must not conceive sensation to be conveyed by any other means than by the nerves. But, observing the constitution of the other organ of the senses, he entertained an idea that the retina re- ceives the impression in a secondary way, and through the choroides, as an intermediate organ ; that, by the light striking the choroid coat, it is agitated, and communicates the motion to the retina ; and we find that through all the organs of the senses, he continues, the nerves are too delicate to be immediately exposed to the naked impressions of external bodies. * Dr. Smith made the stream of light through the key hole of a dark chamber fall upon th's point of the retina, opposite to the termination of the optic nerve, but he found it quite insen- sible even to this degree of light. M Picquet asserts, thatv cry luminous objects make a faint impression on the centre of the optic nerve. But Dr. Priestley says, that a candle makes no impression on that part of his eye. f Against this hypothesis, the size of the insensible spot was urged by Marriotfe. Bernoulli calculated that this spot is a circle, the •diameter of which is a seventh part of the diameter •of the eye, and that the centre is twenty-seven parts of its diameter from the point opposite 'So the pupil, and a little above the middle. OF THE RETINA. 187 Another objection to the opinion, that the retina is the seat of sensa- tion, has been lately urged, viz. that the thickness of this coat, together with its transparency, allows of no particular surface for receiving the image ; and that its transparency would cause a partial dispersion, which would produce a confusion in vision.* If these opinions require serious refutation, we have it in the effects of the diseases of the retina, optic nerve, and brain. But the thalami nervorum, the optic nerve, and its expansion into the retina, seem scarce- ly to have ever occurred to these speculators, as worthy of notice in this investigation. The following appears to me the true account of this matter. The outer or posterior surface of the retina (being that which is towards the newly discovered membrane) is the proper seat of vision. That it must be a surface on which the object is represented, is evident from the con- sideration of the extreme minuteness of the objects painted there. Now it is to be considered that at the point where the optic nerve comes through the coats of the eye, there is no posterior surface peculiarly adapted to receive the impression of light; and as well might we expect the optic nerve to be sensible to the impression of light in any point of its extent from the brain to the eye, as at this; for here the inner sur- face of the retina only is formed; there is no posterior surface upon which the rays can impinge. The doubts regarding the cause of this spot giving no sensation, have arisen from the idea, that the internal surface of the retina, or its substance, felt the impression of the rays of light. At the same time it is evident, that the choroid coat, and its secretion is in a most remarkable manner subservient to the retina, as the instru- ment of vision : for, when the secretion is black, it absorbs the rays ; and animals which have such a pigmentum nigrum, see best during the full day; again, when the surface is of a shilling nature, it repels the rays, and this contributes to strengthen the sensation; and such animals are fitter for seeing in obscure light; nay, further, if the surface of the choroid be coloured, the animal will see objects of that colour the best, because the colour of the choroid depends upon its reflecting more of the coloured ray, than of the others of which light is composed. But as animals see which have no paint on the choroid, neither such as wifl absorb, nor such as will strongly reflect the rays, and which have merely the surface of the choroid with its coloured blood-vessels in contact with the retina; so it is evident, that it is not the deficiency of the choroid coat, nor the want of the black paint at the entrance of the optic nerve, which prevents the sensation, but really, that there is here no surface formed and organized to receive the impression of the light; the internal surface not being the sensible surface of the retina. * M. Le Cat thought the pia mater was the sentient part of the nerve. It was, there- fore, a kind of confirmation of his opinion to suppose the choroid to be the seat of vision, as he teaches that (he choroid coat is a production of the pia mater. He conceived (hat the retina moderated the impression of light upon the choroid coat, as the cuticle dulls the im- pression on the papillse of the tongue. 188 OF THE RETINA. FURTHER OBSERVATIONS ON THE RETINA. It has already been observed, that vision is the combined operation of the external organ, nerve, and brain; consequently, the destruction of the function may be produced by disease of the retina, of the optic nerve, or of the brain. Any partial injury, pressure, electricity, or gal- vanism, influencing the retina, will cause the sensation of light or fire be- fore the eye.* Because here, or in its corresponding part of the brain, is the organ of vision ; and no idea but of light is this organ capable of exciting in the mind. Disease in the retina, nerve, or corresponding part of the brain, causing total blindness, while the cornea and humours of the eye remain pellucid, is called amaurosis. It is, in general, to be considered as a paralytic affection. Amaurosis f has been found to fol- low strokes on the head; concussion and compression of the brain; blood effused within the skull; or tumours pressing on the nerve or brain. J An amaurosis spasmodica has been enumerated by authors. This kind of blindness has been supposed to arise in consequence of the stricture of the optic nerve by the origins of the recti muscles; as far as I have observed, no action of these muscles can affect the optic nerve before it perforates the coats of the eye. If it were to be attri- buted to the operation of these muscles, I should rather suppose it to be occasioned by their spasmodic action on the ball of the eye, by which the function of the retina may be disordered ; but I think it is more pro- bable that the same irritation which is acting on the motory nerves of the eye, does, in this instance, affect also the optic nerve and retina. However, distention of the coats of the eye, by increased secretion of the humours, destroys the sensibility of the retina. In the hydrophthal- mia, there is in the beginning a short-sightedness, so that objects are seen only when near the eye. Thus far we might account for the defect of vision by the alteration of the focus of the cornea and hu- mours ; but by and by, as the eye enlarges, as it becomes turgid, and the coats more distended, the pupil becomes stationary, and the vision is lost before the aqueous humour has become turbid. § * Light from pressure on the eye. See Cartesius, cap. ix. lib. de Meteor, and the Oph- thalmographia of Briggs, coruea. + Amaurosis ; gutta serena ; cataract a nigra ; which last name is from the blackness of the, pupil in consequence of the transparency of the lens. | “ Ipse vidi bis in pueruiis scrophulosis amau rosin, etiam subito ingruentem ; secto cada- vere inveni glandulam strumosatn nervis opticis incumbentem.” Sauvages Nosol. From many observations we find that tumours and extravasations, which must compress gradually, do yet produce an instantaneous effect. In Bonetus*, we have many cases of blindness from abscess in the anterior part of the brain; from fluid on the surface, and in the ventricles ; from steatomatous tumours ; from coagulum of blood, and from a hydatid pressing on the union of the optic nerves; and lastly, from a calculus in the optic nerve. For a case of blindness from pressure upon the eye and its displacement, and consequent elongation of the optic nerve, by an encysted tumour in the orbit, with gradual recovery after operations, See Med. Ob. and Enquir, vol. iv. p. 371. J To complete such a case, we may further observ e, that there is now an accession of pain, a tension over the forehead and pericranium, and there is sometimes accompanying it a swelling and insensibility of the side of the face. So luxation or displacement of the eye by tumours, causes blindness, by extending the optic nerve or compressing the eye-ball and consequently the retina. * Pe Oc ul. A flee(ibus, Ob. 2. OF THE RETINA. 189 The connexion and sympathy betwixt the retina and the viscera of the abdomen is very particular. We have proofs of this in the disorder of the stomach having an immediate effect on the sensibility of the re- tina. A very particular effect of this kind is the temporary loss of vision in one half of the field. This I have often experienced for a short time. Dr. Wollaston has founded some observations on the same ex- perience. On looking to the name on a door, he could see only one half of it. Allied to this, but greater in degree, is the amaurosis which attacks hysterical women suddenly, with head-ache and violent pain. From such sympathy of parts arise the amaurosis biliosa, verminosa, in- termittens, arthritica, &c. Similar attacks of blindness have been found to alternate with convulsions.* Commencing cataracts and opacities of the cornea, and of the hu- mours in general, give occasion to spots and obscurities in the vision ; but we have at present to consider those only which depend on the state of the nerve. Errors of vision are not easily to be distinguished from those of the imagination proceeding from the brain; Error opti- cus, or hallucinatio, from delirium : one distinction of the former is, that we can correct the deception by the assistance of the other senses, while, in the latter, the mind is disturbed. Old people are often troubled with the appearance of dark irregular spots flying before their eyes. In fever also, it is very common to see the patient picking the bed-cloaths, or catching at the empty air. This proceeds from an appearance of motes or flies passing before the eyes, and is occasioned by an affection of the retina, producing in it a sensa- tion similar to that produced by the impression of images ; and what is deficient in the sensation, the imagination supplies ; for, although the resemblance betwixt those diseased affections of the retina and the idea conveyed to the brain may be very remote, yet, by that slight resem- blance, the idea, usually associated with the sensation, will be excited in the mind. M. de la Hire attributed the fixed spots to drops of extravasated blood on the retina, and the flying ones, to motes in the aqueous hu- mours f ; but we shall show presently, that this apparent motion of the motes before the eyes may be a deception. After turning round upon the heel for some time, objects apparently continue in motion. Dr. Por- terfield supposed this to proceed from a mistake with respect to the eye, which, though it be at rest, we conceive to move the contrary way to that in which it moved before; from which mistake, with respect to the motion of the eye, the objects at rest will appear to move the same way the objects are imagined to move, and, consequently, will seem to conti- * The following is an ingenious account of the manner in which this may be produced, though to me it is not satisfactory : —“ Non infrequens caecilas post couvulsiones graves et irequentes, sed a nemine quod sciam recte descripta causa; hanc non ah humoris affluxu de- duce, ut voluerunt, sed quia in magnis illis per paroxysinas convulsionum partium omnium, et oculorum simul contortionibus in quibus ssepe quoque convulsi, admodumque exerti et inflexi apparent, attracto sic nimium et tenso nervo optico, illis adnatoilloque simul contorto et lasso, spiritusque visorii transitu iinpedito, oculos visione privari contingit, atque inde provenire di- ligente examine et consideratione invenimus.” Platerus Prax. lib. i. c. 7. f Guttula cruoris retinae insidens et nigricans, omnem lucem intercipiet unde phantasma obscurum vel nigrum ; reruin si dilutus cruor radios rubros transmittat tunc maculam rubrarrt videbit aeger ut omnia trans vitruru inspecta rubra sunt.” Sauvage, vol. iv. p. 287. 190 OF THE RETINA. nue their motion for some time after the eye is at rest. How superior is simple experiment to the most ingenious speculation ! Dr. Porterfield is presuming in all this, that the eye is at rest when the body is stationa- ry, after turning round rapidly on one foot. But the fact is, that the eyes continue in motion after the body is at rest, but owing to a disorder in the system of sensation we are not sensible of it. Dr. Wells, in making an experiment, in which it was necessary to look upon a luminous body, was seized with giddiness, and he found, that the spot on the retina, af- fected by the great excitement of the luminous body, did not remain sta- tionary, but, when made apparent by looking upon the wall or any plane, was moved in a manner altogether different from what he conceived to be the direction of his eyes. In making the experiment after looking some time at a candle, and then turning himself round till he became giddy, he afterwards directed his eyes to the middle of a sheet of paper, he saw the dark spot (caused by the former brilliancy of the candle on the retina) take a course over the paper, although he conceived that the position of his eyes remained stationary. He then directed a person to repeat this experiment, and then bade him look stedfastly to him, and keep his eyes fixed ; but instead of being stationary, they were seen to move in the socket; though, of this the person himself was quite insen- sible. * From these experiments, we may conclude, that spots which seem to move before the eyes are not, on that account, solely to be attributed to opacity of the humours or cornea, since the appearance of motion may be given to those motes, though occasioned by an affection of the nerve ; especially, if the unusual sensation be attended with giddiness. Giddi- ness, however, is not necessary to such sensation ; when my eyes are fatigued, and, sitting in my room, I look towards the window, I see be- fore me small lucid circles which seem to descend in quick succession ; upon attending more particularly to my eyes, I find them in perpetual motion ; my eye is turned gradually downward, which gives to the spec- trum the appearance of descending ; but it regains its former elevation with quick and imperceptible motion. During the slow inclination of the eye downward, the motes or little rings seem to descend ; but in lifting the eye again, the motion is so quick, that they are not perceived, f There is a kind of umbra seen before the eyes which are occasioned by the vessels of the retina. Of this kind is the suffusio reticularis of Sauvages, in which the person sees ramifications which strike across the sphere of vision and are synchronous with the pulse, showing its de- pendence on the full and throbbing pulsation of the head. There are also corruscations seen before the eyes in consequence of a blow upon the eye-ball, and accompanying violent head-ache, vertigo, phrenitis, epilepsy, &c. Whatever forces the blood with great violence to the head, as coughing, vomiting, sneezing, will cause, for the instant, such corruscations, by means of the disturbed circulation through the retina. J * The author has pursued this subject further, both in a succeeding part of the volume, and in the Pi,il. Transac. for 1823. f Sauvages. This appearance has been attempted to be explained upon the supposition of a very sensible state of the retina, which perceives the gutulif* exuding from the pores of the cornea, and which, falling over its surface, gives the appearance of their descending. But it is only felt when the retina is exhausted or disturbed by pressure on the eye-ball. See Sau- vages Sufi'usioScir.tillans et Suff. Dana^s. | This was my opinion, as well as that of other physiologists ; but I have proved it to be incorrect. The effect contemplated proceeds from the sudden action of the muscles of the evelids. OF THE RETINA. 191 We arc particularly called upon to attend to the connexion betwixt the iris and the retina. In amaurosis, the sensibility of the retina being entirely lost, the pupil is consequently immovable and dilated.* But we must recollect, that if one eye be sound, the pupil of the diseased eye follows, in some degree, the movement of the iris of the sound eye. If one eye be shut, the pupil of the other eye will dilate ; if the hand be put over the eye-lids of the shut eye, the pupil will still further dilate.'}' We find several instances of vision indistinct during full day-light, and perfect in the crepusculum. This we have explained by the dilata- tion of the pupil allowing the rays of light to pass the partial opacity of the lens ; it, of course, has no connexion with the disease of the retina. There are also instances of vision being more than naturally obscure in the twilight, which is owing to a degree of insensibility. J The night blindness, however, is not to be entirely attributed to a degree of con- tinued insensibility in the nerve. The attacks are irregular, and allied to the intermitting amaurosis. It has been epidemic, and the following cases seem to ally it with the paralytic affections § A man, about thirty years old, had, in the spring, a tertian fever, for which he took too small a quantity of bark, so that the returns of it were weakened without being entirely removed; he therefore went into the cold bath, and after bathing twice, he felt no more of his fever.— Three days after his last fit, being then employed on board of a ship in the river, he observed, at sun-setting, that all objects began to look blue, which blueness gradually thickened into a cloud, and not long after he became so blind as hardly to perceive the light of a candle. The next morning, about sun-rise, his sight was restored as perfectly as ever. When the next night came on, he lost his sight again in the same manner; and this continued for twelve days and nights. He then came ashore, where the disorder of his eyes gradually abated, and in three days was entirely gone. A month after he went on board of another ship, and after three days’ stay in it the night blindness returned as before, and lasted all the time of his remaining in the ship, which was nine nights. He then left the ship, and his blindness did not return while he was upon land. Some little time afterwards, he went into another ship, in which he continued ten days, during which time the blindness returned only two nights, and never afterwards. In the August following, he complained of loss of appetitite, weakness, shortness of breath, and a cough; he fell away very fast, had frequent shiverings, pains in his loins, dysury and vomitings ; all which complaints * There are, however, cases of Amaurosis a myOsI, in which tnere is a contracted and im- movable pupil, and children are born with an insensibility of the organ in which the pupil is not greatly dilated. I would be willing to attribute the peculiarity of the pupil anti appa- rent amaurosis in newly born children 10 the remains of the tnembrana pupiliaris. f The sympathy of the iris with the retina I do not conceive to be immediate, but through the intervention of the brain; and the degree of dilatation to the pupil, I should hold to depend on the strength of the common sensation of both eyes. By this only can we account for the sensibility of the retina of one eve affecting the iris of the other, or the disturbance of the brain, in comatose diseases, destroying the sympathetic connexion betwixt the retina and pupil. } Estimmanis differentia inter splendorem et activitatem luminis candelas et lunae : lumi- nis Solaris vis est ad vim luminis candelse 16 pedis distantis, observante D. Bonguer ut 11664 ad 1; et ad lumen lunae in pleni lunio, ut 374,000 ad 1 demonstrante D. Euler Mem. de 1’Acad. de Berlin, an. 1750, pag. 299. non mirum itaque si vis toties major sufficeret ad succutiendam retinam quam tanto minor non afficiebat. Sauvages Amblyopia Crepuscularia. $ By Dr. Heberden. 192 OP THE RETINA. increased upon him till the middle of November, when he died. He had formerly been employed in lead-works, and had twice lost the use of his hands, as is usual among the workers in this metal. See Medical Trans- actions, published by the college of Physicians in London, vol. i. p. 60. Pye*, servant to a miller, at the 6th mill on the Limehouse wall, about forty years of age, came to me October 2d, 1754, for advice and assistance. He told me, that about two months ago, while he was em- ployed in mending some sacks, near the setting of the sun, he was sud- denly deprived of the use of his limbs and of his sight. At the time he was attacked with this extraordinary disease, he was not only free from any pain in his head or his limbs, but on the contrary, had a sensation of ease and pleasure ; he was, as he expressed himself, as if in a pleasing dose ; but perfectly sensible. He was immediately carried to bed, and watched till midnight; at which time he desired those who attended him to leave him, because he was neither sick nor in pain. He continued the whole night totally blind, and without a wink of sleep. When the day light of the next morning appeared, his sight returned to him gradually as the light of the sun increased, till it became as per- fect as ever ; when he rose from bed, his limbs were restored to their usual strength and usefulness, and himself in perfect health. But on the evening of the same day, about the setting of the sun, he began to see but obscurely, and his sight gradually departed from him, and he became as blind as on the preceding night; though his limbs con- tinued as well as in perfect health ; nor had he from the first night, any complaint from that quarter. The next day, with the rising sun, his sight returned ; and this has been the almost constant course of his disease for two months past. From the second night, the symptoms preceding the darkness were a slight pain over the eyes, and a noise in his head, which he compared to a squashing of water in his ears. After near two months continuance of the disease, on September the 29th, the patient was able to see all night ; on the 30th September, Oc- tober 1 and 2, he was again blind all night ; on the 3d, he was able to see ; on the 4th, he was blind till 12 ; on the 5th, was blind. From this he had no return of his complaint till June 1755 ; from which time till the 3d of October, when I again saw him, he had three or four attacks; from the 3d till the 10th, he had an attack every evening.—He had at this time a purging. I ordered him an electuary of bark and nutmeg, which succeeded in removing the blindness ; but the diarrhoea continued wasting him. On the 20th, delirium came on ; on the 21st, he became deaf; he died on the 25th, after having suffered from fever, pain in his bowels, and continued diarrhoea ; but the defect in his eyes never re- turned after the 10th. This man had clear bright eyes : when his sight failed him the pupils were enlarged about one-third in diameter. Medi- cal Facts and Enquiries, vol. i. p. 111. I could give other cases from my note-book, but these are sufficient. Boerhaave gives us an example of imperfect vision, from a discord- ance between the contraction of the iris and the excitement of the re- tina ; so that the pupil did not dilate in the proportion to the decay of light. | * Case by Dr. Samuel Pye. f In old people there is an obscurity of vision, from a diminished sensibility of the retina ; and the iris does not take a quick succession of contraction and dilatation with the change of light. OP THE RETINA. 193 When inflammation extends within the eye, or when the retina is ex- cited by sympathy with the ophthalmia of the outer membranes, it may happen that the patient is totally blind during the day, and yet sees on the approach of evening, because, from the sensibility of the retina, the pupil is absolutely shut, but as the light is diminished the pupil is gradu- ally relaxed, and the obscure light admitted, and this obscure light, from the irritable state of the retina, gives a vivid sensation incomprehensible to the by-standers. Our judgments of the strength of sensations are comparative merely; when we have been accustomed to strong impres- sions, lesser ones are disregarded. The greater light destroys the capa- city of the retina for receiving slighter and more delicate impressions ; while, on the other hand, the absence of light reserves to us the power of seeing objects the most faintly illuminated. We are every day be- coming more acquainted with iho invisible properties of light; and we have frequent experience of darkness being relative, and that which we should call total darkness is very often but a fainter light. One man will see distinctly, when another is quite deprived of the power of discerning objects. A man in prison seems to have the light gradually admitted to him ; and many animals are in quick pursuit of their prey, while we are groping our way with the assistance of our other senses. Animals which seek their prey in a light which is darkness to us, have, most probably, a greater degree of sensibility of the retina. But they have also a more conspicuous apparatus in the largeness of their eyes, and the dilatability of their pupil, while the sensibility which this provi- sion gives, is often guarded from the light of day by the membrana nicti- tans, and by an iris capable of great contraction. Their iris possesses also a great power of contraction in narrowing the pupil during the day, as it is capable of dilating during the night, to the whole extent of the cornea. In the human eye, also, the strict sympathy between the iris and retina is a guard to the latter. But it has often happened that, in using optical instruments, the retina has been hurt by the intensity of the light from the concentrated rays : a lesser degree of this defect we have given us in the following instance :* “ Being occupied in making an exact meridian, in order to observe the transit of Venus, I rashly directed to the sun, by my right eye, the cross hairs of a small telescope. I had often done the like in my younger days with impunity ; but I suffered by it at last, which I mention as a warning to others. I soon observed a remarkable dimness in that eye, and for many weeks, when I was in the dark, or shut my eyes, there ap- peared before the right eye a lucid spot, which trembled much like the image of the sun seen by reflection from water. This appearance grew fainter, and less frequent by degrees, so that now there are seldom any remains of it. But some other very sensible effects of this hurt still re- main : For, first, the sight of the right eye continues to be more dim than that of the left; secondly, the nearest limit of distinct vision is more remote in the right eye than in the other, although, before the time men- tioned, they were equal in both these respects, as I had found by many trials ; but, thirdly, what I chiefly intend to mention is, that a straight line in some circumstances, appears to the right eye to have a curvature in it. Thus when I look upon a music book, and, shutting my left eye, * Viz. by Dr. Reid. 194 OP THE MEMBRANA PUPILLARIS. direct the right to a point of the middle line of the five which compose the staff of music, the middle line appears dim indeed at the point to which the eye is directed, but straight; at the same time the two lines above it and the two below it appear to be bent outwards, and to be more distinct from each other and from the middle line, than at other parts of the staff to which the eye is not directed. Fourthly, although I have re- peated this experiment times innumerable within these sixteen months, I do not find that custom and experience take away this appearance of cur- vat are in straight lines. Lastly, this appearance of curvature is percep- tible when I look with the right eye only, but not when I look with both eyes; yet I see better with both eyes together than even with the left eye alone.” Herschel, in making his observations on the sun, found the irritation to proceed from the red rays,* (being thnsp nf thp rays of light which have the property of producing heat in the greatest degree); he found, when he used red glass to intercept the too vivid impression of light on his eyes, that they stopped the light, but produced an insufferable irrita- tion from the degree of heat. But when he used green glass it trans- mitted more light, and remedied the former inconvenience of an irritation arising from heat. He concluded, that in the darkening glasses for te- lescopes, the red light of the sun ought to be entirely intercepted. Boer- haave mentions an instance of the retina being injured by the long use of the telescope, and he himself was hurt by a similar cause. These injuries are owing to the intrusion of light highly concentrated, and over which the pupil has no command ; it is a degree of intensity which the organ is not prepared to counteract. OF THE MEMBRANA PUPILLARIS. The membrana pupillaris is an extremely vascular membrane, which is extended across the pupil of the foetus. It was discovered by Haller, Albinus, Wachendorf,f and Dr. William Hunter, at the same time or without correspondence with each other. HallerJ, after injecting, with oil of turpentine and cinnabar, a foetus of the seventh month, saw through the cornea the vessels of the iris inject- ed, and some ramifications from them produced into the space of the pupil. From conviction that no vessels ramified without an involving membrane, he naturally concluded, that a membrane was drawn across the pupil of the foetus, though in this instance, it was about to disappear. In several other foetuses of the seventh month he confirmed his first observation; and, cutting off the cornea, he observed the membrane im- pelled forward by tire humours behind like a little vesicle. Albinus, in his first book of Academical Annotations, thus describes the way in which he detected this membrane. In the same child in whom he had filled the vessels of the crystalline lens, he also first ob- served the membrane which closes the pupil, and in which the vessels were injected that came from the margin of the pupil. Upon looking * See a curious instance of red colours producing convulsions in an epileptic patient.— Sandifort Thus. vol. iii. pag. 314. f In Commercio Norico, A. 1740, hebd. 18, as quoted by Haller. | De nova tunica pupillarn foetus claudente. Oper. Minor. OP THE MEMBRANA PUPILLARIS. 195 through the cornea, he could see no distinction of parts, but all seemed vascularity. He conceived, at first, that these were the vessels of the uvea, and that it had quite contracted, and had shut the pupil; then that, they were the vessels of the capsule of the crystalline lens; but hav- ing cut into the eye, he found it to be this membrane. Dr. Hunter, speaking of this membrane, and of Albinus’s claim to the discovery, says, “ In justice to this great anatomist, I must declare that I believe this, both because he asserts it, and because I know from the circum- stances it was hardly possible he could miss taking notice of it in that child.” “ I have always observed,” he continues, “ both in the human body and in the quadruped, that there is a great resemblance to one an- other in the vessels of the capsula crystallini and of the membrana pupill®. In an injected foetus, I always find both nearly in the same state : if one be filled only with the blood that is drove before the in- jection, so is the other; if one be filled partly with injection, and partly with blood, the other is in the same condition; if one by good fortune be finely and minutely filled with injection, the other is so too; if one be burst by extravasation, the other is commonly in the same state; and when the foetus is so near its full time that the one cannot be injected, neither can the other.”* Dr. Hunter, speaking further of the artery of the crystalline capsule, says, “ that it does not terminate at the great circle of that humour. Its small branches pass that circle, and run a very little way on the an- terior surface of the crystalline humour before the points of the ciliary processes; then they leave the humour and run forwards, supported on a very delicate membrane, to lose themselves in the membrana pupil- Ise.” He continues: “ The membrana pupillae receives two different sets of arteries, one larger, from the iris, and the other much smaller, but very numerous, from the crystalline capsule.” Now I think that every expression in these excerpts confirms the opi- nion I entertain, that these vessels which are seen filled with red blood, and which take their course through the humours, are subservient mere- ly to the membrana pupillaris. The first time I observed the membrana pupillaris, was in the eye of a child born at the full time. I had injected the child very minutely with size and Vermillion, and the iris was beautifully red and the pupil quite transparent and black, and not obscured by any extravasation of the injection into the aqueous humour, upon very narrowly observing the circle of the iris, I saw distinctly a small injected vessel pass out from the edge of the iris, and crossing the pupil, divide into two branches, which ran into the opposite margin of the iris. This was the remains of the membrane, but so delicate and so perfectly transparent, that the presence of it was only to be presumed from the vessel which was seen to cross the pupil. Since that time I have often seen it in the early months, and parti- cularly strong about the seventh month of the foetus. It is then an opa- que, and very vascular membrane, and generally it has spots and streaks of extravasation in it. The vascular structure of this mem- brane is very particular, and I can assign no other reason for this than that it may be a provision for its rapid absorption. It has evidently two * See Medical Commentaries, p. 63. foot-note. 196 OF THE HUMOURS OF THE EVE. sources of vessels, viz. the vessels of the capsules and those of the iris; but whether the arteries come by the one source, and the veins depart by the other, I cannot determine. In one preparation I see the vessels with their trunk in the membrana pupillaris, and the branches sent over the surface of the iris. The larger and flat venous-like vessels of the membrane are distribut- ed in a beautiful net-work, in the form of the lozenge of a Gothic window. They have a free communication with each other. In their whole course the vessels seem nearly of the same size, (which also is like the cha- racter of a venous net-work,) and they terminate apparently in the mar- gin of the iris. Haller makes a comparison betwixt this membrane, which closes up the pupil, and that matter which is accumulated in the passage of the ear in the foetus. But there is no analogy.— As the waters of the am- nios might otherwise be in contact with the membrane of the drum of the ear, and injure what necessarily is of a dry and arid nature, this matter accumulated in the ear of the foetus defends it. But at the time when the membrana pupillaris exists in its full strength and vascularity, no light is admitted into the eye—the foetus is lying in the womb. Towards the ninth month, the membrane has become transparent, and if not totally absorbed, it is torn by the first motion of the pupil, and altogether disap- pears. It can therefore have no effect in obscuring the light, and prevent- ing it from exciting in too great a degree the eye of the newly-born child. I offer with some hesitation the following rationale: it is the nature of the iris to contract its circular fibres during the operation of light, so as to stretch the membrane, and to close or nearly close the pupil; that, on the other hand, the pupil is completely dilated through thq operation of the radiated fibres of the iris in darkness :—To the question, then, why it is not dilated during the foetal state ? The answer, I think, may be this:—The iris is not loose in the foetal state, it is connected and stretched to the middle degree of contraction and dilatation by the mem- brana pupillaris. Were the iris in a full state of contraction, during the life of the foetus, it could not receive its full nourishment, proper degree of extension, and due powers ; but being preserved stationary and ex- tended, the disposition to contraction, which it must have when the re- tina is without excitement, is counteracted, until it is about to receive by the birth of the child, that degree of excitement which is to keep up the balance betwixt the two classes of fibres : those which dilate and those which contract the iris. OF THE HUMOURS OF THE EYE. OF THE AQUEOUS HUMOUR. The aqueous hnmour is perfectly limpid. The use which I have as- signed to the aqueous humour explains its nature and the extent of the chamber which contains it, viz. that it distends the cornea, and allows the free motion of the iris ; it consequently fills the space between the lens and cornea. The usual description is, that it is lodged in two chambers ; the one before the iris, called the anterior chamber of the aqueous humour, and the other behind the iris, called the posterior chamber of the aqueous hu- mour. OP THE HUMOURS OF THE EYE. 197 This posterior chamber was, at one time, conceived to be of great ex- tent,* and authors spoke of depressing the lens into the posterior cham- ber of the aqueous humour, t It is found, now, that betwixt the lens and iris there is no space to which we ought to give this name of cham- ber. Heister, Morgagni, and M. Petit (medecin) first demonstrated the ex- treme smallness of the posterior chamber, and after them Winslow con- firmed the fact, that the iris moved almost in contact with the anterior surface of the lens. M. Petit gave the clearest proof of the smallness of the posterior chamber, by freezing all the humours of the eye, and dissecting them in their solid state. Without this expedient it was impossible to prove the relative size of the two chambers; for, whenever the cornea was cut, the aqueous fluid escaped, and the lens pushed forward. When the eye was frozen, and then dissected, it was found that the ice, which took the shape and dimensions of the anterior chamber, was much larger than that found in the posterior chamber indeed the latter was formed of a very thin flake of ice. The thin piece of ice in the posterior chamber indi- cated as much fluid only betwixt the iris and lens as might allow a free motion to the iris. These experiments were instituted in the course of investigating the question of the nature of the cataract. The conclusion that the posterior chamber of the aqueous humour contained but one fourth of the whole aqueous humour, was admitted with great difficulty and after much contest. It determined the question, whether the cataract was a membrane or the opaque lens ; for, as those who maintained that it was a membrane, said it could not be the lens, because the lens was far distant from the iris, it was necessary for their opponents to prove that the lens was close upon the pupil, and that the posterior chamber of the aqueous humour was very small. It is agreed that in the adult, the quantity of the aqueous humour amounts to five grains ; in the foetus it is red, turbid, and weighs about a grain and a half, owing, in part, to the comparatively greater thickness of the cornea. As it is natural to conceive that the aqueous humour flows from a vas- cular surface, it is the most generally received opinion, that it is derived from the points of the ciliary processes and surface of the iris. Haller, particularly, and after him Zinn. have thought that the ciliary processes were the secreting bodies; but there is one argument, which, in my mind, determines that these are not the sole secreting parts, viz. that while the membrana pupillaris closes up the communication betwixt the two chambers, I have observed the anterior one to be full of the fluid, which of course must have been supplied from another source than the ciliary processes. I suppose, therefore, that the villous surface of the iris is the proper secreting surface of the aqueous humour.§ Zinn ob- * Viz. by Heisler. They were called the first and second chambers by M. Brisseau. + There certainly appears sufficient room for this in Vesalius and Briggs’ plates: these plates have misled many. t See Acad. Roy. des Sciences, 1723. Mem. p. 38. § The opinion of Nuck is now out of the question. He thought that he had discovered par- ticular aqueducts, which conveyed the aqueous humours into the anterior part of the eye; but these are found to be nothing more than the short ciliary arteries which pierce the fore part of the sclerotica. M. Mery and Bonhomme (see Zinn, p. 143.) observed, in an adult, the pu- pil closed with the membrane; and, in this instance, there was scarcely any fluid in the ante- rior chamber, whilst the posterior was turgid with fluid. 198 OP THE HUMOURS OF THE EYE. serves, that Haller saw the membrana pupillaris distended and bulged forwards by the aqueous humour in the posterior chamber. It is scarce- ly necessary to say, that this must always take place when the cornea is first opened in demonstrating that membrane, whether there be a watery fluid behind it or not. But I believe I shall be able to prove, that the secretion of the ciliary processes can have little power of filling the posterior chamber, even from the connexion of membranes behind the membrana pupillaris of the foetus. The aqueous fluid is perpetually un- dergoing the change of secretion and absorption, and this is the reason of its quick renewal when it has been allowed to escape by puncture of the cornea. The ancients were not ignorant of the quick regeneration of this fluid. It was proved to the moderns by a charlatan, Josephus Burrhus. Before the physicians of Amsterdam he punctured the cornea of a dog ; then instilling his liquor under the cornea, he bound up the eye ; in a few days he took off the bandage, and showed them the cor- nea again distended with the aqueous humour. It was soon found that the instilled fluid was of no kind of consequence. Redi and Nuck made many experiments, and it was found that the aqueous humour was regenerated in the course of twenty-four hours. It is generated much more quickly than this. When the disputes regarding the cataract ran high, and when, to make new distinctions in the disease was taken as a mark of practical know- ledge and of acuteness, there was a kind of cataract attributed to the aqueous humour. When the aqueous humour became turbid, white, and opaque, and obscured the pupil, they were absurd enough to call this a cataract. The turbid state of the aqueous humour is at once distinguish- able from the opaque lens, because it obscures the iris as well as the pupil. Pus is formed in the chambers of the aqueous humour, in consequence of deep inflammation, contusions, &c. and from the same cause, some- times, proceeds a bloody effusion. When the pus has lodged in the an- terior chamber of the aqueous humour, it would appear, upon the autho- rity of Galen, that an oculist of his day performed a cure by shaking the patient’s head !* It is an operation of oculists to puncture and allow the pus to flow out, and some have even syringed out the pus with water but this must have been on the principles of Jos. Burrhus’s exhibition ; for the natural secretion is here the best diluent. When we recollect the nature of the parts with which the pus lies in contact, we cannot be san- guine in the hope of such an operation saving tire eye. Sometimes, there remains, after operation on the cornea, or in consequence of ulce- ration, a continued flow of the aqueous humour; the consequence is a subsiding of the cornea it becomes corrugated, opaque, and from the contact of the iris, apt to adhere to the iris. In consequence of this sup- * Mouchart says, he has often seen the oculist Woolhouse-repeat this cure, by shaking his patient’s head over the side of the bed. He attributed the cure to the falling of the pus into the posterior chamber, which, he supposes, has parts more capable of absorbing it. t They were at variance regarding the place at which to puncture for this discharge :—Some did it behind the iris; there we know there is a crowd of vessels: the best place is the lower edge of the cornea before the iris. It seems to have been no uncommon accident, in this ope- ration, to find the lens protruded through the pupil. The reason of this has been already ex- plained. $ Rhytidosis, seu subsidentia et corrugatio cornea’. OF THE HUMOURS OF THE EYE. 199 puration, there sometimes follows an absolute obstruction of the pupil, from the coalescing and adhesion of the edges of the iris.* THE VITREOUS HUMOUR. The vitreous humour, as already explained, occupies almost entirely the great ball of the eye. It is consequently beyond the lens, and keeps it at the requisite distance, to cause the rays from objects to concentrate and impinge upon the retina. The vitreous humour is considerably denser than the aqueous humour. | Its involving membrane is called membrana hyoloides sive vitrea.J The peculiar appearance of this humour, its glairy-like consistence, is not owing to its density, but to the manner in which it is contained in'its membranes. From being contained in a cel- lular structure of perfectly pellucid membranes, it has the adhesion and consistence of the white of an egg. This membranous structure of the vitreous humour has been demonstrated by acids and by freezing. When frozen, it was found to consist of pieces of ice connected by strong membranes, which separated with difficulty, and showed their torn frag- ments ; and M. Demours lifted the transparent membranes with the point of a needle. Although the vitreous humour appears to be gelati- nous, it is not so in reality, and when it is taken from the coats of the eye, it retains the shape for a time, but gradually subsides by the fluid exuding from the membranes, and this is accelerated by puncturing it. OF THE CRYSTALLINE LENS. The crystalline humour is a small body, of the shape of an optician’s lens, of great power. It is of perfect transparency, and of density much greater than the vitreous humour. Its density to that of the vitreous hu- mour is calculated to be as 1114 to 1016. But the crystalline is no1: of uniform density, for the centre forms a denser nucleus, surrounded by con- centric layers, successively diminishing in density to the surface, where there is the liquor Morgagni surrounding the solid substance and con- tained within the capsule. The form of the crystalline is that of a compressed sphere, the anterior surface being more compressed or flatter, though, in a degree, convex. According to Petit, the anterior surface is the segment of a sphere whose diameter is 7, 8, or even 9 lines. The posterior surface is a sphere of 4 or 5, or 5lines in diameter. As I have said, the internal structure of the lens is quite peculiar, and resembles neither the vitreous nor the aqueous humour. By maceration it splits into lamellae, and at the same time bursts up into equal parts, so that there is first a stellated-like fissure, and then it separates into pretty regular divisions. After maceration in acids, the lens can be frittered out into minute shreds and fibres. § From its form, density, and central nucleus, it has great power of con- verging the rays of light; and in an eye properly constituted, it con- centrates them accurately to the surface of the retina. For this reason it is placed before the vitreous humour, and socketed in its anterior part. * Viz. Synisesis. There occasionally occurs congenital imperforation of the pupil, f It is, according to Dr. Monro, in the proportion of 1016 to 1000. t Ophthalmograpkia, authore G. Briggs, 1676. Cantab 5 See further of the muscularity of the lens, 200 OF THE HUMOURS OF THE EYE. It is contained in a capsular membrane, the tunica aranea improperly called *, which membrane is continued from, or connected with, the membranes of the vitreous humour ; but this is a subject which requires a more particular investigation. OF THE CAPSULE OF THE 1 ENS AND VITREOUS HUMOUR. Fuj.i, Here we have the appearance of the Petitian canal blown up ; a is the lens, b the vitreous humour, c the Petitian canal. It is not found full of any fluid, it is only the laminae of membrane inflated, and it is best de- monstrated when the eye is slightly putrid by cutting off the cornea, and with it a small circular portion of the sclerotica, and taking with these the iris also, when the lens presents itself seated firmly in its capsule on the vitreous humour. Now laying back the ciliary processes, we make a fine puncture with a lancet by the side of the lens, and then blow gently into it with the blow-pipe. Every anatomist acknowledges the existence of the Petitian canal, and a distinct capsule to the lens is also pretty generally allowed. But many deny that the vitreous membrane has two plates, without observ- ing that the existence of the Petitian canal is a proof of the splitting of the membrana vitrea, on the fore part at least. Some believe that the vitreous membrane splits and involves the lens, and forms its capsule; but the difficulty, on this supposition, is still to account for the formation of the canal which surrounds the lens ; for as the fluids on the surface of the lens and within its capsule have not admission to the canal, the canal must be distinct; and, indeed, sometimes we blow up the cir- cular canal, and sometimes, by a wrong puncture, the capsule of the lens itself; but not both at once. Seeing, then, that these cavities are distinct, some anatomists have ad- mitted that the membrana vitrea is double ; that the lens has its proper capsule; and that the lamina of the vitreous membrane, coming near the margin of the lens, splits and involves it in a second coat. Others have supposed the anterior layer of the vitreous humour does not pass * Opkthalmographia, OP THE HUMOURS OF THE EYE. 201 over the anterior surface of the proper capsule of the lens, but only adheres to the edge of the capsule of the lens, and forms the Petitian canal. There are yet others who have described the mombrana vas- culosa of the retina, as forming the capsule of the lens. This is one of those pieces of anatomy which provokes us to continued research, and mortifies us with disappointment. If this piece of anatomy, when investigated in the eye of an adult, is difficult to be understood, it in in- finitely more complicated in the eye of the foetus; and, for my own part, I cannot reconcile my experience with any former opinion. I conceive that it is the membrana vasculosa tunicae retinae, or membrana vasculosa Ruyschii, which forms the vascular capsule of the lens in the foetus, and also the canal of Petit in the adult. The crys- talline lens has, in the first place, its proper capsule, which surrounds it on all sides ; again, the transparent web of membrane that is continued onward from that part of the retina which has upon it the pulpy and nervous expansion, splits when it approaches the margin of the lens. One lamina goes round behind the lens, and the other passes a little before it, forms an adhesion to the capsule of the lens, and is then re- flected off to the points of the ciliary processes and to the membrana pupillaris of the foetus.* Betwixt these split laminae of the continued membrane of the retina, the canal which surrounds the lens is formed. The membrana vitrea is simply reflected over the back of the lens, and has no part in forming the Petitian canal. Where the retina advances forward upon the ciliary processes, it forms an adhesion, beyond which the medullary part is not continued ; but the membrana vasculosa pass- ing onward, as I have described, embraces the lens, and the lamina, which passes behind the lens and before the vitreous humour, receives and conveys the artery of the capsule; on the fore part of the lens the anterior lamina only touches the capsule of the lens, adheres, and is then reflected off to form the membrana pupillaris. In this account I am supported by the most careful investigation, and by the simplicity of this system of vessels: for it will be observed, that it is on the membrana vasculosa alone, that the vessels, carrying red blood in the foetus, are supported, and that it shows throughout the same character for vascularity. Again, I think it probable that this membrane which passes before the lens, viz. the membrana pupillaris, and that which passes behind the lens, forming the vascular capsule of the lens, disappear at the same time; or if this posterior and vascular mem- brane which passes behind the lens is not totally absorbed, it becomes thin, loses its vessels, and is more intimately united to the membrana vitrea. * In the foetus, as far as I have observed, the proper capsule of the lens and the membra- na pupi Haris, lie in contact, but they do not adhere ; and while the membrana pupillaris is perfectly red with injection, there is none to be seen on the fore part of the capsule. There is, indeed, no part of that surface which is afterwards to secrete the aqueous humour, which could secrete that fluid, betwixt the surface of the lens and membrana pupillaris; so complete is the adhesion of the adventitious and vascular tunic of the lens to the membrana pupillaris. 202 ACTION OF THE LENS. ACTION OF THE LENS ON THE RAYS OF LIGHT. Before leaving this interesting subject, we must endeavour to shew the application of these anatomical facts to the function of the lens. When we look upon a magnifying-glass, and see objects through it, we at the same time see the surfaces; that implies that the rays of light, striking these surfaces, are in part reflected and in part refracted. But if we put the magnifying-glass into water we no longer see the surfaces ; and yet we see through the glass. The reason is this: when a ray of light passes from one medium into another, it has a disposition to re- flection, in proportion to the difference of density ; so that the ray passing through air is reflected from the surface of the glass; passing through water it is not reflected, but refracted, entering through the glass. In the same manner, if the surface of the lens had been exposed to air, or if the exterior surface of the lens had been as dense as its interior nucleus, we should have seen that surface on looking into the eye ; that is to say, the rays of light would have been reflected in part, instead of all entering by refraction. From such views, we see why the lens consists of concentric layers, increasing in density inwards, and why its exterior surface is surround- ed with the liquor Morgagni. We perceive also the advantage of the cornea being moistened; for the lacrymal secretion has the same influ- ence on the light in entering the cornea that the liquor Morgagni has on the rays entering the lens. The reader will perceive that this effect of the gradual succession of density is different from the effect attributed by Mr. Ramsden, and in addition to it. He observed that the dispersion of the refracted rays, producing the coloured rays, was to be observed only where there was a sudden density interposed in the course of the ray; and therefore that the gradual variation of the lens would prevent such dispersion.* On the whole, therefore, we must conclude that this curious structure of the lens gives an image both more intense and truer in its colours than would be produced otherwise. OP THE DISTRIBUTION OF THE CENTRAL ARTERY AND VEIN OF THE RETINA. I am the more anxious to give the accurate distribution of these ves- sels, that Walter’s account of them has tended much to derange that simple and natural view of this system which observation authorizes us to take. The arteria centralis retinae arises from the ophthalmic artery.t Some- times it is derived from the ciliary arteries before they enter the coats of the eye, and often there is more than one branch entering the optic nerve. J Arising from this source, there are many branches which are * It is affirmed by Dr. Young, on Experiments, that the dispersive power of the eye is one third of that of crown-glass. He suggests that this effect may be owing to the aqueous htt- aaovsr. Trans. Roy. Soc. for Nov. 1800. | See Haller, Fascic. vii. tab. vi. fig. 2. 4- 7. i Haller, F. vii. p. 42. OF THE CENTRAL ARTERY. 203 distributed to the retina, whilefa branch passes onward from the lamina cribrosa through the vitreous humour, to the capsule of the lens. This vessel does not pass exactly in the centre of the vitreous humour, but to one side of the axis of the eye. When it arrives near the capsule of the lens, it divides into three or four branches, which, reaching the cap- sule, spread beautifully on the back part of it.* The branches of the arteria centralis retinae, which are distributed in the retina, are subservient to its support, and are consequently as visible in the adult as in the foetus ; and, where the membrane of the retina has been described as adhering to the point of the ciliary body, these vessels of the retina unite to or inosculate with the vessels of the ciliary pro- cesses. Walter objects to the description of the arteria, centralis retinae given by Haller and others : he says, decidedly, that there are no arteries dis- tributed to the retina, and that anatomists have deceived themselves in supposing those vessels which ramify on the retina, to be arteries, when, in reality, they are veins ; he conceives, that the free return of the injec- tion from the extremities of the arteries into the veins has misled them. I am at a loss to conceive what notions Professor Walter can have en- tertained regarding this vein distributed in the retina, without an accom- panying artery. It is a supposition contrary to the general frame of the economy, and l would oppose to it, with confidence, my own experience ; since in the ox and other animals, I have seen the veins of the retina turged with blood, and exceedingly distinct; yet, when I injected the trunk of the artery at the root of the optic nerve, I found a set of vessels injected on the surface of the retina quite different from the turgid veins, and which could be no other than the arteries distributed to the retina. I must conclude that there is no peculiarity in the distribution of vessels in the tunica vasculosa retinae. We frequently observe that the trunks of veins and arteries, destined to the same final distribution, take a different course; but in their final distribution, I know no instance in which they do not ramify with parallel branches interwoven with each other. The vena centralis retin-®, as it is described by Haller, i3 some- times a branch of the ophthalmica cerebralis, but often it rises from the cavernous sinus, amongst the origins of the external and inferior recti muscles of the eye ; after giving off many small twigs to the periosteum and fat of the orbit, it passes obliquely from behind, forward, and inward, perforates the sheath of the optic nerve, and, after supplying the sheath, dips into the surface of the nerve.—It is now the comes arteri® centralis retin®. It enters through the cribriform plate of the optic nerve, and spreading generally in large and remarkable branches on the retina, these make free inosculations with each other, and finally inosculate with the veins of the ciliary processes. Whether a branch of the vena centralis retin® is sent off to accom- * Walter (de venis oculi) says, the arteria centralis retina, having perforated the mem* brana hyoloidea, passes through the middle of the vitreous humour, and scatters some twigs on the small cells of the vitreous humour. It does not, he says, run through the vitreous hu- mour in a straight line from behind forward, nor does it divide into a great number of branches in the posterior part of the capsule of the lens, like radii front a centre, as Zinn has described. He asserts that the lens receives its vessels from the investure of the membrana hyoloidea, and that they run back front the edge of the lens towards the posterior convexity. 204 OF THE PELLUCID MEMBBANES. pany the branch of the artery which takes its course through the vitreous humour, I have not been able to determine. OF THE VASCULARITY OF THE PELLUCID MEMBRANES. It’ we cut through the sclerotic and choroid coat, round the optic nerve as it enters the eye, and afterwards cut up the outer coats towards the cornea, the humours fall out from these coats, and will remain suspended in a fluid, hanging by the optic nerve and closely embraced by the retina : we have now to review these parts taken collectively, independent of the outward and proper coats, and, as I have classed them, as constituting the internal globe of the eye. The first peculiarity which strikes us here is the perfect transparency of all the parts within the embrace of the retina. As there are, in the adult and healthy eye, no vessels to be seen in the transparent membrane and humours, it becomes a question whether nature has provided for the support and nourishment of those parts by other means than the common circulation of red blood through vessels'? Now, I am inclined to think, that there ia r»o inrough them ; and I believe, that this would be much more generally allowed were there not something like a proof remaining in men’s minds that these humours and tunics were sup- plied with red blood in the foetus ; whence they deduce the natural con- sequence that, in the adult state, these vessels are only shrunk so as to convey only colourless fluids. I have, therefore, to give my reasons why I think that these vessels of the foetus are not subservient to the humours ; and, I think, I shall prove that when they have once disappeared, they are no longer pervious vessels ; that, though those parts which they are sup- posed to supply, should become inflamed and vascular in the adult, these vessels which were apparent in the foetus do not become enlarged ; that they do not administer in any way to inflammation and disease, but that a new source is given, and that vessels are formed which were at no former period discernible. Why should there be red blood transmitted to the pellucid membranes and humours of the foetus ? Why is not that state of circulation, which nourishes and supports the parts in the adult state sufficient for their growth and the progress to perfection which they undergo in the foetus ? Why is the capsule of the lens only crowded with vessels carrying red blood, while the proof of vessels passing to the cells of the vitreous coat stands upon some very rare and vague assertions, and such as can be naturally explained by the appearance of those vessels which merely pass through the vitreous humour for a different destination ? I believe this is a view which has been little attended to ; but, upon the most minute enquiry, and upon examining the preparations of the vascularity of the eye of the foetus, I can see no vessels passing intr the humours and carrying red blood, which are not finally distributed to the membrana pupillaris. When we lay open the eye of a foetus, after a very minute and successful injection, we see vessels which all proceed from the centre of the optic nerve, passing through the vitreous humour to the back of the capsule of the lens, viz. the branches of the arteria centralis retinae. This artery divides very often into many branches be- OF THE PELLUCID MEMBRANES. 