A MANUAL 
OF 
Normal Histology 
AND 
Organography 
BY 
CHARLES HILL, Ph.D., M.D. 
ASSISTANT PROFESSOR OF HISTOLOGY AND EMBRYOLOGY AT THE NORTH- 
WEST c.nN UNIVERSITY MEDICAL SCHOOL; WniCWlTO1, P U K 1U I'.fA. t 
PROFESSOR OF ZOOLOGY, UNIVERSE Y OF^VSHINGTON 
Illustrate I 
i 
PHILADELPHIA AND .MlON 
W. B. SAUNDERS C^MPAN| 
1906 Copyright, 1906, by W. B. Saunders Company 
PRESS OF 
W. B. SAUNDERS COMPANY 
PHILADELPHIA PREFACE. 
This manual is written in the interest of element- 
ary students. The fundamental facts in histology 
have therefore been presented in as clear and 
concise a manner as possible, and theories advanced 
only to simplify the facts and aid the memory in 
their retention. The figures have been selected 
with considerable care and are intended to illus- 
trate the salient points of the text. They are to 
be studied as critically as the text, and to further 
facilitate such a study the descriptive terms are 
placed on the figures rather than in foot-notes. 
The oral cavity deserves more attention than 
is usually given this subject. Neglect of proper 
care of teeth is a common failing, and the cause 
may be traced directly to a lack of knowledge 
of their structure and function. This chapter has 
therefore been enlarged. The author is- greatly 
indebted to Professor Frederick B. Noyes, of the 
Northwestern University Dental School, for con- 
tributing most excellent figures on this subject. 
His critical essays form the basis for the descriptive 
part of this chapter. 
The author believes most thoroughly in the 
laboratory method of study. He believes, too, 
that the laboratory work should precede the class- 
11 12 
PREFACE. 
room work, for which 4 his manual is written. 
Laboratory technique, however, is so extensive a 
subject that a laboratory text, or the teacher's 
personal outlines, should be used for this particular 
work. In conformity with this view, only the funda- 
mental principles of laboratory technique arc out- 
lined in the text. 
Lastly, the subjects treated have been made funda- 
mental and brief, that the teacher in charge may 
supplement the chapters by collateral work as may 
fit the particular course offered. It is therefore a 
basis on which the instructor may build and com- 
plete his ideal elementary course in histology. 
Charles Hill. 
July, 1906. CONTENTS. 
Page. 
Introduction 17 
Preparation of Material 17 
CHAPTER I. 
Development 26 
The Cell 36 
CHAPTER II. 
Tissues 45 
Epithelial Tissue 45 
Supporting Tissue 57 
Connective Tissue 58 
Cartilage 66 
Bone 69 
Muscular Tissue 77 
Nervous Tissue 86 
CHAPTER HI. 
Circulatory System, Blood, Marrow, and Lymphatic Organs 100 
Heart 100 
Arteries and Veins 101 
Blood 105 
Marrow 109 
Lymphatic System 113 
Thymus Gland 117 
Spleen 118 
CHAPTER IV 
Digestive System 124 
Mouth 124 
Teeth 131 
Tongue 160 
Pharynx 168 
Esophagus 170 
Stomach 172 
Small Intestine 180 
Large Intestine 186 
13 14 
contents. 
Page. 
CHAPTER V. 
Digestive Glands :... . 193 
Salivary Glands 193 
Pancreas 198 
Liver 202 
CHAPTER VI. 
Organs of Respiration 217 
Larynx 217 
Thyroid Gland 221 
Parathyroids 224 
Trachea and Bronchi 225 
Lung 228 
CHAPTER VIL 
The Urinary Organs 239 
Suprarenal Bodies 239 
Kidneys 243 
Ureters 255 
Urinary Bladder 257 
CHAPTER VIII. 
Reproductive Organs in Male 261 
Testicles 261 
Penis 274 
Prostate Gland 280 
CHAPTER IX. 
Reproductive Organs in the Female 283 
Ovaries 283 
Fallopian Tubes 295 
Uterus 299 
Pregnancy 309 
Mammary Gland 314 
CHAPTER X. 
The Skin 319 
Hairs 325 
Nails • 331 
Glands of skin 333 CONTENTS. 
15 
CHAPTER XI. 
Peripheral Nerve Terminations 339 
Motor Nerve Endings 339 
Sensory Nerve Endings 341 
CHAPTER XII. 
Spinal Cord 349 
CHAPTER XIII. 
The Brain 362 
Medulla 364 
Summary of Tracts, their Origin and Terminations 372 
Pons 372 
Cerebellum 375 
Cerebral Cortex 381 
Neuroglia 384 
Blood-vessels of Central Nervous System 387 
CHAPTER XIV. 
The Eye 389 
Tunica Externa 392 
Tunica Media 396 
Tunica Interna 399 
Refracting Media 406 
Blood-vessels 408 
CHAPTER XV. 
Organ of Hearing 415 
Development of Labyrinth 429 
CHAPTER XVI. 
Olfactory Organ 431 
CHAPTER XVII. 
Laboratory Directions 434 
Preparation of Elastic Fibers 436 
Standard Fixing Solutions 442 
Standard Stains 445 
Index 449 A MANUAL OF 
NORMAL HISTOLOGY 
AND 
ORGANOGRAPHY. 
INTRODUCTION. 
PREPARATION OF MATERIAL. 
I. Spreads.-Thin spreads or smears are made 
upon cover glasses or on glass slides. The specimens 
are then studied, stained or unstained, but always 
in some liquid medium. They may be fixed and 
mounted permanently by treating the preparations 
just as if they were sections. Blood, marrow, nerve 
cells from brain or cord, and scrapings from organs, 
as the liver, may be prepared in this way. 
II. Teasing.-Muscle, tendon and nerve fibers are 
easily prepared in this way. The teasing, or spread- 
ing, may be done in water and glycerin, or small 
pieces may be dehydrated with alcohol and then 
teased in oil, or even in balsam, thus making a per- 
manent mount. Alcohol and oil harden the tissues, 
and satisfactory teasing is therefore more difficult. 
17 18 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
III. Dissociation or Maceration of Tissue Ele- 
ments- 
i. Alcohol, 25 per cent.; time, twenty-four 
or forty-eight hours. 
2. Strong acids, as hydrochloric or nitric; 
time, twenty-four hours. 
3. Caustic potash, 25 per cent.; time, ten 
to thirty minutes. 
To obtain columnar and goblet cells of the intestine, 
remove several inches of the colon, clean carefully 
by passing water through it, and then distend the 
piece with 25 per cent, alcohol, ligating both ends. 
Next day open the bowel and make light scrapings 
from the mucous surface and place these in a vial 
containing equal parts of alcohol (50 per cent.) and 
glycerin. Shake the vial and the cells will dis- 
seminate throughout the fluid. The 25 per cent, 
alcohol dissolves the cement that holds these epi- 
thelial cells together. If desired, a little stain may 
be added to the glycerin preparation. 
The epithelium of the bladder may be obtained in 
the same manner, by distending the organ with 25 
per cent, alcohol; also, the ciliated cells of the 
trachea, although in this case no distention is 
possible. All these cells come away very easily, 
and the scraping must be carefully done. 
Tubules of the kidney are readily obtained by 
treating small pieces with acid. In twenty-four 
hours, remove the pieces to equal parts of alcohol 
and glycerin, and shake. A drop of this will show 
all forms of tubules and glomeruli. The former are 
practically equivalent to epithelial casts, clinically 
so important in urinary analysis. PREPARATION OF MATERIAL. 
19 
The caustic potash reaction is more rapid. Pieces 
of tissue may be treated with this on the glass slide 
and examined in the fluid. Care must be observed 
that the alkali does not get on the lens of the micro- 
scope. 
IV. To Prepare Tissue for Sectioning in Celloidin 
or Paraffin. 
i. Fixing and Hardening. - Fixing consists in 
rapidly killing the cell and preserving its constitu- 
ents, nucleus and cytoplasm, before disintegration 
can take place. Most fixing agents coagulate the 
protoplasm and cell contents. 
(a) Heat.-Cover-glass preparations may be fixed 
by heating them in an oven or over a gas flame to 
ioo° or even 1500 C. 
(6) Fluids. 
(1) Acids-osmic, 1%; chromic, 1%; ni- 
tric, 10%; etc. 
(2) Salts-mercuric chloride saturated, 
potassium bichromate, 3%; etc. 
(3) Alcohol, 95%, or absolute. 
(4) Formalin, 5%. 
Acids and salts may be used separately as above, 
but as a rule different combinations are used, 
formulae of which are given on another page. 
(c) Precautions. 
(1) Fix living tissues, if possible. 
(2) Fix small pieces, so that fluids may 
readily penetrate. 
(3) Heat hastens the penetration. 
(4) Change as often as the fluid becomes 
cloudy. 20 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
(5) Use a large quanitity of fluid (50 to 100 
times the volume of the tissue). 
2. Washing. 
(a) Water.-If there is a chemical change between 
the fixing agent and the tissue, use water. This is 
most frequently the case. The specimens should be 
very thoroughly washed, preferably in running 
water, for twenty-four hours or more. 
(6) Alcohol.-When alcohol is indicated, use the 
grades 50%, 70%, 95%, and leave in 80%. When- 
ever picric acid forms a part of the fixing agent, 
alcohol wash must be used. 
3. Dehydrating. 
(a) We dehydrate to preserve the tissue from 
action of bacteria. 
(&) In order that imbedding fluids, which do not 
mix with water, may penetrate the tissue. Alcohol, 
the grades ending with absolute alcohol, is always 
the agent used. 
4. Imbedding with Celloidin, Evaporation Method. 
(a) A bsolute A Icohol and Ether, Equal Parts.-After 
thorough dehydration in absolute alcohol, the tissue 
is transferred to absolute alcohol and ether, equal 
parts, where it is left for twenty-four hours. 
(6) Thin celloidin, 4%, made by dissolving cel- 
loidin shreds in equal parts of absolute alcohol and 
ether. The tissue may be left any length of time in 
thin celloidin, the longer the better. 
(c) Thick celloidin, 10%; time, twenty-four hours 
or longer. 
5. Mounting on Block and Evaporation of Ether. 
(a) Cover surface, of perfectly dry block, with thin 
celloidin. PREPARATION OF MATERIAL. 
21 
(6) Remove the tissue from thick celloidin and place 
upon block, in the proper position for cutting. 
This is called orienting. A piece like a nerve may 
have to be supported with needles, and these re- 
moved later. 
(c) Add thick celloidin, from time to time, and open 
any air bubble that may appear. Leave the speci- 
men in air until the ether has evaporated so that the 
celloidin does not feel sticky to the touch. The 
usual time will be ten to twenty minutes. 
(d) Transfer to Chloroform Vapor.-Pour a little 
chloroform over the bottom of a dish. Set the 
blocks in this so that the liquid does not reach the 
tissue. Cover tightly and leave for thirty minutes. 
(e) Transfer to chloroform liquid by immersing the 
tissue. Time, thirty minutes. 
(/) Transfer to 80% alcohol, where blocks may be 
left permanently. 
6. Imbedding with Paraffin or Fusion Method. 
(a) Intermediate Stage.-The tissue is taken out of 
absolute alcohol, where it has been thoroughly 
dehydrated, and is then treated with some fluid 
that is miscible on the one hand with absolute 
alcohol, and on the other with paraffin. Liquids 
used are- 
(i) Chloroform. 
(2) Cedar-wood oil. 
(3) Turpentine. 
(4)- Xylol. 
Tissues left in oils become brittle. From one to two 
hours are usually sufficient, depending upon the size 
of the piece to be imbedded. Chloroform will harden 
the tissue to a less degree than the other fluids. 22 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
(6) Melted Paraffin.-The melting-point of paraf- 
fin should vary according to the room temperature 
where the sections will be cut. The following table 
gives the relation of melting-point of paraffin to this 
temperature: 
Paraffin melting-point. Room temperature. 
45° C 15° to 17° C. or 60° to 65° F. 
48° C 22° C. or 70° F. 
55° C 24° C. or 75° F. 
Tissues are left in melted paraffin from two to six 
hours. 
(c) Solidification of paraffin may be accomplished 
by means of- 
(i) Watch glasses. 
(2) Metallic frames. 
(3) Paper trays. 
(4) Tea-lead trays. 
The paraffin is poured into these trays, and the 
tissue quickly transferred to it. The piece is then 
oriented, and as soon as the paraffin has cooled 
enough to form a crust, the whole block is placed in 
cold water, where the paraffin is quickly cooled so 
as to avoid crystallization. The block is then ready 
to be cut in sections. 
A. Advantages of Celloidin Imbedding. 
1. No heat is necessary. 
2. Large sections may be cut, because 
penetration is more complete than 
is the case with paraffin. 
3. Unnecessary to remove celloidin to 
stain; sections are therefore easily 
handled. PREPARATION OF MATERIAL. 
23 
B. Disadvantages of Celloidin Sections. 
i. Slow process-at least three days. 
2. No thin sections. 
3. Celloidin may take the stain, particu- 
larly with saffranin. 
4. Serial sections difficult to make. 
5. More expensive. 
C. Advantages of Paraffin Imbedding. 
1. Accommodates very small objects. 
2. Thinner sections may be cut. 
3. Rapid process. 
4. Cheaper than celloidin method. 
D. Disadvantages of Paraffin Imbedding. 
1. Must use heat, which is injurious to 
tissues. 
2. Must remove paraffin to stain sections, 
and the latter therefore tear easily. 
3. Proper room temperature necessary 
when sections are cut, in order to 
conform to melting-point of paraf- 
fin. 
7. Cutting Sections.-Use the whole edge of the 
knife in cutting celloidin sections, and keep the 
knife wet with 70% alcohol. When cutting paraf- 
fin sections, the knife is placed at right angle to the 
block. Always trim away superfluous paraffin. 
8. Staining celloidin sections. 
1. Alcohol, 95%. 
2. Water. 
3. Hematoxylin, ten minutes. 24 
NORMAL HISTOLOGY AND ORGANOGRAPHY 
4. Water. 
5. Acid alcohol, HC1 0.5 to 1%; leave the 
sections in this until all stain is 
washed out of the celloidin. 
6. Water. 
7. Eosin, 0.5% solution, one to three 
minutes. 
8. Alcohol, 35%. 
9. Alcohol, 95%. 
10. Xylol creosote (beechwood creosote, 20 
parts; xylol, 80 parts). 
11. Mount in Canada balsam and cover. 
The sections must become perfectly transparent in 
the xylol creosote. If they are cloudy or milky, 
water is present; and the sections must be returned 
to alcohol, 95%, and the process repeated. Sections 
that curl should be flattened out when lifted out of 
95% alcohol, because in this the sections are soft. 
In xylol or in water the sections are hard. 
9. Staining Paraffin Sections.-Since the paraffin 
has to be removed the sections first have to be fixed 
to the glass slide or cover glass. 
(1) Spread fixative on slide. Albumin fixative 
consists of egg albumin and glycerin, equal parts. A 
very thin spread is all that is necessary. Schaellin- 
baum fixative consists of clove oil 4 parts and thin 
celloidin 1 part. A thicker spread of this is used. 
(2) Place section upon slide and heat gently. 
(3) Xylol or turpentine to remove the paraffin. 
(4) Absolute alcohol to remove the oil. 
(5) Alcohol, 95%. 
Stain on the slide, or immerse the whole slide in PREPARATION OF MATERIAL. 
25 
the stain, following directions as for celloidin sec- 
tions. 
Stain in bulk before imbedding in paraffin when- 
ever this is possible, as then the sections may- 
be mounted from xylol directly into balsam. An 
excellant way to get sections smooth is to float them 
on warm water-not so warm as to melt the paraffin 
-and then lift them out upon the glass slide. 
Decant surplus water and put away for twenty-four 
hours to dry. Next day remove paraffin with xylol 
and stain according to above directions. 
Review of Preparing Tissues. 
i. Fixing and hardening 
2. Washing. 
3. Dehydrating. 
4. Imbedding in celloidin. 
5. Mounting on block and evaporation of 
ether. 
. 6. Imbedding in paraffin. 
7. Cutting sections. 
8. Staining celloidin sections. 
9. Staining paraffin sections. CHAPTER I. 
DEVELOPMENT. 
Histology is that branch of science that treats of 
cells and their derivatives. These cells, in the adult, 
are modified according to their intrinsic qualities, 
environment, function, and varied experiences, 
which enable us to classify them and ultimately 
place them in a few elementary groups. 
The ovum, or starting-point of every individual, 
is a cell. Hitman embryology comprises its intra- 
uterine development. Ontogeny is a broader term. 
It includes not only embryology, but the develop- 
mental history of an individual up to old age or the 
senile condition. There is another form of develop- 
ment, much slower, but just as certain as ontogeny. 
This affects not only the individual, but, collectively, 
every member of the animal group. In the study of 
races there is ample evidence that structural changes 
have slowly but gradually taken place. This 
broader developmental history, or history of a race, 
is known as phylogeny. It is closely interwoven with 
the ontogenetic development, so much so, that the 
latter in large part repeats the former, or one's 
phylogenetic history is repeated in the ontogeny. 
In development, therefore, the phylogenetic or 
intrinsic qualities of a cell are important factors. 
These factors constitute heredity. There is further 
26 DEVELOPMENT. 
27 
evidence that these factors are lodged in the chro- 
matin of the cell nucleus. 
Environment is the other great factor that brings 
about a structural modification. It is between 
environment on the one hand, and heredity on the 
other, that a specialization and differentiation of 
cells, tissues, and organs is produced. 
A cell is a spacially limited mass of protoplasm 
which, under certain conditions, will assimilate, grow, 
Fig. i;-Formation of the polar bodies in the ova of Asterias gla- 
cialis (Hertwig): ps, polar spindle; pb', first polar body; pb", second 
polar body; n, nucleus returning to condition of rest. 
and reproduce itself. A tissue is a complex of 
similarly differentiated cells and their derivatives. 
An organ is a complex of tissues, forming a body with 
a definite internal structure and external form. 
Ovulation and Maturation.-The ova develop in 
the ovaries and are differentiated very early during 
embryonic life. The estimated number of ova in 28 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
each ovary is 35,000. It is a remarkable phenomenon 
that for many years these units show no attempt at 
development or cell division. At the age of puberty 
one or more or these cells pass periodically from the 
ovaries, approximately every twenty-eight days in 
the non-pregnant woman. This process is known as 
ovulation, and continues up to the time of the meno- 
pause, which appears generally at the age of forty- 
five. 
As soon as the ovum is liberated from the ovary, a 
Fig. 2.- Portions of the ova of Asterias glacial is, showing the ap- 
proach and fusion of the spermatozoon with the ovum (Hertwig): a, 
fertilizing male element; b, elevation of protoplasm of egg; b', b", stages 
of fusion of the head of the spermatozoon with the ovum. 
mitotic division of the nucleus takes place, and the 
ovum extrudes or produces what is called the first 
polar body. This is a form of budding, the polar 
body receiving one-half the original nucleus of the 
ovum. Without delay, a second division of the 
nucleus in the ovum takes place, and a second polar 
body is produced. This is also an equal division of 
the nucleus, but this time there is a reduction of one- 
half the number of chromosomes. The significance DEVELOPMENT. 
29 
Male pronucleus. 
Female pronucleus. 
Male pronucleus. 
Female pronucleus. 
Segmentation nucleus. 
Fig. 3.- A, fertilized ovum of echinus (Hertwig): the male and 
the female pronucleus are approaching; in B they have almost fused; 
C, ovum of echinus after completion of fertilization (Hertwig). 30 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
of this reduction has led to many theories. During 
the process the nucleus loses its membrane, is much 
reduced in size, and is now known as the female 
pronucleus. All these preliminary changes are 
known as maturation of the ovum. Without fer- 
tilization, further development of the ovum does not 
seem possible, in higher forms, and the cell is in- 
variably lost. 
Fertilization.-By this is meant the union of a 
spermatozoon with the ovum, or, more technically, 
the union of a male and a female pronucleus. This 
Fig. 4.- Diagram of the division of the frog's egg (Hertwig): 
A, stage of the first division. B, stage of the third division. The 
four segments of the second stage of division are beginning to be divi- 
ded by an equatorial furrow into eight segments; p, pigmented surface 
of the egg at the animal pole; pr, the part of the egg which is richer in 
protoplasm; d, the part which is richer in deutoplasm; sp, nuclear 
spindle. 
union takes place in the upper part of the oviduct. 
Maturation always precedes fertilization. If a 
spermatozoon enters the ovum before the polar 
bodies are extruded, the spermatozoon remains inert 
within the cell until maturation is completed. The 
ovum, thus reinforced, enters upon an aggressive 
growth, a phenomenon quite in contrast with its 
preceding history. DEVELOPMENT. 
Segmentation or Cleavage.-Following fertilization 
the ovum multiplies rapidly by mitosis. The union 
of male and female nuclei restores the reduced num- 
Fig. 5.- Cleavage in egg of frog, 1 to 16 cell stage. 
Fig. 6.- Blastula of triton tamiatus: fh, segmentation cavity; rz, mar- 
ginal zone; dz, cells with abundant yolk (Hcrtwig). 
ber of chromosomes, which remain constant and even 
in number for every succeeding division. By re- 32 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
peated divisions, a spherical mass of cells is produced, 
known as the morula stage. 
Blastula.-The spherical mass quickly develops 
into a hollow sphere, lined by a single layer of cells, 
and is then a blastula. The cavity of the blastula 
is the segmentation cavity. 
Gastrula.-A more vigorous growth seems to 
take place at one point of the blastula, producing 
lateral pressure and an invagination at that place 
so as to form a two-layered cup-like structure--in 
Fig. 7.- Blastula and gastrula of amphioxus. 
some eggs a blastoderm-known as the gastrula. The 
gastrulae vary considerably according to the different 
forms of cleavage. It is an established fact that all 
metazoa pass through the morula, blastula, and 
gastrula stages, respectively, in the course of their 
development. The cup-like cavity of the gastrula is 
known as the archenteron or coelenteron, and is 
destined to develop into the alimentary canal. The 
pore or external opening of the coelenteron is called 
the blastopore. 
The gastrula has two layers of cells: an outer, the ■ 
n: rlBrncnr.cn arfi )o noiiBinacn/•• . s atiungstU <£ - j 
.. , U1H no . d. •: r . 'r. (noarnorfT n-jIiA) ritn ■ PLATE I. 
i, 2, 3, Diagrams illustrating the segmentation of the mammalian 
ovum (Allen Thomson, after von Beneden). 4, Diagram illustrating 
the relation of the primary layers of the blastoderm, the segmentation- 
cavity of this stage corresponding with the archenteron of amphioxus 
(Bonnet). DEVELOPMENT. 
33 
ectoderm, and an inner, the entoderm. The cells of 
the entoderm are much larger than the cells of the 
ectoderm and there is thus a structural difference. 
In cleavage that results in a two-layered blastoderm 
the term hypoderm is used, which is thus morpho- 
logically equivalent to the entoderm. 
The two-layered gastrula is rapidly invaded by a 
third layer of cells, the mesoderm, which develops 
between the first two layers and ultimately fills that 
Fig. 8.- Sagittal section through an egg of triton (after the end of 
gastrulation): ak, outer germ-layer; ik, inner germ-layer; dz, yolk- 
cells; dl and vZ, dorsal and ventral lips of the coelenteron; ud, coelen- 
teron; d, vitelline plug; mk, middle germ-layer (Hertwig). 
cavity. This cavity, which is the segmentation 
cavity of the blastula, permanently disappears. 
The origin of the mesoderm has long been a con- 
tested question. The favored theory seems to be 
that for higher forms, at least, it develops from the 
hypoderm. 
The mesoderm, although at first a solid mass of cells, 
is an invaginated fold in which a cavity soon appears, 
having an inner layer of cells that affiliates closely 34 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
with the hypoderm cells, and an outer layer that ap- 
plies itself to the ectoderm. The hypoderm with 
its mesoderm layer is known as the splanchno pleurc, 
while the ectoderm and its mesoderm is the so- 
Fig. 9.- Transverse section of chick embryo 22 hours old 
matopleure. The new cavity thus produced is the 
coelom, or body cavity, and is destined to become the 
pleural and peritoneal cavities. The mesoderm on 
Fig. io.- Transverse section of a sheep embryo, 17 | days (Bonnet) 
each side of the neural canal becomes symmetrically 
blocked by means of a longitudinal fold and many 
transverse folds; thus many segments or joints are DEVELOPMENT. 
35 
produced, known as myotomes or mesoblastic somites. 
From these develop bone, voluntary muscle, and the 
dermis of the skin. 
While these progressive changes are going on in the 
mesoderm, a longitudinal dorsal groove develops in 
the ectoderm. By a median fusion of the margins of 
the groove, it is transformed into a longitudinal canal, 
the neural canal, which develops into the brain and 
spinal cord. 
Fig. ii.-Rabbit embryo of the ninth day, seen from the dorsal 
side (after Kolliker). The stem-zone (sfe) and the parietal zone (pz') 
are to be distinguished. In the former 8 pairs of primitive segments 
have been established at the side of the chorda and neutral tube; ap, 
area pellucida; rf, medullary groove; vh, fore-brain; ab, eye-vesicle; 
mh, mid-brain; hh, hind-brain; uw, primitive segment; stz, stem-zone; 
pz, parietal zone; h, heart; ph, pericardial part of the body cavity; vd, 
margin of the entrance to the head-gut (yordere Darmpjorte), seen 
through the overlying structures ; af, amniotic fold ; vo, vena ompha- 
lomesenterica. 
This brief embryonic growth has been productive 
in specialization and differentiation of cells. In no 
case will the cells of one germ layer reproduce, re- 
place, or function for the cells of any of the other 
layers. As derivatives of these three germ layers we 36 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
are able to give the following table (Minot, "Em- 
bryology," 1903): 
A. Ectoderm. 
i. Epidermis. 
(<z) epidermal appen- 
dages. 
(5) lens of eye. 
2. Epithelium of 
(a) cornea. 
(5) olfactory cham- 
ber. 
(c) auditory organ. 
(d) mouth 
(oral glands), 
(enamel organ), 
(hypophysis). 
(<?) anus. 
(y) chorion 
(fetal placenta). 
(g) amnion. 
3. Nervous system. 
(a) brain 
(optic nerve), 
(retina). 
(5) spinal cord. 
(c) ganglia. 
(d) neuraxons. 
B. Mesoderm. 
i. Mesothelium. 
(a) epithelium of per- 
itoneum, pericar- 
dium, pleura, uro- 
genital organs. 
(5) striated muscles. 
2. Mesenchyma. 
(a) connective tissue, 
smooth muscle, 
pseudo - endothe- 
lium, fat-cells, 
pigment cells. 
(5) blood. 
(c) blood-vessels. 
(d) lymphatics. 
(f) spleen 
(/) supporting tis- 
sues, cartilage, 
bone. 
(g) marrow. 
C. Entoderm. 
i. Notochord. 
2. Epithelium of 
(a) digestive tract, 
esophagus, stom- 
ach, liver, pan- 
creas, small intes- 
tine, yolk-sack, 
large intestine, 
cecum, vermix, 
rectum, allantois 
(bladder). 
(5) pharynx, Eusta- 
chian tube, ton- 
sils, thy m us, para- 
thyroids, thyroid. 
(c) respiratory tract, 
larynx, trachea, 
lungs. 
Fig. 12.- Diagram of a typical cell. 
THE CELL. 
The cell is a limited mass of protoplasm which, 
under certain conditions, is capable of assimilation, 
growth, and reproduction. Histologically the cell DEVELOPMENT. 
37 
is a nucleated mass of protoplasm. In some cells, as 
bacteria, no nucleus has been found. The nucleus, 
as a rule, is constantly present in animal tissue, and 
forms an essential part of the cell. Whenever it is 
lost or destroyed, the cell dies. 
Protoplasm is a viscid, transparent jelly-like sub- 
stance. Wherever we find protoplasm we find life, 
and wherever we find life we find protoplasm. 
Every particle of protoplasm has its origin in some 
antecedent protoplasm, and so on, in an unbroken 
scries, all life is traced back to the earliest primitive 
form of protoplasm. As to the structure of proto- 
plasm there are three theories: 
i. That it is a fluid homogeneous substance. 
2. That it consists of minute spherical globules, 
like an emulsion. 
3. That it is a mass of interlacing fibrils, forming a 
complex reticulum. 
In many cells the protoplasm, at or near the sur- 
face, is quite dense, forming what is then called the 
ectosarc. The more vicsid central portion is the 
endosarc. 
The constituents of a typical cell and cell contents 
are: 
1. Cytoplasm, the protoplasm that surrounds the 
nucleus, consisting of,- 
(a) Spongioplasm, a reticulum or fibrillar network; 
(&) Hyaloplasm, a fluid portion, also called cy- 
tolymph; 
(c) Cell membrane, often absent in animal cells. 
2. Nucleoplasm or karyoplasm, the protoplasm of 
the nucleus,- 38 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
(a) Nuclear membrane, frequently absent; 
(5) Chromatin, network that stains easily; 
(c) kinin, closely applied to the chromatin, does 
not stain; dissolves in distilled water; 
(d) Nuclear sap, a fluid perhaps analogous to the 
hyaloplasm; 
(e) Nucleolus, spherical body that stains heavily; 
Fig. 13.-Mitotic division of cells in testis of salaman'der (Benda and 
Guenther). 
(/) Nuclear net knots, or karyosomes, false nuclei 
that are nodal points formed by interlacing chro- 
matin network; 
(g) Nuclear membrane, amphipyrennin; 
(A) Centrosome, a small spherical body often found 
in the cytoplasm near the nucleus. It is looked upon 
as the dynamic center in cell division. DEVELOPMENT. 
39 
3. Cell Inclusions.-These are foreign bodies en- 
closed in the cytoplasm, such as vacuoles, pigment, 
fat or oil, crystals, starch, and chlorophyl. The 
last two are found almost exclusively in plant cells. 
Mitosis or Karyokinesis.-Mitosis is indirect cell 
division, and refers to the changes manifest in the 
nucleus during such division. The process may be 
divided into four phases- 
i. Prophase. The first manifestation of mitosis 
appears in the centrosome. This little body is, 
therefore, looked upon as the dynamic center of the 
cell. The centrosome divides and each half passes 
to opposite poles of the nucleus. The chromatin 
network, which really consists of chromatin granules, 
is transformed into a skein of threads known as a 
spirem or mother skein. These threads break up into 
a definite number of segments known as chromo- 
somes. The chromosomes are even in number, and, 
for a given species, a constant number is always 
present. In the human cell there are sixteen chro- 
mosomes,-according to some, twenty-four. To- 
ward the close of this stage, each chromosome 
forms a loop and is finally arranged symmetrically 
around the equator of the nucleus, with the free ends 
of each loop turned away from the center. This 
symmetrical figure is known as monaster. During 
this stage the nuclear membrane usually disappears. 
The nucleolus also vanishes, just how is not clear. 
The net knots disappear with the formation of 
chromatin loops. 
During these changes the achromatic substance- 
linin and nuclear sap-has formed a central spindle 40 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
with each apex directed toward a centrosome. This 
spindle consists of fine threads or lines directed 
toward the centrosomes. A like radiation becomes 
manifest in the cytoplasm, each line being directed 
toward, or from, one or the other centrosome. This 
radiation is absent from the protoplasm immediately 
surrounding each centrosome, forming a clear field 
called the attraction sphere. The lines that extend 
Fig. 14.- Diagram of mitosis. 
into the cytoplasm are known as polar rays. Those 
that form the spindle seem to be attached to the 
curved portions of the chromatin loops. 
2. Metaphase.-This stage begins with the chro- 
matin loops arranged radially in the equatorial plane 
of the nucleus. The most important change in 
mitosis now takes place, in that each chromosome DEVELOPMENT. 
41 
loop divides lengthwise to form two daughter chromo- 
somes. This is an equal division, both qualitative 
and quantitative. The curved portion of each 
daughter loop passes along the rays of the achro- 
matic spindle and approaches one or the other cen- 
trosome. There are three theories as to the mech- 
anism involved: 
(i) It is affirmed that the threads of the spindle 
contract and pull each daughter loop toward its 
centrosome. 
(2) The rays may elongate and push each loop to- 
ward the opposite centrosome. According to this 
theory there should be twice as many lines or rays 
between the loops as there are spindle rays from each 
centrosome, an observation recorded by some in- 
vestigators. 
(3) The centrosomes may be fermenting centers 
of chemical change, and the explanation, therefore, 
a chemical one. 
At the close of the metaphase the daughter loops 
arrange themselves respectively around each cen- 
trosome forming what is known as a diaster or 
daughter star. The free ends of these are turned 
away, and the curved portions of each are turned 
toward the centrosome. 
3. Anaphase.-During this period the changes 
manifest in the prophase are reversed. The chro- 
matin loops are gradually transformed into twisted 
skeins of threads, called daughter skeins, which 
ultimately produce the normal chromatin reticulum. 
The nuclear membrane and nucleolus reappear. A 
constriction of the cytoplasm is manifest for the first 42 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
time. This constriction appears in the plain passing 
between the daughter nuclei. 
4. Telophase.-In this stage the cell divides com- 
pletely. Each daughter cell gradually assumes the 
normal condition of the parent cell from which it had 
its origin. The time required for complete division 
varies from one to several hours. 
Amitosis is the direct cell division and occurs sel- 
dom as a normal process. The nucleus merely con- 
stricts producing two or more fragments. In this 
way polynucleated cells are formed, such as white 
blood corpuscles, giant cells, and surface epithelial 
cells of the bladder. 
Laws of Cell Cleavage.- (1) The cleavage plane is 
always equatorial to the nucleus. 
(2) The position of the nucleus depends on (a) the 
shape of the cell, and (b) on the distribution of food 
material or secretions. If the cytoplasm is eccentric 
in the cell, the nucleus is associated with it. 
(3) When each plane of division is parallel to the 
preceding plane, a filament is produced. This is the 
law in some plants, as spirogyra, nostoc, etc. 
(4) When each plane is at right angle to the pre- 
ceding plane and in two dimensions, a surface of cells 
is formed, as simple epithelium. 
(5) When each plane is at right angle to the pre- 
ceding plane and in three dimensions, a volume or 
an organ is formed with three dimensions, as the 
morula stage in embryos. 
General Considerations.-The subject of cell divi- 
sion has given rise to much discussion. While we 
are unable to control mitosis, the following are 
factors that modify cell growth: DEVELOPMENT. 
43 
i. Trauma.-Following a cut or a bruise the ad- 
jacent cells are stimulated to rapid multiplication 
and the wound heals. 
2. Heat.-There is a mean temperature for the 
maximum multiplication of cells which varies with 
the species. In man this mean temperature is blood 
heat, 98.6°. 
3. Electricity.-By stimulating protoplasmic ac- 
tivity, electricity no doubt is a factor in influencing 
normal cell growth. Just how this is accomplished, 
and to what extent, is a much-disputed problem. 
4. Light.-A very important factor in promoting 
multiplication, or decreasing it, or even destroying 
certain cells, as bacteria. The different rays of 
light have each a specific effect. 
5. Nourishment.-Proper food is a stimulant. 
6. Chemical.-Certain salt solutions, as sodium 
and potassium salts, have a stimulating effect. 
7. Exercise.-Regular systematic exercise prompts 
a healthy growth. Massage acts in the same way. 
Pathological tumors are abnormal growths of nor- 
mal tissues. In many of these tumors the cells 
multiply rapidly by mitosis, resulting often in un- 
equal division of the chromosomes, or chromatin 
loops, but whether this is a cause or a consequence 
can be argued with equal force. We are unable to 
produce these tumors experimentally, and, unfor- 
tunately, we are often unable to stop their mul- 
tiplication of cells. 
The surface of a sphere increases as the square of 
its diameter, while the volume increases as the cube 
of the diameter. As the cells depend upon their 44 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
surface area for the absorption of food and elimination 
of waste, and as the volume increases at a greater 
rate than the surface area, the reduction in size of a 
cell becomes a necessity. 
Much significance is attached to the fact that 
mitosis brings about an equal division of the chro- 
matin or chromosomes. If for any reason an un- 
equal division obtains, the cell becomes abnormal 
and a monstrosity, with death, follows. Experi- 
mentally this may be done with an egg cell, which, if 
anesthetized, allows more than one spermatozoon to 
enter, resulting in an unequal division of the female 
pronucleus and an abnormal development. That 
chromatin is the bearer of hereditary qualities is a 
postulate based upon the observation that mitosis 
results in an equal division of the chromosomes. 
What these unrevealed biological units are, is a 
matter of much controversy. CHAPTER II. 
TISSUES. 
A tissue is defined on page 27. There are four 
kinds of tissues,-(1) Epithelial tissue; (2) Support- 
ing tissue; (3) Muscular tissue; (4) Nerve tissue. 
I. EPITHELIAL TISSUE. 
Epithelium lines surfaces, external or internal, 
and forms the secreting 
cells of glands (see table, 
page 36). The cells have 
a regular form, usually a 
cell wall, a distinct nu- 
cleus that is rich in chro- 
matin and therefore 
stains easily, with hema- 
toxylin, and generally 
form distinct layers, ex- 
cept in glands. Blood 
and lymph vessels are 
absent from these layers, 
but nerve fibers enter the deeper strata. 
Epithelial tissue is classified as: (1) simple or 
(2) stratified. 
1. Simple epithelium, consisting of a single layer 
of cells. 
(a) Simple squamous, flat single layer of cells, 
Fig. 15.--Epithelium cells from 
skin of frog. 
45 46 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
found in the alveoli of the lung and in Bowman's 
capsule of the kidney. 
(5) Simple cuboidal, found forming the wall of 
most ducts, as the bile duct, pancreatic duct, portions 
of kidney tubules, and ducts of salivary glands. 
(c) Simple columnar, ciliated or non-ciliated. 
Fig. 16.- Squamous epithelial cells from the mouth. 
This is the most common form of simple epithelium. 
The alimentary canal, below the diaphragm, has 
simple columnar; also portions of the kidney tubules. 
Fig. 17.- Simple columnar cells from intestine. 
Simple ciliated is found in the oviduct, uterus, cen- 
tral canal of the spinal cord, and smaller bronchi. 
(d) Pseudo-stratified.-In this type all the cells 
rest on a common basement membrane, but the 
nuclei rest at different levels, which give the tissue 
the appearance of being stratified. Frequently TISSUES. 
47 
this tissue is ciliated, as is the case in portions of the 
respiratory tract. 
2. Stratified epithelium, consisting of several 
layers of epithelial cells. 
Fig. 18.- Ciliated epithelium from trachea. 
(a) Transitional, consisting of two or three layers 
of cells, found in the wall of the bladder, ureters, 
pelvis of kidney, and prostate portion of male 
urethra. In this case the surface layers of cells are 
Fig. 19.- Epithelial cells from the bladder. 
flat, often polynucleated and form a mosaic pattern 
upon the second layer, which is pear-shaped, with 
the broad ends forming depressions into the first 
layer of cells. The third layer consists of smaller, 48 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
irregular, interstitial cells that fill the spaces between 
the spaces of the pointed ends of the second row. 
(6) Stratified Squamous -In this case the super- 
ficial layers are flat and the deeper ones cuboidal 
Fig. 20.- Section of bladder epithelium 
or columnar. This is the most extensive of the 
epithelial tissues. It forms the epidermis of the 
Fig. 2i.- Section of epidermis of skin from palm-surface of finger. 
skin, the walls of the oral cavity and the esophagus, 
the epithelium of the conjunctiva, external auditory 
canal, vagina, and the external sheath of hair 
follicles. TISSUES. 
49 
(c) Stratified columnar, ciliated or non-ciliated. 
This is found in the olfactory mucous membrane, the 
first part of many gland ducts, palpebral conjunc- 
tiva, portions of the male urethra, vas deferens, and 
portions of the larynx. 
General Considerations.-The epithelial cells are 
simpler and more embryonic than the cells of the 
other tissues. They are continually multiplying 
throughout life, to re- 
place the superficial 
layers that are con- 
stantly exfoliating 
from the surfaces. If 
any of these surfaces 
are injured, the cells 
marginal to the injury 
repair the loss by a 
gradual growth cover- 
ing the denuded sur- 
face. As a consequence 
of this mitotic activity, 
we find these cells fre- 
quently in pathological growths as epithelial growths 
or epithelioma. If the tumor is malignant it is a 
carcinoma or cancer. It is a remarkable fact that, in 
the adult, epithelium is able to produce cells only 
of its own kind,-i. e., squamous cells produce 
squamous epithelioma, and columnar cells columnar 
epithelioma. Epithelial tissue, however, is easily 
modified, as is evidenced by calloused hands, pro- 
duced by heavy labor, and the cornification of nails, 
Hair linrtK and fppfh 
Fig. 22.-Section of stratified epithe- 
lium from esophagus. 50 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
Since the blood supply never penetrates epithelial 
layers, it is evident that the superficial layers of cells 
receive less nourishment, and this, perhaps, ac- 
counts for the constant exfoliation. It is also evi- 
dent that anything that will increase the blood 
supply will increase the nourishment, as friction, 
massage, and hot applications. The nourishment, 
at best, is not very good, which explains the ease 
Fig. 23.- Section showing corneal epithelium of the eye, 
with which skin grafts are made. Epithelial cells 
will live for twenty-four hours or more in normal 
salt solutions, and will even multiply in favorable 
culture media. 
The nerve termination among the epithelial cells is 
an important relation which, in large part, controls 
their metabolism. A disturbed nervous system may 
impair or even cause a destruction of epithelial cells. TISSUES. 
51 
Cilia are exclusively confined to epithelial cells. 
There are three theories to account for the motion 
of cilia: 
i. The contraction may be intrinsic in the wall of 
the cilium. This theory is supported by the fact 
that the cilium or flagellum of a spermatozoon will 
show motility when severed from the rest of the cell. 
2. Contraction of the base where the cilia are 
attached. The cilia will continue to vibrate if a 
fragment of the cell protoplasm remains attached to 
them. 
3. The cilia are supposed to be hollow tubes with 
walls of unequal elasticity. By forcing the proto- 
plasm rapidly into these tubes ciliary motion is 
produced. Pseudopodia are produced in this man- 
ner, and the morphological relation of pseudopodia 
and cilia is a close one. 
The one great physiological action of epithelium 
seems to be to secrete fluids. Consequently epithe- 
lium is found lining all cysts wherever the cyst is 
located,-in the ovary, the skin, or in connection 
with the alimentary tract. Conversely, a cyst may 
be formed wherever epithelium is found. 
Lastly, it is of the greatest importance that stu- 
dents should be able to recognize epithelial cells. 
The diagnostic points of this recognition are: 
1. The oval or round distinct nucleus, usually 
rich in chromatin. 
2. The regularity of the cells,-i. e., the cells of 
one class are alike, either squamous, or columnar, or 
ciliated. 
3. They appear in compact layers or strata, not 52 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
loosely thrown together, and blood- and lymph- 
vessels are absent. 
Glands.-A gland is an organ, situated beneath the 
surface of the body, whose epithelial cells produce a 
fluid that is not directly used in the metabolism of the 
body. If the fluid is a waste the product is an ex- 
cretion; if it has a utility it is a secretion. Certain 
epithelial cells, known as goblet cells, are very 
numerous in the simple epithelium forming the 
lining of the stomach and intestine, particularly so 
in the lower part of the 
bowel. These cells func- 
tion as glands and secrete 
mucus for the protection 
of the surface. In case 
of irritating media, such 
as undigested food or 
poisons, extensive mucus 
is poured out over the sur- 
face, thus protecting''the 
delicate inner lining. In 
some cases of constipation this mucus secretion is 
impaired. Salts or drugs that increase the func- 
tional activity of these cells correct such complica- 
tion. On the other hand, too extensive a secretion 
may be corrected by drugs, as opiates that inhibit 
the physiological action of these cells. Constipation 
may be due to inertness of the musculature of the 
intestinal wall, in which case other remedies correct- 
ing this disturbance are indicated,-massage, hydro- 
therapy, and drugs that act on the musculature. 
Physiologically, gland cells are either mucous or 
Fig. 24.- Skin and simple alveolar 
glands from the salamander. TISSUES. 
53 
serous. In mucous cells the mucus secretion collects 
at one extremity of the cell as a clear glistening drop. 
The cytoplasm and nucleus are crowded to the op- 
posite end. In serous cells the nucleus is more 
centrally placed and the serous secretion is stored 
up as minute granules distributed throughout the 
Fig. 25.- Simple tubular gland from stomach 
cytoplasm, more especially in that portion of the cell 
lining the free surface. Some glands are mucous, 
some are serous, and some are mixed. . 
Mucous Membrane.-A mucous membrane con- 
sists of a lining of epithelial cells, basement mem- 
brane, and membrane propria. The basement mem- 
brane is largely an clastic cellular secretion on which 54 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
the epithelial cells rest, although at times flattened 
connective-tissue cells seem to enter into its forma- 
tion. The membrana propria is a connective-tissue 
production consisting of connective-tissue cells, 
fibers, and blood- and lymph-vessels. Mucous mem- 
Fig. 26.- Cells from different glands : a, Pancreas; b, submaxillary 
gland; c, liver. 
branes line cavities or tubes that communicate with 
the surface of the body, such as the alimentary canal, 
respiratory tract, and urogenital system. 
Serous Membrane.-A serous 
membrane has the same histo- 
logical elements as the mucous 
membrane. The epithelial lining 
is simple squamous, and these 
cells secrete a serous fluid, more 
viscid and more of a lubricant 
than mucus. Serous membranes 
enclose cavities that do not com- 
municate with the surface of the 
body, as the pleural, pericardial, and peritoneal 
pavities and cavities of joints, forming in the latter 
case synovial membranes. Sheaths or bursae of 
tendons have serous membranes. 
Fig. 27.- Goblet or 
mucous cells from intes- 
tine. TISSUES. 
55 
As to form, glands are classified as-■ 
i. Simple. 
(a) Simple tubular-gastric glands, sweat 
glands, and uterine glands. 
Fig. 28.- Diagram of different forms of glands. 
(6) Simple alveolar-smallest sebaceous 
glands, and skin glands in amphib- 
ians. 
2. Compound. 
(a) Compound tubular-kidney, prostate, 
liver, testis. 56 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
(&) Compound alveolar or racemose-sali- 
vary glands, mammary gland, lung, 
pancreas, sebaceous glands. 
A dehisent gland is one whose cells pass away 
with the secretions, as is the case with the ovary and 
testis. A follicular gland is one that is made up of 
follicles, such as the thyroid gland. The thyroid, 
thymus, and spleen are usually spoken of as "duct- 
less glands." The thymus and spleen are lymphoid 
organs, not secreting in function, and therefore along 
with lymph nodes should not 
be classified as glands. Their 
classification will be further 
discussed when the histology 
of these organs is described. 
Endothelium.-This term 
is growing obsolete. The 
cells lining closed cavities 
used to be so designated, 
such as peritoneal and pleural 
cavities, circulatory systems, 
and cavities of joints. These 
cells, however, are epithelial 
cells and the membranes they 
form are serous. The word "epithelium" conveys 
the idea of cells of a definite form, pattern, and 
structure. The word "endothelium" conveys no 
idea as to structure. 
Peritoneum and Pleura.-These are true serous 
membranes, the structure of which is described on 
page 54. Elastic fibers are particularly abundant 
in the membrana propria, giving strength to both 
Fig. 29.- Epithelium or 
endothelium from mesentery. 
Silver nitrate stain. TISSUES. 
57 
peritoneum and pleura, so that these membranes are 
readily sewed in surgical cases. Physiologically 
these membranes are of the greatest importance: 
i. It is claimed that the simple pavement epithe- 
lial cells of the peritoneum can produce a secre- 
tion that clots, and in this manner adhesions are 
quickly formed. This is of the greatest importance 
in preventing the spreading of an infection, as in 
peritonitis. 
2. These cells act as phagocytes and feed upon 
bacteria in case of an infection. According to one 
view they can destroy living bacteria. A second 
theory is that they act as scavengers and remove 
only dead bacteria. 
Stomata and stigmata have been frequently de- 
scribed as minute openings in these membranes to 
facilitate the absorption of fluids. Stomata are 
said to have guard cells to regulate the size of the 
opening, and were supposed to be specially abundant 
in the peritoneal lining of the diaphragm. The exist- 
ence of stomata has lately been strenuously denied. 
The rapid absorption of peritoneal fluid is a well- 
established fact. If stomata are absent the ab- 
sorption is purely one of osmosis or dialysis. It 
should be remembered that drainage is along 
lymphatic channels and therefore from the pelvis 
toward the thorax. 
IT. SUPPORTING TISSUE. 
The supporting tissue consists, in large part, of cell 
products whose main function is to give support. 
It is divided into three classes: connective tissue, 58 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
cartilage, and bone. Macroscopically these classes 
differ greatly, because of differences in the inter- 
cellular substances found in each, but the cellular 
substances show a remarkable similarity. Nerve 
fibers make no connection with these cells. The 
cells, therefore, have an independent existence, 
quite unlike epithelial cells, muscle and nerve cells 
that always retain a mutual connection with each 
other, forming a complex called a syncytium. The 
supporting tissue cells are, therefore, peculiarly in a 
Fig. 30.-Connective-tissue cells from 
a chick embryo. 
Fig. 31.-Connective-tissue 
cells from Wharton's jelly of 
the umbilical cord. 
class by themselves, many of them being roving or 
wandering cells. 
1. Connective Tissue. 
The elements of this tissue consist of cells and cell 
products, in the form of connective-tissue fibers, 
which penetrate and give consistency and support to 
every organ in the body. 
i. Connective-tissue Cells. 
(a) Embryonic Connective-tissue Cells.-These are 
flat, stellate cells found in embryos and in the um- 
bilical cord. Those of the cord, with the matrix in TISSUES. 
59 
which they are imbedded, form a soft, pulpy mass 
known as Wharton's jelly, or mucous tissue. These 
cells are loosely associated in no definite order, their 
stellate processes interlace and sometimes appear 
to come in direct contact. Their nuclei are round, 
or oval, or elongated, forming what is known as the 
spindle-shaped and pointed nucleus, often resem- 
bling the cigar-shaped and rounded nucleus of a plain 
muscle cell. The nuclei are rich in chromatin, and 
therefore stain heavily with hematoxylin. Blood- 
and lymph-vessels mingle freely with these cells; in 
Fig. 32.-Two pigment cells from the dermis of a salamander. The 
pigment is in the cytoplasm. 
fact, this association is constant. The so-called 
granulation tissue in healing wounds consists of em- 
bryonic connect!ve-tissue cells, always bleeds easily, 
because of its vascularity, and painless because of 
absence of nerve endings. 
(b) Pigment Cells.-These are connective-tissue 
cells in which pigment is stored in the cytoplasm, 
never in the nucleus. The cells are extensively 
branched, large and flat. In amphibians and rep- 
tiles they are abundant in the dermis of the skin, and 
enable the animal to change its color, as is the case 
with the tree toad and the chameleon. In the human 60 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
body connective-tissue pigment cells are limited to 
the choroid coat and iris of the eye, to birth-moles, 
and to the piamater of the brain. The pigment 
may be of any color, the constituent being melanin, 
a coloring material probably derived from the blood. 
(c) Fat Cells.-These are 
connective-tissue cells with 
a large storage of fat. The 
fat occupies the center of 
the cell as a big drop which 
crowds the cytoplasm and 
nucleus to one side, closely 
pressed against the cell 
wall, which is unusually 
conspicuous. The cells 
are large and spherical. Since fat is dissolved by 
alcohol, these cells in sections are distorted, polyhe- 
dral, and appear more like irregular spaces than any- 
thing else. Normal fat is 
not to be confounded with 
pathological fat found in 
fatty degeneration of 
organs. In the latter case 
the fat appears as little 
droplets diffused through 
the cytoplasm of the dis- 
eased cells, and is pro- 
duced at the expense of protoplasm, a destructive 
process or katabolism. Normal fat is a constructive 
process or anabolism, and is therefore a storage of food 
or potential energy. Its production, physiologically, 
is not clearly understood. It may be produced from 
Fig. 34.-Normal fat cell. 
Fig. 33.-Pigment cells from 
the choroid coat of the eye. 
These cells are of connective- 
tissue origin. 61 
TISSUES. 
a proteid diet, but its production is more easily 
prompted by a fatty diet and the carbohydrates. 
Cold prompts its production, as is clearly manifest 
in hibernating animals when the cold season ap- 
proaches, and the increased weight of animals, as a 
rule, during the winter season. 
Fig. 35--Fat cells as they appear in sections treated with alcohol. 
Alcohol dissolves the fat. 
The usual stain for fat is osmic acid, in which fat 
acts as a reducing agent, precipitating black osmium. 
Any reducing agent will do this, as is made evident 
by the black color of the cork in a bottle containing 
osmic acid solution, fat being absent from cork. 
Other connective-tissue cells, as Plasma cells, Wan- 
dering cells, and Mast cells, are frequently described. 
These resemble normal constituents of blood and 
lymph to which they may belong. 
2. Connective-tissue Products. - These products 
may be a jelly-like substance or fibers. Connective- 
tissue cells are always associated with these products. 
There are two theories as to the production of fibers. 
(a) The fibers may be processes of the cytoplasm 
that lose their cell connection. 62 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
(b) The connective-tissue cells may secrete a 
homogeneous matrix, which later becomes striated, 
producing fibers in a manner as fibrin is formed in 
clotting blood. 
Connective tissue is classified 
according to its matrix into: 
i. Mucous Connective Tissue. 
-This consists largely of embry- 
onic connective-tissue cells and 
a jelly-like matrix or ground sub- 
stance which gives a reaction for 
mucus. It is found in the um- 
bilical cord and in embryonic 
tissue. 
2. Reticular Connective Tissue.-This is a reticulum 
of interlacing fibrils and is found in adenoid tissue, 
lymph nodes, spleen, and membrana propria of 
Fig. 36. - Reticular 
tissue from a lymph 
gland. 
Fig. 37.-Teased tendon, showing 
fine wavy white fibers. 
Fig. 38.--Cross section of tendon. 
mucous membranes. Also, to a limited extent, in 
bone marrow. 
3. White Fibrous Connective Tissue.-This consists 
largely of white nonelastic fibers. The fibers are TISSUES. 
63 
parallel to each other, not branched, and yield gela- 
tin on boiling. The fibers swell up when treated with 
acetic acid. They are 
found in tendons, the apo- 
neuroses, and ligaments, 
the fascia of muscles, the 
dura mater, and the fibrous 
capsules of many organs. 
4. Yellow Fibrous Con- 
nective Tissue.-The matrix 
in this consists of elastic 
fibers that are branched, 
and usually coarser than 
the white nonelastic fibers. They do not swell up 
when treated with acetic acid and yield elastin on 
Fig. 39.-Longitudinal section 
of tendon. 
Fig. 40.-a, Yellow elastic fibers from the teased ligamentum 
nuchae of the ox; b, Cross section of a portion of the ligamentum nu- 
chae of the ox. The elastic fibers are grouped in bundles with a few 
intervening connective-tissue cells. 
boiling. Like the preceding, the fibers are fre- 
quently grouped into bundles with a limited supply 
of blood-vessels and connective-tissue cells. This 64 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
tissue is found wherever elasticity is required, as in 
the ligamentum nuchae and subflava, in the walls 
of arteries, and in the membrana propria of the 
peritoneum and pleura. 
5. Areolar Connective Tissue.-This is really a mix- 
ture of interlacing bundles of white and yellow 
elastic fibers. It is found subcutaneously to the 
skin, to which it imparts elasticity. Areolar tissue 
is vascular and favors, therefore, a rapid spread of 
bacteria. Over bony prominences there is a limited 
supply of areolar tissue and the skin at these places 
has restricted mobility. It 
is at these points that the 
spread of an infection, such 
as erysipelas, is checked. 
General Considerations. 
-On account of the embry- 
onic condition of connec- 
tive-tissue cells these, like 
epithelial cells, are fre- 
quently met with in patho- 
logical tumors. If the tumor is malignant it is 
called a sarcoma, and is as fatal to life as carcinoma, 
or cancer. If the tumor is made up largely of fat 
cells, it is called a lipoma, and if the fibrous elements 
predominate it is a fibroma. 
The production of connective tissue is often 
nature's method of checking the spread of a disease. 
This tissue is produced as a wall in advance of a 
spreading infection, and if the bacteria are unable to 
penetrate this barrier, the disease soon becomes self- 
limiting. This accounts for the swollen infected 
Fig. 41.-Elastic fibers of the 
mesentery. 65 
TISSUES. 
parts, and also for the redness which is due to the 
extensive blood supply which is always associated 
with this tissue. Such a swollen tumor is called 
an induration or congestion. In this manner a whole 
or a part of an organ may be affected. The con- 
nective-tissue fibers are absorbed with difficulty or 
not at all, and a permanent mark or scar remains 
as an evidence of the injury. In a healing wound, 
particularly if infected, these fibers are abundantly 
produced, and its redness is evidence of its extensive 
vascularity or blood supply. Later, these fibers 
contract, which occludes the blood, and then the 
color changes from a red to a white scar that no 
medical treatment can remove. 
Pigmentation is a most important subject. Pig- 
ment appears, as a rule, in the cytoplasm of cells, 
seldom between the cells. It is not confined to con- 
nective-tissue cells, but is common to epithelial cells, 
as the deep layer of the epidermis giving the color of 
races; is found in the retina cells, where it is always 
black, and in hair and nails. It appears in the cyto- 
plasm of muscle cells, particularly in old heart 
muscle,where it is found near the ends of the nuclei, 
and is nearly always present in nerve cells, giving a 
gray color to this tissue. Pigmentation is an ac- 
companiment of many diseases, particularly skin 
diseases. It is also produced under the influence of 
light, as freckles, that can only be removed by the 
normal exfoliation of the epithelium. 
The production of pigment seems to depend upon 
the blood. As blood is absent from epithelium there 
are two theories as to the manner in which the cells 66 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
obtain it: (a) they may receive it directly from the 
blood, or (6) connective-tissue cells may elaborate 
it and deliver it secondarily to the epithelial cells. 
That the pigment is not intrinsic to epithelial cells is 
proved by the fact that colored skin grafted on a 
white man soon turns white, and white skin grafted 
on a colored person turns black. The fruitless at- 
tempts to change one's color are well known. 
A melanotic sarcoma is a pigmented connective- 
tissue tumor, very malignant, whose cells disseminate 
very rapidly throughout the body, producing every- 
where new tumors. These cells have their origin 
from normal pigmented connective-tissue cells, and 
therefore are supposed to come from birth-marks, or 
the choroid of the eye, or the piamater of the brain. 
The etiology of such tumors is unknown. Fortu- 
nately they are rare. 
The diagnostic points by which connective-tissue 
cells are known are: i. The easily stained round, 
or oval, or spindle-shaped nucleus. 2. The cells are 
loosely thrown together, not in compact layers or 
strata. 3. The stellate cells, although the proc- 
esses are often inconspicuous and not readily de- 
tected. 4. The tissue is vascular where cells are 
abundant. 
2. Cartilage. 
Cartilage is supporting tissue in which the inter- 
cellular substance predominates and yields chondrin 
upon boiling. The cartilage cells are typical con- 
nective-tissue cells, and occupy lenticular spaces in 
the matrix called lacunce. Cartilage is surrounded 
by a dense connective-tissue membrane called the TISSUES. 
67 
perichondrium, in which smaller blood-vessels ramify. 
Blood- and lymph-vessels are absent from the car- 
tilage matrix. According to the structure of the 
matrix, cartilage is classified as,- 
Fig. 42.-Section of hyaline cartilage from the trachea. 
1. Hyaline Cartilage.-This is the simplest and 
most common form of cartilage. The matrix appears 
Fig. 43.-Two groups of cells from hyaline cartilage: A, Two 
cells found just beneath the perichondrium; B, Four cells found deeper 
in the cartilage matrix. 
to be a homogeneous substance, although many fine 
interlacing fibrils are present. The lacunae near the 
perichondrium have their long axis parallel to the 68 
NORMAL, HISTOLOGY AND ORGANOGRAPHY. 
surface, while deeper in the matrix the long axis is 
often at right angles to the surface. Each lacuna 
nonfainc ono or tnoro nnrtilaoro cells. T11C Cartilage 
surrounding lacunae 
usually stains differ- 
ently from the bal- 
ance of the matrix. 
This cartilage oc- 
curs as articular carti- 
lage of joints, at the 
end of ribs, and in the 
nose, the larynx, the 
trachea, and bronchi. 
2. Elastic Carti- 
lage.-Elastic cartilage differs from the hyaline vari- 
ety in having typical interlacing, branched elastic 
fibers that form a dense network. This cartilage is 
found wherever elas- 
ticity is required, as in 
the external ear, the 
Eustachian tube, epi- 
glottis, part of ary- 
tenoid cartilages, and 
cartilages of Wirsung 
and Santorini. 
3. White Fibrous 
Cartilage.-In this va- 
riety the white fibers 
predominate. As a rule these fibers run parallel in 
bundles and do not branch. A granular matrix 
intervenes between the fibers. Fibrous cartilage 
is found in the intervertebral disc, in the sym- 
Fig. 44.- Section of elastic cartilage 
from epiglottis. 
Fig. 45.- Section of white fibrocarti- 
lage from symphysis pubis. TISSUES. 
69 
physis pubis, and in the insertion of the round 
ligament. 
General Considerations.-Cartilage tumors are 
known as chondroma, and are common. Like 
cartilage they are of slow growth and therefore 
harmless. The absence of blood accounts, in large 
part for the inactivity of the cartilage cells, both in 
the normal and pathological condition. Further- 
more, cartilage cells are enclosed in the matrix in a 
manner that inhibit their multiplication. Cartilage 
therefore grows by apposition or acquisition, not by 
intussusception, like most tissues. 
Cartilage slowly ossifies with age. During this 
process loops of blood-vessels enter the matrix from 
the perichondrium, and lime salts are deposited ad- 
jacent to the cartilage cells. This process will be 
further described under bone development. 
The identification of cartilage is very easy, as the 
matrix has a marked affinity for many stains. 
3. BONE. 
Bone is the chief supporting tissue of the body, 
and consists of a calcified intercellular substance, 
mostly calcium phosphate, and connective-tissue 
cells, or bone cells. Organic substance constitutes 
one-third the weight, and inorganic substance two- 
thirds the weight of bone. The bone cells, some- 
times called bone corpuscles, are flattened stellate 
cells with many slender processes, and a well defined 
round or oval nucleus. Like cartilage cells they lie 
imbedded in lenticular spaces called lacuna. These 
lacunae, however, communicate with adjacent la- 
cunae by means of numerous capillary tubes called 70 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
canaliculi, into which extend the slender cell proc- 
esses. Through these canaliculi the imprisoned 
cells receive their nourishment and give up their 
waste products. 
Haversian System.-This consists of a Haversian 
Fig. 46.- Haversian system with only one lacuna sketched. 
canal, containing an artery, vein, and nerve, bone 
lamallae concentrically arranged around the canal, and 
from two to six rows of concentrically arranged cells 
with their lacunae and canaliculi. The canals average 
0.05 mm. inch) in diameter. 
The canals, as a rule, run parallel 
with the shaft of the bone, but com- 
municate freely with each other. 
The blood penetrates as far as the 
Haversian canals but the lymph 
reaches each bone cell through the 
finer canaliculi. The nerve termi- 
nates in the wall of the blood-ves- 
sels and has no connection with the bone cells. 
Haversian systems occupy a central zone in a bony 
shaft. External and internal to this zone compact 
lamellae are present, arranged parallel to the surface. 
Fig. 47.- Bone 
cell or corpuscle. 
The cell occupies a 
lacuna. TISSUES. 
71 
Fig. 48.- Segment of a transversely ground section from the shaft 
of a long bone, showing all the lamellar systems. Metacarpus of man 
(Bohm and Davidoff). 72 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
In the circumferential lamellae canals, called Volk- 
mann s canals, convey blood-vessels to the Haver- 
sian canals. In the angular interstices, between the 
Haversian systems, lamellae and canaliculi are found 
arranged like those of the circumferential lamellae. 
The shafts of long bones contain a marrow cavity. 
At the ends the marrow cavity disappears, and the 
bony structure becomes spongy with many inter- 
stices and is then called cancellate bone. The middle 
of flat bones is made up of a like loose structure 
called diploe. 
Fig. 49.-Portion of a transversely ground disc from the shaft of a 
human femur (Bohm and Davidoff). 
Periosteum.-The periosteum is a dense, fibrous, 
connective-tissue membrane that covers the bone 
and is derived from the perichondrium of the carti- 
lage. It is composed of two layers, (a) an inner 
layer that contains many elastic fibers and osteo- 
blasts, or bone-forming cells, known as the osteo- 
genetic layer, and (6) an outer layer of coarse, 
white, fibrous bundles where numerous blood-vessels 
ramify and send branches to the Haversian canals. TISSUES. 
