UC-NRI

,

THE LIBRARY

OF

THE UNIVERSITY
OF CALIFORNIA

PRESENTED BY

PROF. CHARLES A. KOFOID AND
MRS. PRUDENCE W. KOFOID

COMPENDIUM

OP

HUMAN HISTOLOGY.

o

COMPENDIUM

OF

HUMAN HISTOLOGY,

BY C. MOEEL,

PROFESSOR AGREGE A LA FACULTE"T>E MEDECINE DE STRASBOURG.

bg Sfotntg-ngfrf

TRANSLATED AND EDITED BY

W. H. VAN BUM, MJX,-<

OP GENERAL AND DESCRIPTIVE ANATOMT IN THE UNIVERSITY OP NEW YORK J
MEMBER OP TIIE PATHOLOGICAL SOCIETY OF NEW YORK, AC., AC.

NEW YOEK:
BAILLlfiRE BROTHERS, 440 BROADWAY.

LONDON:
H. BAILLIEKE,

219 BEGENT ST.

MELBOUENE :
F. BAILLIEKE.

PAEIS:

J. B. BAILLIEEE ET FILS,
ETTB HAUTEFETJILLE.

MADEID :
C. BAILLT-BAILLIEEE,

CALLE DEL PRINCIPE.

1861.

T4)OJ:(

in

Entered according to Act of Congress In the year 1869, by

BAILLIEKE BROTHERS,

In the Clerk's Office of the District Court of the United States, for the Southern District of

New York.

B. CKAIGILE.V1),

Printer, Stereotyper, and Electrotypar,
CTaiton JJutfiJt'ng,

81, 83, and 85 Centre Street.

EDITOR'S PREFACE.

I HAVE prepared M. Morel's Compendium of His-
tology for the use of the American medical student
in consequence of the excellence and fidelity of its
plates, and the clear and concise manner in which all
that is positively known of the science, up to the pre-
sent moment, is set forth in the text.

An original work of the same character and simi-
larly illustrated would involve a much greater
expense, even if the same degree of merit could have
been attained.

Histology, at the present day, is the progressive
department of anatomical science, and its rapidly
accumulating facts form the basis of modern physi-
ology and pathology. Still in its youth, it is advanc-
ing steadily from year to year, and to keep pace with
its progress, we must draw constantly upon all reli-
able sources of information. In our young and busy
country the laborers are as yet too few, and too much,
of necessity, employed in the active and practical
duties of the medical profession, to institute original

vi EDITOR'S PEEFAOE.

and systematic researches in minute anatomy to any
great extent, and hence we are mainly indebted for
our knowledge of it to our brethren of the old world.
To solicit the attention of the student to the sub-
ject of general anatomy, and to furnish him with an
attractive text-book in a less elaborate form than the
excellent works of Todd and Bowman, the Cyclo-
paedia of Anatomy, &c., &c., is the object with which
I have prepared the present volume for the press.
I trust it may serve the purpose of an introduction to
the more extensive works on the subject, and also to
the numerous and faithful laborers in this department
of science in Europe, and especially in Germany,
where it is most successfully cultivated.

YORK, October, 1860.

CONTENTS

PAGE

INTRODUCTION, " *V ., . . ^p&.L . ȣ.?/jaV'i."L .w.*:rr*,'; 9

CHAPTER I.

CELLS AND EPITHELIAL MEMBRANES, . . ru^ . . 11

CHAPTER H.

FIBRES; CONNECTING TISSUE, 17

CHAPTER IH.

CARTILAGE — BONE — TEETH, 26

CHAPTER IV.

MUSCULAR TISSUE, •* •••,- :v/« .- . . , . -v . 45

CHAPTER V.

ELEMENTS OF NERVOUS TISSUE, . ." ' . . . .58

viii CONTENTS.

CHAPTER VI.

PAGE

VESSELS. — ARTERIES. — VEINS. — CAPILLARIES, AND LYM-
PHATICS, 71

CHAPTER VII.

GLANDS. 84

Of '* p- V* '";<" T^ <lVr f"\ *" "\

CHAPTER VHI.
SKIN AND ITS APPENDAGES, 145

CHAPTER IX.

INTESTINAL Mucous MEMBRANE, .... . '^)\f ^: 155

CHAPTER X.

ORGANS OF SENSE, . ^itii^uJ . . 111?'^!. <^VL . 170

EXPLANATION OP THE PLATES, . 1] . . . .185

COMPENDIUM

OP

HUMAN HISTOLOGY.

INTRODUCTION.

THE science of Histology has for its object the study
of the organic elements of the human body, in refer-
ence to their forms, the various changes which they
undergo, and the part which they perform in the con-
struction of its several tissues and organs.

In the present state of the science all of the simple
elements of which the body is composed may be re-
duced to one of the following typical forms, viz :
1st, structureless material ; 2d, cells ; 3d, fibres ; 4th,
crystalline substance.

Structureless material, or amorphous substance,
exists either as a liquid or solid ; in the former con-
dition it is of constant occurrence, in the latter it con-
stitutes the basis or fundamental substance of several
of the tissues, e.g. bone, cartilage, etc.

The cell, in the largest acceptation of the term, is a
vesicle, varying greatly in shape, as well as in size, and
consisting essentially of an envelope, and contained
material of diverse appearance and nature.

1

10 INTRODUCTION.

The fibre, also variable in size, is either homoge-
neous throughout (connective fibre), or it takes the
form of a tube, the walls of which are readily distin-
guishable from its contents (muscular fibre, nerve
fibre, etc.).

In the normal state of the human body crystalline
substance has, up to the present time, been found only
in the internal ear, where it constitutes the otoliths,
and in the encephalon ; it is not positively deter-
mined that the concretions, composed of concentric
layers, which are found in the pineal gland, are crys-
talline in their nature.

CHAPTER I.

Cells and Epithelial Membranes.

SECT. I. The simple cell is the organ which above
all others is especially endowed with vital power, it
is the formative element, in fact, of all the simple
tissues, and is therefore, of necessity, our first object
of study.

In every perfect cell we recognise the following
parts : (1) A containing membrane, transparent, struc-
tureless, and exceedingly thin and delicate — the cell-
wall ^ within this envelope (2) a liquid substance,
generally transparent and granular, surrounding an-
other vesicle, which usually presents a more strongly
marked outline and thicker walls than those of the
cell, called the nucleus, or cyto blast ; and finally, (3)
in the midst of the granular contents of this latter,
we can detect, ordinarily, a granular body larger than
the rest, known as the nudeolus. (PI. I. fig. II. 1, 2,
3. PL II. fig. VI, VII. PI. XIII, fig. I).

Whenever these constituent parts cannot be recog-
nised in a cell, it is to be inferred that it has already
undergone transformation from its original condition,
as we find to be the case, for example, in blood glo-
bules (PI. I. fig. I. 1), and fat cells (PL I. fig. V.)

The contents of the cell, exclusive of its nucleus
and nucleolus, have been described as ordinarily
liquid, transparent, and finely granular. Sometimes,
however, these transparent granules are replaced,

of

12 CELLS AND EPITHELIAL MEMBRANES.

entirely or in part, by minute masses, or grains, of an
opaque and very dark colored substance (pigment),
such as are to be seen, for example, in the pigment
cells of the choroid, of the iris, and in many iierve-
cells. (PL II. fig. I, II., PI. XIII. fig. I. 6.) There
are cells, also, which in their normal condition con-
tain numerous minute spherical globules with a clearly
defined, dark outline, and possessing a very highly
refractive power ; these little pearl-like bodies are
nothing more than free fat, and are known as oil-
globules. Hepatic cells always contain a variable
quantity of them, and globules of colostrum are filled
with them. (PL I. fig. Ill, PL XVIII. fig. VI. 2.)
The same is true of the cells of sebaceous glands.

The presence of oil globules in a cell which nor-
mally contains none, is evidence of its approaching
degeneration, and indicates arrest, or, at least, tem-
porary perversion of its physiological development.
This is to be seen in the pulmonary epithelial cells
while tubercular deposit is taking place ; it is also the
anatomical lesion of the cells of renal epithelium in
Bright's disease. Finally, crystals are sometimes
formed in the cells of adipose tissue. (PL II. fig. IV.)

When cells, and especially young cells, are sub-
jected to the action of acetic acid under the micro-
scope, both the cell wall and its contents very soon
begin to grow pale, but their nuclei become more dis-
tinct; after a time the cell wall melts down and dis-
appears, but the nucleus retains its natural appear-
ance. If, in place of acetic acid, caustic potash
be applied in the same manner, even though largely
diluted, the cell begins at once to swell up, grows

CELLS AND EPITHELIAL MEMBRANES. 13

pale, and finally disintegrates entirely ; its elementary
molecules, or granules, alone seem to possess the pro-
perty of resisting the action of this chemical agent.

Although varying greatly in shape, all cells may be Different
arranged under one of the following distinctive types :
1st, spherical cells ; 2d, many-sided cells ; 3d, scales ;
4th, conical or cylindrical cells ; 5th, ciliated cells ;
6th, fusiform cells ; 7th, branching, or star-shaped
cells.

To the first class belong the embryonic ovule, and Giobuiaror

w spherical cells.

the cells developed directly from it ; newly formed
cells in the adult, and, in general, all cells which float
in a liquid medium.

The second class includes the deeper seated cells of Polygonal or

many-sided cells

many of the epithelial membranes ; the epithelial and 8cale8-
cells of glands composed of clustered follicles, and of
some glands of tubular structure. Cells in the form
of scales are found only in the superficial layer of the
epidermis and epithelium of the tongue.

The deep layer of almost all the epithelial mem- comcai ceiis.
branes which present a stratified arrangement of their
cells, the epithelium of the intestinal canal, and of its
tubular follicles, and that of a large proportion of the
excretory ducts of glands, are made up of conical or
cylindrical cells, (PL XXIII. fig. II. 3, PL XXVI. fig.
VI. fig. XL)

The free surfaces of the epithelial cells lining the cmated ceiis.
walls of the air passages, uterus, fallopian tubes, etc.,
are furnished with a great number of minute hair-like
projections (called cilia from their resemblance in
shape to an eye-lash) .which possess during life a
peculiar vibratile motion, always in the same direc-

14 CELLS AND EPITHELIAL MEMBRANES.

tion ; these constitute the fifth class, and are known
as ciliated cells. (PL I. 'fig. VII.)

