CLASS-BOOK
OF
PHYSIOLOGY;
FOR THE USE OF
SCHOOLS   AND  FAMILIES.
COMPRISING
THE STRUCTURE AND FUNCTIONS OF THE ORGANS OF MM,
ILLUSTRATED BY
COMPARATIVE REFERENCE TO THOSE OFy^NFERIOR ANIMALS,
     BY B. N. COMINGS, M. D.
AUTHOR OF PRINCIPLES OF PHYSIOLOGY, OUTLINES OF PHYSIOLOOY,
      THE PRESERVATION OF HEALTH, ETC., ETC.
     WITH TWENTY-FOUR PLATES,
AND NUMEROUS ENGRAVINGS O NW OOP,
      COMPRISING IN ALL ABOVE TWO HUNDKEQyflGUA^S,'i'L •'.< .<;'"••


            NEW-YOEK: £       '-  l/
    D. APPLETON & CO. 200 BROADWAY."'
18.13. 

ENTERED, ACCORDING TO ACT OF CONGRESS, IN THE YEAR 1852, BY

                    B.   N.   COMINGS,

IN THE CLERK'S OFFICE OF THE DISTRICT COURT OF CONNECTICUT.
FOUNDRY OF S. ANDRUS  AND  SON,
         • HARTFORD.
    W. C. Armstrong, Typographer. 
PREFACE.
   The '• Principles of Physiology" which has been so highly commended
 by all literary men, who have examined its merits, although well adapted
 to more advanced institutions, has been thought too large and expensive
 for the major portion of our schools.  To meet the demand for a lower
 priced book, and comply with the desires of numerous friends of edu-
 cation, the Class-Book of Physiology is now offered to the public.
   The unanimous verdict of teachers in favor of the general plan of
  he "Principles of Physiology," has induced the author to pursue the
 same method of illustration, and,  if possible, bring to a higher perfection
 the original plan of that work.   It has been his constant study in  this
 treatise to  explain and illustrate to  the student, fully and clearly, as
 many of the most  practical  principles of Physiology,  as  could be
 included in  the moderate limits of the present volume.
   That Human Physiology can be made more easy of comprehension—
 more profitable, and more attractive to the young, by appropriate refer-
 ences to  the Comparative  Physiology of the  inferior animals, than  by
 any other method—is an established  fact  in  the  mind  of the author,
 though he must leave it for others to judge of the success with which
 this plan has been developed.
   Physiology owes much of its present eminence, as a deeply interest-
 ing and progressive science, to observations made on the structure and
 functions of the  same organs  in the lower orders  of animals as are
 found to exist in man.  Take from Human Physiology the light derived
 from Comparative Physiology, and it would become  what it was centu-
 ries ago, an obscure and comparatively uninteresting science.
   The young universally feel  a deep interest  in the animated beings
 which they see around them. The horse, the ox, the dog, and birds and
 insects, are  all objects of admiration and wonder to the  philosophic
 mind  of youth;  and  when they learn that  each  possesses organs
 approximating more or less  in  structure to their own, their sympathies
are enlisted, they feel a deeper  interest  in  their  own organization,
acquire more  noble and  exalted views of the position they occupy
in the scale of being, and learn to appreciate  more truly the evidences
of an all-wise design in the works of their Creator. 
4
PREFACE.
   Physiology cannot but be considered, by every intelligent and reflect-
 ing mind, a deeply interesting and practically important study.   It makes
 us acquainted with the structure and uses of the organs of life, and the
 laws  by which they may be  preserved in health and vigor.   When  a
 knowledge of the principles of Physiology shall  be diffused through
 all classes of society, the sum-total of human happiness will be greatly
 increased, and more permanent enjoyment of health, and  more exalted
 exercise of all  the physical and intellectual .powers, will be secured to
 each individual.
   This science has  peculiar  claims  to the attention  of every teacher
 who would be successful in his profession.   It  presents,  in their  true
 light, those facts  which lie at the foundation of mental development,
 and suggests the  best means  of promoting intellectual growth.
   For the convenience of those who have not had sufficient experience
 to dispense with questions, they have been  put at the bottom of each
 page, but there is left  ample  scope for teachers to  propose many more.
 For those who may be advanced in study, or who may review the
 book, a description of the figures  and plates  are recommended as an
 useful exercise.
  Carpenter,  Roget, Wilson,  Pereira, Bourgery,  Aitken, Kirkes  and  t
Paget, Horner, Hussall, Aggassiz, Wyman, Chambers, Griscum, and vari-
ous other authors, have been consulted in the preparation of this work.
  The author is  under obligations to the publisher of  "Principles of
Physiology" for permission to use the figures and such portions of the
text of that work as  he found suited to his purpose.
New Britain, May, 1853. 
                      CONTENTS.


                                                          PAOIC
INTRODUCTION,............................................................    9
CHARACTERISTICS OF ORGANIC AND INORGANIC MATTER,.............    9
DEFINITIONS,...............................................................    10
                         CHAPTER I.
CHARACTERISTICS OF PLANTS AND ANIMALS,..........................    15
                         CHAPTER II.
STRUCTURE AND COMPOSITION OF ANIMAL BODIES,....................    19
                        CHAPTER  III.
THE BLOOD,................................................................    27
CIRCULATION OF THE BLOOD,............................................    29
                         CHAPTER IV.
RESPIRATION,..............................................................    47
                         CHAPTER V.
ANIMAL HEAT,.............................................................    53
                         CHAPTER VI.
DIGESTION,.................................................................   67
MASTICATION,...............................................................   67
INSALIVATION,.............................................................   72
                        CHAPTER VII.
ABSORPTION,...............................................................   93
                        CHAPTER  VIII.
NUTRITION,.................................................................   98
                         CHAPTER IX.
SECRETION,..................................................................  101
                         CHAPTER X.
THE SKIN,..........................•.........................................  109 
6                         CONTENTS.

                         CHAPTER  XI.                      paok
THE NERVOUS SYSTEM,....................................................  119
NERVOUS SYSTEM OF MAN,................................................  12,
SPINAL CORD,...............................................................  12a
MEDULLA OBLONGATA,....................................................  131
THE BRAIN,..................................................................  n'2
FUNCTIONS OF THE CEREBELLUM,.........................................  141
FUNCTIONS OF THE CEREBRUM,...........................................  1J"
CONNEXION OF THE MIND WITH THE BODY,..............................  149
                        CHAPTER XII.
THE SENSES,................................................................  153
   SENSE OF TOUCH,......................................................  153
   SENSE OF TASTE,.......................................................  155
   SENSE OF SMELL,......................................................  161
   SENSE OF HEARING,...................................................  161
   SENSE OF SIGHT,.......................................................  170
                        CHAPTER  XIII.
ANIMAL MOTION,..........................................................  192
THE MUSCLES,..............................................................  219
                        CHAPTER XIV.
THE VOICE,..................................................................  234
                        CHAPTER  XV.
THE HUMAN FORM,.......................................................  239

SYNOPSIS OF LAWS OF HEALTH,..........................................  251
INDEX AND GLOSSARY,........ ........................................  253 
LIST OF FIGURES.
FIQ piOg		F1Q l'AQ.T.	
1. Parent Cells,	20	36. Single Gland of Small Intestine, .	90
2. Fasciculi and Fibres of Cellular Tissue, 21		37. Lymphatics, ....	94
	<x>	38. Diagram of Mucous Membrane,	95
4. Corpuscles of Human Blood.	28	39. Appearance of Lymphatics, .	95
5. Dorsal Vessel of the Spider,	30	40. Section of Kidney,	104
6. Circulation in Crustacea,	30	41. Structure of Parotid Gland, .	104
7. Circulation in Fishes, ,	31	42. Nervous System of Ascidia,	121
8. Circulation in Reptiles,.	31	43. Nervous System of Pecten, .	122
9. Circulation in Man, .	32	44. Nervous System of an Insect, .	123
10. Diagram of the Pericardium,	32	45. Nervous System of Sphinx, .,	124
11. Section of Right Side of the Heart	33	46. Brain of a Cod—of a Shark,	126
12. Valves of a Vein, ....	36	47. Brain of a Bird, ....	12G
13. Capillaries in a Frog's Foot,	36	48. Portion of Spinal Cord,	129
	48	49. Skull of European,	144
15. The Serpula, ....	49	50. Skull of Negro, ....	144
16. Respiratory Apparatus of Insect, .	50	51. Capricorn Beetle, ....	153
17. Interior of a Snail, .	51	52. Vertical Section of the Nasal Cavily	162
18. Lungs of an Ostrich,	52	53. Bones of the Ear, ....	167
19. Air Cell,.....	52	54. Cavity of the Tympanum, .	167
20. The Larynx, Bronchial Tubes, &c.	53	55. Interior of the Eye,	181
21. Human Thorax,	54	56. Section of the Eye, .	181
22. Development of Teeth, .	69	57. Refraction of Rays of Light,	184
23. Dental Capsule,	69	58. Image on the Retina,	189
23'. Human Teeth, ....	69	59. Bones in the Foot and Leg of a Deer	,213
24. Section of a Human Tooth,	70	60. The same of a Horse,	213
25. Jaw and Teeth of Rabbit, .	70	61. Bones of the Arm,.	220
26. Teeth of Herbivorous Animal,	71	62. Bones and Muscles of the Humerus	,225
27. Teeth of Carnivorous Animal,	71	63. Tail-Fin of a Whale, .	226
28. Teeth of Insect-eating Animal,	71		233
29. Teeth of Frugivorous Animal,	71	65. Larynx of a species of Duck,	235
30. Teeth of a Rattle-Snake, .	71	66. Larynx of a Rook, .	235
31. Section of Mouth and Throat,	73	67. Vertical Section of the same,	235
32. Stomach of the Sheep, .	76	68. Human Larynx, viewed sideways,	236
33. Section of the Stomach,	80	69. Vertical Section of the Larynx, .	236
34. Mucous Membrane, . ...	81	70. Front View of the Larynx,	236
35. Tubular Follicle of the Stomach, .	82	71. Bird's-eye View of the Human do.	237
 
LIST   OF   PLATES.
 PLATES.                                                               PAGB.
     I.    Comparative View of the Organs of Circulation,.....13
    II.    General View of the  Circulating Apparatus of Man,  ....    17
   III.    Organs of Circulation,..........25
   IV.    Organs of Circulation.—Heart and Lungs,......39
    V.    Organs of Respiration,     ,.........45
   VI.    Organs of Respiration,                   ,.....57
  VII.    Organs of Digestion,...........77
 VIII.    Organs of Digestion,..........87
   IX.  • The Skin,.............109
    X.    The Skin,.............117
   XI.    The Brain and  Spinal Cord,.........139
  XII.    The Nerves,............147
 XIII.    Organs of Sense,............159
 XIV.    Organs of Vision.—The Eye,.........173
  XV.    Organs of Vision.—The Eye,.........179
 XVI.    Organs of Vision.—The Eye,.........    187
 XVII.    Organs of Motion.—The Bones.—Anterior View,.....195
XVIII.    Organs of Motion.—The Bones.—Posterior View,    ....    201
 XIX.    The Extremities,............209
  XX.    Organs of Motion.—The Bones.—Comparative View,  ....    217
 XXI.    Organs of Motion.—The Muscles.—Lateral View,.....223
 XXII.    Organs of Motion.—The Muscles.—Posterior View,  ....    231
XXIII.    The Human Form, in various Positions,.......240
XXIV.    The Human Form in various Positions, and Public School Play-grounda,  253 
CLASS-BOOK  OF  PHYSIOLOGY.
                    INTRODUCTION.
  1. All  bodies in  which  evidence  of life  has been
observed, possess certain parts or organs, which are essen-
tial to the existence  of the  individual.  A plant or an
animal exists by means of its appropriate organs,  and the
matter of which they are composed is therefore called
organized or organic matter.
  2. Minerals  exhibit no signs of life,  but  they continue
to exist  without any  distinction  of parts or organs, and
belong to the kingdom of unorganized or inorganic matter.
A piece  of quartz,  for  instance, may be broken into any
number  of fragments, each  of which will  retain  all the
characteristics  of the original mass.
  3. Minerals  may grow or increase in size by the super-
addition of new particles to their surface;  but they are not
nourished, like organized beings, by interposing new par-
ticles between  those which already  form their substance.
  4. In  plants and animals, each part is essential to the
completeness of the individual being, and no part or organ
can maintain an independent existence.  If a rose be cut
from its stem, or an  arm be amputated  from  the body,
it immediately dies, and loses its original characteristics.
  5. A plant is dependent upon its roots and its' leaves for
vitality, and an animal cannot  live without its heart, its
lungs, and its  stomach.

  What are essential to the existence of all living bodies'?  What is the matter
of which such bodies are composed  called?  What is the matter found in
minerals called ?  Do minerals growl  How?  Are they nourished?  What
is essentia! to the completeness of a plant or animal?  Can any organ main-
tain an independent existence?  Upon what parts is a plant dependent for its
vitality?  Upon what parts is an animal dependent? 
10
CLASS-BOOK OF PHYSIOLOGY.
  6. There are two conditions in which we may study or-
ganized matter: namely, as living beings and as dead bodies.
  7. The science of Physiology is  derived from the first
method, and the science of Anatomy from the second.
  8. Physiology makes us  acquainted with the uses to
which the different parts are subservient, and the laws by
which they are governed.
  9. Anatomy teaches the number,  size,  situation, form,
texture, and composition of the various parts, with their
relations to each other.
  10. Anatomy and Physiology, in their most extended use,
apply to all organized beings, though they are  naturally
divided into the several branches of Vegetable Anatomy
and Physiology, and Animal Anatomy and Physiology.
  11. Animal Anatomy and Physiology are again divided
into Comparative Anatomy  and  Physiology, and Human
Anatomy  and Physiology.
  12. Comparative Anatomy and Physiology are devoted
to the lower orders of animals.
  13. Human Anatomy and  Physiology  are limited in
their application to man.
  14. The divisions of Physiology into Comparative and
Human are usually made  as a matter of convenience in
study, and not because the Physiology of man is peculiar
to him  alone: for the same organs which exist in man,
may be found in greater or less perfection  in nearly all the
lower orders of organized beings.
  15. Comparative and Human Physiology naturally illus-
trate each  other, and thereby become more interesting and
more easily comprehended.

  In what conditions may we study organized matter?  What science  is
derived from  the first, and what from the second method?  With what does
Physiology make us acquainted?  What  does  Anatomy teach?  How are
Anatomy and Physiology naturally  divided?   How are animal Anatomy
and Physiology divided? To what orders of animals are Comparative Anato-
my and Physiology devoted?  Why is Physiology divided into Comparative
and  Human? 
\ 
PLATE   I.
  COMPARATIVE  VIEW  OF THE ORGANS  OF CIRCULATION.


  Fiourb  1.---Circulation in the Insect—a, The dorsal  vessel, divided into valvular
partitions, by the successive contraction of which, the blood is propelled forward,  J, 4,
Canals which carry the blood to the head,  c, c, Canals passing backward for  the  supply
of the body, and returning the blood to the posterior end of the dorsal vessel.—The course
of the circulation is indicated by the direction of the arrows.
  Fiourk 2.---Circulating Apparatus of the Lobster.—In the lobster and crab, the heart
has but a single cavily, and the veins are indistinct, consisting merely of irregular channels
excavated in the tissues,  a, The  heart; b, c, Arteries which go to the head  and to the
antenna or feelers; d, The hepatic artery, or artery of the liver; e, /, Arteries  which sup-
ply the thorax and abdomen.----After the blood has been propelled through these arteries
by the heart, it passes into the great vein, g, g, from all parts of the body.   Thence it
passes to the gills, h, where it is exposed to the action of the air, and is then  returned to
the heart by the branchial veins, i, which correspond to the pulmonary veins of Man.

  Figure 3.---Sectional View of the Circulating Apparatus of the Lobster.—a, The heart.
o, b, Venous sinuses,  c, c, Branchial arteries,  d, d, The gills or branchiae,   e, e, Branchiul
veins, terminating in the heart.

  Fiqurz 4.----Circulating Apparatus of Fish.—a, The auricle, having a single  cavity,
to which the blood is sent from all parts of the  body.   4, The ventricle, which receives
the  blood from the auricle, and propels it to the arterial bulb, e, into the branchial artery,
d.  The branchial artery is sub-divided into the arteries of the gills, e, in which the blood
is aerated.  /, /, The dorsal artery, or aorta, which receives the aerated blood from the
gills, and distributes  it to all parts of the body,  g, The vena cava, or great hollow vein,
which conveys the blood back again to the auricle.  A,  Vena porta?, that branch of tho
vena cava which conveys the blood from the abdominal organs,  i, The intestine,   k, The
kidneys.

  Figure 5.---Circulating Apparatus of Lizard.—a, Left auricle,  b, Right auricle.—
One of these receives the venous blood from the system, and the other receives the  arte-
rializcd  blood from the lungs,  c,  The single ventricle, which'receives the blood from both
auricles, and transmits it partly into the lungs and partly into  the aorta,  d, d, Arches of
the  aorta,  e, Carotid artery, which distributes the blood to the head,  f, Pulmonary vein,
which conveys the blood from the lungs to the heart, g, Brachial artery, which  goes to
the fore-legs.   A, A, Pulmonary artery, in which the blood is  submitted to tho inlluenct!
of air in the  lungs,  t, The lungs,  j, The  stomach, k, Vena  portae.  /, Intestines, m.
Ventral aorta, or that portion,of  the aorta contained in the  abdomen,   n, Kidneys, o,
Liver and vena purtae. p, Inferior vena cava, which conveys the blood from all the lower
parts of the body to  the heart,  j, Superior vena cara, through which the blood of the
upper parts of the body is sent to the heart.

  Figure C.---Heart of Tortoise.—a, Right auricle,   4, Single Ventricle,  c, Left auri-
cle., d, d, Pulmonary artery,  e,  e, Pulmonary vein. /, Vena cava,  g, Right aorta. A
Left nnrtn. 
PI 1
 
 
PLANTS AND ANIMALS.               15
                     CHAPTER  I.
          CHARACTERISTICS OF  PLANTS  AND ANIMALS.
  16. Plants and animals are distinguished from alf unor-
ganized bodies by the process of nutrition and the property
of reproducing their kind.   Plants are nourished by the
inorganic elements found in the earth and air around them.
The materials of their growth are received  in the form of
a liquid or a gas,  already prepared  for their use.
  17. Animals are nourished  by the organic materials of
vegetables or of other animals.   Animals always possess
a stomach or  a digestive cavity,  in which their food is
received, to undergo a  process of preparation before it can
be absorbed into their  tissues.
  18. Sensation and voluntary  motion are peculiar  to
animals alone, and are therefore called animal functions.
  19. Plants  and animals both have  a limited period of
existence, which varies with every species.  In some, this
period  is confined to a  single day; in many plants, to a
single summer: while  some animals live more than a cen-
tury, and some trees—as the oak and olive—are supposed
to live a thousand years.
  20. The natural age  of man is usually estimated at about
seventy years, though  instances occasionally occur of indi-
viduals who  survive  an hundred or more years.  The
duration  of man's life  is less uniform than that of any
other class of animals.   In some communities, the average
age  at death is only ten  or twelve years;  in others, it is
nearly forty.   In  all cases, individuals and communities
are long-lived just in  proportion  as their localities, occu-

  How are plants and animals distinguished from unorganized  bodies?  How
are plants nourished ?  How are animals nourished ?  What do animals Hiwaya
possess?  What functions are peculiar to animals alone?  What is snid of the
period of existence of plants and animals?  What is the natural age of man?
How does it vary in different communities?   In proportion to what are com
munities  and.individuals long-lived?
           2 
16                CLASS-BOOK  OF  PHYSIOLOGY.
pations,  and  habits of life  are  favorable to  health;   for

health  and life  are blessings lent to man only as conditions

of obedience  to the laws of his organization



                              PLATE   II.


GENERAL  VIEW OF THE CIRCULATING APPARATUS OF MAN.
  The course and  relative positions of the principal arteries and veins of the Systemic
circulation are shown in this plate.  The arteries commence from the great arterial trunk
called the  aorta, and their branches are distributed to all parts of the system.  The venous
branches, which accompany the arteries, unite into two great veins, the superior and infe-
rior vena cava, which convey the blood back to the heart.
  a, The left ventricle of the heart,  b, The right auricle,  c, The superior vena cava,  d,
The root of the pulmonary artery,  e,  e, The aorta, which is seen arching backward over
the heart, and passing downward into the  abdomen, where it divides into its two great
branches, the iliac arteries,  through which the blood passes to the lower extremities.  /,
The inferior vena cava, which accompanies the descending aorta and its  branches, and
returns the blood from the lower extremities. The dotted lines represent the outlines of
the kidneys.

      PRINCIPAL DIVISIONS  OF THE AORTA AND  VENA  CAVA.
  It should be remembered that most of the branches which spring from the great artery
and vein, are double—that is, each right branch has a corresponding one at the left side
—so that there are, for instance, the right and the left carotid arteries, the  right and the
left jugular veins, &c.
  From the arch of the aorta are sent  off those arteries which are distributed to the head
and arms.  The principal ones among these are named as follows:
  g, The carotid artery, which nscends in the side of the neck, and divides  into the  tem-
poral artery, A, which is distributed in the temple, and the facial artery, i, which supplies
the face; and also  sends a branch, called the internal carotid, to the parts within the skull.
  j, The sub-clavian artery,  lying  beneath  the clavicle or collar-bone.  That part of the
continuation of this artery which passes through the axilla or arm-pit, is called the axillary
artery, k ;  that which lies in the upper arm, the brachial artery, /;  and in the fore-arm
it divides into the radial and ulnar arteries, m, n, which are distributed  to the hand and
fingers in the manner indicated in the plate.
  The principal branches of tho descending aorta are named as follows.
  The iliac artery, o, which, on passing into the thigh,  becomes the femoral artery, p, and
in the leg divides into the tibial and peroneal arteries, q, r, which form numerous brunches
for the supply of the leg and foot.
  Before dividing into the iliac arteries, the descending aorta gives off several important
branches;  as the coeliac artery, from which the stomach and liver are supplied ; the renal
artery, which goes to the kidneys, and the mesenteric artery, to the  intestine's • besides
many other sub-divisious in various parts of its course.
  The branches of  the vena cava generally accompany those of the aorta in their distribu-
tion, as  shown in  the figure,  and are often  called by the same names.  Tho principal
divisions of the ascending vena cava are:-The jugular  vein, s, which accompanies tho
carotid artery.  The sub-clavian vein,  t, which accompanies the artery of tho same name
and receives tho blood from the arm and hand.                              '       '
  The inferior vena cava, like the aorta, divides into two great branches, the iliac veins  «
the sub-divisions of which accompany those of the arteries, and are called by the  same
names.  The manner in which the superficial veins ramify and anastomose with each othP,
is shown on the upper and lower extremity of the left side. 
 
 
OF ANIMAL BODIES.
19
                    CHAPTER  II.
        STRUCTURE AND  COMPOSITION OF ANIMAL BODIES.
  21. The component substances  of animal bodies may be
divided into fluids and solids:
  22. The fluids are found mostly in the form of chyme,
chyle, lymph, and blood.   About thirty pounds of fluid
can be drawn directly from a man who weighs one hun-
dred and fifty pounds.  By exposure to a process of evap-
oration, the body may then be reduced to twelve or fifteen.
Perfectly dry mummies  are sometimes found  to  weigh
only seven or eight.   Hence the fluids  may  be said to
constitute by far the largest proportion of the body.
  23. The fluids'vary exceedingly at different  periods of
life.   In youth,  they are very abundant, making the form
plump and round.  In old age,  they are greatly dimin-
ished, leaving the form shrunken  and wrinkled.
  24. The fluids contain in solution the materials for the
formation of the solid tissues, and are also  the medium
through which  all the waste particles are carried out of
the system.  The fluids and solids, being alternately con-
verted into each other, do not differ essentially in their
chemical elements.
  25. The human  body  has been found,  by chemical
analysis, to contain the  following elementary substances:
Oxygen, hydrogen, nitrogen, carbon, sulphur, phosphorus,
silicon,  chlorine, fluorine,  iron, and sometimes  mangane-
sium, aluminum, and copper.
  26. The first  four are most constant and most abundant,
and are named essential elements.
  27. The solid portions  of the body are called tissues.
  How are the substances which compose animal bodies divided ?  How many
pounds of fluid may be drawn from the body of a man weighing one hundred
and  fifty  pounds?  How  can the weight of the body be  farther reduced?
When are the fluids  most abundant and when least abundant?  How many
elementary substances are there in the human body?  WhicrFare the  foui
essential elements?  What are the solid portions of the body called? 
20            CLASS-BOOK  OF PHYSIOLOGY
  28. The tissues, in their primary formations, are made
up of granules, nuclei,  cells, filaments, and fibres.
  29. Granules are particles of various sizes, from immea-
surable minuteness  to  the ten-thousandth of an inch in
diameter.  Granules are found floating in milk, chyle, and
other animal fluids, and imbedded in most of the tissues.
                        30. Nuclei are the germ and cen-
                     tre around which  cells are formed.
                     (Fig. 1.)
                        31. Cells are minute bubbles, vesi-
                     cles or scales.   Their natural shape
                     is oval or spheroidal, but they often
                     become  flattened or many-sided  by
                     pressure, as may  be  illustrated  by
  ng. i.-parent cells.— filling a vial with a strong solution
    a, a, Parent cells.        n     •     ,       j ,-\
    b, b, secondary cells.    of soap m water, and then  inverting
    c, e, Nuclei.          ^ whe]Q if. ^ be fi]]ed ^^ bubbles>
each one of which will assume a form in accordance with
the position  it occupies.   The cells perform a  highly im-
portant process in  all animal and vegetable  structures.
The solid portions  of  plants, and the tissues of  animal
bodies, are formed directly by the deposition of cells, or
by the indirect elaboration of their fluid contents.   They
are concerned, not only in the functions of nutrition, in
the development and restoration of parts, but in absorp-
tion and secretion.   They are developed into  tissues in
various ways.  In some, the cell-membranes become elon-
gated, and are folded and divided into threads or filaments
of exceeding fineness.
  32. Tubules,  or  little tubes,  are  several cells elongated,
and placed end to end—the partitions being removed.
  33. Filaments, or fibrils, are exceedingly delicate threads,
composed of minute particles, usually arranged in parallel
bundles or fasciculi.  {Fig. 2.)
  Of what are the tissues made up? What are granules?  Where are gran-
ules found ? ^Vhat are cells?  How are cells developed into tissues? Whal
are tubules? What are filaments? 
OF  ANIMAL  BODIES.
21
Fig. 2.—Fasciculi and fibres of cellular tissue.  A, White fibrous element, with cell-nuclei visible in it
 B, Yellow fibrous element, showing its branching fibrils. C, Finer fibrils of the yellow element.
   34.  Fibres are larger than fibrils, but are similar in other
respects.
   35.  A  tissue is the union or interlacement of one or
more of these primary structures.
   36.  An organ fs an instrument composed of tissues, and
designed  for action.  Its action is  called its function or
use.   Thus, the liver is an organ, and  the secretion of bile
its function.
   37.  An  apparatus consists of  a number of  different
organs, arranged for the performance of some one office.
The teeth,  mouth, stomach, intestines, &c, belong to the
digestive apparatus.
   38.  A system is a connected series of similar parts,  such
as the muscular or the nervous system.
   39.  The  number of tissues which  make up the different
organs of  animals  is variously stated,  according to the
minuteness of description which different anatomists adopt.
  What are fibres?  What is a tissue?—an organ?  What is an apparatUB?
—a system ?
       2* 
22            CLASS-BOOK OF PHYSIOLOGY.
^.3._A magnified representation of a portion ln futures of the  ribs, the
         of areolar tissue.          external air passes  from the
lung  into  this  tissue, and continues inflating it till the
whole body becomes enormously distended with  air,  caus-
ing suffocation and death.   In the progress of disease, the
watery portions of the blood are  sometimes  effused into
this  membrane, causing dropsy.   When  the  finger  is
pressed on a dropsical limb, a hollow or depression is pro-
duced by the forcing out of the fluid  from this tissue  at
that particular point.
  41. The cellular  tissue  is found in  every part of the sys-
tem, except in compact portions of bone, teeth, and cartilage.
Its chief use seems to  be to connect together organs and
parts  of organs which  require a certain degree of motion
on each other.  It possesses great power of extensibility
and elasticity.
  42. Yarious  names have been  assigned to the cellular
membrane, corresponding to the different positions in which
it is found.  When inclosing those organs not exposed to
  What tissue is the primary form of all others?  How is the cellular tissue
formed ?  How is the cellular tissue sometimes inflated ? Where is the cellular
tissue found?  Wha't is its chief use?  What  different  names have been
given to the cellular tissue ? 
OF ANIMAL  BODIES.
23
the air, it receives  the name of serous membrane, from
a fluid secreted in*it, called  serum.  In the lining of
the respiratory passages and of the alimentary canal, it is
called  mucous membrane, from  a secretion  of mucous
which  is poured out from numerous glands beneath  its
surface.  Where it  forms a covering for the body, it is
known as the dermoid membrane, or skin. 
PLATE   III.
ORGANS OF CIRCULATION.
  Figure 1.----Front View of the Heart.—a, Right auricle,  b, Right ventricle,  c, Left
auricle,  d, Left ventricle,  e, Aorta. /, Pulmonary artery,  g, Superior vena cava.  A, A,
Coronary veins and arteries—the nutrient vessels of the heart.
  Fioure 2.----Section of the Heart, showing its  Cavities and Partitions or Septa.—a,
Right auricle,   b, Right ventricle,   c, Left  auricle,  d, Left ventricle,  e, Aorta.  /, Pul-
monary veins,  g, Superior  vena cava, j, Right pulmonary veins,  k, Left pulmonary
veins.
  Figure 3.----Ideal View of the Circulation.—a, Right auricle.  b\ Tho entrance of the
Buperior vena cava,  c, The inferior vena  cava,  d, Tricuspid valves, e, Right ventricle.
/, Pulmonary artery,  g, g, Branches of pulmonary artery.  A, A, Capillary vessels of tho
lungs,   i, Pulmonary  veins,  j, Left auricle.  A, Bicuspid valve.  I,  Left  ventricle,  m,
Arch of the aorta,  n, n, Arteries which distribute the blood to the head and upper ex-
tremities,  o, Descending aorta,  p, p, Capillary vessels of the systemic circulation.
  Figure 4.----Capillaries.—This  figure represents a highly magnified view of the  ar-
rangement of the  capillaries, between the branches of the arteries and veins, as found in
an intestinal villus,   a, Arteries,   b, Veins. 
Hartford, Conn 
 
THE BLOOD.
27
                    CHAPTER  III.

                        THE BLOOD.
  43. Ix all organized beings, the process of nutrition is
carried  on by means of a circulati ng fluid.  In plants, this
fluid is  called sap; in animals, it is called blood.
  44. The blood of insects is white or colorless.   In fishes,
it is red in the gills,  heart, and liver;  but nearly colorless
in the main bulk of the body.   In  the mammalia, birds,
and reptiles, it is of a dark purple color when drawn from
a vein,  and of a bright scarlet  when it  comes from an
artery.   It emits  an odor  peculiar  to the animal from
which it is taken.
  45. In a few minutes after blood is taken from a living
animal,  it begins  to coagulate, and become solid,  like  a
soft jelly.  If allowed to stand  for a few hours, the clot
will be found diminished in size, but firmer than before,
and floating in the midst of a yellowish fluid, called  serum.
  46. The serum,  or liquid, which remains  after coagula-
tion, is  composed principally of albumen and water.
  47. Albumen forms a very large proportion of the brain,
the spinal cord, and nerves.   It is perfectly colorless when
pure, and is coagulated or hardened by either heat or acid.
An example of it may be found  in the white of an egg.
  48. The  ivater of the blood is always one of its most
important constituents, and always forms by far the greater
proportion of its bulk—one thousand parts of the blood
containing from seven to eight  hundred parts  of  water.
The amount given off in perspiration, the state of the at-
mosphere, the fluid drank,  and many other circumstances,

  How is the process of nutrition carried on in organized beings?   What is
this fluid called in plants?—in animals?  What is the color of the blood in
insects?—in the mammalia, birds and reptiles?  How does the blood coagu-
late?  Of what is the serum composed?  Of what tissues does albumen form
a large proportion ?  What are some of the characteristics of albumen ? What
proportion of the blood is water?  What circumstances influence the quantity
of the blood ? 
28            CLASS-BOOK OF PHYSIOLOGY.
increase or diminish this portion of the blood, and make
it subject to frequent variations in quantity.
   49.  The clot or crossamentum is composed of fibrin and
numerous red particles, called blood discs or corpuscles.
   50.  Fibrin is white when obtained pure,  as  it may be
by repeated washings.   Its peculiar  property is to coagu-
late spontaneously.   It forms the basis of the muscles, and
is found in lymph and chyle.  It is also found in solution
in the serum, as the blood flows  in the vessels of a living
part, but coagulates soon after the blood is exposed to the
air, and forms first a jelly-like mass,  and then, as  the con-
traction progresses, it  entangles the coloring matter,  and
presses out the serum—thus forming an  imperfect analysis
of the blood.
   51.  The blood discs, which contain the coloring matter,
have a size and form peculiar to each species of animal in
which they exist.   In man, they are little round cells, flat-
tened like a piece of money, and from T7Votns to  ^tot^s

Fig i.—A, Corpuscles of human blood, magnified five hundred diameters, a, Particles collected in a
 columnar form. B, Red particles of the blood of the common fowl, b, A particle seen edgeways.
of an. inch in diameter.   {Fig. 4.)   In birds, reptiles, and
fishes, they become necessarily larger, till, in some species
of fish, they present a surface about  six  times as large as
those found in man.  The number of the blood discs cor-
respond very much to the temperature of the animal.  In
warm-blooded  animals,  they form  from  twelve to fifteen

  Of  what is the clot composed?  What i3 the color of fibrin when pure?
What is its peculiar property?  In what is it found?  How does the coagu-
lation  of the blood form  an imperfect analysis of the blood?  What is the
color and  form of the blood discs?  What is the  size of the blood discs in
different animals? 
THE BLOOD.
29
per cent, of the whole mass of the blood; in birds, fifteen
per cent.; in man, twelve or thirteen per cent.  In  some
of the cold-blooded animals—in fishes, for example—they
form only five or six per cent, of the whole weight of the
blood.  The coloring  matter of the blood  discs contains
nearly seven per cent, of iron.   In certain diseases, in
which the proportion of iron is diminished below the natu-
ral standard, the capacity of maintaining animal heat has
been found correspondingly reduced.   In such cases, some
preparation of iron has been found the best remedy.  From
these facts it is  inferred that the blood discs  perform an
important office in maintaining animal heat.
   52. By chemical analysis,  the blood is found to have
nearly the same elements, combined in  the same propor-
tions as they exist in the flesh of the animal.   It is there-
fore better fitted to renovate the tissues, and to carry.nu-
triment to every part of the system—to furnish at one
point the elements of  bone;  at another, those of muscle;
at another, those of brain, and so on.  The blood also
takes up  and carries off, through appropriate organs, all
waste particles; thus maintaining in the body a continuous
round of organization and  decomposition—of growth and
decay—a perpetual change of particles, new and old.

         CIRCULATION OF THE  BLOOD.

   53. The organs by means of which the blood is carried
from one part of the body to the other, constitute the cir-
culatory apparatus,  and the course of the blood through
the organs is called its circulation.
   54. If we commence with those animals which are lovv-

  What the number?  Under what circumstances is the iron found to be
diminished ?  What is the remedy in such cases ?  In what vital process do
the blood discs perform an important office?  What elements is the blood
found to possess by chemical analysis?  What does the blood carry to every
part of the system?  What does the blood take up and carry off?   What
is the circulating apparatus?  What the circulation ?  What is the condition
of the circulatory apparatus in different orders of animals? 
30
CLASS-BOOK OF  PHYSIOLOGY
est in the scale of organization, we shall find the apparatus
for circulating the  blood  exceedingly simple,  though it
becomes  more and  more  complicated  as  we ascend to
higher orders.
   55. In insects,  the blood is sent to various parts of the
body by the alternate contractions of  different portions of
a central vessel which runs  along the back, and thus forms
a rudimentary heart.  (Fig. 5, and fig. 1, Pl. I.)
    Fig. 5.—Dorsal Vessel of the
      Spider.—a, the abdomen ; i,
      the dorsal vessel or heart; c, u
      trunk passing to the head ; (/, </,
      vessels communicating with the
      organs of respiration.

   56.  Among  the Crustacea—of which the crab, lobster,
craw-fish, &c, are examples—there is a single sac or ven-
tricle, which receives the blood from the gills, and propels
it  to other parts of the body.   (Fig. 6,  and fig.  2, Pl.  I.)
   57.  In fishes, we have a distinct heart with two cavities
—an  auricle or  reservoir, and a ventricle or  propelling
organ.  (Fig. 7, said fig. 4, Pl. I.)
   58.  Eeptiles and  the perfect amphibia, such as the frog

  How is the blood sent to the various parts of the body in insects?  How
in  the Crustacea?   What is tne circulating apparatus  in fishes?—what in
reptiles ?
Fig. 6.—Circulation in Crustacea.
 —a, heart; b, gills; c, circulation
 through  the body; d, arteries; e,
 veins. 
THE BLOOD.
81
and the snake, have two auricles and one ventricle.  (Fig.
8, and figs. 5 and 6, Pl. I.)
          Fig. 7.—Circulation in Fishes.—a.  Fig. 8.—Circulation in Rep-
           heart; b, auricle; c, ventricle; d, circu-   tiles.—o, heart; b. ventri-
           lation through the gills, or lesser circu-   cle; c, c, auricles.
           lation; g, circulation through the body,
           or greater circulation;  e, arteries; /,
           veins.
        59. In  the mammalia (those animals which nurse their
     young) and in birds, we find parts equivalent to two hearts,
     such as exist in fishes, with a  complete double circulation.
     (Fig. 9.)   The heart is constructed on the same general
     plan in the  entire group of warm-blooded animals, so that
     the heart of an  ox, a  sheep,  or  a dog, may  be  taken  to
     illustrate the human heart.
        60. The form of the double heart  is somewhat  like a
     pear, as represented in fig. 1, Pl. II.  and fig. 1, Pl. III.
     In man, it is situated  in  the front part of the thorax, be-
     tween the lungs, with its  base  or broader  part  inclining
<     obliquely backward and upward towards the right shoulder,
     and its apex pointing forward and to the left side, between
     the fifth  and sixth- ribs,  where its beatings are  most dis-
     tinctly felt.
        Describe the heart, as found in mammalia and in birds? What is the form
     of the double heart?  Where is  the heart situated in man?
            3 
32
CLASS-BOOK OF  PHYSIOLOGY.
   61.  The heart is  protected from friction against  other
organs by a smooth serous  membrane, called pericardium
by anatomists, and the heart-case by butchers.  The peri-
cardium is not  only spread over  the external surface of
the heart,  but is reflected or doubled on itself in such  a
manner as to  form a closed sac or  bag, as represented
in fig. 10.
Fig. 9.—Circulation in Man.—a,
 right auricle; b, right ventricle;
 c, left auricle; d, left ventricle;
 e, aorta; /, vena cava; g, pulmo-
 nary artery; A, pulmonary veins.
-7»
Fig. 10.—Diagram of the Pericardium.—
 o, o, auricles; v, v, ventricles; p.p. pericar-
 dium.
   62. The heart  itself is divided in the direction  of its
length, into two halves, each  representing a single heart.
The walls of  the  left  half are thicker and stronger  than
those of the  right.    The reason is obvious:  the right
sends its contents only to the lungs, in its immediate prox-
imity, while the left propels the blood  to all parts  of the
system.   The walls of the auricles are also much thinner
than those of the ventricles, which require greater strength
to act as propelling organs.   The office of  the auricles is

  How is  the heart  protected from friction against other organs?   Describe
the pericardium.   How is the heart divided? Which  half has the thicker
and stnnghtest waKs?  Why are the walls of the left half thicker and stronger

It^  I' Twl     , ° ihC Wa"S °f thC aUrk1e ComPare with  *«e of Thr
ventricle?   What  is the office of the auricle? 
THE BLOOD.
33
Section or Right Side
only to receive  the blood as  it flows from the veins, and
their walls are accordingly thin and flabby.*
   63. The auricles and ventricles
are  separated from each other by
triangular folds  of membrane (fig.
11) on the right side, called trims-  c
pid valves (three-pointed), and  on
the   left  bibuspid  (two-pointed)
valves.   These valves are attached
to the walls of the ventricle by lit-  c
tie muscular cords, which prevent
them from  being forced up  into
the auricle during the contractions  c-
of the ventricle.   (Figs. 3 and 4,
Pl. IV.)  This simple mechanism Fji
is so perfect as wholly to prevent  °F the heart.—a, right auricle;
      J-           ■     j    sr         j, ventricle; c, orifice between the
the flowing back Of the blood into  tricuspid valves, d; e, c, ascending
           °                          and descending vena? cavae;/, pul-
the auricle.                           monary artery.
   64. There  are also  three valves at the  entrance of the
aorta or large artery, and the same number  at  the orifice
of  the  pulmonary artery.  These six valves are  named
semi-lunar, from the half-moon  shape of the folds of mem-
  How are  the auricles and ventricles separated from each  other?  How
are the valves attached to the  walls of the ventricle?  Describe the semi-lunar
valves.
  *The comparative thickness of the walls of the ventricle, and. the
structure of the valves, may  be illustrated most easily by examining the
heart of some animal.  For this purpose, the main vessels should be cut
i»ft" high up, and all  the fatty portions carefully removed with  a knife.
The pericardium should be opened one-half the distance round  the
!ii';irt, and then  turned off  to  expose the heart, or to be replaced at
iiltMsure.  The comparative thickness of the walls of the ventricles is
seen by making a transverse section through the heart, about one-third
the  distance from the apex to the base.  By a perpendicular incision
through each  of the external walls to the margin  of the auricle, the
cuspid valves, with their delicate tendons, are fully exposed.  The
auricles may be cut away at their margins.  The semi-lunar valves may
be exposed, by cutting away successive portions of the aorta and pul-
monary artery. 
34
CLASS-BOOK OF PHYSIOLOGY.
 brane.   They are attached to the walls of the artery at its
 exit from the ventricle, and each fold forms one-third of a
 circle.   (Figs. 4 and 6,  Pl. IV.)
   65.  When either set of  valves  become diseased, or fail
 to perform their office perfectly, the heart becomes irreg-
 ular and labored in its action, and in some instances sud-
 den death ensues.
   66.  The  arteries, veins, and capillaries are the channels
 of communication between the heart and the various  parts
 of the body.
   67.  The arteries are cylindrical tubes, composed of three
 principal coats—external, middle, and internal.
   68.  The external, or resisting coat,  forms a strong tough
 investment to  the artery, and gives  it its power of resist-
 ance to the heart's actions.
   69.  The  middle, or fibrous coat, is composed of elastic
 tissue, disposed in an oblique direction around the artery,
 and has for its office to equalize the flow of blood through
 the vessels.  If the heart impelled the blood  through an
 inelastic tube, at each impulse of the heart  a  quantity of
 blood would be ejected with a jerk from the other end of
 the tube, and it would cease to flow in the intervals of the
 heart's  contractions.  The elasticity  of this coat enables
 the vessel to accommodate itself to the quantity of blood
 which may be thrown into it, and its alternate distention
 and contraction serves to continue the propulsion of the
ventricle to the remotest extremities of the arteries with a
constant flow of blood.
  70. The contractile power of the middle coat enables the
arteries to close their divided extremities when they have
been cut or torn, so as sometimes to prevent hemorrhage.
If the artery be large, a ligature is usually found necessary;
  What consequences follow disease of the  valves?  What vessels are the
channels of communication between the heart and the various parts of the body ?
 Describe the arteries?  What is the use of the external coat of the artery?
Of what is the middle or fibrous coat composed?   What advantages are de-
rived from the elasticity of the middle coat ?  How is hemorrhage sometimes
 arrested in the smaller arteries? 
THE BLOOD.
35
but the  smaller branches seldom  require it.  This con-
traction of the divided end may be increased by the appli-
cation of cold or of stimulating substances, or by simply
pricking  or  twisting the  cut end of  the artery.  Fatal
hemorrhage is thus often prevented by irritating applica-
tions, or by the violence with which the vessels  are torn
asunder.
   71.  The internal coat is a thin serous membrane, which
lines the interior of the artery, and gives it a smooth, pol-
ished  surface, along which the blood  may flow with  the
least possible amount of resistance  from friction.
   72.  The arteries gradually diminish in size towards their
extremities, and finally terminate in minute hair-like ves-
sels, which are too small  to  be seen with the naked eye.
As they approach their extremities,  the divisions  and
ramifications  of the  arteries  are exceedingly numerous,
forming frequent communications or anastomoses with each
other; so that in case of obstructions in  one of the main
trunks,  numerous  lateral branches keep  up a supply of
arterial  blood to parts that  would  otherwise perish for
want of it.   These anastomoses are very numerous in the
arteries of the limbs and about the joints.
   73.  The veins are composed of three  coats, like the arte-
ries, but are much thinner in structure, and do not retain
a  cylindrical  form when emptied of their contents, but
become  flattened or collapsed,  The veins commence by
minute vessels in the capillaries, and unite to form larger
and larger branches, till  they terminate in large trunks
which return  the blood to the heart.  The velocity of the
blood  in the  veins is less than in the arteries, and their

  What is usually necessary to arrest  hemorrhage  from the large arteries?
How may the contractions of the divided end of  an  artery be increased?
Desciibe the internal coat.   How do the extremities of the arteries finally ter-
minate?  How is the danger of obstruction in the large trunks obviated ?  Of
how many coats are the veins composed? What  is their structure?  How
do the veins commence ?  How does the velocity of the blood in the veins
compare with that of the arteries'1
       3* 
86
CLASS-BOOK OF  PHYSIOLOGY.
diameter correspondingly greater.  When the  veins are
liable to pressure from the muscles between which  they
run, they are abundantly furnished with valves, similar
in form to the semi-lunar valves of the aorta and pulmo-
nary artery.  The free margins of the valves are turned
towards the heart, so as to prevent any backward movement
of the blood.   By pressing a finger on one of the veins of
the back of the hand, near the wrist,  and drawing it tow-
ards the knuckle, one or more of these valves can be easily
found.  (Fig. 12.)
  Fig. 12.—Valves of a Vein.—a,  Fig. 13.—Capillaries in Frog's Foot
    vein laid open; b, b, b, valves.              magnified.
  74. The capillaries (hair-like vessels) in man are  about
3 ^ o-th of an inch in diameter.  They are so minutely dis-
tributed to every part of the body, as to render it impossi-
ble to puncture  the  skin without wounding  several of
these microscopic vessels.  In the capillaries, the blood is
brought  in  immediate contact with  the tissues, and parts
with its nutritive elements.  They are the medium through
which the functions  of nutrition and  secretion are per-
formed, and the channels of communication between the
arteries and veins.   Fig. 13 shows a magnified represent-
ation of these vessels in the foot of a frog.  Fig. 4, Pl. III.,
displays their arrangement in the human intestine.
  What is said of the valves in the veins?  Describe the capillaries?  What
functions are performed through the capillaries? 
 
PLATE  IV.
ORGANS OF  CIRCULATION.-HEART  AND  LUN08
  Figure 1.----Front  View of Heart and Lungs.—Both  organs  are  stripped of theii
envelopes, the pleurae and pericardium.  The right lung is drawn aside, so as to uncover
the heart and large vessels.  The left lung is deeply dissected, to show the disTribution and
mode of ramification of the air-tubes and blood-vessels.
  a, The larynx,  b, The trachea.—The right lung is somewhat shorter than  the left, and
is divided into three lobes, c, d, e, while the left lung has but two lobes,/, g.  The surface
of the lobes is sub-divided into lobules, by the intersection of great numbers of depressed
lines.  A, Right auricle of the heart,  i, Right ventricle,  j, Left auricle.   A-, Left ventricle.
I, The aorta.  ?«, The pulmonary artery.  ■«, Left pulmonary veins.—These veins are four
in number, two for each  lung; and they return to  the heart the blood which has been
conveyed into the lungs by the pulmonary artery. The division of the pulmonary artery
into right and left branches, cannot be seen in this figure, being hidden by the  aorta,  o,
The superior  vena cava,  p, Root of the right innominate artery, springing from the arch
of the aorta,  q, Root of the left sub-clavian artery,  r, Root of the left carotid artery.
  Figure 2.---Back View of the Heart and f.ungs.—a, Larynx.   A, Trachea,  c, Right
bronchus,  d, Left bronchus,   e, Left auricle of the heart.  /, Left ventricle,   g, Right
pulmonary  veins.  A, Left pulmonary veins,  i, Left pulmonary artery.  /', Section of the
iorta.  k, Trunks of the brachio-cephalic veins (those which belong to the arms and head).
I, The opening of the inferior vena cava.—The sub-divisions of the pulmonary arteries and
veins, and of the air-tubes or bronchi, are seen accompanying each other in  the  left lung
in both figures.
  Figure 3.----Mitral Valve.—a, Membrane which forms the valve,  b, b, Columns ten-
dinas, cords by which the folds are drawn together.
  Figure 4.---A portion of  Tricuspid Valve.—a, Membrane of one of the folds,  b, b.
 Columns tendinis,  c, c, Portions of the walls of the ventricle.

   Figure  5.----Semi-lunar Valves, with Aorta laid open.—a, a, a, Folds of membrane.
 *, A portion of the aorta.