205 lore it arrives at the capsule of the lens: now, if these be filled with blood, or but partially injected, they have the appearance of being branches distributed to the vitreous humour, and not to the lens. This appearance is still more apt to deceive us when the lens is separated from the vitreous humour, and when the vitreous humour is otherwise dis- turbed, for then the vessels shrink and seem to terminate in the midst of the vitreous humour. When the injection is perfect there is no such ap- pearance. On the back of the lens we see a profusion of vessels; but I think I may positively say that these vessels do not penetrate into the lens it- self, hut are merely on the capsule, and that having made the circuit of the lens, they terminate in the membrana pupillaris and ciliary body. I can observe no villi on the inner surface of the capsule of the lens, nor any appearance of its being a secreting surface, to lead me to suppose that these vessels secrete the lens, as Walter supposes they do ; nor, af- ter the most successful injection of the capsule of the lens and of the coats of the eye in general, can I observe the slightest stain of colour in the pellucid state of the lens, nor betwixt its white fibres when it be- comes opaque. Nor have I observed, at any time, a single branch of these vessels, which are so profuse on the back of the lens, distributed to the anterior part of the capsule ; on the contrary, they all terminate abruptly at that line, a little forward from the utmost verge of the lens, where they are united to the vessels of the membrana pupillaris and cilia- ry processes. Were these vessels of the capsule provided for the secre- tion of the lens, or were those vessels the trunks of lesser branches, which pierce into the substance of the lens, they would appear also on the fore part of the capsule. If I am accurate in these observations, we are authorised to deduce this conclusion:—that these vessels which we see running through the vitreous humour and capsule of the lens, and which are sometimes seen filled with red blood or injected with size and vermillion, are not the ves- sels of the humours, but vessels in their passage to the membrana pupil- laris, and that they disappear totally when that membrane is absorbed. They are injected when the membrana pupillaris is injected; they are more difficult to fill when that membrane is becoming pellucid and tender towards the latter period of gestation; and with the annihilation of the membrane follows the disappearance of the vessels carrying red blood through the transparent humour of the eve. In confirmation of the total annihilation of these central vessels of the vitreous humour, I have found that, when disease comes upon the lens of the adult, the vessels, which are apparent in consequence of in- flammation, do not proceed through the old tract from the centre of the optic nerve and through the vitreous humour to the lens, but that they come from the extremity of the retina and laterally, and thence spread over the back of the lens. An eye, which I had lately an opportunity of examining, confirmed me in this opinion. I assisted my brother in an operation on the eye, in which, the anterior part being diseased, it was cut away. I had scon an opportunity of retiring and examining the parts with Dr. Monro. I ob- served then an opaque spot on the posterior surface of the lens, which was indeed in the capsule, and to this spot there came vessels over the margin of the lens from the extremities of the vessels of the retina; 206 ANATOMY OF THE HUMOURS. but, in the vitreous humour there were no vessels to be seen, nor any branches passing into the lens obliquely from behind, as they do in the foetus. SOME SURGICAL OBSERVATIONS CONNECTED WITH THE ANATOMY OF THE HUMOURS. I have already mentioned, as the principle of the operation of extract- ing the lens, that the simple action of the muscles surrounding the eye- ball, is sufficient to protrude the lens, if the incision of the cornea be of proper dimensions relative to the size of the lens. No doubt, if there have been thickening inflam nation, and perhaps preternatural adhesions of the membranes surrounding the lens, the operation will necessarily be- come more complicated; the lens will not glide at once over the cheek when the incision of the cornea is completed. But still, I think, we are not to allow ourselves to consider it as a step of the operation, in any cir- cumstances, that the ball of the eye is to be pressed ; because, in that case, the membranes of the lens give way suddenly, and part of the vi- treous humour unavoidably is protruded with it, or the edge of the lens is turned obliquely to the pupil, and the vitreous humour escapes by the side of it. It is better to destroy the adhesions with the instrument, and to scratch the capsule of the lens so that it may burst: whence it is evident that it is necessary, in order to insure the correct performance of the operation of extraction, that the lens should press equally forward on the pupil, and that the pupil should be allowed to dilate. From this it ap- pears how loose the ideas of those are who can speak of trying first to couch, and if that is not found to succeed, then to perform the operation of extraction. I conceive the attempt with the needle to preclude the operation of extracting, for these reasons :—An unsuccessful attempt to depress will, in general, be a laboured and reiterated motion of the point of the needle, which must occasi n inflammation and an adhesion firmer than is natural. Again, in couching, the lens is removed from the axis of the eye so far only that, in the case of the extracting being attempted, it no longer equally opposes itself to the pupil, the consequence of which must be the escape of the vitreous humour and the detention of the lens. In regard to the place at which the couching-needle is to be introduc- ed, we may observe, that we are directed by the older surgeons to pierce the sclerotic coat very near to the edge of the cornea, because they were afraid of hurting the lens with the needle. The idea then entertained was, that the cataract was a membrane hung behind the pupil and be- fore the lens. The older surgeons had the idea that the needle entered before the lens and passed at once into the aqueous humour. We are to disregard these injunctions of surgeons who directed the needle to be introduced with the idea of avoiding the lens ; for, while their notions regarding the disease were erroneous, their rules of operating could not be correct ; accordingly, we find them dilfering in their directions as to the place of piercing the cornea ; some directing us to pierce it at the distance of one line from the edge of the cornea, others at the distance of four lines and a half. Now that we know the place of the cataract, and know also that it is the opaque lens, we can be at no loss to introduce the needle correctly. ANATOMY OP THE HUMOURS. 207 If', says M. Petit, vve pierce the sclerotic coat one line from the edge of the cornea, we pierce the tunica conjunctiva, sclerotica, choroid, vitre- ous humour, and ciliary processes before the needle enters the cataract. In this puncture, we wound the most vascular part, and, indeed, every de- licate part of the eye ; for even in this most anterior course, the retina is equally lacerated with the others.* But if we pierce the sclerotic coat, three lines from the edge of the cornea, we avoid the ciliary liga- ment and body, and processes ; and by directing it a little forward, in a line towards the opposite margin of the iris, we shall find the point of the needle advancing through the opaque lens ; for, although the lens be so opaque as to prevent the light fron« striking the retina, it is so far transparent, in general, that the needle is distinctly seen catering its sub- stance, and can be then directed so as to transfix the cataract without hurting the iris. We have seen that there is no posterior chamber of the aqueous hu- mour fit to contain the depressed crystalline lens. The belief, which even some modern surgeons have entertained of the possibility of de- pressing the lens into the aqueous humour, is a remnant of those inac- curate notions respecting the size of the posterior chamber of the aque- ous humour and the place of the lens, which have long been corrected. With this, also, I think ought to have been forgotten, the idea of the ris- ing of the lens after it has been depressed by the cataract floating in the humours.—The fact I am confident is this : when, after transfixing the cataract, we endeavour to dislodge it by depressing the point of the needle, we separate the adhesion between the humours and the points of the ciliary processes ; we do not, however, unsocket the lens from the fore part of the vitreous humour, but when the lens descends with the point of the needle from before the pupil, the vitreous humour revolves with it ; the consequence of which is, that when the needle is with- drawn, the lens rolls round with the vitreous humour : but as the lens only is opaque, as its firm connexion with the vitreous humour, and even the rolling of the vitreous humour itself cannot be seen, this rolling of the lens appears to be the consequence merely of its own buoyancy in the aqueous humour. This adhesion of the lens to the vitreous humour, I have been sensible of during its depression, from the elastic nature of the resistance which I felt. When the lens parts from its socket in the vitreous humour, and when it is depressed with such a turn of the nee- dle as puts it under the anterior part of the vitreous humour, it cannot rise again ; there is no motion of the eye which can replace it ; there is no aqueous fluid, in which, if it were of less specific gravity, it could rise : it lies under, and, in part, imbedded in the vitreous humour An- other idea is, that it rises with the needle : but no one, who understands what is to be done in the operation of the needle, will raise it again op- posite to the pupil after the lens is depressed ; it ought to be withdrawn without again elevating the point. But what has always appeared to me as the most unaccountable cause that can be assigned for the rising of the cataract, is the action of the muscles of the eye. I It has been ex- * In our most modern system of surgery, we are directed to enter the needle one-tenth of an inch. To my certain knowledge, not only the ciliary body has been injured by this direc- tion, but even the root of the iris has been seen to be pushed forward on the point of the needle. t See Mr. Benjamin Bell’s System of Surgery. 208 OF THE EYE-LIDS. plained how the lens is protruded by the action of the muscles when the cornea is cut and the aqueous humour let out; for then the uniform re- sistance of the eye is broken, and there is a motion of the humours to- wards the breach, and the lens, lying behind the pupil, is the first part to be protruded forward ; but when it lies under the anterior part of the vi- treous humour (and there it must lie if it is at all displaced,) or in what- ever situation it happens to be, from that it cannot be moved by the ac- tion of the recti muscles ; for they embrace the eye on every side, and their action operates uniformly, so that they cannot affect a body im- mersed in the midst of the humours. For the same reason that we should decline the operation of extracting, after attempts have been made to depress with the needle, I should refuse when the pupil is rug- ged and irregular, because th© dlB©ae© may h© more extensive than it appears to be. Thus cataracts brought on by falls, or blows, or punc- tures of the eye, are less favourable, as there is danger of the inflamma- tion having gone deep, and having affected the other humours in a way which cannot be known, since the opaque lens is betwixt us and them. A frequent cause of the failure of the operation of depression is the displacement of the lens backwards ; for when it seems to have gone down with the needle, it has slipped from under it and started backward. In this case the pupil appears clear, but the patient gains little advan- tage ; for the cataract, though removed from the pupil, is still in the si- tuation to obstruct the light. OF THE EYE-LIDS, OF THEIR GLANDS, AND OF THE COURSE OF THE TEARS. Having completed the description of the eye, as the organ of vision, we have now to attend to its connexions, its adventitious membranes, the glands of the eye-lids, and the course of the tears. It is plainly ne- cessary that the eye should not be loose in the socket ; but that, in its rolling motion, it should still be attached ; and that, although the delicate anterior surface must be exposed, the internal parts of the socket should be defended from the intrusion of extraneous bodies. This is accom- plished by the tunica conjunctiva. The tuN'CA conjunctiva, or adnata, is the inflection of the com- mon skin of the eye-lids. It goes a little back into the orbit, and is again reflected, so as to come forward and cover the fore part of the eye-ball. Here it is pellucid, and the white coat of the eye shines through it. It covers the cornea also ; and here it is perfectly transparent; loses its character of vascularity, and is assimilated to the nature of the cornea. As this coat is a continuation of the common integuments, it is, like them, vascular and liable to inflammation. The tunica conjunctiva, is the most common seat of ophthalmia. In the commencing inflammation, we see the vessels turgid or blood-shot; by and bye, they elongate towards the surface of the cornea ; the patient complains of dimness ; the dim- ness becomes apparent to the surgeon ; spots of opacity then form in the cornea ; and the vessels of the conjunctiva are seen taking their course over the turbid surface of the cornea. In this stage of the inflammation, OF THE EYE-LIDS. 209 by cutting the turgid vessels of the conjunctiva, we interrupt the source of blood for a time, and procure a small evacuation ; but these vessels soon coalesce again, and the flow of blood is renewed. A variety of ap- pearances are produced by this process of inflammation, and these have appropriate names. The tunica albuginea is the thin tendinous coat formed by the inser- tion of the recti muscles, which expand over the anterior part of the eye, I would admit this into the enumeration of the coats of the eye, merely to prevent confusion of names, and to make intelligible the descriptions of some of the older writers. It is not properly a coat. Where the con- junctiva covers the anterior part of the eye, the white sclerotic coat is seen under it; and in consequence of this, the tunica conjunctiva is some- times called albuginea. A very material part of the structure of the eye still remains to be described, an apparatus by which the surface of the eye is preserved from injury, kept moist, and perfectly transparent. The eye-lids are composed of the common integuments, with this difference only, that they have a cartilaginous margin to give them shape, and muscular fibres, in the duplicature of their membrane, to give them motion. A small semilunar cartilage, which lies like a hoop in their edge, keeps them of a regular figure, and so as to close neatly over the eye. This cartilage having a triangular edge, and the base of the angle forming the flat surface of the margin of the eye-lid, they meet with the most perfect accuracy. Either end of this hoop-like cartilage is connected with the periosteum at the corners of the eye, so as to move with its fellow as upon a hinge. This cartilage of the eye-lid is called tarsus. The msibomean glands.—These are very elegant little glands which lie under the inner membrane of the eye-lids. About twenty or thirty ducts of these glands open upon the tarsus of each eye-lid. These ducts run up under the vascular membrane of the inside of the eye-lids ; and minute glandular follicles, to the amount of about twenty, are at- tached to each of these ducts. These glands exude a white albuminous matter, which defends the edge of the eye-lid from the acrid tears, and closes them more accurately by its unctuosity. This matter is soluble in the tears.* The vascularity of the inner surface of the eye-lid is sub- servient to these glands ; for the vessels forming their ramifications round the little glands, secrete the matter into them. This is the seat of the ophthalmia tarsi; and following this inflammation, the edges of the eye-lids, and the mouths of the ducts, are sometimes eroded with little ulcers. These ducts are the seat of the stye. This is an inflammation and closing up of the mouth of one of the ducts, which then swells up into a little hard granule in the edge of the eye-lid, accompanied with inflammation of its cyst or surrounding membrane. OF THE SECRETION AND COURSE OF THE TEARS. The lachrymal gland is seated in the upper and outer part of the orbit, and behind the superciliary ridge of the frontal bone. It is of a flattened form, and is depressed into a hollow of the bone. Several ducts * Majendje- 210 OP THE SECRETION OP TEARS. from this gland open upon the inner surface of the upper eye-lid. 13y the reflection of the membrana conjunctiva from the eye-lid over the surface of the eye-ball, dust and motes are prevented from getting behind the eye-ball; and when they have got under the eye-lids, the extreme sensi- bility of the tunica conjunctiva excites the lachrymal gland, and the or- bicular muscles of the eye-lids, (which, by its pressure, accelerates the flow of the tears,) and the dust or motes are washed out. The puncta for absorbing the tears and conveying them into the nose, being at the inner angle or canthus of the eye-lids, we see the intention of the ducts of the lachrymal gland opening on the inside of the upper eye-lid to- wards the outer angle : for, by this means, the tears are spread over all the surface of the eye-ball, by the motion of the eye-lids, before they de- cline into the puncta. But the tears do not flow only when the gland is excited by dust; their secretion is perpetual, and, together with the mo- tion of the eye-lids, they continually moisten the surface of the eye-ball. Even during sleep it is supposed they continue to flow; and here we may admire a provision for their conveyance towards the inner canthus, in the inclination of the tarsus to each other; for the eye-lids meet only on the outer edge of the broad surface formed by the tarsus, the conse- quence of which is, that a kind of gutter is left in the angle by the inner edges of the tarsus not meeting, which permits the tears from the ducts of the lachrymal gland to flow towards the puncta lachrymalia when the eye-lids are shut. The puncta lachrymalia are the mouths of two ducts which form the beginning of a canal for drawing off the tears from the eye into the nose. These puncta are placed at the inner canthus of the eye, one on the termi- nation of the tarsus of the upper eye-lid near the nose, and the other at the corresponding extremity of the lower eye-lid: they are surrounded by a rigid substance ; and their open mouths absorb by capillary attrac- tion. These canals lead the tears into the lachrymal sac, and thence the tears pass into the nose. The caruncula lachrymalis is that little body like the granulation of a wound which lies in the inner angle formed by the two eye-lids. Very small hairs are seen to sprout from it, and some small sebaceous follicles open upon its surface. Connected with the caruncula lachryma- lis is the membrana or valvula semilunaris. This is a fold or dupli- cature of the adnata, which appears like a distinct vascular membrane. It is drawn from under the caruncula lachrymalis, when the eye-ball is directed outward, so as then to appear like a web spread over the white of the eye near the inner canthus. By directing the eye towards the nose, this membrane is again accumulated about the caruncula. Of this more presently. [This is a small muscle situated on the orbitar face of the lachrymal sac, which was first introduced to the notice of American, French, and Eng- lish anatomists in the year 1823, by W. E. Horner, M. D. Adj. Pro- fessor of Anatomy in the University of Pennsylvania. The following is his description of the muscle, given in the 2d volume of his Special Anatomy, vol. ii. p. 408, &c. “ It arises from the posterior superior part of the os unguis, just in ad- vance of the vertical suture between the os planum and the os unguis. Having advanced three lines, it bifurcates; one bifurcation is inserted THE TENSOR TARSI. OP THE SECRETION OF TEARS. 211 along the upper lachrymal duct, and terminates at its punctum, or near it; and the lower bifurcation has the same relation to the lower lachry- mal duct. The base of the caruncula lachrymalis is placed in the an- gle of the bifurcation. The superior and the inferior margins of the muscle touch the corresponding fibres of the orbicularis palpebrarum, where the latter is connected with the margin of the internal canthus of the eye, but may be readily distinguished by their horizontal course. The nasal face of this muscle adheres very closely to that portion of the sac which it covers, and also to the lachrymal ducts. The lachrymal sac rises about a line above its superior margin, and extends in the or- bit four lines below its inferior margin. The orbital face of the mus- cle is covered by a lamina of cellular membrane, and between this lami- na and the ball of the eye are placed the valvula semilunaris, and a con- siderable quantity of adipose matter. As the bifurcated extremities of the muscle follow the course of the ducts, they are covered by the tunica conjunctiva. When this muscle is examined from behind, the eye-lids being in situ, it becomes obvious that it is concave on its orbital surface, and consequently convex on the nasal; that the muscle is an oblong body, half an inch in length, and about three lines wide, bifurcated at one end ; and that it arises much deeper from the orbit than any acknowledged orgin of the orbicularis. The superior fork, however, has a few of its fibres blended with the ci- liaris. In regard to the use of this muscle. Its attachment to the posterior face of the sac is such, that it draws the orbital parietes of the sac away from the nasal, and dilates the sac, from the nasal face of the latter be- ing fixed to the bones. As this muscle has a cylindrical concavity on its orbital side, it is evident that when it contracts the fibres become straight, or nearly so, like the fibres of the diaphragm, and the cavity of the sac is enlarged after the same manner as the cavity of the tho- rax. A tendency to a vacuum being thus produced by it, the valves or folds of the internal membrane of the sac, permit the vacuum to be filled more readily through the puncta than from the nose; and the puncta being continually bathed in the tears of the lacus lachrymalis, both in the waking and in the sleeping state, the tears are constantly propelled through them by atmospheric pressure. The evacuation of the sac is no doubt accomplished by its own elasticity, and by the con- traction of the orbicularis; probably in a chief degree by the latter, because in persons who have epiphora, or a tendency to obstruction in the nasal duct, the accumulation of tears and matter principally takes place at night, when the action of the orbicularis is suspended by sleep. For these reasons we should argue, that this little muscle is active all the time, both night and day. To Dr. Physick I am indebted for sug- gesting another use for this muscle ; that of keeping the lids in contact with the ball of the eye. Some persons possess unusual voluntary power of this muscle, of which I have seen two examples ; one in a lady; another in a gentleman, a student of medicine. In each instance the individual could shorten so much the internal angle of the eye-lids, as to conceal it, along with the puncta, in the internal canthus of the orbit.” In a note Dr. Horner remarks :—“ My claims (to the discovery of this muscle) have been unequivocally admitted by Messrs. Breschet and 212 OP THE SECRETION OF TEARS. Jourdan, of Paris, anatomists of unusual distinction, in the translation which they have made of J. F. Meckel’s Manual of Anatomy, vol. iii. p. 219; by Gery, in the Melanges de Chirurgie £trahgere, Geneva, 1824, p. 415 ; and by Professor Giuseppe Trasmondi, in the Arcadica Journal of Rome, vol. xix. p. 1. 1823.” The discovery of this muscle was claimed by Flajani for Duverney; and Schobingcr, his pupil, was referred to for a more especial description, which he gave in a dissertation published in Haller’s Opera Minora. To all the claims and objections, Dr. Horner replied in the Philadelphia Medical and Physical Journal of Nov. 1824, to which the reader is re- ferred. For ourselves, we have no doubt of the credit being due to Dr. Horner for teaching this very interesting piece of anatomy to the American, French, and English Anatomists, whose works were, previ- ous to his researches, altogether silent on the subject. But this appears not to have been the case with all the German anatomists, as may be seen by the following extract from Rosenmiiller’s excellent compendium, of which we shall shortly publish a translation for the use of students of medicine. “ Before the tear-bag lies the ligamentum palpebrale internum and orbicularis palpebrarum : behind the 1 ear-bag is a small muscle, musculus sacci lacrymalis, which arises from the posterior edge of the lachrymal fossa, and terminates on the posterior surface of both tarsi.”* This extract is from the third edition of Rosenmiiller, published in 1819, at Leipzig. He describes it as a fact long known and well es- tablished. J. D. G.] The lachrymal sac and duct lie in the os unguis or os lachry- male. This sacculus is a bag of an oblong or oval figure; it is sunk into the fossa of the os unguis, and defended by the frontal process of the superior maxillary bone; and it is covered by the ligamentous connexion of the orbicularis muscle. This sac is the dilated upper end of the nasal duct ; and into it the two canaliculi lachrymales (the extre- mities of which are the before-mentioned puncta), open as distinct tubes. Two coats are described as forming the lachrymal sac : a nervous, white, external coat; and a vascular, pulpy, pituitary membrane. This sac, diminishing towards the lower part, and being received into the com- plete canal of the bone, becomes the nasal duct. Taking a course downward and backward, it opens into the nose under the inferior spon- gy bone. The lachrymal sac and duct are by some said to be muscu- lar, which it is conceived is necessary to enable them to convey the tears into the nose ; or it may be, that they act like a syphon, the duct, reach- ing down into the nose, being like the long leg of the syphon, and draw- ing the tears in at the openings of the puncta. The lachrymal sac and duct are very frequently diseased and obstruct- ed. For example, after small-pox, syphilis, or in scrophulous consti- tutions, the inner membrane of the sac being of the nature of the pitui- tary membrane of the nose, inflames, swells, and adheres. The eonse- *' “ Vor dern Thiiinensack liegt das ligamentum pafpebrale internutri mil dem orbicularis palpebrarum; hinler dem Thiauensack einer Kieiner lVlukel, musculus sacci lacryrnalis dor von dem hinteren Rande der Fossa lacrytnalis entspringt und sich an der hintereu Fliiche beidcr Tarsorum endiget.1’—Haudbuch der anatomic des menschlicheu Kgrpers u. s. f. von bo h arm Christian. Rosenmuller. Oritto verbesserte auflage Leipzig foci K. F. Koehler, 1819. ON THE MOTIONS OP THE EYE. 213 quences of this are, first, a swelling of the lachrymal sac in the inner angle of the eye, and a watery or weeping eye ; upon pressing the tu- mour, the tears, mixed with mucus, are forced back through the puncta ; by and bye the sac inflames and suppurates ; matter is discharged by pressure of the sac : and, lastly, it is eroded and bursts out, discharging the tears and matter on the cheek. This is the complete character of the fistula lachrymalis. While the sac bursts outwardly, it often does further mischief within, by making carious the thin lamina of bone in which it lies. MOTIONS OF THE EYE-BALL AND EYE-LIDS. We do not reflect on those actions of our frame which are most admira- ble in themselves, which minister continually to our necessities, and perfect the exercise of our organs, until we be deprived of them ; like unnatu- ral children, unconscious or unmindful of indulgence, we feel only the loss of benefits. “ With much compassion,” says the religious philoso- pher, “ as well as astonishment at the goodness of our loving Creator, have I considered the sad state of a certain gentleman, who, as to the rest, was in pretty good health, but only wanted the use of these two little muscles that serve to lift up the eye-lids, and so had almost lost the use of his sight, being forced as long as this defect lasted, to shove up his eye-lids with his own hands !”* Two objects are attained through the motion of the eye-ball. First, the control and direction of the eye to objects ; secondly, the preserva- tion of the organ itself, either by withdrawing the surface from injury, or by the removal of what is offensive to it. Without keeping this distinc- tion before us, we shall not easily discover the uses of the parts. There is a motion of the eye ball, which, from its rapidity, has escaped observation. At the instant in which the eye-lids are closed, the eye-ball makes a movement which raises the cornea under the upper eye-lid. If we fix one eye upon an object, and close the other eye with the fin- ger in such a manner as to feel the convexity of the cornea through the eye-lid, when we shut the eye that is open, we shall feel that the cornea of the other eye is instantly elevated; and that it thus rises and falls in sympathy with the eye that is closed and opened. This change of the position of the eye-ball takes place during the most rapid winking mo- tions of the eye-lids. When a dog was deprived of the power of clos- ing the eye-lids of one eye by the division of the nerve of the eye-lids, the eye did not cease to turn up when he was threatened, and when he winked with the eye-lids of the other side. In patients deprived of the motion of the orbicularis palpebrarum by paralysis, we see every effort to close the eye-lids attended with a turning up of the eye-ball. Nearly the same thing I observed in a girl whose eye-lids were attached to the surrounding skin, owing to a burn ; for the fore part of the eye- ball being completely uncovered, when she would have winked, instead of the eye-lids descending, the eye-balls were turned up, and the cornea was moistened by coming into contact with the mouths of the lachrymal ducts. * Paley’s Natural Theology. 214 ON THE MOTIONS OF THE EVE. The purpose of this rapid insensible motion of the eye-ball will be un- derstood on observing the form of the eye-lids and the place of the lach- rymal gland. The margins of the eye-lids are flat, and when they meet, they touch only at their outer edges, so that when closed there is a gut- ter left between them and the cornea. If the eye-balls were to remain without motion, the margins of the eye-lids would meet in such a manner on the surface of the cornea, that a certain portion would be left un- touched, and the eye would have no power of clearing off what obscured the vision, at that principal part of the lucid cornea which is in the very axis of the eye; and if the tears flowed they would be left accumulated on the centre of the cornea, and winking, instead of clearing the eye, would suffuse it. To avoid these effects, and to sweep and clear the surface of the cornea, at the same time that the eye-lids are closed, the eye-ball revolves, and the cornea is rapidly elevated under the eye-lid. Another effect of this motion of the eye-ball is to procure the dis- charge from the lachrymal ducts ; for by the simultaneous ascent of the cornea, and the descent of the upper eye-lid, the membrane on which the ducts open is stretched, and the effect is like the elongation of the nipple, facilitating the discharge of tears. By the double motion, the descent of the eye-lid, and the ascent of the cornea at the same time, the rapidity with which the eye escapes from injury is increased. Even creatures which have imperfect eye- lids, as fishes, by possessing this rapid revolving motion of the eye, avoid injury and clear off impurities. I may observe in passing, that there is a provision for the preserva- tion of the eye, in the manner in which the eye-lids close, which has not been noticed ; while the upper eye-lid falls, the lower eye-lid is moved towards the nose. This is a part of that curious provision for collect- ing offensive particles towards the inner corner of the eye. If the edges of the eye-lids be marked with black spots, it will be seen that when the eye-lids are opened and closed, the spot on the upper eye-lid will descend and rise perpendicularly, while the spot on the lower eye- lid will play horizontally like a shuttle. To comprehend certain actions of the muscles of the eye, we must remember that the caruncle and membrane called semilunaris, seated in the inner corner of the eye, are for ridding the eye of extraneous matter, and are, in fact, for the same purpose with that apparatus which is more perfect and appropriate in beasts and birds. In quadrupeds there is a gland for secreting a glutinous and adhesive fluid, which is seated on that side of the orbit next the nose ; it is quite distinct from the lachrymal gland; it is squeezed by an apparatus of muscles, and the fluid exudes upon the surface of the third eye-lid. This third eye-lid is a very peculiar part of the apparatus of preserva- tion. It is a thin cartilage, the posterior part of which is attached to an elastic body. This body is lodged in a division or depression of the orbit on the side towards the nose. When the eye is excited, the eye- ball is made to press on the elastic body, and force it out of its recess or socket; the consequence of which is the protrusion of the cartilagi- nous third t-ye-lid, or haw, as it is termed in the horse. By this me- chanism the third eye-lid is made to sweep rapidly over the surface of the cornea, and by means of the glutinous fluid with which its surface is bedewed, it attaches and clears away offensive particles. ON THE MOTIONS OF THE EYE. 215 In birds the eye is an exquisitely fine organ, and still more curiously, and as we might be tempted to say, artificially protected. The third eye-lid is more perfect ; it is membranous and broad, and is drawn over the surface of the eye by means of two muscles which are attached to the back part of the eye-ball and by a long round 'endon, that makes a course of nearly three parts of the circumference of the ball. The lachrymal gland is small, and seated low, but the mucous gland is of great size, and seated in a cavity deep and large, and on the inside of the orbit. As the third eye-lid is moved by an apparatus which cannot squeeze the mucous gland at the same time that the eye-lid is moved, as in quadrupeds, the oblique muscles are particularly provided to draw the eye-ball against the gland, and to force out the mucus on the surface of the third eye-lid. It flows very copiously; and this is probably the reason of the smallness of the proper lachrymal gland which lies on the opposite side of the orbit. We already see two objects attained through the motion of these parts ; the moistening the eye with the clear fluid of the lachrymal gland, and the extraction or rather the protrusion of offensive particles. There is another division of this subject no less curious : the different conditions of the eye during the waking and sleeping state, remain to be considered. If we approach a person in disturbed sleep, when the eye- lids are a little apart, we shall not see the pupil nor the dark part of the eye, as we should were he awake, for the cornea is turned upwards un- der the upper eye-lid. If a person be fainting, as insensibility comes over him the eyes cease to have speculation; that is, they want direction, and are vacant, and presently the white part of the eye is disclosed by the re- volving of the eye-ball upwards. So it is on the approach of death ; for, although the eye-lids be open, the pupils are in part hid, being turned up with a seeming agony, which however is the mark of increasing insen- sibility. It will now be admitted that the variety of motions to which the eye is subjected, require the complication of muscles which we find in the or- bit : and it must be obvious to the most casual observer, that unless these various offices and different conditions of the eye be considered, it will be in vain to attempt an accurate classification of the muscles of the orbit. OF THE ACTIONS OF THE MUSCLES OF THE EYE, AND THEIR NATURAL CLASSIFICATION. The muscles attached to the eye-ball are in two classes, the recti and obliqui. The recti muscles are four in number, and come from the bot- tom of the orbit, and run a straight course forwards and outwards ; they embrace the eye-ball, and are inserted at four cardinal points into it. The obliqui are two muscles having a direction backwards and out- wards ;* they embrace the eye-ball, one passing over it obliquely, the other under it obliquely. That the recti muscles perform the office of directing the axis of the eye, turning it round to every point in the sphere of vision, there are many * We may say so, tor although the superior oblique muscle comes from the back of the orbit, yet, by passing through the trochlea, it has a course backwards and outwards to it in- sertion. 216 ON THE MOTIONS OF THE EVE The muscles of the eye seen in front. A. B. C. D. The recti mus- cles ; voluntary muscles. E. The superior oblique mus- cle or trochlearis. a. the trochlea cut ofT from the boue and left attached to the tendon. It is a loop through which the tendon runs. b. The tendon of the troch- learis muscle expanding and running to its inser- tion. G. The inferior oblique mus- cle. It is seen, like the tendon of the superior ob- lique, to run backwards and outwards. proofs. In the first place, their origin, course, and insertion, accurately fit them for this office ; and they are obviously equal to it, unassisted by other muscles. In the next place, from man down to the cuttle-fish, the voluntary motions of the eyes are the same, and the origin, course, and insertion of these muscles are similar, while the other muscles vary with the change of apparatus which is around the eve. The muscle of the eye seen in profile. A. B C. D. Three of the recti muscles. They arise together from the perios- teum of the bottom of the orbit, and are inserted into the anterior part of the sclerotic coat of the eye. E. The superior oblique muscle, or trochlearis. a. The trochlea. b. The reflected tendon inserted into the back and outer part of the sclerotic coat. G. The inferior oblique muscle. c. Its origin from the anterior part of the orbit. d. Its insertion into the back and outer part of eye-ball. The oblique muscles of the eye stand contrasted with the recti in every respect; in number, size, and direction. Yet it is a received ON THE MOTIONS OP THE EYE. 217 opinion, that they antagonize the recti, and keep the eye suspended. To this opinion there are many objections. 1. In creatures where the eye is socketed on a cup of cartilage and cannot retract, the oblique muscles are nevertheless present. 2. Where a powerful retractor mus- cle is bestowed in addition to the recti muscles, the oblique muscles have no additional magnitude given to them. 3. In matter of fact, the human eye cannot be retracted by the united action of the recti as we see quadrupeds draw in their eyes, which is an argument against these muscles being retractors, and therefore against the obliqui being their opponents, to draw it forward. By dissection and experiment it can be proved, that the oblique mus- cles are antagonists to each other, and that they roll the eye in opposite directions, the superior oblique directing the pupil downwards and out- wards, and the inferior oblique directing it upwards and inwards. But it is proved that any two of the recti muscles are equal to the direction of the pupil in the diagonal between them, and there is no reason why an additional muscle should be given, to direct the pupil upwards and inwards more than upwards and outwards, or downwards and inwards. It is evident, then, that the oblique muscles are not for assisting the recti in directing the eye to objects, but that they must have some other ap- propriate office. If we proceed farther, it must be by experiment. To these, other objections, no less strong, may be added. We have just found that certain very rapid motions are to be performed by the eye-ball; now it can ’be demonstrated, that a body will be moved in less time by a muscle which is oblique to the line of motion, than if it lay- in the line on which the body moves. If the oblique muscles were ei- ther opponents or coadjutors of the recti, there appears no reason why they should be oblique, but the contrary ; for as the points of their in- sertion must move more rapidly than those of the recti, they are unsuit- able. On the other hand, that there may be no difference in the time of the action and relaxation of the several classes, we see a reason why one rectus should be opposed by another, and why there being occasion for one oblique, its antagonist should also be oblique. In proportion as a muscle gains velocity by its obliquity, it loses power; from the obliquity, therefore, of these muscles believed to be opposed to the recti, and from there being two of them to four of the latter, they are disproportioned in strength, and the disproportion proves that the two classes of muscles are not antagonists. EXPERIMENTAL ENQUIRY INTO THE ACTION OF THESE MUSCLES. I. I divided the superior rectus or attollens in a rabbit, and felt some- thing like disappointment on observing the eye remain stationary. Shortly afterwards, on looking to the animal while it was feeding, I saw the pupil depressed, and that the animal had no power of raising it. The explanation I conceive to be this : during the experiment the eye was spasmodically fixed by the general action of the muscles, and par- ticularly by the powerful retractor, a muscle peculiar to quadrupeds. But on the spasm relaxing, and when the eye was restored to the influ- ence of the voluntary muscles, the recti, the voluntary power of raising 218 ON THE MOTIONS OF THE ETE. the eye being lost by the division of the superior muscle, the eye was permanently depressed. II. Wishing to ascertain if the oblique muscles contract to force the eye-ball laterally towards the nose, I put a fine thread round the tendon of the superior oblique muscle of a rabbit, and appended a glass bead to it of a weight to draw out the tendon a little. On touching the eye with a feather, I had the pleasure of seeing the bead drawn up. And on repeating the experiment, the thread was forcibly drawn through my fingers. By experiments made carefully in the dead body, (having distended the eye-ball by dropping mercury into it to give it its full globular figure,) I had found that the action of the superior oblique muscle is to turn the pupil downwards and outwards, and that the inferior oblique just reverses this motion of the eye. In the above experiment there is abundauce of proof that the superior oblique muscle acted, and yet the pupil was not turned downwards and outwards, therefore both oblique muscles must have been in action. Their combined action draws the eye-ball towards the nose. In the violent spasmodic affection of the eye, when it is painfully irrita- ted, I believe that all the muscles, both of the eye-ball and eye-lids, are excited. In quadrupeds, I have ascertained that the oblique muscles act ■when the haw is protruded, but I have also found that the retractor oculi alone, is capable of forcing forwards the haw. But quadrupeds having an additional apparatus of muscles to those of the human eye, are not suited for experiments intended to illustrate the motions of our eyes. The monkey has the same muscles of the eye with man. III. I cut across the tendon of the superior oblique muscle of the right eye of a monkey. He was very little disturbed by this experiment, and turned round his eyes with his characteristic enquiring looks, as if nothing had happened to affect the eye. IV. I divided the lower oblique muscle of the eye of a monkey. The eye was not, in any sensible manner, affected : the voluntary motions were perfect after the operation. V. On holding open the eyes of the monkey, which had the superior oblique muscle of the right eye divided, and waving the hand before him, the right eye turned upwards and inwards, while the other eye had a scarcely perceptible motion in the same direction. When the right eye was thus turned up, he seemed to have a difficulty in bringing it down again. From experiments it is proved, that the division of the oblique muscles does not in any degree affect the voluntary motions by which the eye is directed to objects. This cannot, however, be said of the involuntary winking motions of the eyes. We have seen that in winking to avoid injury, the oblique muscles were in operation ; and that the inferior oblique muscle gained in the power of elevating the eye-ball by the division of the superior ob- lique. its opponent. ON THE MOTIONS OF THE EYE. 219 These revolving motions accompanying the winking motions of the eye-lids, are of the utmost consequence to the preservation of the organ. A case which was some time under my observation proved this. By a defect of motion, the eye and eye-lids remained fixed, and the conse- quence was that the cornea inflamed and became opaque. Another cu- rious circumstance in this case was, that when the eye-lids were closed, the patient still saw red light through the affected eye, the reason of which was that the eye-ball did not turn up when the eye-lid was closed. It we close the eyes opposite to the window or before a candle, and continue to attend to the sensations of the eye, we shall still see red light coming through the eye-lids. But if we make an effort to close the eye-lids (though they be already shut), we shall be in momentary darkness, because during the effort the eye-balls are then turned up. Thus it appears that the dropping of the eye-lid would make but an imperfect curtain before the eye, and the eye, to be entirely protected from the light, must have the pupil turned upwards. * ON THE TWO CONDITIONS OF THE EYE, ITS STATE OF REST, AND OF ACTIVITY. The eye is subject to two conditions : a state of rest with entire obli- vion of sensation, and a state of watchfulness, during which both the op- tic nerve and the nerve of voluntary motion are in activity. When the eye is at rest, as in sleep, or even when the eye-lids are shut, the sensa- tion on the retina being then neglected, the voluntary muscles resign their office, and the involuntary muscles draw the pupil under the upper eye-lid. This is the condition of the organ during perfect repose. On the other hand, there is an inseparable connexion between the ex- ercise of the sense of vision and the exercise of the voluntary muscles of the eye. When an object is seen, we enjoy two senses ; there is an impression upon the retina; but we receive also the idea of position or relation which it is not the office of the retina to give. It is by the con- sciousness of the degree of effort put upon the voluntary muscles, that we know the relative position of an object to ourselves. The relation existing between the office of the retina and of the voluntary muscles, may be illustrated in this manner. Let the eyes be fixed upon an illuminated object until the retina be fa- tigued, and in some measure exhausted by the image ; then, closing the eyes, the figure of the object will continue present to them : and it is quite clear that nothing can change the place of this impression on the retina. But notwithstanding that the impression on the retina cannot be changed, the idea thence arising may. For by an exertion of the volun- tary muscles of the eye-ball, the body seen will appear to change its place, and it will, to our feeling, assume different positions, according to the muscle which is exercised. If we raise the pupil, we shall see the body elevated, or if we depress the pupil, we shall see the body placed below us ; and all this takes place while the eye-lids are shut, and when no new impression is conveyed to the retina. The state of the retina is here associated with a consciousness of muscular exertion ; and it shows I * In the case above alluded to, the patient had lost both motion and the common sensibility of the eye, the office of the fifth nerve was lost, yet the optic nerve retained its power, and he could see. 220 OF THE MOTIONS OF THE EYE. that vision in its extended sense is a compound operation, the idea of po- sition of an object having relation to the activity of the muscles. We may also show, by varying this experiment, that an agitated state of the muscles, or a state of action where the muscles are at variance or confused, affects the idea of the image. If we look on the luminous bo- dy so as to make this impression on the retina, and then cover the face so as to exclude the light, keeping the eye-lids open, and if we now squint, or distort the eyes, the image which was vividly impressed upon the retina instantly disappears as if it were wiped out. Does not this circumstance take place, because the condition of the muscles thus un- naturally produced, being incongruous with the exercise of the retina, disturbs its operation 1 If we move the eye by the voluntary muscles, while this impression continues on the retina, we shall have the notion of place or relation raised in the mind ; but if the motion of the eye-ball be produced by any other cause, by the involuntary muscles, or by pressure from without, we shall have no corresponding change of sensation. If we make the impression on the retina in the manner described, and shut the eyes, the image will not be elevated, although the pupils be ac- tually raised, as it is their condition to be when the eyes are shut, be- cause there is here no sense of voluntary exertion. If we sit at some distance from a lamp which has a cover of ground-glass, and then fix the eye on the centre of it, and then shut the eye and contemplate the phan- tom in the eye ; and if, while the image continues to be present of a fine blue colour, we press the eye aside with the finger, we shall not move that phantom or image, although the circle of light produced by the pressure of the finger against the eye-ball moves with the motion of the finger. May not this be accounted for in this manner : the motion produced in the eye-ball not being performed by the appropriate organs, the voluntary muscles, it conveys no sensation of change to the sensorium, and is not associated with the impression on the retina, so as to affect the idea ex- cited in the mind ? It is owing to the same cause that, when looking on the lamp, by pressing one eye, we can make two images, and we can make the one move over the other. But, if we have received the im- pression on the retina so as to leave the phantom visible when the eye- lids are shut, we cannot, by pressing one eye, produce any such effect. We cannot, by any degree of pressure make that image appear to move, but the instant that the eye moves by its voluntary muscles, the image changes its place ; that is, we produce the two sensations necessary to raise this idea in the mind ; we have the sensation on the retina com- bined with the consciousness or sensation of muscular activity. These experiments, and this explanation of the effect of the associated action of the voluntary muscles of the eye-ball, appear to me to remove an obscurity in which this subject has been left by the latest writers. In a most scientific account of the eye and of optics, lately published by Dr. Brewster, it is said on this question, “ We know nothing more than that the mind residing, as it were, in every point of the retina, refers the impres- sion made upon it, at each point, to a direction coinciding with the last portion of the ray which conveys the impression.” The same author says, “ Kepler justly ascribed erect vision from an inverted image to an operation of the mind, by which it traces the rays back to the pupil, and ON THE MOTIONS OF THE EYE. 221 thus refers the lower part of the image to the upper side of the eye.” What can be here meant by the mind following back the ray through the humours of the eye ? It might as well follow the ray out of the eye. A greater authority says, we puzzle ourselves without necessity. “ We call that the lower end of an object which is next the ground.” No one can doubt that the obscurity here, is because the author has not given himself room to illustrate the subject by his known ingenuity and pro- foundness. But it appears to me, that the utmost ingenuity will be at a loss to devise an explanation of that power by which the eye becomes acquainted with the position and relation of objects, if the sense of mus- cular activity be excluded, which accompanies the motion of the eye-ball. Let us consider how minute and delicate the sense of muscular motion is by which we balance the body, and by which we judge of the position of the limbs, whether during activity or rest. Let us consider how imper- fect the sense of touch would be, and how little of what is actually known through the double office of muscles and nerves, would be attained by the nerve of touch alone, and we shall be prepared to give more impor- tance to the recti muscles of the eye, in aid of the sense of vision : to the offices performed by the frame around the eye-ball in aid of the in- strument itself. OF THE EXPRESSION OF THE EYE, AND OF THE ACTIONS OF THE OBLIQUE MUSCLES IN DISEASE. During sleep, in oppression of the brain, in faintness, in debility after fever, in hydrocephalus, and on the approach of death, the pupils of the eyes arc elevated. If we open the eye-lids of a person daring sleep or insensibility, the pupils will be found elevated. Whatever be the cause of this, it will be found that it is also the cause of the expression in sickness, and pain, and exhaustion, whether of body or mind : for then the eye-lids are relaxed and fallen, and the pupils elevated so as to be half covered by the upper eye-lid. This condition of the eye during its insensible unexercised state, we are required to explain. It is a fact familiar to pathologists, that when debility arises from af- fection of the brain, the influence is greatest on those muscles which are, in their natural condition, most under the command of the will. We may perceive this in the progressive stages of debility in the drunk- ard, when successively the muscles of the tongue, the eyes, the face, the limbs, become unmanageable; and, under the same circum- stances, the muscles which have a double office, as those of the chest, lose their voluntary motions, and retain their involuntary motions, the force of the arms is gone long before the action of breathing is affect- ed. If we transfer this principle, and apply it to the muscles of the eye, we shall have an easy solution of the phenomena above enumerated. The recti are voluntary muscles, and they suffer debility before the ob- lique muscles are touched by the same condition ; and the oblique mus- cles prevailing, roll the eye. If it be farther asked, why does the eye roll upwards and inwards ? We have to recollect, that this is the natural condition of the eye, its position when the eye-lids are shut and the light excluded, and the recti at rest and the obliqui balanced. 222 ON THE MOTIONS OF THE EYE. Although I am aware that medical histories do not often lead to the improvement of strict science, yet I am tempted to describe the condi- tion of a patient now under my care, because it exhibits a succession of those phenomena which we seek to explain. He presented himself to me in the hospital, with a distinct squint, the left eye being distorted from the object. On the eye-lid of the right eye there was a deep ve- nereal ulcer; the man was in danger of losing the right eye, and re- quired prompt assistance ; but before he could be brought under the in- fluence of mercury, the inflamed sore became deeper and the cornea opaque. The superior rectus muscle being, as I suppose, injured by the increasing depth of the sore, the pupil became permanently de- pressed. The sight of the right eye being now lost, the left eye came into use; it was directed with precision to objects, he had no difficulty in using it, and it daily became stronger. After a few weeks, medicine having had its influence, the sore on the upper eye-lid of the right eye healed, the inflammation and opacity of the eye gradually diminished, the light became again visible to him; first it was yellow, and then a deep purple. And now the muscles re- sumed their influence, and the eye was restored to parallel motion with the other, and so as considerably to embarrass the vision. But the in- flammation of the upper eye-lid had been so great, as to diminish its mobility; and what appeared most extraordinary, the lower eye-lid as- sumed the office of the upper one, and a very unusual degree of motion was remarked in it. It was depressed when he attempted to open the eye, and elevated and drawn towards the nose, when he closed the eye. But the upper eye-lid was not only stiff, but diminished in breadth; so that notwithstanding the remarkable elevation of the lower eye-lid, their margins could not be brought together, and we could perceive the mo- tion of the eye-ball; in his attempt to close the eye we constantly saw the pupil elevated, and the white part of the eye exposed. I shall now attempt the explanation of these phenomena. The impression upon the left eye had been weak from infancy, and the retina being unexercised, the recti, or voluntary muscles, wanted their excitement, and were deficient in activity ; the involuntary muscles therefore prevailed, and the pupil was turned upwards and inwards, and consequently removed from the axis of the other eye. But when that other eye became obscured, the left eye being the only inlet to sensation, the attention became directed to the impression on the retina, the volun- tary muscles were excited to activity, and they brought the eye to bear upon objects. This eye improved daily, because the natural exercise of a part is its stimulus to perfection, both in function and in growth. When the right eye became transparent, aud the light was admitted, the volun- tary muscles of that eye partook of their natural stimulus, and com- menced that effort in search of the object, which in the course of a few days brought the eye to its proper axis, and both eyes to parallelism. The next thing that attracts our attention in this short narrative, is the revolving of the eye-ball. It has been explained in a former part of the paper, that when the eye-lids are shut, the recti, or voluntary muscles, resign their office, and the inferior oblique muscle gains power, and the eye-ball traverses so as to raise the pupil. It will not have escaped ob- servation, that the pupil of this eye was depressed, and could not be ele- vated by a voluntary act for the purpose of vision, owing, as we have ON THE MOTIONS OF THE EYE. 223 supposed, to the injury of the rectus attollens, at the same time that it was thus raised involuntarily, in the attempt to shut the eye; a proof that this insensible motion is performed by the lower oblique muscle, and not the superior rectus muscle. The circumstance of the lower eye-lid assuming the functions of the upper one, and moving like the lower eye-lid of a bird, reminds me of an omission in the account of authors. They have sought for a de- pressor of the inferior eye lid, which has no existence, and is quite un- necessary ; for the motion of the M. levator palpebrce superioris opens wide the eye-lids, and depresses the lower eye-lid, at the same time that it elevates the upper eye lid. If we put the finger on the lower eye-lid when the eye is shut, and then open the eye, we shall feel that during this action the eye-ball is pushed outwards; and we may observe, that the lower eye-lid is so adapted as to slip off the convex surface of the ball, and is consequently depressed. The reason of this is, that the muscle which raises the upper eye-lid passes over a considerable part of the upper and back part of the eye-ball, and the origin and insertion of the muscle being under the highest convexity of the ball, that body must be pressed forwards in proportion to the resistance of the upper eye-lid to rise. In the preceding case the upper eye-lid being stiff and unyielding, both the origin and the insertion of the levator palpebrce became fixed points ; consequently, the action of the muscle fell entirely on the eyo- ball itself, whereby it was forced downwards and forwards in an unusual manner, and so depressed the lower eye-lid to an unusual degree. Thus the muscle became a depressor of the inferior eye-lid, instead of an ele- vator of the upper eye-lid ! The motion of elevation in the lower eye- lid was of course performed by an increased action of the lower portion of the orbicularis palpebrarum. But it has been observed, that the shutting of the eye-lids is not the only part of the act of preservation, and that the motions of the eye-lids are attended with a rolling of the eye-ball. How is this relation between the eye-lids and eye-ball established ? This leads to an examination of the fourth nerve, which could not be done before. THE FOURTH NERVE. We have seen that it takes its origin from the brain, at a part remote from all the other nerves which run into the orbit. It threads the intrica- cies of the other nerves without touching them, and is entirely given to one muscle, the superior oblique. We may observe, too, that this singularity prevails in all animals. What office can this nerve have in reference to this one muscle ? Why is its root, or source, different from the other nerves,—from the nerve of vision, the nerve of common sensibility, and the nerve of voluntary motion? We now reflect, with increased interest, on the offices of the oblique muscles of the eye, observing that they perform an insensible rolling of the eye-ball, and hold it in a state of suspension between them. We have seen that the effect of dividing the superior oblique was to cause the eye to roll more forcibly upwards, and if we suppose that the influence of the fourth nerve is, on certain occasions, to cause a relaxation of the muscle to which it goes, the eye- ball must be then rolled upwards.