Fusiform ce'.is. Fusiform cells are found principally in tissues of
recent origin which are undergoing fibrous transfor-
mation ; cicatrices are formed by this class of cells,
and some tumors are composed almost entirely of
them. (PI. IV. fig. IV.)

^he ^as^ c^ass comPrises those cells in which the
cell wall is developed into tubular or filiform prolon-
gations or branches. Examples : Most nerve cells of
the nervous centres and ganglia ; the cells of the ex-
ternal surface of the choroid ; bone cells, plasmatic
cells, etc. (PL XIII. fig. I., fig. II., PL V. fig. IV., PL
III. fig. IV.)

Every cell must derive its origin from another pre-
viously existing cell. In the present state of science
but two modes are known in which cell generation is
accomplished in human histology: endogenous gene-
ration, and multiplication by cleavage.

In endogenous generation the process is not always
exactly the same ; sometimes the nucleus of the pri-
mitive cell developes itself into two secondary nuclei,
each of which on the disappearance of their common
envelope, surrounds itself by a portion of the granular
contents of the cell, and a new cell wall making its
appearance on its surface, (Kolliker), the infant cell is
thus completed; (segmentation of the yelk). In
other cases the young nuclei, instead of making their
appearance first in the interior of the nucleus of the
primitive cell, develope themselves directly from the
granular contents, and then grow into perfect cells in
the mode already described ; e.g. cells of foetal mar-
row. (PL VI. fig. IV.)

CELLS AND EPITHELIAL MEMBRANES. 15

The mechanism of the process of generation by
cleavage is as follows :

The primitive nucleus developes itself into two
secondary nuclei, or, two nuclei may exist, from* its
formation, in the primitive cell ; then the cell wall
contracts like an hour-glass enclosing a nucleus in
either end, and finally a separation takes place at the
contracted portion, the result of this metamorphosis
being two perfect new cells ; (Ex. cells of cartilage,
cells of epithelium of intestine).

SECT. II. EPITHELIAL MEMBRANES. — The term Epi-
thelium is applied to a class of membranes formed
exclusively of cells, and ordinarily very thin and deli-
cate. They invest all of the free surfaces which the
body presents ; thus the external integument is every-
where clothed with an expansion of epithelium, or
epidermis, and the same is true of all mucous, serous,
and synovial membranes, and of the membranes lining
the cavities of the secreting glands, blood-vessels, and
lymphatics. In view of the different shapes of the
cells of which epithelial membranes are composed,
they are divided into three groups, or classes: 1st,
polygonal or scaly epithelium ; 2d, cylindrical or co-
nical ; and 3d, ciliated epithelium.

Epithelial cells are in some instances spread out so
as to form a simple lamina ; in others they are found
in several layers, one superimposed upon another.
The first mode of arrangement constitutes simple epi-
thelium / the second is known as stratified epithelium.

Heretofore the study of cells and epithelial mem-
branes has been too much neglected ; and yet there
are, in truth, no histological elements of more import-

16 CELLS AND EPITHELIAL MEMBKANES.

ance — from whatever point of view they may be
regarded. For is not the simple cell the constituent
or formative element of all the normal tissues, as well
as of those which result from diseased action ? And
of the latter, those over which our remedies exert the
least power are composed almost exclusively of cells.
Still farther : those organs of the body which hold
the highest rank in view of the importance of their
functions, which, in other words, possess the greatest
amount of vital force, consist in the greatest propor-
tion of cells; whilst the elementary fibre, and the
organs mainly formed by it, perform functions which
are simply mechanical.

CHAPTER II.
Fibres ; Connecting Tissue.

4

THE essential elements of connecting tissue* are
fibres, and cells. Its fibres are of two kinds, viz:
connective fibres properly RO called, and elastic fibres.
Its cells are diminutive in size, generally branched,
but sometimes fusiform, and have received from Vir-
chowf the name vi plasmatic cells.

The elementary connective fibre is so exceedingly fibSLectIve
delicate in its proportions that it is impossible to
measure its dimensions. Generally collected in fas-
ciculi or bundles, they run parallel with each other,
their outlines showing a slightly wavy or undulating
disposition. In certain organs, tendons, for example,
all the fasciculi of connective fibres are parallel
to each other. (PL III. fig. I. ; fig. III. 1 , PL IV. fig.
I. 1; fig. II. 1.) In the aponeuroses, the skin, the
mucous, serous, and synovial membranes, they interlace
so as to form a tissue or web, with meshes of varying
size. (PL II. fig. IX.) These facts are readily de-
monstrated by examining a small fragment or slice
from the surface of an aponeurosis or tendon,, care

* The term connecting tissue is employed throughout the present work
to designate that tissue heretofore generally known as cellular, areolar
or filamentous tissue. — (Ed.)

t Rodolphe Virchow, Professor of Pathological Anatomy in the Uni-
versity of Berlin. — (Ed.)

18 PTBRKH; CONNECTING TISSUE.

being taken to cut in the direction of the fibres of the
latter.

Elastic fibres are of larger size than those just de-
scribed ; the smallest, measure T-ro o-th of aline in breadth,
but they may reach ^th of a line (elastic coat of veins,
PI. XVI. fig. IV. 1). Their outlines are clearly
marked by one, and more frequently by two black
lines, between which is to be seen an entirely unor-
ganized and transparent substance. They give off
branches, also, in every direction, and these divisions
uniting again with each other, form a network of
variable closeness. Ordinarily, the principal branches
of a fasciculus of elastic fibres run parallel with each
other, as in the yellow elastic ligaments of the spine,
(PL III. fig. V. 1) ; but the secondary branches which
they give off present very well marked undulations,
and most frequently curl upon themselves. (PL III.
fig. V. 2 ; PL XV. fig. VI. 1.) Following this de-
scription it is hardly possible to confound elastic and
true connective fibres with each other, but we possess
additional means of bringing out their distinctive
characteristics, by the use of certain chemical reagents.
Thus, when we subject the connective fibre to the
action of acetic acid, it becomes so pale as to be unre-
cognisable, and finally dissolves entirely in the liquid ;
the same result follows, and even more rapidly, on the
application of diluted caustic potash. These reagents
produce no alteration whatever in the appearance of the
elastic fibres ; dilute caustic potash is even employed in
preparing clean and perfect specimens of them. To effect
this, a piece of yellow elastic ligament is to be boiled
for fifteen or twenty minutes in water containing some

FIBRES; CONNECTING TISSUE. 19

of the alkali. All of the other elements which enter
into the composition of the ligamentous tissue are dis-
solved, whilst the elastic fibres remain unchanged.

The cellular element of connecting tissue (the plas-
matic cell) is a reeent discovery ; we are indebted to
Virchow for the first thorough exposition of its nature,
and especially of its important pathological relations.*

Plasmatic cells are minute corpuscles, sometimes piasmatic ceiis,
fusiform, but more frequently star-shaped, with sharp
outlines, and connected with each other by means of
their branching prolongations, so as to constitute a
network similar to that formed by the cells of bone.
(PL III. fig. II. 1 ; fig. III. 2 ; fig. IV. 3.)

In tendons, we find piasmatic cells arranged in a
longitudinal series, between the fasciculi of connective
fibres. (PL III. fig. II. and III. ; PL IV. fig. I.) In
the skin and mucous membranes they are distributed *

* It will have been already noticed by the reader, familiar with the
present attitude of Histology in Germany, that our author has fully
adopted the somewhat novel views of the celebrated Professor of Berlin.
The assertion in the preceding chapter, that every cell must take its
origin from a previously existing cell, is one of the new doctrines of Vir-
chow, who denies that cells ever make their appearance by spontaneous
generation, according to the generally received pathology of the present
day, in an appropriate blastema or exudation, and insists that they a^e
always produced by endogenous growth, or by fissure and cleavage of
preexisting nuclei and cells.

The discovery of the so-called piasmatic cell, as an element of con-
necting tissue, was first announced by Virchow at Wurzburg, where
he was then professor, in 1851, and these cells play a most important
part in the new pathological views which have since been so ably deve-
loped in his more recent and elaborate work on " Cellular Pathology,"
published at Berlin in 1858. Their existence was at first disputed by
Henle, but admitted by Kolliker, Leydig of Wurzburg, Weber of Bonn,
and most other German authorities. — (Ed.)

20 FIBRES; CONNECTING TISSUE.

more irregularly. In studying the cells in tendon,
both longitudinal and transverse sections must be
examined, in order to see them well ; their branching
disposition can be clearly recognised only in the
latter. (PL III. fig. IV. 3.)

Plasmatic cells are most advantageously studied,
however, in the cornea ; its entire substance, between
the two layers of epithelium which invest its anterior
and posterior surfaces, consists of an amorphous ma-
terial in which we find myriads of star-shaped cells
arranged in regular concentric lines running parallel
with its surfaces. The numberless branches given
off by the cells, on every side, anastomose in such a
manner as to form a very beautiful network. Very
dilute acetic acid must be applied to the section under
examination ; if the acid is too strong the branches of
the cells are rendered invisible, and the cells them-
selves appear simply fusiform, or spindle-shaped. (PI.
II. fig. V.)

In the way of normal development, these plasmatic
cells may transform themselves into cartilage cells, as
in some tendons in old age, the inferior extremity of
the tendo achillis, for example, and the cartilaginous
enlargement of the peronceus longus, where it plays
over the cuboid bone. This transformation is effected
by the disappearance of the branches of the cell, and
the production of an external envelope, which thickens
into cartilage. (PI. IV. fig. I. 2 ; fig. II. 2.)

They are metamorphosed in a like manner, in the
periosteum, into bone cells, by investing themselves
with a coating of earthy salts ; it is also through the
agency of these cells that layers of new bone are de-

FIBKES; CONNECTING TISSUE. 21

posited by the periosteum in certain stages of perios-
titis. Senile opacity of the cornea is likewise ex-
plained by the appearance of oil-globules in the inte-
rior of its plasmatic cells. Finally, the researches of
Virchow tend to prove that all, or nearly all, of the
morbid formations developed in the meshes of the
connecting tissue throughout the body, are traceable
to the perverted growth of plasmatic cells.