73 
The periosteum is anchored to the compact bone by 
means of bundles of fibers (Sharpey's pbers) that 
pass concentrically or parallel to the Haversian 
systems. 
Blood Supply,-The compact bone is supplied 
with blood from the periosteum. Larger blood- 
vessels, called perforating -vessels, pass directly 
through the bony shaft and supply the marrow. 
In removing bone, as a rib, the periosteum is not 
taken away, and because of the latter's vascularity 
and osteogenetic layer, the removed part regenerates. 
On the other hand, infected marrow and diseased 
bone may be removed from the inner surface until a 
mere shell remains of the once solid shaft. If all 
the infection is removed a regeneration follows. 
Development of Bone,-The development of bone 
is either intramembranous or endochondral. In the 
latter a cartilage stage intervenes, otherwise the 
history in each case is the same. A synopsis of 
endochondral development is as follows: 
i. A solid shaft of hyaline cartilage, non-vascular 
and without any marrow cavity. 
2. In the center of this shaft the cartilage cells 
enlarge, their lacunae enlarge and coalesce, particu- 
larly along lines extending toward the ends of the 
bone. The rosette produced by this excavation is 
called the primary areola of Sharpey. 
3. Lime salts are deposited in the thin walls of 
these spaces, making calcified cartilage. 
4. Osteogenetic cells and blood-vessels from the 
periosteum enter the cartilage spaces. The carti- 
lage cells disappear with this invasion and the ex- 74 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
cavation, begun by the cartilage cells, is further en- 
larged by the bone cells. The excavated areas are 
now called the secondary areolae of Sharpey, the 
cavities having a rich blood supply quite in con- 
trast with the primary areolae. The marrow cavity 
Fig. 50.-Longitudinal section through a long bone (phalanx) 
of a lizard embryo. The primary bone lamella originating from the 
periosteum is broken through by the periosteal bud> Connected with 
the bud is a periosteal blood-vessel containing red blood-corpuscles 
(Bohm and Davidoff). 
is excavated and the shaft'becomes longitudinally 
porous. 
5. Osteogenetic cells attach themselves to the wall 
of these enlarged Haversian canals and become en- 
closed in lime deposits, forming thus the outer lam- 
ellae and outer row of bone cells of each Haversian tissues. 
75 
system. Cells with lamellae are added centripetally 
to this outer row and thus ultimately complete the 
Haversian system, leaving a 
small central canal contain- 
ing vessels and a nerve. 
Ossification begins in the 
center of the cartilage shaft 
and proceeds gradually 
toward each end, so that all 
the above changes occur at 
one and the same time. 
After birth these changes go 
on at the ends of the bone, 
so long as it keeps growing. 
During this period the bone 
is made thicker by deposits 
from the periosteum forming 
the circumferential lamellae of 
bony shafts. These lamellae 
are added without the inter- 
vention of a cartilage stage 
and therefore represent intra- 
membranous development. 
Regeneration of Bone.- 
The embryonic process of 
developing bone is repeated 
every time a broken bone 
heals. As a rule the carti- 
lage stage does not intervene. 
A synopsis of the healing 
process of a simple fracture 
is as follows: 
Fig. 51.- Longitudinal 
section through area of 
ossification from long 
bone of human embryo 
(Huber). 76 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
i. Hemorrhage and clot. The fibrin of the clot 
tends to hold the broken ends in apposition. The 
parts are swollen and red, due to the influx of blood. 
2. Organization of the clot. Connective-tissue 
cells and white corpuscles enter the clot, feed upon 
it and ultimately replace it, the connective-tissue 
cells meanwhile producing fibers. The organized 
clot is a more substantial fabric and more firmly 
holds the broken ends in apposition. 
3. Osteogenetic cells enter the organized clot and 
deposit lime salts, producing a primary callus. The 
connective fibers shrink, pulling the broken ends 
firmly together, producing a sensation known as 
knitting of bone. The primary callus surrounds the 
bone, and may even fill the marrow cavity. 
4. Haversian systems are formed, uniting the 
broken ends. These systems appear just as de- 
scribed under development of bone. 
5. Primary callus is absorbed and marrow cavity 
excavated. Bone cells called osteoclasts are sup- 
posed to be active factors in this absorption. 
General Considerations.-Bone does not grow in 
the same sense as other tissues do. Any increase in 
size is due to apposition of bone lamellae upon those 
already formed. Accompanying and often pre- 
ceding bone production we usually find a destructive 
or excavating process. It is believed two classes of 
cells bring about these changes: (a) Osteoclasts that 
cause bone absorption, and (6) osteoblasts that en- 
gage in bone production. The latter are supposed 
to be particularly abundant in the osteogenetic 
layer of the periosteum. TISSUES. 
77 
Bone tumors are not uncommon and are called 
osteoma. They are of slow growth, usually as- 
sociated with bone, and harmless. 
On account of the great vascularity, a broken bone 
heals more rapidly than a broken tendon, or liga- 
ment, or a broken cartilage. An old bone is brittle 
and the healing process a slow one on account of the 
increase of earthy matter and a decrease of the 
organic. 
An infection beneath the periosteum is a felon. 
The periosteum is firmly attached to the bone by 
Sharpey's fibers and the pressure produced by an in- 
fection beneath it gives rise to extreme pain, which 
is instantly relieved by an incision. An inflam- 
mation in the bone is called an ostitis, while if it is 
located in the marrow cavity it is called an osteo- 
myelitis. 
HI. MUSCULAR TISSUE. 
Muscular tissue consists of elongated cellular ele- 
ments in which contraction takes place along the 
long axis of the cell. This contraction is intrinsic to 
the muscle cytoplasm, and of this the spongioplasm 
seems to be the active agent. The word sarcode and 
its derivatives is used in describing muscle proto- 
plasm. This word was introduced by Dujardin, in 
1835, and was later replaced by the word protoplasm. 
1. Smooth, Non-striated or Involuntary Muscle.- 
This is the simplest form of muscle tissue. The cells 
are mononucleated, elongated, or spindle-shaped, 
and vary in length from 40 to 200 /z. The nucleus 
occupies the center of the cell, is rich in chromatin, 
and oval, with blunt ends, or cigar-shaped. The 78 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
cytoplasm is longitudinally striated, the striations 
being due to fibrils or sarcostyles, which are, structur- 
ally, probably analogous to the spongioplasm. 
Between the fibrils there is a homogeneous sub- 
stance, the sarcoplasm, which is analogous to the 
hyaloplasm. These cells have no cell wall. The 
ends overlap each other and are held together by a 
delicate cement substance. Nerve fibers from the 
sympathetic nervous system reach the muscle cells 
and terminte in small granules upon the muscle 
cytoplasm. 
Fig. 52.- a, Cell from smooth muscle of intestine; b, Cross section of 
smooth muscle of intestine. 
Smooth muscle is found in the wall of the tubes of 
the body, and invariably in thin layers, with one 
exception-the wall of the uterus-where the muscle 
may be an inch in thickness. Plain muscle is found 
in the wall of the alimentary tract, trachea and 
bronchi, bladder, ureter, uterus, Fallopian tubes, 
urethra, vas deferens, blood-vessels, lymph-vessels, 
large ducts of glands, nipple, hair-follicles, Eusta- 
chian tube, spleen, prostate gland, ciliary muscles, 
and iris of the eye. tissues. 
79 
2. Cardiac Muscle.-The heart ontogenetically is 
a modified blood-vessel, and its muscle, therefore, 
has the same origin as smooth muscle. Heart- 
muscle cells are oval or brick-shaped and mono- 
nucleated, the oval nuclei occupying the center of 
Fig- 53--Longitudinal section of heart muscle fibers. 
the cell. Longitudinal fibrils and, in addition, a 
fine cross striation, are present in the cytoplasm, 
resembling the cross stri- 
ation of voluntary mus- 
cle. This cross striation 
is explained under Vol- 
untary Muscle, and 
therefore will not be 
given here. The cells 
are joined together, end 
to end, by delicate ce- 
ment lines and laterally 
may unite with adjacent cells by means of protoplas- 
mic processes. In the cytoplasm adjacent to the ends 
of the nuclei, normal fat is frequently present and 
also some pigment. The latter is more prominent 
in old hearts, to which it imparts a brown color. 
Fig. 54.--Cross section of heart 
muscle fibers. 80 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
At present the exact structure of the heart muscle 
is a disputed question. In sections, many breaks 
or artifacts resemble the cement lines separating 
adjacent cells. The longitudinal fibrils are said to 
penetrate the cement and thus establish a con- 
tinuity of protoplasm between adjacent cells. The 
presence or absence of a cell wall, analogous to the 
sarcolemma of voluntary muscle, is also disputed. 
3. Voluntary Muscle.-A voluntary muscle fiber 
is a multinucleated, greatly elongated cell, which 
may attain a length of 12 cm. (5 inches). These 
fibers are arranged parallel to each other and grouped 
into bundles, called fasciculi. Each fasciculus is 
Fig- 55--Voluntary muscle fiber. The sarcoplasm has broken, show- 
ing the smooth sarcolemma. 
surrounded by connective-tissue cells and fibers in 
which many blood-vessels ramify. A finer fabric of 
connective tissue penetrates the fasciculus and gives 
support to the individual fibers. The connective 
tissue that enters a fasciculus is called the endo- 
mysium, and that which surrounds a fasciculus is 
called the perimysium. Fasciculi are grouped into 
coarser bundles and these collectively make up a 
muscle. The muscle is in turn enveloped in a firm 
connective-tissue layer called the epimysium. In 
gross anatomy the latter constitutes the deep fascia 
of muscle. In tough meat the connective-tissue 81 
TISSUES. 
element is extensively developed and the fasciculi 
are large and coarse. 
Each muscle . fiber has a delicate,' transparent, 
smooth cell wall called the s ar colemma. The oval 
distinct nuclei lie immediately beneath the sarco- 
lemma in higher vertebrates, but in lower forms and 
in all embryos the nuclei lie deeper in the muscle 
protoplasm. These nuclei have the same structure 
as the nuclei of any other tissue, but the cytoplasm 
shows a distinct and regular cross and longitudinal 
striation, characteristic of only one other tissue- 
the cardiac muscle. The 
longitudinal striation is 
due to the presence of 
delicate fibrillae called 
sarcostyles, which is an- 
alogous to the spongio- 
plasm of other cells., A 
more homogeneous and 
fluid substance intervenes 
between the sarcostyles, 
called sarcoplasm, and is 
in turn analogous to the hyaloplasm of other cells. 
The sarcostyles are not uniformly or evenly dis- 
tributed in each muscle fiber, but are grouped into 
bundles. In cross sections the fiber has therefore 
a honeycomb structure, the minute areas being 
known as Cohnheim's fields. A single Cohnheim 
field represents the cut ends of a single bundle of 
fibrils or sarcostyles. 
The cross striation is more intricate to explain. 
This striation consists of alternating light and dark 
Fig. 56.- Cross section of three 
voluntary muscle fibers. 82 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
bands. The dark bands are doubly refractive to 
light, or anisotropic, while the light bands are singly 
refractive, or isotropic. The dark bands represent a 
predominance of the sarcostyle substance, and the 
light bands a predominance of the sarcoplasm. In 
the middle of the light band a dark line can be seen, 
known as Krause's membrane. In the middle of the 
dark band a light-colored line is present, known as 
Hensen's median disc. The latter disappears when 
Fig. 57.--Diagram of voluntary muscle fiber; A, Fiber relaxed; B, 
fiber contracted. 
These transverse markings are all due to the dis- 
tribution of the sarcoplasm and the regular con- 
strictions of the sarcostyles. The sarcostyles are 
not of uniform dimensions, but at regular intervals 
show dilatations alternating with constrictions. The 
dilatations appear at regular intervals and in the 
same transverse plane of the muscle fiber, thus 
giving rise to the dark band. Krause's membrane 
is not a membrane, but represents minute nodal 
points of the sarcostyles, placed in the same trans- TISSUES. 
83 
verse plane of the fiber and in the middle of the light 
band. The light band represents an abundance of 
sarcoplasm and it is in this sectional area that the 
sarcostyles suffer a constriction. As Hensen's me- 
dian disc is a light line in the middle of the dark 
band there must be 
a deep constriction, 
if not a complete 
constriction of the 
sarcostyles at this 
point. 
The whole muscle 
fiber between the 
two Krause's mem- 
branes is called a 
sarcomere, and con- 
sists of a median 
dark band and the 
proximal halves of 
the adjacent light 
bands. A single 
fibril or sarcostyle 
between two of 
Krause's mem- 
branes is called a 
sarcous element. 
It is believed that 
muscular contractil- 
ity is particularly a function of the sarcostyles and 
that the sarcoplasm serves more as a storage of energy 
or food. As to color there are two kinds of muscle, 
white and red. In white meat, as the muscle of the 
Fig. 58.-Part of a longitudinal sec- 
tion through the line of junction be- 
tween muscle and tendon. At the line 
where the tendon fibrils join the sarco- 
lemma (o), the nuclei of the muscle are 
very numerous. Sublimate preparation 
(Bohm and Davidoff). 84 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
breast of a bird, the fibers have a poor supply of 
sarcoplasm and a predominance of sarcostyles. In 
red meat the fibers are rich in sarcoplasm and have a 
less supply of the sarcostyle protoplasm. In the 
myology of man both kinds of fibers are present. 
The white fibers are more powerful but have less 
endurance; that is, if held in tetanic contraction 
with no interval of rest they would tire quicker than 
the red fibers. The pectoral muscle of birds is 
powerful, but would soon tire but for the interval 
of rest that intervenes between the strokes of the 
wing; that is, during its upward movement. 
Fig. 59.-Three voluntary muscle fibers from an injected muscle, show 
ing network of blood-capillaries. 
Blood Supply.-Blood-vessels follow the con- 
nective tissue of a muscle, and penetrate to the 
individual fibers where they break up into capil- 
laries. These vessels run, as a rule, parallel to the 
fibers, forming a network with anastomosing 
branches. They extend in a varicose manner 
between the fibers in such a way that when a muscle 
contracts they readily adjust themselves, without 
breaking. 
Nerve Supply.-Medullated nerve fibers accompany TISSUES. 
85 
the blood-vessels and terminate beneath the sarco- 
lemma in special end plates called muscle plates. 
These will be described under special nerve endings. 
Non-medullated or sympathetic nerve fibers also 
accompany blood-vessels, but they innervate the in- 
voluntary musculature of arteries and veins. 
Distribution.-Voluntary muscles are the skeletal 
muscles, and make up the bulk of the body. 
Striated fibers are present in the upper part of 
the esophagus, and also constitute the platysma 
muscle of the skin. 
Union with Tendon and Bone.-The muscle 
fibers terminate abruptly with tendon fibers. This 
is not a direct end-to-end union, but the tendon 
fibers fuse with the sarcolemma at an angle. In the 
same way the muscle fibers unite with the periosteum 
of the bone. At this point Sharpey's fibers are 
particularly abundant and firmly anchor the peri- 
osteum to the compact bone lamella?. 
General Considerations.-A muscle tumor is called 
a myoma. Tumors of plain muscle are common in 
the wall of the uterus. They are benign, of slow 
growth, and usually harmless. A tumor of striated 
muscle fibers is very rare. The tissue is highly 
specialized and the fibers therefore do not multiply 
readily. If a muscle is injured or cut the voluntary 
fibers regenerate partly from the cut end and partly 
from free muscle nuclei that are shed into the wound. 
The physiological action of plain muscle is slow, 
producing peristaltic contractions. That of volun- 
tary muscle is rapid, as in the wings of insects. 
Voluntary muscles, while more powerful, tire easily. 86 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
Plain muscle has a wonderful endurance. The 
pain produced by violent action of plain muscle is 
in direct proportion to the degree of contraction. 
Some examples are: the colicky pains of the intestine ; 
labor pains; pains due to calculi in the ureter or bile 
duct; or the pain in appendicitis produced by con- 
traction of the plain muscle of the appendix. These 
pains have many things in common They may 
last for hours, they remit and recur with regularity, 
and they come in waves. 
An infection in a muscle, as a psoas abscess, bur- 
Fig. 60.-Diagram of a neuron. 
rows in the fascia,-that is, spreads along the con- 
nective-tissue septa, perimysium and endomysium. 
The quality of meat depends on the amount of con- 
nective tissue. In tough meat the fasciculi are 
coarse and perimysium abundant. In tender sir- 
loin the reverse prevails. 
IV. NERVOUS TISSUE. 
Nervous tissue is most highly specialized of all 
tissues and consists of elements called neurons. A 
neuron is a nerve cell with all its processes. These 
cells vary greatly in size; usually they are large. 87 
TISSUES. 
They have one or more processes, no cell wall, and a 
distinct nucleus. The nucleus has a conspicuous 
nucleolus, a prominent nuclear membrane, but a 
small supply of chromatin. 
The cytoplasm is usually pigmented, the pigment 
being collected to one side of the cell. It is this 
pigment that gives nervous tissue a gray color 
wherever these cells are found. Fat and vacuoles 
are also usually found in the cytoplasm. The proc- 
esses of nerve cells are: 
Fig. 6t.-Transverse section through the sciatic nerve of a frog. 
At a and b is a diagonal fissure between two Lantermann's segments; 
as a result, the medullary sheath here appears double (Bohm and 
Davidoff). 
i. Axis cylinder (Deiters^ process, axon, neurite, 
or neuraxon), which is usually a long protoplasmic 
process that physiologically carries an impulse away 
from the cell. Collaterals are nerve processes that 
leave the axis cylinder at right angles. They are 
commonly found near the nerve cells, but may ap- 
pear at a node of Ranvier some distance away from 
the nerve cell. 88 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
2. Dendrites, which are usually short processes, 
very much branched, and physiologically carry an 
impulse toward the nerve cell. A collection of 
nerve cells constitutes a ganglion, while a nerve 
plexus is a reticulum or interlacing of nerve fibers. 
Nerve cells are classified, according to the number 
of their processes, into unipolar, bipolar, and 
multipolar. 
Nerve Cells.--i. Unipolar nerve cells.-These are 
nerve cells with but one process. If a nerve cell 
Fig. 62.- Section of spinal ganglion. 
has but one process that process must be an axis 
cylinder. If a nerve cell has many processes only 
one is an axis cylinder, the others are dendrites. 
Unipolar nerve cells are found in the olfactory mucous 
membrane. They are columnar or cylindrical and 
each gives rise to a basal process, the axis cylinder, 
which remains non-medullated and extends through 
the cribriform plate to enter the olfactory lobe of the 
cerebrum. This class of nerve cells is common in 
invertebrates. 89 
TISSUES. 
2. Bipolar Nerve Cells.-Bipolar nerve cells have 
two processes,-one axis cylinder and one dendrite. 
Nerve cells of the spinal ganglia and ganglia of the 
Fig. 63.--Two bipolar nerve cells from the spinal ganglion 
cranial nerves belong to this class. These cells 
apparently are unipolar, but their embryology 
clearly shows the single process to be morphologically 
equivalent to two. In 
this particular case 
the long peripheral 
process carries an im- 
pulse to the cell, and 
this long process is 
therefore a dendrite. 
The short process that 
unites the ganglion 
with the central ner- 
vous system is the 
axis cylinder. These 
large bipolar cells are 
surrounded by a cap- 
sule of connective-tissue cells. The cells are large and 
the single compound process very soon divides into 
the two processes mentioned above. The cytoplasm 
Fig. 64.-Three ganglion cells from 
a spinal ganglion of a rabbit embryo. 
The cells are still bipolar. Their proc- 
esses come together in later stages, 
and finally form the T-shaped structure 
seen in the adult animal; chrome-silver 
method (Bohm and Davidoff). 90 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
of these cells has a fibrillar structure, this striation 
having a close relation to the fibrillae of the axis 
cylinder. 
The spinal ganglia are situated on the posterior 
or sensory root of the spinal nerves and within the 
vertebral canal. The Gasserian, geniculate, audi- 
tory, jugular, and petrosal ganglia of the cranial 
nerves are morphologically equivalent structures. 
The nerve cells of all these ganglia 
are bipolar, with the exception of a 
few cells said to be multipolar. In 
addition to nerve cells, nerve fibers 
and connective-tissue elements 
make up the histology of these gan- 
glia. A liberal blood and lymph 
supply is always present. 
3. Multipolar Nerve Cells.- 
These are nerve cells with many 
processes, only one of which is an 
axis cylinder. They constitute by 
far the bulk of nerve cells and are 
found in the brain and spinal cord 
and in ganglia along the sympa- 
thetic nervous system. The cells 
vary in size from 4 /i in the granular 
layer of the cerebellum to 150 [t, the largest nerve 
cells of the spinal cord. Chromatophile granules, 
vacuoles, fat, and a fibrillar structure is found 
associated with the cytoplasm. Large multipolar 
nerve cells, called cells of Purkinje, are found in the 
cerebellum and will be described with the histology 
of that organ. 
Fig. 65.-Gan- 
glion cell with a 
process dividing at 
a (T-shaped proc- 
ess); from a 
spinal ganglion of 
the frog (Bohm 
and Davidoff). TISSUES. 
91 
Nerve Fibers.-i. Medullated Fibers.-Medullated 
nerve fibers usually consist of three parts, (a) axis 
cylinder, (6) medullary sheath, (c) neurilemma. An 
axis cylinder is a cell process that carries an impulse 
away from the nerve cell. It is a slender cytoplasmic 
process and may be very long, as is the case with 
Fig. 66.-Ganglion cell from the Gasserian ganglion of a rabbit; stained 
in methylene-blue (intra vitam) (Huber). 
the motor fibers that come from nerve cells in the 
anterior horn of the spinal cord and extend, without 
interruption, to muscles in the distal parts of the 
limbs. The axis cylinder presents a longitudinal 
striation, a fibrillar structure, that is supposed to be 
continuous with the cytoplasmic striation of the 92 
NORMAL HISTOLOGY AND ORGANOGRAPHY 
Fig. 67.-Motor neurons from the anterior horn of the spinal cord of 
a new-born cat; chrome-silver method (Huber). 
Fig. 68.-A nerve cell with branched dendrites (Purkinje's cell), 
from the cerebellar cortex of a rabbit; chrome-silver method (^ohm 
and Davidoff). TISSUES. 
93 
cell body. The fibrils are imbedded in a fluid pro- 
toplasmic substance, the neuroplasm, and the whole 
surrounded by a delicate membrane, the exolemma. 
Implantation cone is an elevation that is sometimes 
Fig. 69.-Pyramidal cell from the cerebral cortex of man; chrome- 
silver method (Bohm and Davidoff). 
present at the junction of the axis cylinder and cell 
body. 
The medullary sheath (white sheath of Schwann) 
is a covering to the axis cylinder. This sheath never 94 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
extends to the nerve cell but begins a little distance 
from it. It consists of fat and neurokeratin. The 
latter, on burning, gives an odor of burnt bone. It 
Fig. 70.-Medullated nerve fibers from a rabbit, varying in thick- 
ness and showing internodal segments of different lengths. In the fiber 
at the left the neurilemma has become slightly separated from the under- 
lying structures in the region of the nucleus (Bohm and Davidoff). 
is this sheath that gives the white color to nerves and 
the white matter of the brain. In osmic acid prep- 
arations, oblique fissures appear in the medullary TISSUES. 
95 
sheath dividing it into sections known as Schmidt- 
Lantermann segments. It is claimed by some that 
these are artifacts. Nodes of Ranvier are regular 
constrictions of this sheath at regular intervals of 
80 to 900 [j.. The smaller the liber the greater the 
distance between these nodes. Tong libers are 
slender, with long distance between the nodes; 
short libers are coarse, with 
short distance between the 
nodes. 
The neurilemma is a thin 
structureless membrane that 
surrounds the medullary 
sheath. An oval nucleus is 
present in this sheath, midway 
between the nodes of Ranvier. 
At each node the neurilemma 
is constricted and touches the 
axis cylinder, which in turn 
may be slightly thickened at 
this point and may give off a 
collateral. Medullated nerve 
fibers with a neurilemma are 
found in the cranial and spinal 
nerves. Medullated fibers 
without a neurilemma are found in the brain and 
spinal cord. The neurilemma gives great strength 
to the fibers. Its absence in the brain and cord ac- 
counts for the pulpy soft nature of this tissue. 
2. Non-medullated nerve fibers with a neurilemma, 
but without a medullary sheath, mingle with the 
medullated fibers. The sympathetic system con- 
Fig. 71.-Longitudinal 
section through a nerve 
fiber from the sciatic nerve 
of a frog (Bohm and 
Davidoff). 96 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
sists largely of non-medullated fibers. Terminal 
branched endings of an axis cylinder, called neuro- 
podia, have neither medullary sheath nor neurilemma. 
The axis cylinder, just as it leaves its nerve cell, is 
likewise uncovered. 
Nerve Trunk.-The fibers that constitute a nerve 
are grouped into bundles called funiculi. Each 
funiculus is enclosed in a connective- 
tissue sheath, the perineurium, which 
sends septa, the endoneurium, in 
among the individual fibers. The 
whole nerve is enclosed in a firm con- 
nective-tissue sheath, the epineurium. 
Blood- and lymph-vessels accompany 
the connective-tissue elements and 
ramify through the nerve just as is 
the case in a muscle. 
Nerve cells with a long axis cylinder 
were classified by Golgi as Type I, and 
with a short axis cylinder as Type II. 
Golgi believed the former to be motor 
in function, and the latter sensory, a 
classification no longer tenable. 
Neuroglia tissue is a delicate sup- 
porting tissue of the brain and cord, 
consisting of cells with many fine in- 
terlacing branches, mossy cells, or spider cells. 
These cells develop from the ectoderm and are onto- 
genetically closely related to nerve cells. Their 
function is to give support, not to conduct nerve 
impulses. 
The great nerve center in the body is the cerebro- 
Fig. 72.-Re- 
m a k ' s fibers 
(non-medullated 
fibers) from the 
pneum o g a s t r i c 
nerve of a rabbit 
(Bohm and Da- 
vidoff). TISSUES. 
97 
spinal system-brain and spinal cord. Next conies 
the sympathetic system, made up of ganglia and 
Fig- 73--Cross section of nerve trunk. 
Fig. 74.- Diagram to show the composition of a peripheral nerve- 
trunk (Huber). 
mostly non-medullated nerve fibers that terminate 
in glands or smooth muscle. Lastly, the peripheral 98 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
system,-nerve terminations formed in tissues and 
organs throughout the whole body. 
General Considerations.-Nerve cells are so highly 
specialized that their multiplication after birth is un- 
known. We never, therefore, find tumors of nerve 
cells. If a nerve cell is cut, the axis cylinder re- 
moved from the nerve cell dies while the end that 
is still attached to the cell regenerates and may 
Fig- 75--Neurogliar cells: a, from spinal cord of embryo cat; b, from 
brain of adult cat; stained in chrome-silver (Bohm and Davidoff). 
restore the lost part. Surgeons unite the ends of a 
cut nerve so that the axis cylinder may develop along 
the old nerve trunk which becomes a path of least 
resistance. 
In amputations the cut nerve may grow into a 
tumor, called a neuroma. Such a tumor would con- 
sist of nerve fibers and the accompanying connective- 
tissue elements. Injury to nerve cells, such as TISSUES. 
99 
brain or ganglia, heal by production of connective 
tissue and accompanying scar. 
The function of the axis cylinder is to conduct 
a nerve impulse. Physiologically such an impulse 
travels away from the cell, but experimentally it may 
pass in the opposite direction, as is the case when a 
nerve is stimulated midway in its course. The axis 
cylinder being made up of fibrils, it follows that such 
a cylinder may conduct more than one impulse, 
which in turn reach different centers through dif- 
ferent collaterals. 
The function of the medullary sheath is to protect 
and nourish the axis cylinder. Experimentally the 
non-medullated nerve fibers will tire quicker than 
the medullated. The nodes of Ranvier are points 
where nourishment from the blood and lymph can 
reach the cylinder. It is affirmed by some that the 
endolemma is only a lymph space surrounding the 
axis cylinder. 
The neurilemma is protective in function and gives 
great strength to the fibers. With nerves that ter- 
minate in muscle fibers the neurilemma is continuous 
with the sarcolemma of the muscle. Proximally the 
neurilemma begins where the medullary sheath takes 
up, always a short distance from the nerve cell, which 
leaves the axis cylinder uncovered as it emerges from 
the cell. 
It is affirmed that the neuron represents the ele- 
mentary unit of nerve tissue, and that neurons are 
merely in contact with each other and not in proto- 
plasmic continuity. This idea constitutes the neuron 
theory. CHAPTER HI. 
CIRCULATORY SYSTEM, BLOOD, MARROW, AND 
LYMPHATIC ORGANS. 
HEART. 
The heart is a muscular organ. Its wall consists 
of three layers, endocardium, myocardium, and 
epicardium. 
i. The endocardium is a serous membrane that 
covers the inner surface. Histologically it consists 
of two layers, an inner lining of simple squamous 
epithelial cells (endothelium or mesothelium), and 
an outer layer composed of connective-tissue fibers, 
connective-tissue cells, and smooth muscle cells. 
The endocardium is reflected over the heart valves 
where the smooth muscle is particularly abundant. 
2. The myocardium is the middle layer and forms 
the mass of the heart wall. It consists of muscle 
tissue, the cardiac muscle already described (page 79). 
This muscle consists of many layers that course in 
different directions with connective-tissue elements 
intervening, in which branches of the coronary 
blood-vessels ramify. 
3. The epicardium is the outer covering, a serous 
membrane, and histologically similar to the endo- 
cardium, with a greater deposit of fat. The epi- 
cardium is reflected to form the pericardium, the 
100 CIRCULATORY SYSTEM. 
101 
epithelial cells secreting a serous fluid that acts as a 
lubricant. 
ARTERIES AND VEINS. 
Arteries and veins are structurally so alike that they 
may be described under one heading. Arteries carry 
blood away from the heart and to the capillaries. 
Veins return the blood from the capillaries and to 
the heart. Arteries have thicker and more elastic 
walls with a larger number of circular fibers. Veins 
are less elastic and have a larger number of longitudi- 
Fig. 76.-Cross section of small artery and vein; A, artery; V, vein. 
nal fibers. The walls of each consist of three layers: 
intima, media, and adventitia. The structural ele- 
ments of each layer is outlined in the following table: 
I. Tunica intima. 
i. Endothelium, simple squamous epithelial 
cells. 
2. Subendothelial layer. 
* (a) White connective-tissue fibers, longi- 
tudinal. 
* This tissue predominates in veins. 102 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
(b) Connective-tissue cells. 
* (c) Elastic connective-tissue fibers, longi- 
tudinal. 
* 3. Henle's fenestrated membrane (elastic in- 
ternal limiting membrane). Interlac- 
ing basketwork of elastic fibers. 
Fig. 77--Cross section of aorta. 
II. Tunica media. 
* i. Smooth muscle, circular. 
* 2. Elastic plates and fibers, longitudinal and 
circular. 
3. Nerves. 
4. Blood capillaries, difficult to demon- 
strate. 
* This tissue predominates in arteries. CIRCULATORY SYSTEM. 
103 
f 5. White connective fibers. 
6. Connective-tissue cells. 
7. Muscle fibers longitudinal, rare. 
III. Tunica adventitia. 
f 1. White connective-tissue fibers, longi- 
tudinal and oblique. 
2. Connective-tissue cells. 
*3. Elastic connective-tissue fibers, longitudi- 
nal (external limiting membrane). 
4. Nerves. 
5. Vasa vasorum (blood-vessels). 
6. Lymphatic 
vessels and 
nodes. 
t 7. Smooth mus- 
cle fibers, 
longitudi- 
nal. 
It should be remem- 
bered that large and 
small arteries differ 
greatly in keeping with their function. In small 
arteries or arterioles, the involuntary muscle is 
conspicuous, as it is the contraction of this muscle 
that regulates the blood supply to an organ. In 
large arteries, as the aorta, the muscle is greatly 
reduced, and elastic elements unusually well de- 
veloped. The muscle, too, is deficient in large 
veins situated deep in the body, as the vena 
cava. The smaller veins have valves, folds of 
Fig. 78.- Cross section of small 
artery. 
* This tissue predominates in arteries, 
f This tissue predominates in veins. 104 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
the intima, so arranged as to equalize the pressure 
from the contained blood. Without these valves 
the thin-walled veins would become greatly dis- 
tended. If for any cause the veins expand so 
that the valves do not act, a permanent disten- 
tion with engorgement of blood follows. The veins 
become distorted and are spoken of as varicose 
veins, a condition quite common to the long saphe- 
nous veins of the lower limbs. 
Capillaries.-These are the finer organic ramifi- 
cations of the circu- 
latory system, and 
unite arteries and 
veins. Histologic- 
ally, the walls of cap- 
illaries consist of a 
single layer of flat- 
tened epithelial (en- 
dothelial or mesothe- 
lial) cells. The blood 
courses very slowly 
through these inter- 
lacing tubes. The white cells penetrate the walls 
and under certain conditions even the red corpuscles 
may do so. According to some investigators, minute 
pores in the epithelial wall, called stigmata and 
stomata, allow this migration. Others deny the 
presence of these pores, in which case the blood ele- 
ments escape by passing between two adjat ent epi- 
thelial cells, after which this opening closes. 
Fig- 79--Cross section of vein. CIRCULATORY SYSTEM. 
105 
The blood is derived from the mesoderm; it is a 
red fluid that consists of (i) a liquid portion, the 
plasma, and (2) solid constituents, the corpuscles. 
There are at least three classes 
of the latter, red corpuscles, 1011116 
corpuscles, and platelets. 
1. Red corpuscles (erythro- 
cytes) in the mammalia are non- 
nucleated, circular, biconcave 
discs. In all the other verte- 
brate groups and in all embryos 
they are nucleated oval and bi- 
convex cells. Each corpuscle 
consists of a red coloring matter, 
hemagiobin, and a more substan- 
tial fabric or reticulum, the 
stroma. The hemagiobin is the 
bearer of oxygen, is readily solu- 
ble in water, leaving the stroma 
or fabric, which is then known as 
a ghost corpuscle. 
The red corpuscles are soft and 
elastic and are covered by an oily 
film. In a fresh spread they ad- 
here to each other by their con- 
cave surfaces forming rouleaux or "money-pile" rows. 
This is purely a physical phenomenon. As soon as 
the oily covering dissolves this combination disap- 
pears. The corpuscles are extremely susceptible to 
changes in the plasma. If water is added they will 
swell up and the hemagiobin begins to dissolve. With 
THE BLOOD. 
Fig. 80.- Red blood- 
corpuscles from man. 106 
NORMAL, HISTOLOGY AND ORGANOGRAPHY. 
evaporation the corpuscles begin to shrink, forming 
minute processes and they are then said to be 
crenated. Evaporation of water produces an in- 
creased percentage of the salts 
in solution. This in turn ab- 
stracts water from the cor- 
puscles and the shrinking or 
crenated condition follows. 
It is estimated that the total 
amount of blood in man is 
one-thirteenth the weight of the body. The average 
normal male, therefore, has approximately 25,000,- 
000,000,000 red corpuscles. The life period of a red 
Fig. 81.- Crenated red 
blood-corpuscles from man. 
Fig. 82.-Red blood-corpuscle of frog; a, flat view; b, side view. 
corpuscle is not definitely known, but physiologists 
tell us it is probably from two to four weeks. Ac- 
cordingly the daily consumption and loss is enormous, 
and is equaled only by as constant and regular a 
production of new cells. Their number in man is 
5,000,000 per cubic millimeter. CIRCULATORY SYSTEM. 
107 
The following table gives the size of the red blood- 
corpuscle in the different groups of animals: 
Man 7.2 to 7.8 /z. Chick .... 12.1 by 7.2 /i. 
Monkey 7.0 /z. Duck .... 12.9 " 8.0 /z. 
Dog 7.5/z. Tortoise.. 21.2 " 12.5/z. 
Cat 6.2 /z. Snake. . . .22.0 " 13.0 /z. 
Horse 5.6 /z. Frog 22.3 " 15.7 /z. 
Guinea-pig . . 7.5 /z. Newt . . . .30.7 " 19.0 /z. 
White Corpuscles.-These are colorless, nucleated, 
plastic, ameboid cells. Their number in man is 
from 7000 to 10,000 per cubic millimeter. They are 
variously classified according to the morphology of 
their nuclei, or the granules in the cytoplasm that 
Fig. 83.- White blood-corpuscles from man. 
take different stains, or as to their origin, or as to 
their function. For practical purposes they may 
be classified as: 
1. Small mononucleated 20%...size 8 to 10 microns. 
2. Large mononucleated 6%. . .size 12 microns. 
3. Polymorphic 1 
, _ / , , neutrophile. . . 70%'. . .size 10 to 12 microns. 
4. Polynucleated J 1 
5. Eosinophile 4%...size 10 microns. 
The percentage of these different cells and their 
total number per cubic millimeter is of the greatest 
clinical value in blood analysis. They are often 108 
NORMAE HISTOLOGY AND ORGANOGRAPHY. 
called 'wandering cells, as they are able to pass 
through the capillary wall and migrate throughout 
the tissues and organs. The polynucleated form is 
readily recognized by its multiple or fragmented 
nuclei. 
3. Blood platelets are small, colorless, round, non- 
nucleated bodies about one-third the size of red 
blood-corpuscles. They are supposed to play an im- 
Fig. 84.- Ehrlich's leucocytic granules (from preparations of 
H. F. Muller): a, Acidophile or eosinophile granules, relatively large 
and regularly distributed; e, neutrophile granules; ft, amphophile 
granules, few in number and irregularly distributed; y, mast cells with 
granules of various sizes; 3, basophile granules; (a, o, and e, from the 
normal blood; y, from human leukemic blood; ft, from the blood of 
guinea-pig) (Bohm and Davidoff). 
portant role in the coagulation of blood. As soon as 
blood is shed they disappear, unless special precaution 
is made to preserve them. They may be preserved 
by picking the finger through a drop of osmic acid. CIRCULATORY SYSTEM 
109 
Their number per cubic millimeter is from 200,000 
to 600,000. 
Hemin Crystals (Teich- 
man's crystals).-These 
come from the hemaglo- 
bin of the blood and when 
found are always a posi- 
tive evidence of blood. 
The crystals can be ob- 
tained from clotted blood, 
no matter how old the 
clot or stain is. Dry 
blood and salt, equal 
parts, are ground to- 
gether on a glass slide, 
a few drops of glacial 
acetic acid are added and 
heat applied until gas- 
bubbles appear. The 
crystals are brown, rhombic, and easily recognized. 
MARROW. 
Bone marrow is either white or red. The white 
marrow occupies the shaft of the bone and is largely 
fat. The red is found in the ends of bones or can- 
cellated portions and is richly supplied with blood. 
Histologically, we find in marrow all the con- 
stituents of blood and connective-tissue elements, 
fibers and cells. In addition, the following are some 
of the more characteristic cells of this tissue: 
1. Hematoblasts or Nucleated Red Blood-corpuscles. 
-These cells contain hemagiobin and a small round 
Fig. 85.- Fibrin from laryngeal 
vessel of child (Bohm and Da- 
vidoff). 110 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
nucleus that stains heavily with hematoxylin. They 
are supposed to be the chief source of the red blood- 
corpuscle, in which case the nucleus must disappear 
either by disintegration or extrusion. 
2. Marrow Cells or Myelocytes.-These are large 
cells with a rather large nucleus that stains lightly. 
3. Eosinophiles.-These are destined to become 
the eosinophile of the blood. 
4. Giant Cells.-These are osteoblasts or osteo- 
clasts. The osteoblasts are supposed, to be engaged 
in bone production, the osteoclasts in bone absorp- 
tion. They are very large cells with many nuclei 
grouped near the center of the cell. 
In the giant cells of tuberculosis the 
nuclei are found near the periphery 
of the cell. 
General Considerations.-There is 
an old saying that "a person is as 
old as his blood." A truer expres- 
sion would be that he is as old as his 
blood-vessels. With age, or dissipation, the blood- 
vessels harden, due to depositions of connective- 
tissue elements. This impairs the free circulation of 
blood and the body, as a whole, suffers. The hard- 
ened condition is spoken of as arteriosclerosis, or 
atheroma. Usually the intima suffers first by becom- 
ing much thickened. Later, a like disturbance takes 
place in the media and adventitia. As superficial 
scars remain permanently, and can not be eliminated, 
so there is no relief for this scar formation of the 
blood-vessels. Under this hardened condition a rup- 
ture of the smaller arteries is not uncommon, par- 
Fig. 86.- Hemin 
crystals from blood- 
stains of man. CIRCULATORY SYSTEM. 
Ill 
ticularly those of the brain, as they have thinner 
walls. Such a disaster is apt to be fatal. 
An inflammation of the heart, as endocarditis, is 
apt to produce a deposit of connective tissue in the 
endocardium, which upon shrinking brings about 
defective valves, with leakage of blood. This in- 
creases the work of the heart, 
and although that organ in 
an emergency can do twenty 
times its normal work, there 
is of course a limit to its 
power, and broken compen- 
sation sooner or later follows. 
The vasa vasorum, that 
carry blood to nourish the 
walls of both arteries and 
veins, are very important 
structures. The coronary 
vessels of the heart belong to 
this class and their course 
is quite definitely known. 
Our knowledge of the rest is 
vague. They ramify through 
the adventitia and to a less 
extent in the media. If a 
blood-clot forms within the 
vessel, loops from the vasa vasorum enter the clot and 
assist in its organization. 
The endothelial cells of the intima, according to 
one theory, are active agents in preserving the 
fluid condition of the blood; that is, inhibiting 
coagulation. If these cells are injured a clot of 
Fig. 87.- Cellular element of 
red marrow. 112 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
blood quickly forms upon the injured or denuded 
surface. Surgeons take advantage of this principle 
and twist or crush the ends of bleeding vessels to 
check a hemorrhage. 
The identification of blood-stains is often a medico- 
legal problem. The corpuscles of the blood pre- 
serve their integrity for a remarkably long period of 
time, so that in a water solution of even an old clot, 
Fig. 88.-Section of red marrow. 
the red blood-corpuscles are readily detected under 
the microscope. Hemin crystals is another evidence 
that the stain is blood. To identify the blood of 
man is practically impossible. Non-mammalian 
blood, as that of a bird, can usually be positively 
recognized by the nucleated red blood-corpuscles 
and their oval form. The practical value of this in 
criminal cases is apparent. CIRCULATORY SYSTEM. 
113 
LYMPHATIC SYSTEM, THYMUS, AND SPLEEN. 
1. Lymphatic Capillaries.-The walls of these 
capillaries consist of a single layer of flattened 
epithelial cells (mesothelial or endothelial). They 
therefore, histologically, resemble the blood-capil- 
laries. They are not so well defined but represent 
rather irregular cavities with numerous constrictions. 
These capillaries, according to one theory, form a 
closed system and open only into the larger vessels. 
Fig. 89.- Section of lymph node. 
Another theory is that at their origin they communi- 
cate with intercellular spaces. 
2. Lymphatic Vessels.-These accompany blood- 
vessels and have very thin walls. Ultimately they 
drain into the large thoracic lymph duct or the short 
right lymphatic duct; each finally opens into the 
venous system at the junction of the subclavian and 
jugular veins. The thoracic duct begins with the 114 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
receptaculum chili, just below the diaphragm and a 
little to the right of the vertebrae, passes upward into 
the thorax to open into the venous system on the 
left side, as given above. The histology of the walls 
of these vessels resembles that of the veins. 
3. Lymph Nodes. These represent adenoid tissue 
and consist of (1) reticular connective tissue and (2) 
lymph cells. Lymph nodes are found throughout 
Fig. 90.- From a human lymph gland. At a are seen the con- 
centrically arranged cells of the lymph nodules (fixation with Flem- 
ming's fluid) (Bohm and Davidoff). 
the body in connection with lymph vessels, fat and 
connective tissue. They serve as filters to the lymph 
and contribute white corpuscles to the blood. 
Structurally, these nodes have a connective-tissue 
capsule, that sends filaments into the node, called 
trabeculae. Within these meshes lymph cells arc 
densely packed around the periphery of secondary 
nodules, which in turn occupy the cortex of each CIRCULATORY SYSTEM. 
115 
node. The center of each nodule is known as the 
germ center or lymph pulp. The periphery of each 
secondary nodule, being densely packed with white 
lymph-corpuscles, takes a darker stain than the 
center. The space occupied by these white corpus- 
cles is called the lymph sinus. The cells of the sinus 
are in circulation while those of the germ center 
remain stationary. 
Fig. 91.- A solitary lymph nodule from the human colon. At 
a is seen the pronounced concentric arrangement of the lymph cells 
(Bohm and Davidoff). 
Lymph nodes represent adenoid tissue and con- 
sist of two elements, (a) reticular connective tissue, 
with many clastic fibers, and (&) lymphoid cells. An 
inflammation of this tissue is therefore called adeni- 
tis. Blood-vessels and nerves ramify through this 
tissue. They enter at one point called the hilum. 
Lymph vessels connect with opposite points of the 
node, the efferent one passing out at the hilum. The 116 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
efferent quickly unites with a second node to which it 
becomes the afferent vessel. In this way the lymph 
nodes are united into chains, always accompanying 
blood-vessels and fascia. 
Solitary lymph nodes are found just beneath the 
epithelium of mucous membranes, particularly in 
the alimentary tract. They resemble secondary 
nodules of lymph nodes. In the lower part of the 
Fig. 92.- A small lobule from the thymus of child, with well- 
developed cortex, presenting a structure similar to that of the cortex 
of a lymph gland (Bohm and Davidoff). 
ileum they are collected into patches called ag- 
minated lymph nodules or Peyer's patches. 
Hemolymph Nodes.-These resemble the lymph 
nodes described above, except that the lymph sinus 
is tilled with blood. When first discovered they were 
believed to be evidence of disease, but they are now 
looked upon as normal structures. They are most 
readily found in the fascia involving the tho- 
racic aorta, and are particularly abundant in the 
sheep. CIRCULATORY SYSTEM. 
117 
THYMUS GLAND. 
The thymus gland is described in this place be- 
cause of its resemblance in the adult to a lymph 
organ. In the embryo it is an epithelial organ that 
develops from the hypoderm of the third and fourth 
visceral clefts. Lymphoid tissue invades this epithe- 
lium and reaches its highest development in a child 
two years old. After this age the lymphoid tissue is 
invaded by connective tissue and fat, so that at the 
Fig. 93.- Section of lobule of thymus gland. 
age of puberty only a remnant of the original struc- 
ture remains. 
In the child the thymus is a paired, elongated, 
lobulated, ductless organ that lies partly in the neck 
and partly in the thorax upon the large blood- 
vessels. Structurally we recognize a capsule with 
trabeculae, pulp and the corpuscles of Hassal. 
i. Capsule and Trabeculae.-The capsule consists 118 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
of dense connective tissue, mostly nonclastic fibers 
and cells. Processes or trabeculae. pass into the or- 
gan from the capsule and divide it up into distinct 
angular lobules. Fibers from the trabeculae enter 
the lobules where they interlace to form a supporting 
reticulum. 
2. Pulp.-This consists of lymphoid cells that fill 
the intersticies of each lobule. The cells are more 
densely packed along the periphery of each lobule, 
so that an outer or cortical layer can be distin- 
guished from a central portion, the medulla. 
3. Corpuscles of Hassal.- 
These are nests of epithelial 
cells that lie in the medulla 
and are remnants that show 
the epithelial origin of the or- 
gan. They stain red with eo- 
sin and arc found in no other 
organ. It is affirmed that 
these epithelial cells continue to grow after birth and 
may be found late in life when only remnants of the 
thymus is present. 
SPLEEN. 
The spleen is a blood-forming organ, very vas- 
cular, purple in color, and with a density slightly 
more than that of the liver. It varies greatly in 
size, the average being five inches long and three 
inches wide. Its surfaces touch the left kidney, the 
cardiac end of the stomach, and the left lower aspect 
of the diaphragm. Its long axis follows the direction 
of the tenth rib. It is practically covered by the 
Fig. 94.-Corpuscle of 
Hassal surrounded by lym- 
phoid cells from the me- 
dulla. CIRCULATORY SYSTEM. 
119 
peritoneum. The structures to be recognized are 
capsule and trabeculae, Malpighian corpuscles, and 
spleen pulp. 
i. Capsule and Trabeculae.-The investing peri- 
toneum forms a serous coat with simple squamous 
epithelium and connective-tissue fibers. Sub- 
jacent to this the spleen is provided with a strong 
Fig. 95.- Portion of section of human spleen. The figure gives a 
general view of the structure of the spleen (Sobotta). 
capsule consisting of elastic fibers, connective-tissue 
cells and involuntary muscle. The spleen is thus 
not only distensible but may pulsate. From the 
deep surface of the capsule processes or trabecula of 
connective tissue and smooth muscle pass into the 
substance of the spleen. From the trabeculae finer 
branches pass to form a fine supporting fabric for 
the whole organ. 120 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
2. Malpighian Corpuscles.-These are lymph pock- 
ets in the adventitia of the smaller arteries. The 
artery rarely passes through the center of the cor- 
puscle, but usually eccentric to or one side of it. The 
lymph corpuscle is liberally supplied with blood. 
3. Spleen Pulp.-This constitutes the bulk of the 
spleen and fills the spaces between the trabeculae. 
The constituent corpuscles of the blood arc present 
in this pulp and splenic cells. The latter are slightly 
Fig. 96.- Section of spleen 
larger than white blood-corpuscles, are mononu- 
cleated and contain pigment and frequently red 
blood-corpuscles. 
Blood Supply.-The splenic artery enters the hilum 
and its branches follow the trabeculae. Ultimately 
the smaller branches enter the spleen pulp. Beyond 
the Malpighian bodies the smaller arteries end in 
minute dilatations known as the ampulice oj Thoma. 
Beyond these the blood flows directly into the meshes circulatory system. 
121 
of the spleen pulp with no other walls than the spleen 
cells. The veins begin in the same way as the 
arteries end. The capillary veins pass directly to 
the trabeculae and ultimately unite at the hilus to 
form the splenic vein which drains into the portal. 
General Considerations.-The invasion of bacteria 
into the system is chiefly along the lymphatics. 
Each lymph node becomes a point of resistance, and 
Fig. 97.- From the human spleen (chrome-silver method) (Bohm and 
Davidoff). 
usually enlarges many times the normal size, far in 
advance of the seat of infection. This is due to the 
absorption of the toxins. Thus the lymph nodes in 
the groin enlarge from an infection in the toe, those 
in the axilla from an infected finger, and those of the 
neck from a bad tooth. If these barriers break down 
the infection becomes systemic, a condition known in 
a general way as blood-poisoning. 122 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
The function of the thymus gland is not known. 
Since its structure resembles the tissue of a lymph 
node it is reasonable to suppose that it has a like 
function. Recently structural changes have been 
observed in this organ in epileptics, but whether 
these changes are a cause or a consequence of the dis- 
ease is not known. 
The lymphoid tissue of the spleen no doubt 
Fig. 98.- Diagram of lobule of the spleen (Mall). 
contributes to the supply of white blood-corpuscles. 
The broken-down red corpuscles found in this organ 
have led to the further idea that the spleen is a 
graveyard for the worn-out red corpuscles of the 
blood. Leucocytes are supposed to feed upon this 
detritus and then migrate to the liver, where it is 
elaborated into the bile pigment of that organ. 
Anything that causes an enlargement of the lymph CIRCULATORY SYSTEM. 
123 
nodes usually causes an enlargement of the spleen. 
Like these nodes the spleen is capable of enormous 
distention, due to the abundance of elastic con- 
nective-tissue fibers. This is particularly so in 
typhoid fever, where the spleen has been known to 
weigh fifteen or twenty pounds. 
On account of the rich blood supply an injury to 
the spleen causes severe hemorrhage, which the 
pulpy condition of the organ renders difficult to 
check, as a suture usually does not hold. In such 
accidents the whole spleen has been removed with- 
out fatal results. Extirpation of the spleen is also 
justified in certain diseases of that organ. CHAPTER IV. 
DIGESTIVE SYSTEM. 
The digestive system consists of alimentary canal 
and accessory digestive glands. 
The Alimentary Canal.-This is a muscular tube 
extending through the body and measures about 
thirty feet in length. The following parts will be 
described: - 
I. Mouth. 
II. Pharynx. 
III. Esophagus. 
IV. Stomach. 
V. Small Intestine. 
i. Duodenum. 
2. Jejunum. 
3. Ileum. 
IV. Targe Intestine. 
1. Vermiform Appendix. 
2. Cecum. 
3. Colon. 
(a) Ascending. 
(6) Transverse. 
(c) Descending. 
(d) Sigmoid Flexure. 
4. Rectum. 
THE MOUTH. 
The mouth is limited by the lips in front, and the 
cheeks laterally. The arched palate forms its roof 
124 DIGESTIVE SYSTEM. 
125 
and the tongue is attached to the movable floor, 
while posteriorly it opens into the pharynx through 
the isthmus or fauces. This cavity is lined by a con- 
tinuous mucous membrane, consisting of stratified 
mucous epithelium placed on a tunica propria. In 
Fig. 99.-Human embryo of about twenty-eight days (His): I-V, 
brain-vesicles; /*, /2, /3, / cephalic, cervical, dorsal, and lumbar flexures; 
ot, otic vesicle; ol, olfactory pit; mx, maxillary process; h', li', heart; 
I, I', limbs; a Is, allantoic stalk; ch, villous chorion. 
the submucosa is found connective-tissue elements 
in which the clastic fibers predominate; also con- 
nective-tissue cells, mucous and serous glands, 
nerves, and nerve endings, blood- and lymph-vessels. 126 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
The mucous membrane is continuous with the skin 
at the outer border of the lips. At this border the 
horny layer of skin begins, otherwise the skin and 
this mucous membrane are similar structures. 
Morphologically, the mouth cavity is to be re- 
garded as a part of the outside surface of the body, 
which, embryologically, has been included by the 
development of neighboring parts. At the time the 
neural folds are closing dorsally to form the brain and 
cord there develops a series of paired, ventral, 
facial pits. These, enumerated from before back- 
wards, are: the lens of the eye, the nasal pit, the 
mouth, and gill clefts. The tissue between the latter 
are called visceral arches, while that one between the 
anterior gill cleft and the mouth cavity is the man- 
dibular arch. The latter is morphologically analogous 
to the visceral arches. In man the gill clefts all 
finally close permanently, but the ectodermal em- 
bryonic mouth cavity ultimately unites with the 
embryonic foregut, thus forming the fauces which 
lead to the pharynx. This final perforation be- 
tween the mouth cavity and the foregut is paired, in 
lower forms, which with other embryonic relations 
confirms the view that the mouth cavity morpho- 
logically represents a median fusion of two gill clefts. 
During this period of development the forebrain 
grows ventrally and the mandibular arch grows in the 
same direction. The space between these structures 
is the beginning of the mouth and the nose, and is 
called the stomodeum. At this time a rounded eleva- 
tion, from the base of the mandibular arch, grows for- 
ward along the base of the forebrain. This growth DIGESTIVE SYSTEM. 
127 
forms part of the maxillary arch, and finally most of 
the upper jaw. In this manner the stomodeum 
Fig. 100.- Development of the face of the human embryo (His): 
A, Embryo of about twenty-nine days; B, embryo of about thirty-four 
days; C, embryo of about the eighth week; D, embryo at end of the 
second month. 
becomes divided into an olfactory region and the 
mouth cavity proper. The stomodeum at this stage 128 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
is a deep pentagonal cavity. Its lower boundary is 
formed by the mandibular arch, while laterally are 
to be found the maxillary processes of each side. 
Its upper boundary is formed by an unpaired growth 
called the nasofrontal or nasal process (Fig. 100.) 
Situated on each side of the nasal process are the 
nasal pits. Each pit divides the nasofrontal process 
into a lateral external portion called the lateral 
frontal protuberance, which forms the outer boundary 
Fig. ioi.- Median section through the head of an embryo rabbit 
6 mm. long (after Mihalkovics). 
of each nasal pit, and a median or central portion 
called the globular protuberance, which constitutes 
the inner boundary of each pit. The two lateral or 
side protuberances grow around the olfactory pits 
and form the alse of the nose, while the two central 
portions develop into the intermaxillary bone con- 
taining the incisor teeth and the center of the lip. 
By studying the text figures a correct idea of these DIGESTIVE SYSTEM. 
129 
relations is readily obtained. It will be seen that 
the line of contact between each lateral protuberance 
and maxillary process forms a groove, the naso-optic 
furrow or lacrimal groove, which later closes to form 
the lacrimal canal. The line of contact between 
each globular protuberance and the maxillary pro- 
cess is less close, and places each nasal pit in wide 
communication with the mouth. A failure of union 
in the latter case causes the deformity of harelip, 
Fig. 102.- Roof of the oral cavity of a human embryo with the fun 
daments of the palatal processes (after His). 
which may be double or single, depending on 
whether both or only one side is involved. 
About the fortieth day, in the human embryo, the 
maxillary processes have grown so far toward the 
median plane that they have met and united with 
the lateral and also the median protuberances of the 
nasofrontal process. The nasal pits are thus sepa- 
rated externally from the oral fossa. With this 
union the arch of the upper jaw is complete, but the 130 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
inclosed space is in one chamber, there being no 
separation between the mouth and nose cavities. 
The formation of a palate, however, effects a separa- 
tion between the two. The rudiments of the palate 
appear as shelf-like projections from the inner or 
oral surface of the upper jaw. A triangular piece 
grows backward from the globular protuberance of 
the nasofrontal process, which ultimately unites 
with horizontal or palatal plates from the maxillary 
arch. In the eighth week of embryonic life, union of 
the palatal plates begins at their anterior extremi- 
ties and proceeds backward. A deficiency in the 
union constitutes the deformity of clejt palate. 
Cleft palate is therefore, embryologically, a later 
development than harelip. Either may occur with- 
out the other, but they are usually found together. 
The cleft of the palate usually turns to one side, 
passing out between the cuspid and lateral incisor 
teeth. A double cleft palate is Y-shaped, the 
center piece in front containing the incisors, and 
representing the anterior triangular piece of the 
rudimentary palate, this piece having failed to unite 
with the lateral palatine plates. This deficiency 
may involve the hard or the soft palate, or it may 
affect both, and even produce a cleft or bifid uvula. 
The completion of the palate definitely separates 
the nasal chambers from the mouth, the only com- 
munication between the two being through the 
posterior nares. The permanent limitations of the 
mouth are thus established from a cavity that 
develops primarily as an ectodermal invagination. 
The ectoderm invests not only the mouth proper, DIGESTIVE SYSTEM. 
131 
but clothes at least the anterior portion of the adult 
pharynx. The tongue, however, is invested with en- 
toderm epithelium and 
so are the Eustachian 
tubes. 
TEETH. 
Morphologica 11 y, 
teeth are appendages 
of the skin, and arc to 
be compared with such 
structures as hair and 
nails. They are thus 
a part of the exoskcl- 
eton and their relation 
to the bones or the en- 
doskcleton is entirely 
a secondary process, 
for the purpose of 
strength and support. 
In many of the fishes 
the mouth generally 
is lined by simple cone- 
shaped teeth that serve 
the purpose of seizing 
and holding the ani- 
mal's prey. In man 
the additional function of masticating the food has 
greatly modified the form and structure of teeth. 
Dentition.-There are twenty deciduous or tem- 
porary teeth that erupt between the ages of six 
months and two and one-half years. In each jaw 
these are,-incisors 4, cuspids 2, molars 4, the dental 
Fig. 103.- The palate and supe- 
rior dental arch (right side): i, Me- 
dian incisors; 2, lateral incisors; 3, 
canine; 4, first bicuspid; 5, second 
bicuspid; 6, first molar; 7, second 
molar; 8, wisdom-tooth; 9, mucous 
membrane of the hard palate con- 
tinuous behind with that of the soft 
palate; 10, the anteroposterior raphe 
of palate; 11, pits on each side of the 
raphe perforated with the orifices of 
glands; 12, anterior rugosities of the 
mucous membrane (after Testut). Designation of 
the Follicles. 
Place of Origin 
of the Epithe- 
lial Cord. 
Period at 
WHICH THE 
Enamel-Or- 
gan First 
Appears. 
Period at 
WHICH THE 
Dental 
Bulb Ap- 
pears. 
Time of the 
Appearance 
of the Fol- 
licular 
Wall. 
Closing of 
the Fol- 
licle and 
Rupture of 
the Cord. 
Periods at 
WHICH THE 
Dentine- 
cap First 
Appears. 
Periods at 
WHICH THE 
Teeth are 
Erupted. 
Periods at 
which the 
Teeth are 
Normally 
Shed. 
Inf. cent, in- > 
cis 
6th month. 
7th year. 
Sup. cent, in- 
cis 
10th month. 
714 years. 
tition. 
Inf. lat. incis. 
Sup. lat. in- 
cis 
16th 
week. 
16th month. 
20th month. 
j- Sth year. 
emporary den 
Inf. cuspids . 
Sup. cuspids, 
ist inf. mo- 
lars .... 
• 
Epithelial lamina. 
From 7th to 
Sth week. 
r 
y 9th week. 
10th week. 
f Beginning 
< of the 
(4th month. 
30th to the 
32d month. 
| 12th year. 
ist sup. mo- 
lars .... 
2d inf. mo- 
lars .... 
17th 
week. 
24th month. 
26th month. 
28th month. 
10th year. 
10% years. 
1 ith year. 
2d sup. mo- 
lars .... 
30th month. 
11% years. 
CHRONOLOGY OF THE DENTAL FOLLICLE IN MAN (Legros and MagiTot). 
132  
' Inf. cent, in- 
cis 
Sup. cent, in- 
cis. .... 
Inf. lat. incis. 
Sup. lat. in- 
cis 
1 
Cord of the 
corresponding 
temporary- 
teeth. 
-{7th year. 
8% years. 
Inf. cuspids. 
Sup. cuspids. 
About the 
16th week. 
f 20th 
I week. 
21st week. 
9th month. 
f ist month 
1 after birth. 
) II to 12 
.J years. 
Permanent dentition. 
ist inf. bi- 
cusp. . . . 
ist sup. bi- 
cusp. . . . 
2d inf. bi- 
cusp. . . . 
2d sup. bi- 
cusp. . . . 
ist inf. mo- 
lars .... 
ist sup. mo- 
lars .... J 
Cord of the 
corresponding 
temporary- 
molars. 
Epithelial 
lamina. 
15th week. 
17th week. 
18th week. 
• 20th week. 
f 6th month 
■< of fetal 
( life. 
| 9 to 10 
j years. 
j- nth year. 
1 From 5 to 
[ 6 years. 
2d inf. mo- 
lars .... 
2d sup. mo- 
lars .... 
Cord of the 
ist permanent 
molars. 
3d mo. after 
birth. 
| ist year. 
ist year. 
ist year. 
3d year. 
1 From 12 to 
J 13 years. 
3d inf. mo- 
lars .... 
3d sup. mo- 
lars . . . . 
Cord of the 
2d permanent 
molars. 
J 3d year. 
f After the 
(6th year. 
After the 
6th year. 
After the 
6th year. 
| 12th year. 
1 From 18 to 
J 25 years. 
133 134 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
formula for one side being,-1.| C.^ M.-f = 10.' The 
second set, or permanent teeth, number thirty-two 
Fig. 104.- Scheme of a longitudinal section through a human 
tooth. In the enamel are seen the "lines of Retzius" (Bohm and 
Davidoff). PLATE II. 
Dissected Skulls Showing the Development of the Teeth 
(Noyes). 
i. Skull at nine months, central incisors just erupted, laterals not yet 
through the gum. The root of the central about half formed. The 
lower first and second temporary molars seen in their crypts. The crypt 
for the lower first permanent molar shown, but the developing tooth has 
dropped out of it. The upper temporary cuspid and first and second 
molars are seen in their crypts. Notice the straightness of the lower jaw. 
2. Skull at one year. Two incisors in each jaw are erupted. The 
first molars are just starting. Notice the formation of the root of the 
lower temporary molars just beginning. Also notice the first permanent 
molar in its crypt with half of the crown formed. 
3. Skull in the second year. The temporary first molar and cuspid 
partly erupted. Notice the development of their roots. Notice the per- 
manent cuspid above and the first molar below in their crypts. 
4. Skull in fourth year. Complete temporary dentition. Notice 
the upper central, lateral cuspid and bicuspid in their crypts; the 
lower incisors, cuspid, first bicuspid, and first permanent molar. 
5. Skull in sixth year. Complete temporary dentition with the 
first permanent molar in place. The lower central incisors have just 
been lost and the permanent ones are just coming through the gum. The 
cuspids, bicuspids and second molar are seen in their crypts. 
6. The left side of the same skull as No. 5. Notice the extent to 
which the roots of the first permanent molar are developed. 
7. Front view of the same skull as No. 6. Notice the position of the 
incisors and cuspids in their crypts. 