   Figure  C.----Semi-lunar Valves.—A, .INiM* of mr-mUraim.   B, Valvc-s of aorta.    'S3 

,J#;V ;--;-.  '"^V^   v- ■  \i'

Fl n . (',
 
 
THE BLOOD,
41
  75. The course of the blood in the circulation of man
may be easily understood, by reference to fig. 4, Pl. III.
Commencing, we will suppose, with the left ventricle (l),
the blood is  impelled through the semi-lunar valves into
the aorta (m), and along  its successive branches to  the
microscopic net-work of the capillaries (p p), which ramify
•through all the tissues of the body.   In'the capillaries, the
blood parts with its nutritive elements, becomes venous,
and is  collected into the small veins, and flows through
their converging branches into the main trunks, the vena3
cavse (b and c), and finally into, the right auricle (a).  From
the right auricle it is emptied through the tricuspid valves
(d) into the right ventricle (e).   This completes  the  great
or systemic circulation.
   76. From  the right ventricle the  blood is impelled
through the semi-lunar valves into the pulmonary arterj^,
and along its branches (g g) to the capillaries of the lungs,
to be exposed to the action of the air.   From the pulmo-
nary capillaries the blood enters in converging streams the
pulmonary veins (i i), which carry it to the left auricle (j),
and this completes the lesser or pulmonary circulation.
It is then emptied through the bicuspid valves (k) into the
left ventricle, where it started on its course.
   77.  At each contraction, the heart of a man in middle
age, whose blood averages about  twenty-eight pounds,
empties itself of two ounces of  blood, with  a  propelling
force of about  four and one-quarter pounds.   The  heart
of such a person contracts about  seventy-five times in each
minute;  so  that,  in every three minutes,  twenty-eight
pounds and two ounces pass through the heart, or a quan-
tity equal to the weight of the entire blood in the body.
  Describe the course of the blood in the circulation  of man. What changes
lake place in the capillaries?  What is the course of the blood from the right
ventricle ?  Of how much blood does the heart of a man in middle age empty
itself at each contraction ?  What is the amount of the propelling force of the
heart?  How many times does the heart contract in a minute? How long a
time will twenty-eight pounds of blood require  to pass through the heart ac-
cording to this estimate? 
42            CLASS-BOOK OF  PHYSIOLOGY.

  78. By the rapidity with which poisons are transmitted
from one part of the system to another, it is estimated that
in man the blood completes its entire circuit of the arte-
ries, capillaries, and veins of the greater or systemic cir-
culation, and  then of the pulmonary circulation,  to  its
original starting point, (the left ventricle,) in less than one
minute.
  79. The frequency of the heart's action varies at  differ-
ent periods of life, being  most frequent in infancy, and
diminishing to old age.  During the first year, the average
number of pulsations in a minute is from one hundred and
thirty to one hundred and fifty.   At the seventh year, the
number is from ninety to eighty-five;  in middle life, it is
about seventy-five; in old age, it  is as low as sixty, or
even fifty.   In the female, the heart beats more frequently
than in the male.   The action of the heart is also accele-
rated or retarded by various  circumstances affecting the
nervous system.  It is quicker  after than before eating,
and slower during sleep than when awake;  in the evening,
than in the morning;  and in the sitting, than in the  stand-
ing position.   Fear, anger, and the stronger passions, move
the heart to violent action.   Melancholy or sorrow  retard
it, both in force and in  frequency.  Hence a  temper of
uniform good-nature  is  always conducive to  long life,
while frequent indulgence in fits of passion induce prema-
ture disease,  and sometimes sudden death.

  How-long a time will be necessary, if we form our opinion from the rapidity
with which poisons are transmitted ? What is the frequency  of the heart's
contractions during the  first year ?—the seventh ?—in middle life ?—in old
age ? What other circumstances affect the frequency of the heart's action ?
What temper of mind is conducive to long life ? 
 
PLATE   T.
                    ORGANS OP  RESPIRATION.


  Figure 1.----Front View of the Cavity of the Thorax.—a, b, c, Lobes of the right lung.
d, e, Lobes of the left lung. /, /, The diaphragm, clothed with the pleura, g, g, Section
of the ribs. A, Appendage to the breast-bone, called the ensiform cartilage,  t, The heart
covered by the pericardium, the left lung being drawn aside to display it.  k, k, Internal
jugular veins.  /, I, Carotid arteries,  m, Larynx.
  Figure 2.---Posterior View of the Cavity of the  Thorax.—a, The larynx,  b, The tra-
chea,  c, e, The right and left bronchi,  d, aorta,  e, The heart. /, /, Tho diaphragm.
  Figure 3.----Lungs of a Frog.—a, Hyoidean apparatus. *, Cartilaginous veins at Um
root of the lungs,  c, c, Pulmonary sacs.
  Figure 4.----Section of the Lung of the  Turtle. 
PL.V
m
l. CICelloioIi'-h.
7654 
 
RESPIRATION.
47
                    CHAPTER IV.

                       RESPIRATION.
  80. Respiration is that process by which a  mutual
interchange  of elements is effected in every living being
between its circulating fluid and the  air.  Plants cannot
be perfected unless  the ascending sap  is exposed to its
chemical action, and animals cannot maintain life without
a perpetual renovation of the blood by its purifying influ-
ence.  There is in every class some provision for exposing
the nutritive fluids to the action of this essential element
of vitality.
  81. In plants, the process of respiration takes  place  in
the leaves.   Carbonic acid (which is composed of carbon
and oxygen) is absorbed from the air,  and decomposed:—
the oxygen is  set free  or escapes from the leaves, and the
carbon  is absorbed by the sap,  and transformed into the
various tissues of the plant.
   82. In animals,  the  process is  reversed.  Oxygen is ab-
sorbed, and carbonic acid, which is pernicious to animal
life, is given off.   Thus the two  great kingdoms of nature
mutually furnish those elements which are essential to the
life of each other.   Plants purify the air for the use of an-
imals, and maintain in it a supply of that element, without
which animals cannot  exist.  Animals, in turn, furnish the
essential element  for  the growth of all vegetable struct-
ures, by parting  with  that  which  is  useless and even
poisonous to themselves.
   83.  In animals,  the  necessary  condition for the function
of respiration is a  membrane supplied with the circulating

  What is respiration ?  What is said of the necessity of respiration in plants
and in animals ?   How does  the process of respiration take place in plants ?
Of what is carbonic acid composed?  How do plants dispose of the oxygen ?
__hov, the carbonic acid.?  How do animals dispose of the oxygen ?—how the
carbon?  How do  plants affect the air?  What is the necessary condition
for trie functions of respiration in animals ?
        4 
43
CLASS-BOOK  OF PHYSIOLOGY.
fluid on one side, and the air on the other.  But the same
principle is so modified in the different groups of animals
as to adapt it to  their various modes of life.   In some, this
is the only condition;  in others, there is a complication of
organs, all tending to make this condition more perfect.
                     84.  Thus, in the lowest groups, of
                   which the hydra is an example (fig. 14),
                   the respiration takes place  through the
                   whole  surface  of  the  animal,  and is
                   called cutaneous respiration.  This kind
                   of respiration  is found to  some extent
                   in all  the higher  orders of animated
                   beings,  and is of no  inconsiderable
                   importance  even  to man.  In  many
                   of  the  cold-blooded  animals   it  is
                   equally important with that performed
                   by the special  organs of  respiration.
                   The frog, for example, will live longer
 mg. m.-the hydra, or  with  his  mouth  and  nostrils com-
   Fiesh-waterPoijpe.    pieteiy closed,  than when his  skin is
2oated with a  substance through which the air  cannot
Denetrate.
   85.  All  the  animals which  possess a  special organ oi
 •espiration  may be divided in  two  large groups, viz:
 vater-breathing and air-breathing animals.   Each of these
groups also present two distinctive  modifications of the
respiratory organs, quite unlike each other.
   86.  In the lowest group of water-breathing animals, the
respiratory organs consist of prolongations of the  cutane-
 )us covering into fringes, such  as are represented in the

  How is this principle modified in different groups of animals ?  How does
respiration take place  in  the hydra ?   What  is this kind of respiration called ?
[n what other orders of animals is this kind  of respiration found ?  What is
said of its importance in cold-blooded animals ?—in the frog ?  In how many
large groups may all the animals which possess a special organ of respiration
be divided?   What modification in each of these? Describe the respiratory
organs in the  lowest group of water-breathing animals. 
RESPIRATION.
49
serpula.  (Fig. 15.)  In different orders of this group of
animals, the fringes are found in very different forms.   In
some, they are attached to the head,  and in  others, to the
side, and  serve  the double purpose of
respiratory and locomotive organs.
  87. In  fishes, which  belong to  the
highest  group of  water-breathing  ani-
mals, the respiratory organs consist of a
series of arches attached  to  the head,
each of  which  is  supplied with  a vast
number  of thin elongated plates, collect-
ively forming gills.
  88. The gills  of fishes  are  made  up
of  numerous little fibres,  sejb  close to
each other, like  the barbs of a feather.
Each fibre contains a slender  plate  of
cartilage, which gives it mechanical sup-  Fis-15-—The serpula.
port, and enables it to preserve its shape while moved by
the streams of water which are perpetually rushing through
the gills.  On the  surface of the fibres are distributed myr-
iads of blood-vessels, spread over every part like a delicate
net-work.   The whole extent  of this surface, exposed to
the action of air absorbed  from the  water, is exceedingly
great.   In the skate it is at least equal to the whole sur-
face of the human body.   The water itself does  not  act
on the respiratory  membrane, but is  merely the vehicle by
which the  air  is brought  in  contact with it.  It is well
known  that fishes cannot live any  length  of time in a
limited quantity of water which has no access  to fresh air.
When they are removed from the water, the filaments of
the gills almost instantly flap together, and adhere in such
  What is said of the form and attachment of the  fringes ?  Describe the respi-
ratory organs of fishes. The gills of fishes are made up of what ? How do the
fibres preserve their shape ? What are distributed on the surface of the fibres ?
What is said of the extent of this surface exposed to the action  of the air
absorbed from the water? How great is it in the skate?  Does the water
itself act on the membrane ?   What does ?  How are fishes effected by being
kept in water which has  no access to fresh air?
 
CLASS-BOOK OF PHYSIOLOGY.
a manner as prevents  the exposure of a great portion of
their surface to the air; but the portion which is exposed
shortly becomes so dry, that  the action of the air on the
blood is soon suspended, and  death ensues from imperfect
oxygenation.
                                    89.  In insects, which
                                  form the  lowest group
                                  of air-breathing animals,
                                  there is  a  special provi-
                                  sion  for conveying air
                                  to the circulating  fluids
                                  through  tubes  of  thin
                                  delicate  membrane. (Fig.
                                  16.)  The abdomen of an
                                  insect is made  up of a
                                  series  of joints, each of
                                  which is composed of two
                                  plates, one on the upper
                                  and one on the  lower
                                  side.   At the  edges of
                           ¥   *  each joint, where the two
                                  plates meet, there  is an
                                  opening, called  the stig-
                                  ma, through which the
                                  air passes into the tubes.
                                  These tubes extend to
                                  every part of the insect,
                                  and convey air to all the
                                  tissues, forming a very re-
Fig. 16.—Respiratory Apparatus or Ins ct.—a,    -i -i -i    -i   ...  ,  o
 head; b, first pair of legs; c, origin of-wing; d, d, marKable  SUDStltUte IOr
 stigmata; e, air-tubes or tracheae ; /, air-sacs.    & circulation of tne blood
through a special organ of respiration.
  90. The highest group of air-breathing animals possess
a distinct  lung, which is found  greatly  modified in the
  What takes place when they are removed from the water to the air?  What
is the cause of death ?  How is air conveyed to the circulating fluids of insects ?
Describe the air-tubes of in'-rct* V.T!i.it do the highest  group of air-breathing
animals possess 1
 
                         RESPIRATION.                      51

different classes of animals that belong to this group.  The
lung is seen in its sim-
plest condition  in the
snail, (fig.  17,) where
it consists of a respira-
tory sac  with a blood-
vessel distributed on its d
surface.
  91. In frogs, the lungs
consist of two bags, on
the walls of which  are
  ,,    „ ,           t i   Fig.11.—Interior of  a  Snail.—a, the heart;  b,
CellS Ot DUt Very Slight  large blood-vessels branching over the sac, c;  d,
 -,    ,    ,              _  artery which conveys the blood to the general sys-
Cieptn;  tne process Ot  tem; e, part of the stomach; /, the liver.
respiration is carried on through the membrane that forms
the  cells.  (Fig. 3, Pl. Y.)
   92. In turtles, the interior of the lungs is divided into
several  cavities  which  communicate  with  each   other.
(Fig. 4, Pl. V.)*
  In what animal is the lung seen in its simplest condition ?   Describe the
respiratory organs of a frog—a turtle.

  * A very beautiful preparation, to show the distribution of the blood-
vessels  over the membrane of the lung, together with the membrane
itself, may be prepared from the lungs of a turtle.  Procure a turtle at
least six or eight inches in length, cut off the head, and  immediately
saw  the lower shell from the upper at the sides, and  then with  a knife
dissect off the muscles from the shell.  When the  shell  is removed,
almost the first object that arrests the attention  is the heart, still per-
forming its  functions with  as  much apparent regularity as if nothing
had happened, which it will continue to do for several hours, though its
action grows more and more feeble.   On either side of the heart, and
partly under the scapulae, the lung may be seen in  a collapsed state.  A
quill should be inserted into the trachea, and the lungs inflated, for the
purpose of rendering their  position more apparent, when  they can be
easily removed with the scissors, though it must  be  remarked that the
slightest  scratch  spoils the preparation.   As  soon  as the lungs are
removed,  they should be  inflated to their utmost capacity, a ligature
applied to the trachea, and then hung in the air to  dry.  In half an hour
you  have an exceedingly handsome and useful preparation, which may
be preserved for anv length of time.
        4* 
62            CLASS-BOOK OF  I'll V^luLuGV.
Fig. 18.—Lungs of the Ostrich.—a,
 the heart; b, the stomach; c, c, the
 intestines; d, the trachea or windpipe;
 e, e, the lungs; /, /, /, air-cells, in
 which are also seen the orifices of the
 tubes through which these air-cells
 communicate with the lungs.
                              93.  In birds, the respiratory
                            apparatus consists of two lungs,
                            which are made up of  numer-
                            ous cells.  The air also passes
                            through the lungs into  large
                            sacs along  the. abdomen, and
                            even into the bones.  (Fig. 18.)
                            Eespiration  in birds is  more
                            frequent than in any other class,
                            and their movements are cor-
                            respondingly more active.  The
                            large amount  of  air contained
                            in the sacs and bones of birds
                            must  also serve  to give them
                            more  lightness and buoyancy
                            for  their aerial flights.
                               94.  The  capacity  of the
                            lungs,  as a respiratory organ,
depends in  each group of animals on  the extent of the
respiratory membrane, which  is  invariably  increased in
proportion as  the cells become more numerous in a given
space.  Thus,  in the  entire group of warm-blooded ani-
mals, where the  function of  respiration  is at  its  highest
perfection, we find  an almost infinite number of  cells.
                  95.  In the human lungs it is estimated
                that there are at least six hundred millions
                of air cells, collectively presenting a surface
                equal  in extent to about  thirty times the
                whole  surface of the body.   Each cell, as is
                represented in^. 19, is constructed on the
                same plan as the single air-sac of the snail,
and consists of a thin delicate membrane, with an artery
  Describe the respiratory organs of a bird.   How do birds compare with
other animals in the frequency of their respirations?  What  special  benefit
do birds derive from the large amount of air contained in their sacs and bones?
Upon what does the capacity of the  lung depend ?  In what group of animals
are  the air cells most numerous?  How many air cells  are there in the
human lunj-1 ?  flow i? each  nir cell constructed ?
Fig. 19.—Air-cell,
 with blood-vessels
 branching over it. 
RESPIRATION.
53
distributed on its surface in minute capillary vessels, which
terminate in veins that carry the blood back to the heart.
   96.  The whole substance of the lungs is thus made up
of these minute cells, with their air and blood vessels.
   97.  The  lungs  are supplied
with air through the larynx and
trachea.  (Fig. 20.)
   98.  The larynx is an irregular
cartilaginous tube, forming the
upper extremity of the windpipe,-
as the whole tube is commonly
called.  The larynx  is situated
immediately below the root of
the tongue,  and forms  the pro-
tuberance in the front part of the
neck,  called "Adam's Apple."
The larynx gives passage to the
air which is inhaled into the
lungs or exhaled from them, and
Contributes essentially tOthe pro- Fig. 20.—a, the larynx; i,the trachea;
 -1   ,.    r.     1      ^            c, bronchial tubes; d, the left lung.
auction ot vocal sounds.
   99.  The trachea is composed of about eighteen cartila-
ginous rings, connected together so as  to  form  a  tube,
which is capable of maintaining a uniform size.
   100. On entering the chest, the  trachea divides into two
trunks, called bronchi, one of which goes to the right and
the other to  the left lung.   As soon as the bronchi  enter
the lungs,  they branch off into numerous divisions and
sub-divisions, their ultimate  extremities  terminating  in
air cells.   (Fig. 1,  Pl. YI.)
   101. The human lungs occupy the greater part o£ the
  Of what is the whole substance of the lungs mainly made up ?  How are
the lungs supplied with air?  Describe the larynx.  How is the larynx situ-
ated, and what is it sometimes called ? What other use has the larynx besides
to give passage to the air?  How is the trachea formed ? How does the tra-
chea divide on entering the chest?  How does the bronchi divide?  Where
are the lungs placed in man ? 
54            CLASS-BOOK OF  PHYSIOLOGY.

chest, the  heart  being the  only organ of much volume
which is included in it.   The size of the lungs in different
individuals corresponds very nearly to the capacity of this
cavity.   Hence, persons with full broad chests rarely suf-
fer from weak or consumptive lungs, while those who have
narrow  and contracted chests are as seldom exempt  from
these evils.
  102.  The chest, or thorax, is a cavity closed on all sides
from the entrance of air, and  its bony walls afford an ad-
mirable protection to the delicate organs included within it.
                             103.  The  walls  of the tho-
                           rax  (fig. 21) are  formed by
                           the breast-bone in front, by the
                           ribs and spine on the sides and
                           back, and by  the diaphragm
                           below.
                             104.  The  ribs, to the num-
                           ber of twelve on each side, are
                           attached to the bones  of the
                           spine  by  slightly  movable
                           joints, and  to the  breast-bone
                           by flexible cartilages. The ribs
                           are also connected to each oth-
                           er by the intercostal muscles.
                             105.  The diaphragm (fig. 5,
                           Pl. VI.)  is a large muscular
                           partition, which separates the
     Fig. 21,-Human Thorax.     c^est frQm fae abdomen.
  106.  The internal surface of the chest is lined through-
out with a serous membrane,  called the pleura, which is
reflected over the external surface of the lungs.  A serous
fluid is constantly exhaled from this membrane, causing
the parts to glide on each other free from friction.
  How may we judge of the size of the lungs in different individuals? De-
scribe the chest.  How are the walls of the thorax formed ?  Describe the
ribs—the diaphragm.  How is the internal surface of the chest lined?—and
how is it kept moist ?
 
 
PLATE  VI,
                     ORGANS  OP  RESPIRATION.


  Figure 1.----The Larynx, Trachea, and Bronchi.—a, The larynx,  b, The trachea.
 c, e, Bronchi,  d, d, d, e, e, e, Outlines of the lungs. /, /, /, &c., Bronchial tube.—These
 tubes continue to ramify, decreasing in size, until they can only be distinguished by the
 microscope,  g, g, g, Lymphatic vessels and ganglia.

  Figure 2.----A Portion of the Tissue of the Lungs, Showing the blood-vessels, capil-
 laries, and air-tubes, magnified fifty diameters.—A vein, a, is represented ramifying with
 an artery, b, around the intricate air-cells, c, c.

  Figure 3.---The Plural Surface of a Portion of Lung, magnified three diameters,
 showing the form and great abundance of the air-cells.

  Figure 4.----Plural Surface enlarged.

  Figure 5.---The Diaphragm,  separated from the Body.—a, The right vault of  tho
 diaphragm, which is higher than the left,  b, b, The right and left crura or pillars of  the
 diaphragm, by which it is attached to the spinal column.

  Figure 6.----Lateral View of the Outlines of the Thorax and Abdomen.—This figure
 Is intended to show the respective positions of the diaphragm and the walls of the chest
 and abdomen, in inspiration.  The dotted lines, a, a indicate the contour of the front of
the chest and abdomen, when the chest is filled with air after inspiration,  b, b, The line
of the diaphragm, when it is  contracted  and flattened in inspiration, pressing  down  the
abdominal contents, and causing the abdomen to project, e, c, The line of the chest and
abdomen, after the air is expired,  d, d, The arch of the diaphragm, when  relaxed in
expiration, rising into tho interior  of the thorax, and drawing inward and downward
its point of attachment to the front of tho body, c. 
■m	\-^ik .,.'/ \
	
-,-'"■:■ Jf	\ -'~^ ■^^^
"%■	Jr" li x ■':
Fij
Fia-5.
^JK

E.C.Kellogg.I'ifl'--
Kartfurd. Conn.. |
      1 
 
RESPIRATION.
59
   107.  In the  process  of respiration,  the cavity of the
chest is constantly increased and diminished in size by. the
alternate  elevation  and  depression of the ribs and aia-
phragm, as explained by fig. 6,. Pl. VI.
   108.  AVhen the lungs are empty, and the respiratory
organs at rest, the ribs hang downward and  inward, and
the diaphragm  extends upward into the cavity, reducing
it to its smallest capacity.  In the act of respiration, which
inflates the  lungs,  the  ribs  are elevated,  increasing the
diameter of the cavity, and the diaphragm is at the same
time  depressed, increasing  its length; thus  making the
capacity of the chest greater in all  directions.
   109.  As  the cavity of the chest  is enlarged,  air rushes
into the lungs, and inflates them, to fill it just.as perfectly
as when at rest.  The lungs are thus comparatively pas-
sive in the respiratory movements, always accommodating
themselves to the size of the cavity in which they are con-
tained.   The active process of respiration is performed by
the respiratory muscles (d, e, i, fig. 21,) attached  to the ribs
and by the diaphragm.
   110.  When the ribs  are confined by a  tight dress or
otherwise, respiration  is  carried on mainly by the dia-
phragm.  When the abdomen is so closely confined or so
distended as to prevent the descent of the diaphragm, res-
piration is performed  by the respiratory muscles attached
to the ribs.
   111.  It is therefore  a law of our organization that  all
parts  of our dress should be loose about the chest and ab-
domen.  When the fullest action of the respiratory organs
is in  any way restrained, respiration becomes correspond-

  How is the cavity of the chest increased and diminished in size?  What is
the position of the ribs and  diaphragm when  the respiratory organs are at
rest? What change takes place in the act of respiration? How is the chest
filled when it is enlarged ?  By what organs is the active process of respira-
tion performed ?  How is respiration carried on when the rifc'«  are confined?
How when the dinphragm ?  Whnt law of our organization do theee parts
teach u«1 
60            CLASS-BOOK OF PHYSIOLOGY.

ingly more frequent and more laborious.  For this reason,
all persons who diminish to  any extent the capacity of the
chest or of the abdomen, breathe oftener than is natural,
and with slight exertions pant for breath, like one who has
been taking most violent exercise.
  112.  Under ordinary circumstances, the number of inspi-
rations  of an  adult are from  fourteen  to eighteen  in each
minute.  In  mental excitement or active  exercise, they
become more frequent.  Infants and young persons breathe
more rapidly  than adults.
  113.  The average quantity of air taken into the lungs
at each inspiration  is about  twenty cubic inches; at  six-
teen inspirations  in each minute, twenty thousand cubic
inches of air pass through the lungs in an hour—making
two hundred  and sixty and  one-third cubic feet in a day.
  114.  As the air passes through the  lungs, it parts with
about one-fourth  of its oxygen, and  receives  nearly an
equal amount of carbonic acid.  It  is also saturated with
watery vapor, and warmed to nearly the same temperature
as the blood.
  115.  In this process, the venous blood is purified of the
waste and worn-out  particles, which  are taken up from the
capillary circulation in the tissues, and converted  into
arterial blood.
  116.  It is estimated that in every minute a quantity of
blood equal to the whole amount in the body is subjected
to this  renovating  process  in the  lungs,  and  in every
twenty-four hours about twenty ounces of watery vapor
and six ounces of carbon are exhaled from the lungs.

  When the action of the respiratory organs is in any way restrained, what is the
effect on respiration ? What is the number of respirations in adults ? How is it
affected by exercise or by excitement ? How much air is taken into the lungs
at each respiration ?  How much air  will pass through the lungs in an  hour?
—in a day ?  How is the  air changed in passing through the lungs?  What
change takes pjpce in the blood during  this process?  How much  blood
is subjected to this  renovating process every minute?  What is exhaled
from the blood ? 
RESPIRATION.
61
  117. If the lungs become diseased, so  that their func-
tion is imperfectly performed, or if the air we breathe is
already charged with impurities which have escaped from
the lungs, or if there be an insufficient supply of air, the
whole system suffers.   The blood is burdened with  an ac-
cumulation of impurities, and the nervous system becomes
depressed and inactive for the want of pure arterial blood,
its natural stimulus.
  118. For this reason, persons who sleep in small imper-
fectly-ventilated rooms, feel  languid and oppressed  in the
morning, instead of being refreshed and invigorated.
  119.  In churches and public assemblies,  when  there is
an insufficient supply of pure air, a feeling of fatigue, lan-
guor, and head-ache is very soon experienced.
  120.  A due supply of pure air may be regarded as one
of  the  most essential conditions  of healthy respiration.
Life cannot be sustained for any considerable time with-
out  air,  nor can  it  be continued in carbonic acid  gas.
Therefore, every apartment we occupy, whether public or
private, should be provided with reliable means  for con-
veying off the poisonous gas and supplying the pure air.
   121.  When we consider the delicate  structure  of the
lungs, and  the absolute necessity of efficient ventilation
we are not surprised  that one-fourth to one-third of our
race  are scourged with lung  diseases; since little  or no
care has been taken to obey this imperious law of animal
existence.
  122.  Every room not provided with that noble ventila-
tor,  a fire-place, should have an aperture for the entrance
of pure air, and another for the exit of the gases thrown

  If the lungs be diseased or the air be impure, what is the effect ?  What is
the effect of sleeping in poorly-ventilated apartments? How are public assem-
blies  affected by impure air ? What is said of the  importance of a due
supply of pure air?  With what should every apartment we occupy be pro-
vided?  What proportion of our race are scourged with lung diseases?  How
should every room be ventilated ?
       5 
62
CLASS-BOOK  OF  PHYSIOLOGY.
off by respiration; and  no  family which neglects  these
conditions of health,  can expect exemption from disease*

  * A very interesting experiment, to illustrate the importance of ven-
tilation, may be made by lowering a lighted taper or candle attached to
a flexible wire into an open-mouthed glass jar, holding one or more
pints.  In a very few minutes carbonic acid will be found sufficient to
extinguish the taper.  That it is carbonic acid may be ascertained by
pouring into the jar lime-water, which immediately  becomes turbid from
the formation  of carbonate of lime.  That carbonic acid is also pro-
duced by respiration may be made to appear by filling and inverting the
jar in water; then pass the end of a tube (or, if  nothing better be at
hand, an open straw,) under the jar, and breathe through the tube into
the jar till the water is  entirely displaced.  The  hand, or a piece of
glass or of brown paper, must now be put snugly  on the mouth of the
jar, which is to be inverted and. placed on the table.  On removing the
hand, plunge the taper into the respired air, and it will be instantly
extinguished.  The necessity for a supply of oxygen may be shown
by  inverting the  jar, and  passing up the lighted taper.   As fast as the
oxygen is consumed, the nitrogen, which is lighter than atmospheric
air, occupies the upper portion of the jar, causing the taper to  grow
dim or be extinguished, according to the position in which it is held. 
ANIMAL HEAT.
63
                    CHAPTER  V.

                      ANIMAL HEAT.

  123. The power of maintaining animal heat is closely
allied with the process of respiration.  In those animals
which possess the most perfect development of the respira-
tory organs, the  animal  heat is maintained at a uniform
temperature, whatever may be the variations  of tempera-
ture in the surrounding medium.
  124. In birds, respiration is  more active  than in  any
other class of animals, and their temperature is uniformly
higher than any  other, ranging from 106° to 112° Fahren-
heit.  In the  mammalia, it is from 95° to 105°.  In man,
at adult age,  it  varies,  in different individuals, from 98°
to 100°.   In fevers, it is several degrees higher: in scarlet
and typhus fevers, as high as 106° or 107°.   In health, it
is about  one degree and a half lower during sleep than
when awake.   Hence we always require additional cloth-
ing during sleep.
  125. In the young of all  animals, the temperature is a
few degrees higher than  in the adult, and respiration is
correspondingly  more frequent; but the  sensibility to cold
is much  greater,  and consequently the power of resisting
it much  less.   For this reason, when young  animals  are
exposed to a low temperature, without protection, the ani-
mal heat rapidly diminishes, and, if  artificial heat be not
afforded, death ensues.
  126. Those animals which possess the power of main-
taining a uniform standard of temperature, are called warm-

  What relation has the power of maintaining animal heat to the process of
respiration. How does the respiration and temperature of birds compare with
other animals ? What is the temperature in the mammalia ?—in man ? What
is it in fevers?  What during sleep ? What is the temperature and respira-
tion of young animals? How do they bear exposure to cold ?  What are those
animals called which possess the power of maintaining a uniform temperature? 
64
CLASS-BOOK  OF PHYSIOLOGY.
blooded animals.  Eeptiles, fishes, and all the lower order
of animals, are cold-blooded.
   127. In the snail, whose respiratory apparatus we have
seen is  exceedingly simple, the temperature is very little
above that of the  surrounding air.  The temperature of
fishes is always nearly  the same as that  of the*water,
rising or falling with the warmth or cold of the sea, river,
or lake which they inhabit.   In reptiles, which come near-
est to warm-blooded animals in the development of the
respiratory organs, there  is the  power to maintain  the
temperature of the body a few degrees higher than  the
surrounding medium,  though  this cannot endure a very
low temperature without becoming torpid.
   128. In some cold-blooded animals, a  most remarkable
provision exists for preserving life when the temperature
of the body is reduced below the freezing point.   As the
cold increases, the organs become more and more inactive,
until at length all the animal functions cease, and torpidity
ensues.   Some species of insects and fishes may be frozen
solid  like ice, and yet retain life, and again become active
when exposed to a proper degree of warmth.  The freez-
ing appears  to produce no chemical change,  either in the
tissues or the fluids; it merely suspends the operation of
their  affinities until, by a  return of warmth,  they are ex-
cited  to action.*

What are those called which do not possess this power ?  What order of ani-
mals are cold-blooded ?   What is  the temperature of the snail ?   What  of
fishes?  What is the temperature of reptiles?  What remarkable provision
exists in some cold-blooded animals for preserving life at a low temperature ?
What examples are given ?  How is this fact explained ?
  * Some very interesting phenomena have been observed in certain
warm-blooded animals, which hybernate or spend the winter in a semi-
torpid state.  One of these hybernating animals, common in New Eno--
land, is a species of marmot, usually called woodchuck.  This animal
enters his den or burrow about the first of October, closino- the entrance
after him with  hard-packed earth.  There he remains until about
the first of April, most of the time enjoying a very profound sleep. 
ANIMAL HEAT.
65
  129. A comparative view of the process of respiration,
in connection with the development of animal  heat, very
clearly shows that the lungs,  under the  influence of the
nervous  system, are  the organs which maintain the  tem-
perature of the body.  The various tissues, together  with
the  food, supply the blood with  carbon,  which combines
with the oxygen of the respired air to form carbonic  acid,
and produce one hundred and thirty-five degrees of heat
for every ounce of carbon.   The chemical combination in
this process is  essentially the  same as that of combustion.
   130.  The lungs, however, must  not be regarded as  the
only source of  animal heat.   For  it is probable that cer-

  What does a comparative view of the process of respiration, in connection
with the development of animal heat, show ?  With what does the carbon of
the blood combine ?  What is formed by this process ?  How does it compare
with combustion ?   Are the lungs the only source of  animal heat ?

and  breathing just often enough to keep himself comfortably warm.
During the five months which he remains in this  condition,  his whole
number of respirations does not exceed thojse of  eight or ten days of
activity in the summer months.   All hybernating animals become enor-
mously fat in the autumn before  they begin their " winter's-nap."  This
fat, which contains a very large proportion of carbon, is gradually ab-
 sorbed, and combined with the oxygen of the lungs, in order to main-
 tain the necessary temperature;  and the animal comes  forth from his
 hiding-place in the spring greatly emaciated, and with a most excellent
 appetite.  During the long period of his sleep, digestion  and the other
 animal functions not necessary to respiration have been entirely suspend-
 ed, and  the  small supply of oxygen indispensable to  his diminished
 respiration has been obtained from the air which penetrates through the
 earth to his burrow.  These animals possess no peculiarity of structure
 by which they are particularly suited to this mode of life.  They seem
 rather to have an  instinctive  impulse to adopt this economical method
 of passing the winter, because, during that  season, their usual  supply
 of food can no longer be obtained.  Indeed, some other animals, whose
 habits do not commonly  lead them to hybemate, have the power of pro-
 longing life in a similar manner; and the same species which hybernate
 in a cold climate will not do so in a warmer one.   This habit of sleep-
 ing through the winter  seems,  therefore, by a wise provision of the
 Creator, to be given to certain animals, in order to supply the failure of
 all other means of maintaining life.
         5* 
66
CLASS-BOOK OF  PHYSIOLOGY.
tain chemical changes, resembling those in the lungs, are
constantly taking place throughout the tissues of the body,
whereby a small amount of heat may be evolved.
  131. The  variations of  atmospheric temperature  have
long since been observed to exert  an important influence
over the health of the lungs.   The diseases of the lungs
prevail most during those  months and in  those localities
where the weather is the most variable, and diminish most
in proportion as the weather becomes more uniform.
  132. To guard  against lung diseases, constant care and
vigilance  must be  exercised to preserve the warmth of the
body as  uniform  as  possible  by  artificial means.  The
clothing  during winter should be  sufficient uniformly to
protect the body against  sudden changes, and it should not
be changed two suddenly or at  too early a season  for the
thinner habiliments of hot weather:  for it is much better
to suffer a little inconvenience from  the heat  of flannels,
in the spring, than to  risk injury to the lungs by taking
them off, as is too  often done on the first warm day.

  What other source is  there ?  What causes affect the health of the lungs ?
When and where do diseases  of the lungs prevail most ?  What is necessary
to guard against lung diseases ?  What care should be exercised in regard to
clothing ? 
DIGESTION.                     67
                    CHAPTER VI.

                        DIGESTION.
  133. Digestion is that process in animals by which the
food is prepared for the nutrition and growth of the body.
  134. The food of plants is  derived  from the earth and
air around them, in a liquid or gaseous state, and is already
adapted to their use.  But the materials from which animals
derive their  nourishment require a certain degree of pre-
paration before they can be taken up by the nutritive fluid.
  135. All animals are therefore provided with organs by
which their  food  is acted upon, so  as to fit it to be con-
veyed into their systems; and in no organs of the body is
the wisdom and skill of the Creator more manifest than in
the means with which  every animal is provided for secur-
ing a subsistence.
  136. In those animals which live on food that  requires
but  little preparation,  the organs of digestion  are very
simple.  In  the class of polypes, for instance, a single sac
or cavity, in which  the food is dissolved,  is all  that is
required.
   137. In the higher  orders, there is an apparatus  for
masticating  or grinding the food;  and instead of the sin-
gle digestive sac  of the polype,  there  are  three  distinct
cavities:  in  the first, the food is mechanically divided;  in
the second, it is reduced to a pulpy mass; and in the third,
its nutritive portions  are taken up, to be conveyed into
the circulating fluid.
                    MASTICATION.
   138. The  apparatus  for masticating or dividing the food
mechanically is found  in accordance with the kind of food
  What is digestion?   From what  source is  the  food of plants obtained?
How do animals derive their  nourishment ? With what organs are all pro-
vided ? In what  animals are the digestive organs very simple ?  What do
we find in the'higher orders? What  is said in regard to the apparatus for
masticating the food ? 
68            CLASS-BOOK OF PHYSIOLOGY.
which the animal requires,  and the rapidity with which
the process of digestion is to be carried on.
  139. If the process of digestion  is to be performed rap-
idly, the food requires division into small portions, so as
to present as large an amount of surface as possible to the
solvent fluid.  Thus, in those animals which chew or mas-
ticate their food most perfectly, the process of digestion
is performed in a few hours;  while  in those which swallow
their  prey whole, as the snake, several days are required.
  140. The apparatus for masticating the food presents a
great  variety  of forms, and is modified  in the  different
orders of animals according  to the kind of food on which
the animal subsists;  and yet it is so strictly in accordance
with each animal's organization, that an experienced anato-
mist can tell, by the  inspection of this apparatus alone, the
class to which the individual belongs.
  141. Insects which  masticate their food are furnished
with jaws of a great variety  of construction, and all admi-
rably adapted for the service they are to perform.  "Some
are sharp, and armed with spines and branches for tearing
flesh; others are hooked, for seizing, and at the same time
hollow, for suction.   Some  are like shears, for gnawing
leaves, and others more  like grindstones, of a  strength
and solidity^ sufficient to reduce  the  hardest  wood  to
powder."
  142. Mastication, in most  of the higher animals, is per-
formed by means of teeth  implanted in the jaws, and so
arranged as to act against each other with a cutting, grind-
ing, or chewing power, according to the nature of the food
on which they operate.
  143. In man and most of the mammalia there are three
kinds of teeth, namely, incisors, canine  and  molars.   The

  How is the food divided when the process of digestion is performed rapidly ?
How do the organs of mastication indicate the class to which each animal
belongs?  What is said of the jaws of insects?   How is mastication per-
formed in most of the higher animals ? How many kinds of teeth are there
in man and the mammalia?            •             . 
DIGESTION.
69
incisors have a thin cutting edge, intended simply to di-
vide the food; the canine have a conical form, adapted to
tearing it in pieces;  the molars are formed  for bruising
or grinding the food.
  144.  There are also two sets of teeth—the temporary or
milk teeth, and the permanent teeth.
      Fig. 22.—Development or Teeth.—a, the      Fig. 23.—Dental
       gum; b, the lower jaw; c, dental capsules.         Capsule.
  145.  The first set, or milk teeth,  (fig. 22,) are twenty in
number—four incisors in the front of each jaw, and  two
canine and four molar teeth on each side.   All these teeth
fall out at from six to eight years of age, and are gradu-
ally replaced by the permanent teeth, (fig. 23,) which are
a                 c             *
  Fig. 23.—Human Teeth.—a, incisors; b, canine tooth; c, bicuspid teeth; d, molars.
thirty-two in  number, sixteen in each jaw, namely: four
incisors, two  canine, four bicuspids  or small molars, and
six true molars.   The last molar does not make its appear-
ance until long  after the rest, and hence it is called the
wisdom-toothi
  146.  The human teeth are composed of three distinct

  Describe each.   How many sets of teeth are there ?  How many teeth are
there in the first set ?   How many in the second ?  When does the last mo-
lar make its appearance ?   Of what are the human teeth composed ?
 
70
CLASS-BOOK OF  PHYSIOLOGY.
structures—the ivory or tooth-bone,  the" enamel,  and the
cementum.  The ivory, which constitutes the main part of
of the tooth, resembles bone in its structure, except it con-
tains a  larger amount of mineral matter,  and is harder
than bone.  The enamel forms a crust over the whole sur-
face of the crown of the tooth, and protects it from wear-
ing out  or decaying.  It is composed of ninety-eight parts
in a hundred of mineral matter, and is the hardest of  all
animal  substances.   The cementum  forms a covering to
the root of the tooth, and serves  to make  its attachment
in the jaw more  firm.  Fig. 24 represents a section of a
human tooth.
   Fig. 24.—Section of          Fig. 25.—Jaw and Teeth of Rabbit.
    a Human Tooth.—
    d, dental cavity.
   147. Other  animals have the enamel distributed differ-
ently.  The incisors  of the rabbit and other rodentia or
gnawing animals have the enamel on the front side of the
tooth—the ivory  being on the back part, is worn off first,
leaving a sharp point of enamel, as represented in fig. 25.
The continual wearing away of the incisors in  this class
of animals is provided for by their constant growth from
below.
   148. In  the horse, ox,  and other grass-eating animals,
the enamel forms upright plates in the  midst of  the ivory
which forms the  main body of the tooth.  The ivory be-
ing the softest, is worn away first, leaving the enamel in

  Describe each structure of the  teeth. How is the enamel distributed on
other animals?  Describe the incisors  of a rabbit.  Describe the teeth of
grazing animnl?.   What is said of the form of the teeth?
 
DIGESTION.
71
Teeth of Herbivorous
 Animal.
projecting ridges, which  are admi-
rably adapted to the grinding action
of the tooth.   (Fig. 26.)
  149.  The  particular form of the Fie-m
teeth of any  animal corresponds
with the nature  of the food on which that animal subsists.
In  those which  live  entirely on  animal flesh, the  molar
teeth are so compressed  as to form cutting edges,  which
work against each other like a pair  of  shears.  (Fig. 27.)
In  animals which live on insects,  the molar  teeth are
raised into conical points,  which lock into corresponding
depressions  in the teeth of the opposite jaw.  (Fig. 28.)
Fig. 27.—Teeth of Carnivorous
        Animals.
Fig. 28.—Teeth of Insect-eating
        Animals.
Fig. 29.—Teeth of Fru-
  givorous Animal.
When the  animal lives on soft fruits, these teeth are sim-
ply raised into rounded elevations.  (Fig.
29.)  When they are destined to grind
harder vegetable substances, their surface
is flat and roughened, as in those of the
horse and ox.
  150.  In fishes and reptiles, the teeth
are short and bent backward, and  are
thus  adapted to seizing and  retaining
their prey,  rather than dividing or tear-
ing it in pieces.  The head of the rattle-
snake is represented by^.  30. In  the
front part  of  the upper  jaw  are two
  What is the form of the teeth in animals which live on flesh?—on insects?
—on fruits ?  What is the form of the teeth in fishes and reptiles ?
Fig. 30.—Rattle-Snake. 
72
CLASS-BOOK OF PHYSIOLOGY.
poison fangs,  consisting of hollow tubes, through which
the poison secreted in the glands on each side of the head
is injected.
   151. The teeth are brought into action by means of the
muscles,  which move the lower jaw in a manner corres-
ponding with  the  nature of the food.  In  flesh-eating
animals,  the lower  jaw  has a  hinge-like action, opening
and shutting like a pair of shears, and the sharpness of their
teeth renders  them a  powerful cutting instrument.   The
jaw of the herbivorous  animals has a lateral motion, by
which the food is ground between the rough surfaces of
the  teeth.   In  the  gnawing  animals, the  lower jaw  is
drawn rapidly backward and forward, and  the teeth are
thus made to act as a powerful file, by which  the  hardest
shell is quickly rasped to a powder.
   152. In  man, we find a combination  of each of the
above movements.   He can move the lower jaw upward
and downward,  from side  to side, and forward and back-
ward, and is thus adapted  to the mastication of a mixed
diet of all the  endless variety of articles upon which he is
accustomed to subsist.

                  INSALI V ATION.
   153. Insalivation  is the  act of blending with the food
the saliva, which is a watery fluid secreted in the parotid,
sublingual and submaxillary glands, and poured into the
mouth during the process of mastication.  The  parotid
glands are situated on each side of the cheek, just below
the ear;  the sublingual, under  the tongue;  and the sub-
maxillary, near the angles  of the lower jaw.
   154. The use of the saliva is to make the food soft and
moist,  so that it can be more easily swallowed,  and be
rendered more solvent in the digestive fluid of the stomach.
  How are  the teeth brought into action ?  How does the  lower jaw act in
different animals?  Describe the movements of the lower jaw in man.  What
is insalivation ?  Where are the salivary glands situated ? What is the use of
the saliva ? 
DIGESTTON.
to
When the organs of mastication are at rest, only saliva
enough is secreted to keep the mouth moist; but its flow
is greatly increased  when the movements of mastication
commence, and when food is taken into the mouth.  The
sight or even the thought of food will frequently cause
the  saliva to  be  poured  out more  freely,  making "the
mouth  water," as it is termed.  During the  progress of
fever, the secretion of saliva ceases or is very much dimin-
ished, and the mouth becomes dry and parched.
   155.  If the food  is imperfectly masticated, or is swal-
lowed very  rapidly, the saliva is also imperfectly mixed
with the food, and the work of digestion becomes  corres-
pondingly more difficult.   In this country, impaired diges-
tion and loss of general health is  a frequent result of
rapid eating.
   156.  When  mastication  has
been completed, the food is trans-
mitted in successive portions to
the stomach by the act of degluti-
tion or swallowing.  The food is
first collected into a  ball or mass
by the action of the muscles of
the cheeks  and tongue, and is
conveyed back  against a sort of
movable curtain (the vail of the
palate),  which  hangs from the
sides of the palate so as to touch
the tongue by its lower  border,
and makes  the  mouth a closed
cavity.  (Fig. 31.)  The  instant
  ,   i  n .   -,      i j. _ •  „.*. j-1,,'^ Fie.  31.—Section of Mouth and
the food IS  brought against tniS  throat.-«, vail of the palate; b,
                     j  n     .1__nharvnx: e, oesophagus; d,trachea;
partition, it opens, and allows the  £ tl^roid' glanQ r f, hu.ynx; ff, saii-
food to pass into the pharynx.  va,-ygia„d; A, tongue.
The oesophagus or food-pipe receives the morsel from  the
   When is the saliva secreted ?  How is the secretion of saliva affected by
 fevers?  How is digestion affected by an imperfect mastication of the food?
 How is the food  transmitted to the stomach ?
        (5
 
74            CLASS-BOOK OF PHYSIOLOGY.

pharynx, and forces it along to the stomach by the alternate
contraction  of its successive portions.   The  undulating
movement produced by the contractions  may be  readily
observed in the oesophagus of a horse while in the act of
drinking.
  157. The form and size of the  stomach varies in differ-
ent animals, according to  the nature of the food to be
digested.  It is found in its simplest condition in the class
of plypes, of which the hydra (fig. 14) is an example.  In
this animal, the stomach is merely a bag or sac with one
opening, as  represented in fig. 4, Pl. VII.  Around this
orifice to  the  stomach  are from six to ten arms, for  the
purpose of seizing its prey, which is swallowed whole, and
readily digested without  any mechanical  division what-
ever.   In the  planaria,  (fig. 1, Pl. VII.)  an animal of a
little  higher organization,  numerous branches  or canals
pass off from the stomach to various parts of the body.
  158. In all  the higher orders, the stomach has two  ori-
fices, and  is  prolonged into a canal, as represented in fig. 5,
Pl. VII.,  called the alimentary canal.   In the carnivorous
animals, whose food is flesh, which is easily dissolved,  the
stomach is very simple in  its structure, and the alimentary
canal comparatively short.
  159. The most complex stomach and the greatest length
of alimentary  canal is found in ruminating animals—as the
ox, sheep, deer, &c.   In this class of animals, the stomach
possesses  four distinct  cavities, as represented in fig.  32,
which represents the stomach of a sheep.  The food is at
first imperfectly masticated in the mouth, and  passed to
the first stomach,  to be mascerated;  it is then passed into
the second  stomach,  where the fluids  are received, and

  What is said  of the form and size of the stomach ?  In what class of ani-
mals is it found in  its simplest condition ?  Describe the stomach of a hydra.
What variation  is found in the planaria ?  Describe the stomach  of the higher
orders of animals.   In what class of animals is the stomach the most com-
plex?  How many cavities are there in the stomach of a ruminating animal?
Describe the  course of the food through the several cavities. 
 
PLATE   fll.
                      ORGANS  OF  DIGESTION.


  Figure 1.---Digestive Apparatus of a Planaria.—a, Mouth, surrounded by a circulai
sucker,  b, Buccal cavity,  c, Orifice of the oesophagus,  d, Stomach,  t, Ramification!
of gastric canals.  /, Cephalic ganglia and their filaments.

  Figure 2.----Digestive  Apparatus of a  Fowl.—a, CSsophagus.  b, Crop,  c,  Second
stomach, in which the gastric juice is secreted,   d, Gizzard,  e, Liver. /, Gall-bladder.
g, Bile ducts, h, Pancreas,  i, Duodenum,  k, Large intestine—its two cseca, /.

  Figure 3.----Digestive  Apparatus of a  Beetle—a, The head and jaws,  b, Crop, c,
The gizzard,  d, The true digestive stomach, surrounded by its follicles,  e, The long ves-
sels which constitute a rudimentary liver.

  Figure 4.----Ideal Representation of the Simplest Form of a Stomach, as found in the
hydra.

  Figure 5.----Ideal  View of the Alimentary Canal, as  found in the higher orders of
animals. 
PL.V1T.
 