Connecting tissue, then, is made up of the three connecting
elements just studied, mingled together in variable
proportions, and, with them, of vessels and nerves,
also variable in number. But it is to be observed
that these latter exist in connecting tissue as accessory vessels.
elements only. Thus, the numerous vessels habitually
formed in certain layers of connecting tissue, as for
example in that which underlies the mucous mem-
brane of the intestinal canal, or some portions of the *
external integument, have nothing whatever to do
with the nutrition of the connecting tissue around
them ; they merely pass through it to their ultimate
destination, and are proportionate in number to the
importance of the function to which they minister —
whether they furnish materials for important secre- *
tions, as in the one case, or in the other, as bearers of
caloric, are destined merely to keep up the heat of a
part.

In the substance proper of connecting tissue the
phenomena of nutrition are of rather a low order.
The simple diffusion of the nutritious fluid exuded
from an occasional blood-vessel suffices to keep up the
vitality of the elements which compose it. This is
confirmed by examination of the structure of a tendon,

22 FIBRES; CONNECTING TISSUE.

or of the cornea. There are few organs so poorly
supplied with blood-vessels as the former ; and in the
latter there are none whatever. It follows, then, that
the fluid from which they derive their sustenance
penetrates by imbibition into their substance, or that
Nerves, it gets there through a net-work of plasmatic cells.
There are very few nerves which properly belong to
connecting tissue; it is true that some of its mem-
branous expansions contain a large number, but they
do not minister either to the nutrition, or to the
general sensibility, of the tissue which surrounds them.
The comparative study of nervous distribution in ten-
dons, and in certain regions of the skin confirms this
view.

We may conclude then that, for its own use, con-
necting tissue is but scantily supplied with blood-
vessels and nerves ; it bears to them mainly the rela-
tion of a mechanical support.

Distribution. Connecting tissue is distributed very generally and
universally throughout the body, either collected in
bundles or fasciculi of fibres, or spread out in the form
of a membranous expansion. It serves as the bond
of union between the several parts of an organ, and
it maintains entire organs in their proper relations to
each other. Alone, it constitutes tendons, ligaments,
aponeuroses, periosteum, perichondrium, the dura-
mater, pia-mater, and sclerotica. As membrane, in-
vested with epithelium, it constitutes the serous, syno-
vial, and mucous membranes, as well as the skin,
and the membranous expansion which forms the basis
of most glands.

The vitreous humor of the eye, and similar hyaline

FIBRES; CONNECTING TISSUE. 23

and gelatiniform tissues, composed of an amorphous
substance, throughout which a variable number of
branching or plasmatic cells are distributed, consist,
probably, of connecting tissue in an embryonic or
imperfectly developed state.

The fibres of connecting tissue develop themselves Development,
from cells of the simplest form, which commence the
process by assuming an elongated shape, then join
each other — end to end, and gradually break up into
fibres within, so (see fig. III. pi. IV.) that each row of
cells thus attached by their extremities, is developed
into a bundle of connective fibres. Whilst the majority
of the original cells are thus transforming themselves
into connective fibres, others assume a star-shape, send-
ing out branching processes, which, joining themselves
to similar prolongations from neighboring cells,produce,
after the disappearance of their nuclei, elastic fibres.
The cells heretofore called u plasmatic" are nothing
more than the star-shaped corpuscles just described,
before taking on their final transformation into elastic
fibres. This is the mode of development of the fibres
of connecting tissue most generally admitted, but we
have recently recognised two other moc[es in which
connective fibres are formed, which have never been
described, and which perhaps are worthy of notice.
A fibrous tumor of the dura-rnater, of an encephaloid
aspect, presents, in its softer portions a series of oval
or fusiform cells, arranged, end to end, in longitudinal
rows (PL IV. fig. IV. 2). In the harder parts of the
same tumor, where to the naked eye it has a distinctly
fibrous appearance, its cells are longer and more
thread-like, their bodies have become more atte-

24 FIBRES; CONNECTING TISSUE.

nuated, and their nuclei, apparently from increasing
compression, have withered and mostly disappeared
entirely. Meanwhile these elongated cells, in contact
by their extremities, have grown together, and thus
become transformed into a continuous fibre. The
essential feature in this process, and that in which it
differs from the usual mode of development, consists
in the fact that there is no tendency observed in the
cell contents to break up into fibres, so that each row
of cells is eventually fused into but one solitary fibre,
and not into a bundle of fibrillse ; (PL IV. fig. IV. 3).

In the other mode of development of connecting
tissue, which we had an opportunity of studying in a
fibrous tumor of the uterus, the formation of the fibre
seemed to be due to the metamorphosis of free nu-
clei. At certain points of the tumor an agglomeration
of oval, or spherical nuclei was observed, imbedded in
a soft amorphous substance (blastema).* The out-
lines of these nuclei were clear and well marked ;
their contents were composed of very fine granules,
in some instances so grouped as to represent a nucle-
olus. Very rarely an outline representing the trace
of a cell-wall could be recognised. They measured
about T iFth of a line in diameter. (PL IV. fig. V).

At other points these nuclei were seen more elon-
gated in their shape, stretching themselves, as it were,
in the blastema in which they were imbedded, and
becoming connected together by their extremities so
as to form one fibre out of each row of elongated

* This term, originally introduced by Schwann, signifies a soft, solid,
hyaline or amorphous materials-such as that in which cell growth usually
takes its origin.— (Ed.)

FIBRES ; CONNECTING TISSUE. . 25

nuclei (PI. IV. figs. VI. and VII.). During -this
process of development of the nuclei the blastema
underwent no change, and showed no disposition to
take on a fibrous arrangement ; it simply diminished
in quantity.

Finally, some observers have asserted that simple
amorphous substance, presenting no trace of orga-
nization, was capable of undergoing spontaneous
transformation into connecting tissue. Thus far we
have failed to recognise this mode of development,
and, moreover, are indisposed to admit the possibility
of the spontaneous generation of a recognisable tis-
sue in an entirely unorganized and amorphous mass
of substance.

CHAPTER III.
Cartilage — Bone — Teeth.

SECT. I. CARTILAGE. — The tissue known as cartilage
consists of cells of characteristic appearance imbedded
in a peculiar material — which we shall designate, as
the fundamental substance of cartilage. This latter
exists in two forms, the one entirely structureless, the
other distinctly fibrous; hence the two varieties of
the tissue : true cartilage and fibro-cartilage.
cartilage ceils. The perfectly formed cartilage cell, such as we find,
for example, in the interior of an adult costal cartilage,
is usually spherical, or many-sided, and of conside-
rable volume (sVth — roth of a line), It consists of an
external envelope with transparent granular contents,
presenting no peculiar features; but the nucleus is
filled with large sized oil-globules to such an extent
that no nucleolus is distinguishable (PL V. fig. I).
Sometimes even the granular contents of the cell are
replaced by these oil-globules so completely as to
give it the appearance of a vesicle filled by a drop of
oil. In childhood, and on the surface of the cartilages
of the adult, the cells are of smaller size and elongated
in shape, and contain very little free fat, especially in
the foetus.

But the distinctive characteristic of the cartilage
cell is the existence of a structureless membrane, or
capsule, which surrounds it completely on all sides,
and which is continuous bv its external surface with

CARTILAGE. BONE. TEETH. 27

the fundamental substance of the tissue. Sometimes
this capsule includes but one cell, and this we see in
examining a cartilage near its surface (PL V. fig. II) ;
more frequently, however, it encloses several, but
rarely more than five or six (PL V. fig. I). >

The fundamental substance of true cartilage is a
hard and elastic material in which no trace of struc-
ture can be detected. In old age, and sometimes
even in adult life, it becomes infiltrated with fat, and
often presents minute cracks — which appearance has
been mistaken for the spontaneous generation of fibres
in a structureless material. But in reality they are
no more fibres than the granular striae of fibrine — to
which they Bear an accurate resemblance.

This fatty transformation, or atrophy, is often found
in the costal cartilages, and is recognisable by the
naked eye in the form of dead white or reddish yel-
low spots.

Cartilage is made up exclusively of the elements
just described. In adult life neither nerves nor blood-
vessels can be recognised in it. The latter, it is true,
are occasionally encountered, but only during the
forming stage of the tissue, or where it is undergoing
transformation into bone, as we shall see hereafter.
Thus, to sum up in a word, true cartilage consists of
a structureless fundamental substance or basis, studded
with minute cavities, lined by a membrane, and en-
closing cells.

Cartilages are enveloped by a membrane called
perichondrium. This membrane is formed by an
interlacement of connective fibres with delicate elastic
fibres, an occasional nervous fibrilla, vessels in vari-

CARTILAGE. BONE. TEETH.

Relations be-
tween cartilage
and bone.

Articular carti-
lage.

Distribution.

able quantity, and plasm atic cells. These latter exist
in greatest number in the deepest portions of the
membrane, and it is to be noticed that those in imme-
diate contact with the surface of the cartilage are not
distinguishable in appearance from cartilage cells
(PL V. fig. II). Are we not justified in concluding
from this fact that the growth of cartilage is effected
by the transformation of these plasmatic cells of its
perichondrium ?

Cartilages are united to bones by immediate con-
tact or apposition ; there is no substance or tissue
interposed between them. Their opposed surfaces
are rough, and their minute elevations and depressions
fit into each other accurately.

It was supposed for a long time that the free sur-
faces of articular cartilage were invested with syno-
vial membrane. Careful examination of the surface
of the cartilage demonstrates, however, that within
the cavity of a joint it is entirely naked ; it is not
even covered by the epithelial layer of the synovial
membrane. It is incorrect therefore to describe
synovial membranes as shut sacs, and as lining the
whole interior surface of an articular cavity. A syno-
vial membrane simply covers the internal surface of
-the capsular expansion which surrounds the joint, or,
to be more exact, it is nothing more than the capsule
of the joint covered internally by a layer of epithe-
lium. It is to be understood, however, that those
ligaments which present a free surface in the cavity
of a joint are also invested by epithelium.

Under the head of true cartilage are included:
the cartilaginous skeleton of the foetus, the costal car-

CARTILAGE. BONE. TEETH. 29

tilages, those of the joints, the cartilages of the nose,
the thyroid, cricoid, and arytenoid cartilages, and
the cartilaginous rings of the trachea and bronchial
tubes.