8. Skull in seventh year. The toothless age. Upper incisors lost 
and the permanent ones not erupted. One lower incisor in place. First 
permanent molar in place, but the roots not fully formed. Crown of the 
second permanent molar seen in its crypt. PLATE II PLATE III. 
Dissected Skulls Showing the Development of the Teeth- 
Continued (Noyes). 
g. Skull in eleventh year. The incisors are in position, but the tem- 
porary molars and cuspids are still in position. The second permanent 
molar is through the bone but not through the gum. 
io. The left side of the same skull. On this side the lower tem- 
porary cuspid and first molar have been lost. Note the position of the 
upper cuspid in these pictures and the distance the root extends toward 
the orbit. The lateral on the left side is not of typical form, but is a 
"peg tooth." 
xi. Skull in the thirteenth year. The lower second molar the only 
remaining temporary tooth. The second permanent molar is in place 
but the roots are not fully developed. The crypt for the third molar 
(wisdom tooth) is seen. 
12. Skull of young adult. The upper centrals are broken. The 
second molars are fully developed and the third molar shows the crown 
fully formed in the crypt. 
13. Skull of adult. This shows the full permanent dentition and 
the roots of the teeth. 
14. Edentulous jaws. Notice the position of the mental foramen. Plate ill DIGESTIVE SYSTEM. 
135 
and in each jaw are divided into,-incisors 4, cus- 
pids 2, bicuspids 4, molars, 3, the dental formula for 
one side being,-I.| C.j- B.| M.f = 16. 
Structure of Teeth.-The parts of a tooth are 
crown, neck, roots and pulp. Its calcareous wall 
consists of enamel, dentin, and cementum. 
Enamel.-The enamel is the hardest tissue in the 
body and covers the exposed portion, or crown, of 
the teeth. Its function is to mechanically protect 
the tooth. This enamel is derived from the ecto- 
derm, while all bone tissues are products of the 
mesoderm. Bone, if injured, may regenerate and 
repair the defect. Enamel does not regenerate if 
injured, the defect being permanent, as the formative 
enamel tissue disappears before the eruption of the 
tooth. Chemically, it is composed of phosphates 
and carbonates of calcium and magnesium, a small 
amount of fluorides, water, and perhaps a very small 
amount of organic material. In consequence of the 
latter, enamel, unlike bone, is soluble in acids, 
leaving scarcely any residue. 
Enamel is composed of two structural elements,- 
(a) enamel rods or prisms (also called fibers), and (6) 
inter prismatic or cement substance, both of which arc 
calcified. These elements have different properties, 
both chemical and physical. The interprismatic 
substance is more readily acted upon by acids, and 
it is therefore possible to etch enamel sections and 
produce a disassociation of the enamel rods. The 
interprismatic substance is not so strong as the rods, 
and in splitting or breaking the enamel the tissue 
usually separates along the cement lines; that is, 136 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
these lines form paths of least resistance, a fact taken 
advantage of in operative dentistry. 
According to Noyes ("Dental Histology''), "the 
enamel rods, or prisms, arc long, slender prismatic 
rods or fibers, five- or six-sided, pointed at both ends, 
and alternately expanded and constricted through- 
out their length. They are from 3.4 to 4.5 microns 
in diameter, some of them apparently reaching the 
entire distance from the surface of the dentin to the 
surface of the enamel, but, as the diameter of the 
rods is the same at their outer and inner ends, and 
as the crown surface is 
much greater than the 
surface of dentin cov- 
ered by enamel, there 
are many rods that do 
not extend through 
the entire thickness. 
These short rods end 
in tapering points be- 
tween the converging 
rods, which extend the entire distance. To ex- 
press this in terms of development, as the forma- 
tion of enamel begins at the surface of the dentin, 
the increasing area of crown surface requires more 
ameloblasts, and as new ameloblasts take their 
places in the layer the formation of new enamel rods 
begins between the rods which were previously 
forming. These short rods are most numerous over 
the marginal ridges and the points of the cusps." 
The rods are not perfectly smooth and even, but 
show alternately expansions and constrictions. 
Fig. 105.-a. Enamel rods in cross 
section; b, Enamel rods, longitudinal 
view. DIGESTIVE SYSTEM. 
137 
They are so arranged that the expansion of adjacent 
rods lie opposite each other; that is, the expansions 
do not interlock with the constrictions. The cement 
substance, therefore, has a reciprocal arrangement. 
Sections ground parallel to the rods show, therefore, 
dark and light lines, described as the striations of the 
enamel, which are caused by the difference in the 
refracting power of the prismatic and interprismatic 
substances. In a ground section across the rods, the 
tissue presents a mosaic pattern, which becomes 
more distinct if treated with acid. 
Fig. to6.- Transverse section of enamel (Noyes) 
Lines of Retzius-These lines or stratification 
bands begin at the tip of the dentin cusps and sweep 
around in larger and larger zones. They thus pass 
obliquely through the enamel and record the growth 
of the crown, as each line was at one time the surface 
of the enamel. They arc to be regarded as traces 
of the strata caused by the periodic deposition of 
lime salts. 
According to Noyes, "the appearance of striation 
is the record in the fully formed tissue of the manner 138 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
of growth, each dark stripe or expansion in a rod 
representing a globule of calcified material. The 
ameloblasts build up the rods by the addition of 
globule after globule, surrounding them with a 
cementing substance and completing the calcifi- 
cation of both. In this sense the striation of the 
enamel may be said to record the growth of the in- 
dividual rods." 
Direction of the En- 
amel Rods.-Upon the 
axial surface the rods 
are usually straight 
and parallel with each 
other, but upon the oc- 
clusal surface they 
change their direction 
by a series of sym- 
metrical curves, and 
often become much 
twisted and wound 
around each other, par- 
ticularly the inner 
ends. In operative 
dentistry it is found 
that the enamel upon the axial surface cleaves 
readily while the gnarled portion upon the occlusal 
surface tends to break away in chunks. 
Fig. no shows the general plan of the arrange- 
ment of the enamel rods in the formation of the 
crown. In the gingival half of the middle third the 
rods are horizontal. Their, inclination, from this 
horizontal direction, gradually increases toward the 
Fig. 107.-Tip of an incisor, 
showing lines of stratification of the 
enamel (Noyes). digestive system. 
139 
root and toward the occlusal surface, so that at the 
apices of the latter surface the rods are placed 
vertical to a horizontal plane. Because of this plan 
Noyes divides all cavities, in dental work, into two 
classes: 
" i.-Those in which the enamel rods are in- 
Fig. 108. - Straight enamel, 
showing dento-enamel junction 
(Noyes). 
Fig. 109. - Gnarled enamel, 
showing dento-enamel junction 
(Noyes). 
dined toward the cavity, characteristic of the oc- 
clusal surfaces. 
" 2.-Those in which the enamel rods are inclined 
away from the cavity, characteristic of axial sur- 
faces" (Fig. in). 
In preparing cavities on the axial surfaces the 140 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
lateral walls should be beveled, as shown in the above 
figure. The historic requirements for strength in 
enamel walls are: 
1. The enamel must be supported upon sound 
dentin. 
2. The rods which form the cavo-surface angle 
must run uninterruptedly to the dentin. 
3. They must be supported by short rods, with 
Fig. no.- Drawing, showing the direction of the rods over the mesial 
marginal ridge of a bicuspid (Noyes). 
their inner ends resting on the dentin and their 
outer ends abutting upon the cavity wall, where they 
will be covered by the filling material. 
4. That the cavo-surface angle be cut in such a 
way as not to expose the ends of the rods to fracture 
in condensing the filling material against them. 
"The first step in the preparation of an enamel 
wall is to determine the direction of the enamel rods 
by cleavage with a chisel or hatchet. Then the wall digestive system. 
141 
Fig. in.- Illustrating the two classes of cavities (Noyes). 
Fig. 112- Labio-lingual section of superior lateral incisor, showing 
a pit cavity (Noyes). 142 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
must be smoothed or trimmed by a shaving motion 
of the chisel, increasing the inclination of the wall 
slightly. This is done so as to be sure and reach the 
rod directions and remove the portions of the tissue 
that has been splintered by the cleavage. Then the 
cavo-surface may or may not be trimmed, as the 
position demands" (Fig. m, Noyes). 
Fig. 113.- A portion of a ground tooth from man, showing enamel 
and dentin (Bohm and Davidoff). 
Grooves, fissures, pits and developmental lines 
are points of weakness and in operative work cavi- 
ties must be excavated so as to establish a strong 
margin, histologically, against which to pack the DIGESTIVE SYSTEM. 
143 
filling. The arrangement of the enamel rods must 
therefore be constantly borne in mind in the opera- 
tive repair of teeth. 
Dentin.-The dentin is the second layer of teeth, 
and not only makes up the mass of a tooth but de- 
termines its form; that is, the number of cusps and 
roots is moulded by the developmental process of the 
dentin. Its histologic form has much to do with the 
penetration of caries. 
Dentin, like bone, develops from the mesoderm, 
and consists of an organic, formative matrix impreg- 
nated with about 72 per cent, of inorganic salts. On 
boiling it yields gelatin. Minute canals of dentinal 
tubules radiate from the central cavity of the tooth, 
which contains the formative organ or pulp. These 
tubules arc from 1.1 to 2.3 microns in diameter and 
are separated from each other by a dentinal matrix of 
about 10 microns in diameter. In the crown the 
tubules branch but little, excepting close to the en- 
amel where they anastomose freely. In the crown 
they radiate in sweeping curves so as to open at 
right angles on the dentinal surface. This produces 
"s" or "f''-shaped curves known as primary curves. 
They also present many wavy curves known as 
secondary curves, which is really the result of an open 
spiral course taken by the tubules. In the body of 
the dentin a few small branches are given off at 
acute angles, but near the enamel junction the tu- 
bules fork and branch freely, forming an anasto- 
mosis that facilitates in the spreading of caries just 
beneath the enamel, the micro-organisms diffusing 
sideways and then penetrating the dentin in the 
direction of the tubes. 144 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
In the root the tubules radiate directly to the ce- 
mentum, showing only the primary curves. Many 
line branches pass in all directions from tubule to 
tubule. The dentin next to the ccmentum contains 
many small irregular spaces that connect with the 
dentinal tubules. They present a granular ap- 
pearance in ground sections, and are therefore 
called the granular layer of Tomes. These spaces are 
tilled by the enlarged ends of the dentinal fibrils, 
which are cell processes of the 
odontoblasts, while the fibrils 
also fill the dentinal tubules. 
The layer of Tomes may some- 
times be found beneath the 
enamel, but is never well 
marked. 
The dento-enamel junction 
presents rounded projections. 
This scalloped appearance has 
given rise to the view that 
certain dentinal tubules pass 
for a short distance into the 
enamel. In ground sections, 
irregularly branched dentinal 
spaces are often found at a uniform depth from the 
surface. These are the inter globular spaces of Czer- 
mak and represent areas of imperfectly developed 
dentin. Lastly, the sheaths of Neumann represent 
the inner wall of the dentinal tubules, and may be 
regarded as differentiated and more resistant ground 
substance. 
The formation of dentin continues for an indef- 
Fig. 114.- Section of den- 
tin at right' angles to the 
tubules (Noyes). DIGESTIVE SYSTEM. 
145 
inite period after the eruption of a tooth. The proc- 
ess is one of apposition, thickening the dentin at the 
expense of the pulp. Finally this growth ceases. 
Irritation of the pulp, or the pulp of some tooth on 
the same side, may lead to the formation of second- 
ary dentin. The latter is an imperfect structure. 
The tubules are smaller and less numerous, while the 
matrix is less compact and shows a deficiency of 
Fig. 115.-Section of dentin in the crown cut in length of the tubules 
(Noyes). 
inorganic salts. Several deposits of secondary 
dentin may thus be produced. 
The Pulp.-The pulp occupies the center of the 
tooth. It consists of connective-tissue cells, con- 
nective-tissue fibrils, a semifluid interfibrillar ground 
substance, nerve plexus largely non-medullated, 
blood and lymph vessels. We may recognize three 
kinds or layers of cells, the most important being the 146 
NORMAL HISTOLOGY AND ORGANOGRAPHY 
odontoblasts, forming the outer surface of the pulp 
next to the dentin. 
i. The odontoblasts form a continuous layer over 
the entire pulp surface, being everywhere in contact 
with the dentin. This layer has been called the 
Fig. 116.-A portion of a cross section through a developing tooth 
(Bohm and Davidoff). The dentin is formed, but has become homo- 
geneous from calcification. Bleu de Lyon differentiates it into zones 
(a and b). At c is seen the intimate relationship of the odontoblasts 
to the tissue of the dental pulp. 
membrane eboris or the "membrane of ivory.'' The 
odontoblasts are mesoderm cells, columnar, some- 
times club-shaped, with basal nuclei and three 
kinds of processes, (i) Each cell has one to three 
long, slender, protoplasmic processes projecting into DIGESTIVE SYSTEM. 
147 
the dentinal tubules, and extending through the 
tubule to the outer surface of the dentin, where they 
completely fill the granular spaces already described 
as the granular layer of Tonies. It is generally 
believed that these processes may transmit im- 
pressions to the sensory nerves of the pulp. (2) 
Each odontoblast shows lateral processes, minute 
but blunt, that interlock with like processes from 
adjacent cells. (3) Usually a single process pro- 
jects from the basal end into the pulp. 
The odontoblasts are dentin-forming cells and 
superintend the formation and calcification of 
primary and secondary dentin. 
2. The layer of Weil represents a layer of connec- 
tive-tissue cells forming a thin zone just beneath the 
odontoblasts. In thin sections this appears as a 
thin layer about half as thick as that of the odonto- 
blasts. 
3. Underneath the layer of Weil the connective- 
tissue cells are numerous and closely packed. To- 
ward the center of the pulp they become loosely but 
uniformly scattered. The cells are small, have a 
single deep-staining nucleus, and the cytoplasm 
stretching out into slender processes in many direc- 
tions, forming stellate cells; or in two directions to 
form spindle cells. 
The connective-tissue fibrils of the pulp are similar 
to those of white fibrous connective tissue, sometimes 
resembling the reticular variety. The vascular con- 
dition of the pulp makes it an organ of nourishment 
for the dentin as well as the mature tooth. 
Cementum.-The cementum covers the dentin in 148 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
the root portion of a tooth. At the gingival margin 
it slightly overlaps the enamel. Near this margin it 
forms a thin layer, but becomes thicker toward the 
apex of the root and between the roots of the bi- 
cuspids and molars. The cementum consists of 
parallel lamellae of bone tissue that contain no 
Haversian canals. Small blood-vessels from the in- 
vesting peridental membrane penetrate the lamellae, 
while other small vessels from the pulp pass through 
Fig. 117.- Cross section of human tooth, showing cement and dentin. 
At a are seen small interglobular spaces (Tomes' granular layer). 
the cementum in the opposite direction. Fibers 
from the investing peridental membrane find attach- 
ment in the cementum. These fibers resemble the 
fibers of Sharpey in bone. The cementum, there- 
fore, furnishes a medium of attachment by which the 
tooth is held in position. 
Cementum is constantly being produced by the 
apposition of new surface layers. In newly erupted DIGESTIVE SYSTEM. 
149 
teeth the cementum is thin and in teeth of old per- 
sons the cementum is thick. This continuous 
growth is necessary in order to establish attachment 
for new fibers of the peridental membrane and to con- 
form to the natural growth of the jaw. 
Between the lamellae, particularly in the apical 
portion of the root where the cementum is thick, 
numerous lacunae are present, resembling those of 
bone. Canaliculi radiate from these lacunae with 
less regularity, however, than in the case of bone. 
They may be confined to one side of a lacuna, usually 
the side toward the surface. 
Bocal thickenings of the cementum, called hyper- 
trophies, are common. These enlargements involve 
one or more of the lamellae and were formerly called 
exostoses, or cementostoses. 
Peridental Membrane.-This is an organic tissue 
that surrounds the root of teeth and occupies the 
space between the cementum and the bony wall 
of the alveoli. Its chief function is to anchor a tooth 
to the j'aw and give support to the gingivus. Its 
chief constituent is white connective-tissue fibers in- 
terspersed with a variety of cells, blood-vessels, 
lymphatics and nerves. 
The fibrous tissue may be divided into two classes: 
coarse, radiating fibers that form the principal bulk 
and perform the principal function of anchorage, and 
a secondary fine variety that interlace with these and 
unite largely with the anastomosing blood-vessels of 
the tissue. The principal fibers connect, on the one 
hand, with the cementum which they enter in bun- 
dles to form the fibers of Sharpey, and on the other 150 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
hand they unite with the periosteum of the bony 
alvoli and the subepithelial tissue of the gum. From 
the upper portion of the cementum these fibers pass 
horizontally, some of them directly to connect with 
the cementum of adjacent teeth and others to 
mingle with the connective tissue of the adjacent 
mucous membrane, thus giving a firm support to the 
Fig. 11S.- Transverse section of peridental membrane in alveolar 
portion (Noyes). 
gingivus, a condition which becomes of primary im- 
portance in the mastication of food. The fibrous 
mat of the gum is usually greater on the lingual side, 
where food is brought against the gingivus with con- 
siderable force. If a crown band is extended too far, 
or if deposits accumulate as in case of uncared-for digestive system. 
151 
teeth, these supporting fibers will be cut off and the 
gingivus drops down and no longer fills the inter- 
proximal space. 
In the alveolar portion the principal fibers not 
only spread out and radiate like a fan, but are in- 
clined downward from their attachment in the ce- 
mentum to their anchorage in the bony wall of the 
alveolus. Some of these fibers are tangential to the 
cementuni and thus support the tooth against a 
rotary strain. The principal fibers thus perform a 
physical function and firmly bind the tooth to the 
adjacent hard and soft tissues. At the alveolar 
border and at the apex of the root they are so ar- 
ranged as to support the tooth against lateral 
strain, while in the rest of the alveolar portion the 
tangential fibers are particularly numerous and sup- 
port the tooth against any rotary force which may 
result from the mastication of food. At the gingivus 
line the fibers blend with the submucosa and bind 
the gum closely to the neck of the tooth. At the 
apex of the root the secondary loose variety becomes 
continuous with the connective tissue of the tooth 
pulp. 
The cellular elements of the peridental membrane 
are the fibroblasts, cementoblasts, osteoblasts, osteo- 
clasts, and epithelial cells, which have been called the 
glands of the peridental membrane. All these cells 
arc interposed between the bundles of supporting 
fibers already described. 
i. The fibroblasts are spindle-shaped connective- 
tissue cells arranged in radiating rows between the 
fibers. They are numerous in young teeth and 152 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
the root. They produce the cementum and there- 
fore resemble the osteoblasts of bone. They have a 
single deep-staining nucleus and irregular processes 
that fit around and between the fibers and also ex- 
tend into the cementum. A cementoblast may be- 
come enclosed in the cementum and thus form a 
lacuna which it completely fills, thus making a 
Fig. 119.- Peridental membrane next to the cementum highly mag- 
nified (Noyes). 
relatively few in old teeth. The single nucleus stains 
deeply, being rich in chromatin. The cells are small 
and, as their name implies, their function is the pro- 
duction of fibers that give support to the tooth. 
2. The cementoblasts arc flat irregular cells that 
fit in and adjust themselves between the fibers so as 
to form a single layer everywhere over the surface of DIGESTIVE SYSTEM. 
153 
cement corpuscle analogous to a bone corpuscle. 
Such an inclusion is the exception in the life history 
of these cells. 
3. The osteoblasts are also connective-tissue cells, 
but cover the bony wall of the alveoli. They lie 
between the fibers and their function is the pro- 
duction of bone which anchors the supporting fibers 
to the alveolar wall. These cells are analogous to 
the osteoblasts of bone. 
4. The osteoclasts are large, bone-destroying, 
multinucleated cells that are often called giant cells. 
They may also act upon and absorb the cementum 
and dentin. They are not constantly present in the 
peridental membrane but appear whenever cal- 
cified tissue is to be destroyed. They apply them- 
selves to the surface to be absorbed and by their 
physiological action excavate cavities in which they 
lie, known as Howship's lacunce. The latter may 
later fill in with new cementum or bone, thus leaving 
a permanent record of the process of absorption and 
repair. The absorption of the roots of deciduous 
teeth results from the physiological action of the 
osteoclasts. If for any cause, such as bacterial in- 
vasion, the osteoclasts fail to appear, the root of 
the deciduous tooth does not absorb but remains as 
a permanent obstruction to the developing new tooth. 
5. Epithelial cells, believed by some to be remains 
of the enamel organ, envelop the surface of the roots 
and are found in both young and old teeth. Their 
function is not known. They appear as cords of 
epithelial cells that anastomose freely to form an en- 
veloping network, which nowhere seems to unite 154 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
with the epithelium of the mucous membrane of the 
mouth. The structure of some of these cords re- 
sembles that of tubular glands, and Dr. Black has 
suggested that their function may be a glandular one. 
They not infrequently enter into the pathological 
conditions of the peridental membrane. 
Blood Supply.-Usually several small blood-vessels 
enter the foramina at the 
apex of the root and pass di- 
rectly to the pulp. Upon 
reaching the pulp these ves- 
sels anastomose freely, form- 
ing an extensive blood plexus. 
A capillary plexus with nar- 
row meshes has been de- 
scribed between the layer of 
odontoblasts and the dentin, 
but does not penetrate the 
latter. Both arteries and 
veins have very thin walls 
and may be easily ruptured. 
The pulp therefore bleeds 
very easily when exposed. 
No accompanying lymphatics 
have been described. 
The peridental membrane, 
being a connective-tissue layer, has a very rich blood 
supply. Vessels enter the membrane near the apex 
of the root, accompanying the nerve at that, place; 
small arterioles penetrate laterally from the Haver- 
sian canals of the alveolar wall, and a third supply 
is derived from the mucous membrane of the gum, 
Fig. 120.- Showing the ar- 
rangement of epithelial cords 
or glands of the peridental 
membrane around the root 
of a central incisor (dia- 
gram by Dr. Black). DIGESTIVE SYSTEM. 
155 
vessels passing over the border of the alveolar proc- 
esses. This vascular condition is important, both in 
health and disease. 
Nerve Supply.-The tooth pulp is supplied with 
nerve fibers from the fifth cranial nerve. Medul- 
lated dendrites of sensory neurons enter the pulp 
cavity through the apical foramen of the root. All 
of them lose the medullary sheath, but do so at 
variable distances in the pulp. The varicose den- 
Fig. 121.- Nerve termination in the pulp of a rabbit's molar, 
stained in methylene-blue {intra vitam): a, Odontoblasts seen in side 
view; b, a number of odontoblasts seen in end view, showing a termi- 
nal branch of a nerve fiber situated between the odontoblasts and the 
dentin (Huber). 
drites ultimately form a loose plexus immediately 
under the layer of odontoblasts and, therefore, 
practically at the periphery of the pulp. Small 
branches pass from this plexus to terminate between 
the odontoblast cells, or pass through the layer of 
odontoblasts, but in no case have they been traced 
into the dentin. The sensitive dentin is, therefore, 
due to an indirect irritation of these nerve endings, 
conveyed to the latter through the medium of the 156 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
dentinal fibrils and the odontoblasts. The pulp is 
very sensitive to traumatic and chemical irritations, 
even when conveyed to it through the constituents 
of the dentin. It is especially sensitive to changes in 
temperature, heat or cold acting alike. It has no 
localized sensation of touch. 
Our knowledge of the nerve supply of the periden- 
tal membrane is not extensive. Both medullated 
and non-medullated fibers are present, the latter 
being a part of the sympathetic nervous system, and 
accompany as well as innervate the small blood- 
vessels. The nerve fibers enter the peridental mem- 
brane in the same manner and from the same sources 
as the blood supply, which has already been de- 
scribed. 
Attachment of Teeth.-In considering the attach- 
ment of teeth it must be remembered that teeth are 
not a part of the osseous system but are dermal 
appendages. The phylogenetic history of this sub- 
ject in vertebrates is very interesting. The de- 
scriptive literature is extensive and many classifi- 
cations of the different forms of attachment have 
been made. Tomes, in his "Dental Anatomy," 
classifies four forms of attachment: (i) by a fibrous 
membrane; (2) hinge-joint; (3) ankylosis; (4) in- 
sertion in a socket. 
The attachment by fibrous tissue is manifest in 
the scaly teeth of sharks. Each cone-shaped tooth 
has a flattened dermal plate. Calcified connective 
tissue is built into this plate, which it unites more or 
less fibrously to the submucous matrix of the mouth. 
Such teeth are practically dermal scales and have no DIGESTIVE SYSTEM. 
157 
direct attachment to the bony skeleton, the 
hinge-joint is merely a modification of the fibrous 
attachment, and is found in many fishes, reaching a 
high degree of development in the poison fangs of 
snakes. The hinge is composed of connective-tissue 
elements. In snakes the fang has a muscular at- 
tachment by which the reptile is able to erect the 
fang. By ankylosis is meant a direct calcified union 
with the bone of the jaw. Such teeth have no 
flattened base, but a calcified pulp which binds them 
firmly to the bony 
skeleton of the 
mouth. Ankylosis 
is confined to the 
teeth of certain 
fishes. 
The development 
of a socket is associ- 
ated with large teeth 
and a consequent 
strong attachment. 
The evolution of a 
socket is well represented phylogenetically in 
reptiles where Wiedersheim makes three classes: 
(i) pleurodont dentition (lacertilia), where "the 
teeth are situated upon a ledge on the inner side 
of the lower jaw, with which they become fused 
basally;" (2) acrodont dentition (chameleon,) where 
"they lie on the free upper border of the jaw;" 
(3) thecodont dentition (crocodiles), where "they are 
lodged in alveoli." In man all the teeth are im- 
bedded in well-developed alveoli of the jaw-bones. 
Fig. 122.- Diagram illustrating the de- 
velopment of a socket, a, Pleurodont 
dentition; b, acrodont dentition; c, the- 
codont dentition. 158 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
Here the function of the teeth is not only to seize 
and bite the food, but also to masticate it and test 
its quality. This change in function accounts for 
the heterodont dentition, which must have arisen by 
a modification of the simple homodont condition 
in which the teeth are all small, conical, and of the 
same size and shape. The primary arrangement of 
the teeth is such that those of one jaw do not 
usually correspond in position with those of the 
other, but rather with the interspaces between them. 
As a rule, the succession of teeth in man is nearly 
always reduced to two functional sets, the deciduous 
Fig. 123.-Diagram illustrating the development of the enamel organ 
of three teeth. 
teeth and the permanent teeth. Traces of an 
earlier set have been found, which may be spoken of 
as a "predcciduous" dentition, and occasionally one 
or more teeth appear which replace corresponding 
permanent teeth, and thus indicate the possibility of 
an extra unrecorded set. An unlimited succession 
of teeth takes place in nearly all vertebrates, except 
with mammals. 
Development of Teeth.-The enamel of the tooth 
develops from the epithelium of the oral cavity. In 
the seventh week of fetal life the mucous epithelium 
covering the gums invaginates to form a dental 
groove. The ridge or shelf thus invaginated is called DIGESTIVE SYSTEM. 
159 
the dental ridge. Early in the third month this 
dental ridge pro- 
duces lateral proc- 
esses along its lin- 
gual side, one for 
each deciduous 
tooth. These epi- 
thelial processes or 
sacs are known as 
enamel organs and 
develop directly into 
the tooth enamel. 
A little later, during 
the third month, a 
second set of proc- 
esses comes from the 
lingual side of the 
dental ridge and in 
like manner forms 
the enamel organs of 
the permanent set of 
teeth. 
The origin of the 
dentin is closely 
associated with the 
enamel organs but 
conies from the con- 
nective tissue under- 
lying these organs. 
This connective tis- 
sue forms dental 
Fig. 124.- Diagram illustrating the de- 
velopment of a tooth. 160 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
papilla, which later become differentiated into the 
dentin and dental pulp. The developing papillae 
gradually become invested by the enamel organ and 
one by one erupt on the surface of the oral cavity 
either as deciduous or permanent teeth. 
It will be observed that the enamel organs are sac- 
like structures consisting of an outer and inner layer 
of epithelial cells. The inner layer envelops the 
dental papillae and is destined to form the enamel 
prisms. The outer layer becomes associated with an 
investing sheath of connective tissue, the dental sac, 
and serves as a temporary protection while the 
enamel is being formed. When the tooth erupts the 
outer lining of epithelial cells disappears. 
The tooth papillae are thus all preformed at the 
time of birth. They remain latent and develop 
regularly into the different teeth according to the 
table on page 132. A serious illness of a child just 
before their eruption may affect their healthy 
growth by interfering with proper nutrition, and 
imperfect and pitted teeth result, which often ac- 
counts for an early decay. 
THE TONGUE. 
The tongue is a voluntary muscular organ that 
occupies the floor of the mouth. In lower verte- 
brates the tongue is a prehensile organ. In many 
fishes it is covered with teeth, its function being to 
capture and hold prey. In frogs and toads it is 
covered with mucous and peculiarly modified to 
capture insects. In reptiles it is often bifurcated, 
very motile, and used to frighten an enemy. In DIGESTIVE SYSTEM. 
161 
woodpeckers it is barbed and clearly a prehensile 
organ. In man, while the organ assists in taking 
Fig. 125.- Papillar surfaces of the tongue, with the fauces and 
tonsils: 1, 1, circumvallate papillae, in front of 2, the foramen cecum; 
3, fungiform papillae; 4, filiform and conical papillae; 5, transverse 
and oblique rugae; 6, mucous glands at the base of the tongue and in 
the fauces; 7, tonsils; 8, part of the epiglottis; 9, median glosso-epi- 
glottidean fold (fraenum epiglottidis) (from Sappey). 
food, its more important function is gustatory, the 
taste organs being located upon its surface. For 162 
NORMAL, HISTOLOGY AND ORGANOGRAPHY. 
description the tongue may be divided into body, 
base, inferior surface, and dorsum. 
Body.-This is chiefly made up of striped muscle 
which may be divided into intrinsic and extrinsic. 
A median septum divides it into two symmetrical 
lateral halves. Connective-tissue elements, nerves, 
the body of glands, and blood-vessels interlace 
freely with the muscle. The musculature is best 
studied in a beef's tongue that has been boiled, and 
is a subject that belongs to gross anatomy. In any 
section of the tongue, muscle fibers will be seen both 
in cross section and in longitudinal section. 
Base.-This is the posterior wide end of the tongue 
that is attached to the hyoid bone. It is covered 
with a smooth mucous membrane, beneath which is 
a rich supply of lymphoid tissue. The latter con- 
stitutes the lingual tonsil. Mucous glands arc abun- 
dant. 
Inferior Surface.-This is covered with smooth 
mucous membrane on which open many mucous and 
serous glands. The surface is divided into two 
halves by a fibrous septum which passes to the floor 
of the mouth and is known as the lingual frenum. 
When this is abnormally short the person is said to be 
tongue-tied, and speech is impaired. 
The Dorsum.-This surface is convex both from 
before backward and from side to side. A median 
depression, or sulcus, divides it into lateral halves. 
The sulcus apex points backward to the foramen 
cecum just in front of the base. This cecum is a 
blind pocket that marks the origin of the middle 
portion of the thyroid gland, and is the remnant of DIGESTIVE SYSTEM. 
163 
the obliterated thyroid duct. The dorsal surface is 
studded with three sets of papillae, to be described in 
detail. 
Papillae.-i. Filiform Papillae.-These are not 
only the smallest but by far the most numerous, and 
give the tongue a velvety appearance. They are 
arranged in divergent rows that extend outward and 
forward from the median sulcus. Each papilla is 
conical, points backward, and is covered by a thick 
Fig. 126.-Section through two filiform papillae of tongue. 
layer of stratified, horny, squamous epithelium. 
The function of these papillae is purely prehensile. 
In carnivorous animals they give the tongue a rasp- 
like structure that serves effectually in cleaning 
bones. It is said that a tiger, in this way, can draw 
blood from a living hand. 
2. Fungiform Papillae.-These are less numerous, 
larger, and supplied with blood, which gives them a 164 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
red color. . They are most numerous at the tip and 
margins of the tongue. Each is like an inverted 
cone and has a covering of eight or ten layers of 
squamous epithelial cells. Many of these papillae 
have taste buds in their lateral walls, analogous to 
those to be described in the third class of papillae- 
the circumvallate. A connective-tissue papilla oc- 
cupies the core of the fungiform. This core has a 
rich supply of blood-vessels which in fevers become 
congested with blood and give the dorsum a 
Fig. 127.-Section of fungiform papilla of tongue. 
Speckled red color, spoken of as strawberry tongue. 
This is particularly the case in scarlet fever. 
3. Circumvallate Papillce.--These are by far the 
largest and are found just in front of the foramen 
cecum. They are about ten in number and are ar- 
ranged in the form of a letter V, with the apex point- 
ing backward. They resemble the fungiform pa- 
pilla?, only they are much larger. Each papilla is 
surrounded by a deep, narrow, circular trench or DIGESTIVE SYSTEM. 
165 
jossa, hence their name. The wall consists of strati- 
fied squamous epithelium and the core of connective 
tissue richly supplied with blood-vessels. From this 
core secondary connective-tissue papillae indent the 
under surface of the stratified epithelial wall. 
Taste Buds.-These are nests of epithelial cells 
that lie in the lateral walls of circumvallate and 
Fig. 128.-Longitudinal section of a human circumvallate papilla 
(Bohm and Davidoff). 
many fungiform papillae, and are closely associated 
with the sense of taste. They resemble small acorns, 
and are made up of columnar cells so arranged as to 
form a central taste canal, which in turn opens by a 
pore into the circumvallate fossa. Two kinds of 
slender epithelial cells are present, (i) tegmental or 166 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
cover cells, principally at the periphery of the bud, 
which support or ensheath (2) the gustatory or taste 
cells. The latter are smaller, more delicate and 
centrally placed, with the distal or free end bearing 
a small process that projects into the inner taste pore. 
The cells of the taste bud occupy the whole lateral 
wall; that is, the base of each cell rests upon the base- 
ment membrane next to the connective-tissue core 
and the distal end extends practically to the sulcus 
Fig. 129.-Two foliate papillae from tongue of rabbit. 
of the papilla. These taste buds, as a matter of pro- 
tection, develop in the lateral wall rather than in the 
exposed dorsal surface of each papilla. 
The nerve fibers of the gustatory nerve are not in 
protoplasmic continuity with the epithelial cells of 
the taste buds, as is the case with the sensory cells of 
the olfactory region. Nerve fibers enter the taste 
buds and terminate in varicosities that interlace 
and come in contact with the gustatory cells of each DIGESTIVE SYSTEM. 
167 
taste bud. It is evident that a food to be tasted 
must first be put into solution to pass into the sulcus 
and stimulate the delicate processes of the gustatory 
cells of taste buds. 
Foliate Papillae.-On each side of the rabbit's 
tongue, some distance back, can be seen a small oval 
patch, with diagonal grooves and ridges, resembling 
the side of a three-cornered file. These patches are 
the foliate papilla. In reality they are not papillae 
but alternating grooves and ridges. In transverse 
section, the lateral walls of the ridges will be found 
beset with taste buds resembling in detail those 
Fig. 130.-Section through Fig. 131.-Cells from a taste 
taste bud. bud: a, taste cells; b, supporting 
cells. 
described in the circumvallate papillae. The rabbit, 
therefore, to relish his clover, should roll the leaves 
over these lateral patches. 
Glands of the Tongue.-Small serous racemose 
glands are associated with the circumvallate pa- 
pillae into the fosses of which their ducts open. 
Glands are otherwise absent over the dorsum of the 
tongue. Over the other parts of the tongue both 
serous and mucous glands are abundantly present. 
Many of these are mixed serous and mucous glands. 168 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
Blood Supply.-The arteries are the lingual, 
which branches to form (i) the dorsal linqual artery 
which anastomoses freely with the tonsillar branch 
of the facial, and (2) the ranine artery that passes 
along the under surface. The veins are the ranine 
and the dorsalis linguce that drain into the internal 
jugular. 
Nerves.-These are (1) the hypoglossal, the motor 
nerve; (2) the lingual, from the inferior maxillary 
of the fifth, which is accompanied by the chorda 
tympani of the seventh, or facial; (3) the glosso- 
pharyngeal, which supplies the taste buds; (4) the 
internal laryngeal. Many fibers of the sympathetic 
system mingle with these nerves. 
PHARYNX. 
The pharynx is the common passage for both 
food and air. It is an expanded portion of the di- 
gestive tube five inches in length and with seven 
openings: one, the fauces from the mouth; two 
posterior nares; two Eustachian tubes; one to the 
trachea, and the orifice of the esophagus. 
The mucous membrane of the pharynx is lined 
with stratified squamous epithelium, except in the 
region of the posterior nares where the epithelium 
is ciliated. In the submucosa there is a generous 
supply of mucous and serous glands and lymphoid 
tissue. The latter is particularly abundant in the 
region of the posterior nares, forming in this location 
the pharyngeal tonsils or adenoids. In early youth 
the adenoids are prone to enlarge so as to obstruct 
normal breathing, a condition that justifies their 
removal. A rich supply of elastic longitudinal DIGESTIVE SYSTEM. 
169 
connective-tissue fibers is also present in the sub- 
mucosa. The submucosa is therefore capable of 
being greatly distended, as is the case in throat in- 
fections, such as diphtheria, where the congestion 
is so great as to interfere with respiration. The 
diphtheria germs and toxins are thus lifted up and 
walled off from the deeper structures and normal 
Fig. 132.-Section through the pharyngeal tonsil of man (Sobotta). 
blood supply. This is nature's method of eliminat- 
ing the disease, with the possible danger to the pa- 
tient of suffocation. 
External to the submucosa come several layers of 
striated muscle fibers forming the pharyngeal muscle, 
the description of which belongs to gross anatomy. 
Tonsil. The tonsils are two oval lymphoid 
masses imbedded in the lateral walls of the pharynx, 170 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
opposite the root of the tongue and between the 
anterior and posterior palatine arches. This lymph- 
oid tissue is covered with the oral mucous mem- 
brane, beset with many depressions or pits known 
as crypts. It is along these crypts that bacteria 
may enter the tonsil, producing an inflammation of 
that organ known as tonsillitis. 
ESOPHAGUS. 
The esophagus is the part of the alimentary canal 
that intervenes between the pharynx and the stom- 
ach, and is a very muscular tube about- ten inches 
in length. Its upper end is opposite the lower bor- 
der of the crycoid cartilage and the sixth cervical 
vertebra. The lower end or cardiac orifice is oppo- DIGESTIVE SYSTEM. 
171 
site the eleventh dorsal vertebra. Two distinct 
constrictions are present, one at the beginning and 
one where it is crossed by the left bronchus. The 
normal distention at these points is about four- 
fifths inch. 
The wall of the esophagus may be divided into 
four coats: mucous, submucous, muscular, and 
fibrous. 
i. Mucous Layer.-This layer is thrown into 
many longitudinal folds and lined, as in the pharynx, 
with stratified epithelium. The tunica propria is 
well developed and may contain solitary lymph 
nodes. Tubular glands resembling those of the 
stomach are found in patches, particularly at the 
extremities of the esophagus. They are entirely 
confined to the mucosa and distinct from the mucous 
glands found in the submucosa. Their function is 
problematic. A muscularis mucosa is present in the 
esophagus just external to the tunica propria, con- 
sisting of longitudinally disposed smooth muscle 
cells. This layer becomes more prominent in the 
alimentary canal below the esophagus. 
2. Submucosa.-This layer lies just external to 
the muscularis mucosa and consists of loose con- 
nective-tissue elements, blood and lymph vessels, 
nerves and the bodies of mucous glands. These 
glands are compound racemose and are particularly 
abundant in the lower part of the esophagus. The 
ducts pass through the muscular mucosa to open on 
the epithelial surface. They secrete mucus for the 
lubrication and protection of this surface. Not in- 
frequently the morning vomit of mucus in chronic 172 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
gastritis comes from excessive secretion of these 
glands. The tissues of the submucosa are loosely 
held together, and sections, therefore, may tear along 
this layer. 
3. Muscular Coat.-This consists of an inner cir- 
cular and an outer longitudinal layer, although the 
fibers of each often interlace. The longitudinal 
layer is particularly strong, often thicker than the 
circular. In the upper half many striated fibers are 
present that are continuous with the pharyngeal 
voluntary muscle. The control of these fibers en- 
ables the dog to return food to the mouth that has 
passed into the upper part of the esophagus. In the 
lower half, only smooth muscle fibers are present. 
The longitudinal layer passes on as the longitudinal 
layer of the stomach and intestine, while the circular 
becomes the diagonal fibers of the stomach and does 
not pass to the intestine. Connective-tissue ele- 
ments interlace and strengthen the whole muscu- 
lature. Foods and liquids are carried along this 
tube by peristaltic contraction of its muscles, and 
in this way cattle and horses can take nourishment 
without lifting their heads. 
4. Fibrous Coat.-This consists of loose connec- 
tive-tissue elements, mostly white fibrous, binding 
the esophagus to adjacent structures. It is not 
well defined and often difficult to demonstrate as a 
distinct layer. 
STOMACH. 
The stomach varies greatly in form and position 
according to physiological conditions. For de- 
scriptive purposes it has two ends, cardiac and py- DIGESTIVE SYSTEM. 
173 
loric; two surfaces, dorsal and ventral; two curva- 
tures, greater and lesser; and two orifices, esophageal 
and pyloric. The most fixed point is the esophageal 
orifice, which is situated opposite the seventh left 
costal cartilage one inch from the sternal junction. 
The most movable portion is the pyloric end, which 
is situated one-half to one and one-half inches to the 
right of a median plane and a variable distance be- 
low the esophageal opening. The distance between 
Fig. 134.-Anterior outlines of stomach. (His' model.) 
the two orifices is about four inches. The full 
length of the stomach is about ten inches, and the 
greatest diameter four inches, with average capacity 
of one quart. These dimensions are subject to 
great variations. 
The stomach wall, like that of other parts of the 
food canal, is-made up of four layers: mucosa, submu- 
cosa, muscularis, and serosa. 
1. Mucosa.-The mucous surface is uneven, due 174 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
to irregular folds. The surface is beset with minute 
pores or circular depressions, called crypts, into 
which the gastric glands open. As in other parts 
of the food canal this layer consists of epithelium, 
membrana propria, and muscularis mucosa. The 
epithelium is simple columnar with the nucleus near 
the bottom of the cell, leaving a clear proximal half/ 
Fig. 135.-Cross section through the wall of a stomach 
to each cell that does not readily stain. The pits or 
crypts are lined by this same epithelium. The 
membrana propria has a rich supply of connective- 
tissue cells and extensive ramifications of blood and 
lymph capillaries. The muscularis mucosa is a thin 
muscle layer, external to the membrana propria, 
and consists of an inner layer of circular and an outer DIGESTIVE SYSTEM. 
175 
layer of longitudinal smooth muscle fibers. A liberal 
supply of connective tissue is associated with this 
muscle. This layer, therefore, offers resistance to 
an invasion of bacteria, while the muscular contrac- 
tion relieves pressure to the rich blood supply in the 
submucosa just external to it, and at the same time 
exerts pressure upon the gastric glands. 
Gastric Glands.- 
Crypt. 
1 hese are widely dis- 
tributed and per- 
haps the most impor- 
tant structures of 
the mucosa. They 
are simple tubular, 
except in the pyloric 
region, where many 
of them are 
branched. Usually 
several glands open 
into each crypt, the 
latter representing 
a circular pit-like 
evagination of the 
epithelial surface. 
The wall of each 
gland consists of 
simple epithelium and two kinds of cells are present: 
(i) chief cells, which are by far the most numerous; 
these are round or cuboid cells, with central nucleus 
that stains blue with hematoxylin; (2) parietal cells, 
which are less numerous, larger, and have a granular 
cytoplasm that takes the red eosin stain. They inter- 
Fig. 136.-Simple tubular gland from 
stomach. 176 
NORMAL HISTOLOGY AND ORGANOGRAPHY 
vene with the chief cells but are placed at the pe- 
riphery of the glands, and communicate with the 
central lumen by means of a network of secreting 
ducts. They are most abundant in the cardiac 
end of the stomach and along the 
middle and inner third of each 
gland. These cells are supposed to 
have something to do with the se- 
cretion of hydrochloric acid. The 
cytoplasm of the chief cells contains 
granules of pepsinogen, which is 
converted into pepsin of the gastric 
juice. During fasting, these gran- 
ules accumulate, and during, or 
after, active secretion they become 
smaller and tend to disappear. 
The mucosa secretes a varying 
amount of mucus for the protec- 
tion of the delicate epithelial sur- 
face. In many forms of indigestion, 
and particularly in poison cases, 
the mucus secretion is very exten- 
sive and serves to keep the irrita- 
ting stomach contents away from 
the epithelial lining. The excess 
of mucus can be removed by stom- 
ach lavage. 
The chief difference between the 
pyloric and cardiac regions of the 
stomach is found in the mucosa, (i) The crypts in 
the cardiac end are shallow, while in the pyloric end 
the crypts frequently extend half way through the 
Fig. 137.-A num- 
ber of fundus glands 
from the fundus of 
the stomach of young 
dog, stained after 
the chrome - silver 
method, showing the 
system of line canals 
surrounding the pa- 
rietal cells and com- 
municating with the 
lumen of the glands 
(Huber). DIGESTIVE SYSTEM. 
177 
thickness of the mucosa. (2) The gastric glands 
are longer than the crypts in the cardiac end; 
towards the pyloric end the glands become shorter, 
tortuous, and pressed closely against the muscu- 
laris mucosa. Many of the pyloric glands are 
branched. . (3) The parietal cells are numerous in 
Fig. 138.-From a section through the junction of the human esophagus 
and cardia (Bohm and Davidoff). 
the gastric region and practically absent in the 
pyloric. The pyloric mucosa, in this way, comes to 
resemble that of the small intestine. In addition 
an occasional' villus or Brunner's gland may be found 
in the pyloric end. 
2. Submucosa.-The submucosa in all mucous 178 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
membranes is highly vascular. Besides blood and 
lymph there is an abundant supply of connective- 
tissue elements, largely elastic fibers, connective- 
tissue cells and fat cells. Nerve cells and nerve 
fibers, known as 
Meisner's plexus, are 
found here and in the 
submucosa through- 
out the alimentary 
canal. 
3. Muscularis.- 
This consists of 
smooth muscle and 
may be divided into 
three layers: (a) an 
inner sheath where 
the fibers run ob- 
liquely; this sheath 
is continuous with 
the circular layer of 
the esophagus; (6) 
a middle circular 
layer which is con- 
tinued as the circu- 
lar layer of the in- 
testine ; (c) an outer 
longitudinal layer 
continuous with the 
longitudinal layer of, 
both esophagus and intestine; nerve cells and 
nerve fibers form a plexus between the longitudinal 
and circular muscle of the whole alimentary tract, 
which is known as the plexus of Auerbach. 
Fig. 139.-From vertical section 
through human pylorus (Bohm and 
Davidoff). DIGESTIVE SYSTEM. 
179 
Fig. 140.-Section through fundus of human stomach in a condition of 
hunger (Bohm and Davidoff) 
Fig. 141.-Section through fundus of human stomach during digestion 
(Bohm and Davidoff). 180 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
4. Serosa. This consists of a thin layer of fibrous 
tissue covered by simple pavement epithelial cells 
and bound down to the muscularis by delicate 
fibrous septa. It is really a part of the peritoneum. 
SMALL INTESTINE. 
The small intestine is about twenty-four feet long, 
and is divided into du- 
odenum, ten inches; 
jejunum and ileum,re- 
spectively, two-fifths 
and three-fifths of the 
remainder. About 
three feet from the 
lower end of the ileum 
Meckel's diverticu- 
lum may be present, 
representing the last 
embryonic closure of 
the intestine. The in- 
testine has the same 
number of layers as 
the stomach. The 
muscularis, however, 
consists of but two 
strata, an inner circu- 
lar and an outer lon- 
gitudinal. 
i. Mucosa.-The 
mucosa is lined by simple columnar epithelium in 
which many goblet cells are present, particularly in the 
deeper folds. The membrana propria and muscularis 
Fig. 142.-Section of small intestine with 
blood-vessels injected. digestive system. 
181 
mucosa arc identical with those described in the stom- 
ach. The mucous surface of the small intestine is much 
increased by means of folds, of which there are three 
mechanisms: valvula 
conniventes, villi, and 
crypts oj Lieberkuhn. 
(a) Valvula Conni- 
ventes.-These arc 
concentric, trans- 
verse, crescentic folds 
of the mucosa, that 
usually form two- 
thirds of a circle, 
although occasionally one forms an entire circle or 
even a spiral. These valves are two or three inches 
Fig. 143.-Portion of the wall of 
the small intestine, laid open to show 
the valvula: conniventes (Brinton). 
Fig. 144.-Mucous membrane of the jejunum, highly magnified 
(schematic): 1, 1, Intestinal villi; 2, 2, closed or solitary follicles; 3, 3, 
orifices of the follicles of Lieberkuhn (Testut) 
long, about one-third inch broad and one-eighth inch 
thick. The inner surface of the small intestine is thus 
thrown up in a series of shelves. This mechanism 
has an analogue in the typhlosole of the earthworm 
and the spiral value of some fishes. 182 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
(b) Villi.-These are tongue-like elevations of the 
mucosa one-thirtieth to one-fortieth inch in height, 
and barely visible to the naked eye. They are 
found on both sides of the valvula conniventes 
and on the general surface of the mucosa. Collec- 
tively they give the surface a velvety appearance. 
The villi are most numerous in the upper part of the 
intestine, where they number fifty to eighty to the 
square inch. They are longer but more slender and 
less numerous in the ileum, where they number 
forty to sixty to the square inch. Their total num- 
Fig. 145.-a, Cross section of a villus; b, cross section of crypt of Lie- 
berkuhn. 
ber in the small intestine is estimated at 4,000,000. 
Each villus has a lining of simple columnar 
epithelium which covers a connective-tissue core. 
A few smooth muscle fibers enter this core from 
the muscularis mucosa. In addition there is a 
rich blood supply and a central lymphatic duct. 
The latter is a part of the lymphatic system of 
the intestine known as lacteals because of the milky 
lymph they contain after each meal. The villi de- 
velop as invaginations of the mucosa and are ex- 
clusively confined to the small intestine. DIGESTIVE) SYSTEM. 
183 
(c) Crypts oj Lieberkuhn.-These are sometimes 
spoken of as intestinal glands. They consist of pits 
or evaginated diverticula of the mucous epithelium 
that open as pores between the bases of the villi. 
The bottom of these crypts rests against the muscu- 
laris mucosa. Goblet cells are particularly numer- 
ous in the epithelial lining of their walls. Crypts 
Fig. 146.-Schematic transverse section of the human small intestine 
(after F. P. Mall). 
are also present in the large intestine and are analo- 
gous to the shorter crypts of the stomach into which 
the gastric glands open. 
Solitary Lymph Nodules.-These are simple nodes 
of lymph tissue situated just beneath the mucous 
epithelium. They are found along the whole ali- 
mentary tract and in all mucous membranes. 184 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
Peyer's Patches, or Agminated Lymph Nodules.- 
These appear as oval elevations on the mucous sur- 
face and are collections of lymph nodules. They 
may be three inches long or less, and one-third to 
one-half inch broad. They number from thirty to 
forty, and are found in the ileum and always in the 
mucous surface op- 
posite the mesen- 
teric attachment, 
the long axis being 
parallel with that 
of the intestine. 
Their bodies usu- 
ally extend to the 
circular muscle 
layer and they 
therefore invade 
the sub mucosa. 
Villi are either 
stunted or altogeth- 
er absent over these 
patches. In early 
youth they are very 
prominent, while in 
middle life they be- 
gin to atrophy, and 
in old age they may entirely disappear. 
The patches are the scat of ulcerations, particu- 
larly in typhoid fever and tuberculosis. The latter 
form transverse ulcers as the bacteria of tuberculosis 
spread along the lymphatics which here are trans- 
verse to the intestine. The typhoid germ produces 
Fig. 147.-Longitudinal section of ileum 
showing part of a Peyer's patch. DIGESTIVE SYSTEM. 
185 
an ulcer whose long axis is parallel to that of the 
intestine. 
Brunner's Glands.-These are branched tubular 
glands whose bodies are situated in the submucosa 
and whose ducts 
pass through the 
muscularis mucosa 
to open between or 
into the crypts of 
Lieberkuhn. They 
are confined to the 
duodenum, partic- 
uarly the upper 
part. Occasionally 
they may be found 
in the pyloric end 
of the stomach. 
The cells resemble 
those of the pyloric 
glands, being cylin- 
drical and finely 
granular. Brun- 
ner's glands are 
easily recognized, 
as they are the only 
glands that lie in 
the submucosa. 
2. Submucosa.- 
The. sub mucosa 
does not differ from the same layer already described 
in the wall of the stomach. 
3. Muscularis.-The muscularis consists of an 
Fig. 148.-Longitudinal section of 
duodenum »near pyloric end, showing 
glands of Brunner. 186 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
inner circular and an outer longitudinal layer of 
smooth muscle. The inner circular is the heavier of 
the two and by its contraction produces many longi- 
tudinal folds in the mucosa. Smooth muscle, wher- 
ever found, is associated with connective-tissue 
elements, but the smooth muscle of the intestine 
has a less supply 
of this than the 
smooth muscle any 
other place in the 
body. 
4. Serosa. - This 
layer is identical 
with the serosa de- 
scribed in the wall 
of the stomach. 
Fig. 149.-Portion of large intestine. 
LARGE INTESTINE. 
The average length of the large intestine is five 
feet. Its divisions are given on page 124. It is dis- 
tinguished from the small intestine by the following 
external features: tcenice coli, sacculce, and appendices 
epiploicce. 
Tcenice Coli.-In the large intestine the longitudinal 
muscle is gathered into three bands or strips known 
as taeniae coli. Each band is about one-quarter inch 
wide and one foot shorter than the intestine to 
which it belongs. The large intestine, therefore, 
becomes sacculated-that is, it is divided by the 
three longitudinal muscle bands into three rows of 
sacculae. If the bands be dissected away the saccules DIGESTIVE SYSTEM. 
187 
disappear and the intestine becomes about one foot 
longer. 
Appendices epiploicce are small pedunculate proc- 
esses that project from the serous coat of the large 
intestine. The pouches are covered by the perito- 
neum and are usually distended with fat. These 
external features 
are the surgeon's 
guide in recogniz- 
ing the large intes- 
tine. Size is a less 
reliable factor. 
Structurally the 
large intestine has 
the same four lay- 
ers as the small in- 
testine. The three 
outer layers are 
identical. The 
mucosa presents a 
smooth surface 
with numerous mi- 
nute circular pits, 
the crypts of Lie- 
berkuhn. As villi 
are absent the mu- 
cosa resembles that of the stomach rather than that of 
the small intestine. The crypts of the stomach are 
shallow, while those of the intestine are deep and 
extend to fhe muscularis mucosa. Each crypt is 
lined by simple columnar epithelium. Goblet cells 
are very numerous in this epithelium. 
Fig. 150.-Cross section of large intes- 
tine, showing many goblet cells in epithe- 
lium. 188 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
Vermiform Appendix.-The appendix, although 
very small, belongs to the large intestine. It is a 
worm-like tube about three inches long and one- 
quarter inch thick, although the length varies 
greatly. It is a blind tube that evaginates from 
Fig. 151.--Transverse section of human vermiform appendix. 
Observe the numerous lymph nodules. The clear spaces in the submu- 
cosa are adipose tissue (Sobotta). 
the lower encl of the cecum. Lymph nodes are 
particularly abundant in the mucosa of the ap- 
pendix. 
In the different parts of the alimentary canal the 
mucosa shows a marked variation, as represented in 
the following table: DIGESTIVE SYSTEM. 
189 
Esophagus. 
Stratified epithelium. 
Mucous glands. 
Crypts absent. 
Villi absent. 
Valvula; absent. 
Stomach. 
Simple epithelium. 
Gastric glands. 
Crypts shallow. 
Villi absent. 
Valvulas absent. 
Small Intestine. 
Simple epithelium. 
Brunner's glands. 
Crypts of Liebcr- 
kiihn. 
Villi present. 
Valvuhe conniven- 
tes present. 
Large Intestine. 
Simple epithelium. 
Crypts. 
Crypts. 
Villi absent. 
Valvula; absent. 
Blood Supply of Stomach and Intestines.-The ar- 
teries of the stomach are all derived from the celiac 
Fig. 152.-Section through fundus of cat's stomach. The blood-vessels 
are injected (Bohm and Davidoff). 
axis, a branch of the aorta. The intestines are sup- 
plied by blood from the superior and inferior mesen- 
teric arteries, branches of the aorta. The arteries 
enter along the line of the mesenteric attachment 
and there form branches that pass transversely 190 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
around the intestine to ultimately penetrate the 
longitudinal muscle layer. Between the two mus- 
cular coats branches are given off to supply the 
muscles themselves. The arteries then penetrate 
to the submucosa where an extensive blood plexus 
is formed. From this plexus branches pass through 
the muscularis mucosa and enter the mucosa. Here 
Fig. 153.-A portion of the plexus of Auerbach from stomach of 
cat, stained with methylene-blue (intra vitam), as seen under low mag- 
nification (Huber). 
they branch into a fine capillary network which in 
the small intestine penetrates to the core of the villi. 
Other branches from this plexus supply the inner 
portion of the circular muscle layer. 
The veins lie side by side with the arteries. Often 
two veins accompany one artery. The blood drains 
into the superior and inferior mesenteric veins; the 
inferior joins the splenic, and the latter unites with DIGESTIVE SYSTEM. 
191 
the superior to form the portal vein. This blood 
thus ultimately passes through the liver. 
Lymphatics of the Alimentary Canal.-The lym- 
phatics begin in the mucosa just beneath the epithe- 
lium. In the small intestine they begin with the cen- 
tral lymph vessel of a villus. These vessels form a 
network in the deeper portion of the mucosa and 
then pass through the muscularis mucosa to form 
an extensive loose plexus in the submucosa. 
Coarser lymphatic vessels lead from this plexus 
through the muscularis, where branches are received 
from a lymphatic plexus located between the two 
muscle coats. 
The solitary lymph nodes of the mucosa contain 
no lymphatics but are encircled at their periphery 
by an extensive lymphatic network. The same is 
true of the lymph nodules in Peyer's patches. 
Nerve Supply of the Alimentary Canal.-The chief 
nerve supply of the alimentary tract consists of sym- 
pathetic neurons whose nerve cells form the centers 
of two plexuses, (i) that of Auerbach, situated 
between the two layers of the muscle coat, and (2) 
that of Meissner in the submucosa. The latter con- 
tains fewer ganglia and finer fibers. The numerous 
small sympathetic ganglia of each plexus are united 
by small bundles of non-medullatecl nerve fibers in 
which a few medulla ted nerve fibers are present. 
From these plexuses the nerve innervation extends 
to the glands and epithelial cells of the mucosa, and 
to the muscularis to end in small varicosities about 
the smooth muscle cells. 
While the nerve innervation is not under will con- 192 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
trol it is capable of being stimulated by cerebro- 
spinal nerves. Medullated nerve fibers from this 
system have been traced to terminal end baskets 
surrounding cell bodies of many of the sympathetic 
neurons of these plexuses. CHAPTER V. 
DIGESTIVE GLANDS 
SALIVARY GLANDS. 
i. Parotid Gland (serous gland).-This is a com- 
pound tubular gland, the largest of the salivary 
glands, situated in the parotid recess at the side of the 
head below and in front of the ear. It is a triangular 
mass that varies in weight from one-half ounce to 
one ounce or more. Its three surfaces are desig- 
nated as superficial, anterior and posterior. The 
gland is divided into lobes and lobules and inter- 
laced with connective-tissue elements from the 
parotid fascia that invests it. 
The parotid, or Stenson's duct, measures from 
one and one-half to two and one-half inches in 
length and one-eighth inch in diameter. It runs 
forward across the masseter muscle, passes around 
the anterior border of this muscle, pierces the buc- 
cinator, then forward a short distance to open on 
the inner surface of the cheek opposite the crown 
of the second molar. This duct is subject to injury 
in facial wounds or operations. 
The gland is an epithelial organ and consists of 
the excretory duct, interlobular, intralobular, and in- 
tercalated ducts, and the distal convoluted tubules or 
alveoli. The excretory duct (Stenson's) is lined by 
stratified epithelium near its end where it opens on 194 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
the mucous surface of the cheek. The rest of the 
duct is lined by two layers of cubical epithelium, 
which is invested by a firm fibrous coat or tunica 
propria. The interlobular ducts lie between the 
Fig. 154.-Section through salivary gland of rabbit, with injected 
blood-vessels (Bohm and Davidoff). 
lobules and have much the same histology as the 
excretory duct, excepting the finer branches where 
the epithelium becomes simple cubical. The intra- 
lobular ducts are found inside the lobules and have a 
simple layer of tall cylindrical cells whose cytoplasm DIGESTIVE GLANDS. 
195 
shows a distinct longitudinal striation. The inter- 
calated pieces, on the other hand, are clothed by a 
single layer of flat, slender, often spindle-shaped 
cells. The epithelial lining of the acini consists of 
typical serous-gland cells. This is a single layer 
of irregular columnar or cubical cells with nuclei 
situated near their basal portion. . When at rest 
the cytoplasm is filled with zymogen granules 
which are used up and largely disappear during the 
process of secretion. Mumps is a specific disease 
of this gland, more technically known as parotitis. 
2. Sublingual Gland 
(mucous gland).-This 
is really a collection of 
compound tubulo-alve- 
olar glands. It is an 
elongated flattened mass 
one and one-half to 
one and three-quarter 
inches in length, situ- 
ated in the floor of the 
mouth, one on each side 
of the median plane, and limited laterally by the 
ramus of the mandible. Its excretory ducts, from 
ten to twenty in number, open separately on the 
summit of papillae visible to the naked eye, which 
are situated just laterally to the base of the frenum 
of the tongue. 
The duct system of the gland is similar to that of 
the parotid, with the exception of the intercalated 
piece, which is absent. The alveoli are less tubular 
than those of the parotid and are lined by simple 
Fig. 155.-From the parotid gland 
of man. 196 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
columnar epithelium with the nuclei situated at the 
base of the cells near the basement membrane. 
These are the chief cells of the alveoli and they se- 
crete mucus, which is first stored up in the cyto- 
plasm in coarse granules 
known as mucigen. • A 
second form of cells, less 
numerous, is found singly 
or in groups in the periph- 
ery of the alveoli and in 
close apposition to the 
basement membrane. 
On account of their shape 
and position they are 
called parietal cells, cres- 
cents of Gianuzzi, or demi- 
lunes of Heidenhain. 
They are finely granular, 
stain red with eosin, and 
are looked upon by some 
as secreting a serous fluid. 
There are three theories 
as to their use: (i) They 
may be considered as 
worn-out chief cells that 
have been crowded to the basement membrane after 
too active a secretion. (2) They may be considered 
as latent undeveloped cells ready to take the place 
of mucous cells that get lost in the process of active 
secretion. (3) They may be considered as normal 
active cells contributing constantly to the salivary 
secretion in a way that is at present unknown. 
Fig. 156.-Model of a small 
portion of a sublingual gland of 
man. The demilunes of Heid- 
enhain are more deeply shaded 
(Maziarski, " Anatomische Hefte, " 
1901). DIGESTIVE GLANDS. 
197 
3. Submaxillary Gland (mixed gland).-In man 
this gland is composed of tubules having a serous 
secretion and similar to those of the parotid gland, 
and tubules with alveolar enlargements like the sub- 
lingual gland that secrete mucus. Its histology, 
therefore, would be a repetition of what has already 
been described in the parotid and sublingual glands. 
The submaxillary gland is next in size to the pa- 
rotid, which it resembles in color and lobulation. It 
Fig. 157.-Section from the human submaxillary gland. 
is placed against the inner surface of the angle of the 
lower jaw in close proximity to the parotid gland. 
It has a complete firm capsule derived from the cer- 
vical fascia. Connective-tissue elements from the 
capsule ramify between the lobes and lobules of the 
gland. 
The submaxillary, or Wharton's duct, is about two 
inches long, passes forward beneath the mylohyoid 
muscle, then along the inner side of the sublingual 
gland to open on the summit of a small papilla situ- 198 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
ated in the floor of the mouth at the side of the fre- 
num of the tongue in close proximity to its fellow 
of the other side. The submaxillary gland of the 
rabbit is a serous gland; that of the dog and cat is 
mucous. 
The accessory 
salivary glands are 
numerous small 
glands of the mouth 
known according to 
their location as la- 
bial, palatine, and 
lingual. They are 
mostly glands with 
mucous secretions. 
Branched tubular 
glands with serous 
secretion occur in 
the tongue, their 
ducts opening into the depressions of the circumval- 
late papillae. 
• PANCREAS. 