 
DIGESTION.
79
rolled into a small ball, to be returned to the mouth, and
undergo a second process of mastication, called  "chew-
ing the cud."   When  the food  is again swallowed, it is
passed into the third and thence into the fourth stomach,
to go through the final process of digestion.
Pylorus.  4th Stom. 2d Stom.   1st Stom.
Fig. 32.—Stomach of the Sheep.
  160. Birds, which  have no means of masticating their
food,  are provided  with a  peculiar modification of the
stomach.  In those which live on grain—as the common
fowl,  quail,  &c.—the  food is first  moistened and softened
in the crop, just as it is in the first stomach of the  sheep.
It is then passed through a second stomach (where it  is
saturated with the gastric juice) into the gizzard.   In the
gizzard,  it undergoes a triturating or grinding  process,
which is  accomplished by means of pieces of quarts or
other angular stones, which the  bird  instinctively swal-
lows  for the  purpose,  and  the  strong  muscular  action
of the organ.  The digestive apparatus of a fowl is repre-
sented in fig. 2, Pl. VII.
   161. A powerful gizzard is also found  in most insects,
but it is placed above the digestive stomach instead of be-
low it, as in birds.   In fig. 3, Pl. VII., is represented the
digestive apparatus of a carnivorous beetle.
  How is the  stomach modified in  birds?  How is  the gizzard placed in
insects ?
         6* 
80
CLASS-BOOK OF PHYSIOLOGY.
   162. By a  comparative view of the  structure of the
stomach in the different groups, we cannot fail to observe
a  regular  gradation, from the simple digestive sac of the
hydra to the complex apparatus of the ruminating animals.
In man, the stomach is intermediate between the  carniv-
orous  and herbivorous mammalia,  and  is  very  clearly
adapted to a mixed diet.
   163. The stomach in man is an oblong membranous bag,
placed obliquely across the abdomen, and just below the
diaphragm.   Its average capacity in the adult is about
one  quart, though it may be distended to contain a much
larger quantity, or  be contracted to a  very  small size.
                                         It has two open-
                                         ings—one towards
                                         the  heart, called
                                         the cardiac orifice,
                                         which receives the
                                         food from the oeso-
                                         phagus—and the
                                         other at the right
                                         orsmallen'dofthe
                                         stomach, called the
                                        . phyloric orifice, for
                                         the   transmission
                                         of food to the small
                                         intestines.   The
                         h.—a, the oesophagus; n      o +i    ,
 6, the cardiac orifice ; c, the great end of the stomach; d, its 10rm 01 tne StOm-
 lesser or pyloric end; d', the pyloric orifice; e, the lesser   r    /J  +"U
 curve; /, the greater curve; g, the rugae or wrinkles of the &CU and  tlie pOSl-
 mucous membrane; h, the pylorous; i,j, the duodenum, +:„„  -.{• :+_ _.-„„
 or first portion of the small intestine; k, the duct through W.OU  OI 1LS Open-
 aVuoCdenum.bile and pancroatic juice are pou,ed into the ings are represent-
                                     %   ediny^. 33.
   164. The stomach possesses three  coats—the outer or
serous, the middle or  muscular, and  the inner or  mucous
coats.   .
  What do we observe by a  comparative view of the stomach in different
animals? Describe the human stomach.   How is it placed?  What is its
average capacity in the adult ?  How many openings has it, and what are they
called?  How'many coats does the stomach possess, and what are they?
 
DIGESTION.
81
   165.  The serous coat is the same as the external coat of
all the organs which are not exposed to the  air.   Its  use
is to secrete a fluid which  lubricates the surface  of  the
organs, and prevents friction between them.
   166.  The muscular coat is composed of numerous mus-
cular fibres,  such as we see in lean  meat.   These fibres
possess great power of contraction, being drawn up and
stretched out  again like  India-rubber without  injury.
Some of these fibres run  lengthwise of the organ, some
wind around it in  the form of rings, and others run  ob-
liquely across it.  By the alternate contracting and relaxing
of these fibres, a great variety of motion is produced during
the  process  of digestion, causing the  food  to be rolled
about and moved  successively over every portion of  the
inner or mucous coat.  In the act of  vomiting, there is a
spasmodic contraction of all the fibres, throwing the con-
tents of the stomach back into the mouth.
   167.  The  mucous  membrane (fig.  34)
lines the inside  of  the stomach with a
very soft and velvety investment.  It is
not  elastic, like the other coats, but is
drawn  into folds when the  stomach is
contracted,  and  spreads out  smoothly
when it is dilated.   This coat secretes a^^r^^JSS
murcous or slimy matter, which protects J£Jf (Jjfh ^mouths
the stomach from being unduly irritated °om ^elST1*1 thebot"
by its  contents,  and it also  pours  out
from numerous little follicles or glands the gastric juice, in
which the food is dissolved.
   168.  The gastric follicles perform  an important part in
the process of digestion.   They are of a tubular form, as
represented in fig. 35, from ^oth to  aiUth of an  inch in
diameter.  When there is no food  in the stomach, these

  Describe the serous coat of the stomach—the muscular coat—the mucous
coat.  What does the mucous coat secrete ?  What is secreted by the gastric
follicles?  What is the use of the gastric juice?   Describe these follicles.
 
82            CLASS-BOOK OF PHYSIOLOGY.
        n       follicles or glands  are  at rest; but imme-
        q^<\   diately on the introduction of food, they
         x9>    commence secreting actively an acid fluid,
                which exudes in drops, running down the
                walls of the stomach, and  soaks  into  the
                substances within it.
                  169. The gastric fluid is a very powerful
                solvent of all proper food of  every kind,
                whether animal or vegetable.   It is indis-
                pensable  to digestion, and is found  do
                where but in the living stomach.
                  170. The amount  of  gastric fluid  se-
                creted  at one time, corresponds with  the
Fig. 35.—onb or the quantity of food which is then needed by
  Tubular Follicles t   .  "-,           ■ i        t -i   •
  or the stomach, the  body  as nourishment. It begins to
                flow as soon as the first mouthful of food
is introduced into the stomach, and continues to be poured
out till the demand  for nourishment is supplied, and then
ceases.  If more food be taken than  is sufficient for  the
wants of the system, it will remain undigested,  and  be-
come a  source of irritation and  oppression; or, being
mixed with that previously received into the stomach,  the
digestion of the whole is retarded.
   171. The sense of hunger is felt when there is a demand
for a  fresh supply of nourishment, and the stomach is in
a condition to pour out its secretion.   If the food be then
swallowed no faster  than the gastric fluid is prepared to be
mixed with it, hunger or the desire  for food will cease
when the secretion ceases, or when just food  enough has
been taken;  but if the food be swallowed  twice as fast as
it can be supplied with gastric juice, the sense of hunger
will  continue till twice as much is taken as is actually re-

  How does the gastric juice act on all kinds of food"?  With what does the
amount of gastric juice correspond?  When is it secreted ?  How is the food
disposed of when more is taken than is required ?  When is the sense of
hunger experienced?  When does it cease to be felt?  What is the conse-
quence of swallowing the food twice as fast as it should be? 
DIGESTION.
88
quired.  Hence, rapid eating creates an unnatural appetite,
frequently causing nervous  irritability, and dyspepsia or
disease of  the  stomach.  In this country, where men are
governed more by the excitement of business than by any
regard to health, rapid eating is a prevailing sin, the con-
sequences  of which are apparent in a greater  proportion
of dyspeptic complaints than are to be found in any other
country.
   172. AVhen the proper kind of food  has been taken in
proper quantities, the  fibres of the muscular coat of the
stomach alternately contract,  pressing the mass of food
backward  and forward, and from  side to side, exposing
every part of it to the action of the gastric juice, until its
solution is complete.  This  process lasts from two to five
hours, or even longer, according to the kind of food and
the thoroughness with which it has been masticated.  The
agitation of the food is assisted by the action of the respir-
atory  organs,  in  alternately raising and  depressing the
diaphragm whenever the air is inhaled or exhaled  from
the lungs.
   173. "The readiness with which the gastric fluid acts
upon the several articles of food is in some measure deter-
mined by  the minuteness of division, and the  tenderness
and the moisture of the substance presented  to  it.  By
minute divisions  of the food, the extent of surface  with
which the digestive fluid can come in contact is increased,
and its action  proportionably accelerated."  Hence, when
the food is thoroughly masticated,  it digests with greater
facility.  Tender  and moist substances also digest more
easily than those that  are tough, hard, and dry; because
they are more easily as well as more thoroughly penetrated
by the gastric fluid.
  174. The value of any particular substance, as an article
  What evils result from rapid eating?  Describe the manner in which the
food is moved backward and forward in the stomach.  How long does this
process last?  What circumstances facilitate the action  of the gastric juice on
the food? 
84             CLASS-BOOK OF PHYSIOLOGY.
of diet, is not in all cases in proportion to its digestibility;
for many substances that are easily soluble  in  the gastric
fluid afford  only a small amount  of nourishment,  while
others that are more difficult of solution are highly nutri-
tious.   Fresh fish, for instance,  may be  digested  in less
than half the time required for beef-steak,  though the beef-
Rteak is decidedly the most nutritious.  A substance, to be
nutritive, must  not only .contain an  abundance of those
elements which go to form the tissues of  the body, but it
must be capable of being digested by the gastric fluid or
some other secretion in the alimentary canal, and of being
assimilated to the blood.
   175.  When digestion  is completed in  the stomach, the
food and gastric juice are thoroughly mixed, and converted
into a pulpy mass, called chyme.  There are many circum-
stances, besides the  nature  of the food, which affect this
process.
   176.  Only a sufficient quantity of food  should be taken
to fairly fill the stomach, and not to distend it.
   177.  Sufficient time  should elapse  after  each meal to
allow the stomach to become empty before a fresh supply
is taken.  This interval in adults should generally be five
or six  hours, though it varies with the kind of food, the
condition of the stomach, and the constitutional peculiari-
ties of each individual.   In young persons, where all the
functions are performed with more activity and vigor, the
intervals between the meals may be much  shorter than
in adults.
   178.  Gentle exercise, both before and  after each meal,
is favorable to digestion;  while excessive exertion, whether
bodily or mental, retards it.

  Is the value of a particular article of diet in proportion to its digestibility I
What properties do  render an article of diet nutritive ?  What is the food
converted into when digestion is complete ?  What should be the quantity of
the food? What time should be allowed between each meal?  Why should
the intervals between the meals be shorter with young persons  than with
adults?  How does exercise affect digestion? 
 
PLATE   VIII.
                       ORGANS  OF  DIGESTION.


  Figure 1.----General View of the Digestive Organs of Jl/an.—This figure is intended
to give a general idea of the forms and relative positions of the organs of digestion.—a,
The oesophagus.  J, The stomach,   c, The duodenum,  d, d, d, Convolutions of the small
Intestine,  e, The coecum.  /, Appendix of the coecum. g, Opening of the small into tho
large intestine,  h, The ascending colon,   i, i, Transverse arch of the  colon, j, The de-
scending colon.  /;, The liver.   /, The gall-bladder,  to, The pancreas', mostly covered by
the stomach, o, The spleen.—In this figure, the liver is raised up and the transverse arch
of the colon  drawn down, in order to show parts which they cover when in their natural
situation.

  Figure 2.----General Aspect of the Abdominal Viscera.—In this figure, the  anterioi
walls of the abdomen are removed, so as to  show the organs  in their  natural positions.
The small intestine is removed.—a, The liver, situated beneath the right arch of  the dia-
phragm,  b, The stomach,  c, Epiploa, or floating folds of the peritoneum,  d,  Summit
of the gall-bladder,  e, e, Large intestine, showing all its courses.

  Figure 3.---The Chyle-Vessels and the  Thoracic Duct.—a, A portion of the Bmall
intestine.  6, b,  Origins of lacteals.  c, Mesentery,  d, Mesenteric glands,  e, Lymphatic
vessels.  /, Thoracic duct,  g,  Aorta,  h, Thoracic duct, curving downward and forward,
to empty its chyle at the junctions  of the left jugular and sub-clavian veins.

  Figure 4.----The Pancreas.—This figure is given to show more clearly the situation
and connexions of the pancreas,  a, The pancreas.  A, The duodenum,  c, The gall-blad-
der, d,  Duct of the gall-bladder, which  communicates with  the hepatic duct, «, which
leads from the liver.  /, Duct of the pancreas, which opens into the common bile-duct,"',
through which the combined secretions of the pancreas and the liver are poured into the
duodenum.

  Figure 5.----The Liver.—Section of the liver, showing the ramifications of the vessels.
The hepatic  vena porta? is a division bf the abdominal vena portse, into which empty all
the veins of the digestive organs.  It sends branches into ull parts of the  liver.  After
these branches have reached the capillary state, they are succeeded by the roots of the
hepatic  veins which unite into three large veins which empty into the inferior vena cava.
a, The right  or  greater lobe,  b, The left or smaller lobe,  c, Groove which lodges the
umbilical vein,  d, Hepatic vena portse.  f,  Hepatic artery. /, Inferior vena cava.

  Figures 6 and 7.---Liver.—Figure 6 represents a horizontal section of two superficial
lobules  of the liver, showing the probable arrangement of the biliary ducts,  a, a, Inter
lobular  branches of the hepatic vein*,  b, b, Trunk of biliary ducts.

  Figure 7  represents a horizontal section of three superficial lobules, showing the two
principal syetems of blood-vessels,  a, a, Inter-lobular veinB proceeding from the hepatic
veins,   b, b. Inter-lobi lar plexuses formed by branches of the portal veins. 
P. (:.KrllU£-y Lith 
 
DIGESTION.                      89
  179. A quiet and tranquil state of mind is also essential
to good digestion.
  180. Drinks taken  in  large quantities materially inter-
fere with the process of digestion.   The juices secreted by
the stomach  itself are  sufficient for the solution of most
articles of diet; and whenever a superabundance of liquid
is swallowed, the first effort of the stomach is  to get  rid
of it.  This  it does by absorbing the liquid at once and
without  change  through the blood-vessels of the mucous
coat.   The digestion  of the more solid materials  is  not
commenced until the liquid is disposed of.
  181. As soon as any portions of the food become suffi-
ciently digested  to mix Avith the gastric fluid, and form
chyme, they  are sent  through the pyloric orifice of  the
stomach into the duodenum, or first portion of the aliment-
ary canal.   (Fig. 33.)   Around  the pyloric  orifice (d), at
the inside,  is a thick band or  valve, called  sphincter.
When digestion is not going on, this sphincter, as well as
a similar one at the  cardiac orifice (b), is so completely
closed that none Of the contents of the stomach can escape.
But towards  the termination of the digestive process,  the
pyloric offers less resistance.  First it yields to allow  the
successively digested  portions to go through it, and after-
wards it allows  the passage of even  undigested portions,
which are always  retained in the  stomach  much longer
than those portions that are readily digested,  and produce
the irritability and suffering so often experienced after eat-
ing indigestible substances.
  182. In the intestinal or alimentary  canal the food is
further acted upon, and undergoes  other changes.
  183.  The alimentary canal is divided into tAvo portions,
named, from their difference in diameter, the small and the

  What effect has the mind  on digestion ?  How do drinks affect digestion
when taken in large quantities?  How does the stomach get rid of the fluids?
What course does the food take when it has become sufficiently digested to
form chyme? Describe the pyloric orifice of the stomach.  Into how many
portions is the alimentary canal divided ?
       7 
90
CLASS-BOOK OF  PHYSIOLOGY.
large intestines.   This distinction is much less marked in
carnivorous animals than  in  those which feed on vegeta-
bles, and the length of the canal differs greatly in the two
orders.   In the tiger, for instance, the intestines are about
three times the length of the body.   In the sheep, they
are about  twenty-eight  times longer  than the body,  or
seven times as long as those of the tiger in proportion to
the size of the animal.  In those animals Avhich live on a
mixed diet, the  intestines are of a  medium length.   In
man, they are about six times the length of the body.
   184. The small intestine, which commences at the pyloric
orifice of the  stomach and terminates  in the large intes-
tine, is about twenty-five feet in length in man, is a narrow
tube with  thin walls, and  is  coiled in various directions,
as represented at d, fig. 1,  Pl. VIII.
   185. The large intestine, or colon, is about five feet in
length, and resembles in appearance a long sac divided into
numerous pouches.
   186. The intestines, like the stomach, have three coats—
the peritoneal or serous,  the muscular, and the mucous.
The mucous membrane of the small intestine is found in
transverse  folds,  which greatly increase the extent of its
surface.
                    187. In the substance of the mucous
                  membrane, glands are imbedded, one of
                  which is represented in fig. 36, and the
                  surface is  studded with minute process-
                  es, termed villi.
                    188. Through these villi the nutritive
Fig. 36.-sinole gland of portions of the digested food is absorbed,
   SMALL ;NTBSTINE-    and conveyed  by a set of vessels, called
lacteals, into the general circulation.
   189. After  the chyme or digested  food has passed out
  What is the length of the alimentary canal in the tiger?—in the sheep?__
in man ?  Describe the small intestine—the large intestine.  How many coats
have the intestines? What glands  are imbedded  in the mucous membrane of
the intestine ?
 
DIGESTION.                     91
of the stomach into the small  intestine, it becomes mixed
with the bile secreted by the liver, and with the juice se-
creted by the pancreas or sweet-bread.
  190. The pancreas is a long narroAV gland, situated partly
behind the right side of the stomach, and within the first
curve  of the  small intestine, as represented at m, fig. 1,
Pl. VIII.   The  fluid which  it secretes  seems to be of a
nearly similar nature with saliva, and is  supposed to assist
in digesting fatty substances, and rendering them fit  for
absorption.
  191.  The liver is the largest gland  in the body.  It is
situated in the right side, beloAV and  in contact with the
diaphragm, and is divided  into several lobes.  At its loAver
side is the gall-bladder, into Avhich the bile is poured, after
being  secreted.  The gall-bladder  thus  serves as a reser-
voir to the bile.  Its duct opens into a duct leading direct
from the liver, and forms Avith  it the common bile-duct,
through which the bile is  poured  into the small intestine
at the same point with the duct from the pancreas.  These
ducts are represented in fig. 4, Pl.  VIII.
  192.  The bile  is a greenish-yelloAV fluid, having  an ex- )
tremely bitter taste and a nauseous  smell. It is constantly^
 ecreted by the liver; but, during  fasting, it accumulates )
in the gall-bladder, whence it is poured out on the intro-'
duction of food into the stomach.
  193.  By the mingling of bile and pancreatic juice Avith
the chyme in the small intestines,  chyle is formed.  The
chyle is a whitish milk-like fluid, with a somewhat saltish
taste.  It is, in fact, imperfectly-formed blood,  and nearly %
resembles blood in  its constituent parts.  The chyle is ab-   j
sorbed as the digested food passes along through the small  J
intestine.  The residue of the chyme, consisting of indi-*/

  What changes does the food undergo after passing out of the stomach?
Describe the pancreas.  What is supposed to be the use of the fluid secreted
by the pancreas?  Describe the liver. How is the gall-bladder  situated?
What are the properties  of the bile ?  How is the chyle formed ? How is ii
absorbed ?
/ 
92
CLASS-BOOK OF  PHYSIOLOGY.
gestible substances, gradually becomes more and more dry
and hard, till it is at length carried into the large intestine,
and thence excreted from the system.
  194. The food and the several secretions mixed with it
are carried through the intestinal canal, and sloAAdy exposed
to the action of  the absorbent vessels by the peristaltic or
vermicular movements  of the intestines.   This movement
is effected by means of the successive  contractions and
dilations of the  intestinal coats, which extend  in a wave-
like manner throughout the tube.   In health,  this move-
ment is slow, and generally unperceiA^ed by the mind; but
it becomes very perceptible  in diarrhea, or when  acceler-
ated by the influence of purgatives.
   195.  The natural movements of the bowels are indis-
pensable to the continuance of health, and they should not
be restrained by tight waist-bands or ligatures  around the
body.   The habit of wearing  garments  that are too tight
is a frequent cause of inactiAre or constipated boAvels, and
finally leads to impaired health and disease.

  What movements  force the passage of the food along the alimentary canal?
What effect does the wearing of tight garments have on the  natural move-
ments of the bowels and on health? 
ABSORPTION.                    93
              v"    CHAPTER VII.

                       ABSORPTION.
  196.  Absorption is that process by which all the various
elements of the body are taken  into the circulation.
  197.  All the tissues of the body, except the enamel of
the teeth, and some of very Ioav organization, as the hair
and nails, possess to some degree the power of absorption.
  198.  Fluids are absorbed most  readily, and none are
absorbed with so great facility as water.  A large propor-
tion of the weight of the body  is due to the water which
its  tissues  absorb.  Muscle, in drying,  loses three-fourths
of its weight, and blood four-fifths.   Mummies have been
found of adult size with all the organs entire, but reduced,
by  the  evaporation of the watery fluids, to  a weight not
exceeding  eight pounds.
  199.  The process of absorption is performed throughout
all the tissues by two sets of vessels, viz: the Igmphatics
or lacteals and blood-vessels.
  200.  The  lymphatics—a portion of which are also lac-
teals—constitute a peculiar and distinct system  of vessels,
which are distributed to every part of the.body  where
there are blood-vessels.  The lymphatics derive their name
from the peculiar limpid fluid or lymph which they convey.
  201.  Those which have their origin in the mucous mem-
brane of the alimentary canal have received the name of
lacteals, from the milky  appearance of the chyle  Avhich
they absorb.
  202. The lymphatics are  minute and delicate vessels,
with walls so thin  that they are nearly invisible  unless
  What is absorption ? What tissues possess the power of absorption ? To
what is a large portion of  the weight owing?  How much of its weight does
muscle lose in drying?—and blood, how much?  To how small a weight have
mummies been found reduced ?  By what vessels is the process of absorption
performed?  What are the lymphatics?  From what do lymphatics derive
their name ?   What are the  lymphatics called that  have their origin in the
mucous membrane ?  Describe the lymphatics.
       7* 
91
CLASS-BOOK* OF PHYSIOLOGY.
distended with some colored substance.  They commence
in closely meshed net-work, or in loops distributed upon
the external surface of  all the organs, and  interspersed
among the proper  elements and blood-vessels of all the
several tissues.
Sm^mmk^^Mv   203. Externally the lymphatics present a
        |fg|||! constricted or knotted appearance, OAving to
Fv.37.-LYMPHATics.the  existence of numerous valves, formed
by semi-circular  folds of the lining  membrane, arranged
in pairs,  (fig.  37,) and  their edges  coming together so
as to prevent the flow  of fluids,  except in the direction
towards the heart.  By this arrangement, all muscular or
external pressure accelerates the flow of lymph, as it does
that of the blood in the veins.  In reptiles and some birds
the flow of the lymph is effected by muscular sacs, called
lymph-hearts.
  204. The lymphatic glands are small, oval, and some-
what flattened or rounded  bodies, composed of a plexus
of minute lymphatic vessels, and a plexus of blood-ves«
sels convoluted or  twisted upon  each other, and  inclosed
in a thin cellular capsule, in such a manner as to form small
knots or kernels,  as they are sometimes called, when they
become inflamed  and SAvollen. In scrofulous persons, these
glands are exceedingly liable to become enlarged, particu-
larly on the sides of the neck and in the armpits.
  205. The contents of the lymphatics pass  through the
lymphatic glands, and undergo a process of digestion, by
which they are renovated and fitted for further use in the
animal economy.
  206. The lacteals, or lymphatics of the alimentary canal,
commence in the villi of the mucous membrane, as repre-

  How do they commence ?  What is the appearance of the lymphatics
externally ?  How  are the valves formed ?  Of what use are the valves ?
How is the flow of lymph effected in reptiles? What are lymphatic glands?
What are they sometimes called when they become inflamed ?  How are the
contents of the lymphatics affected by passing through these glands ?  How
do the lacteals commence ? 
ABSORPTION,
95
Fig. 38.—Diagram of Mucous Membrane.—A, in the
 intervals of digestion; B, during digestion; a, a, absorb-
 ent vessels ; *, b, absorbent cells of a villus;  c, c, pits or
 follicles between the villi.
senled in fig.  38.
Each villi resem-
bles in appearance
a  minute  papilla
or point in the mu-
cous  membrane,
and is formed of an
extremely delicate
membrane, termed
epithelium Avhich
contains a plexus
of lacteals, all
forming a fine net-
work in the sub-
mucous tissue, (fig.
39.)  Each  villus  sends  forth only p^r-
one  lacteal  vessel, and this so small |j
as to be imperceptible to the  naked ;
eye.                                 ||
   207. As the lacteals issue from the | ■ ^
villi, they unite  to form large trunks, t,' '
and, passing through  the mesenteric 1,.
glands, join in one common trunk the £_./,
thoracic duct,  and may thus be com-
pared to  the  roots  of a tree,  which Fig. 39.— appearance oflym-
l          .                ,            phatics in the mucous MEM-
commence m numberless minute fibres  brake of the stomach.—a,
.  ,,    .,    j n  vt   ■ •   .  n    • +  superficial layer;*, deep layer.
in the soil, and finally join to form its
main trunk, the body of the tree.
   208.  The thoracic duct is the main trunk, into which the
contents of  the  lymphatics  and  lacteals are emptied.   It
commences  in front of the second  lumbar vertebra,  and
passes up  in front  of the back-bone to  discharge its con-
tents by a valvular opening into the large vein just beneath
the clavicle or collar-bone.
   Describe a villus.  What do the lacteals unite to form ?  Through what
gland* do the lacteals pass ?  Describe the thoracic duct.  Into what does the
thoracic duct discharge its contents ?
 
98
CLASS-BOOK OF PHYSIOLOGY.
   209.  Absorption by lymphatics or lacteals takes place
■: hrough the Avails or coats of the  vessels, and these are so
 onstituted that only those materials Avhich  are suited to
ibrm lymph and chyle can traverse them.   This system
 ►f vessels therefore possesses the  remarkable property of
■selecting those elements which are in a state of organiza-
tion to fulfil certain specific purposes in the animal economy,
 md all others are rejected.  Hence,  the lymph and chyle
invariably present  nearly the  same characteristics and
contain the same elements.
   210.  But blood-vessels do not seem to possess any such
power of selecting materials as has been attributed to lym-
phatics and lacteals;  for any substance, Avhether gaseous,
Liquid, or a soluble, or a minutely divided solid, may be
absorbed by a  blood-vessel provided it is capable of per-
meating its walls.
   211.  In the alimentary canal, the fluids are taken up by
the veins, and the more solid materials by the lacteals.
   212.  From the skin, absorption is performed mainly by
the veins, though it is a well-known fact that various poi-
sonous  and medicinal substances take effect through the
lymphatics.  When irritating substances are rubbed on the
skin, red streaks soon appear in  the course of the lym-
phatics, and the lymphatic glands become swollen and in-
flamed.   In like manner, poisonous substances  acquired
through slight wounds, such as are received in dissecting
dead bodies in a certain state of decomposition, or by the
sting of insects or by the bite of reptiles, extend along the
course of these, and produce fatal  consequences.
   213. There are peculiar conditions of the body in which

  How does absorption by lymphatics or lacteals take place ?  What materials
jan traverse the walls of the lymphatics? What remarkable property does
this system- of vessels possess?  Do blood-vessels possess any power of select-
ing materials?  What substances maybe absorbed by blood-vessels?  How
are substances taken up in the alimentary canal ?  How is absorption per-
formed from the skin?  How are poisons known to take effect? Under what
circumstances does absorption from the skin take  place with great activity? 
ABSORPTION,
97
the absorption of fluids through the skin is performed with
very great activity.  Persons Avho are suffering from thirst,
receive great relief by applying Avater to the skim   When
the natural amount of  fluids in the body has been  dimin-
ished  by excessive perspiration,  or by long  abstinence
from  fluids,  the Aveight of the body may be increased
several ounces or pounds by immersion in a Avarm bath.
—-214. It is on account of the increased activity of the
absorbents that contagious disease is acquired more easily
after   fasting than after a full meal.   Fear, anxiety  of
mind, as well as every thing that depresses  the tone and
vigor of the system,  renders  it more susceptible to  dis-
  ase  through  the  increased  activity  of the  absorbents.
Hence, epidemics that are  propagated by an impure state
of  the atmosphere are most fatal  among those who have
the most  dread of disease, and thus a quiet mind and an
easy  conscience are the best safeguards against contagious
disease.
^ 215. The necessity  for a constant supply  of food arises
from the continual decomposition which is taking place in
the living body.   By this process, materials for nutrition
are all the Avhile set free, Avhich it is the special  office of
the.lymphatics  to take up and  pass through a  kind of
second digestion, thereby  fitting them for further use in
forming the tissues of the  body.  By this process of inter-
stitial absorption, animals may live for a  long  time on
their own solids.  Hibernating animals, for instance, which
retire to their  Avinter-quarters  loaded Avith fat, gradually
become, lean, and spend from four to five months  of the
year   with no  supply of  nutriment,  except  such as  is

  Why are contagious  diseases acquired more easily after fasting than after
a full meal?  What causes render the  system more susceptible  to disease?
Among what class of persons are epidemics most fatal?  What are  the best
safeguards against contagious diseases?  What creates a necessity for a con-
stant supply of food ? What materials are taken up by the lymphatics?  How
may animals live for a long time on their own solids?  What is said in regard
to hybernating animals? 
98
CLASS-BOOK OF PHYSIOLOGY.
  derived from the  enormous quantities  of fat which, they
  lay in store during the period of their activity.
/"" 216. The  mucous  membrane is the  most  important
i  channel through which all the neAV materials for the nour-
ishment  and growth  of  the body are introduced.  The
(more nutritive  portions  are taken up  chiefly by the lac-
\teals, while liquids are absorbed by the veins.
    217. In the lowest tribes of animals,  and in the earliest
  condition of the  higher  groups, absorption  by the skin
  seems  equally important to the maintenance of  life with
  that which takes place from the digestive cavity.


                     CHAPTER VIII.
                          NUTRITION.
    218. Nutrition is that vital process by Avhich the aliment-
  ary materials are converted into organized tissue.  It consists
  essentially in a deposition in each tissue of the body of those
  elements which maintain its life and growth.
v"- 219. It is the function  of the digestive organs to prepare
(  from the food  the elements of nutrition.   By the process
v.  of absorption,  they are taken  from the  digestive  cavity,
yand emptied through  the thoracic duct  into the large vein,
t  and thence into the right side of the heart, to be  passed
\ through  the lungs into the left side, and  from thence dis-
 tributed  by the arteries to all parts of the body.
    220. The peculiar  process by which the nutritive ele-
  ments of arterial  blood are formed into tissues,  is called
  nutrition.   But it is very evident  that this  process  is
  dependent for  its  perfection  upon other  circumstances.
  There must not only  be  an abundant supply of nutritive
    Through what channel are the materials for the nourishment and growth
  of the body chiefly taken up? What portions are taken up by the lacteals,
  and what by the veins?  What is said in regard to  absorption by the  skin?
  What is nutrition?  In what does  nutrition  essentially consist?  By what
  organs are the elements of nutrition prepared ? How are the elements of
  nutrition taken up?  What  circumstances may be  regarded as essential to
  nutrition ? 
NUTRITION.
99
food, but the food must be Avell digested;  the  absorbents
must transfer its nutritive portions, to the  general  circula-
tion. The heart and lungs must also perform their functions
properly.  If there is a failure in any of these particulars,
the body cannot be perfectly nourished.  Hence, it  not
unfrequently happens that the causes of deficient nutrition
are not easily comprehended.  Appetite, digestion, absorp-
tion, respiration, and circulation, may all be regarded as
indispensable to a healthy nutrition.
   221. The tissues of the body are constantly undergoing
a series of rapid changes, in which the particles are decom-
posed and removed, to be replaced by neAV ones, which in
their turn die and pass aAvay.  Yet every atom removed
is  supplied with a new one, so perfectly resembling  the
original,  that the identity of an  adult person is maintained
through  a series of years Avith the same  form, size, and
features,  and in  many instances the same weight, when
perhaps not a particle of the  original matter that consti-
tuted his body is retained.  Each part and organ  exactly
maintains  its form and composition during the successive
changes of many years.
   222. Each individual particle  or atom has  its own
period of  life, which is long or  short according to  the
character of the tissue  in which it is found.  In  muscle,
for instance, it is supposed the changes are much  more
frequent than in bone.   The milk-teeth exist for a limited
period, and are then partially absorbed, and fall out, to be
replaced by  a  more permanent set.  The hair of quad-
rupeds, the feathers of birds,  and the antlers of deer,  are
shed and reproduced annually with nearly the same form,
color, &c.
   223. It is supposed that every action of any of the parts
of the body is  attended with a change of particles. When
  What changes are the tissues constantly undergoing? How are the  par-
ticles removed from the body supplied?  What is said  of the life of  each
individual particle ?  In what tissue are the changes the most frequent? What
takes place with every action of any part of the body? 
100
CLASS-BOOK OF PHYSIOLOGY.
  we  move an arm, for instance, some of the atoms in the
  muscles which produce the motion die, and leave their
  places, being replaced by others.
    224. The rapidity of the changes may also be supposed
  to be in proportion to the activity of the parts.   In those
  who take much exercise, the atoms Avhich  compose the
  body must be changed much oftener than in the indolent
  and sedentary.   In the same manner, the exercise of par-
  ticular limbs will cause them to appropriate a much larger
  amount of  nutritive matter.  An individual Avho walks
  much, will therefore develop more fully the muscles of the
  lower limbs;  Avhile  the blacksmith will develop  more
  fully the muscles of the arms.  But a palsied limb, Avhich
  has fallen into disuse, will emaciate and groAV smaller.
 ,r'" 225. Physiologists have  never been  able to determine
( with certainty by what means each tissue selects from the
 \kblood just those elements which form its own composition.
/ We must therefore regard it as one of those ultimate facts
  in nature,  Avhich  lie beyond the  limits of our present
\ knowledge.
    226. It is supposed, however, "that the process of nutri-
  tion consists in the groAvth of individual cells  composing
  the  fabric, and that these  derive  their  support from the
  organic compounds Avith which they are supplied by the
  blood,  and  that the structure composing every  separate
  portion of the  body  has what may be termed a special
  affinity for some particular constituents of the blood, caus-
  ing it to absorb from that fluid, and convert  into  its own
  substance, certain of its elements."
 /~227. When the  amount of alimentary materials  con-
 \ verted into tissue exceeds the waste of the decaying ele-

    How is this illustrated by a movement of the arm ?  The rapidity of the
  changes are in proportion to what?   What is the effect of exercising particu-
  lar limbs?  Have physiologists been able to determine the means by which
  each tissue selects those elements which form its own composition? In what
  is the process of nutrition supposed to consist?  When is the body said to
  increase in size? 
SECRETION.
101
 / ments, the body is  said  to  grow old, or increase  in  size.
   When the nutrition is less than the loss by decomposition,
   the body becomes emaciated.  In the earlier periods of life,
\  nutrition goes on rapidly, speedily producing the renewal
 \and groAvth of the various parts of the  body.  When the
 ,-nDody has attained its full size, the process of nutrition be-
   comes less active as life advances.  In middle life, nutrition
!  just equals the loss by decomposition; in old age, the body   j
 \  becomes so imperfectly nourished,  that it is  literally worn  -•''
 \ out Avith years.
                    CHAPTER IX.

                        SECRETION.
  228'. Secretion is the process in plants and animals by
which various materials are separated from the circulating
fluid.  From the sap of different plants, in Avhich chemical
analysis  cannot detect the slightest difference,  the most
opposite and varying products are elaborated.  Thus, the
sap of the poppy produces the narcotic opium; that of the
cherry-laurel, the deadly prussic acid; that of the olive, its
oil.   Acids are obtained from some; alkalies, from others;
SAveet juices, nutritive principles,  oils,  and resins, from
others;  different  secretions  are obtained  from different
parts of  the same plant.   In animals, the nutritious milk
is secreted  in one organ; bile in another; mucus, saliva,
urine, &c, in others; and  yet we  are wholly ignorant of
the reasons why, by the same process and out of the same
fluid, so  many different secretions  are formed.  All that
we know is in regard  to  the structure of the organs con-
cerned in elaborating those various secretions.

  When is it said to become emaciated ?  How does the activity of nutrition
vary at different periods of life ?   What is secretion ?  What is said of the
secretions obtained from the sap of plants?  What are some of the secretions
obtained from  the sap of plants?  What are some of the secretions obtained
from animals?
       8 
102          CLASS-BOOK OF PHYSIOLOGY.
   229. The process of secretion, both in the animal and
 in the plant, is performed by cells, which are arranged in
 different methods, according to the structure of the organ
 in Avhich they are found.   Those cells seem to  have  the
 poAver of separating the peculiar secretion of each organ
 from the  blood of the membrane with which they are con-
 nected.   At parts where it is necessary that the  secretion
 should be particularly abundant, the secreting surface is
 increased by great, numbers of little bags or follicles lined
 with cells.
   230.  There are tAVO kinds of materials which are secreted
 from the blood of  man, namely, those which go to form
 such products as may serve some useful purpose in the
 animal economy, called secretions, and those which Avould
 be injurious, if retained in the system, called excretions.
  231.  The two principal  divisions  of  the secreting ap-
 paratus are membranes and glands.   The principal secret-
 ing  membranes  are the serous and  mucous  membranes
 and  the skin.
  232. The  serous membrane forms closed sacs, which
 envelop all the organs of the body not exposed to the air,
 and  also line the cavities in Avhich those organs are con-
 tained.  The brain, heart, lungs,  and the organs inclosed
 in the abdomen, are all protected  by this membrane.  A
 gaseous fluid is constantly secreted by it, which makes its
 surface smooth and moist, so as to render the movements
 of the organs free and easy, and prevent any friction where
 the surfaces come in contact with each other.
  233. A peculiar variety of  the same membrane is found
 at the ends of the bones, Avhich  secretes a thick fluid to
 lubricate the joints,  called synovial fluid, from its resem-
 blance to  the white of an egg.
  How is the process of secretion performed in animals and in plants ?  What
 power do the cells seem to possess?  How is the secreting surface increased
in particular parts ?  What two kinds of materials are secreted from the blood
of man? What are the principal divisions of the secreting apparatus?  What
organs are protected by the serous membrane ? What is secreted by the serous
membrane I  How are the ends of the bones protected ? 
SECRETION.                  103
  234.  The mucous membrane lines all  those passages
which communicate with the air—'as the nose, the larynx,
the bronchi and their minute ramifications in the lungs, and
the whole digestive apparatus—from the mouth through
the intestines.  It secretes a peculiar viscid fluid, called
mucus, which serves to moisten and defend this membrane,
and aid in  the exercise of smell and taste.   When the
mucous  membrane becomes irritated or inflamed,  as in
common  colds, causing catarrh, or in diarrhea and dysen-
tery,  it secretes a large amount of  mucus, Avhich some-
times becomes quite thick and hard, like the white of an
egg when boiled or hardened by alcohol.
  235. The most important of the secreting glands are the
liver,  the  kidneys, the salivary and lachrymoJ glands.
  236. The liver is found in some form in nearly all ani-
mals  which possess a digestive cavity.  In man and the
mammalia, it is made up of a vast number of minute lob-
ules,  of irregular form.  Each lobule contains a mass of
cells,  and a plexus of biliary ducts, Avith three  blood-ves-
sels ;  namely, the hepatic artery, the  portal vein, and the
hepatic vein.   (Figs. 5  and 6, Pl. VIII.)
  237. The hepatic artery furnishes nourishment to the
substance of each lobule; the portal vein provides blood for
the secreting operation; and the hepatic vein carries  back
the blood derived  from both sources.   The bile is taken
up from each lobule by the plexus  of biliary ducts which
finally unite into a common duct.
  238.  The function of the liver in  secreting  bile  is of \
very great importance to health.  When the liver becomes'"')
inactive, or ceases to perform its office perfectly from any'
  What passages are lined by the mucous membrane?  What is the secretion
of the  mucous membrane called ?  What is its use ? What  are the most
important of the secreting glands ?  In what animals is the liver found ? Of .
what is the  liver made up in man and the mammalia ? What does each
lobule contain ?   Describe the use of tbe hepatic artery—the portal vein—the
hepatic vein.  How is the bile taken up from each  lobule ?   What is said
of the  function of  the liver?   How is the health affected by inaction of
the liver ? 
                                                              I

  104           CLASS-BOOK OF PHYSIOLOGY.

  other cause, the health very soon becomes impaired, caus-  \
  ing head-ache, languor,  and  nausea, if not more serious  J
  disease.  The object of the secretion of bile is to separate
'.—from the blood those materials Avhich Avould  be injurious
  if retained in the system, though in the form  of bile they/
  afford important aid to the process of digestion.
    239. The kidneys also secrete or separate from the blood
  certain superfluous or Avaste materials.
  240. The external or cortical substance of each kidney is
composed of an infinite number of ramifications of blood-
vessels.  The central or medullary part is formed of nu-
merous straight  tubes, which are collected into  conical
bundles, all terminating in one common basin or pelvis, as
it is called.  (Fig.  40.)  As the urine is secreted in the
pelvis of  the kidney it is conveyed  by the tubes, named
ureters, into the bladder.
  241. The  salivary glands,  including the parotid, sub-
maxillary, and lingual, and the lachrymal  glands, are all

  What is the object of the secretion of bile? What is the function of the
kidney ? Of what is  the cortical substance of the kidney composed ?  Of
what the central or medullary portion ?  What do the salivary glands include 1 
SECRETION.                    105
similar  in structure.  They are composed of an aggrega-
tion of  small  lobules, the cells  of which  open by minute
ducts, Avhich  converge  and unite into larger  and larger
ducts, and  at last into  a common trunk, through which
their contents are carried to the point Avhere the peculiar
fluid of each is  needed.  The  structure of the parotid
gland is  represented in fig. 41.
   242.  The quantity and  character of the  secretion are
influenced by variations in the quantity  of blood, and of
the peculiar materials for any secretion Avhich it contains,
and by the condition of the nervous system. An increase
in the  quantity of blood which  passes through a gland,
generally increases its  secretions.  Through the nerves,
various emotions of the mind influence the secretions: the
thoughts of food increase the flow of  saliva, and grief or
pain produces a  Aoav of tears.   In the  case of milk, not
only the quantity, but the quality, of the secretion is influ
enced by the state of the mind.
   243.  The office of excretion  is especially performed by
the lungs, the liver, the kidneys, and the skin.   The lungs
throw off carbon and hydrogen, in the form of carbonic acid
 and vapor.   The liver  separates the  same elements  from
 the blood,  in the form of a peculiar fatty matter; the kid-
 neys, in the form of urine; and the skin, in that of sweat.
 If the  excretions,  or either of them, be checked, they
 speedily accumulate in  the blood, and  often  lead to the
 most deleterious results.

   Of what are the salivary and lachrymal glaads composed ?   What circum-
 stances influence the quantity  and character of the  secretions? How do
 emotions of the mind influence the secretions?  By what organs is the func-
 tion of  secretion performed?  What substances are thrown off from the
 lungs ?—the liver ?—the kidneys ?—the skin ?
        8* 
106
CLAbS-BOOK OF  PHYSIOLOGY.
                     CHAPTER  X.

                        THE SKIN
  244.  The skin is the external covering of the body, and
consists of tAVO  principal layers.  The epidermis, or scarf-
skin,  and the dermis, or true  skin.
  245.  The  epidermis  is  made up of  cells in  different
stages of drying.   Those  nearest to  the  true skin  are
rounded or oval in form, and, as they approach the surface,
lose by evaporation the fluid they contain,  and are  gradu-
ally converted into scales or  scarf-skin.   The outer layers
of the epidermis are constantly being Avorn off, and neAV
layers as constantly formed from Avithin.  Thus, each layer
is gradually  pushed from Avithin, outward.
  246.  The epidermis is raised from the true  skin  in  the
formation of a blister, and portions of a considerable extent
peal off after some diseases, such as scarlet fever.  It is also
removed with the hair, in the process of dressing the hides
of animals,  leaving the true skin Avith a smooth surface.
The minute scales of Avhich  the surface of the scarf-skin
is composed, are constantly cast off by ablution and fric-
tion of the skin.  On the scalp, these scales are removed
in the form of "dandruff"  or scarf.
  247.  The pigment cells, containing  the coloring  matter
Avhich causes the different varieties of  complexion, are de-
posited in the soft layers of the cuticle  next to the true
skin.   (Fig. 8, Pl. IX.)  In Albinoes there is no Coloring
matter: the skin presents a uniform and pearly whiteness,
and the hair is also Avhite and colorless.
  248.  The epidermis  is not  provided with either  nerves

  What are the principal layers of the skin ?  How is the epidermis formed ?
What becomes of the external layers of the epidermis ?  How is the epider-
mis raised from  the true skin ?  How are the  minute,scales of which the
surface of epidermis is composed, cast off?  How are the different varieties
of complexion caused ?  Where are the pigment cells deposited ?   Why is
the epidermis a hard, insensible membrane ? 
 
PLATE    IX.
                                 THE SKIN.


  Figure 1.----A Portion of the Epidermis of the Palm of the Hand, magnified by a simple
lens, Showing the direction of the rugae or wrinkles, and the arrangement of the apertures
of the sudoriferous Kiauus.

  Figure 2.---A portion of the same, magnified one hundred diameters.

  Figure 3.---A Transverse Section of the  Ridges of the Epidermis of the Palm of Vie
Hand, Showing a side view of the apertures of the sudoriferous glands, their spiral ducts,
the thickness of the epidermis in that situation, its composition of layers of cells, and its
mode of connexion with the true skin.

  Figure 4.----A Portion of the Epidermis from the back of the Hand, Showing tho dis-
position of the folds in that situation, the arrangement of the papillae, the disposition of
the hairs, and the apertures of the sudoriferous  and sebaceous glands, magnified with  a
simple lens.
  Figure 5.----A piece of the same,.magnified one hundred diameters, Showing that each
Line is a furrow or groove, a provision which allows of very great extension of the epidermis.

  Figure 6.----A Square of Cuticle, seen upon its internal surface.—a, The sulci, or
depressions, which correspond  with the ridges  of  the  external  surface, b, The ridges
which correspond with the furrows of the external surface.

  Figure 7.----The Under Surface of the Epidermis, Showing the pigment-cells, which
contain the coloring matter of the skin.—These cells are seen  to be collected  principally
In the furrows  between the papillas.

  Figure 8.----The Pigment Cells of the Negro, Showing that his darker complexion is
owing to the darkness of the color of the pigment contained in these cells. 
 
 
THE SKIN.
Ill
or blood-vessels, and is therefore a hard, insensible mem-
brane, investing the true skin, and protecting it from im-
mediate contact with external objects.  Where the friction
or pressure to which it is exposed is very great, it becomes
quite thick and  horn-like.  Thus,  on the palms of the
hands and the soles of the feet, it is much thicker than
any Avhere else.
   249. The epidermis is marked on the surface by a net-
work of lines, Avhich are more numerous and larger near
the joints, where they form  deep Avrinkles.  It is perforated
by numerous openings or pores, for the passage of hairs
and for the perspiratory ducts.   (Figs. 1, 2, 3, Pl. IX.)
   250. The dermis or true skin is a firm, elastic membrane,
composed of innumerable fibres, interwoven in every di-
rection by a vast number of blood-vessels, lymphatics,
and nerves.
   251. Within and beneath the true skin lie the perspira-
tory glands,  the hair follicles, and  the  sebaceous  or oil
glands.  Its outer surface  is studded with an infinite num-
ber of minute conical elevations, called papilloe.  (Fig.  5,
Pl.  X.)
   252. Each pappilla is composed of a minute blood-vessel
and a nerve, both of which form a loop, or are bent several
times upon each other.   The blood-vessel is usually the
capillary termination of a vein in an artery.   These pa-
pillae are the seat of the sense of touch, and are so numer-
ous over all the external parts of the body that the skin
cannot be punctured by the finest needle without wounding
some one of them.   They  are the most numerous in those
parts of the  body most exposed to  the  action of foreign
agents, or where the sense of touch is most acute.  They
are most prominent and most densely set on the ends of
  How is the eperdermis affected  by pressure ?  How is it marked on the
surface ? By what is the epidermis perforated ?  Describe the dermis or true
skin.  What lies beneath the true skin ?  Of what is each papilla composed?
What is the blood-vessel ?  What sense is located in the papillae ?  Where are
they the most densely set ? 
112           CLASS-BOOK OF PHYSIOLOGY.
the fingers and in the palms of the hands, Avhere each
raised line is composed of a double toav of them.
  253.  The perspiratory glands are imbedded in the fatty
layer beneath the skin, through which the ducts pass Avith
a beautiful spiral coil, as represented 'v&fig. 3, Pl. IX., and
fig. 1, Pl. X., and open at the surface obliquely, so as to
form  a  kind of  valvular opening.  These glands are very
numerous over all parts of the body, being on an average
about 2800 to   every square  inch of  surface, or about
7,000,000 in all.
  254.  Fluid is  constantly exhaled from the perspiratory
glands,  and carried off by evaporation as fast as it reaches
the surface, in the form of insensible perspiration.  During
actiAre exercise,  or exposure to heat, it is poured off more
rapidly, accumulating on the surface in drops, and is then
called sensible perspiration.  In warm, dry Aveather, Avhen
evaporation takes  place rapidly, the amount of insensible
perspiration may be  very great.   It  has been  estimated
that from two to three pounds are daily exhaled from the
skin of  an adult, though the amount of insensible perspira-
tion may be very materially increased or diminished ac-
cording to the quantity of fluid taken  into the system.
  255.  This Avatery exhalation serves a very important
purpose in the animal economy in  maintaining a uniform
standard of heat,  and  in  carrying  off substances  that
would be highly injurious if retained in the  system.  The
most  abundant  matters thus carried off are  carbonic acid
and water.
  256.  The sebaceous  or oil glands are also imbedded in
the fatty layer beneath the skin: their ducts open either
  Where  are the perspiratory glanas  located ?   How do the perspiratory
ducts pass through the skin ?  How numerous are the perspiratory ducts ?
What is constantly exhaled from the perspiratory ducts?  What is sensible
and  what insensible  perspiration?  How much is estimated to be exhaled
from the skin of an adult daily ?  How may the perspiration be increased or
diminished ?  Of what use in the animal economy is this watery exhalation ?
What matters are carried off?  Where  are the oil glands located ?  Where
do their ducts open? 
THE SKIN.
113
 on the surface of the skin or directly into the follicles of
 the hair.  They are most numerous in those parts  largely
 supplied with hair, as the  scalp and face, and are  thickly
 distributed in the nose, lips, and ears.   The oily secretion
 of these glands serves to keep  the skin supple and soft,
 and prevents it from drying and cracking.
   257. Along the margin  of the eyelids there is a row of
 these glands, which keep the lids smooth, and prevent the
 tears from trickling over their edges.   Occasionally one of
 these glands becomes inflamed, and forms what is called a
 stye.  In  the passage  of the ears,  another set of these
 glands secretes the ear-Avax.
   258. The hair and nails are both regarded as appendages
 to the  skin, and  contribute to its defence.  Each hair
 originates in a small follicle or body in the fatty substance
 just beneath the skin. (Fig. 2, Pl. X.)   Sebaceous glands
 open into these follicles, and furnish the oily material with
 which the  hair is anointed and softened.  The coloring
 matter of the hair is secreted by cells within the follicles,
 and through a deficiency of this secretion the hair becomes
 gray, and finally white.   The shape of individual hairs is
 cylindrical for the smaller kinds, and oval for those which
 grow to any length.  When left to their natural growth,
 the end or  tip of the hair is  always  conical or pointed;
 and in most animals  the portion of the  hair next to the
 skin is smaller than  the more distant  portion.   After the
 growth of the hair has reached a certain point, its nutrition
 ceases, and  the hair falls  off, to be replaced by another.
 In most animals, this occurs periodically, and  is called
 moulting, or shedding of the coat.  In the same  manner
  In what  parts are the oil glands most numerous ?  Of what use is the oily
 secretion ?  What purpose do these glands serve on the margin of the eyelids ?
 What are  these glands called when they become inflamed?  What are
 regarded as appendages of the skin ?  How does each hair originate ?  How
 are the hairs softened ?  How is the coloring matter secreted ? What causes
the hair to become gray?  What is the form of each hair?  What is the
form of the end of hair?   What  part of the hair is the smallest in most
animals ?   How do most animals shed their hair ? 
114
CLASS-BOOK OF PHYSIOLOGY.
the antlers of deer are produced very rapidly till they have
attained their growth, when they begin to harden  at the
base, gradually obstructing the vessels which nourish them,
and then fall off, to be again replaced by a new and more
beautiful production.
  259. The nails are produced from the true skin by an
organization of cells similar to  the epidermis.  Each nail
is inserted between a fold of the skin, which is reflected
backward to the root of the nail, and then passed forward
beneath its under surface, to  which  it adheres.  (Fig.  3,
Pl. X.)  In  the process of groAvth,  additions are made  to
its  under surface  and to the free edge of its root  at the
same  time, so  that growth in  thickness and groAvth  in
length proceed together.
  260. The use of the nails is to support  and  protect the
ends of the fingers in grasping, and they  are  particularly
useful in taking hold of minute objects.
  261. The  structure of the scales, feathers,  hoofs, and
horns of different animals, like  that  of the nails and hair,
is similar to the epidermis, to  which they belong.  The
feathers of birds are remarkable for the wonderful manner
in which they combine strength and lightness with surpass-
ing beauty.  The stem or body is formed by an apparatus
which may  be likened to a hair follicle; but there are
some additional parts, for the  production of the  laminse
that form the vane of the feather, which are joined to the
stem during its production.  These laminas, when perfectly
formed,  are  connected by minute  barbs at their edges,
which hook into one another, and thus give to the entire
vane  a very strong resisting surface.   The  substance  of
which feathers consist is a very bad  conductor of heat;
and when they are  lying one upon the other, they form
an  admirable protection against cold and moisture.
  In what manner do deer shed their antlers ?  How are the nails produced ?
Describe the insertion of the nail and the process of its growth ? What is the
use of the nail ?  What do the feathers, hoofs, and horns of animals resemble
in their structure ?  For what are the  feathers of birds remarkable ?  How
are they formed ? 
 