Fibro-cartilage differs from true cartilage only in
the nature of its fundamental substance or basis,
which, instead of being structureless, is fibrous. The
fibres of which it consists are of the elastic variety, at
least in most fibro-cartilages (PL V. fig. III). The
intervertebral discs and the semi-lunar cartilages of
the knee-joint we have found to be the only excep-
tions to this rule ; their fundamental substance con-
sisting almost entirely of connective fibres.

The principal fibro-cartilages are those of the Distribution.
external ear and Eustachian tube, the epiglottis, the
little cartilaginous masses at the summits of the ary-
tenoid cartilages, the intervertebral discs, and inter-
articular cartilages.

Cartilage, like all other tissues, is developed from Development,
embryonic cells. Those cells which are about to take
on the cartilaginous transformation, secrete from their
external surfaces an enveloping membrane, which
becomes their capsule, whilst a solid structureless
material is deposited around them, constituting the
fundamental substance. In the formation of fibro-
cartilage a portion only of the original formative cells
take on the changes above described, whilst the
remainder transform themselves into connective and
elastic fibres.

The growth of cartilage is effected in part by the Growth.
endogenous multiplication of its cells (vide sect. 1,
chap. 1), and in part by the addition of new tissue to

30 CARTILAGE. BONE. TEETH.

its surface, derived from ihe plasmatic cells of the
perichondrium as already described. It lias not been
demonstrated that cartilage is ever reproduced when
destroyed by disease or injury ; it is replaced by
transformed plasmatic cells, as far as the process can
be traced.*

To study the structure of cartilage very thin slices
should be cut from it by means of a razor.

SECT. II. BONE. — To study advantageously the mi-
nute anatomy of bone, sections as thin and delicate
as possible, should be made with a saw in every direc-
tion through its substance, and the laminae thus pro-
cured should be rubbed down with moistened pumice
stone, and afterwards polished upon a fine whetstone.
It is well also to examine, in connexion with these,
the delicate and transparent scales which form the
walls of the cancelli of the spongy portion of the bony
tissue ; they can be readily detached, and when placed
between two slips of glass, and moistened with a drop
of water, are ready for use.

structure of In a transparent lamina of bone thus prepared,

when placed under the microscope, there are always
two elements to be recognised, and these alone con-
stitute true osseous tissue, viz. bone cells, and the

* There are many points connected with the histology of cartilage, and
especially of articular cartilage, still unsettled, and in consequence of the
important bearing of this knowledge upon the principles of surgery, as
applied to diseases of joints, I cannot refrain from calling attention to the
admirable papers of Mr. R. Harwell, F.R.C.S.E., Ast. Surgeon Charing
Cross Hosp'l, Lond., in the No. for October, 1859, of the Medico- Chirur-
gical Review, and in the No. for February, 1860, of the Edinburgh Me-
dical Journal. They are complementary to the researches of Ecker,
Goodsir, and Redfern, and comprise the fullest knowledge of the subject
yet acquired by science. — (Ed?)

CARTILAGE. BONE. TEETH. 81

medium in which they are found, which we shall
designate as the fundamental substance of hone. This
latter consists of a whitish structureless material —
opaque, or transparent, according to the thickness of
the section. It is composed, chemically, of earthy
salts, and an organic substance by means of which the
earthy particles are held together.

The cells of bone (called also osseous corpuscles,
osteo-plastic cells, and laounce) bear some resemblance
in their shape and outline to the star-shaped or
branching plasmatic cells already described. They
are minute fusiform bodies, slightly flattened laterally,
and measuring from TJ7th to T~d of a line in length.
From their exterior a delicate tracery of minute
thread-like prolongations radiate in every direction,
anastomosing with each other, and with those of neigh-
boring cells. Under a magnifying power of from 350
to 400 diameters it can be distinctly seen that these
filiform appendages of the cells of bone are hollow in
their interior, and are, in fact, very minute tubes or
canaliculi ; their mode of communication is likewise
very apparent, (PL V. fig. IV). The more delicate
scales of the spongy variety of bone, and the cemen-
tum of the teeth, present in fact no other constituent
elements ; but this is not true of the more dense or
cortical substance of bone, or of scales of greater thick-
ness. On placing a transverse section of a long bone
under the microscope, it is at once apparent that its
cells are grouped after a certain fixed plan. In fact
they are arranged very regularly in concentric circles
around a larger central opening — which is the trans-
verse section of the track of a blood-vessel, or in other

32 CARTILAGE. BONE. TEETH.

words, a Haversian canal. Very many of the canaliculi
from the nearest circle of bone-cells are also to be seen
running into the Haversian canal. In the long bones
the Haversian canals run parallel with the axis of the
shaft of the bone, and communicate with each other
at short intervals by transverse anastomotic branches
(PL VI. fig. I. 1, 2, 3). In the short and flat bones
they also pursue a determinate course, and anastomose
in a similar manner. These canals, which contain
the bloodvessels of the osseous tissue, tunnel its fun-
damental substance in all directions, terminating
either upon the external surface of the bone, or in its
medullary cavities. The nutrition of bone is effected
by means of the parts just described. The very
numerous orifices of the canaliculi in the walls of the
Haversian canal receive the nutritious fluid which
exudes through the walls of its contained bloodvessel,
and convey it throughout the network which they
and their parent bone-cells or lacunae form, to the
outermost of the series of concentric circles,
periosteum, The fibrous membrane which invests bone exter-
nally, called periosteum^ resembles perichondrium in
its structure ; it is an interlacement, or rather a felting,
of connective and elastic fibres, traversed by some
nerves and very numerous bloodvessels, and studded
with plasmatic cells which, as we shall see, play an
important part in the formation and growth of bone.
(PL VI. fig. V.) '

tiees(hlll8iy e**~ ^e medullary cavities of bones are filled by mar-
row, which is in direct contact with their walls, for
the prevalent idea that the walls of these cavities are
lined by an internal periosteum, or medullary mem-

CARTILAGE. BONE. TEETH. 33

brane, is incorrect. These names have been applied
to the scattered fasciculi of connecting tissue by which
the blood-vessels and fat cells of the marrow are sup-
ported.

Marrow is found only in the cancelli and medul- Marrow,
lary canals of bone ; neither the Haversian canals
nor the canaliculi contain it. In the foetus it is of a
reddish color and possesses some consistency ; in the
adult it is met with in this form only in the smaller
cancelli of spongy bone, and in short and flat bones ;
in the medullary canals of long bones, and in the
larger cancelli of their spongy substance, it is yellow
in color and almost diffluent. Thus, there are two
varieties of marrow, which differ in their histologi-
cal elements as well as in their physical properties.
The red, or foetal marrow, is made up of an aggre-
gation of spherical cells, each containing fine granular
matter and one large nucleus. Some of these cells have
several nuclei, and attain a large size (TVth to TVth
of a line). It is worthy of remark, in passing, that
the cells of foetal marrow' are identical in appearance
with certain forms of so-called cancer cells. This
variety of marrow is richly supplied with blood-ves-
sels, which traverse its substance, accompanied by
delicate filaments of connecting tissue.

The cells of yellow marrow are nothing more than
vesicles filled with liquid *fat, or ordinary fat cells.
In some of them the nucleus can be still recognised,
and others again resemble so closely the cells of foetal
marrow as to suggest a series of transitional changes,
by which it is rendered probable that the ordinary
yellow marrow is nothing more than foetal marrow.

Arteries and
nerves of bone.

34 CARTILAGE. — BONE. TEETH.

the cells of which have undergone the process of fatty
degeneration.

Of the two varieties the red, or foetal marrow, is
more richly supplied with blood-vessels.

The arteries of bone are derived from its perios-
teum; one class of them, the smaller vessels, pene-
trate the compact substance and pursue the same
course as the Haversian canals which they occupy ;
the other class, larger, and known as nutritious arte-
ries, enter separate canals of their own, and thus
reach the medullary cavities, where they terminate
by supplying the marrow and anastomosing with the
vessels of the first class. The veins, as a rule, present
the same calibre and pursue the same course as the
arteries with which they correspond ; in some instan-
ces, however, they assume a larger size and different
arrangement, as in the sinuses of the diploe, and of
the bodies of the vertebrae. Up to the present time
lymphatics have not been demonstrated in bone. Its
nerves, which are numerous, ordinarily follow the
course of the arteries, and supply the marrow as well
as the bone; before penetrating its substance they
give off branches to the periosteum. There is reason
to believe that they terminate by free extremities.
bonveelopmont of ^ne development and growth of bone is accom-
plished in two ways : by ossification of the cartila-
ginous skeleton of the fcetus/ and by transformation
of the deeper layers of the periosteum.

The first mode of development is best studied in
very thin sections of a young bone, made just at the
line of junction of the cartilage and bone. On exa-
mining, in the first place, the cartilaginous portion of

CAETILAGE. BONE. TEETH. 35

the section, it is to be observed that its cells are dis-
posed in parallel rows, and that some of them are
quite altered in appearance. One portion of them
differs in no respect from ordinary cartilage cells,
whilst the remainder have already changed in form,
the change being confined mainly to their nuclei.
The nucleus, for example, has become very irregular
in its outline, and by sending out prolongations in
every direction, has put on a decided resemblance to
a bone-cell. It is imbedded in a finely granular sub-
stance limited by a pale circular or oval line, the cell
wall ; outside of this another line is to be seen in
close proximity to the first, and surrounding the cell ;
this is the capsule of the cartilage cell. (PL VI. fig.
III. 2, 3, 4.)

In view of these facts it is pretty evident that the
osseous cell, or lacuna, is identical with the nucleus
of the original cartilage cell, in a more advanced
stage of development.

The process of ossification is completed by the
elongation of the filiform prolongations, or canaliculi,
given off from the nuclei of the cartilage cells, which
terminate by anastomosing with the canaliculi of
neighboring nuclei ; and meanwhile earthy salts have
been brought by the bloodvessels and deposited in
the fundamental substance of the cartilage, as well as
in the interior of its cells. Neither the walls of these
cells, nor their enveloping capsule, disappear imme-
diately after the ossification of their contents ; by the
addition of dilute hydrochloric acid to a portion of
recently ossified bone they can both be rendered
visible — prssenting their usual appearance.