* * The nerves have been considered so generally as instruments for stimulating the mus* !es, without thought of their acting in the opposite capacity, that some additional illustration 224 ON THE MOTIONS OF THE EYE. The course of inquiry leads us, in the next place, to observe the vi- cinity of the root of this fourth nerve to the origin of the respiratory of the fa e, and we find them arising from the same tract of fibrous sub- stance. The column of medullary matter which constitutes that part of the medulla oblongata from which the respiratory nerves arise, termi- nates upwards, or at its anterior extremity, just under the corpora quad- rigemina, and there the fourth arises. Is it possible, then, we say, that there can be any correspondence between the general act of respi- ration, and the rolling of the eye ? Led thus to make the experiment, I was gratified to find it so easy to give the proof. On stopping the nos- trils with the handkerchief, every effort to blow the nose will be attended by a rapid rising of the cornea under the upper eye-lid. And on every occasion when the eye-lids suffer contraction through the agency of the respiratory nerve of the face, as in sneezing, the eye-ball is rolled up- wards, undoubtedly through the agency of the fourth nerve. It is plain that we must consider the nerves and muscles of the eye- lids in a double capacity, in their voluntary and involuntary actions. In the first, the motions of the eye-lids combine with the whole muscles of the eye-ball, as we may perceive in the voluntary contractions and squeez- ing of the eye ; but in the insensible and involuntary motions of the eye- lids, there would be no sympathy with the muscles of the eye-ball, and therefore no correspondence in the motion of these parts, without a nerve of the nature of the fourth ; that is, a nerve which having diverged from the root of the respiratory nerves, takes its course to the oblique muscles. In one word, the connexion of its root declares the office of this nerve. The expression of the eye in passion confirms the truth of this rela- tion being established by a respiratory nerve, and consequently by a nerve of expression. In bodily pain, in agony of mind, and in all this class of passions, the eyes are raised and dragged, in conjunction with the changes to which the other features are subjected. If it be asked now, as it has been asked for some hundred years past, why the fourth nerve goes into the orbit, where there are so many nerves, why it is so distant in its origin from the other nerves, and why it sends off no twig or branch, but goes entirely to one muscle of the eye 'l the answer is, to provide for the insensible and instinctive rolling of the eye-ball; and to associate this motion of the eye-ball with the winking motions of the eye-lids; to establish a relation between the eye and the extended respiratory system: all tending to the security or preservation of the organ itself. may be necessary here. Through the nerves is established the connexion between the mus- cles, not only that connexion by which muscles combine to one effort, but also that relation between the classes of muscles by which the one relaxes while the other contracts. I ap- pended a weight to a tendon of an extensor muscle, which gently stretched it and drew out the muscle; and I found that the contraction of the opponent flexor was attended with a weight, which indicated the relaxation of the extensor. To establish this connexion between two classes of muscles, whether they be grouped near together, as in the limbs, or scattered widely as the muscles of respiration, there must be particular and appropriate nerves to form this double bond, and to cause them to conspire in relaxation as well as to combine in contraction. If such a relationship be established, through the distribution of nerves, between the muscles of the eye lids and the superior oblique muscles of the eye-ball, the one will relax while the other contracts. DISTANCE OF OBJECTS. 225 OF THE MANNER IN WHICH THE EVE ADAPTS ITSELF TO THE DIS- TANCE OF OBJECTS. This is a question which many have endeavoured to answer, and ma- ny have failed ; the proof of this is, that there is not one explanation of the manner in which the eye adapts itself to the distance of objects, but many explanations equally ingenious. One opinion is, that the eye is at rest when we see the distant parts of a landscape, but that the direction of the eye to the nearer objects is at- tended with an effort. This effort is the action of the straight muscles of the eye compressing the ball of the eye, so as to lengthen the axis as much as is necessary to allow the pencils of rays to unite in points upon the retina. To this opinion it is objected, that in some animals the sclerotic is hard, and not capable of changing its figure ; that in man, the pressure would be unequal; that the unelastic retina would be thrown into irregu- lar tolds ; that these muscles, being voluntary muscles under the will, we should be more conscious of their operation than we are ; and that, while the mind remains attentive to distant objects, no voluntary exer- tion of these muscles can affect the distinctness of the objects. Again, to make the eye change its accommodation from the distinct vision of objects, at six inches to fourteen feet five inches, would require such a pressure as might lengthen the axis of the eye one tenth part, which again would form an oval that would derange the retina. Another opinion is, that when the eye sees the nearest objects it is at rest, and that, in attending to distant objects, the straight muscles draw back the fore part of the eye into the socket, and thus shorten the axis. To this opinion, of course, the same objections lie as to the supposition that the axis is lengthened by the operation of the muscles. I must say, that it appears to me, if the effect contemplated were refer- able to the changing the configuration of the eye, we would be sensible of a shift in the position of all objects seen lateral to the axis of vision, and that, by looking to objects afar oft', we should diminish or extend the field of vision laterally. I can observe no such effect. There are some who have entertained an opinion, that the iris, by its contraction, operates so on the circular margin of the cornea, where it is connected with the sclerotic coat, as to make the cornea more con- vex, and thus increase its power of concentrating the rays and enable the eye to see near objects distinctly. To account for this power in the iris, Dr. Jurm, the proposer of this hypothesis, supposes that there is a greater muscular ring in the margin of the iris connected with the edge of the cornea ; the existence of these muscular fibres is not demonstrated, but he says, since the lesser muscular ring in the inner margin of the iris is not proved by ocular inspection, and yet is justly inferred from its ef- fects, viz. the contraction of the pupil ; in the same way, “ the change “ of conformation in the eye has not yet been adequately accounted for, “ bid may be fairly made out by supposing the existence of the greater “ muscular ring.” His conclusion is in these words :—“ When we u view objects nearer than the distance of fifteen or sixteen inches, 1 u suppose the greater muscular ring of the iris contracts, and thereby 226 DISTANCE OF OBJECTS. “ reduces the cornea to a great convexity ; and when we cease to view “ these near objects, this muscular ring ceases to act, and the cornea, by “ its spring, returns to its usual convexity suited to fifteen or sixteen <{ inches. In which condition the elasticity of the cornea on the one “ side, and the tone of the muscular ring on the other, may be consi- “ dered as two antagonists in a perfect equilibrium.” To this opinion it is objected, that the iris is not rooted in the cornea, but in the sclerotic coat, which is firm in man, and inflexible in many ani- mals. We have also to consider, that this delicate and invisible circle of muscular fibres has not only to contract the margin of the cornea, but, in this action, to alter the configuration of the whole eye. The eye-ball is a whole equally distended, and no part of it can suffer con- traction without a resistance from the whole of the coats : besides, in this case, the alternation of light and the brightness of objects would be perpetually obscuring the image, by the play of the iris causing an alte- ration of the focus of the cornea. But Dr. Jurin did not attribute the whole effect to the action of the iris. He thus explains the use of the fluid surrounding the lens and the membranous capsule :—When the eye is to be suited to greater distances, he supposed that the ligamentum ciliare contracts its longitudinal fibres, and, by that means, draws the part of the interior surface of the capsule, into which these fibres are inserted, a lit- tle forward and outward. By this action, he supposed that the fluid, within the capsule of the lens, flows from the middle towards the mar- gin ; and, consequently, the centre of the capsule of the lens is reduced to a less degree of convexity ; and that the elasticity of the capsule, and the tone of the ligament, may be looked upon as two antagonists perfect- ly in equilibrio with one another. In the state of rest, the eye is con- ceived, by Dr. Jurin, to be adapted to the middle distance ; by the in- crease of the convexity of the cornea, to be adapted to nearer vision ; and by the change in the capsule of the lens, to be fitted to distant objects. To this last supposition it is objected, that there is a simplicity in the operations of nature ; that the change wrought upon the capsule of the lens is insufficient to account for the whole effect, and that, therefore, there is a presumption that it has no share in producing the change ; that there are no muscular fibres in the ciliary processes ; and lastly, that this fluid, being of density but little, if at all, removed from the aqueous humour, any alteration of its form can have but a very insigni- ficant effect. ♦ It has occurred to others *, that the oblique muscles of the eye-ball, being thrown in opposite directions round it, they may have the effect of elongating the axis of the eye : Again, that the action of the orbicularis muscle of the eye-lids, by compressing the eye-ball, assists in accom- modating the eye for seeing near objects more distinctly. Dr. Monro makes a set of experiments to prove the effect of the orbicularis' mus- cle of the eye-lids ; but I conceive that he has deceived himself, in as- cribing to the compression of the eye-lids, an effect partly produced by a voluntary effort, but in a way which is not understood, and partly by the contraction and dilatation of the pupil, from the degree of opening of the eye-lids. If he be right in his way of accounting for the effects * Hambergerus, Briggs, Keif. Monro. DISTANCE OF OBJECTS. 227 produced in the experiments which he details, they ought to have the ef- fect of precluding the necessity of all further hypothesis ; so fully does the action of the orbicularis muscle seem to him adapted to the end pro- posed. In the first experiment, when he opened his eye-lids wide, and endeavoured to read a book, the letters on which were so near the eye as to be indistinct, he found that he could not do it. In the second ex- periment, keeping the head in the same relation to the book, he brought the edges of the eye-lids within a quarter of an inch of each other, and then made an exertion to read, when he found he could see the letters and words distinctly. When I try this experiment I find the action of the eye-lids to have no sensible effect, unless they are brought very close together : then I do indeed find that they have a most remarkable effect. But in this situation the eye-lids cover the cornea so much, that if they have any effect at all upon the cornea, it must be to compress and flat- ten it, and not to give it a greater convexity. The smaller the opening of the eye-lids, the greater I found the effect; I conceive it to be pro- duced by the optical effect of the eye-lashes correcting the too great converging of the rays ; and the same effect I found to be produced by the marginal hairs of two flat camel-hair brushes, although the eye-lids were kept open. Dr. Monro concludes that, in this action of the eye, 1st, the iris, 2ndly, the recti muscles, 3dly, the two oblique muscles, and, 4thly, the orbicularis palpebrarum, have all their share in accommo- dating it to the distance of objects, and in giving perfect vision. Very ingenious experiments are made by Dr. Young*, to determine whether there be any change in the length of the axis of the eye-ball. He considers it as necessary to account for the power of the eye in adapting it to the distance of objects, that the diameter should be en- larged one seventh : its transverse diameter diminished one fourteenth; and the semi-diameter shortened one thirtieth of an inch. To deter- mine this he fixed the eye, and at the same time he forced in upon the ball of the eye the ring of a key, so as to cause a phantom very accurate- ly defined to extend within the field of perfect vision ; then looking to bodies at different distances, he expected, if the figure of the eye was altered, that the spot, caused by the pressure, would be altered in shape and dimensions ; he expected that instead of an increase of the length of the eye’s axis, the oval spot caused by the pressure of the key, re- sisting this elongation, should have spread over a space at least ten times as large as the most sensible part of the retina; but no such effect took place ; the power of accommodation was as extensive as ever, and there was no perceptible change either in the size or in the figure of the oval spot. Again, he placed two candles so as exactly to answer to the extent of the termination of the optic nerve; he marked accurately the point to which the eye was directed ; he then made the utmost change in its focal length, expecting that, if there were any elon- gation of the axis, the external candle would appear to recede outward upon the visible space ; but this did not happen ; the apparent place of the obscure part was precisely the same as before. A favourite opinion of late has been, that the lens has a power of al- tering its degree of convexity, and thus accommodating itself to the distance of objects. As to the fibrous structure of the lens, there can * Philos. Trans, for 18IOi 228 DISTANCE OF OBJECTS. be no doubt: first it is rent by fissure, then split into lamina, and can hr finally teased out into fibres. This structure was first observed by Leeuwenhoeck. The fibrous structure and muscularity of the lens was brought for- ward by Descartes, as explaining some actions of the eye ; but was again neglected, till more lately, that it has been revived by the inser- tion of Dr. Young’s Observations on Vision in the Philosophical Trans- actions.* The following are Dr. Young’s observations on the appear- ance of the lens :—“ The crystalline lens of the ox is an orbicular con- “ vex transparent body, composed of a considerable number of similar “ coats, of which the exterior closely adheres to the iuterior. Each of “ these coats consists of six muscles, intermixed with a gelatinous sub- f( stance, and attached to six membranous tendons. Three of the ten- “ dons are anterior, three posterior ; their length is about two thirds of “ the semi-diameter of the coat; their arrangement is that of three “ equal and equidistant rays, meeting in the axis of the crystalline ; one “ of the anterior is directed towards the outer angle of the eye, and one u of the posterior towards the inner angle, so that the posterior are “ placed opposite to the middle of the interstices of the anterior ; and “ planes passing through each of the six and through the axis, would (c mark on either surface six regular equidistant rays. The muscular fkfibres arise from both sides of each tendon; they diverge till they “ reach the greatest circumference of the coat, and having passed it, u they again converge till they are attached respectively to the sides of <£ the nearest tendons of the opposite surface. The anterior or poste- “ rior portion of the six viewed together, exhibits the appearance of “ three penaiforme radiated muscles. The anterior tendons of all the “ coats are situated in the same planes, and the posterior ones in the “ continuations of these planes beyond the axis. Such an arrangement “ of fibres can be accounted for on no other supposition than that of muscularity. The mass is inclosed in a strong membranous capsule, i: to which it is loosely connected by minute vessels and nerves; and 11 the connexion is more observable near its greatest circumference. Be- il tween the mass and its capsule is found a considerable quantity of an u aqueous fluid, the liquid of the crystalline.” These muscular fibres could not be excited by Dr. Young so as to change the focal power. The same author states, that nerves enter the leas. I cannot sav I see any tending that way. Supposing that these * ■•'•foe vol. for 1793. DISTANCE OF OBJECTS 229 are muscular fibres *, from their closeness and direction, they would stand acknowledged as forming the strongest and most powerful muscle of its size in the whole body; yet they act only on themselves which re- quires the least possible degree of power. Again, how are they relax- ed ? What power is their antagonist ? As to the tendons 1 do not see their use. Does not the lens act merely on itself? It can require no concentrating of its fibres into tendons; for tendons are found in other parts of the body only where it is necessary to concentrate the whole power of the muscle so as to operate on one point. We know that the transparency of a substance depends on a certain arrangement of its fibres. Would not this change of position in the lens affect its transparency ? The effect is observed in the cornea. However successfully the admirable methods of Dr Young may have decided the matter as to the conformation of the eye-ball, he has not sa- tisfied me that the power of adaptation is in the lens. We learn from Sir Everard Home,! that Mr. John Hunter has proved the lens to be laminated, and those laminee to be composed of fibres ; and upon the same authority, we learn that his opinion was in favour of the muscularity of its structure. Sir E. Home wished to follow out this subject, by including it in the Croonian Lecture. He, with the assistance of Mr. Ramsden, thought he had determined that a patient after the ex- traction of the cataract, still retained the power of adapting the eye to the distances of objects. Dr. Young, on the contrary, is positive that in those who have lost the crystalline humour by operation, the focal dis- tance is totally unchangeable. By Mr. Ramsden’s ingenious contrivance, the head was fixed accurate- ly and at the same time a microscope was adapted to observe the changes in the convexity of the cornea as the eye was directed alternately to near and to distant objects. In these experiments, the motion of the cornea became distinct, its surface remained in a line with a wire which crossed the glass of the microscope when the eye was adjusted to the distant objects, but projected considerably beyond it when adapted to the near ones, and the space through which it moved was so great as readily to be measured by magnifying the divisions on the scale, and comparing them. In this way it was estimated that it moved the 830 part of an inch (a space distinctly seen in a microscope magnifying 30 times), in the change from the nearest point of distinct vision to the distance of 90 feet. In the evidence from anatomical structure, I cannot think Sir E. Home so happy. He was desirous of determining more accurately than had hitherto been done, the precise insertion of the tendons of the four straight muscles, so as to know whether their action could be extended to the cor- nea or not; he found them to approach within j of the cornea before their tendons became attached to the sclerotic coat. But he did not stop here; he stripped oft' with them the anterior lamina of the cornea. Now, as it is supposed, in these experiments, that the action of the recti muscles upon the sides and back part of the ball compresses the humours, and makes them flow forward so as to distend the cornea: if the extremities of the tendons be inserted into the edge of the cornea and even pass • The fibrous structure of the lens is represented according to Leeuwenhoeck. f See Philos. Trans. 230 DISTANCE OF OBJECTS. over it, as Sir E. Home has demonstrated, their effect would be to flat- ten the cornea, by drawing out and extending its margin. This is a cir- cumstance which Dr. Monro has remarked; and he has found “all the tendinous fibres of the recti muscles firmly attached to the sclerotic coat at the distance of a quarter of an inch from the cornea, and no appearance that any part of them, or that any membrane produced by them, is con- tinued over the cornea.” Dr. Young’s experiment appears to be decisive of the question as re- gards the cornea. He destroyed the influence of the cornea, and still the eye possessed its range ! He did this in the most ingenious manner, by inserting upon his eye a lens with its circular case full of water. The water touched the cornea, and intervened betwixt the cornea and the glass. Consequently, as the power of the cornea exists only by the dif- ference of density of the air and cornea, and as by the interposition of water this power was destroyed, the eye continuing in possession of its ability to adapt itself to distances, this property could not depend on the cornea. Amongst the variety of opinions, the innumerable, ingenious, but con- tradictory experiments for discovering the manner in which the eye adapts itself to the distance of objects, 1 am, for my own part, much at a loss to determine which 1 should prefer. I have often doubted whether these experimenters were not in search of the explanation of an effect which has no existence. I have never been able to determine, why a very slight degree of convexity in the cornea of a short-sighted eye should be so permanent during a whole lifetime, were the cornea elastic in the manner supposed, and capable of being altered in its convexity by the action of muscles. A near-sighted person, with the assistance of a concave glass, can command the objects to the distance of some miles, and with the glass still held to his eye, can see minute objects within three inches of the eye. Now I cannot conceive how the concave glass should give so great a range to the sight: as there can be no change in the glass, it must be the eye which adapts itself to the variety of dis- tances ; yet, without the glass, it cannot command the perfect vision of objects for a few feet. Again, a short-sighted person sees an object dis- tinctly at three inches distant from the eye ; at twelve feet, less distinct- ly ; and when he looks upon the object at twelve feet, the objects beyond it are confused, just as they appear to other men ; but when he directs his attention to the more remote objects, those nearer become indistinct. Now this indistinctness of the object, seen when he examines narrowly the objects beyond them, would argue (did we admit this muscular pow- er in the eye of adapting itself to objects) that the cornea or the lens has become less convex, were we not previously convinced that the ut- most powers of the eye could not bring the object at the distance of twelve feet, or any other intermediate distance, to be more distinctly seen than the fixed and permanent constitution of the eye admits. I cannot help concluding, therefore, that the mechanism of the eye has not so great a power of adapting the eye to various dis ances as is gene- rally imagined, and that much of the effect attributed to mechanical power is the consequence of the motion of the pupil, the effect of light and of at- tention. An object looked upon, if not attended to, conveys no sensation to the mind. If one eye is weaker than the other, the object of the strong- er eye alone is attended to, and the other is entirely neglected : if we look OP VISION. 231 through a glass with one eye, the vision with the other is not attended to. Now objects, as they recede from us, become fainter and fainter in their colours, and the general effect upon the eye is different from those which are near ; and as it happens that the mind must associate with the sensa- tion before it be perfect, there is, consequently, an obscurity thrown over distant objects when we contemplate near ones ; as, on the other hand, the images of near ones are not attended to when the mind is oc- cupied with distant ones, although they be nearly in the line with the dis- tant object examined. The mind, not the eye, harmonizes with the state of sensation, brightening the objects to which we attend. In look- ing on a picture, or a panorama, we look to the figures, and neglect the back-ground ; or we look to the general landscape, and do not perceive the near objects. In short, we experience the whole phenomena pre- sented to the eye when the shades and colours of nature are presented to us from a plane surface, as when the eye opens on all the varieties of a natural scene. It cannot be an adaptation of the eye, but an accommo- dation and association of the mind with the state of impression. or VISION. The eye is certainly the noblest of the organs of sense. It is that with which we should part the most unwillingly, and of which, when deprived, we are most helpless. A celebrated philosopher says, how much more noble is that faculty by which we can find our way in the pathless ocean, traverse the globe, determine its figure and dimensions, delineate every region of it; by which we can measure the planetary orbs, and make discoveries in the sphere of the fixed stars ! VV hile an- other says, it is the universe itself! We are present with the stars which beam upon us, at a distance, that converts to nothing the wide di- ameter of our planetary system. The other senses are the ties which bind us to our dwelling-place, whilst the eye retains the unbounded free- dom of the celestial origiu.* Yet notwithstanding the perfection of the sense of seeing, much of this perfection is gained by the other senses, and particularly by that of touch. If the human body were motionless and inert, the sensation conveyed by the eye would be very imperfect; we should be able to conceive neither the distance nor the figure of ob- jects. But, as it is, the visible magnitude of an object is the sign of its real magnitude ; which knowledge we have acquired by other means. When we look upon an object, we have its visible figure before us, as the sign of its real figure, which, by experience, that is, by motion of the hand, by approach, and the actual comparison with our own bodies, we have in a manner more perfect previously ascertained. Without this combination of actual experience and true knowledge, with the associat- ed signs in the eye, vision would be a continual delusion. Upon other occasions, we are apt enough to acknowledge the powers of association. But the connexion of ideas is in no instance more Con- * Brown 232 OK VISION. stant and secret than in those conveyed by sight and touch. AVhen a solid body is presented to view, we see only the light and shade ; but this raises in our mind the associated ideas from the sense of touch, of solidity, convexity, and angularity, “ the visible idea exciting in us those “ tangible ideas,” which, in the free and promiscuous exercise of our senses, usually accompany it. It is thus that we attribute to the sense of sight what is the act of the memory and judgment.* We have seen that the picture of an object is formed in the bottom of the eye. It was formerly sufficient to say, that the mind contemplates this image. We should say now that this image is conveyed into the sensoriuin by the optic nerve. This is an hypothesis merely ; and we have no more consciousness of the object being in the brain or sensori- um than in any other part of the body : we may rather say, that the im- pression made on the organ, nCrves, and brain, is followed by sensation, and that the intelligence is the joint operation of the whole.! Lastly, the metaphysician calls our sensations the signs of external objects; be- cause the object itself is not presented to the mind, nor is there an ac- tual resemblance betwixt the object and the sensation of it, but merely a connexion established by nature, as certain features are natural signs of anger ; or by art, as articulate sounds are the signs of our thoughts and purposes. We are now naturally led to the consideration of some points, the full comprehension of which require the knowledge both of anatomy and of the principles of optics. PARALLEL MOTION OP TIL. eYPS. The axis of the eye is a line drawn through the middle of the pupil and of the crystalline lens, and which consequently falls upon the mid- dle of the retina. The axes of the eyes, it is evident, are not always parallel ; for when both eyes are directed to a near object, the axes of the eyes meet in that object; but when we direct the eyes to the ob- jects in the heavens, they may be considered as perfectly parallel in their axis, though perhaps not then mathematically so. To an observer, the eyes seem always moving in parallel directions ; but nature has given us the power of varying them so, that we can direct them to the same point, whether remote or near. This, however, is in some measure ac- quired by custom, and lost by disuse. A child has much difficulty in al- tering the distance of its eyes, which is the occasion of the vacancy Of its stare ; and we observe that a patient who has long lost one eye is in- capable of directing the axis of the blind eye without looking with the other, and even then, the blind organ does not follow the other with that perfect accuracy which exercise gives when both eyes are sound. By * See Dr. Jurinon Mr. Molyneux’s problem, Smith’s Append, p. 27. f Euclid, and others of the ancients, contended that vision was occasioned by the emission of rays from the eye to the object. He thought it more natural to suppose, that an animate substance gave out an emanation, than that the inanimate body did. In 1560, the opinion was confirmed that the rays entered the eye.—The sensation was not always believed to be in the retina : it was by some believed that part of the sensation was to be attributed to the crys- talline. Kepler, in (600. showed, geometrically, how the rays were refracted through all the humours of the eye so as to form a distinct picture on the retina ; and also he showed the effect of glasses on the eyes. See further, regarding the opinions of the ancients. Boer- haave, Prelect. Acad. tom. iv. p. 282. OF VISION 233 practice and straining, the axes of the eyes may be further altered from the natural parallelism. A child born blind turns its eyes in every possi- ble direction, as -it does its hands, without concert; but when the vision is perfect, there is a power which directs the eyes and leads to paral- lelism. There is a particular sensible spot in the retina, which m akes it ne- cessary to distinct vision that this spot shall receive the concentrating rays of light; and the natural constitution of the eyes is such, that this spot in one eye shall have a relation to that of the other: that the axis of both should be accurately in the middle of the eye-ball, the child very soon acquires the power of directing the eyes with a simultaneous and corresponding effort. By voluntary squinting or depressing one of the eyes with the finger, objects appear double, because the optic axis is changed in the distorted or depressed eye, and the picture is no longer painted on correspond- ing points of both retinae. This simple experiment leads us to consi- der what is the constitution and correspondence of the eyes, that when each has the picture of the object impressed upon it, we should only see it single if the eyes are sound and perfect. Fig.lG. Fig. 17. For example; the object a is exactly in the centre of the axis of both eyes, consequently, it is distinctly seen; and it appears single, be- cause the rays from it strike upon the points of the retina opposite to the pupils in both eyes. Those points have a correspondence ; and the ob- ject, instead of appearing double, is only strengthened, in the liveliness of the image. Again, the object b will be seen fainter, but single, and correct in every respect. It will appear fainter because there is only one spot in each eye which possesses the degree of sensibility necessa- ry to perfect vision; and it will appear single, the rays proceeding from it having exactly the same relation to the centre of the retina in both eyes. Though they do not fall on the centre of the retina, they fall on the same side of the centre in both eyes. But if the eyes are made to fix steadfastly on an object, and if another object should be placed be- fore the eyes within the angle which the axis of the two eyes make with the first object, it will be seen double, because the points of the re- tina, struck by the rays proceeding from the nearer object, do not cor- 234 OF VISIO-V. respond in their relation to the central point of the retina. Thus, the eyes b b, having their axis directed to a, will see the object c double .somewhere near the outline d d. Because the line of the direction of the rays from that body c does not strike the retina in the same relation to the axis a b in both eyes. Upon this principle, we may easily explain why objects, which are much nearer the eyes, or much more distant from them than that to which the two eyes are directed, appear double. Thus, if a candle is placed at the distance of ten feet, and I hold my finger at arm’s length between my eyes and the candle, when I look at the candle, I see my finger double, and when I look at my finger, I see the candle double. This double vision occurs to us all frequently ; but unless we make the experiment purposely, we do not attend to it. Ma- ny other instances of the harmony, and of the want of it in the eyes, particularly the reverse of what these diagrams show, may be easily produced, viz. the seeing two objects single : for, if we look at a half- penny and a shilling, placed each at the extremity of two tubes, one exactly in the axis of one eye, and the other in the axis of the other eye, we shall see but one piece of coin, and of a colour neither like the shilling nor like the halfpenny, but intermediate, as if the one were spread over the other. This relation and sympathy between the corresponding points of the two eyes is, therefore, to be considered as a general fact, viz. that pictures of objects falling upon corresponding points of the two retinas present the same appearance to the mind as if they had both fallen upon the same point of one retina; and pictures upon points of the two retinas which do not correspond, and which proceed from one object, present to the mind the same apparent distance and position of two objects, as if one of those pictures were carried to the point corresponding with it in the other retina. Several animals, we see, direct their eyes by very different laws from those which govern the motion of ours ; but we are not to reason upon their sensations by the laws of vision of the human eyes: we must take it as a principle, that nature has been bountiful to them also ; and that the result of organization in their eyes is perfect vision. In birds (if we except the owl) the eyes diverge, and are directed to op- posite sides. As the owl seeks his prey in the night, it may be necessa- ry to the distinctness of bis vision in weak light, that both eyes be di- rected to the object. Most fishes have their eyes directed laterally, though there are exceptions ; as those fishes which are flat, and swim at the bot- tom, have their eyes directed upward. In many insects, the surface of the eye has no resemblance to the cornea of viviparous animals; but when examined with the microscope, it is seen to consist of a number of tubercles, each of which is a distinct eye. in others, the eye is removed to the extremity of the movable tenaoulie. Very large animals, as the whale, elephant, rhinoceros, hippopotamus, have, in proportion to their bo- dies, very small eyes : so have the animals which live much under ground; and, in general, a large eye is a sign of the animal being able to see in obscure light, because there is proportionably a greater number of rays admitted into the eye. For the same reason fishes have a peculiarly large eye and dilatable pupil, because the water is a more obscure me- dium, and, from the occasional roughness of its surface, much darkened and variable. OF VISION. 235 We must conclude, that in these varieties of tne eyes, where there is a difference in number, position, and natural motion, there are different laws of vision adapted to these peculiarities and the exigencies of the animals. If we are to judge from anology, we may suppose, that in many animals there is no correspondence between points of the two retinas, or it is of a different kind from ours. In those which have im- movable eyes, the centre of the two retinas will not correspond so as to give the idea of one object, but of distinct objects, in their respective places; and, indeed, I conceive that in such the offices of the eye must be much circumscribed; they will, perhaps, only distinguish degrees of light: and in such as turn their eyes in all directions, independently of each other, they would seem to possess a perception of the direction in which they move them, as we have of the motion of our arms. This consideration leads to a very curious subject. SQUINTING. The student cannot feel satisfied on the subject of the motions of the eyes, unless he understands this very common defect. In the first place, we must observe that there is a complaint, where, the muscles of the eye being primarily affected, the eyes are distorted. The images then fall on parts of the retina which have no correspond- ence, and the effect for a time is double vision. Afterwards there is single vision, without amendment of the distortion, but merely from the weaker impression on one eye being neglected. But this is not the very common case of squinting, where, with very evident obliquity of the eyes, there is single vision from the beginning. This common case of squinting, I apprehend, could not be understood whilst there was a neg- lect of the classification of the muscles of the eyes and an ignorance of their distinct offices. It now appears, that the recti muscles of the eye-ball are in activity during attention to the impression on the retina; but that when that attention is withdrawn, the recti muscles are relieved, and the eye-ball is given up to the influence of the oblique muscles. This takes place in sleep, in fainting, and intoxication. When the nerve is deficient in one eye, and the sensibility less than in the other, the recti muscles are unex- erted; the obliqui preponderate; and the state of equilibrium betwixt the two obliqui is when the eye-ball is turned, and the pupil presented upwards and inwards. Thus we perceive that by founding on a just view of the anatomy, the whole train of facts connected with this curious sub- ject accord, and the explanation of squinting is simple. Whereas, be- fore it was necessary to take a great deal for granted, and to suppose an effort of the muscles of the weak eye necessary to draw it out of the other one; it being presumed that a weaker impression, in addition to a full natural one, must be an injury to vision. We have seen, that there is a point in both retinas more acutely sensi- ble to the impression of light and the image of objects, than any other part of all its concave surface. In a sound eye, this point is immediate- ly opposite to the pupil. There is a coincidence betwixt this point and the axis of the eye; and when we look to an object, its image strikes this point of the retina.* If the greater sensibility of the nerve should * This was M. de la Hire’s opinion.—He had an idea also that squinting was produced by the obliquity of the object. Roth of these opinions are refuted bv Dr. Jurin. 236 OF VISION. lie in its proper place, and some cause should produce such an action of the muscles and distortion of the eye as we see in a squint, then the image will be double ; for it no longer falls on corresponding points of the retina of each eye, and separate images are conveyed to the brain. If, however, this distortion continues, the single vision is gradually restored. Is there, then, in this case produced a new correspondence betwixt points of the retina which were before discordant] We find that this is not the case, by a very simple experiment.—In a person who squints, one of the eyes is directed to the object and the other appears to be turned from it: if the sound eye be shut, and the person be directed to look to an object with the other, it is directed to it with the proper and natural axis. Now this shows us that the sensibility of the proper spot in the bottom of the eye is not altogether lost. But most people who squint have a defect of fvision in the distorted eye, while the eye directed to the object has its natural sensibility to light. Now the mind does not attend easily to two impressions, the one being weaker than the other : in a short time the weaker impression is entirely neglected, and the stronger only is perceived.—So in squinting, the impression on the eye in a short time ceases to be attended to, the strong and vivid impression is alone per- ceived, and single vision is the consequence; while the eye, thus natu- rally excited, has the due degree of energy and activity of the recti, or voluntary muscles, but the other eye has no impression, and no such ex- citement as the natural stimulus on the retina affords to the recti mus- cles, and therefore it is drawn into that position which is its state of rest; the eye is as if asleep. What is very extraordinary in squinting,is the correspondence in themus- cles of the eye, notwithstanding the great distortion of the eye-ball; for, when both eyes are open, as the sound eye turns in all variety of directions to the surrounding objects, the other eye still follows it, but preserves its dis- tance, so as in a manner to avoid all interference. But this is explained on the view stated. There is a preponderance of the oblique muscles over the recti, by which the eye is turned from the true line of the axis, without being altogether withdrawn from the influence of voluntary effort. Blows on the head, drinking, and smoking, and a variety of irritations, occasion convulsions and distortion of the eyes, but they, at the same time, cause double vision. This is evidently produced by the affection of the mus- cles moving the eye-ball (since a change of the sensibility of the retina could not give occasion to distortion during a state of insensibility) ; we may, therefore, conclude, that squinting is sometimes the consequence of irregular action of the muscles, independent of the condition of the retina.* We can distort our eyes by an unnatural effort, but we cannot squint, that is to say, we can bring our eyes into such a forced situation that we * In Smith’s optics, there is a case of squinting and double vision occasioned by a blow. In Burton’s Dissertation, in the Acad. Roy. des Sc. 1743, squinting after long continued pain of the head. In the Mem. Roy. do I’Acad, des Sc. 1718, Hist. p. 29. there is a curious in stance of false vision. I find also quoted several cases of strabismus from sudden fright, in Kphem. Germ. cent. 3. &4. obs. 152. p. 349 lb. dec. 3. an 8. & II. ob. 57. d. 114 lb. dec. 3. an. 9. & 10. obs. 67. “ Novi Juvenem paralysi obnoxium, cui cum caeteris oculi sintstri tnusculis relaxa- tis, adikicens fortius conlrahereter propter oculum ita distortuni objectum quodcunque duplex apparebat, nec quod verum esset distinguere protest.” Willis de anima Brut. P. Physiol, p. 77. An instance of the loss of corresponding motions of the eyes, and strange illusions of sight. See in the Enquiry into the Nature of Mental Derangement by Dr. Crichton, vol. i. p- OF SOUN£>. 237 cannot see any thing distinctly ; but we cannot keep one eye distinctly upon an object and turn the other from it.—Such a position of the eyes, at least, (and which is exactly that of those who squint unintentionally,) I cannot by any means accomplish.* This shows the strict correspond- ence betwixt the moving muscles of the eve-balls. By this experiment, we shall find the difficulty of that method of correcting the squint pro- posed by Dr. Jurin, or of commanding motions of the eyes different from those which have been bestowed by nature, or acquired by habit. But habit I believe to be much more seldom the origin of squinting than is gene- rally supposed. It is said, by Dr. Reid and others, that we see young people, in their frolics, learn to squint, making their eyes either converge or diverge when they will to a very considerable degree : why should it be more difficult for a squinting person to learn to look straight when he pleases 1 The reason of the greater difficulty is obvious,—that in mak- ing the eyes converge or diverge the will is acting upon both eyes equally ; but to distort one eye inward or outward, and at the same time to keep the other fixed, is to me like an absolute impossibility. But the reason of the difficulty of correcting squinting is, as I have stated, that the vo- luntary muscles of the eye are deficient in their natural stimulus, which is the exercise and enjoyment of the sense of vision. A frequent effect of the weakness left by long fevers in children is a squint which gradually goes off as the strength is restored. It is ob- served, also, that squinting and double vision are, in some fevers, a concomitant with delirium and phrenitis. This symptom proceeds, in all likelihood, from an unequal tension of the muscles of the eye-ball. The double vision is the effect of discordance in the action of the mus- cles, f OF THE EAR. OF SOUND, AND OF THE EAR IN GENERAL. Sound is the effect of impression on the auditory nerve, by which a corresponding change is produced in the brain, and the perception of sound excited. It may be produced by the vibration and motion of the air, but not without the intervention of solids. The human voice, for example, does not depend merely on the percussion of the air, but on that vibration, as combined with the tension and consequent vibration of the glottis, excited by the current of air. However, the vibrations which produce sound are not those which are visible or are felt by the finger; sound depends on a more minute motion of the particles of bo- dies, and is only cognizable by the appropriate organ, the ear. * It is said that astronomers, who are much user! to attend only to the impressions of one eye, are sometimes able to squint at pleasure. See Mr. Home, Phil. Trans. 1797, p. 17. t This has been more lately explained by the author in a distinct dissertation, and he hopes to pursue the subject further. See Philos. Trans. 238 OF SOUNU. There is no body impervious to sound, or, in other words, incapable of transmitting the vibration. That sound is communicated through the medium of the air, we know from the circumstance, that a bell, when struck in a vacuum, gives out no sound; and again, from this, that the condensed state of the atmosphere affords an easier communi- cation of sound, and conveys it to a greater distance. The velocity of the impression transmitted by the common air is computed at 1130 feet in a second ; and sound, when obstructed in its direct motion, is reflect- ed with a velocity equal to that with which it strikes the solid body by which its progress is interrupted. That water conveys the vibrations producing sound has been proved by experiment. It was once the saying of naturalists, that to suppose fishes to have the organ of hearing, would be to conceive that an organ were bestowed upon them without a possibility of its being of use. But w'e are assured of the fact, that, on the tinkling of a bell, fishes come to be fed * ; and it was the custom for the fishermen on the coast of Britany to force the fish into their nets by the beating of drums f, as our islanders are at present accustomed to do when the larger fish get entangled amongst the rocks. We are told, that in Chi- na, they use a gong for the same purpose. These facts were once of importance, though more accurate observation has now made them su- perfluous. The Abbe iVollet took much pains to decide the question, whether water was a medium for sound. After considerable prepara- tion, and acquiring a dexterous management of himself in the water, (for which he takes great merit to himself,) he found that he could hear un- der water the sound of the human voice, and even distinguish conver- sation and music. The human ear being an organ imperfectly adapted to this medium of sound, these experiments do not inform us of the relative powers of air and water in the transmission of sound. But another experiment of the Abbe Nollet proves, what indeed to me is sufficiently evident, from the structure of the ear of fishes, viz. that the water transmits a much stronger vibration than the air. When he sunk under water and struck together two stones which he held in his hands, it gave a shock to his ear which was insupportable, and which was felt on all the surface of his body, like that sensation which is produced when a solid body held in the teeth is struck by another solid body.f He observed in other experiments, that the more sonorous the bodies struck were, the less vivid was the impression; by which it would ap- pear, that water, though it conveys an impression more strongly to the ear than the air, is not equally adapted to the resonance and variety of tone. Indeed, this is a natural consequence of the water, a fluid of greater density being in close contact with the sounding body, and suppressing its vibration. In these facts, we shall find the explanation of some pe- culiarities in the structure of the ears of fishes. Thus, we see, that the vibration of a solid body is continued through the air, and through water, until reaching the organ of hearing, it pro- duces the sensation of sound. Sound, it will be evident, is also com- * Boyle. f M. l’Abb6 Nollet, Acad. R. des Sciences. Naturalists were very incredulous of the effects said to be produced by music on lobsters. Some may be so still; but there is no doubt that they possess the organ of bearing. See Scarpa Disquisition.es Anatomicce de Auditu in Insectis, &c. i These experiments were repeated by Dr. Monro. See his Book of Fishes OP THE EARS OP ANIMALS. 239 municaied through solids. When we put the ear to one end of a log of wood of thirty feet in length, and strike upon the other, we are sensible of the impression ; and when a solid body applied to the bones of the head, or to the teeth, is struck, we are sensible of the noise * ; and this is felt even by those who are deaf to impressions conveyed through the air : indeed it is partly in this way that we are to judge whether deafness may be cured by operation, as depending upon some injury of the me- chanism of the organ, or whether it be an incurable affection of the nerve, or brain itself. If the sound be perceptible when conveyed through the teeth, or when a watch, for example, is pressed upon the bone behind the outer ear, we are assured that the internal organ is un- affected ; and upon enquiring farther into the case, we may find that the deafness proceeds from some disease of the outer tube of the ear, or of that tube which leads into the throat, and that it can be remedied. GENERAL VIEW OF THE VARIETIES IN THE EARS OF ANIMALS, t There is in the scale of animals a regular gradation in the perfection of the organ of hearing. But, in the human ear, we find united all the variety of apparatus for communicating the vibration to the internal or- gan, and along with this the most extensive distribution of nerves in the labyrinth, or inmost division of the ear, to receive that impression. The ultimate cause of this more complex structure is the greater pow- er with which man is endowed, of receiving through the ear various im- pressions of simple sounds : language, music, and various modifications of the sense, of which the lower animals are probably incapable. As, in treating of the anatomy of the eye, we do not attempt to inves- tigate the manner in which light acts upon the retina, in producing the sensation of colours, but endeavour merely to explain the structure of the eye : to show how the coats support and nourish the humours ; how the humours serve to concentrate the rays of light, and assist their im- pulse upon the retina : so, in the same manner, in explaining the struc- ture of the ear, we need not investigate the philosophy of sound, nor the nature of those impressions which are made by it on the sensorium through the nerves ; our views are limited to the structure of the ear : we have to observe the mechanism by which the strength of vibrations is increased and conveyed inward to the seat of the sense, and the manner in which the neive is expanded to receive so delicate an impression. The method of studying this subject, which is at once the most in- structive and the most amusing, is to trace the various gradations in the perfection of the organ, through the several classes ot animals. It is chiefly by comparing the structure of the viscera, and the organs of sense in animals and in man, that comparative anatomy is useful in elucidating the animal economy. For example, in the stigmata and air-vessels of insects and worms ; in the gills of fishes ; in the simple cellular structure * Perhaps we cannot call this sound. t In the following short account of the comparative anatomy of the ear* although I have ta- ken every assistance in my power from books, I have described the structure, in all the exam- ples, from my own dissections and observations. 240 OF THE EARS OF ANIMALS. of the lungs of amphibia ; in the more complicated structure of the lungs of birds ; we observe one essential requisite through the whole gradation, viz. the exposure of the circulating fluids to the action of the air. And in this variety of conformation, we see the same organ so modified as to correspond with the habits and necessities of the different classes of ani- mals. In the same manner, with regard to the circulating system, we are taught the explanation of the double heart in the human body, by tracing the variety of structure through the several classes of animals ; from the simple tube circulating the fluids of insects, the single ventricle of fishes and reptiles, the double auricle and perforated ventricle of am- phibia, up to the perfect heart of the warm-blooded animal. The organs of generation, and the economy of the foetus in utero, is, in the same degree, capable of illustration from comparative anatomy. But most especially, in the structure of the ear, is there much scope for this kind of investigation. We find such varieties in the ear of reptiles, fishes, birds, and quadrupeds, as lead us, by gradual steps, from the simpler to the more complex structure. The simplest form of the organ of hearing is that in which we find a little sac of fluid, and on the inside of the sac the pulp of a nerve ex- panded. If an animal, having such an organ, breathe air, a membrane closes this sacculus on the fore part; and, by means of this membrane, the vibrations of the air are communicated to the expansion of the nerve through the fluid of the sac. But if the animal inhabits the water only, it has no such membrane to receive the impression ; the organ is in- cased in bone or cartilage, and instead of the exterior membrane, some small bone or hard concreted matter is found suspended in the fluid of the sac nerve. The sound passing through the waters, is in such case, conveyed to the organ not by any particular opening, but through the bones of the head ; and this concrete substance partaking of the tremu- lous motion, communicates an undulation to the fluid, and through it an impression to the nerve.* For example, in the crab and lobster, we find a prominent bony pa- pilla or shell, which is perforated ; a membrane is extended across the perforation ; and behind this membrane there is a fluid, in which the nerve is expanded, and which receives the impulse conveyed to the membrane. In the cuttle-fish, there is no external opening ; there is merely a little sac under the thick integuments : this sac has in it a small concretion or bone for receiving the vibration ; which, in this ani- mal, is conveyed by a more general impression upon the head than in the instances last mentioned ; and the vibrations of this loosely poised bone or concrete, seems equal to the provision of the membranes which, in the crab, closes up the external opening in the perforated shell. In fishes, there is a considerable variety of structure. Those which remain perpetually under water have not the outer membrane, nor any apparatus for strengthening the first-received undulations of sound. But such as lie basking on the surface of the water, and breathe through lungs, have an external opening—a canal leading to the membrane, and * It is conceived by some that the antennae of insects convey to them the vibration of bo- dies, and that they may be considered as an imperfect variety of this organ They may re- ceive an impression from the vibration of the air, but as their nerves are nerves of touch, it cannot be sound which they experience. OF THE EARS OF ANIMALS. 