PLATE  X.
                                 THE  SKIN.


  Fiourb 1.----A Section of all the Layers of the Ski?i.—a, The epidermis,  b, c, The two
layers of the  cutis vera,  d, A sweat-gland, surrounded by cells of fat, and sending its
spiral duct upward through all the layers of the skin to the surface.
  Figure 2.----A Section of the Skin, Showing the hair follicles and sebaceous glands.
a, a, Sebaceous glands, opening into the hair follicle.  6, A hair, with its follicle, c, sur-
rounded by fat-cells.
  Figure 3.----A Section of the Thumb, Showing the manner in which the nail is inserted
between the folds of the skin.—a,  The last bone  of the thumb,   b, The cuticle reflected
upon the root of the nail,  c, The nail,  d, The  cuticle of the point of the thumb, contin-
uous with that at the inner surface of the nail.
  Figure 4.----Papilla of the Skin, magnified, containing expansions of the nerves and
of the capillary blood-vessels.
  Figure 5.----The Spiral Arrangement  of the Papilla at the  ends of the Fingers, in
which the sense of touch is especially seated. 
Fis.l
PL.X
Fie. 5

If
111
fife
 
 
CHE  NERVOUS  SYSTEM.
119
                      CHAPTER  XI

                     THE JsERVOUS SYSTEM.
    262.  The nervous system of man and the higher animals
  consists of the brain, the spinal cord, the ganglia, and the
  nerves.
    263.  The brain is the centre of sensation.  The spinal
  cord, the ganglia, and the nerves are conductors of nervous
  impressions.
    261.  The office of the nerves is to convey impressions
  made upon their extremities to the  brain, the organ  by
  which the mind becomes conscious of external objects, and
  to convey impressions' from  the  brain to the ultimate dis-
  tributions of the nerves.
    265.  The nerves are divided into tAVO classes—nerves of
  sensation and nerves of motion.  Thus, if the hand be acci-
  dentally placed in contact with a hot iron, the feeling of pain *
  is communicated to the brain by the  nerves  of sensation,
  and the impulse to remove the hand is immediately return-
  ed from the brain by the nerves of motion. Nerves of sen-
  sation and nerves of motion have a separate origin from the
  nervous centre, though they are  apparently the  same in
  structure, and are usually in the same bundle of nerve fibres.
v"" 266.  Nerves have no power of originating impressions.
V Those of sensation are stimulated  by external agents, and"
/those of motion by the will or some other force generated
V. in the nervous centres.
    267. Nervous force moves along a nerve,  like the elec-
  tric fluid along a wire, without the lapse of an appreciable
  period of time in its passage.  Each nerve-fibre can carry
  only one  kind of an  impression:  a nerve of motion can
    Of what does the nervous system consist ?  Of what is the brain the centre ?
  What is the office of the nerves ?  How are the nerves divided ?  What illus-
  tration can you give of the function of both ?  Have the two classes of nerves
• the same origin from the nervous centre ? Do nerves originate  impressions ?
  How is each class of nerves stimulated ? How does nervous force move along
  a wire ?  Can a single nerve-fibre convey more than one kind of impression?
  What doesra nerve of motion convey ?  A\rhat a sensitive fibre ? 
120
CLASS-BOOK OF PHYSIOLOGY,
   convey only motor impulses; a sensitive fibre can transmit
   only such as may produce  sensation, as that of light or
   sound.
  ^"268. The fibres of motor nerves, Avhich are distributed
 f  to the muscles, spread forth from their trunks into branches,
 \  which anastomose with each other, forming a kind of net-
 \work through the muscle; but  the nerves of sensation,
 ^•hich start from the skin, and convey impressions to the
 I  brain, originate in minute elevations  or papillae  on the
 \ surface of the true skin, and in their infinite ramifications
  \is seated the sense of touch.
    N269. In order that an individual may become conscious
   of  what  is passing around him, an impression must be
   made by external objects upon the organs of the sensitory
   nerves in the papillae, and this impression must be con-
   ducted by the nervous trunk to the brain, and  then it
 \becomes  a sensation.   On the other hand, before the mind
 /"can cause any movement  of the  body to be here formed,
 >  an emotion or act of the will must  produce a change at
[  the origin of the motor nerves in the brain, and  this
y  change must be  conducted along those nerves to the mus-
 \  cles,  where  it excites  a  contraction or muscular effort
 ^suited to the required purpose.
     270. There  is another kind  of movement which does
   not seem to be excited by impressions made on the brain.
   They are called reflex  movements, because impressions of
   this  class are conducted only to  certain  nervous centres,
   and  are  then  reflected back to the organ  whence they
   originated.
     271. Movements of this class are more particularly con-

    How are  the motor fibres distributed to the muscles ? How do the nerves
   of sensation originate ? What sense is seated  in the ramifications  of the
   nerves of sensation ?   How does  an individual become conscious of what is
   passing around him ? What takes place before any movement of the body can
   be effected ?  What are those movements called which do not seem to be
   excited by impressions made on the brain ?  Why are they called reflex move-
   ments? In what ehanges arc  the reflex movements particularly concerned? 
THE NERVOUS SYSTEM.              121
cerned in those changes which have for their object  the
maintenance of organic life, such as the movements of the
digestive canal, the respiratory movements, or the contrac-
tion of the  eyelids and pupil,  to exclude a portion of  the
rays of light when they are too intense for the retina.
  272. The nervous centres of reflex action are the ganglia
and the  spinal cord.  The exercise of this power by  the
ganglia and spinal cord is a remarkable  arrangement, by
which those processes that are in constant action for  the
maintenance of life are performed without any exercise
of the will or any consciousness of the mind.   It  is to be
feared that,  if the  brain was made  sensitive to all  the
digestive  and  respiratory movements, the mind of many
individuals Avould be constantly occupied Avith vigilant
inspection of these hidden processes of nature.
  273. The true nature of reflex action can be more easily
comprehended by studying the comparative development
of the nervous system in different groups of animals, and
by  noting the poAvers of its simplest, compared with its
most  perfect developments.
  274. One of the simplest forms of the
nervous  system is found in the ascidia,
(fig. 42,) one of the lowest of the class of
mollusca.  In this and similar animals,
we find only a single ganglion or nervous
centre.  At a is seen the orifice by which
water enters for supplying the stomach
with food, and at b that  through which
it passes out again.  Between  these ori-
fices is the single ganglion, c, which sends
filaments to both  orifices, and also  over  Fig 42-lNERVOUa SYg.
the surface of the envelop  or  mantle, d.    TE:*or abcim*.
  What are the centres of reflex  action ?  What particular  advantage  may
be supposed to result from this arrangement ?  How may the true nature of
reflex action be more easily comprehended ?  In what animal is one of the
simplest forms of the nervous system found ?  Describe the nervous system of
the ascidia and the phenomena of life exhibited by that animal.
       9*
 
122           CLASS-BOOK  OF PHYSIOLOGY.

These animals are mostly fixed to one spot during their
Avhole existence.   The continual entrance and exit of the
currents of Avater constitute the only phenomena of life
which they exhibit, except Avhen the current draws in an
injurious substance.   The  mantle then contracts, causing
a jet of water to issue from each orifice, and throw off the
offending material.  This little animal has no eyes or other
organ of special sense.   The small tentacula or feelers, at
the upper orifice, are  the only parts Avhich seem to  be
peculiarly sensitive;  and the irritation-caused by the con-
tact  of a  hard substance Avith these, or Avith the general
surface of the body, produces an instinctive contraction of
the mantle, for the purpose of getting rid of the irritating
cause.   This contraction can only be  performed by the
aid of a nervous system, which has the power of receiving
impressions, and of exciting the most distant parts of the
body to act in accordance with them.
                           275. Those animals which  in-
                        habit bivalve  shells exhibit the
                        powers of respiration, sensation,
                        and voluntary motion, and pos-
                        sess  a corresponding develop-
                        ment of the nervous system.  In
                        the nervous system of the pecten
                        or scallop-shell, (fig. 43,) there is
                        a large ganglion at B, which dis-
                        tributes branches to the gills and
                        mouth,  and regulates  the  re-
ng. 43.-nervous system of  pec- spiratory movements.  Another
 SS^gSffifftfi&5 ganglion, c, is connected with the
 the foot; e, oesophagus.         thick fleshy part  on which  the
animal crawls, and which is called its foot.   Near the sides
of the oesophagus, e, are situated two other  ganglia, A, a,
the nerves of which  are distributed to the  sensitive ten-
tacula which guard  the mouth.  These  two cephalic

  Describe the nervous system of the pecten.
• 
THE NERVOUS  SYSTEM.
123
ganglia, or  ganglia of the  head,  evidently correspond to
the brain of higher animals, being the instruments of sen-
sation and voluntary power, and  they exert a controlling
direction over the  movements of the animal; while  the
pedal  and  bronchial  ganglia (those  of the  foot and  of
respiration) minister  to  the reflex actions of the organs
supplied by them.
   276. In animals of  higher orders, the ganglia are more
numerous as the  variety  of functions to be  performed
becomes greater; and in proportion as Ave ascend the scale,
the cephalic ganglia  become more and more developed,
and more and more elevated above the oesophagus, until
they finally meet on the  central line above it, and, in  the
more perfect animals, take their  place in the top of  the
head—overlooking, as it Avere, all the other" organs.
   277.  The nervous system of in-
sects  whose actions are  generally
energetic and rapid, and in Avhich
the apparatus of motion (Avings and
legs) is highly developed, presents
a marked difference from that of
the Mollusca,  Avhich  are usually
inert and sluggish.   It consists of a
large  ganglion in the head, analo-
gous  to the brain  of vertebrated
animals, and a chain of ganglia, one
for each segment of the body, uni- ^ 44.-NERvoua svSTEM of a„
ted by a double cord,  as in fig. 44.         lNSECT-
In the larva or caterpillar, before it is changed into the per-
fect insect, the nerves  arising from the ganglia are chiefly
distributed to the muscles of the legs, and the ganglia  are
only repetitions of each other, being nearly of uniform size;
but in  the perfect  insect, the wings and legs, which con-

  What is said of the ganglia in the higher orders of animals ?  How does
the nervous system of insects compare with  that of the Molusca ?  Of what
does the nervous system of insects consist ?  How are the ganglia united ?
 
124           CLASS-BOOK  OF PHYSIOLOGY.
stitute the apparatus of locomotion, are confined to the
thorax, and the segments  of the abdomen have no legs.
Accordingly, the ganglia of the thorax, in the perfect insect,
are found to be very much  increased in size, and sometimes
concentrated in one mass, while those of the abdomen are
much smaller.
                        278. This difference is  shoAvn in
                     fig. 45, where A represents the nerv-
                     ous  system of the caterpillar, from
                     which is produced a species of sphinx
                     or hawk-moth, and B that of the moth
                     itself.  In B, the cephalic ganglion is
                     much larger than that of A, since it
                     has become connected with more per-
                     fect  eyes and other organs of sense.
                     The ganglia which supply the wings
                     and  legs (those next below that of the
                     head) are also greatly enlarged and
                     concentrated, while  the abdominal
                     ganglia are diminished, and some of
                     them are wanting.  The whole chain
                     is also  considerably shortened, the
                     body of the moth not being so long
                     as that of the caterpillar.
                        279.  The chain of ganglia in in-
                     sects is found to consist of two dis-
                     tinct tracts—one is  composed of
                     nerve-fibres  only, and passes from
the cephalic ganglion over  the surface of all the other gang-
lia, giving branches to the nerves which proceed from each
other, while the other tract connects the ganglia themselves.
Thus, each  segment of the insect  has  a distinct nervous
connection with its own ganglion, and a sympathetic  con-
nection with the others, extending to the cephalic ganglion,
  How do the ganglia of the perfect insect differ from that of the larva or
caterpillar?  Describe Fig. 45, with the difference  between A and B.  Ex-
plain the arrangement of the ganglia of insects.
Fig. 45.—Nervous System of
 Sphinx-ligustri.—A, that of
 the caterpillar;  B, that of the
 perfect insect. 
THE NERVOUS  SYSTEM.            125
which seems to have a controlling influence over all the
rest, and alone to possess the faculty of sensation.  Hence,
the motions produced by the ganglia of the trunk, when
the head of the insect is removed, although they may seem
to indicate sensation, are  found to be only reflex in their
nature—a certain irritation producing a certain movement
without choice,  and probably without  consciousness,  on
the part of the animal.
   280.  Thus,  if the head of a centipede be cut off while
it is in motion, the body will continue to move as before;
or if the body be divided as many times as it has segments,
each portion will still continue to move,  but all conscious-
ness seems to be lost: for as the decapitated body comes in
contact with an obstacle equal to its own  height, it remains
fixed against  it,  the legs moving as before,  but without
change of direction or the ability of surmounting the ob-
stacle—being no longer subject to the will of the animal,
but performing reflex movements by the influence of their
own ganglia.
   281.  In vertebrated animals, (those Avhich possess a back-
bone or spinal column) the ganglia are no longer scattered
through the body, but are united into one continuous mass;
and this  mass, constituting  the  brain and spinal cord, is
inclosed within  the skull and vertebral  column, in such a
manner as  to be protected  from the injuries  to which it
would otherwise be liable.   The brain in the higher ver-
tebrata consists of a principal  mass, called the cerebrum,
which occupies all the front and  upper  part of the skull,
and is divided into two hemispheres or  halves by a mem-
branous partition, running from back to front, and of a
smaller mass, called the cerebellum, situated  beneath  the
cerebrum, at  the back part of the skull.  At the base of
the cerebrum there are  two ganglia,  the olfactory and
   How is it shown in the case of the centipede that consciousness depends on
the cephalic ganglia ?   How are the ganglia arranged and protected in verte-
bral animals ?  Of what parts does the brain of the higher vertebrata consist ?
What ganglia at the base of the cerebrum ? 
126          CLASS-BOOK OF PHYSIOLOGY.

the optic, Avhich belong to the nerves of smell  and sight.
All these  parts in  the human brain will be particularly
described.
                               282. In the brain of a fish,
                             (fig. 46,) the  parts just men-
                             tioned are beginning to ac-
                             quire considerable  develop-
                             ment.   The  cerebral hemis-
                             pheres (c, h), the optic ganglia
                             (o, p), the  cerebellum (c, e),
                             are plainly to be distinguish-
                             ed, and their relative sizes are
                             in proportion to the intelli-
                             gence of the animal.  Thus,
Fig. 46.-A, brain of a cod; b, brain of the the ganglia which control the
shark; ol, olfactory ganglia; v, spinal cord. gense of gight are very large,
since this  sense is possessed in  a very high  degree by
fishes;  while the cerebral hemispheres, to which belong
more especially the manifestations of will and thought, are
correspondingly smaller. •  The cerebellum also, which, as
we shall see, is connected with the  poAvers of motion, is
large, as we should expect to find it in animals possessed
of the power of rapid movement, and is larger in the ac
tive and rapacious  shark  than in  the less energetic cod.
                 The spinal cord  is large, and  is divided
                 at the top, so as to form an opening be-
                 tAveen its  tAvo halves.   In man, as we
                 shall see, this opening becomes entirely
                 closed.
                    283. In  birds,  the brain has made  a
                 considerable  advance towards Avhat it
                 finally becomes  in  man.  The cerebral
^.47.-BRi.iN of a bird, hemispheres (a>  ^ 47^ are  greatly in-
creased in  size,  and cover  in the olfactory ganglia entirely
  What is said of the brain  of a fish ? Describe Fig. 46.  What parts are
large and what small in a fish ? What is the comparative size of the cerebral
hemispheres in birds ?
 
THE NERVOUS  SYSTEM.
127
and the  optic gangha (b) partly.  The cerebellum  (c) is
also much more developed, as we should expect from the
variety of movements performed by birds, but is as yet un-
divided into lobes.  The spinal cord (d) is still of consider-
able size, and is much enlarged  at the points from Avhich
originate the nerves of the Avings and legs.  As might be
inferred  from these improvements in the structure of the
brain,  the intelligence of birds is vastly superior to that
of the animals  previously considered,  and they are the
first in the ascending scale which are capable of education
or training.  Did the limits of this work permit, we might
thus go  on to trace  the progressive development of the
brain through individual species of  birds and  mammalia,
and to show at each step a corresponding advance in  intel-
ligence as we approximate to man.
  284. In man,  the  cerebral developments  are greatly
increased, while the spinal cord is diminished in size.   The
surface of the brain is not smooth, but divided  by furrows
into a series  of convolutions, by which the surface over
which the blood comes in relation Avith the nervous mat-
ter is greatly increased, thus adding  to the activity of  the
organ.  The tAVO hemispheres are more closely connected
Avith each other by fibres  running across from each side.
The cerebellum is divided into tAVO hemispheres.

           NERVOUS  SYSTEM  OF MAN.
  285. The nervous system of man  and of  the higher
animals consists of two portions—the cerebrospinal and the
sympathetic  or* ganglionic.  The  cerebro-spinal system is
composed of the brain and  spinal cord, with  the nerves
which proceed from them to the  skin and muscles.   It has
  What is said of the cerebellum ?—the spinal cord ?  How do birds compare
in intelligence with the animals previously considered ?  How are the cere-
bral developments in man ?—how the spinal cord?  How is the surface of the
brain in man ?  Of what does the nervous system of man or the higher ani-
mals consist ?  Of what is the cerebro-spinal system composed ?  What has
it been called ? 
128           CLASS-BOOK OF  PHYSIOLOGY.

been called  the nervous system of animal life, because it
is  that  by which sensations are  received and voluntary
motions  executed, and with which the mind is more im-
mediately connected.   The sympathetic system is connected
Avith the nutritive processes alone, and from  its influence
over  the organs of the  thorax and  abdomen, has been
called the nervous system of organic life.   It  consists of a
chain of ganglia, communicating Avith each other by nerv-
ous cords, extending from the  head along each side of the
oack-bone.   Nerves proceed from it to  the organs of di-
gestion and secretion, and to the heart and blood-vessels.

                 •/spinal  cord.
   286.  The spinal cord is a long  irregular cylindrical col-
umn  of nerve substance, surrounded by a  membranous
envelop, and inclosed within a long canal, formed by the
vertebras (or pieces of the back-bone).  It extends from the
head to the first or  second vertebra of the  loins,  and is
composed of both white  and  gray nervous matter.   The
white matter constitutes its greater portion, and is situated
externally, while the gray matter occupies its central part.
The spinal cord consists of two symmetrical halves, united
in the middle line by a set of converging fibres, called a
commissure, but separated anteriorly and posteriorly by a
vertical fissure—the posterior  fissure being deeper, but not
so wide and distinct as the anterior.   Each lateral half is
marked by two longitudinal furrows, which  divide it into
three columns or tracts, called anterior, lateral, and poste-
rior.   There is a considerable  enlargement of the cord  in
the lower part of the neck, at the part from which arises
the large nerves which supply the upper extremities; and
a similar enlargement is also found in  the loins, at the
origin of nerves which go to the lower extremities.
  With what is the sympathetic system connected, and what has it been call-
ed ?  Of what does it consist ?  What is the spinal cord ?  How is the canal
in which it is lodged formed?  What is the extent of the spinal cord?—and
 of what does it consist ?  How are the two halves  united ?  How is each
 half divided ?  What enlargements in the spinal cord ? 
* THE NERVOUS SYSTEM.
129
)rtio:i of thb
-   287.  The number  of nerves given  off  by the  spinal
cord  is thirty-one on each side: eight pairs in the  region
of the neck; twelve in that of the back, corresponding to
the twelve pairs of ribs; five in the loins, and six in the
pelvis.   Each of these nerves arises by two distinct roots,
one springing from the anterior column,
and the other from the posterior  column
of the cord, as in fig. 48—a pair of roots
on each side, corresponding to each verte-
bra.  These roots (the posterior ones hav-
ing first formed a ganglion) soon  unite in
a single trunk, which thus combines the
properties possessed by both.  The poste-^v^p^^
rior set of roots  consists  exclusively of  tl^?n^k^l
those fibres which convey impressions to   "sler&rTootT^lanJ-
the spinal cord and brain, and thus form   Si^n&medt/both'i
the nerves of sensation; Avhile the anterior   /> branch.
roots consist of fibres which convey nervous  influence
from the brain  and spinal cord to the muscles,  and form
the  nerves of  motion.  Thus,  if the spinal cord of  an
animal be laid  bare,  and  the posterior  set  of roots  be
touched, acute pain is  obviously produced;  while, if the
anterior roots be irritated, violent motions of the muscles
^supplied by the injured nerves are occasioned.
   288.  The spinal cord is  both a conductor of nervous
impressions and a nervous centre of reflex  action.   "When
an impression is made on the extremity of a spinal nerve,
it is transmitted to the spinal cord, and thence conducted
to the brain, where alone it  can be perceived by the mind.
In like manner,  the stimulus of the will which originates
in the brain is conducted along the cord, and thence to the
   How many nerves  are given off by the spinal cord?  How many pairs are
given off in the neck—back—loins—pelvis?  How does each nerve arise from
the spinal cord?  Of what fibres do the posterior  roots consist?—the ante-
rior ?  What would  be the  effect of irritating the anterior or the  posterior,
if the spinal cord of an animal was laid bare?  What two functions does the
spinal  cord perform ?  Explain how it acts as  a  conductor of nervous im-
pressions.
        10 
130          CLASS-BOOK OF  PHYSIOLOGY.
nerves.   In case  the spinal  cord is lacerated or  torn
asunder at any point, as sometimes happens in fracture
of the spine, this communication  to and fro between the
brain and the nerves is interrupted, so that the will has
no longer any control over the parts below the injury, nor
is the mind conscious of any injury that may be inflicted
on them.   Thus, if the cord be severed in the loins, sensa-
tion and  the  power of voluntary motion  in  the loAver
extremities Avill  be lost, Avhile they will be in full exercise
in the upper extremities.
  289. The spinal cord is also a  nervous centre of reflex
action.  During sleep, when the  brain is inactive,  respira-
tion and all those movements necessary to  life go on as
usual:  liquid  poured into  the mouth  is swallowed—the
body changes its  position.  An animal whose cerebrum
has been  removed, does the same things.   A pigeon, for
instance, has been kept alive for several  months  in that
condition; running Avhen  pushed, flying when   thrown
into the air, drinking  when  its beak Avas  plunged into
water, and swallowing food Avhen placed in its mouth, but
at all other times appearing in a  profound sleep.
   290. From  such facts, it is evident that the spinal  cord
must possess  a  great degree  of  independent poAver; but
it differs from that of the brain in this, that it  is exerted
without  the concurrence of the  judgment  and the  will;
and the  movements produced by it are rather like  those
of an automaton, set in  motion by pulling certain wires or
touching certain springs.  Thus, the motions of a decapi-
tated animal  are  never spontaneous, but always  excited
by a stimulus of some kind.

  What are the effects of lacerating or dividing the cord? Explain how the
spinal cord is a nervous centre of reflex actions?  Does the spinal  cord pos-
sess any degree of independent power?  How does it differ from that of the
brain ? 
THE NERVOUS  SYSTEM.
131
                MEDULLA  OBLONGATA.
 f  291. At its upper part the spinal cord becomes greatly  \
/  enlarged, and forms a bulb-shaped body, called the medulla   \
j   oblongata,  which is inclosed Avithin the skull, and through
   which the connection between the spinal cord  and the  /
 , brain is preserved.  Its columns are continuous Avith those .
  ^>i the spinal cord, but are more prominent,'and it contains \
:   a larger quantity of gray matter.  It is connected with the  ;
   nerves of  respiration, mastication, and deglutition, and /
   may be considered as the common centre of the cerebro^/
  Nspinal system.
     292. The medulla oblongata differs from the rest of the
   spinal cord in its functions mainly  in  the importance and
   extent of the actions governed by it.  Like the cord, it is
   a conductor of nervous  impressions;  but it  has a wider
   extent of function, since all impressions which pass to and
   from the brain and spinal cord must be transmitted through
   it.  Motor impressions are transmitted through its anterior
   columns, and sensitive impressions through  its posterior
   columns.   Thus, if one of its anterior  columns be divided,
   the animal will lose the  poAver of motion in one half of
   the body,  while its sensation will remain unimpaired.
     293. The functions of the medulla oblongata, as a nerv-
   ous centre, are more immediately important to the main-
   tenance of life than that of any other part of the system.
   The nervous force necessary for deglutition  and respira-
   tion is generated in this  organ.  It has  been proved by
   repeated experiments  that  the entire brain  may be cut
   away, in successive portions, and life yet continue  for a
   considerable  period, and the respiratory movements be
     Where is the medulla oblongata?  How is it formed?  What is said of its
   columns?  With what functions  are its nerves connected?  How does the
   medulla oblongata differ from the  rest of the spinal cord?  Of what import-
   ance to the maintenance of life are the functions of the medulla oblongata?
   By what experiments has it been proved  that life can be maintained so long
   as this portion remains uninjured? 
132           CLASS-BOOK  OF PHYSIOLOGY.
uninterrupted.  Life may also continue Avhen the spinal cord
is  in  like manner cut away from below upAvard as high
as the phrenic  nerve, which commences near the throat.
In some of the amphibia, (tortoises, frogs, &c.,) the brain
and spinal cord have both been thus removed, and still
respiration  and life  continued so  long as the  medulla
oblongata Avas untouched.  But a very slight wound at its
central portion will produce suffocation and sudden death.
   294. The power  of reflex action is more apparent in this
than in any other portion of the nervous centres.   By this
power, the respiratory movements are carried on.  Thus,
the application of stimuli to many parts of the body,  the
nerves of Avhich transmit impressions to the medulla, will
cause respiratory movements  by  reflection through  the
nerves which proceed  from the medulla  to the muscles
concerned in respiration.   This accounts for the " catching
for breath" produced by dashing cold water in  the face,
Convulsive movements are also produced  through  the
agency of this part of the cord.  In  those convulsions
which result from  the  teething  of children, in lock-jaw,
and other like  diseases, death usually ensues from suffoca-
tion—the muscles of respiration becoming so fixed that the
air cannot be breathed.

                    THE  BRAIN.
   295. The human brain consists of two principal portions
—the cerebrum or large brain, and the cerebellum or small
brain—protected by their membranes, and inclosed within
the cranium or skull.   The cerebrum,  which  constitutes
nearly seven-eighths of the whole  mass, occupies all the
upper and anterior portions of the cranium, and is divided
  What has been 6aid of the power of reflex action in this portion?  What
effects are produced on the respiratory movements by stimuli applied to other
portions of the body? How are convulsions often produced? What is usually
the immediate cause of death in such cases? Of how many portions does the
brain consist, and what are they called?  What portion of the cranium is
occupied by the cerebrum? 
THE NERVOUS SYSTEM.
133
into tAvo hemispheres or lateral halves.  These are con-
nected by transverse bands or  commissures of nervous
matter, and each  hemisphere has three prominent masses
or lobes—one at the forehead, one at the temples, and one
at the back of the head.   Its surface is intersected by deep
fissures and eminences, which produce those Avinding ine-
qualities called convolutions.
   296. The nervous tissue of the cerebrum is composed
of Avhite and gray substances, disposed in a peculiar man-
ner: a layer of the  gray substance occupies the surface,
and folloAvs all the irregularities of the convolutions, while
the Avhite substance is placed in the central parts.   Thus,
each convolution consists of  a layer of gray substance at
the outside and of white substance Avithin.  The manner
in which the two substances are thus arranged to form the
convolutions,  may be rudely illustrated by taking  two
pieces of  cloth,  laying one upon the other, and collecting
them up into folds in a globular shape.  By such arrange-
ment, the  surface over which the blood comes in contact
with the  nervous matter is  greatly increased, and it is
interesting to know that in man  the convolutions are more
numerous and  extensive,  and  the depressions between
them deeper, than  in any other  animal.  The brain is
most abundantly supplied with blood—the amount sent to
it having been  estimated as high as one-fifth of that con-
tained in  the  whole body,  though one-tenth Avould be
probably  nearer the truth.
   297. ToAvards the  base and centre of the cerebrum, the
surface is inflected inward, so as  to form an intricate inter-
nal  cavity, several compartments of which are called ven-

  How is the cerebrum divided ?  How are  the two halves connected to-
gether?  What is the external appearance of each hemisphere"? Ofwhatis
the nervous tissue of the cerebrum composed ?  How are the white and gray
Bubstances disposed ?  How may the manner in which the two substances are
disposed be  illustrated? What is the effect  of this arrangement?  What
proportion of the whole amount of blood has been estimated to be sent to the
brain ? What are the internal cavities railed ?
       10* 
134           CLASS-BOOK  OF PHYSIOLOGY.
tricles.  They  communicate with  each other, and serve
still further to increase the cerebral surfaces.  It is in these
ventricles  that collections of  serous  fluid take place, in
cases of what is called "dropsy of the brain," or Avater in
the head.
  298. The cerebellum is situated  at the back of the head,
below the cerebrum.   It is divided into two lateral lobes,
and, instead of waving  convolutions, its  surface presents
a number of plaits with furrows between them.   It is com-
posed,  like the cerebrum, of gray and white matter,  and
the Avhite matter presents, on  a vertical section of one of
the lobes,  a tree-like appearance, called  arbor vitce (tree
of life).
  299. The membranes Avhich surround  and protect  the
brain are three in number, and are called the dura mater,
the pia mater,  and the arachnoid.  These  membranes are
also prolonged downwards, so as to form  a tubular sheath
to the spinal cord.   The dura mater (hard mother) was so
called  by the old anatomists, because they supposed it to
be the origin or mother  of all the hard, firm membranes
of the body, and the pia  mater (tender mother) Avas  also
thus named by them,  as  being  the origin of the  soft
membranes.
 ' 300. The dura mater is  a strong,  dense, fibrous mem-
brane, which forms the external envelop of the brain,  and
is in contact  with the bones of the skull,  to  Avhich it
strongly adheres.  It is separated into two layers, the inter-
nal of which is doubled on itself, so as to form two remark-
able processes:  the one, from  its  resemblance in shape to
a sickle, is called falx cerebri, and is interposed between
the two hemispheres of  the brain, so  that Avhen  the head
  How do they communicate with  each other?  Where is the cerebellum
situated?—how is it divided?  Of what  two substances is it composed?
What is the  appearance of the matter when divided vertically?  How is
the brain protected ?  What was the origin of the name applied to the dura
mater and pia mater ? Describe the dura mater.  What is that portion  of the
dura mater called which divides the two hemispheres ? 
THE NERVOUS  SYSTEM.
135
rests on one side, the uppermost hemisphere is prevented
from pressing upon the lower.   The other process is called
tentorium cerebelli, and is  extended over the  cerebellum,
so as to prevent the  pressure of the cerebrum upon the
latter when the head is in  an erect position.  There is also
a smaller process, called falx cerebelli, which separates the
two hemispheres of the cerebellum.
   301.  The arachnoid (spider's web)  membrane, so called.
from its extreme thinness,  lies beneath the dura mater, and
is spread over the entire  surface of the brain.  It corres-
ponds in  its use to the serous membranes of the heart and
other organs, and serves to keep the opposite  surfaces of
the dura  mater and the pia mater, between which it lies,
moist and smooth.
   302.  The pia mater is a loose transparent web, in which
a multitude of blood-vessels cross each other in every pos-
sible direction.   Minute branches of these vessels, in im-
mense numbers,  penetrate the brain, to which they afford
nutriment, at the same time that they serve as a means of
attachment between the brain and  membrane.  The pia
mater follows all the convolutions, entering all the cavities
of the brain,  and is also prolonged  over the  spinal cord
and •the nerves, constituting one of the most  important
membranes of the body.
   303.  Twelve pairs of nerves  are  given off from the
brain, and are named as follows: 1st pair, Olfactory nerves;
2d, Optic Nerves; 3d, Motores Oculorum;  4th, Patheticus;
5th, Trifacial nerves; 6th, Abducentes;  7th, Portia dura,
or facial  nerves;  8th,  Portio Mollis, or  auditory nerves;
9th, (xlosso-pharyngeal nerve; 10th, Pneumogastric nerve;
11th, Hypo-glossal  nerve; 12th,  Spinal accessory nerve.
^X 304.  The first pair is distributed to the inner membrane
\pf the nose, and transmits  to the brain the impression pro-
  "What other processes are there ?   Describe the arachnoid membrane. De-
scribe the pia mater.  How many pairs of nerves are given off from the brain ?
What are they called? Where is the first pair distributed, and what is  its
size ?—the second ? 
186
CLASS-BOOK OF  PHYSIOLOGY.
 /^duced by odors.   The  second pair is  distributed to the
/  retina of the eyes, and in like manner conveys the im-
;   pression of sight.   The third, fourth, and sixth pairs are
   nerves of motion only,  and are distributed to the muscles
\  which move the eyes.   The fifth pair is for the most part
 \ a nerve of sensation only; it is divided into three branches
  ^sr-fhe f[rst of which, called the ophthalmic nerve, passes
  / into the orbit or cavity in which the eye is lodged, and is
   then distributed to the forehead and temples.   The second
   branch,  or superior maxillary, supplies the cheeks, nose,
   and  upper-lip with sensitive  filaments.   The  third, or
   inferior  maxillary, which, like the spinal  nerves, has also
   a motor root, imparts the poAver of moving to the masti-
   cating muscles,  and gives  sensibility to  the parts about
\ the mouth.
  \   305. The seventh pair is the general motor nerve of the
   muscles  of the face; the eighth pair is the nerve of hear-
   ing, and is distributed to the  internal ear; the  ninth pair
   supplies the back of the mouth and pharynx, and is con-
   cerned in the act of swallowing; the tenth pair originates
   from the medulla oblongata,  and supplies the lungs and
   air passages, as also the heart and stomach; the  eleventh
   pair  gives  motion  to the tongue; and the twelfth pair is
   concerned in respiration.  All these nerves are supposed
   to contain two sets of filaments—one communicating with
   the cerebral hemispheres,  and the  other with  the spinal
   cord.  Plate XI., fig. 4, represents a section of the brain,
   showing the arrangements  of these nerves.  That of the
   nerves proceeding from the spinal cord is seen in Plate
   XL, Jig.  1.

     What are the third, fourth, and sixth pairs ?  What is the fifth pair ?  How
   is it divided ?  Where is each branch of the fifth distributed ?   What is the
   seventh pair?—the eighth?  What is the origin of the ninth pair? What
   organs does it supply ? To what parts do the eleventh and twelfth give motion?
   What two  sets of filaments are all these nerves supposed to contain ? 
XI 
/
PLATE   XI.
                       THE  BRAIN  AND SPINAL CORD.


        Figure I.----Anterior View of the Brain and Spinal Cor.i, isolated from the Skeleton,
      —a, b, Right and left hemispheres of the brain, the left hemisphere covered by the arach-
      noid and pia-mater; the right hemisphere naked, displaying the convolutions,  c, d, Right
      and left lobes of the cerebellum,  e, The medulla oblongata.  /,/, The spinal cord, cov-
      ered by the pia-mater on the right side, and showing the origins of the spinal nerves on
      the left.   At/,/, are seen the two enlargements of the  cord, in  the neck and the loins,
\     g1 to Si The eight cervical pairs of nerves;  h to h, The twelve dorsal pairs; i to t, Tho five
 \   lumbar pairs; k, k,  The six sacral pairs.   I,  Lateral column of the cord,   m,  Posterior
      column.

        Figure 2.----A Section of the Brain and Spinal Cord, inclosed in the Skull and Verte-
      bral. Column.—a, The cerebrum, b,  cerebellum,  c, c,  The spinal cord.—The vertebra
      are cut through, so as to display a lateral view of the cord.

        Fioure 3.----The Cerebellum.—A, Anterior view.  B, Posterior view.

   s"^ Figure 4.---A Vertical  Section of the Brain, showing  the Origins of its Nerves.—
 f    a, a, The cerebrum, with its convolutions,   b, The cerebellum, displaying the arbor-vitae
/     upon its  section,   c, The  medulla oblongata,  d, The corpus callosum, a band of fibres
      which connects the two hemispheres of the brain,  e, The eye. | /, The first pair of nerves.
I   \ g, The second pair. 1 h, The third pair,  n, The fourth pair. Ij, The fifth pair,  k, The sixth
 \    pair. /, The seventh pair,  m, The eighth pair,  n, The ninth  pair,  o, Tho tenth pair.
     p, The eleventh pair, q, The twelfth pair,   r, Spinal nerves.
        Figure 5.---A  Horizontal  Section of the Brain,  showing its  Interior.—a, a, The
      cineritious or gray substance at the  outside  of the brain, following  the convolutions.
      ft, *, The white or medullary substance at the inside of the brain,  c, c, The lateral and
      middle  ventricles. 
Fi°. 2
 
 
THE nervous system.              141
      FUNCTIONS  OF THE  CEREBELLUM.

  306. Much discussion has taken place in regard to the
functions of  the cerebellum.  It seems to be noAV agreed,
however, by the  most  intelligent physiologists, that it is
the organ Avhich is more especially connected Avith motion.
Numerous experiments have been made on living animals,
all  of which go  to shoAV that, after the removal of the
cerebellum,  the  power of  executing those  movements
necessary to locomotion is lost.   The faculties of volition
and sensation remain;  but the power to walk, fly, or even
stand, is uniformly lost, from the inability to combine the
action of the muscles in groups.
  307. From facts of this character, it seems to be  most
probable that the function of the cerebellum is to harmon-
ize and regulate the actions of the voluntary muscles.   In
accordance with this  theory, Ave find that those  animals
which possess variety  of motions, or muscular action in
the  highest  degree, are endowed with a cerebejlum cor-
respondingly large.
  308. In the animals of the  cat tribe, which use  their
limbs for  seizing their prey, and which  are  capable of
great muscular exertion,  the cerebellum is larger  than in
those whose  limbs are subservient  to  locomotion only.
In  birds, the variety of whose  movements is still greater,
it is  larger than  in most of the  mammalia.  It acquires
its  highest development  in  man,  as might  be expected,
from the muscular combinations necessary to maintain the
erect position, and to  perform the  intricate and varied
movements of the human hand.

  What is said in regard to  the functions of the cerebellum?  How is it
regarded by the most intelligent physiologists?   What  do experiments on
living animals show in regard to the formations of the cerebellum ?  What is
most probably the function then, of the cerebellum ? What is said in regard
to the development of the cerebellum in the cat tribe and in birds?  In what
class does the cerebellum acquire  its highest development ? 
142
class-book of physiology.
  309. The influence  of each half of the cerebellum ia
directed to muscles on the opposite sides of the body;  and
it would appear that, for the right ordering of movements,
the action of its tAVO halves must be ahvays mutually bal-
anced and adjusted.

         FUNCTIONS  OF THE  CEREBRUM.
  810. The cerebrum  is the  organ through which the
phenomena of thought and intelligence  are  manifested.
By its means, we reason upon  the ideas excited  by sensa-
tions, we judge and decide upon our course of action, and
put that decision into practice  by issuing a mandate Avhich
is conveyed by the nervous trunks to the muscles.
  311. It is a common, but erroneous idea, that reason is
peculiar to man, and that the actions of the lower classes
of animals are due  to  instinct alone.   There can be no
doubt  that reasoning processes, exactly resembling those
of man, are performed by many animals: such, for instance,
as the  dog, the horse, and the  elephant.  We  must admit
that an animal reasons when it profits by experience, and
obviously adapts its actions to the  end it desires to gain,
especially when it departs from its natural instincts to do
this.  The presence of intelligence is also perceived in the
differences of character found in various individuals of the
same species.   Thus, some dogs are stupid, others saga-
cious,  some ill-tempered, others good-tempered;  just  as
there are stupid men  and intelligent men, ill-tempered
men and good-tempered men.  But the actions  of insects
seem to be wholly instinctive,  so that we  observe no dif-
ference of temper or capacity in them.
  312. Birds, however, which resemble insects in many
  What is said in regard to the influence of each half of the cerebellum?
What is the function of the cerebrum?  Is reason peculiar to man?  When
may an animal be  said to reason?  How may we discover  the presence of
intelligence in animals ? What example is given of different degrees of intel-
ligence in an animal ?  What seems to be the nature of the actions of insects?
What is said in regard to birds? 
THE NERVOUS SYSTEM.
143
of their instinctive tendencies, exhibit  a remarkable dis-
tinction in their actions.  In escaping from  danger,  in
obtaining food, and in constructing their habitations, the
actions of birds, like those of insects, are instinctive.  But
in adapting their operations to  peculiar circumstances,
birds display a variety and fertility of resource not  to  be
found in insects;  and birds also learn by experience, and
may be educated, while insects observe perfect uniformity
in all their actions.
   313. The relative  amount of  intelligence in  different
animals bears a pretty constant proportion to the size and
development of  the  cerebral hemispheres.   Size alone,
hoAvever, does not produce all the difference.   In ascend-
ing from the lower to the higher animals, a marked ad-
vance in the complexion of the  brain is observed: the
convolutions become more and more  prominent, giving a
proportionably increased surface  for  the  entrance of the
blood-vessels, and an equally increased amount of the gray
matter which seems to be the real centre of all the opera-
tions of the organ.  Still,  the size of the cerebrum, com-
pared with that of the spinal cord and the  ganglia at its
top, usually  affords a  tolerably  correct  measure  of the
intelligence of  the  animal.  The  same rule holds good in
comparing different men, if due allowance be made for the
comparative activity of their general functions, or, in other
words, for their differences in temperament.
   314. Thus, two men whose brain is of the same size may
differ widely in mental vigor, because the general system
of one performs its functions more actively and energetic-
ally than that of  the other.   For the same reason, a man
  In what actions do birds seem to be governed by instinct, and in what by
intelligence?  How does the amount of intelligence in different animals com-
pare with the development of the cerebral hemispheres  Is  all the difference
produced by size  alone?  What other circumstances are to be taken into the
account? What is said of the size of the cerebellum, compared with that of
the spinal cord ?  How does this rule  hold in regard to different men ? Why
may two men whose brains are of the same sfee differ widely in mental vigor?
Under what circumstances will a large brain surpass a small one in power ?
        11 
144           CLASS-BOOK OF PHYSIOLOGY.
of small brain, but whose general habit is active, may have
a more powerful  intellect than  another of much  larger
brain, but whose system is sluggish and inert.  But of two
men  alike in temperament, arid having the same general
configuration of head, it cannot be doubted that the one
with  the larger brain will surpass the other.  It is a strik-
ing fact,  that almost all those  persons who have been
eminent for their acquirements, or for  the  influence of
their  talents over their fellow-men, have had large brains.
This  was  the case,  for  example, with Newton, Byron,
Cuvier, Cromwell, and Napoleon.  The  average weight of
the brain  is  about  three pounds two  ounces.   That of
Cuvier weighed four pounds eleven and a half ounces, and
those of Byron and Cromwell are said (though the fact is
doubtful) to have weighed nearly six pounds. In idiots,
on the contrary, the brain is usually very small—in some
instances weighing only one and a half pounds.
  315. The  size of the  brain may be pretty correctly
estimated by the facial angle.  This angle is obtained by
drawing a horizontal  line (c, d, Jigs. 49  and 50) from the
Fig. 49.—Skull of European.         Fig. 50.—Skull of Nbgro.
entrance of the ear to the floor of the cavity of the nose,
and a second line (a, b) from the most prominent part of
the forehead to the front of the upper jaw, so as to inter-
sect the other.  This line will evidently be more inclined
to the former, and  the  angle formed by the two will be

  What has been said in regard to the size of the brain in men who have been
distinguished for their talents? What examples are given of large brains?
How is the brain in idiots ?  How may the size of the brain be estimated ? 
 
                                       5L
PLATE  XII.
THE NERYES.
  Figure 1.----Posterior View of the Principal Nerves.—The general arrangement of
the nervous centres and the distribution of the nervous trunks are shown in this figure.—
The spinal column is laid open, so as to display the cord, with the nerves which pass from
it.  The muscles of the left side and limbs are dissected, to show the course of the princi-
pal nerves.
  a, The hemispheres  of the cerebrum,  b, The  lobes of the cerebellum,  c, The  spinal
cord,  d, The facial nerve, the principal motor nerve of the  face, e, The brachial plexus,
a net-work of nerves, originating by several roots from the spinal cord, nnd going to sup.
ply the arm.—From this plexus proceed—/, the scapular nerve; g,  the median  nerve; A,
the ulnar nerve; i, the musculo-spiral nerve ;j, the intercosto-humeral (nerve of Wrisberg).
From the spinal cord proceed—the  intercostal nerves, k, k, running between the ribs; the
nerves forming  the luobar plexus,  I, from which the front  of the  leg is supplied; those
forming the sacral plexus, m, which supplies  the back of the leg.  The chief branch of
the sacral plexus is the great sciatic nerve, n, which divides into the tibial nerve, o, the
peroneal or fibular nerve,p. and many other branches.  The nerves seen on the right  side
of the figure, are  the  ramifications of the sub-cutaneous nerves, branching beneath the
skin, in which they are finally lost.  Some of the superficial veins are also represented. 
 
 
THE NERVOUS  SYSTEM.
149
more acute in proportion as the face is more projecting
and the forehead more retreating;  while it will be nearer
a right angle, if the forehead be prominent and the muzzle
projecting but little.   Hence, the facial angle Avill indicate
the proportion which the brain bears to the face.
  316. This angle  is more open in man than in any other
animal, and it varies greatly in the various races of men.
The difference between the facial angle of the  European
and American head, and that of the negro, is seen in figs.
49  and 50.  In the one, it is about  eighty degrees, and in
the other  about seventy.   In  monkeys,  it varies from
about  sixty-five to thirty degrees, and as we descend still
lower, it becomes still more acute.