36 CARTILAGE. BONE. TEETH.

It is asserted by some observers that it is the car-
tilage cells themselves, and not their nuclei, which
are thus transformed into bone cells. They describe
the cell-wall as becoming wrinkled, and undergoing
the changes which we have attributed to its nucleus,
whilst the nucleus itself fades away and finally dis-
appears entirely. (PL VIL fig. II.) In opposition to
the authorities by whom this statement is endorsed,
we are disposed to persist in the belief that it is the
nucleus of the cartilage cell which becomes trans-
formed into the osseous cell, or lacuna, of bone.
F<etai Marrow. The cells of ossifying cartilage which remain un-
changed during the process just described, eventually
assume the character of foetal marrow. At first they
become the seat of active endogenous development,
in consequence of which they increase, together with
their enveloping capsules, very considerably, in size.
PL VI. fig. IV. 4.) Very soon they come in contact
with each other, their capsules becoming welded
together (PL IV. 5), and the partitions which thus
result, melting away as they lie arranged in longi-
tudinal rows, a medullary canal is thus formed filled
with young cells and free oil-globules, wrhich, in fact,
constitutes foetal marrow. (PL IV. 6.) Whilst the
process of ossification is going on, numerous blood-
vessels derived from its perichondrium are seen
ramifying through the substance of the cartilage.
These seem at first to be simply hollowed out of the
cartilage ; but later in the process the cartilage cells
immediately around them become elongated and fusi-
form in shape, and seem by their subsequent union
to form walls for the vessels.

CAKTILAGE. BONE. TEETH. 3 7

The process of ossification from periosteum is less
complicated than that just described, by which car-
tilage is converted into bone. This fibro-vascular
membrane contains, as we have already stated, a large
number of little star-shaped or plasmatic cells.
When, by the addition of acetic acid, the ordinary
connective fibres of the membrane are made to dis-
appear, more than one layer, composed of elastic fibres
and branching cells, is brought in view, in which
both the form and arrangement of osseous cells are
faithfully represented. (PL VII. fig. 1, 3.) In the
deepest layers of the periosteum, where ossification
takes place, the plasmatic cells are seen to be more
numerous, and farther advanced in development than
elsewhere. The blastema in which they are imbedded
is also deeper in color, and this is explained by the
presence, already, of earthy salts. (PL VI. fig. V. 2,
3.) In fact the process of ossification is thus almost
perfected, for the plasmatic cell requires only to be
imbedded in and surrounded by earthy matter, to
become a cell of bone. However, the process is not
always effected in so simple a manner, for sometimes
the plasmatic cells do not present their usual star-
shaped prolongations, and in this case the filiform
processes, which ultimately form canaliculi, only make
their appearance whilst the incrustation of their cell-
walls is actually taking place.

From our own investigations it is evident that the
ossification of the cranial bones is effected entirely by
the changes just delineated in their periosteal cover-
ings. (PL VII. fig. I.) The new deposits of bony
matter which take place in some grades- of perios-

38 CARTILAGE. BONE. TEETH.

teal inflammation are explained in the same man-
ner.

separation of The reparation of bones after fracture or exsec-
tion, or where a portion has been gouged out in an
operation, is accomplished by a process analogous to
that which the periosteum performs in ossification.
The gelatiniform mass which forms between the frag-
ments of a broken bone, in an excavation produced
by the gouge, or even in a medullary cavity,, contains
usually some fibrillae of connective tissue, together
with a large number of blood-globules and oval
nuclei (fibro-plastic), which are subsequently con-
verted into bone cells. It is easy to follow the suc-
cessive transformations of these nuclei by the micro-
scopic examination of a very thin lamella of bone to
which this gelatiniform material is still adherent.
These are the several steps of the process : at a little
distance from the bone, the oval nuclei possess a very
regular outline, but as we trace them nearer to its
surface they are observed to change their shape ;
their outlines wrinkle, and send out linear prolonga-
tions radiating in every direction; at the same time
earthy matter is deposited around them, by which
they become gradually encrusted, and thus the meta-
morphosis into bone is completed. (PL XXVII.

4 1.)

Reparation or reproduction of bone in' a medullary
canal, and in the cancelli of its spongy portions, is
not accomplished by medullary membrane, which, as
we have already asserted, has no existence, nor yet
by the aid of an imaginary cartilage, which, in any
case, would be but transitory. The phenomena of

CAETILAGE. BONE. TEETH. 39

ossification here are entirely analogous to those we
have observed in the deeper strata of periosteum,
both in its healthy state, and when inflamed. In all
these cases the osseous cell, in the absence of which
the tissue of bone cannot exist, is developed from
another cell or its nucleus — that is to say from the
essential organic element — which is always present
both in the periosteum, and in the contents of the
medullary cavities.

SECT. III. — TEETH. A tooth consists of a central Teeth,
portion which constitutes nearly the whole of the
organ, and of an outer lamina which accurately invests
its external surface. The central mass, or ivory, has
a cavity in its interior — variable in size and shape,
which communicates externally through a narrow
canal situated at the extremity of the root; this
cavity contains the pulp (PL VIII, fig. I. 1, 2). The
portion of the external lamina which invests the
crown of the tooth is the enamel (fig. I. 4) ; that
which covers its root is the cementum (fig. I. 3).

The ivory is composed of fundamental substance, ivory,
traversed by minute canals. The former, structure-
less and transparent when viewed in thin section, is
identical with the fundamental substance of bone, and
the canals which it contains resemble closely the
'canaliculi of bone-cells. They take their origin in
the central cavity of the tooth, and thence radiate to
the surface of the ivory, where they terminate ; it is
an exception to the rule for them to pass beyond this
limit and to penetrate the exterior lamina (PL VIII.
fig. III. 2). At their commencement some are single,
others arise from a common trunk, and others again

40 CAETILAGE. BONE. TEETH.

take their origin from minute cavities in the deeper
strata of the fundamental substance; these latter,
however, always communicate with the central cavity
of the tooth (PL VIII. fig. II. 4). With a magni-
fying power of 350 to 400 diameters, the canals can
be seen to be sharply limited by two very fine but
distinct lines, to be slightly wavy or undulating in
their course, and to run, mainly, parallel to each
other. Their lateral branches can also be distin-
guished, radiating in every direction, anastomosing
with each other, and thus forming an universal net-
work, which permeates, everywhere, the fundamental
substance of the ivory. (PL VII. fig. III. 1, 2 ; PL
VIII. fig. II).

At their origin the canals are larger than at their
termination, measuring, on an average, from r-nrcrth
to T^o-th of a line. Sometimes they present, in their
course, small spindle-shaped enlargements (PL VIII.
fig. II. 3), and they terminate, as a rule, in irregularly
shaped cavities which are the interspaces between
minute glob . ar masses of the fundamental substance
(PL VIII. ng. II. 5). It is to be noticed that these
inter-globular spaces, as they have been designated,
communicate freely with the bone-cells of the cemen-
tum, to which, in fact, they bear no little resem-
blance.

Enamel. The 'enamel forms a hard and homogeneous lamina
moulded accurately upon the surface of the crown of
the tooth, and terminating, at its neck, by a thin
edge, which seems to insinuate itself between the
ivory and the terminal margin of the cementum. It
is composed exclusively of five or six-sided prisms,

CAETILAGE. BONE. TEETH. 41

placed side by side, without any appreciable inter-
vening substance (PL VIII. fig. IV. 1). Examined
in vertical section they are observed to undulate
slightly, and to assume a direction perpendicular to
the nearest surface ; moreover, they are generally
parallel with each other, except upon the irregularly
shaped surfaces of the molar teeth, where they form
divergent bundles (PL VIII. fig. III.). Their sub-
stance is wholly amorphous ; sometimes it is crossed
by transverse lines ; its chemical nature seems to
connect it with the epithelial formations. Some
observers have asserted that the enamel is invested
externally by a delicate structureless layer, which
they designate as the cuticle of the enamel.

The cementum, by which the root of the tooth is
covered externally, is true bone ; it consists of funda-
mental substance, and bone-cells of variable size and
irregular in their arrangement. Haversian canals are
absent, except where its structure has been altered
by inflammation. The periosteal investment of the
alveolar sockets also covers the surface of the ce-
mentum.

The pulp of the tooth, which occupies its central r>entaipuip.
cavity, is connected with the periosteum of the socket
by a pedicle which penetrates the orifice at the
pointed extremity of its root. It is made up of deli-
cate connective tissue, interspersed with plasmatic
cells, and largely supplied by blood-vessels and
nerves — the terminal arrangement of the latter being,
as yet, imperfectly made out. The presence of lym-^
phatic vessels in the pulp is uncertain. During the Development of
sixth week of foetal life, the free borders of the niax-

3

42 CAETILAGE. BONE. TEETH.

illary bones begin to show distinct longitudinal
depressions or grooves, at the bottom of which minute
granulations make their appearance, which are the
germs of the teeth ; it is from these that the ivory is
developed. Shortly afterwards partitions make their
appearance by which the groove is divided up into
separate apartments, with a germ at the bottom of
each — recalling in their appearance the circumvallate
papillae of the tongue. Still later the margins of
these compartments, as they grow, rise above the
level of the germs, contract by approaching from
opposite sides, and finally unite together. Hereafter
the germ is enveloped on all sides in a cavity which
takes the name of the dental sac.

Dental sac. The walls of the sac are at first formed by two dis-
tinct layers, which afterwards become one. The
external layer, which later becomes the periosteum
of the socket, is made up of very vascular connecting
tissue ; the internal layer, of the same nature as the
preceding, but more delicate in structure, contri-
butes, according to M. Magitot,* to the subsequent
formation of the enamel.