241 behind the membrane, bones to convey the vibration to the internal parts, and these internal parts are nearly as perfect as in terrestrial animals. In neither of the species of fishes, the cartilaginous nor spinous fish- es, is there a proper external opening, as in animals breathing air. They receive the impulse from the water, upon the integuments and bones of the head ; but within the head, and in the seat of the sense they have a most beautiful apparatus for receiving and conveying those general vi- brations to the expanded nerve. There is in every ear, adapted to hear- ing under water, a bone or concretion, placed so as to vacillate easily, and which is destined to agitate the fluid in which it is suspended with a stronger vibration than could be produced merely by a general impulse. Besides this provision in fishes, there is a very elegant structure for still further increasing the surface destined to receive the impulse, and for ex- posing to that impulse or vibration a larger proportion of the expanded nerve. It consists of three semicircular tubes, which penetrate widely within the bones of the head. They are filled with a fluid, and have in their extremities a division of the nerve which is moved or otherwise affected by the vibration of the fluids contained within the tubes. There is a slight variety, however, in the ear of cartilaginous fishes. In the head of the ska te, for example, there is under the skin, at the back of the head, a membrane extended across a pretty regular opening. This, however, is not considered as the opening of the ear; but a pas- sage like a mucous duct, which is beside it, has given occasion to a con- troversy between Professors Scarpa and Monro ; and it may not be out of place to inquire a little into this disputed point. We have seen that water conveys the sound of vibrating bodies with a shock almost intolerable to the ear, and with a particuliar and distinct sen- sation overthe whole body. We see, also, that, in the greater number of fishes, there is confessedly no external opening, the whole organ is plac- ed under the squamous bones of the head. Yet the cartilaginous fishes, which are supposed to have an external ear, swim in the same element, and are in no essential point peculiar in their habits. And we should receive with caution the account of any peculiarity in the organ of hear- ing of one class of fishes, which is not common to all inhabiting the same fluid. Such animals, as occasionally pass from the water into the air, must have a membrane capable of vibrating in the air ; but, even in them, it is expanded under the common integuments, and protected by them. Were it otherwise, when the creature plunged into the water, it would be assailed with that noise (confounding all regular sounds), of which man is sensible when he plunges under water. It appears oppo- site to the general law of nature, to suppose any species of fish to have that delicate membrane which is intended to convey atmospheric sounds; while other creatures living in the water have no such provision. When we come to examine the ear of the skate, we find, that what Dr. Monro conceives to be the outward ear of the fish*, is really, as * “ In the upper and back part of the head of a skate and in a large fish weighing 150 “ pounds, at the distance nearly of one inch from the articulation of the head, with the first “ vertebra of the neck or atlas, two orifices capable of admitting small sized stocking wires “ at the distance of about an inch and a quarter from each other, surrouuded with a firm, 14 membranous ring, may be observed. These are the beginnings of the Meatus Auditorii :' Exterai.” Treatise on the Ear, p. 208 242 OF THE EARS OF ANIMALS. represented by Scarpa, a mucous duct merely * ; which does not lead in- to the sacculi of the vestibule and semicircular canals, as appeared to Dr. Monro ; and that to suppose this would be to acknowledge the free access of air and water to the immediate seat of the organ, and to the soft pulp of the auditory nerve, a thing not to be believed, t To me it appears, that this narrow duct cannot be considered as the external ear; because we find in the skate a proper membrane under the thin integu- ments for transmitting the sound, quite unconnected with the duct; and upon following this mucous duct, we find it taking a circuitous course, and filled with a strong gelatinous matter ; it is every where narrow, and filled with a glutinous secretion. It has no membrane stretched across it, and bears no resemblance to the external ear of any other animal. We may conclude, then, that fishes have no external opening like ter- restrial animals ; that, instead of this outward provision, they have the movable bone within the organ. Although the cartilaginous fishes have a membrane extended over part of the organ, which, in the spinous fish- es, is completely surrounded with bone, it is not to be considered as capa- ble of the tremulous motions of the membrana tympani of terrestrial ani- mals, but may be considered as analogous to the membrana fenestrae ovalis; and, since it lies deep under the integuments, we have no reason to believe that sound is transmitted to the organ of hearing in fishes, any otherwise than through the general vibration of the head. The organ of hearing in amphibious animals, demonstrates to us a dif- ference in the manner in which the sensation is received; for they have both the outer membrane to receive the vibration of the air, and a mecha- nism of small bones to convey this motion into the seat of the sense ; and they have, besides, within the ear itself, a chalky concretion ; a pro- vision plainly intended for propagating the motion communicated through the water. In serpents, birds, and quadrupeds, we shall hereafter trace the various gradations in the perfection of this organ. We shall find, that, as the animal rises in the scale, the cavities and tubes of the ear are extended and varied in their form. Now, I conceive that, while the multiplied forms of the tubes and sphericles of the internal ear afford a more ex- panded and susceptible surface for receiving impressions, the consonant forms of the parts enable them to receive a stronger vibration, and a more perfect and modified sound. A chord of a musical instrument will vibrate when another in exact unison with it is struck. The vibration communicated to the air is such as is adapted to the tension of the symphonic chord; and no other per- cussion of the air, however violent, will cause it to sound. Again, the air passing through a tube of certain dimensions, will not communicate to it a motion, nor call forth its sound, while the air, passing in equal quantity through a tube of one degree of difference, will rise into a full note. What holds true in regard to the unison of chords, is also true of cylinders, or even of the walls of a passage or room, a certain note will * Scarpa, speaking of this opinion of Dr. Monro, says, “ qua in re vehementer sibi halluci- “ natus est, ostia niinirum ductuurn mucosorum,ut manifestum est, pro auris meatibus acci- 4‘ piens. Etenim omnino nulium est in cartilagineis piscibus ostium auditus extusadapertum, “ ovalis sub cornmuni integumento reconditajacet et tooperfa.” f “ Quod et absurdum est et a rei veritate quam maxima alienum,” Vid. Anatomies Di•- ifuttittffnes de and it n ttolfactu, auctore A. Scarpa. OF THE ORGAN OF HEARING. 243 cause the resonance of the passage or room, as a certain vibration will call forth the sound of the tube of an organ: because it is in all these instances necessary that the impulse be adapted to the position of the surfaces and their powers of reverberation. These few facts illustrate what I mean, by saying, that the various forms of the internal ear of animals, as they advance in the scale, give additional powers to their organ. In the first example of the simple ear, where a bone vibrates on the expanded nerve, I should conceive that the sensations were in consequence of this simple percussion capable of little variety ; but in animals where, besides this simpler mechanism, there are semicircular canals, and more especially in those animals which have siill a farther complication of the forms of the ear, certain sounds will be peculiarly felt in each of these several cavities and convolutions ; and while the sensation is becoming more distinct, by the perfection of the organ, it admits also of a greater variety of sounds or notes : so that a certain state of vibration will affect the semicircular canals, (one or all of them,) and produce the sensation of sound, which would not at all affect the vibration of the simple lapilli lying in their sac. DESCRIPTION OF THE ORGAN OF HEARING IN PARTICULAR ANIMALS. IN THE LOBSTER AND CRAB. In these animals, the structure of the ear is very simple ; but it ap- pears to me that Professor Scarpa, in his description, has imagined the organ to be more simple than it is in nature. In the lobster, there projects from near the root of the great antenna, an osseous papilla of a peculiarly hard and friable nature. In the point of this papilla we observe a foramen, and a membrane stretched over it. This is the seat of the organ of hearing. It is described as containing a sac of a pellucid fluid, which adheres to the membrane, while the au- ditory nerve is expanded upon the lower surface of the sac. Now, the lobster, being an animal which can live on land as well as in water, Scarpa gives this as an instance of a structure calculated to receive the sensation of sound equally well from the water or from the atmosphere. But, to me, it does not appear to be so exceedingly simple ; while there is evidently a provision for the reception of the vibration communicated through the water, though it does not indeed strictly resemble that which is commonly found in the ears of fishes. There is suspended behind the sacculus, and in contact with the nerve, a small triangular bone, which when pulled away * is found to hinge upon a delicate cartilage. This bone seems intended, by its being thus suspended in the neighbourhood of the pulp of the auditory nerve, for impressing upon that nerve the vibration from the water. The lobster, then, has, like the amphi- bious animals, a double provision for receiving the communication of sound either from the water or from the air.t * See fig. 2. t From the mucous like transparency of the nerve in the lofastefr, it is difficult to ascertain its exact relation to this bone. 244 OF TIIE ORGAN OF HEARING, The ear of the crab differs from that of the lobster in this, that, under the projection, there is a movable case of bone, to which we see a small antenna attached. Within this is the organ of hearing; and there is here an internal provision for the transmission of sound to the auditory nerve, which consists simply in a few circumgyrations of a pellucid and flexible cartilage : an inspissated fluid surrounds this cartilage, while the auditory nerve is expanded behind it. Of the ear of fishes.—In the heads of fishes there is a cavity sepa- rated by a thin vascular membrane from that which contains the brain. Within this cavity there is a sacculus distended with a fluid, and contain- ing a small bone ; * on the inside of this bag, (which is called the saccu- lus lapillorum,) a great proportion of the auditory nerve is expanded. In the cartilaginous fishes, there are three lapillit contained in their proper capsules, and surrounded with a gelatinous matter,J each of the lapilli having its appropriated division of the acoustic or auditory nerve dis- tributed upon it in a beautiful net-work. This cavity in the head of fishes, resembles the centre of the labyrinth in the human ear, which is called the vestibule. Within the vestibule there is a limpid fluid, intersected every where by a delicate and transpa- rent cellular membrane ; and the parts within the vestibule are supported in their place by this tissue, which is similar to that which supports the brain in fishes. Besides this central part of the organ in fishes, there are departing from the vestibule three semicircular cartilaginous canals, within which, are extended membranous canals. These membranous tubes contain a fluid distinct from that contained in the common cavity of the vestibule, nor have they any communication with the sacculi, which contain the la- pilli, although they are in contact with them. § These cartilaginous ca- nals are of a cylindrical form, and, being as transparent as the fluid with which they are surrounded, are not readily distinguished in dissec- tion. Each of the cartilaginous canals is dilated at one of its extremi- ties into a little belly, which is called the ampulla. The auditory nerve in cartilaginous fishes || is first divided into two fasciculi, which are again subdivided into lesser nerves. These go to the three sacculi lapillorum, and to the ampullul® of the semicircular ca- nals. Before the division of the nerve which goes to the sacculus pierces it, it forms a singular and intricate net-work of filaments. The branch to the ampullula is raised on a partition which stands across as if to receive the undulations of the fluid coming along the tube. In the spinous fishes, the three semicircular canals unite in a common belly ; but in cartilaginous fishes, the posterior semicircular canal is dis- tinct from the others. In fishes, all the parts of the ear are filled with a matter of a gelati- nous consistence, or viscid fluidity ; and the whole sacculi and semicir- cular canals are surrounded with fluid. That jelly is the most suscepti- * See plate, fig. 3. t In many of the spinous or squamous fishes there is only one. In cartilaginous fishes, these bodies are not like bone, but like soft chalk. In the spinous fishes, on the other hand, they are of the shape of the head of a spear, and hard like stone. t The gelatinous matter is rather before the bones, and distending the little sacculi. j So Professor Scarpa asserts, in contradiction to others. jj The fifth pair of nerves in fish answers to the seventh in man ; has the same division into the portio mollis and dura. OF THE ORGAN OF HEARING. 245 ble of vibration, is evident when we fill a glass, and allow a body to fall into it ; for then the delicate vibration is communicated to the finger on the outside of the glass, or by striking the glass, we may observe the tremulous motion of the jelly. The semicircular canals, containing such a fluid, are well adapted to receive the extensive vibrations commu- nicated through the bones of the head, and to convey them to the nerve expanded in the ampulla. From the simpler to the more perfect aquatic animals, we may trace several links of the chain by which nature advances towards the perfect structure of the ear. We return now to observe, in the first example of terrestrial animals, the most simple state of that part of the organ which receives the sensation ; but while the structure of the internal organ is the most simple, the mechanism for receiving the vibration and convey- ing it to the internal ear is modified and adapted to the atmosphere. OF THE EAR IN REPTILES AND AMPHIBIOUS ANIMALS. In reptiles, which form the intermediate class of animals betwixt fishes and quadrupeds, the ear has also an intermediate structure ; in some individuals of this class the ear resembles that of fishes, such as we have described; while, in others, it resembles more nearly the com- mon structure of terrestrial animals. In the salamandra aquatica, a variety of the lizard, there is a foramen ovale*, deep under the integuments. In this foramen there is carti- lage, in immediate contact with which there is a common sacculus ly- ing in the cavity or vestibule ; and in this little sac there is found a cretaceous matter; there are here, also, semicircular canals, with am- pullulae, and a common belly connecting them. In this animal, then, it is evident, the ear is similar in structure to that of the cartilaginous fishes.f In the frog, the outward apparatus is different, but the internal ear is simple.J Under the skin of the side of the head, a little behind the prominent eye, we find a large circular opening, which tends inward in a funnel-like form: and from the upper part of the circle of this meatus find a small elastic bone, or cartilage suspended. This bone is in contact with the common integuments of the head, which are stretched over the little cavity. This first bone is placed at a right an- gle with a second bone, and both are lodged in a proper tympanum.§ This second bone swells out towards its inner extremity, and is accu- rately applied to the foramen ovale. The foramen ovale opens into a cavity which we must call the vestibule, and which, in this creature, is peculiarly large in proportion to its size. This vestibule contains a sac, upon which the nerve is expanded ; it contains also a chalky soft con- cretion, which is of a beautiful whiteness, and of a regular figure when * This is the appropriated appellation of the opening, which leads from the outer cavity of the ear, or tympanum, into the seat of the proper organ where the nerve is expanded. f It is said by naturalists, that the salamander never has been heard to utter a cry; and as dumbness is in general coupled with deafness, it is natural to suppose it has no ears. This is to consider the organ as subservient to conversation ! J See plate, fig. 5 and 6 j This tympanum being a cavity containing air, has communication with the mouth by a tube, which we shall afterwards find called Eustachian tube. Several have erroneously des- cribed this animal as receiving sounds through the mouth. 246 OF the organ of hearing. first seen, but has no solidity.* The vestibule here, as in all other ani- mals, being the immediate seat of the sense, is filled with fluid. In serpents, the mechanism external to the seat of the organ is less complete than in the frog. From the scales behind the articulation of the bone which keeps the lower jaw extended, a little column f of bone stretches inward and forward. This bone has its inner extremity en- larged to an oval figure, and is inserted into the foramen ovale. This creature has no membrana tympani, nor does it appear to have so good a substitute as the frog : the outer extremity of the bone seems rather attached to the lower jaw by a cartilaginous appendage and small liga- ment.;]; Within the skull, serpents have the little sac, with the cretace- ous matter and semicircular canals, united by a common belly. § In the turtle, we find a proper tympanum, and by lifting the scaly integuments from the side of the head a little above the articulation of the lower jaw, we open this cavity. Through this cavity there ex- tends a very long and slender bone, which, upon the outer extremity, is attached by a little elastic brush of fibres to the cartilaginous plate under the integuments, while the inner extremity is enlarged, so as to apply accurately to the foramen, which opens into the vestibule ; and a passage also opens from the cavity of the tympanum into the fauces. In this animal, as in all which we have classed under the present divi- sion, the internal ear consists of a central cavity, or vestibule, which contains a sac with fluid, and cretaceous matter, and of three semicircu- lar canals connected by a common belly. This common belly of the semicircular canals has no communication with the sacculus vestibuli, which contains the cretaceous matter, further than as it lies in contact with it, and as they both lie surrounded bv a fluid ; they equally receive the impression of the little bony column, the extremity of which vibrates in the foramen ovale. There being enumerated forty or more varieties of the lacerta or lizard, many of these have very different habits. Some of them never pass int > the water, but inhabit dry and dusty places. The lacerta agi- lis, or common green lizard, which is a native both of Europe and of India, is nimble, and basks, during the hot weather, on the trunks of old trees and on dry banks ; but on hearing a noise it retreats quickly to its hole. It has the skin over the tympanum extremely thin, and such as to answer precisely the office of the membrane of the tympanum. So all the varieties of reptiles which, in their habits and delicacy of hearing, resemble terrestrial animals, have either the membrane of the tympanum ora skin so delicate as to produce the same effect; while those which inhabit the water, have a rough integument, or a hard scale, drawn over the tympanum. Besides this, some have a small muscle at- tached to the bone, which runs across the tympanum; it is like the ten- sor tympani, and is another step towards the proper structure of the ter- restrial ear. * See fig. 6. d. f Plate, fig. 7. b. | See Scarpa, tab. v. fig ix. $ Serpents are affected by music : and they will raise and twist themselves with every va- riety of lively motion to the pipe and tabor. OP THE ORGAN OP HEARING. 247 of the ear in birds. Comparing the internal ear of birds with that of the animals which we have already described, we find a very important addition. We find here the internal ear (or labyrinth, as we may now call it,) consist- ing of three divisions ; the vestibule, or middle cavity ; the semicircu- lar canals ; and the cochlea ; which last is an additional part, and one which we have not in the class of animals already described. Leading into these three cavities, there are two foramina ; the fenestra rotun- da, and the fenestra ovalis ; and both these openings have a mem- brane stretched over them in the fresh state of the parts. The first, the fenestra ovalis, or foramen ovale receives the ossiculus auditus, which is in birds like that which we have already described in reptiles.* This ossiculus connects the membrana tympani (which is here of a regu- lar form) with the vestibule, and conveys the vibration of the atmosphere to it. The semicircular canals are here also three in number, and are distin- guished by the terms minor, major, and maximus ; but as the major and minor coalesce at one of their extremities, and enter the vestibule to- gether, the semicircular canals open into the vestibule by only five fora- mina in place of six. Each of the semicircular canals is dilated at one extremity into an elliptical form, while the other extremity is of the na- tural size of the diameter of the tube. These canals are formed of the hard shell of bone, and are surrounded with bone, having wider and more open cancelli. In the dry state of the parts, we find a cord passing through the semi- circular canals, which some have called the zonula nervosa. But these are the membranous canals, which are contained within the bony ones, dried and shrunk up. Within the bony cavities of the labyrinth, there is laid a pellucid membrane which contains a fluid, has the nerves expanded upon it, and is the true vestibule and semicircular canals; while the bony case, which we have described, is merely the mould of these, and the support of their delicate texture.I The cochlea, one of the three divisions of the labyrinth, is but im- perfect in birds, when compared with that part of the organ in quadru- peds and in man. The cochlea in birds consists merely of two cylin- ders, formed of cartilage, which are united toward their further extremi- ty. While the opposite extremities diverge, and while one of these cy- linders opens into the vestibule, the other opens outward into the cavity of the tympanum. J * Mr. Home, in his lecture on the muscularity of the membrana tympani, (vid. Phi!. Trans. A. 1800,1 says, in birds this membrane has no tensor muscle to vary its adjustments, but is always kept tense by the pressure of the end of the slender bone. This is a very im- perfect account of the mechanism of the tympanum in birds. There are two bones, or one small bone with a cartilage, which lies along the membrana tympani. This elastic cartilage has two little tendons attached to it. Even the slender bone which stretches from the carti- lage to the foramen ovale, the inner extremity of which is enlarged to fill up that hole, seems have a small tendon inserted into it; but whether this be a muscular or ligamentous con- nexion I am unable at present to say. f On drawing out the sacculus vestibuli and semicircular canals from the bony partof the ear of a bird, I find the membranous semicircular canal to consist apparently of the same pellucid elastic matter with those of fishes. i We find Mr, Home saying that the cochlea is neither absolutely necessary to fit the or- 248 OP THE HUMAN EAR. That which, more than any other circumstance, distinguishes the or- gan of birds from that of animals inhabiting the waters, is the want of the bone or stony concretion in the sacculus vestibuli. OF THE HUMAN EAR. The anatomy of the human ear will naturally be considered under three heads : the external ear; the tympanum; and the labyrinth. The outward ear requires no definition. From the outward ear there is a cartilaginous tube, which leads into the tympanum. The tympanum is the cavity within which is placed that mechanism of bones and muscles which increases the strength of the vibration, and conveys it inwards to the labyrinth. The labyrinth is the general name of those intricate canals which contain the expanded nerve ; it is the proper seat of the sense. OP THE EXTERNAL EAR. The external ear is formed of elastic cartilages, covered with very thin integuments. The apparently irregular surfaces of the outer ear will be found, upon examination, to be so formed that the sinuosities lead gradually into each other, and finally terminate in the concha or im- mediate opening of the tube of the ear. By the constant motion of the external ear of quadrupeds, we see its importance to them both in col- lecting sound, and judging of its direction. (We must not forget, how- ever, in estimating the mobility of this apparatus, that the ears are used like the tail, to free them from flies.) In most men, the motion of the ear is lost, but some men still retain it; and this is very remarkable, that when the more internal mechanism of the ear is injured, and ceases to strengthen the sound before it conveys it inwards to the labyrinth, the external ear resumes the office to which it was originally adapted, and by a degree of motion and erection, assists the hearing. In Europeans, the outward ear is in a great degree flattened to the head by the dress ; but in eastern nations, and in ancient statutes, we see the ears stand prominent, and bear a part in the symmetry and expression of the whole head. The muscles moving the cartilages, besides, being intended to direct the ear, appear to have a more essential use in giving a due ten- sion to the cartilages. These cartilages are surrounded with their pecu- liar perichondrium ; but as to their vessels and nerves, it seems very su- perfluous to give a minute description of them here. "an to be impressed by sounds communicated through the air, nor to render it what is termed a musical ear; and that is sufficiently proved by that part being wanting in birds, whose or- gan is particularly adapted to inarticulate sounds. That the cochlea is not necessary to the communication of sound through the atmosphere, we have seen from the examination of the ear of reptiles. But since we see that it forms part of the labyrinth in birds, we may be led to doubt Mr. Home’s conclusion OF THE HUMAN EAR. 249 When the cartilages are dissected they appear thus : a. The helix.—It is the out- er margin, the edge of which is turned over, and forms the cavi- tas innominata. BCD. The ANTHELIX. It is very prominent ; of a triangu- lar shape ; and within the outer rim or margin. e. The sc a ph a, which is a de- pression or cavity on the anteri- or part of the anthelix. F. The ANTITRAGUS. g. The tragus.—These are the two prominent points which approach each other, and form the margin of the great cavity of the ear. l. The concha, or great cavity of the ear, and which is the trumpet- like opening of the meatus auditorius externus. The few pale coloured fibres which are found on the cartilages, are scarcely to be recognized as muscles.* The lobe of the ear, or that part which hangs down and is pierced for the ear-ring in women and savages consists of skin and cellular substance merely. The meatus auditorius externus, is the tube which leads into the tympanum. This tube is partly bony and partly cartilaginous. The outer portion of the tube is cartilaginous, and about three quarters of an inch in length, and is divided by fissures. The deeper part of the tube is formed in the bone, as we find upontw ning to the description of the tem- poral bone. Glands of the passage.—The cuticle, covering the inside of the tube, is very fine, and there project from it many small hairs which stand across the passage. Under the skin there is a set of small glands, which pour their secretion into the tube, and are called the glandulje cERUMENosiE. j‘ These glands, secreting the wax of the ear, have their little ducts opening betwixt the roots of the hairs ; and this secretion with the hairs which stand across the passage, guards the internal parts of the ear from insects. The whole passage, consisting of the canal of the temporal bone and the cartilaginous tube placed upon it, has an oblique direction. It first passes upward and forward, and then makes a slight curve to descend to the membrane of the tympanum. T his external tube of the ear, being of the nature of a secreting sur- face, and exposed to the air, is liable to inflammation. There follows a dryness of the passages, and then a more fluid secretion. If the in- flammation of the tube should extend within the bones, then, like the af- fections of all parts surrounded with solid bone, the pain is extreme and * See Valsalva & Santorini. + “ H® figuram obtinent variam ; ma jor tameri harum pars ve! ad ovalem, ve! ad sph*ri- “ cam accettit colore tinguntur flavo ab humore in earum follicnlis contento qui ob assidnam “ fibrarum carnearum reticnlariurn pressionem, per cntia correspondf ntia t'orair-ina in :neatu3 “ auditorii cavitatern transmittitur. Valsalva da sure homansi, p. 10. 250 OF THE HUMAN EAR. the danger considerable : there is not only suppuration in the tympanum and destruction of the membrana tympani, but the disease may be still further communicated internally. Hildanus gives us an observation of the effects of a ball of glass dropt by accident into the ear, in which the inflammation was so extensive, and the pain so excruciating, that the whole side of the head, and even the arm and leg of that side were affect- ed, in consequence of the brain partaking of the inflammation. Such things as peas and cherry-stones and pins are very apt to be put into the ear by children ; and awkward attempts to extract the foreign body, very often push it further in ; and acrid fluids put into the ear to kill insects, have forced them deeper, with such an increase of pain as has thrown the patient into a condition little short of delirium. A defective or too profuse secretion from the glands of the tube will cause a degree of deaf- ness ; and sometimes the wax is so indurated as to cause a very obsti- nate deafness.* In the foetus, the concha and meatus externus are narrow, and there is secreted a thick white stuff, which defends the membrane of the tym- panum from the contact of the waters of the amnios. This, after birth, falls out in pieces along with the secretion of the wax; but, in some in- stances, it has remained and become very hard. OF THE TYMPANUM OR MIDDLE CAVITY OF THE EAR. THE ANATOMY OF THE TYMPANUM. In the foetus, the cavity of the tympanum is superficial, compared with that of the adult; for what forms a tube in the latter, is in the. for- mer merely a ring, which is attached to the squamous portion of the temporal bone upon this circular bone the membrane of the tympa- num is extended. The tympanum is a very irregular cavity, intermediate betwixt the membrane which is extended across the bottom of the external tube, and the labyrinth or internal ear. It contains no fluid, as the labyrinth does ; but is really a cavity, having a communication with the external air through a tube which leads into the fauces. The tympanum communicates also backwards with the cells of the mastoid process. J The inner extremity of the meatus externus forms a circle which is pretty regular, and upon which the membrane of the tympanum is extended. That part of the cavity of the tympanum which is opposite to the termination of the- mea- tus externus, is very irregular. It has in it the foramen rotundum and the foramen ovale ; and betwixt these, there is an irregular bony tubero- * See Valsalva, p. 10. “ Tails surditalis a dnodecim annis afftigentis curatio.” The old- er writers treat of the “ Auditus l*sio a surdibusaurium lapidescentibus.” See Bonetus, U ■fill. Cassertus Placantinus. De audilus orga.nolib. 1. cap. 20. p. 90. There is also mention made ofan adventitious membrane closing up the passage,and stretched above the mem- flrana tymparii. This is produced by a foul secretion, and resembles that which stuff's up the passage in the foetus. See Fabricius de Chirurg. operat. cap. de aur. Chirurg. Vkslingius Anat. cap. 16. See experiments on the Solvents of the Ear-wax by Dr. Haygarth, Med. Obs. and Enquiries, vol. iv. p. 198. He gives the preference to warm water over every other solvent. j See plate 8. fig. 3. | When Valsalva, in a case of ulceration and caries on the process, threw in his injections, he found them flowing out by the mouth : viz. by the Eustachian tube through the tympanum. See Val. de aure humana, p. 89. OP THE HOMAN EAR. 251 DESCRIPTION OP THE FIGURE. The outer ear in outline. The tube of the ear is seen closed at the inner part by the membrane of the tympanum. The chain of bones in the tympanum is seen. And the Eustachian tube leading from the tympanum into the throat. sity, called the tubercle, from which there stretch back some exceedingly small spiculse of bone, which connect themselves with the margin of the irregular cavity of the mastoid process. On the opposite side of the ca- vity there is a small eminence, with a perforation in its centre, called the Pyramid. The foramen ovale* is in the bottom of a deep sinus; it is not strictly of an oval form, but has its lower side straight, while the upper margin has the oval curve. This opening leads into the vestibule ox- central cavity of the labyrinth. The foramen rotundum is more irregular than the oval hole. It does not look directly forward, like it, but enters on the side of an irre- gular projection : it does not lead into the vestibule, but into one of the seal® of the cochlea. In the recent state of the parts, the periosteum covering the surface of the cavity of the tympanum, takes away some- thing of its irregularity; we trace the internal periosteum backwards into the mastoidean cells. The Eustachian tube | extends forward from the cavity of the tym- panum, and opens behind the palate. J In the dry bones, the Eusta- chian tube is more like an accidental fissure, than a regular passage, es- * Fenestra oval is. f Iler a paiato ad aurem. 1 By some older writers, the Eustachian tube is called aqueduct, because they conceived that humours were evacuated from the tympanum by this passage. 252 OF THE HUMAN’ EAR. sential to the economy of the ear. It appears thus irregular in the bones, from the tube being towards the back of the nose, composed ot a moveable cartilage cohered with a soft membrane ; as the tube ap- proaches the opening behind the palate, it widens into a trumpet shape ; and the extremity of the tube is governed by muscular fibres. Within the cavity of the tympanum, on the upper part of the Eustachian tube, there is a small canal, giving origin to the laxator tympani. This canal has been called the spoon-like cuvitu. There can be no doubt that the Eustachian tube is designed for ad- mitting the free access of air into the cavity of the tympanum, that, by preserving a due balance betwixt the atmosphere and the air contained within the ear, the motion of the membrane of the tympanum may be free. This, at least, we know, that, when the extremity of the Eusta- chian tube is closed, we suffer a temporary deafness which can be ac- counted for only by the confined air wanting a due degree of elasticity to allow the vibration of the membrane of the tympanum. I conceive it to be necessary, that the air in the tympanum be changed occasionally, which is accomplished by some actions of the throat and fauces, as swallowing, forcing a new body of air into the Eustachian tube. The extremity of the Eustachian tube, next to the throat, may be tempora- rily obstructed by the cynanche tonsillaris, which is frequently attended with pain, stretching from the throat to the ear; or it may be closed by inflammation and adhesion of its mouth, by adhesion of*the soft palate to the back of the fauces, by polypus in the nose, reacning down into the fauces and compressing it, &c.* OF THE MEMBRANA TYMPANI. A. The bony margin of the outer auditory foramen, B. Membrana tympani. C. The malleus. I). The incus. E. Orbiculare. F. The stapes. The membrane of the tympanum is extended over the circular open- ing of the bottom of the meatus externus. It has a little of an oval shape, and lies over somewhat obliquely, so that its lower margin is further inward than the upper. Its use is, to convey the vibration or os- cillation of the atmosphere, collected by the outer ear, inwards to the chain of bones in the tympanum. Although this membrane be tense, it is not stretched uniformly like the parchment of a drum, but is drawn into a funnel-like shape by the adhesion of the long process of the mal- leus to its centre. It consists of two layers of membrane, and has, na- turally, no perforation in it; and the experiments of air, and the smoke of tobacco sent from the mouth through the ear, succeed only in those * The following case is from Valsalva :—“ Quidam plebeius ulcus gerebat supra uvulam “ in sinistra parte, quodquitlam eam,quam invaserat partem exeserat atque abstuleret sic, ut “ ulceris cavitas cum extremosinistrae tub* orificio communicaret. Igitur quoties homo mol- “ lem turundam remediis imbutam in ulceris cavitatem intrudebat: toties illico sinistra aure w evadebat surdus, talisque permanebat toto ex tempore quo turunda in ulcere relinquebatur,” p.90. OF THE HUMAN EAR. 253 who have had the membrane of the tympanum partially ruptured or eroded by ulceration. This membrane is transparent; and when we look into the tube of the ear, and direct a strong light into it, we observe it to be of a shining tendinous appearance. The inner lamina of the membrana tympani is very vascular. It has, indeed, been said to resemble the iris, both in its prolusion of vessels, and in the manner of their distribution.* This is carrying the conceit of their analogy too far. I have observed an artery of a very large size (compared with the surface to be supplied) running by the side of the long process or handle of the malleus. In this course, it is giving out small branches ; and when the trunk arrives at the extreme point of the long process of the malleus, it divides into two branches, the ex- treme subdivisions of which run towards the margin of the membrane. This artery is, nevertheless, too small to require us particularly to avoid it in the puncturing of the membrane for deafness, produced by obstruc- tion of the Eustachian tube. The opinions regarding the muscularity of the membrane of the tym- panum, shall be reserved until we have considered the whole mechanism of the parts in the tympanum. The vibrations of the membrane of the tympanum are transmitted to the fo- ramen ovale by four moveable bones; the malleus, incus, os orbiculare, and stapes. These bones are named from their shape, and the names assist in con- veying an idea of their form. They are so united by articulation and small liga- ments, as to form an uninterrupted chain; and, while they transmit the vi- bration, their mechanism is such, that they strengthen the impulse. They have also small muscles attached to them, by which it is probable, the whole apparatus has a power of adapting the degree of tension to the force of the impulse com- municated to the membrane of the tym- panum. I conceive that they increase the power of the ear for receiving the weaker sounds, and are, at the same time, a guard to the internal parts, from such violent shocks as might in- jure the nerve. How necessary it sometimes is to damp and suffocate, in some de- gree, piercing sounds, we must all be sensible; and in those who are habitually exposed to the sudden eruption of sound, the susceptibility of the nerve is injured, and they become very deaf. We have, in a late publication, an example of this in blacksmiths, in whom, it is common to OF THE CHAIN OF BONES IN THE TYMPANUM. Malleus. Incus. Orbiculare. Stapes. * See Mr. Home’s lecture on the structure and use of the membrana tympani. Phil. Trans Part I. 1800. 254 OF THE HUMAN EAR. find a degree of deafness; and we find old artillery-men quite deaf, from the long practice of their profession. The malleus receives its name from a resemblance to a hammer or mallet: it is, in some degree, like a bludgeon; the great head stands obliquely off from the body of the bone (if such it may be called) like the head of the thigh-bone. Anatomists can scarcely be blamed, if, in describing the processes of this bone, they forget the body. I should consider that part as the body of the bone which stretches down from the circular margin f the tympanum, and is attached to the membrane, or what we should consider as the handle of the mallet. This part of the bone stands at an angle with the head and neck; tapers towards the extremity, and is a little curved down towards the membrane. From the larger end of the body of the bone there stands out an acute pro- cess ; and from the neck attaching the bulbous head to the body of the bone, there stands out a very slender process, which is often broken off. The great head of the bone does not form a regular ball to be socketed in the body of the incus; there are irregularities in the contiguous sur- faces of both the bones. The incus is the second bone of the chain; it receives its name from its resemblance to the blacksmith’s anvil. It more resembles a molar tooth with two roots. On the surface of the body, it has a de- pression like the surface of the first molaris. Into this depression of the incus the head of the malleus is received. The shorter of the two processes, and the body of the bone lie on the margin of the circular open- ing of the tympanum; and the acute point of this process is turned back into the opening of the mastoid cells. The long leg or process of the incus hangs down free into the tympanum,* and has attached to its point the os orbiculare. The os orbiculare or lenticular bone is like a grain of sand in size, and is the smallest bone of the body : it is a medium of articulation be- twixt the incus and stapes; and were it to be magnified, it would resem- ble the body of a vertebra f The stapes J or stirrup is well named, for it has a very close resem- blance to a stirrup-iron; the little head is articulated with the os orbi- culare ; the arch of the bone is exactly like that of the stirrup-iron, but elegantly grooved within, so as to give lightness to the bone. It has a membrane stretched across it. The base answering to that part of the stirrup-iron upon which the foot rests, is not perforated, nor is it of a re- gular form, but is flat on one side, corresponding with the foramen ovale. It is this base of the bone which is attached to the membrane stretched over the foramen ovale. CONNEXION AND MOTION OF THESE BONES. The malleus hanging on that part which we have called the neck of the bone, has the long handle or body of the bone stretched down upon the membrane of the tympanum. It is destined to receive the oscil- lations of that membrane. * See plate 4. fig. 1. d. f Soemmerriug supposes he has disproved the existence of this bone, j See plate 9. %. 1. c. OF THE HUMAN EAtt. 255 The head of the malleus is so articulated with the incus, that the de- gree of motion communicated to that bone is much increased. From this scheme, we see, that the head of the malleus is so articulat- ed with the body of the incus, that the centre of motion of the incus is ia a line drawn through the centre of its body, and, consequently, that the extremity of the long process, to which we see the os orbiculare and stapes attached, moves through a greater space than that which receives the impulse of the head of the malleus. Thus, a very small degree of mo- tion communicated by the head of the malleus to the body of the incus, must be greatly increased in the extremity of the long process of the in- cus, and, consequently, this mechanism of the bones essentially assists in giving strength to the vibration which is transmitted inward to the seat of the nerve. The os orbiculare stands simply as a link of communication betwixt the extremity of the incus and the upper part of the stapes, and its use is evidently to promote the accurate and perpendicular motion of this long lever of the incus upon the head of the stapes; for, if this bone had not been so placed, the motion of the long lever of the incus must have given an obliquity to the impulse upon the stapes. The base of the stapes almost completely fills up the foramen ovale. It is seated on a mem- brane which is stretched over the foramen.* The stapes, then, acts like a piston on a membrane of much less circumference than that of the membrana tympani. From all which considerations, we may learn how much the vibration produced by the agitation of the air in the outer canal of the ear is increased, before it strikes upon the fluids of the labyrinth, OF THE MUSCLES WITHIN THE TYMPANUM.! The laxator tympani arises from the upper part of the edge of the tympanum, near the part to which the membrane of the tympanum ad- heres, and is inserted into the handle of the malleus, near the root of its shorter process. The tensor tympaniJ arises from the upper part of * Valsalva has the following observation, see page 24. “ Olim namque in cujusdam surdi “ cadavere surditatis causam in eo sitam inveni nempe quod indicata membrana in substan- “ tiam osseam indurata, unum continuatum os constituebat cum basi stapedis et margine fe* “ nestree ovalis.” t Musculus processus minimi mallei. Valsalva. { Musculus processus majoris mallei. 256 OE THE HUMAN EAR. the Eustachian tube ; it lies along the side of the tube, and is inserted into the handle of the malleus be- low the slender process. The ex- ternal or superior* muscle of the malleus, which is denied by some anatomists to be of the nature of muscle, comes from the fore and upper part of the tympanum, and is fixed by a small tendon to the pro- cessus gracilis of the malleus. The stapedius | is the small- est muscle, and is attached to the smallest bone. It has a small round fleshy belly, taking its origin from the pyramid, and is inserted by a round small tendon into the head of the stapes. As all these muscles are inserted either into the malleus or stapes, and not into the middle bones, it would appear that their operation is chiefly upon the membranes of the tympanum, and of the foramen ovale, through the medium of the bones immediately attached to them. Sir E. Home, in the Philosophical Transactions for 1800, asserts that the membrana tympani is muscular ; that its fibres run from the circum- ference towards the centre ; and that they are attached to the malleus. But what is the supposed use of this muscular membrane 1 Sir E. Home says, it is principally by means of this muscle that accurate per- ceptions of sound are communicated to the internal organ ; that it is by means of this muscle that the membrana tympani is enabled to vary its degree of tension, so as to receive the vibrations in the quick succession in which they are conveyed to it. But we have seen, that the tension and relaxation of the membrana tympani is already sufficiently provided for; “ the malleus has three muscles by which it is moved : one of t£ them is called the tensor, from its pulling the malleus inward, and “ tightening the membrane of the tympanum; the other two act in an “ opposite direction, and relax the membrane.We should naturally suppose this to be sufficient; but, according to Sir E. Home, these mus- cles act only to bring the membrane into such a degree of tension, as to enable the minuter changes of the muscular membrane to have their full effect; and that the play of these muscles gives the perception of grave, and acute tones. But the more favourite idea of Sir E. Home is, that, upon the accu- rate adjustment of the membrana tympani. the difference between a mu- sical ear, and one which is too imperfect to distinguish the different notes in music, depends ; that this judgment or taste is owing to the greater or less degree of nicety with which the muscles of the malleus render the muscular membrane capable of being truly adjusted ; if the tension be perfect, all the vibrations produced by the action of the radiat- ed muscle will be equally correct, and the ear truly musical. A. Laxator tympani. Externus mallei. Teasor tympani. Stapedius. * Musculus processus minoris. Valsalva. t This muscle is particularly strong in the horse, where it was first discovered by Casscrius t Sir E. Home’s Lecture. OF THE HUMAN EAR. 257 Sir E. Home proceeds upon the idea, that the membrane of the tym- panum is like a musical instrument, or, as he expresses himself, like a monochord; but he is fundamentally wrong in supposing, that it requires a more delicate organ to be perceptible of musical tones than of articu- late sounds or language. In the first place, we may require an explana- tion of the use of that muscle which is inserted into the stapes. This stapedius muscle would seem to have the same use, and to affect that bone in the same manner, in which the muscles of the malleus affect it. Surely Sir E. Home will not go so far as' to say, that the membrana fe- nestrse ovalis is also muscular. It may be further worthy of attention, in considering this subject, that whatever affects the membrane of the tympanum, affects, also, the membrane of the vestibule. In the paper already quoted, the following case is given, as illustrating the manner in which the loss of the natural action of the muscles affects the ear, in regard to its capacity for music. A gentleman, thirty-three years of age, who possessed a very correct ear, so as to be capable of singing in concert, though he had never learned music, was suddenly seized with a giddiness in the head, and a slight degree of numbness in the right side and arm. These feelings went off' in a few hours, but on the third day returned ; and for several weeks he had returns of the same sensations. It was soon discovered that he had lost his musical ear ; he could neither sing a note in tune, nor in the smallest degree perceive harmony in the performance of others. For some time, he himself thought he had become a little deaf, but his medical attendant was not sensible of this in conversation. Upon going into the country, he de- rived great benefit from exercise and sea-bathing. In this case, continues Sir E. Home, there appeared to be some affec- tion of the brain, which had diminished the action of the tensor muscles of the membrana tympani, through the medium of the nerve which regu- lates their actions ; this gradually went off, and they recovered their ac* tion. Another case is given of a young lady who was seized with a phren- zy which lasted several years, when, from being without a musical ear, she came to sing with tolerable correctness, to the astonishment of her friends. We now proceed to put the incorrectness of this reasoning, concerning the muscular power of the membrane of the tympanum, in a more parti- cular point of view, leaving to Sir E. Home’s paper only the merit of in- genuity. Sir A. Cooper was led to pay particular attention to the action of the membrane of the tympanum, from being consulted in a case where the membrane was lost with little injury to the function of the organ.* * Case. This gentleman had been attacked, at the age of ten years, with an inflammation and suppuration in his left ear, which continued discharging matter for several weeks : in the space of about twelve months after the first attack, symptoms of a similar kind took place in tne right ear, from which matter issued for a considerable time. The discharge, in each in- stance, was thin, and extremely offensive to the smell; and in the matter, bones, or pieces of bones, were observable. The immediate consequence of these attacks was a total deafness, which continued for three months r the hearing then began to return : and, in about ten months from the last attack, was restored to the state in which it at present remains. Having filled his mouth with air, he closed the nostrils, and contracted the cheeks; the air thus com- pressed, was heard to rush through the meatus auditorius with a whistling noise, and the hair hanging from the temples became agitated by the current of air which issued from the ear. When a candle was applied, the flame was agitated in a similar manner. Sir A. Cooper then passed a probe into each ear, and he thought, the membrane dn the left 258 OF THE HUMAN EAR. He found, that, instead of the total annihilation of the powers of the or- gan, the gentleman was capable of hearing whatever was said in compa- ny, although the membrane of both ears was destroyed. He could eveu hear better in the ear in which no traces of the membrane remained. This gentleman was only in a small degree deaf from the loss of the membrane ; but his ear remained nicely susceptible of musical tones, “ for he played well on the flute, and had frequently borne a part in a “ concert ; and he sung with much taste and perfectly in tune.” This case puts aside, at once, that theory which supposes the musical ear to depend on the minute play of the muscles of the tympanum. It appears, from these and other instances, that the membrane of the tympanum may be destroyed, that the bones may be washed out by mat- ter formed in the tympanum, and still the patient retain the use of the organ. But this is only while the stapes retains its place ; for if this bone be destroyed, the membrane of the foramen ovale will be destroyed, and the fluids of the labyrinth be allowed to flow out, or be otherwise lost. We see that, if the chain of bones, and only a part of the mem- brana tympani be left, still this shred of membrane, if it be not detached from the handle of the malleus, will vibrate in the air, and communicate those motions through the other bones to the vestibule. We see, also, that though the bones only remain, and though they be detached from the membrane of the tympanum, the sound will still be communicated. We see, that a rupture of the membrane will not destroy the organization so far as to prevent the hearing, unless there follow clots of blood or in- flammation, suppuration, or fungus. When Sir A. Cooper found that the membrana tympani could be torn without injuring the organ, he did not stop short in his investigation : but as he found, by daily experience, that obstruction of the Eustachian tube caused deafness, he thought of puncturing the membrana tympani, as a cure for that kind of deafness. He expected, by this operation, to give elasticity to the confined air. Accordingly, by puncturing the membrane of the tympanum with a small trocar, he found, with much satisfaction, tiiat the hearing was instantly restored. * Valsalva made a good distinction, when he said, that the membrane of the tympanum was not absolutely necessary to hearing, but only to perfect hearing. We have, in this fact, the explanation of the following circumstance, amongst many others : “ In naturali surditate a conforma- “ tionis vitio inter tandem istud experimentum, (viz. an ossiculi et “ membrana tympani aliquis sit usus auditum,) quod inopinato et felici- “ ter successit cuidam, qui intruso auri scalpio in aurem profundissime “ disrupit tympanum, fregitque ossicula et audivit.”f Willis also knew, side was entirely destroyed, since the probe struck against the petrous portion of the temporal boue. 1 he space usually occ upied by the meinbrana tympani was found to be an aperture without one trace of membrane remaining. On the right side, also, a probe could be passed into the cavity of the tympanum ; but here, by producing it along the sides of the meatus, some remains of the circumference of the membrane could be discovered, with a circular opening in the centre about the fourth of an inchin diameter. Si e Trans. Roy. Soc. for 1800. Parti, p. 151. * I am only afraid that such punctures will not continue open, as in Valsalva’s experiments they healed up very soon. But, when there is no other ingress and escape to the air in the tympanum but through the punctured hole, it may tend to keep it open. See much of this in Morgagni, Epist. An. XII. The membrana tympani is very vascular. I have it red with in- jection. See Ruysch. fig. 9. tab. 9. Epist. An. VIII. . t Biolatius Enchirid. Anat. lib. 4. c. 4. See also Bonetus de Aurinm Affect, Observ. IV. OF THE HUMAN EAR. 259 that the destruction of the membrana tympani did not deprive the person of hearing. Vid. de Jlnima Brutorum. A most ingenious paper is given to the Philosophical Transactions, by Dr. Wollaston, in which it is shown that the exterior apparatus of the ear, and especially the parts in the cavity of the tympanum, are intended to give us the perception of acute and delicate sounds. OF THE DISEASES OF THE TYMPANUM. Valsalva denied the existence of periosteum to these bones of the tympanu n, while he allowed that they had minute vessels distributed on their surfaces : but these vessels he supposed to creep along the na- ked bone independently of any membrane. This, however, is contrary to all analogy.* These bones, as well as the cavity of the tympanum, are covered with a very fine membrane or periosteum, which, after a minute injection, is seen covered with many small and distinct vessels, as well as with intermediate extravascular effusions of the injection, as happens in injecting in other membranes. When the tympanum becomes diseased, there is fetid matter collected, the membrane of the tympanum suffers, and the small bones are some- times discharged. In such a case, we have little farther to do than, by injections, to prevent the matter from accumulating. But, let us not con- found this serious cause of deafness with the slighter suppurations in the outer passage of the tube : although such suppurations in the tube of the ear are apt, when neglected, to destroy the membrane of the drum or tympanum, and to spread disease to these internal parts. Authors make a display of the diseases of the membrane of the tym- panum under the titles relaxatio, tensio nimia, induratio, and diruptio tympani. f We have seen how little rupture of the me brane affects the hearing, and may thence conclude, that these fantastic opinions about tension and relaxation of the membrane deserve little notice. The idea of relaxation of the membrane of the tympanum, I have no doubt, has arisen from the effect of cold and moist weather in injuring the hear- ing ; but deafness from this cause is not produced by relaxation of the membrane of the tympanum, but by swelling of the mouth of the Eusta- chian tube.j Induration of the membrane is less of an imaginary disease, since there are instances of the membrane becoming thickened by inflam- mation, or cartilaginous, or osseous. The membrana tympani has been found to adhere to the extremity of the incus.§ Independently of the want of elasticity, which such an adhesion must produce, the vibration of the bones is prevented, and a degree of deafness is inevitable. Fungous or polypous excrescences from the glands in the outer pas- sage of the ear, press back and destroy the membrane of the tympa- num. In the cure of these by the knife, caustic, or ligature, there is * See Ruysch. Epist Anat. VIII. tab. 9 f See Du Verney de Organo Auditus, p. 41. j “ Relaxatio fit ab humore superfluo qui membranam hanc humectat et symptoma hoc “ communiter cum obstructione meatus ex tumore glandularum conjunctunri est, de qua jam “ supra dictum est: muitum auteni facit ad difficultatem audiendi in persnis quae defluxioni- “ bus catarrhosis obnoxi* sunt et per eandem rationem austri nebul* et aer plurius audi- “ turn minuuntut experiri quotidie possumus.” Du Verney loc. cit. P. 41. i See the London Philosophical Transactions for 1800, Part I. p. 5* 260 OF THE HUMAN EAR. much danger of injuring the membrane. Fungous tumours project from the membrane itself. A stroke upon the head will cause bleeding from the ear. This is often a sign of concussion of the brain ; that is to say, a shock so severe as to rupture the membrane of the tympanum, will most probably injure the brain.* After bleeding from the ear, some- times suppuration follows and blood flowing thus from the membrane of the tympanum, or other part of the ear, runs back into the cavity of the tympanum, and, filling it with coagulum, causes deafness, by obstruct- ing the free motion of the bones and membrane. Sir A. Cooper, in a case of this kind, punctured the membrane, and, after a discharge of blood which continued for ten days, the hearing was gradually restored. It is supposed by that gentleman, that the blood effused, becomes, in some instances, oganized, so as to obliterate the tympanum, causing per- manent deafness. The dangers in suppuration and caries of the tympanum is that the disease may penetrate backward into die mastoid cells and labyrinth, or into the brain itself; for inflammation and suppuration so confined amongst the deep recesses of the bone, must give great torture, and be apt to extend the mischief to the brain ; or the bone becoming carious, matter may be thrown out on the inside of the cranium, the effect of which must be mortal. Such I have seen to be the effect of suppura- tion deep in the ear. In a man who had been deaf for many years, and who was killed suddenly by a fracture of the skull, I found the cells of the temporal bones filled with matter, and a thin greenish fluid lay be- twixt the temporal bone and dura mater. I have since found the caries of the petrous bone from this cause fatal in young people Valsalva gives us a case of injury of the head, in which the patient was relieved while the discharge of pus by the ear was free ; but he died when it was entirely suppressed. J But, after such suppuration as we should naturally think must totally destroy so delicate an organization, we are sometimes agreeably sur- prised with a gradual recovery of the function. This is owing to the nerve accommodating itself or becoming sensible to a less forcible im- pression, and by the ear acquiring new properties. I have already men- tioned that the destruction of the mechanism of the tympanum arose sometimes from suppurations beginning in the outward ear; and we may suppose that the apparatus within the tympanum, when partially hurt, is sometimes capable of being, in some degree, replaced by a natural pro- cess ; of which the following case from Valsalva is a remarkable proof. I lately examined the ears of a woman whose hearing had been much injured by an ulcer of the tympanum and caries oi the small bone. I found the ear in which she was deaf without a membrana tym- pani, and the stapes only remaining of the bones, and a fibrous mass, like an excrescence, in the tympanum. But, in the tympanum ot the opposite ear, I found the membrani tympani almost entirely eroded ; so # When Valsalva found the ventricles of the brain full of blood, and blood also in the tympanum, he supposed that the blood in the latter was derived from the brain through cer- tain foramina which he discovered. See p. 30. ■f See Valsalva, p. 16 | Valsalva, p. 83. See also a case in Bonetus de Aurium Affect. Observ. I. and Gul. Ballonius Epid. et Ephem. lib 2. p. 270. When the matter was suppressed, there came pain of the head, and weight, which yielded to no remedy ; on dissection, there was found an abscess within the skull. In Bonetus, loc cit., a case is related, in which an ignorant sur- geon compressed a fistulous ulcer in the ear, and so caused the death of the patient. OF THE HUMAN EAR. 261 that the malleus and incus were uncovered, and distinctly seen. I could even observe, that the long process of the incus, which should be articu- lated with the head of the stapes, was separated from it: but nature had curiously restored the eroded membrane. Thus, from the edge of the injured membrane, a new membrana tympani was obliquely stretched across the cavity of the tympanum, so as to exclude the malleus and in- cus from that cavity, but including the head of the stapes, as if nature, finding the separated bones no longer necessary, had attached the mem- brane to the head of the stapes.”