The pancreas is a tabulated compound racemose 
gland analogous in its structure to the salivary 
glands. It is situated transversely across the pos- 
terior wall of the abdomen, so deep in the body and 
so closely associated with other organs that but 
little is known of its diseases. Its length varies 
from six to eight inches, its breadth one and one-half 
inches and thickness from one-half to one inch. The 
right extremity, or head, rests in the concavity of 
Fig. 158. - A number of alveoli 
from the submaxillary gland of dog, 
stained in chrome-silver, showing some 
ofthefine intercellular tubules (Huber). DIGESTIVE GLANDS. 
199 
the duodenum and the other end touches the spleen. 
It lies behind the peritoneum and, unlike the salivary 
glands, it is not enclosed in a fibrous capsule, and is 
therefore looser and softer in its texture. 
The pancreas develops as two evaginations of the 
alimentary canal and embryologically, therefore, 
Fig. 159.-From section through human pancreas (sublimate) (Bohm 
and Davidoff). 
has two ducts. One of these, the pancreatic duct, 
or duct of Wirsung, opens jointly with the bile duct 
on the summit of an elevated papilla, situated at the 
inner side of the descending portion of the duodenum. 
This duct extends the length of the pancreas and 
receives in its course the short ducts from the various 
lobes composing the gland. 200 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
The second duct, or duct of Santorini, loses its 
connection with the alimentary canal and comes to 
open into the duct of Wirsung. It is a very short 
tube, inferior in position and secondary in impor- 
tance. 
Histologically, the ducts are lined by a mucous 
membrane of simple columnar epithelial cells that 
are morphologically continuous and analogous with 
the epithelial cells of the intestine. This mucous 
Fig. 160. •-Scheme showing relation of three adjoining alveoli to 
excretory duct, illustrating origin of centro-acinal cells (Bohm and 
Davidoff). 
membrane is ensheathed by a coat of connective- 
tissue elements, fibers and cells, all of which are 
associated with more or less fat. 
The acini resemble in form and size those of the 
salivary glands. The parietal cells are absent. The 
chief cells are columnar, the nucleus near the base of 
the cell, and the cytoplasm loaded with zymogen 
granules. During physiological activity these gran- 
ules are greatly reduced. In addition, centro-acinal DIGESTIVE GLANDS. 
201 
cells are present. These arc smaller and flatter 
than the chief cells and occupy a central position of 
many acini. They represent an invagination of the 
neck of the acinus and are best understood by re- 
ferring to Fig. 160. 
Areas oj Langerhans.-These arc ova? cell masses 
that measure 0.2 to 0.3 mm. They are found in the 
lobules of the pancreas, always associated with the 
connective tissue but having no connection with the 
Fig. 161.-Section from an injected pancreas of the dog 
pancreatic tubules. The areas are surrounded by a 
rich supply of coarse capillary blood-vessels. The 
individual cells are epithelioid, smaller than those 
of the acini, and finely granular. In many respects 
they resemble the liver cells. It is believed that the 
secretions from these cells is absorbed by the blood 
and modifies the distribution and elimination of 
sugar. The areas thus have a compensatory rela- 
tion to the liver and may do in part the work of that 
organ. A marked disturbance in these areas has 202 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
been observed in diabetes, but whether a cause or 
consequence is not known. 
LIVER. 
The liver is a large compound tubular gland whose 
terminal ducts anastomose. In this respect it differs 
from any other gland in the body. It develops as a 
ventral evagination of the intestinal wall and in 
close proximity to the origin of the pancreas, so that 
in the adult the ducts of these two organs have a 
Fig. 162.-Posterior and inferior surfaces of the liver (Nancrede) 
common opening at the apex of a papilla, as already 
mentioned in the description of the pancreas. If an 
obstruction occurs at this opening, it is possible for 
the pent-up bile to invade the pancreas. The ven- 
tral liver diverticulum quickly bifurcates to form 
respectively the right and left lobes of the liver. 
By repeated divisions the bile system of the organ is 
built up, forming an elaborate anastomosis of the 
finer bile capillaries. It follows, therefore, that the 
liver cells are genetically related to the pancreatic DIGESTIVE GLANDS. 
203 
cells and sister cells of the columnar epithelium of 
the alimentary tract. 
The fully developed liver consists of five lobes: 
right lobe, left lobe, quadrate, caudate, and spigelian 
lobes. Five fissures: umbilical, duchis venosus, 
transverse, gall bladder, and vena cava fissures. Five 
ligaments: ligamentum teres (remnant of the umbilical 
vein), falciform, coronal, and two lateral ligaments. 
Fig. 163.-Diagram of liver lobule. 
The description of these structures belongs to gross 
anatomy. 
The liver is the largest gland in the body, weigh- 
ing from three to four pounds, or one-fortieth the 
weight of the whole body. It measures ten to 
twelve inches in its transverse diameter, six to seven 
inches in its antero-posterior, and about three inches 
thick at the back part of the right lobe, which is the 204 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
thickest part. This heavy organ is held in position 
not only by its ligaments but by the abdominal pres- 
sure, and also by the connective tissue of the vena 
cava, which forms a dorsal fissure between the right 
and left lobes. 
The organ is enclosed in a firm connective-tissue 
capsule {capsule oj Glisson), which is very dense over 
the lower surface in the region of the fissures, par- 
Fig. 164.-Injected blood-vessels in liver lobule. 
ticularly the transverse, where the blood-vessels and 
bile duct enter. Septa from this capsule ramify 
between the lobes and lobules, and finer branches 
interlace between the liver cells, giving everywhere 
support and consistency to the organ. Here, as in 
every organ, blood-vessels, lymph-vessels, and fat are 
associated with this connective-tissue fabric. The 
capsule is closely invested with peritoneum, except- 
ing a circular area bounded by the coronal ligament, DIGESTIVE GLANDS. 
205 
where the capsule, and therefore the liver, is in direct 
apposition with the lower surface of the diaphragm. 
The blood supply of the liver consists of the hepatic 
artery, and a branch of the celiac axis, and the portal 
•vein, formed by the junction of the splenic and supe- 
rior mesenteric veins. The portal vein is by far the 
larger vessel. These vessels accompany the bile- 
Fig. 16c-Section through liver of pig, showing chains of liver-cells 
(Bohm and Davidoff). 
duct, and wherever one branches the others do, even 
to the finer terminations between the liver lobules. 
The duct, vein and artery form the ventral border 
of the forq/men of Winslow. Their relation at this 
place is, bile duct to the right, artery to the left, and 
vein between and behind the other two. This rela- 
tion is an important one in the surgery of these parts. 206 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
The Portal Canal.-This consists of an artery, a 
bile duct, and a vein, with accompanying lymphatics 
and connective tissue. Sections of the portal canal 
may be found between the liver lobules where the 
vessels are small, or between the liver lobes where the 
structures are large. The bile duct can be recog- 
nized by the columnar simple epithelium and the 
artery and vein by their respective histology. In 
Fig. 166.-Reticulum (Gitterfasern) of dog's liver (gold-chlorid method) 
(Bohm and Davidoff). 
pathological sections, where the lobules can no 
longer be recognized, the portal canal usually re- 
mains patent and is therefore a valuable criterion 
in the identification of this tissue. 
The common bile duct is formed by the junction of 
the hepatic and cystic ducts at the mouth of the 
transverse fissure, and passes downward anterior to DIGESTIVE GLANDS. 
207 
the foramen of Winslow to open into the descending 
part of the duodenum three and one-half to four 
inches beyond the pylorus. It passes obliquely 
through the intestinal wall, where it is joined by the 
pancreatic duct, and opens by a common orifice on 
the bile papilla, as already described. The common 
bile duct is about three inches long and one-quarter 
inch in diameter. 
The histology of the bile ducts resembles that of the 
gall bladder. There is on the inside a mucous mem- 
brane clothed with simple columnar epithelium rest- 
ing upon a base- 
ment membrane. 
Smooth muscle 
cells are found in 
the m e m b r ana 
propria of the mu- 
cosa. The sub- 
mucosa is a nar- 
row vascular layer 
composed of con- 
nective-tissue elements. The muscularis consists of 
an inner circular layer and an outer longitudinal 
layer of smooth muscle. On the outside is a strong 
connective-tissue coat whose fibers are continuous 
with the capsule of Glisson. 
The passage of bile into the intestine is not a pas- 
sive but an active process. The smooth muscle of 
the bile duct contracts in a peristaltic manner, and 
the bile is thus expelled into the intestine, periodi- 
cally, in jets. This activity is normally under con- 
trol of the nerves, largely a reflex action of the sym- 
Fig. 167.-Section of portal canal of liver. 208 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
pathetic nerves associated with the intestine. If 
there is an obstruction to the free passage of bile, as 
in the passage of a calculus, the musculature of the 
ducts contracts violently and spasmodically, giving 
rise to the characteristic pain of plain muscle con- 
traction described on page 86. If the obstruction 
occurs in the hepatic or the common duct, the liver 
becomes saturated with bile which is absorbed by the 
blood, and jaundice follows. If the obstruction is 
in the cystic duct the liver does not suffer and there is 
no jaundice. 
Smaller Excretory Bile Ducts and Gall Bladder.- 
Small bile ducts of the liver begin within the liver 
lobules, where they form a complex system of anas- 
tomosing channels or tubes called bile canaliculi. 
Interlobular Ducts.-The bile canaliculi unite to 
form interlobular ducts that lie between the liver lob- 
ules. These unite into larger and larger ducts and 
converge to pass out through the transverse fissure, 
where five or six ducts are found. The latter unite 
into two short main ducts that drain respectively 
from the right and left lobes of the liver. 
The hepatic duct is formed by the union of the two 
main ducts at the bottom of the transverse fissure 
and thus receives the bile from the whole liver. It is 
from one to one and one-quarter inches in length and 
one-quarter inch in breadth, and extends downward 
from its origin, taking an irregular course, to its 
junction with the cystic duct, which unites with it to 
form the common bile duct. 
The gall bladder, with its cystic duct, is an evagina- 
tion of the bile duct. The gall bladder is a pear- DIGESTIVE GLANDS. 
209 
shaped receptacle for the retention of bile, and has a 
fundus, body, and neck. It is usually about three 
inches in length and one to one and one-quarter 
inches in diameter with a normal capacity of one to 
one and one-half fluidounces. Structurally it has 
an outer coat of perito- 
neum, a middle coat 
of connective-tissue 
elements, with a liberal 
mixture of smooth 
muscle fibers, and an 
inner coat of mucous 
membrane raised into 
folds and covered with 
simple columnar epi- 
thelium. 
The cystic duct begins 
at the neck of the gall 
bladder and extends 
downward to its junc- 
tion with the hepatic 
duct, with which it 
forms an acute angle. 
It takes an irregular 
course and is from one 
and one-quarter to one 
and one-half inches 
long; therefore longer 
than the hepatic duct, but only about one-half its 
diameter". 
Liver Lobules.-These are minute units of the liver 
about the size of a pinhead. They are cylindrical 
Fig. 168.-Portion of gall bladder 
and bile ducts: i, Cavity of gall 
bladder; 2, cavity of calyx; 3, groove 
separating the calyx from the bladder; 
4, promontory; 5, superior valve of 
calyx: 6, cystic canal; 7, common 
bile duct; 8, hepatic duct (Testut). 210 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
or irregularly polyhedral in shape, about 2 mm. in 
length and 1 mm. in breadth. Their arrangement 
is quite irregular except just beneath the capsule 
where they usually lie with their apices toward the 
surface. Each lobule has a connective-tissue in- 
vestment in which the finer branches of the portal 
Fig. 169.-Injected blood-vessels in liver lobule of rabbit (Bohm and 
Davidoff). 
canal ramify. This investment is particularly dense 
in the pig, which renders the organ in this animal 
very fibrous and tough, quite unfit for the market. 
In certain chronic liver diseases the same condition 
obtains, when the organ is spoken of as the "hob- 
nailed" or "nutmeg" liver. DIGESTIVE glands. 
211 
In the center of each lobule is a blood-vessel known 
as the intralobular vein, while the small veins be- 
tween the lobules are called the interlobular veins. 
These two sets of veins are connected by irregular 
blood capillaries that radiate from the periphery of 
the lobule to its center. They are typical capillaries 
whose walls consist of but a single layer of flattened 
Fig. 170.-Human bile capillaries. The capillaries of one lobule are 
seen to anastomose with those of the adjoining lobule (below, in the 
figure) (chrome-silver method) (Bohm and Davidoff). 
endothelial cells. The blood in the portal vein 
passes to the interlobular veins, then through the 
capillaries to the intralobular vein. The latter 
opens into sublobular veins which unite to form the 
hepatic veins, and these in turn open into the vena 
cava just below the diaphragm. The arterial blood 
of the hepatic artery supplies the connective tissues, 212 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
the walls of the bile ducts and blood-vessels, and 
doubtless some of this arterial blood finds its way 
into the liver capillaries 
where it blends with the 
venous blood from the 
portal vein. 
From the center of each 
lobule toward its periph- 
ery irregular strands of 
liver cells radiate and 
freely anastomose with 
each other, as well as in- 
terlace between the blood 
capillaries. These are called hepatic cords and con- 
sist of double irregular rows of liver cells. The 
cords constitute the 
bile capillaries and 
unite at the periph- 
ery of the lobule 
with the bile ducts 
of the portal canal, 
situated between the 
lobules. The bile 
capillaries, there- 
fore, are very fine 
tubes lying between 
the liver cells that 
constitute its walls. 
These tubes anasto- 
mose freely with 
each other and are the terminal endings of the bile 
passages or its secreting portions. The liver, as a 
Fig. 171.-Schematic diagram 
of hepatic cord in transverse sec- 
tion. At the left the bile capillary 
is formed by four cells, at the right 
two; the latter type occurs in 
the human adult (Bohm and 
Davidoff). 
Fig. 172.-From the human liver, 
showing the beginning of the bile ducts 
(chrome-silver) (Bohm and Davidoff). DIGESTIVE GLANDS. 
213 
gland, thus differs from all other glands (i), that the 
secreting tubules anastomose, and (2) that the wall 
of the secreting portions consists of but two cells. 
The liver cells 
have no cell wall. 
They are large poly- 
hedral or irregular 
epithelial cells, con- 
taining sometimes 
two, but usually one, 
nucleus. The cyto- 
plasm is granular, 
containingbile drops 
and vacuoles. The 
function of these 
cells is twofold: (1) to secrete bile into the bile cap- 
illaries, and (2) receive and contribute sugar to the 
blood capillaries. In junction with this it is affirmed 
that definite cyto- 
plasmic or intracellu- 
lar channels exist, 
particularly for the 
passage of bile. 
These channels end 
in minute dilatations 
within the cells, from 
which finer passages 
lead to and arborize 
around the nucleus. 
According to some 
investigators, the finer passages may penetrate the 
nucleus and are then called intranuclear canals. 
Fig. 173.-Diagram of liver cells, show- 
ing bile passages. 
Fig. 174.-Diagram of liver cells, 
showing bile ducts and blood capillaries. 214 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
Fig. 175.-From preparation from the liver of a rabbit, showing 
the so-called stellate cells of Kupffer: a, Stellate cells; b, liver cells 
(Huber). 
Fig. 176.-Part of a section through liver lobule from dog, showing stel- 
late cells (Bohm and Davidoff). digestive glands. 
215 
Whether this intracellular system is an artifact due 
to manipulations or a normal condition is at present 
unsettled. In either case the liver cells play a deli- 
cate role, and a slight functional disturbance may 
allow the bile to escape to the blood capillaries, with 
jaundice as a natural sequel. In such a case there 
may or may not be any pain depending on the pres- 
ence or absence of an obstruction in the bile duct. 
Stellate Cells of Kupffer.-These are uniformly 
distributed in the lobules. The cells are irregular, 
elongated, and end in two or three pointed projec- 
tions. They are smaller than the hepatic cells and 
are seen only after a special method of treatment. 
According to Kupffer these cells belong to the endo- 
thelium of the intralobular blood capillaries, and 
possess a phagocytic function. 
Lastly, each lobule is interlaced by a fine reticular 
connective fabric that comes from the connective- 
tissue investment of the lobule. This gives support 
and consistency to the lobule. 
Lymphatics of the Liver.-These may be divided 
into (i) the interlobular lymphatics, which accom- 
pany and in some places surround the blood-vessels, 
and (2) sub peritoneal lymphatics on the surface of 
the organ which in the upper portions communicate 
through the ligaments with the thoracic lymphatics. 
Nerves of the Liver.-The liver receives medullated 
fibers from the left pneumogastric and non-medul- 
lated fibers from the solar plexus. The nerves reach 
the organ between the two layers of the small omen- 
tum and accompany the portal canal, therefore enter 
the liver at the transverse fissure. The sympathetic 216 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
fibers innervate the walls of the blood-vessels. The 
medullated pass to the liver lobules where they lose 
the medullary sheath and then accompany the he- 
patic cords or bile capillaries to ramify ultimately 
between and around the liver cells. CHAPTER VI. 
ORGANS OF RESPIRATION AND THYROID 
GLAND. 
The organs of respiration comprise the larynx, 
trachea, bronchi and lungs. More than forty per 
cent, of all deaths are directly due to diseases of this 
tract, which renders a thorough knowledge of this 
system of primary importance. These organs de- 
velop as a ventral median outgrowth of the fore-gut, 
and the mucous epithelium is therefore derived from 
the entoderm. The primitive connection with the 
alimentary canal is maintained in the adult, the upper 
extremity of the larynx opening on the anterior wall 
of the pharynx. 
THE LARYNX. 
The larynx in the male averages 44 mm. in length, 
43 mm. transverse diameter, and 36 mm. antero- 
posterior diameter. In the female these dimensions 
are 36 by 41 by 26 mm. It is a cartilaginous mus- 
cular tube that contains the two vocal cords, the latter 
being transverse folds of mucous membranes. 
In the wall arc three single symmetrical cartilages, 
the thyroid, cricoid, and cartilage of the epiglottis; and 
three pairs, namely, two arytenoids, two corniculce 
laryngis (cartilages of Santorini), and two cuneiform, 
making in all nine pieces. The two last pairs are very 
217 218 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
small, while only the thyroid and cricoid are visible 
on the front and sides of the larynx. The cartilage 
of the epiglottis, the arytenoids, the corniculae laryn- 
Fig. 177.-- Articulations and liga- 
ments of the larynx, anterior view: 
A, Hyoid bone, with a its greater, 
and a' its lesser cornua; 1-5, liga- 
ments; 6, lateral cricothyroid artic- 
ulation; 7, junction of cricoid and 
trachea (Testut). 
Fig. 178.-Articulations and lig- 
aments of the larynx, posterior 
view: A, Hyoid; B, thyroid, with 
b and b' its cornua; C, cricoid; D, 
arytenoids; E, cartilages of San- 
torini; F, epiglottis; G, trachea; 
1-6, ligaments; 2, opening for su- 
perior laryngeal artery; 7, junc- 
tion of trachea and cricoid (Tes- 
tut). 
gis, are of the elastic or yellow fibrous variety and do 
not tend to ossify with age. The rest are composed of 
the hyaline cartilage, which tends to ossify with age. 
Many pairs of muscle control the manipulation of ORGANS OF RESPIRATION. 
219 
these cartilages, regulating the vocal cords and 
modulating the voice. 
The mucous membrane of the larynx is continuous 
Fig. 179.-Vertical section through the mucous membrane of the human 
larynx (Bohm and Davidoff). 
with that of the mouth and particularly sensitive 
about the upper part above the glottis. This mu- 220 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
cous membrane is covered in the greater part of its 
extent with stratified columnar ciliated epithelium. 
The cilia are found higher up the front wall than on 
each side, reaching in the former to the base of the 
epiglottis and at the sides to a point just above the 
false vocal cords. Above these points the epithelium 
is stratified squamous, like that of the pharynx. 
Upon the true vo- 
cal cords the epi- 
thelium is also 
stratified squa- 
mous. Mucous 
glands are found 
everywhere in 
this membrane 
but are particu- 
larly abundant 
upon the epiglot- 
tis. 
The membran a 
propria, on which 
the epithelial cells 
rest, is not only 
very vascular but 
has a rich supply 
of elastic fibers 
and other connective-tissue elements. It is this tis- 
sue that becomes edematous and greatly swollen in 
infections, such as diphtheria. This is nature's 
method of eliminating the disease, with, however, the 
accompanying danger of suffocation. 
The vocal cords are transverse elastic ligaments 
Fig. 180.-Diagram to illustrate the 
thyro-arytenoid muscles; the figure repre- 
sents a transverse section of the larynx 
through the bases of the arytenoid carti- 
lages: Ary, arytenoid cartilage; p.m, proc- 
essus muscularis; p.v, processus vocalis; 
Th, thyroid cartilage; c.v, vocal cords; Oe 
is placed in the esophagus; m.thy.ar.i, in- 
ternal thyro-arytenoid muscle; m.thy.ar.e, ex- 
ternal thyro-arytenoid muscle; m.thy.ar.ep, 
part of the thyro-ary-epiglottic muscle, cut 
more or less transversely; m.ar.t, transverse 
arytenoid muscle. (Redrawn from Foster.) ORGANS OF RESPIRATION. 
221 
covered with a very thin mucous membrane. They 
are attached anteriorly to the thyroid cartilage, 
close to each other, and diverge posteriorly to their 
attachment in the arytenoid cartilages. The glottis 
is the slit-like opening between the vocal cords. 
THE THYROID GLAND. 
The thyroid gland is not a part of the respiratory 
tract, but it is so closely associated with this tract in 
development and in position that it seems advisable 
to describe the 
organ in this 
place. The gland 
is a highly vas- 
cular body con- 
sisting of two lat- 
er al lobes and 
connected by a 
transverse bar, 
the isthmus. The 
rudiments of the 
lobes develop 
from the epithe- 
lium of the fourth gill cleft, while the isthmus and a 
large part of the lobes come from the floor of the 
mouth, the thyroglossus duct at the base of the 
tongue being a remnant of this origin. The gland 
is therefore an epithelial organ derived from the ento- 
derm. 
In position the gland lies low down in the neck 
and in close apposition to the trachea. The isthmus 
crosses in front of the trachea and covers the second 
Fig. 181.-Section from thyroid gland, show- 
ing vesicles or alveoli. 222 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
and third cartilage ring. 1 he lateral lobes are closely 
applied to the sides of the trachea and extend up- 
ward to cover the lower part of the thyroid cartilage. 
Each lobe measures about two inches in length, one 
and one-quarter inches in breadth, and one-half inch 
in depth. The gland, however, is subject to great 
variations both in size, form, and position. It is gen- 
erally larger in females, and appears to undergo a 
periodic enlargement during each menstruation. It 
reaches its maxi- 
mum growth at pu- 
berty, and is fre- 
quently much di- 
minished in size in 
old age. 
Structure.-The 
thyroid gland is in- 
vested by a thin 
layer of areolar tis- 
sue which not only 
binds it fast to the 
trachea, but divides 
it into small lobules 
of irregular size and 
form. It is a duct- 
less gland consisting of epithelial vesicles varying in 
size from .05 mm. to 1 mm. in diameter. These vesi- 
cles vary greatly in form and are grouped and held to- 
gether by areolar connective tissue in which many 
blood-vessels ramify. These vesicles are generally 
filled with colloid substance, a yellow viscid fluid, that 
in sections stains a yellowish red with eosin. They are 
Fig. 182.-Portion of a cross sec- 
tion of thyroid gland of a man; c, col- 
loid substance (Sobotta). ORGANS OF RESPIRATION. 
223 
lined by a simple cubical epithelium made up of two 
kinds of cells, (i) a smaller number of colloid cells 
engaged in the production of colloid, and (2) inter- 
vening chief cells which replace the former in case 
they are lost. It is affirmed by some that the two 
kinds of cells represent merely different stages of 
secretion. 
The thyroid, being an epithelial organ, may be the 
seat of a cancer. Goiter is a more common thyroid 
tumor, consisting of accumulations within its vesi- 
cles of colloid substance; or an increase of the con- 
nective-tissue elements; or a multiplication of the 
thyroid vesicles. Removal of the thyroid produces 
myxedema, while a congenital absence of the gland 
is the cause of cretinism. In the latter case, thyroid 
extract, regularly administered, will establish a nor- 
mal growth of the child. In exophthalmic goiter the 
thyroid gland is enlarged, but in this case the en- 
larged thyroid is a symptom of a more general disease 
involving other organs and systems. The thyroid 
gland may be removed and grafted almost anywhere 
in the body. It will readily grow in its new position 
and assume its normal function with good results. 
Vessels and Nerves.-The arteries of the thyroid 
gland are the superior and inferior thyroid arteries on 
each side, to which is sometimes added a fifth vessel, 
the thyroidea ima. The organ has, therefore, a very 
rich supply of blood. The smaller vessels and capil- 
laries ramify in the connective-tissue elements be- 
tween the gland vesicles. The veins, which are also 
large, form an extensive plexus near the surface of 
the gland, from which a superior, middle, and inferior 224 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
vein are formed on each side. Extensive lymphatics 
accompany the blood system. The nerves are derived 
from the middle and inferior cervical ganglia of the 
sympathetic. They accompany the blood-vessels, 
whose walls they innervate, sending also branches 
that extend close to the base of the epithelial cells. 
PARATHYROIDS. 
The parathyroids are two flattened bodies, one- 
fourth to one-half inch in diameter, that are con- 
Fig. 183.-From parathyroid of man (Huber.) 
stantly present and placed in close proximity to the 
upper and posterior surface of the lobes of the thy- 
roid gland. They consist of solid masses of epithelial 
cells. Lymphoid follicles are usually closely asso- 
ciated with these masses. The' function of these 
little bodies is not known; however, if the thyroid 
gland be removed and the parathyroid left, the effect 
of a complete thyroidectomy is not obtained. ORGANS OF RESPIRATION. 
225 
THE TRACHEA AND BRONCHI. 
The trachea extends from the cricoid cartilage, a 
point opposite the lower border of the sixth cervical 
vertebra, to the level of the intervertebral disc be- 
Fig. 184.-The trachea and bronchi. 
tween the fourth and fifth dorsal vertebrae, extend- 
ing therefore one to two inches into the chest. The 226 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
trachea measures from four to four and one-half 
inches in length, and three-fourths to one inch in 
width. It is smallest at its commencement, and, 
although quite uniform in its dimensions, is usually a 
little wider midway between its two ends. 
At the lower end the trachea bifurcates to form 
the right and left bronchi, which pass each to the root 
of the corresponding 
lung. The right bron- 
chus is larger than 
the left and more 
nearly vertical, so that 
in looking down the 
trachea more of the 
right than of the left 
bronchus can be seen. 
The right bronchus di- 
vides into branches, 
one to each root of 
the three lobes of the 
right lung, while the 
left gives off- two 
branches, one to each 
lobe of the left lung. 
Structure.-In the 
wall of the trachea 
there are from sixteen to twenty C-shaped cartilage 
rings that make a little more than two-thirds of a cir- 
cle. The outer surface of these cartilages is flat, but 
the inner surface is convex from above downward, so 
as to give greater thickness in the middle than at the 
edges. The cartilage is of the hyaline variety and is 
Fig. 185.-From longitudinal sections 
of trachea. ORGANS OF RESPIRATION. 
227 
enclosed in a periosteum. The cartilage rings are held 
together by a strong elastic fibrous tissue, which not 
only occupies the space between them but is pro- 
longed over their surfaces, so that each ring appears 
imbedded in this tissue. Each cartilage terminates 
abruptly behind by rounded ends, between which 
Fig. 186.-Transverse section through human bronchus (Bohm and 
Davidoff). 
stretches a thin layer of smooth muscle tissue. This 
muscle not only unites the ends but is also found in 
the intervening space between the cartilage rings, 
along the posterior wall of the trachea. Outside of 
the transverse fibers are a few fasciculi having a lon- 
gitudinal direction. 
The cartilage rings of the bronchi resemble those 228 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
of the trachea in being incomplete behind. The 
right bronchus has from six to eight rings, while the 
left has from nine to twelve. The left bronchus is 
longer but narrower. 
The mucous membrane is smooth and contains a 
considerable amount of lymphoid tissue and many 
mucous glands. The epithelial lining consists of 
long columnar ciliated cells, often very irregular and 
even branched at their fixed ends. One or two rows 
of small irregular cells intervene between the basal 
ends of the ciliated cells, and this epithelium is 
therefore stratified although very thin. The cells 
rest upon a basement membrane through which 
nerves pass to reach the sensitive epithelium. Ex- 
ternal to the basement membrane, in what consti- 
tutes the membrana propria, there is a strong layer 
of longitudinal clastic fibers. This tissue extends 
the whole length of the air passages, and gives not 
only great elasticity but is an obstruction to invading 
bacteria. A vascular submucosa, not very exten- 
sive, intervenes between the mucosa and the carti- 
lage. In this may be found the bodies of small race- 
mose mucous glands, the largest being in the poste- 
rior wall. The excretory ducts of these glands open 
on the inner surface. Lymphoid tissue is present 
both in the mucosa and the submucosa. 
THE LUNG. 
The lungs occupy the greater part of the chest 
cavity, of which they form an accurate mould. The 
right lung is the larger and has three lobes, while the 
left has two. Each lung is suspended freely in this ORGANS OF RESPIRATION. 
229 
cavity and is attached only by a small part of its 
flattened or mesial surface called the root. The 
outer surface of each lung it covered by a serous 
membrane, the visceral pleura, which is reflected 
over the chest wall, where it is called the parietal 
pleura. The histology of the pleura is identical with 
that of the peritoneum. 
Each lobe has one bronchus which divides rapidly 
into smaller bronchi. The latter, instead of having 
cartilage rings, are supplied with small cartilage 
plates. These plates are not present in bronchi 
whose diameters are less than o.i mm. Mucous 
glands are rather numerous but also disappear in 
bronchi less than o.i mm. in diameter. These 
smaller bronchi differ further from the larger ones 
in having a circular layer of smooth muscle that in- 
tervenes between the cartilage plates and the mucous 
membrane. The contraction of this muscle reduces 
the caliber of the smaller bronchi and thus regulates 
the amount of air that passes to the lung tissue. In 
asthma there is a spasmodic or more or less chronic 
contraction of this muscle tissue, which causes diffi- 
culty in breathing. The air is forced through the 
narrow tubes, and this brings about a dilatation of 
the terminal passages and a hypertrophy of the 
chest muscles, the latter being due to the forced 
efforts in securing sufficient air. Asthmatic patients, 
therefore, have resonant lungs and usually an en- 
larged chest. The primary trouble in this disease 
is not in this smooth muscle tissue, but seems to 
involve the nervous system and the innervating 
nerves. Smooth muscle is present in all the bronchi, 230 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
even in the smallest tubes whose diameters measure 
0.2 mm. 
Structure of the Lung.-The structure of the 
smaller bronchi, which form a part of the lung tis- 
sue, has just been described. Our knowledge of the 
terminal air passages has recently been greatly in- 
creased by the work of Dr. Miller, of the University 
of Wisconsin, whose account will be followed. The 
smallest bronchioles, whose diameters are 0.2 mm., 
are called terminal, or respiratory bronchi. In these 
Epithelium. 
Longitudinal 
clastic, fibers. 
I nvoluntary 
muscle. 
Cartilage. 
Mucous gland. 
.1 ir sacs. 
Fat cells. 
Fig. 187.-Section from lung showing portion of small bronchus and 
adjacent lung tissue. 
tubes the character of the epithelial lining changes. 
Patches of small pavement epithelial cells appear 
among the ciliated cells, while at the end of the res- 
piratory bronchus all are of the pavement variety. 
At this point the tube, slightly dilated, opens into 
three to six distinct chambers called atria. Each 
atrium opens into a variable number (2 to 5) of 
larger irregular spaces called air sacs, the walls of 
which have concave spherical depressions called air ORGANS OP RESPIRATION. 
231 
cells, or alveoli. Simple pavement epithelium lines 
the atria and air sacs, consisting of two varieties of 
cells: (i) small nucleated elements, and (2) larger 
non-nucleated plates. The latter line the alveoli 
and are applied directly against the blood capillaries, 
while the nucleated elements intervene at the free 
margin of the alveoli. Before birth the air sacs are 
collapsed and all the pavement epithelium is com- 
posed of nucleated cells. With the first breath of 
air the air sacs become distended, not uniformly, 
but to form vesiculated walls, the small vesicles being 
the alveoli. The walls of the latter suffer greater 
distention, due to a less resistance offered by the 
opposing blood capillaries, and the nucleated cells in 
this region become changed to non-nucleated plates, 
through which an exchange of gases takes place dur- 
ing the functional activity of the lung. The atria 
and air sacs vary in size according to their distention 
with air. An average diameter is 1.0 mm. for the 
atria, and 1.0 by 1.5 mm. for the air sacs. Each air 
sac has from six to eight air cells, or alveoli, that also 
vary greatly in size, an average diameter being 0.25 
mm. One system of atria and air sacs constitute a 
lobule and is separated from adjacent lobules by in- 
tervening areolar tissue. The base of each lobule is 
directed toward the surface of the lung and the apex 
towards its root. These lobules can be seen in a 
macroscopic surface examination of the lung. 
The elastic fibers of the membrana propria, de- 
scribed in the wall of the trachea and bronchi, ex- 
tend to the distal end of the air passages, where they 
spread out to form a thin reticular fabric just ex- Fig. 189. 
Figs. 188 and 180.-Two sections of cat's lung (Bohm and Davidoff). 
232 ORGANS OF RESPIRATION. 
233 
ternal to the pavement epithelium, giving great 
elasticity to the air sacs and functions in the expul- 
sion of air during normal breathing. The term in- 
fundibulum is sometimes applied to the distal air 
passage lined by pavement epithelium. 
The following is a resume of the tissues found in 
the walls of the respiratory passages: 
Fig. 190.-Inner surface of human alveolus treated with silver nitrate, 
showing respiratory epithelium (after Kolliker). 
i. Epithelium extends the whole length. In the 
trachea and bronchi this is stratified ciliated. In the 
atrium and air sacs it is simple pavement and made 
up of two kinds of cells, namely, nucleated and non- 
nucleatcd. 
2. Elastic fibers extend the-whole length. In the 
respiratory parts the fibers form a reticulum just 234 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
external to the pavement epithelium and give elas- 
ticity to the lung tissue. 
3. Mucous glands are found in the walls of the large 
passages down to tubes 1.0 mm. in diameter. 
4. Cartilage is found in the trachea and bronchi 
down to tubes 1.0 mm. in diameter. In the trachea 
and larger bronchi the cartilage forms C-shaped 
rings, while in the 
smaller tubes the car- 
tilage appears in 
plates. 
5. Smooth muscle is 
found in the larger 
passages down to 
tubes 0.2 mm. in di- 
ameter, or down to 
the respiratory parts. 
In the trachea and the 
larger bronchi this 
muscle is placed in the 
posterior wall and be- 
tween the ends of the 
cartilage rings. In 
the smaller bronchi it forms a circular layer between 
the lining epithelium and the cartilage plates. 
Blood Supply.-The lungs, like the liver, receive 
blood from two sources, arterial blood through the 
bronchial vessels, and venous blood through the pul- 
monary artery. The bronchial arteries, from one to 
three for each lung, are much smaller than the pul- 
monary vessels, and carry blood for the nutrition of 
the lung. They arise from the aorta or from an 
Fig. 191.-Scheme of lung lobule 
(after Miller): b. r., respiratory 
bronchiole; d. al., alveolar duct (ter- 
minal bronchus); a, a, a, atria; 5. al., 
air sacs; a. p., air-cells or alveoli. ORGANS OF RESPIRATION. 
235 
intercostal artery and follow the bronchial tubes 
through the lung, to be ultimately distributed in 
three ways: i. They supply the bronchial lymph 
glands, the coats of the large blood-vessels, and the 
walls of the bronchial tubes, forming in the latter 
an outer and an inner plexus for the irrigation of the 
muscle coat and the mucous membrane. 2. They 
supply the interlobular areo- 
lar tissue; and 3, They spread 
out over the surface of the lung 
beneath the pleura. The 
bronchial veins do not have so 
extensive a distribution be- 
cause some of the blood sup- 
plied by the bronchial arteries 
returns by the pulmonary 
veins. The superficial and 
deep set of bronchial veins 
unite at the root of the lung 
to drain on the right side into 
the large azygos and on the 
left into the left upper azygos 
vein. 
The pulmonary artery, 
which supplies the venous 
blood, is a very large vessel 
that gives branches to each 
lobe of the two lungs. The relation of the pul- 
monary artery to the bronchi is different on the two • 
sides. On the right side the first branch of the pul- 
monary artery turns backward below the bronchus 
of the upper lobe, and then passes along the posterior 
Fig. 192.-'Reconstruc- 
tion in wax of a single atri- 
um and air sac with the 
alveoli: V, Surface where 
atrium was cut from alveolar 
duct; P, cut surface, where 
another air sac was re- 
moved; A, atrium; 5, air 
sac with air cells (alveoli) 
(after Miller). 236 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
surface of this bronchus. On the left side the corre- 
sponding artery turns backward above the level of 
the first bronchial branch. The bronchus to the 
upper lobe of the right lung is therefore called an 
eparterial bronchus. All the other bronchi are be- 
low their respective arteries and are called hyparterial 
bronchi. Because of these relations it is believed 
that the upper lobe of the right lung has no homo- 
logue on the left side, and that the middle lobe on 
the right side is homologous to the upper lobe on the 
left. The pulmonary ar- 
tery divides with the 
bronchi and closely ac- 
companies them along 
their posterior or superior 
walls. The correspond- 
ing veins pass along the 
anterior or inferior walls. 
These blood-vessels are 
very large, often as large 
as the bronchial tubes, 
but in no case do they 
supply blood to the walls 
of the bronchi. At the apex of the pulmonary 
lobule, the pulmonary artery breaks up into several 
small twigs, one for each antrum, supplying blood 
to an extensive capillary plexus that spreads over 
the surface of atria and air sacs. The capillary 
meshes are very dense, and the capillary tubes very 
large, so that the intervening spaces are barely wider 
than the capillaries themselves. Because of the large 
size of the lung capillaries it is possible for fine 
Fig. 193.-Section from in- 
jected lung showing capillaries of 
an air sac. ORGANS OF RESPIRATION. 
237 
shreds from a blood clot, or emboli in the blood, to 
filter through and reach the left side of the heart by 
the pulmonary veins. If so, these emboli are 
c|uickly carried by the blood current around the 
aorta and up the right carotid, as the latter is the 
most direct route. This course takes them to the 
right side of the brain, in which the capillaries are 
narrow, and where the emboli lodge often with fatal 
results. Such emboli or shreds of blood clots pri- 
marily enter the venous system at the seat of a bone 
fracture, or in the walls of the uterus after parturi- 
tion, or from clots of blood anywhere in the system. 
The pulmonary veins carry blood from the pul- 
monary capillary plexus. Each venous radicle 
drains an area corresponding to several air cells or 
alveoli. At first these small veins take an inde- 
pendent course in the interlobular tissue, but after 
they have attained a certain size they accompany 
the arteries and the bronchi, and, as a rule, along the 
lower and front aspect of the latter. At the root of 
the lung there are formed two pulmonary veins on 
each side which open separately into the left auricle. 
The pulmonary veins have no valves, and unlike the 
veins of other organs are more capacious than their 
corresponding arteries. 
Lymphatics.-The lymphatics of the lung are very 
extensive and accompany the two blood systems. 
We may therefore divide them into two sets, a 
bronchial and an alveolar. The bronchial consists of 
an elaborate, fine plexus that ramifies through the 
mucosa and submucosa of the bronchial tubes. This 
set anastomoses freely with a second plexus just ex- 238 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
ternal to the smooth circular muscle layer of the 
bronchi. Lymph nodes are interpolated every- 
where in these plexuses. Just beneath the pleura, 
all over the surface of the lung, lymphatics ramify 
and drain toward the root of the lung, where they 
join the lymphatics located in the bronchial walls. 
The alveolar set accompany the pulmonary vessels. 
These lymphatics have their origin in a plexus that 
surrounds the respiratory or alveolar portions of the 
lungs, and then accompanies the pulmonary arteries 
and veins along the external surfaces of the bronchial 
tubes to the root of the lungs, where they ultimately 
unite with the bronchial lymphatics. While lym- 
phatic nodes are present everywhere, they are par- 
ticularly abundant at the root of the lung. As 
tuberculosis spreads along the lymphatics, the dif- 
ferent clinical aspects of this disease depend to a 
considerable extent on which of these systems be- 
comes involved. 
Nerves.-The nerves of the lung come from the 
pneumogastric and the sympathetic, and are made 
up of medullated and non-mcdullated fibers. They 
enter at the root of the lung and accompany the 
blood-vessels to the terminal air passages, where 
they arborize about the lung alveoli just external to 
the epithelial lining. Many nerve ganglia arc located 
along their course and many fine fibers are given off 
that innervate the musculature and epithelial lining 
of the bronchial tubes and the walls of the blood- 
vessels. CHAPTER VII. 
THE URINARY ORGANS. 
The following organs will be considered under this 
topic: Suprarenal bodies, Kidney, Ureter, and Blad- 
der. The urethra will be described in connection 
with the generative organs. 
THE SUPRARENAL BODIES. 
The suprarenals, morphologically, belong to the 
nervous system, but their close proximity to the 
kidneys makes it advisable to describe them here. 
They are two triangular flattened organs covered 
with fat that lie one on either side of the spine, in 
close proximity to the upper kidney border. The left 
one is slightly larger and measures from one and 
one-fourth to two and one-half inches from above 
downward, one and one-fourth inches from side to 
side, and one-sixth to one-eighth inch in thickness. 
. Embryologically, the organs consist of a cortical 
part that develops in connection with the Wolfpan 
body and therefore comes from the mesoderm, and a 
medulla which is associated with the sympathetic 
nervous system and is derived, at least in part, from 
the ectoderm. The medulla decomposes very rapid- 
ly after death, and the organ then resembles a cap- 
sule; hence the name, suprarenal capsule, is often 
used. 
239 240 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
Each suprarenal is invested in a hbrous capsule and 
a liberal supply of fat. The capsule contains many 
elastic fibers and some smooth muscle cells. 
The cortex shows a radial structure and has been 
divided into three zones, which are not very well de- 
fined. 
i. The zona glomerulosa, next to the capsule, con- 
sists of a row of columnar epithelial cells folded in 
such a way as to form oval bodies or elongated heads 
separated by strands of connective tissue from the cap- 
sule. The oval nuclei are in the middle of the cells. 
2. T h e z o n a 
fasciculata makes 
up the larger por- 
tion of the cortex 
and consists of 
anastomosing col- 
umns of epithelial 
cells, a continua- 
tion of the zona 
glomerulosa. 
Each column has two rows of polygonal cells that are 
smaller than those of the glomcrula?. 
3. The zona reticularis borders on the medulla. 
Here the columns anastomose and freely interlace. 
The cells resemble those of the fasciculata. Con- 
nective tissue ramify between the columns, hence 
the radial appearance of the cortex. 
The medulla is coarsely vascular. The cells are 
smaller than those of the cortex and are grouped in 
round or oval masses. These cells are finely gran- 
ular, often pigmented, and stain a brown color. 
Fig. 194.-Cross section of suprarenal body of 
man. PLATE IV. 
Diagrammatic Representation of the Development of the Genito- 
urinary System, the Wolffian Body and its Derivatives 
Being Colored Red, the Mullerian Duct and its Derivatives, 
Green (Heisler): 
i, Indifferent type; 2, indifferent type, later stage, the Wolffian and 
Mullerian ducts and the primitive ureter now opening into the urogenital 
sinus; 3, male type, lower ends of Mullerian ducts fused to form the sinus 
pocularis; 4, female type. PLATE IV. THE URINARY ORGANS. 
241 
Numerous ganglion cells are present and many nerve 
fibers. 
Blood-vessels.-Each suprarenal body receives 
three arteries,-one each from the aorta, the phrenic, 
and the renal. The arteries break up into small 
branches, most of which enter the medulla through 
the hilum. Some branches ramify in the capsule 
Fig. 195.-Section of suprarenal cortex of dog (Bohm and Davidoff). 
and from there enter the cortex, where they form 
capillaries around the columns of epithelial cells. 
Those that enter the medulla form a coarse plexus 
in this part, and then send smaller capillaries into the 
cortex to anastomose with those from the capsule. 
The veins pass out from the center, usually one from 242 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
each organ. The vein from the right suprarenal 
enters the vena cava, while that from the left empties 
into the renal. Lymphatics accompany the blood- 
vessels. 
Fig. 196.-Arrangement of the intrinsic blood-vessels in the cortex and 
medulla of the dog's adrenal (Fig. 17, Plate V, of Flint's article in " Con- 
tributions to the Science of Medicine," dedicated to Professor Welch, 
1900). 
The nerves are exceedingly numerous and come 
from the solar and renal plexuses of the sympathetic, 
and medullated fibers from the phrenic and pneumo- 
gastric. They ramify freely among the ganglionic 
cells of the medulla and between the cells of the cor- 
tex, particularly those of the glomerulosa. THE URINARY ORGANS. 
243 
The function of the suprarenal body is not-known. 
Its extirpation in the dog is followed by death in a 
few days. There are at least three interesting clini- 
cal features connected with this organ: 
i. Suprarenal extract, taken internally, increases 
arterial tension by contracting the small arterioles. 
The extract has the same effect when sprayed upon 
surfaces, therefore it is much used in nose, throat, 
and eye work, to check hemorrhage and reduce con- 
gestion. 
2. The cortical cells may produce a malignant 
growth called a hypernephroma. The malignant 
cells may invade and replace the kidney. The 
growth usually spreads to the liver and adjacent or- 
gans, causing death in one to three years. 
3. Addison's Disease is a chronic, usually tubercu- 
lar, inflammation of the suprarenal bodies, fatal in 
one or two years. It is accompanied with a striking 
bronze pigmentation of the skin, and digestive and ner- 
vous disturbances. It is a rare disea'se of middle life. 
The above facts support the view that the organ 
secretes a substance that is regularly gathered up by 
the blood. This secretion may control, in a measure, 
arterial pressure. The organ is also a relay in the 
sympathetic nervous system which, when destroyed, 
as in Addison's Disease, accounts for the gastric and 
nervous symptoms. 
THE KIDNEYS. 
The kidneys, two in number, are compound tubular 
epithelial glands derived, embryologically, from the 
mesoderm. They are situated behind the peri- 244 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
toneum, one on each side of the vertebral column and 
on a level with the last dorsal and the upper two or 
three lumbar vertebrae. They are held in position 
by the renal vessels, by a loose areolar tissue that 
surrounds them which contains much fat, and by 
the abdominal pressure. Each kidney measures 
four inches in length, two and one-half inches in 
breadth, and one and one-fourth to one and one- 
half inches in thickness. 
Their developmental history is rather complex 
and can be but briefly given here. It involves the 
history of the pronephros, mesonephros, and meta- 
nephros, three sets of excretory organs which re- 
place each other in the sequence in which they are 
mentioned. 
i. The pronephros, or head kidney, develops in 
connection with the nephrotomes of the first three or 
four embryonic somites. These nephrotomes unite 
with a longitudinal duct, the pronephric duct, 
which opens posteriorly into the cloaca. With this 
organ fluid from the celomic or peritoneal cavity 
can be eliminated, and also waste products from the 
blood, as a tuft of blood capillaries or glomerulus 
is present near the peritoneal opening of each ncphro- 
tome. This kidney is exceedingly rudimentary in 
mammals and functional only in larval stages of 
amphibians and in bony fishes. 
2. The mesonephros, or Wolfpan body, develops 
in connection with the nephrotomes posterior to 
those that form the pronephros. The pronephric 
duct becomes the Wolffian duct and drains from the 
peritoneal cavity in the same manner as in the head THE URINARY ORGANS. 
245 
kidney. The glomerulus in this case is situated in 
the wall of the nephrotome, which makes the meso- 
nephros a more efficient organ. The mesonephros 
is an elongated segmented organ and a permanent 
structure in amphibians. It is an embryonic organ 
in birds and mammals, in which it is replaced by 
the metanephros. 
3. The metanephros, or permanent kidney, develops 
as a diverticulum from the cloacal end of the Wolffian 
duct. The diverticulum lengthens into a tube, the 
ureter. The upper or anterior end of the tube 
Fig. 197.-Kidney of new-born infant, showing a distinct separation 
into reniculi; natural size. At a is seen the consolidation of two adjacent 
reniculi (Bohm and Davidoff). 
branches to form a number of smaller tubes, the uri- 
niferous tubules of the kidney. The surrounding 
mesoderm becomes condensed and vascular, inter- 
lacing between the tubules to form the adult kidney. 
The development of the urinary system is closely 
associated with that of the generative system, and 
will be referred to again when the latter is described. 
Structure.-The hilus of the kidney is an opening 
through which the ureter and blood-vessels pass. 
On making a longitudinal section of the kidney, it 
will be seen that the hilus leads to an expanded fis- 246 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
sure, the renal sinus. The pelvis is a funnel-shaped 
expansion of the ureter that occupies a large portion 
of the sinus. The contents of the sinus may be re- 
moved, when the exposed wall will be found to be 
kidney substance. 
Each kidney is 
enclosed in a 
smooth fibrous cap- 
sule of areolar tis- 
sue, a part of which 
also lines the sinus. 
The capsule is 
finely vascular and 
can easily be de- 
tached. If it ad- 
heres to the kidney 
substance it is evi- 
dence of disease. 
It is customary 
to describe the kid- 
ney as made up of 
two layers, an out- 
er, or the cortex, and 
an inner, the me- 
dulla, although 
there is no sharp 
line dividing the 
two. The medulla 
consists of ten or 
twelve separate conical masses called Malpighian, or 
medullary pyramids, so arranged that their bases bor- 
der on the cortical layer and their apices point toward 
Fig. 198.-Longitudinal section 
through the kidney: 1, Cortex; 1', medul- 
lary rays; 1", labyrinth; 2, medulla; 2', 
papillary portion of medulla; 2", boun- 
dary layer of medulla; 3, transverse sec- 
tion of tubules in the boundary layer; 4, 
fat of renal sinus; 5, artery; *, transverse 
medullary rays; A, branch of renal artery; 
C, renal calyx; U, ureter (after Tyson 
and Henle). THS URINARY ORGANS. 
247 
the renal sinus where they form papillae. The 
medullary substance is more dense than the cortical 
and is strictly striated, which is due to the radiating 
course of the tubules in this part. At the base of 
each Malpighian pyramid these tubules pass up into 
the cortical substance and are grouped to form 
cone-like masses called medullary rays, or pyramids of 
Fig. 199.-Section through cortex and medulla of kidney. 
Ferrein, the apex of each being in close proximity to 
the periphery of the kidney. There are thus a great 
many medullary rays for each Malpighian pyra- 
mid. The portions of the kidney that intervene 
between the medullary rays are called the labyrinth, 
and consist largely of convoluted tubules. The 
cortical substance not only covers the bases of the 248 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
Malpighian pyramids, but sends prolongations be- 
tween them down to the renal sinus. These cortical 
prolongations are called the columns of Bertini, of 
which there are as many as there are Malpighian 
pyramids. 
It is convenient to describe the kidney tubules as 
consisting of nine parts. Each tube commences in 
the labyrinth of the cortex with (i) an invaginated 
dilatation called Bowman's capsule. This capsule 
is lined by simple squamous epithelium which, 
when invaginated, makes two layers, the lumen of 
the tube being between these layers. Into the in- 
vaginated cavity is crowded a tuft of blood capil- 
laries called a glomerulus. A liberal supply of con- 
nective tissue blends with these capillaries. The 
capsule and glomerulus are frequently called a 
Malpighian corpuscle. At the base of the cap- 
sule each tube is constricted, forming (2) the neck, 
after which it becomes much convoluted and wide, 
forming (3) the proximal convoluted tubule. The 
cells of this part are large with very thin cell 
walls. The cytoplasm immediately around the nu- 
cleus is granular, but toward the basement membrane 
it is striated with lines at right angles to the mem- 
brane. The tube now approaches the medulla, 
becomes nearly straight, but rapidly narrows to 
form (4) the spiral portion. It now passes straight 
down a Malpighian pyramid, where it makes a short 
curve, and returning thus forms (5) the loop of 
Henle. This loop has a narrow descending limb 
with a short curve, and a wider ascending limb. 
The narrow descending limb and curve has simple THE URINARY ORGANS 
249 
flat epithelium, so that the lumen is practically as 
Fig. 200.-Diagram of kidney tubule. 
large as that of the preceding part. The ascending 250 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
limb is larger but the epithelium takes on the char- 
acteristic of the proximal convoluted tube, although 
the cells are a little smaller and may contain pig- 
ment granules. The ascending limb passes straight 
up a medullary ray, from which it emerges to again 
enter the cortex, where it becomes irregular in out- 
line forming (6) the irregular tubule, which quickly 
becomes much twisted and coiled to form (7) the 
distal convoluted part. In the irregular part the 
Fig. 201.-Section of a portion of the labyrinth of the kidney cortex. 
cells are very unequal in size and a rod-like structure 
of the cytoplasm is very distinct, while the basement 
membrane is said to be absent. The cells of the 
distal convoluted tube are rather long, with a distinct 
membrane and a highly refractive-appearance of the 
protoplasm. Near the basement membrane minute 
projections from adjacent cells may be seen to inter- 
lock. Finally, this portion terminates in (8) a 
short junctional tubule, which leaves the cortex and THE URINARY ORGANS. 
251 
enters a medullary ray to join the last part (9), the 
collecting tubule. The latter passes straight through 
the Malpighian pyramid to open on its surface in a 
small pore. In its course the collecting tube receives 
not only other junctional tubules but also unites 
with other collecting tubes. The junctional part is 
narrow but its lumen relatively large, being lined by 
clear flat or cubical cells. The collecting tubes are 
large and have a lining of simple cubical epithelium. 
It will be ob- 
served that the 
loop of Henle, 
junctional and 
collecting tub- 
ules, form the 
medulla, and 
the other parts 
are found in 
the kidney cor- 
tex; that their 
walls consist of 
simple epithe- 
lium which is 
flat in the capsule, neck, and descending limb of 
Henle's loop; while large cubical or columnar cells 
with granular and rod-like structure of the cytoplasm 
are found in the convoluted parts and ascending 
limb of Henle's loop; and a low cubical epithelium 
invests the junctional and collecting tubules. 
Casts.-It is common in high fevers and in diseases 
of the kidney to find moulds of the uriniferous 
tubules in the urine. In high fevers blood may 
Fig. 202.-Section of a portion of kidney 
medulla. 252 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
enter and congeal in the uriniferous tubules, the 
kidney secretion forces out this obstruction, which 
then appears in the urine as a blood cast. A 
clear serum mould is called a hyaline cast. In more 
chronic cases the cells of the tubules are carried away 
and the mould is then called an epithelial cast. The 
cells may have decomposed, when it becomes a 
granular cast. Hyaline casts often show granula- 
tions and are then also called granular casts. Finally, 
fatty degenerations may appear and form fatty 
casts. The recognition and identification of casts 
form an important subject in clinical analysis. If 
small pieces of kidney are treated with strong hydro- 
chloric acid and the detritus thus produced be ex- 
amined in glycerin, under a low magnification, many 
pieces of the uriniferous tubules are readily ob- 
served. These pieces are practically identical with 
the epithelial and granular casts of the diseased 
kidney. 
Blood-vessels.-The kidneys are highly vascular 
and receive a large amount of blood in proportion to 
their size. The renal artery and renal vein pass 
through the hilum, the artery between the vein and 
ureter. In the renal fissure the artery breaks up 
into four or five branches which lie external to the 
pelvis of the ureter. These branches pass directly 
to the columns of Bertini, where they break up into 
smaller vessels and rise to the level of the Mal- 
pighian pyramids. ' At this level they pass across 
the pyramids, between the latter and the cortex, 
forming what are called arterial arches. The ar- 
teries form incomplete arches across the base of the THE URINARY ORGANS. 
253 
pyramid, while the accompanying veins, in this 
place, form complete venous arches across the base 
of the pyramid. From the arches interlobular 
arteries pass 
outward be- 
tween the me- 
dullary rays 
and among the 
convoluted tu- 
bules, taking a 
direct course 
toward the sur- 
face of the kid- 
ney. At inter- 
vals they give 
off curved short 
branches which 
pass directly to 
the glomerulus 
of a Malpig- 
hian corpuscle, 
where they 
break up into 
a spongy mass 
o f capillaries. 
A vein, smaller 
than the artery, 
emerges from 
the glomerulus 
close to the 
point where the artery enters. The artery is called 
the vas afferens and the smaller vein the vas efferens. 
Fig. 203.-Diagram of blood supply of kidney. 254 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
The latter, instead of uniting with other veins to form 
larger trunks, as is the case in other organs, passes 
directly to the convoluted tubules, where it forms 
a dense capillary system that ramifies everywhere 
over the walls of these tubules. Many of the effer- 
ent vessels from the lowermost glomeruli, that is, 
those nearest the medulla, break up into pencils of 
straight vessels called pseudo-arteria recta, which 
pass directly into the medulla to form capillaries 
around the tubules of this part. 
Interlobular 'veins convey the blood from the kid- 
ney cortex to the venous arches at the base of the 
pyramids. Near the periphery of the kidney other 
veins converge to form a stellate appearance just 
beneath the capsule. These stellate veins, which 
also receive blood from the capsule, ultimately pass 
inward through the cortex to join the venous arches. 
The blood supply of the medulla is to a great ex- 
tent independent of that to the cortex, excepting that 
supplied by the false arteriae rectae. Branches from 
the concave side of the arterial arches pass directly 
into the medulla, where they form bunches of pencils 
of small parallel vessels, the arteria recta, which sup- 
ply blood to the walls of the uriniferous tubules of 
this part. Veins return this blood to the venous 
arches that lie between the cortex and medulla. 
These arches form veins that pass through the col- 
umns of Bertini and ultimately drain into the renal 
vein, which passes through the hilum to join the 
inferior vena cava. 
On account of this extensive blood supply any 
renal disturbance is, as a rule, accompanied by a cor- THE, URINARY ORGANS. 
255 
responding circulatory disturbance. Conversely, a 
disturbed circulation or an enlarged heart is indica- 
tive of a possible nephritis. 
Nerves.-The nerve supply is derived from the 
cerebrospinal system and the sympathetic. Many 
of these supply the blood-vessels, which they always 
accompany, but some arborize among the renal 
tubules, particularly those of the renal cortex. 
THE URETERS. 
The ureters are two muscular tubes that conduct 
the urine from the kidneys to the bladder. The 
dilated commencement of each ureter is called the 
pelvis and lies with its base in the renal fissure, and 
extends through the hilum to the lower portion of 
the kidney where the ureter proper begins. Tatcral 
expansions of this pelvis extend to and enclose the 
papillae of the Malpighian pyramids, on the surface 
of which the collecting tubules open. These ex- 
pansions are called calyces. 
The ureters measure from fourteen to sixteen 
inches in length, and one-fourth inch in diameter. 
Each ureter lies behind the peritoneum and passes 
downward and inward to the brim of the pelvis, and 
then forward and inward to the base of the bladder. 
The ureters are about two inches apart as they enter 
the wall of the bladder, through which they pass 
obliquely for three-fourths inch to open on the 
inner surface in two narrow and slit-like openings. 
The oblique passage through the bladder wall acts 
as a valve to prevent a return flow of urine. 
Structure.-The walls of the ureter consist of an 256 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
outer fibrous, a middle muscular, and an inner mucous 
layer. The latter has many longitudinal folds and 
is lined by transitional epithelium of four or five 
layers of cells. The superficial cells are flat, or low 
cubical, and may contain two nuclei. Their lower 
surfaces have depressions that fit upon the rounded 
ends of the second layer, which consists of oval or 
pear-shaped cells. Between the apices of the latter 
are two or three rows of small, irregular interstitial 
cells. Mucous 
glands have 
been described 
in the renal pel- 
vis and so have 
lymphoid nod- 
ules, but the 
presence of 
glands in the 
ureter of man 
is doubtful. 
The membrana 
propria is com- 
posed of areolar 
tissue which 
becomes gradually loose toward the muscularis. This 
membrane is like others of its kind, having a limited 
blood supply. The muscular coat is composed of 
smooth muscle cells and consists chiefly of a circular 
layer between two thin longitudinal layers, particu- 
larly well defined in the lower part of the ureter. 
The fibrous coat is relatively thick and strong, con- 
tributing fibrous elements that interlace the muscle 
tissue. 
Fig. 204.-Cross section of the ureter. THE URINARY ORGANS. 
257 
The function of the ureter is an active one. A few 
drops of urine enter the ureter and are propelled 
along by the peristaltic contraction of its muscula- 
ture, which forces the urine in intermittent jets into 
the bladder. In case of overdistention the force ex- 
erted by this mechanism is sufficient to rupture the 
bladder. In case of an obstruction in the ureter, 
as in the passage of calculi, a violent contraction of 
the smooth muscle follows, accompanied by severe 
pains. In surgical operations ureters have been 
sewed into the upper end of the bladder, or even into 
the intestine. In the latter case the kidney usually 
becomes infected with bacteria from the bowel. 
THE URINARY BLADDER. 
The urinary bladder is a receptacle for the reten- 
tion of urine, with an average capacity of one pint, 
although capable of much greater distention. When 
empty it lies wholly within the pelvis, but if dis- 
tended it rises into the abdomen. When moderately 
filled it has a rounded form, but when completely 
distended it becomes egg-shaped, the larger end, 
called the base or fundus, being directed downward 
and backward toward the rectum, and its smaller 
end, the summit, resting against the anterior ab- 
dominal wall. When distended the peritoneum 
covers the bladder, excepting a triangular space of 
two inches above the symphysis pubis known as the 
space of Retzius. This is of surgical importance, 
as the bladder can be opened through this space 
without going through the peritoneum. 
The mucous membrane on the inner surface of the 258 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
bladder is loosely attached to the muscularis, and is 
slightly corrugated or folded in the contracted form 
of the organ. At the lower part of the bladder is 
found the orifice leading into the urethra, and im- 
mediately behind this is a smooth triangular surface 
called the trigone. The' orifices of the ureters are 
found at the posterior angles of the trigone, and in 
the distended bladder are about one and one-half 
inches apart and about the same distance from the 
urethral orifice. When the bladder is distended 
this space is diminished. An exact knowledge of 
these relations 
is important in 
any attempt to 
pass a catheter 
into the ureter. 
Histology of 
the Bladder.- 
There is a mu- 
cous, submu- 
cous, muscular, 
and serous coat to the bladder. The mucous mem- 
brane resembles that of the ureters, with which it is 
continuous. It is covered with a transitional epithe- 
lium whose cells vary according to the distention of 
the bladder. As a rule, epithelial cells have but very 
little elasticity and mucous membranes, therefore are 
frequently much folded. The bladder cells are capable 
of considerable distention, when they become very 
flat. When the organ contracts they accommodate 
themselves to this condition and become cubical. The 
cells of the surface layer are squamous and have 
Fig. 205.-Section through the mucosa of the 
bladder. THE URINARY ORGANS. 
259 
concave depressions into which the rounded ends of 
the second layer or pear-shaped cells are adjusted. 
Two or more layers of irregular interstitial cells inter- 
vene between the apices of the pear-shaped cells. 
The interstitial cells divide regularly by karyokinesis 
and are then crowded to the surface to replace the 
superficial cells that normally exfoliate. There are 
no glands in the bladder, but solid cell projections 
are sometimes found that resemble glands. The blad- 
der is a part of the allantois, a vesicular evagination 
of the hind-gut. The bladder epithelium, therefore, 
Fig. 206.-Epithelial cells from the bladder. 
is of hypodermic origin, while that of the ureter is 
from the mesoderm. 
A vascular submucosa intervenes between the mu- 
cosa and the muscularis. This is a thin layer of 
areolar tissue, but sufficient to give the mucosa 
apparent elasticity and enable it to move upon the 
muscularis. 
The muscular coat consists of smooth muscle fibers 
which may be divided into bundles of outer longi- 
tudinal fibers, a middle strong circular layer, and an 
imperfect inner longitudinal or diagonal stratum. 260 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
At the urethral opening the middle layer is thickened 
to form a sphincter muscle, according to some au- 
thors. The bladder musculature forms a basket- 
work fabric, and when much distended intervals 
may arise in its walls which become points of weak- 
ness through which the mucosa may protrude, when 
the organ is said to be sacculated. 
Vessels and Nerves.-The bladder is supplied with 
blood from the superior and inferior vesicle arteries, 
and in the female also from branches of the uterine 
artery. The veins form large plexuses, particularly 
around the neck, sides and base. They eventually 
drain into the internal iliac. The nerve supply is 
from the third, fourth, and sometimes the second 
sacral nerves, and from the hypogastric plexus of the 
sympathetic. The latter are nearly all non-medul- 
lated. CHAPTER VIII. 
REPRODUCTIVE ORGANS IN THE MALE. 