We know already that the dental germ takes its
origin, by a pedunculated root, from the bottom of
the sac ; from a point diametrically opposite to
this springs another germ similar to it in nature,
which, as we shall see hereafter, gives origin to the
enamel.
of The dental germ (whence the ivory is developed)

* Emile Magitot has a paper on the structure of the teeth in the
Archives Medicates, Paris, Jan. 1858, and has sinoe>ritten on the subject
in same Journal.— (Ed.}

CAKTILAGE. BONE. TEETH. 43

rich in blood-vessels, which reach it through its pedi-
cle, contains, besides, a large number of nuclei and
young cells of an oval • form, together with some
connective fibrillae ; its nerves, which appear some-
what later, accompany its vessels. It is covered by
an amorphous membrane* which, as Magitot has
shown, is incorrectly regarded as a portion of the
internal layer of the wall of the dental sac. This
border belongs really to the germ, and takes no part
in the subsequent formation of the ivory. Beneath
this there is a stratum of oval cells, arranged very
regularly side by side, with their long diameters per-
pendicular to the surface of the germ. The peripheral
extremity of each cell elongates into a thread-like
tube, which by degrees increases in size, and gives off
minute lateral branches ; in this manner a great
number of minute canals are formed, which run
parallel with each other to the* extreme limit of the
germ, communicating largely by their ramifications.
Thus the canalicuii of the ivory of the tooth are
developed from the superficial cells of its germ, each
cell, according to Kolliker,f by a process similar to
wire-drawing, elongating itself into a complete canal.
Whilst the dental canals are being thus developed,

* Homogeneous basement membrane of Todd and Bowman. In his
account of the development of the teeth the author mainly follows
Goodsir.— (Ed.}

t A. Kolliker, Professor of Anatomy and Physiology in the University
of Wufzburg (Bavaria), author of the " Manual of Human Microscopic
Anatomy," which has been twice translated into English ; first by Pro-
fessors Busk and Huxley, and published by the Sydenham Society,
1853-54; and more recently, in a revised edition, by Dr. George
Buchanan, under the author's supervision. Parker, London. 1860.

44 CAKTILAGE. BONE. —TEETH.

an amorphous substance is poured out in the intervals
between them, an exudation furnished, no doubt, by
the deeper cells of the germ, and which subsequently
becomes the fundamental substance of the ivory of
the tooth. Finally, its development is completed by
the infiltration of the fundamental substance with
calcareous salts, and what remains of the original
Development germ becomes atrophied and forms the dental pulp.
The germ of the enamel, having attained its com-
plete development, envelopes entirely the base of the
germ of the ivory, which we have traced to its com-
plete ossification. Superficially it is made up of con-
necting tissue rich in blood-vessels ; more deeply
there are only star-shaped cells imbedded in amor-
phous material ; and finally the stratum immediately
in contact with the dental germ, is formed by an
epithelial layer, whose cells, long, narrow, and pris-
matic in shape, resemble closely the prisms, already
described, of the enamel. Thus it is more than pro-
bable that the enamel is formed directly by the
°f petrifaction of these elementary bodies. The lower
partions of the dental sac give origin to the cemen-
tum, taking on the process of ossification in the same
manner as periosteum.

In view of the fact that connecting tissue, under
certain circumstances, undergoes transformation into
cartilage and bone, as well as into the substance of
the teeth, these tissues, being all analogous in nature,
are grouped together, by some authorities, in one
family.

The preparations required for the study of the
structure of the teeth are prepared in the same man-
ner a*s sections of bone.

CHAPTER IV.
Muscular Tissue.

THE essential element of muscular tissue, i.e. the
contractile element, presents, in its intimate structure,
both cells and fibres. The cell is a transitory ele-
ment, or rather is found only in those organs in which
an incomplete stage of development is persistent.
The fibre, in two distinct forms, constitutes the bulk
of all recognised muscles. The two varieties are
known as the striped, and the smooth or unstriped
muscular fibre.

Smooth, or unstriped muscle. — When a small por- structure of

smooth muscu-

tion of certain muscular organs, the muscular wall of larfU)re-
the intestine, or of the bladder, for example, is placed
beneath the microscope, it is found to consist appa-
rently of long, pale, spindle-shaped bodies, each one
of which is provided with an elongated nucleus
having a clear and distinctly marked outline, and
surrounded by a substance so finely granular as to
appear almost amorphous. More attentive exami-
nation, however, reveals the real nature of these
nucleated bodies — the essential contractile elements ;
in place of a spindle-shaped cell, it is soon recognised
as a true fibre, presenting, as we trace it in the direc-
tion of its length, a regular succession of contractions
and enlargements. These fibres, instead of running
parallel with each other, cross at very acute angles,
and in such a manner that their points of intersection

46 MUSCLES.

a

seem to correspond always with their narrow or con-
tracted intervals, or, as it is still described by some,
with the tapering points of the fibre-cells. A cir-
cumstance which has doubtless served to perpetuate
this erroneous view is that these fibres break very
easily when an attempt is made to isolate them, and
as the rupture always -takes place at one of the con-
stricted portions of the fibre, which tapers off as it
breaks, in consequence of its elasticity, it results that
each fragment thus detached presents a regular spin-
dle shape. (PL XIV. fig. VIII.) But if a section is
made across the course of the fibres, polygons are
brought into view, varying very considerably in dia-
meter (jioth to lioth of a line), but never of a size
so small as to be recognisable as the terminal point
of a spindle-shaped corpuscle. (PI. IX. fig. II.) The
same section shows also the mode in which these
fibres are grouped together so as to form fasciculi of
muscle. Between the fibres which are thus in imme-
diate contact with each other, forming fasciculi, there
is no intervening substance whatever ; but they are
surrounded by an investment, or sheath, of connecting
tissue which also includes the blood-vessels and ner-
vous filaments by which they are supplied. (PI. IX.
fig. II. 4.)

contractile ceiiB. The contractile fusiform element, or fibro- cellular
corpuscle, is found only in those organs whose nor-
mal condition is one of imperfect development — as
for example, in the smallest arteries, of a diameter of
from 7V th to ?Vth of a line. In vessels of this class
the middle or muscular coat consists of this element
in its purest form. It is not difficult to demonstrate

MUSCLES. . 4

that the contractile element of which it is composed
is a spindle-shaped, or fusiform, corpuscle of variable

length, in the interior of which a nucleus, which

.
approaches more nearly the circular shape than that

of the true smooth or unstriped fibre, is recognisable,
(PL XV. fig. VII. 2, 3.) We find this fusiform cor-
puscle in the walls of the villi of the small intestine,
in the muscles of the hair-bulbs, and perhaps also in
other organs. It is as yet an unsettled question
whether the dartos is made up of this element, or of
the fully developed unstriped fibre.

The distribution of the smooth, or unstriped mus- Distribution of

smooth muscular

cular tissue, limited at first to organs possessed of
obvious contractility, is daily increasing in extent.
Thus, its presence has been demonstrated in the villi
of the intestines, in the excretory ducts of most of the
glands, in the middle coat of arteries, veins, and lym-
phatics, in the genital organs of the female (uterus
and appendages, vagina, and corpora cavernosa of the
clitoris) ; in the genital organs of the male (corpora
cavernosa penis, prepuce, prostate, seminal vesicles,
&c ) ; in the vascular tunic of the eye ; and, finally,
throughout the whole extent of the skin, where it is
very unequally distributed. It is found in connexion
with the hair-bulbs and sebaceous follicles ; and by
its presence, the phenomenon of horripilation, or
goose-flesh, is explained. Some portions of the ex-
ternal integument are unusually rich in unstriped
muscular fibres ; for example, the prepuce, and the
skin of the nipple, and in some instances, of the whole
female breast. The elongation and rigidity of the
nipple are due entirely to their contraction, and not,

48

MUSCLES.

*

Development of
unstriped muscu-
lar fibre.

as generally supposed, to a turgescence, or erection,
similar to that of the corpora cavernosa.

Smooth, or unstriped muscular fibres are developed
from formative cells, which at first elongate, and then
become attached by their extremities. In some organs
and localities this mode of development is incom-
plete ; the metamorphoses of the formative cells are
arrested in their earlier stages, and thus the exist-
ence of the contractile fusiform corpuscle — the fibre-
cell of Kolliker, is explained. Hereafter we shall
see that the true striped muscular fibre passes through
the two stages we have just described before it
assumes its ultimate and definite form, so that, in a
general histological survey of the entire muscular
tissue of the body, it may be considered as repre-
senting, in its several constituent portions, different
and progressive degrees of development of the same
formative element — of which the striped fibre is the
last and most perfect form.

In the muscular tissue of the uterus during preg-
nancy we recognise the development of new muscular
fibre of the smooth variety. According to Kol-
liker this takes place only during the first six months
of gestation. In its deeper strata an immense num-
ber of cells is recognisable, measuring from T^orth to
sVth of a line, and we can trace them through the
several phases of their development into smooth mus-
cular fibres. After delivery, and whilst the uterus is
diminishing in bulk, the larger proportion of these
muscular fibres become infiltrated with fat, break
down, and disappear entirely by absorption ; it is by
this process of fatty atrophy that the uterus returns,
after child-birth, to its original dimensions.

MUSCLES. 49

i

Striped Muscle. — The tissue of muscle in its sim-
plest element — the primitive fibre — is variable in its
physiognomy, presenting to the eye but two con-
stant features, viz : an external envelope, with con-
tents marked by transverse stripes. (PL IX. fig. V.
and PL X.)

The primitive fibre is usually polygonal, rarely striped fibre.
cylindrical ; its envelope, called myolemina or sarco-
lemma,* is readily recognisable, either without any
previous preparation, or by the aid of chemical re-
agents, as a perfectly structureless membrane. Nei-
ther in the living nor dead fibre, neither in the state
of contraction nor of relaxation, can any folds or
wrinkles be detected in it corresponding with the
cross stripings of its contents. On its internal sur-
face, at regular intervals, oval nuclei (PL X. fig. II. 3 ;
PL IX. fig. V. 3) are visible — the last traces of the
cellular origin of muscle. It is exceedingly elastic.

On examining its contents, the most marked fea-
tures observed are the transverse stripes, equidistant
from and parallel with each other. Occasionally
longitudinal striae are to be detected in muscular fibre
instead of the transverse stripes, and in rare instances
both the longitudinal and transverse stripes are pre-
sent. (PL X. fig. II. 4, 5.) If this contained sub-
stance is still farther analysed by the aid of chemical
re-agents (chromic acid, alcohol, etc.) or prepared by
boiling, and even sometimes without the employment

* This term was introduced by Bowman, who first investigated and , .
described the sarcolemma, and its relation to the primitive muscular fibre
of the striated variety. V. Cyclop, of Anat. and Physiology, Art. Muscle,
and Todd and Bowman's Phyt* Anat.— (Ed.}

50 MUSCLES.

of these artificial means, it becomes evident that it is
composed of two distinct constituents — one granular
and the other amorphous, the latter being very vari-
able in amount, and serving as a connecting medium
to the former — which is thus imbedded in it. (PL IX.
fig. V. 5.) These minute granules — the sar cents ele-
ments of Bowman (PL X. fig. II. 5), are slightly flat-
tened in the direction of the length and breadth of
the fibre, and measure, on an average, nnr <rth of a line.
These little bodies seem to be the active agents in the
production of the contractility of muscle ; it is in
them, and in their relation to the amorphous material
by which they are enveloped, that we are to look for
the power which the muscular fibre possesses of
changing its size and shape.