* We have already remarked, that, when the organ of one side is injured, we hear so much better with the other, that we attend only to the sensation conveyed by it, and neg- lect the duller sensation. The consequence of this is, that the bad ear becomes worse. It is much like that effect which takes place in eyes by squinting. OF THE LABYRINTH. DESCRIPTION OF THE FIGURE. The labyrinth first cut out of the solid bone, and then opened, so as to shew the cavities. The central one, the vestibule; the semicircular canals ; and the cochlea, so laid open as to exhi- bit part of the scala vestibuli and srala tympani. The chain of bones is attached, the stapes resting on the foramen ovale. The labyrinth is the internal ear ; the proper seat of the sense of hear- ing. It consists of the vestibule or middle cavity ; of the semicircular canals; and of the cochlea. It has its name from those cavities and tubes leading into each other in so intricate a manner, as to be followed out with much difficulty. We understand that the cavities hitherto described in the human ear contain air, and communicate with the atmosphere : but, in the cavities we have now to describe, the nerve is expanded, and there is, in contact with it, not air, but an aqueous fluid. In treating of this division of our subject, we have, first, to attend to the forms of the cavities, as seen when sections are made in the dry bones next to the soft parts contained in those cavities; and, finally, to the distribution of the nerves. To give an idea of the exquisitely delicate and complex structure of the many canals, excavations, openings, sulci, and foveae, of the bones ; of the tubuli, sacculi, and partitions of the membranes; and, lastly, of the soft expansions of the nerves, without the assistance of plates, would be impossible. Albinus, in his academical annotations, begins very for- mally a chapter on the ear; but, after a few words, dismisses the subject, referring merely to his plates. * See Valsalva de Aure Humana. Tract, p. 79. In those deaf from birth it has been twice found that the incus was wanting. See Bontius de/Lur. Affect. Observ. IV. 262 OF THE HUMAN EAR. The vestibule, or central cavity of the labyrinth, is of an oval form, and about a line and a half in diameter. * It has two remarkable pits or hollows in it, and has numerous foramina opening from it into the neigh- bouring cavities, besides lesser foramina for transmitting that portion of the nerve which is distributed on the sacs contained in it. One depres- sion or fovea is in the back or lower part of the vestibule, another in the outer and superior part of it : the one is circular, the other semi-oval. Morgagni, and other anatomists, examining the dry bones, speculated on their use in reverberating the sound in the cavity ; but we must not regard them in this unnatural state ; on the contrary, they contain in the living subjects membranous sacculi filled with fluid, in which membranes the nerve is finally distributed. That foramen over which the stapes is placed, and which is called the foramen ovale, transmits the vibration into the vestibule. For the foramen ovale opens directly into the vesti- bule, and through the vestibule, only, does the vibration of the bones in the tympanum reach the other parts of the labyrinth. Semicir' ULar canals.—When we have cut into the vestibule, by taking a way that portion of the os petrosum which is behind the meatus auditorius internus, we see five circular foramina : these are the openings of the semicircular canals. There are three semicircular canals ; and they are distinguished by the terms, the superior or vertical, the posterior or oblique, and the exterior or horizontal. The one which, in this view, is nearest, is the opening common to the inner ends of the posterior and superior semicircular canals. When we pass a bristle into this common foramen, and direct it upward, it passes along the superior semicircular canal, and will be seen to descend from the upper part or roof of the vestibule, almost perpendicularly on the foramen ovale, which is open, and immediately opposite. If, again, we pass a bristle into the foramen which is near the bottom of the cavity, (and which will be just upon the edge of the fracture that has laid open the vestibule, if not included in it,) it will come out by the opening common to the superior and posterior semicircular canal. It has passed, then, along the posterior canal. The two openings of the exterior or horizontal canal are upon the back part of the vestibule ; and the canal itself takes a circle which brings its con- vexity to the confines of the mastoid cells. These canals are formed of a very hard brittle bone, their calibre is so small as not to admit the head of a common pin ; they form somewhat more than a half circle ; and of each of them, one of the extremities is enlarged like the ampullula of fishes. Valsalva imagined that the enlarged extremities of these tubes were trumpet-like, to concentrate and strengthen weak sounds. We shall find, on the contrary, that there is in the human ear, as in fishes, a particular expansion of the nerve in these extremities of the tube, oppos- ed to the circulatory vibration of the fluids in the canals. The cochlea.—The third division of the labyrinth is the cochlea. It is so named from its resemblance to the shell of a snail, or from the man- ner in which its spiral lamina turn round a centre like a hanging stair. It has been minutely, but not simply described ; and indeed, there can be nothing more difficult, than to describe it in words. When the os petrosum is cut from around the cochlea, it is seen to be of a pyramidal shape, and to consist of a scroll making large circles at * Du Verney GEuvres Anatomiques. OP THE HUMAN EAR. 263 the base, and gradually lesser ones towards the apex. It is formed in the most anterior part of the petrous bone, and has its apex turned a little downward and outward ; and the base is opposed to the great cul de sac of the internal meatus auditorius. The spiral tube, of which the cochlea is composed, forms two turns and a half from the basis to the point; and it consists of the same hard and brittle matter with the semicircular canals. When the whole coch- lea is cut perpendicularly in the dry state of the bones, and when the membranes have shrunk away or spoiled, the sides of the spiral canal appear like partitions, and are, indeed, generally described as such. In consequence of the spiral tube of the cochlea having its sides cut per- pendicularly as in this figure, the cochlea appears as if divided into three circular compartments or successive stages; but there is really no such division ; because the spiral turnings of the tube lead from the one into the other. What gives particular intricacy to the. structure of this part of the labyrinth, is the lamina sfirai.is.* This spiral partition runs in the spi- ral tube of the cochlea, so as to divide it in its whole length ; and, in the fresh state of the parts, this lamina of bone is eked out by mem- brane, so as to form two perfectly distinct tubes. These tubes are the scalje cochleae ; they run into each other, or communicate at the apex of the cochlea ; but at the base, the one turns into the vestibule, and the other opens into the tympanum by the foramen rotundum. In the middle of the cochlea there runs down a pillar, which is the centre of the circumvolutions of the scalm. It is called the modiolus. This pillar is of a spongy structure; and through it the nerves are trans- mitted to the lamina spiralis. The modiolus opens towards the apex of the cochlea like a funnel; and when we take away the outward shell of the apex of the cochlea, which is called the cupola, we look into this expansion of the upper part of the modiolous as into a funnel; it is therefore called the infun- dibulum. The infundibulum is that part which, in a perpendicular section, we should call the upper partition n f The scalae or divisions of the spiral tube of the cochlea, have a com- munication at their smaller extremities in the infundibulum; and as, again, their larger extremities do not open into the same cavity, but one into the vestibule, and the other into the tympanum, the vibrating motion, which is communicated through the cochlea, must pass either from the tympanum into the foramen rotundum, circulate round the modiolus by the scala tympani, pass into the lesser extremity of the * A, Lamina spiralis. B, Scala vestibuli. C C, Scala tympani. D, The hook of the la- mina spiralis in the infundibulum. t That is, supposing the cochlea to rest, on its base, which it does not 264 OP THE HUMAN EAR. scala vestibuli in the infundibulum, and circulate through it towards the base of the cochlea, until it pass into the vestibule ; or it must pass from the scala vestibuli into the scala tympani. The first is the opi- nion of Scarpa and others. But I trust it will afterwards appear, that the oscillations of sound are in the first place conveyed into the ves- tibule, and thence circulate round both the semicircular canals and cochlea. In the dry bones, when we cut into the cochlea, there appears a spiral tube, as I have described ; with a partition running along it, and, of course, taking the same spiral turns with it towards the apex. This is the bony part of the lamina spiralis ; but, as the membrane which ex- tends from its circular edge quite across the spiral tube of the cochlea, has shrunk and fallen away in the dry state of the parts, the lamina spiralis is like a hanging stair, and the seal® are not divided into dis- tinct passages. In this bare state of the shell of the cochlea, when we cut away the cupola or apex of the cochlea, and look down upon the infundibulum, we see the extreme point of the lamina spiralis rising in an acute hook-like point. The modiolus or central pillar, and the lamina spiralis which encir- cles it, are of the most exquisite and delicate structure; for, through them the portion of the seventh nerve destined to the cochlea is con- veyed. To say that the modiolus is formed of two central bones, is saying that there is no central column at all; or, that the modiolus is the cavity seen in the bottom of the meatus auditorius; and to affirm, at the same time, that the modiolus is a nucleus, axis, or central pillar, is a contradiction in terms. When we break away the shell of the cochlea, and break off also the spiral lamina, we find the little funnel-like depression in the bottom of the meatus internus, reaching but a little way up into the centre of the cochlea.—We find this depression of the meatus auditorius internus per- forated w'ith innumerable small holes ; and these foramina are so placed as to trace a spiral line, because they give passage to the nerves going to the spiral lamina, and must take the form of the diminishing gyrations of the lamina spiralis. In the centre of these lesser foramina, which are seen in the bottom of the great foramen auditorium internum, there is a hole of comparatively large size, which passes up through the mid- dle of the pillar. The modiolus is formed of a loose, spongy texture, and resembles the turns of a cork-screw ; and this spiral direction is a necessary consequence of the lamina spiralis, being a continuation of the spongy or cribriform texture of the modiolus. Internal periosteum of the labyrinth.—We find that the vesti- bule, the semicircular canals, and cochlea, besides their soft contents, which we have yet to describe, have their proper periosteum, which, af- ter a minute injection, appears vascular; and this, as it has appeared to me, is particularly the case with the last-mentioned division of the laby- rinth. I see very considerable vessels distributed on the vestibule ; par- ticularly, I see their minute ramifications on the circular fovea, while ve- ry considerable branches are seen to course along the semicircular ca- nals. In the cochlea, I see distinct branches of vessels rising from the root of the lamina spiralis, and arching on the seal®, to the number of ten in the circle ; and, after a more minute injection, I have found the ON THE HUMAN EAR. 265 osseous part of the lamina spiralis tinged red, and the membranous part of a deep scarlet.* We have observed the meatus auditorius internus to be a large oval foramen in the posterior surface of the pars petrosa of the temporal bone. This tube transmits the seventh or auditory nerve. It is about live lines in diameter, but increases as it passes inward ; and appears to terminate in two deep fovea, which are divided by an acute spine. But the auditory foramen only appears to terminate in these fovea, for they are each perforated by lesser holes, which lead into the three divisions of the labyrinth, whilst a larger one conveys a portion of the nerve through the cavities of the temporal bone altogether, and out upon the side of the face. This larger foramen is in the upper part of the supe- rior and lesser fovea. It first ascends to near the surface of the petrous part of the temporal bonet, and then descends and turns backward, and takes a course round the tympanum above the foramen ovale; and close by the posterior semicircular canal. Its termination is the foramen sty- lo-inastoideum. J Where this canal of the portio dura advances towards the surface of the pars petrosa, it is joined by a very small canal which extends from the videan hole on the fore part of the inclining face of the bone : again, after it has passed the tympanum, it is joined by a short canal which receives the corda tympani, after it has passed the tympa- num. The other foramen which is in the upper and lesser fovea of the mea- tus internus, is rather a cribriform plate, as it is a deep pit with many fo- ramina in it. These lead into the vestibule, and form the macula cri- brosa vestibuli.§ In the inferior and larger fovea, we observe several dark spots, which, when more narrowly examined, are also distinguish- ed to be cribriform plates, or collections of lesser foramina. We parti- cularly observe that conical cavity which is perforated with many little pores for transmitting the nerve into the cochlea, and which we have al- ready mentioned. From the form which these foramina take, this is named the tractus spiralis foraminolosus. These foramina, after passing along the modiolus cochleae, turn at right angles, and pass be- twixt the plates of the lamina spiralis. Besides the tractus spiralis foraminolosus the bottom of the larger fo- vea has many irregular foramina, which are like cancelli: for very deli- cate spiculse of bone stand across some of them. There is a range of these foramina which stretches from the tractus spiralis. This may pro- perly be called the tractus calthratus rectus |j ; they do not lead into the vestibule, but into the beginning of the lamina spiralis, where it divides the two scalae cochle®, and turns the orifice of one of them, (by a beautiful curve,) out into the tympanum. Nearer to the ridge which divides the two fovese of the meatus inter- nus, there is a little pit which has also a cribriform plate (like that which is in the upper fovea, and is called macula cribrosa); opposite to this point * In a preparation before me, I see a considerable artery derived from the basilar artery, entering the meatus auditorius internus. From this trunk, I conceive that most of therse arte- ries which I have described are derived. + In the foetus, it becomes here superficial. 4 This is the aqueduct of Fallopius. § See Scarpa, Plate VII. fig. i. m. || Tractus spiralis foraminolosi initium. Scarpa. 266 OF THE HUMAN LAR. the inside of the vestibule is rough and spongy: it transmits a portion of the nerve to the sacculus in the hemispherical sinus of the vestibule.* of the soft parts contained in the labyrinth. Within the vestibule, semicircular canals and cochlea, there are soft membranes independent of the periosteum. These form sacculi and tubes which contain a fluid, and have the extreme branches of the portio mollis distributed among them. Betwixt the soft and organized sacculi and tubes and the periosteum of the osseous labyrinth, a watery fluid is exuded Sacculus vestibuli.—The hemispherical and semi-elliptical foveae which we have described in the vestibule, contain, or at least receive par- tially, two sacculi. The sacculus which is in the hemispherical cavity, receives the most convex part of the sacculus vestibuli. This sac is distended with a fluid, and is pellucid, and fills the greater part of the vestibule ; for only a part of it is received into the fovea. It forms a complete sac, and has no communication with the other soft parts of the labyrinth, though lying in contact with the alveus communis, presently to be mentioned ; and being surrounded with an aqueous fluid, it must re- ceive the impressions of sound in common with them. Alveus communis ductuum semicircularum.—This sacculus lies in the semi-elliptical fovea of the vestibule, or like the other sacculus, is in part received into it. This sacculus receives the extremities of the tubuli membranacei which lie in the semicircular canals ; it is a little bag common to them, and connecting them altogether, as in fishes ; it is fill- ed with fluid, and is so pellucid, as to be distinguished with much diffi- culty. Upon pressing the common sac, or the ampullulae of the semi- circular canals, the fluids are seen to circulate along the membranous tubes of the canals. These two sacculi in the vestibule lie together, and firmly adhere, but do not communicate ; yet (as may be easily imagined) they cannot be separated without tearing the partition. Tubuli membranacei. —The tubuli membranacei are the semicircu- lar tubes which pass along the osseous semicircular canals, and to which the latter are subservient, merely as supporting them. They are con- nected by means of the common alveus in the vestibule, and form a dis- tinct division of the organ. It was believed by anatomists formerly, that the osseous canals had the pulp of the nerve expanded on their periosteum. But we find, on the contrary, that the membranous tubuli do not touch the bones, but are connected with them by transparent cellular membrane-like mucus. Each of the semicircular membranous tubes has one extremity swelled out into an ampulla of an oval form, answering to the dilated extremity of those osseous tubes which we have already described. These am- pullse have the same structure and use with those formerly mentioned in describing the ear in fishes. When the central belly of these tubes is punctured, both the ampullae and the membranous canals fall flaccid. Besides those vessels which we have described running along the peri- osteum of the cavities of the labyrinth, vessels also play upon the sac- * Scarps. OP THE HUMAN EAR. 267 euli and membranous tubes. The ampullae of the tubes are, in a parti- cular manner, supplied with blood-vessels.* In the cochlea there is also a pulpy membrane, independent of the periosteum; but of this 1 can say nothing from my own dissection. OF THE NERVE. As the seventh pair of nerves arise in several fasciculi, they form what would be a flat nerve, were it not twisted into a cylindrical form adapted to the foramen auditorium internum. While these-fasciculi are wrapped in one common coat, they are matted together. In the canal, the nerve is divided nearly into two equal parts ; t to the cochlea and to the vestibulum and semicircular canals. Those fasciculi, which are des- tined for the vestibule, are the most conspicuous ; and on the portion des- tined for the ampullae of the superior and external canal there is formed a kind of knot or ganglion. Before the auditory nerves pass through the minute foramina in the bottom of the meatus auditorius, they lay aside their coats, and become more tender and of a purer white colour : and by being still arther sub- divided by the minute branching and divisions of the foramina, they can- not be followed, but finally expand in a white pulpy-like substance on the sacs and ampullae. We must, however, recollect that there was a difference to be observed in the apparent texture of these expanded nerves in the lower animals : we may observe here, also, that part of the nerve which is expanded on the common belly or sacculus tubulorum, is spread like a fan upon the outer surface of the sac, and has a beauti- ful fibrous texture ; but upon the inside of the sac upon which it is finally distributed it loses the fibrous appearance. We must suppose its final distribution to be in filaments so extremely minute that we may call it a pulp ; though by the term it must not be understood that an unorga- nized matter is meant. That part of the nerve which stretches to the ampullae, immediately divides into an opaque white mucous-like expansion. Beyond these ampullae, there has been no expansion of the nerve discovered in the membranous tubes. The sacculus vestibulij is supplied by a portion of the nerve which perforates the macula foraminolosa, in the centre of the osseous excava- tion, or that which receives into it part of the sac. This part of the nerve is expanded in a soft mucous-like white matter in the bottom and sides of the sac. A division of the nerve, as we have already explained, passes from the meatus auditorius internus through the cribriform base of the mo- diolus into the cochlea. Owing to the circular or spiral form of the fora- mina when the nerve is drawn out from the meatus, its extremity appears as if it had taken the impression of these foramina from the extremities of the torn nerves preserving the same circular form. These nerves, • “ Caeterum universum hoc canaliculorum membranaceorum alvejque communis machina- “raentum, sanguiferisvasisinstruitur, quorum crassiora, circum alveum communem, serpen- «* tino incessu ludimt; crebra et conferta alia ampullae imprimis recipiunt ob qtiam cau«am “ rubellffi pleromque sunt et cruore veluti suffusae.” Scarpa, p. 47. | Of the portio dura we have already spoken, j i. e. In opposition to the sacculus tubulorum 268 OF HEARING. passing along the modiolus and scalre cochleae are in their course subdi- vided to great minuteness. Part of them perforate the sides of the modiolus, whilst others pass along betwixt the two plates of the lamina spiralis, and out by the minute holes in the plates and from betwixt their edges. Lastly, a central filament passes up through the centre of the modiolus, and rises through a cribriform part into the infundibulum to supply the infundibulum and cupola. Where the nerves pass along the lamina spiralis, their delicate fibres are matted together into a net-work. According to the observations of Dr. Monro, they are quite transparent on their extremities. OF HEARING. When aerial undulations were, by the experiments on the air-pump, first proved to be the cause of sounds, philosophers looked no further to the structure of the ear than to discover an apparatus adapted for the reception of such vibrations. When they observed the structure of the membrane of the tympanum, and its admirable capacity for receiving these motions of the atmosphere, they were satisfied, without consider- ing the immediate objects of sensation. In the same way, an ignorant person, at this day, would rest satisfied with the fact that sound was re- ceived upon the drum of the ear. But after so minutely explaining the anatomy of the ear, it becomes us to take a general survey of a structure the most beautiful which the mind can contemplate. We can- not say that it surpasses in beauty the structure of other parts of the body: but the parts are adapted to each other, in a manner so simple, efficient, and perfect, that we can better understand and appreciate the harmony of their structure than that of organs, which perform their functions by qualities and actions almost entirely unintelligible to us. We see that the external ear collects the vibrations of sound as it moves through the atmosphere in circular undulations proceeding from the sonorous body: we may observe, that where the necessities of ani- mals require them to be better provided with this external part of the organ than man, the superiority is in the increased sensibility to sounds, and in judging of their direction. Notwithstanding it is obvious that the horse and ass, for example, use their ears to judge of the direction of sound, experiments of cutting off these appendages, we are told, have not hurt the power of the organ ; and man, from the perfection of the internal organ, excels all animals in the capacity of the ear for articulate and musical sounds. From the external ear we observe, that the trumpet-like tube conveys the sound inward to the membrane of the tympanum. Behind the mem- brane of the tympanum, there is a cavity which, in order to allow of the free vibration of the membrane, contains air.—When this air is pent up, by the swelling or adhesion of the Eustachian tube, the elasticity of the air is diminished, and the membrane prevented from vibrating.* * See Recherckes, &c. relatives 4 Porgane de Panic eta la propagation des sons, par M. Perolle, SttcieU Pc. de Medicine, tom. iii. OF HEARING. 269 In the tympanum, we have seen that the operation of the chain of bones is to increase the vibration received upon the membrane of the tympanum, and to transmit it to the membrane of the foramen ovale. In the cavity of the tympanum we observed two foramina, the foramen ovale and the foramen rotundum, both of which lead into the labyrinth ; but one of them (the foramen ovale) into the vestibule, the other (the foramen rotundum) into a scala of the cochlea; now it becomes a ques- tion, whether the oscillations of sound pass by one or by both of these foramina ? It is contended, that the sound passes in both ways, that is, along the solid bones, and through the air of the tympanum. Did it pass through the air, why is there all this expense of apparatus ?—why a mem- brane of the tympanum : for unless the impressions of sound were to be conveyed, as powerfully through the air, as by the bones, why are they at all ? If the air were the medium, then the chamber containing it should be direct and regular. Again, it is with the same inconsistency maintained, that the tympanum is more capacious in the elephant and in nocturnal birds, so as to increase the acuteness of hearing. The obvious objection to this is, that the walls of the cavity are irregular in a singular degree, with minute cells, spines and processes, presenting no where a regular concave for reverberation. If a person should show me an irregular piece of rock crystal, opaque white, from the variety of its reflecting surfaces, and say it was a lens, I would as soon believe it was a magnifying glass, as that the cells of the cavity of the tympanum were for reverberating and directing the sounds. An absolute Confusion of ideas has led to the opinion, that the fora- men rotundum receives the undulation of the air. It is not enough to state to those physiologist*, that the foramen ovale is directly opposite the membrane of the tympanum, and the foramen rotundum turned away from it. No, they say, that is the very reason, because it does not receive the impulse direct, but by reverberation, and obliquely. If there were any hope of arguing against these opinions, we might state the matter thus. If the sounds arrived from different sources, and came in various directions, they might (if the surfaces were regularly adapted) be reverberated to some common centre, and thereby strength- ened (of which we have an example in the outward ear) ; but the sound comes only by the motion of the membrane of the tympanum, through the tube of the ear; it is already concentrated, and if it were now to be directed against the walls of these passages, it might be dissipated, but how is it to be concentrated again ?—and if concentrated, in what de- gree can it be stronger than when it entered the tympanum ? In the labyrinth there is no air, but only an aqueous fluid : now this, we have seen, conveys a stronger impulse than the atmosphere ; strong- er in proportion to its greater specific gravity and want of elasticity; for an elastic fluid like air may be compressed by concussion, but an inelastic fluid must transmit fairly every degree of motion it receives. But if the fluid of the labyrinth be surrounded on all sides ; if, as is really the case, there can be no free space in the labyrinth, it can par- take of no motion, and is ill suited to receive the oscillations of sound. Against this perfect inertia of the fluids of the labyrinth I conceive the foramen rotundum to be a provision. It has a membrane spread 270 OF HEARING. over it, similar to that which closes the foramen ovale. As the foramen ovale receives the vibrations from the bones of the tympanum, they cir- culate through the intricate windings of the labyrinth, and are again transmitted to the air in the tympanum by the foramen rotundum. Without such an opening there could be no circulation of the vibration in the labyrinth ; no motion of the fluids communicated through the contiguous sacculi, nor through the scalae of the cochlea ; because there would be an absolute and uniform resistance to the motion of the fluids.—But, as it is, the provision is beautiful. The membrane of the foramen rotundum alone gives way of all the surfaces within the laby- rinth, and this leads the course of the undulations of the fluid in the la- byrinth in a certain unchangeable direction. To me it appears, that to give a double direction to the motion of the fluids, or to the vibration in the labyrinth, far from increasing the effect, would tend to annihilate the vibrations of both foramina by antagonizing them. The common idea is, that there is a motion communicated through the membrane of the foramen rotundum along the scala tympa- ni, and another through the foramen ovale into the vestibule, and through the vestibule into the scala vestibuli ; and that the concussion of these meet in the infundibulum of the cochlea. But as there is no space for motion in the fluids, in either the one or other of these tracts, the vibra- tion must have been received in the infundibulum at the same time that the motion was communicated to the membranes of the foramen ovale and rotundum ; for if a tube full of water, a mile in length, loses one drop from the extremity, there must be an instantaneous motion through the whole to supply its place. The evident consequence of this double im- pulse would be (if they were of the same strength) to suppress all motion in the fluids of the labyrinth. But we have shown that the strength of vibration communicated to the foramen ovale and foramen rotundum are not the same ; for the mecha- nism of the bones in the tympanum is such as to accumulate a greater force or extent of motion on the membrana ovalis than is received upon the membrana tympani; therefore the lesser vibration which is commu- nicated through the medium of the air in the tympanum, cannot be sup- posed capable of opposing the stronger vibration which is conveyed from the foramen ovale through the labyrinth. Besides, the air in the tympa- num has a free egress, and cannot therefore strike the membrane on the foramen rotundum forcibly. For these several reasons, I conceive that Scarpa’s account of the manner in which the sound is conveyed is erroneous : * As to the immediate seat of the sense of hearing, there cannot, after what has been explained regarding the distribution of the nerves, remain any controversy ; though before the structure of the ear was so well un- derstood, some imagined that the vestibule, others that the middle part of the semicircular canals, was the seat of hearing ; others, again, that the lamina spiralis was better adapted for receiving the vibrations of sound. It is evident that the soft expansion of the nerve, in all the three divisions of the labyrinth, is destined to receive the undulation of the con- tained fluids, and that this motion of the fluids gives to the nerve, or to the nerve and brain conjointly, the sensation of hearing. * Scarpa, p. 61. OF HEARINfc. 271 Since we have, in seme measure, traced the structure of the ear from the animals of a simple structure to those of a more complicated organi- zation, and have observed some parts of the ear common to all animals, some peculiar to certain orders ; and since all have the sense of hear- ing, more or less acute, it becomes natural to enquire what are the parts of the organ the most essential to the mere perception of sound, and what parts conduce to a more perfect state of the sense. All the external apparatus of the ear is not necessary to give the ani- mal the simple perception of sound.— There are many classes of ani- mals altogether without them, and even in man we see that they are not absolutely necessary ; since, when deprived of them by disease, he still enjoys the sense. He* is deprived of no essential variety of the sensa- tion ; he is capable of perceiving the distinctions of articulate sound ; and still possesses his musical ear. The external apparatus of the ear, the membrane of the tympanum, and the little bones, receive, concen- trate, and increase the tremors of the external air, and render the lesser motions or more acute impressions audible. They are not essential to hearing. These are the parts calculated only to receive the minute un- dulations of the air, and to perfect our sense of acute sounds. It would appear, that the simple sac of the vestibule is sufficient to receive the impression in some animals, and that in many the vestibule and semicircular canals form all the organ of hearing. It is evident, therefore, that these are the most essential parts. We find, however, that the cochlea exists, though it be imperfect, in birds; that it is fully formed only in man, and in quadrupeds: from which we may conclude, that it is subservient to the more exquisite sen- sations. We are not, perhaps, warranted in concluding that any one part of the organ of hearing bestows the pleasures of melody and har- mony, since the musical ear, though so termed, is rather a faculty de- pending on the mind. Yet, when we see that the sacculi of the vesti- bule is c >mrnon to all creatures ; and the semicircular canals common to fishes, birds, and beasts ; and when, in the lamina spiralis of the cochlea, we see a more perfect preparation for variety of impression; and which, by comparative anatomy is marked as the perfection of the organ of hearing, we are naturally drawn to observe this part more nar- rowly. Even after studying, with all diligence, the anatomical structure of the ear, we cannot but be astonished with the varieties to be found in the sensation ; for example :—“ The ear is capable of perceiving four or five hundred variations of tone in sound, and probably as many different degrees of strength; by combining these, we have above twenty thou- sand simple sounds that differ either in tone or strength, supposing every tone to be perfect. But it is to be observed, that to make a perfect tone, a great many undulations of elastic air are required, which must all be of equal duration and extent, and follow one another with perfect regularity ; and each undulation must be made of the advance and re- coil of innumerable particles of elastic air, whose motions are all uni- form in direction, force, and time. Hence we may easily conceive a prodigious variety in the same tone, arising from irregularities of it oc- casioned by constitution, figure, situation or manner of striking the so- norous body; from the constitution of the elastic medium, or its being disturbed by other motions; and from the constitution of the ear itself 272 OF HEARING. upon which the impression is made. A flute, a violin, a hautboy, a French horn, may all sound the same tone, and be easily distinguishable. Nay, if twenty human voices sound the same note, and with equal strength, there will still be some difference. The same voice, while it retains its proper distinctions, may yet be varied many ways : by sick- ness or health, youth or age, leanness or fatness, good or bad humour. The same words, spoken by foreigners and natives, nay, by different provinces of the same nation, may be distinguished.”* There are several interesting subjects which have not met with suffi- cient attention. On what does this variety in the sensation depend ? Does the vibration strike on different parts, and re-echo along different passages of the labyrinth, so as to move particular divisions of the audi- tory nerve ? Or does the whole fluid of the labyrinth move in every sound, and is every filament of nerve struck ? I must suppose that the first opinion is true. It appears necessary, to account for that extraor- dinary compass and variety in the sensations of this organ. And if the varieties in the impression had resulted from a pulse agitating indiscri- minately the whole nerve, it would seem that the object would have been better accomplished by the uniform expansion of the medulla of the nerve over all the surfaces and cavities, as in the eye. But as, on the conirary, the medullary matter lies in patches, it is probable that those are the centres where undulations of sound meet, reflected from the surrounding vaults. In an elliptical chamber, a person standing in one of the foci is heard in a whisper by a person stand- ing in the other focus : for by the regular elliptical form, the waves or pulses are reflected to the foci. The vestibule has regular concavities, which we can imagine to produce such a concentration of sound. The cavity of the tympanum, on the contrary, hav- ing no such regularity of form, (as I have argued above,) can produce no such concentration of the pulses of sound. Another difficulty presents in accounting for the direction of sound. Authors have left us quite in the dark on this subject. That two ears, by receiving the impressions unequally as we turn the head, affords a means of judging of the directions of sounds, is obvious; but we possess the same power through the operation of one ear. Some have been so hardy as to explain this on the supposi- tion that the impressions are received on the head, and that we judge in this manner of the direction of them; which were, I think, to make the ear a superfluous ornament. Are the sounds reflected from the different surfaces of the outer ear, so as differently to affect the mem- brane of the tympanum and the adjoining muscles 1 it is not easy to prove this. Does ventriloquism throw any light on this subject ? If we know how we are deceived in the direction of sounds, we may learn by what means we judge of them. This would make the modifications of the intensity of impression the means by which we judge of the direc- tion of sound. It may countenance such an explanation if we con- sider the nicety with which we judge of the distance of a sonorous * Reid’s Enquiry, p. DISEASES OF THE INTERNAL EAR. 273 body ; we judge, at least, as accurately of distance by the ear as by the, eye. I must again repeat that the cochlea is the more important part of the organ, or rather the refined and higher part of the apparatus ; for the vestibule is universal, and the semicircular canals common to fishes, birds, and quadrupeds. We think that we find in the iamina spiralis the only part adapted to the curious and admirable powers of the hu- man ear, for the enjoyment of melody and harmony. It is in vain to say, that these capacities are in the mind and not in the outward organ* It is true, the capacity for enjoyment, or genius for music, is in the mind. All we contend for is, that those curious varieties of sound which constitute the source of this enjoyment, are communicated through the ear, and that the ear has mechanical provisions for every change of sensation. There is no part of the proper organ which appears susceptible of the variety of musical notes but the scala of the cochlea. Its breadth is in regular gradation of parts from the base towards the point or apex; and whether the fibres were to be taken as the cords of a harp, or the tubes like the ora of a wind instrument, every gradation of sound may be supposed to have here its corresponding organ to vibrate, and by its vibration to move a distinct part of the auditory nerve. Let us then turn to the consideration of the effects of these musical tones upon the mind. There is nothing more curious than the relations established betwixt the senses and the ruder bodily operations. We have seen how the motions of the body and limbs added to the perfection of the eye, an organ which we should suppose neither required nor admitted addition of powers from so unexpected a source. The motions of the limbs are in constant relation to the enjoyment received through the ear, from the tatooing with the fingers on the table to the richest combination of sounds from a whole orchestra; for, in all this compass of enjoyment* rythm is a necessary part. Rythm is a regular and agreeable return of an expected note with which the body readily accords. We cannot walk, nor jump, nor dance, nor strike with a hammer, without feeling a desire that the stroke should be in a certain regulated succession. This is rythm, and is a necessary part of music. Melody is something more, it is a succession of notes which bear a relation in the time of their vibrations; the sound still dwelling on the memory is succeeded by sounds which, from the pro- portions of their vibrations, are agreeable and melodious. Harmony is the concurrence of sounds which correspond in certain of their vibra- tions. Music has another power over us by a resemblance to the ex- pression of human suffering and passion, by which a melody is conti- nually suggesting circumstance of interest, while by association it un- locks the memory, and keeps the mind revolving in agreeable reverie. OF THE DISEASES OF THE INTERNAL EAR.- Of all the causes of deafness, that which proceeds from an organic disease of the brain is, of course, the most dangerous. In apoplectic afFections, with faultering of speech and blindness, deafness is also pro* duced by the general affection of the brain. But worst of all is the 274 DISEASES OF THE INTERNAL EAR. ease where a tumour of the brain, or betwixt the cerebrum and cerebel- lum, compresses the origin of the nerves.* I have, however, observed, that a tumour in the vicinity of the origin of the auditory nerve, though it ran its course so as to prove fatal, had rather a contrary effect on the or- gan of hearing; and while the pupil of the eye remained stationary, and the man saw indistinctly, he had a morbid acuteness of hearing. This had probably been produced by the surroundinginflammation having ex- tended to the origins of the auditory nerves. The auditory nerve often becomes morbidly sensible, and the patient suffers by the acuteness of per- ception, or is distressed with the tinnitus aurium, which is, in this case, analogous to the flashes of light which sometimes affect the eye in total darknes , and which those experience who are totally blind, or have cata- ract. So morbidly acute does the sensation sometimes become, that the slightest motion of the head will excite a sensation like the ringing of a great hell close to the ear. 7 With delirium, vertigo, epilepsy, hys- teria, the increased sensibility of the organ becomes a source of painful sensation. The ear is sometimes affected by sympathy of parts: for example, from foulness of the stomach and bowels, as it is termed ; and the same reason may be assigned for the complaint of hypochondriacs, that they are molested with strange sounds. In the case of intestinal worms, we find the patient complaining of murmuring and ringing in the ears.J Of the organic diseases of the labyrinth, there is little on record. It would appear, that the fluids become often so altered in their consistence as to prove an absolute destruction to the organ. Mr. Cline found in a per- lon deaf from birth, that the whole labyrinth was filled with a substance like cheese. A disease of the auditory nerve, like that of the retina in the gutta serena, is no unfrequent complaint.§ Deafness, in acute fever, is a good sign; because, say authors, it ar- gues a metastasis of the morbific matter. We should rather say, be- cause it argues a diminution of the morbid sensibility of the brain, jj But the surcharge of the vessels of the brain or of the auditory nerve will also produce deafness and unusual sensations in the ear ; as in sup- pression of the menses and haemorrhoids, in surfeit, &c., in which cases it is often preceded by vertigo and head-ach. There occurs a very curious instance of analogy betwixt the ears and eyes, in the following cases :—“ A certain eminent musician, when * Vidit Clariss. Dom. Drelincurtius Tumorem sleatomatis consistentia pugnique magnii Incline, cerebrum et cerebellum inter, eo loco ubi conariuin uti'ique substeritur cho- roidis plexus alee, spatio semestri a sensibili laesicne, caecitatem primo, surditatem subinde, omnium clenique sensuum et functionum animalium abolitionem et necem ipsam intulisse.” Bonnet, vol. i. p. 123. ob. 53. In Sandifort Obs. Anatom. Path. torn. i. p. 116. there is ati -instance in which the auditory nerve had a cartilaginous tumour adhering to it. •}• F. Hoffmann. Consult, et Respons. Cas. xxxix. We must not, however, take his rea- soning after what we have seen of the structure of the ear, that the viscid pituita, separated in the concha, cochlea, and labyrinth, resolved into halitus endeavouring to escape, produces the susurrus et tinnitus aurium. | Hoffmann. Med. Consult. Bocrhaave. The sympathy is sometimes exerted in a contrary direction. Sauv. § Dysecoea (atonica) sine organorum sonos transmittentium vitio evidente. Cullen. Copho- sis Sauv. Cophosis a Parucusi distinguitur ut amaurosis ab amblyopia respectiva. Sauv. 11 But the difficulty of knowing when the deafness is the result of disease, or inalconfor- malion in the parts transmitting the sound tothe nerve, and when in the brain and nerve, has fed to more uncertainty and coufusion with regard to the species and varieties of the disor- ders of the car than in the eye ; where the transparency of the humours assist in the detini- ffor*. OF THE SENSE OF SMELLING. 275 he blew the German flute, perceived at the same time the proper sound of it, and another sound of the same rythm or measure, but of a dif- ferent tone. Ilis hearing seemed thus to be doubled. It was not an echo; for he heard both sounds at one and the same moment: neither were the sounds accordant and harmonious, for that would have been sweet and pleasant to his ear. Having for several days persisted in his attempts, and always been shocked with this grating sound, he at last threw his flute aside. The day before he first became sensible of this strange affection, he had imprudently walked in a very cold and damp evening, and was seized with a catarrh in the right side. Whence, pro- bably, it arose that the natural tone of that ear was altered : the sound appeared more grave, and dissonant from that received by the left ear. Having recovered from the catarrh, the distinct hearing of his ear was restored.” Sauvages, who relates this case, subjoins another:—“ Very lately,” says he, “ a foreigner came for advice in a similar situation. He com- plained, that when any person spoke to him, he heard the proper sound of the voice, and at the same time another sound accompanying it an octave higher, and almost intolerable to him. As it must have hap- pened, that, if the accompanying sound had preserved the true octave above the voice, and been synchronous with it, the ear would have re- ceived them as one sound, and been pleased with their concord : it is probable that the accompanying sound was not in unisofi with the true.” Sauvages, vol. iii. p. 352. OF THE NOSE AND THE ORGAN OF SMELLING. OF THE SENSE OF SMELLING. Smelling seems to be the least perfect of the senses. It conveys to us the simplest idea, and is the least subservient to the other senses. The sensation it presents to us we can less easily recall to memory; and the associations connected with it are less precise and definite than those of the senses of hearing and seeing; finally, we would lose this sense with less regret than any other. Animal and vegetable bodies, during their life, growth, putrefaction, and fermentation, and, most probably, all bodies whatever, are perpetu- ally giving out effluvia of great subtilty. Those volatile particles re- pelling each other, or diffused in the atmosphere, are inhaled by the nose, and convey to the pituitary membrane of the nose the sensation of smell. Even in the outward form and structure of the nose, there is a relation to the exercise of this sense ; the lateral cartilages of the nose, or those which form the nostrils, possess a degree of elasticity adapted to pre- serve the passage open and free. They have muscles adapted to move them, to expand them when greater freedom of respiration is required. 276 OF THE SEICSE OF SMELLIXG. and to contract them in order to diminish the stream of air, and to give it more force to penetrate to the upper cavities of the nose. The carti- lage which joins to the septum of the nose is also flexible and moveable by muscles, which curve the nose or draw down the point; thus, in smelling, the air, which in ordinary respiration passes freely backwards, is directed upwards to the aethmoid bone ; these cartilages perform another office in giving that flexibility to this prominent feature, which enables it to elude injuries and at the same time protect the bones of the nose: but their chief use is in connexion with the sense; for it may be observed, that when we draw the air in, in smelling, the nostrils are compressed, which gives more force to the air received, and at the same time the di- rection of the stream of air is changed. When we breathe with the nostrils stationary or expanded, the air passes directly backwards, but when it is drawn in, in smelling (the nose being drawn down), a direc- tion upwards is given to the stream of air, so that it is made to circulate about the cells of the aethmoid bone, where the olfactory nerve is ex- panded. Immediately within the nostrils, there are two cavities separated by the bony partition, which has been already described in treating of the bones. These cavities enlarge as they proceed inward, and open back- ward into the throat, and, consequently, communicate with the mouth. They extend upward and sideways into the cells of the bones of the face : and the pituitary membrane is extended over the surfaces of these wind- ing passages, and over the irregular surfaces of the nose, formed by the projecting cartilages of the aethmoid and lower spongy bones ; which, also, have already been sufficiently described. The cavities of the nose lead into many cells in the bones of the face, which, though not the immediate seat of the sense, are subservient to the organ by permitting a circulation of the air, and thus carrying the effluvia into contact with the nerve. No doubt these cavities are also useful in giving vibration and tone to the voice. The cavities of the nose are con- tinued upwards into the frontal sinuses, and into the cells of the aethmoid bene ; backward and upward into the sphenoid sinus ; and upon the sides into the antra Highmoriana or sinuses of the upper maxillary bones. The membrane covering the surface of these bones is called the mem- Brana Schneiderian a, the mucous or pituitary membrane. It is of a glandular structure, or is lubricated by the mucus discharged by the folli- cles on its surface. This secretion on the surface of the membrane, is to defend its delicate and sensible structure from the effects of the air, while it preserves the sensibility of the surface and the delicate expand- ed nerve. It seems of a nature to allow the effluvia to penetrate it. A very particular provision has been made against the too powerful ef- fect of smells while the membrane is inflamed, and, consequently, in a state of great sensibility. When the membrane is inflamed, the secre- tion is altered, and the effluvia does not penetrate, nor does it affect the nerve in its state of extreme sensibility. We have already described the course of the first pair of nerves or the olfactory nerves, and also those branches of the fifth pair of nerves which are distributed to the membrane of the nose. These, it were superfluous to recapitulate here. The olfactory nerve alone is the organ of smelling, and the branches of the fifth pair bestow merely common sensibility to the membrane. OF THE SENSE OF SMELLING. 277 I have traced branches of the fifth nerve into all the cavities of the face, and we feel that they possess sensibility. In applying volatile salts to the nostrils, we can distinguish a painful sensation to rise into the frontal sinuses different from the sense of smelling. When the root of the nose has been broken in and the cavity opened, experiments have been made by sending effluvia upwards into the frontal bone, and no sense of odours was experienced : but when they were admitted down- wards to the {Ethmoid bone, the first nerve was affected, and the sense exercised. This sensible and nervous membrane, being also glandular and secreting, is very vascular ; and this vascularity, this glandular struc- ture, and its exposed state, makes it liable to frequent disease : and, when diseased, when tumours and polypi form in it, we must never forget the extreme thinness and delicacy of the surrounding bones, which, when they are either pressed upon by tumours, or have their membranes eroded, are soon totally destroyed. It is with manifest design, that this organ which so particularly admonishes us of the effluvia diffused in the air we breathe, should have been placed in the entrance to the canal of the lungs. It is, in some measure, a guard to the lungs, as the sensibili- ty of the tongue guards the alimentary canal. That the humidity of the membrane either preserves the sensibility of the nose, or is a solvent, in which the effluvia dissolving affect the nerves, is evident ; for the sense is lost when the membrane becomes dried. The sensibility is also affect- ed in various ways by too abundant a mucous discharge, or by an altera- tion of its natural properties ; by the infarction and thickening of the membrane, as in ozfena ; by obstructions preventing the current of air through the nose, as in polypi, &c. The acuteness of sensation in this organ is most probably lost by our habits, by our relying on other senses, by the incessant application of ar- tificial odours to the organ. Those who have believed in the variety of the human species, and the approximation of some tribes to the brute, dwell much on the acuteness of sensation enjoyed by negroes, and their wider nostrils.* There is nothing more curious than the spontaneous exercise of the organs of the senses. Thus we have bad taste in the mouth, ringing in the ears, sparks of fire before the eyes, when there has been no outward impression made upon the organ ; and so have we rarer examples of disease putting even the organ of smelling into exercise. A young gen- tleman, a student, was attacked with a complaint in his Schneiderian membrane, which changed the nature of its secretions. During this disease he was assailed with the most disagreeable odours, a circum- stance not so uncommon ; but the unpleasant exercise of the sense was sometimes relieved by his experiencing the most delightful and fragrant effluvia, which were not in existence, but proceeded either from the spontaneous operation of the organ of sense, or from morbid irritation upon it. * Pallas says, the Calmuck, by applying his nose to the hole of a fox, or any other beast, can tell whether he be at home or not.—See Whits of Manchester. 278 OF THE MOUTH AND TONGUE. OF THE MOUTH, SALIVARY GLANDS, THE ORGAN OF TASTE, &c. OF THE MOUTH AND TONGUE. The mouth is that cavity anterior to the velum or fleshy palate ; the posterior cavity is the fauces ; the mouth is for mastication and speech, the posterior cavity is a common passage, admitting the food to be con- veyed into the oesophagus, and the air to be drawn in from the nostrils into the trachea. The lips and cheeks are formed of the skin and reflected mucous membrane, with muscular fibres intervening to give them pliancy and motion, and with minute glands to discharge the moisture on their inner surfaces. The glands of the lips are called glandules labiales, and are very nu- merous; those of the cheeks are called the glandules buccales. OF THE TONGUE. The body of the tongue consists of muscular fibres, with intermin- gled fat and cellular membrane, nerves, and blood vessels. The base of the tongue is that part which is backward, and is con- nected with the os hyoides : the apex is anterior. The surface applied to the roof of the mouth is called dorsum. On this surface there is to be observed a middle line, dividing the tongue into two lateral portions ; a division which is very accurately preserved in the distribution of the blood vessels and nerves of either side. On the dorsum, towards the base, the surface is rough with the papilla? maximoe and foramen cmcum Morgagni.* These papillae are like small glands seated in little superficial fossulae, so that their broad mushroom- like heads alone are seen; but they are connected with the bottom of the fossulae by short stems or necks. This is considered as a glandular apparatus. The foramen caecum is, in truth, only an enlarged appara- tus of the same kind, for, in the bottom of this foramen, many glan- dular papillae stand up ; and in its bottom small foramina have been ob- served, which are generally conceived to be the mouths of small sa- livary ducts. Morgagni himself, however, seems only to have seen a small duct opening into this foramen in one subject of many which he examined. In Haller's opuscula there is a dissertation on the Ductus Coschwizianus, which was supposed to carry the saliva from the sub- lingual gland to the middle of the tongue, and also into the throat, but * Adversar, Anat. VI. Animad, XCIII. OF THE MOUTH AND TONGUE. 279 it turns out to be a vein only. It is curious to observe the necessity the author discovered for these ducts, when he thought he had found them.* The secreting mucous surface begins here, towards the root of tho tongue, to resemble the glandular structure of the oesophagus, which by bedewing the surface of the morsel, fits it for an easy passage through the gullet. This roughness of the root of the tongue is, at the same time, a provision for the detention of the sapid particles, and consequent- ly prolonging of the sensations of taste. The papillje of the human tongue are divided into four classes. 1. These larger papillae upon the root of the tongue are the truncatae; and they are often studded on the dorsum of the tongue in a trian- gular form. 2. The fungiformes are obtuse papillae found more for- ward on the tongue; they are little hemispherical tumid papillae, with an obtuse surface. These are interspersed among the third division, the most numerous and universally prevalent papillae, viz. villosi or conoideae; they are, as Soemmerring says, of various forms, angular, conical, obtuse. 4. The vaginatae are the more important papillae, however; they are endowed with peculiar sensibility to sapid bodies ; are to be distinguished by their superior redness and brilliancy, and are placed upon the point and edges of the tongue. The tongue is invested with the cuticle and rete mucosum, like the skin in other parts. The lower surface of the tongue is similar to the general lining membrane of the mouth, being a soft villous and secret- ing surface. It is reflected off upon the bottom of the mouth, where it forms the frenulum linguje. This ligament seems evidently intend- ed to limit the motion of the point of the tongue backwards. A very false opinion has prevailed, that the shortness of this ligament, or its being continued too far forward toward the point of the tongue, prevents the child from sucking. The tongue, as I conceive, would sufficiently perform the necessary action on the mother’s nipple, although its lower surface were universally adhering to the bottom of the mouth. But, observe the bad consequences which may arise from yielding to the ob- stinate importunity of the nurse, and cutting this frenulum. The ranine vein or artery which runs near it may be cut, and the child will continue sucking and swallowing its own blood; and children have actually died, and the stomach has been found distended with blood ! But there is a another more dreadful accident from this cutting of the frenum linguae. A child, says M. Petit, whose frenum had been cut almost immediately after its birth, was suffocated and died five hours afterwards. They be- lieved that the operation was the cause of the child’s death ; they sent for me to open the body. I put my finger into its mouth, and I did not find the point of the tongue, but only a mass of flesh which stopped up the passage from the mouth into the throat. I cut up the cheeks to the masseter muscles, to see what had become of the tongue. I found it turned like a valve upon the fauces, and the point actually swallowed into the pharynx. “ Some time after,” continues M. Petit, ‘ I was call- ed to the child of Mr. Yarin, Sellier du Roi, whose frenum they had cut two hours after its birth, and who, a little after, had fallen into the same ■ Vater, who injected these ducts, found thetn terminating in a gland near the os hyoides ; and the opinion was, that they had even a connexion with the thyroid gland. Heister was of the same opinion 280 OF THE SALIVARY GLANDS. situation with the child I have now mentioned, and was nearly suffocated. My first care was to introduce my finger : the tongue was not, as yet, entirely reversed into the throat. I brought it back into the mouth; in doing which, it made a noise like a piston when drawn out of its syringe.” M. Petit waited to find the effect of its sucking, and after hearing the action of deglutition for some minutes, the child fell again into the same state of suffocation. Several times he reduced the tongue, and at last contrived a bandage to preserve it in its place ; but, by the carelessness of the nurse, the accident recurred, and the child was suffocated during the night. There can be no better illustration of the use of the frenum linguae. OF THE SALIVARY GLANDS. The sources of the saliva are very numerous : the parotid or superior maxillary glands, and socim parotidis ; the inferior maxillary or Submax- illary glands; the sublingual glands; and (according to the opinion of many) the glandular follicles of the root of the tongue, the palate, and even the buccales and the labiales, or glands of the cheeks and lips, are also to be enumerated, as sources of saliva. But the chief source of the saliva is in the proper salivary glands. The parotid gland, as its name implies, is that which lies near to the ear. It is the largest of the salivary glands ; and it is of much im- portance for the surgeon to observe its extent and connexions. A great part of it lies before the ear, and betwixt the ear and jaw. It extends over the masseter muscle, and upwards to the zygoma. But there is al- so a great part of it which lies below the tip of the ear, and betwixt the angle of the jaw and the mastoid process. Its surface is unequal, and composed of little masses or lobules of gland, united by a cellular mem- brane. The duct of this gland was discovered by Needham, and after- wards by Steno : it is very often called Steno’s duct. When it is inject- ed with quicksilver, the branches are seen distributed in a most beautiful and minute manner amongst the lobuli of the gland, like the branching of veins. These brandies have a direction upward from the gland, and unite into a trunk, which passes from the upper part of the gland across the cheek over the origin of the masseter muscle : it then pierces the buccinator muscle, and opens upon the inner surface of the cheek, oppo- site to the second dens molaris. This duct has strong white coats ; but, although the mouth of the duct is very small, the duct itself is dilatable.