Under this heading are included (i) the testes and 
their ducts, (2) epididymis, (3) penis, and (4) pros- 
tate gland. 
THE TESTICLES. 
The testes are two glandular organs for the produc- 
tion of spermatozoa, suspended in the scrotum by 
the spermatic cord. Each testicle is about one and 
one-half inches long, one and one-fourth inches 
wide, and nearly one inch thick from side to side. 
The corresponding dimensions of the ovary are, one 
and one-half by three-fourths by one-half inches. 
The coverings of the testes are, (1) skin, (2) dartos; 
these two form the wall of the scrotum. The skin is 
thin and pigmented. The dartos is a reddish tissue 
continuous with the two layers of superficial fascia 
of the groin. It is vascular and consists of smooth 
areolar tissue and smooth muscle fibers. The latter 
give involuntary contractility to the scrotum and 
produce folds or rugae in the skin. (3) Intercolum- 
nar fascia, which is a thin connective-tissue layer 
closely associated with (4) the cremasteric fascia. 
The latter is continuous with the internal oblique 
muscle. (5) The infundibuliform fascia comes next 
and is a continuation downward of the fascia trans- 
versalis. (6) The tunica vaginalis envelops each 
261 262 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
testicle and is derived from the peritoneum during 
the descent of the organ. It is therefore a serous 
coat that has the same histology as the peritoneum, 
and may be divided into two parts, one the visceral 
portion that invests the surface of the organ, and the 
other the parietal portion that is reflected over the 
surface of the infundibuliform fascia. The interval 
between these portions constitutes the cavity of the 
tunica vaginalis, and it is in this space that hydro- 
Fig. 207.-Cross section of human testicle. 
cele fluid collects. (7) The tunica albuginea comes 
next and is a thin fibrous covering. This tunic 
sends fibrous cords or trabeculae into the testis, 
which divide the organ into lobules. It is par- 
ticularly dense along the posterior margin of the 
organ where it also invests the vas deferens, forming 
at this margin a mediastinum called the corpus of 
Highmore. (8) The tunica uasculosa is a delicate 
vascular layer that covers the inner surface of the REPRODUCTIVE ORGANS IN THE MATE. 
263 
tunica albuginea. The three tunics just mentioned 
form the wall or capsule of each testicle, and are so 
closely associated that it is difficult to distinguish 
one from the other. 
Structure.-The testis is a compound tubular gland 
divided into three hundred to four hundred lobules. 
Each lobule is conical in shape with the apex directed 
toward the mediastinum and the base toward the 
surface of the organ. The lobules differ in size ac- 
cording to their 
position. Each 
lobule represents 
several coiled tu- 
bules which, when 
unraveled, aver- 
age two feet in 
length. There 
are at least six 
hundred to eight 
hundred of these 
tubules to each 
testicle. Their 
walls are lined with stratified epithelium which is in- 
vested with a thin layer of connective-tissue ele- 
ments. The epithelium rests upon a basement 
membrane and may be arranged in at least three 
irregular groups or layers: i. A layer of cubical 
cells, with small nuclei, rests upon the basement 
membrane. The cells of this layer are called sper- 
matogonia. The columns of Sertoli, or sustentacular 
cells, also belong to this layer. These columns 
are elongated columnar cells that extend from the 
Fig. 208.-Section of convoluted tubules of 
testicle. 264 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
basement membrane inward toward the lumen 
of the tube. They give off lateral processes that 
form a reticulum about groups of young spermatozoa, 
to which they give both support and sustenance, 
according to the views of some authors. 2. Within 
the first layer there are one or two rows of large cells 
with large deep-staining nuclei. These are the 
spermatocytes. The latter multiply rapidly and 
continually to form, 3, spermatoblasts or sper- 
matids. The spermatids are small spherical cells 
and each one in due time develops into a spermato- 
zoon. The latter ripen regularly in groups which 
seem to cluster about individual sustentacular cells. 
The nucleus of the spermatids elongate and each 
little spherical cell gradually assumes the form of a 
mature spermatozoon. The different stages in this 
development can be worked out by a study of the 
spermatids as seen in the different tubules. In the 
cross section of a single tubule all the spermatids 
will be in the same stage of development. The 
spermatozoa when mature are crowded into the 
lumen of the convoluted tubules, where they mix 
with a viscid secretion which probably comes from 
the epithelial wall. The convoluted seminiferous 
tubules end blindly near the surface of the testis, 
where they are also said to anastomose with each 
other. In the other direction, each tubule becomes 
straight and forms the tubuli recti, which approach 
the mediastinum and function as excretory ducts. 
These erect tubules anastomose to form the rete 
testis. 
Interstitial Elements of the Testis,-Like any other REPRODUCTIVE ORGANS IN THE MARE. 
265 
organ the testicle has a fine reticulum of connective 
tissue that is associated with the capsule or tunica 
albuginea. This reticulum consists of areolar tissue 
that not only intervenes between the lobules, but 
interlaces between the seminiferous tubules. Blood 
and lymph vessels are everywhere associated with 
this tissue. In addition to ordinary connective- 
tissue cells, there is associated with this reticulum 
patches of cells that re- 
semble epithelium and 
have yellowish granules 
or pigment. These are 
called interstitial cells, 
and, like the areas of 
Langerhans of the pan- 
creas, are supposed to se- 
crete products regularly 
absorbed by the blood. 
We can postulate a pos- 
sible function of these 
cells when we consider 
the function of the testi- 
cle and its influence on 
the body as a whole. 
(i) Physiologically the testis exerts a marked influ- 
ence on the development of the body. (2) It is ac- 
tively engaged in the production of spermatozoa. 
(3) It is essential for the act of copulation. 
Early castration in domestic animals is a striking 
evidence of the influence the testicle exerts upon 
development. The change manifest is both physi- 
cal and mental. As the infantile testis does not 
Fig. 209.-Sustentacular 
cells (cells of Sertoli) of the 
guinea-pig (chrome-silver me- 
thod) ; profile view: c, c, Depres- 
sions in the sustentacular cells 
due to pressure from the sper- 
matogenic cells; d, basilar por- 
tion of sustentacular cells 
(Bohm and Davidoff). 266 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
produce spermatozoa, it is believed that the secre- 
tions from the interstitial cells react upon the devel- 
opment of the body as a whole. While the semi- 
niferous tubules function in the production of sper- 
matozoa, it is not clear that the accumulation of 
semen prompts the sexual act. For instance, the 
testicles sometimes do not descend into the scrotum 
but remain in the body cav- 
ity. Frequently such testi- 
cles are of the infantile type, 
that is, no semen is devel- 
oped; and yet the copulation 
act in such males is not only 
possible, but the sexual crav- 
ings may be actually exagge- 
rated. The interstitial cells 
of such testicles are well de- 
veloped and the male is other- 
wise normal. Again, the im- 
potency that sometimes 
comes with old age is said to 
be due to impaired functional 
activity of the interstitial 
cells rather than to lack of 
spermatozoa. We have no specific medical treat- 
ment for such cases, extracts from normal testes 
having been tried without satisfactory results. 
Spermatogenesis and Spermatozoa.-The develop- 
ment of spermatozoa begins in man in early youth 
and usually continues into old age. This phenom- 
enon is in marked contrast to ovulation in woman, 
where there is a cessation or menopause at about the 
Fig. 210.-Human sper- 
matozoa, side and flat view. REPRODUCTIVE ORGANS IN THE MALE. 
267 
age of forty-five. The explanation offered to ac- 
count for this difference in the sexes is sought in the 
blood supply to the generative organs. There is a 
decrease in the nourishment to the ovaries as the 
menopause approaches, due to a contraction of the 
blood-vessels that supply the organ. The testes, on 
the other hand, have a liberal supply of blood 
throughout life. 
A study of the stratified epithelium of the semi- 
niferous tubules will reveal spermatozoa in all stages 
of development. Cells in the spermatogenic layer 
divide by normal karyokinesis to produce the second 
layer or spermatocytes. Each spermatocyte divides 
twice to produce four spermatids, which develop 
regularly into four spermatozoa. The development 
of four spermatozoa is regarded as analogous to the 
maturation of the ovum, which results in a ripe 
ovum and three polar bodies. The first division of a 
spermatocyte is regarded as normal mitosis. The 
second division is regarded as atypical, resulting in 
the reduction of one-half the original number of 
chromosomes; and the resulting nucleus, when it 
becomes the nucleus of the ripe spermatzoon, is 
called the male pronucleus. The union of male and 
female pronuclei, which takes place in fertilization, 
is supposed to reestablish the normal number of 
chromosomes, a number that is regularly maintained 
in all later cell divisions. 
Structure of Spermatozoa.-A spermatozoon is a 
minute cell, about 0.055 mm. long and consisting of 
a nucleus or head, a middle piece or body, and a vibra- 
tile tail. In man the head is a flattened ovoid, ap- 268 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
pearing pear-shaped or pointed in one view and 
rounded in another. It contains the nucleus and 
stains heavily with nuclear dyes. It measures about 
0.0045 mm. long, 0.0025 mm. broad, and 0.0015 mm. 
thick. 
The middle piece, or body, is cylindrical in man, and 
measures about 0.006 mm. in length, and 0.001 mm. 
in thickness. In some animals, as the rat, a spiral 
thread can be seen coiled about the periphery, 
whilst through its center a slender filament seems to 
pass and be continuous with the central filament of 
the tail. This filament ends in a terminal enlarge- 
ment placed in close proximity to the nucleus and 
known as the terminal globule. 
The tail is about 0.045 mm. long and tapers toward 
the extremity, ending in an extremely delicate fiber, 
the end piece. Again, in the rat this end piece 
seems to be the terminal part of the central filament 
of the middle piece, which thus extends the whole 
length of the tail. The spermatozoon is propelled 
forward by a spirally lashing movement of the tail, 
similar to the movement of cilia. Movement of 
cilia, however, ceases as soon as they are removed 
from their cell, which is not the case with the tail of a 
spermatozoon, in which motion seems to be an in- 
trinsic quality. So long as spermatozoa remain in 
the male passages they are inert, but become active 
as soon as expelled. 
Spermatozoa differ a great deal in the different 
species of animals. They are very hardy cells, and 
in the female passages may live for days and even 
weeks. In some domestic birds, as turkeys, they REPRODUCTIVE ORGANS IN THE MALE. 
269 
live at least a month, while in bats copulation takes 
place in the fall and fertilization follows in the spring. 
Excretory Ducts of the Testis.-These ducts are 
the tubuli recti, rete testis, vasa efferentia, epididy- 
mis, and vas deferens. 
Tubuli Recti.-The seminiferous tubules, towards 
the mediastinum, unite at acute angles to form a 
Fig. 211.-Diagram of human testicle, longitudinal section. 
series of short parallel straight tubes called the tu- 
buli recti. They are clothed by a simple layer of low 
cubical epithelium. 
The rete testis consists of a reticulum of tubules 
formed by an anastomosis of the tubuli recti in the 
mediastinum. They are lined by simple columnar 
epithelium. 
The -vasa efferentia are tubules that lead from the 270 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
upper portion of the rete testis through the tunica 
albuginea to the epididymis. There are about fif- 
teen of them. They are lined by simple columnar 
ciliated epithelium, and represent tubules that em- 
bryologically belong to the mesonephros. Outside 
of the epithelium is a thin investment of areolar 
tissue in which smooth muscle cells interlace. 
The epididymis is a very much coiled canal, about 
twenty feet long, formed by the confluence of the 
vasa efferentia. 
At the upper 
and posterior 
border of the 
testis the vasa 
efferentia and 
epididymis 
form a globular 
mass of tubules 
called the glo- 
bus major. At 
the lower and 
posterior bor- 
der there is a smaller mass of coiled tubules formed 
by the epididymis, and called the globus minor. 
The epididymis is lined by simple epithelium which 
is ciliated in most places, but interposed are patches 
of nonciliated cells. The latter form small areas that 
resemble glands. External to this epithelium there 
is a thin layer of smooth muscle fibers which blends 
with vascular areolar tissue. 
The vas deferens begins at the lower margin of the 
globus minor and is a direct continuation of the 
Fig. 212.-Cross section of epididymis. REPRODUCTIVE ORGANS IN THE MALE. 
271 
canal of the epididymis. It is a duct about twelve 
inches long, but when unraveled and extended it is 
eighteen to twenty inches in length. At first it is 
rather tortuous, but soon becomes straight and 
ascends along the inner border of the epididymis to 
pass directly to the external abdominal ring, taking 
a vertical course and forming a part of the spermatic 
cord. It then passes through the inguinal canal, 
and reaching the 
internal abdomi- 
nal ring, turns 
quickly down- 
ward and inward 
to the side of the 
bladder upon 
which it descends, 
curving backward 
and downward to 
the neck of the 
bladder, where it 
enters the urethra 
through the pros- 
tate gland. In its 
abdominal course it lies external to the peritoneum, 
and along the bladder wall it arches between the 
latter and the ureter. Along this wall it becomes 
sacculated and near its terminus gives off a lateral, 
enlarged, and sacculated diverticulum, the seminal 
vesicle. The distal end beyond the opening of the 
seminal vesicle, is a narrow straight tube called the 
ejaculatory duct. 
Structure.-The wall of the vas deferens has three 
Fig. 213.-Cross section of vas deferens. 272 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
coats, an inner mucous, a middle muscular, and an 
outer fibrous. The mucous membrane generally 
presents two or three longitudinal folds and is lined 
with simple columnar epithelium. According to 
some investigators it may be ciliated in places and 
even resemble the transitional epithelium of the 
ureters. The membrana propria resembles that of 
other mucous membranes. No glands are present. 
The muscular layer is of the smooth variety. It con- 
sists of a strong inner circular and an outer longi- 
tudinal layer. Near the epididymis an extremely 
thin layer of longitudinal muscle fibers is present 
inside of the circular layer. The fibrous layer con- 
sists of loose areolar tissue, with which are asso- 
ciated blood and lymph vessels. 
Paradidymis.-This consists of a set of branched 
tubules that leads off as blind diverticula from the 
canal of the epididymis or the vas deferens. There 
is one diverticulum or several of them. The length 
of these tubules when unraveled varies from two to 
twelve inches, and histologically they resemble the 
structure of the vasa efferentia. Morphologically the 
paradidymis is analogous to the parovarium found 
in the broad ligament of the ovary, the origin of 
both being associated with the development of the 
tubules of the mesonephros. 
Hydatid of Morgagni.-There are two of these 
bodies. One of them, more constant than the other, 
lies usually between the globus major and the testi- 
cle and is called the sessile hydatid. It is a small 
cone-shaped body of epithelial cells and represents 
the peritoneal end of Muller's duct, the analogue of REPRODUCTIVE ORGANS IN THE MALE. 
273 
the fimbriated end of the Fallopian tube in the 
female. The other is less constant and lies usually 
just external to the globus major and is called the 
stalked hydatid. It is an epithelial body and repre- 
sents vestiges of the peritoneal end of the pronephric 
or Wolffian duct. The stalked hydatid is also 
present in the female, where it resembles a small 
cyst closely associated with one of the fimbriae of the 
Fallopian tube. 
The distance passed by the spermatozoa, before 
being eliminated by the urethra, is approximately 
twenty-four feet. The chief ducts and their lengths 
are: seminiferous tubules, each two feet long; epi- 
didymis, twenty feet; and vas deferens, two feet. 
The spermatozoa are themselves perfectly inactive 
in making this passage. During the copulation act 
they are discharged probably from the whole length 
of the vas deferens by peristaltic contraction of this 
duct, and not only from the seminal receptacle as 
formerly supposed. The supply of spermatozoa 
is extensive. If each testicle has eight hundred 
seminiferous tubules, each two feet long, then there 
are sixteen hundred feet of epithelial lining for each 
organ engaged in the production of spermatozoa. 
The semen consists of a fluid part, secreted mainly 
by accessory reproductive glands, and cell elements 
or spermatozoa that develop in the testes. In man 
there are about sixty thousand spermatozoa to each 
cubic millimeter of semen. 
Vessels and Nerves.-The spermatic artery supplies 
the tubules of the testicles and the epididymis with 
blood directly from the abdominal aorta. It is a 274 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
long, slender artery that joins the spermatic cord 
as the latter passes through the inguinal canal. As 
the vessel approaches the testicle, it sends branches 
to the epididymis and then divides into other 
branches that ramify among the seminiferous 
tubules. The vas deferens receives a slender 
branch from one of the vesical arteries. This is 
called the artery of the vas deferens, and reaches as 
far as the testis, where it anastomoses with the 
spermatic artery. 
The spermatic veins begin in the testis and epi- 
didymis and pass out at the posterior border of the 
organ, where they unite into large veins that form 
a plexus along the spermatic cord. Inside the abdo- 
men this plexus unites to form a single trunk, the 
spermatic vein, which on the right side opens into the 
vena cava, and on the left side into the renal veins. 
The lymphatics are very extensive and accompany 
the veins. They terminate in the lymphatic glands 
which encircle the large blood-vessels in front of the 
vertebral column. 
The nerves are derived from the sympathetic 
system. There is a spermatic plexus that accom- 
panies the spermatic artery, and some libers from the 
hypogastric plexus that accompany the artery of the 
vas deferens. 
THE PENIS. 
The penis is a vascular organ composed principally 
of two corpora cavernosa, one corpus spongiosum, 
which encloses the urethra, and the glans, which is 
really the distal end of the corpus spongiosum. 
The integument of the penis is very thin and loosely REPRODUCTIVE ORGANS IN THE MALE. 
275 
attached. It is devoid of fat and hair and darker in 
color than the skin generally. Over the glans it is 
redoubled in a loose fold, the prepuce or foreskin. 
The inner layer of this fold is attached firmly to the 
base of the glans or cervix, and from there it becomes 
closely adherent to the glans as far as the orifice of 
the urethra, where it meets the mucous membrane 
of the latter. Over the glans it is red, thin, and 
moist, and beset with numerous large vesicular and 
Fig. 214.-Cross section of penis: a, through the glans; b, through the body. 
nerve papillae, but devoid of glands, excepting 
around the cervix, where large sebaceous glands are 
numerous, called glands of Tyson, which secrete a 
white, waxy, odoriferous substance, the smegma. 
The corpora cavernosa are two parallel cylindrical 
masses of erectile tissue that lie in the dorsum of the 
penis. They blend together in the anterior portion, 
and toward the root of the penis diverge to become 
firmly attached to the pubic and ischial rami. The 
anterior extremity of the corpora cavernosa is cov- 
ered by the glans penis. 
Structure of Corpora Cavernosa.-There is a median 276 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
fibrous septum between the two corpora cavernosa 
which becomes thin anteriorly and incompletely 
separates the two bodies. There is an external 
fibrous investment, very strong and elastic. This 
is composed mostly of longitudinal bundles of white 
fibers with interlacing elastic fibers. • These fibers 
are intimately associated with the median septum 
and also with connective-tissue trabeculae that 
ramify through the substance of the cavernous 
bodies. The substance of the latter is called erectile 
tissue and is of a spongy nature. The trabeculae 
anastomose and interlace freely to form a multitude 
of interstices or cavernous spaces. These are filled 
with venous blood, and are really a complex system 
of veins lined by a layer of flattened epithelium as 
in other veins. In the anterior portion of the penis 
the venous labyrinth of one corpus cavernosum 
intercommunicates with that of the other through 
the incomplete septum. In the erectile condition 
the corpora cavernosa are distended with blood 
which is carried away by two sets of veins, the one 
set joining the prostatic plexus and the pudendal 
veins, and the other draining into the dorsal vein 
of the penis. The arterial blood is supplied mainly 
by branches of the pudic arteries, but the dorsal 
artery of the penis sends a few branches through the 
fibrous sheath, particularly in the forepart of the 
organ. The arteries ramify in the trabeculae and 
terminate in minute capillary branches that open 
into intertrabecular spaces. Some of the smaller 
arteries project into the spaces, forming peculiarly 
twisted or looped vessels called helicine arteries. REPRODUCTIVE organs in the male. 
277 
The corpus spongiosum is also composed of erectile 
tissue, but is a single cylindrical body that lies below 
and between the corpora cavernosa. Its posterior 
extremity is much enlarged and rounded, and is 
called the bulb. This lies in the ventral portion of 
the root of the penis just in front of the triangular 
ligament. Anteriorly the corpus spongiosum forms 
the glans penis, which caps the corpora cavernosa. 
The border of the glans is rounded and projecting 
and is called the corona glandis, behind which is a 
constriction of the penis, the cervix. In the whole 
of its extent the corpus cavernosum encloses the 
urethra. 
Structure of Corpus Spongiosum.-'This resembles 
the erectile tissue of the corpora cavernosa, and like 
the latter is distended with blood during erection, 
but is less rigid. The venous labyrinth is a finer 
meshwork and the trabeculae and fibrous tunic is 
much thinner. In the glans the meshes are particu- 
larly small and uniform. Plain muscle fibers enclose 
the urethra and also form a part of the external coat. 
Urethra in the Male.-The male urethra extends 
from the bladder to the end of the penis, in length 
about eight and one-half inches. Its walls are 
in apposition, excepting during the passage of urine 
or semen. The urethral cleft in the glans is vertical; 
in the body of the penis it is transverse; and through 
the prostatic portion near the bladder it is crescentic. 
It is lined by a mucous membrane, external to which 
is a double layer of smooth muscle fibers, the inner 
fibers disposed longitudinally and the outer circular. 
For descriptive purposes the urethra is divided into 278 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
a prostatic portion, a membranous portion, and a 
spongy or penile portion. 
i. The prostatic portion is about one and one- 
fourth inches in length and passes through the 
prostate gland. This is the widest portion of the 
urethra and passes vertically from the neck of the 
bladder to the triangular ligament of the perineum. 
In cross section the canal is crescentic with its con- 
vexity turned forward. The lining membrane pre- 
sents longitudinal folds, and along the posterior 
wall is a prominent median ridge which gives rise to 
the crescentic form of the urethra when seen in sec- 
tions. This ridge is called the crista, or verumon- 
tanum. The longitudinal groove on each side of the 
crista is called the prostatic sinus, which is pierced 
by numerous orifices of the prostate gland. In the 
middle of the crista is the orifice of a blind recess, 
and at the lateral margins of this arc the slit-like 
openings of the seminal or ejaculatory ducts. The 
median or blind recess is a cul-de-sac which passes 
upward and backward for a distance of one-fourth 
to one-half inch, and is called the sinus pocularis 
or masculine uterus. It represents embryologically 
the fused ends of Muller's duct, and is therefore mor- 
phologically equivalent to the female uterus. The 
epithelium of this part of the urethra resembles that 
of the bladder and is of the transitional variety. In 
the sinus pocularis it is said by some to be simple 
ciliated like that of the uterus. 
2. The membranous portion is about three-fourths 
inch in length and lies between the two layers of the 
triangular ligament. It is the narrowest part of the REPRODUCTIVE ORGANS IN THE MARE 
279 
urethra, not more 
than one-fifth 
inch in diameter, 
and curves so as 
to be directed 
downward and 
slightly forward 
beneath the pubic 
arch. The epi- 
thelium in this 
part varies. Por- 
tions of it resem- 
ble that of the 
bladder, but more 
often it presents 
the appearance of 
p s e u do-stratified 
with two or three 
layers of nuclei. 
3. The spongy 
portion is by far 
the longest and 
most variable in 
length and direc- 
tion. Its length is 
about six inches, 
and its entire 
course is in the 
corpus callosum. 
The epithelial lin- 
ing near the meat- 
us is stratified 
Fig. 215.-Diagram of male bladder and 
urethra, front view. 
Fig. 216.-Diagram of male bladder and 
urethra, posterior view. 280 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
squamous, and directly continuous with the skin. 
The rest of this portion is lined by columnar pseudo- 
stratified epithelium with two or more rows of nuclei. 
The whole length of the urethra, excepting its distal 
end, is beset with small racemose mucous glands called 
glands of Littre. These vary much in size, some 
of them being sacculated. Most of them open in the 
floor of the urethra, their ducts passing obliquely for- 
ward through the lining membrane. In urethral infec- 
tions these glands become involved, as a rule, which 
increases the difficulty of eliminating the disease. 
The Urethra in the Female.-The female urethra 
is about one and one-half inches in length, and cor- 
responds to the male urethra between the bladder 
and the opening of the ejaculatory ducts. It is 
directed downward and forward parallel to the an- 
terior wall of the vagina, to which it is attached. 
The transverse diameter of the closed tube is about 
one-fourth inch, but it is capable of great disten- 
tion, sufficient to admit the index finger. The ex- 
ternal orifice, or meatus, is a vertical slit with prom- 
inent margins, on which may be seen the orifices of 
two small glands, called Skene's glands. The latter 
are subject to infection in urethral disturbances and 
often give rise to severe irritations. 
THE PROSTATE GLAND. 
The prostate gland is a muscular as well as glandu- 
lar organ that surrounds the prostatic portion of the 
male urethra. It atrophies in the adult after cas- 
tration, and remains undeveloped if the testicles 
are removed in infancy, which supports the view REPRODUCTIVE ORGANS IN THE MALE. 
281 
that it is an accessory organ of generation. Its size 
varies considerably, but its average transverse or 
longest diameter is one and one-half inches, its 
antero-posterior diameter about three-fourths inch, 
and its vertical diameter one and three-fourths 
inches. Since the urethra, and also the ejaculatory 
ducts, pass through the organ, the gland on this 
account may be divided into three lobes. The 
wedge-shaped portion that lies between these ducts 
and the cervix of the bladder is called the middle 
Fig. 217.-Section from the prostate gland. 
lobe, and the rest of the gland is spoken of as the 
lateral lobes. It is the latter that often hypertrophy 
in old age and are removed in prostatectomy. The 
gland lies in close apposition to the rectum, and with 
the finger in the latter it can readily be palpated. 
The prostate is a compound tubulo-alveolar gland 
whose ducts open into the prostate portion of the 
urethra. Smooth muscle fibers not only surround the 
organ, but interlace radially toward its center, form- 
ing a network in whose meshes the glandular parts are 
located. Areolar tissue and blood-vessels accom- 282 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
pany the muscle tissue. The alveoli of the glands 
are lined by simple columnar epithelium, which 
sometimes show two rows of nuclei. These alveoli 
contain a serous acid coagulum and usually oval 
laminated concretions called prostatic bodies. The 
latter are more numerous in old men. The numer- 
ous excretory ducts unite to form twelve to fifteen 
collecting tubes which open into the urethra, most 
of them into the prostatic sinus. These ducts are 
lined by simple columnar epithelium, except near 
their terminations where it is transitional. The 
organ dorsal or in front of the urethra is mostly 
smooth muscle tissue. 
In old people the prostate gland frequently hyper- 
trophies and produces urethral stricture with reten- 
tion of urine. Prostatectomy or the removal of the 
lateral lobes, usually corrects this defect, but is a 
serious operation on account of the commonly feeble 
condition of these patients. 
Cowper's glands are a pair of small oval bodies 
about the size of a pea, situated in the space between 
the triangular ligaments and in close proximity to 
the membranous portion of the urethra. They are 
compound tubulo-alveolar mucous glands lined by 
simple cubical epithelium. Their excretory ducts, 
one for each gland, are one and one-half inches long 
and run forward near each other to open into the 
floor of the bulbous portion of the male urethra. 
In the female the analogue of these bodies is called 
the glands of Bartholin. They open into and lie in close 
apposition to the female urethra. They may be pal- 
pated in the lateral walls of the vestibule of the vagina. CHAPTER IX. 
REPRODUCTIVE ORGANS IN THE FEMALE. 
Under this head will be described the ovaries, 
Fallopian tubes, uterus, vagina, and mammary 
gland. 
THE OVARIES. 
The ovaries are two dehiscent glandular organs 
that develop from the mesoderm in close apposition 
to the mesonephros. Each ovary measures about 
one and one-half inches in length, three-fourths 
inch in breadth, and nearly one-half inch in thickness. 
In early fetal life the ovaries lie close to the kidneys, 
but later they pass down into the pelvis where they 
lie in close proximity to the iliac fossa. The exact 
position varies considerably, but in the majority of 
cases they will be found placed against the side wall 
of the pelvis with their long axis parallel to that of the 
body. Each ovary is held in position by a suspen- 
sory ligament, which is a peritoneal fold that passes 
downward from the brim of the pelvis and contains 
the ovarian vessels and nerves, and also by the ova- 
rian ligament, which passes to the uterus and is 
really a reduplication of the broad ligament. The 
Fallopian tube partly encircles the ovary and also 
contributes to its support. 
Capsule of the Ovary.-The external surface of the 
283 284 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
ovary is of a pale color and in early life is smooth and 
even, but in later life it becomes rough and marked 
by pits and scars. This is caused by the rupture of 
Graafian follicles and the expulsion of ova. It is 
covered by an epithelium which is continuous with 
that of the peritoneum, but differs from the latter 
Fig. 218.-Diagram of female genitalia. 
in being lined by cubical cells instead of the simple 
pavement variety. This ovarian epithelium is the 
germinal epithelium of embryos, from which the ova 
and the other epithelial cells of each Graafian follicle 
are derived. The germinal epithelium rests upon a 
rather dense investment of fibrous - tissue, analo- REPRODUCTIVE ORGANS IN THE FEMALE. 
285 
gous to a like structure in the testicle, and is there- 
fore called the tunica albuginea. This is not a dis- 
tinct tunic but rather a condensed part of the ova- 
rian matrix. It is not well defined, and is difficult 
to demonstrate in sections. 
The medulla is practically the core of the ovary 
and consists of a fibro-muscular matrix well supplied 
Fig. 219.-Section from ovary of adult dog. At the right the stellate 
figure represents a collapsed follicle with its contents. Below and at the 
right are seen the tubules of the parovarium (copied from Waldeyer). 
with blood- and lymph-vessels. In this substance 
may be found connective-tissue cells, connective- 
tissue fibers and a limited supply of smooth muscle 
fibers. 
The Cortex.-Between the medulla and the cap- 
sule is the cortex. It is a broad zone, not well de- 
fined, in which are found the same elements as in the 286 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
medulla, and in addition Graafian follicles in different 
stages of development, and in older ovaries also cor- 
pora lutea. 
Young Graafian Follicles.-Early in embryonic life, 
when the ovary is clothed with the germinal epi- 
thelium which later becomes the epithelium of the 
capsule, epithelial buds or strings of epithelial cells 
push their way into the ovarian cortex. These buds 
soon lose their connection with the germinal epithe- 
lium and form little groups or nests of cells known as 
young Graafian follicles. In each follicle one cell 
takes a central posi- 
tion and is the egg 
cell or ovum, des- 
tined, under proper 
conditions, to de- 
velop into a new be- 
ing. The ovum in- 
creases rapidly in 
size, receiving pro- 
tection and possibly 
nourishment from the investing cells. The repro- 
ductive cells, both ova and spermatozoa, can thus be 
traced directly from the germinal epithelium, which 
is of mesodermic origin and closely related to the 
pavement epithelium of the peritoneum. 
The Graafian follicles occupy the cortical layer of 
the ovary. They are all formed during embryonic 
life, and whatever influence environment has upon 
the offspring, that influence leaves its impression not 
upon the origin of the reproductive cells, but upon 
their later development. At time of birth it is esti- 
Fig. 220.-Section from ovary of young 
dog. REPRODUCTIVE ORGANS IN THE FEMALE. 
287 
mated that there are thirty-five thousand eggs or 
ova to each ovary. Only a small number of these 
ripen and become discharged as mature eggs. The 
extrusion of these eggs from the ovary is known as 
ovulation, and in woman is supposed to occur during 
the menstruation period, one from each ovary. 
Menstruation in a normal woman extends generally 
over a period of thirty-two years, between the ages of 
thirteen and forty-five. If thirteen eggs ovulate 
yearly from each ovary, there will be a possible total 
Fig. 221.-Young Graafian follicles: a, follicle with one layer of epithe- 
lial cells; b, follicle with two layers of epithelial cells. 
of eight hundred and thirty-two that may ripen dur- 
ing the life of a woman, allowing no interruption for 
pregnancies. After the menopause, ovulation is 
supposed to cease. 
The Ripe Graafian Follicle.-It has already been 
stated that only a small number of the young ova 
ripen and ovulate. These mature in the following 
manner: The ovum of such follicles occupies a cen- 
tral position where it accumulates food and grows 
into a large spherical cell. The investing epithelium 288 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
forms at first a single layer of cells. These remain 
small and multiply rapidly, forming two layers of 
cells between which, at one side of the follicle, a 
cavity appears. As the follicle grows larger this cav- 
ity, which is eccentric in position, becomes filled 
with a fluid called the follicular fluid. The ovum 
remains attached to the side of the follicle and be- 
comes surrounded by several layers of cells called 
the discus proligerus. The outer layer also multi- 
Fig. 222.-Ripe Graafian follicle. 
plies, forming eight to twelve layers of cells and is 
then called the stratum granulosum, to which the 
discus proligertis is attached. External to the 
stratum granulosum a connective-tissue envelope 
forms, called a theca. This theca develops from the 
ovarian stroma and consists of two layers, an ex- 
ternal, the theca fibrosa, and an internal, the theca 
vasculosa, the latter being supplied with a fine 
plexus of lymph- and blood-vessels. The mature REPRODUCTIVE ORGANS IN THE FEMALE. 
289 
Graafian follicle is thus a sphere that measures from 
one-twentieth to one-sixth of an inch in diameter, 
and lies immediately beneath the surface epithelium 
of the ovary. 
The manner in which such follicles rupture has 
been variously explained. One rational theory is 
Fig. 223.-From ovary of young girl (Bohm and Davidoff) 
that the pressure of the accumulated follicular liquid 
obliterates the blood-vessels in the theca vasculosa 
next to the ovarian epithelium. This establishes a 
point of least resistance at this place, the follicle 
ruptures, and the follicular fluid with the ovum is 
discharged upon the surface of the ovary, the 290 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
stratum granulosum and most of the discus pro- 
ligerus remaining behind in the ovary. 
The Ovum.-The ovum has already been men- 
tioned as a large spherical cell with a large accumu- 
lation of food material. It measures 0.2 mm. in 
diameter and is barely visible to the naked eye. 
When examined under the microscope, even before 
the rupture of its follicle, it is found encircled by a 
clear substance called the zona pellucida, which upon 
a closer examination may be found to contain trans- 
verse striations, hence it has also been called zona 
radiata. It is not uncommon for a few of the epi- 
thelial cells of the dis- 
cus proligerus to re- 
main attached to this 
layer, if so they arc 
called the corona radi- 
ata. The zona pelluci- 
da is a secretion from 
the adjoining cells, and 
one theory of the trans- 
verse striations is that they are produced by minute 
cellular processes from the cells that form the corona 
radiata; that is, the first row of epithelial cells in- 
vesting the ovum. It is affirmed by some that these 
processes are in direct communication with the sub- 
stance of the ovum and are the means by which 
elaborated food material is contributed to the latter. 
The zona pellucida no doubt serves to strengthen 
the delicate ovum after its expulsion from the ovary. 
The transverse striae in this membrane may serve a 
further purpose as primitive channels for the entrance 
Fig. 224.-The ovum. REPRODUCTIVE ORGANS IN THE FEMALE. 
291 
of spermatozoa, only one of which penetrates the 
substance of the ovum. 
The substance of the ovum is known as the vitellus. 
It is a soft semifluid substance composed of cyto- 
plasm in which is deposited a liberal supply of food 
material called deutoplasm. The nucleus of the 
Fig. 225.-Scheme of the development and maturation of an ascaris 
ovum (after Boveri): P. B., Polar bodies. (From "Ergebn. d. Anat. u. 
Entw.," Bd. I.) 
ovum is called the germinal vesicle, which is placed 
to one side of the cell. The nucleus is unusually 
large, about 0.05 mm. in diameter, and has all the 
characteristics of an ordinary cell nucleus. This 
was first described by Purkinje in the ovum of birds 
in 1835. There is a well-defined nuclear membrane 292 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
which encloses a clear nuclear substance in which 
there is a limited amount of chromatin, and the nu- 
cleus, therefore, does not stain heavily. The nucleo- 
lus, on the other hand, is very prominent and is 
called the germinal spot. Not infrequently two 
nucleoli may be found. There is some doubt whether 
a cell membrane to the ovum is present before fer- 
Fig. 226.-Schematic diagram of spermatogenesis as it occurs in 
ascaris (after Boveri). ("Ergebn. d. Anat. u. Entw.," Bd. 1.) 
tilization. After fertilization such a membrane 
appears and is called the vitelline membrane. As a 
rule each Graafian follicle contains one ovum; in rare 
cases follicles are found with two and even with three 
ova. 
When a Graafian follicle ruptures and an ovum is REPRODUCTIVE ORGANS IN THE FEMALE. 
293 
expelled, a great activity is at once manifest in the 
ovum, whether it is fertilized or not. The nucleus, 
which is near the margin of the ovum, divides in a 
few hours, extruding what is termed the first polar 
body. This is normal cell division, or mitosis. A 
second division quickly follows, resulting in a second 
polar body. Meanwhile the first polar body may 
also divide. This second division results in a reduc- 
tion of one-half the number of chromosomes, and 
the nucleus thus reduced is called the female pro- 
nucleus, which is now ready to unite with the male 
pronucleus of the spermatozoon and complete the 
process of fertilization. The phenomenon manifest 
in the extrusion of the polar bodies is known as 
maturation oj the ovum, and seems to be an attempt 
on the part of the ovum to develop into a new indi- 
vidual without the process of fertilization; that is, 
parthenogenetically. If the ovum is not fertilized, it 
shows no further activity and is lost. If the ovum 
is fertilized it continues to divide regularly and in a 
short time develops into the embryo. 
The developmental history of ova is full of interest. 
They are very numerous and develop so very early 
in embryonic life. During childhood they grow 
large and accumulate a liberal storage of food, while 
the sister epithelial cells that form the Graafian fol- 
licle remain small and multiply rapidly to form the 
ripe follicle. This latent condition extends over a 
period of fifteen to forty years. When the ripe fol- 
licle finally ruptures and the ovum is eliminated, a 
rapid segmentation quickly follows resulting in the 
extrusion of the polar bodies. This is followed by a 294 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
second passive period, unless fertilization takes 
place, when the ovum rapidly develops into a new 
being. By far the large majority of the ova remain 
undeveloped in the ovarian cortex, where they seem 
to pass merely a passive existence. We have no 
explanation of these phenomena beyond attributing 
them to heredity, the nature of which is still highly 
speculative. 
The Corpora Lutea.-A corpus luteum is the modi- 
fied Graafian follicle after its rupture and discharge 
Fig. 227.-Section of corpus luteum. 
of the ovum. This follicle remains permanently 
in the cortex of the ovary as a scar. When the 
rupture takes place the follicular cavity fills up with 
an exudate and an infusion of blood from the rup- 
tured blood-vessels. This coagulum is quickly in- 
vaded by white blood-corpuscles, connective-tissue 
cells from the theca, and epithelial cells from the 
stratum granulosum. The corpus luteum thus ulti- 
mately shows a uniform distribution of epithelial REPRODUCTIVE ORGANS IN THE EEMALE. 
295 
cells and connective-tissue cells. If the ovum be- 
comes fertilized and pregnancy follows, the corpus 
luteum continues to grow until it becomes many 
times larger than the original Graafian follicle, causing 
a rounded elevation at that point on the surface of 
the ovary. This kind is called a true corpus luteum. 
On the other hand, if the ovum is not fertilized the 
corpus luteum shrinks and becomes smaller than the 
original follicle. This kind is called a false corpus 
luteum. The corpus luteum is at first well defined 
by the investing follicular theca, but after a time its 
limits are less distinct, so that as age advances the 
ovarian stroma becomes gradually pervaded with 
cells like those of the corpora lutea. 
THE FALLOPIAN TUBES. 
The Fallopian tubes are two ducts for the passage 
of ova from the ovary to the uterus. They differ 
from the ducts of other glandular organs in being 
detached from the organs whose secretions they con- 
vey. They are from four to five inches long and 
pass almost horizontally outwards from the fundus 
of the uterus. When they reach the ovary they 
ascend along the pelvic floor and nearly encircle each 
organ, passing up the external and down the internal 
or mesial margins. Each tube is enclosed in the free 
margin of the broad ligament, which is a peritoneal 
fold that also contains the round ligament of the 
uterus, the ovary, parovarium, and numerous blood- 
and lymph-vessels. 
For descriptive purposes each duct is divided into 
an isthmus, an ampulla, a neck, and a fimbriated ex- 296 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
tremity. The isthmus is smooth and round, about 
one inch in length, and opens into the fundus of the 
uterus by a small orifice that will barely admit an 
ordinary bristle. It is a straight and narrow part of 
the duct, about 2 to 3 mm. in diameter. The am- 
pulla encircles the ovary and is at least twice the size 
of the isthmus. It is also less firm to the touch, 
Fig. 228.-Cross section of ampulla of Fallopian tube. 
being flabby while the isthmus is cord-like. The 
neck is an annular constriction between the ampulla 
and fimbriated extremity, the latter being a funnel- 
shaped expansion of the ovarian end of the tube, 
which terminates in a number of irregular processes 
called fimbriae. The fimbriae vary considerably in 
size and number. Many of them are branched, and REPRODUCTIVE ORGANS IN THE FEMALE. 
297 
one is particularly long and attached to the upper 
end of the ovary. 
Structure.-The Fallopian duct is a muscular tube 
lined the whole length by a mucous membrane 
clothed with simple ciliated columnar epithelium. 
This mucous membrane is thrown up into longitudi- 
nal folds that are very broad and numerous in the 
wide portions of the tube and in the narrow portions 
less conspicuous. It is continuous on the one hand 
Fig. 229.-Cross section of isthmus of Fallopian tube. 
with the mucous membrane of the uterus, and at the 
other end of the tube with the serous lining of the 
peritoneum, being one example of a direct conti- 
nuity of a mucous and a serous membrane. Glands, 
so numerous in the mucous membrane of the uterus, 
are absent in the Fallopian tube. 
The mucosa rests upon a thin vascular submucosa 
composed of areolar tissue. External to the sub- 
mucosa there is a muscular coat consisting of a thick 
inner circular layer and a thin outer longitudinal 298 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
layer of smooth muscle libers. Externally the tube 
is practically enclosed by the peritoneum, forming a 
serous covering. 
Embryologically, each Fallopian tube represents a 
Mullerian duct, which is derived from the mesoderm. 
In the male the Wolffian duct develops into the vas 
deferens. This duct, which is rudimentary in the 
female, is called Gartner's duct, and lies parallel to 
the Fallopian tube, between the latter and the round 
ligament. The round ligament extends from the 
uterus to the internal abdominal ring in nearly the 
same position as the vas deferens does in man. 
Fertilization, as a rule, takes place in the upper 
part of the Fallopian tube. In cases of tubal preg- 
nancy the ovum does not reach the uterus but finds 
lodgment in the tube. The much-folded mucous 
membrane allows considerable distention, but ulti- 
mately the rapidly growing embryo ruptures the 
tube, with serious complications resulting from in- 
ternal hemorrhage. Usually the ova pass down the 
tube on the corresponding side, but it is possible for 
the ova from one ovary to pass down the tube of the 
opposite side. Experimentally, the right ovary and 
the left tube may be removed in the dog and the ani- 
mal still become pregnant. 
The ovaries have a marked influence on the devel- 
opment and mentality of a woman and their removal, 
prior to the menopause, is followed by deleterious 
results, much the same as the removal of the testes 
in the male. While extracts from certain organs, 
such as the thyroid gland and the suprarenal bodies, 
have specific medicinal properties, extracts from the REPRODUCTIVE ORGANS IN THE EEMALE. 
299 
ovaries give no satisfactory results. Its potency is 
manifest only by the living organ in the performance 
of its normal function. The ovary or fragments of 
it will readily grow in other parts of the body, and 
has been successfully grafted from one animal to an- 
other. 
The Parovarium, or Epoophoron.-The organ 
bearing this name lies in the broad ligament lateral 
to the ovary and between the latter and the tube. 
It consists of a number of closed epithelial tubules 
which can usually be seen by holding this part of the 
ligament up against the light. Embryologically 
they represent the upper portions of the Wolffian 
duct and some of the attached tubules of the meso- 
nephros, and correspond to the epididymis in the 
male. 
The paroophoron represents vestiges of tubules 
similar to the parovarium, situated in the broad liga- 
ment below the ovary. They correspond to the 
paradidymis in the male. 
Being lined by epithelial cells, either of these or- 
gans may develop into parovarian or paroophoron 
cysts, the former being more common. 
• THE UTERUS. 
The uterus, or womb, is a hollow muscular organ, 
with thick walls, placed in the pelvic cavity between 
the bladder and rectum. In case of pregnancy it 
receives and nourishes the ovum and later expels the 
fetus at the end of pregnancy. During gestation, 
and also periodically during menstruation, it is sub- 
ject to marked physiological and structural changes. 300 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
It is therefore an organ in which great activity is 
manifest during the greater part of adult life. 
The fully developed virgin uterus is a pear-shaped 
organ, flattened from before backward, free above, 
Fig. 230.-Arrangement of uterine muscle, as seen from in front after 
removal of serous coat (Helie). 
and connected below with the vagina, into which its 
lower extremity projects. Its average dimensions 
are, three inches in length, two inches in breadth at 
its upper and widest part,.and one inch in thickness. REPRODUCTIVE ORGANS IN THE FEMALE. 
301 
For descriptive purposes it is divided into fundus, 
body, and neck, or cervix. 
The fundus is the broad convex upper end that 
lies above the attachment of the Fallopian tubes. It 
is chiefly this part that expands in case of pregnancy. 
The body is the part between the fundus and neck. 
This part tapers downward with convex sides. The 
Fig. 231.-A, Isolated muscle-elements of the non-pregnant uterus 
B, cells from the organ shortly after delivery (Sappey). 
neck, or cervix, is about one inch long, cylindrical, 
and projects into the anterior part of the upper end 
of the vagina. The projecting portion is called the 
'vaginal part, and has a transverse oval aperture, 
called the os uteri, which communicates with the 
cavity of the uterus. The latter is a triangular 302 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
cavity, so flattened that the anterior and posterior 
uterine walls touch each other. The base of the 
cavity is in the fundus and is convex downwards. 
The two Fallopian tubes open into the upper angles 
each by a small aperture that will barely admit a 
bristle. The cavity tapers gradually toward the 
cervix, where it becomes constricted to form the in- 
ternal os. The peritoneum covers the fundus and 
Fig. 232.-Cross section of wall of uterus. 
body of the uterus, and posteriorly extends down- 
ward to clothe the upper posterior wall of the vagina. 
It is then reflected back over the rectum, forming a 
a sac called the pouch of Douglas. This makes it 
possible to open the peritoneal cavity by a puncture 
through the upper posterior vaginal wall, an operation 
which establishes free drainage to the female pelvis. REPRODUCTIVE ORGANS IN THE FEMALE. 
303 
Anteriorly the peritoneum docs not cover the whole 
uterus, but at the junction of the body with the 
neck, it is reflected back over the bladder wall form- 
ing the utero-vesical pouch. 
Structure.-The histology of the uterus resembles 
that of the Fallopian tubes, and the layer of the one 
is continuous with that of the other. Embryologi- 
cally, these two structures, and also the vagina, de- 
velop from the Mullerian ducts, the uterus and 
Fig. 233.-Diagonal section of the uterine mucosa. 
vagina representing the fused lower ends of Muller's 
ducts. The whole uterus, including the epithelial 
lining, is therefore of mesodermic origin. The uter- 
ine wall is composed of a mucosa, muscular, and 
serous layer. The Fallopian tube has a submucosa 
which is absent in the uterus. 
The mucosa, or endometrium, is the inner layer and 
is lined by simple columnar ciliated epithelium, 
which at the external os changes to the stratified 
variety of the vagina. It has a rich supply of 304 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
branched tubular mucous glands which, in the cer- 
vix, are very large and have a tendency to become 
sacculated. These glands extend radially as far as 
the muscularis, and some of them may even pene- 
trate a short distance into the muscle coat. The 
gland ducts are lined by ciliated epithelium, while 
in the deeper portions cilia are absent and the epi- 
thelium becomes simple cubical, resembling a glandu- 
lar type. Most of these glands take a tortuous or 
spiral course, and are separated from each other by 
an interstitial tissue composed of connective-tissue 
cells. These cells are of the embryonic type, rich in 
chromatin and therefore stain heavily with nuclear 
dyes. The relative amount of interstitial and 
glandular tissue in a normal uterine mucosa should 
be approximately equal parts. The connective 
tissue predominates in interstitial endometritis, and 
the glandular tissue in adenitis. The whole uterine 
mucosa is unusually thick and very vascular. In a 
mature woman it is normally subject to marked 
periodic changes resulting from menstrual condi- 
tions, which reach a high degree of complexity in 
case of pregnancy. 
The Muscular Layer.-The muscularis is an unusu- 
ally thick layer of smooth muscle cells which in the 
non-pregnant uterus measure forty to sixty mi- 
crons, while at the end of pregnancy the cells measure 
four hundred to six hundred microns in length. 
These muscle cells are arranged in bundles with a 
considerable amount of connective-tissue fibers and 
cells interlacing them, imparting strength and elas- 
ticity to the uterine wall. There has been consid- REPRODUCTIVE ORGANS IN THE FEMALE. 
305 
erable discussion as to the exact disposition of the 
different layers of this musculature which, in a gen- 
eral way, may be divided into three strata: (i) an 
inner layer of longitudinal fibers, by some called 
the muscularis mucosa; (2) a middle circular layer, 
and (3) an outer thin layer of fibers that run diago- 
nally or somewhat irregularly. The inner layer is 
much the thickest; none, however, is sharply de- 
fined. 
The serous coat is the peritoneal lining which con- 
sists of connective-tissue elements and an invest- 
ment of simple pavement epithelium. 
Vessels and Nerves.-The arteries that supply the 
uterus are arranged in two pairs,-the uterine and 
ovarian. The uterine artery is a branch of the an- 
terior division of the internal iliac. It reaches the 
upper portion of the vagina, and then ascends in a 
very tortuous manner along the lateral border of the 
uterus to the fundus, where it divides into two 
branches, one of which anastomoses with the ovarian 
artery and the other supplies the Fallopian tube. 
From the ascending portion many side branches are 
given off which penetrate the uterine wall and ramify 
in the muscle tissue and the mucosa. These 
branches are very tortuous so that the uterus 
can expand in pregnancy without breaking the 
vessels. 
The veins are very large and have no valves. 
They form large sinuses mostly along the lateral 
walls, from which the blood is collected into two 
trunks: (1) the uterine vein accompanies the uter- 
ine artery and empties into the internal iliac vein; 306 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
(2) vessels communicate with the ovarian or pam- 
piniform plexus which drains through the ovarian 
veins. 
The lymphatics begin in the interstitial substance 
of the mucosa, and uniting with lymphatics from 
the muscularis, emerge to form a rich plexus just 
beneath the serous covering. This plexus drains 
along two channels: (i) by lymphatic vessels that 
accompany the uterine veins; (2) vessels that ac- 
company the ovarian veins. The blood and lymph 
drainage is therefore in two directions. That of the 
fundus is toward the ovary, and that of the body and 
cervix is in the opposite direction along the uterine 
vessels. This is of clinical importance in the spread 
of infections. 
The nerves are non-medullated fibers from the in- 
ferior hypogastric plexus, and medullated from the 
third and fourth cervical. The non-medullated sup- 
ply the muscle while the medullated fibers have been 
traced to the mucosa, where they form a plexus from 
which fibers pass to the surface epithelial cells. An- 
other set arborize about the mucous gland cells. 
Sympathetic-nerve ganglia are associated with the 
non-medullated fibers. 
Menstruation.-This consists of a hemorrhagic and 
mucous discharge from the uterus, which recurs 
about every twenty-eight days in the non-pregnant 
woman between the ages of thirteen and forty-five. 
It is accompanied by more or less severe systemic 
disturbances of a neurotic nature, and also by in- 
creased activity of the glandular system as a whole. REPRODUCTIVE ORGANS IN THE FEMALE. 
307 
Enlargement of the thyroid gland usually accom- 
panies the menstrual flow. 
From five to ten days before the menstrual flow 
begins there is a marked hyperemic condition of the 
Fig. 234.-Uterus during menstruation, cut open to show the swelling 
of the whole organ, and particularly the mucous membrane: A, Mucous 
membrane of cervix; B, C, mucous membrane of corpus, much thickened; 
D, muscular layer; E, uterine opening of tube; F, os internum (the mu- 
cous membrane tapers down to these openings) (Courty). 
uterine wall. The congestion of blood causes a 
marked swelling and growth of the uterine mucosa, 
so that it attains a thickness of 6.0 mm. This mu- 
cosa is then called the decidua menstrualis. After 
these changes have occurred the menstrual flow be- 308 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
gins and usually lasts for four days. This results 
in a complete or partial exfoliation of the superficial 
part of the mucous membrane of the uterine fundus 
and body, but does not involve the cervix. The 
exfoliation begins at the internal os and advances 
progressively toward the fundus. The restoration 
of the mucosa proceeds in the same order, from be- 
low upward, and in the course of five or six days the 
mucous membrane is restored. The epithelial lining 
regenerates from the free ends of the mucous glands 
that did not partake in the exfoliation. 
The uterus is thus a seat of great physiological 
activity. During at least one-half the menstrual 
period of twenty-eight days there are marked struc- 
tural changes manifest in the uterine mucosa. In 
such an active organ pathological disturbances are 
naturally of frequent occurrence. 
Menstruation and ovulation are related phenom- 
ena, and yet there is evidence that neither one de- 
pends on the other. Pregnancies may occur before 
the menstrual period is inaugurated. Even at the 
early age of nine years pregnancy has been reported; 
also in mature women after confinement, but before 
menstruation has reappeared, pregnancy may occur. 
A woman who does not menstruate does not become 
pregnant, as a rule, but there are exceptions. Ovu- 
lation, therefore, may go on without menstruation, 
and there is evidence that menstruation may prevail 
without ovulation. For a further discussion of this 
subject, see Raymond's "Human Physiology." REPRODUCTIVE ORGANS IN THE FEMALE. 
309 
PREGNANCY. 
During pregnancy the mucous membrane of the 
uterus becomes modified into a membrane called the 
decidua gravitatis. This membrane may be divided 
into (i) the decidua serotina or basalis, that part of 
the mucosa to which the ovum is attached and in 
which the placenta develops; (2) the decidua re- 
flexa, that which envelops the ovum, and (3) the 
decidua ver a, the part that lines the rest of the 
uterus. 
In the early stages of pregnancy the changes in the 
uterine mucosa resemble those of the decidua men- 
strualis. At the end of the first half of pregnancy 
the decidua serotina is 1 cm. thick. The epithelial 
lining has disappeared and two layers can be recog- 
nized: (1) a superficial compact layer, and (2) a deep 
spongy layer. The compact layer consists of con- 
nective-tissue elements and some very large pig- 
mented cells called the decidua cells. These cells 
usually have one large nucleus, but some of them 
may be polynucleated. The cells are thirty to one 
hundred p in diameter, and oval or elongated, re- 
sembling epithelial cells, although they are supposed 
to develop from the interstitial connective-tissue 
cells of the normal mucosa. They are of diagnostic 
value in uterine curetments where they become a 
probable evidence of pregnancy. In post-mortems 
they have no medico-legal significance, as these cells 
may be found in the decidua menstrualis. In the 
spongy layer the connective-tissue cells form septa 
between the flattened and sacculated as well as tor- 310 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
tuous mucous glands. Blood-vessels also form a 
plexus in the spongy layer. 
The decidua reflexa disappears during the first 
months of pregnancy, while the decidua serotina 
enters into the formation of the placenta. 
Placenta.-The placenta is a vascular organ for 
the nourishment of the fetus, and serves the purpose 
of bringing the fetal and maternal blood into closest 
proximity without actually blending. The organ 
Fig. 235.-Section of the decidua serotina at the margin of the placenta. 
may be divided into an embryonic part, the placenta 
joetalis, and a maternal part, the placenta materna. 
The latter is the modified uterine mucosa or decidua 
serotina. 
The fertilized ovum usually finds lodgment in the 
fundus of the uterus. Very early it becomes en- 
closed in an envelope of its own production called 
the chorion. This chorion has an outer epithelial Plate V 
i. Semi-diagrammatic section of gravid uterus, showing contained ovum of about five weeks (modified from Allen Ihomson). 
2. Semi-diagrammatic section of uterus, showing relations of fetal and maternal placenta (Ahlfeld). REPRODUCTIVE ORGANS IN THE FEMALE. 
311 
layer and an inner connective-tissue layer, the latter 
being vascular. It is this vascular chorion that enters 
into intimate relations with the uterine mucosa 
to form the placenta, the former the fetal part and 
the latter the maternal part. These parts become 
intimately associated. 
The chorion very early produces a large number of 
villi which invade the mucosa, where they ultimately 
become large and much branched, like the root of a 
tree. These are the chorionic villi and belong to 
the fetal pla- 
centa. Each 
villus consists 
of a connective- 
tissue core with 
an epithelial 
lining. The 
fetal blood cir- 
culates through 
the connective- 
tissue core 
while the maternal blood bathes the external sur- 
faces of the villi. The terminal ramifications of 
each villus becomes firmly anchored in the uterine 
mucosa, while the branched lateral twigs float freely 
in the maternal blood spaces or intervillus sinuses. 
These villi serve a double purpose. They attach 
the fetal placenta firmly to the uterus, and establish 
a close relation between fetal and maternal blood 
whereby the embryo receives proper nourishment. 
Upon closer examination each villus should present 
in cross section an outer layer of simple squamous 
Fig. 236.-Cross section of two human chorionic 
villi at end of pregnancy. 312 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
epithelial cells and a core of connective-tissue cells 
in which two or more small capillary blood-vessels 
ramify. The epithelium of the villi undergoes great 
alterations and may entirely disappear, to be re- 
placed by isolated accumulations of large round 
nuclei that stain intensely with nuclear dyes, and 
that form protuberances on the surfaces particularly 
of the large villi. These are called zellknoten, or 
cell knots. Their origin and significance is doubtful. 
In the earlier months of pregnancy the epithelial in- 
vestment of each villus is clothed externally by a 
continuous protoplasmic mass, called the syncytium, 
containing small and irregularly scattered nuclei. 
It is generally supposed that the syncytium repre- 
sents the modified and disintegrated uterine epi- 
thelium and is therefore of maternal origin. Some 
embryologists affirm that in some villi there is a 
membrane external to the syncytium which mor- 
phologically represents the epithelial wall of the 
uterine blood-vessels. The maternal blood, how- 
ever, very soon breaks through the capillary spaces 
of the uterine mucosa and enters the intervillus 
sinuses clothed by the syncytium. The fetal cir- 
culation is a closed system and nowhere is there a 
direct intermingling of fetal and maternal blood. The- 
oretically the exchange of gases, in the early stages 
of development, takes place through (i) the epi- 
thelial wall of the maternal capillaries; (2) the uter- 
ine epithelial lining, probably represented by the 
syncytium; (3) the epithelial lining of the chorion, 
and (4) the epithelial wall of the fetal blood capilla- 
ries. The first of these membranes is not always Diagrammatic Section through the Human Placenta at the Middle of the Fifth Month (after Leopold). 
The fetal placenta consisting of the chorion (???) with its villi (z), has grown into the maternal placenta; the villi 
present attached points (Zd,^2) and free processes (?/); sp is the spongy layer of the decidua serotina, in which the separa- 
tion takes place along the line Tr; CS is the compact layer forming the inner part of the uterine placenta, which consists of 
the basal plate (BP), the closing plate (SP), the arteries (a), the cavernous blood-spaces (c), and the marginal sinus. 
Plate vi reproductive: organs in the female. 
313 
present, as maternal blood ruptures this wall. The 
second investment, or syncytium, disintegrates. 
The third also disappears, at least in parts, or be- 
comes so thin that it can scarcely be detected. Ulti- 
mately, therefore, the fetal and maternal blood is 
practically separated by only one membrane, the 
epithelium of the fetal capillaries. 
The maternal placenta does not differ structurally 
from the histology of the decidua already described 
except in degree of complexity. There is an inter- 
nal compact portion and a deeper spongy layer. The 
latter rests against the uterine muscularis and is very 
vascular. Numerous blood- 
vessels penetrate the compact 
layer to open freely into the 
intervillus sinuses already de- 
scribed. These blood-vessels 
usually take a very tortuous 
course, and they are thus able 
to adjust themselves to contractions and expansions 
of the uterine wall. Decidual cells are especially 
conspicuous in the compact layer of the placenta. 
These cells are sometimes present in the spongy 
layer but never in the chorionic villi or fetal portions 
of the placenta. 
The fetal blood reaches the placenta through the 
umbilical cord. There is regularly present two ar- 
teries and one vein, imbedded in a gelatinous con- 
nective-tissue matrix known as Wharton's jelly. 
The blood in the arteries is carried to the placenta 
and is venous. That in the vein returns from the 
placenta and is arterial. After birth, when the pla- 
Fig. 237.-Four decidual 
cells from decidua serotina. 314 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
centa comes away, it is always at tlie expense of the 
uterine mucosa, which leaves a raw, bleeding surface. 
The uterine muscles at once contract, reducing the 
uterine cavity and checking the hemorrhage. A 
normal mucous membrane at once regenerates, the 
ciliated epithelium and mucous glands developing 
from remnants of glands that were not entirely ob- 
literated by the placental growth. As a rule regular 
menstruation is inaugurated when lactation ceases, 
but there are exceptions to this. A second preg- 
nancy may follow without any intervening menstrual 
period, but this is rare. 
THE MAMMARY GLAND. 
The mammary gland is a skin gland that is present 
in both sexes. In the second month of embryonic 
life there is a linear thickening of the skin, extending 
from each axilla to the groin, and at regular inter- 
vals in this ridge a series of mammary glands develop 
in many vertebrates. In the human race only one 
pair is produced, which represents the fourth or fifth 
pair of this series. In rare cases accessory mam- 
mary glands are found in man both above and below 
the normal pair. 
In childhood the mammary gland is identical in 
both sexes, but with approaching puberty it enlarges 
in the female, reaching its highest development at 
the end of pregnancy. The menopause brings 
about a retrogression and shrinkage of the organ. 
The gland is therefore to be considered an accessory 
sexual organ. 
The mammary gland is a segregation of fifteen to REPRODUCTIVE ORGANS IN THE FEMALE. 
315 
twenty separate compound tubulo-alveolar glands 
which open separately on the nipple by an equal 
number of pores. These glands are arranged radi- 
ally and enclosed by a variable supply of fat and 
connective tissue in such a way that it is possible to 
divide the breast into fifteen to twenty lobes, which 
may be further divided into lobules. Each pore 
leads to a narrow 
vertical tube, the 
lactiferous duct, 
which widens just 
below the base of 
the nipple to form 
a receptacle called 
the milk sinus, be- 
yond which it 
again becomes a 
narrow tube. 
The latter be- 
comes branched to 
form interlobular 
ducts that open 
into distal dilata- 
tions or alveoli, which constitute the secreting por- 
tions of the gland. 
The lactiferous ducts and sinus are lined with 
simple columnar epithelium, which becomes strati- 
fied near the orifices where it is directly continuous 
with the stratified epithelium of the skin. The finer 
structure of the alveoli varies according to the func- 
tional activity of the organ. During lactation the 
alveoli are distended with milk. The cells of the 
Fig. 238.-Diagram of one-half of mammary 
gland, dissected to show gland. 316 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
simple glandular epithelium become distended with 
the products of secretion that consist of granules and 
deposits of fat. The granules liquefy and along with 
the fat globules are discharged into the alveoli as 
milk. Many particles of fat are taken up by migra- 
ting white corpuscles, called phagocytes, which mix 
with the secretion and thus become converted into 
the colostrum corpuscles of early lactation. The 
gland cells after secretion accumulate a second sup- 
Fig. 239.-Section of a portion of the mammary gland. 
ply, and this process is repeated many times. The 
secreting cell does not disintegrate as is the case in 
the sebaceous glands of the skin. 
When the gland is not engaged in the secretion of 
milk, many of the alveoli shrink up and disappear, 
while the remaining ones become much reduced in 
size, and the gland as a whole is smaller. The cells 
of the alveoli become columnar, resembling the cells 
that line the ducts. The epithelium rests upon a REPRODUCTIVE ORGANS IN THE FEMALE. 
317 
basement membrane and a membrana propria, the 
latter containing basket cells whose processes mingle 
with the glandular epithelium. 
The interstitial tissue just external to the alveoli 
is composed of connective-tissue cells that stain 
heavily with nuclear dyes, while in the intervening 
spaces between the alveoli, connective-tissue fibers 
and fat cells are abundant. A supply of plain.muscle 
fibers intervene and surround the ducts in the nip- 
ple. The fibers placed longitudinally function in 
the erection of the nipple, while the circular ones 
constrict the ducts. 