In fact, according as these ultimate corpuscles
approach each other more closely in the direction of
the length of the fibre than in the direction of its
breadth, it will assume the fibrillated appearance
(PL X. fig. II. 4, 5), or, in the opposite case, the
appearance of discs piled upon one another. This
latter disposition of the sarcous elements presents a
more striking appearance, when between the discs
which result from their arrangement in transverse
rows, a large amount of the amorphous hyaline sub-
stance is present, as in fig. V. (PL IX. 5).

To sum up in a word : the ultimate fibre of striped
muscular tissue is composed of an external envelope
of simple structureless membrane, which contains a
granular material of soft consistence ; and the varia-
tions in appearance of the striae by which it is marked,
are due to the varying relations which these granules
are capable of assuming to each other,

MUSCLES. 51

1 he striped muscular fibre is continuous throughout
its whole length, and this corresponds accurately with tongue'
that of the fasciculus, or bundle, of which it forms a
constituent part. Up to the present time we know
of but two organs which constitute exceptions to this
law, and these are the heart and the tongue. The
muscular fibres of the heart are branched, and form
very frequent anastomoses, recalling the disposition
of the columnce carnece of the ventricles, and explain-
ing the admirable correspondence and unity of action
in the movements of the organ (PL X. fig. III). The
fibres of the tongue give off branches only in its sub-
mucous layer of muscular tissue, and these do not
appear to anastomose. They terminate by pointed
extremities which are attached to minute fasciculi of
connective fibres, which seem to act as their tendons
— at least this is the opinion of most authorities.
The ultimate fibres of striped muscle are united
together by delicate lamellae of connecting tissue
(perymisium), and thus constitute secondary fasciculi.
These again, surrounded by sheaths of the same
material, but somewhat more dense, form tertiary
fasciculi ; and, finally, the entire muscle is enveloped
by a still stouter sheath which forms its external
perymisium. In this outer membrane we find the
ramifications of the nerves and nutritious vessels of
the muscle.

The striated fibre terminates by a rounded extre- Termination of

J striated fibres.

mity, which is simply in close apposition with its
tendon. Nevertheless Kolliker asserts that this
arrangement, which is certainly the most common of
all, is found to exist only where the muscular fibre

52 MUSCLES.

meets its tendon obliquely ; but where it is conti-
nuous, in the same line with the tendinous fasciculus
with which it corresponds, the two tissues blend
together insensibly, without any line of demarcation
at their point of contact.*
Aspect of the We cannot close our description of muscular fibre

striated fibre dur-

antraction. wjt}lout remarking that Weberf long since demon-
strated that it does not wrinkle during contraction.
It becomes shorter by increasing in breadth and
thickness, at the same time, just like a cylinder of
caoutchouc after being stretched. The zigzag wrin-
kling occurs only where the extremities of the fibre, as
it shortens, do not return by the same line in which
it was elongated. It is very easy to verify the exact-
ness of Weber's assertion by examining, under the
microscope, the glosso-laryngeal muscle of the frog,
when under the influence of galvanic stimulus.
Nerves of mus- T}ie nerves of striped muscle are supplied both by
the cerebro-spinal axis, and the sympathetic system ;
but those derived from the latter source are very few
in number.

'" " In the human body the smooth muscular tissue nowhere forms large
isolated muscles, as in the case of the recto-penal muscles of mammals,
for example, but occurs either scattered in the connective tissue, or in
the form of muscular membranes. In both cases its bundles are either
arranged parallel to each other, or united to form networks ; and, even
in man, are connected in many places with tendons of elastic tissue, as
first detected by me in the tracheal muscles, and in the cutaneous feather
muscles of birds." Kolliker, Manual of Human Microscopic Anat.
London, 1860, p. 65.— (Ed.)

t This is not the celebrated Weber, Professor of Anatomy at Leipzig,
and famous for his researches on the structure of the placenta, the ske-
leton, joints, etc., but E. Weber, author of an elaborate article, " Muskel-
bewegung," in Wagner's Handworterbucb, 1846. — (Ed.)*

MUSCLES. 53

As they enter the substance of a muscle, its nerves
are united in bundles, and pursue a course almost at
right angles to its fibres. Very soon they divide and
subdivide, gradually approaching the same direction
as the fibres of the muscle, and finally the smaller
branches run almost parallel with them (PL XI). In
their course, the nervous filaments separate sometimes
from each other without anastomosing; and, again,
they unite after separating, in such a manner as to
form loops, and even many series of loops, or a net-
work of anastomoses.

As to the mode in which nervous filaments ter-
minate in muscle, the following is the result of our
examination of different muscles of the frog. At the
points where the little bundles of nerves separate,
the majority of their primitive fibres present a dis-
tinct contraction in diameter, a strangulation, to half
their previous size. From these contractions two
branches usually, sometimes three, take their origin ;
and these, after running a short distance, undergo a
similar contraction and branching. Finally, the ter-
minal fibres taper off quite rapidly, soon show but a
single outline, and at last seem to lose themselves on
the sarcolemma (PL XIV. fig. I).

Can we infer from these facts a similar distribution
of the nerves of striated muscle in man ? From the
researches of Valentin,* confirmed in part by Kol-
liker, it would seem not. Both of these authorities
assert that they have seen nervous fibres terminating

* G. Valentin, Professor of Anatomy and Physiology in the Uni-
versity of Berne, author of the treatise on " Nemologie1'1 in the Encyclo-
pedie Anatomique, Lehrbuch der Physiologic, etc., etc.«-~(.E$.)

54 MUSCLES.

by loops, in the muscles of the smaller mammiferse,
and in man. Lebert* also has given a representation
of nerves terminating by loops, in the muscles of the
abdomen, and in the tongue of the frog.

Remak has discovered microscopical nervous gan-
glia in the auriculo-ventricular septa of the frog's heart,
and very rightly ascribes to their influence the persist-
ence of the rhythmical pulsations of the organ, when
isolated from the body, as well as the continued regu-
lar contractions in the septum itself, when this has
been detached from the rest of the heart.

From the observations of Reichert, who has care-
fully studied the distribution of the nerves of the
frog's heart, it would appear that each muscular fibre
is in relation with several nervous filaments. Volk-
man has sought to establish the numerical proportion
of large and slender fibres which enter the substance
of a striped muscle ; he has counted twelve slender
fibres in an hundred.

Very little is known of the mode of distribution of
its nerves to the non-striated muscular tissue. It may
be asserted, probably, with truth, that it is much less
richly supplied with nerves than the striated variety ;
the middle coat of the arteries affords evidence of
this.

* H. Lebert, at present Professor of Clinical Medicine in the University

of Breslau, author of Physiologic pathologique, 2 vols. Paris, 1845 ; thje

" Traite & Anatomic pathologique" now in course of publication, and

numerous papers in the Annales des Sciences Naturelles, and elsewhere.

t Bogislav Keichert, Professor of Anatomy at Berlin, successor to
Muller.— (Ed.)
k t Professor of Anatomy at Dorpat, Livonia.— (Ed.)

MUSCLES. 55

Of tke diverse theories put forth as to the mode of
development of muscular tissue, we shall notice only
that which seems to us most in conformity with ascer-
tained facts.

Muscular tissue is derived originally, like all the
other tissues, from the primordial cells of the embryo,
which, at first, everywhere the same, undergo a spe-
cial metamorphosis in order to form each and every
histological element.

The embryonic cells which are about to form mus-
cular fibres at first increase in length, and then,
coming in contact with each other by their narrowing
extremities, finish by uniting together. Afterwards,
the partitions formed by these lines of union disap-
pear, and we have, as a result of the process, tubes
of structureless membrane presenting constrictions
(which mark the line of fusion of the original cells),
and intervening expansions, each of which contains a
nucleus (PL IX. fig. IV. 1, 2, 3). At this period
their diameter varies from ToVoth to 4¥<rth of a line.
During the process of transformation the contents of
the cells, at first hyaline, become granular, and the
granules, which bear some resemblance to oil-globules,
assume a regular arrangement either in longitudinal or
transverse rows (PL IX. fig. IV. 4, 5, 6). Still later,
the muscular fibre, thus formed, increases in thick
ness, assumes a cylindrical shape, and its several cha-
racteristic features become more and more obvious ;
the division of its interior into fibrillse is noticed, and
also the appearance of a large quantity of nuclei, which
take their origin by endogenous multiplication. If, at
this moment, the extremity of a fibre is examined on

56 MUSCLES.

transverse section, it is found that the changes just
described take place from its circumference towards
its centre, very rarely in the opposite direction. Fi-
nally, the fibrillse increase in number, whilst their
newly formed nuclei are absorbed, and the mus-
cular fibre gradually puts on its permanent appear-
ance.

The following is a summary, in two words, of this
process — which seems best borne out by facts : fusion
of embryonic cells, T\ hich by their union form a tube,
or myolemma; metamorphosis of its contents into
elementary granules, and their subsequent develop-
ment into fibrillse or discs.

During the earlier periods of development and
growth of the fibres of muscle, they are enveloped by
a large number of elementary cells — some oval in
shape, others smaller and round. Of these, the
greater proportion are destined to form the connect-
ing tissue and other parts which constitute a com-
plete muscle ; and the rest, after having contributed,
no doubt, to the growth of the persistent elements of
the tissue, fade and disappear. The muscular fibres
of the heart are developed in accordance with the
same rules, with this exception, that, in place of the
fusion and subsequent transformation of simple cells,
these phenomena are accomplished by means of
branching, or star-shaped cells ; hence arises the
branching character of the fibres of this organ. The
fibres of muscle, having attained their complete
development, remain permanently, for an indefinite
period, in this state, and the metamorphoses which
occasionally occur in their interior, are marked

MUSCLES. 57

by a very feeble amount of vital activity. Up to
the present time the mode in which muscular fibre
is reproduced, has not been satisfactorily made
out*

* Wounds of muscles never heal by means of transversely striated mus-
cular substance; . . . they heal simply by means of a tendinous
cicatrix. An instance of new formation of muscular tissue has been seen
by Rokitansky in a tumor of the testicle of an individual eighteen years
old ; and another by Virchow, in an ovarian tumor. Kolliker, op. cit.