* The socia parotidis is a small gland, not constantly to be found, seated on the upper side of the duct of the parotid gland, and just under the margin of the cheek bone. It opens by a lesser duct into the great- er duct of Steno. Sometimes, however, instead of one considerable gland, there are several small ones, seated in the course of the great duct, and opening into it by several minute ducts. The submaxillary gland is of a regular oval figure, and is seated under the angle of the jaw ; it lies under the platysma myoides on the tendon of the digastric muscle ; it is defended by the angle of the low- * A friend of mine having introduced a silver tube into the salivary duct to cure a fistula, it slipped in and was lost; that is, it was necessary in the end to cut it out by an operation behind the angle of the jaw. VELUM palatinum. 281 er jaw, where it is generally connected with or involves the root of the facial artery. It is regularly lobulated ; and its duct passes forward be- tween the genio-glossus and mylo-hyoideus, and under the sublingual gland. The openings of the submaxillary ducts, or ducts of Wharton, are very easily distinguished. They open under the tongue very near each other, on each side of the frenum linguae ; so that they appear as if tied down by the frenum. Wrhen these are excited to discharge their fluids, they become a little erected ; their open mouths are seen distinct- ly, and even the tortuous course of their canal in the bottom of the mouth may be seen. The subungual gland is of a flat and elongated form ; it lies close under the tongue between the genio-hyo-glossus and mylo-hyoideus mus- cles. It is the smallest of the three great salivary glands. The two sublingual glands stretching close under the tongue, are separated from the cavity of the mouth only by the membrane of the mouth. The duct of the sublingual gland opens into the duct of Wharton at the same time that it opens by small lateral ducts, with loose pendulous mouths upon the lower surface of the tongue. The glandulce molares are seated betwixt the masseter and buccinator muscles : they properly belong to the class buccoles. These are small glands, in some measure incorporated with the cheek. The glandular lab tales are more distinct, and can be insulated by dissection : they are round and flat, and sunk in the substance of the lips. All these glands secrete into the mouth. From the general surface of the lips, tongue, cheek, and palate, there is a fluid exhaled. This exhaling surface, and all those glands are excited to action by the same stimulus, the excitement of the morsel in the mouth. The saliva moistens the surface of the mouth, assists in manducation, prepares the food to be swallowed and acted upon by the stomach, and accelerates digestion. As the mouth is an exhaling sur- face, so is it an imbibing and absorbing surface. Calomel may be rub- bed upon the mouth so as to salivate. VELUM FALATINUM ; UVULA ; ARCHES OF THE PALATE ; AND AMYGDALAE. The velum pendulum palati is the vascular and fleshy membrane, which, hanging from the bones of the palate, divides the mouth from the fauces. It is not a simple membrane, but has betwixt its laminae many glands, which open upon its surface by little follicles, and it is thickened and strengthened by muscular fibres, so that it is more like a fleshy parti- tion, stretching backward and eking out the palate, than a hanging mem- brane. The edge of the velum palati is not square, but turned into elegant arches ; and, from the middle of the arches of the palate, hangs down the uvula, so named from its resemblance to a grape. It is a large, soft, and glandular papilla, peculiarly irritable and moveable, having in it muscular fibres, and hanging from the moveable soft palate. It seems to hang as a guard over the fauces, and, by its sensibility, in a great degree governs the operation of these parts. It is also part of the organ of the voice. The arches of the palate or fauces descend on each side from the 282 AMYGDALAE- velum palati. They are muscular fibres, covered with the soft vascular and follicular membrane of the fauces.* There are two on each side. These arches stand at some distance from each other, so that the isth- mus of the fauces resembles the double-arched gateway of a citadel, or rather the arched roof of a cathedral, with the uvula hanging as an orna- ment from the central union of four semicircular arches ; for the arches which are apart below are joined above. Behind the soft palate is the cavity of the fauces, and into that cavity there are openings from the nose. The use of the velum is, that, in swallowing, it may be drawn up like a valve upon the posterior opening of the nose ; and there being at the same time, an action of the arches of the palate, the whole are brought into a funnel-like shape, which di- rects the morsel into the pharynx and gullet. In this action, the direc- tion of the food assists the valvular action of the veltim ; but, in vomiting, the nose is assailed with the contents of the stomach. The velum also is a principal part of the organ of the voice ; it divides the air which is- sues from the lungs, and directs it either into the cavity of the mouth or nose. Amygdalae.—Betwixt the arches of the palate, on each side,'lies a large oval gland of the size and shape of an almond. These are the tonsils or amygdalae. The amygdala is a mucous gland : it is loosely covered with the investing membrane of these parts : its surface is seen, even in a living person, to be full of large cells like lacunae ; these com- municate ; and into these the lesser mouths of the ducts open. On a narrower inspection of the amygdala, we may describe its structure thus : within the arch of the palate, and before the arch of the fauces, there is a fossa of an oval shape, and on the surface of the membrane a number of cells open like the mouths of veins. When the arches and the amygdala are dissected, out behind these holes, we feel a gland, as it were one solid body ; but on further dissection from behind, the cellular membrane being taken away, instead of one large gland, there are a number of lesser ones. These glands discharge their secretions into the oblique passages just described ; and from these lacunae the mucus is pressed out when the morsel is pushed backward. From the loose tex- ture, and from its being a vascular and secreting body, exposed to the im- mediate vicissitudes of weather, the amygdala is often inflamed, and then it impedes the action of the surrounding muscular fibres in the action of deglutition. The use of the amygdala is evidently to lubricate the passage of the throat, and facilitate the swallowing of the morsel; and, for this reason, are the mouths of its ducts cellular and irregular, that they may retain the inucus until ejected by the action of deglutition. In this operation, the amygdalae are assisted by numerous lesser glands, which extend all over the arches of the palate and pharynx. * See Vo). I. Constrictor Isthmi faucium and Palato-pharyngeus. OP THE SENSE OF TASTING. 283 OF THE SENSE OF TASTING. On the surface of the tongue are to be observed many papilla? ;* in which the extremities of the gustatory nerve terminate ; they are the or- gans of the sense of tasting. These papillae arise from the true skin of the tongue ; they are extremely vascular; they are covered by the rete mucosum, and a very line cuticular sheath. These papillae are to be seen on the point and edge of the tongue, as pretty large vascular soft points which project from an opaque and white sheath. If you take a pencil and a little vinegar, and touch or even rub it strongly on the sur- face of the tongue, where those papillae are not, the sensation only of a cold liquid is felt; but when you touch one of these papillae with the point of the brush, and at the same time apply a magnifying glass, it is seen to stand erect and rise conspicuously from its sheath, and the acid taste is felt to pass as it were backward to the root of the tongue. The exqui- sitely sensible papillae are placed only on the point and edge of the tongue ; for the middle of the tongue is rough and scabrous, not to give the sensation of taste, but to break down the solid morsel against the roof of the mouth, and press the sapid juice from it, so that it may run over the edge of the tongue. The more delicate and vascular papillae would be exposed to injury if situated on the middle of the tongue. Before we taste, the substance dissolved in the saliva flows over the edges and point of the tongue, and then only comes in contact with the organ of taste. It would appear that every thing, which affects the taste, must be solu- ble in the saliva; for without being dissolved in this fluid, it cannot enter readily into the pores and inequalities of the tongue’s surface. We have already noticed, that by the peculiar form of the larger papil- lae at the root of the tongue, the fluids lodge, and the gratification of the palate is prolonged. A curious circumstance, in the sense of taste, is its subserviency to the act of swallowing. When a morsel is in the mouth and the taste is perfect, our enjoyment is not full : there follows such a state of excitement in the uvula and fauces, that we are irresistibly led to allow the morsel to fall backward, when the tongue and muscles of the fauces seize upon it with a convulsive grasp, and convey it into the stomach; it is only then that the measure of enjoyment is full. Were not this appetite of the throat and uvula connected with the action which impels the food into the stomach, the complete enjoyment of the sense of taste alone would satisfy, and would have rendered unnecessary the disgusting practice of the Roman Gourmand, who forced himself to vomit that he might resume the enjoyment of eating. But, as it is, the connexion of the stomach and tongue is such, that the fulness of the stomach precludes the further enjoyment of the sense of taste. The senses of smelling and taste have their natural appetites or relish; but they have also their acquired appetites, or delight in things which to un- sophisticated nature are disagreeable: so that we acquire a liking to snuff, tobacco, spirits, and opium ; “ Nature, indeed, seems studiously to have set bounds to the pleasures and pains we have by these two * Albinus Ann. Acad. lib. i. c. xv. 284 OP TOUCH AND £>F THE SKIN. senses, and to have confined them within very narrow limits, that we might* not place any part of our happiness in them ; there being hardly any smell or taste so disagreeable that use will not make it tolerable, and at last, perhaps, agreeable : nor any so agreeable as not to lose its relish by constant use. Neither is there any pleasure or pain of these senses which is not introduced or followed by some degree of its contrary which nearly balances it. So that we may apply the beautiful allegory of Socra- tes : that although pleasure and pain are contrary in their nature, and their faces look different ways, yet Jupiter hath tied them so together, that he who lays hold of the one draws the other along with it.” OF THE SKIN AND OF THE SENSE OF TOUCH. OF THE SKIN. The skin may be divided, by the art of the anatomist, into four la- minae or membranes, distinct in texture and appearance, and use, viz. the cuticle, or epidermis; the corpus tnucosum, or reticular tissue; the cutis vent, dermis, corium, or true skin: but from the surface of this last there is separated a vascular membrane, below which is the surface of the true skin ; lastly, we may enumerate the tela cellulosa as consti- tuting a part of the general integument, giving lodgment to the glands of the skin and to the bulbs of the hairs. The cuticle, or epidermis, or scarf skin, is the most superficial of these layers: it is a transparent and insensible pellicle which serves, in some degree, to resist the impression of external bodies on the sur- face of the body, and to blunt the otherwise too acute sensation of the cutis vera.* In n an it is very thin, unless in parts which are ex- posed to the contact of hard bodies, as the palms of the hands and soles of the feet. The thickness of the cuticle there, however, is not altogether the effect of labour and walking, but there is even in the early feetus a provision for the defence of the skin of the feet, by the supply of a thicker cuticle. When the cuticle is drawn from its foot, that part upon the sole is white, opaque, and thick, whilst, in the leg, it i3 transparent and more delicate, j This is also particular, that by la- bour or continued pressure on the cuticle it does not abrade and be- come thin and tender, but thicker, harder, and the part more insensi- ble, so as even to acquire a horny hardness and transparency. Of this we have an example in the hands of smiths and other workmen, and in * It is unaccountable that so great a man as Morgagni could suppose the cuticle (o be the tnere effect of air and pressure on the surface, of live true skin. Adversar. Anatom, ill. 3. r A lb ini. Annot. Acad. OF TOUCH AND OF THE SKIN. 285 u remarkable manner in the feet of those who have been accustomed to walk bare-foot on the burning sands. It is thus a protection to the foot in a state of nature. But if the skin be too much or too quickly exerted, instead of forming additional layers of cuticle, a serous fluid is thrown out from the true skin, which separates the cuticle in blisters ; and this over-action of the skin will throw off the cuticle, as we see to be the consequence of the irritation of plasters or cataplasms, scalding water, exanthematous diseases, erysipelas and mortifications, &c. When the foot comes to be unnaturally pinched in shoes, the hard leather works perpetually on a point of the toes and blisters the foot; but if in a less- er degree and longer continued, it excites the formation of cuticle in the skin below, which thrown outward by succeeding layers of cuticle, at last forms a corn or clavus, and which, like a small nail, has a broad head with a conical point shooting into the tender skin.* The cuticle is perforated by the extremities of the perspiring and ab- sorbing vessels, and by the ducts of the glands of the skin, and by the hairs. Indeed, when the small pores of the skin or foramina are exa- mined narrowly, the cuticle is seen to form sheaths which enter into them, and which, when torn out, are like little tubes having a perforated point; for when, by maceration, the cuticle is separated from the skin, as we draw it off we see little processes of the cuticle, which enter into the pores of the skin. In the dead body the cuticle may be separated by permitting putrefac- tion to go on, and for this purpose the skin is put in maceration f : Ruysch separated it by extending a portion of skin and pouring boiling water upon it. + Vesalius and Malpighi practised the coarser way of carrying a red hot iron near the skin. Mr. Cruickshanks enumerates three classes of processes of the cuti- cle : there appear evidently two. The first lines the pores through which the hairs pass : these are the longest. The second class is easily dis- tinguished on the inside of the cuticle, which covers the palms of Ihe hands or soles of the feet, or indeed on any part of the cuticle ; and they appear in regular order on those parts of the cuticle which correspond with the parallel or spiral ridges of the cutis : these enter into the pores of the true skin. The surface of the cuticle is uniform next the skin ; but, on the outer surface, it is rough and squamous. These squamae are the portions of the cuticle, which, breaking up, are rubbed off; for there is a perpetual change, by the formation of new cuticle under the old. and the abrasion or disquamation of the old surface. When I say that the cuticle is uniform, I must not forget to speak of the regular lines observable on both its surfaces, and which are especial- ly observable on the tips of the fingers, and which are a very particular part of the organ of touch. The ulcerative process has no power over the cuticle, so that when the matter of an abscess has reached the cuticle, its progress is stopt until the cuticle is burst by the distension This is one reason of the greater pain of abscesses in the soles of the feet and palms of the hand, where the cuticle is very strong. § * De clavo pedis, vide Albini, Acad. Aimot. lib. vi. cap. vi. et vide tab. ii. fig. 1. + Santorini Observ. Anat. cap. i. § i. | De hum. C. fabrica, lib. ii. c. 6. 5 See Hunter on Blood and Inflarn. p. 4(59. 286 OF TOUCH AND OF THE SKIN. OP THE STRUCTURE AND GROWTH OF THE NAILS. The nails are naturally connected with the cuticle, for they remain attached to it: in exanthematous diseases, when the cuticle exfoliates, the nails are also pushed off; and in death they both separate from the true skin by maceration and beginning putrefaction. The nails are to give firmness and resistance to the points of the fingers. Although they take a very universal adhesion, it is chiefly from the root that they grow and shoot out to the point of the fingers, to which they adhere firmly. Over the root of the nail the cuticle projects, and under it the rete mu- cosum is extended ; and under this, and defended by it, are the papillae of the skin. Like the cuticle, the nails are without vessels or sensation : they are undergoing a perpetual growth, by their roots, and are worn down by la- bour. When cherished, they grow to an amazing length, and curve a little over the points of the fingers. It was supposed that the nails were formed by the extremities of the tendons, which, extending beyond the flesh, were dried and hardened * ; and the celebrated Albinus describes the nail as formed by the conversion of the papillae which lie under it |: they are more properly conceived to be a continuation of the epidermis. J W e cannot believe, even on the authority of Albinus, that the nervous filaments which lie fasciculated under the nail are converted into the nail, merely because the under surface of the nail is reticulated like these filaments. For it is evidently reticulated like the soft filaments, in order to give lodgment to them, to have a corresponding surface with them. The nails differ from the cuticle in not scaling or exfoliating like it, but in growing from a root like a hair. OF THE HAIRS. The hairs grow from a bulbous root, seated in the cellular mem- brane. This bulb is vascular, and has connexion, by vessels, with the cellular texture. It consists of a double membrane; the outer is a kind of capsule which surrounds the other, and stops at the pore in the skin, and does not form part of the hair. Betwixt these capsules, there is a cellular tissue, and the space is commonly found filled with a bloody fluid. In the bottom of the inner sac, there is a small body, called mon- ticule by Duverney, from which the hair is seen to arise ; and if this is left when the bulb of the hair is pulled out, the hair will be regenerated. The root of the hairs, says Winslow, is covered by a strong white membrane, which is connected with the skin and cellular membrane. Within the root, there is a kind of glue, some fine filaments of which advance to form the stem, which passes through the small extremity of the bulb to the skin. As the stem passes through the root, the outer membrane is elongated in form of a tube, which closely invests the stem and is entirely united with it. And many authors agree, that the hair does not perforate the cuticle, but takes from it a vagina which accom- panies it in all its length. § The hair serves as a distinction in the human tribes. The European * Riol-anus. f Annof. Acad. vol. i. lib. ii- cap. iv. { Winslow. 5 Albinas Acad. Annot. 1. vi. cap. ix. and Morgagni Adversar. et Epist. An. iii. 6 4. OF TOUCH AND OF THE SKIN. 287 has the longest hair, next him the Asiatic, then the American, and lastly the African.* A common opinion is entertained that hair on the body is a mark of strength ; but I have observed our famous boxers, when in high condition, are smooth, fair, and clear in the complexion of their bodies ; while men of a dark sallow hue are generally hairy on the trunk and shoulders. Betwixt hair and wool, or betwixt the hair on different parts of the body, there is no distinction in the anatomical structure. In the growth of hair and wool, however, there is a difference. They are both produced annually ; but wool is shed at once, and leaves the animal bare, whilst the hair falls off gradually, and the young and the old hairs are together growing at the same time. Hair is of uniform thickness in its whole length ; whereas wool is variable in the thickness of its filament:—further it has been found that the thicker part grows during the warmer times of the season; that it is thicker in summer, and finer in the spring and autumn. This shows us how the fleece becomes coarse and hairy in a warm climate. RETE MUCOSUM. The rete or corpus mucosum, or Reticulum Malpighi, lies betwixt the cuticle and the surface of the true skin. It is a mucous layer, pervaded by the little fibrillge passing betwixt the skin and cuticle. I consider it as a soft bed to envelope and preserve the papilla; of the skin, and as intended to become cuticle in due succession. It was considered, by Albi- nus, as of a nature adapted to imbibe the fluids through the cuticle, and as a production of the epidermis. Meckel believed it to be only a mucous fluid, inspissated into the form of a membrane ; and that it was dissolved by putrefaction, while the skin and cuticle remain firm. It is the seat of colour in the skin, and is of a white transparency in the albino, and in the inhabitants of temperate climates. It is black in the negro ; copper- coloured in the mulatto; yellow in the Egyptian.'!' From the experi- ments of Priestley, on the effects of coloured cloth in absorbing light, we should argue that the blackness of the negro’s skin was ill calculated for enduring the heat of warm climates. But it has been, on the other hand, argued that the black colour facilitates the radiation of heat, and that, as the heat of the body is greater than the heat of the atmosphere, the blackness will upon the whole, tend to preserve the body cool. The rete mucosum changes its shades of colour in Europeans, from the ef- fect of light; but this tanning seems to have no strict resemblance to the permanent colour of the negro’s skin. It soon reaches its maximum by the influence of the sun, and soon it wears off again. And this de- * M. White of Manchester tells us he has seen a lady with hair six feet in length:—a Prus- sian soldier, whose hair trailed on the ground. f Malpighi de sede nigredinis in Ethiope. ft has appeared to me that there was a great deal of colour in the cuticle of the negro, and so Morgagni, “ nigricante et fusco colore in- fectas.” Adversar. II. Animad. IV. See also Blumenbach de generis humani Varietate. The colour of the skin belongs to tribes, and is only in a certain degree affected by climate. Humboldt, Essai Politique sur la Nouvelle Espagne, observes that climate", which has such an effect on Europeans, has little or none on the Indian complexion ; tribes of a temperate climate are darker than those inhabiting a province less cool and temperate. The Indians on the tops of the Andes are as dark as the inhabitants of the plains. Hum- boldt also asserts (contrary to Volney) that, in the provinces of Spanish America the children of Indians are copper-coloured from the moment of their birth. OF TOUCH AND OF THE SKIN. gree of blackness does not attach to the offspring.* When the rete muco- sum is destroyed by ulceration, it is imperfectly regenerated, and does not possess its former colour. In a negro, the inner surface of the rete mu- cosum is blacker than the outer surface ; the inner surface of the cuticle is softer and darker than the outer surface.! Mr. White argues, that if this blackness were the effect of the sun, that part most exposed would be the blackest. But though I agree with him in thinking that the black- ness of the negro is not owing to climate, yet I see this argument of his is incorrect; for it is not the direct influence of the sun which tans ; no such effect comes of exposing dead skin; it is the excitement of the living vascular surface in the formation of new matter, or the discharge of colouring matter into the rete mucosum. While the rete mucosum has its peculiar use of defending the delicate surface of the papillae of the skin, I conceive it to be undergoing a per- petual change ; to be thrown off in succession from the vascular surface of the skin, and in its turn to form the cuticle by its outer layers. The inner surface of the rete mucosum is softer and more pulpy ; the out- ward surface more allied to the cuticle, which gives occasion to Mr. Cruickshanks to say it is double. VASCULAR MEMBRANE OF 'THE TRUE SKIN. Under the rete mucosum, and on the surface of the skin, there is a soft vascular membrane, which is still above the porous and glandular true skin. It was first demonstrated by injections in subjects who had died of small-pox, and it is so much strengthened by other inflammatory actions of the vessels of the skin, as to be capable of demonstration. It was at first supposed that this vascular membrane was the rete mucosum successfully injected ; but afterwards it was found, that it was distinct from the rete mucosum. J Mr. Cruickshanks conceives that it is cuticle in its state of formation, and that the rete mucosum is in fact a cuticle advancing to the state of perfect maturation. I should rather believe that this is a vascular surface, not. changeable, nor losing its vascularity, to be thrown off in form of rete mucosum : but, in itself, the organized surface, which is to secrete the rete mucosum, and which secretion does in succession become cuticle. This vascular surface of the skin, for such I must suppose it, (although it be capable of being separated by long maceration and putrefaction, into something like a distinct mem- brane,) is the seat of the small-pox pustule, and probably of all other cu- taneous diseases. § * See the Gradation in Man, by Charles White of Manchester. Some have said that ex- treme cold also tans the skin, as the Laplanders, the Esquimaux Indians and Greenlanders, are dark ; opposed to this, we find the Finlanders and Norwegians fair beyond other Europeans. There is much in the habits of life: a painter will not find his carnation tints amongst the poor, nor in the skin of a Highlander—yet where so pure as in the Highland lady ? f Foropiuions regarding the cause of colour in the skin, see Albinus desede ct causa Co- (oris JEthiopum, Lugd. Batav. 1737.—Haller clement. Physiolog. page 20.—Blumenbach de generis humani varietate nativa, Got. 1795, page 122., and note t Mr. Baynham, who discovered this vascular surface, conceived that he had injected the rete rnucosum. Ruysch and others mentioned by Albinus, supposed they had injected the cuticle when most probably they had torn off the vascular membrane, or, as Albinus alleges, Acad. Annot. lib. vii. c. iii. in taking oft’ the cuticle they had torn up the vascular papillae along with it. f Of the slough of the small-pox pustule, see Dr. Adam’s Morbid Poisons. Appendix. OF TOUCH AND OF THE SKIN. 289 Thus there are three lamina above the true skin, distinguished by their character ; the cuticle, the rete mucosum, and the vascular mem- brane : but as some have divided the rete mucosum into lamina, Mr. Cruickshanks has separated two vascular layers from the surface of the skin. They who are fond of such minute subdivisions, may thus enume- rate five lamina or membranes, before coming to the porous surface of the true skin. OF THE TRUE SKIN. The true skin is the dense, elastic, and vascular membrane which is un- der these outer layers already treated of. It consists of a net-work of firm filaments, having in their protection sebaceous glands, exhalent and ab- sorbent vessels, nerves, the papillre or organized extremities of the nerves, and the roots of the hairs. These are sufficient to give it both some substance and firmness. While it has firmness, strength, and elasticity to defend the body, it is also an organized surface, performing important functions in the economy ; and the healthy condition of the system depends upon it nearly as closely as on the action of the lungs or of the surface of the intestines. The skin is dense on the outer surface, while the internal layers are loose, and gradually degenerate into the cellular substance. Our sol- diers and sailors have a way of marking their skins with gunpowder or with vermilion, which is indelible. They prick the skin and insert the colouring matter into it, where it remains without producing inflamma- tion, and unabsorbed. But this is no proof of the unchangeable nature of the skin as regards its colour, or whatever else may distinguish the nations and tribes of man.* On narrowly observing the surface of the skin, we find it irregularly porous. Some of these are the ducts of sebaceous glands, which are lodged in the skin. They transmit the hairs also, and are the perspiring, and, probably, the absorbing pores ; or, at least, within these larger pores the absorbing and transpiring vessels terminate. These pores are most remarkable about the nose, mouth, palms of the hands, and soles of the feet. Into these pores of the true skin, as we have mentioned, little sheaths of the cuticle enter, and through these sheaths the perspir- ing matter must consequently escape : but perspiration is the action of living parts : in d; ath, the action of the perspiring vessels ceasing, the pores of the cuticle are no longer pervious to the fluids, and there is no perspiration or exudation through them, even when the dead surface is exposed to heat, it dries only where the cuticle is off. OF THE ORGAN OF TOUCH.t The villi of the skin project above its surface, like the pile of velvet. They vary much in size, and in some places are very much prolonged. They conduct the sensible extremities of the cutaneous nerves to form the organ of the sense of touching I see that these sentient fila- * I allude to the ingenious Essay of the Rev. S. S. Smith of the American Philosoph. Soci- ety, on the Causes of the Variety in the Human Complexion and Colour. | Albinus Dissertatio de Sede et Caus. Color. iEthiop. Malpighi, Exercit. de Tact. Organ. \ Videde Papillis Cutis, Alhini, Ac. Annot. lib vi. c x. and Ruysch 290 OF TOUCH AND OF THE SKIN. ments are very vascular at their extremities. When the hand is mi- nutely injected, and there seems a general blush of redness over it: when the cuticle is taken off, and we examine the villi with a powerful magnifying glass, their extremities are seen bulbous and red. We know that even in nerves there is no sensibility without blood be supplied, and I look upon this high degree of vascularity as a provision for great sen- sibility. These fine filaments are placed in the softest bed possible. Examine the minute ridges of the cuticle, and you may distinguish them to be quite regular ; the ridge which is prominent externally corresponds with a depression or minute sulcus within. In these sulci, or in the inter- stices of the ridges of the cuticle, there is a soft matter in which the villi lie secure, yet ready to receive the impression made through the insensible cuticle. Of the nature of the sensation conveyed by the nerves of the sense of touch we are as ignorant as of that conveyed by the other nerves. Some are accustomed to consider this as an inferior sense, for no better reason than that it is more common to the surface of the body, whereas it is the most important, and that which ministers to the other senses and to our necessities most of all:—it is the sense necessary to the existence of every living creature. Nor is it, as they suppose, a universal sense. It is as much limited to the external surface of the body as the sense of vision is to the eye. Nay more, it is that sense which gives correctness to all the others, at least if we are right in attributing the perception of hardness, softness, solidity, figure, extension and motion, to the exercise of this sense. If the sense of touch be that change arising in the mind from the applica- tion of external bodies to the skin, then certainly the organ has high ex- ercise, and is of all the senses the most valuable. But it appears to me that these qualities, of hardness, softness, solidity, figure, extension, and motion, would be known to us, although we had no nerves in our finger ends at all, by what I would call the muscular sense. We may acquire a conception of these qualities by moving our body or our mem- bers, by pressing upon an object and feeling the resistance it occasions. Much might be said on this subject, but it is evident that these two senses, that of motion or action, and of feeling, must be closely allied and mutually useful to each other. FUNCTION OF THE SKIN. The function of the skin has a very extensive connexion with the due performance of the internal organs of the animal economy. The perspired matter from the skin consists principally of water and carbon. The carbonic acid produced in the process, is by the union of the carbon with the oxygen of the atmosphere. The perspired fluid holds also in solution several salts and excrementitious matter of animal sub- stance. Resides the insensible perspiration, there is an oily exudation from the glands of the skin, which appears to be useful in giving pliancy and softness to the scales of the cuticle. This oily secretion is copiously secreted in the negro ; and it appears as a means of protection against OF TOUCH AND OF THE SKIN. 291 the powerful influence of the sun, in as much as it prevents the cracking and breaking of the squamce of the cuticle. It preserves the skin soft and perspirable. The softness of the negro’s skin is remarkable ; and this softness and coolness of the skin is observable in all the degrees of propinquity to the negro. It has been long observed that the surface of the body, immersed in water, gave out bubbles of air. Lavoisier found that this air precipi- tated lime water. Cruickshanks, Abernethy, Jurin, continued these experiments illustrative of this function of the skin in giving out car- bonic acid ; but these have been overthrown by Professor Woodhouse of Philadelphia, who proved that the air so collected upon the surface was attracted from the water and not exhaled by surface. Nevertlieless carbon is discharged by the skin, and the quantity is found to depend on the vigour of circulation, and of the constitution ; and when discharged from the skin as I have said, the attraction of the oxygen of the atmosphere forms the carbonic acid. Thus the func- tion of the skin is brought to resemble, in the most essential particular, the function of the lungs; and I believe all animal surfaces whatever will be found to partake of this function, the discharge of the useless carbon from the system. The powers of the human system are, in all respects, superior to that of brutes ; and the provision for the human body inhabiting the differ- ent climates of the globe, is most particular. It has been proved that man, for a short time, can support existence in a heat of 260° of Fahr. It is proved, that while he can live in indulgence under the line, he can inhabit a country so cold as to drive away the white bear of the polar regions. A ship’s crew have wintered in 76° of northern latitude, and the powers of the living body sustained life while spirits and mercury were frozen. Although there are experiments by Dr. Fordyce, which prove that animals possess a power of resisting heat independent of perspiration, still, undoubtedly, the free or checked perspiration of the surface is a means of equalizing the temperature of the body. According to the activity of the circulation is the heat of the body, and according to the activity of the circulation is the perspiration in health. By this per- spiration, and the change of the perspired fluid unto vapour, the heat of the body is carried off. In a cold atmosphere, perspiration ceasing, the vital heat is retained ; in a warm atmosphere, the perspiring actien being excited, the heat of. the body is prevented, or rather carried off. The authorities are contradictory in regard to the absorption by the surface, unaided by friction, abrasion, or ulceration.* The more important function of the surface is to be contemplated in its effect on the general activity of the vascular system, and in the vi- carious action which takes place betwixt it, the stomach and intestines, and the kidney and lungs. The similarity of function performed in the lungs and by the skin, would lead us to attend to the injury of the for- mer by the impression of cold on the surface, and the checked per- spiration. The fact that perspiration is altered in degree by the pro- gress of digestion, would lead us to attend to the many occasions in * Hollo on Diabfites, Dr. Currie, Abbe Fontana, Dr. Watson. 292 OF TOUCH AND OF THE SKIN. which we see the disorders of the viscera effecting changes on the skin; the imperfection of the function of perspiration, when digestion and the function of the viscera are deranged, would lead us not only to mark the symptoms of internal disease on the skin, but to take the means of exciting the latter as a remedy for the former. In the same manner will the secretion of the kidney be influenced by the state of the skin and of perspiration: need I add that the health and strength of the circulation, and of course the health of all the functions, is in- fluenced by the excitement of the skin. Some practitioners take the stomach, and others the bowels, and others the liver, on which they harp continually; let any one take the skin as his object of care, and his practice will have equal success, his cases and facts become soon as numerous, while his connexion with general science will be more in- timate ; and if he introduce his system by showing that health is en- joyed when the various functions, which together form the animal eco- nomy, are perfect, and that one function cannot be in health without the whole be also, he will, in my opinion, have better claims to public fa- vour than any who have yet flourished in it by promulgating doctrines in regard to the functions and diseases of individual parts. THE ANATOMY OF THE VISCERA OF THE ABDOMEN. VIEW OF THE SYSTEM OF THE VISCERA, AND OF THE STRUCTURE OF GLANDS. INTRODUCTORY In this last division of the work we have to comprehend the anatomy and functions of the several viscera of the abdomen and pelvis : we must consider them not only as individual parts, but as connected together and as forming with the lymphatic and circulating systems of vessels that chain of dependence and relation which constitutes the animal economy. It is necessary to take here a general view of the economy of the intes- tinal canal and absorbing system, including at the same time something of the history of opinions regarding secretion and the structure of glands. It will be understood, that these introductory observations are meant on- ly to combine the several parts, and to prevent that manner of descrip- tion, which is necessary to accuracy and minuteness, from leading us to consider the several parts as distinct and insulated. An animal body is never for a moment stationary : the remotest part i3 in action, and is suffering an incessant change. From the first mo- ment of animal existence a revolution is commenced : we, by slow de- grees, advance in activity and strength, and ripen to maturity; but by as slow and as sure gradations we decline to feebleness and infirmities. The more rapidly animals advance in the first stage of their progress, so is their decline proportionally rapid. But it is not in observing the changes of the animal body from youth to age that the operations of the economy appear the most interesting. It is when we find the living body to consist of parts performing a va- riety of functions, and these connected and mutually dependent; when see we the circulating fluid throwing out fluid and solid secretions to build up and support the body, which is in incessant and daily decay. Again, our admiration must be strongly excited when we observe the system to consist of fluids and solids, and the existence of the animal to depend upon the balance of different powers, the fluids separating and combin- ing in new affinities, and forming the various secretions ; and the solids possessing life and action, and controuling the affinities and influencing the combinations of the circulating fluids. Forgetting that animation is the essential character of living bodies, that it influences the chymical affinities, and varies the attraction of particles, physiologists have too 294 SYSTEM OP THE VISCERA. much endeavoured to explain the phenomena of animated nature by il- lustrations, formerly drawn from mechanics, and hydraulics, ar.d in the present day from chymistry. In a body in which there is life, there is a perpetual waste : first by se- cretions, which for particular purposes are thrown into the cavities, and afterwards carried out of the body entirely, by the excretions of the kid- ney, by the perspiration from the surface, the exhalation by the lungs, the secretions of the intestines. But more than this, there is a decom- position of the solids of the body which are carried into the circulating fluids, and finally dismissed from the system. Lastly, we observe, that even the powers of muscular motion, nay, the powers of the mind and of the senses, are exhausted by exercise, and renovated through the in- fluence of the circulation. The continued action of a muscle is follow- ed by feebleness, and the continued impression of the rays of light ex- hausts the retina, so that the object becomes first faint and then vanish- es ; and these, and all the other powers peculiar to life, are supported by means of the circulating arterial blood. Since there is waste of the solids and fluids, and exhaustion of the energies of the system, so also there must be a source of supply, and means of renewing its activity, and there must be a perpetual motion in the particles of the living frame. Accordingly, animals have appetites requiring the supply of food and drink, and the calls of hunger and thirst stand in relation to the necessities of the body. When food is re- ceived into the first passages, there is thrown out from the stomach a fluid which dissolves it, changes its properties, and is itself essentially altered. The work of assimilation is thus begun. As this converted fluid takes its course through the intestines, it is more and more changed ; more nearly assimilated to the nature of the fluids of the animal; and having still additional secretions united to it, particularly the bile, it is by these means purified from the grosser parts, and fitted for absorption. This fluid, which is now called chyle, is absorbed by a particular and appropriate system of vessels, which, from their conveying this white and milky-like fluid, are called the lacteals. The lacteal vessels carry the chyle to the thoracic duct, the trunk of the absorbing system ; but not directly; for the chyle is deposited in the mesenteric glands, from which it is again absorbed and carried forward. Or if we suppose these glands to be merely convoluted vessels, its flow is at least delayed, so that it is not at once thrown into the mass of circulating fluids. We find then that the stomach performs digestion, and the spleen, we will venture to atfirm, is subservient to it. The secretion of the liver we find to prepare the chyle for absorption, while at the same time it is the pe- culiar stimulus to the intestines. The pancreas pours out a fluid which tempers the acrid bile. The superior part of the intestinal canal absorbs the nutritious fluid or chyle, while the gross remains of the food move on to he deposited in the great intestines. The great intestines are not only receptacles, but form at the same time an extensive secreting and absorbing surface useful in the economy : since it is, at the same time, a secreting and an absorbing surface of great extent. The lacteal vessels, which take up the chyle, are but branches of the system ot absorbents—which is a system consisting of two great divi- sions, the lacteals and lymphatics: the first receiving the nutritious fluids from the intestinal canal, and the latter being absorbents, taking up SYSTEM OF THE VISCERA. 295 the fluids which have been thrown out upon the cavities and surfaces of the body; and we presume upon their absorbing the solid parts of the body also. Thus the new fluids, rich in supplies, are mingled with those which are fraught with the waste and decomposition of the sys- tem. The thoracic duct, the trunk of this system, conveys these fluids thus mingled together into the right side of the heart, where they are re- ceived into the vortex of the circulating red blood. These fluids, now agitated and wrought up with the blood in the cavities of the heart, are sent through the circulation of the lungs, and submitted to the influence of their action and the exposure to the atmospheric air. When chyle is formed in the stomach and intestines, it is observed to consist of albumen, serum, globules, and salts : but the change which it may undergo by its reception into the lacteals, its being deposited in their glands, its mingling with the lymph, its agitation in the heart, have not been observed, though it is natural to suppose, that by degrees it is assimi- lated in its nature to that of the circulating blood, and does at last be- come perfectly similar by the operation of the lungs. By the exposure of the circulating fluids to the atmosphere in the lungs, the carbon of the blood is thrown off, and the blood, resuming it3 purity, is again suited to circulate in the body. What is life ? we see it in its effects only ; we can in no other way comprehend it. Is the blood alive as the solids are ? both are alive : that is to say, they have properties which distinguish them from inanimate matter. The term will only be objectionable to those who have defined life to be the effect of the re-union of the several parts composing an animal body. The blood possesses properties while circulating in the vessels distinct from those which it shows out of the body ; and these do not depend on the agitation and incessant motion, nor on the degree of heat, nor on any similar circumstance, but apparently on some secret in- fluence which the vessels exert over it. There are produced from the blood a variety of fluids by organs which are called glands, and the formation or separation of these fluids is se- cretion. But the solid parts of the body ought to be considered as se- cretions, equally with the matter which flows from the ducts of glands. For there is formed and deposited from the blood, during the round of its circulation, bone to support the incumbent weight of the body : mus- cular fibre, to give it motion: nervous matter giving it sensibility, as well as all the other variety of solids and fluids. The only difference betwixt these solid depositions from the blood and the glandular se- cretions, is, that the former are still within the influence of the vascular system, and that they are decomposed and reabsorbed, conveyed again into the mass of circulating fluids before they can be finally expelled from the body, while the latter are poured into receptacles, which make their exit by ducts. The chymists have observed the division of animal bodies into solids and fluids; but the subdivisions of these are very inaccurate. The fluids they have distinguished into three classes ; 1st, Recrementitious humours, which go to nourish and support the body : 2dly, The ex- crementitious fluids, which are carried out of the body by certain emunctuories ; and the 3d are of a compound nature, being partly re- crementitious and partly excrementitious. We must observe, how- ever, that the fluids enumerated under these heads show it to be a ve- 296 SYSTEM OP THE VISCERA. ry incorrect arrangement. The first division comprehends the fat, the marrow, the matter of internal perspiration, and the osseous juice. The second comprehends the fluids of insensible transpiration, the sweet, mucus, cerumen, urine, faeces. And the last division compre- hends the saliva, the tears, the bile, the pancreatic juice, the gastric and the intestinal juice, the milk, and the seminal fluid. To attend to their arrangements of the solid parts of animals serves as little useful purpose ; for we find substances unlike in structure and discordant in function. From this short view of the system we understand how the powers are spent in action, and the fluids exhausted by deposition and secretion, and how essential to life the functions of those parts are which act upon and assimilate the food. It is the consideration of those organs which forms the subject of the first section of what remains of the pre- sent volume. As in the consideration of these functions the structure of the glandular organs becomes a chief subject of inquiry, it will be natural at present to consider the opinions which have been entertained regarding their structure. The peculiar nature of that organization by which the several secre- tions are formed, has eluded absolute proof by experiment or dissec- tion. It is imagined that there are some organs which do little more than separate the parts of the blood like to the exudation by exhaling arteries. But neither in the exhalent arteries nor in the simple organs can I imagine a mere straining of the blood, but rather that the same principle of activity influences all, and that the several varieties of se- cretion depend upon an action modified by the living property in the secreting part. The fluids in circulation and the vessels containing them reciprocally affect each other: we know that a change on the state of the circulating fluids will alter the nature of the glandular ac- tion, and an excitement of the gland will still more powerfully change the nature of the secretion; the active power of the solids appearing to be an agent which controls and directs the chymical affinities. The term gland is applied to certain solid or firm bodies, with regular and smooth surfaces, which are in great number over the whole body. The functions of many of these bodies are known. They are found to have ducts which convey away a secreted fluid ; but in many of them we discover no duct, and can but obscurely guess at their use. We are struck with the variety of form in the secreting organs. We see a simple surface pouring out its fluids ; or a simple canal into which the arteries throw out their secretion. We find again the secreting ves- sels and their ducts convoluted and massed together, forming such firm glandular bodies as I have just mentioned ; of which kind are the solid abdominal viscera. In the glandular viscera there are greater varieties in form than in any of the other parts of the body ; but with these varia- tions there is no corresponding change of function. I am of opinion that the forms of the solid abdominal viscera result entirely from their si- tuation. The liver is convex upwards, because the diaphragm is con- cave ; and it is irregularly concave downwards, because in contact with the duodenum, colon, and gall bladder. The same may be said of the spleen, the pancreas, the kidney : their form has reference to place, and has nothing further to do with their functions. The form, in short, re- sults from a system of packing more than any thing else. SYSTEM OP THE VISCERA. 297 When we dissect the glands we do not find them to have much simi- larity in structure. Thus the substance of the liver, the kidney, the tes- ticle, &c. are quite unlike. There is also a very remarkable difference in the length, size, and form of blood vessels passing into the glands, and of the ducts coming out of them. In considering the opinions of physiologists or anatomists regarding glandular secretion, and the structure of glands, we find in the first in- stance that the old physicians contented themselves with saying that the glands or viscera possessed a peculiar power to select and separate the fluids from the blood. The next class had recourse to hypothesis : they spoke of the separation of certain parts by means of fermentation,* or by a kind of filtering through the pores or vessels of glands ; that these pores allowed only particles of a particular size or figure to pass them.f It was opposed to this hypothesis, that the thinner fluids must have run through the organs destined for the grosser secretions. But when a theory such as this is received, no argument nor proof seems neces- sary to overthrow it. Resting upon authority alone it stood until it was overturned by the fashion of new doctrines : one equally puerile was raised upon its overthrow. We observe, says the founder of this theory,J that wet or oiled paper, will only transmit fluid of that kind with which it is previously imbued, it will not transmit the oil when wetted, nor will the water make any im- pression on the paper when previously oiled. Upon these facts are to be raised a theory of secretion ! Betwixt the secreting vessels and the ducts, in the peculiar tissue of which glandular structure consists, there is interposed a fluid of that particular kind which is required to be secret- ed, and when the blood is driven against this tissue so imbued, no fluid but of a nature resembling that already deposited can be transmitted. By this hypothesis they explained secretion ; making it to depend on the attraction and repulsion of the particles of the blood by fluids previously secreted. We may surely leave this class of physiologists accounting for the original deposition of the fluids in the glands without a wish to search with them further into this mystery. Commentators on this the- ory, by taking into the system the action of the nerves, indicated that they did not altogether forget that the body was alive.§ Another set of physiologists attributed the whole effect of secretion to the velocity of the blood in the glands or secreting vessels ;|| others, to the length and curves of the vessels, and their action upon the fluids. Again, others have been satisfied with the round assertion that the vital action was the essential cause of secretion. This must be acquiesced in, while yet there may remain an inquiry as to the structure and the means employed. While a power exists in an animal body, directing its actions, perhaps both in the solids and fluids, and in the mutual influence which they exert, the form, length, and activity of the vessels and ducts give opportunity and time for the operation of that principle upon which the secretion depends. Let us attend to the observations of anatomists, and to the appearance which the glandular viscera present under the knife. * Van Helmont. Vieussens, &c. fCharleton, Descartes, Borelli, Verheyn, &c. &c. | Winslow. Helvetius. 5 Conor, Tentarnen epistolare de Secretione, || Boerhaave, Pitcairn, &c. 298 SYSTEM OP THE VISCERA. It is not perfectly clear what the older anatomists meant by the ex- pression Parenchyma. It however saved them the trouble of investiga- tion. They meant flesh, yet not muscular substance, but such as the liver presents. This matter they seem to have conceived to be formed by the blood. Thus Highmore describes the liver to be formed of the blood of the umbilical vein : the opinion originally of Erasistratus. Previous to the time of Malpighi it is fruitless to trace the opinions of anatomists regarding the structure of glands. He was the first who sought to throw light upon this obscure subject by anatomical investigation, and he made a more rapid progress than has been done by any man since his day. If we take into consideration the difficulties he had to encounter in a new field, and the prejudices of the learned with which he had to combat, his merits will be found greater than even those of Ruysch. The opinions of Malpighi were received by those who, forsaking the authorities of names, saw the importance of the study of anatomy. Ruysch himself gave credit to the opinions of Malpighi in the early part of his life. But Ruysch’s more attentive observations being in contradic- tion to those of Malpighi, his maturer judgment rejected that anato- mist’s proofs, and with a boldness in which he was never remarkably deficient, he invented a new theory, or at least alleged new facts, and swayed men’s opinions with an absolute authority. Malpighi was an Italian, and born near to Bologna. Whilst yet a young man, being sunk under the accumulation of family distress, absorbed in grief, and lost to the consideration of his interest, he received comfort and assistance from his master, who urged him to embrace the medical profession. His progress was rapid. After studying at Padua, he was called to fill one of the chairs in Bologna. He was then solicited by Fer- dinand II., Duke of Tuscany, to be professor in the university of Pisa. Here he was associated with liberal men; and now only in his second professorship did he learn to despise the scholastic learning of the time, and betook himself to experiment as the only means by which philosophy could be raised from the oppressive barbarism of the schools. Malpighi and Borelli were associated; they dissected together; they suggested observations to each other; they doubted, and canvassed freely each other’s opinions, and were to each other an excitement and encourage- ment to perseverance and industry. They were supported by govern- ment ; popular in their teaching, while they collected round them the learned men of the time. This was the origin of the famous Academy del Cimento. Malpighi was, after this, professor in Messene, and died in the Quirinal palace at Rome, of a stroke of the apoplexy,* after hav- ing been some time physician to Pope Innocent XII. Malpighi had many enemies, and even some of his colleagues were animated against him with a dishonourable jealousy. Many laughed at his studies and occupations as frivolous and absurd. Something must be allowed for men who had laboured with diligence to become learned ; for these, his opponents, had passed their lives in the study of the Arabian writers. With them studies were enforced which held science in subjection; stu- dies which, in place of invigorating, served only to chill and paralyse exer- tion, and retard ingenious investigation. Even Borelli, but from other motives, opposed and censured some of the dissertations of Malpighi. Malphigi has been considered as the inventor of this department of •* Much coagulated blood was found in the ventricles of his brain by Raglivi. SYSTEM OP THE VISCERA. 