 CONNECTION OF THE  MIND  WITH  THE BODY.
  317. The brain,  as appears from  what has already been
said,  is the connecting link between the  mind and the
body.   All the organs of the body may be said to be the
agents of the mind, inasmuch as the mind  manifests itself
through them all.  Thus, the  hand, the eye, the muscles
which control the features, are all made to express, more
or  less forcibly, the varied emotions of the mind.  The
mind, too, controls, to  a  certain extent, the operations of
the various functions of the body, to which it gives a shape
and form in correspondence with itself.
  318. In this view, we may regard the entire body as an
assemblage of organs for the  manifestation of the  mind.
But the influence  of the mind  upon the body is recipro-
cated by that of the body upon the mind.  If the body
can be made to suffer from the condition of the mind, the
  In what class is the facial angle more open than in all others ?  How does
it vary in different races? What is the facial angle of  an European or an
American—of a negro—of a monkey? What may we regard as the connect-
ing link between- the mind and the body ? How may we regard all the organs
of the  body?  What parts are  made to express the emotion of the mind?
What control does the  mind exert over the body?  What then may we
regard the body ?  How is the influence of the mind upon the body reciprocated ?
       11* 
150           CLASS-BOOK 'OF PHYSIOLOGY.
mind itself is not less affected by the condition of the body.
A single illustration will suffice to shoAV this fact: Melan-
choly,  or  depression of spirits from any cause whatever,
will often produce disease and derangement of the liver;
and, on the  other hand, a  derangement  of the liver will
almost always insure melancholy, though no  other  cause
exists.
  319. But the intellect is not limited in its  influence to
the organic  and animal functions:  it also stamps itself
upon every lineament  and feature of the man.  Thus, as
we ascend in -the scale of being, intelligence becomes more
highly developed, and is marked by a more perfect organ-
ization of the  brain and nervous system.  The nervous
power  in man is  at its highest point, as is shoAvn by the
very liability to disease or derangement of the vital func-
tions, arising from the sympathy between the physical and
intellectual powers.   The mere animal has no desires to
gratify but  those of appetite.  These satiated, he has no
anxiety for the future—no repinings for the past;  he is not
wasted by care, nor harassed by toil and disappointment.
Man, on the contrary,  is the constant subject  of exciting
and depressing influences—of functional  and  organic de-
rangements,  growing out of his  complex nature.  Ever
restless, never  satisfied, he  is constantly on the rack of
physical and mental torture.   He consequently obtains
the highest perfection and excellence when he  obeys most
perfectly the laws of his nature, and retains the  physical
and the intellectual  in the most complete harmony of
development.
  320. Hence, in the education of the young, the powers
of the body and mind should be cultivated together.  The

  What illustration is given to show this fact?  Upon  what does the intellect
Btamp itself?  As we ascend the scale of being, how is intelligence marked ?
How is it shown that the nervous power is at its highest point in man ? What
is said in regard to the cares and anxieties of man, compared with other
animals ?  When does man obtain the highest perfection ? What should be
observed in the education of the young ? 
THK NERVOUS SYSTEM.             151
mind should not be excited to such a degree as to overtask
the brain, nor so neglected as to leave the latter without a
proper  degree of exercise.  One extreme wastes the vital
energies while yet immature; the other degrades heaven-
born powers  to  a level with the brute.   The injudicious
course,  so often pursued, of stimulating  the intellect  of
what is called a "precocious child," too often results in
misery  in the sufferer itself, and in disappointment  to  its
unwise  friends.  Such children rarely fulfill the promise
of their earliest years, and the anxious parent usually
sees the brilliancy of their youth fade into dullness or dis-
ease in  after-life.
  321.  During the first six or  eight years, the most im-
portant object in the education  of the young is to develop
the physical powers, and secure vigor and strength to the
body.   If there  is a tendency to an early development  of
the  intellectual  poAvers, special care should be  taken  to
restrain the exercise of the mind, till the physical powers
shall become  strong and healthy, rather than fan the flame
already kindled till it consumes the citadel of life.
  322.  In the subsequent development of the intellectual
faculties, gradual and uniform progress is greatly to be pre-
ferred to rapid strides in  knowledge.  They who at first
rush furiously up the rugged path of science, are sure very
soon to tire or fall sick by the way.  Nor should the mind
ever be confined too long on any particular study;  a suit-
able variety  not only  refreshes the mind, but affords a
more harmonious  development of all the powers.   The
young  especially require  variety:  their  minds  are con-
stantly  on the alert for something neAv—something to see,

  What is said in regard to neglecting or exciting the mind  What is the
result of either extreme?  What is often the result of injudicious stimulating
of the intellect of precocious children?  What is the most important objec'
during the first six or eight years? What should be done if there is a tendency
to an early development of the intellectual powers ?  What is to be preferred
in the subsequent  development of the intellectual faculties?  What is said in
regard to  variety of study? 
152
CLASS-BOOK OF PHYSIOLOGY.
handle, and  taste—or for some  new  thought  or truth.
Continued application, for a great length of time, is wholly
incompatible with their natural impulses, and fatigue very
soon  ensues when it is attempted;  for the mind seeks
variety with the same irresistible tendency that the body
seeks change of position.
   323.  In more mature years, the mind should be trained
to earnest and patient thought, but not with unremitting
toil.  The best thinkers are those who  possess the  power
of exerting their brains Avith the  most energy for a limited
period  of time, and Avho  then  take  liberal relaxation.
The brain thereby exercises the poAver  of prompt, ener-
getic  action;  and when it  acts, it  is  to some purpose.
Those who keep the  brain  constantly at work, either be-
come dull and lazy thinkers, or are prematurely worn out.
The men Avho  have  done the most for the world and for
the race, are men of vigorous thought and liberal exercise
—men who take care of the body while they work the
mind.   The  reason why genius  so  often finds an early
grave, is because the  intense exitement it creates in the
brain soon exhausts the physical energies.

  How should the mind be trained in more  mature years ?  Who are usually
the best thinkers?  What  is the effect of keeping the brain constantly at
work ?  Who are the men  who have done the  most for the world ? Why
does genius so often find an  early grave ? 
THE SENSES.
153
                    CHAPTER  XII.

                       THE SENSES.
   824.  There are  five senses:  touch, taste, smell, hearing,
and sight.  The office of the senses is to make us acquainted
with the material world around us,  and the states of our
own bodies.   Our knowledge of the properties of matter,
and our  ideas  of form,  taste, odor,  and sound, are  all
obtained from  impressions made on the mind through
the senses.
                  SENSE  OF TOUCH.
   325.  The sense of touch is the most universally diffused
of all the senses, existing in greater or  less perfection in
all animals.  In some, as in man, nearly the whole exterior
of the body is endoAved with it; but in others  it is limited
to certain parts in which it is specially seated.  In insects,
the surface of the  body  is  covered  with  an insensible
shell, and  the  organs of
touch are the antennas, or
feelers.   These  are pro-
longations from the por-
tion of  the head near the
mouth; they are often of
very great length,  as in
fig. 51, usually contain-
ing a  great  number  of
points, and are very flex-
•ii     ,i  , ,i         t_   Fig. 61.—Capricorn Beetle.—a, a, antennae.
lble, so  that they can be   *                   ' '
turned toward any object  the insect  may wish to examine.
In walking, the antennse  are used  almost incessantly in
touching the surfaces over which they pass, and they seem

  How many senses are there ?  What is the office of the  senses ?  How do
we obtain our ideas of form, taste, odor, and sound ? Which of the senses
is the most universally diffused ?  What is the extent in man?  How is it
limited in other animals ?  What are the organs of touch in insects 1
 
154           CLASS-BOOK OF  PHYSIOLOGY.

to be the  medium of some kind of correspondence with
each other; for ants or bees are seldom seen to meet with-
out reconnoitering one another with their antennas.
  326. In  fishes, the body is so covered by scales as to be
nearly insensible.  In those animals  Avhich are covered
with hair,  the sense of touch is most perfectly developed
in those  parts which are most uncovered, and are brought
in contact  with the substances on which they feed.   The
sensibility of the lips of the horse, for example, is very
gTeat.  The carnivorous animals are usually provided with
long hairs or "whiskers"  each of which at  its root is in
contact with a filament of nerve.   (Fig. 6, Pl. X.)
  327. In most of the mammalia, the lips and tongue are
employed  as the chief organs of touch.   In the elephant,
this sense is possessed very acutely by the little finger-like
projection at the end of its trunk;  and in the bat, it seems
to  be  diffused over  the  whole membrane  of which  the
wings are  formed.
  328. In  man, the  true skin is studded with minute
papillas,  and each papilla is provided with a termination or
a loop of a sensitory nerve.   The whole external surface
of the body is thus more  or less highly endowed with  this
faculty,  according as  the papillae are more or less numer-
ous in any particular part.  In the hand, and especially at
the extremities of the fingers, these papillae  are extremely
numerous,  and the  sense of touch  is  here most acute.
(Figs. 4  and 5, Pl. X.)   The hand is capable  of a great
variety of movements, as well as a high degree of improve-
ment by education.  In the blind,  who learn to read with
  What is  the condition of the body in fishes ? Where is the sense of touch
most perfectly developed in animals which are covered with hair? What is
said of the  lips of the horse and the whiskers of carnivorous animals? What
are the chief organs of touch in most of the mammalia ?  In what parts is
it possessed very acutely by the elephant and the bat ?  With what is the true
skin in man studded ?  With what is each papilla provided ?  Where are the
papilla the most numerous, and the sense of touch the most acute ?  What is
said of the  improvement of the hand by education ?  How do the blind  learn
to read ? 
THE SENSES.
155
facility by  simply touching  the raised  letters, this sense
acquires most wonderful acuteness and precision.
   329. In animals, the sense  of touch is almost wholly
confined to the surfaces of the body, while the deeper parts
are  comparatively free  from it, though not  insensible to
pain from injury or disease.  In case  of an ordinary cut
or bruise, or a surgical operation, the most acute suffering
arises from the violence inflicted on the  sensitive nerves
near the surface.  Thus, a Avound that is only "skin deep,"
will sometimes cause quite  as  much immediate pain as" a
more serious injury to the deep-seated parts.  The sense of
Touch may therefore be regarded as an ever-watchful sen-
tinel, placed  on the exterior of our bodies to guard Avith
untiring vigilance the delicate  textures within.

                 SENSE OF  TASTE.
   830. Taste is that  sense by which we judge of certain
properties of matter—as SAveet, sour, bitter, &c.  Its chief
purpose is  to direct animals  in the choice of food.  Like
the  sense of touch,  it is not excited except by the  direct
contact of particular substances;  and only those substances
which are soluble in water, or in  the fluids of the mouth,
make any impression on this organ.  Substances that are
not  soluble, are said to be either insipid or tasteless.
   331. The sense of taste, in the higher animals, is con-
fined principally to the  mucous membrane of the tongue,
Avhich is very thickly set, especially on its upper surface,
Avith papillae.   The papilla? of the  tongue have some re-
semblance in structure  to those of the skin, though they
are far more highly organized.   (Fig. 1,  Pl. XIII.)
  332. The papilla? of  the  tongue  are  of various  forms

  To what parts is the sense of touch almost wholly confined in all animals ?
Where is the pain the most acute in cases of injury?  What may we regard
the sense of touch ?  What is taste ?  What is its chief purpose ?   How is
the sense of taste excited ? What is said of substances that are not soluble?
To what parts is the sense of taste chiefly confined ?   What is said of the
papillae of the tongue ?—of their form and size 1 
156
CLASS-BOOK OF PHYSIOLOGY.
and sizes:  some are conical; others are enlarged and flat-
tened at the top;  some are elevated above the surface of
the tongue; and others are imbedded beneath it.   The
fungiform  papillae, which  are supposed to be the special
instruments of the sense of taste, are composed of numer-
ous loops  of  capillary vessels,  Avith  a bundle of nerve-
fibres, as represented in fig. 5, Pl. XIII.
  333.  The tongue itself is made up of muscular substance,
Avhich accomplishes the various movements required in the
act of mastication, and in the production of sounds.  It
possesses nearly the same  structure in the other mamma-
lia as in man.   In birds, it is usually cartilaginous or bony
in its texture, and destitute of nervous  papillae, so that
their  sense of taste cannot be very  acute.  Several of
them use  their tongues for other purposes.   The wood-
pecker, for instance, (fig.  6, Pl.  XIII.) whose  tongue is
sharp and  forked, transfixes insects with it;  and the par-
rot uses it to  keep steady the nut or  seed which is being
crushed between  its mandibles.   In some  reptiles,  the
tongue  is large and fleshy; in others,  as the serpent tribe,
it is sharp  and forked,  and possessed  of very great quick-
ness of motion.  In the frog and chameleon, it serves as
an organ of prehension, and is  darted out with great ra-
pidity to catch the insects on which  these animals feed.
The tongue of the fish is generally in  a more rudimentary
state; it is fixed in the  throat,  and often covered with
teeth.   The tongue of the bee forms a little tube, through
which it draws up  the juices of flowers.
  334.  Most of the lower animals are instinctively directed
in the choice of their food by the sense of taste, rejecting
what is pernicious, and selecting whatever is adapted to

  Describe the fungiform papillae ? Of what is the tongue itself made up ?
What is the structure of the tongue in birds ?  For what other purposes is the
tongue of some birds used ? What is said of the tongue in reptiles ?__in ser-
pents ?—in the frog, and the chameleon ?  What of the tongue of the fish
and the bee ?  How are most of the lower animals directed in the choice of
their food ? 
 
PLATE  XIII.
                          ORGANS OF SENSE.

  Figure 1.----The Dorsum, or Upper Surface of the  Tongue.—a, Tho epiglottis,  b,
The root of the tongue,  c, c, Mucous  glands, covering the root of the tongue,  d, d, d,
The large papillaj, arranged in two oblique lines, meeting at the middle of the root of the
tongue.  Spreading over the rest of the surface are seen the small papillae, in great num-
bers and of different shapes and sizes.
  Figure 2.----The Inferior Surface of the Tongue.—This figure represents the lower
side of the tongue laid Open, so as to show the distribution of the nerves,   a, The hyoid-
bone, to which the base of the tongue is attached,  b, b, The stylo-glossus muscles, reaching
from tho tongue to the  styloid processes of the temporal-bone, e, c.  Their action is to
draw the tongue backward, d, The hypo-glossal nerve.—Minute filaments of these nerves
are spread throughout the tongue and in its papillae.
  Figure 3.----Organ of Hearing:  Vertical Section of the Organ of Hearing.—a, b, e,
The external  ear.  d, Entrance  to the  auditory canal.  /, Auditory canal,  e, e, Petrous
portion of the temporal-bone,  in which  the internal ear is excavated,  g, Membrane of
the tympanum, h, The tympanitic cavity or drum of the ear.   (For the relative positions
of these bones, see fig. 54,  page 167.)  i, Cells excavated in the temporal-bone,  j, Opening
from the ear-cavity into these cells.—On the side of the cavity opposite  the membrana
tympani, are seen the fenestra ovalis and rotunda, which open into the vestibule.   /, The
vestibule, k, The Eustachian tube,  to, Semi-circular canals,  n, Cochlea,  o, Auditory
nerve, p, Canal, by which the carotid artery enters the skull,  q, Part of the glenoid fossa)
which receives the head of the lower-jaw.  r, Styloid process of the temporal-bone.

  Figure 4.----A magnified representation of the Labyrinth, laid open, so as to display
its Cavity—a, The vestibule,  b, The cochlea,  e, The partition by which the cochlea is
divided into two parts,   c, The fenestra ovalis.  d, The fenestra rotunda. /, /, /, The
semi-circular canals,  g, Portion of the temporal-bone.

  Figure 5.----Capillary Plexus of Papilla of Human  Tongue.
  Fioure 6.---Tongue of a Woodpecker.
Figure 7.---Tongue of a Giraffe, 
LE.C.ICe:   -i.LiB 
 
THE SENSES.
161
   their Avants.   Man is  guided more by reason than by in-
   stinct,  and  his  taste  is very much influenced  by habit.
   Thus, many substances that are exceedingly disgusting at
   first, become  by  use highly  grateful.   Innumerable  in-
   stances of those acquired tastes are observed in all  ages,
   and in every  state of society.   Thus, epicures  in  various
   stages  of civilization  make use of meat,  fish,  and  eggs,
   after decomposition has commenced, or  after those articles
   of food are in what is called a "ripe condition;" and mul-
   titudes, from  all classes of society, chew tobacco, the most
   disgusting of  all Aveeds, as a SAveet morsel.
     335. The susceptibility of the organs of taste to pleas-
   urable sensations, depends very much on the condition of
   the stomach,  even in health.  Accordingly, the relish or
   the pleasure Avith which we partake of any particular arti-
   cle  of food, diminishes as hunger is appeased.   If indul-
   gence  of the  appetite is  persisted in beyond  the actual
   demand  for food, nausea or  disgust will very soon super-
   vene, and compel even the glutton to desist.   The sympathy
(   subsisting between the organ of taste and the stomach, is
   an  important and wise  provision, informing us Avhen a
   sufficient amount of food has been taken.

                     SENSE OF  SMELL.
     336. Smell is the sense by which Ave  perceive odors.
   Certain  bodies seem to possess the property of diffusing
   through  the  air in extreme minuteness the particles  of
   which they are composed, and of exciting a peculiar sensa-
   tion in the organ of smell.  Those particles which emanate
   from odorous bodies are so exceedingly minute, that many

     How is man guided ?  How do substances naturally loathsome come to be
   agreeable ?  What examples are given ?  Upon what does the susceptibility
   of the organs of  taste to pleasurable  sensations depend ?  What ensues if
   indulgence of the appetite is persisted in beyond the actual demand for food ?
   What is said in regard to the sympathy of the organ of taste with the stom-
   ach? What is smell?   What properties do certain bodies seem to possess?
   What is said of the particles which emanate from odorous bodies ? 
162
CLASS-BOOK OF PHYSIOLOGY.
substances do not seem to lose Aveight by freely imparting
their scent to an  unlimited  quantity of air.  Musk, for
instance, will impart its scent to a room that is constantly
open for many years, without any appreciable diminution
of Aveight.  But there are other bodies, such as camphor,
Avhich lose Aveight by loss of particles from  their surface
Avhen freely exposed to the air.
  337.  The special seat of the sense of smell is in the thin
and  delicate  membrane which lines  the  internal surfaces
of the nasal cavities.   It is called Schneiderian membrane,
from the man who first described its structure.
  338.  The  acuteness of this  sense  seems very nearly in
proportion to  the  amount of Schneiderian membrane, or
to the extent of  surface which the  nasal cavities present.
                            Hence, in all those animals re-
                            markable for acuteness of scent
                            —as the deer,  sheep, and dog
                            —the nose is very large, and
                            its internal surface greatly in-
                            creased by the curiously con-
                            voluted  form  of the internal
                            or turbinated bones.   Fig. 52
                            is a vertical  section of the
R§As5IrcAEvTTv.-a, moCuTth°r b°,iosi™, nasal cavities in man, shoAving
 a&^^^.^E*^ now tnis membrane is increa*
 j£Zi;^^o«S?SLi sphen°idal ed in surface by the turbinated
                            bones,/; g, h.
  339.  When air  charged  with odorous particles  passes
over the  Schneiderian membrane, in  the  act of ordinary
respiration, or in the voluntary efforts of snuffing  air, some

  How long will musk scent a room without any apparent loss of its particles?
What is  said of bodies which lose weight by loss of particles? Where  is
the special seat of the sense of smell?  What is the membrane called? The
acuteness of this sense is in proportion to what ? What  is said of the size  of
the nose in those animais which are remarkable for acuteness of smell? How
is the interior surface of the nose greatly increased?  Explain the manner  in
which the odorous particles are made to act on the Schneiderian membrane?
 
                      THE  SENSES.                  163

of the particles come in contact with it, and act upon the
delicate extremities of the olfactory nerves, with which the
membrane is thickly set.   If this membrane is either too
moist or too dry, the odorous particles make no impression
on it.  Thus,  in colds or in fevers, the sense of smell is
almost entirely lost for the  time.
  340. All animals do not perceive the same odors equally
well.  Carnivorous animals excel in detecting the odors
of animal substances, and of tracking other animals by the
scent, but  have  no apparent sensibility to the  odors of
plants and flowers.  Herbivorous animals  are peculiarly
sensitive to the latter, but their sensibility to animal odors
is much  less acute.   Some  herbivorous animals, however,
possess very great acuteness of smell in regard to animal
odors.  Thus, the deer and the antelope frequently scent
the approach  of  the hunter, and make their escape, unless
he steals upon them  in a direction contrary to that of the
Avind.  In this class  of animals, the sense of smell seems
to be an important means by Avhich they are warned of
the presence of their enemies.
  341. Herbivorous animals undoubtedly require an acute
susceptibility to the odors of plants, to guide them in select-
ing their food from a variety of plants,  some of which are
highly deleterious, if not destructive, to animal life.
  342. The wonderful scent of the dog is Avell known.
The certainty with which he  detects  the foot-steps of
animals, long after  they have passed—the facility with
which he traces the progress of his master through crowded
streets, recognizing the emanations which his foot has left
among all the  diversity and multitude of odorous parti-
cles—is truly astonishing.   In like manner, the deer-hound

  Under what circumstances do the  odorous particles fail to make any impres-
sion? Do all animals perceive the same odors equally well? In what do car-
nivorous animals excel?—in what herbivorous? What is said of the deer and
antelope?  Of what special use does the sense of smell seem to be to this
class of animals ? How do the herbivorous animals seem to be  guided in
eelecting their food ?  What is said of the scent of the dog ?—the deer-hound ?
       12* 
164           CLASS-BOOK OF PHYSIOLOGY.

pertinaciously pursues his  victim, and follows its traces
through the herd of its  fellows,  among which it vainly
seeks for protection.
  343.  Birds and fishes do not in general possess the sense
of smell in as high perfection as quadrupeds, though they
do not appear to be  entirely destitute of it.  Many insects
are able to distinguish odorous  substances at considerable
distance; but physiologists are not agreed as to the loca-
tion of the organs of smell.
  344.  Like all the senses, that of smell is greatly improved
in acuteness by education.   In  the blind, especially, it
becomes next to that of touch, the sense  on which they
place the greatest reliance, and by which they distinguish
individuals from each other.   The Indians of Peru, accord-
ing to Humboldt, can ascertain by the smell, in the middle
of the night, whether a visitor be an European,  an Amer-
ican, an Indian, or a jSTegro.   Sometimes the smell becomes
morbidly sensitive:  there  are  those who sicken at  the
scent of cheese, or  faint at that of a cat.  An eminent
French physician was exceedingly annoyed  during an
illness, in which his smell  became remarkably acute, by
the odor of copper;  and after a careful search, the source
of his annoyance was  found to be a brass pin, which had
fallen among the bed-clothes.

              SENSE  OF  HEABING.
  345.  Hearing is the sense by which we perceive sounds.
The ear is  the  special organ of  hearing,  though all  the
parts which are  found in the higher orders of animals are
not  essential  to constitute  an  organ of hearing.   The
essential part of this organ is a nerve, endowed with the
peculiar property of  receiving  and transmitting to  the

  What is said of the sense of smell in birds and fishes ?—what of insects ?
How may the sense of smell be improved ?   How is it in the blind ?   What
is said of the Indians  of Peru?  What examples are given in which this sense
has become morbidly sensitive ?  What is  hearing ?  What is the special
organ of hearing?  What is the essential part of this organ? 
THE SENSES.                   165
brain the impressions derived from the vibrations of the
air or Avater Avith which the animal is surrounded.
   346. Thus, in some of the loAver animals—as the crab,
lobster, &c.—the ear consists of a cavity in the side of the
head, lined with a membrane on which the nerve is dis-
tributed,  and  filled with a watery fluid.   In some, this
cavity is  completely  shut  in by  its bony walls, and in
others there is a small aperture  covered by a membrane,
upon which the external medium can  act.   This cavity,
Avhich corresponds with the vestibule in higher animals, is
the Avhole organ in lower animals;  it is the essential part
in all, and is never omitted in the  most perfect develop-
ments of the organ.
   347. All other parts may be regarded as  superadded to
the vestibule, to render this essential organ more perfectly
adapted to the wants of each group of animals.  Thus, in
the lowest fishes, a single semi-circular canal is superadded
to the vestibule; a little higher, there are two;  and in  all
other fishes, three  semi-circular canals.  In animals which
live in the air, there are added other parts, which  adapt
the organ more perfectly to this element.
   348. In man, and most  of the mammalia, we find the
ear composed of three parts—the external^ the middle, and
the internal ear.
   349. The external ear is a fibro-cartilaginous appendage,
placed on the outside of the head, to receive and conduct
the sounds to  the  interior.   In most of the quadrupeds,
the external ear is very large, and capable of being turned
in any direction at the will of the animal, as in the horse,

  Describe the ear, as found in the crab, lobster, &c. ?  How is it inclosed in
some species?  With what in higher animals does this cavity correspond?
Is  this part ever omitted in the most perfect development of the organs?
What may all other parts be regarded?  What parts are added in fishes?
What other pans are added in animals which live in  the air? Of how many
parts is the ear  composed in man and most of the  mammalia?  What are
these parts?  Describe the external ear. What peculiarity has it in most of
the quadrupeds ? Do men ever popses? the power of moving the external ear? 
166           CLASS-BOOK  OF PHYSIOLOGY
deer, and hare.   Some men  also possess  the power  of
moving the external ear, though to a very limited extent.
  350. Persons who are partially deaf may make  use  of
ear-trumpets, by which the vibrations of sound are col-
lected from a greater extent  of surface,  and  thereby act
with greater intensity on the drum of the ear;  or, in case
this is destroyed, on the internal ear.
  351. The canal (fig.S, Pl. XHI.) into which the external
ear collects the sonorous vibrations, passes inwards until
it is terminated by the tympanum or the membrane  of
the  drum of the ear, which separates the external from
the middle ear.  This canal is about an inch in length, and
is protected from the entrance of insects and dust by short
hairs, which grow across the tube.
  352. In reptiles and birds, there is no external ear, and
the tympanum is found  on the surface of the head, where
it can be easily seen, just back of the eye, as in  the frog.
In birds, it is found in a slight depression in the head, sur-
rounded by a tuft of feathers.  In man, it is a rough, tense
membrane, stretched across the auditory passage, in  a
manner similar to the parchment on a drum, with its edges
set  in a bony groove.
  353. The middle ear, which is also called the tympanitic
cavity or drum of the ear (h), is an irregular bony  cavity,
filled with air.   It communicates with the external air by
means of the Eustachian tube, which terminates  in the
back part of the throat.  The use of this tube seems to be
to produce an equilibrium  between  the air contained  in
the drum of the ear and  the external ear.   In severe colds,
 What may be made use of to collect the vibrations of sound by persons who
are partially deaf?  What effect does it  have on the vibrations of sound?
What is said of the canal into which the external ear collects the sonorous vibra-
tions?  How is it separated from the middle ear?  What is its length?  How
is it protected from insects? Have reptiles and birds any external ear? Where
is the tympanum formed  in frogs?—in birds?  Describe it in man.  What
other name is applied to the middle ear?  With what is it filled ? How does
it communicate with the external air ?  Where does this tube terminate ?
What is its use?  What effect do colds sometimes have on this tube? 
THE SENSES.
167
this tube is frequently obstructed, causing "ringing in the
ear," confusion of sound, and partial deafness.
        a                      vol
Fig. 53.—Bones or       Fig. 54.—Cavity or the Tympanum, with
   the Ear.              the bones in their places.
   354.  Within the drum of the ear (fig. 3, Pl. XIII.) there
 is a very curious arrangement of small bones, which con-
 nect the tympanum  to the membrane of the internal ear.
 These bones, which are represented in figs. 53 and 54, are
 so arranged as to form a continuous chain of bones.  When
 the tympanum vibrates, they move backward and forward
 in such a manner that the slightest vibration is  communi-
 cated to the membrane of the internal ear.  In birds and
 reptiles, instead of a chain of bones, there is a single bone,
 Avith  one extremity  attached  to the tympanum and the
 other to the membrane that incloses the internal ear.   This
 bone'can easily be seen pressing against the tympanum in
, the ear  of a bird by removing the skin and  feathers from
 the head.
   355.  The internal ear or labyrinth is composed of three
 cavities—the  vestibule, the  semi-circular  canals, and the
 cochlea.

   What peculiar arrangement within the ear?  How are these bones ar-
 ranged ?  How do they move with the vibrations of the tympanum ?  What
 substitute  for  a chain  of bones do we find  in birds and reptiles? How
 can  this bone be seen  in the ear of a bird ?   How many cavities has the
 internal ear ? 
168
CLASS-BOOK OF PHYSIOLOGY.
   356.  The vestibule (porch or entrance) corresponds with
the simple sac that constitutes the whole organ 'of hearing
in the lower animals, and is the essential part in all.  It is
separated from the middle ear by a bony partition, Avhich
is perforated by two small holes, called, from their form,
foramen ovale (oval opening), and foramen rotundum (round
opening).  The first is closed by a membrane, on which
the stapes, one of the small bones, rests, and the other by
a membrane similar  to the tympanum.
   357.  The semi-circular canals are passages  running off
from the upper part  of the vestibule, in the form of three
arched tubes.  These canals are found in fishes, and in all
animals  which live in the air.  Their use  is supposed to
be to assist in producing an idea of the direction of sounds.
   358.  The  cochlea, so called from its resemblance to a
snail-shell, is a spiral  canal, running off from the lower
part  of  the vestibule.   It is  peculiar to those animals
which live  in the air, and has been supposed to be the
organ by which we judge of the pitch of sounds.  It also
affords a greater extent of surface  for the spreading out
of the nervous fibres.
   359.  All the above cavities of the internal ear  are lined
with a delicate membrane, on which the extremities of the
auditory nerve are  minutely  distributed,  and are filled
with a watery fluid,  in which filaments of the nerve are
also found floating.  These terminations of the  auditory
nerve constitute the  real organ by  which impressions of
sound are received  and transmitted to the brain.  The*

  With what does the vestibule correspond ?  How is it separated from the
middle ear?  How is this partition perforated?  How are these openings
closed ?  What  are the semi-circular canals ?   In what animals are  those
canals found ?  What is their use ? From what does the cochlea derive its
name ? What is the form  and position of the  cochlea ?  To what class of
animals is it peculiar ?  What has been supposed to be the use of the cochlea ?
How are the cavities of the internal ear  lined ?  What is distributed on this
membrane ? With what are these cavities filled ?  What constitutes the
real organ by which impressions of sound are received and transmitted ?  How
are the vibrations of sound  communicated to the nerve ? 
THE SENSES.
169
 vibrations of sound are communicated to the nerve through
 the medium of a watery fluid.
   360. Sound travels through the air at the rate of about
 twelve and a half miles in  a minute;  through water, its
 velocity  is  four times  greater;  and  the intensity of the
 vibrations of sound in air and water are in about the same
 proportion*   Hence,  the impressions  of  sound  on the
 nerves Avhich are the immediate  seat of hearing are much
 more intense in the watery fluid, Avhich 'fills the cavities
 of the internal ear,  than they could be if those cavities
 Avere filled with air.   For the same reason, animals Avhich
 live in the air require an apparatus for hearing more com-
 plicated than those animals which live in the Avater.   Ac-
 cordingly, we find in those animals which live in the air,
 the addition of just  those parts  that Avould communicate
 the vibrations of sound from the air  to the  fluid of the
 internal  ear with  the  greatest intensity.   Thus, a  tense
 membrane, like  that of the drum of the ear, Avith air on
 both sides, is better adapted than any other animal struc-
 ture to receive the  vibrations  of  the air; and the arrange-
 ment of the bones Avhich connect this membrane with that
 of the internal ear, is equally well fitted for the office of
 conducting those vibrations to the fluid of the internal ear.
   361. Still, the faculty of hearing will not be  entirely
 lost if the drum of the  ear is destroyed;  so that the vibra-
 tions of sound act directly on the  membrane of the internal
  At what  rate  does sound travel through the air?  What  is its velocity
 through water ?  What advantage  then is  gained by the nerves receiving
 impressions  through water instead of air ?  Why do animals which live in air
 require an apparatus more complicated than those  which live in water?
 What parts  do we find added in those animals which live in air?  What is
 said in regard to the adaptation of the tympanum and the bones which con-
 nect it to the internal ear to  receive the vibrations of the air?  Will the
 faculty of hearing  be entirely lost if the dmm is destroyed ?   How will the
hearing be affected by its  loss?
  * The difference in the intensity of the vibrations of sound in air and
water may be easily perceived by striking two stones  together with
equal force—first in the air and then under water, with the head immersed. 
170           CLASS-BOOK OF PHYSIOLOGY.
ear,  though  it will be  greatly  impaired,  rendering  the
individual partially deaf.
  362. The faculty of hearing may be very much increased
in acuteness  by cultivation;  but this  increase depends
rather upon  the habit of attention to the faintest  impres-
sions made upon the organ, than upon any change of  the
organ itself.   Thus, the  Avatchful Indian, recognizes foot-
steps, and can even distinguish the tread of a friend from
that of a foe, while his Avhite companion, who lives among
the  busy hum  of cities, is  unconscious of  such slight
sounds.   Yet the latter may be a musician, capable of dis-
tinguishing the tones of all the different instruments in a
large orchestra—of following any one of them through the
part which it performs—and of detecting the least discord
in the blended  effects of the whole—effects which would
be to the Indian only a  confused mass of sound.

                 SENSE OF  SIGHT.
  363. Sight is  the sense by  which we are enabled to
perceive luminous impressions;  and through these we be-
come acquainted with the form, size, color,  and position
of objects that transmit  or reflect light.
  364. The eye  is the organ  of sight.   It consists essen-
tially in an instrument capable of making a distinct picture
of surrounding objects  on the  expanded  surface of  the
nerve of sight.
  365. Some of the inferior animals, such as the leech,
seem to  be guided in their movements by  certain dark
spots on their surface, supposed to be  rudimentary eyes,
though no fully developed eyes  have as yet been dis-
covered.  In some of the star-fishes those eye-spots  are
found at the extremity of the rays, as in fig. 1, Pl. XYI.
  How may the faculty of hearing be increased in  acuteness? Upon what
does  this increase seem to depend? What examples are given of the habit
of attention? What is sight?  What is the organ of sight?  In what  does
it consist essentially?  How do  some of the inferior animals seem to be
guided in their movements ? 
 
PLATE  XIY.
ORGANS OF  VISION-THE  ETE.
  Figure  1.----The Left  Eyeball, showing the Posterior Surface of the Retina.- a, A
small transparent spot, situated near the optic nerve, called the foramen of Soemmering,
surrounded by a yellow halo, the limbus luteus.   b, The optic nerve, cut off at its entrance
into the retina,  c, The central artery of the retina, d, d, Ramifications of the artery on
the inner wall of the retina, seen through the outer layers.

  Figure  2.----The Globe of the Eye, magnified, and seen in front.—This figure repre-
Bonts the second or choroid coat, the sclerotica being removed,  a, The pupil,  b, The iris.
c, c, The ohoroid membrane,  d, d, The ciliary nerves, running from every part of the cir-
cumference towards the iris,  e, e, The ciliary arteries.

  Figure  3.----The Globe of the Eye, seen in the same view.—The iris is removed, in
order to display the ciliary processes, and their position in regard to the lens.  The ciliary
nerves and arteries are the  same as in fig. 7.

  Figure  4.----The Anterior Half of the Globe of the Eye, seen from behind.—The lens
and the vitreous humor are removed, a  The pupil,   b, b, The posterior surface of the
iris, called, from its dark  grape-like color, uvea,  c, c, The  ciliary processes,  d, d, The
internal surface of the choroid and sclerotic,

  Figure  5.----The Posterior Half of the Globe of the Eye, showing its internal surf ace.
—a, a, The cut edges of the sclerotic, choroid, and retina,  b, b, The internal surface  of
the  retina,  e, The foramen of Soemmering,  d, The optic nerve,  e, Branches of the
central artery of the retina.

  Figure  6.----The Fibres of the Iris, detached.—a, The pupil,   b, The circular fibres at
the central margin of the iris, by the action of which the pupil is diminished or enlarged.
e, c, The radiating fibres, which proceed from the external border of the circular fibres.

  Figure  7.----A Portion of the Pigment Membrane of the  Choroid Coat, highly magni-
fied..—-It is seen to consist  of regular six-sided  plates, the tissue of which is filled with
grains of coloring matter.

  Figure  8.----Compound Eyes of the Bee, highly magnified, showing the Division into
Facets, and also the Conical Shape of each separate Portion.—A, Facets still more highly
magnified.  B, The same with hairs growing between them.

  Figure 9.----A, Front View of the Crystalline Lens.  B, Side View of the Lens.—a.
Its anterior and least convexity,  b, Its posterior and greatest convexity.
  Figure 9.----Front  View of the Crystalline Lens.

  Figure 10.----Side View of the Crystalline Lens.—a, Its anterior and least convexity,
b, Its posterior and greatest  convexity.

  Figure 11.----The Crystalline Lens, after being immersed in boiling water.—The lines
on its surface show its division into three parts.

  Figure 12.----The Three Segments of the Crystalline Lens.—The faces of the segments
show the concentric  layers  of which  it is composed (like the coats of an onion).  The
nucleus, or central portion of the lens, is seen on one of the segments, and on  the other
two  are corresponding depressions. 
Fi 2-1
Fi<5.  6
Fig. 7

Fl6.ll.
E.  AUooA.Lith.

Ry.1'2.
   .:i.-ulford C. 
\ 
THE SENSES.
175
  366. Most insects  are  furnished with compound eyes,
AA'hich consist of several hexagonal facets, (fig. 8, Pl. XIV.)
united together in such  manner as to form a large, dark-
colored protuberance on  each side of the head.   Each of
these facets  is an eye in  itself.  In  some insects, these
facets are exceedingly numerous.  In the eye of a butter-
fly, 17,000 have been counted;  in some species of beetle,
25,000;  in the common  horse-fly, 4,000.  These numer-
ous eyes, no tAVO of which  have the same direction, seem
to compensate  for the inability of the insects to move the
head without moving the whole body, since they are pro-
vided Avith an  eye in every direction.
   367. Spiders are  furnished with from six to fourteen
eyes, situated  on the most prominent part of  the  back,
instead of on the sides of the head.  (Fig. 3, Pl. XYI.)
   368. In the snail and some  other mollusks there are
only two eyes, situated  on or near the tip of  a flexible
stalk—the tentacula, (fig. 2, Pl. XYI.)  which can  be
extended in  any direction at the pleasure of the animal.
In lobsters and crabs the eye is placed at the extremity of
a  long tube, which  can  be moved in various directions,
and extended or withdrawn.
   369. In all the higher  animals there are only tAvo eyes,
Avhich are constructed on the same general plan, with some
variation in the form of particular parts, adapting the eye
to the medium with which different animals are surrounded.
   370. The form  of  the  eye is nearly globular in all, and
placed in a bony socket (the orbit) in the head.  The orbit
is  lined with a cushion of fat, on which the eye rests and
rolls with very great ease.   When a person becomes very
  With what are most insects provided ?  Of what are those compound eyes
made up?   What is each facet? How numerous are these facets?  How
many in the eye  of a butter-fly—in the beetle?  What seems to be the use
of so large a number?  With how many eyes are spiders provided?  How
many eyes are there in the snail, and how are they situated ?  How is the eye
placed in crabs and lobsters ? How many eyes are there in all the higher
animals ?  What is the form of the eye, and how is it placed ?  How is the
orbit lined ? 
176
CLASS-BOOK OF PHYSIOLOGY.
much emaciated, this cushion of fat is gradually absorbed,
alloAving the eye to recede into the orbit.
  371. The  eye is  admirably protected  against insects,
dust, and other foreign substances, by the eye-brows, eye-
lids, and eye-lashes.
  371. In birds and reptiles  there is a thin transparent
membrane which  is  draAvn across the eye by a muscle
that passes through  a  loop in the membrane, (fig. 4, Pl.
XYI.)  This nictating membrane is so transparent as not
to prevent the power of vision, while it protects the eye
from too strong light, and guards it against foreign bodies.
  373. The horse is provided with a beautiful contrivance
for protecting the eye,  called the haw.  It is a triangular-
shaped cartilage, admirably adapted to the convexity of
the eye, and so arranged that  it is made  to sweep across
the eye at the will of the animal,  and shovel up any dust
or insect that may fall upon it.
  374. The anterior surface of the eye is covered by the
conjunctiva—a thin mucous membrane, which is reflected
upon the lids, so as to form their internal surface.
  375. The conjunctiva is  constantly  moistened by the
mucus from its surface, and by the tears  that are secreted
in the lachrymal glands, and  poured upon the inner sur-
face of the upper lid by seven or  eight tubes.  The  lach-
rymal gland (fig. 2, Pl. XY.)  is situated  at the upper or
outer angle of the orbit.  It is continually pouring  out  a
watery fluid, which  moistens the globe of the eye, and
keeps it free from impurities.   This secretion is increased
by mental  emotion,  and by irritation of  the  eye.   The
tears pass out from the eye by tAVO lachrymal ducts, Avhich
  What takes place when a person becomes very much emaciated ?   How is
the  eye protected against insects, dust, &C. ? What membrane is there in
birds and reptiles?  How is it drawn across  the eye ?  How does it  protect
the eye without preventing sight? With what is the  horse provided?  De-
scribe the  haw ?  How is the interior surface of the eye covered ?   How  is
the conjunctiva moistened?  Where is the lachrymal gland situated ?  What
is continually pouring out from this gland ?  How is this secretion increased 1
How do the tears pass out of the eye ? 
 
PLATE   XV.
                  ORGAN  OP  VISION.-THE  EYE.


  Fioure 1.----Both Eyes, with their Muscles, as they appear upon a horizontal section
through the orbits, immediately above the eyes—as if the upper part of the head were
removed, as far down as the top of the eyes, the observer looking at them from above.
They are represented in this position, in order to show clearly the situation and action of
the superior oblique  muscle, and  also the crossing or decussation of the optic nerve.  The
letters of reference indicate the same parts in figures 1 and 3.
  a, The optic nerve,  s, figure 1, The chiasma or commissure of the optic nerve, whence
each nerve extends forward and outward, passes into the eye at t, and becomes continuous
with the retina,  b, The common oculo-motory nerve, which is distributed to five of the
muscles of the eye.   k,  Trunk of the fifth pair, a branch of which constitutes the ophthal-
mic nerve, and gives sensibility to the different parts of the eye.—The distribution of this
nerve is seen  in the left eye in figure 1. /, Artery of the eye.  c, The elevator muscle of
the upper eyelid,   d, The superior rectus, or elevator of the eye.   «, The inferior rectus,
or depressor of the eye.  /, The internal rectus,  g, The external rectus,  h, figure 1, The
superior oblique muscle.  ?n, Its pulley, i, figure 3, The inferior oblique muscle.  In figure
1, parts of several of these muscles are removed, in order to display the others distinctly.
  Figure 2.----The Lachrymal  Apparatus.—a, The lachrymal gland,  b, b. The lachry-
mal ducts, which collect the tears, and transmit them to the lachrymal sac, c, whence they
pass into the cavity of the nose.
  Figure 3.----The Right Eye,  with its Muscles, displayed in the cavity of the orbit, on
the vertical plane of  a section corresponding to the middle of the arch of the eyebrow :—
that is, as if the right  side of the head were removed, as far as the middle of the right eye-
brow, leaving the eye in its place, to be seen from the right. 
EL. TV.

J!  Harlfonl 
 
                       THE SENSES.                    181
                                           *
commence in a small opening in the edge of each lid, near
the corner of the eye, and unite to form the lachrymal sac
that lies upon  the side of  the upper parts of the nose.
From  the lachrymal sac a canal passes down to the interior
of the nose, Avhere the tears pass off in vapor Avith the breath.
   376. The Avails of the eye are composed of three coats:
the sclerotic,  the cornea, and the choroid coat.  Its interior is
occupied by three humors:  the aqueous, the crystalline,
and the vitreous.
   377. The sclerotic, (fig. 55,) so named from its firmness
and density, constitutes about four-fifths of the  globe of
the eye.  It is a tough fibrous structure, admirably adapted
to protect and  support this delicate organ.
       Fig. 55.—Interior or the Eye.     Fig. 56.—Section of the Eye.
c, cornea; s, sclerotic; s, portion of the sclerotic turned back to show the subjacent parts;
 ch, choroid ; r, retina; n, optic nerve; ca, anterior chamber; i, iris; p, pupil: cr, crys-
 talline lens; cp, ciliary processes; v, vitreous humor; b, b, conjunctiva.
   378. The cornea (c, fig. 55) is a dense transparent struct-
ure, convex in front and concave posteriorly.   It resem-
bles a Avatch-glass in form, and is  received into a circular
groove in the margin of the sclerotic, in the same manner
that a watch-glass is inserted  into the case.  It occupies
about one-fifth of the front part of the eye, and  projects
forward beyond the sclerotic.   In some individuals and

  Where is the lachrymal sac situated, and how do the tears escape from it ?
Of what are the walls of the  eye composed ? How is its interior occupied?
Describe the sclerotic.  Describe the  cornea.  How is it received into the
sclerotic?  What portion of the eye does it occupy ?  What is said in regard
to its prominence at different periods of life and in different animals? 
182
CLASS-BOOK OF PHYSIOLOGY.
  in some animals it is more prominent than in others, and
  it is also more prominent at  some  periods of life than at
  others.  In fishes, and in some water-birds, it has only a
  slight projection forward, as represented in figs. 5 and 6,
  Pl. XYI.
    379. The choroid coat, (ch, fig. 55,)  which  is  a  thin,
  delicate structure, consisting mostly of  blood-vessels and
  nerves, lines the interior of the sclerotic.   The internal
  surface of the choroid is covered by a layer of black pig-
  ment cells.  (Fig. 7, Pl. XIY.)
 / """380. The aqueous humor, which occupies the anterior
/ chamber of the  eye, (fig. 56,) is  nearly pure water.   It
1 gives  prominence to the cornea, causing it to be more or
 'sLess convex, according to the amount of this fluid.
r   3,81. The vitreous humor, which resembles thin jelly or
f  melted glass  in consistence,  occupies the greater  part of
!  the globe of the eye behind the iris.
V  382. The crystalline humor resembles thick jelly  or
  soft gristle.  It has the  form  of  a double-convex  lens,
  Avhence it has  received the name of crystalline lens.  In
  those  animals which have only slight projections of  the
  cornea, it  is nearly spherical.   (Figs. 5  and 6,  Pl. XYI.)
  It is suspended in its place by the ciliary process, (fig. 3,
  Pl.  XIY.) a set of little bands from the  choroid coat.
    383. The aqueous and vitreous humors are separated
  from each other by the iris,  (fig. 2, Pl. XIY.)  a kind of
  curtain, which  divides  the  anterior from  the  posterior
  phamber of the  eye.  The iris receives its name from  the
  great variety of its colors.  It is perforated in the centre by
  an opening, called the pupil.  (Fig.  2, Pl. XIY.)  In man,
  this pupil is round, and dilates or  contracts according to
  the amount of light and the sensibility of the optic nerve.
   What fluid occupies the anterior chamber of the eye ?  How does it affect
  the form of the cornea ?  Describe the vitreous  humor—the crystalline humor.
  What is the form of it ? How is it suspended in its place ?  How are the
  aqueous and vitreous humors separated from each other ?  From what does
  the iris receive its name ?  What opening has the iris in the centre?  What
  is the form of the pupil in man ? 
THE SENSES.                   183
When the  light  is  very  strong, it  is  but a  speck, and
enlarges to  nearly half the size of the iris in the dark.   In
birds,  especially in  oavIs,  its motions are  more  free and
extensive than in man.
  384. The blackness of the pupil  is owing to the dark
color of the internal surface of the choroid.  In Albinoes,
which are destitute of coloring matter,  the pupil, as well
as the iris,  are a bright red, from the numerous  capillary
blood-vessels of the choroid.   In many quadrupeds—as
the ox, the lion, and the cat—a portion of the surface of
the choroid is covered with a bluish layer of bright metallic
lustre, by Avhich the light is brilliantly reflected, when the
eye is seen  in certain directions, causing the eyes to appear
in an obscure light like two balls of fire.
  385. In  animals whose range  of  vision is  required to
extend widely in a horizontal direction—as in the deer,
cow,  &c.—it  is lengthened horizontally, so as to give a
wide side-view.  In the carnivorous  animals—as the lion,
cat, &c.—which watch their prey in situations either above
or below them, the pupil is elongated vertically.
  386. Inside of the choroid coat, and at the back part of
the eye, is  the  retina, which consists of a delicate film of
nervous fibres,  spread out from the optic nerve as soon as
it has passed through the sclerotic and choroid coats.
  387. The globe of the eye is moved by six muscles—
four recti or  straight, and two oblique—all of which are
lodged in  the  orbit.  The superior rectus  or straight
muscle (fig. 3,  Pl. XY.) rolls  the eye  upward, and the
inferior rectus  turns it  downward.  The internal rectus
rolls the globe inward, or toward the nose, and the external

  How does it vary  in size ?  To what is the blackness of the pupil  owing?
What is the color of the pupil and iris in albinoes? What peculiar appearance
has the eye in many quadrupeds?  What is the  form of the pupil in grazing
animals?—in carnivorous animals? What  is situated inside of the choroid
coat?  Describe  the retina.  How is the globe of the eye moved? How
does the superior rectus move the eye ?—the inferior rectus ?—the  internal
rectus?—the external rectus? 
184
CLASS-BOOK OF PHYSIOLOGY.
 rectus turns it outward.  The  superior  oblique,  a very
 remarkable muscle, has its origin at the back of the orbit,
 passing forAvard through a little cartilaginous pulley, and
 then turning backward, to be  inserted into the sclerotic
 coat.   The  direction of its  action  is thus  changed,  like
 that of a rope which  is passed through a block in an
 ordinary pulley.   The use of this muscle is to roll the eye
 downward and inward.  The  inferior  oblique turns it
 upward and outward.
   388. The coats and humors of the eye seem  admirably
 adapted  to  modify the rays of light, which fall  on the
 nerve of sight in such a manner as to make the impression
 clear and distinct.  All the parts of the eye are constructed
 in such strict accordance with  the  laws of light,  that it
 excels all other optical instruments  in perfection and  ac-
 curacy.  Human skill has thus  far effected only an imper-
 fect imitation  of the  instrument  designed  by  Infinite
 Wisdom.
   389. It is well knoAvn that Avhen the rays of light pass
 obliquely from the air through a dense medium, they are
 refracted or bent out of their course, as in fig. 7,  Pl. XYI.,
               a       and that the  refraction is in propor-
                       tion as the rays fall  more  or  less
                       obliquely.  Thus, if a piece of money
                       be placed in a cup  (fig. 57) in such
                       a position that the  side of the cup
                       will just hide the money from sight,
                       and then let the cup be filled with
         Fig- 57.        water, the money will be distinctly
 visible from the refraction of the rays of light.  For the

  Describe the superior oblique ?  What is the use. of this muscle ?  In what
direction does the inferior oblique turn the  eye ?   To what do the coats and
humors of the eye seem adapted?  How does the eye compare with optical
instruments ?  How are the rays of light affected by passing obliquely from a
rarer to a denser medium ?  The refraction is in proportion to what ? What
examples are given, illustrating the refraction of the rays of light in passing
from air to water ?
 