The nipple docs not 
develop until after 
birth. Its normal po- 
sition is in the fourth in- 
tercostal space, about 
four inches from the 
sternum. It is clothed 
with stratified pig- 
mented epithelium and 
devoid of hair follicles 
and sweat glands. The skin immediately around 
the nipple is also pigmented, forming an areola with 
numerous small papillae, giving a rough or wrinkled 
appearance. Besides large sweat glands, twelve or 
more large sebaceous glands, called glands of Mont- 
gomery, are present in this area. These glands open 
at the apices of the small papillae just mentioned, 
and are usually considered as accessory milk glands. 
Vessels and Nerves.-The arteries that supply the 
breasts are the long thoracic, the internal mammary, 
Fig. 240.-Section through two alveoli 
of mammary gland. 318 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
and the intercostals. These anastomose freely and 
approach the gland from all directions. The -veins 
are equally extensive. They accompany the arteries 
and bear the same names. Lymphatics are very 
numerous and form extensive lymph spaces around 
the alveoli of the gland. For the most part they 
drain to the lymph glands in the axilla, but from the 
deeper part of the breast they drain along the course 
of the internal mammary artery. CHAPTER X. 
THE SKIN. 
The skin covers the entire body and is directly 
continuous with the mucous membranes of the ali- 
mentary canal and urogenital organs at their 
external orifices. It contains sensory nerve endings 
and in the deeper layers there is a liberal supply of 
both blood- and lymph-vessels. It is the chief factor 
in regulating body temperature, and is an efficient 
mechanical protection to the deeper tissues, while the 
sweat and sebaceous glands render it an important 
excretory organ. Hairs and nails represent modi- 
fications of the superficial layers. It varies consid- 
erably in thickness, being 4 mm. thick on the palms 
of the hand and 0.5 mm. over the back and shoul- 
ders. The color is imparted by pigmentation and 
the blood supply. The color is characteristic of races 
and variable in the different parts of the body as well 
as subject to modification depending on age and dis- 
ease. The skin moves freely upon the deeper tissues, 
excepting over bony prominences where it is more 
firmly attached. On the palm of the hand and the 
sole of the foot it is also bound down to the subjacent 
tissues. The external surface presents in places 
numerous permanent ridges which correspond with 
rows of underlying papillae, and which in criminals 
are utilized for the purposes of identification. The 
319 320 
NORMAL HISTOLOGY AND ORGANOGRAPHY 
hair follicles appear with regularity in external de- 
pressions practically all over the body, forming dis- 
tinctive patterns. Cutaneous blood-vessels and 
Fig. 241.-Section of skin through palmar surface of fingers. 
tendons form ridges and lines readily detected by 
the unaided eye, and over which the skin is freely 
movable. THE skin. 
321 
Structurally the skin or integument consists of 
two chief strata that may be subdivided into layers 
in the following manner: 
I. Epidermis epithelial layers derived from the 
ectoderm. 
i. Corncum or horny layer,-superficial 
epithelial plates. 
2. Stratum lucidum,-absent where the 
skin is thin. 
3. Stratum granulosum,-absent where the 
skin is thin. 
4. Malpighian or germinal layer,-nucle- 
ated growing cells. 
O O 
II. Dermis or corium,-connective-tissue elements 
from the mesoderm. 
1. Papillary layer. 
2. Reticular layer. 
Epidermis.-The horny layer of the epidermis 
forms the outer covering of the skin and consists of 
several layers of scaly epithelial cells in which the 
nuclei have disappeared. The cells are dead and 
constantly exfoliating superficially, while new strata 
are regularly added from below. Bacteria are 
usually present in its external parts, and in surgi- 
cal operations, therefore, the skin is thoroughly 
scrubbed, a process that removes most of this layer 
and renders the field of operation practically sterile. 
At birth the horny layer is less compact and of a red 
color. It is then called the Ternix caseosa, which 
exfoliates in a few days, when the complexion 322 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
changes to that of the particular race to which the 
child belongs. 
The strata lucidum and granulosum are two thin 
layers that lie between the corneum and the Mal- 
pighian layers and are best developed in the sole of 
the foot and the palm of the hand. Each consists 
of two or three rows of epithelial cells. The stratum 
lucidum overlies the stratum granulosum and is a 
o 
refractive layer consisting of cells with disintegrating 
Fig. 242.-Section of epidermis of skin from palm surface of finger. 
nuclei, and possessing a homogeneous substance 
called eleidin. The latter is colored with eosin but 
does not take nuclear dyes. The cells that compose 
the stratum granulosum possess many granules 
called keratohyalin granules, which are regarded as 
products of cell disintegration. These granules in- 
crease in size and coalesce to form the semifluid sub- 
stance called eleidin of the stratum lucidum. The 
granules take nuclear dyes; the eleidin does not. THE SKIN. 
323 
The Malpighian layer is macle up of growing epi- 
thelial cells and constitutes the deeper parts of the 
epidermis. Its lower surface is beset with numerous 
depressions that receive connective-tissue papillae 
from the dermis. The epidermis and dermis thus 
interlock by means of an extensive system of papillae 
from each layer. The Malpighian layer is thicker than 
the horny layer, excepting in the sole of the foot and 
the palm of the hand. It consists of ten to fifteen 
layers of epithelial cells. The cells in the lower row 
are columnar and are so arranged that their long axis 
is vertical to that surface. In colored races these 
cells are pigmented and impart to the skin the par- 
ticular color of the race. Pigmentation has been 
discussed on page 65, to which the reader is re- 
ferred. The other cells of the Malpighian layer are 
cubical or flattened and so placed that their long 
axis lies parallel to the surface of the body. The 
cells of the deeper strata have numerous minute 
short processes and have been called prickle cells. 
These processes form intercellular bridges, which 
give rise to a complex system of minute intercellular 
channels that permit more freely the passage of 
nourishment. These cells are constantly dividing 
and adding new strata to the horny layer that is ex- 
foliating at the same rate. 
The dermis, corium, or cutis vera, is of connective- 
tissue origin and lies just beneath and intimately 
associated with the epidermis. It may be divided 
into a papillary portion, next to the epidermis, and 
a deeper reticular portion which shades off into the 
subdermal fascia. The papillary portion consists of 324 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
vascular and nerve papillae that fit into depressions 
on the lower surface of the epidermis. The two 
layers of the dermis pass into each other without any 
sharp line of demarcation. In both layers there is 
an abundance of connective-tissue fibers, both clastic 
and non-clastic, forming what has been termed areo- 
lar tissue. These fibers form bundles that interlace 
to produce a network, particularly in the reticular 
or deep portions. In the meshes of this reticulum 
are to be found the bodies of the sweat glands, and a 
variable amount of adipose tissue, while hair follicles 
with their sebaceous glands find lodgment in the 
dermis with greater regularity. It is the dermis, 
and particularly the areolar tissue, that gives elas- 
ticity and mobility to the skin. The epidermis is 
not very elastic, consequently wrinkles of the epi- 
dermis are formed when the fat is absorbed, and 
also in old age, by shrinkage of the areolar tissue. 
A variable amount of muscle is everywhere present 
in the dermis. Smooth muscle is associated with 
the hair follicles, forming the arrector pili muscle. 
In the face and neck voluntary muscle fibers may be 
traced into the papillary layer, while a third set of 
muscle elements is associated with the sweat glands. 
The latter is of the smooth variety and will be de- 
scribed along with the sweat glands. 
The dermis everywhere is very vascular.' Blood- 
and lymph-vessels ramify freely through it, but in 
no case do they enter the epidermis. Nerve fibers, 
on the other hand, enter the Malpighian layer of the 
epidermis and arborize around and between the 
epithelial cells. In the dermis these fibers form an THE SKIN. 
325 
extensive nerve plexus, from which some terminal 
fibers proceed to the hair follicles, and others to 
special nerve papillae in the dermis. These and 
other nerve terminations will be described as 
peripheral nerve endings in another chapter. 
HAIRS. 
The hairs arc distributed practically over the 
whole surface of the body, with the exception of the 
palms of the hand, the soles of the feet, and the red 
border of the lips. They are distributed with con- 
siderable regularity, as a 
rule one hair for each fol- 
licle, but there may be two 
and sometimes three. The 
part of the hair buried in 
the skin is called the root, 
and the part that projects 
beyond the surface is the 
shaft. The lower part of the 
root is thickened to form 
the hair bulb, into which is 
pushed from below a vascu- 
lar connective-tissue projection called the hair papil- 
la. The root is inserted deep in the skin, usually 
reaching the subdermal elements. It is placed 
diagonally to the surface and becomes enclosed in a 
specially modified wall made up of several layers de- 
rived partly from the epidermis and partly from the 
dermis. 
Most hairs are composed of three layers: an outer 
cuticle, a middle cortical, and a central portion, the 
Fig. 243.-Portion of a hair. 326 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
medulla. In thin and light hairs the medulla is usu- 
ally absent. 
The hair cuticle, or outer hair membrane, is made up 
of structureless transparent epithelial scales that 
overlap each other in the direction of the distal end 
of the hair. A hair feels smooth, therefore, if pulled 
through the fingers from the root to the free end. 
These scales overlap each other sometimes to such 
an extent that the cuticle has the appearance of 
being stratified. The scales are derived from epi- 
thelial cells that have become cornified, and they 
are thus closely related to the horny epithelial plates 
of the epidermis. 
The cortical substance forms the main bulk of the 
hair and lies just beneath the cuticle. The cortex 
consists of spindle-shaped nucleated cells which 
show a distinct fibrillar structure, giving the whole 
hair the appearance of being longitudinally striated. 
Pigment granules are deposited in these cells and 
between them, to which the hair owes most of its 
color. Numerous small spaces filled with air are 
frequently formed between the cells of the cortical 
layer, and these give a white color to hairs that have 
a scanty supply of pigment. Hairs that have en- 
tirely lost their pigment and have none of these air 
spaces, are gray but not white. 
The medullary substance forms the axis of the 
hair and may be absent, but is usually present in 
thick hairs. It is made up of nucleated cubical 
epithelial cells forming two or three rows in thick- 
ness. Pigment is also present in the medullary 
cells. THE SKIN. 
327 
Hair Follicles.-The hair follicles are the pits in the 
skin occupied by the roots of the hairs. These pits 
are placed diagonally to the surface, and in the scalp 
where the skin is thick they are at least half an inch 
in length. It is estimated that the normal scalp 
has about one hundred and twenty thousand of these 
follicles, or an average of eight hundred to the square 
inch. Each follicle is really a minute tubular de- 
Fig. 244.-Cross section of a hair follicle 
pression or invagination of the skin, and its wall is 
therefore made up of constituents from both the epi- 
dermis and the dermis. These layers may be tabu- 
lated as follows: 
I. Outer tunic. 
i. Connective-tissue fibers arranged longi- 
tudinally. 
2. Connective-tissue fibers, circular. 
3. Glassy membrane. 328 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
II. Outer root sheath; resembles Malpighian 
layer of the epidermis. 
III. Inner root sheath. 
i. Henle's layer,-non-nucleated ele- 
ments. 
2. Huxley's layer,-nucleated cells. 
3. Root sheath,-structureless membrane. 
The outer tunic is derived from the dermis and is 
of connective-tissue origin. Externally there is a 
layer of connective-tissue fibers arranged longitudi- 
nally, in which may be found a few connective- 
tissue cells and a delicate plexus of nerve fibers. 
The non-elastic connective-tissue fibers predominate, 
but the elastic variety is also present. Internal to 
the longitudinal fibers is a compact circular layer of 
non-elastic connective-tissue fibers, and internal to 
this is the glassy membrane, a very thin hyaline 
sheath often difficult to find. The outer tunic in- 
vests the lower half of the root sheath. This tunic, 
in the so-called tactile hairs of many mammals, has a 
rich nerve innervation and a liberal blood supply. 
In such hairs nerve fibers have been traced to the 
glassy membrane, while others apparently penetrate 
to tactile cells in the outer root sheath. 
The root sheaths encase the root of the hairs and 
are derived from the epidermis, being therefore of 
ectodermal origin. The outer root sheath is a direct 
continuation of the Malpighian layer and diminishes 
in thickness toward the bottom of the follicle. It is 
composed of nucleated epithelial cells which possess 
intercellular bridges and a fibrillar protoplasm. 
This sheath always stains heavily with nuclear dyes. TIII5 SKIN. 
329 
The inner root sheath is less conspicuous, and in good 
sections will be found to consist of an outer layer of 
two rows of non-nucleated elements, representing 
cornified epithelial cells and called Henle's layer, and 
Fig. 245.-Cross section of the human scalp, 
internal to this about two rows of nucleated cells, 
called Huxley's layer. These layers are absent from 
the upper half of the follicle. Internal to Huxley's 
layer, and in direct contact with the root of the hair, 
is the root sheath, which has much the same structure 
as the hair cuticle. Many scaly plates are imbricated 330 
NORMAL, HISTOLOGY AND ORGANOGRAPHY. 
upon each other and interlock with those of the hair 
cuticle in such a manner that if a hair is pulled out 
the root sheath comes away with it, the break taking 
place along Huxley's and Henle's layers. 
The hair papilla indents the lower end of the root 
and is of connective-tissue origin. It has a rich 
blood supply which contributes nourishment to the 
adjacent epithelial cells of the root which arc con- 
stantly dividing. It is this cell division that brings 
about the growth of a hair. If the papilla is de- 
stroyed the hair dies. When a hair is pulled out 
with its root the papilla and some adjacent epithelial 
cells usually remain uninjured. The epithelial cells 
in due time reproduce a new hair. 
The arrector pili muscle consists of bundles of 
smooth muscle fibers that pass obliquely downward 
from the upper surface of the dermis to be inserted 
in the connective-tissue tunic of the hair follicle near 
its lower extremity. The insertion of these fibers is 
always on the side toward which the hair inclines, so 
that when the fibers contract the root is drawn to a 
vertical position and the hair becomes erect. 
The hair on the scalp grows approximately at the 
rate of twelve inches a year, or one inch a month. 
The average duration of a hair is about four years. 
Many vertebrates, as horses and cattle, shed their 
hair annually, every spring, a phenomenon called 
moulting. In mankind the hair of the scalp is con- 
stantly dropping out and being replaced by growths 
of new shafts. Occasionally hair grows where it 
normally does not belong and for cosmetic effect 
requires removal. This is done by electrolysis, the; skin. 
331 
which consists in passing an electric needle down 
along the root of each hair to the hair papilla, which 
is then destroyed by a weak current of electricity. 
The hair is then readily removed and does not re- 
turn. The loss of hair on the scalp is due to a va- 
riety of causes, many of which we cannot explain. 
It often accompanies a prolonged illness, such as 
typhoid fever, and is then doubtless due to a general 
emaciation resulting in lack of proper nourishment 
of the scalp. The loss of hair in such cases is only 
temporary. Certain neurotic diseases result in a 
permanent loss and the same may be attributed to 
some germ diseases of the scalp that infest and de- 
stroy the hair papillae. In other cases baldness 
seems to be hereditary. It naturally follows that a 
healthy condition of the scalp will contribute to a 
rich growth of hair. Regular massage with a stiff 
brush no doubt accelerates the blood flow and thus 
brings about a better nourishment and growth to the 
hair. 
The natural preservation of hair after death is 
well known. In Egyptian mummies the hair is well 
preserved even to its natural color. The hair is thus 
an important factor in the identification of unknown 
deceased persons. 
THE NAILS. 
The nails are epidermal structures that are mor- 
phologically analogous to the hoofs and claws of 
lower animals. Each nail may be divided into a 
body, the part that is exposed, and the root that is 
hidden from view and lies in a fold of the skin. The 332 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
lateral margins are also covered by a fold of the skin 
called the nail 'wall. The nails have a pink color 
imparted by the subjacent blood, excepting near the 
root, where there is an opaque area called the lunula. 
The lunulae diminish in size from the thumb to the 
little finger. 
Each nail rests upon a very vascular dermis which 
has been called the nail bed. 
This connective-tissue bed 
has many fine longitudinal 
ridges and alternating 
grooves which fit closely 
into corresponding grooves 
and ridges on the lower sur- 
face of the nail. Each nail 
consists of two parts: a deep soft stratum that rep- 
resents the Malpighian layer of the epidermis, and an 
external hard cornified layer that represents the 
Fig. 246.-Thumb nail. 
Fig. 247.-Longitudinal section of nail. 
horny layer. The former consists of nucleated 
polygonal prickle cells which fill the furrows and 
cover the nail bed several cells deep. Under the 
root of the nail this layer is strongly developed 
and is called the matrix. It is from this matrix THE SKIN. 
333 
that the growth oi the nail takes place, and there- 
fore if the nail is to be permanently removed the 
matrix must be destroyed. This matrix ends an- 
teriorly in a curved line which forms the margin 
of the lunula already described. A stratum granu- 
losum is present in the upper portion of the matrix 
and absent in the other portions of the nail. 
The external cor- 
nified layer consists 
of flat epithelial 
scales in which rem- 
nants of a nucleus 
may frequently be 
found. Thesescales 
are derived from 
epithelial cells and 
overlie each other, forming hardened lamellae called 
nail leaves. 
THE GLANDS OF THE SKIN. 
Sweat glands are coiled simple tubular glands dis- 
tributed over the whole surface of the skin, with the 
exception of the inner surface of the prepuce, the 
glans penis, and the red borders of the lips. In the 
axilla and around the anal opening they are excep- 
tionally large and often branched. They are most 
numerous on the palm of the hand and the sole of 
the foot, where they number two thousand seven 
hundred to the square inch. On the forehead there 
are one thousand two hundred, and on the cheek 
about five hundred to the square inch, while over the 
back they are the least numerous. Their total num- 
Fig. 248.-Cross section of nail 334 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
ber over the whole body has been estimated at nearly 
two million four hundred thousand, which, with an 
average length of an inch, makes the united length 
approximately two and one-half miles. This vast 
secreting surface is constantly secreting moisture, 
either as insensible or sensible perspiration. The 
amount of this perspiration within a given time 
Fig. 249.-Undersurface of the epidermis, separated from the cutis 
by boiling. The sweat glands may be traced for a considerable part 
of their length; a, Sweat gland ; b, longitudinal ridge; c, depression, 
d, cross ridge (Bohm and Davidoff). 
varies considerably, but in the average person in 
good health it is estimated at about two pints every 
twenty-four hours. 
The excretory ducts open on the surface of the 
skin by numerous sweat pores along the crests of the 
epidermal ridges. These pores are barely visible to 
the naked eye. The duct is spirally twisted in the 
stratum corneum and enters the dermis between two THE SKIN. 
335 
dermal papillae; that is, at the apex of an epidermal 
papilla. In the dermis it takes a sinuous or nearly 
straight course and penetrates to the lower stratum 
of the skin, or even deeper, to the subcutaneous con- 
nective tissue. This distal end is very much coiled 
and constitutes the secreting portion of the gland. 
In the epidermis the duct has no other wall than the 
epithelial cells of the various layers through which 
it passes, but in the dermis the wall is composed of a 
single layer of short cubical cells outside of which 
there is a delicate basement membrane. The se- 
creting portion is also 
lined by simple epithe- 
lium, but the cells are 
larger and have a fine- 
ly granular protoplasm. 
Between the gland cells 
and the basement mem- 
brane there is found in 
the larger glands, a single 
layer of lion-striated mus- 
cle cells arranged longitudinally. This muscle 
is derived from the ectoderm, being modified 
epithelial cells. All the other musculature in 
the body comes from the mesoderm. The muscle 
of the sweat glands probably aids these glands in ex- 
pelling their products of secretion. Non-medullated 
nerve fibers of the sympathetic system form a deli- 
cate network just external to the basement mem- 
brane called the epilamellar plexus. From this 
plexus delicate fibers pass through the basement 
Fig. 250.-Cross section of deep 
portion of sweat gland. 336 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
membrane to ramify between the gland cells, where 
they end in clusters of small terminal granules. The 
physiological activities of the sweat glands is thus 
directly under the control of the nervous system 
and does not depend on the blood supply, a fact 
that may also be demonstrated by physiological 
experiments. 
Fig. 251.-Model of a sebaceous gland with a portion of the hair 
follicle, reconstructed by Born's wax-plate method (Huber). 
Sebaceous glands are associated with hair follicles, 
into which they pour their contents. They are also 
found on the red borders of lips, the labia minora, 
the glans and prepuce, where hairs are absent. 
They are simple branched alveolar glands that se- 
crete an oily substance called sebum. This is a THE SKIN. 
337 
fluid at the temperature of the body, keeps the skin 
soft and flexible, and also supplies a natural dressing 
for the hair. In the scalp there may be an exces- 
sive secretion of sebum which dries and exfoliates 
with the horny epidermis as dandruff. 
Each hair follicle has two or more sebaceous 
glands that vary in size from 0.2 to 0.5 mm. The 
excretory duct is short and wide and opens into the 
upper third of the follicle. This duct is lined by 
stratified epithelium that is directly continuous with 
the outer root 
sheath of the hair 
follicle. The cells of 
the alveoli are very 
large and contain fat 
globules that vary 
in size and give a 
reticular appearance 
to the cytoplasm. 
The nuclei are rela- 
tively small. The 
cells completely fill 
the alveoli so that the latter appears to be solid. 
The cells disintegrate and change directly into secre- 
tion, which is then poured into the follicle as sebum. 
The renewal of lost cells takes place by constant 
proliferation of basal cells. 
It is quite common in the scalp to find sebaceous 
cysts, or wens, which result from an occlusion of the 
duct and an enlargement of the gland. These cysts 
are lined by a simple layer of epithelium and filled 
with a white, waxy, or semisolid fluid quite analo- 
Fig. 252.-Section of two alveoli of a 
sebaceous gland. 338 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
gous to the sebum. Wens are of slow growth and 
cause no disturbance, unless they get very large or 
become infected by being carelessly opened. The 
radical cure consists in their complete removal, in- 
cluding the epithelial wall. CHAPTER XI. 
PERIPHERAL NERVE TERMINATIONS. 
Physiologically, nerve endings may be classified as 
motor or sensory. 
MOTOR NERVE ENDINGS. 
(The Telodendria of Nerve Fibers in Muscle Tissue.) 
i. In Striated Muscle.-The nerve endings in stri- 
ated muscle are called muscle-end plates, or sole plates. 
In the higher vertebrates these are found in the 
muscle sarcoplasm just beneath the sarcolemma of 
each muscle fiber. A motor nerve fiber as it ap- 
proaches its termination becomes much branched 
so as to innervate from ten to twenty muscle fibers. 
The axis cylinder enters the sarcoplasm where it im- 
mediately terminates in a web-like, flat end-brush with 
numerous dilatations. The axilemma, or Henle's 
sheath, is continuous around the brush. The me- 
dullary layer stops short at the level of the sarco- 
lemma; that is, at the surface of the sarcoplasm. 
The neurolemma is continuous with the sarcolemma 
of the muscle fiber. The adjacent sarcoplasm of the 
muscle fiber is granular and a liberal supply of muscle 
nuclei is also present in the proximity, which results 
in an elevation of the muscle fiber at the point of 
nerve contact known as Doyer's elevation. 
339 340 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
2. In non-striated and in heart muscle the nerve 
termination is more simple. The muscle is supplied 
with neurons from the sympathetic system, most of 
which are of the non-medullated variety. These 
fibers branch repeatedly to form an extensive 
Fig. 253.-Motor endings in striated voluntary muscles. From 
Pseudopus Pallasii. Asa consequence of the treatment the arborescence 
is shrunken and interrupted in its continuity. The end plate is in con- 
nection with two nerve branches (Bohm and Davidoff). 
primary plexus surrounding the muscle bundles. 
From this plexus non-medullated fibers, that is, 
just the axis cylinders, penetrate the heart muscle, 
or the involuntary muscle, where they anastomose 
to form a delicate secondary plexus, from which lat- 
eral short twigs pass to end in minute dilatations or 
granules upon the muscle cells. PERIPHERAL NERVE TERMINATIONS. 
341 
SENSORY NERVE ENDINGS. 
(IWodendria of Dendrites.) 
The sensory nerve terminations are essentially 
the terminals of dendrites as distinguished from the 
motor plates which are the terminals of axones. 
The cell bodies of these sensory neurons are found 
in the spinal and cranial ganglia, often at a consid- 
erable distance from the sensory termination. In 
Fig. 254.-Motor nerve ending on 
heart muscle cells of cat; methylene- 
blue stain (Huber, De Witt). 
Fig. 255.-Motor nerve 
ending on involuntary non- 
striated muscle cell from 
intestine of cat; methy- 
lene-blue stain (Huber, 
De Witt). 
this case the dendrite is a long one, medullated, and 
structurally identical with an axis cylinder or axone. 
The nerve impulse is, however, normally carried 
toward the nerve cell, while in axones the impulse 
goes the opposite way. As stated in another place, 
such sensory neurons have a long dendrite that ex- 
tends peripherally and a short axone that passes 
centrally; that is, to the spinal cord or brain. 342 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
These sensory endings form tclodendria or end- 
brushes that vary in complexity according to the 
tissue elements that take part in their formation. 
i. Free Sensory Nerve Endings.-These are the 
simplest forms of nerve endings and occur in epi- 
Fig. 256.-Nerves of epidermis and papilla from ball of cat's foot 
(Bohm and Davidoff). 
thelial tissues and in some parts of the connective 
tissues. The sensory nerve fibers near its termina- 
tion repeatedly branch, the latter retaining the 
medullary sheath. The branches appear always at 
the nodes of Ranvier. From this coarse plexus a PERIPHERAL nerve terminations. 
343 
finer non-medullated system of branches appear 
which innervate the epithelium and terminate in 
varicosities, discs, or minute granules that lie in appo- 
sition to epithelial 
cells. Similar free 
terminations occur 
in tendons, and liga- 
ments, and other 
fibrous connective 
tissue. 
2. Tactile Cells.-These are also called Grandry's 
corpuscles, and may be found in the duck's bill just be- 
neath the gum- 
my epithelium. 
The cells are of 
epithelial origin, 
oval, and meas- 
ure about 50 // in 
diameter. One 
to five cells are 
surrounded by a 
connective-tis- 
sue capsule. 
These cells are 
superposed o n 
each other, with 
their long axes 
always parallel 
to the surface of 
the bill. A me- 
dullated nerve fiber may be traced to the cap- 
sule, which it penetrates and then becomes non- 
Fig. 257.-Tactile cells from the bill of a 
duck. 
Fig. 258.-Corpuscle of Herbst from bill of 
duck (Bohm and Davidoff). 344 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
medullated. The latter terminates in tactile discs 
that are interposed between the tactile cells. A 
group of three cells will have two discs; five cells 
will have three discs. 
3. Corpuscles of Herbst.-These are much larger 
bodies and may also 
be found in the bills 
of aquatic birds, in 
close association 
with the tactile cells 
just described. 
They are ovoid 
bodies 75 /i wide and 
150 [i long. There 
is an inner core sur- 
rounded with con- 
nective-tissue lamel- 
lae. The core con- 
tains the axis cylin- 
der, which is thick- 
ened at the end and 
is encased between 
two rows of cells that 
seem to have the 
same function as 
Grandry's corpus- 
cles. The nerve fiber 
enters at the end of the corpuscle and becomes 
non-medullated only after reaching the inner core. 
4. Meissner's Corpuscles.-These are found beneath 
the epidermis of man, particularly of the hand and 
foot, and occupy the dermal papillae of the dermis. 
Fig. 259.-Meissner's tactile corpus- 
cle; methylene-blue stain (Dogiel, "In- 
ternat. Monatsschr. f. Anat. u. Phys.," 
vol. ix). PERIPHERAL NERVE TERMINATIONS. 
345 
They are oval bodies and approximately the same 
size as the corpuscles of Herbst. There is a thin 
connective-tissue capsule and a loose complex core. 
One or more medullated nerve fibers enter at the 
lower end of the corpuscle. These soon become 
non-medullated and their axoncs then make a vari- 
able number of spiral turns which interlace, branch, 
and are beset with 
many granules or 
varicosities. One 
or more axis cyl- 
inders occupy the 
center of the core. 
5. Genital Cor- 
puscles. - These 
are oval or round 
bodies located in 
the mucosa, just 
beneath the epi- 
thelium of male 
and female geni- 
talia. Their size 
varies from o. 1 
mm. to 0.4 mm. 
They are sur- 
rounded by a thick fibrous capsule and each cor- 
puscle is innervated by one to ten medullated nerve 
fibers. The latter become non-medullated after 
passing through the capsule, and the axones then 
form a complex core quite analogous to that of 
Meissner's corpuscle. In fact, the two are very 
similar structures. 
Fig. 260.-Genital corpuscle from the 
glans penis of man; methylene-blue stain 
(Dogiel, " Arch. f. mik. Anat.," vol. xli.) Fig. 261.-Pacinian corpuscle from mesentery. 
Fig. 262.-Neuromuscular nerve-end organ from the intrinsic plantar 
muscles of dog; from teased preparation of tissue stained in methylene- 
blue. The figure shows the intrafusal muscle fibers, the nerve fibers and 
their terminations; the capsule and the sheath of Henle are not shown 
(Huber and De Witt, "Jour. Comp. Neurol.," vol. vn). 
346 PERIPHERAL NERVE TERMINATIONS 
347 
6. Pacinian Corpuscles.-These are oval bodies 
and the larger ones are easily 
visible to the naked eye, being 
over 2 mm. long. Structurally 
they seem related to the corpus- 
cles of Herbst. They are found 
in the dermis of the hand and 
foot, particularly along the lower 
surface of the fingers and toes. 
They are also found in the joints, 
the peritoneum, pleura, pericar- 
dium, and are especially abun- 
dant in the mesentery. The 
greater portion of the corpuscle 
consists of concentric lamellae of 
connective-tissue origin. Be- 
tween these flat endothelial cells 
intervene. A granular core 
forms the axis of the corpuscle, 
in the center of which the axis 
cylinder maybe traced. Usually 
one large nerve fiber goes to each 
corpuscle. After entering the 
core this forms a plexus of fine 
branches and becomes non-med- 
ullated. 
7. Tendon and Muscle Spin- 
dles.-A tendon spindle is an ex- 
pansion of tendon bundles en- 
closed in a well defined connec- 
tive-tissue sheath. The nerve 
fiber enters the middle of the spindle, divides re- 
Fig. 263.-Neuroten- 
dinous nerve-end organ 
from rabbit; teased 
preparation of tissue 
stained in methylene- 
blue (Huber and De 
Witt, "Jour. Comp. 
Neurol.," vol. x). 348 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
peatedly, becomes non-medullated and finally ter- 
minates in varicosities or expanded clavate ends. 
The muscle spindle is a collection of delicate muscle 
fibers enveloped in a dense perimysium sheath, the 
whole being innervated by sensory nerve endings 
much as in tendon spindles. The sensory endings 
both in tendon and muscle transmit the sensation 
of extension which becomes the basis for coordinate 
movements. CHAPTER XII. 
THE SPINAL CORD. 
The spinal cord is an organ composed largely of 
neurons, with which are associated blood-vessels, 
connective-tissue elements, and a limited amount of 
epithelial and muscle cells. It represents the ter- 
minal portion of the cerebrospinal axis and is a 
direct continuation of the encephalon. It is one of 
the first organs to develop in the embryo where it 
makes its appearance as a dorsal ectodermal groove. 
This neural groove gradually closes to form a canal 
which lies at first just beneath the ectoderm and 
later becomes encased in connective-tissue layers and 
the bony axial skeleton. 
The cord is bilaterally symmetrical and flattened 
dorso-ventrally. It presents two enlargements: 
(i) the upper or cervical, which extends from the 
third cervical vertebra to the second thoracic and 
corresponds to the origin of the nerves of the arm, and 
(2) the lower or lumbar, which extends from the 
ninth thoracic vertebra to the terminal cone at the 
level of the body of the second lumbar vertebra. 
The lumbar enlargement marks the origin of the 
nerves of the leg. From the apex of the terminal 
cone there extends a slender rudimentary prolonga- 
tion, the filum terminale, which, with the spinal 
nerves of this region, is called the cauda equina. The 
349 350 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
spinal cord, therefore, does not extend the whole 
length of the vertebral canal but only to the level of 
the second lumbar vertebra. Its length is about 
eighteen inches, its diameter one-half inch or less. 
Membranes of the Cord or Meninges.-i. The 
Dura.-This is a thick strong membrane composed of 
Fig. 264.-Portion of spinal cord and membranes dissected. 
white fibrous tissue which forms the outer covering 
of the cord. Many blood-vessels find lodgment in 
this membrane. It is analogous and continuous 
with the dura of the brain, the most striking differ- 
ence being that the dura of the cord does not form THE SPINE. 
351 
the internal periosteum of the vertebral canal. Be- 
tween the dura and the vertebrae is a space called 
the epidural space, which is filled with areolar tissue, 
fat, and a plexus of spinal veins. 
2. The Pia.-This is a thin connective-tissue 
layer that lies close to the surface of the cord, dips 
into the anterior fissure, and also sends fibers or 
trabeculae into the cord substance. Many small 
blood-vessels accompany this layer. 
3. The Arachnoid.-This is a delicate membrane 
between the other two, but much nearer the dura. 
Its external surface is clothed with a single layer 
of flat epithelial cells which secrete a serous fluid. 
The arachnoid is therefore a serous membrane. 
Fissures.-1. Posterior Median Fissure.-This is. a 
median dorsal fissure that extends the whole length 
of the cord. It is extremely narrow but deep, as it 
penetrates to the central gray matter, being inti- 
mately connected with the two sides in its course. 
The single septum is derived from the neuroglia tis- 
sue, and not from the pia, which sends no prolonga- 
tion of any kind into it. 
2. Anterior Median Fissure.- This also extends 
the whole length of the cord. It is shallower but 
wider than the posterior fissure and does not quite 
reach the central gray matter. The pia forms a 
fold into this fissure with which is associated many 
blood-vessels. The two median fissures or clefts 
divide the cord into a right and a left half, each 
practically identical with the other. 
3. Postero-lateral Groove.--This is a shallow de- 
pression on each side of the posterior fissure and 352 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
marks the entrance into the cord of the dorsal roots 
of the spinal nerves. In a like position, anteriorly, 
is the exit of the anterior roots of the spinal nerves, 
but there is no depression or groove as in the case of 
the posterior roots. The two roots of the spinal 
nerves divide each half of the spinal cord into three 
regions or major tracts known as the posterior, 
Fig. 265.-Schematic diagram of the spinal cord in cross section after 
von Lenhossek, showing in the left half the cells of the gray matter, in 
the right half the collateral branches ending in the gray matter (Huber). 
lateral, and anterior columns. The posterior column 
is limited by the posterior fissure and the posterior 
roots, the lateral is the region between the roots, 
and the anterior lies between the anterior root and 
the anterior fissure. 
Spinal Nerves - Thirty-one pairs of nerves arise 
from the side of the cord. These are classified into THE SPINE. 
353 
8 cervical, 12 dorsal, 5 lumbar, 5 sacral, and 1 coc- 
cygeal. Each nerve is attached to the cord by a 
dorsal and a ventral root. Each root, before uniting 
with the cord, breaks up into secondary bundles and 
spreads out like a fan, making a continuous linear 
attachment. The dorsal ganglion is located upon 
the dorsal within the vertebral canal, near the union 
of the two roots. 
Gray Matter of the Cord.-The gray matter of the 
cord is centrally located and takes the form of a 
capital letter H. The gray matter in each lateral 
half resembles a crescent which is joined to the op- 
posite side by an isthmus, in the center of which is 
the central canal. The latter is usually obliterated 
in the adult man, and is filled as well as surrounded 
by the gelatinous substance of Rolando, which is a 
reticular structure. That part of the isthmus above 
the central canal is called the posterior gray com- 
missure, while the gray matter ventral to the canal 
is the anterior commissure. 
Each crescent may be divided into a posterior, 
lateral, and anterior horn. The anterior horn is the 
largest and the lateral horn is the smallest. The 
posterior horn is pointed and approaches near to the 
posterior lateral groove. The apex of this horn is 
called the zona terminalis. At the base of this apex 
there is a reticular substance called the zona reticu- 
laris, while next to this and apparently capping the 
posterior horn is a gelatinous mass, similar to that 
which surrounds the central canal, called the sub- 
stantia gelatinosa of Rolando. 
The nerve cells of the posterior horn are irregularly 354 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
distributed and some of them are particularly small 
and have a stellate appearance. At the base and 
mesial surface of this horn there is a group of large 
nerve cells called the column of Clarke. This column 
extends from the second lumbar up through the 
dorsal region of the cord to the cervical. In the 
cervical region it is absent; however, Stilling's nu- 
cleus of this region may represent a remnant of the 
column of Clarke. At the base of the dorsal horn, 
deeper down and lateral to Clarke's column, another 
group of nerve cells may be found that is called 
Waldeyer's central cell column. This is reciprocal 
with Clarke's column; that is, in the dorsal region 
where Clarke's column is conspicuous, only rem- 
nants of Waldeyer's tract can be found, while in the 
other regions of the cord this cell tract is particu- 
larly prominent. 
The lateral horn is a small lateral prominence at 
the side of the gray crescent. In the substance of 
this, a small collection of nerve cells may be found, 
while just beneath this a number of nerve fibers pass 
out into the white matter. These have been called 
the processus reticularis. 
The anterior horn is not only large but presents a 
blunt, rounded appearance. The nerve cells of this 
horn are very large and have been classified according 
to their position into antero-mesial, postcro-mesial, 
antcro-lateral, and postero-lateral. The axis cylin- 
der of most of these cell bodies goes to form the an- 
terior root of the spinal nerves. They therefore 
carry only motor impulses. 
White Matter of the Cord.-The white matter of THE SPINE. 
355 
the cord consists of medullated nerve fibers. Most of 
these fibers have no neurilemma, and the cord there- 
fore is soft and pulpy, in contrast to the nerve 
trunks whose fibers have a neurilemma which with 
the connective-tissue elements make nerves tough 
and strong. The white matter practically encloses 
the gray. The fibers which compose it vary com 
Fig. 266.--Cross section of the spinal cord, dorsal region. 1, Zona 
terminalis; 2, zona reticularis; 3, substantia gelatinosa of Rolando; 4, 
stellate cells of posterior horn; 5, column of Clarke; 6, Waldeyer's 
central cell column; 7, cells of lateral horn; 8, central canal; 9, antero- 
mesial cells; 10, postero-mesial cells; n, antero-lateral cells; 12, pos- 
tero-lateral cells. 
siderably in size, both large and small being mixed 
up together. In sections of the adult healthy cord 
no evidence of definite tracts of fibers can be seen. 
We know, however, that longitudinally arranged 
groups of fibers run a definite course, have definite 
connections, and carry impulses that result in defi- 
nite sensations and actions. The physiological evi- 356 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
dence of this fact is experimental and positive. A 
nerve fiber detached from its cell body dies. In 
this way tracts will degenerate in the cord, some 
above and some below a transverse cut. The em- 
bryological evidence rests on equally positive facts. 
In development certain tracts acquire medullary 
Fig. 267.-Cross section of the spinal cord, lumbar region. 1, zona 
terminalis; 2, zona reticularis; 3, substantia gelatinosa of Rolando; 4, 
stellate cells of posterior horn; 5, column of Clarke; 6, Waldeyer's cen- 
tral cell column; 7, cells of lateral horn; 8, central canal; 9, antero- 
mesial cells; 10, postero-mesial cells; n, antero-lateral cells; 12, postero- 
lateral cells. 
sheaths earlier than others. This fact has greatly 
extended our knowledge of the white matter in the 
cord. The pathological evidence is a third factor. 
Certain diseases produce degenerate lesions in the 
cord. Proper interpretations of these lesions have 
enabled us to map out definite nerve tracts in the 
cord, and to determine their relations as well as pos- THE sriNE. 
357 
sible functions. The information evolved from 
these sources makes a classification of tracts, in the 
cord, possible. 
Tracts of the Cord.-Posterior Region. 
i . Column of Goll.-This lies adjacent to the dorsal 
fissure and extends the whole length of the cord. 
Its fibers arborize about nerve cells in the nucleus 
gracilis of the lower region of the medulla. 
2. Column of Burdach.-This extends parallel to 
the column of Goll between the latter and the pos- 
terior horn of gray matter. It extends the whole 
length of the cord and its fibers arborize about nerve 
cells in the nucleus cuneatus of the medulla, adjacent 
to the nucleus gracilis. The column of Goll becomes 
wider in the upper portions of the cord and that of 
Burdach narrower. This is due to nerve fibers that 
gradually pass into the column of Goll from the col- 
umn of Burdach on their way to the brain. 
3. Comma Tract.-This is a small tract found in 
the column of Burdach, and represents sensory 
fibers from the posterior roots of the spinal nerves 
that pass down the cord for a short distance, and 
then turn into the anterior horn of gray matter to 
arborize about nerve cells of this region. 
4. Lissaur's Marginal Ground Bundle.-This is a 
small commissural tract placed near the surface of 
the cord just lateral to the entrance of the posterior 
root fibers. It is formed by some of the fibers of 
this root. The tract extends the whole length of 
the cord, but each individual fiber runs but a short 
distance and then turns inward to arborize about 
nerve cells of the posterior horn. 358 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
These four tracts are composed almost entirely of 
nerve fibers that enter the cord by the posterior 
roots of the spinal nerves. They are therefore sen- 
sory tracts and forward impulses toward the brain. 
The termination of the postcrier root fibers may be 
enumerated as follows: 
i. Column of Goll, Burdach, comma tract, Lis- 
saur's tract. 
2. Arborize about the cells in Clarke's column. 
3. Arborize about the cells in posterior horn. 
4. Arborize about the cells in anterior horn on 
same and opposite side. 
Lateral Region.-The tracts of this region are: (1) 
Direct Cerebellar; (2) Gowers's, or Ascending Antero- 
lateral; (3) Crossed Pyramidal; (4) Lowenthal's, 
or Antero-lateral Descending; (5) Mixed Lateral. 
1. The Direct Cerebellar.-This is a band of fibers 
that lies at the surface of the cord just lateral to the 
dorso-lateral groove. Its nerve fibers arc derived 
from the cells of the column of Clarke, consequently 
the tract extends from the last dorsal up to the 
medulla on the same side. It is an ascending or 
sensory tract, and, as it is traced upward, becomes 
wider from the acquisition of axones from the col- 
umn of Clarke. It enters the cerebellum through 
the inferior peduncle and finally terminates in the 
cerebellar cortex of the superior worm on both sides, 
chiefly the opposite. 
2. Gowers's tract lies just in front of the direct 
cerebellar and also at the surface of the cord. It is 
an ascending or sensory tract and some of its fibers 
are supposed to reach the cerebellum by passing THU SPINE. 
359 
through the formatio reticularis of the medulla, and 
making a backward turn through the superior med- 
ullary velum of the same side. 
Other fibers of this tract have been traced to the 
corpora quadrigemina, the thalamus, substantia 
nigra, and the lenticular nucleus of the cerebrum. 
The fibers of this tract extend the whole length of 
Fig. 268.-Cross section of spinal cord cervical region. 1, Zona ter- 
minalis; 2, zona reticularis; 3, substantia gclatinosa of Rolando; 4, 
stellate cells of posterior horn; 5, column of Clarke; 6, Waldeyer's cen- 
tralcellcolumn; 7, cells of lateral horn; 8, central canal; 9, antero-me- 
sial cells; 10, postero-mesial cells; 11, antero-latcral cells; 12, postero- 
lateral cells. 
the cord and probably have their origin in the cells 
of the posterior horn. 
3. The crossed pyramidal tract is a large and 
well-defined bundle that lies just beneath the direct 
cerebellar; that is, between this and the posterior 
horn. Below the point where the direct cerebellar 360 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
begins, the crossed pyramidal comes to the surface 
of the cord. The fibers of this tract have their origin 
in the large pyramidal cells of the cerebrum in the 
region of the area of Rolando. Traced downward 
from this source, they cross in the lower part of the 
medulla to the opposite side of the cord, making at 
this point the motor decussation. As it descends the 
tract gradually diminishes in size, due to the fact 
that fibers leave it to arborize around the large 
motor cells of the anterior' horn. In this way the 
entire tract is ultimately exhausted near the lower 
extremity of the cord. It is thus a descending or 
motor tract that governs the opposite side of the 
body from where it has its origin. 
4. Lowenthal's tract is closely associated with 
Gowers's. Its position is anterior and mesial to 
Gowers's, encroaching some upon the anterior region 
of the cord. The fibers of this tract are supposed to 
come from cells in Deiters' nucleus of the medulla 
which may be regarded as an internode between the 
cerebellum and the medulla. This tract descends 
as far as the lumbar region and its fibers are supposed 
to arborize around the motor cells of the anterior 
horn of the spinal cord. 
5. The mixed lateral bundle represents the re- 
mainder of the lateral region. Its fibers probably 
come from cells in all parts of the gray matter of the 
cord, and from cells on the opposite side of the cord. 
At intervals these fibers ultimately reenter the gray 
matter and arborize about nerve cells. It is there- 
fore an intersegmental or commissural tract, both 
sensory and motor. THE SPINE. 
361 
Anterior Region. 
i. Direct Pyramidal Tract.-This is a small well- 
defined tract that lies next to the antero-median 
fissure. As a rule this tract can only be traced down 
to the middle of the dorsal region. These fibers 
originate jointly with those of the crossed pyramidal 
tract; that is, from the large pyramidal cells of the 
cerebral cortex. The fibers, however, do not cross 
in the medulla but pass directly down the cord on 
the same side. The fibers cross in the cord at inter- 
vals in its course, making use of the anterior com- 
missure to reach the opposite side, where they ar- 
borize around the cells of the anterior horn in a 
manner like those of the crossed pyramidal. It 
thus follows that the motor cells on one side of the 
cerebrum control the muscular contraction on the 
opposite side of the body, either through the crossed 
or the direct pyramidal tract or through both. 
2. The anterior ground bundle is really a part of 
the mixed lateral tract already described. It is 
composed of ascending and descending fibers that 
have both their origin and their termination in the 
gray matter of the cord and is therefore an inter- 
segmental or commissural tract. 
3. Anterior White Commissure.-This is composed 
of medullated nerve fibers passing parallel to the 
gray commissure between the latter and the bottom 
of the anterior fissure. It is a decussation of fibers 
of a mixed variety, many of them being derived 
from the direct pyramidal tract as already stated. CHAPTER XIII. 
THE BRAIN. 
The brain, or encephalon, develops jointly with 
the spinal cord, and represents the anterior extremity 
of the cerebrospinal axis. The average weight of 
the brain is about forty-eight ounces, while the cord 
weighs less than one ounce. Like the cord it is an 
organ in which all the elementary tissues may be 
found but in which the neurons predominate. 
During embryonic growth the brain and cord are a 
hollow tube and this cavity is never obliterated r but 
remains in the brain as its ventricles. Develop- 
mental history further discloses the fact that the 
brain, like the cord, is made up of definite segments 
or joints called neuromeres. These primary units 
are soon replaced by three larger vesicles called 
primary fore-brain, mid-brain, and hind-brain. It 
is generally affirmed that the first of these repre- 
sents 3 neuromeres, the second 2 neuromeres, and 
the third 6 neuromeres. Later the primary fore- 
brain divides to form the cerebrum and the 'tween- 
brain, while the hind-brain also divides to form the 
cerebellum and medulla. In the adult brain, there- 
fore, five divisions may be recognized, each of them 
presenting a central canal or cavity as designated in 
the table below: 
362 THE BRAIN. 
363 
Primary Divisions. 
Fore-brain or prosen- 
cephalon 
1. Telencephalon or cerebrum. 
2. Thalamencephalon, or dien- 
cephalon, or 'tween-brain. 
Secondary Divisions. 
Cavity. 
Lateral ventricle. 
Third ventricle. 
Mid-brain. 
Hind-brain or rhomb- 
encephalon 
3. Mesencephalon or mid-brain. 
4. Metencephalon or cerebel- 
lum. 
5. Myelencephalon or medulla. 
Aqueduct of Sylvius 
Upper part of fourth 
ventricle. 
Fourth ventricle. 
The brain is thus a hollow multiple organ. Its 
central cavity is lined with a serous membrane, the 
ependyma, which secretes a serous fluid, the cerebro- 
spinal fluid. The outer vascular investments are the 
meninges, which serve as a delicate packing between 
the brain wall and the bony vault of the cranium. 
The Meninges.-These are three connective-tissue 
investments to the brain that are practically identical 
and continuous with those already described inclos- 
ing the cord. It will be sufficient, therefore, to men- 
tion the points wherein these membranes slightly 
differ. 
The dura of the brain forms the periosteum of the 
investing bones, while each segment of the vertebral 
column has its own periosteum. Several broad 
prolongations of the brain dura extend between the 
different divisions of the brain. These are the ten- 
torium between the cerebrum and the cerebellum; 
the falx cerebri which dips into the great fissure be- 
tween the two lobes of the cerebrum, and the falx 
cerebelli, which is a small median septum between 
the cerebellar hemispheres. At the basal skull fora- 
mina, the dura accompanies the cranial nerves and 
is continuous with the areolar sheaths of these 
nerves. 
The pia is composed mostly of areolar tissue and 364 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
small blood-vessels. It is the nourishing tissue of 
the brain and clothes its entire surface, dipping 
down to the bottom of fissures, and sending strands, 
associated with blood-vessels, into the brain sub- 
stance. The brain pia is more vascular than that of 
the cord. 
The arachnoid is a web-like membrane between the 
dura and the pia, but much nearer the dura. The 
space beneath the dura is called the subdural space, 
and is small. That between the arachnoid and pia 
is larger and is called the subarachnoid space. The 
former has a little serous fluid, and the latter is filled 
with lymph and some cerebrospinal fluid. This 
fluid reaches the external surface of the brain through 
a small foramen or pore in the thin roof of the fourth 
ventricle. Trabeculae intervene between all these 
membranes. 
THE MEDULLA. 
The medulla is about one inch in length, and rep- 
resents the continuation of the spinal cord. Its 
lower extremity is at the lower margin of the fora- 
men magnum. From this point it passes upward 
in nearly a vertical direction to its upper extremity 
at the lower border of the pons. Being the nerve 
center for the large cranial nerves, the medulla is the 
most vital part of the brain, and the best protected. 
Its lower portion resembles the cord, having the same 
fissures and grooves. The upper portion is ex- 
panded in such a manner as to bring its cavity or 
fourth ventricle to the dorsal surface. This ex- 
panding process has carried the dorsal tracts later- THE BRAIN. 
365 
ally, leaving a very thin roof, consisting of the 
ependyma and a vascular pia, to cover the ventricle. 
The lower half of the fourth ventricle is found in the 
upper half of the medulla, while the upper half of 
this ventricle extends into the pons region and is 
overlaid by the cerebellum. The central canal of 
the cord opens into the lowest point of this ventricle 
and therefore extends through the lower half of the 
medulla, but nearer its dorsal surface. The lower 
Fig. 269.-Dorsal view of the medulla, pons and mid-brain. 
half is therefore spoken of as the closed 'medulla 
while the upper part, that has the ventricle, is 
called the open medulla. 
Two ridges, the funiculus gracilis and funiculus 
cuneatus, may be recognized on the dorsal surface of 
the medulla, and represent the continuation of the 
columns of Goll and Burdach. The funiculus gra- 
cilis terminates anteriorly in a blunt expansion 366 
NORMAL HISTOLOGY AND ORGANOGRAPHY 
called the clava. On the dorsal aspect of the 
open medulla is 
found the restiform 
body, which passes in- 
to the inferior pedun- 
cle of the cerebellum 
and represents fiber 
tracts, the most im- 
portant being the di- 
rect cerebellar tract. 
The lower half of the 
fourth ventricle is V- 
shaped and its apex 
is called the calamus 
scriptorius, from its 
resemblance to a pen. 
In its floor three tri- 
angular areas are 
found, called trigo- 
num vagi, trigonum 
hypoglossi, and area 
acusticce. It is in 
these areas that we 
find, respectively, the 
origin of the tenth, 
twelfth, and eighth 
cranial nerves. The 
striae acusticce are 
transverse ridges in 
the floor of this ventri- 
cle, extending across 
its middle part from 
the median sulcus to 
Fig. 270.-View, from below, of the 
connection of the principal nerves 
with the brain: I', the right olfactory 
tract; II, the left optic nerve; II', the 
right optic tract (the left tract is seen 
passing back into i and e, the internal 
and external corpora geniculata); 
III, the left oculomotor nerve; IV, the 
trochlear; V, V, the large roots of the 
trifacial nerves; -|-the lesser roots 
(the + of the right side is placed on 
the Gasserian ganglion); 1, the oph- 
thalmic; 2, the superior maxillary; 
and 3, the inferior maxillary divi- 
sions; VI, the left abducens nerve; 
VII, VIII, the facial and auditory 
nerves; IX-XI, the glossopharyngeal, 
pneumogastric, and spinal accessory 
nerves; XII, the right hypoglossal 
nerve; C,, the left suboccipital or first 
cervical nerve (Nancrede). THE BRAIN. 
367 
the lateral margins, and represent nerve libers of 
the eighth cranial nerve. 
On the lateral surface of the medulla a prominent 
oval elevation appears called the olivary body, 
which represents a crescent collection of nerve cells. 
Just dorsal to the olivary body is the continuation 
of the dorsal groove of the cord, and it is from this 
groove that fibers of the ninth, tenth, and eleventh 
cranial nerves emerge. Near the anterior extremity, 
at the lower margin of the pons, is the superficial 
origin of the seventh and eighth nerves. The origin 
of these nerves corresponds to the entrance into the 
cord of the posterior root of the spinal nerves. Just 
median or ventral to the olive is a groove that cor- 
responds to the points of exit of the anterior root of 
the spinal nerves. From this groove the fibers of 
the twelfth cranial nerve escape. 
The ventral region of the medulla presents a 
median fissure, the continuation of the anterior 
fissure of the cord. The upper end of this fissure 
forms a pit at the lower margin of the pons, called 
the foramen cecum. Just lateral to this cecum, and 
curving around the pons, is the superficial origin of 
the sixth pair of cranial nerves. On each side of the 
median fissure is a longitudinal ridge called the pyr- 
amids which represents the fibers of both the crossed 
and the direct pyramidal tract. Near the lower ex- 
tremity of the medulla the fissure seems partly 
obliterated by ridges recrossing. These represent 
pyramidal fibers crossing to form the crossed pyr- 
amidal tract, and constitute, therefore, the motor 
decussation. Just below the olive curved striae may 368 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
be seen, that appear to come from the median fissure 
and sweep around the olive and enter the cerebellum 
through the restiform body and inferior peduncle. 
These are called the superficial arcuate fibers, and 
many of them come from the nerve cells of the olive 
of both the same and the opposite sides. 
Sections of the Medulla. - Cross Sections of the 
Closed Medulla.-These verify the surface markings 
Fig. 271.-Cross section of the closed medulla. 
already described. In the dorsal region is the funiculi 
gracilis and cuneatus, fiber tracts of the columns 
of Goll and Burdach. Beneath these are the nuclei 
of gracilis and cuneatus, nerve cells around which 
arborize the telodendria of the fibers of the columns 
of Goll and Burdach. From these nerve cells axones 
spring that sweep downward and across to the oppo- 
site side, and in crossing form the sensory decussa- THE BRAIN. 
369 
tion. It thus happens that the sensory impulses also 
cross and reach the opposite side of the brain. Ex- 
ternal to the nucleus gracilis is the substantia gelati- 
nosa of Rolando, a continuation of that of the cord. 
Just external to this is a cross section of nerve 
fibers, the ascending root of the fifth nerve. The 
central area of each half of the section shows a large 
number of scattered nerve fibers interlacing and in 
cross sections. This area is called the formatio 
reticularis. Anterior to it, a collection of nerve cells 
represents the olivary body, median and dorsal to 
which a second and smaller collection of cells consti- 
tute the mesial olivary nucleus. The bulk of the 
anterior portion shows a cross section of the pyra- 
mids. Some of these fibers may be seen to sweep 
to the opposite side, thus making the motor decus- 
sation. In doing so they seem to pass over in large 
alternate bundles, rather than uniformly, as is the 
case with the sensory decussation. At the anterior 
surface on each side of the median fissure and sweep- 
ing around the pyramids are the superficial arcuate 
fibers, and also a collection of nerve cells, the arcuate 
nucleus. 
In cross sections of the open medulla the resem- 
blance to that of the cord is less distinct. The thin 
roof of the fourth ventricle is usually broken, leaving 
a dorsal expanded cleft. The lateral margin or 
remnant of the roof is called the lingula. Just be- 
neath the floor and close to the median sulcus are 
the nerve cells of the twelfth nerve. Lateral but in 
close proximity to these are the nerve cells of the 
tenth nerve. The axones from these cells may be 370 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
traced through the substance of the medulla to their 
ventral exit. The superficial origin of the twelfth 
nerve is just anterior to the olive, and the fibers of 
the tenth nerve may be traced to their superficial 
origin just dorsal to the olive. In serial cross sec- 
Fig. 272.-^Cross section of the open medulla. 
tions it will be seen that the nuclei of the other cra- 
nial nerves, from the sixth to the twelfth, lie in the 
floor of the fourth ventricle. 
The fasciculus solitarius is a bundle of nerve fibers, 
cut in cross section, and placed just lateral to the THE BRAIN. 
371 
nucleus of the tenth nerve. This bundle represents 
fibers from the ninth and tenth nerves. Just in- 
ternal or mesial to this bundle are a few cells called 
the solitary nucleus. This is probably a motor nu- 
cleus of the ninth and tenth nerves. Lateral to the 
solitary fasciculus are the fibers of the large restiform 
body on their way to the cerebellum. 
The posterior longitudinal bundle is a tract of 
nerve fibers that appears in cross section just an- 
terior to the nucleus of the twelfth nerve, and lies in 
close apposition to the median plane. The formatio 
reticularis occupies the greater part of the center of 
each lateral half of the medulla, and presents the 
same appeareance as in sections of the closed med- 
ulla. Likewise the cells of the olivary body, which 
in the open medulla form a large conspicuous nu- 
cleus that takes the form of a U with wavy sides, and 
with the open extremity turned inward and upward. 
Nerve fibers from its hilum sweep across to the oppo- 
site side and some curve around to join the arcuate 
fibers of the same side. Of the latter there arc two 
sets,-the superficial that passes around the anterior 
pyramids, and a deep set that curves upward and 
outward to reach the lateral surface just above the 
olive. Here they join the superficial set and pass 
to the cerebellum through the inferior peduncle. 
The arcuate nucleus extends into the open medulla 
and lies in its ventral surface near the median fissure, 
while the anterior pyramids form two large conspicu- 
ous masses anterior and mesial to the olives. 372 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
SUMMARY OF TRACTS, THEIR ORIGIN AND TERMINA- 
TIONS. 
Columns. 
Origin of Axones. 
Terminations. 
I. 
Column of Goll . . . ■ 
i. Cells of dorsal ganglion. 
2. Cells of posterior horn. 
i. Nucleus gracilis. 
2. 
Column of Burdach . 
i. Sameascolumn of Goll. 
i. Nucleus cuneatus. 
3- 
Comma tract 
i. Dorsal ganglion . . . . 
i. Cells of post. horn. 
4- 
Lissaur's tract . . . . 
i. Dorsal ganglion . . . . 
i. Cells of post. horn. 
5- 
Direct cerebellar . . . 
i. Cells of col. of Clarke . 
i. Cerebellum. 
i. Cerebellum. 
6. 
Gowers's tract . . . . 
i. Cells of post, horn . •] 
2. Corp, quadrigemina. 
3. Thalamus. 
4. Substantia nigra. 
5. Lenticular nucleus. 
7- 
Lowenthal 
i. Cells of cord 
1. Cells of ant. horn. 
8. 
Lateral ground bundle. 
i. Cells of cord 
1. Cells of cord. 
9- 
Crossed pyramidal . . 
i. Cerebral cortex . . . . 
1. Cells of ant. born. 
IO. 
Direct pyramidal . . . 
i. Cerebral cortex . . . . 
1. Cells of ant. horn. 
II. 
Ant. ground bundle . . 
i. Cells of cord 
1. Cells of cord. 
The sensory tracts are Nos. I, 2, 3, 4, 5, 6. The motor tracts are Nos. 7, 9, 10. 
The mixed tracts are Nos. 8, 11. 
THE PONS. 
The pons represents the anterior basal portion of 
the hind-brain. It is an oval body, one inch long, 
one inch thick, and about one and one-half inches 
broad. It is a junctional piece between the medulla 
and the mid-brain and the overlying cerebellum. 
The upper half of the fourth ventricle is confined to 
its dorsal aspect; that is, between the pons and the 
cerebellum. Viewed from the ventral surface it 
presents the appearance of a rhomboid with stria- 
tions that pass transversely and become constricted 
laterally to form the middle peduncles of the cere- 
bellum. 
The fifth cranial nerve, with its large sensory root 
and its small motor root, is attached to the ventral 
aspect of the pons, nearer its upper than its lower 
border. The anterior pyramids seem to enter the 
pons from below, and emerge above the pons, where 
they become lost in the crus cerebri. THE BRAIN. 
373 
In a transverse section the pons presents the fol- 
lowing parts: 
I. White matter. 
1. Transverse fibers-(a) superficial, (6) 
deep. 
2. Longitudinal fibers-(a) superficial (an- 
terior pyramids), (6) deep. 
Fig. 273.-Cross section through the lower part of the pons. 
3. Fibers of fifth, sixth, seventh, and 
eighth cranial nerves. 
4. Formatio reticularis. 
5. Median raphe. 
II. Gray matter. 
1. Nucleus pontis. 
2. Superior olive. 374 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
3. Nuclei the origin of fifth, sixth, seventh, 
and eighth cranial nerves. 
Transverse Fibers.-The superficial and the deep- 
set of transverse fibers of the pons pass into the cere- 
bellum through the middle peduncle. Some of the 
fibers arc commissural between the two halves of the 
cerebellum, while others connect with the nuclei 
pontis on the same side or the opposite side. In the 
lower portion of the pons, near the medulla, the deep- 
set are called the trapezium, on account of their 
trapezoid arrangement. 
Longittidinal Fibers.-The superficial set repre- 
sents mostly longitudinal bundles of the anterior 
pyramids that interlace the transverse fibers. The 
deep-set are near the dorsal aspect of the pons and 
comprise at least three groups: (i) the posterior 
longitudinal bundle near the median raphe in which 
are found fibers from the antero-lateral column of the 
cord; (2) the lemniscus or fillet, a continuation of the 
sensory decussation; (3) the fasciculus teres, just 
dorsal to the posterior longitudinal bundle, and 
which contain fibers of the seventh cranial nerve. 
Fibers of the cranial nerves pass through the 
medulla from their nuclei in the dorsal portion to 
their various superficial exits on the ventral surface. 
The' format™ reticularis is similar to that described 
in the medulla. The median raphe is also a contin- 
uation of that described in the medulla. 
Gray Matter of the Pons.-The nuclei pontis are 
nerve cells that are scattered among the superficial 
transverse fibers and arc nodal points forming con- TllE BRAIN. 
375 
nections between the medulla, cerebellum, and 
higher brain centers. The superior olive lies in the 
formatio reticularis and is seen only in the lower 
portions of the pons. The nuclei of the cranial 
nerves are found in the dorsal aspect, most of them 
just beneath the floor of the fourth ventricle. 
Fig. 274.-Section through the human cerebellar cortex vertical to 
the surface of the convolution. Treatment with Muller's fluid (Bohm 
and Davidoff). 
THE CEREBELLUM. 
The cerebellum is next in size to the cerebrum and 
overlies the fourth ventricle. It is characterized by 
transverse curved sulci which divide it into lamellae, 
giving the organ a foliate appearance. A cross sec- 
tion of the lamellae shows a central core of white 376 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
matter with a gray cortex, giving the section the 
appearance of a branching tree, hence the name arbor 
vitro. A section taken in this plane presents the 
following layers: 
i. Molecular layer-on the outside. 
(i) Small cortical cells. 
(2) Stellate cells. 
(3) Cells of Purkinje. 
2. Granular layer. 
(1) Granular cells. 
(2) Large stellate cells. 
3. Medullary substance-core of nerve fibers. 
(1) Centripetal neuraxes from Purkinje cells. 
(2) Centrifugal neuraxes. 
(a) Mossy fibers. 
(ft) Climbing fibers. 
(3) A few ganglion cells forming the central 
gray nucleus. 
Molecular Layer.-The small cortical cells are 
found in all parts of this layer, but more especially 
near its periphery. They are multipolar cells and 
but little is known of the distribution of their neu- 
raxes. The stellate cells are evenly distributed, and of 
particular interest are their neuraxes. The latter pos- 
sess two types of collaterals. One set forms branches 
among the cortical cells, while a second class branches 
at a level with the Purkinje cells, where it forms a 
basket-like net around the bodies of these cells. The 
cells of Purkinje are the largest nerve cells in the body 
(about 60 ti in diameter or seven times the diameter 
of a red blood-corpuscle). They form a single row Fig. 275.-Schematic diagram of the cerebellar cortex: A, by ordinary nuclear staining (omitting the layer of 
Purkinje's cells); B, vertical to the surface of the convolution; C, longitudinal section through the convolution; B and 
C, by the chrome-silver method (Bohm and Davidoff). 