299 anatomy, which the French, curious in distinctions, have called the ana- lytic method. He showed the impropriety of the term Parenchyma, as applied to the substance of glands. He proved that the lungs, for ex- ample, (which they also called Parenchymatous) were not fleshy, and had no resemblance to the glandular viscera of the abdomen. He taught, that though glands are smooth on their outer surface, they consist of lo- bules connected by cellular membrane : and, upon a still more minute investigation, that they consist of innumerable little follicles or sacs ; that these are interposed betwixt the arteries which convey the fluids and the excretory ducts going out from them; that the arteries, or the vasa eflerentia, after ramifying and encircling these bodies, pierce them and secrete the fluids into them. On other occasions he describes these lit- tle glandular bodies as appended to the ramifications of the arteries, like fruit hanging by the branches of a tree. Malpighi threw in his liquid injections ; dissected and examined with the microscope ; made careful observations and experiments on living animals; and, lastly, attended in a particular manner to the phenomena of disease. By disease, no doubt, parts swell out and are magnified, and become distinct; but it is not a good test of the natural structure. Fig.i. a a a denotes the follicles of the most simple glands, bbb single ducts from each follicle, a, pouring their fluids into a common excretory canal d, c, which at length are thrown off by the aperture c. Ruysch studied at Leyden, under Van Horne, and at a very early age attached himself to anatomy and botany. At this time he brought him- self into notice by a defence of the professors against one Bilsius, who, although he was learned and acute, had attacked them with all the wea- pons of a Charlatan. Returning to his native country, he was raised to the professorship of anatomy and botany in Amsterdam. It was here that Ruysch made those discoveries in anatomy, and that wonderful and sudden progress in practical anatomy, which not only raised him above his contemporaries, but has been the admiration of all since his time. Though new and various methods of preparing the body have been dis- covered since the time of Ruysch, yet there has been no approach to the elegance with which he displayed the structure of minute parts. It has been said, that, while others preserved the horrid features of death, Ruysch preserved the human body in the softness and freshness of life, even to the expression of the features. We must, no doubt, ascribe some part of this encomium to the exaggeration naturally arising from the novelty of the thing. But as to his superiority in the manner of dis- playing the minute vessels of delicate parts, and his methods of preserv- ing the parts in liquors, transparent and soft, and so as to float in their natural folds, there can be no doubt. Neither can the minuteness and 300 SYSTEM OF THE VISCERA. success of his injections be denied: we have too many occasions in which we must resort to the catalogue of Ruysch’s museum for the true anatomy, to doubt his great success, or to question the truth of those encomiums which have been bestowed upon him. Kings, princes, ambassadors, and great generals, but more than these, all the learned men of the time, crowded to the museum of Ruysch. We must not blame him, if, whilst others were merely speculating about the structure of parts, he, surrounded by so princely a museum, should simply have laid open his cabinets, and bid them satisfy themselves whether or not he was right. Ruysch’s preparations went to contradict the opinions of Malpighi. His injections, pushed more minutely, showed those round bodies which are to be seen in some of the glandu- lar viscera (and which Malpighi took to be little bags into which the se- creted fluid was poured) to be merely convoluted arteries. Ruysch taught, that the minute arteries, after making these convolutions, termi- nated in the beginning of excretory ducts; that there was no substance or apparatus interposed, but that the vessels and ducts were continuous. His opinions being formed upon the strength of more minute prepara- tions, and a stiperior dexterity of anatomical investigation, few anatomists chose to be outdone, or to acknowledge they could not see what he saw. This I believe to be one reason of the rapid progress of Ruysch’s opi- nion. It may be further observed, that it was not in the mere fact of there be- ing follicles, in which Malpighi and Ruysch differed ; for the latter con- ceded that there were hollow membranes, but contended that these were not glands.* The opinions of Malpighi and Ruysch have held the schools in per- petual controversy ; most anatomists, however, leaning to the authority of Ruysch. There follows these a crowd of French academicians, who with Boerhaave, may be considered as mere commentators on the origi- nal authorities of Malpighi and Ruysch. Some of these argue for se- cretion by continuous vessels, and contend that the arteries terminate in the excretory ducts ; others, that the secretions are made into follicles ; and some, as Boerhaave, insist that both are right in their observations, and in the proofs which they have adduced, that secretion is in part per- formed by continuous vessels, partly by a more intricate glandular appa- ratus. Of the secretions discharged from the glands it may be sufficient to say, that many of them are destined to be useful to the further operations of the economy ; that they are all liable to be absorbed upon any ob- struction to their evacuation; and that as far as experiments on brutes .go, all the animal secretions may be even injected into the circulating fluids without greatly disordering the system.! The blood carried into the glands has nothing peculiar in its appear- ance and sensible qualities ; the idea once entertained, that the blood suing from the heart immediately commences a separation of its parts * Their difference of opinion is expressed in the following words of Ruysch : “ Adeoque discrepantia inter magnum ilium virum et inter me est, qnotl ille putat humores delabi in glandulas dictas simplicissimas,—ibi foreri mutari: Ego puto, quod arteri* ultim® siiccos ■faciant, et factos ibi deponant.” f Haller, by experiments, proved that several kinds of foreign matter may be' conveyed into the circulating blood ; and Bichat has made the experiment of injecting all the animal ■ secretions into the. veins of brutes. SYSTEM OF THE VISCERA. 301 for the several secretions, is quite unsustained; and if it deserves a serious refutation, we have it in the varieties to be observed in the dis- tribution of the arteries to the glands ; for a different origin of a secreting artery would in that, supposition change the secretion.* In some of the glands the arteries and veins have a peculiar appear- ance ; they are convoluted, and reflected so curiously, as to have given rise to the idea of their preparing the blood for the secretion ; thus in the spermatic cord the vessels have been called thevusa pnparantia. But this convolution of vessels is for another purpose. Nothing peculiar has been observed in the distribution of nerves to the glands. They are comparatively small. They have been cut, and still the secretion has gone on. As however most of the higher and dis- tinguishing properties of life reside in the nervous system, so it is rea- sonable to suppose that not only the various sympathies and sensibilities which the glands possess are derived from the nerves, but also that the secretions which they separate from the general mass of blood, is owing to an influence of life residing in their nerves. An imperfect know- ledge of anatomy, and especially of the connexions and relations of the nervous system, gives rise to very useless experiments. Is it not strange that experimenters should think that they cut off nervous energy by cut- ting through the nerve ? This is still proceeding upon an old-fashioned opinion, that the brain secretes the nervous spirits, and the nerves dis- pense them ! Let us be satisfied with knowing a little. The life residing in the gland is an agent controlling the affinities. The liver or the kidney se- crete bile and urine, not because they have a certain form, or certain length of vessels, but because the affinities of the constituent parts of the blood are controlled by the living principle in the gland. As the forms of the parts which throw out secretions have a great va- riety, it may be useful in this introductory view to point out these vari- eties, and their appropriate names.| In the first place, although in ge- neral language the term gland implies a secreting body, yet this does not follow from the definition of that word. According to Hippocrates, it is a tumid round body, soft, smooth, and shining. Many such bodies, and which we cail glands, have no excretory ducts, and do not secrete a fluid ; while most secreting parts admit of no such definition. When, again, we admit the definition of authors who have taught their peculiar opi- nious regarding their structure, we have a still less admissible description. Thus Malpighi defined a simple gland to be “ a hollow membrane with a duct;” and Ruysch says, “some glands are entirely composed of a hollow membrane and an outlet or duct, but principally of vessels. These definitions of glands being optional and uncertain, it is neces- sary to use names appropriated to the several varieties of form in secret- ing parts. Indeed the term gland is useless as conveying any know- ledge of the structure of which the viscera are composed. We must observe, however, that there is a division of glands still in use into conglobate and conglomerate. This first implies a gland simple * Bichat has examined the blood of the carotid artery, and of the spermatic artery, without being able to observe any difference. f The terms acini, cotulae, crypt*, folliculi.glanclula:, lacunae, loculi, utricuii, have been al- most promiscuously used; being so many names for bundles, bags, bottles, holes, and par- titions. 302 SYSTEM OF THE VISCERA. in its form, the latter a gland having the appearance of an assemblage of several glands.* There is no gland that has not more or less the ap- pearance which is described as conglomerate ; that is, consisting of se- veral parts, united by cellular membrane ; and the distinction is attended with no advantage. Acini (the stones of grapes, literally,) form the last subdivision which we observe in the viscera, as in the liver ; they are round bodies, not re- gularly invested with membranes, and which can be teased out into par- cels of minute vessels, f Cryptce (implies cells or cavities) are numerous in the body. We have an example of them in the great intestines.J Ruysch, denying the de- finition of Malpighi, says, Crypta signifies a soft body, consisting of ves- sels not completely surrounded with a membrane, and resolvable by boil- ing or maceration. § Folliculi are little bags appended to the extremity of the ducts, into which the secretion is made, and from which it is evacuated by the ducts. Lacuna- are little sacs opening largely into the passages, (as in the urethra,) and into which mucus is secreted, which, lodging there, for a time to be discharged when occasion requires the lubrication of the pas- sage. The best example of this structure is at the root of the tongue, when the glandular textures have been swollen by inflammation. Finally, we have to recollect that every part of the body secretes ; that every surface is a secreting surface ; and even that surface which is produced by an incision no sooner ceases to bleed, than a secretion be- gins. And that an ulcer in the skin or flesh becomes by habit similar to those organs, the peculiar functions of which is to secrete some mat- ter useful in the system. This fact corrects the notions which we should otherwise be apt to receive of the action of secretion, requiring a com- plicated apparatus, from contemplating the more complicated glandular organs. OF THE ABDOMEN IN GENERAL, AND OF THE PERITONEUM. The abdomen is that division of the body which is betwixt the tho- rax and pelvis. It is bounded above by the arch of the diaphragm ; be- hind, by the spine ; on the sides and fore part by the abdominal muscles; and below, the abdominal viscera are supported by the alae ilii and the os- sa pubis. The abdomen contains the viscera, which are for the purpose of receiving and assimilating the food, and the organs immediately con- * As the salivary glands and the pancreas. Farther, the lymphatic glands are generally called conglobate glands, being smooth, and apparentlj simple in their structure; but these, when injected, take exactly the appearance which should naturally be described by the term conglomerate, consisting of many little cavities. These lymphatic glands, belonging to a distinct system, require no farther particular definition to distinguish them, i See farther of the acini of the liver for example. | Ruysch ad VirumClar. H. Boerhaave, p. 53. j “ Cryptarum vascula possum docere, sed sunt tam subtilia, ut reptatus non possit distin- gui: tantum circum afftisa rubedo per repletionem videtur.” Ruvsch ad Her. Boerhaave, P• 77. «F THE REGIONS OP THE BELLY. 303 nected with them. Nature, by the classification of the parts in the great cavities, declares a connexion of these parts in function, which is never to be lost sight of. We speak of the cavity of the abdomen ; but it is an inaccuracy of language : for there is really no cavity. The parietes of the abdomen, viz. the abdominal muscles and peritoneum, closely embrace the con- tained viscera. To understand what is meant by the cavity of the ab- domen : to understand the connexion of the several viscera, and the manner in which they lie contiguous, while they adhere at certain points only, we must attend to the peritoneum. But, in the first place, let us notice the outward divisions of the belly. To give greater accuracy to the description of the seat of the viscera, or, perhaps, rather more strictly to connect the knowledge of the in- ternal parts with the outward marks of the belly, it has been long cus- tomary to mark certain arbitary divisions on its surface, which are call- ed regions. OF THE REGIONS OF THE BELLY. 304 OF THE PERITONEUM. The epigastric region (a) is the upper part of the belly, under the point of the sternum, and in the angle made by the cartilages of the ribs. Upon the sides covered by the cartilages of the ribs are the hypochondriac regions, or the right and left hypochondrium (b b). These three regions make the upper division of the abdomen, in which are seated the stomach, liver, spleen, pancreas, duodenum, and part of the arch of the colon. The space surrounding the umbilicus, betwixt the epigastrium and a line drawn from the crest of one os ilii to the other, is the umbilical region (c), and here principally are the small intestines. The hypogastric region is of course the lowest part of of the belly, consisting of the angle betwixt the umbilical region, the spines of the ossa ilii and the pubis (n). The two lateral spaces be- twixt the false ribs and the spine of the os ilii, and behind the line per- pendicular to the spine of the ilium, are the iliac regions (e. e), and behind those the lumbar regions, or the loins : here the kidnies are seated and part of the colon. The hypogastric is divided into three, the pubic in the middle (a), and an inguinal on each side (b b). OF THE PERITONEUM. The peritoneum, like all the other membranes of the body, consists of an expansion of dense cellular membrane; yet it is what is called a proper or true membrane; being a white firm thin contexture of cellular substance, in which no fibre or striated appearance is to be ob- served.* By its outer surface it adheres to the adipose mem- brane, on the inside of the abdo- minal muscles, and to the sur- face of the several viscera; its inner surface is smooth, and forms no adhesion while the parts are sound and healthy; j its outer surface is looser in its texture, and by the splitting of its lamina, it may be traced in- to the common cellular mem- brane. The cellular membrane on the outside of the peritonaeum is in some places short, firm and dense ; as on the liver, the spleen, the uterus, and the in- testines : but it is longer, lax, and fatty, where it attaches the peritonaeum to the muscles and tendons of the abdomen. * The meaning of some anatomists saying that the peritoneum is a double membrane, wii1. be seen below. or THE PERITONEUM. 305 The peritoneum has no termination; or it is a sac; yet. so curiously is it involved with the viscera, that though we say the viscera are con- tained in the abdomen, yet, accurately speaking, they are without the peritoneum, and consequently do not lie in the abdominal cavity.* Let us follow it in its inflections, and suppose that we have opened the sac, (that is, the cavity of the belly,) we find it first expanded on the lower surface of the diaphragm ; and at some of the interstices or per- forations of that muscle or its tendon it comes in contact with the pleu- ra, and adheres to it by cellular substance. From the diaphragm the peritoneum is reflected off to the liver (a.), forming the ligaments of that viscus, and, expanded over its surface, it forms its outer membrane. From the diaphragm it is also sent off upon the oesophagus and sto- mach, and prolonged to the spleen on the left side (as it is to the liver on the right) so as to form the ligaments of the spleen. The aorta, the great vena cava, the thoracic duct, and the kidnies, are behind the peritoneum; that membrane being stretched before them. But the intestines are also in the same respect behind this general in- vesting membrane ; for it is merely reflected from the spine and psoas muscles, and from the great vessels running down upon the spine, so as to involve the intestines and form their outer coat (b). As it stretches towards the intestines, it involves the vessels of the intestines in the du- plicature, and forms the mesentery (c). The peritoneum also lines the abdominal muscles d ; it is reflected from the diaphragm upon the surface of the transversalis and rectus ab- dominis muscles. Here it is united to them by a loose adipose mem- brane, and from the abdominal muscles it is continued upon the inside of the pubes. From the pubes it ascends upon the bladder of urine E; descends again behind the bladder; and there, making another re- flection to mount over the rectum f, and form the meso-rectum, it leaves betwixt the rectum and bladder a particular sacculus ; or if the uterus intervene, the peritoneum having descended on the back part of the fundus of the bladder, it is again in a similar manner reflected over the uterus g. The kidney h is behind the peritoneum; but so are the other viscera. The only difference in their relation to this membrane being, that they hang further into its embrace. From this detailed description we see that the peritoneum has no ter- mination ; that it is continued from the surface of the diaphragm to that of the abdominal muscles ; from that over the bladder and rectum ; from the rectum in the whole length of the intestinal canal; and from the in- testinal canal up upon the diaphragm. We see then what is meant when it is said that it is a shut sac ; we understand by the cavity of the perito- neum merely the inside of this sac ; and that when distended with fluid, the fluid is contained betwixt the peritoneum lining the abdominal mus- cles, and that part of it which invests or forms the outer membrane or coat of the intestines. This fluid, whether collected there by disease or thrown in by experiment, has no natural outlet, nor does it transude in the living body.j * The figure represents an ideal section of the abdomen ; the edge of the peritoneum is represented by the dotted line. f We not unfrequently find an accurate general description in authors, but some incorrect- ness in the subordinate detail; which throws back the ideas of the reader into confusion. Such is the enumeration of the holes or perforations of the peritoneum, “ pour donner pas- 306 OF THE USE OF THE PERITONEUM. BLOOD-VESSELS OF THE PERITONEUM. As the peritoneum is a membrane of great extent, and investing a variety of parts, its vessels come from many sources. It receives arte- ries and veins from the mammary vessels ; from the phrenic and epigas- tric vessels; from the lumbar arteries and veins ; and from the ilio-lum- bales, circumflexse ilii, renal, and spermatic arteries. It receives nerves from the intercostal, lumbar, and diaphragmatic nerves. It would appear that disease has given rise to the opinion that the peri- toneum has in it many little glands. This is controverted decisively by Morgagni: there are no glandular bodies in the peritoneum. OF THE USE OF THE PERITONEUM. The peritoneum serves as a dense and outer coat to the abdominal viscera ; conveys the vessels to them, as in the example of the mesente- ry ; and, having its inner surface smooth and lubricated by a watery se- cretion, it allows the parts to lie in contact, (they being strongly com- pressed by the surrounding abdominal muscles and diaphragm,) and at the same time allows in the intestinal canal a capacity of motion without friction. There is no internal surface or cavity, as it is called, of the living body, which is not moistened by an exudation from the vessels of the sur- face. Thus it is with the peritoneum. An exhalation from the ex- treme arteries bedews its surface, and is again taken up by absorbent vessels ; so that it does not accumulate in health, nay, even fluids pour- ed into the abdominal cavity will be taken up by the absorbents.* When the abdomen is opened in animals alive, or recently killed, as in the shambles, a vapour is seen to exhale from the peritoneum, having a peculiar animal odour. Yet we ought not to say that this vapour is col- lected in the dead body : for before the opening of the peritoneum, or the death of the animal, it is not in a state of vapour, but is condensed into a watery exudation. | We see the capacity of secretion of the peritoneum very well in her- nia, where the peritoneal surface will in a very short time pour out a great quantity of serum. One great use of the peritoneum is to retain the viscera in their sage A l’cesophage, A la veine-cave,” &c. See Anatom. Chirurg. par M. Palfin. We see that there are no such perforations, that the oesophagus never enters into the cavity of the pe- ritoneum nor does the rectum pass out from its cavity. This was indeed explained by Ferne- lius, in op; sition to Galen. See a description of the inflections of the peritoneum, by Bar- tholin.—Specimen llistori* Anatomicte Analect. Ob. I. * See Nuck Sialograph, c. ii. p. 17. “ Qua copia in statu secundum naturam secernatur dictu difficile est; ad uncias certe col- lecta aquula in sani homiuis abrlomiue reperitur. (Kaawn, 543.) In homine, cui sponte ab- domen sub umbilico ruptuin erat ad quinque & sex libras de die effluebat.” (Journ. de Med. 1757. M. Aug. ut denique 800 libr. eflluxerent.) This, however, proves nothing of the na- ture or quantity of the secretion ; this has probably been an inflammation and abscess of the peritoneum, which we have seen pours out such a quantity of fluid, thin and serous, as quick- ly to drop through the bed-clothes upon the floor. f This vapour I have seen arising from the intestines of the human body during the opera- tion for hernia ; and also when the omentum and intestines have escaped in consequence of a wound of the belly. OP THE USE OF THE PERITONEUM. 307 place, says Haller; for when it is wounded, they escape, and sometimes with a sudden impetus, which makes it difficult to reduce or retain them.* But this is not from the want of the embracing of the peritoneum, but from the tendons or muscles which support the peritoneum, being cut; for when there is a deficiency in the support given by the abdominal mus- cles, or their expanded tendons, the peritoneum does not prevent the viscera from being protruded, but easily yields to their forcible protru- sion, and forms a sac involving this hernia. Nor do the processes of the peritoneum, which have received the name of ligaments, nor the mesentery, nor mesocolon, sufficiently resist the prolapsus of the viscera when they have escaped from the pressure of the surrounding muscles. Sufficient example of this we have in her- nia of the intestines, in which the mesentery is greatly elongated, or in the displacement of the stomach, or in the prolapsus and procidentia uteri. The peritoneum which forms the sac of hernia retains little elasticity, and does not shrink into tho belly when freed from the outer adhesions ; but the general peritoneum will allow great distention, as in ascites, and quickly contract to its former dimensions on the evacuation of the fluid; and so that part of the membrane which invests the stomach and intes- tines, the bladder of urine and gall bladder, has considerable elasticity, since it suffers thesejparts to be distended and again returns to its former dimensions. The consideration of the insufficiency of the peritoneum to retain the viscera leads us to attend to a circumstance of the greatest impor- tance connected with the viscera of the belly. The abdomen is every where (except towards the spine) surrounded by muscles. Above we see the diaphragm; before, and at the sides, the abdominal muscles ; and even below, the parts in the pelvis are surrounded and compressed by the levator ani, in such a manner that the whole of the viscera suffer a continual pressure. This pressure upon the viscera appears to be uni- form and constant, notwithstanding the alternate action of the abdominal muscles and diaphragm as muscles of respiration : but it must be occa- sionally very violent, as during exertions ; in pulling, for example, or in straining, as a sailor must do in working of the great guns ; or when pul- ling at the oar, or when balancing himself upon his belly over the yard- arm. And indeed by such violent and general compression of the visce- ra of the belly, ruptures are sometimes produced, of the worst kind, and followed by an immediate train of urgent symptoms. The viscera having in general delicate outer coats, and no ligaments capable of supporting them, and being very vascular, require the aid of this pressure of the surrounding muscles ; and the great venous trunks, which take their course through the abdomen, are in a particular manner indebted for their security to the pressure of the abdominal parietes. We must recollect also the bad consequences which result from the sud- den relaxation of the abdomen ; as in women after delivery, or in con- sequence of withdrawing the water of ascites without due compression of the belly; languor, faintness, and even death, are sometimes pro- duced, apparently by the balance of the vascular system being destroyed. Some good authors in former times have described the peritoneum as * Element. Physiol, tom. ii. p. 330. 308 OF THE OMENTA. a double membrane.* This was no farther a mistake than as they con- sidered the cellular membrane, which lies without the peritoneum, as a part of it. It is necessary to recollect this in order to understand the meaning of their calling the sheath of the cellular membrane, which ac- companies the vessels passing out from the abdomen, productions of the peritoneum. The vaginal productions of the peritoneum are the sheaths of the common cellular substance which accompany the aorta and oeso- phagus into the posterior mediastinum ; or which give a bed to the sper- matic vessels, or passing under Poupart’s ligament accompany the ves- sels of the thigh. They are improperly termed productions of the peri- toneum. # The proper productions or prolongations of the peritoneum are of a very different kind; they are the ligaments and plicae, the mesentery, mesocolon, and omenta. OP THE LIGAMENTS AND FOLDS FORMED BY THE PERITONEUM. There are certain ligaments and plicae formed by the peritoneum, which to enumerate will carry us again over all the extent of its surface. When this membrane is reflected off to the oesophagus from the dia- phragm, it forms, 1. the ligamentum, dextrum ventriculi; and 2. the vinculum oesophagi. In the same manner is formed, 3. the ligamentum inter cesophagum et lienem, which we may trace into the omentum majus, presently to be described. From the spleen we may trace the mem- brane into, 4. the plica renalis and capsularis; 5. another plica or du- plicature may be traced from the kidney to the colon, and on the right side, 6. the plica duodeno-renalis, viz. from the kidney to the duodenum. When we turn up the liver, we are led to observe the five ligaments to that viscus, to be described in their proper place, and from the liver stretching to the kidney we find the 7. ligamentum hepatico-renale still tracing the convolutions of the intestines, and following the mesentery or ligament of the small intestines, into the mesocolon, or ligament of the great intestines, and the mesorectum or process of the peritoneum to the rectum ; we there see the 8. plica semilunaris, which is before the rec- tum, and behind the bladder of urine. The young anatomist ought to trace all these processes of the peri- toneum, both to comprehend the great extent of this membrane, and more especially to learn the relations of the viscera to each other. OF THE OMENTA. The omenta are fatty membranes which hang over the face of the bowels. They are considered as secondary processes of the peritoneum, because they are not formed by the peritoneum reflected off from the spine upon the intestines, as the mesentery is, —it being a primary pro- cess ; but they are reflected from the peritoneal surface of the stomach and intestines. Anatomists distinguish the omentum majus, or colico- gastricum: the omentum minus, or hepatico-gastricum; omentum coli- cum, dextrum et sinistrum ; and, lastly, the appendices epiploicce. The omentum, or epiploon, meaning thereby the great omentum, is % floating membrane of extreme delicacy, expanded over the surface of * See Anat. Chirurg. par M. Palfin, tom. ii, p. 55, and note «. OF THE OMENTA. 309 the small intestines, and attached to the great arch of the stomach and intestinura colon. Although this membrane be of extreme delicacy and transparency in the young subject,* yet it is much loaded with fat, and appears transparent in the interstices only; and in advanced age it loses much of its delicacy, and acquires a degree of consolidation or firmness, and is often irregularly collected into masses, or adheres preternaturally to some of the viscera. The omentum majus hangs suspended from the cellular connexion betwixt the arch of the stomach and the great transverse arch of the co- lon ; or rather it forms that connexion betwixt the stomach and colon. It consists of two membranes, or is as a sac, collapsed and hanging from the stomach and colon |, one of the sides being the peritoneum re- flected off from the oesophagus and along all the great arch of the sto- mach, and the other that which comes from the arch of the colon. And further, each of these laminae may be supposed to consist of two lami- nae ; for example, where the omentum is formed by the meeting of the pe- ritoneum from the lower and upper surfaces of the stomach ; these two uniting, form the upper lamina ; and where the lower layer of the omen- tum comes off from the colon, it is also formed by the peritoneum re- flected in the same manner from both sides of that intestine ; so with some truth the omentum is supposed to consist of four laminae of mem- branes of extreme tenuity ; but these four layers cannot be demon- strated. The great omentum extends from the bosom of the spleen transversely, until it terminates on the right side of the arch of the co- lon, where the omentum colicum begins. The great omentum varies considerably in extent. In a child it is short; in the adult further extended over the viscera : sometimes it reaches only to the umbilicus ; sometimes it is allowed to extend its mar- gin into the pelvis, so that in old people it is very apt to form a part of the contents of hernia ; often it is wasted and shrunk ; sometimes col- lected into masses leaving the surface of the intestines. My reader must now find his way into the marsupium, or purse of the omentum, viz. the porta nmenti, the celebrated foramen of Winslow. It will be found to be a slit betwixt the ligamentum hepatico-colicum and hepatico-duodenalis, being under the biliary vessels and vena porta:. Upon blowing into this opening, in a young subject, three omenta are distended, viz the omentum hepatico-gastrum, the colico-gastricum, and the colicum. This opening serves as a communication betwixt the cavities of the omentum and the general peritonaeal cavity ; but I am inclined to think it is very frequently destroyed by adhesions.| As this opening points to- wards the right side, Dr. Monro thinks it a sufficient reason for introduc- ing the trochar on the right side in the operation of tapping for ascites (contrary to the usual caution of avoiding the liver, which is so often dis- eased in this case) ; by operating on the left side he thinks the water will not be allowed to flo w from the sac of the omentum. It appears to * “ Praeterea tenenimas esse ut nulla membranarum huraanarum, retina oculi excepta, aeque sit tenera.”.—Haller, vol. vi. lib. 20. § 1. par 12. While its delicacy is remarkable in the young subject, the retiform vessels (vid. Ruysch. Ther. II. Q. V. Spigel. LVIII. &c. have the fat accumulated in their tract, as if it were thrown up by them to a side; but often, the fat increasing, obscures the vessels. | Marsupium the common term.—See Winslow, IV. p. 352. 1 Winslow, Duverney, and Haller. 310 OP THE OMENTA. me that it will flow equally well from whatever point of the belly the water is drawn. OF THE OMENTUM MINUS, OR HEPATICO GASTRICUM. This is a membrane of the nature of that last mentioned, but in gene- ral less loaded with fat. It is extended from the liver to the lesser arch of the stomach. It passes off from the lower surface of the liver at the transverse fossa ; from the fossa ductus venosi ; invests the lobulus Spi- gellii; involves the branches of the cceliac artery ; and is extended to the lesser curvature of the stomach and the upper part of the duodenum.* OMENTUM COLICUM. This is a continuation of the great omentum upon the right side of the great arch of the colon : where it rises from the caput coli; but it sel- dom extends its origin from the colon the length of the caput coli. It is inflated with the great omentum. APPENDICES EPIPLOIC.*, OR OMENTULA INTESTINI CRASSI These are little fatty and membranous processes which hang pendu- lous from the surface of the colon: they are of the same texture and use with the greater omentum and right colic omentum. We have mentioned that the omenta are double reflections from the peritoneum, and consequently they may be inflated so as to demonstrate them to be perfect sacs. To do this it is not required to puncture any part of them ; for by the natural opening just described, the whole may be inflated in a young subject, and in a healthy state of the viscera. There is a considerable variety in the form of the omentum of ani- mals! ; but still they seem to show the same provision of covering the intestines, filling up the inequalities which arise from the rounded forms of the viscera, and still further lubricating and giving mobility to the in- testines. J The surface of the omentum, however, seems merely to fur- nish a fluid exudation like the general surface of the peritoneum ; and the idea which has been entertained of the oil or fat exuding is not cor- rect^ The use assigned to the omentum of being subservient to the func- tion of the liver is deservedly neglected. || * Macilentius est, etvasa habet minora.” Winslow. Haller. Indeed, it seems rather to answer the general purpose of a cellular membrane conveying vessels, than the purposes of the omentum majus. f Haller Element. Physiol, tom. vi. lib. xx. § 2 and 3. | We must not suppose that because a madman stabs himself in the bellv, and there is af- terwards found adhesion of the intestines to the wounds, the omentum has not done its office, (see Boerhaavii Pretectiones, vol. i. § 45.) no more can we give credit to the tale told by Ga- len (De Usu Partium, I. iv. c. 9.) of the gladiator who lost part of the omentum, and ever af- ter had a coldness in his guts! At least, we cut out a great part of the omentum from a man without any such sensation being the consequence now a-days. 5 “ Et dum halitu pingui & ipsa obungit & peritoneum.” Haller loc. cit. Boerhaave, Morgagni Adversar. III. Auiraad. VI. jj Viz. by supplying a gross oily matter to the venae portae. OF THE ABDOMEN. 311 OF THE VISCERA OF THE ABDOMEN. Having understood the nature of the general investing membrane of the abdomen, and what is meant by its cavity and its processes, we take a general survey of the economy of the viscera, before entering upon the minute structure of the parts individually. The contents of the abdomen are thus enumerated in elementary works on anatomy. 1. The membranous visceka, viz. the stomach, the small and great intestines, the gall-bladder, mesentery, the mesocolon, and ligamentous processes, and the omenta. 2. The solid viscera, viz. the liver, spleen, pancreas, the kidnies, and renal capsules, the mesenteric glands. But a natural order in the arrangement of these viscera is to be preferred. The organs destined to receive the food, and to perform the first of those changes upon it, which fit it (after a due succession of actions) for becoming a component part of the living body, are the stomach and intestines primarily ; the glandular viscera, the liver, pancreas, and the spleen, are subservient or secondary organs. I have been accustomed in my lectures to divide these parts into those which have action and mo- tion, and those which are quiescent or possessed of no power of contrac- tion. Thus the stomach, intestines, gall-bladder, and bladder of urine (though this belongs to the pelvis) have muscular coats, and the power of contracting their cavities: while the liver, spleen, pancreas, and kid- nies, have no muscularity. This division of the viscera may lead to important distinctions in pa- thology. During inflammation, it is observed, that though the parts possessing a power of contraction may sometimes lie inactive without pain, yet in those parts when roused to action there is excruciating pain. On the other hand, it often happens that the glandular and solid viscera are the seat of long continued disease, which is attended only with a dull or low degree of pain; and the anatomist is often struck upon examin- ing the body after death with the wide ravages of a disease, which gave no sign during life. We divide the intestinal canal into three parts; the stomach, the small intestines, the great intestines. The small intestines are subdivided into the duodenum, jejunum, and ileon. The great intestines are subdivided into the csecum, colon, and rectum. The stomach is the seat of the digestive process : in the duodenum the food receives the addition of the secretions from the liver and pan- creas, and is still further changed; in the long tract of the jejunum and ileon the nutritious part is absorbed ; and in the great intestines the foul sediment becoming fieces, is carried slowly forward, suffers a further ab- sorption of fluid, lodges in the lower part of the colon, and then in the rectum or last division of the canal. From this view it is apparent that each division of the intestinal canal is marked by some peculiarity in its use or function ; we must carefully examine their minute structure as individual parts ; at the same time that we do not allow ourselves to forget the connexion, the relation of the organs, and their economy as a whole. With this intention, following the course of the food, we treat first of the oesophagus. 312 OF THE (ESOPHAGUS. OF THE (ESOPHAGUS. The oesophagus or gullet is a cylindrical muscular tube, which con- veys the food to the stomach. It is continued from the pharynx down behind the larynx and trachea and close before the spine, and continu- ing its course in the back part of the thorax, it perforates the diaphragm, and expands into the upper orifice of the stomach. Although with many authors I call it a cylindrical tube, and it may take this form when dissected from the body and inflated, yet during life it lies collapsed with its inner membrane in close contact. It is dilated only by the passing down of the food or drink, and then partially only, since the matter taken into the stomach does not flow as through an in- active tube, but the morsel is transmitted by a succession of contractions of its fleshy coat. The upper part of this tube is called the pharynx. It may be des- cribed as being expanded like a funnel; it is attached to the occipital bone, pterygoid processes of the sphenoid bone, and jaw-bones; and fur- ther down it is kept expanded upon the horns or processes of the os hyoides. The lower part of this funnel may be said to terminate in the (Esophagus; for although the tube be continuous and there be no absolute difference in the texture of the pharynx and the cesophagus, yet the tube is attached in such a manner to the cricoid cartilage as sufficient- ly to mark the termination of the pharynx and the commencement of the oesophagus. It is here that the tube is narrowest and least dilatable, owing to its connexion with the cricoid cartilage. This is a point of the anatomy which must be particularly studied by the surgeon, for here he will meet with difficulty in attempting the introduction of instruments, and here is the seat of stricture. This bag is very fleshy, being sur- rounded with muscular fibres, which take their origin from the neighbour- ing fixed points ; as the styloid process, the horns of the os hyoides, the thyroid cartilage ; bv which it is enabled to grasp and contract upon the morsel when it has been thrust by the tongue behind the isthmus fau- cium. This strong tissue of muscular fibres which surrounds the pha- rynx, continued down upon the oesophagus in the form of a sheath, which has been called tunica vaginalis. I believe we can with propriety enumerate no more than two proper coats of the oesophagus ; its muscular and internal coat: for that which is sometimes considered as the outer coat, is only the adventitious cel- lular membrane, and the nervous coat is merely cellular tissue connect- ing the muscular and inner coats. The muscular coat of the cesophagus greatly surpasses in strength and in the coarseness of its fibres any part of the whole tract of the intestinal canal. There may be very distinctly observed in it two layers of fibres ; an external one consisting of strong longitudinal fibres, and an internal one of circular fibres. These laminae of fibres are more easily separated from each other than those in any other part of the ca- nal.* But an idea is entertained that the one or other set of fibres, * It appears that the oesophagus can be ruptured in two ways ; across, by the tearing of the longitudinal fibres; and longitudinally, by the separation of the longitudinal fibres. This, though a rare accident, takes place in violent vomiting or straining to vomit; and, in the first instance, the tearing across of the oesophagus seems to be the effect of the action of the OP THE (ESOPHAGUS. 313 the circular and internal ones, are for contracting the tube, and the outer ones for elongating and relaxing it. I believe on the other hand that they contract together, conducing to one end, deglutition.* What is called the tunica nervea is the cellular connexion betwixt the muscular and inner coat; it is very lax, insomuch that the muscu- lar coat and the inner coat are like two distinct tubes, the one contained within the other, and but slightly attached. This appearance is pre- sented particularly when the oesophagus is cut across. The inner coat of the oesophagus is soft and glandular; villi are described as being distinguishable on its surface, and it is invested with a very delicate cuticle which dulls the acute sensibility, and prevents pain in swallowing. It in every respect resembles the lining membrane of the mouth. The power, however, which the oesophagus seems to possess of resisting heat depends not on the insensibility bestowed by the cuticle, but is owing to the rapid descent of the hot solids or liquids swallowed; for when they happen to be detained in the gullet they produce a very intolerable pain. This inner coat has an exhaling sur- face, like the rest of the body, with particular glands to secrete and pour out that mucus which lubricates the passage for the food. These glands suffer ulceration and schirrous hardening, and are a terrible cause of obstruction to swallowing. The inner coat is capable of a great de- gree of distention, but it is not very elastic ; or, at least, contraction of the muscular coat throws it into longitudinal folds, or plicae. In the neck the oesophagus lies betwixt the cervical vertebrae and the trachea, but is at the same time in a small degree towards the left side. At the bottom of the neck it perforates the membranous fascia, and enters the thorax. Here the surgeon should take good heed of the relation of the tube to the fascia, for I have seen a stricture imagined to be present from an instrument resting on this membranous connexion. When the oesophagus has entered the thorax it descends, retiring a little the same time, and passing behind the bifurcation of the tra- chea and the arch of the aorta, when it descends farther upon the dor- sal vertebrae, it lies rather to the left side; escaped from the aorta, it lies on the right side of it, and as it passes further down it gets more and more before the aorta. This is sufficiently apparent when we at- tend to the relation of the perforations in the diaphragm for transmitting the aorta and the oesophagus. Behind the oesophagus, in the thorax, there are one or two lymphatic glands, which were understood by Vesalius to belong to the oesophagus. What deceived him is an appearance to be observed in these glands. The lymphatics, or the small branches of veins, are generally filled with a black matter, which, extending to the coats of the oesophagus, resem- ble very much the ducts of the glands going to open into the oesophagus. These gland* in the posterior mediastinum are sometimes diseased, and enlarged so as to compress the oesophagus, and to cause so permanent an obstruction of deglutition as to occasion death. The inner coat of the oesophagus shows so very different a texture diaphragm on the oesophagus. By this accident the fluids of the stomach are poured into the cavity of the thorax. * See farther of the muscular coat of the intestines. “It was at one time supposed that the muscular fibres of the oesophagus had a spiral direction.” See Verheyen, and Morgagni Adversar. iii. 1 314 OF THE STOMACH. from that of the stomach, and this difference is marked by so very ab- rupt a line ; the delicate cuticular lining terminates so abruptly, the one for transmission merely, the other for the lodgment of the food and for di- gestion, as sufficiently to indicate the different offices performed by the oesophagus and stomach. OF THE STOMACH. The stomach is that capacious membranous bag into which the oeso- phagus delivers the food, and in which the process of digestion is per- formed. The food of animals is of various kinds, and the form and structure of the stomach varies according to the nature of the food. Animal food affords a rich aliment in a state nearly prepared for supply- ing the deficiencies of the living system. In such animals as live on flesh the stomach is simple in its form, and possesses little muscular property. On the contrary, vegetable food has a smaller proportion of nutritious matter in it, requiring for its separation a more complicated and tedious process of maceration, trituration, and digestion. Therefore in brutes living on vegetable matters we observe a more intricate system of reservoirs, for separating and preparing the food for the operation of the digesting stomach or true stomach. The human stomach is simple com- pared with the stomach of the herbivorous animals, but more curiously guarded to retain and fully to operate upon the food than the carnivorous stomach. Since I am entering on this subject I may add, that the length and in- tricacies of the intestines hold always a relation to the form of the sto- mach. If the food of an animal be of difficult digestion, and offer little nutriment, as it requires a complicated stomach to prepare their food, so will it require to be carried through intestines long and intricate, that op- portunity may be given for the whole nutritious matter to be absorbed out of the mass, and turned to use. But if, on the contrary, the food be rich in nutritious matter, the intestines will be shorter, more direct, and have less of that apparatus intended to delay the course of the contents. SEAT, FORM, DISPLACEMENT OF THE STOMACH. The stomach lies under the margin of the ribs of the left side, and chiefly in the left hypochondrium, but stretches into the epigastrium. Its greater extremity is on the left side, in contact with the diaphragm ; to- wards the right, the shelving edge of the left lobe of the liver is betwixt it and the diaphragm. On the lower part it is separated by the mesoco- lon and arch of the colon, from the small intestines ; and to the greater extremity the spleen is attached by vessels and by the loose intertexture of the omentum. The stomach may be said to be a conical sac ; the ex- tremities of which being made to approach each other, gives it the curve of a hunter’s horn, and this is the reason that the anatomist describes these parts ; the superior or cardiac orifice into which the oesophagus expands ; the lower or pyloric orifice, which leads into the duodenum: the lesser curvature and greater curvature of the stomach ; and the great bag or extremity towards the left where the spleen is attached, and the inferior or lesser extremity extending to the right side, and in a direction obliquely downwards. OF THE STOMACH. 315 The lesser curvature of the stomach extends from betwixt the two ori- fices ; including in its embrace the spine, the aorta, and the small central lobe of the liver, while the lesser omentum is attached to it.—The great- er curvator of the stomach is the outline of its distended belly, which rises above the arch of the colon, when the stomach is full, and is mark- ed by the course of the gastro-epiploic vessels. In the foetus the stomach lies more perpendicular than in the adult. In the adult when the stomach is distended the lower orifice is nearly on a level with the upper one ; but when the stomach is empty, and sub- sides, it falls considerably lower; so that whilst the stomach lies across the abdomen it is also tending obliquely downwards. The ensiform car- tilage will be found to present to the middle of the stomach; and the lower orifice, when in its natural situation, is opposite to the fossa umbi- licalis of the liver; the upper orifice is kept constantly in one place from the stricter connexion of the oesophagus with the diaphragm. Both orifices of the stomach present backward, but more especially the upper one, the lower one being pointed backward and downward. By the distension of the stomach the great arch is extended, the ori- fices are directed more backward and towards each other, and the greater extremity draws upon the oesophagus. By these means I conceive that there is sometimes produced a difficulty of the stomach discharging its contents when greatly distended, the orifices being in some measure turned both from the oesophagus and duodenum. The stomach being liable to varieties in its degree of distention, the natural relation of parts must be consequently altered. It ought to be particularly recollected, that in the living body the stomach is supported and bound up by the intestines ; so that the great curve is forwards ; and the broad anterior surface which the stomach presents in the dead body is turned directly upward, and the inferior downward.* By the collapsing of the stomach and the consequent falling down of the liver, some have explained the sensation of hunger, conceiving that the unea- * Thus the gastro-epiploic artery presents directly forward, and has been wounded by a stab here. 316 OF THE STOMACH. sy sensation proceeds from the liver being allowed to hang upon the broad ligament.* From the great simplicity of mechanical expla- nation, physicians have eagerly indulged in them, but it will in general be found, that when they are applied to the explanation of the phenome- na of a living body they lead to erroneous notions. in describing the human stomach as a conical bag, curved, I speak of what we shall commonly observe in the dead body. But sometimes I have found the stomach divided into two sacs, and more frequently have I seen a contraction in the centre of the stomach, from muscular action. The two last subjects for public demonstration, I found divided into two sacs. Riolan demonstrated this in 1642. Schneider and Dionis have given us such instances, and Morgagni has expressed an opinion that these were not divisions, but only contractions of the stomach. In fact, we meet with a permanent, as well as an occasional form of the human stomach, in which there is a division into two sacs. Sir Everard Home is of opinion that the cardiac and pyloric portions, thus divided, perform distinct offices. OF THE COATS OF THE STOMACH. The coats or membranes forming the stomach are the outer, the mus- cular, the nervous or vascular, the villous, and the three cellular coats. For some of these subdivisions, however, I see no use, nor are they au- thorized by the natural appearance of the coats of the stomach. When there is a distinction in texture, structure, of function, and where these laminae can be separated, we shall consider them as coats ; but a mere intermediate tissue of vessels, or the connecting cellular membrane, are improperly considered as distinct tunics. First coat.—From what has been already said of the peritoneum, it will readily be allowed that the outer coat of the stomach is formed by the peritoneum, a coat common to all the intestines. Were this not sufficiently evident in itself, it might be ascertained by dissecting the peri- toneum from the cardiac orifice of the stomach, where it will be found reflected-from the diaphragm. This coat is firm, simple in its texture. * Winslow. OF THE STOMACH. 317 having no apparent fibrous texture, and smooth on its outer surface, with many minute vessels. Under the peritonaeal coat is the first cellular coat, being in fact a short cellular tissue betwixt the peritonaeal coat and the muscular coat. Muscular coat.—The muscular coat of the stomach consists of se- veral laminae of fibres; less distinct, however, than those of the oeso- phagus, or, in other words, more loosely and irregularly distributed.* These muscular fibres of the stomach do not run in an uninterrupted course, but split, rejoin, and form a kind of retiform texture, through which the coats beneath are at intervals discernible. This structure would appear to bestow a greater power of contraction on the stomach. The strong longitudinal fibres which are seen upon the oesophagus form the outer stratum of the muscular coat of the stomach, and they extend from the oesophagus and cardiac orifice in a stellated form along the up- per curvature, and downward upon the great end or sacculus ventriculi. Then we have to observe a set of circular fibres, which, forming rings upon the great end, extend over all the stomach, like the circular fibres of the arteries. These fibres do not each encircle the stomach en- tirely ; but while their general direction is circular, they are so in- terwoven that no one fasciculus can be followed to a great extent. These are called the transverse fibres or stratum , while the deepest layer consists of the continued circular fibres of the oesophagus. These fibres are strong upon the cardiac orifice, and may be presumed to form a kind of sphincter ; but they diminish as they are remote from the superior orifice. The lower or pyloric orifice of the stomach, how- ever, is more carefully guarded by muscular fibres ; having in the duplica- ture of the inner coats a distinct circular ring of muscular fibres. The cellular tissue, being intermingled with the muscular fibres, con- nects and strengthens them, and gives the appearance of little white lines interwoven with the muscular fibres, and which some have described as small tendons.! There is also to be observed a broad ligamentous band on the two flat surfaces of the stomach towards the pylorus. They are like the bands of the colon, but not nearly so strong or evident. They are formed by the denser nature of the cellular tissue, and more intimate union betwixt the first and second coats. * The most genera! opinion is, that there are three layers of fibres in the stomach. Some describe an external longitudinal series ; a middle transverse stratum; and again the inter- nal fibres running longitudinally. See Galeati Acad, de Bologne. + See Winslow, sect. viii. p. 57. 318 OF THE STOMACH. OF THE PYLORUS.* The pyloric orifice of the stomach deserves more particular attention. When the stomach is distended and dried, and a section is made of its lower orifice, a delicate membrane appears hung across, and which is perforated with a circular opening. When the stomach is hardened in spirits, and a section of this part made, the pylorus is seen to be a dupli- cature or process of the inner coats of the stomach ; and by more par- ticular dissection, it will be found that this circular fold or membrane, is formed by the drawing of a more powerful fasciculus of circular fibres which guard this lower orifice.! OF THE ACTION OF THE MUSCULAR COAT. Upon considering the weakness of the muscular fibres of the stomach, and the membranous nature of the whole coats, it appears that the ge- neral action of the stomach is slow, regular, and by no means a forcible contraction ; not an apparatus for triturating the food, but merely giving motion to its contents. But regarding the extreme sensibility ot the sto- mach, and the gradual and regular succession of action, much will be found that is worthy of attention-! It would seem that the morsel is sent down into the oesophagus by a succession of actions, preceded by a per- fect relaxation ; and that when the food arrives at the superior orifice of the stomach, by the same relaxation preceding the contraction, the mus- cular fibres of the upper part of the stomach yield and receive the food compressed by the oesophagus. Attending to the form of the stomach, we see a provision for the reception of the food into the great sacculated fundus on the left extremity. And here we shall find that there is a great- er profusion of vessels for the secretion of the juices of the stomach, and a set of muscular fibres, probably relaxing and yielding to receivti the food, and excited to action only when the process of digestion has been in part or entirely accomplished. Often, on dissection, I see the sac or left extremity of the stomach distended, when towards the right extremity it is like the intestine in form. We have proof, that when the * Quasi Janua custos. j See H. P. Leveling de Pyloro. Sandefort Thesaurus, vol. iii. ! See Haller’s Experiments. Opera Minora, Ventriculi Motus peristalticus. OP THE STOMACH. 319 lboil has remained the usual time in the great sac of the stomach, and comes in succession to be presented at the lower orifice, if the stomach be healthy, and the change upon the food perfect, the lower orifice is re- laxed, and yields to the contraction of the muscular fibres of the sto- mach, and the contents of the stomach are passed into the duodenum : but if the food has been of an indigestible nature, it is rejected. The pyloric fibres refuse the necessary relaxation, and by the unnatural ex- citement, an antiperistaltic motion is produced, and the matter is again thrown into the great end of the stomach, or rejected by vomiting.* There is in the natural action of the stomach a stimulus, followed by a regular succession of motion in its fibres, conveying the contents from the upper to the lower orifice of the stomach. Of this excitement and action we are not conscious ; but when the action is disordered by an un- usual excitement, the lower orifice is not unlocked, the action becomes violent (the reverse of what naturally takes place,) and pain or uneasy feelings are produced. Upon this principle may be explained the nausea and vomiting which take place at certain times after eating, when balls or concretions are lodged in the stomach. While the food lies in the greater extremity, or in the body of the stomach, and the ball or concre- tion with it, there is no great excitement; but when it has suffered the necessary change, and is approaching to the pyloric orifice, this part, be- ing as it were a guard upon the intestines, is suddenly excited, vomiting is produced, and the ball is thrown into its old place in the sacculus or great end. An attempt has been made to distinguish the affections of the sto- mach according as they proceed from the vitiated secretion, or the dis- ordered muscular action. For example, it has been said, if there is pain when the stomach is empty, then it is owing to the secretions of the stomach hurting the coat; if there be pain when the stomach is full, or at regular periods after taking food, then is it proceeding from dis- ordered muscular action. This is settling the whole difficulty on too easy terms. The functions of the muscular fibre and of the secreting vessels are not thus distinct. The motion of the stomach itself and the secretions into it are actions conducing to a general result, and na- ture has secured the end by combining the means ; and vitiated fluids poured into the stomach, even by its own vessels, are attended with ir- regular spasmodic pains. This great sensibility, producing effects almost like intelligence, is apparent in the more common disorders of the stomach. We shall find the meteorismus ventriculi (the great distention of the stomach by fla- tus) existing for weeks, and yet the food passing in regular course through its orifices. We shall find very frequently food of difficult di- gestion lying in the stomach and oppressing it for days, while food more recently received may have undergone the natural changes, and have, at all events, passed through the pylorus into the duodenum. Owing to the same slow and successive actiorrof the stomach, it of- ten happens that ulceration and scirrhous pylorus, or other obstruction of the lower orifice of the stomach, is attended with pain, nausea and vomiting only at stated intervals after taking food; i. e. at the time in * It would seem that the upper orifice of the stomach has a power of contraction on unu- S'.ia! stimuli being applied, tlaller loc. fit. Exp. ccciii. 320 OF THE STOMACH. which the food should be sent into the intestines in the natural course of action. The muscular fibres of the stomach are excited by stimuli, applied not to their substance, but to the contiguous coats ; and betwixt the de- licate surface of the inner coat and the muscular fibres there is the strictest sympathy and connexion. The same connexion holds in a less intimate degree betwixt the outer coat and the muscular fibres; for when a part on the surface of the stomach of a living animal is touch- ed with acid or stimulating fluids, the part contracts.