 
PLATE   XVI.
                  ORGANS  OF VISION-THE  EYE.

  Figure 1.---Eye-spots of a Star-fish, at the extremities of the radii.

  Figure 2.---Eyes of a Snail, on the extremities of the tentacular
  Figure 3.---Eyes of a Spider, on the anterior part of the back.

  Figure 4.---Nictating Membrane of a Bird.—A, Nictating membrane, covering one-
half the suiface of the eye.  B, The muscles bjt which the membrane is drawn across the
eye. The muscle a forms a loop at b, through which the muscle c acts as through a pulley
by its tendon d, which is inserted into the edge of the nictating membrane at c.

  Figure 5.---Eye of a Fish, with very slight convexity of the cornea, and the lens
nearly spherical, so as to compensate for  the want of refractive  power in the anterior
part of the eye.

  Figure 6.---Eye of a Duck, with a similar formation.

  Figure 7.---Refraction of Light.—a, The ray of light falling obliquely on a dense me-
dium at b, is refracted to c, instead of pursuing its original course to d; when it passes into
a rarer medium again at c, it is again refracted in a new course down to d, instead of/.

  Figure 8.---The Lenses.—a, Single convex lens,   b, Single concave lens,  c, Double
convex lens,  d, Double concave lens, e, Concavo convex lens.

  Figure 9.----Short-sightedness—The image formed in front of the retina.

  Figure 10.---Long-sightedness—Tho image formed back of the retina.

  Figure 11.---Eye of a Lynx.—a, Ciliary process, by which  the lens, b, is  moved
backward and forward, to adapt it to different distances.

  Figure 12.---Eye of an  Eagle.—a, Fan-like muscle, attached  to  the lens, to  change
its position.

  Figure 13.---Eye of an Owl, surrounded by a  kind of bony case, which causes the
anterior portion of the eye to become more, and the posterior portion less convex, when-
ever the eye i* drawn back into the socket. By this means the focal distance is changed,
and the eye adapted to different distances. 
PL. XVI
 
 
THE SENSES.
189
same reason an oar  or  a  stick, when  partly immersed in
water,  will appear bent in proportion to its obliquity.
  390. The rays of light which fall upon  the cornea of
the eye are refracted toAvards the pupil, both by the  dens-
ity  of  the cornea and  aqueous  humor, and  by the con-
vexity of the cornea, Avhich  causes the rays  to fall on it
more obliquely.
  391. After passing through the pupil, the rays of light
continue to be refracted by the crystalline  lens and vitre-
ous  humor, so that they meet in a focus  on  the retina,
Avhere a complete inverted image or picture of the object
is thus formed.   This is
shown in fig. 58, where,
for the sake of  conve-
nience, two rays only are
represented  as  issuing
from each of the  two extremities of an object, a, c.   Those
rays cross each  other  in the middle of  the eye—those
from a being brought to a focus at b, and  those from c at
d;  and as all the other  rays are refracted in the same man-
ner, a complete inverted  picture of the object  is formed at
the back  of the eye.
  392. The inverted image may be easily seen by remov-
ing the fat and muscle from the eye of a white rabbit, and
bringing  a lighted candle in front of it, when an inverted
image may be  distinctly seen on the retina  through the
transparent  coat of the  sclerotic;  or  it may be seen by
removing the sclerotic  from the back part of the eye of a
sheep  or an ox.  In either case, the eye should be fresh,
as the cornea and humors soon lose their transparency,
and the image becomes indistinct.*
  How are the rays of light refracted towards the pupil ?  How are the rays
of light affected by the crystalline lens and the vitreous humor?  What is  the
position of the image on  the retina ? Describe Figure 53.  How may the
inverted image be seen ?
  * To show the retina of the eye, clip off the muscular and adipose
substance about it,  then describe  with the knife a circle about the
       14
 
190            CLASS-BOOK OF PHYSIOLOGY.
  393.  The black pigment, which is situated in the inter-
nal surface  of the choroid, and immediately "behind  the
retina, absorbs the rays of light as soon as they have passed
through the retina, and prevents them from being reflected
from one part of the eye to another, causing confusion and
indistinctness in the  picture.   The black pigment also
diminishes the intensity of the impression of light on  the
retina.   In  Albinoes,  (in whose eyes  the pigment is defi-
cient,) vision is not  only extremely  imperfect, but  the
strong sunlight is even painful to the  eye.   Hence, Albi-
noes  can  see most  clearly when twilight comes  on,  or
during cloudy  days, or by moonlight.
  394.  The ordinary forms of  defective vision, known as
short-sightedness  and  long-sightedness,  are  caused  by
defects in the refractive poAver  of the eye.
  395.  In  short-sightedness, the refractive  power is  too
great, causing  the rays to be brought  to  a focus forward
of the retina, unless the object be held very near the eye,
so as to increase the angle at which they fall on the cor-
nea.  (Fig. 9, Pl. XYI.)  In most  cases of. short-sighted-
ness,  the  cornea  is too convex  from an excess of  the
aqueous humour.
  396.  Short-sightedness is frequently caused in students
  What is the use of the black pigment on the internal surface of the choroid ?
How, does  the light affect the eye in Albinoes ?  How are short and long-
sightedness caused?  What is the defect in short-sightedness?  What is the
form of the cornea in short-sightedness?  How is it frequently caused  ?

entrance of the optic nerve  that shall  include one-fourth of the ball of
the eye; holding the eye in the thumb and fingers of the left hand,
gradually  and carefully cut through the sclerotic to the choroid coat, at
a single point in the circle already described, and then complete the dis-
section in water by carefully insinuating the sharp point of the scissors
between the coats, and clipping  round  the circle.   The slight attach-
ment of the choroid to the sclerotic may  now be  separated with the
back of the knife till the detached portion of the sclerotic can be clipped
off, leaving the nerve entire.  The dissection is  now complete; and, if
well performed, inverted images of objects can be seen  on the retina as
in life. 
THE SENSES.                   191
and artisans by the habit of holding objects near the eyes,
till they adapt themselves to a short focal distance, and it
may be remedied by perseverance in the opposite practice.
Thus, sailors, from the long habit of using their eyes in
search of distant objects, acquire the ability of recognizing
objects at  a  distance that would  be  unobserved  by  a
landsman.
   397. If short-sightedness has continued from birth, it
can  seldom be remedied,  except by  the use  of concave
glasses, the curvature of which compensates for the excess
of the convexity of the eye.   If the  glasses' used be toe
concave, they will increase the difficulty;  while those that
are  not quite concave enough, will  have a  tendency to
remedy it.  If glasses can be  dispensed with, or if they
are* changed  for those less concave every few years, the
difficulty will gradually diminish,  till, in advanced  life,
the eye assumes the natural form.
   398.  In long-sightedness, (fig. 10, Pl. XYI.) which is
commonly met with in persons in advanced life, the re-
fractive power of the eye is not sufficient to bring the rays
to a focus on the  retina, but back of it, unless the object
be held at a long distance from the eye.   At  this period
the eye is not sufficiently convex, from the decrease of its
fluids.  This difficulty may be remedied  by perseverance
in the habit of holding objects as near the eye as possible,
or wearing spectacles with convex  glasses,  which  shall
compensate for the deficiency of the convexity of the eye.
   399. The eye is the most delicate of the organs of sense,
and is more liable to disease than any other.   In many
persons the  conjunctiva  is  exceedingly sensitive,  and
   How may short-sightedness be remedied ?  What power do sailors acquire
by the habit of viewing objects at a distance ?  What kind of glasses may be
used to remedy short-sightedness?  What will be the effect of using glasses
that are too concave ?—not quite concave enough to compensate for the con-
vexity of the eye ?  How does the eye gradually  return to its natural form ?
What is the cause of long-sightedness?   What change in the eye diminishes
its convexity? How may the difficulty be remedied ?  What is said in regard
to the liability of the eye to become diseased? 
192           CLASS-BOOK OF PHYSIOLOGY.
becomes inflamed from very slight causes.   Exposure to
dust, to Avind, or to a strong light, not unfrequently induces
severe inflammation.   The optic nerve is  also liable to
serious injury from exposure to a strong light, from too pro-
tracted  application to study, or from using  the eyes with
insufficient light.  Disease of the eyes may be prevented by
a careful regard to their strength, by refraining from their
use in improper light, and by affording them rest as soon
as a sense of fatigue begins to be experienced.  Moderate
ablution at bed-time, and liberal washing in cold water on
rising in the morning, will be found of great service in
promoting strength and vigor.


                   CHAPTER  XIII.
                      ANIMAL  MOTION.
  400.  The power  of voluntary motion is  characteristic
of all animals.
  401.  The organs of voluntary motion are the bones and
muscles.
  402.  The bones constitute the frame-work of  the body,
and give strength and firmness to the entire organization.
  403.  The muscles form the greatest part of the mass of
the body, and constitute what is commonly known as flesh
or lean  meat.
  404.  The  principal  hard parts in animals are  shells,
crusts, and  bones.  Shells  are  almost destitute  of animal
matter,  being nearly the same in composition as a piece of
marble.   Crusts, such as the  covering of the lobster, con-
tain a considerable quantity of animal matter, though less
than is  found in bones.

  What parts are liable to become inflamed or t"» be injured by improper use ?
What causes induce disease ?  How may disease be prevented ?  What power
is characteristic of all animals?  What are the organs of voluntary motion?
What do  the bones constitute?—what the muscles?  What are the principal
lard parts in animals ?  What is the composition of shells ?—of crusts ? 
 
PLATE   XVII.
ORGANS OF  MOTION.-THE  BONES.
  Figure 1.----Front View of the Human Skeleton.—At the right half of this figure, the
bones are represented in their natural connexions, and divested of all covering.  At the
left side, the joints are covered by their ligaments.  The outer lines show the form of the
body when covered with flesh.
  The Head.—a, The frontal-bone,  b, The parietal-bone,  c, The temporal-bone.  e,The
superior maxillary-bone.  /, The malar-bone,  g, The nasal bones,  h, The vomer,  i, The
inferior maxillary-bone,  k, The orbits.  /, /, Sutures.
  The Trunk—1, 1, The spinal column.  2, The sternum.  3, 3, The ribs.   4, The oa
innominatum, or haunch-bone. 5, The sacrum.
  The Superior Extremities.—6, The clavicle.  7, Acromion process of the scapula,
which articulates with the clavicle.  8, The humerus.  9, The elbow-joint.  10, The radius.
11, The ulna.   12, Bones of the carpus.  13, Bones of the metacarpus.  14, The phalanges.
  The Inferior  Extremities.—15, The hip-joint.  16, The femur, or thigh-bone.  17,
The patella.  18, The tibia.  19, The fibula.  20, Bones of the tarsus.  21, Bones of the
metatarsus.  22, Bones of the toes.  On the left side of the figure, I indicates the ligaments
of the shoulder,   m, Ligaments of the elbow,  n, Ligaments of the wrist, s, Ligaments
of the hip-joint,  o, Ligaments of the knee, and tendon of the extensor muscle of the leg.
p, Ligaments  of the ankle,  q, Large vein and artery of the arm.  r, Large vein and artery
of the leg.
   Figure 2.---A Bone deprived of its earthy portion by maceration in a dilute acid, and
tied in a  knot, to show its flexibility.
   Figure 3.---A Section of the  Femur, showing its cancellous structure.
   Figure 4.----A Dorsal Vertebra.—a, The body of the vertebra, b, The spinal foramen.
c, c, Articulating processes,  d, d, Transverse processes, e, Spinous  processes.
   Figure 5.----A Lumbar Vertebra, to show  the greater thickness and strength of its
body and processes.
   Figure 6.----The Lower  Jaw.—a, The condyle, which  articulates with the temporal-
bone, b, The coronoid process,  c, The ramus.
   Figure 7.----Vertebra of a Fish.—9, End view.  B, Side view of the same.
   Figures 8 and 9.----These figures are designed to show the minute structure of bone.
Figure 8 represents a cross-section of bone, highly magnified,  a, a, Orifices of small tubes,
called, from their discoverer, Haversian canals.  They usually run in the direction  of the
length of the bone, the membrane lining the hollow of which is prolonged into their canals.
 This  membrane  contains innumerable small blood-vessels, and  the interior of the bone
is thus supplied with blood.  Around each of the  Haversian  canals are seen concentric
circles of some small dark spots, which are found to be flattened cavities or bone-cells,
from which proceed numerous minute tubules.  These open into the sides of the Haver-
sian  canals,  and communicate from one bone-cell to another, thus transmitting the
nourishment with which they are supplied by the blood-vessels throughout the substance
of the bone.  Figure 9, represents a longitudinal section of bone, highly magnified, showing
the Haversian canals seen lengthwise, their connexion with each other, and the direction
of the bone-cells. *These figures are from HassalCs Microscopic Anatomy. 
pl xvn
ICeTlogS Iith
Hartford, Conn. 
 
ANIMAL  MOTION.
197
  405. At first, bones exist in a state of cartilage, and are
gradually converted into bone  by a deposition of phos-
phate and carbonate of lime.
  406. The lime of the earthy portion of the bones  is
continually increasing till old age, while the animal por-
tion is  gradually diminishing.  In children, the animal
matter constitutes about one-half;  in adults, one-fifth;  and
in old age, one-eighth of the whole composition.
   407.  In children, the bones  are soft and flexible, and
admirably adapted to sustain the numerous falls and acci-
dents, to which  they are liable,  without injury.  At this
age, the bones are not easily broken, though they are bent
and twisted from their natural form.   Thus, infants are
not unfrequently made "bow-legged," by  efforts to bear
their weight on their limbs  before they have acquired the
proper proportion of earthy  matter to give them the requi-
site strength.  If not encouraged by  parental  ambition,
nature does not incline the young  infant to  make the effort
to  stand or walk until the period when the bones have
become quite stiff and hard.
   408.  The bones do not arrive at their perfect state until
about the twentieth year.  Previous to this  period, the
form of the bones may be easily changed by improper
habits.  Indeed, some change may be effected in many of
the bones at a much later period  of life.
   409. As the animal matter of  the bones diminishes  in
old age, they  become hard and brittle.  In an aged per-
son, a very slight slip or miss-step is sufficient to produce a
fracture.  Fortunately, the failure and decline of  all the
other powers  compel this class  of persons to move with so
   In what state do bones exist at first ?  How are they converted into bone ?
 Which portion of the bones continues to increase and which to diminish to
 old ase?  What  proportion of the  bones is animal matter in children 7—in
 adults?-in old age?  What is the  condition of the bones in  children ?
 To what injury are the bones most liable at this age ? How are infants made
 bow-legged ?  At what age do the bones arrive to perfection ?  What is the
 cTdittaf of the bones in old age ?  To what injury are the bones of the aged
 liable ? 
198           CLASS-BOOK OF  PHYSIOLOGY.
 much care and caution, that the frailty of this part of the
 system is but seldom tested.
   410. The earthy and animal portions of the bones can
 be easily separated from  each other.   To obtain the ani-
 mal portion, we have only to soak the bone a few days in
 a diluted acid.   When the earthy matter is then dissolved,
 the animal matter which  is left becomes so soft and  plia-
 ble, that a bone of sufficient length can easily be tied into
 a knot, as represented in fig. 2, Pl. XYII.
   411. By exposing a bone to the action of a hot fire, the
 animal matter will be consumed, leaving it so brittle that
 it may be  easily crumbled into fragments.
   412. The bones of nearly all the higher animals present
 a great  variety of form  and  structure, according  to the
 position they occupy.
   413. The principal bones of the extremities are long
 and cylindrical, and consist of a shaft and two extremities.
 The shaft  of a  long bone  is dense and hard  in structure,
 and hollow in  the centre, forming a cylinder or a double
 arch—a form which, it is well  known, receives the greatest
 amount of strength.  The  extremities of the long bones
 are broad and expanded, so as to present a large surface to
 articulate with  adjoining  bones, and their internal struc-
 ture is cellular and cancellous, so as to secure as much bulk
 as possible in proportion  to the quantity of matter.   The
 internal structure of the long bones may be seen by a" sec-
 tion of the thigh-bone, fig. 3, Pl. XVII.
   414. The different bones of the body are united to each
 other by articulations and joints.
   415. The different bones of the cranium and skull, which
 surround and protect the brain, are very firmly united by

  How can we separate  the  animal  from the earthy portion of the bones ?
 How the earthy portion?  What is said of the bones of the  higher animals?
 What is the form of the principal bones of the extremities?  Describe the
shaft, and the extremities of a long bone. How are the different bones of the
body united to each other?  How are  the different bones  of the cranium
united together ? 
 
PLATE   XVIII.
ORGANS OF  MOTION.-THE  BONES.                 1
   Figure 1.----Posterior View of the Human Skeleton.—The Head.—a, The frontal-bone.
 b, b, The parietal bones,  c, The left temporal-bone,  d, The occipital-bone.
   The Trunk.—1, 1, 1, Spinous processes of the vertebrae,  t, t, t, Transverse processes  j
 of the vertebra;. 2, 2, The ribs.  3, The os innominatum, showing its three parts, viz: a, ']
 the illium ; b, the ischium ; c, the os pubis.  4, The sacrum.  5, The coccyx.             -I
   The Superior Extremities.—0, The scapula. 7, Acromion process of the scapula.
 8, The clavicle.  9, Head of the humerus placed  in the glenoid cavity of the scapula.  10,  |
 Shaft of the humem?.  11, 12, Internal and  external condyles of the humerus.  13, The
 olecranon process of the ulna, which articulates with the pulley-like surface at  the lower  J
 end of the humerus, forming the elbow-joint.   14, Shaft  of the ulna.  15,  Shaft of the  |
 radius.   16, Lower extremity of the radius, which articulates with the bones of the carpus. . j
 17, Bones of the carpus.  The first row consists of four boms, viz: a, the scaphoid-bone ;  ;
 b, the semi-lunar-bone;  c, the cuneiform-bone;  d, the pisiform-hone.  The second row  I
 consists of four bones, viz: c, The trapezium. /,  The trapezoid-bone.  g, The os magnum.  |
 ft. The unciform-bone.—18, 18, Bones of the  metacarpus.   19, 19, 20, 20, 21, 21,  First, sec-  •
 Olid, and third ranges of finger bones.
   The Inferior Extremities.—22, Head of the femur, placed in  the acetabulum or  |
 cotyloid cavity of the haunch bone.  23,24, Projections called trochanter major and minor,
 to which the  muscles of the hip are attached. 25, Shaft of the femur. 26, 27, External
 and internal condyles of the femur.  28, Upper extremity  of the tibia, which  articulates
 with the lemur. 29, Shaft of the  tibia.   30, The internal  malleolus, a projection of the
 tibia which forms the inner ankle.  31, The  fibula.  32, External malleolus, a projection  ,.
 of the fibula  which forms the outer ankle.  33, Bones  of the tarsus.  34, Bones of the  i
 metatarsus.   3.3, Bones of the  toes.  The ligaments of the various joints are  seen on the  j
 left side of this figure.
  Figure 2.----The Knee-joint—A, The knee-joint, with the patella removed,  a, a, The  '
 condyles of the lemur, covered with cartilage, b, b, The two semi-lunar cartilages, which
 form cup-shaped depressions for the reception of the condyles,  c, The anterior crucial
 ligament which passes from the tibia to the femur.  B, Section of the knee-joint, showing  !
 the reflections of the synovial membrane, a, The cancellous structure of the lower  part  ]
 of the femur,  b, The tendon of the extensor muscle of the leg.  c, The patella,  d, The , ]
 ligaments which attach the patella to the head of the  tibia,  e, The cancellous structure  |
of the head of the tibia.  /, The anterior ligament,  g, The posterior ligament.  The synovial  !
 membrane may be traced along the under surface of the patella and  its ligaments, and
 then over the head of the tibia, over the posterior ligaments, and then over the lower part
of the femur.
  Figure 3.----A Section of the Hip-joint.—a, The head of the femur,  b, b, The capsular  •
ligament, embracing the cavity of the hip-bone and the head of the femur, and keeping
 both bones firmly together,  c, A round ligament attached to the inside of the cavity and
to the head of the femur.
  Figure 4.---The Bones of the foot, seen upon the upper surface.—a, The OS calcis, or
 heel-bone,  b, The astragalus,  which articulates with the lower end of the tibia,   c, The
cuboid-bone,   d, The scaphoid-bomi.  c, e. f, Cuneiform bones. 
 
 
                       ANIMAL MOTION.                203

   sutures (seams), which are formed  by the interlocking of
   the ragged edges of one bone into corresponding notches
   in the  adjoining one.  These bones are thus so firmly
   united together in man at adult age,  that it is difficult to
   separate them, except by  breaking away some of the pro-
   jecting parts.
      416.  The bones forming joints are firmly bound together
   by muscles and ligaments, and the end of each bone cov-
.   ered over by a thin layer  of cartilage, which has a smooth
   glassy surface.  Each joint is inclosed by a sac or capsule
   of serous membrane, which secretes a peculiar fluid, called
   synovial fluid.  The office of the synovial fluid is to  keep
   the joints constantly moist and supple.
      417.  After a  severe injury to  the joint, the synovial
   fluid  is  sometimes  secreted in excess, causing " dropsy of
   the joint."
      418.  The beautiful  smoothness  of the  surfaces of the
   cartilages,  and the manner in which  the bones are bound
!   together by ligaments and muscles,  may be seen  by ex-
   amining the knee-joint of any of  our  domestic animals.
|   In fig. 2, Pl. XVIII., is a section of the knee-joint in man,
   showing the reflection of its synovial membrane.
     419.  There are several kinds of joints in the body, the
   most  important of which are the hinge-joint at the elbow
   and  knee,   and the ball-and-socket joint at the hip and
   shoulder.
     420. In  the hip-joint, the socket is much deeper than
   at the shoulder—an arrangement evidently designed  to
   give greater security against dislocation in a part on which
   the weight  of the whole trunk must press in walking,  run-

     How are the sutures formed? What is said of their firmness at adult age?
   How are the bones forming joints bound together? How is the end of each
   bone covered?  How is each joint inclosed? What is the office of the  syno-
   vial fluid?  How is this fluid sometimes affected  by an  injury?  How may
   the structure of a joint be seen?   How many kinds of joints are there?
   What is said of the hip-joint ?  What circumstance seems designed to pre-
   vent dislocation at the hip-joint ? 
204
CLASS-BOOK OF PHYSIOLOGY.
ning, leaping, &c.   There is also a strong cord, fastened by
one end to the top of the thigh-bone, and by the other to
the socket in which it moves.
  421.  The skeleton of man is formed  by the union of
about two hundred and  fifty bones,  and is divided into
head, trunk, and extremities.
  422.  The head includes  the  bones of  the face and the
cranium; the trunk  includes all the bones immediately
attached to the spine,  except  the head; the extremities
embrace all the bones of the shoulders, arms,  and  legs,
which are called upper and lower extremities in man, or
the anterior and posterior extremities in  quadrupeds.
  423.  The face is formed by the union of fourteen bones,
which serve for the lodgment and protection of the organs
of sight, smell, and taste.
  424.  The cranium  or skull is a bony case, of an  oval
form, occupying the upper and back  part of the  head, and
serving for the protection of the brain, which is  lodged in
its cavity.   Its walls are made  up of eight bones, which
are firmly united to each other in such a manner that every
part is admirably adapted to resist external force.
  425.  The cranium is constructed on the principle of the
arch,  the bones at the base of the skull overlapping those
above so firmly, that a separation is rarely, if ever, effected
during life, and only with great difficulty after death.
  426.  The spinal column or back-bone, as it is commonly
called, consists in man of thirty-three different bones, called
vertebrae, which are divided  as follows,  in man:  seven
cervical vertebrae,  (vertebrae of the  neck,)  twelve  dorsal
vertebrae, (vertebrae of the back,) five lumbar  vertebrae,
(vertebrae of the loins,) five sacral vertebrae, four cocygeal

  Of how many bones is the skeleton of man formed ?  How is it divided ?
What bones are included in the head ?—the trunk ?—the extremities ?  Of
how many bones is the face formed?  Describe the cranium.  Its walls are
made up of how many bones ? On what principle is the cranium constructed ?
How is a separation of the bones prevented?  Of how many bones does the
spinal column consist?   How are they divided? 
ANIMAL  MOTION.
205
vertebrae.  All these vertebrae are separate at the time of
birth,  but the five sacral vertebrae  are soon after united
into one piece—the sacrum-—and the four coccygeal ver-
tebrae  are also united into one piece, the coccyx.
  427. The number of the cervical  vertebrae is the same
in all the mammalia.   Birds have a  much larger number:
the swan, which  is remarkable for the gracefulness and
beauty of its neck, has twenty-three vertebrae, the crane
has seventeen, and the swallow thirteen.
  428. The number of the dorsal vertebrae is the same as
the number of the ribs on each side.  In man, there  are
twelve dorsal vertebrae, in the lion thirteen, and  in  the
elephant twenty.
  429. The  vertebrae  are perforated by  an aperture, so
that when they are all united, they form a continuous tube
or canal for the lodgment of the spinal cord.
  430. By the division of the spinal column into so large
a number of separate bones, very great freedom of motion
is allowed, with only a slight bend at any particular point.
  431. Each vertebrae consists of a body, which is situated
in front of the spinal canal in man, and below it in quad-
rupeds ; and of seven processes or projections, which serve
to form the spinal canal, and  unite  the vertebrae  to each
other  by affording attachments for the muscles.
  432. In man and the other mammalia,  the two surfaces
of the body of the vertebrae are nearly flat, and are sepa-
rated  from each other by a disc of fibro-cartilage.
  433. In reptiles and fishes, a different  plan is adopted.
In  serpents, one  surface  of each vertebra is concave  and
the  other convex, and thus  the convex surface  of each

  What change takes  place with the five sacral vertebrae ? What  is said of
the number of the cervical vertebrae in the mammalia ?—in birds ? How many
cervical vertebrae has  the crane and the swallow? What do the vertebra
form when united together?  What is gained  by the division of  the spinal
column into so many separate pieces?  Of what does each vertebrae consist?
What is the form of the two  surfaces of the. body of the vertebrae ?  What is
the form in fishes and reptiles ?  What kind of a joint do they form ?
        15 
206
CLASS-BOOK OF PHYSIOLOGY.
 vertebra fits into the concave surface of the next, in such
 a manner that the whole spine becomes a series of ball-
 and-socket joints—an  arrangement  which  is remarkably
 adapted to the peculiar movements of those animals.
   434. In fishes, both surfaces are concave, and between
 each vertebra there  is  interposed a  bag, containing fluid,
 and  having two convex surfaces, over which those of the
 vertebrae can freely  play.  Very great freedom of motion
 is  thus acquired,  though  the strength  is proportionably
 diminished.  But great  strength is  not required by ani-
 mals whose bodies are supported by a  medium which  is
# nearly of the same density with themselves.
   435. The extreme flexibility of fishes enables them to
 propel their bodies by the  movements of the tail and
 hinder parts from side to side, their fins being used  prin-
 cipally for influencing their direction.
   436. Man is the only animal whose spine seems adapted
 to the erect attitude.  Its form has  some resemblance to
 the letter  S, being  a # double  curve, and it thus forms a
 kind of spring that  is admirably adapted to diminish the
 shock produced by a sudden jar, as  in the act of jumping
 upon the feet from a height.   The bodies of the vertebrae
 are also broader, in  proportion to their size, than in other
 animals, while the spinal processes,  which form the ridge'
 along the back, are  considerably shorter  In quadrupeds
 which maintain a horizontal position of the spinal column,
 the spinal processes are very long, for the attachments of
 muscles to support the head.  In figs. 9 and 10, Pl. XIX.,
 may be seen a comparative  view of the vertebrae in the
 lion and ox.
   437. The ribs, which  are twelve on  each side in  man,
 are attached  by one extremity to the transverse processes
   How are the two surfaces separated in fishes ? How do fishes propel their
 bodies?  For what purpose are fins used ? What attitude is peculiar to man ?
 What is the form of the spine in man ?  What  advantage is obtained by this
 form ?   How do the vertebrae in man differ from those of all other animals ?
 What is said of the spinal processes in quadrupeds ?  How many ribs arc
 there in man ? What are the attachments of the ribs? 
 
    PLATE   XIX.
    __----                       £
THE  EXTREMITIES.
  Figure  1.----Anterior Extremity of Man.—a, Scapula, or shoulder blade,  b, The
humerus, or principal bone of the arm.  e, The radius,  d, The ulna,  e, The carpus, or
wrist.  /, The metacarpus, or palm,  g, The phalanges, or fingers.
  In figures 2, 3,4,5,6,7, and 8, the corresponding bones are indicated by the same letters
as in figure 1.
  Figure  2.---Anterior Extremity of the  Deer.
  Figure  3.---Anterior Extremity of the Lion.
  Figure  4.---Anterior Extremity of the  Whale.
  Figure  5.---Anterior Extremity of the Bat.
  Figure  6.---Anterior Extremity of the  Bird,
  Figure  7.---Anterior Extremity of the  Sloth.
  Figure  8.---Anterior Extremity of the  Monkey.
  Figure  9.----Skeleton of the Lion.—a, The skull,   b, The cervical vertebra,  c, The
dorsal vertebrae,  d, The lumbar vertebras, e, The sacrum. /, The caudal vertebra, which
compose the tail,  g, The ribs,  h, The scapula,  i, The humerus,  j, The fore-arm.—In
this part, corresponding to the fore-arm of  man, the two  bones are united into a sintle
one.  k, Bones of the wrist, or carpus.  /, Bones of the metacarpus, or hand,  m, The
phalanges,  n, The femur, or thigh-bone, united to the bones of the pelvis,  o, The patella,
or knee-pan.  p, The tibia;  the two bones of the leg being united into one.  q, Bones of
the  tarsus, or ankle,  r. Bones of the foot and toes.—In the lion, the bones of the arm are
stout and long, and the fingers short and compact, collectively combining freedom of motion
and strength, and admirably adapting this class of animals to the sudden springs with
which they pounce upon their prey.
  Figure  10.----Head and Shoulders of an Ox.—a, The skull,  b, The cervical vertebra?.
c, The dorsal vetebrae, which are very long, for the attachment of the muscles which sup-
port the neck and head,   d, The scapula, or shoulder-blade. 
E.C.lCelloM.Liih
145 
 
ANIMAL MOTION.
211
   of the dorsal vertebrae, and by the other to cartilages which'
   are continuations of the ribs.  The cartilages of the first
   seven, or true ribs, (aa,fig. 1, Pl.  XVII,) are united to the
   Bternum or breast-bone; the  cartilages  of the  five lower
   ribs (bb,fig. 1, Pl. XVII)  are not directly connected with
   the sternum, and are hence called false ribs.
     438.  The sternum, or breast-bone, (fig. 1, Pl. XVII) is
   flat in man, but in those animals which have need of great
   strength in the upper limbs it is  increased in  breadth, and
   furnished with a projecting keel'or ridge for  the attach-
   ment of powerful muscles.   In the turtle tribe, it is so far
   extended as to afford  a  complete protection  to the under
   side of the animal.
     439.  The  extremities, which  have  been  regarded  as
   appendages to the trunk, are four in number in all  the
   vertebrated  animals,  and  are constructed on the  same
   general  plan, though they  are widely different  in general
   appearance.   The fin of a fish, the wing of a bird, the leg
.  of a  lion  or a  deer, and the arm of  man, are evidently
   adapted to very different uses, and are apparently destitute
   of any very striking resemblance to each other;  yet, when
   those same limbs are stripped of the skin and muscles,
   they will be  found to possess the  same essential parts,
   slightly  modified, according to their several uses.
     440.  One of the superior extremities of man, and one
   of the anterior extremities of a deer, a lion, a  whale, a bat,
   and a bird, are represented by the same letters in figs. 1,
   2, 3, 4,  5, and 6, Pl. XIX.
     441.  The scapula, or shoulder-blade, is a large flat bone,
   attached to the  back part of the trunk by muscles.  In
    How many of the cartilages are attached  directly to the breast-bone?
   What are the five lower ribs called ? What is the form of the  breast-bone in
   man ?—in  those animals which have  need of great strength in  the upper
   limbs ?  What is said of it in the turtle ?  How many extremities are there
   in all the vertebrated animals? What is said of their construction?  What
   illustrations are given ?  Describe the scapula or shoulder-blade.  How is it
   attached to the trunk? What advantages are derived from this  kind of
   attachment ?
          15* 
212
CLASS-BOOK OF  PHYSIOLOGY.
animals which walk on all-fours, this kind of attachment
secures much greater elasticity  of movement,  and also
diminishes the force of the shock in the acts of leaping or
running.   In man, it  gives  greater freedom of motion to
the arm.
  442. The clavicle, or collar-bone,  is attached at one ex-
tremity to the  shoulder-blade,  and at the  other to the
sternum or breast-bone.  It acts as  a brace to separate the
shoulders,  and it is accordingly strongest in those animals,
the action of whose superior extremities tend to draw them
together; while  it is  comparatively weak, or  altogether
deficient, in  those animals, the action of whose limbs nat-
urally tends  to keep them asunder.   Thus, in birds, there
is not only a strong clavicle, but a  second bone also, tend-
ing to keep the  shoulders apart.  In the lion, deer, &c, it
is entirely  wanting.
  443. The arm is supported  by a  single long and cylin-
drical bone,  c, the humerus.  In the  fore-arm,  there are
two long bones,  the radius and ulna (d, e), which lie par-
allel to each  other.  The radius is on the outer or thumb
side of the  fore-arm,  and the ulna on  the inside.  The
radius and ulna  are connected with one another by liga-
ments at their extremities, and by  a strong fibrous mem-
brane, that passes between their adjacent edges along their
entire length.  Those  bones  rotate freely on each other, in
such a manner that either the palm or back of the hand
may be turned.   In most quadrupeds, the radius and ulna
are so firmly united together as to be incapable of rotation.
  444.  The  hand is anatomically divided into  three por-
tions—the carpus, metacarpus, and phalanges.  The carpus,
  What are the  attachments of the clavicle ?  What is the use of this bone ?
In what animals is it strongest?  In what animals weakest?   How is it in
birds ?—in the lion, deer, &c. ? How is the arm supported ?  How many bones
are there in the fore-arm, and what are they called ?  On which side is the
radius?—the ulna?  How are the radius and  ulna connected to each other?
How do these bones rotate on each other?  In what condition are the radius
and ulna in  most quadrupeds?  How  is the hand  anatomically divided ?
Describe the carpus—the metacarpus—the phalanges. 
ANIMAL  MOTION.                213
which is nearest the wrist-joint, is composed of eight small
bones, which are firmly united to each other by ligaments
■—the metacarpus, which consists of five long cylindrical
bones, resembling the bones of  the fingers so much, that
in the  skeleton they might  be easily mistaken for their
joints.   The fingers are formed by a series of small bones,
called phalanges, of  which  there  are only  two  in  the
thumb, and three in each of the fingers.
  445. As the foot and ankle,  which correspond to  the
wrist and hand in man,  are designed for solidity in quad-
rupeds, we find in different  parts that there  is only  one
solid piece for two, three,  or more
bones  in  corresponding parts in
man, though those solid pieces are
found originally to have been sev-
eral distinct bones that  have after-
wards united.   Thus, in the rumi-
nating animals, as  the deer  and
horse (figs. 59 and 60),  the number
of  phalanges  is reduced to  two in
each foot, and in the horse there is
but one, which is enveloped by the
hoof.
   446. The structure of the lower
extremities has a very great analogy
to that of the upper, the principal
differences being such as are necessary to make the lower
extremities more  solid, and better adapted  to serve as
organs of locomotion, instead of organs of prehension.  _
   447. The lower extremities are connected with the spine
 by  a bony case or  basin, called the pelvis.   The thigh,

  How many phalanges are there in the  thumb ?-in the fingers ?  How are
 the foot and ankle in quadrupeds made more solid than the wrist and hand
 in man»  Are these parts found solid originally ?  How many phalanges are
 there in the deer ?-in the horse?  How do the upper and lower extremities
 differ from each other? How are the lower extremities connected with the
Fig. 59-
Fig. 60.
spine
?  How is the thigh supported ? 
214
CLASS-BOOK OF PHYSIOLOGY.
like the arm, is supported by a single long cylindrical bone,
called the femur, which is bent at the upper extremity at
an angle, and  its rounded head separated from the main
bone by a narrow portion, called its neck.  The lower end
of the thigh-bone spreads into long condyles, on which
the large bone of the leg moves backward and forward.
  448. The leg has two bones, but they do not possess the
power of  rotating on each other like the fore-arm.   The
main bone, or tibia, is much  larger than the fibula, which
is  a  long slender bone,  running parallel with the tibia,
and  apparently serving  no  other  purpose than  to give
attachment to the muscles.   The upper end of the tibia is
broad, and has two shallow depressions, in which  the  con-
dyles of the femur or thigh-bone are received.
  449. In front of the knee-joint is a  small bone,  called
the patella, which serves the  double purpose of protecting
the joint and  changing the direction of the tendon which
comes down from the thigh.
  450. The foot is composed, like the hand,  of three dis-
tinct portions—the tarsus, the metatarsus, and the phalanges
or toes.  There are seven bones in the tarsus, all of which
are larger than those of the carpus.   The  metatarsus is
composed of five long bones in man.   The toes, like the
fingers, have three phalanges, each, except the great-toe,
which has only two.  The tarsus  and metatarsus form a
kind  of arch  on the inside  of the foot, which serves to
lodge and protect the vessels  and nerves that descend from
the legs to the toes.   This arch also serves to deaden the
shock that would be experienced every time the  foot was
put to the ground; for by the elasticity of the ligaments
which bind  these  bones together, a kind of spring is
  What is the form of the upper extremity ?—of the lower extremity ?  How
many bones form the leg ?  What is  their comparative size ? Describe the
tibia.   What bone in front of the knee-joint ? What  is its use ?  Of how
many portions is the foot composed, and what are they called ?  How many
bones in the tarsus?—the metatarsus?  How many phalanges are there in the
toes?  What do  the tarsus and metatarsus  form? What advantages are
derived from this form of the foot ? 
 
PLATE   XX.
               ORGANS  OF MOTION.-THE BONES.


  Figure 1.----Skeleton of the Camel.—-The black ground in this and the two following
figures shows the outline of the form when clothed with flesh,  a, The skull,  b, The cer-
vical vertebrae,  c, The dorsal vertebra?.—The spinous processes of these vertebra  are
much longer and larger than those of man, for the purpose of giving attachment to  the
strong muscles and ligaments by which the heavy neck and head are supported,  d, The
lumbar vertebrae,  e, The sacrum. /, The caudal vertebrae, which  compose the tail,  g,
The ribs,   h, The scapula,   i, The humerus,  j, The fore-arm.—In this part, corresponding
to the fore-arm of man, the two bones are united into a single one.   k, Bones of the wrist
or carpus.  I, Bones of the metacarpus or hand,  m, The phalanges,  n, The femur, or
thigh-bone, united to the bones of the pelvis,  o, The patella, or knee-pan.  p, The tibia;
the two bones of the leg being united into one.  q, Bones of the tarsus or ankle,  r, Bones
of the foot and toes.—In animals which do not possess fingers, the bones of the fore-arm,
wrist, and hand  are always few in number.  Thus, in the camel, and  in  all herbivorous
quadrupeds, the fore-arm has only one bone;  the wrist, about  four; the  hand, only one,
with sometimes  the rudiment of another; while some species have two toes, and others
only a single one.                                                           t

  Figure 2.---Skeleton  of  the Vulture.—vc, Cervical vertebrae, fifteen  in number,  b,
Dorsal and lumbar vertebrae,   vs, The sacrum,  vq, Vertebrae of the tail,   st, The breast-
bone, or sternum, cl,  The clavicle,   h, The humerus,  o, The two bones of the fore-arm.
ca, Bones of the wrist, imperfectly developed,  ph, Bones of the hand and fingers.  /, The
thigh-bone,  t, The two bones of the leg. ta, The shank or ankle bones.

  Figure 3.---Skeleton of  Turtle.—a, Cervical vertebrae,  b, Scapula,   c, Clavicle,  d,
Coraooid-bone.   e, Dorsal vertebrae.  /, Ribs incorporated with the dermal plates which
form the shell,  g, Marginal plates,   h, Pubic bones,  t, Femur, k, Tibia.  /, Fibula.

   Figure 4.----Skeleton of the Perch.—a, b, First and second dorsal fins,  c, The caudal
or tail-fin.  d, The anal-fin.  e, One of the ventral fins, which correspond to the  legs. /,
One of the pectoral fins, which are analogous to the an#s.  The spinous  processes of the
vertebrae are long, and are connected with another set of boues, by which they are con-
tinued upward, so as to form the frame-work of the fins which arise from the back.  The
whole number of vertebrae is forty-two, of which twenty-one are dorsal and twenty-one
caudal or coccygeal.  The number of pairs of ribs is the same as that of the dorsal vertebras. 
PI. XX
 
 
ANIMAL  MOTION.
219
formed, which yields for a moment to the shock, and then
recovers itself.
  451. In animals which walk on all-fours, the difference
of direction in which the bones of the  legs are connected
with the spine, prevents a jar from extending to the body.
In those animals which obtain  their food by sudden  and
extensive leaps—such as the cat, tiger, and lion—there is
an arrangement of the bones admirably adapted to dimin-
ish  the  shock produced by a sudden descent of the body
upon the ground.

                   THE  MUSCLES.

  452.  The muscles are the  moving power  by which the
parts of the skeleton are set in motion.
  453.  Each muscle,  if examined carefully, is found to be
made of a number of bundles of fibres, and  each fibre is
formed  of numerous smaller fibres or fibrils.   The  primi-
tive fibrils are only about To.^ooth.of an inch in diameter.
Each fibre, which extends from one end of the muscle to
the other, is supplied with one or more loops of nervous
filaments.  Through  the  influence of the nervous system,
the muscular tissue is capable of being excited to sudden
and forcible contraction.   In contracting, the two ends of
a muscle approach each other, and swell out in the middle
to a corresponding degree. • Thus, the whole muscle, when
shortened  by the drawing  together  of its two ends, is
greatly enlarged in diameter, especially towards the middle.
  354.  The energy of muscular contraction depends, in a
great degree, upon the power of the  stimulus which is
transmitted to the muscles from the brain.

  In animals which walk on all-fours, how is a jar prevented from extending
to the body?  How are the parts of the skeleton set in motion ?  Of what is
each muscle made up ? What is the size of the primitive fibrils ?  With what
is each fibre supplied?  How is the muscular tissue excited to contraction ?
What change takes place in a muscle when it contracts ?  When is the muscle
enlarged most in diameter? Upon what does the energy of the muscular
contraction depend? 
220
CLASS-BOOK OF PHYSIOLOGY.
   455.  This is frequently observed in instances  of great
nervous excitement, as when a person is under the influ-
ence of violent passion or insanity.  A delicate female is
thus often a match for three or four strong men,  and can
even  break cords and bands that would hold the most
powerful man.
   456.  In the production of animal motion, the bones not
only serve as  points  of  attachment for the muscles, but
they constitute a series  of levers  for the application of
muscular  force.
   457.  Most of  the muscles act  on  the  bones at  great
mechanical disadvantage, though it is a law in mechanics
that what is lost in power is gained in time.  Thus, in
fig. 76,  the muscle  (a) which arises from the top  of the
                         Fig. 61.
shoulder,  and is inserted at e, a short distance from the
elbow, acts at a great mechanical loss of power in raising
the fore-arm^ but its contraction to a very slight extent
will raise the hand through a considerable space.   Thus,
since the muscle is inserted about one-sixth of the distance
from the elbow to the wrist, it will require a force  of con-
traction in the muscle equal  to six pounds to raise one
pound at  the wrist, while its contraction of one inch will

  In what cases of great nervous excitement  is this frequently observed ?
What example is given ? What other purpose do the bones serve besides
affording attachment for the muscles? How do most of the muscles act on
the bones ?  What law of mechanics in regard to this ?  Explain Figure 65
What force in the muscle will be required to raise one pound at the wrist, ? 
 
P1.21.
I  C K"elli>'i».Lith
Hirttnti 
PLATE   XXI.
ORGANS OF  MOTION--THE MUSCLES.
   LATERAL  VIEW OF  THE  PRINCIPAL  MUSCLES OF THE  HUMAN  BODY.

  Muscles of the Head and Neck.—1, The occipito-frontalis muscle, which elevates the
eyebrows, and wrinkles the forehead, expressing astonishment or attention.  2, The orbic-
ularis palpebrarum, which closes the eyelids.  3, Triangularis nasi, which compresses the
nostrils.  4, The levator labii superioris, which raises the upper lip and expands the nos-
trils, expressing disdain.  5, Zygomaticus major.  6, Zygomaticus minor: These muscles
raise the upper lip and draw it outward.  7, Orbicularis oris.—Only half of this  muscle
is seen on the plate.  It extends completely around the mouth, which its action is to close.
It  also assists the lips in whistling, blowing and sucking.  8, The buccinator, or trumpet
er's muscle.—It elongates the mouth  transversely, and is greatly used in  blowing wind-
instruments.   9, Depressor labii inferioris, which  draws down the under lip, expressing
chagrin, disgust.  10, Depressor anguli oris, which depresses the angle of the lips.  11,
The masseter.—This powerful muscle is the essential agent in mastication.   It raises the
lower-jaw, and brings its teeth strongly against those of the upper-jaw.  12, Omo-hyoideus,
extending from the edge of the scapula to the hyoid-bone, which it depresses.   13, Sterno-
hyoideus, a depressor of the larynx.  14, The digastricus, an elevator of the larynx and a
depressor of the lower jaw.  15, The Sterno-cleido-mastoideus, extending  from the tem-
poral-bone to the sternum and clavicle.—When one of these contracts, it draws the head
to its own side; when both contract, the bead is carried forward. 16, The upper portion
of the trapezius.—(See Plate XXII.)  17, 18, Scalenus posticus and anticus, which ele-
vate the ribs and assist in  respiration.
   Muscles of the Trunk.—19, The pectoralis major, a large muscle,  attached to the clavi-
cle, sternum and ribs, and to the humerus.  It draws forward the shoulder, and also ele-
vates the ribs, acting as a muscle of inspiration.   20, The serratus magnus, a powerful
muscle, lying beneath the  pectoral muscle.—It is  divided into slips  or digitations, which
extend from the ribs to the scapula.  It is a muscle of inspiration, the contraction of its
slips tending to separate the ribs and thus dilate the chest.  21, 21, &c. External inter-
costal muscles, which  elevate the  ribs.   22, The transversalis abdominis.  This muscle
draws the front  of the abdomen inward, thereby pushing up its contents against the dia-
phragm, in the act of expiration.  23, Rectus abdominis, which draws the  chest forward
toward the pelvis, and assists in straightening the trunk when it has been thrown backward.

   Muscles of the Superior  Extremities.—24, The deltoid muscle.  This thick and powerful
muscle is attached to the scapula and to the  humerus.   Ordinarily it elevates the arm;
but when the body is raised by the arms, as in climbing, it draws up the trunk.  25, The
biceps brachialis.—This Is the large muscle whose projection is felt in front of tho arm.
It is a flexor of the fore-arm.   26,26,26, Portions of the triceps brachialis.—(See Pl. XXII).
27, The pronator teres.—This muscle, being attached to  the radius, and having its fixed
insertion on the humerus, rolls the radius inward, and thus turns the palm of the hand
downward.  28, The supinator longus.—This  muscle acts as an antagonist to the last, and 
222
CLASS-BOOK  OF  PHYSIOLOGY.
turns the hand upward.  29, The flexor carpi radialis.  30, The palmaris longus.  31
Flexor carpi ulnaris — These three muscles are flexors of the wrist upon the fore-arm.
Their white and slender tendons are attached  to the carpal and metacarpal bones.  32,
Tendons of the flexor sublimis digitorum, which bend the second range of the finger-bones
upon the first.  33, Extensor carpi radialis longior.—This muscle  extends  the wrist upon
the fore-arm.  34, Extensor communis digitorum.—(See Pl. XXII.)  35, Lower portion
of the abductor pollicis longus.   36, Lower portion of the extensor pollicis brevis.—These
two muscles draw the thumb outward, and bend it on  the carpus.  37, Extensor carpi
ulnaris.—(See Pl. XXII.)
  Muscles of the Inferior Extremities.—-38, The rectus internus.—This muscle is a flexor
of the leg.  39, The sartorius or tailor's muscle, the  longest muscle in the body.—By its
action the legs are bent inward, so as to  cross' each other.  40, The rectus femoris.  41,
The vastus internus.  42, The vastus externus.—These three muscles extend the leg upon
the thigh. 43, Portion of the adductor magnus.—This muscle draws backward the thigh
at the hip.   44, A  portion of the gluteus raaximus.—(See Pl. XXII.)   45, The gluteus
medius.  46, A tendinous expansion called the fascia-lata, forming part  of the femoral
aponeurosis.  47, The tendon of the vastus femoris,  which contains the  patella. 48, The
triceps surae, or extensor of the foot, composed of  three large fasciculi.—(See Pl. XXII.)
49,The peroneus longus; its tendon passes behind and beneath the outer ankle,in a pul-
ley-like groove, and is inserted into the first  metatarsal-bone.  By its  contraction, this
muscle extends and rotates the foot.  50, The tibialis anticus— This muscle is attached
by its tendon to a bone of the instep, and bends the  foot upward.  51, The extensor digi-
torum communis.—Its four tendons are seen proceeding under the annular ligament of
the tarsus, and diverging to the four smaller toes.  This muscle extends the joints of the
toes, and  bends the foot upon the leg.  52, Annular ligament of the tarsus.  53, Adductor
pollicis pedis.—(See Pl. XXII.) 
                    ANIMAL MOTION".                 225

move the wrist through six inches
of space.   In the same manner the
muscle b, fig. 62, which lies on the
back of the arm, and is attached to
a short projection of the ulna be-
hind the elbow, acts with a similar               i
disadvantage in regard to power,          Fig. 62.
though it has a corresponding advantage in point of time.
   458. Under ordinary circumstances, the energy of mus-
cular  action depends on the condition  of. the  muscles
themselves.  Those muscles which are firm,  plump, and
high-colored, act with greater force than  those which are
pale and flabby.  In  the sedentary and inactive, the mus-
cles are smaller in size and less vigorous  than in those
whose habits are more active.   "Within certain limits, the
muscles increase, both in size and power,  by use.   In the
smith, who makes  constant use of his arms, the muscles
are  proverbially  large and powerful; in the pedestrian,
the muscles of the legs become developed.
   459. The free exercise of the muscles not only increases
the general strength,  but greatly improves the vigor  and
health of all the physical powers.
   460. The energy of muscular contraction appears to be
greater  in insects, in  proportion to their  size, than in any
other animals.  Thus, a flea will leap sixty times its own
length,  and move as many times its own weight.   The
same  muscular power, in a man of six feet, would enable
him to leap a  distance of over three hundred feet, and to
   If this muscle contracts one inch, through what space  will it move the wrist?
Under ordinary circumstances, upon what  does the energy of muscular con-
traction depend?  What kind of muscles  act with greatest energy? What
is said of the muscles in the sedentary and inactive?   How are the muscles
affected by use ?  What is  said of the arms of the smith, and the legs of the
pedestrian ?  What is said of the influence of exercise on the muscle?, and on
the health of all the powers ?  In  what animals is the energy of muscular
contraction greatest in proportion to size ?  How far will a flea leap ?  How
 far would the same muscular power in man enable him to leap ?  How much
would it enable him to lift ?
 