377 378 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
of cells, placed with considerable regularity some 
distance apart, along the inner margin of the molec- 
ular layer. Their neuraxes arise from the basal 
end of the cell body and extend through the granular 
layer and enter the medulla as the centripetal fibers. 
The other extremity of the cell body passes into one 
or more prominent dendrites that arise toward the 
Fig. 276.-Cell of Purkinje from the human cerebellar cortex. Chrome- 
silver method (Bohm and Davidoff). 
periphery of the cerebellum. These dendrites 
branch freely in one plane, like an ivy growing 
against the wall, and this plane is always at right 
angles to the lamellae of the cerebellum, and therefore 
sections of the cerebellum should be made in this 
plane. The brain. 
379 
Granular Layer.-This layer is densely packed 
with nerve cells- of two varieties. The granular 
cells are most numerous, small, and have only a few 
dendrites that end in hook-like telodendria. The 
neuraxes from these cells pass vertically into the 
molecular layer, where many of them form a T- 
shaped division, the two end branches passing par- 
allel with the laminae and therefore into a plane 
vertical to that of the den- 
drites of the Purkinje cells. 
Large stellate cells form the 
second variety of this layer. 
They are few in number 
and lie close to the mo- 
lecular. Their dendrites 
branch in all directions and 
their neuraxes form telo- 
dendria among the granu- 
lar cells. 
The medullary substance 
may be divided into centrif- 
ugal fibers,-those that 
carry nerve impulses toward 
the granular and molecular 
layers, and centripetal fibers; 
those that carry impulses in the opposite direction. 
The latter are the neuraxes of the cells of Purkinje. 
The centrifugal fibers are the mossy fibers, that form 
mossy telodendria in the granular layer, and also so- 
called climbing fibers that pass through the granular 
layer and connect with the dendrites of Purkinje 
cells, up which they seem to climb. Collaterals are 
Fig. 277.-Granular cell 
from the granular layer of 
the human cerebellar cortex. 
Chrome-silver method (Bohm 
and Davidoff). I'ig. 278.-Portions of vertical section of human cerebral cortex, 
treated by the Golgi method. The figure shows the arrangement of the 
different cells of the cerebral cortex (Sobotta). 
380 THE BRAIN. 
381 
given off in their passage through the granular layer. 
The central gray nucleus forms the central core of 
each lateral cerebellar hemisphere. It forms a cap- 
sule of gray matter from whose hilum many nerve 
fibers pass, the majority to enter the superior cerebel- 
lar peduncle. 
THE CEREBRAL CORTEX. 
The cerebrum is such an extensive and complicated 
organ that only a description of the cortex in the 
region of the fissure of Rolando will be given here. 
From without inward this region presents, rather 
indistinctly, the following layers: (i) molecular 
layer; (2) small pyramidal cells; (3) large pyr- 
amidal cells; (4) polymorphic cells; (5) medullary 
substance of nerve fibers. It is to be borne in mind 
that this cortex presents many fissures and minor 
folds into which the pia dips, and that a transverse 
section is any plane that is vertical to the folded 
surface. 
1. The molecular or outer layer is composed chiefly 
of nerve fibers which interlace in all directions but 
which have chiefly a direction parallel to the external 
surface. The chief dendrite of the pyramidal cells 
terminates in this layer in tuft-like telodendria, and 
also ascending neuraxes, mostly from the polymor- 
phous cells. The cells of this layer are few, and have 
been described as polygonal, spindle-shaped, and 
triangular, or stellate. Their neurons are nearly all 
confined to this layer, the axones of only a few reach 
down to the deeper layers. 
2. The layer of small pyramidal cells is not well 382 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
defined and usually not so broad as the molecular 
layer. The nerve cells have a triangular body, the 
apex being directed toward the surface of the cortex. 
From this apex a primordial dendrite ascends and 
Fig. 279.-Large pyramidal cells from the human cerebral cortex. 
Chrome-silver method (Bohm and Davidoff). 
gives off a number of branches that end in terminal 
filaments or telodendria in the outer layer, frequently 
at the brain surface. Several short dendrites arise THE BRAIN. 
383 
from the basal surface of the cell body where also 
the axone is attached. The latter passes toward 
the medullary 
substance, and 
near the cell 
body is pro- 
vided with col- 
laterals that 
connect with 
adjacent neu- 
rons. 
The layer of 
large pyramidal 
cells comprises 
a broad area. 
The cells meas- 
ure 20 [1 tO 30 // 
in diameter, be- 
ing twice as 
large as those 
of the preced- 
ing layer. In 
all other re- 
spects the cells 
of this layer re- 
semble the 
small pyram- 
idal cells. 
Their dendrites 
and axones also occupy the same relation as those 
of the preceding layer. 
4. The layer of polymorphic cells usually includes 
Fig. 280.-Schematic diagram of the cerebral 
cortex: a, Molecular layer with superficial (tan- 
gential-) fibers; b, striation of Bechtereff-Kaes; 
c, layer of small pyramidal cells; d, stripe of 
Baillarger; e, radial bundles of the medullary 
substance; /, layer of polymorphous 'cells 
(Bohm and Davidoff). 384 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
a few large pyramidal cells, and it is not well defined 
from the preceding layer. There is present in this 
layer: (i) multipolar cells with short neuraxes (Golgi 
cells) whose dendrites project in all directions; and 
(2) cells with slightly branched dendrites and with 
neuraxes passing toward the surface of the brain 
where they terminate in the molecular outer layer. 
The cells of this layer are triangular or spindle-shaped 
and vary considerably in size. 
5. The medullary substance is composed of a mass 
of nerve fibers that take a radial course and in which 
we can detect no structural difference. Physio- 
logically, however, we can divide them into four 
classes as follows: 1, projecting or centrifugal fibers 
which indirectly connect the cerebral elements with 
the periphery of the body; that is, they carry im- 
pulses away from the nerve center; 2, commissural 
fibers that connect corresponding jjarts of the two 
cerebral hemispheres through the corpus callosum; 
3, association fibers that connect different parts of 
the same hemisphere; 4, centripetal fibers or terminal 
fibers,-those that come from cell bodies in the same 
or the opposite hemisphere, or in some more distant 
nerve center, and that ultimately arborize about 
nerve elements in the cerebral cortex. In a strict 
sense the second and the third class fall under either 
the centrifugal or the centripetal group. 
THE NEUROGLIA. 
The neuroglia tissue represents a special form of 
supporting elements found exclusively in the central 
nervous system and in the retina. It develops from THE BRAIN. 
385 
the ectoderm while all other supporting tissues are 
derived from the mesoderm. The development of 
neuroglia cells is closely associated with the origin of 
neurons, as both are derived from epithelial cells that 
lie primarily near the central canal of the nervous 
system. The embryonic neuroglia cells are called 
spongioblasts, while those that develop into true 
nerve elements are 
called neuroblasts. 
Both kinds pass out 
very early and per- 
manently lodge in 
the gray matter. 
The neuroglia ele- 
ments appear as 
cells with many ra- 
diating, slender pro- 
cesses that are usu- 
al ly unbranched, 
and because of 
their peculiar ap- 
pearance have been 
called spider cells or 
mossy cells, or astro- 
cytes. The cell 
bodies contain but 
very little protoplasm, and their shape is modi- 
fied according to their surroundings, being triangu- 
lar, or quadrangular, or polyangular, the protoplas- 
mic processes arising from their angles. According 
to the length of their processes attempts have been 
made to classify them as short-rayed astrocytes, pos- 
Fig. 281.-Neurogliar cells: a, from 
spinal cord of embryo cat; b, from brain 
of adult cat; stained in chrome-silver 
(Huber). 386 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
sessing a few short processes, and long-rayed astro- 
cytes, having many long, slender processes. The 
former appear among the nerve cells only, the latter 
are found both in the gray and the white matter. 
Fig. 282.-Typical neuroglia cells, from cross section of the white mat- 
ter of the human spinal cord, stained after Benda's selective neuroglia 
tissue staining method (Huber, "Studies on Neuroglia Tissue," 
Vaughan Festschrijt, 1903). 
Not infrequently detached processes may be found 
and processes that can be traced directly through 
the bodies of adjacent astrocytes. The neuroglia 
thus forms a delicate web-like fabric that interlaces The brain. 
387 
the whole central nervous system, to which it gives 
substance and support. It is to be remembered that 
supporting tissue of mesodermic origin does the same 
thing, especially in the cord. The connective-tissue 
elements usually accompany the nutrient blood- 
vessels. 
BLOOD-VESSELS OF THE CENTRAL NERVOUS SYSTEM. 
The spinal cord receives its blood supply from a 
plexus of blood-vessels in the pia mater. There is an 
anterior median artery just in front of the anterior 
fissure. Some two hundred branches from this 
vessel pass at right angles directly into the fissure 
and enter the gray matter, where each divides into 
a right and left branch that enclose the central 
canal. Each arterial branch ultimately bifurcates, 
just in front and external to the cell column of 
Clarke, forming minute ascending and descending 
terminals, which become lost in an extensive capil- 
lary system of the central gray matter. The white 
matter receives its blood supply from a plexus of 
vessels situated on the dorsal and lateral surfaces of 
the cord. From this system small branches enter 
the cord anywhere and form capillaries among the 
nerve fibres; that is, supplies blood to the white 
matter. The gray matter has a more liberal blood 
supply than the white matter. 
The brain substance also receives its blood supply 
from a plexus of blood-vessels in its pia. The capil- 
laries are particularly numerous and closely meshed 
wherever the nerve cells are segregated, that is, 
in the ganglion centers. In the cerebellum the gran- 388 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
ular layer is the most vascular. The arterioles have 
thin walls, and in old age may become brittle and 
may easily rupture. 
No lymphatic vessels with definite walls have been 
discovered in the central nervous system. The 
blood-vessels are, however, surrounded by peri- 
vascular spaces which probably function as lymph 
channels. CHAPTER XIV. 
THE EYE. 
The eyes begin to develop during the fourth week 
of embryonic life, and appear then as a pair of lateral 
evaginations of the fore-brain. A pair of vesicles 
are thus formed called the primary optic vesicles. 
When the latter reach the ectoderm an invagination 
of these vesicles takes place, like pushing in one 
side of a hollow rubber ball. The cavity of the 
primary optic vesicle becomes obliterated by this 
process, and a new vesicle forms, called the secondary 
optic vesicle. It will be observed that the cavity of 
this vesicle is practically the same as would be pro- 
duced by an invagination of the brain wall. Later 
it will be seen that this cavity corresponds to the 
space occupied by the vitreous humor of the adult 
eye, while its wall becomes the retina. The stalk 
that connects this vesicle to the brain is the optic 
stalk, in which later optic nerve fibers appear. 
At the time the secondary optic vesicle is forming 
there is a disc-like thickening of the adjacent ecto- 
derm, which soon invaginates and becomes con- 
stricted as an ectodermal vesicle. This is the lens, 
which later takes a position at the mouth of the 
secondary optic vesicle. The latter presents, at this 
stage, a fissure in its ventral surface called the cho- 
roid fissure. Connective-tissue cells migrate through 
389 390 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
this fissure and fill the cavity of the secondary vesicle. 
Fig. 283.-Part of a section through the head of an early human 
embryo, showing the connection of the primary optic vesicles with the 
fore-brain (His): olj, Olfactory area of epiblast; ch., part of fore-brain 
which gives rise to cerebral hemispheres; th, thalamencephalon; p.o.v., 
primary optic vesicles. 
Fig. 284.-Three successive stages of development of the eye, showing 
formation of secondary optic cup and crystalline lens in human embryos 
of 4 mm. (A), 6 mm. (B), and 8 mm. (C) (Tourneux): a, a, primitive 
optic vesicles; b, external layer of secondary optic cup (future pigment 
layer of retina); c, inner layer of cup (retina proper); d, lens pit (thick- 
ened and depressed ectoderm); e, lens vesicle. 
These cells form the vitreous humor, while the choroid THE EYE 
391 
fissure closes and permanently disappears. The ex- 
ternal coats of the eye-that is, the sclera and the 
choroid-develop from the surrounding connective 
tissue. 
Fig. 285.-Plastic representation of the optic cup with lens and vitre- 
ous body (Hertwig): ab, Outer wall of the cup; ib, its inner wall; h, 
cavity between the two walls, which later disappears entirely; Sn, fun- 
dament of the optic nerve (stalk of the optic vesicle with a furrow on 
its lower surface); aus, optic (choroid) fissure; gl, vitreous body; I, lens. 
The parts of the adult eyeball may be tabulated as 
follows: 
I. Tunica externa. 
i. Sclera. 
2. Cornea. 
II. Tunica media. 
i. Choroid coat. 
2. Ciliary body. 
3. Iris. 
III. Tunica Interna. 
1. Retina. 
2. Pigment membrane. 
The refracting media, or transparent media of the 
eye traversed by a ray of light, are: 
1. The cornea. 392 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
2. Aqueous humor. 
3. Lens. 
4. Vitreous humor. 
TUNICA EXTERNA. 
1. The sclera is a dense connective-tissue covering 
of the eye that terminates anteriorly in the cornea. 
It is of interest to note that, in birds of prey, horny 
plates develop in the sclera for the better protection 
Fig. 286.-Diagram of the eye. 
of the eye. Posteriorly the sclera is perforated by 
the entrance of the optic nerve. Connective-tissue 
fibers, known as the lamina cribrosa, pass across this 
point and interlace the optic fibers, while others 
sweep backward along the optic nerve as its external 
envelope. 
The sclera consists of interlacing bundles of con- The eye. 
393 
nective-tissue fibers closely felted together. The 
tendons of the ocular muscles are continuous with 
the scleral fibers. The external scleral surface is 
clothed with a layer of flattened endothelial cells 
which belong to the capsule of Tenon. The latter is 
a loose connective-tissue fabric that invests the eye- 
ball, and is so intimately connected with the eye 
muscles that coordinate 
movement of the arti- 
ficial eye, or glass shell, 
is made possible after 
the enucleation of an 
eye. Pigmentation is 
regularly present at the 
corneal margin and the 
surface next to the 
choroid. This inner 
pigmented scleral sur- 
face is lined by a layer 
of flattened endothelial 
cells, forming a sepa- 
rate membrane a n d 
called by some the lam- 
ina jusca; generally, 
however, it is regarded 
as the outermost layer 
of the choroid and known as the lamina choroidea. 
2. The Cornea.-The cornea is inserted into the 
sclerocorneal junction in which is found an annular 
venous sinus, the canal of Schlemm, which may ap- 
pear as a single canal or as several canals. The 
cornea is a perfectly transparent medium and free 
Fig. 287.-Section of the cornea of the 
eye. 394 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
from red blood corpuscles, the nearest blood supply 
being that of the sclerocorneal margin in the region 
of the canal of Schlemm. 
Histologically the cornea is made up of five layers: 
i, the anterior epithelium; 2, the anterior elastic 
membrane, or Bowman's membrane; 3, the ground 
substance, or substantia propria; 4, Descemet's 
membrane; 5, the endothelium of Descemet's 
membrane. 
The corneal epithelium is of the stratified squamous 
variety, a little thicker near the corneal margin than 
at its center. It is related to the epidermis of the 
skin, the cells being provided with short prickles 
that are very difficult to demonstrate. This epithe- 
lium forms an efficient and important protection to 
the front of the eye. The anterior elastic membrane 
measures 8 p in thickness, about the width of a red 
blood corpuscle, and becomes thinner towards the 
sclerocorneal junction. It is a compact layer of con- 
nective-tissue fibrils and is regarded by some as a 
basement membrane to the overlying epithelium. 
Nerve fibers penetrate this membrane to connect 
with the corneal epithelial cells. The substantia 
propria constitutes the bulk of the cornea. It con- 
sists of bundles and lamellae of connective-tissue 
fibrils, and peculiarly flattened cells called corneal 
corpuscles. The fibrils of each lamella are cemented 
together and run parallel to each other and to 
the corneal surface, but so arranged that those of ad- 
jacent lamellae cross at an angle of about twelve 
degrees. 
The lamellae arc also cemented to each other. The THE EYE. 
395 
corneal cells have irregular processes and lie in special 
cavities called corneal spaces, in which are also found 
a varying number of leucocytes. These spaces seem 
to be part of a complicated lymphatic system, and 
communicate with each other by means of a complex 
system of canals. While blood does not irrigate the 
cornea, lymph does, freely and extensively. The 
posterior elastic or Descemet's membrane resembles the 
Fig. 288.-Corneal spaces of a dog (Bohm and Davidoff) 
anterior elastic membrane, and may be separated 
into shreds of fine, elastic, connective-tissue fibrils. 
The endothelium of Descemet's membrane is Com- 
posed of low, hexagonal cells forming a single layer. 
It will be found that Descemet's membrane with its 
investing endothelium is reflected to form the an- 
terior layer of the iris, enclosing therefor the anterior 
portion of the aqueous chamber. 396 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
TUNICA MEDIA. 
i. The Choroid Coat.-The choroid is the vascular 
tunic of the eye, and may be divided into four layers. 
From without inward these are named: i, lamina 
suprachoroidea; 2, lamina vasculosa Halleri; 3, 
lamina choriocapillaris; 4, glassy layer, or vitreous 
membrane. This entire tunic is derived from the 
Fig. 289.-Section through the human choroid (Bohm and DavidofT). 
mesoderm and is largely composed of connective- 
tissue elements. 
The Lamina Suprachoroidea.-This layer is closely 
applied to the sclera, and is composed of a loose 
fabric of areolar tissue in whose meshes are con- 
nective-tissue cells and lymph spaces lined with 
endothelium, known as perichordeal lymph spaces. THE EYE. 
397 
Pigment cells are also present. The lamina vascu- 
losa is the broadest layer and is also composed of 
areolar tissue. The blood-vessels constitute its 
principal portion, and they are so distributed that the 
larger ones, the veins, occupy its outer portions. 
The lamina chor io capillaris consists chiefly of capil- 
Fig. 290.-Section through the ciliary body. 
lary vessels that are particularly abundant in the 
region of the macula lutea, or yellow spot of the 
retina. In other respects this layer resembles the 
lamina suprachoroidea, except that pigment cells 
are absent. The glassy or -vitreous membrane is but 
2 g thick, homogeneous, clothes the inner choroid 398 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
surface, and also forms a lining membrane against 
which the pigment cells of the retina are applied. 
2. The Ciliary Body. -The ciliary body is that por- 
tion of the tunica media extending between the ora 
serrata of the retina and the base of the iris. On the 
inner surface of this body there are about seventy 
meridional folds called the ciliary processes. Second- 
ary folds and processes appear on and between the 
primary folds, while the whole surface is clothed 
with two rows of epithelial cells, the pars ciliaris 
retinae. Of these the outer layer is deeply pig- 
mented and represents the outer layer of the second- 
ary optic vesicle, while the inner layer is non- 
pigmented and develops from the inner layer of the 
optic vesicle. The greater bulk of the ciliary body 
is made up of smooth muscle tissue called the ciliary 
muscle, or muscle oj accommodation. This muscle 
may be divided into three portions. The outer por- 
tion is made up of meridional fibers. The middle 
division of radial fibers have their origin near the 
canal of Schlemm, from which they spread out like 
a fan. The inner portion is near the base of the iris 
and the fibers are circular. The combined action of 
these fibers is to pull the choroid coat forward and 
inward and thus slacken the tension on the suspen- 
sory ligament of the lens, as this ligament joins with 
the epithelial cells of the ciliary body as well as with 
the hyaloid membrane that encloses the vitreous 
humor. Under this condition the lens becomes 
more convex and the eye is focused to near objects. 
3. The Iris.-The iris is a pigmented circular cur- 
tain that occludes the rays of light from the periphery THE EYE. 
399 
of the lens. The circular opening in the iris is the 
pupil. Three layers may be recognized in the iris, 
enumerated from before backward, as follows: i 
anterior endothelium; 2, stroma with sphincter 
muscle; 3, pigment epithelium, or pars iridica retinae. 
The anterior endothelium is a single layer of cells that 
is continuous with the posterior endothelium of the 
cornea. The stroma forms the bulk of the iris and 
is very vascular and muscular. Targe pigment cells 
are present and a fine reticular tissue. Smooth 
muscle fibers, the sphincter muscle of the pupil, 
encircle the pupil. Along the posterior surface 
radial fibers probably function as a dilator muscle 
of the pupil. The posterior epithelium, or pars 
iridica retinae, is a direct continuation of the pars 
ciliaris retinae and extends to the margin of the pupil. 
It is composed of two layers of cells and both, in this 
case, are pigmented. 
TUNICA INTERNA. 
The inner tunic is the retina of the eye, which may 
be divided into ten layers, named from within out- 
ward as follows: 
1. Internal limiting membrane. 
2. Layer of nerve fibers. 
3. Ganglion cell layer. 
4. Inner molecular layer. 
5. Inner nuclear layer. 
6. Outer molecular layer. 
7. Outer nuclear layer. 
8. External limiting membrane. 
9. Rods and cones. 
10. Pigment layer. 400 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
(1) The internal limiting membrane is a very deli- 
cate homogeneous layer formed by lateral expansions 
of processes of neuroglia elements. It is closely ap- 
plied to (2) the optic nerve fibers. The latter are non- 
medullated and radiate toward the entrance of the op- 
tic nerve, composed of both centrifugal and centrip- 
etal axones. The latter arise from (3) the ganglionic 
cells, that are irregularly distributed along the inner 
Fig. 291.-Section of retina of the eye. 
border of the retina. These cells are large, multi- 
polar, and their dendrites extend outward and con- 
tribute to the substance of (4) the inner molecular 
layer. The latter is a network of neuroglia fibrils 
and nerve processes, contributed in part by the cells 
of (5) the inner nuclear layer. This layer is com- 
posed of several rows of nucleated cells of which some 
are sustentacular, or neuroglia elements, some bi- 
polar ganglion cells, and others multipolar ganglion THE EYE. 
401 
cells situated in the outer region of this layer and 
expanding in a horizontal direction. (6) The outer 
molecular layer, like the inner molecular, is a net- 
work of fibrils, processes from all the ganglion cells 
of the retina and also neuroglia elements. The ex- 
ternal portion of this molecular layer is not so densely 
packed with fibrils and has been called Henle's fiber 
layer. (7) The outer nuclear layer is composed of 
many compact rows of nuclei and is the most con- 
spicuous layer in stained sections of the retina. The 
cell bodies enclosing most of these nuclei are the 
visual units of the eye and are called rod-visual and 
cone-visual cells, as the rods and cones are merely 
processes of these cells. The cells are elongated units 
whose long axis is placed radial to the eye, and whose 
multiple processes enter the outer molecular layer 
as already mentioned. The cone-visual cells are 
least numerous and their nuclei are placed at regular 
intervals in the outer portion of the layer. Their 
nuclei are somewhat larger than the nuclei of the 
other cells. Rod-like neuroglia elements give sup- 
port to the visual cells. (8) The external limiting 
membrane invests the outer nuclear layer. It is a 
thin, transparent, homogeneous membrane, derived 
from the neuroglia tissue, and forming a dividing line 
between the rods and cones and the outer nuclear 
layer. (9) The rods and cones are processes from the 
visual cells whose nuclei form the bulk of the outer 
nuclear layer. The rods are 40 g to 50 g in length, 
and consist of two segments, the outer being doubly 
refractive to light, and may be separated into numer- 
ous transverse discs by the action of certain reagents. 402 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
The inner segment shows a superficial longitudinal 
striation, due to impressions from fiber baskets of the 
neuroglia network. The cone is 15 // to 25 // long 
and its inner segment considerably broader than the 
rod. The rods are more numerous than the cones, 
three or four of the former intervening between two 
of the latter. (10) The pigment layer forms a com- 
pact background to the rods and cones. It consists 
of hexagonal cells that contain black pigment gran- 
ules. The inner surfaces of these cells possess thread- 
like filaments that interlace between the rods and 
cones. The nuclei of these cells lie in the outer ends 
of these cells, the so-called basal plates, and are not 
pigmented. The granules are mobile and their dis- 
tribution in the cells varies according to the illumi- 
nation of the retina. In strong light the pigment is 
evenly distributed throughout the cytoplasm, while 
in weak light it is collected at the outer portion of 
each cell. This single row of pigment cells represents 
the outer layer of the primary optic vesicle, while 
the other nine layers of the retina develop from the 
inner layer of this vesicle. 
The neuroglia elements of the retina differ from 
those of the brain in that they form radial sustentac- 
ular fibers, called fibers of Muller, which penetrate 
the retina to the rods and cones. Each fiber repre- 
sents a modified epithelial cell which terminates in 
basal plates, the latter forming the limiting mem- 
branes of the retina. The end plates that form the 
external limiting membrane give off externally short, 
inflexible fibrils, which form -fiber-baskets enclosing 
the basilar portions of the rods and cones. The THE EYE. 
403 
bodies of Muller's fibers are very plastic and adjust 
Fig. 292.-Schematic diagram of the retina according to Ramon y Cajal: The line fl, after pass- 
ing through a Muller's fiber, crosses a bipolar rod cell, then two bipolar cone cells, and finally ends in 
the body of a bipolar cone cell (Bohm and Davidoff). 
themselves to the pressure exerted by the various 404 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
elements that constitute the different layers of the 
retina through which they pass. 
In certain areas of the retina there are peculiar- 
ities that differ from the above description. These 
areas are: (i) the macula lutea, or yellow spot; 
(2) the optic papilla, or blind spot; (3) the ora ser- 
rata; (4) the pars ciliaris retinae; (5) the pars iridica 
retinae. 
1. The macula lutea, or yellow spot, is a crater- 
like area of the retina that lies in the visual axis of 
Fig. 293.-Section through human macula lutea and fovea centralis. 
As a result of treatment with certain reagents, the fovea centralis is deeper 
and the margin more precipitous than during life (Bohm and Davidoff). 
the eye. The central depression is called the jovea 
centralis. Its margin is somewhat thickened and 
presents all the layers of the retina, while in the fovea 
the layers are practically reduced to the cone-visual 
elements. From this center the cell bodies of the 
cones radiate in curves to reach the outer molecular 
layer, which gives rise to obliquely directed fibers 
known as Henle's fiber layer. The macula lutea is 
the most sensitive spot in the retina and derives its THE BYE. 
405 
name from the yellow pigment held in solution within 
the cell layers. 
2. The optic papilla, or blind spot, is the point of 
entrance of the optic nerve. It is found a little to 
the nasal side of the macula lutea. From the center 
of this papilla the nerve fibers spread out radially to 
supply the various parts of the retina. The optic 
fibers lose their medullary sheaths in their passage 
through the sclera and the choroid, so that the optic 
nerve at this point becomes suddenly thinner. Be- 
Fig. 294.-Section through point of entrance of human optic nerve 
(Bohm and Davidoff). 
cause of this and the fact that the fibers curve radi- 
ally, there is produced a deep circular depression in 
this region. At this point the retina is absent, the 
choroid coat is interrupted, while connective-tissue 
fibers of the sclera, called the lamina cribrosa, inter- 
lace and cross the optic fibers. 
3. The ora serrata is that portion of the retina that 
marks the posterior limit of the ciliary body. At 
this point there is a rapid diminution of the retinal 
layers until but two rows of cells remain, the outer 
one pigmented. The optic fibers and visual cells 406 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
disappear first. Then the outer molecular layer is 
lost, so that the nuclear layers become confluent. 
Ultimately but two rows of cells remain, which are 
continued over the ciliary body as the pars ciliaris 
retinae, already mentioned in the description of the 
ciliary body. The ora serrata forms a zigzag line 
which marks the posterior border of the ciliary folds. 
The iridica retinae has already been described in 
connection with the description of the iris. 
REFRACTING MEDIA. 
The refracting media of the eye are the cornea, 
aqueous humor, lens, and the vitreous humor. The 
cornea is described on another page. 
i. The aqueous humor is a structureless fluid re- 
sembling lymph that fills the chamber of the eye in 
front of the lens. The iris is suspended in this fluid 
and divides the chamber into an anterior and a 
posterior compartment. The fluid is largely a se- 
cretion from epithelial cells, or, according to some, 
from epithelial glands said to be located in the region 
of the ciliary body. The vitreous humor is re- 
placed if accidentally lost. 
2. The Lens.-The origin of the lens has already 
been described as an ectodermal invagination in the 
form of a vesicle. The cells of the posterior wall of 
this vesicle form the bulk of the lens. These cells 
become long and slender and are known as the lens 
fibers, while the cells of the anterior wall remain low 
and cubical and form the anterior epithelium of the 
lens. Surrounding the lens on all sides is the lens 
capsule. This capsule is a homogeneous membrane, The Eye. 
407 
thicker on the anterior surface of the lens than on the 
posterior, and with certain reagents appears to be 
made up of lamellae. The latter connect with fibers 
of the suspensory ligament. 
In adults the anterior epithelium forms a single 
layer of flattened or cubical cells which extend as far 
Fig. 295.-Crystalline lens: A, longitudinal fibers; B, posterior surface 
view of anterior epithelium (Leroy). 
as the equatorial margin of the lens. At this mar- 
gin the cells increase in height to form the lens fibers. 
These are flattened hexagonal prisms, thickened at 
the posterior ends. They pass in a meridional direc- 
tion from the anterior surface backward, and are 408 
NORMAL, HISTOLOGY AND ORGANOGRAPHY. 
held together by a small amount of cement sub- 
stance. 
The suspensory ligament connects the capsule of the 
lens with the epithelium of the ciliary body and the 
hyaloid membrane of the vitreous humor. From 
this point the fibers pass forward and inward to be- 
come inserted into the capsule of the lens. The in- 
sertion occupies a wide zone at the equator of the 
lens, which reaches some distance on the anterior and 
posterior surfaces. Between these fibers there is 
consequently a canal around the lens, divided by 
septa, the canal of Petit, which communicates by 
minute openings with the anterior chamber. 
3. The vitreous humor fills the chamber of the eye 
back of the lens. It is a transparent tissue that 
contains about 98 per cent, of fluid substance and 
fine interlacing fibers, as well as a few connective- 
tissue cells and leucocytes. Toward the surface the 
fibers are more densely arranged, forming the hyaloid 
membrane which encloses the entire vitreous body. 
The origin of the vitreous humor has been described 
in connection with the developmental history of the 
eye. 
BLOOD-VESSELS OF THE EYE. 
The arteries of the choroid are derived from the 
short posterior ciliary, the long ciliary, and the an- 
terior ciliary arteries. The short posterior penetrate 
the sclera in the vicinity of the optic nerve, and 
supply blood to the choroid of that region. These 
arteries also anastomose with branches from the 
retinal vessels. The long posterior ciliary penetrates THE EYE. 
409 
the sclera near the optic nerve, and course forward 
between the choroid and the sclera to the ciliary 
body. It supplies blood to the ciliary muscles, the 
ciliary processes, and the iris. The anterior ciliary 
arteries lie close to the straight ocular muscles and 
penetrate the sclera near the sclerocorneal junction. 
They give off branches to the iris and the ciliary body, 
anastomosing with branches from the long posterior 
ciliary artery. Veins return the blood from these 
regions and bear the same names as the arteries 
they accompany. 
Fig. 296.-Vertical section through the eyeball and lids (Pyle) 
The retina is supplied with blood from a central 
artery and vein that enter and leave the retina at the 
optic papilla, or blind spot. Each divides into a 
superior and inferior papillary artery and vein. The 
latter again divide into two branches, making in all 
four arteries and four veins known according to their 
position as superior and inferior nasal, and superior 
and inferior temporal vessels. Within the retina 410 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
itself a coarse plexus of vessels blends with the nerve 
fiber layer. This connects with a fine network lying 
Fig. 297.-Vertical section of the upper eyelid of man (Sobotta.) 
within the inner nuclear layer. The visual cell layer 
is non-vascular. The Eye. 
411 
The eyelids are two movable folds 
of the skin whose inner surface is 
covered by a mucous membrane, 
the conjunctiva. The skin on the 
outer surface is thin, movable, and 
presents fine hairs with small seba- 
ceous glands, and also a few sweat 
glands. At the lid margin papilla; 
are developed and the epidermis is 
thickened. Along the outer bor- 
der there are two or three rows of 
large hairs, the eyelashes, the poste- 
rior row of which possesses seba- 
ceous glands and modified sweat 
glands, called the glands of Moll. 
The eyelids are further provided 
each with twenty-five to thirty 
large glands, known as Meibomian 
or tarsal glands, whose ducts open 
on the palpebral margin just in- 
ternal to the eyelashes. Each 
gland has a large central duct lined 
by stratified epithelium and into 
which numerous branched alveoli 
open. The latter resemble the al- 
veoli of sebaceous glands. The 
Meibomian glands lie close to the in- 
ternal surface of the eyelids and 
their cells undergo a fatty change 
and give out a fat-containing secre- 
tion. 
In each lid there exists a frame- 
Fig. 298.-Mei- 
bomian or tarsal 
gland, reconstructed 
after Born's wax- 
plate method (Heu- 
ber). 412 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
work of condensed fibrous tissue, which gives con- 
sistency and shape to the lid, and is termed the tar- 
sal plate, or tarsus. The orbicularis oculi muscle lies 
beneath the subcutaneous tissue of the outer surface 
and is composed of voluntary muscle fibers that arch 
between the angles of the eyelids. 
Fig. 299.-Lacrimal and Meibomian glands, the latter viewed from 
the posterior surface of the eyelids. (The conjunctiva of the upper lid 
has been partially dissected off, and is raised so as to show the Meibomian 
glands beneath.) 1, Free border of upper, and 2, free border of lower lid, 
with openings of the Meibomian glands; 5, Meibomian glands exposed, 
and 6, as seen through conjunctiva; 7, 8, lacrimal gland; 9, its excretory 
ducts, with 10, their openings in the conjunctival cul-de-sac; II, con- 
junctiva (Testut). 
The conjunctiva is a mucous membrane that lines 
the inner surface of the eyelids and is reflected over 
the front of the eye. Over the cornea it forms the 
anterior stratified epithelium, and has already been 
described. The line along which it is reflected on to 
the globe of the eye is called the jornix. The pal- The EYE. 
4i3 
pebral portion adheres intimately to the tarsal plate 
and presents numerous papillae. It is covered by a 
layer of columnar cells beneath the bases of which 
are small flattened cells. Goblet cells are to be found 
among these cells. Over the globe of the eye it ad- 
heres closely to the sclera, and this portion of the 
conjunctiva is perfectly smooth and is composed of 
stratified squamous epithelium. The conjunctiva 
that clothes the eyelid is thinner than that which 
covers the cornea and any for- 
eign particle, therefore, tends 
to cling to the eyelid rather 
than to the eye. 
The Lacrimal Apparatus.- 
This consists of (i) the lacri- 
mal or tear gland, (2) the lac- 
rimal canals, and (3)'lacrimal 
sac, or nasal duct. 
The lacrimal gland is a 
branched tubular gland situ- 
ated in the upper and outer 
part of the orbital cavity. Its 
structure resembles that of a 
serous gland. The ducts, which are numerous, are 
clothed with stratified epithelium and open on the 
conjunctival surface, over which the secretion is 
evenly distributed by the action of the eyelids. 
The lacrimal canals begin as two minute orifices 
at the apices of the papillae lacrimales situated near 
the inner canthus. They are lined by stratified 
epithelium and open directly into the lacrimal sac. 
The latter is lined with simple pseudostratificd epi- 
Fig. 300.-1, Canalicu- 
lus; 2, lacrimal sac; 3, na- 
sal duct; 4, plica semilu- 
naris; 5, caruncula lacri- 
malis (Leidy). 414 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
thelium, having two strata of nuclei, and represents 
the upper expanded portion of the nasal duct. 
This duct has a similar epithelium and opens into 
the inferior meatus of the nose. Ciliated epithelium 
has been described as being present in the nasal duct, 
and also mucous glands in the lower parts. CHAPTER XV. 
THE ORGAN OF HEARING. 
The organ of hearing consists of three portions,-- 
external, middle, and internal ear, the last being the 
essential part, as within this are the peripheral termi- 
nations of the auditory nerve. 
i. The External Ear.-The pinna or auricle pro- 
jects from the side of the head and is covered with a 
thin layer of skin, in which are found hairs, sebaceous 
glands, and sweat glands. A cartilage matrix of 
this portion is of the clastic variety with interposed 
areas of non-elastic cartilage. The lower lobe is free 
from cartilage and is composed of adipose tissue. 
The external auditory meatus is the passage leading 
inward from the concha as far as the tympanic mem- 
brane. Its average length is about one inch. This 
tube may be divided into an external cartilaginous 
portion and an internal osseous portion. The skin 
lining the cartilaginous portion is clothed with coarse 
hairs and possesses modified sweat glands called 
ceruminous glands. These are branched, of the 
tubulo-alveolar variety, and empty into hair fol- 
licles near the surface of the skin, or on the surface 
of the skin in the neighborhood of the hair follicles. 
The skin of the osseous portion is supplied with 
neither hair nor glands, but possesses slender papillae. 
415 416 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
At the bottom of the auditory canal is the tympanic 
membrane. It is an elliptical disc placed at an ob- 
lique angle to the ear canal, with its antero-infcrior 
border most distant from the outer orifice. This 
membrane is composed of three layers, an external 
cutaneous, a middle fibrous, and an inner mucous. 
The external layer is continuous with the integu- 
mentary lining of the meatus and consists of a thin 
layer of cutis covered by epidermis. The middle 
layer, or membrana propria, consists of two sets of 
fibers,-external or 
radial fibers next to 
the integument, and 
internal or circular 
fibers next to the in- 
ner mucous lining. 
The circular fibers 
are numerous near 
the circumference 
but scattered and 
few in number near 
the center. In the 
upper and anterior margin of the membrane is a 
small triangular area that is thin and lax and is 
called the pars flaccida. The main portion of the 
membrane is, on the other hand, tightly stretched 
and termed the pars tensa. Both radial and circular 
fibers are absent from the pars flaccida. 
2. The Middle Ear.-The middle ear, or tympanic 
cavity, is a small air chamber in the tympanic bone, 
intervening between the inner end of the external 
auditory meatus and the outer wall of the internal 
Fig. 301.-External ear (Randall). THE ORGAN OF HEARING. 
417 
ear or labyrinth. It is lined by a mucous membrane 
and contains the bones of the ear, malleus, incus, and 
stapes. The mucous membrane is folded over these 
ossicles and has a pseudostratified ciliated epithe- 
lium, having two strata of nuclei. Cilia are, how- 
ever, absent on the surface of the auditory ossicles, 
their ligaments, and the tympanic membrane. The 
Fig. 302.-Semidiagrammatic section through the right ear: G, Exter- 
nal auditory meatus; T, membrana tympani; P, tympanic cavity; o, 
fenestra ovalis; r, fenestra rotunda; B, semicircular canal; 5, cochlea; 
VI, scala vestibuli; Pt, scala tympani (Czermak.) 
tympanic cavity communicates with the mouth by 
a narrow canal, the Eustachian tube, which transmits 
air and conveys mucous secretion from the middle 
ear. This tube is about one and one-half inches in 
length and is directed downward and inward from 
the anterior part of the tympanum to open on the 418 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
upper part of the nasopharynx by a wide orihce. 
Its anterior part, about one inch in length, is enclosed 
in cartilage, while its posterior portion is encased in 
bone. The mucous membrane is ciliated and glands 
are absent. 
3. The Internal Ear.-The internal ear is the es- 
sential part of the 
organ of hearing 
and consists of a 
bony and a mem- 
branous labyrinth. 
The latter is 
contained within 
the former and 
represents the 
same general 
shape, the two 
being separated 
by a lymph space 
containing the 
perilymph. A se- 
ries of cavities 
constitute the 
bony labyrinth, 
which are named 
from before back- 
wards-cochlea, vestibule, and semicircular canals. 
The membranous labyrinth situated within these 
cavities consists of the membranous cochlea, utriculus, 
and sacculus, and membranous semicircular canals. 
(1) Vestibule, Utriculus, and Sacculus.-The vesti- 
bule forms the central portion of the bony labyrinth 
Fig. 303. - Otoscopic view of left 
membrana tympani : 1, Membrana flac- 
cida; 2, 2', folds bounding the former; 
3, reflection from processus brevis of 
malleus; 4, processus longus of incus 
(occasionally seen); 5, membrana tym- 
pani; 6, umbo and end of manubrium; 
7, pyramid of light (Morris). THE ORGAN OF HEARING. 
419 
and communicates behind with the bony semicircu- 
lar canals, and in front with the cochlea. Its outer 
wall forms the inner wall of the tympanic cavity, 
and in it is seen the fenestra avails, into which the 
foot of the stapes is adjusted. The posterior part 
of the vestibule receives five apertures that lead to 
the semicircular canals, while its anterior part leads 
by an elliptical opening into the scala vestibuli of the 
cochlea. 
Fig. 304.-Right bony labyrinth, viewed from outer side: The figure 
represents the appearance produced by removing the petrous portion of 
the temporal bone down to the denser layer immediately surrounding 
the labyrinth (from Quain, after Sommering). 
The utriculus and sacculus are two sac-like struc- 
tures enclosed in the bony vestibule. The two are 
indirectly connected by the ductus endolymphaticus, 
which is a Y-shaped channel that terminates in a 
blind recess, the saccus endolymphaticus. The latter 
lies against the dura on the posterior surface of the 
temporal bone. 
The zdriculus is larger than the sacculus and occu- 420 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
pies the postero-superior portion of the bony vesti- 
bule. It communicates by five apertures with the 
membranous semicircular canals. Its wall is com- 
posed of fibrous tissue, lined internally with a single 
layer of columnar epithelium. The floor and an- 
terior wall is thickened to form the macula acustica 
utriculi, which is innervated by fibers of the auditory 
nerve. The epithelium of this region is composed 
Fig. 305.-Membranous labyrinth of the right ear from five-months hu- 
man embryo (from Schwalbe, after Retzius). 
of two kinds of cells: (i) slender sustentacular cells 
resting on a basement membrane, and (2) hair cells, 
or auditory cells. The latter support a number of 
stiff hairs and constitute the neuro-epithelium, 
around which arborize the neurons of the auditory 
nerve. Crystals of calcium carbonate, known as 
otoliths, are found on the surface of the epithelium. 
The sacculus occupies the lower portion and fore THE ORGAN OF HEARING. 
421 
part of the bony vestibule. It is oval in shape, 
smaller than the utriculus, its longest diameter 
measuring about 3 mm. From its lowest part a short 
canal, the duct of Hensen, opens into the ductus 
cochlearis. Anteriorly there is an oval, whitish 
thickening, the macula acustica sacculi, innervated by 
the neurons of the auditory nerve. The histology 
of the sacculus is like that of the utriculus. 
(2) Semicircular Canals.-There are three osseous 
canals situated behind and above the vestibule. 
The superior canal is vertical, the external is hori- 
zontal, and the posterior is vertical. They open into 
the vestibule by five apertures, since the inner ex- 
tremity of the superior and the upper extremity of 
the posterior join to form a common duct, the 
canalis communis. Each canal presents an en- 
largement or osseous ampulla near its origin with 
the vestibule. The membranous semicircular canals 
partly fill the bony canals, to which they conform. 
The peripheral border of each canal is fixed to the 
periosteum of the bony canals while the opposite part 
is free. Each canal is dilated in the bony ampulla 
to form a membranous ampulla. These canals com- 
municate with the utriculus and possess a fibrous 
wall clothed with simple pavement epithelium, ex- 
cepting in the ampullae, where it is columnar. In the 
latter slender sustentacular cells intervene between 
shorter neuro-epithelial cells, or hair cells,, similar to 
those of the maculae. The neurons of the auditory 
nerve arborize around the bases of the hair cells. 
(3) The Bony and Membranous Cochlea.-The bony 
cochlea assumes the form of a short cone and con- 422 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
sists of a spirally arranged tube which forms from 
two and one-half to two and three-quarter coils 
around a central pillar termed the modiolus. The 
length of this tube is about 30 mm. and its diameter, 
near the base of the cochlea, about 2 mm. The 
Fig. 306.-Longitudinal section of the cochlea of a cat. This figure 
gives a general view of the cochlea. The cochlear duct is met with six 
times in the section (Sobotta). 
modiolus is about 3 mm. in height and transmits the 
nerve. A flat shelf of bone, the lamina spiralis, 
winds around the modiolus like the thread of a screw, 
and projects about half-way into the cochlear tube 
and thus incompletely divides' this tube into two 
passages, of which the upper is named the scala vesti- THE ORGAN OF HEARING. 
423 
buli, and the lower the scala tympani. A mem- 
brane-the membrana basilaris-stretches from the 
free edge of the bony lamina spiralis to the outer 
wall of the cochlea and completes the scala vestibuli 
Fig. 307.-Section through one of the turns of the osseous and mem- 
branous cochlear ducts of the cochlea of a guinea-pig: I, Scala vestibuli; 
m, labium vestibulare of the limbus; n, sulcus spiralis internus; o, nerve 
fibers lying in the lamina spiralis; p, ganglion cells; q, blood-vessels; a, 
bone; b, Reissner's membrane; De, ductus cochlearis; d, Corti's mem- 
brane; /, prominentia spiralis; g, organ of Corti; h, ligamentum spirale; 
i, crista basilaris; k, scala tympani (Bohm and Davidoff). 
and the scala tympani, but the two communicate 
at the apex of the cochlea. The scala tympani 
begins at the fenestra rotunda, in the inner wall of the 424 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
tympanum just below the fenestra ovalis, and the 
scala vestibuli leads to the perilymphatic space of 
the vestibule. The fenestra rotunda is closed by 
the tympanic membrane. 
From what has been stated it is evident that an 
injection into the scala tympani through the fora- 
men rotunda will pass into the scala vestibuli at the 
apex of the cochlea, and travel down the passage 
above the lamina spiralis to ultimately reach the 
perilymphatic space of the vestibule and exert press- 
ure against the base of the stapes through the fenes- 
tra ovalis. 
The membranous cochlea (ductus cochlearis or scala 
media) forms a spiral canal inside the bony cochlea, 
and ends at the apex , of the latter in a blind ex- 
tremity, the lagena. This scala media lies near the 
free margin of the lamina spiralis and just above 
the membrana basilaris. It thus forms a spiral tube 
that gradually increases in size from its lower to its 
upper or distal end. Its lower end communicates 
with the sacculus through the ductus reunions of 
Hensen. Triangular in transverse section it has a 
roof, called Reissner's membrane, which separates it 
from the scala vestibuli. Its outer wall is the peri- 
osteal lining of the bony cochlea, while its floor is the 
outer border of the lamina spiralis and the membrana 
basilaris. This membranous labyrinth is clothed 
throughout its whole length by a single layer of 
epithelial cells. 
Reissner's membrane consists of an exceedingly 
thin connective-tissue lamella lined on the vestibular 
side with a single layer of endothelial cells, and on the The organ of hearing. 
425 
cochlear duct by a single layer of flat epithelial 
cells. 
The outer wall of the scala media is the periosteal 
lining of the bony cochlea which is thickened and 
modified to form what is termed the ligamenturn 
spirale cochleae. The ligament has a projection, the 
crista basilaris, to which the outer edge of the mem- 
brana basilaris is attached. The inner surface of 
Fig. 308.-Organ of Corti: At x the tectorial membrane is raised; c, 
outer sustentacular cells; d, outer auditory cells; /, outer pillar cells; g, 
tectorial membrane; h, inner sustentacular cells; i,p, epithelium of the 
sulcus spiralis internus; k, labium vestibulare; e, tympanic investing 
layer; in, outer auditory cells; n, n, nerve fibers which extend through 
the tunnel of Corti; o, inner pillar cell; q, nerve fibers; b, b, basilar mem- 
brane; a, epithelium of the sulcus spiralis externus; r, cells of Hensen; 
s, inner auditory cell; I, ligamentum spirale (after Retzius). 
this wall is clothed with simple epithelium of the 
columnar type,, which in places appears to be strat- 
ified and to possess darkly granulated cells. 
On the floor of the scala media and resting on the 
basilar membrane is the complicated structure 
termed the organ of Corti. This consists of the fol- 
lowing structures: (i) Corti's rods or pillars; (2) 426 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
hair cells (inner and outer); (3) supporting cells of 
Deiters; (4) the cells of Hensen and Claudius; (5) 
the lamina reticularis, and (6) a cuticular membrane, 
the membrana tectoria. 
1. The rods of Corti form two rows, an inner and an 
outer. The bases of the two rows are planted on the 
membrana basilaris, some little distance apart, and 
the outer ends come in contact so that between the 
two rows above and the basilar membrane below 
there is enclosed a triangular tunnel, the tunnel of 
Corti. This tunnel increases both in height and 
width toward the apex of the cochlea. The inner 
rods number nearly six thousand. The outer rods 
number about four thousand, and are longer than the 
inner. They are also more inclined toward the bas- 
ilar membrane and form with it an angle of about 
forty degrees. 
2. The hair cells are placed on each side of the rods 
and thus form an inner and an outer set. The inner 
hair cells form a single row and number about three 
thousand five hundred, so that each cell is sup- 
ported by a little more than one rod. Their free ex- 
tremities are surmounted by about twenty fine hair- 
like processes arranged in the form of a crescent. 
Each cell is oval and contains a large nucleus. The 
lower end is rounded and reaches about half-way 
down the rod, and in contact with this end are the 
arborizations of the nerve terminations. To the 
inner side of these cells are several rows of columnar 
cells that function as supports. The outer hair cells 
number about twelve thousand, and form three rows 
in the basal coil and about four rows in the upper two THE ORGAN OF HEARING. 
427 
coils. The free extremity of each cell supports some 
twenty hair-like processes, while the outer extremity 
reaches half-way to the basilar membrane and is in 
contact with nerve arborizations. 
3. Deiters' supporting cells alternate with the rows 
of the outer hair cells. Their lower ends expand 
upon the basilar membrane, and the upper end tapers 
Fig. 309.-Section of Corti's organ from guinea-pig's cochlea: ST, 
scala tympani; FC, tunnel of Corti; a, bony tissue or spiral lamina; b, b, 
fibrous tissue covering same continued as substantia propria of basilar 
membrane; c, c, protoplasmic envelope of Corti's pillars (e, e,); d, 
endothelial plates; /, heads of pillars containing oval areas; g, head 
plates of pillars; h, h', inner and outer hair cells; m, membrana retic- 
ularis; k, I, cells of Hensen and Claudius; n, n, nerve fibers; i, cells of 
Deiters (after Piersol). 
and extends to the free surface of the hair cells. 
Each cell has a nucleus near its middle and contains 
a bright thread-like structure, called the supporting 
fiber. 
4. The cells oj Hensen are outer supporting cells and 
consist of several rows just outside of Deiters' cells, 
where they form a well-marked elevation on the floor 428 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
of the scala media. The columnar cells just external 
to this elevation are named the cells of Claudius. 
5. The lamina reticularis is a thin cuticular 
structure which lies over Corti's organ and extends 
from the outer rods as far as Hensen's cells. This 
membrane has numerous small apertures into which 
the outer hair cells project. 
6. The membrana tectoria is an elastic membrane 
attached to the free margin of the lamina spiralis and 
reaching outward as far as the outer row of hair cells. 
This membrane has no nuclei and shows fine radial 
striations. The membrane is supposed to act as a 
damper to the hair cells. 
The Auditory Nerve.-The auditory nerve divides 
into two main parts, the ramus 'vestibularis and the 
ramus cochlearis. The vestibularis divides into 
three branches which are the macula acustica, utric- 
uli, and the ampullae of the inferior and external 
semicircular canals. The ramus cochlearis supplies 
a branch to the macula acustica sacculi and one to 
the ampulla of the posterior semicircular canal. The 
remainder of the ramus cochlearis is distributed to 
the hair cells of Corti's organ. Near the base of the 
osseous spiral lamina there is situated, in a special 
bony canal, a ganglion called the spiral ganglion of 
the cochlea. The ganglion cells are bipolar, having 
a dendrite that extends inward through the lamina 
spiralis to the organ of Corti, and a neuraxis that 
passes out the modiolus and thence to the medulla. 
Some of the dendritic processes pass through the 
tunnel of Corti, so called tunnel fibers, to reach the 
outer hair cells. THE ORGAN OF HEARING. 
429 
DEVELOPMENT OF THE LABYRINTH. 
The epithelial lining of the membranous labyrinth 
is derived from the ectoderm and develops as a vesic- 
ular invagination on each side of the epencephalon. 
After being constricted off from the ectoderm this 
vesicle develops a dorsomesial evagination, which 
gradually grows larger and becomes the ductus endo- 
Fig. 310.-Three transverse sections showing development of otic 
vesicle of human embryo (Tourneux): A, from embryo of 3 mm., showing 
auditory pit; B, from embryo of 4 mm., showing the transformation of 
the pit into the otic vesicle; C, from embryo of 6 mm., showing otic 
vesicle detached from surface ectoderm, and presenting a posterior 
diverticulum, the recessus vestibuli. 
lymphaticus. By means of folds and constrictions 
the dorsal utriculus and ventral sacculus are formed, 
and also the semicircular canals which connect with 
the utriculus. The membranous cochlea or scala 
media grows both in a longitudinal and a spiral 
direction, retaining its connection with the sacculus 
through the canalis reuniens. This complex mem- 430 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
branous labyrinth becomes invested with developing 
bone, and is filled with endolymph and surrounded 
with perilymph. The developmental history of the 
middle and external ear is closely associated with 
that of the first gill cleft of which they primarily 
form an associate part. CHAPTER XVI. 
OLFACTORY ORGAN. 
The olfactory region may be divided into the vesti- 
bule, respiratory organ, and the olfactory organ. 
i. The 'vestibule is cov- 
ered with a continuation 
of the skin, which grad- 
ually takes on the char- 
acter of a mucous mem- 
brane. The epithelium 
is of a stratified squa- 
mous variety, and pre- 
sents hairs, sebaceous 
glands, and mucous 
glands. The vestibule 
comprises the region of 
the anterior nares. 
2. The respiratory re- 
gion is lined by ciliated 
epithelial cells, the nuclei 
of which are placed at 
various levels. Hairs 
and sebaceous glands are 
absent, but branched al- 
veolar glands having 
mucous and serous cells 
are present. Numerous 
leukocytes are usually found upon the surface. 
Fig. 311.-Olfactory mucous 
membrane; a, sustentacular cells; 
b, olfactory cells; c, basal cells; d, 
submucous fibrous tissue; e, glands 
of Bowman; /, nerve fibers (Leroy). 
431 432 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
3. The olfactory region is usually confined to the 
superior turbinated bone and to the adjacent nasal 
septum. In the fresh condition the region may be 
Fig. 312.-Diagram of the connections of cells and fibers in the ol- 
factory bulb: olj. c, cells of the olfactory mucous membrane; olj. n, 
deepest layer of the bulb, composed of the olfactory nerve fibers which 
are prolonged from the olfactory cells; gl, olfactory glomeruli, containing 
arborization of the olfactory nerve fibers and of the dendrons of the mitral 
cells; me, mitral cells; a, thin axis-cylinder process passing toward the 
nerve-fiber layer, n. tr, of the bulb to become continuous with fibers of 
the olfactory tract; these axis-cylinder processes are seen to give off 
collaterals, some of which pass again into the deeper layers of the bulb; 
ri, a nerve fiber from the olfactory tract ramifying in the gray matter of 
the bulb (Schafer). 
distinguished by its yellow color, which is due to 
pigment in the sustentacular epithelial cells. 
The olfactory cells are true bipolar ganglion cells. 
The upper process of these cells reaches to the free OLFACTORY ORGAN. 
433 
surface of the epithelial layer and is short. It ter- 
minates in six to eight short firm hairs. The lower 
thinner process is a neuraxone which passes through 
the cribriform plate to terminate in telodendria in 
the region of the olfactory bulb. The sustentacular 
cells are long columnar elements with oval nuclei. 
They give support to the ganglion cells. 
Targe branched tubular glands are present, called 
the glands of Bowman. They secrete an albuminous 
or serous fluid. Beneath the epithelium there is a 
rich supply of capillary blood-vessels and lymphatics. 
Fibers from the trigeminal nerve terminate in telo- 
dendria among the epithelial cells of the entire 
olfactory region. CHAPTER XVII: 
LABORATORY DIRECTIONS. 
The following is a brief outline of the tissues to be 
prepared for a laboratory course accompanying the 
text. Special technique is cited whenever indicated, 
otherwise standard laboratory methods may be em- 
ployed. This outline is abbreviated and should be 
expanded according to the skill of the instructor or 
student and according to the laboratory equipment. 
Mitosis. 
i. Growing point of onion or lily root tip, hardened 
in Flemming or corrosive sublimate, and cut in longi- 
tudinal section. 
2. Testicle of grasshopper taken in June, or ova, 
or skin stripped from tail of growing tadpoles. Iron 
hematoxylin stain is excellent. 
Epithelium. 
i. Isolated epithelial cells from intestine, trachea 
and bladder (see Introduction). 
2. Epithelium exfoliated from skin of frog (pieces 
gathered from water where frogs are kept). 
3. Fresh cells scraped from mucous surface of 
cheek. 
4. Sections of intestine, cornea of the eye, and skin. 
5. Endothelial cells of mesentery. 
Prepare endothelium as follows: 
(1) Kill a small animal, as a rat. 
434 LABORATORY DIRECTIONS. 
435 
(2) Open abdominal cavity. 
(3) Wash out cavity with sterile water; do not 
handle the mesentery. 
(4) Fill cavity with | per cent, silver nitrate 
solution, 5 min. See that mesentery is 
bathed. 
(5) Wash cavity with | per cent, nitric acid 
solution, 5 min. 
(6) Fill cavity with alcohol 95 per cent, one-half 
to one hour, as convenient. 
(7) Remove mesentery with intestine attached. 
(8) Immerse in fresh 95 per cent, alcohol one to 
twelve hours. 
(9) Cut intestine away from mesentery and im- 
merse the latter in fresh 95 per cent, alcohol, 
one-half to one hour. 
(10) Transfer mesentery to clove oil and expose 
to sunlight in shallow wide dish, three to live 
hours. Direct sunlight is not good. 
(11) Cut mesentery into small pieces and mount 
in balsam. Handle mesentery as little as 
possible during the whole process. 
Glands. 
1. For simple mucous and serous glands make 
cross sections of the skin of a salamander. 
Connective Tissue. 
1. Sections of young umbilical cord and of em- 
bryos show connective-tissue cells. 
2. Sections of fat and teased fresh pieces of fat. 
3. Salamander skin, dehydrated and mounted 
with lower side up shows connective-tissue pigment 
cells. 436 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
4. Brown connective-tissue pigment cells may be 
scraped from the choroid coat of the eye after re- 
moving the retina. 
5. Sections and teased preparations of ligamentum 
nuchae of the ox. 
6. Sections and teased preparations of a tendon. 
7. Elastic fibers of the mesentery of a rat. 
PREPARATION OF ELASTIC FIBERS. 
(1) Fill abdominal cavity of a rat with 95 per cent, 
alcohol, one hour. 
(2) Remove intestine with mesentery attached 
and place in fresh alcohol. 
(3) Cut away the mesentery and stain. 
Orcein 1 part. 
Alcohol, 95 per cent 100 parts. 
Hydrochloric acid 1 part 
Stain for one to twelve hours. The fibers should 
appear dark brown. If stained too deeply, treat 
with acid alcohol, | per cent, hydrochloric acid. If 
too red, dip the pieces in ammonium hydroxid 
water supersaturated with crystals of picric acid. 
Cartilage. 
i. Cartilage sections may be cut with a razor from 
bone joints obtained at a meat market. 
2. Sections of trachea for hyaline variety. The 
sections must be cut thin and not overstained. 
Bone. 
i. Ground sections, mounted dry. A dry white 
and fat-free bone is the best. With a turning table 
ring a glass slide with balsam. Before the balsam 
sets the bone may be mounted dry by covering LABORATORY DIRECTIONS. 
437 
with circular cover glass, which sticks to the ring of 
balsam. 
2. Sections of decalcified bone. Place a fresh 
bone in 95 per cent, alcohol to fix and harden soft 
parts. Next day begin process of decalcification. 
Use nitric or hydrochloric acid, | to i per cent., using 
a large quantity and changing fluid twice daily. 
Nitric acid may be used in i to io per cent, strength. 
Time required varies from one to seven days. By 
means of sharp needles it is possible to determine 
when decalcification is complete. -After decalci- 
fication wash in running water for twenty-four hours. 
Muscle. 
i. Smooth muscle. Pieces stripped from the 
intestinal wall may be stained for twenty-four hours 
with dilute hematoxylin. Tease in glycerin and 
alcohol, or, for permanent mounts, dehydrate and 
tease in oil. 
2. Cross sections of the intestine will show smooth 
muscle in cross and in longitudinal sections. 
3. Pleart muscle. Teased specimens and very 
thin sections. 
4. Voluntary muscle. Sections of a tongue will 
show fibers both in cross and in longitudinal section. 
5. Injected muscle. Sections should be cut very 
thick to show capillaries. Such muscle carefully 
teased is very satisfactory. 
6. Fresh voluntary fibers may be teased in 
alcohol and glycerin. 
Nervous Tissue. 
1. For bipolar cells study sections of the spinal 
ganglion. 438 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
2. For multipolar cells study sections of the cere- 
bral cortex and spinal cord stained with Cox-Golgi 
method, as follows: 
Potassium bichromate 20 parts. 
Corrosive sublimate 5 per cent. 
sol 20 parts. 
Distilled water 40 parts. 
Potassium chromate, 5 percent. 
sol 16 parts. 
Specimens remain in this two weeks or two 
months; after which wash thoroughly twenty-four 
hours. Cut sections free-hand as thin as possible 
and place them in a saturated solution of lithium 
carbonate for twenty-four hours. Transfer to 95 
per cent, alcohol, and then to clove oil, from which 
they are mounted in balsam on a glass slide and 
covered with a cover glass. 
3. Fix a sciatic nerve with 0.5 per cent, osmic acid. 
Wash thoroughly in water and tease either in glyc- 
erin or dehydrate and tease in oil. Study structure 
of medullated fibers. 
4. Make cross section of sciatic nerve. 
Blood. 
1. Dip a thin strip of filter paper in the blood of a 
frog and make a spread either on a cover glass or a 
glass slide. Dry in air and fix in 95 per cent, alcohol. 
Stain with hematoxylin and eosin. Wash in water 
and dry in air, after which the specimen may be 
mounted in balsam. 
2. Study fresh specimens of human blood for 
rouleaux and crenated red blood corpuscles. 
3. Thin blood spreads may be made: 
(1) On glass slides by placing a drop of blood near LABORATORY DIRECTIONS. 
439 
one end and with the end of a second slide spread it 
by making a single stroke toward the opposite end. 
(2) Placing a small drop between two cover 
glasses and drawing them apart in such a way that 
their surfaces are always parallel. 
(3) Saturate the end of some thin blotting paper 
and make a spread either on a cover glass or a glass 
slide. 
4. Spreads are dried in air and then fixed, by 
heat (1200 C.), for two hours, or equal parts of 
absolute alcohol and ether for two hours. They 
are then dried and stained. Wright's stain is a 
short method and fixes and stains a film at the same 
time. 
(1) Stain a blood film with Wright's fluid one 
minute. 
(2) Distilled water 2 min. Add in drops upon 
cover glass or slide. 
(3) Wash in water until the film of blood becomes 
pink. 
(4) Dry between filter paper and mount in balsam. 
(For preparation of Wright's stain see "Pathological 
Technique," Mallory and Wright, Third Edition.) 
5. Blood platelets are obtained by pricking the 
finger through a drop of 1 per cent, osmic acid. 
6. Flemin crystals. Grind together on a slide 
equal parts of dry blood and salt. Add glacial acetic 
acid and cover with cover glass. Heat until gas 
bubbles escape. Examine with high-power of micro- 
scope. 
Red Marrow.-With a pair of pinchers squeeze a 
drop from the end of a rib and spread on slide or 440 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
cover glass. Fix and stain as for blood. A spread 
may be made from the end of the femur or any of the 
long bones. 
Blood-vessels. 
i. Sections of the aorta. 
2. Small arteries can be found in sections of the 
tongue or any other organ. 
3. Sections of any large vein. 
Lymphatics, Thymus Gland, Spleen. 
1. Sections of lymphatic nodes. 
2. Sections of thymus gland. 
3. Sections of the spleen. 
These tissues must be cut thin and not overstained. 
Digestive System. 
1. Teeth. Ground sections, technique as for bone. 
2. Tongue. Section foliate papillae of rabbit for 
taste buds. 
3. Cross section of esophagus. 
4. Sections of cardiac and pyloric end of stomach. 
5. Small intestine. Injected specimen must be 
cut thick. 