* The stomach is considered as less irritable than the intestines, because it is alleged that a stronger dose of a medicine is required to prove emetic than to act as ajiurgative: but we ought to consider that the action thus excited in the intestines is merely an acceleration of their secretions ; while vomit- ing is the interruption of the usual action, requiring such a violent ex- citement as to invert the natural action. But there is something more than this ; as the function of the sto- mach differs from that of the intestines, so may the quickness of their action. Thus in the stomach a gradual change is to be produced upon the food, requiring time and a slow degree of motion; but in the in- testines there is a greater agitation of their contents, and a quicker ac- tion of their coats, to bring the fluids into more general contact with the absorbing surface, and to give greater activity probably to the ab- sorption by the lacteals. I am inclined to think that the stomach is the most irritable part of the body, and susceptible of the most minute dis- tinctions in the nature of the stimuli applied to it. The phenomena of the living animal, and experiments in those re- cently killed, sufficiently prove the contractile powers of the two ori- fices. Experiments have been made which show the powers both of the cardiac and of the pyloric orifices in retaining the contents of the stomach after the oesophagus and duodenum have been cut across. The stomach of a rabbit has been squeezed in the hand after cutting the duodenum, without any of its contents being permitted to escape and in similar experiments, the finger being introduced into the lower orifice of the stomach of an animal yet warm, the fibres of the pylo- rus were found to contract strongly upon it. Upon forcibly compres- sing the stomach, the food will be made to pass into the oesophagus much more readily than into the duodenum ; which is another proof iiow necessary the natural series of action is to the relaxation of the pylorus. Rumination.—As it is found that some individuals ruminate, and that even such a habit may be acquired, it must be right to say a few words on this subject.—In the ruminating quadrupeds the food passes into the paunch. The paunch consists of a larger and smaller cavity, and from the lesser cavity the food is regurgitated into the mouth, to suffer mastication. When a second time swallowed, it is let into the third cavity, and from the third it passes into the fourth cavity, and from that into the intestines. The human stomach cannot perform an * “ In ea sede qui tangitur, contrahitur, sulcusque profundus nascilur, et rug®; cibusquo aliquando propellitur ut A sede; contracta fugiat. Minds tamcn quam inlestina. ventriculus irritabilisest: hinc emetica fortiora necesse est purgantibus.”—Haller, f See a paper 3d. vol. of Sandifort, Thes. An excellent plate of the Pylorus, given with this Dissertation,—Morgagni Adversar. HI, IV. de Ventriculi Struct. OF THE S'fOMACH. 321 operation so complicated as this. But the different directions which the food takes in the stomach of the ruminant animals, in consequence of the motions of the muscular fibres closing or adjusting the slits of the (Esophagus, or the openings of the several bags, proves to us that many silent and curious operations may be going forward even in the human stomach. Something we might suppose would be learned from the feelings of such men as chew the cud ; but it happens that the best recorded instance occurred in one, a mere brute in intellect.* Here the morsel was brought up from the stomach by a very slight effort; it was chewed and swallowed; after a pause another morsel was brought up, and underwent the same process, and was swallowed. He ate his food voraciously and without chewing. There is no history of dissec- tion on record except on the authority of Fabricius ab Aquapendente, who found the oesophagus remarkably muscular. Op vomiting.—When there is an unusual or unnatural irritation on the stomach, or when it is violently stimulated or opposed in its natural course of action, the motion becomes inverted; and drawing by sympa- thy other muscles to its aid, the contents of the stomach are evacuated by vomiting. Thus where the food takes changes inconsistent with healthy digestion; or when solid matters lodge in the stomach ; or when secretions of the duodenum pass into the stomach, or unusual actions are propagated backwards upon the stomach from the upper portion of the canal; or when emetics are taken, which are unusual stimuli; or when there is inflammation in the stomach, which, from giving greater sensibility, produces the same effect with more violent stimuli; or when the coats are corroded or ulcerated ;—vomiting is produced. That vo- miting may be produced by the inverted motion of the stomach and (Eso- phagus alone, is apparent from experiments upon living animals, where the abdominal muscles are laid open, and from cases in which the stomach has lain in the thorax, and yet been excited to active vomiting.f Again, it is equally evident that, when the stomach is excited to vomiting, there is consent of the abdominal muscles, by which they are brought into vio- lent and spasmodic action ; not alternating in their action, as in the motion of respiration, but acting together, so as greatly to assist in compressing the stomach : but at the same time, the action of these muscles, how- ever forcible their contraction, cannot alone cause vomiting; nor has the action of these same muscles any tendency to produce such an effect on other occasions, in which the utmost contraction of the diaphragm and abdominal muscles is required to the compression of the viscera. Many have conceived that vomiting is entirely the effect of the action of the abdominal muscles and diaphragm. Such, for example, has been the opinion not only of J. Hunter, but of Duverney, and of M. Chirac in Hist, de PAcad. des Sciences, 1700. M. Littre opposed this notion, and contended before the Academy, that the contraction of the diaphragm was the principal cause of vomiting. M. Lieutaud in 1752 supported the idea that vomiting is the effect of the action of the stomach. He found, upon dissection, in a patient whose stomach had resisted every kind of emetic, that it was greatly distended and become insensible; and concluded that the want of action in the stomach, and consequent loss of * By Sir Everard Home. 7 See Wepfer de Cicuta Aquatica, p. 68—Sausage’s Vonlitus. 322 OP THE STOMACH. the power of vomiting, was a strong proof of the action being the effect of the contraction of the stomach only. There are other more curious instances of disease of the stomach preventing the muscular con- traction in any violent degree, and consequently the absence of the usu- al symptom of vomiting:—an instance of this kind will be seen in Dr. Stark’s work. In my Museum 1 have a preparation of a stomach, in which the walls had become so thick that they could no longer suffer con- traction by the muscular fibres; the consequence of which was that, although the inner coat of the stomach was in a raw and ulcerated state, there was no active vomiting. There is a very curious experiment by M. Magendie which has much puzzled men’s minds. He cut out the stomach of a large dog, and sub- stituted in its place a bladder which he fastened to the oesophagus, and having excited vomiting, by pouring emetic solution into the veins, the contents of this bladder were discharged as from the natural stomach. The. conclusion has been too hastily formed, that the stomach has there- fore nothing to do with the action of vomiting. But it ought to be recol- lected, that the bladder represents a relaxed stomach, whereas the stomach is muscular and active, and capable of resisting the action of the abdominal muscles and diaphragm, unless there be a consent of the action of the stomach and the action of the muscles of respiration. Thus if we could suppose that a man had a distended bladder for a stomach, whilst he ex- erted himself forcibly and retained his breath the contents would be dis- charged. So would they if he lay with his belly over a yard-arm. But no such discharge takes place from the natural body, because the upper orifice of the stomach resists ! This resistance does not take place in vomiting ; and therefore, I say, the stomach has to do with vomiting, in spite of all the cruelties which have been committed. The lower ori- fice is contracted, the coats of the stomach are contracted, and the upper orifice is relaxed in the act of vomiting : while the power of ejecting the contents is very principally owing to the violent throes and contractions of the abdominal muscles and diaphragm. The singultus is the partial exertion of the sympathy betwixt the upper orifice of the stomach and tho diaphragm, by which a kind of weak spas- modic action is excited in it, but without a concomitant inverted action in the stomach and oesophagus. It is a convulsive and sonorous inspira- tion, owing to an irritation of the upper orifice of the stomach and oeso- phagus, but not exactly of that kind which causes inversion of the natural actions of the stomach. Thus we have the singultus from gluttonous distention of the stomach, from some medicines and poisons, from some crude aliment, or even from some foreign body sticking low in the (Eso- phagus, or from inflammation. The borborigmi and rumination seem to be gentler inverted actions of the upper orifice of the stomach and oeso- phagus, unassisted by any great degree of compression of the stomach by the abdominal muscles and diaphragm. The full action of vomiting is preceded by inspiration, which is a pro- vision against the violent excitement of the glottis, and the danger of suffocation from the acrid matter of the stomach entering the wind-pipe; for by this means the expiration and convulsive cough accompanying or immediately following the aytion of vomiting, frees the larynx from the ejected matter of the stomach. But the action of the diaphragm is far- ther useful by acting upon the mediastinum, which embraces the (Eso- phagus, and no doubt supports it in this violent action. OF THE STOMACH. 323 The subject is very interesting, but I must enlarge no more upon it here. NERVOUS OR VASCULAR COAT OF THE STOMACH. What Haller calls the nervous coat, is the cellular structure in which the vessels and nerves of the stomach ramify and divide into that de- gree of minuteness which prepares them for passing into the innermost or villous coat It may with equal propriety be called the nervous, the vascular, or the great cellular coat.* Taking it as the third distinct coat of the stomach, it is connected with the muscular coat by the se- cond cellular coat, and with the villous coat by the third cellular coat. Strictly, however, it is the same cellular membrane, taking here a looser texture to allow of the iree interchange and ramification of vessels. When macerated, it swells and becomes like fine cotton, but has firmer and aponeurotic-like filaments intersecting it; it can be blown up so as to demonstrate its cellular structure.! It is in this coat that anatomists have found small glandular bodies lodged, especially towards the extre- mities or orifices of the stomach. Villous coat.J—This is the inner coat, in which the vessels are finally distributed aud organized to their particular end. It is of greater extent than the outer coats of the stomach; which necessarily throws it into folds or plicae. These folds take, in different animals, a variety of forms : but they are simple in man : from the oesophagus they are continued in a stellated form upon the orifice, but form no valve here. In the body of the stomach they are more irregular, sometimes retiform, and sometimes they form circles or squares, but they have generally a tendency to the longitudinal direction. Inthe pyloric orifice the villous coat forms a ring, called the valve of the pylorus, which, however, has no resemblance to the •valve in its form or action. This ring is not formed by the inner coat of the stomach alone, but by the inner stratum of fibres of the muscular coat, the vascular and cellular coats, and the inner or villous coat. The effect of all these coats, reflected inward at the lower orifice, is to form a tumid and pretty thick ring, which appears like a perforated circular membrane when the stomach has been inflated and dried; but in neither state is its direction oblique so as to act as a valve. It seems capable of resisting the egress of the food from the stomach, or the return of the matter from the duodenum, merely by the action of the circular fibres which are included in it. In the inner surface of the stomach of those dying suddenly, and who were previously in health, plicae, may be observed more or less distinct according to the state of contraction of the muscular coat of the sto- mach. But in those dying of disease and with relaxed stomach, no folds of the inner coat of the stomach are to be seen. The reason of this the reader should comprehend. The matters contained in the sto- mach after death, being no longer controuled, enter into chymieal decom- position, which extricates flatus, and the gas distends the stomach. This distention removes the plicae of the inner coat, and indeed changes the whole form of the stomach. * To call it cellular coat, however, would be to confound it with the three cellular coats generally enumerated by authors, t Winslow, sect. viii. p. 64. | For a highly interesting description of the appearances of the mucous membrane of the stomach and bowels, in health and disease, see Horner’s valuable communication published in the 1st No. of the American Journal of the Medical Sciences. J. D. G. 324 OF THE STOMACH. The glands of the human stomach are very small, but in great num- bers around the termination of the oesophagus. In this description I am looking to the plate of Sir Everard Home. Brunner described the glands of the stomach as seated on the curvatures. Glands are dis- tinctly to be seen in the stomach of birds and many quadrupeds, and in fishes and serpents * But it is to Sir Everard Home that we owe the most careful observations on this subject. His lectures on this subject delivered in the College of Surgeons had that grave character of investi- gation befitting the place, while they possessed an interest beyond ex- ample. | Gastric fluid.—There is secreted into the stomach a fluid, which is the chief agent in digestion. The most common opinion is that it flows from the extreme arteries of the villous coat in general. When pure, it is a pellucid, mucilaginous liquor, a little salt and brackish to the taste, like most other secretions, and having, in a remarkable degree, the power of retarding putrefaction and dissolving the food. It acts on those substances which are nutritious to the animal, and which are pecu- liarly adapted to its habits. It seems to be a peculiarity in the human stomach, that it has a great- er capacity for digesting a variety of animal and vegetable bodies. But perhaps the natural power of digesting is diminished as the stomach gains the power of dissolving a variety of substances. In other creatures, a sudden change of food excites the stomach to reject it, and the powers of the stomach are found incapable of acting duly on the aliment, though time so far accommodates the gastric fluid to the ingesta, that the diges- tion becomes perfect. Mr. Hunter speaks of the power of cattle eating and digesting their secundines. J I have seen the membranes coiled in the bowels of a cow ; but I too hastily concluded this to be the cause of death. I am corrected by the authority of Dr. Jenner and Dr. Adams. The fact is sufficiently ascertained, that the nature of the digestive pro- cess may be so far altered that graminivorous animals may be made to eat flesh, and carnivorous animals brought to live upon vegetables. This throws us back from the simple idea which we should be apt to en- tertain of the nature of the change produced by digestion, viz. that it is chymical. For we see that the nature of the solvent thrown out from the stomach, and its chymical properties, may be changed by an altera- tion in the action of the coats of the stomach. Thus we are baffled in our inquiries, and brought back to the consideration of the living proper- ty, which can so accommodate itself to the nature of the aliment. The gastric fluid has been collected from the stomachs of animals af- ter death, by sponges which the animal has been made to swallow, or which have been thrust down into its stomach, incased in perforated tubes. And, lastly, it has been obtained by exciting the animal to vomit- ing, when the stomach was empty ; for the secretions of the stomach are then poured out unmixed with food.§ Although by these means a fluid may be obtained which may properly be called the succus gastri- cus, yet it must contain a mixture of the saliva, and secretions from the glands of the oesophagus and pharynx, with the glandular secretions of the stomach, and the general vascular secretion from the surface of the * Haller. f These Lectures are now published. | See Observations on Digestion. § By Spallanzani. OF THE STOMACH. 325 stomach. It is a fluid, then, upon which the chymist can operate with no hope of a successful or uniform result. And, indeed, chymistry seems no farther to assist us in forming an accurate conception of the changes induced upon the fluids in the alimentary canal, than that the more perfect, but still very deficient, experience of the modern chymist successfully combats the speculations of the chymists of former ages. For example, it was formerly supposed that digestion was a fermentation, and that this fermentation was communicated and propagated by the gas- tric juice. It is now found that the gastric juice has properties the re- verse of this ; that it prevents the food from taking an acid or putrefac- tive fermentation; that it acts by corroding and dissolving the bodies received into the stomach; and that it is itself at the same time convert- ed into a new fluid, distinct in its properties.* It is almost superfluous to observe,| that the gastric juice has no power of acting upon the coats of the stomach during life ; whether this be owing to the property, in the living fibre, of resistance to the action of the fluid, or that there is a se- cretion bedewing the surface, which prevents the action, it is not easy to say; but more probably it is owing to the resistance to its action in- herent in a living part. J Mr. Hunter supposed it necessary that the animal should be in health, immediately preceding death, in order that the secretion of the gastric juico may be natural and capable of dissolving the dead sto- mach : but I have found the stomach of children, who have died after a long illness, digested by the secretion of the stomach. See Examples in my Collection. Of digestion.—By trituration and mastication, and the union of the saliva in the mouth, the food is prepared for the more ready action of the stomach upon it. In the mouth, however, no farther change is induced upon it than the division of its parts. But in the stomach, the first of those changes (probably the most material one) is performed, which by a succession of actions fits the nutritious matter for being re- ceived into the circulation of the fluids of the living body, and for be- coming a component part of the animal. For now the gastric juice, acting on this fluid mass, quickly dissolves the digestible part, and en- tering into union with it, produces a new fluid, which has been called chyme, a thick or viscid and turbid fluid. The mass changes its sensi- ble and chymical properties ; and when it has suffered the full action * The most curious fact is that property of the coats of the stomach, or of the fluids lodging in the coats of the stomach, by which milk and the serum of the blood are coagulated. It has been found that a piece of the stomach will coagulate six or seven thousand times its own weight of milk. This action seems a necessary preparation for digestion, which shews us that the most perfect and simply nutritious fluid is yet improper, without undergoing a change, to be received into the system of vessels. For example ; milk and the white of eggs are first coagulated, and then pass through the process of digestion. See J. Hunter, Animal Economy, Observations on Digestion. f I do think it a very self-evident fact, notwithstanding Dr. Adam’s taunting manner of quoting these words. See that very interesting work on Morbid Poisons, preface, xxxvi. | Mr. Hunter is one ureat authority on this subject, &c. See also Morgagni Adversar. III. A. XXIV. Dr. Adams on Morbid Poisons, preface; and Mr. A. Burns’s (of Glasgow,) Paper. Edin. Journal, Ap. 1810. Amongst other curious facts stated by Mr. Burns is this, that he has found all the length of the alimentary canal dissolved into a pulpy glutinous mass. I may say that connected with the discussion, there may enter a question as to what is the cause of a ten- derness sometimes to be observed in all the membranes of the body. I have examined the vis- cera of a negro, where the intestines were particularly tender, but the pericardium and valves the heart more remarkably so still. 326 OF THE STOMACH. of the stomach, by the gradual and successive muscular action of the stomach, it is sent into the duodenum. The food is converted into chyme by the operation of the gastric fluid, by an operation peculiarly animal, a process of life. And the conversion of the food into a new substance is unattended by any chymical change, strictly speaking, if by chymistry we understand the mutual influence of dead matters in forming compounds, or separating and extricating the constituent parts. Animal or vegetable matter in the heat and moisture of the stomach would quickly fall into the fermentations; but the living properties of the stomach prevent this. I speak of the stomach in health; when weak, then the symptom announcing the diminished power is the ex- trication of gas, or the formation of acids, with oppression and uneasy sensations. The contents of the stomach consist of air, partly swal- lowed, partly extricated of the watery secretions of the coats, and of chyme. The stomach being stimulated by fulness, by flatus, and more still by the peculiar irritation of the food prepared by digestion, the muscular coat is brought into action, and the contents of the stomach delivered into the duodenum. A case is on record which finely illustrates the function of the sto- mach. A woman was presented in the clinical ward of La Charity, to Corvisart, who had a fistulous opening in the left side of the epigastric region, which communicated with the stomach, and through which part of the villous coat of the stomach could be seen, of a vermillion co- lour, and covered with mucus, and having certain plicae. The vermicular undulations of these rugae of the inner coat of the stomach could be observed. Three or four hours after this woman took food, she felt an irresistible desire to raise the dressings from the fistula. Then flatus was forcibly discharged with the food, which was reduced into a greyish pulp, having neither acid nor alkaline properties. After emptying the stomach, which she washed by sending through it a pint of infusion of camomile, she found perfect ease. In the morning a small quantity of fluid like saliva, ropy and clear, was found at the ori- fice. This was probably the gastric fluid; it possessed neither acid nor alkaline qualities. On her death the hole in the stomach was found eight fingers’ breadth from the left extremity, or one third of the whole length of the stomach distant from the pyloric orifice. From this case we learn, 1. that the stomach is subject to a gentle vermicular motion ; 2. that the food received into the stomach is retain- ed three or four hours in the great left extremity of the stomach ; 3. that when it has undergone the process of digestion there, it is convey- ed, with rather a sudden impulse, into the pyloric extremity of the sto- mach ; 4. that the chyme thus formed, has undergone an animal pro- cess, becoming neither acid nor alkaline. Contemplating this illustration of the function of the stomach as a digesting organ, with the according action of its muscular fibres above described, a solid ground-work is af- forded for the pathology of this organ. Hunger and thirst. —We are solicited to take food by the uneasy sensation of hunger, and by the anticipation of the voluptuous sating of the appetite, and by the pleasures of the palate. Hunger is considered as the effect of the attrition of the sensible coats of the stomach upon each other by the peristaltic motion of the stomach and compression of OF THE STOMACH. 327 the viscera. This is too mechanical an explanation. It' the sensation proceeded merely from such attrition of the coats of the stomach, food received into the stomach would be more likely to aggravate than to as- suage the gnawing of hunger : to excite the action of the stomach would be to excite the appetite ; and an irritable stomach would be at- tended with a voracious desire of food. Something more than mere emptiness is required to produce hunger. By some, hunger is supposed to proceed from the action of the gastric fluid on the coats of the sto- mach ; by others it is attributed to the dragging of the liver, now no longer supported by a full stomach. Hunger is like thirst, a sense placed as a guard calling for what is necessary to the system, and depending on the general state of the body. Morbid craving may proceed from many causes; a tape worm has occasioned bulimia, and spirits and high sea- soning excite the appetite even when the stomach is full, but natural hun- ger has reference to the state of the general system. Thirst is a sensation seated in the tongue, fauces, oesophagus, and stomach. It depends on the state of the secretions which bedew these parts, and arises either from a deficiency of secretion or from an unusual- ly acrid state of it. It would appear to be placed as a monitor calling for the dilution of the fluids by drink, when they have been exhausted by the fatigue of the body and by perspiration, or when the contents of the stomach require to be made more fluid—the more easily to suffer the ne- cessary changes of digestion. The change on the secretion of the tongue and fauces from disorder of the stomach, is not, I imagine, a consequence of an influence commu- nicated along the continuous surface. It has its origin in this natural con- stitution of the parts ; the connexion which nature has established be- twixt the stomach and tongue, betwixt the appetite and the necessi- ties of the system. The state of the tongue, the loose or viscid secre- tions of the throat and fauces, even the secretion of the saliva, and the ir- ritability of the larynx, are all influenced by the state of the stomach. The more permanent and demonstrable effects on the tongue are princi- pally attended to ; which perhaps is the reason that we only know by this that the stomach is disordered, not how it is affected. The cardiac orifice is the chief seat of all the sensations of the sto- mach, both natural and unusual, as it is the most sensible part of the sto- mach. Indeed we might presume this much by turning to the descrip- tion and plates of the nerves ; for we shall find that this upper part of the stomach is provided in a peculiar manner with nerves, the branches of the par vagum. The sympathy of the stomach with the rest of the intestinal canal, the connexion of the head and stomach in their affections, the effect of the disorder of the stomach on the action of the vascular system and of the skin, and the strict consent and dependence betwixt the stomach and dia- phragm and lungs, and in a particular manner with the womb, testicle, &c.—and again, the connexion of the stomach with the animal econo- my, as a whole,—must not escape the attention of the student of medi- cine. 328 OF THE INTESTINES. OF THE INTESTINES. That portion of the alimentary canal which extends from the lower orifice of the stomach to the anus is called the intestines. It is divided into the small intestines, and the great intestines ; the small intestines are subdivided into the duodenum, jejunum, and ileon. The great intes- tines are subdivided into caecum, colon, and rectum. The marked difference of function is betwixt the small intestines and the great intestines. But betwixt the form and capacity of the stomach, the form and capacity of the small intestines, and the form and capacity of the great intestines, there is always a certain relation preserved in the different classes of animals. The small intestines are estimated to be in length 26 feet, or from four to five times the length of the body, and the great intestines one length of the body, or about six feet. The younger the subject, the longer the intestinal canal. In an infant they were found to be upwards of eleven times the length of the body. In a child of one foot nine inches they were upwards of eight times the length of the body. In a child three feet one inch they were found to be seven times and one half the length of the body.* Is this difference to be accounted for by supposing that a different food is applicable to the several ages, or is it an increase of absorbing surface accommodated to the necessities of the body while growing! In the carnivorous animal the whole of the canal is shorter, being about five times the length of the animal: for example, in the lion. In the herbivorous animals the intestines are longer and more complicated, affording means for the retention or the delay of the descent of the food. Of the small intestines, the first portion is that division extending from the orifice of the stomach to the part where it is encompassed by the mesocolon. It is called the duodenum. * Sir Everard Home’s Lectures OF THE INTESTINES. 329 DESCRIPTION OF THE FIGURE. A. The stomach, b b. The duodenum, c. The gall bladder, d. The pancreas and its duct. e. The ductus hepaticus. p. Ductus cysticus. g. The ductus com- munis coledochus, joined near where it pierces the gut by the pancreatic duct. THE DUODENUM Stands distinguished from the general tract of the small intestines by its shape, connexions, and situation. It has been called duodenum, because it was usual to measure its extent by the breadth of twelve fingers. It is greatly larger than any other part of the small intestines ; irregular and sacculated; more fleshy ; and, although it has fewer pli- cae, it is more glandular and more vascular: but its greatest peculiari- ty, and that which must convince us of its importance in the animal economy, and of the necessity of attending to it in disease, is this, that it is the part which receives the biliary and pancreatic ducts, and in which a kind of second stage of digestion takes place. This intestine takes a course across the spine from the orifice of the stomach. First it goes in a direction downward ; then it passes upward till it touches the gall-bladder; then making a sudden turn it descends directly near to the right kidney, and it enters its vagina, or in other words, is in- volved in the mesocolon; and whilst so embraced, it takes a sweep to- wards the left side, obliquely across the spine, and a little downward; from this description it is obvious that it must be longer than the breadth of twelve fingers, and indeed I call duodenum all that portion of the intestine which is above the mesocolon, preferring a natural to an arbitrary boundary.* As in this extent, besides being tied down to the spine by the mesocolon, it has no mesentery, and the peritonaeum is reflected off from it, covering it imperfectly : of these reflections we have to remark the ligamentum duodeno-renale, and ligamentunu duo- deno-hepaticum already described. Although we shall presently treat of the coats of the small intestines in general, yet it may not be improper here to observe what are an- nounced as peculiarities in the coats of this first division. The first or peritoneal coat is imperfect, as must already be understood: for it does not invest the whole circumference of the gut; it ties it down more closely, or it merely contains it in its duplicature, while a greater pro- fusion of cellular membrane accompanies this than the other divisions of the intestines. The muscular coat is stronger than that of the je- junum and ileon ; the plies formed by the inner coats, smaller than those of the other part of the small intestine, and having more of a glandular structure. At the lower part of the first incurvation of the duodenum, the inner coat forms a particular process like to those which are called valvulae conniventes ; and in this will be discovered the open- ing of the biliary duct, within which also the ductus pancreaticus gene- rally opens. It is not without some reason that anatomists have considered the * Rusych calls it “ Intestinum digitale, vel intestinum rectum brevissimum.” Adversar. Anat. II. See a good description of the duodenum by M. Laurent Bonazzoli, in the Transactions of the Academy of Bologna. And the Dissert. L. Claussen. de duodeni situ et nexu. Sandi* fort. Thes. V. III. Monro, Medical Essays. 330 OK THE SMALL INTESTINES. duodenum as a second stomach, calling it ventriculus secundus, and sue* centuriatus ; for there is here performed a change upon the food, con- verting the chyme (as they have chosen to call it,) which is formed in the stomach, into perfect chyi.e. But to suppose that the chyme is perfected in the duodenum, is to suppose the biliary and pancreatic se- cretions necessary to the formation of chyle; a point which is not al- lowed ; for many suppose that the bile is merely a stimulus to the in- testines, holding a control over their motions ; others, that it is useful only in separating the chyle from the excrement; or again, that the bile is decomposed, part entering into the composition of the chyle, while the other goes into that of the faeces ; it seems to bestow upon them a power of stimulating the intestinal canal in a greater degree ; and as the chyle is formed occasionally without the presence of bile, we may be induced the more readily to allow that the bile does not, in the natu- ral actions and relations of the system, enter into the composition of the chyle. At all events, we see that it is the bile which is the peculiar stimulus of the intestinal canal, and that when interrupted in its dis- charge from the ducts, the motions of the belly are slow, and costive- ness is the consequence. There are poured into the duodenum, from the liver and pancreas, se- cretions which have an extensive effect on the system of the viscera ; and we must acknowledge that the derangement of these secretions ope- rate as a very frequent and powerful cause of uneasiness, and therefore that the duodenum must often be the seat of uneasy and distressing symptoms. We may observe that, from the course of the duodenum, pain in it should be felt under the seventh or eighth rib, passing deep, seeming to be in the seat of the gall-bladder, and stretching towards the right hypochondrium, and to the kidney, and again appearing as if on the loins. We may observe farther, that from the connexions of this portion of the intestine, and from the manner in which it is braced down by the mesocolon, spasm, when flatus is contained in it, will sometimes produce racking pains. Nay, farther, when the irregularities of digestion affect the duodenum, and spasm and indigestion follow ; the distention causes it to press upon the gall-bladder, and the pressure and excitement toge- ther cause an irregular, and often an immoderate flow of bile, which with the acrid state of the food, produces anxieties and increased pain, inverted motion, and vomiting. We must not forget, that the inverted action of the stomach draws quickly after it the inverted motion of the duodenum. It may be of con- sequence to attend to this in the operation of an emetic, for the stomach will sometimes appear to be discharging foul and bilious matter, which we naturally may suppose to have been lodged in it, but which has ac- tually flowed from the duodenum, or has even come recently from the ducts in consequence of the operation of the vomit.* From a defect in the natural degree of the stimulating power of the bile, it will accumulate in the duodenum, occasioning anxiety and loss of appetite, and even congestion of blood and a jaundiced skin ; we may certainly affirm that these at least are often connected. Such accumula- tion in the duodenum must be attended with a languid action of the * Indeed vomiting, in consequence of the concussion and compression it gives the whole contents of the abdomen, acting in a particular manner on the liver, affords most powerful means of operating upon the infarction and remora of the blood in the hepatic system. OF THE SMALL INTESTINES. 331 whole canal, and inactivity of the abdominal viscera, because the peri- staltic motion is begun here in the natural action of the intestines ; and if the proper stimulus be deficient here, so it will probably be in the whole system of the viscera. Hence the necessity of rousing the activity of the liver by evacuating the whole canal. I may further observe, that it has been the opinion of the most respec- table old physicians, those whose knowledge of diseases has been drawn from an acquaintance with anatomy, from the frequent inspect on of dead bodies, and the observation of the symptoms during life, that the study of the diseases connected with the duodenum is the most important which can occupy the attention of the medical enquirer.* OF THE JEJUNUM AND ILEON, OR INTESTINUM TENUE. The small intestines, under the name of jejunum and ileon, occupy the space in the middle and lower part of the abdomen, the great mass forming convolutions in the umbilical region. The canal of the small intestines is gradually and imperceptibly diminished in diameter as it is removed from the lower orifice of the stomach ; so that the diameter of the gut at the termination of the ileon in the caput coli is considerably smaller than where it forms the duodenum. This tract of the small in- testines performs the most important function of the chylopoetic viscera (if any can be said to be peculiarly important where the whole is so strictly connected); for here the food is moved slowly onward through a length of intestine four times the length of the body, and exposed to a surface amazingly extended by the pendulous and loose duplicatures of the inner coat. Here the fieces are gradually separated from the chyle, and the chyle adhering to the villi is absorbed and carried into the system of vessels. The jejunum \ is the upper portion of the small intestine. Its extent is two-fifths of the whole. Its convolutions are formed in the umbilical region. The ileon.—The lower portion lies in the epigastric and iliac regions, and surrounds the jejunum on the sides and lower part, and forms three- fifths of the whole extent of the intestine from the termination of the duo- denum at the mesocolon to the beginning of the colon. The coats of the ileon are thinner and paler, and more transparent than those of the jejunum, and the diameter of the gut is less; the valvular projections of the inner coat are less conspicuous, so that there is less of a fleshy feel- ing communicated to the touch ; and the mucous glands become more apparent in the lower portion, than in the upper vportion of the small in- testine. There is sometimes found a lusus in the lower part of the ileon before it passes into the colon ; a blind pouch or ccecum is, as it were, attached to the ileon, resembling the caput coli. I have found many instances of this, and several specimens may be seen in my Collection. Sometimes there is more than one csecum in the course of the ileon. J * See Sandifort, vol. iii. p. 288. See Hoffman, t So named from its being rrlore generally empty. | The appendices caecales of the ilieon have given birth to a curious question in the pathology of hernia. See “ Hernia ab ilii diverticulo.” Morgagni, Adv. Anat. III. “ Hernie par 1’appendice de l’ileon.” LKTTRE.Mem. de l’Acad. Royale des Sciences, an 1700: Ruysch, Palfin, &c. See cases of anus at the groin in the Museum. 332 OK the small intest.ines. the peritoneal coat and mesentery. The peritoneal coat of the small intestines is of the same nature with that of the stomach. It is thin, smooth, and possessing a certain de- gree of elasticity. On the surface it has a moisture exuding from its pores: and it firmly adheres to the muscular fibres beneath by a very dense cellular substance. Its transparency makes the muscular fibres, blood-vessels, and lymphatics easily distinguishable ; and when it is dissected or torn up, the longitudinal muscular fibres will be found in general attached to it. Its use is to give a smooth surface, and to strengthen the intestines, and in a great measure to limit the degree of their distention. The peritoneal coat of the intestine is continued and reflected off upon the vessels and nerves which take their course to the intestine ; or, what is the same thing, and indeed is the more common description, the two lamina of the peritoneum which form the mesentery after proceeding from the spine and including the vessels, nerves, and glands belonging to the tract of the intestine, invest the cylinder of the intestine under the name of peritoneal coat.* The mesentkry is composed of membranes, glands, fat, and the se- veral systems of vessels, arteries, veins, lacteals, and nerves. As in reality it is a production of the peritoneum, it may be said to arise from the mesocolon, or the mesocolon from the mesentery, reciprocally. But at present we may trace the mesentery from the root of the mesocolon— for the jejunum, emerging from under the embrace of the mesocolon, carries forward the peritoneum with it; and the laminas of the perito- neum, meeting behind the gut, include the vessels which pass to it and form the mesentery. This connexion of the small intestines by means of the prolongation of the peritoneum, while it allows a very conside- rable motion, preserves the convolutions in their relations, and prevents them from being twisted or involved. But it is by the walls of the ab- domen that the intestines, as well as the more solid viscera, are sup- ported ; for when the bowels escape by a wound, a portion of an intes- tine will hang down upon the thigh, unrestrained by the connexion with the mesentery. The mesentery begins at the last turn of the duodenum, or beginning of the jejunum. Its root runs obliquely from left to light across the spine. Here it has consequently no great extent ; but as it stretches to- ward the intestines, it spreads like a fan, so that its utmost margin is of very great extent, being attached to a portion of the canal, which we have estimated at four times the length of the body. In the middle of the small intestine, the mesentery has its greatest extent or breadth ; towards the beginning of the duodenum and the termination of the ileon, it is short- er, and more closely binds down the intestine. MUSCULAR COAT OF THE INTESTINES. The peritoneum is united to the muscular coat by a verv delicate and dense cellular membrane ; which in the enumeration of the coats we * See the Plan of the Peritoneum. OP THE SMALL INTESTINES, 333 must call the first cellular coat, but which really does not deserve the name of a distinct coat; for, as already said, the outer lamina of the muscular coat is raised with the peritoneum, and adheres intimately to it. The fibres of the muscular coat of the intestines are simpler than those of the stomach ; for here there are only two sets of fibres, the longitudinal and circular fibres. The outer stratum consists of the very minute and delicate longitudinal fibres. Indeed, when the system has been exhausted by a long and debilitating illness, with scarcely any excite- ment of the intestinal canal, these fibres are not to be observed. In a man who has been cut suddenly off by disease, or who has died a vio- lent death, they are more demonstralde ; and in diseases where there ha- been congestion and excited action in the intestines, they become of course still stronger and more discernible. The internal stratum of the muscular fibres is much stronger and more easily demonstrated. These fibres will be observed much stronger about the duodenum and upper part of the jejunum, but they become weaker and more pellucid towards the extremity of the ileon. Tracing any particular fibre of the circular stratum, it is found to form only a segment of a circle, a part of the cir- cuit of the intestine. It seems lost amongst neighbouring fibres or cel- lular connexions ; but still, taken together, the circular muscular fibres uniformly surround the whole gut.* To account for that action of the intestines which urges on the food, we may suppose a greater degree of irritability and activity to reside in the upper portion, where of course is commenced that action which is successively propagated downwards, carrying the faeces into the lower part of the canal. Some anatomists have ingeniously imagined that the inner stratum of fibres surrounds the intestine not in a circular direction, as was asserted by Willis, but obliquely and in a spiral course; from which followed a simple explanation of their effect, since the contraction of the fibre winding lower in the intestine, pursued the contents with a uniform, progressive constriction. Physiologists have made a distinction in the motion which they have observed in the intestines of living animals. The one they call the ver- micular. and the other the peristaltic motion. Upon looking into the bel- ly of a living animal, or of one newly killed, there may be observed a motion among the intestines, a drawing in of one part and a distention and elongation of a other part of the convolution. This motion has some resemblance to the creeping and undulating motion of a reptile, and has got the name of vermicular motion. On the other hand, the direct contraction of the gut by the constriction of the circular fibres is the pe- ristaltic motion. We must not however allow ourselves, from the loose expressions of authors, to imagine, that these circular and straight fibres act separately : on the contrary, excited by the same stimulus, they have a simultaneous motion to the effect of accomplishing the perfect con- traction of the gut and propulsion of its contents, j' While the stimulus is natural, the contractions of the muscular coat are in a regular succession from above downward, and, the lower part contracting before the upper is completely relaxed, the food must be * Morgagni Adversaria Anatomica III. Animadversio V. t Neither can I allow that the acting of the longitudinal fibres in one portion of an intes- tine dilates that which is below,otherwise than through the compression of food and flatus. 334 OF THE SMALL INTESTINES. urged downwards into the lower portion; the lower becomes relaxed at the same time that the upper portion is contracted.* ANTI PERISTALTIC MOTION. When the successive contraction of the muscular fibres of the intes- tines is opposed in its natural course downward, either by a violent sti- mulus (the effect of which is to cause a more permanent contraction in the coats, and one which does not readily yield to the relaxation that fol- lows, as in the natural contraction,) or when there is a mechanical and obstinate interruption to the contents of the bowels ; then is the natural action reversed. This antiperistaltic motion arises thus ; a portion of the intestine being constricted, and not yielding to the contraction which, in the natural action of the gut, should follow in order, the gut must be stationary for a time, until the part above that which is contracted be- comes relaxed ; then the contents of the intestine finding a free passage upwards, and that portion contracting and propelling the matter still up- wards and retrograde ( since it is opposed by the contraction below,) a series of retrograde or antiperistaltic motions are begun and propagated. The course of the action being changed, the cont raction of the gut is not follow'ed by the dilatation of the portion below, but by that above. By this means the matter of the lower portion of the intestinal canal is car- ried into the upper part, and there acting as an unusual stimulus, it aggra- vates and perpetuates the unnatural action. From experiments it ap- pears, that a permanent irritation will cause an accelerated motion in both directions; that from the point stimulated there will proceed downward the regular series of contractions and dilatations, while the motion is sent upwards and retrograde from the same point of the intes- tine toward the stomach.| And this observation, the exhibition of me- dicine and the diseases of the intestines confirm. But farther we may observe, that the food is not uniformly moved downwards ; it is shifted and agitated by an occasional retrograde motion, thus : * From the experiments of Haller and others, it is proved that the irritability of the intes- tines long survives that of the heart: that the intestines are in general in lively motion, when f Haller, !oc,cit., Exper. 244- OF THE SMALL INTESTINES. 335 The portion of the intestine included under a, contracts and sends its contents into b. b contracting, sends its fluid contents in part back- ward into a, but in a greater proportion into c. While the contents of the middle portion are sent into the lower part in a greater proportion than into the higher division, the tendency of the food will be in its na- tural course, downward ; whilst at the same time it sutlers an alternate motion backward and forward; so that it is more extensively applied to the absorbing surface of the intestines. The stimulus to the intestines is matter applied to their inner coat; and although there is much sympathy in the whole canal, yet unless there be matter within a portion of the canal, that particular part has little action. Accordingly, when there is obstruction to the course of the aliment, by whatever cause it may be produced, the portion below becomes shrunk and pale, and free from the ef- fects of inflammation ; while that stimulated by the food, being in a high state of excitement, irri- tated by the presence of matter which it is unable to send forward, evacuated only partially by an un- natural and highly excited retrograde action, it becomes large, thick in its coats, strong in its mus- cular fibres, and greatly inflamed, till it terminate at last in gangrene.* The unusual excitement of the muscular fibres produces a very curious effect in the intus-sus- ceptio, which is the slipping of one portion of the gut within another. This may be produced by applying acrid matter to the intestines of living animals ; and I have no doubt that it has been produced by giving purges too strong and stimu- lating in cases of obstruction of the bowels. By the contractions of the muscular coat greatly ex- cited, the intestine is not only diminished in dia- meter so as to resemble an earth-worm f, but in length also. This great contraction of the outer coats accumulates the vascular and villous coat as if into a heap; which from the compression of the muscular coat is forced into the neighbouring re- laxed portion. This first step leads only to a succession of actions; for the fibres of the relaxed or uncontracted part, sensible to the pre- sence of this accumulated and turgid villous coat, contracts in succes- no motion can be observed in the stomach; but that sometimes the motion of the stomach continues longer than that of the intestines. It is proved also that the action of the intestine is adequate to the motion downward and the discharge of faeces, without the aid of the ab- dominal muscles. See Mem. par Haller sur les Mouvemens des Intestines: and Opera Minora, p. 393. * Ha; gives an experiment illustrating the cause of ileus. He tied a ligature about the intestine of a cat, and found no antiperistaltic motion excited. This is not wonderful; it is the excitement arising from matter within the gut, to which there is no exit, and not the structure of it, which is the cause of the violent symptoms. Many cases in the Museum will give the young student a correct judgment on this subject. Vide Scholium sub tit. Calculus insignis Ilii. Observ. F. Biumi. Sandif. Thes. vol. iii. The figure represents the intas-susceptio. a. The invaginated portion, k. The includ- ing portion. f See Haller’s Experiments, Optra Minora, and “ Dissections of the Atrophia Ablactato- rtun with plates; by Dr. Cheyne. Sandifort. vol. ii. p. 381. in Dysentarise.—Ibid. 244. 336 OF THE SMALL INTESTINES. sion so as to draw a part of the contracted gut further downwards. If the irritation is done away or ceases quickly, as in the experiments on ani- mals, another turn of the intestine coming into play distends this, and un- does the iritus-susceptio. But if the cause continues, the intus-susceptio is continued ; the included part of the gut is farther forced into the other. By these means the vessels going to the included part are interrupted ; the villous coat swells more and more ; and several feet of the upper portion of the intestine is often in this way swallowed down. It is not however in the natural course downward that this preternatural action always proceeds; for, as the excitement is violent and unlike the usu- al stimulus of food, and as we know that an unusual excitement is ve- ry apt to cause an inverted action, it often happens that the intus-sus- ceptio is formed by the lower portion of the gut being included in the part above. VASCULAR COAT. The third coat of the intestines, is a stratum of cellular membrane in which the vessels of the gut are distributed. It might with equal propri- ety be called the cellular coat; and is indeed what some anatomists have called the third cellular coat. By inverting the gut and blowing strongly into it, the peritoneal coat cracks and allows the air to escape into this coat; which then swells out, demonstrating its structure to be completely cellular.* Its use evidently is to suffer the arteries, veins, and lymphatics to be distributed to such a degree of minuteness as to prepare them for reflection into the last and innermost coat, and for en- tering into the structure of the villi: for they come to the extremity of the mesentery as considerable branches, but forming in this coat many branches, and these subdividing, their extreme branches are finally dis- tributed to the inner coat. This is the coat in which, in some parts of the intestines, little glands or cryptse are lodged. VILLOUS COAT. The most curious part of the structure of the intestines is the villous or inner coat; for by its influence is the chyle separated from the gene- ral mass of matter in the bowels, and carried into the system of vessels. To this, all we have been describing is merely subservient. The villous coat has a soft fleecy surface ; and being of greater ex- tent than the other and exterior coats, it is thrown into circular plaits or folds which hang into the intestine, and take a valvular form. They have the name of valvule conniventes. Some of them go quite round the inside of the intestine; others only in part. They are of larger or smaller extent in different parts of the canal : for example, they begin a very little way from the lower orifice of the stomach irregularly, and tending to the longitudinal direction; further down they become broader, more numerous, and nearly parallel; they are of greater length, and more frequent in the lower part of the duodenum and upper part of the jejunum. These valvular projections have their edges quite loose and floating in the canal, and from this it is evident that they can have * An experiment to which Albinus attaches much importance. See also, in the Acad, de Bologma, a paper by Mr. ft. G. Galeati on the fleshy coat of the stomach and intestines. OP THK SMALL INTESTINES. 337 no valvular action. Their use is to increase the surface exposed to the aliment; to enlarge the absorbing surface; and at the same time to give to it such an irregularity that the chyle may lodge in it and be detained. Into the structure of these plicae of the villous coat, the vas- cular or cellular coat enters, and generally in the duplicature a small ar- terial and venous trunk will be observed to run. That these plicae are formed chiefly by the laxity of the connexion and the greater relative ex- tent of the inner coat, is apparent upon inverting the gut, and insinuating a blow-pipe under the villous coat, for then you may distend the cellular substance of the vascular coat so as entirely to do away the valvulae con- niventes. The pile or lanuginous surface from which this coat has its name, is to be seen only by a very narrow inspection, or with the magnifying glass. It is owing to innumerable small filaments which project from the surface like hairs at first view, but of a flat or rounded figure as they are exhibited in a state of fulness and excitement or depletion. They con- sist (as appears by the microscrope) of an artery and vein, and lacteal or absorbing vessels, and to these we may surely add the extremity of the nerve. They have a cellular structure ; they are exquisitely sensible ; and when stimulated by the presence of fluids in the intestines, are erected and absorb the chyle. They are the extremities of the lacteal absorbing system, and their structure is subservient to the absorption by the mouth of the lacteal vessel.* But the surface of this coat is not only an absorbing one, it also pours out a secretion ; and indeed, as a secreting surface, upon which medicines can act, it is to us one of the most powerful means of correcting the dis- ordered state of the system. The fluid which is supplied by the sur- face of the intestines is called the liquor intericus ; a watery and semi- pellucid fluid, resembling the gastric fluid. This fluid physiologists have affected to distinguish from the mucous secretion of the glands of the inner surface of the intestines; but it is impossible to procure them se- parate. | GLANDS. Anatomists have observed small mucous glands seated in the cellular membrane of the intestines, J the ducts of which they describe as open- ing on the villous surface of the intestines. They are seen as little opaque spots when the intestine is cut in its length and held betwixt the eye and the light. They have been chiefly observed in the duodenum; few of them in the general tract of the small intestines. Little collec- tions or agmina of glands are observed, which increase in frequency * See further of their structure under the title of the Lacteal and Lymphatic System, where the subject of absorption and the structure of the villi is treated. Dr. Hunter and Mr. Cruic kshanks observed about fifteen or twenty orifices in each villus. These com- municated with radiated branches of absorbents, which together formed the trunk of one of the lacteal vessels. f It has been supposed that the fluids excreted from the surface of the intestines were furnished by very minute foramina (which are visible by particular preparation) in the inter- stices of the villi. See the letter of Malpighi to the Royal Society of London, on the pores'- of the stomach; and the paper by M. Galeati, in the Bologna Transactions, on the Inner Coat, which he calls the Cribriform Coat. These pores, according to Galeati, are visible throuch the whole tract of the canal, and particularly in the great intestines. f Peyevus. Bibiio. Manget. Brunnerus de glandulis duodeni. Morgagni Adversar. A(*» iii. riii. These he supposed additional pancreatic glands- 338 OP THE SMALL INTESTINES. toward the extremity of the ileon. It is natural to suppose that as the contents of the intestines become in their descent more acrid and stimu- lating, there will be a more copious secretion of mucus in the lower in- testines for the defence of the villous coat. According as these bodies are found single or in collections, they have been called glandul® solita- riae or agminatse. Sometimes they are called glandulae Peyeri or Brun- neri. in concluding the view of the small intestines, we cannot fail, I think, to express a correct idea of their function ; the matter ejected from the stomach is a greyish, pultaceous turbid mass. In the small intestine we find that a precipitation or separation of feculent matter has taken place from the nutritious part. This nutritious matter called chyle is a pure milky fluid, and coagula- ble ; so that already the most remarkable character of the circulating blood is assumed by the digested matter. And what is still more curi- ous, already do we see that consent established betwixt the containing and the contained fluids which is the source of all the actions of a living body. The chylous or nutritious matter from which the feculency is se- parated, is attracted by the surface of the villous coat of the intestine, and in an animal killed some time after taking food, the matter may be seen coagulated upon the inner surface of the intestine. Some are of opinion that the chylijication is produced by the action of the bile, and that the effect of it is to precipitate the effete matter ; but I am more inclined to believe that it is the office of the part of the intes- tines we are now considering, to separate by attraction the chyle from the mass of ingesta : for supposing that we were to give the office to the bile, that would be a mere precipitation, and could not explain the attrac- tion of the chyle to the villi * ; nor the manner in which the fine nutri- tious fluid was imbibed by the lacteals, while the faeculent part is passed down. There is a preparation of the alimentary matter ; but is not the absorption by the lacteals like the action of the roots of plants ? They must exercise a selection, and possess a power of separating ; nor is it more wonderful that the orifices of vessels should affect the morbid fluid, than that they should retain the power we so readily acknowledge them to possess, of separating and changing the blood in the act of secretion. It is more natural to suppose, that this very peculiar property oflife, the coagulation, is bestowed through the influence of the villous surface of the intestine, than produced by the mere pouring in of a secretion like the bile. FUNCTION OF THE SMALL INTESTINES. * In Sir. A. Cooper’s lectures in the College of Surgeons, this attachment of the chyle to the villi was considered as a discovery. But the statement will be found in former editions of this work-