226
CLASS-BOOK OF PHYSIOLOGY.
lift a weight of over ten thousand pounds.  A species of
beetle can support a weight equal to at least five hundred
times that of its own body; and another, by the power of
its  jaws, has  been known to gnaw a hole of an  inch in
diameter in the side of an iron canister in which it had
been confined.  The rapidity of the movements in insects is
also so great, that the vibrations of the wings in some species
have been calculated at several hundred, and, in some of
the smaller insects, at several thousand in a second of time.
  461.  The various kinds of progression in different ani-
mals are called swimming, crawling, flying, walking, running,
jumping, &c.
  462.  In fishes, the body is propelled through the water
by the tail, on the same principle as a boat in impelled by
sculling.  The tail being vertical,  in most cases its stroke is
horizontal, and the body is propelled forward by the resist-
ance of the water to its broad expansion", as it strikes from
Fig. 63.—Tail-Fin of Whale.
side to side, by the alternate contraction of the muscles
which extend  from the long process of the vertebrse  to
the tail.   In the whale, the tail (fig. 63) is expanded hori-

  What is said of some species of beetle ?  What is said of the movements
of insects?  What  are the various kinds of progression in animals called?
How is the body in  fishes propelled through the water?  How is the stroke
made against the water in most cases ?  What propels the fish ? How is  the
tail expanded in the whale, and how is its stroke made ? What is said  of the
structure of the tail ?—of the power of the whale ? 
ANIMAL  MOTION.
227
zontally, so that its stroke is vertical.  The texture of the
tail is such, that it is insensible to pain, and it is so tough
that it is rarely torn or injured.   The whale is therefore
capable of inflicting a tremendous blow without any pain
to itself,  and of cutting a strong boat asunder, or of driv-
ing it Avith the swiftness of an arrow to the depth of many
fathoms.
  463. The  fins  of  fishes are used principally to give
direction to the body as it is propelled through the water.
  464. In serpents,  progression is effected by undulations
of the spine, or by bringing the two extremities  of the
body near together, and  then, the  tail  being fixed, the
head is projected forward the  length  of the body:  again
the tail is brought forward, and the same process repeated.
Sometimes, instead of this alternate contracting,  the whole
body is brought  into a spiral coil,  and by the contraction
of all the muscles on one side, and then by a sudden con-
traction  of the muscles of the opposite side,  the whole
body is  propelled, as  by the  unwinding  of a powerful
spring,  with an  impulse which raises it to  some  height
from the ground.
  465. Flying has some resemblance  to swimming, both
being executed in a fluid medium, which, to a certain ex-
tent, buoys up the body and offers resistance to its progress.
Water, however, affords more support to the body and a
greater  resistance to the propelling organs.  Birds are
especially  adapted to flying  by their formation.  Their
bones excel those of all other animals in combining strength
and lightness.   All the long  bones are hollow cylinders
filled with air.   The breast-bone, which resembles in form
the keel of a ship,  presents a very large surface for the
attachment of the muscles, and it is also connected very
  For what are the fins  of fishes principally  used 1  How is progression
effected in serpents ?  What other mode of progression is there in some ser-
pents? What does flying resemble ? How are birds adapted to flying?  In
what respect do the bones of birds excel all other  animals ? What  are  the
long bones ?  What does the breast-bone  resemble ?
       16* 
228
CLASS-BOOK OF  PHYS10LOOV.
firmly by the ribs to the vertebrae of the back.  The whole
bony apparatus of the body is thus very strongly knit
together, and yet the entire skeleton is exceedingly light—
the body being suspended in the  air by the resistance it
affords to the wings.   The muscles which are attached to
the breast-bone are much larger than  in other animals;
while the muscles on  the back, that raise the wings,  are
correspondingly smaller.   The greatest power of the wings
is consequently in 4;he  downward direction.  In the effort
to fly, the wings are expanded, brought down with con-
siderable  force, and then brought up to the body, being
raised again in such a form as  to offer the  least  possible
resistance to the air.
  466. In many birds  the rapidity of flight is very great,
much  greater  than by  any other mode of progression.
The Eider-duck is said  to fly ninety miles an hour, and
some species of hawk one hundred and fifty.
  467. Walking is produced by the alternate contraction
and extension of the limbs.  In man, one foot  is placed in
front upon the ground while the other  is extended or car-
ried backward, and its length increased,  carrying  forward
the whole body.  In  quadrupeds, two feet are placed on
the ground at  once.
   468. In running, the  body momentarily quits  its sup-
port on the ground at intervals, the foot in advance not
being planted on the ground at the time, the hinder one
quits it.   In this action,  the ostrich probably surpasses all
other  animals, as it is said to outstrip the swiftest grey-
hound at its greatest speed.
   469. In trotting, the fore-foot of one side and the hind-
  What is gained by this peculiar form ?  How is the bony  apparatus united
 together ?  What is said of the skeleton ?  How is  the body suspended in the
 air ?  What is said of the muscles which are attached  to the breast-bone ?__to
 the back ?  In what direction  is the greatest  power of the wings ?  Describe
 the movement of the wings in the effort to fly ?  What is said of the rapidity
 of flight in birds?  What examples?  How is walking produced?  How is
 it produced in man?—in quadrupeds?   Describe running.  What animal
 surpasses all others in running?  Describe  trotting. 
 
PLATE   XXII.
ORGANS OF  MOTION.-THE  MUSCLES.
                     POSTERIOR VIEW OF THE  MUSCLES.

  The right side of the figure displays the outer or superficial layer of muscles.  On the
left side, they are represented clothed with their fasciae or aponeuroses, which form a
tendinous membrane.
  Muscles of the Head and Neck.—l, The occipitalis.—This muscle draws the scalp back-
ward and downward, giving the expressions of joy or surprise.  2, Muscles of the ear,
3,  The masseter.  4, The sterno-cleido-mastoideus.  5,  The splenius.—When  the  two
splenii act together, they draw the head backward, elevating the chin; when one acts, it
bends the head and neck to one side.
  Muscles of the Trunk.—6, The trapezius.—This muscle is attached to the spinous pro-
cesses of the dorsal vertebra? and to the scapula.  It carries the shoulder backward.  7i
The latissimus dorsi.—a, a, Its tendinous or aponeurotic portion.—This broad muscle draws
down the arm, or, if the arm be fixed, it draws the trunk towards the shoulder.  8, Part
of the  obliquus externus.—This muscle compresses  and raises up  the contents of the
abdomen.

  Muscles of the Superior Extremities.—9, Posterior portion of the deltoid muscle.  10,
The infra-spinatus.—This muscle turns the shoulder outward, and assists in keeping the
head of the humerus in its socket.  11, 11, 11, The three portions of the triceps  extensor
cubiti.—This muscle is fixed by its tendon to the olecranon process of the ulna, and  by its
contraction it extends the  fore-arm.  12, The extensor communis  digitorum.—Its four
tendons pass under the annular ligament, and go to the four fingers ; so that it  becomes
an  extensor of the whole hand, as well as of each of the phalanges.  13, The  extensor
proprius of the little-finger.—By means of this slender muscle, the little-finger can be sep-
arately extended.  14, The extensor carpi ulnaris.—This muscle extends the hand on the
wrist.  15,  Flexor carpi ulnaris.  16, Tendon of the long extensor of the thumb.  /, An-
nular ligament of the carpus.

  Muscles  of the Inferior  Extremities.—17, The gluteus maximus.—This large,  thick
muscle is of greater volume than any other in the body, and is the principal agent in pre-
serving its equilibrium. It extends from the iliac bones to the femur, and acts as an ex-
tensor of the thigh.   18, The biceps femoris.—This  strong muscle, extending  from the
pelvis  to the tibia, bends the leg, and also extends the pelvis upon  the leg, keeping it
erect.  19, The semi-tendinosus.—This muscle  bends the leg  upon the thigh, turns the
point of the foot downward and inward, and  keeps the  pelvis erect when  standing.  20,
The vastus externus.  21,21, The triceps surae, consisting of three portions—the gastrocne-
mii, a, b, and the soleus, c;  it terminates in the strong tendon of Achilles, d.  It forms the
extensor muscle of the foot. 
$h
m
'■.    »«  . -,

E..C.Kelto««.Lrfli.
 
 
ANIMAL  MOTIOxX.
233
foot of the other one  are  raised and carried forward  to-
gether; and when  these are set down, the other fore and
hind foot are raised and advanced.
   470. In leaping, the
body is projected into
the  air by the sudden
extension of the joints,
especially those of the
hinder parts of the body
which have been previ-
ously bent, and having
traversed a greater or
less distance, the body
comes again   to  the
ground.  The hare, rab-
bit,  squirrel, kangaroo,
&c, are especially adap-
ted to this kind of pro-
gression  by the length
of the posterior extrem-
ities, which are nearly double that of the anterior, as may
be seen in fig. 64.
Fig. 64.—Kanoaroos.
Describe leaping. 
284            CLASS-BOOK OF PHYSIOLOGY.
                    CHAPTER XIV.

                         THE VOICE.
  471.  The voice in animals and  in man consists essen-
tially in  the production of sounds  expressive of ideas,
feelings, passions, and desires.
  472.  Insects  and  all water-breathing animals  may be
said to be mute, since they have  no voice.  Insects, how-
ever, possess the power of producing  sounds  by  certain
movements which to some extent are characteristics of the
different  species.  The shrill chirp of  the cricket  is  pro-
duced  by rubbing the wing-cases against each other.   The
harsh  shriek of the grasshopper  is caused by friction of
the legs against the wings.   The  shrill  trumpet sound of
the mosquito and the busy hum of bees and flies  are  pro-
duced  by the  rapid motion of the  wings  while  flying.
Other sounds are caused by the jaws in the act of masti-
cating,  as the remarkable "death-watch" so called.*
  473.  In the air-breathing vertebrata, the production of
sounds depends upon the passage of air through a certain

  In what does the  voice consist?   What animals may be said to be mute?
Why may they be said to be mute ? How do insects produce sounds ?  How
is the chirp of the cricket produced ?  How is the sound of a grasshopper
caused?—the mosquito?—bees and flies?  How are other sounds caused?
How is sound produced in air-breathing vertebrata ?
     * "-----—---------------------A wood-worm,
        That lies in old wood, like a hare in her form!
        With teeth or with claws, it will bite or will scratch,
        And chamber-maids christen this worm a death-watch;
        Because, like a watch, it always cries click!
        Then woe be to those in the house who are sick!
        For sure as a  gun they will give up the ghost,
        If the maggot cries click when it scratches the post:
        But a kettle of scalding hot  water ejected,
        Infallibly cures the timber affected:
        The omen is broken, the danger is over,
        The maggot will die, and the sick will recover." 
THE VOICE.
235
portion of the  respiratory tube.  In  reptiles, it is at the
point where the trachea or windpipe opens into the pharynx
that the vibratory apparatus is situated.  The sounds pro-
duced by this class  is very simple, being  little else than
a hiss.
  474.  In birds, the situation of the vocal organ is very
different.   The trachea opens into the pharynx, as in rep-
tiles, by a mere slit, but the most essential  organ is at the
lower extremity of the trachea, near its  division into the
bronchi.  This apparatus, which seems to be  a kind  of
drum, is variously formed in different species.   In fig. 65
Fig. 65. -Larynx of a spe-    Fig. 66.—Larynx of Rook. Fig. 67.—Vertical
     cies of Duck.                           section of the same.
  a, trachea; b, a kind of beny drum; c, bronchial tpbes.
is a representation of the  larynx  of a species  of duck;
fig. 66 represents the larynx of a rook;  and fig. 67 a sec-
tion of the same.   At a, in each of the above figures, is
seen the larynx;  at b, a  sort of bony drum; and at c, the
bronchial tubes.   In the most esteemed singing-birds these
parts are much more  complicated than in birds not distin-
guished  for their vocal powers.
  475. In man and the mammalia, the vocal organ is situ-
ated at the upper part of the windpipe, and is called the

  Where is it produced in reptiles ?  How are the vocal organs situated in
birds ?  What does the apparatus resemble ?  In what birds is it most com-
plicated ?  Where is the vocal organ situated in man, and what is it called^
From what does it receive its peculiar form? 
236
CLASS-BOOK OF PHYSIOLOGY.
larynx.   The larynx receives its peculiar form from four
cartilaginous  pieces, called the thyroid, the cricoid and  the
arytenoid cartilages.
Fig. 68.—Human Larynx,
 viewed sideways.—A, hy-
 oid-bone; /, point of origin
 of muscles of the tongue; t,
 thyroid cartilage; a, pro-
 jection in front, commonly
 called Adam's Apple;  c,
 cricoid cartilage; tr, tra-
 chea; o, posterior side of
 the larynx, in contact with
 the oesophagus.
Fig. 69.—Vertical Sec-
 tion of the Larynx.—
 ar, arytenoid cartilages;
 v, veDtricle of the glottis;
 e, epiglottis. The other
 references as before.
Fig. 70.—Front View
 of the Larynx.—
 The interior wall is
 marked by the lines
 a, a, b, b,; li, inferior
 ligaments of <the glot-
 tis, or  vocal eords;
 Is, superior ligaments-
 The other references
 as before.
  476. The thyroid, (fig. 68,) is  much the largest and is
composed of two symmetrical halves, which meet in front,
and form the proturberance in man called " Adam's Apple."
It rests below on  the cricoid  cartilage, and  is  connected
above with the hyoid-bone of  the tongue (h).
  477. The cricoid cartilage (c), which is placed below the
thyroid (t),  is the base of the larynx;  it has the form of a
ring, and is much  deeper behind than in front.
  478. The arytenoid cartilages are two small cartilaginous
bodies, placed upon  the upper surface of  the back of the
cricoid cartilage, where there is an open space Left between
the  two  halves of  the  thyroid cartilage.   When joined
together, the  arytenoid  cartilages resemble the mouth or
spout of a pitcher.
  Which of the cartilages is the largest?  Of what is it composed?  What
protuberance does it form?  What is above and below the thyroid cartilage?
Where is the cricoid cartilage placed?   What is  its form?  What are  the
arytenoid cartilages? How  are they placed?  What do they resemble when
joined together? 
THE VOICE.
237
   479. The chordce vocales, or vocal cords, (a, a, fig. 71,)
which  are  the instruments  principally concerned in the
production of sound,  and  also in the  regulation of the
aperture through which the
air passes into the trachea,
are  stretched across from
the  arytenoid cartilages to
the  interior  angle of  the
thyroid cartilage.   By the
meeting of the vocal cords
in front,  and their separa-
tion  behind, the  aperture
has the form of a V, but by
the drawing together of the
arytenoid cartilages until the cords touch, the aperture  is
completely closed.   In this manner, the amount of air per-
mitted to pass" the larynx is regulated, and a protection af-
forded against the entrance of solid substances, though there
is the additional guard of the epiglottis, which is pushed
down in  the act of swallowing upon the open space above.
   480. In the ordinary acts of inspiration, the arytenoid
cartilages are wide apart, so that the aperture between the
vocal cords is as large as possible; but in the production
of vocal  sounds the aperture is narrowed, and the vocal
cords made tense, so as to vibrate with the passage of air,
in a manner resembling the vibration of the tongue of an
accordeon, or the reed of a clarionet.   The different sounds
are caused by the different degrees of tension of the vocal
cords.  When the tension is feeble, the tone will be grave
and dull, and when it is great, the tone  will be acute.
   481.  The tension of the vocal cords is regulated by the
  What are the vocal cords, and how are they situated? What is the form
of the aperture between the vocal cords ?  How is it closed?  Of  what other
use is it besides to regulate the passage of air?  What other guards has the
larynx ?  What is the condition of the aperture in the ordinary acts of inspi-
ration, in the production of vocal sounds?  What does the vibration of the
vocal cords  resemble?  How are different sounds caused?   What tone is
produced when the tension is feeble ?—when it is great ?
       17
 
238
CLASS-BOOK OF PHYSIOLOGY.
will with most remarkable precision, and without any con-
sciousness on the part of the individual of the means by
which the desired result is produced.   The average length
in the male in a state of repose is about  TVotns of an incll»
while  in the state of greatest  tension it is about TVotns
of an inch, making a difference of yVo^s or }th of an inch.
In the female the difference is less than |th of an inch.
In this space of |th or |th of an inch, there cannot be less
than  two or three hundred different degrees of tension in
what may be called a natural voice, while in a voice highly
cultivated, as in some celebrated vocalists, there  must be a
much larger number—perhaps from one to two  thousand.
   482. Loss of voice, such as occasionally occurs in pub-
lic speakers, is caused, not by "bronchitis," as  is generally
supposed, but by relaxation  of the vocal cords to such an
extent as to lose all control over the size of "the aperture
between them.  In ordinary colds, these cords  are some-
times slightly inflamed, producing hoarseness.  In inflam-
mation of the vocal cords, the mucous membrane which
lines  the larynx,  the trachea,  and not unfrequently the
bronchi, may be  similarly affected, and hence the disease
is commonly called "bronchitis."
   483. The voice and the  power  to produce articulate
sounds, by which man  communicates ideas to his fellows,
is one of the most remarkable faculties  in his possession,
and one in' which he is vastly superior to all other animals.
By cultivation, the voice can  be  made greatly to surpass
its natural  powers, and increase its capacities for contrib-
uting to man's usefulness and  pleasure,  as a  social being.
   How is the tension of the vocal cords regulated ?  Have we any conscious-
 ness of the tension of the vocal cords?  What is their average length in the
 male in a state of repose ?—in the greatest tension ?  What is the difference
 in the female ?  How many different degrees of tension are there in a natural
 voice ?—in a highly cultivated voice?  How is loss of voice caused?  What
 other parts are sometimes affected when the vocal cords are inflamed? What
 is said of the power of producing articulate sounds?  How may the voice be
 greatly improved? 
 
PLATE   XXIII.
THE HUMAN FORM.
  Fioure 1.---A Lady writing, and resting on her left elbow, with the right shoulder
raised.
  Figure 2.---A Lady writing, in a Correct Position.
  Figure 3.---A Boy bent forward too much in writing.                       a
  Figure 4.---A Boy resting on his left elbow.
  Figure 5.---A Boy writing in a Good Position.
  Figure 6.---A Good Attitude in standing.
  Figure 7.----ft Man walking erect.
  Figure 8.---A Man stooping while walking.
  Figure 9.---A Round-shouldered or Consumptive  Form, caused by tho habit  of
Indulging in such attitudes as represented in figs. 3 and 8.
  Figure 10.---A Lady riding, with her spine bent in such a manner as to produce
curvature.
  Figure 11.---A Lady riding correctly.
  Figure 12.---A Boy at School, on an old-fashioned bench, so high that his feet cannot
touch the floor, and without any support for the back.
  Figure 13.---A Boy at School, in a chair, just right—easy, convenient, and perfectly
adapted to his comfort and health.
  Figure 14.---A Person bolstered up in Bed, in such a manner as to form a curvature
of the spine.
  Figure 15.---A correct position  in Bed. 
 
 
THE HUMAN FOEM.
243
                        CHAPTER  XV.

                       THE HUMAN FORM.
      484. The  sublime privilege of standing  and walking
    erect has been exclusively granted to man, and has always
    been given as one of those characteristics that indicate his
    vast superiority over all other animals.  An erect form is
    therefore equally essential to the  gracefulness and dignity
    of his external appearance, and to the health of the vari-
    ous internal organs which perform the vital functions.
      485. The man whose attitude is erect and commanding,
    has a nobleness of appearance that never fails to commend
    him to our respect and esteem; while he who walks with
    his face to the earth, as if  bowing  beneath a burden of
    guilt, or stooping to some debasing act that leads him to
    shun the face of other men, has an air of inferiority, and
    seems to inspire more of contempt  or  pity than of ad-
    miration.
      486. An erect attitude, and an  open breast, is of no less
    importance to health  than to personal appearance.  For
    any deformity which can affect in any degree the form of
    those  cavities which  contain the organs of circulation,
    respiration, and digestion, must be more or less prejudicial
    to the perfect action of those vital organs.
*     487.  Deformities are sometimes the result of unavoid-
    able disease of some of the bones, but they are generally
    caused by the habitual indulgence in improper positions.
      488.  During childhood the bones are soft  and pliable,
    and easily accommodate themselves to any position which
    is habitual.  Thus, the bone of the thigh  is often  perma-

     What has always been given as one of the characteristics of man ? What
    is said of the importance of an erect form ?  What impression does a man of
    erect form make on us?—one of a stooping form?  What must be the effect
    upon health of any deformity of the cavities which contain the vital organs ?
    How are deformities usually caused ?  What is the condition of the bones
    during childhood ?  How may the bone of the thigh be bent ?
          17* 
244           CLASS-BOOK OF PHYSIOLOGY.
nently bent by compelling children to sit on a bench so
high there is no support for the limbs, except at the centre
of the thighs, which rest on the edges of the seat, as in fig.
12, Pl. XXIII.
   489.  The most common deformities are those of the spine
and ribs.  The ribs  are perhaps more easily changed in
form than other bones of the body.  They are long slender
bones, attached to the spine by ligaments which admit of
free motion to the breast-bone by flexible cartilages.  Their
very structure  is such, that the constant pressure of the
clothing, day after  day, needs to be  only very slight to
bend the rfbs downward and inward, as represented in fig.
6, Pl. XXIV.;  and it is not necessary that  there should
be very great strength of ligature, or any repeated acts o*
violence, to materially diminish the capacity of the chest,
provided-a  sufficient  length of time be  allowed to bring
about the result in a genteel way.   "Snug-fitting'1'' dresses,
from fourteen to twenty, are the only appliances  needed
to make a young lady sadly deformed  in chest for life.
  490. The deformities of the spine are caused in a variety
of ways.  The spinal column is composed  of twenty-four
separate bones, placed one above the other, and separated
from  each other  by a  layer  of  elastic cartilage.   The
spine is maintained in the erect attitude by the action of
numerous muscles and  ligaments.  When these become
weakened by inaction, or by the constant pressure of dress,
some portion of the spine is allowed to.bend  either for-
ward or backward, or to the right or left side.  An equal
portion  above  or below bends in  an  opposite direction,
thus forming two curves.  The elasticity of the cartilages
  What are the most common deformities ?  What bones of the body are
more easily changed in form than  any other ?  Describe the  ribs, and  the
manner they are attached to the spine and the breast-bone.  How are the
ribs  effected by tight dress? How much pressure is necessary to produce
deformity of the ribs?  How may a young lady be  deformed for life ?  How
are the deformities of the spine caused ?   Describe the spinal column.  How
is it maintained in the erect attitude?  What takes place when the muscles
become weakened?  How does the deformity become permanent? 
THE HUMAN FORM.
245
is  such that they very soon yield to any position  which
becomes habitual, and thus the deformity gradually be-
comes permanent.
   491.  The  same curvature of the spine may be effected
by the habit of inclining to one side or the other while
sitting, and whenever the habit is formed, there is a con-
stant disposition  to  persist in it.  The habit, not unfre-
quent, commences in resting one elbow, usually the left,
on the desk at school, and very soon the same attitude is
observed at the  centre-table  at  home; then follows the
habit of reclining in bed in such a manner as to favor the
same form of the spine.   Little by little, the spinal column
deviates from a perpendicular line till there is a permanent
deformity.   Artizans, clerks, writers, and  persons  whose
occupations require the use of the right hand chiefly, are
exceedingly liable  to a slight  curvature,  with marked
prominence of the  right shoulder-blade,  unless constant
care is observed to prevent it.  Teachers and parents can-
not  be too vigilant  of the habits of those committed  to
their charge.   The  seats in school-rooms should  be  so
constructed as to favor correct positions. When a child is
compelled,  for the want of any proper support, to sit sev-
eral hours each day in a bent position, as  represented  in
fig.  12, Pl. XXIII., the anterior edges of some of the car-
tilages will be absorbed and become thinner, and at adult
age, he will stand and walk as represented in figs. 8 and 9,
Pl.  XXIII.
   492.  Youth should always be furnished with such recre-
ation as shall call into exercise the various muscles of the
body.  Time for amusement is not alone  sufficient; such
a  variety should be afforded at every school and seminary
as shall call into vigorous use the muscles of the  limbs,
the arms, the body, and the chest.  Facilities for exercise
   In  what other way may curvature of the spine be caused ?   How does  the
habit ofincliningtoone side frequently commence? With what kind of exer-
cise should youth always be furnished ?  Is time for amusement sufficient ]
What parts should be exercised in amusement ? 
246           CLASS-BOOK OF PHYSIOLOGY.
similar  to  those represented in figure 9, Plate XXIV.,
should be considered as belonging to the  necessary fixtures
which are  indispensable  to every well-regulated  school.
Teachers, too, would not only take  better care of  their
own health, but would increase their usefulness to those
committed  to their charge,  if they would consider it not
beneath their true calling to give practical lessons in re-
gard to the physical as well as the intellectual exercises of
their pupils.   Too little attention is devoted to  the phys-
ical education of the young, in most of our institutions of
learning, and it is to be hoped that, with a more general
diffusion of the  principles of physiology, this most essen-
tial element for the future usefulness and well-being of
the young  will cease to be neglected. 
 
PLATE   XXIV.
                              HUMAN  FORM.

  Figure 1.----A Lady reading, in a good position.
  Figure 2.----A Lady leaning forward^ and resting on one elbow, in aposition favoring
lateral curvature of the spine.
  Figure 3.----A Lady sewing, in a good position.
  Figure 4.----A Lady occupying such aposition in sewing as toproduce antero-posterior
curvature of the spine.
  Figure 5.----Outlines of a Female Figure, after it has been permanently remodelled by
fashionable dress.
  Figure 6.----Part of the Skeleton of the same, with the thorax reduced to about half its
natural size.
  Figure 7.----Outlines of a Natural Female Figure.
  Figure 8.----Part of the Skeleton of the same.
  Figures 9 and 10.----Public School, with Playrgrounds for Boys and Girls, supplied
with appropriate facilities for recreation and exercise. 
Pi6  9
 
 
RULES FOR THE PRESERVATION OF HEALTH.
  Every apartment we occupy should be provided with
some efficient means of ventilation, by which the impure
gasses may be conducted off, and a constant supply of pure
air secured.
  The meals should always be taken at uniform intervals,
and the appetite not indulged at irregular hours.
  The food should be plain and substantial, and not taken
in haste or in a passion.
  Fruit and vegetables, when fully ripe, are conducive of
health, if used in  moderate quantities with  other  food.
Berries should be used within twenty-four  hours  after
picking,  or they are liable to become highly injurious
from  the commencement of the process of  acetous fer-
mentation.
  After  dinner there  should  be at least half an hour's
leisure and rest from active labor.   Students and men of
sedentary habits  should take not less than an hour for
recreation or gentle exercise.
  Children under three years of age  enjoy better health
without animal food, and from three to seven it should be
allowed only in moderate quantities.
  The clothing should always be adapted to the season of
the year, and as nearly uniform as possible, though the
habiliments of winter should not be exchanged for  those
of summer till the weather becomes  permanently  warm
and mild.   By wearing an abundance of warm clothing
during winter,  less  food  and  less  artificial heat are
required, and there is less susceptibility to  colds from
exposure to sudden changes of temperature. 
252          CLASS-BOOK OF PHYSIOLOGY.
  Sleeping apartments should be cool and well ventilated.
Hair beds are much better than feathers.
  Children of all ages should spend some portion of every
day, when not stormy, in the open air.
  Children under seven  years should not be confined in
school  more than  four  hours  each  day, and that time
should be broken by frequent recesses.
  Students should  train their minds to act with correct-
ness and energy for limited periods of time,  and then use
a spare diet, with three or four hours daily exercise in the
open air, and occasional vacations of complete exemption
from study.
  Young persons of both sexes,  whatever their occupa-
tion, should spend  at least two  hours  each day in active
exercise in the open air.
  Every person in full health should wash all over iD
cold water every morning.
 
GLOSSARY  AND  INDEX.
            THE  FIGURES KEFER  TO  THE  PARAGRAPHS.


                                  A

Abdo'men (L. dbdo, to hide).  So called  from  its containing the intestines,
  &c.   [89.]
Abdtjc'tor (L. abduco, to draw from).   Abducent.  A muscle, whose office
  is to draw one part of the body away from another.
Absorp'tion.  The act or process of imbibing or swallowing.  [31-196.]
Absorb'ents.  Vessels which imbibe, as lymphatics and lacteals.   [199.]
Albi'no.  A white descendant of black parents.
Albu'men (L. alius, white).  Albumen is of two kinds,  animal and veget-
  able: 1. Animal albumen exists in two forms, the liquid and the solid.  In
  the liquid state, it is a thick glairy fluid, constituting the  principal part of
  the white of egg.  In the solid state, it is contained in several of the  tex-
  tures of the body, as the cellular membrane, the skin, glands and vessels.—
  2. Vegetable albmnen closely resembles animal albumen, and has been
  found in wheat, rye, barley, peas, and beans.  [46.]
Amphib'ia.  The second class of the Vertebrata, comprising amphibious ani-
  mals, which commence  their larva  state as fishes, and undergo various
  degrees of metamorphoses in advancing towards the condition of reptiles,
  as the frog, &c.  [150.]
An'imal-heat.   [123.]
Anastomo'sis (Gr. and, through, and stoma, a mouth).  The communication
  of vessels with  each other, as of the arteries with the  veins, which, by
  touching at numerous points, form a net-work or reticulation.   See Inos-
  culation.
Anat'omy (Gr. anatemno,  to cut up).   The  science of organization;  the
  science  whose object is  the examination of the organs or instruments of
  life.   Animal anatomy is divided into  human  anatomy and comparative
  anatomy, according as it treats of the organization of the  human body, or
  of that of other animals.   [9.]
An'tenn.e.  The horns or feelers of insects.
Aor'ta (Gr. air, air, tereo, to  keep; as having been formerly supposed to
  contain only air.)  The great artery  of the heart.   It is distinguished into
  the ascending and descending.  [65.]
Aq'ueous.   Watery.
Arach'noid Mem'brane (Gr. arachnS, a spider, and eidos, likeness).   The
  fine  cobweb-like  membrane situated between the dura  and pia mater.  It
  is the serous membrane of the cerebro-spinal centres.   [299.]
         18 
254
CLASS-BOOK  OF  PHYSIOLOGY.
 Ar'bor Vi't.£.  Literally, tree of life.  A term applied to  .ik-  urLorescent
   appearance presented by the cerebellum, when cut into vertically.   [298.]
 Ar'tery (Gr. air, air, and tereo, to hold).   A vessel which carries the blood
   from the heart; formerly supposed, from its being found empty after  death,
   to contain only air.
 Arytenoid (Gr. arutaina, a ewer, and eldos, likeness).   A term applied to
   two triangular cartilages of the larynx.   [478.]
 Au'ditory (L. audio, to hear).  Belonging to parts connected with the sense
   of hearing.   [359.]
 Auric'ula (L. dim of auris, the ear).  An auricle ; the prominent part of the
   ear.   Also, the name of two cavities of the heart.   [57.]
 Automat'ic Motions (Gr. automatos, of his own accord).  Those muscular
   actions which are not dependent on the mind.
 Autom'aton.  A self-moving machine.
                                    B
 Ball-and-Sock'et.  A species of movable articulation, as that of the hip.
 Bicuspida'ti (L.  cuspis, a  spear).   Having two tubercles; as applied to  the
   two first pairs of grinders in each jaw.
 Bi'lis.   Bile, gall, or choler;  the secretion of the liver.   [63.]
 Bil'ious.  A term employed to characterize a class of diseases caused by a
   too copious secretion of bile.
 Bi'valve.   An animal having two valves.
 Brain.   [295.]—Of a fish.  [282.]—Of a bird.   [283.]
 Bronch'us (Gr. brongchos, the windpipe,from brecho, to moisten). The wind-
   pipe ;  a  ramification of the trachea ;  so called from the ancient belief that
   the solids were conveyed into the stomach by the oesophagus, and the fluids
   by the bronchia.   [100.]
 Bronch'ial-tubes.  The minute ramifications of the bronchi, terminating in
   the bronchial cells, or air cells of the lungs.
 Bronchi'tis.   Inflammation of the bronchi, or ramifications of the trachea.
 BuR'siE Muco'sje (mucous bags).  Small sacs situated about the joints, being
   parts of the sheaths of tendons.
                                   C"

 Cje'cum,  or Cce'cum (L. ccecus, blind).   The first part of the colon, or blind
   intestine.
 Cal'lus (Latin, hardness).   New bone, or the substance which serves to join
   together the  ends of a fracture, and to restore destroyed portions of bone.
 Can'cer.   Literally, a crab.   The term is  applied  to  the disease  from  the
   claw-like spreading of the veins.
 Canine'-Teeth (L. canis, a dog). Eye-teeth; the four immediately adjoining
   the incisors.  [143.]
Cap'illary (L. capillus, a hair).   Reserpbling  a hair in  size; a term applied
  to the vessels which intervene between the minute arteries and veins.
Capsu'la (L. dim. of capsa, a chest).  Literally, a little chest   A capsule or
bag, which incloses any part.   [144.] 
GLOSSARY AND  INDEX.
255
Car'bon (L. carbo, a coal).  A substance well known under the form of coal,
  charcoal, lamp-black, &c.  In chemical language, it denotes the  pure  in-
  flammable principle of charcoal;  in its state of absolute purity, it constitutes
  the diamond.
Carbon'ic Acid.   Carbon and oxygen combined.   [12-114.]
Car'dia (Gr. kardia, the heart).  The entrance into  the stomach, so called
  from being near the heart.   [159.]
Car'diac (Gr. kardia, the heart).  Relating to the  heart.
Carniv'orous (L. caro-voro).   Eating flesh.
Carot'id (Gr. karoo, to induce sleep).   The  name of two  large arteries of
  the neck; so called from an  idea that tying them would induce stupor.
Car'pus (Gr. karpds, fruit).  The wrist.   The ossa carpi? or carpal bones,
  are eight in number, and form two rows.  [444.]
Car'tilage.   Gristle.   It is attached to  bones, and must be distinguished
  from the ligaments of joints  and tendons of muscles.  [88.]
Cau'da Equi'na, or horse's tail; the final division of the spinal cord ; so  called
  from the disposition of the nerves which issue from it.
Cerebel'lum (dim. of cerebrum).  The little brain, situated behind the larger,
  or cerebrum.   [295.]
Cer'ebrum (Gr. kdre, the head).  The brain ; the  chief portion  of the brain,
  occupying the whole upper cavity of the skull.  [281.]
Cer'ebro-sfinal.  System.   [285.]
Cer'vix.  The neck;  the hinder part of the neck: the  fore part is called
   collurn.
Chest.  Thorax.  An old English term, commonly  traced  to  the Latin
   cista.—" When it is considered that the same word was  anciently used for
   a basket,  the  appropriation of it to the human thorax will appear quite
   natural to any one who has ever seen a skeleton."—Forbes.   [102.]
Chyle (Gr. chulds,  juice).  The milk-like  fluid absorbed by the lacteal
   vessels.   [22.]
Chylifica'tion (L. fio, to become).  The process  by which the chyle is sepa-
   rated from the chyme.
Chyme (Gr. chumos, juice).  The semi-fluid matter which passes from the
   stomach into the duodenum.  [22-175.]
 Chymifica'tion  (L. fio, to become).   The process by which the aliment  is
   converted into chyme.
 Cil'iary (L. cilia, eyelashes).  Belonging to the eyelids.  [371.]
 Cil'iary Cir'cle or Lig'ament.  A kind of grayish ring, situated between
   the choroid membrane, the  iris, and the sclerotica.
 Cil'iary Pro'cesses.   Small membranous bodies, surrounding the crystalline
   lens in a radiating form.
 Cineri'tious (L. cineres, ashes).  Ash-colored; a  term applied to the exterior
   or cortical part of the brain,
 Clavic'ula (dim. of clavis, a key).  The clavicle, or  collar-bone ; so called
   from its resemblance to an ancient  key.   [442.] 
256             CLASS-BOOK OF  PHYSIOLOGY.
 Coc'cyx (Gr. kdkkux, a cuckoo).   The  lower  end of the  spine; so called
   from its resemblance to the cuckoo's beak.  [426.]
 Coch'lea (Gr. kochlos, a conch).   A cavity of the ear, resembhng the spinal
   shell of  the snail.   [358.]
 Co'lon (Gr. kolon, quasi koilon, hollow).  The first of the large  intestines,
   commencing at the coecum, and  terminating at the rectum.  [185.]
 Co'ma (Gr. koma, drowsiness, from kid, to lie).  Drowsiness ; lethargic sleep;
   dead sleep; torpor.
 Com'missure (L. commissura).  To joint or sever the place where two bodies
   or parts of a body  meet and unite.
 Con'dyle (Gr. kondulos, a knuckle).  A rounded eminence in the joints of
   several bones, as of the humerus and the femur.   [447.]
 Congestion (L. congero. to amass).  Undue fullness of the blood-vessels.
 Conjunctiva (L. conjungo, to unite).   The  mucous membrane which lines
   the posterior surface of the eyelids, and is continued over  the fore-part of
   the globe of the eyelid.  [374.]
 Cor'acoId  Pro'cess  (Gr. korax, a crow, and eidos, likeness).  The upper
   and  anterior point of the scapula; so called from  its resemblance to a
   crow's beak.
 Co'rium.   Leather.   The deep layer of cutis, or true skin, forming the basis
   of the support to the skin.
 Corn'ea (L. cornu, a horn).  The  anterior transparent portion of the globe
   of the eye.  [376.]
 Corpus'culum (L. dim. of corpus, a body).  A corpuscle, or little body.
 Cra'nium (Gr. kdra, the head).   The  skull, or cavity which contains the
   brain, its membranes, and vessels.  [295.]
 Crib'riform (L. cribrum, a sieve, and forma, likeness).  The name of the
   plate of the ethmoid-bone, from its being perforated like a sieve.
 Cri'cos  (Gr. krikos, a ring).  Whence Cricoid, the name  of the ring-like
   cartilage  of the larynx.  [477.]
Crys'talline (Gr. krustallos, ice).  A term  applied to the lens  of the eye
   [376.]
Cuboi'des (Gr. kubos, a cube, and eidos, likeness).  The  name of a bone of
   the foot, somewhat  resembling a  cube, situated at  the fore and outer part
   of the tarsus.
Cunei'form (L. cuneus,  a  wedge, and forma,  likeness).   Wedgelike; the
   name of three bones of the foot.
Cu'ticle (L. dim. of cutis).   The epidermis, or scarf-skin.   [247.]
Cu'tis (Gr. Mtos, the skin).   The true skin, as distinguished from the cuticle,
   epidermis, or scarf-skin.

                                  D
Degluti'tion (L. deglutio, to swallow).   The act of swallowing.  [156.]
Di'aphragm (Gr.  didphragma, a  partition).   The  midriff: the  transverse
   muscular partition which separates the thorax from the abdomen.   [103.] 
GLOSSARY AND  INDEX.
257
 Diges'tion (L. digero, from diversim gero, to carry into different parts).  In
   Physiology, the change of the food into chyme by the mouth, stomach, and
   small intestines;  and the absorption and distribution of the more nutritious
   parts, or the chyle, through the system.  [133.]
 Dor'sum (Latin).  The back; the round part of the back of a man or beast.
   Whence Dor'sal,  appertaining  to  the back,  as  applied to  a region,
   ligaments, &c.   [426.]
 Drop'sy (L. hydrops,  from  the Gr. udrops, water).  An effusion of serous
   fluid into any of the natural cavities of the body.
 Duode'num (L. duodeni, twelve).   The twelve-inch intestine ; so called from
   its being equal in length to the breadth of  twelve fingers; the first portion
   of the small intestines, beginning from the pylorus.  [181.]
 Du'ra Ma'ter (hard-mother).   The outermost membrane of the brain. [299.]
 Dys'entery (Gr. dus, badly, and entera, the  bowels).  Inflammation of the
   mucous lining of the large intestines.
 Dyspep'sia (Gr. dus, and pepto, to digest).   Indigestion;  difficulty of diges-
   tion.  [171.]
                                   E
 Efflu'via (L. effluo, to flow out).  Exhalations, vapors, &c.
 Elasticity.  The  property  or power  by  which a  body  compressed  or
   extended returns to its former state.
 Eleva'tor (L. elevo, to raise).  A name applied to certain muscles, whose
   office it is to elevate any part.
 Enam'el.  The hard exterior surface of the teeth.   [146.]
 Enceph'alon  (Gr. in,  in, kephale, the  head).   The brain;  the contents  of
   the skull, consisting of the cerebrum, cerebellum, medulla  oblongata, and
   membranes.
 Epider'mis (Gr. epi, upon,and derma, the skin).  The cuticle, or scarf-skin;
   the thin horny  layer which protects the surface of the integument.  [244.]
 Epiglot'tis.   A cartilage of the larynx, situated above the glottis.
 Epip'loon (Gr. pleo, to sail).   The omentum;  a membranous expansion which
  floats upon the intestines.
 Epithe'lium (Gr. tithemi, to place).  The cuticle on the red part of the lips,
   and on the mucous membranes in general.
 Eth'moid (Gr. ithmds, a sieve, eidos, likeness).   Cribriform,  or sieve-like; a
   bone of the nose, perforated  for the transmission of the olfactory nerves.
 Eustach'ian-tube.   The  canal which extends  from the tympanum to the
   pharynx, called after Eustachius, its discoverer. [353.]
Excre'tion (L. excerno, to separate from).  A general term for the perspira-
   tion, faeces, &c, which  are  separated and  voided from the blood or the
  food.   [230.]
Expira'tion (L. expiro, to breathe).   That part of the respiration in which
   the air is expelled.   Compare Inspiration.
Exuda'tion.   Transpiration.   The  flow of  liquid  from  the surface of the
  skin or membrane, an ulcer, &c.
         18* 
258             CLASS-BOOK OF  PHYSIOLOGY.
                                   F
Fa'cet.  A little face, a small surface.
Fa'cial (L, fades, the face).  Belonging to the face; as facial nerve, facial
  vein, &c.
Falx.   A  scythe  or  sickle.  The  sickle-like processes of the  dura mater,
  situated between the lobes of the cerebrum and cerebellum.  [300.]
Fas'cia (L. fascis, a  bundle).  Literally, a scarf or large band.  Hence it is
  applied to the aponeurotic expansion of a muscle.
Fascic'ulus (L. dim.  of  fascis, a bundle).  A  little  bundle ; a handful.
  Thus,  a muscle consists of fasciculi of  fibres.  [33]
Fau'ces.   The gullet or upper part of the throat; the  space surrounded by
  the velum palati, the uvula, the tonsils, and the posterior part of the tongue.
Fe'mur, Fem'oris.   Os femoris.   The thigh-bone, the longest, largest, and
  heaviest  of all  the bones of the body.   [447.]
Fenes'tra (Gr. phainb, to  shine).   Literally, a window;  an entrance into
  any place.  Hence the terms fenestra ovalis and rotunda, or the oval and
  round  apertures of the internal ear.
Fi'bre (L. fibra, a filament).  A filament or thread, of  animal, vegetable, or
  mineral composition.  [28]
Fi'bril.   A small filament, or fibre, as the ultimate division of a nerve.  The
  term is derived from fibrilla, L. dim. of fibra, a filament.
Fi'brin.   A tough fibrous mass, which, together with albumen,  forms  the
  basis of muscle.  [49.]
Fi'bro-car'tilage.  Membraniform cartilage: a substance intermediate  be-
  tween proper cartilage and ligament.   [349.]
Fib'ula.   Literally, a clasp, or  buckle.  It denotes the lesser  bone of the
  leg.  [448.]
Fil'ament (L. filum,  a thread, forma, likeness).  Thread-like;  applied to
  the papilla? at the edges of the tongue.
Fis'sure.  A cleft, a longitudinal opening.
Flex'or (L. flecto, to bend).  A muscle which bends the part into which it
  is inserted.  Its antagonist is termed extensor.
Flu'ids.   Substances which have the  quality of fluidity, and are, in conse-
  quence, of no fixed shape.
Fol'licle (L. dim. of follis, a pair of bellows).  Literally, a little bag, or scrip
  of leather; in anatomy, a very minute secreting cavity.  [168.]
Fora'men (L. foro, to pierce).  An opening.  [356.]
Fos'sa (L. fodio, to dig).   A ditch or trench; a little depression, or sinus.
Func'tion  (L. fuvgor, to discharge an office).  The office  of an organ in the
  anii: al or vegetable economy, as of the heart in circulation, of  the leaf in
  respiration, &c.   [18.]
Fu'siform  (L. fusus.a spindle, forma, likeness).  Spindle-shaped; a term
  applied to certain muscles. 
GLOSSARY AND  INDEX.
259
                                  G
Gall'-bladder.  A membranous reservoir, lodged in  a fissure on the under
  surface of the.right lobe of the liver, and containing  the bile.  [191.]
Gall'ducts.   These are the cystic, proceeding from  the gall-bladder;  the
  hepatic, proceeding from the liver; and the ductus communis choledochus,
  resulting from the union of the two  preceding.
Gan'glion (Gr. gangglion,  a nerve-knot).  A small  nervous centre, or an
  enlargement  in  the  course of a nerve, sometimes  termed a  diminutive
  brain.   [262.]
Gas'ter.   The Greek  term  for the stomach.
Gas'tric  (Gr. gaster, the stomach).   Pertaining to  the  stomach; as  the
  gastric juice, &c.
Gas'tric Juice.  The peculiar digestive fluid secreted by the stomach.  [167.]
Gel'atine (L. gelu, frost).  The principle of jelly.  It is found in the skin,
  cartilages, tendons, membranes, and bones.   The purest variety of gelatine
  is isinglass.
Gin'glymus (Gr. gigglumos, a hinge).   The  hinge-like joint; a species of
  articulation admitting of flexion and extension.
Giz'zard.  Of bird.  [160.]  Insect.   [161.]
Gland (L. glans, glandis, an acorn).  A soft body, composed of various tis-
  sues, vessels, nerves, &c,  usually destined to separate some fluids from the
  blood.   [150.]
Gle'noid  (Gr. glene, a cavity, eidos, likeness).   The name of a part having
  a shallow cavity, as the socket of the shoulder-joint.
Glob'ules Red (L. dim. of globus, a ball).  The  red coloring matter of the
  blood; a peculiar animal principle.
Glos'sa, or Glot'ta (Gr.  glotta).   The  tongue; the  organ of speech.—
  Glosso-.  Terms compounded  of this word  belong  to  nerves or muscles
  attached to the tongue.
Glot'tis.  The aperture of the larynx between the arytsenoi'd cartilages.   It
  is covered by a cartilage called  the epi-glottis.
Grax'ule.  A small particle.
Great Symfathet'ic   A nerve formed  by a collection  of filaments from
  every nerve, which join each other at the adjacent ganglia.
                                  H
Hjem'atosin (Gr. haima, blood).  A characteristic constituent of the blood,
  derived from the globules.
HjEm'orrhage.  A rupture  of a  blood-vessel;  a bursting forth of blood;
  loss of blood.
Herbiv'orous  (L. herba, and vora).  Eating herbs.
Hepat'ic  A  term applied to any part belonging to the liver.   [236.]
Hexag'oxal.  Having  six sides and six angles.
Hu'merus.  The  bone  of the upper-arm.  [443.]
Hu'mor (L. humeo, to be moist).   An aqueous substance; as the humors of
  the eye. 
260
CLASS-BOOK OF  PHYSIOLOGY.
Hy'dra (Gr. udor, water).   A polype indigenous in our brooks, destitute of
  a stomach, brain, viscera, or lungs.  [84.]
Hy'giene (Gr. to be well).   Health; the preservation of health; that part
  of medicine which regards the preservation of health.
Hyoi'des  (the Greek letter upsilon).   A bone situated  between the root of
  the tongue and the larynx.
Hvro-GAs'TRiUM.  The lower anterior region of the abdomen.
Hypo-glos'sal.   The name of the lingualis, or ninth pair of nerves, situated
  beneath the tongue.   [303.]