6. Sections of ileum for Peyer's patches. 
7. Large intestine, including vermiform appendix. 
Digestive Glands. 
1. Sections of parotid and submaxillary gland. 
2. Pancreas. Injected pancreas for areas of 
Langerhans. 
3. Liver, including sections of injected organ cut 
thick. 
Organs of Respiration. 
1. Sections of thyroid gland. 
2. Sections of trachea. LABORATORY DIRECTIONS. 
441 
3. Lung, including thick sections of injected organ. 
Urinary Organs. 
i. Suprarenal bodies. 
2. Kidneys. Sections of injected kidney and 
kidney pieces macerated with hydrochloric acid 
(see Introduction). 
3. Sections of ureters. 
4. Bladder, preferably sections of one distended 
with fixing fluid. 
Reproductive Organs. 
1. Sections of testes with epididymis attached. 
2. Vas deferens. 
3. Sections of penis, preferably of baby or a fetus. 
4. Prostate gland, preferably an old one. 
5. Ovaries. Old enough to show corpora lutea. 
6. Fallopian tubes. Sections of fundus and isth- 
mus. 
7. Uterus. 
8. Placenta, preferably at half term. 
9. Mammary gland. 
The Skin and Appendages. 
1. Sections of palm surface of finger. 
2. Sections of the scalp, tangential and cross. 
3. Nails. Sections of finger of fetus are very 
good. 
Peripheral Nerve Endings and Spinal Cord. 
1. Sections of duck's bill. Iron hematoxylin 
stain. 
2. Pacinian corpuscles may be found in sections 
of the skin of the finger or in the connective tissue 
of sections of the pancreas. They may be teased 
out from the mesentery. 442 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
3. Spinal cord. The cord of the horse or ox is 
very satisfactory. 
Brain. 
1. Sections of cerebral cortex. 
2. Sections of cerebellar cortex cut across the 
folds. 
3. Sections of closed and open medulla. 
4. Sections of the pons. 
Sections of the medulla and pons should be cut 
thick and stained with Pal-Weigcrt method. 
Celloidin method of imbedding is preferable. 
The Eye. 
1. Sections of the whole eye imbedded in celloidin. 
2. Sections of the cornea. 
3. Sections of the retina. 
4. Sections of the eyelid. 
The Internal Ear. 
Sections of the cochlea must be decalcified. 
Cochlea of a young kitten is very satisfactory. 
STANDARD FIXING SOLUTIONS. 
Carnoy's Acetic-alcohol Mixture. 
Glacial acetic acid 1 part. 
Absolute alcohol 3 parts. 
Pieces one centimeter thick are fixed in one-half to 
one hour. The after-treatment is with absolute 
alcohol. 
Osmic Acid.-One-half to one per cent, aqueous 
solution. 
Fix for three to twenty-four hours and then wash 
thoroughly in running water. LABORATORY DIRECTIONS. 
443 
Flemming's Solution. 
Osmic acid, 1 per cent, aqueous 
solution 10 parts. 
Chromic acid, 1 per cent, aque- 
ous solution 25 parts. 
Glacial acetic acid, 1 per cent, 
aqueous solution 10 parts. 
Distilled water 55 parts. 
Fix for twenty-four hours or more and wash thor- 
oughly in running water. 
Flemming's Strong Solution. 
Osmic acid, 2 per cent, aqueous 
solution 4 parts. 
Chromic acid, 1 per cent, aque- 
ous solution 15 parts. 
Glacial acetic acid 1 part. 
This is a good fixing agent for nuclear structures 
and therefore for mitosis. 
Corrosive Sublimate. 
Saturated solution in distilled water. Fix for 
twenty-four hours or more and wash in running water. 
After twenty-four hours, transfer to 70 per cent, 
alcohol to which a few drops of iodin and potassium 
iodid have been added. The iodin removes any 
crystals of sublimate that may have formed. 
Picric Acid. 
Saturated aqueous solution. Fix for twenty-four 
hours, or longer, after which wash in 70 per cent, 
alcohol. 
Picrosulphuric Acid. 
Picric acid, saturated aqueous 
solution 100 parts. 
Sulphuric acid, concentrated... 1 part. 
Distilled water 200 parts. 
After-treatment same as for picric acid. 
Nitric Acid.-Aqueous solution, 3 to 10 per cent. 444 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
Fix for several hours and wash thoroughly in running 
water. 
Chromic Acid.-Aqueous solution | to i per cent. 
Small pieces are fixed for twenty-four hours. Wash 
in running water and pass through the ascending 
grades of alcohol, preferably in the dark. 
Muller's Fluid 
Potassium bichromate 2.5 gm. 
Sodium sulphate 1.0 gm. 
Water 100 c.c. 
Fix for several weeks, preferably in the dark. At 
first the fluid should be changed daily. Wash in 
running water for twenty-four hours and place 
directly in 70 per cent, alcohol. Dehydrate prefer- 
ably in the dark. 
Zenker's Fluid. 
Potassium bichromate 2.5 gm. 
Sodium sulphate 1.0 gm. 
Corrosive sublimate 5.0 gm. 
Glacial acetic acid 100 gm. 
It is better to add the acetic acid just before using 
and not to add it to the stock solution. Fix tissues 
in this fluid for six to twenty-four hours. Wash in 
running water twenty-four hours and transfer to 
alcohol, using the grades. Sublimate crystals are 
removed by iodized alcohol as with corrosive subli- 
mate solutions. 
Formalin. 
Formalin (40 per cent. Formal- 
dehyde) 5 to 10 parts. 
Water 90 parts. 
Small'pieces are fixed in twelve to twenty-four hours. 
As sections do not stain well after this fixation, it LABORATORY DIRECTIONS. 
445 
is better to transfer the pieces to some standard salt 
solution and then wash and dehydrate. 
Potassium Bichromate and Formalin. 
Potassium bichromate 2 per 
cent, aqueous solution 90 parts. 
Formalin 10 parts. 
Fix for several days or weeks. Wash in running 
water and dehydrate with alcohol. This is a good 
fixation for the central nervous system. 
STANDARD STAINS. 
Aqueous Borax-carmin Solution. 
Borax 8 gm. 
Carmin 2 gm. 
Water 150 c.c. 
Grind together the borax and carmin. Add the 
water and in twenty-four hours filter. Stain sections 
for twelve hours or longer. Treat with acid-alcohol 
as necessary. 
Alcohol Borax-carmin Solution. 
Carmin 3 gm. 
Borax 4 gm. 
Water 93 c.c. 
Alcohol, 70 per cent 100 c.c. 
Filter and stain as for the aqueous solution. 
Cochineal Solution. 
Cochineal, powdered 7 gm. 
Alum, roasted 7 gm. 
Water 100 c.c. 
Boil down to one-half its volume, stirring freely. 
When cool filter and add a few drops of carbolic acid. 
This fluid does not overstain and acts rapidly. After 
staining wash in distilled water, as alcohol precipi- 
tates the alum. 446 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
Alum-carmin (Grenacher). 
Alum solution, 3 per cent, to 5 
per cent 100 c.c. 
Carmin 1 to 5 gm. 
Boil for fifteen minutes, cool and filter. Add enough 
water to replace that lost by boiling. Wash the 
sections in water after staining. 
Bohmer's Hematoxylin. 
Hematoxylin 1 gm. 
Alcohol, absolute 10 c.c. 
Potassium alum 10 c.c. 
Distilled water 200 c.c. 
Dissolve the hematoxylin in alcohol and the alum in 
water. Add the first to the second solution while 
continually stirring. Allow this preparation to 
stand in an open jar for two weeks, to ripen, when 
the color will change from violet to blue. After 
filtering the stain is ready. 
Delafield's Hematoxylin. 
Hematoxylin crystals 4 gm. 
Absolute alcohol 25 c.c. 
Ammonium alum, sat. aq. sol. .400 c.c. 
Alcohol 95 per cent 100 c.c. 
Glycerin 100 c.c. 
Dissolve the hematoxylin in absolute alcohol and add 
the alum solution. Place in open vessel for four 
days, filter, and add the 95 per cent, alcohol and 
glycerin. In a few days filter again. 
Ehrlich's Hematoxylin. 
Hematoxylin crystals 2 gm. 
Absolute alcohol 60 c.c. 
Glycerin saturated with 60 c.c. 
Distilled water J ammonia-alum 60 c.c. 
Glacial acetic acid 3 c.c. 
Expose to light for a long time. It is ready for use 
when it acquires a deep red color. LABORATORY DIRECTIONS. 
447 
Heidenhain's Iron Hematoxylin. 
Sections that have been fixed in sublimate solu- 
tions are placed in a 2.5 per cent, aqueous 
solution of ammonium sulphate of iron for four to 
eight hours. Rinse thoroughly in water and place 
in a hematoxylin solution prepared as follows: 
Hematoxylin crystals 1 gm. 
Absolute alcohol 10 c.c. 
Distilled water 90 c.c. 
Dissolve the hematoxylin in the alcohol and add the 
water. This solution should stand in an open vessel 
for four weeks, and before using should be diluted 
with an equal volume of distilled water. 
Stain the above sections twelve to twenty-four 
hours, rinse in top water and return to ammonium 
sulphate of iron solution until black clouds cease to 
be given off from the sections. Rinse in distilled 
water, dehydrate, and mount in balsam. 
This is a good stain for mitosis. 
Anilin Stains. 
These are basic or acid stains. The basic stains 
are safranin, methylene-blue, methyl green, gentian 
violet, methyl violet, Bismarck brown, tliionin, and 
toluidin blue, and stain nuclei. The acid stains are 
eosin, erythrosin, acid fuchsin, orange G. and nigro- 
sin, and stain cytoplasm. 
These stains are used in water solutions and of 
| to i per cent, strength, to which a little alcohol 
may be added. 
Pal-Weigert Method of Staining Sections of Brain 
or Cord. 
Mordant celloidin sections for twenty-four hours 448 
NORMAL HISTOLOGY AND ORGANOGRAPHY. 
in 3 to 5 per cent, aqueous solution of potassium 
bichromate. Wash in water and transfer to the 
following stain: 
Hematoxylin crystals 1 gm. 
Alcohol 95 per cent 10 c.c. 
Lithium carbonate, sat. aq. sol. 1 c.c. 
Water 90 c.c. 
Dissolve the hematoxylin in alcohol first, and then 
add the balance at the time of using. Stain the 
sections in this for twenty-four hours. Wash in 
water and transfer to a 0.25 per cent, fresh solution 
of potassium permanganate for one-half to two min- 
utes. Wash freely in water and place in the follow- 
ing Pal solution: 
Oxalic acid 1 gm. 
Potassium sulphate.- 1 gm. 
Water 200 c.c. 
This will differentiate the gray and white matter 
in one to three minutes. The nerve fibers should 
stain blue. If the sections are too dark they may 
be carried through the permanganate and Pal's so- 
lution a second time. Transfer to water for several 
hours, dehydrate, and mount in balsam. 
For a more complete description of laboratory 
methods, including injections, fixing of tissues, and 
special staining methods, see the following texts: 
"Pathological Technique," Mallory and Wright, 
Third Edition. 
" Microtomist's Vademecum," Fee. 
Bohm-Davidoff-Huber, " Flistology," Second Edi- 
tion, 1904, INDEX. 
Accessory thyroid glands, 197 
Accommodation, muscles of, 398 
Acetic-alcohol, Carnoy's, 442 
Achromatic substance, 39 
Acid, chromic, 444 
nitric, 443 
osmic, 442 
picric, 443 
picrosulphuric, 443 
Acrodont dentition, 157 
Adenoids, 168 
Adventitia of blood-vessels, 103 
Agminated lymph nodules, 184 
Air cells of lung, 230 
sacs of lung, 230 
Alimentary canal, classification, 
124 
lymphatics of, 191 
nerve supply of, 191 
Alveoli of lung, 231 
Alum carmin, 446 
Amitosis, 42 
Ampullae of Thoma of spleen, 120 
Anaphase, 41 
Anilin stains, 447 
Anisotropic muscle, 82 
Anterior gray commissure of 
cord, 353 
ground bundle, 361 
horn of cord, 354 
Appendices epiploicae, 187 
Aqueous humor, 406 
Arachnoid of brain, 364 
of cord, 351 
Arbor vitae of cerebellum, 376 
Arch, mandibular, 126 
maxillary, 127 
Archenteron, 32 
Arcuate fibers, 368, 369, 371 
Arcuate nucleus, 369, 371 
Area acusticae, 366 
Areas of Langerhans, 201 
Areolar connective tissue, 64 
Arrector pili, 330 
Arteries, 101 
helicine, 276 
Arteriosclerosis, 110 
Asthma, 229 
Atheroma, 110 
Atria of lung, 230 
Attraction sphere, 40 
Auditory meatus, 415 
nerve, 428 
Auerbach's plexus, 178, 191 
Axis cylinder of nervous tis- 
sue, 87, 91 
Bartholin's glands, 282 
Bertini's columns, 247 
Bile duct, 206, 208 
Bipolar nerve cells, 89 
Bladder, 257 
mucous membrane of, 258 
trigone of, 258 
vessels and nerves of, 260 
Blastophore, 32 
Blood, 105 
crenatedred blood cor- 
puscles, 105 
ghost corpuscles, 105 
hemin crystals, 109 
hemoglobin, 105 
platelets, 108 
red blood corpuscles, 105 
rouleaux, 105 
stroma, 105 
white blood corpuscles, 107 
449 450 
INDEX 
Blood-poisoning, 121 
Blood supply of bone, 72 
of brain, 387 
of large intestine, 189 
of lungs, 234 
of muscle, 84 
of small intestine, 189 
of spinal cord, 387 
of stomach, 189 
of teeth, 154 
of tongue, 168 
Blood-vessels, 101 
adventitia of, 103 
arteries, 101 
capillaries, 104 
general considerations, 110 
intima, 101 
media, 102 
of central nervous system, 387 
of eye, 408 
of kidney, 252 
of suprarenal bodies, 241 
stigmata and stomata, 104 
vasa vasorum, 103 
Body cavity, 34 
Bone, 58, 69 
blood supply of, 72 
canaliculi, 70 
cancellate, 72 
development of, 73 
diploe, 72 
endochondral, 73 
general considerations, 76 
Haversian system, 70 
intramembranous, 73 
lacunae, 69 
ossification of, 75 
osteogenetic layer, 72 
primary areolae of Sharpey, 73 
regeneration of, 75 
secondary areolae of Sharpey, 
74 
Sharpey's fibers, 72 
Volkmann's canals, 72 
Bones of ear, 417 
Borax carmin, 445 
Bowman's capsule of kidney, 248 
glands, 433 
Brain, 362 
arachnoid of, 364 
blood-supply of, 387 
development of, 35, 362 
Brain, divisions of, 362 
dura of, 363 
meninges of, 363 
pia of, 363 
Bronchi, 226 
eparterial, 236 
hyparterial, 236 
respiratory, 230 
Brunner's glands, 185 
Burdach's columns, 357, 358, 
365, 368 
Calamus scriptorius, 366 
Canal of Petit, 408 
of Scldemm, 393 
Canaliculi, bone, 70 
Cancellate bone, 72 
Capillaries, 104 
lymphatic, 113 
Capsule, lens, 406 
of Glisson, 204, 207 
of kidney, Bowman's, 248 
Tenon's, 393 
Cardiac muscle, 79 
Carmin, alum, 446 
borax, 445 
Carnoy's acetic-alcohol, 442 
Cartilage, 58, 65 
elastic, 68 
general considerations, 69 
hyaline, 67 
lacunae of, 65, 67 
of trachea, 226 
white fibrous, 68 
Cartilages of larynx, 217 
Casts of kidney, tubular, 251 
Cauda equina, 349 
Cell, 27 
air, of lung, 230 
cleavage of, laws of, 42 
column, Waldeyer's central. 
354 
cortical, 376 
decidual, 309 
defined, 27, 36 
Deiters' supporting, 427 
fat, 50 
general considerations, 42 
giant, 110 
goblet, 52 
inclusions of, 39 INDEX 
451 
Cell, membrane of, 37 
mossy, 96 
multipolar, 90 
nerve, bipolar, 89 
of posterior horn, 353 
unipolar, 88 
of connective tissue, 58 
of Hansen, 427 
of liver, 213 
of marrow, 110 
parietal, of salivary glands, 196 
pigment, 59 
plasma, 61 
polymorphic, of cerebrum, 383 
prickle, 323 
Purkinje's, 376 
pyramidal, of cerebrum, 383 
spider, 96 
stellate, of cerebellum, 376 
of Kupffer, 215 
tactile, 343 
wandering, 61, 108 
Celloidin imbedding, 20 
advantages of, 22 
disadvantages of, 23 
sections, staining of, 22 
Ccmentoblasts, 151, 152 
Cementum, 147 
Ccntro-acinal cells of pancreas, 
200, 201 
Centrosomes, 38, 40 
Cerebellar tract, direct, 358 
Cerebellum, 375 
arbor vitse of, 376 
climbing fibers of, 379 
cortical cells, 376 
granular layer, 379 
inferior peduncle of, 366 
medullary substance, 379 
mossy fibers, 379 
Purkinje's cells, 376 
stellate cells, 376 
Cerebrospinal system, 96, 97 
Cerebrum, 381 
fibers of, 383 
medullary substance, 384 
molecular layer, 381 
polymorphic cells, 383 
pyramidal cells of, 383 
Ceruminous glands, 415 
Cervical enlargement of spinal 
cord, 349 
Chondrin, 65 
Chorion, 310 
Chorionic villi, 311 
Choroid coat, 396 
fissure, 389 
Chromatin, 38, 39 
Chromic acid, 444 
Chromosomes, 31, 41 
daughter, 41 
in mitosis, 39 
Ciliary body, 398 
muscles, 398 
processes, 398 
Circulatory endocardium, 100 
epicardium, 100 
heart, 100 
myocardium, 100 
system, 100 
Circumvallate papillae of tongue, 
164 
Clarke's column, 354, 358 
Clava, 366 
Cleavage, 31 
of cell, laws of, 42 
Cleft palate, 130 
Climbing fibers of cerebellum, 
379 
Cochineal solution, 445 
Cochlea, 418, 421 
Coelenteron, 32 
Cohnheim's fields, 81 
Collaterals, 87 
Colostrum, 316 
Column of Bertini, 247 
of Burdach, 357, 358, 365, 368 
of Clarke, 354, 358 
of Goll, 357, 358, 365, 368 
of Sartoli, 263 
Comma tract, 357, 358 
Commissure, posterior gray, of 
cord, 353 
Cone, implantation, 93 
Conjunctiva, 411, 412 
Connective tissue, 57, 58 
areolar, 64 
cells of, 58 
classification, 62 
embryonic, 58 
diagnostic points of, 65 
fibers of, 61 
general considerations, 64 
products of, 61 452 
INDEX 
Connective tissue, reticular, 62 
white fibrous, 62 
yellow elastic, 63 
Corium, 323 
Cornea, 393 
Corneum, 321 
Corona radiata, 290 
Corpora cavernosa, 274 
structure of, 275 
lutea, 294, 295 
Corpus spongiosum, 274 
structure of, 277 
Corpuscles, genital, 345 
ghost, 105 
Grandry's, 343 
Malpighian, of kidney, 248 
of spleen, 120 
Meissner's, 344 
of Hassal, 118 
of Herbst, 344 
of Highmore, 262 
Pacinian, 347 
red blood, 105 
crenated, 105 
white blood, 107 
Corrosive sublimate, 443 
Cortex of kidney, 246 
Cortical cells, 376 
Corti's organ, 425 
rods, 426 
Cowper's glands, 282 
Cremasteric fascia, 261 
Crenated red blood corpuscles, 
105 
Crescents of Gianuzzi, 196 
Cretinism, 223 
Crossed pyramidal tract, 359 
Crus cerebri, 372 
Crypts of Lieberkuhn, 183 
of stomach, 174 
Crystals, hemin, 109 
Cutis vera, 323 
Cutting sections, 23 
Cystic duct, 206, 208, 209 
Cytoplasm, 37 
Cysts, sebaceous, 337 
Czermak's interglobular spaces, 
208 
Dandruff, 337 
Dartos, 261 
Daughter chromosomes, 41 
skein, 41 
star, 41 
Deciduae, 307 
Decidual cells, 309 
Decussation, motor, 300, 367, 
369 
sensory, 368 
Dehydrating, 20 
Deiters' nucleus, 360 
supporting cells, 427 
Demilunes of Heidenhain, 196 
Dendrite, 88 
Dentin, 143 
secondary, 145 
Dentition, 131 
acrodont, 157 
pleurodont, 157 
thecodont, 157 
Dermis, 323 
Descemet's membrane, 394, 395 
Deutoplasm, 291 
Development, general, 126 
of bone, 73 
of brain, 35, 362 
of teeth, 158 
Diaster, 41 
Digestive glands, 193 
Diploe, 72 
Direct cerebellar tract, 358 
pyramidal tract, 361 
Discus proligerus, 288 
Dissociation of tissue elements, 
18 
Diverticulum, Meckel's, 180 
Doyer's elevation, 339 
Duct, Hensen's, 421 
hepatic, 208 
lactiferous, 315 
of Santorini, 200 
of Wirsung, 199 
Ductus endolymphaticus, 419 
reuniens of Hensen, 424 
Dura of brain, 363 
of cord, 350 
Ear, bones of, 417 
external, 415 
internal, 418 
labyrinth of, 418 
middle, 416 INDEX 
453 
Ectoderm, 32, 33 
Ectosarc, 37 
Ejaculatory duct, 271 
Elastic cartilage, 68 
Eleidin, 322 
Embryology, 26 
Embryonic connective tissue, 58 
Enamel, 135 
rods, directions of, 138 
Encephalon, 326 
Endocardium, circulatory, 100 
Endochondral bone, 73 
Endolymphatic duct, 419 
Endometrium, 303 
Endomysium, 80 
Endoneurium, 96 
Endosarc, 37 
Endothelium, 56 
End-plate, muscle, 339 
Enlargement, lumbar, of spinal 
cord, 349 
Entoderm, 33 
Environment, 37 
Eosinophiles, 107, 110 
Eparterial bronchus, 236 
Epicardium, circulatory, 100 
Epidermis, 321 
Epididymus, 270 
Epidural space, 351 
Epimysium, 80 
Epineurium, 96 
Epithelium, 46, 47, 49 
Epoophoron, 299 
Erythrocytes, 105 
Esophagus, 170 
Eustachian tube, 417 
Excretory ducts of testicle, 269 
Exolemma, 93 
Exophthalmic goiter, 223 
External ear, 415 
Eye, 389 
blood-vessels of, 408 
coats of, 391 
refractory media of, 406 
tunica externa of, 392 
Fallopian tubes, 295 
development of, 298 
structure of, 297 
Falx cerebelli, 363 
cerebri, 363 
Fascia, cremasteric, 261 
intercolumnar, 261 
Fasciculi of muscle, 80 
Fasciculus soiitarius, 370 
teres, 374 
Fat cells, 50 
Fauces, 125 
Fenestra ovales, 419 
rotunda, 423 
Ferrein's pyramids, 247 
Fertilization, 30 
Fibers, arcuate, 368, 369, 371 
climbing, of cerebellum, 379 
medullated nerve, 91 
mossy, 379 
nerve, 91 
non-medullary, 95 
of cerebrum, 383 
of connective tissue, 61 
posterior root of, termination, 
358 
Sharpey's, 72 
Fibrils of nervous tissue, 91, 92 
Fibroblast, 151, 152 
Fibroma, 64 
Filiform papillae of tongue, 163 
Fillet, 374 
Filum terminale, 349 
Fissure, choroid, 389 
Fissures of liver, 203 
of spinal cord, 351 
Fixing and hardening tissues, 19 
Flemming's solution, 443 
Fluid, Muller's, 444 
Foliate papillae of tongue, 167 
Follicle, Graafian, 286, 287 
Follicles of hair, 327 
Follicular fluid, 288 
Foramen cecum of medulla, 367 
of tongue, 162 
of Winslow, 205 
Formalin, 444 
potassium bichromate and, 
445 
Formatio reticularis, 369, 371, 
374 
Fovea centralis, 404 
infundibuliform, 267 
Free sensory nerve endings, 342 
Frenum, lingual, 162 
Fungiform papillae of tongue, 
163, 164 INDEX 
454 
Funiculus cuneatus, 365, 368 
gracilis, 365, 368 
of nervous tissue, 96 
Gall bladder, 208 
Ganglia, 88 
Ganglion, spinal, 89 
spiral, 428 
Gastric glands, 175, 176 
Gastrula stage, 32 
Gelatinosa substantia Rolando, 
353 
Genital corpuscles, 345 
Germ layer, derivatives of, 36 
Germinal spot, 292 
vesicle, 291 
Ghost corpuscles, 105 
Giant cells, 1 10 
Gianuzzi's crescents, 196 
Glands, classified, 55 
defined, 52 
of Bartholin, 282 
of Bowman, 433 
of Littre, 280 
of Moll, 411 
of Montgomery, 317 
of penis, 274, 275, 277 
of Tyson, 275 
Glisson's capsule, 204, 207 
Globus major, 270 
minor, 270 
Glottis, 221 
Goblet cells, 52 
Goiter, 223 
exophthalmic, 223 
Goll's column, 357, 358, 365, 
368 
Gowers' tract, 358 
Graafian follicle, 286, 287 
follicular fluid, 288 
stratum granulosum, 288 
theca, 288 
Grandry's corpuscle, 343 
Granular layer, Tomes', 144 
Granules, zymogen, of pancreas, 
200 
Gray commissure of cord, pos- 
terior, 353 
matter of pons, 373 
of spinal cord, 353 
Ground bundle, anterior, 361 
Hair, $25 
follicles of, 327 
papillae of, 330 
Hairs, tactile, 328 
Hansen's cells, 427 
Hardening tissues, 19 
Harelip, 129 
Hassal's corpuscles, 118 
Haversian system of bone, 70 
Heart, circulatory, 110 
Heidenhain's demilunes, 196 
Helicine arteries, 276 
Hemin crystals, 109 
Hemoglobin, 105 
Hematoblasts, 109 
Hematoxylin, 446 
Hemin crystals, 109 
Hemolymph nodes, 116 
Henle's layer, 328, 329 
Hensen's duct, 421 
ductus reuniens, 424 
median disc, 82, 83 
Hepatic cords, 212 
duct, 208 
Herbst's corpuscles, 344 
Heredity, 26 
Highmore's corpuscles, 262 
Hilus of kidney, 245 
Histology, 26 
Humor, aqueous, 406 
vitreous, 390, 408 
Huxley's layer, 328, 329 
Hyaline cartilage, 67 
Hyaloid membrane, 408 
Hyaloplasm, 37 
Hydatid of Morgagni, 272 
Hyparterial bronchi, 236 
Hypoderm, 33 
Imbedding, 20 
celloidin, 20 
advantages of, 22 
disadvantages of, 23 
paraffin, 21 
advantages of, 23 
disadvantages of, 23 
Implantation cone, 93 
Inferior peduncle of cerebellum, 
366 
Infundibuliform fascia, 267 
Infundibulum of lung, 233 INDEX 
455 
Intercolumnar fascia, 261 
Interglobular spaces of Czermak, 
144 
Internal ear, 418 
Interstitial elements of testes, 
264, 265 
Intestine, large, 186 
blood-supply of, 189 
coats of, 187 
sacculae of, 186, 187 
small, 180 
blood-supply of, 189 
mucosa, 180 
muscular layer, 185, 186 
serosa, 186 
submucosa, 185 
villi of, 182 
Intima of blood-vessels, 101 
Intramembranous bone, 73 
Involuntary muscle, distribu- 
tion of, 78 
Iridica retinae, 406 
Iris, 398 
Isotropic muscle, 82 
Jaundice, 208 
Jelly, Wharton's, 59, 313 
Karyokinesis, 39 
Karyoplasm, 37 
Karyosomes, 38 
Keratohyalin, 322 
Kidney, 243 
blood-vessels of, 252 
Bowman's capsule of, 248 
cortex of, 246 
development of, 245 
hilus of, 245 
labyrinth of, 247 
Malpighian corpuscle of, 248 
medulla of, 246 
medullary rays of, 247 
nerves of, 255 
pelvis of, 246 
renal sinus, 264 
structure of, 245 
tubules of, 248 
Knots, nuclear net, 38 
Krause's membrane, 82 
Kupffer's stellate cells, 215 
Laboratory directions, 434 
Labyrinth of internal ear, 418 
of kidney, 247 
Lacrimal apparatus, 413 
groove, 129 
Lacteals, 182 
Lactiferous duct, 315 
Lacunae, bone, 69 
of cartilage, 65, 67 
Lamina choroidea, 393 
cribrosa, 392, 405 
fusca, 393 
reticularis, 428 
spiralis', 422 
Langerhans, areas of, 201 
Lantermann-Schmidt segments, 
95 
Large intestine, 186 
blood-supply of, 189 
coats of, 187 
sacculae of, 186, 187 
Larynx, 217 
cartilages of, 217 
mucous membrane of, 219 
Lateral horn of cord, 354 
Laws of cell cleavage, 42 
Layer, Henle's, 328, 329 
Huxley's, 328, 329 
Malpighian, 323 
Tomes' granular, 144 
Weil's, 147 
Lemniscus, 374 
Lens, 389, 406, 407 
capsule, 406 
Leukocytes, 107 
Lieberkuhn's crypts, 183 
Ligaments of liver, 203 
Ligamentum spirale cochleie, 
425 
Lingual frenum, 162 
Lingula, 369 
Linin, 38 
Lipoma, 64 
Lissaur's marginal ground bun- 
dle, 357 
Littre's glands, 280 
Liver, 202 
blood-supply of, 205 
cells of, 213 
fissures of, 203 
function of, 213 
ligaments of, 203 456 
INDEX 
Liver, lobes of, 203 
lobules of, 204 
lymphatics of, 215 
nerves of, 215 
Lowenthal's tract, 300 
Lumbar enlargement of spinal 
cord, 349 
Lungs, 228 
air cells of, 230 
sacs of, 230 
alveoli of, 231 
atria of, 230 
blood-supply of, 234 
infundibulum of, 233 
lobules of, 231 
lymphatics of, 237 
nerves of, 238 
respiratory bronchi, 230 
structure of, 230, 233 
Lunula, 332, 333 
Lymph duct, thoracic, 113 
node, agminated, 184 
function of, 121 
solitary, 1 16 
Lymphatic capillaries, 113 
vessels, 113 
Lymphatics of alimentary canal, 
191 
of liver, 215 
of lungs, 237 
of mammary glands, 318 
of testicle, 274 
Macula acustica sacculi, 420 
utriculi, 420 
hi tea, 404 
Malpighian corpuscle of kidney, 
248 
of spleen, 120 
layer, 328 
pyramids, 246 
Mammary glands, 314 
lymphatics of, 318 
nerves of, 317 
vessels of, 317 
Mandibular arch, 126 
Marrow, 109 
cells of, 110 
myelocytes, 110 
Masculine uterus, 278 
Maturation, 27, 29, 293 
Maxillary arch, 127 
Meatus, auditory, 415 
Meckel's diverticulum, 180 
Median raphe, 374 
Medullated nerve fibers, 91 
Medulla, foramen cecum of, 367 
of kidney, 246 
pyramids of, 369, 371 
Medullary rays of kidney, 247 
sheath, 91, 93 
substance of cerebrum, 384 
Meibomian glands, 411 
Meissner's corpuscles, 344 
plexus, 178, 191 
Melanin, 60 
Melanotic sarcoma, 65 
Melting-point of paraffin, 22 
Membrane basilaris, 423 
cochlea, 424 
eboris, 146 
tectoria, 428 
Meninges of brain, 363 
of cord, 350 
Menstruation, 287, 306 
Mesial olivary nucleus, 369 
Mesoblastic somites, 35 
Mesoderm, 33 
Mesonephros, 244, 245 
Metanephros, 245 
Metaphase, 40 
Middle ear, 416 
Milk sinus, 315 
Mitosis, 39 
chromosomes in, 39 
Mixed lateral bundle, 300 
Modiolus, 422 
Molecular layer of cerebrum, 
381 
Moll's glands, 411 
Monaster, 39 
Montgomery's glands, 317 
Morgagni's hydatid, 272 
Morula stage, 31, 32 
Mossy cells, 96 
fibers, 379 
Mother skein, 96 
Motor decussation, 300, 367, 
369 
nerve endings, 339 
Moulting, 330 
Mounting tissues on block, 20 
Mouth, 124 INDEX 
457 
Mucigen, 196 
Mucous coat of small intestine, 
180 
of stomach, 173 
membrane, defined, 53 
of larynx, 219 
of trachea, 228 
tissue, 59 
Muller's fluid, 444 
Multipolar cells, 90 
Mumps, 195 
Muscle, 77 
anisotropic, 82 
blood supply of, 84 
cardiac, 79 
ciliary, 398 
Cohnhcim's fields, 81 
endomysium, 80 
end plate, 339 
epimysium, 80 
fasciculi of, 80 
general considerations, 85 
Hensen's median disc, 82, 83 
involuntary, distribution of, 
78 
isotropic, 82 
Krause's membrane, 82 
myoma, 85 
nerve supply, 84, 85 
non-striated, peripheral nerve 
terminations in, 340 
of accommodation, 398 
of skin, 324 
perimysium, 80 
red, 84 
sarcolemma, 81 
sarcomere, 83 
sarcoplasm, 81 
sarcostyle, 78, 81 
sarcous element, 83 
spindle, 348 
striated, peripheral nerve ter- 
minations in, 339 
voluntary, 80 
distribution of, 85 
white, 83, 84 
Muscular layer of small intes- 
tine, 185, 186 
of stomach, 178 
of uterus, 304 
tissue, 77 
Myelocytes, 110 
Myocardium, circulatory, 100 
Myoma, 85 
Myotonies, 35 
Myxedema, 223 
Nails, 331 
Nasofrontal process, 128 
Nerve, auditory, 428 
cells, bipolar, 89 
of posterior horn, 353 
unipolar, 88 
endings, free sensory, 342 
motor, 339 
sensory, 341 
fibers, 91 
medu Hated, 91 
non-medullary, 95 
plexus, 88 
supply of alimentary canal, 
191 
of muscles, 84, 85 
of teeth, 155 
of tongue, 168 
terminations, peripheral, 339 
in non-striated muscle, 
340 
in striated muscle, 339 
trunk, 96 
Nerves of kidney, 255 
of liver, 215 
of lungs, 238 
of mammary gland, 317 
of suprarenal bodies, 242 
of testicle, 274 
of uterus, 305 
spinal, 352 
Nervous system, central, blood- 
vessels of, 387 
tissue, 86 
axis cylinder, 87, 91 
bipolar, nerve cells, 89 
classification of, 88 
collaterals, 87 
dendrite, 88 
endoneurium, 96 
epineurium, 96 
exolemma, 93 
fibrils, 91, 92 
funiculus of, 96 
ganglia, 88 
general considerations, 98 458 
INDEX 
Nervous tissue, implantation 
cone, 93 
medullary sheath, 91, 93 
medullated nerve fibers, 91 
multipolar cells, 90 
nerve fibers, 91 
plexus, 88 
trunk, 96 
neuroma, 98 
neuron, 86 
theory, 99 
neuroplasm, 93 
neuropodia, 96 
node of Ranvier, 95 
non-medullary nerve fibers, 
95 
perineurium, 96 
Schmidt-Lantermann seg- 
ments, 95 
spinal ganglion, 89 
unipolar nerve cells, 88 
Net knobs, nuclear, 38 
Neumann's sheaths, 144 
Neural canal, 35 
groove, 349 
Neuroglia, 96, 384 
Neuroma, 98 
Neuromere, 362 
Neuron, 86 
theory, 99 
Neuroplasm, 93 
Neuropodia, 96 
Nipple, 317 
Nitric acid, 443 
Nodes, hemolymph, 116 
lymph, 114 
function of, 121 
Ranvier's, 95 
solitary lymph, 183 
Nodules, agminated lymph, 184 
Nuclear membrane, 443 
net knobs, 38 
sap, 38 
Nuclei pontis, 374 
Nucleolus, 38 
Nucleoplasm, 37 
Nucleus, 37 
arcuate, 369, 371 
cuneatus, 357 
Deiters', 360 
gracilis, 357 
mesial olivary, 369 
Nucleus, solitary, 371 
Stilling's, 354 
Odontoblasts, 144, 146 
Olfactory organ, 431 
Olivary body, 367, 371 
nucleus, mesial, 369 
Olive, superior, 375 
Ontogeny, 26 
Optic papilla, 405 
vesicle, primary, 389 
secondary, 389 
Ora serrata, 405, 406 
Organ, defined, 27 
of Corti, 425 
Osmic acid, 442 
Ossification of bone, 75 
Osteoblasts, 76, 110, 153 
Osteoclasts, 76, 110, 153 
Osteogenetic layer of bone, 72 
Os uteri, 301 
Otoliths, 42 
Ovaries, 283 
tunica albuginea, 285 
Ovulation, 27, 28, 287 
Ovum, 26, 286, 290 
Pacinian corpuscle, 347 
Palate, 130 
cleft, 130 
Pal-Weigert stain, 447 
Pancreas, 198 
centro-acinal cells of, 200, 201 
zymogen granules of, 200 
Papilla of hair, 330 
of tongue, 163 
circumvallate, 164 
filiform, 163 
foliate, 167 
fungiform, 163, 164 
optic, 405 
Paradidymis, 272 
Paraffin imbedding, 21 
advantages of, 23 
disadvantages of, 23 
melting-point of, 22 
sections, staining of, 24 
solidification of, 22 
Parathyroids, 224 
Parietal cells of salivary glands, 
196 INDEX 
459 
Parotid glands, 91, 93 
Parotitis, 195 
Paroophoron, 299 
Parovarium, 299 
Pars ciliaris retinae, 398 
Patches, Peyer's, 116, 184 
Peduncle, inferior of, cerebel- 
lum, 366 
Pelvis of kidney, 246 
Penis, 274 
glands of, 274, 275, 277 
Pepsin, 176 
Pepsinogen, 176 
Pcrichondrion, 67 
Peridental membrane, 149 
Perimysium, 80 
Perineurium, 96 
Periostium, 72 
Peripheral nerve terminations, 
339 
in non-striated muscle, 
340 
in striated muscle, 339 
Peritoneum, 56 
Petit's canal, 408 
Peyer's patches, 116, 184 
Pharyngeal tonsils, 168 
Pharynx, 168 
Phylogeny, 26 
Pia of brain, 363 
of spinal cord, 351 
Picric acid, 443 
Picrosulphuric acid, 443 
Pigment cells, 59 
Pigmentation, 65 
Placenta, 310 
Plasma cells, 61 
Platelets, blood, 108 
Pleura, 56, 229 
Pleurodont dentition, 157 
Plexus, Auerbach's, 178, 191 
Meissner's, 178, 191 
nerve, 88 
Poisoning, blood-, 121 
Polar bodies, 28, 29, 293 
rays, 40 
Polymorphic cells of cerebrum, 
383 
Pons, 372 
gray matter of, 373 
trapezium of, 374 
white matter of, 373 
Portal canal, 206 
Posterior gray commissure of 
cord, 353 
horn of cord, 353 
longitudinal bundle, 371, 374 
root-fibers, termination of, 
358 
Potassium bichromate and for- 
malin, 445 
Pregnancy, 309 
Preparation of material, 17 
Preparing tissue, review of, 
25 
Prepuce, 275 
Prickle cells, 323 
Processus reticularis, 354 
Pronephros, 244 
Pronucleus, 30 
Prophase, 39 
Prostate gland, 280 
Prostatic sinus, 278 
Protoplasm, 37 
Pupil, 399 
Purkinje's cells, 3.76 
Pyramidal cells of cerebrum, 
383 
tract, crossed, 359 
direct, 361 
Pyramids, Malpighian, 246 
of Ferrein, 247 
of medulla, 369, 371 
Ranvier's node, 95 
Raphe, median, 374 
Receptaculum chili, 114 
Red blood corpuscles, 105 
crenated, 105 
muscle, 84 
Refractory media of eye, 406 
Regeneration of bone, 75 
Reissner's membrane, 424 
Renal sinus, 246 
Reproductive organs in female, 
283 
Respiratory bronchi, 230 
Restiform body, 366 
Rete testis, 264, 269 
Reticular connective tissue, 62 
Retina, 399 
Retzius' lines, 137 
Review of preparing tissue, 25 460 
INDEX 
Rods of Corti, 426 
Rolando's substantia gelatinosa, 
353, 369 
Rouleaux, 105 
Saccule of large intestine, 186, 
187 
Sacculus, 418, 419, 420 
endolymphaticus, 419 
Salivary glands, 193 
accessory, 197 
parietal cells of, 196 
Santorini's duct, 200 
Sap, nuclear, 38 
Sarcode, 77 
Sarcolemma, 81 
Sarcoma, 64 
melanotic, 65 
Sarcomere, 83 
Sarcoplasm, 81 
Sarcostyle, 78, 81 
Sarcous element of muscle, 83 
Sartoli's column, 263 
Scala tympani, 424 
vestibuli, 424 
Schlemm's canal, 393 
Schmidt-Lantermann segments, 
95 
Sclera, 139 
Sebaceous cysts, 337 
glands, 336 
Sebum, 336 
Secondary dentin, 145 
Sections, cutting, 23 
Segmentation, 31 
Segments, Schmidt-Lantermann, 
95 
Semen, 273 
Semicircular canals, 418, 421 
Seminal vesicles, 271 
Sensory decussation, 368 
Sensory nerve endings, 341 
free, 342 
Serous coat of small intestine, 
186 
of stomach, 108 
membrane, defined, 54 
Sharpey's fibers, 72 
primary areolae, 73 
secondary areolae, 74 
Sheaths of Neumann, 144 
Sinus, milk, 315 
pocularis, 278 
prostatic, 278 
renal, 246 
Skein, daughter, 41 
mother, 39 
Skin, 319 
layers of, 321 
muscle of, 324 
Small intestine, 180 
blood-supply of, 189 
mucosa, 180 
muscular layer, 185, 186 
serosa, 186 
submucosa, 185 
Smegma, 275 
Sole plates, 339 
Solidification of paraffin, 22 
Solitary lymph node, 116 
nucleus, 371 
Somatopleure, 34 
Somites, mesoblastic, 35 
Spermatids, 264 
Spermatoblasts, 264 
Spermatocytes, 264 
Spermatogenesis, 266 
Spermatogonia, 263 
Spermatozoa, 266 
structure of, 267 
Sphere, attraction, 40 
Spider cells, 96 
Spinal cord, 349 
anterior gray commissure 
of, 353 
horn of, 354 
arachnoid of, 351 
blood supply of, 387 
cauda echina, 349 
central canal of, 353 
cervical enlargement, 349 
dura of, 350 
filum terminale, 349 
fissures of, 351 
gray matter of, 353 
lateral horn of, 354 
lumbar enlargement, 349 
membranes of, 350 
meninges of, 350 
origin of, 35 
pia of, 351 
posterior gray commissure 
of, 353 
Sclera, 139 
Semen, 273 INDEX 
461 
Spinal cord, posterior horn of, 
353 
tracts of, 357 
summary, 372 
white matter of, 354 
ganglion, 89 
nerves, 352 
Spindle muscle, 348 
Spiral ganglia, 428 
Spirem, 39 
Splanchnopleure, 34 
Spleen, 118 
function of, 122 
ampulla of Thoma of, 120 
in typhoid fever, 123 
Malpighian corpuscle of, 120 
Spongioplasm, -37 
Staining celloidin sections, 22 
paraffin sections, 24 
Stains, 445 
anilin, 447 
Pal-Weigert, 447 
Stellate cells of cerebellum, 376 
of Kupffer, 215 
Stenson's duct, 193 
Stigmata, 57 
of blood-vessels, 104 
Stilling's nucleus, 354 
Stomach, 172 
blood-supply of, 189 
crypts of, 174 
glands of, 175 
mucosa, 173 
muscular layer, 178 
serosa, 108 
submucosa, 177 
Stomata, 57 
of blood-vessels, 104 
Stomodeum, 126 
Stratum granulosum of ovum, 
288 
granulosum of skin, 322 
lucidum, 322 
Striae acusticse, 366 
Striated muscle, peripheral 
nerve terminations in, 339 
Stroma, blood, 105 
Subarachnoid space, 364 
Sublingual gland, 195 
Submaxillary gland, 197 
Submucous coat of small intes- 
tine, 185 
Submucous coat of stomach, 
177 
Substantia gelatinosa of Ro- 
lando, 355, 369 
Superior olive, 375 
Supporting tissue, 57 
Suprarenal bodies, 239 
blood-vessels of, 241 
clinical features, 243 
nerves of, 242 
structure of, 240 
Sweat glands, 333 
Sympathetic system, 97 
Syncytium, 58, 312 
Tactile cells, 343 
hairs, 328 
Taeniae coli, 186 
Tarsal glands, 411 
plates, 412 
Taste buds, 165 
Teasing, 17 
Teeth, 131 
attachment of, 156 
blood supply of, 154 
cementum, 147 
dentin, 143 
development of, 158 
enamel, 135 
rods, directions of, 138 
lines of Retzius, 137 
nerve supply, 155 
secondary dentin, 145 
structure of, 135 
Telophase, 42 
Tendon spindle, 347 
Tenon's capsule, 393 
Tentorium, 363 
Testes, interstitial elements of, 
264, 265 
Testicle, 361 
excretory ducts of, 269 
function of, 265 
lymphatics of, 274 
nerves of, 274 
structure of, 263 
vessels and nerves, 223 
Theca, 288 
Thecodont dentition, 157 
Thoma, ampullae of, 120 
Thoracic lymph duct, 113 462 
INDEX 
Thymus gland, 117 
function of, 121 
Thyroglossus duct, 221 
Thyroid gland, 221 
structure of, 222 
vessels and nerves of, 223 
Thyroidima, 223 
Tissues, classified, 175 
defined, 27 
Tomes' granular layer, 144 
Tongue, 160 
blood supply of, 168 
foramen cecum of, 162 
glands of, 167 
nerve supply of, 168 
papillae of, 163 
circumvallate, 164 
filiform, 163 
foliate, 167 
fungiform, 163, 164 
Tonsil, 169 
pharyngeal, 168 
Trachea, 225 
cartilage of, 226 
mucous membrane of, 228 
structure of, 225 
Tracts of cord, summary, 372 
Trapezium of pons, 374 
Trigone of bladder, 258 
Trigonum hypoglossi, 366 
vagi, 366 
Tubular casts of kidney, 251 
Tubules of kidney, 248 
Tubuli recti, 264, 269 
Tunica albuginea, 262, 285 
externa, of eye, 392 
vaginalis, 260, 261 
vasculosa, 262 
Tympanic cavity, 416 
Tympanic membrane, 416 
Typhlosole, 181 
Typhoid fever, spleen in, 123 
Tyson's glands, 275 
Unipolar nerve cells, 88 
Ureters, 255 
function of, 257 
structure of, 255 
Urethra in female, 280 
in male, 277 
Urinary organs, 239 
Uterus, 299 
masculine, 278 
muscular layer, 304 
structure of, 303 
vessels and nerves of, 305 
Utriculus, 418 
Valvula conniventes, 181 
Vas deferens, 270 
structure of, 271 
Vasa efferentia, 269 
vasorum, 103, 111 
Veins, 101 
Vermiform appendix, 188 
Vernix caseosa, 321 
Verumontanum, 278 
Vestibule, 418 
Villi, chorionic, 311 
of small intestine, 182 
Visceral arches, 126 
Vitelline membrane, 292 
Vitellus, 291 
Vitreous humor, 390, 408 
membrane of, 397 
Vocal cords, 220 
Volkmann's canals, 72 
Voluntary muscle, 80 
distribution of, 85 
WaldEyEr's central cell col- 
umn, 354 
Wandering cells, 61, 108 
Washing tissues, 20 
Weigert-Pal stain, 447 
Weil, layer of, 147 
Wens, 337 
Wharton's duct, 197 
jelly, 59, 313 
White blood corpuscles, 107 
fibrous cartilage, 68 
connective tissue, 62 
matter of pons, 373 
of spinal cord, 354 
muscle, 83, 84 
Winslow's foramen, 205 
Wirsung's duct, 199 
Wolffian body, 244 
duct, 244 INDEX. 
463 
Yellow elastic connective 
tissue, 63 
Zellknoten, 312 
Zenker's fluid, 444 
Zona pellucida, 290 
radiata, 290 
reticularis, 353 
terminalis, 353 
Zymogen, 195 
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delphia. Octavo volume of 405 pages, with 196 illustrations, 32 
of them in colors. Cloth, $2.50 net. 
WITH 196 ILLUSTRATIONS, 32 IN COLORS 
The fact of embryology having acquired in recent years such great interest 
in connection with the teaching and with the proper comprehension of human 
anatomy, it is of first importance to the student of medicine that a concise and 
yet sufficiently full text-book upon the subject be available. In this edition 
the work has been thoroughly revised, and such additions have been made as 
the progress of the science has rendered necessary. Moreover, the entire 
work ha* been generally improved. The chapter treating of the Deciduae 
and the Placenta has been rewritten, as has also the greater part of that upon 
the Chorion. In addition to these changes, several new illustrations have 
been added. 
PERSONAL AND PRESS OPINIONS 
G. Carl Huber, M. D., 
Professor of Histology and Embryology, University of Michigan, Ann Arbor. 
" I find the second edition of 'A Text-Book of Embryology ' by Dr. Heisler an improve- 
ment on the first. The figures added increase greatly the value of the work. I am again 
recommending it to our students." 
William Wathen, M.D., 
Professor of Obstetrics, Abdominal Surgery, and Gynecology, and Dean, Kentucky 
School of Medicine, Louisville, Ky. 
" It is systematic, scientific, full of simplicity, and just such a work as a medical student 
will be able to comprehend." 
Birmingham Medical Review, England 
" We can most confidently recommend Dr. Heisler's book to the student of biology or 
medicine for his careful study, if his aim be to acquire a sound and practical acquaintance 
with the subject of embryology." 
9 10 
SAUNDERS' books on 
McFarland's 
Pathogenic Bacteria 
Fourth Edition, Rewritten and Enlarged 
A Text=Book upon the Pathogenic Bacteria. By Joseph 
McFarland, M. D., Professor of Pathology and Bacteriology in 
the Medico-Chirurgical College of Philadelphia; Pathologist to 
the Medico-Chirurgical Hospital, Philadelphia, etc. Octavo 
volume of 629 pages, finely illustrated. Cloth, $3.50 net. 
RECENTLY ISSUED 
This book gives a concise account of the technical procedures necessary in 
the study of bacteriology, a brief description of the life-history of the important 
pathogenic bacteria, and sufficient description of the pathologic lesions accom- 
panying the micro-organismal invasions to give an idea of the origin of symp- 
toms and the causes of death. The illustrations are mainly reproductions of 
the best the world affords, and are beautifully and accurately executed. The 
chapters upon Infection and Immunity have been greatly extended by the 
addition of many new facts. I he value of the work has been consider- 
ably enhanced by the introduction of a large number of references to the 
literature. 
PERSONAL AND PRESS OPINIONS 
H. B. Anderson, M. D-, 
Professor of Pathology and Bacteriology, Trinity Medical College, Toronto. 
" The book is a satisfactory one, and I shall take pleasure in recommending- it to the 
students of Innity College." 
The Lancet, London 
It is excellently adapted for the medical students and practitioners for whom it is 
avowedly written . . The descriptions given are accurate and readable, and the book 
should prove useful to those for whom it is written." 
New York Medical Journal 
1 • "The author has succeeded admirably in presenting the essential details of bacterio- 
logical technic, together with a judiciously chosen summary of our present knowledge of 
pathogenic bacteria." BACTERIOL OGY AND PA THOL OGY. 
Eyre's 
Bacteriologic Technique 
The Elements of Bacteriologic Technique. A Laboratory 
Guide for the Medical, Dental, and Technical Student. By J. W. 
H. Eyre, M. D., F. R. S. Edin., Bacteriologist to Guy's Hospital, 
London, and Lecturer on Bacteriology, Medical and Dental Schools, 
etc. Octavo, 375 pages, with 170 illustrations. Cloth, $2.50 net. 
This book presents, concisely yet clearly, the various methods at present 
in use for the study of bacteria, and elucidates such points in their life-his- 
tories as are debatable or still undetermined. The illustrations are numerous 
and practical. 
Medical News, New York 
"Of the many laboratory guides constantly being issued, this book is undoubtedly the 
best that has reached us." 
Warren's 
Pathology and Therapeutics 
Surgical Pathology and Therapeutics. By John Collins 
Warren, M. D., LL.D., F. R. C. S. (Hon.), Professor of Surgery, 
Harvard Medical School. Octavo, 873 pages, 136 relief and 
lithographic illustrations, 33 in colors. With an Appendix on 
Scientific Aids to Surgical Diagnosis, and a series of articles on 
Regional Bacteriology. Cloth, $5.00 net; Sheep or Half Mo- 
rocco, $6.00 net. 
SECOND EDITION, WITH AN APPENDIX 
In the second edition of this book all the important changes have been 
embodied in a new Appendix. In addition to an enumeration of the scientific 
aids to surgical diagnosis there is presented a series of sections on regional 
bacteriology, in which are given a description of the flora of the affected 
part, and the general principles of treating the affections they produce. 
Roswell Park, M. D., 
In the Harvard Graduate Magazine. 
" I think it is the most creditable book on surgical pathology, and the most beautiful medi- 
cal illustration of the bookmakers' art that has ever been issued from the American press." 
11 SAUNDERS' BOOKS ON 
Diirck and Hektoen's 
Special Pathologic Histology 
Atlas and Epitome of Special Pathologic Histology. 
By Dr. H. Durck, of Munich. Edited, with additions, by 
Ludvig Hektoen, M. D., Professor of Pathology, Rush Medical 
College, Chicago. In two parts. Part I.-Circulatory, Respira- 
tory, and Gastro-intestinal Tracts. 120 colored figures on 62 
plates, and 158 pages of text. Part II.-Liver, Urinary and 
Sexual Organs, Nervous System, Skin, Muscles, and Bones. 123 
colored figures on 60 plates, and 192 pages of text. Perpart: 
Cloth, $3.00 net. In Saunders' Hand-Atlas Series. 
The great value of these plates is that they represent in the exact colors 
the effect of the stains, which is of such great importance for the differentia- 
tion of tissue. The text portion of the book is admirable. 
William H. Welch, M. D., 
Professor of Pathology, Johns Hopkins University, Baltimore. 
" I consider Diirck's 'Atlas of Special Pathologic Histology,' edited by Hektoen, a very 
useful book for students and others. The plates are admirable." 
Sobotta and Huber's 
Human Histology 
Atlas and Epitome of Human Histology and Microscopic 
Anatomy. By Privatdocent Dr. J. Sobotta, of Wurzburg. 
Edited, with additions, by G. Carl Huber, M. D., Professor of 
Histology and Embryology, and Director of the Histological 
Laboratory, University of Michigan, Ann Arbor. With 214 
colored figures on 80 plates, 68 text-illustrations, and 248 pages 
of text. Cloth, $4.50 net. In Saunders' Hand-Atlas Series. 
Lewellys F. Barker, M. D., 
Professor and Head of the Department of Anatomy, University of Chicago. 
" I congratulate you upon the appearance of this volume. The illustrations are 
certainly very fine, and Dr. Huber has made important contributions to the text. The 
book should have a large sale." 
12 PHYSIOLOGY. 
American Text-Book of Physiology 
American Text=Book of Physiology. In two volumes. 
Edited by William H. Howell, Ph. D., M. D., Professor of 
Physiology in the Johns Hopkins University, Baltimore, Md. 
Two royal octavo volumes of about 600 pages each, fully illus- 
trated. Per volume: Cloth, $3.00 net; Sheep or Half Morocco, 
$3-75 net. 
SECOND EDITION, REVISED AND ENLARGED 
Even in the short time that has elapsed since the first edition of this 
work there has been much progress in Physiology, and in this edition the 
book has been thoroughly revised to keep pace with this progress. The 
chapter upon the Central Nervous System has been entirely rewritten. A 
section on Physical Chemistry forms a valuable addition, since these views 
are taking a large part in current discussion in physiologic and medical 
literature. 
The Medical News 
"The work will stand as a work of reference on physiology. To him who desires to 
know the status of modern physiology, who expects to obtain suggestions as to further 
physiologic inquiry, we know of none in English which so eminently meets such a demand." 
Stewart's Physiology 
A Manual of Physiology, with Practical Exercises. 
For Students and Practitioners. By G. N. Stewart, M. A., 
M. D., D. Sc., Professor of Physiology in the University of 
Chicago. Octavo volume of 911 pages, with 395 text-illustra- 
tions and colored plates. Cloth, $4.00 net. 
JUST ISSUED-NEW (5th) EDITION 
This work is written in a plain and attractive style that renders it particu- 
larly suited to the needs of students. The systematic portion is so treated that 
it can be used independently of the practical exercises, which constitute an 
important feature of the book. In the present edition a considerable amount 
of new matter has been added, especially to the chapters on Blood, Digestion, 
and the Central Nervous System. 
Philadelphia Medical Journal 
" Those familiar with the attainments of Prof. Stewart as an original investigator, as a 
teacher and a writer, need no assurance that in this volume he has presented in a terse, 
concise, accurate manner the essential and best established facts of physiology in a most 
attractive manner." 
13 SAUNDERS' BOOKS ON 
Levy and Klemperer's 
Clinical Bacteriology 
The Elements of Clinical Bacteriology. By Drs. Ernst 
Levy and Felix Klemperer, of the University of Strasburg. 
Translated and edited by Augustus A. Eshner, M. D., Pro- 
fessor of Clinical Medicine, Philadelphia Polyclinic. Octavo 
volume of 440 pages, fully illustrated. Cloth, $2.50 net. 
S. Solis-Cohen, M. D., 
Professor of Clinical Medicine, Jefferson Medical College, Phila. 
" I consider it an excellent book. I have recommended it in speaking- to my students." 
Lehmann, Neumann, and 
Weaver's Bacteriology 
Atlas and Epitome of Bacteriology : including a Text- 
Book of Special Bacteriologic Diagnosis. By Prof. Dr. 
K. B. Lehmann and Dr. R. O. Neumann, of Wurzburg. From 
the Second Revised and Enlarged German Edition. Edited, 
with additions, by G. H. Weaver, M. D., Assistant Professor 
of Pathology and Bacteriology, Rush Medical College, Chicago. 
In two parts. Part I.-632 colored figures on 69 lithographic 
plates. Part II.-511 pages of, text, illustrated. Per part: 
Cloth, $2.50 net. In Saunders' Hand-Atlas Series. 
Lewis' Anatomy and Physiology 
Anatomy and Physiology for Nurses. By LeRoy 
Lewis, M. D., Surgeon to and Lecturer on Anatomy and Physi- 
ology for Nurses at the Lewis Hospital, Bay City, Michigan. 
i2mo of 317 pages, with 146 illustrations. Cloth, $1.75 net. 
JUST ISSUED 
The author has based the plan and scope of his work on the methods he 
has employed in teaching the subjects, and has made the text unusually sim- 
ple and clear. 
14 PATHOLOGY, BACTERIOLOGY, AND PHYSIOLOGY. 
Senn's Tumors Second Revised Edition 
Pathology and Surgical Treatment of Tumors. By Nicholas 
Senn, M. D., Ph. D., LL.D., Professor of Surgery, Rush Medical Col- 
lege, Chicago. Handsome octavo, 718 pages, with 478 engravings, 
including 12 full-page colored plates. Cloth, $5.00 net; Sheep or 
Half Morocco, $6.00 net. 
" The most exhaustive of any recent book in English on this subject. It is well 
illustrated, and will doubtless remain as the principal monograph on the subject in 
our language for some years."-;Journal of the American Medical Association. 
Stoney's Bacteriology and Technic eT* 
Bacteriology and Surgical Technic for Nurses. By Emily 
M. A. Stoney, Superintendent of the Training School for Nurses at the 
Carney Hospital, South Boston, Mass. Revised by Frederic R. Grif- 
fith, M.D., Surgeon, New York. i2mo of 278 pages, profusely illus- 
trated. Cloth, $1.50 net. 
" These subjects are treated most accurately and up to date, without the super- 
fluous reading which is so often employed. . . . Nurses will find this book of the 
greatest value."- The Trained Purse and Hospital Review. 
Clarkson's Histology 
A Text-Book of PIistology. Descriptive and Practical. For the 
Use of Students. By Arthur Clarkson, M. B., C. M. Edin., for- 
merly Demonstrator of Physiology in the Owen's College, Manchester, 
England. Octavo, 554 pages, with 174 colored original illustrations. 
Cloth, $4.00 net. 
" The volume in the hands of students will greatly aid in the comprehension of a 
subject which in most instances is found rather difficult. . . . The work must be con- 
sidered a valuable addition to the list of available text-books, and is to be highly 
recommended."-New York Medical Journal. 
Gorham's Bacteriology 
A Laboratory Course in Bacteriology. For the Use of Medical, 
Agricultural, and Industrial Students. By Frederic P. Gorham, 
A. M., Associate Professor of Biology in Brown University, Providence, 
R. I., etc. I2ino of 192 pages, with 97 illustrations. Cloth, $1.25 net. 
" One of the best students' laboratory guides to the study of bacteriology on the 
market. . . . The technic is thoroughly modern and amply sufficient for all practical 
purposes."-American Journal of the Medical Sciences. 
j, • 1 . Recently Issued 
Raymond s Physiology New (34 Edition 
Human Physiology. By Joseph H. Raymond. A. M.. M. D., Pro- 
fessor of Physiology and Hygiene, Long Island College Hospital, New 
York. Octavo of 685 pages, with 444 illustrations. Cloth, $3.50 net. 
"The book is well gotten up and well printed, and may be regarded as a trust- 
worthy guide for the student and a useful work of reference for the general practi- 
tioner. The illustrations are numerous and are well executed."- The Lancet, London. 
15 16 
BACTERIOLOGY, PHYSIOLOGY, AND HISTOLOGY. 
Ball's Bacteriology Recently Issued-Fifth Edition, Revised 
Essentials of Bacteriology : being a concise and systematic intro- 
duction to the Study of Micro-organisms. By M. V. Ball, M. D., late 
Bacteriologist to St. Agnes' Hospital, Philadelphia. I2mo of 236 pages, 
with 96 illustrations, some in colors, and 5 plates. Cloth, $1.00 net. 
In Saunders' Question- t ompend Series. 
" The technic with regard to media, staining, mounting, and the like is culled from 
the latest authoritative works."-The Medical Times, New York. 
Budgett's Physiology New^Edftion 
Essentials of Physiology. Prepared especially for Students of 
Medicine, and arranged with questions following each chapter. By 
Sidney P. Budgett, M. D., Professor of Physiology, Medical Depart- 
ment of Washington University, St. Louis. l6mo volume of 245 pages, 
finely illustrated with many full-page half-tones. Cloth, $1.00 net. In 
Saunders' Question-Compend Series. 
" Contains the essential facts of physiology presented in a clear and concist 
manner."-Philadelphia Medical Journal. 
» , 1 t * Just Issued 
Leroy s Histology New (3d) Edition 
Essentials of Histology. By Louis Leroy, M. D., Professor of 
Histology and Pathology, Vanderbilt University, Nashville, Tennessee. 
I2mo, 275 pages, with 92 original illustrations. Cloth, $1.00 net. In 
Saunders' Question-Compend Series. 
" The work in its present form stands as a model of what a student's aid should be; 
and we unhesitatingly say that the practitioner as well would find a glance through 
the book of lasting benefit "-The Medical World, Philadelphia. 
Bastin's Botany 
Laboratory Exercises in Botany. By the late Edson S. Bastin, 
M. A. Octavo, 536 pages, with 87 plates. Cloth, $2.00 net. 
Barton and Wells' Medical Thesaurus 
A Thesaurus of Medical Words and Phrases. By Wilfred M. 
Barton, M. D., Assistant Professor of Materia Medica .and Therapeu- 
tics ; and Walter A. Wells, M. D., Demonstrator of Laryngology, 
Georgetown University, Washington, D. C. I2mo, 534 pages. Flexible 
leather, $2.50 net. 
, , , Fourth Ed* on. Revised 
American Pocket Dictionary Recent Issued 
American Pocket Medical Dictionary. Editeo by W. A. 
Newman Dorland, M. D., Assistant Obstetrician to the Hospital of 
the University of Pennsylvania. Containing the pronunciation and defi- 
nition of the principal words used in medicine and kindred sciences, 
with 64 extensive tables. Handsomely bound in flexible leather, with 
gold edges, $1.00 net; with patent thumb index, $1.25 net. 
" I can recommend it to our students without reserve."-J. H. Holland, M. D., 
Dean of the Jefferson Medical College, Philadelphia.