                                  I, J
Ich'or. • A  thin acrid discharge, issuing from wounds, ulcers, &c.
Jeju'num  (L. jejunus, hungry).   The upper  two-fifths of the small intestines,
  so named  from this portion being generally found empty.
Il'eum (to turn  about).  The lower three-fifths of the small  intestines, so
  called from their convolutions, or peristaltic motions.
Il'iac-Bone.  Another  name for the os  innominatum,  derived from the cir-
  cumstance that this compound bone supports the parts which the ancients
  called ilia, or the flanks.
Il'iac Region.   The region situated on each side of the hypogastrium.
In'cus (an anvil).  A small bone of the internal ear, with which the malleus
  is articulated ; so named from  its fancied resemblance to an anvil.
In'dex (L. indico, to point out).   The fore-finger ; the finger usually employed   ,
  in pointing at any object.
Infra-sfina'tus.  A muscle arising from the scapula  below the spine, and
  inserted into the humerus.
Innomina'tus (L. in, priv.,  nomen, name).   Hence Innominatum os, a bone
  composed of three portions, viz:  1, The ilium, or haunch-bone.  2,  The
  ischium, or hip-bone.  3, The os pubis, or share-bone.
Insaliva'tion.   [153.]
In'stinct.  This convenient term admits of the following significations : 1
  The Instinctive Faculty; or  that faculty which  leads the  duckling,  un-
  taught,  into the water; the beaver to build its hut; the bee its  comb; the
  hen to incubate her eggs, &c.; and, 2.  The Instinctive Motions; or those
  involuntary actions which are  excited mediately through the nerves—a part
  of the reflex function.
Integ'ument (L. in,  and tego, to cover).  The covering of any part  of the
  body, as the cuticle, cutis,  &c.
Inter-cos'tal.   The name  of  two sets  of  muscles between  the ribs—the
  external and the internal.  [104.]
Intes'tines  (L.  intus,  within).  That part  of the alimentary canal  which
  extends from the stomach  to the anus.   [183.]
I/ris.   Literally a rainbow;  and hence applied to the rainbow-like membrane
  which separates the anterior from  the posterior chamber of the eye.  [377.]
Ju'gular.   Belonging  to the neck; applied  chiefly to the principal veins of
  the neck. 
                    'glossary and  index.                 261

                                  K
Kingdom.  A term denoting any of the principal divisions of nature; thus
  we have the organic kingdom, comprehending substances which organize;
  and the inorganic kingdom, comprehending substances which crystallize.
Knee'pan.   Patella; the small round bone at the front of the knee-joint.
Kid'neys.  Two oblong glands, which secrete the urine.  [235.]

                                  L
La'bia.  The lips.  They are laterally united  by means of  two acute angles,
  which are called their commissures.
Lab'yrinth.  The name  of a series of cavities of the inner ear;  viz: the
  vestibule, the cochlea, and the semi-circular  canals.
Lach'ryma.   A tear;  the fluid secreted by the lachrymal gland, and flowing
  on the surface of the eye.
Lac'teals (L. lac, milk).  Numerous minute  tubes which  absorb  or take up
  the chyle, or milk-like fluid, from the alimentary canal.  [188.]
Lac'tic Acid (  L. lac, lactis, milk).  An acid produced whenever milk, and
  perhaps most animal fluids, become spontaneously  sour.
Lam'ina.  Literally, a small plate of  any metal.  A term applied  to the,
  foliated structure of bones or other organs.
La'rynx (Gr. larungx, the  larynx).   The superior  part  of the  trachea,
  situated immediately under the os hyoides.  [97.]
Lens (L. lens, lentis, a bean). Properly, a small roundish  glass, shaped like
  a lentil, or bean.  [391.]
Lig'ament (L. ligo, to bind).  A membrane of a flexible but compact texture,
  which connects the articular surfaces of bones and cartilages;  and  some-
  times protects the joints by a capsular envelope.
Lix'gua (L. lingo, to lick).  The tongue; the organ  of taste and speech.
Liv'er.  The largest glandular apparatus in the body, the  office of  which is
  to secrete  the bile.  [191.]
Lob'ulus (L. dim. of lobus,  a lobe).  A lobule, or small lobe.  [236.]
Lum'bi.  The  loins; the inferior part  of the back; whence  Lumbar, the
  designation of nerves, arteries, veins,  &c, belonging to the region  of the
  loins.
Lungs.   The organs of respiration.  [95]
Luxa'tion (L. luxo, to put out of joint).  Dislocation ; or the removal of the
  articular surface  of bones out of their proper situation.
Lymph (L. lympha, water).  A  colourless liquid which  circulates in the
  lymphatics.   [22.]
Lymphat'ics (L. lympha,  water).   Minute tubes which pervade  every part
  of the  body,  which they absorb, or take up,  in the form of lymph.  [99.]
                                  M
Magne'sium.   A metal having the color and lustre of silver.
Malleo'lus (L. dim. of malleus, a mallet).  The ankle, so called  from its
  resemblance  to a mallet. 
262             CLASS-BOOK OF  PHYSIOLOGY.

Mamma    (L. mamma, a teat).  The fifth class of the Vertebrata, consisting
  of animals provided with mammary glands for the suckling of their young
  after birth.
Man'dibles.   The jaws of a tyrd.
Mas'seter (Gr. to chew).  A muscle which assists in chewing.
Mas'toid (Gr. a breast).   Shaped like the breast or nipple; as applied  to a
  process, and a foramen of the temporal-bone.
Mea'tus (L. meo, to pass, to flow).  Literally,  a passage.
Medul'la.  Marrow ; a kind of fixed oil, occupying the cavities of bones.  [2.]
Medul'la Oblongata. The upper enlarged portion of the spinal cord. [291.]
Medul'la Spinalis.   The spinal marrow or cord.
Medul'lary.   The designation of the white substance of the  brain.  [339.]
Mes'entery (Gr. between the bowels).   The membrane which connects the
  small intestines and the posterior wall of the abdomen.
Meta-car'pus (Gr. after,  the wrist).  That part of the hand which is situated
  between the carpus and the fingers.
Meta-tar'sus.  That  part of the foot which is situated between the tarsus
  and  the toes.  [250.]
Mid'riff.  Diaphrgm.  The muscle which divides the body into the thorax
  and the abdomen.
Mi'tral Valves (L. mitra, a mitre).   The name of two valves which guard
  the left ventricle of the heart.
Mo'lar (L. mala, a mill-stone).   The double or grinding teeth.  Those with
  two fangs are called bicuspid, or false molars.
Mol'luscs.  Animals without an internal skeleton or articulated covering.
Mo'tor (L. moveo, to move). A mover; a part whose function is motion.
Mu'cus.   The liquid secreted by the  mucous surfaces, as of the nostrils,
  intended as a protection to the parts exposed to external influences.
                                  N
Narcot'ics (Gr. stupor).   Medicines which induce sleep or stupor, as opiates.
Na'sus.  The nose, or organ of smell;  whence nasal, belonging to the nose.
  [336.]
Nerves (L. nervus, a string).   White  cords arising from the brain or the
  spinal marrow, and distributed to every part of the system.  [250.]
Neural'gia.   Nerve-ache, or pain in the nerve.
Neu'ron (Gr.).   A nerve; a cord arising from the  brain  or spinal marrow;
  whence Neurilemma, the sheath of a nerve  and  Neurology, the doctrine
  of the nerves.
Nic'tating.  Winking.
Ni'trogen.  Azote.  An elementary principle, constituting four-fifths of the
  volume of atmospheric air.
Nu'cleus.  The  kernel  of a nut.  The  centre around which particles are
  aggregated.
Nutri'tion (L. nutrio, to nourish).   The process of nourishing the frame
  [16-218.] 
GLOSSARY AND  INDEX.                 263
                                   0
Obli'quus.   Oblique or slanting; not direct, perpendicular or parallel, applied
   to several muscles.
Obtura'tor (L. obturo, to stop up).  The name of two muscles of the thigh,
   and of a nerve.
Oc'ciput (L. ob caput).  The back part of the head; the part opposite to the
   front or sinciput.
(Esoph'agus (Gr. to carry, to eat).   A canal  leading from  the mouth to the
   stomach.   [153.]
Oleag'inous (L. oleum, oil).  That  which contains, or resembles, oil.
Olec'ranon.  The large apophysis, constituting the elbow, or head of the ulna.
Olfac'tory (L. olfacio, to smell).  Belonging to the smell; the name of the
   first pair of cerebral nerves, &c.   [282.]
Omen'tum.   The caul; a fold or  reflexion of the peritoneum.
Omo (Gr. the shoulder).  Words  compounded with this term belong to mus-
   cles attached to the scapula.
Op'tic.  Belonging to  the sight.  [281.]
Orbicula'ris.  The name of two muscles of the face.
Or'bit (L. orbita, an orbit, a track).  The cavity under the forehead, in which
   the eye is fixed.   [370.]
Or'gan. A part which has a determinate office in the animal economy.  [36.]
Organization.   A term applied  to a system, composed of several individual
   parts, each of which has its  proper function, but all  conduce to the exist-
   ence of the entire system.
Or'igin (L. origo).  The commencement of a muscle from  any part.  Its
   attachment to the part it moves is  called its insertion.
Os, Ossis.   A bone;  a portion of the skeleton, constituting a passive organ
   of locomotion, as distinguished from a muscle, or active organ of this faculty.
Ossifica'tion.  The formation of bone;  the opposition of calcarious phos-
   phate, or carbonate, on the soft solids of animal bodies.
Ot'olites  (Gr.  the ear,  a stone).  Calcarious  concretions found  in the
   labyrinth of fishes and fish-like amphibia, which, by being in contact with
   the membranous parts of the labyrinth, increase by their  resonance the
   sonorous vibrations.
Ox'ides.  Substances combined with oxygen, without being in the state of
   an acid.
Ox'ygen.  A gas which forms about a fifth of atmospheric air, is capable of
   supporting flame, and is essential to the respiration of animals.

                                   P
Pan'creas.   A gland, situated transversely across the posterior wall of the
   abdomen.  In cattle it is called the sweet-bread.  [189.]
Pancreat'ic Juice.  The peculiar fluid secreted by the pancreas.   [163.]
Papil'la.  The term papilla denotes the small  eminences which constitute
  the roughness of the upper surface  of the tongue.  [27.] 
264
CLASS-BOOK OF PHYSIOLOGY.
Paral'ysis.   Palsy ;  the total loss, or diminution, of sensation or of motion,
  or of both.
Parot'id.  The name of the large salivary gland situated near the ear.  [153.]
Par'ies  Pari'etis.  The  wall  of a  house, or any other building; whence
  Parietal, belonging to the walls of  an organ.
Patel'la (L. dim. of patina, a pan).  Literally, a small pan.   The knee-pan.
Pathet'ic (Gr. passion).  A name given by Willis to the fourth pair of nerves,
  because the eyes, by means of these, express certain passions.  [303.]
Pec'toral (L. pectus, the breast).  Pertaining to the breast.
Pectoral'is.   The name of two muscles of the trunk.
Pe'dal (L. pedules).  Pertaining to a foot.
Pel'vis (Gr. a basin).  The basin, or large bony cavity which  terminates the
  trunk inferiorily.  [110.]
Pericar'dium  (Gr.  around the heart).   A fibro-serous  membrane  which
  surrounds the heart.  [61.]
Pericra'nium.  The periosteum or membrane which covers the bones of the
  cranium.
Perios'teum.  The membrane which surrounds the bones.
Peristal'tic   A term applied  to the vermicular contractions of the  intes-
  tines upon themselves.
Peritonje'um.  The serous membrane which lines the interior of the abdomen,
  and invests all the viscera contained therein.
Permeabil'ity  (L. per, through, meo, to pass).   That property of certain
  bodies by which they admit the passage of other  bodies through their
  substance.
Perspira'tion (L.  perspiro, to breathe through).  The watery vapor  which
  is constantly passing off through the skin.  [254.]
Pha'lanx.   A battalion in the Macedonian armies, composed of 16,000 men.
  Hence the term  phalanges is  applied to the bones  of the fingers and toes,
  from their regularity.
Pha'rynx (Gr. the throat).  A musculo-membranous bag, situated  at the
  back part of the mouth, leading to the stomach.
Phre'nes (Gr. the mind).   The diaphragm; so called because the  ancients
  supposed it to be the seat of the mind.   Hence the term Phrenic, a desig-
  nation of the internal respiratory nerve, which goes to the diaphragm.
Phrenol'ogy (Gr. an account).   A description  of the  mind; a  science,
  introduced by Gall and Spurzheim, by which particular characters  and pro-
  pensities are indicated by the conformation, and protuberances, of the skull.
Physiol'ogy (Gr. phusis,  nature,  logos,  an account).   The  science which
  treats  of the properties of organic  bodies, animal and vegetable,  of the
  phenomena  which they  present, and of the  laws which  govern their
  actions.  [8.]
Pi'a Ma'ter.  A vascular membrane, investing  the  whole  surface  of the
  brain.  [299.]
Pigmen'tum Ni'grum (L. pingo, to paint).   A dark brown substance, which
  covers the outer and inner surface of the choroid membrane. 
GLOSSARY AND  INDEX.
265
Pin^na..  The fin of a fish.   A  portion of the external  ear, termed pinna
  auricula, or the auricle, representing a kind of funnel,  which collects the
  vibrations of the  atmosphere.   The other portion  is termed meatus, and
  represents a tube, which conveys the vibration to the tympanum.
Pitu'itary Membrane.  A  designation of the Schneiderian membrane,
  which lines the cavities of the nose.
PlIu'ra.  [106.]
Plex'us (L. plecto,  to  weave).  A  kind of net-work of blood-vessels, or
  nerves.
Plana'ria.  [157.]
Pneu'mo-Gas'tric Nerves (Gr. pneumon, the lung, gaster, the  stomach).
  The  par vagnum, nervi vagi, or eighth pair of nerves, distributed  to the
  stomach.
Pol'ype.   A species of fresh-water insect.  [136.]
Por'tal Circula'tion.   A  subordinate part  of  the  venous  circulation, in
  which the blood makes an additional circuit before  it joins the  rest of the
  venous blood.
Por'tal Vein (L. vena porta).  A vein  originating  from  the organs within
  the abdomen.   [46.]
Por'tio Du'ra.   The hard portion of the seventh pair of nerves, or facial.
  [303.]
Por'tio  Mol'lis.   The soft portion of the seventh pair of nerves, or audi'
  tory.   [303.]'
Potas'sium.  The metallic base of the well-known alkaline substance potassa.
Prehen'sion.  A taking hold, a seizing.
Prism (Gr.  prisma, from prio, to saw).   A solid glass in  the  form of a tri-
  angle, so  termed from its separating a ray of light into its constituent parts.
Pro'cess.  Apophysis.   A process, or eminence of a bone.  Also, a lobe, or
  portion of the  brain.
Prona'tion (L. pronus, bending downward).   The act of turning  the palm
  of the hand downwards, by rotating the radius upon the ulna by means of
  the pronator muscles.
Prona'tor  (L. pronus, bending  downward).  The  name  of two muscles
  which turn the radius and the hand inwards and downwards.
Prox'imate Prin'cifle.  A term  applied, in analyzing any body, to the prin-
  ciple which is  nearest to the natural constitution of the body, and more
  immediately the object of sense, as distinguished from intermediate or ulti-
  mate principles.  Ultimate principles are the elements of which proximate
  principles are composed.
Pso'as (Gr. psoai, the loins).   The name of two muscles of the loins.
Pul'monary, pulmonic, (L. pulmo, the lungs).  Relating or  belonging to the
  lungs.
Pulse (L. pulsus, a stroke).   A beating or striking;  and, hence, the  stroke
  or beat of an artery.  [69.]
Punc'tum (L. pungo, to prick).  A point; that which is without extent.
Punc'ta Lachryma'lia. The external commencements of  the lacrymal ducts,
           19 
266
CLASS-BOOK OF PHYSIOLOGY.
 Pd'pila (L. dim. of pupa, a puppet).   The pupil, or the round aperture in th«
   centre of the iris of the eye.   [384.]
 Pylo'rus  (Gr. pule, a gate;  dm, care).   Literally, a gate-keeper.  The
   lower and contracted orifice of the stomach, guarding the entrance  into
   the bowels.
                                 Q                                 #
 Quartz.   A species of silicious minerals.
                                  R
 Ramification  (L. ramus, a branch, fio, to become).  The issuing of a small
   branch from  a large one, as of the minute branches from the larger arteries.
 Ra'mus.  A branch of a tree; the designation of portions of several bones.
 Rec'tum (L. rectus, straight).  The last portion of the intestines.
 Rec'tus (L. straight).  The name of several muscles.
•Refrac'tion (L. refractus, broken back).  That property of light, by which
   a ray becomes bent, or refracted, when passing from a rarer into a denser
   medium,  and vice  versa.  [389.]
 Respira'tion.   The function of breathing.
 Ret'ina (L. rete, a net).   The net-like expansion of the optic nerve on the
   inner surface of the eye.  [271.]
 Ri'ma.   A  fissure, a crack, or cleft; a narrow longitudinal opening.
 Roden'tia (L.  rodo, to gnaw).  Glires, or  gnawing  animals, as  the  beaver,
   the hamster, the rat, &c.
 Ru'ga.  A wrinkle.   Hence the terms rugose, wrinkled, and rugosity, ap-
   plied to a wrinkled surface, as the mucous membrane of the stomach.
 Ruminan'tia (L. rumino, to chew the cud).   Animals which chew the cud,
   as the deer.
 Rumina'tion.   A voluntary regurgitation of food for further mastication;
   peculiar to the ox, sheep, and other animals having numerous stomachs ; ii
   is commonly called chewing the cud.  [159.]
                                    S
 Sac (L. saccus, a bag).  A term applied to a small cavity, as the lacrymal
   sac.  [90.]
 Sa'crum (L. Sacred).  The bone  which forms the basis of the vertebral col-
   umn, so called from  its  having been  offered in sacrifice, and  hence con-
   sidered sacred.  [426.]
 Sacro-.  A term  applied  to parts connected with  the sacrum; hence  we
   have sacro-iliac symphysis, sacro-spinal ligament, sacro-vertebral angle, &c.
 Sali'va.   The insipid, transparent, viscous liquid, secreted  by  the  salivary
   glands, principally the parotid.  [153.]
 San'guis.   Blood; the fluid which circulates in the heart, arteries, and veins.
 Sarto'rius (L. sartor, a tailor).   The muscle by means of which the tailor
   crosses his legs.
 Scap'ula.  The shoulder-blade.
 Schneide'rian  Membrane.  The pituitary  membrane, which  eecretes  the
   mucous of the nose; so named from  Schneider, who first described it. [337.] 
GLOSSARY AND  INDEX.                 267
Sciat'ic Nerve.  The termination of the sacral  or sciatic plexus; it is the
  largest of all the nerves.
Sclerotica (Gr. sklerds, hard).  The dense fibrous  membrane which, with
  the cornea, forms the external tunic of the eye-ball.
Seba'ceous  (L.  sebum, suet).   Suety; a term applied to follicles which
  secrete  a peculiar oily matter, and are abundant in some parts of the skin,
  as in the nose, &c.  [257.]
Secre'tion (L. secerno,  to  separate).   A substance secreted or separated
  from the blood, by the action of a secreting organ.   [31.]
Seg'ment.  A part cut off or divided.
Sep'tum (L. sepes, a hedge).  A partition which separates two cavities.
Serra'tus (L. serra, a saw). The name of three muscles of the side and back.
Se'rum.   The thin yellowish fluid constituent of the blood.   [45.]
Sin'ciput.  The fore part of the head.  The back part is called occiput.
Sin'ew.   The ligament which joins two bones.
Si'nus.  A gulf.   Hence it denotes a cavity or cell within the substance of a
  bone, as of  the forehead; also a large venous canal, as those of the dura
  mater.
Skel'eton (Gr. skillo, to dry up).  The dry bony frame-work of an animal,
  which sustains the other  organs.
Sphinc'ter (L. sphinggo, to contract).  A muscle, whose office it is to close
  the aperture around which it is placed.  [181.]
Spi'nal Cord.  Medulla spinalis.   The medullary matter contained within
  the spina, or vertebral column.   [263]
Spleen   A spongy organ, situated at the left and behind the stomach.
Splint'bone.   The  fibula, or small bone  of the  leg;  so named  from its
  resembling a surgical splint.
Sta'pes.  Literally, a stirrup.  A stirrup-like bone of the internal ear.   [356.]
Ster'num.  The breast-bone.  [438.]
Stigma'ta.   The apertures in the  bodies of insects  communicating with the
  trachea? or air-vessels.
Stom'ach of the Hydra.   [157.]
    "           Planaria.   [157.]
                Sheep.   [159.]
    «           Bird.  [160.]
                Man.   [163.]
Stu'por (L. stupeo, to be senseless).   A state of insensibility.
Stye  (L. stihan, Saxon, a springing up).   Stian.  A  little  inflammatory
  tumor on the eye-lid.
Sub-.  A Latin preposition, denoting a position beneath any body.
Sub-cla'vian.  Situated under the clavicle.
Sub-cla'vius.   A  muscle arising  from the cartilage of the  first rib,  and
  inserted into the lower surface of the clavicle.
Sub-cutan'eous.  Beneath the skin.
Sub-lin'gual.  Beneath the tongue. 
268              CLASS BOOK OF  PHYSIOLOGY.
 Sub-max'illary.  Beneath the jaw.
 Su'dor (L. sudo, to sweat).  Sweat; the vapor which passes through the
   skin, and condenses on the surface of the body.
 Sudorif'erous Canals.   Minute spiral follicles, distributed over the whole
   surface of the skin, for the secretion of the sweat.
 Su'ture (L. suo, to  sew).   A seam; the junction of the bones of the  cra-
   nium by a serrated line, resembling the stitches of a seam.
 Sympathetic  Nerve.   A nerve consisting of a chain of ganglia, extending
   along the side of the vertebral column from the head to the coccyx, com-
   municating with all the other nerves of the body, and supposed to produce
   a sympathy between the affections of different parts.
 Syno'via (Gr.  don, an egg).  A peculiar liquid, found within  the  capsular
   ligaments of the joints, which it lubricates.

                                   T
 Tar'sus.   The instep; the space between the bones of the leg and the meta-
   tarsus.   [450.]
 Tears.  The peculiar fluid which lubricates the  eye.
 Teeth.  [143.]
 Tem'pora  (L. pl. of tempus, time).   The temples, or that  part of the head
   on which the hair  generally begins to turn  gray, thus indicating  the age;
   whence temporal,  pertaining to the temples, as temporal bones.
 Tena'city (L.  teneo, to hold).   The degree of force with which the particles
   of bodies cohere, or  are held together.
 Ten'don (L. teino, to stretch).  A fibrous cord at the extremity of a muscle,
   by which the muscle is attached to a bone.
 Ten'sor (L. tendo, to stretch).  A  muscle which stretches any part.
 Tentac'ula.   A filliform process or organ on the bodies of various  animals.
 Tento'rum (L. tendo, to stretch).   A tent, or pavilion, as  Tentorium cere-
   belli, a roof of dura mater thrown across the cerebellum.   In leaping  ani-
   mals, it is a bony substance.
 Tho'rax (Gr. thorax).   The chest; or  that  cavity of the body which con-
   tains the heart and lungs.  [60.]
 Thora'cic Duct.  The great trunk formed by the junction of the absorbent
   vessels.   [209.]
 Thy'roid (Gr.  thureos, a shield).  The name given to a shield-shaped  car-
   tilage of the  larynx,  and  of a gland situated on the trachea.
 Tib'ia. Literally, a flute or pipe.  The shin-bone; or the great bone of the leg.
 Tib'ial, tibialis, pertaining to the tibia.
 Tis'sue.  A web,  or web-like structure, constituting the elementary struc-
   tures of animals and plants.  [17.]
 Ton'sils (L. tondeo, to clip, or shear).  The  round  glands situated  in  the
   thorax, between the pillars of the  velum palati.
Trach'ea (Gr.  trachus, rough).  The wind-pipe.   The term is derived from
   the inequality of its cartilages.   [99.]
Tract (L. traho, to draw).   A drawing in length ; a region;  a space. 
GLOSSARY AND  INDEX.
269
Tri'ceps.  Having three heads.  Applied to several muscles.
Tricus'vid.  Having three points;  a term applied  to three triangular folds
   or valves situated between the  right auricle and the right ventricle of the
•   heart.  [63.]
Trifa'cial.   Triple-facial; a term  applied  to the fifth pair  of nerves, the
   grand sensitive nerve of the head and face.
Trochan'ter (Gr.  trochdo, to run or roll).   The name of two processes of
   the thigh-bone—the major and the minor.
Troch'lea (Gr. irochos, a wheel).   A kind of cartilaginous pulley.   Hence
   Trochlearis, a name of the  obliquus superior, or that  muscle of the eye
   which masses through the trochlea or pulley.   [387.]
Tu'nic  The upper  garment of  the Romans.  Hence it is applied to several
   membranes of the  body.
Tur'bina*xd Bones (L. turbo, a top).  Two bones of the  nostrils, so called
   from th*»»r being formed in the shape of a top, or  inverted cone.  They
   are  also called the  inferior  spongy bones, to distinguish them from the
   upper spongy bones.
Tym'panu-"  (Gr. tumpanon,  a drum).  The  drum of the ear.  [351.]

                                    U
 Ul'na  (G*  blent, the cubit).    The large  bone of the fore-arm, so  named
   from its Vnng often used as a measure, under the term ell.  [143.]
Uve'a  (L uva, grape).   The posterior surface of the iris, so called from its
   resemb'>nce in colour to a ripe grape.
U'vula tx>. dim. of uva, a grape).   The pendulous body which hangs down
   from t?  < middle of the soft palate.
                                    V
Vaccina tion  (L.  vacca, a  cow).   The act  of inserting vaccine  matter;
   inocuKtion for the  cow-pox.
Vac'cut-i (L. vaccus, empty).   Literally, an empty place.  This  term gen-
   erally denotes the interior of a close  vessel, from which the atmospheric
   air ard  every other gas has been extracted.
Valve  - u. valva, folding-doors).  A close lid affixed to a tube or opening in
   some lessel, by means of a hinge, or  other movable  joint, and which can
   be or-ned only in one direction.   Hence it signifies a little  membrane
   whic'i prevents  the return  of fluid in the blood-vessels and absorbents.
 VAL'vr.LA (L. dim. of valve).  A little valve.
Vas, Vasis.   Plural  Vasa.   A vessel, or any utensil to hold liquor.
Vas'cu* iR System.  That part of the animal  economy which relates to the
   vesseH
Ve'nou .  Belonging to a vein.  [75.]
Ventb  c'ulus (L.  dim.  of venter, the belly).   The  term  ventricle  is  also
   applied  to two cavities of the heart, and to several  cavities in other parts
   of the body.
Ver'miform (L. vermis, a worm, forma, likeness).  Worm-like.
            19* 
270             CLASS-BOOK OF  PHYSIOLOGY.
Vermic'ula.  Having a worm-like motion.
Ver'tebra (L. verto, to turn).  A bone of the spine, so named from its turn-
  ing upon the adjoining  one.  [286.]
Ver'tebral.   Connected with the vertebra.
Vertebra'ta. Animals which have an internal skeleton, supported by a ver-
  tebral column.  [281.]
Ves'sicle (L. dim. of vesica, a bladder).   A little bladder.
Ves'tibule (L. vestibulum, a threshhold).  A small oval cavity of the inter-
  nal ear, so named from its forming an entry to the cochlea and semi-circu-
  lar canals.  [46.]
Vill'us.   Literally, the shaggy hair of beasts.   Some of the membranes of
  the body, as the mucous membrane of the intestinal canal, present a sur-
  face of minute papillae,  termed villi, villosities, resembling  a downy tissue,
  continually covered with fluid.
Vit'reous  Body  (L.  vitrum,  glass).    Vitreous humour.   A  transparent
  mass, resembling melted glass, occupying the globe of the eye, and inclosed
  in the hyaloid membrane.   [376.]
  Voice.   [471.]
                                 W
Warm-blooded.   A term applied to the mammalia and  birds which have a
  two-fold circulation.  [128.]
                                 X
Xy'ph'oid (Gr. xiphos, a sword, eidos, likeness).  Sword-like; a  term applied
  to the cartilage of  the sternum.
                                  Z
Zool'ogy  (Gr. zobn, an animal, logos, a description).  That branch of Nat-
  ural History which treats of  animals.
Zygomat'icus (Gr. zugbs, a  yoke).   A name given to  two muscles of the
  face, which are attached to the zygoma or arch formed by the  processes of
  the bones.
 
D. Appleton &  Coi's Educational Publications.
Prof.  Mandeville's  Beading Books.

  *** The annexed series of Reading Books are  very extensively introduced and cob*
mended by hundreds of the most experienced teachers in the country.  " Prof. Mande-
ville's system is eminently original, scientific and practical, and destined wherever It it
tetrc-duced  to supersede at once all others.

   I. P3IM ART, or FIRST HEADER.  Price  10 cents.
   II. SECOND READER.  Price 16 cents.
   These two Readers are formed substantially on the same plan; and the second is a
continuation of the first.  The design of both is, to combine a knowledge of the meaning
and pronunciation of words, with a  knowledge of their grammatical functions.  The
parts of speech are introduced successively, beginning with the  articles, these are fol-
lowed by the demonstrative pronouns; arid these again  hy others, class after class,  until
all that are  requisite to form a sentence have been  separately conside' id;  when the
common reading lessons begin.
   The Second Reader reviews the ground passed over in the Primary, but add* largely
to the amount of information.   The child is here  also taught to read writing  as  w ell aa
printed matter; and in the reading lessons, attention is constantly directed to the differ-
ent ways in which sentences are formed and connected, and of the peculiar manner in
which each of them is delivered.   All who have examined these books, have pro-
nounced them a decided and  important advance on every other of the same class in
use.
   III. THIRD READER.  Price 25 cents.
   IV. FOURTH READER.  Price 33 cents.
   In the f\v< two Readers, the main object is to make  the pupil acquainted with the
moaning and t'unrrwns of words,  and to impart facility in pronouncing them in senten-
tial cnniHTtwn : the leading desien of these is to form a  natural, flexible, and varied de-
livery.  Aceiu-diiiLriy, the Third Header opens with a series of exercises on  articulation '
and modulation, c>n!aining numerous examples for practice on the elementary sounds
(including en-ors to lie corrected) and on the different movements of the voice, produced
by sentential structure, by emphasis, and hy the  passions.  The habits formed by these
exercises, which should be tlioronghly, as they can be easily mastered, under intelligent
instruction, find scope for improvement and confirmation in the  reading lessons which
follow, in the same book and that which succeeds.
   These lessons  have  been selected with special reference to the following peculiari-
ties: 1st Colloquial character; 2d. Variety of sentential structure; 3d. Variety of sub-
ject matter; 4th. Adaptation to the Progressive development of the pupil's mind; and,
as far as possible, 5th. Tendency to excite moral  and religious emotions.   Great pains
have been taken to make the books in these respects, which are, in fact, characteristic
of the whole series, superior to any others in use; with what success, a brief comparison
will readily show.
   V. THE FIFTH READER; or, COURSE OF  READING.  Price 75 cents.
   VL THE ELEMENTS OF READING AND ORATORY.   Price $1.
   These books are designed to cultivate the literary taste,  as well as the understanding
and vocal powers of the pupil.
   The  Cotjese op  Reading comprises three parts ; the first part containing a more
elaborate description of elementary sounds  and the parts of speech  grammatically con-
sidered, than was deemed necessary in the  preceding works; here indispensable: pari
second,  a complete classification and description  of every sentence to be found in the
Eno-lish, or any other language; examples of which in every degree of expansion, from
a few words to the half of an octavo  page in length, arc adduced, and arranged to  be
read; and as each species has its  peculiar deliverv as well as structure, both are learned
at the san.e time; partthi.-d, paragraphs;  or sentences in their connection unfolding
ztncral  thoughts, as in the common reading books.  Ii may be observed that the selec-
tions of sentences in part second, and of paragraphs in part third, comprise some of the
finest gems in the language: distinguished  alike  for beauty of thought and facility of
diction!   If not found in a school book, they might be appropriately called "elegant
extracts."
   Tire Elements op Reading  and Okatory closes the series  with  an exhibition of
Lie whole  theory and art of Elocution exclusive of gesture.  It contains, besides the
alassification of sentences already referred to, but here presented with fuller statement
and illustration, the laws of punctuation and delivery deduced from it.-.the  whole fol«
towed by carefully selected pieces for sentential analysis and vocal practice.
Q 
            D.  Appleton <fc CVs Educational Publication*.


               PROF.  EDWARD  C.  MARSHALL.

 Book of  Oratory;

     A New Collection of Extracts in Prose, Poetry, and Dialogue: contain-
     ing Selections from Distinguished American and  English Orators, Di-
     vines, and Poets, of which  many are Specimens  of the Eloquence of
     Statesmen of tho Present Day.  For  the Use of Colleges,  Academies,
     and Schools.   One vol. 12mo., of 500 pages.  $1.

   This work contains a larger number of elegant extracts than any similar one, from
 the first American and English Authors, among whom are Webster, Clay, Everett, Cal-
 boun, "Wirt, Randolph, Prentiss, Channing, Dewey, Burke, Brougham, Shakspeare, By-
 ron, Scott, Hood, Bryant, and Longfellow, together with a complete digest of specimens
 if the oratory and poetry of all parts of the Union.
                            OPINIONS OF THE PRESS.
   " A large and admirable selection of pieces for declamation, copious and varied, and
 well chosen with reference to speaking.  The range of selection is almost universal, at
 least among modern writers in prose, verse, and drama.  They make a spirited  collec-
 tion of thought and rhetoric.  The editor is a practical teacher of elocution, and evidently
 has a wide acquaintance with literature.  It is as good a work of the kind as we evei
 saw."—Evangelic.
   " It is an admirable collection of pieces for declamation, taken principally from emi-
 nent American orators."—Tribune.
   " This is an exceedingly judicious and  tasteful selection  of extracts from various
 /unds of composition,  designed for the use of schools, academies, and colleges.  A large
 proportion of the extracts are from our most distinguished statesmen, and may be con-
 sidered a monument of honor or patriotism, not less than of eloquence.  There  is a
 freshness and grace about the work that will render it peculiarly attractive."—Albany
 Argun.
   " This is an excellent reading book for public seminaries.   The  selections are made
 with good taste, are brief, and of every variety.  The entire field of American speeches
 and publications has been explored to gather them.  They include extracts from Chan-
 ning and Dewey, and  Beecher and Dow, Jr., from Webster, Clay, and Cass, from Black
 Hawk and  Eed  Jacket.  They are  generally specimens of elegant composition,  ex-
 pressive of patriotic and manly thought, and pure and noble sentiment."—Journal cj
 Commerce.
   " It contains  a copious  and excellent selection from the best orators, divines, and
 poets of England  and America, and will be found of great value to the teacher of elocu-
 tion and rhetoric. It will doubtless become a standard work in schools and colleges."
   "It comprises some five hundred  pages of the  best selections we have ever seen
 compiled. It is worthy a place in every family library."—New Haven Register.
   "This work contains a collection of extracts in prose and poetry, with selections from
 the speeches of the most eminent American and English orators, suitable for exercises
 in public speaking.  It is designed for the use of colleges, academies, and schools, and is
 the be">t compilation for that purpose we have ever seen.  The selections are very judi-
 ciously made, and are calculated to interest the scholar, as well  as to furnish him with
 models after which to form his style."—Evening Post.
   "This compilation  for the use of students in elocution has been  prepared with great
 judgment by the author, who has  had much  experience in  this branch  of education,
 having been for many years a professor of elocutioi^it West Point  A principal feature
 in this work is that the selections have buen  mostly made from the speeches of great
 orators of the present century, and many of them are specimens of tts eloquence ot dis-
 tinguished statesmen of our nnion."—Phil. Advertiser.
   " This work is a complete cyclopedia of specimens of English and American oratory
and poetry, for the use of colleges and schools, selected and arranged with skill and good
taste.  The plan of the work, which is quite original, and will commend itself to every
mind, is to present the best specimens which can bo obtained of the oratory and poetry
of all parts of the Union, and of living authors.  This has not been attempted so thor
oughly in any similar work, and as this is decidedly the Book of Oratory of the Union
wo doubt not that it will be eminently successful."—Home Journal.
               PROP. EDWARD  C. MARSHALL.
The First Book of  Oratory.
    One volume 12mo.   Price 62 cents. 
D. Applcton &  Co?% Educational Publications.
                          PROF.  LATHAM.


A Hand-Book  of  the  English Language ;

    For the Use of Students of the Universities and Higher Classes ol
    Schools.  12mo.  $1 25.


   TlHs is an abridgment, or a compendium, by the author, of his large and celebrated!
work on the English language;  and must prove an invaluable aid to every intellicent
teacher of English Grammar. It is quite unlike any work that has heretofore been pub-
lished among us, except it may be some that have borrowed largely from this  treasure-
bouse of information on the  English language.  It is divided into seven  Parts.   The
first and second parts, occupying nearly SO pages, are devoted to the history and analysis
of the English language, designed to show the various elements of which this  language
Is composed, and the manner in which these elements were  introduced gradually into
the language.
   These parts contain the results of very extended and profound study, and furnish in-
formation of great value to the student.   After this follows the grammatical parts of the
work, strictly so called, in which the learned grammarian treats in Part III. of sounds,
letters, pronunciation, and spelling, concluding with an historical sketch of the English
Alphabet: in Part IV., of Etymology, under its various usual  heads;  in  Part V., of
Syntax; in Part VI., of Prosody;  and in Part VII., of dialects of the English language.
Biich is the general plan of a work which cannot fail to receive a cordial welcome among
the scholars of America, coming to them, as it does, with the seal of English  approval
on it, as the work of the age on English Grammar, and presenting, as it does, on its very
face, the evidence of profound and patient scholarship and  philosophical discrimiuation
and analysis.
   " We should be glad to see this excellent work introduced into all our  colleges and
higher schools of learning.  The ethnology of the English  language is too rarely under-
stood.  Most men of education seem to think their native  tongue a  vulgar study, and
confine their researches to the dead languages,  or to modern dialects, which are far in-
ferior in variety and power to the noble idiom  in which Milton sung and Addison wrote.
Dr. Latham's profound and acute investigations have enabled him to throw a flood of
light on the derivations of words, and the mutations of orthography.  His larger trea-
tises have given him a name among the most learned  ethnologists, and this summary of
the results of his labors will make him more widely known among general readers."—
Commercial Advertiser.
   "A work of great research, much learning, and to every thinking scholar, it will ba
a book of study.   The Germanic origin  of the English language,  the* affinities of the
English with other languages, a sketch of the Alphabet, a  minute investigation of tho
Etymology of the language, &c, of great value  to every philologist—O&serper.
                           G. F.  GRAHAM

 English  Synonymes, Classified and Explained;

    With Practical Exercises.   Designed fcr Schools  and  Private Tuition.
    With an  Introduction  and Illustrative Authorities, by Henry Eked,
    LL.D.  12mo.  §1.

   "This is one of the best books recently published in the department of language, and
rMl do much to arrest the evil of making too common use of inappropriate words. The
work is well arranged for classes, and can be made a branch  of common school study.
The excellent and elaborate work of Crabb is adapted to the private study, and has beea
used by many scholars and professional men with great profit, but never could find us
olace in the school-room; consequently, this important department of study has been left
Kch meanrrcommon conversation and miscellaneous reading might afford.
   »TlnTwork  is Xirably arranged.   The Synonymes are  treated with reference to
their character,  as generic and specific;  as active and passive; as positive and negative;

IBd«'l clasfinXPs boSoykHdbe organized in every school"- Teachers' AOvocaU 
U.  Applcton <& Uo.\$ Educational Publications.
                   PROP. G. P. QUACKENBOS.

First  Lessons  in  Composition,

    In which the Principles of the Art are Developed, in connection with
    the Principles of Grammar;  embracing full Directions on the Subject
    of Punctuation:  with Copious Exercises.   12mo.  45 cents.

   %* This work has received tho universal approbation of Practical Teachers and tba
Ififcss  of the United States.

  From the Principal, and assistant  Teachers, of the Mechanics'1 Institute, 2T. Y.
   "With  feelings of unfeigned pleasure, I have examined the 'First Lessons In Conn
position,' by G. P. Quackenbos.
   " This work possesses the rare merit of combining what is new with what is already
familiar in publications of the science upon which it treats.   The matter which is com-
prised  in the first  fifty  pages is invaluable.  If the pupil be faithfully trained in these
preliminary exercises, he will be amply prepared to appreciate the principles detailed i»
the latttr part of the volume.  It is,  without  question, the best treatise that has ap.
E eared on the subject which it professes to illustrate, as every part can be made availa-
 le to  pupils by the judicious teacher; and it appears to be admirably adapted to mew*
the present requirements of schools.
                               J. T. BERGEN, Professor of Belles-lettres.
                               M. C. TRACY, Principal of Mec. Inst. School
                               J. OVERACRE.
   " This book presents an exceedingly simple method of learning the principles ot
Grammar,  and it is so  completely adapted even to the understanding of the youngest
pupil,  that it  cannot fail to be  a  great assistant to the teachers of schools.   It is pre-
pared  with much skill and judgment, and from the suggestions  of long experience. It
will be found to possess & more than ordinary intrinsic value."—N. Y. Courier <&
Enquirer.
                   PROF. JOHN W. S.  HOWS.

The  Shakspearian  Reader;

    A Collection  of the most approved Plays of Shakspeare, carefully ra
    vised ;  with Introductory and Explanatory Notes, and a Memoir of the

    Author.   Prepared expressly for the use of Classes  and the Family
    Reading Circle.   12mo.  $1 25.

   "At a period when the fame of Shakspeare Is "striding the wortd like a colossus,"
 nd editions of his works are multiplied with a profusion that testifies the desire awak«
ened in all classes of society to read and study his imperishable compositions,—there
needs, perhaps, but little apology for the following selection of his works, prepared ex-
pressly to render them unexceptionable for the use of Schools, and acceptable for Family
reading.  Apart from tho fact, that Shakspeare is the  " well  spring" from which may be
traced the origin of the purest poetry in our language,—a long course of professional ex-
perience has satisfied me  that a  necessity exists lor the addition  of a work like the
present, to our stoek  of Educational Literature.  His  writings are peculiarly adapted for
the purpose of Elocutionary exercise, when the system  of instruction pursued  by the
Teacher is based upon the true principle of the art, viz.—a careful analysis of the struo-
ture and meaning of language, rather than a servile adherence to the arbitrary and me
ehanical rules of Elocution.
   "To impress upon  the  mind of the pupil that words are the exposition of thonei f,
and that in reading, or speaking, every shade of thought and feeling has iis appropriate
shade of modulated tone, ought to be the especial aim of every Teacher: and an  atitho?
like Shakspeare, whose every line embodies  a volume of meaning, should surely form
on« of our  Elocutionary Text Books.  *  * *  Still, in preparing a selection'of hia
Works for the express purpose contemplated in my design, I have not hesitated to exer-
cise a severe revision of his language, beyond that adopted in any similar undertaking
«" Bowdler's Family Shakspeare" not  even excepted;—and simply, because I  practi-
cally know the impossibility of introducing Shakspeare as a  Class Book, or as a satisfac-
tory Reading Book  for Families without this precautionary revision."— Extract from
the Preface. 
           D. Appleton & Co. s Educational Publications.


                     THOMAS  ARNOLD,  D. D.

The   History  of  Borne.

    Beprinted entire from the last London Edition.  Three volumes in on*
    6vo.  $3.

   "Arnold's History of Rome Is a well known standard work.  Full and accurate M
Hiebuhr, but much more readable and attractive; more copious and exact than Knight-
ley or Schmitz, and more reliable than Michelet, it has assumed a rank second to none
In value and importance.  Its style is admirable, and it is every where imbued with the
truth-loving  spirit for which Dr. Arnold was pre-eminent.  For Colleges and School!
this History is invaluable; and for private, as well as public libraries, it is indispensable."
                     THOMAS ARNOLD,  D. D.

Lectures  on  Modern  History.

    Edited,  with a  Preface and Notes, by Henry Eeed, LL. D.  12mo,
    $1 25.

   Extract from the American Editor's Preface :—"In preparing this edition, I have
bad in view its use, not only for the general reader, but also as a text-book in education,
especially in our  college course of study. *  *  * * The introduction of this work
gs a text-book I regard as important, because, as far as my information entitles me to
■peak, there is no book better calculated to inspire an interest in historical study.  That
It has this power over the minds of students I can say from  experience, which enables
me al»o to add, that I have found it excellently suited to a course of college instruction.
By intelligent and enterprising members of a class especially, it is studied as a text-
book with zeal and animation.

   " These Lectures, eight in number, furnish the best possible introduction to s philo-
sophical stndy of modern history.  Prof. Reed has added greatly to the worth and inter-
est of the volume, by appending to each lecture such extracts from Dr. Arnold's othei
writings as would more fully illustrate its prominent points.  The Notes and AppendU
which he has thus furnished are exceedingly valuable."—Evening Post.
             PROP.  FREDERICK KOHLRAUSCH.

A  History  of Germany ;

    From the Earliest Period to the  Present  lime.  Translated from the
    last German Edition, by James D. Haas.   With a  Complete Index,

    prepared expressly for this Edition.  8vo.  $1 75.

"Messes. Appixton:
   " Gentlemen,—Having adopted Kolrausch's History of Germany, as a text-book rot
•n advanced class in history, I take great pleasure in stating that I have found no work,
In a wide range of historical instruction, both ancient and modern, devonred with more
avidity by my pupils,  or resulting in  their greater profit  Next to the history of our
»wn country and that of England, I know of none so important to be familiarly under-
stood by our American  youth, as the History of Germany;  in its bearings on modern
eiviliwrtion, the Protestant Reformation, the progress of literature, the advancement, o!
the Arts and Sciences, and high classical scholarship, as well as also our own very origin
and language.                               ,                ...           .,
   "The  history of a nation with whose  past and present we especially, not to say the
whole civilized  world,  have  such vital connections, though unknown perchance to a
ereat extent to our educated men of a preceding generation, ought now to be introduced
every where at once into all our high schools, as an essential part of a course of liberal
MtaMtinn                                  " YOUTS, &C,

    " Bsookmtn, Jan. 24i/t, 1852."
             7 
D. Appleton & Goh Educational Publications.
                 PROP.  GEORGE  W.  GREENE.

History of the Middle Ages.

    For Colleges and Schools (chiefly from the French).  12mo.  $1 25.

   "No portion of history has been less studied, either by old or young, than that of the
middle ages.  This is owing in a great degree, we believe, to the defective text-books
which have hitherto been in use,  for the period in question is itself one of the most in-
teresting and important in the annals of mankind.   It was  the birth-time of modern
society—the source and fountain  of modern civilization—the period in which a larg«
portion of the civil and religious institutions which we now meet highly prize had thei/
origin.
  ~" The work before us, compiled principally from the French, by Professor Qreene,
of Brown University, is the fruit of much learning and research. It furnishes  a brief,
though clear and well digested, exposition of the leading revolutions of the middle ages,
and is designed to introduce the  student to an acquaintance with those various and
complicated agencies which, out of barbarism and decay, slowly built up  the nations of
Modern Europe.   The plan is judicious, and the execution is in the admirable  literary-
taste which always characterizes the writings of Mr. Greene. The period embraced  in
the work reaches from the first general irruption of .the barbarians at the beginning of
the fifth century, to the fall of Constantinople, near the middle of the fifteenth—a period
crowded with momentous changes  in both the civil and ecclesiastical  affairs of the
world—marked by the rise and fall of numerous dynasties, and by the utter extinction
of the ancient civilization and the formation of another entirely new.
   " We hope to see this work generally adopted as  a text-book in schools and colleges
where History is made a part of the course of instruction, for wo feel assured that both
instructors and pupils will find it  admirably suited to explain the interesting and impor>
tant period to which it relates."—Providence Journal.
                 PROP.  GEORGE  W.  GREENE.

Atlas  of  Mediceval Geography ;

    Designed to accompany the above.  One volume Svo.   (In press.)

   Contents :—Map 1. The Roman Empire and Northern  Barbarians  in the Fourth
Century.  Map 2. Europe in the Sixth Century.  Map 3. Europe in the times of Char-
lemagne.  Map 4. Europe in the second half of the Tenth Century.  Map 5. Europe in
the time of the Crusades.  Map 6.  Europe at the end of the Fourteenth Century.
                          E. M. SEWELL.

 The First  History of Rome ;

    With Questions.  16mo.  50 cents.

                                          " Norfolk Academy, Norfolk, Va.
   "I must thank you for a copy of ' Miss Sewell's Roman History.' Classical teachers
bave long needed just such a work: for it is admitted by all how essential to a propel
comprehension of the classics is a knowledge of collateral history.  Yet most pupils are
construing authors before reaching an age to put into their hands the elaborate works
we have heretofore had upon Ancient History.  Miss Sewell, while she gives the most
important facts, has clothed them in a style at once pleasing and comprehensible to th«
most youthful mind.
                              " R. B. Tschttdi, Prof, of Ancient Languages"
                          E. M.  SEWELL.

The First History  of  Greece;
   With  Questions, on  the Plan  of the First  History of Rome.   16mo
   {In press.)
           H 
 
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