CHAPTER V.

Elements of Nervous Tissue.

THE analysis of nervous tissue reduces its anato-
mical elements to two forms, ^iz. the fibre, and the
cell.

ne™etflSe.of The fibres of nerve tissue present variations in the
details of their structure; sometimes consisting of a
tube of a certain diameter, with envelope and con-
tents perfectly distinct ; whilst, at others, on the con-
trary, the envelope and its contents so blend together
as to constitute a simple homogeneous fibre.

The envelope of the nerve tube is entirely struc-
tureless, and possessed of a certain amount of elas-
ticity. Immediately in contact with its internal sur-
face we find a soft amorphous substance of an albumi-
nous and fatty nature — this is the nervous marrow,
or medullary sheath. In fresh nerve fibres this me-
dulla is homogeneous, and constitutes a regular tube ;
but soon after death it becomes disintegrated, and
separates itself into lumpy masses, between and upon
which the envelope contracts so as to give the fibre a
varicose appearance (PL XII. fig. I.). Finally, the
central axis of the tube is occupied by a cylinder of
amorphous material, of an albuminous nature, more
compact and more tenacious than the medulla, which
is known by the name of axis-cylinder (PL XII. fig.
I. 7). It is exceedingly difficult to make out the axis-

ELEMENTS OF NERVOUS TISSUE. 59

cylinder in fresh nerve tissue ; but occasionally it*can
be detected protruding from the broken extremity of
a nerve tube. In order to render it more distinct, a
number of chemical reagents are employed ; amongst
these, dilute chromic acid seems to be the most effi-
cacious. In nerves still alive, so to speak, those, for
example, of a specimen of muscle still capable of con-
traction— we can distinguish only the envelope of the
tube with uniform <?r homogeneous contents; the
axis-cylinder is not recognizable — hence it has been
regarded as -the result of post-mortem, or artificial
change.

To repeat : in a nerve tube we observe, first, two
outer parallel lines representing the enveloping mem-
brane ; then, within these, two other parallel lines,
which mark the limits of the medulla; and finally, in
its centre, two more lines, always parallel, which
form the outlines of the axis-cylinder, when it is visi-
ble (PI. XII. fig. I. 5, 6, 7). The diameter of these
tubes varies from rsad to 26-6-th of a line.

There are other fibres, smaller than those just Fine nerve fibres.
described, in which but two parallel lines on each
side of the tube can be made out — one of which cor-
responds to the envelope, and the other to its con-
tents. The most minute fibres of all (Wo o-th to TTO o-th
of a line) are simple solid cylinders, limited by two
exterior lines only, in which it is impossible to dis-
tinguish the envelope from the material contained
within it. In the first of these it has been supposed
that the medulla was absent — the envelope and axis-
cylinder alone remaining, and that the latter, or most
minute of all, was formed by the axis-cylinder alone.

60 ELEMENTS OF NERVOUS TISSUE.

This, however, is not, as yet, susceptible of demon-
stration. Nerve fibres remain" entire whilst in the
nervous centres, and throughout their whole course ;
but, at their peripheral extremities, most of them
divide into branches. This fact is perfectly made out
as far as the nerves of motion are concerned, as we
have already seen whilst studying the structure of
striped muscle. It is probably true also of the nerves
of mucous membranes, and of the external integu-
ment.

Their mode of termination, which has been a sub-
ject of research for so many minute anatomists, is not
yet definitely established for all the tissues. It ap-
pears to be susceptible of demonstration that in the
ganglia, and other nervous centres, nerve fibres are in
contact with nerve cells. It is equally beyond doubt
that in the muscles, and in certain regions of the skin
and mucous membranes, nerve fibres, after undergoing
division, terminate by free extremities (as in muscle),
and sometimes by again anastomosing with each other
(as in the skin and mucous membrane of the tongue).
The experiments of Prof. Cl. Bernard, on the phe-
nomena of recurrent sensibility, tend to prove that a
large proportion of sensitive fibres end by forming
loops. We shall see hereafter that in the eye, the
ear, and the olfactory mucous membrane, they termi-
nate by contact with nerve cells, as in the nervous
centres. Finally, in the integument of the palm of
the hand and sole of the foot, we find, in fibres of
sensation, two peculiar modes of termination, viz. the
corpuscles of Pacini and corpuscles of Meissner, which
we are about to describe.

ELEMENTS OF NERVOUS TISSUE. 61

The corpuscles of Pacini* are little ovoid, < r rather
ellipsoid bodies, attached by one extremity, by means
of a very delicate pedicle, to the nerves of the fingers
and toes. They consist of a central cavity inclosing
the extremity of a nerve fibre, and an external enve-
lope. This latter resembles the cornea in its struc-
ture ; it is made up of a number of amorphous
lamellae, overlay ing each other concentrically, between
which we find a great number of plasmatic nuclei
disposed in regular series (PL XIV. fig. II. 2). The
more superficial lamellae lose themselves on the sur-
face of the pedicle. The central cavity is filled with
a fine granular substance, in which the outlines of
very pale cells can sometimes be distinguished. Fi-
nally, in the central axis of the cavity is a nerve
fibre, which is remarkably pale, and, for this reason,
not easy to discover. By tracing it onward it is seen
to terminate in a slight bulb (PL XIV. fig. II. 4),
whilst below, it is found occupying the centre of the
pedicle, through which it is continuous with the ner-
vous twig on which the Pacinian corpuscle is situated.
Some authors have represented the nervous filament
as dividing, in the interior of the cavity of the cor-
puscle, into two or three terminal branches.

Pacinian corpuscles are found also in other loca-
lities than in connexion with the nerves of the
fingers and toes. Kolliker has met with them in
connexion with the cutaneous nerves of the arm and
forearm, on the back of the hand and foot, and in
the terminal branches of the internal pudic, inter-

* Nuovi organ! scoperti nel corpo umano del Dottore Filippo Pacini,
Pistoja, 1840.— (Ed.}

62 ELEMENTS OF NERVOUS TISSUE.

costal, and sacral nerves, and, finally, in the great sym-
pathetic plexus which surrounds the abdominal aorta.
°f The corPusc^e °f Meissner,* or tactile corpuscle, is a
minute microscopical organ which occupies the inte-
rior of some of the papillae of the true skin. To get
a view of them, it is necessary to make very delicate
sections of the skin of the palmar surface of the last
phalanges of the fingers or toes, and to apply dilute
acetic acid to the section under the microscope. Its
shape, like that of the Pacinian corpuscle, resembles
an ellipse (PL XXIII. fig. II. 6). Its structure con-
sists of a faintly striated substance studded with plas-
matic nuclei (fig. II. 9) arranged transversely. At
the inferior, or attached extremity of the corpuscle, a
nervous filament is seen applying itself to its surface,
in the inequalities of which it seems to lose itself by
describing tortuous curves which are only occasionally
visible. Whether it ends by becoming continuous with
the substance of the corpuscle, or by simple division,
or by forming a loop, has not as yet been made out.
Kolliker has found these tactile corpuscles in the
papillae of the vermilion borders of the lips, in the
fungiform papillae of the point of the tongue, on the
nipple, the glans penis and clitoris ; but they are
encountered in greatest number in the skin covering
the last row of phalanges of the fingers and toes.
Nervous ceiiu. Nerve cells, or corpuscles, vary exceedingly both in
size and shape. In all of their forms they present,
however, every element of a perfect cell. Thus they
have a very delicate cell-wall, so thin and delicate, in

* Successor to Rudolf Wagner in the chair of Physiology at Got-
tingen.— (Ed.)

ELEMENTS OF NERVOUS TISSUE. 63

fact, as to have led some to doubt its existence.
They contain a pale, finely granular substance, toge-
ther with a variable amount of pigment, as a general
rule (PL XIII. fig. I. 6). The nucleus is spherical in
shape, and much more distinctly marked in its out-
line than the cell itself, and amongst the granules
which it contains the nucleolus is readily distin-
guished by an unusual degree of brilliancy. In the
ganglia there are some cells which, outside of their
own proper cell-wall, are enveloped by another, a
second and much thicker envelope, consisting of
structureless or very delicately fibrillated material,
full of oval nuclei (PL XIII. fig. I. 8). This seems
to be partially developed connecting tissue belonging
to the proper stroma of the organ.

In regard to their form, nerve cells are either ^ape of nerve
simply spherical, or furnished with one, two, three
or more, tubular prolongations of their cell walls (PL
XII. fig. VI. ; PL Xllirfig. I). The spherical cells
seem to be merely in contact with the neighboring
nervous elements amongst which they are situated ;
but the multipolar or caudate cells are continuous,
by their prolongations, with nerve fibres, or their
caudate processes anastomose with each other, as can
be readily seen in the grey matter of the cerebellum.

Nerve cells, associated with other elements, are Distribution,
found in the grey matter of the cerebro-spinal axis,
and in the ganglia of the cerebro-spinal nerves and
those of the great sympathetic. They are also found
in the nerves which traverse the substance of organs,
in which they form microscopic ganglia. Finally, as
we have already intimated, the nervous fibres of the

64 ELEMENTS OF NERVOUS TISSUE,

retina terminate in globular masses, and likewise
those of the internal ear, and olfactory mucous mem-
brane.

of Nerves, whether in main trunks or branches, are
bundles, consisting of nerve fibres in variable number ;
these are grouped together in primitive and secon-
dary fasciculi. The primitive fasciculi consist of a
few fibres surrounded by delicate connecting tissue,
faintly fibrillated and studded with plasmatic cells ;
this is called the neurilemma, from its analogy with
the myolemma of striated muscular fibre (Robin*).
Secondary fasciculi are made up of primary bundles,
which are held together by a much denser membrane
consisting of ordinary connecting tissue.

In large nervous trunks, fibres of every size are
found ; but those of largest size are most abundant in
the anterior roots of the spinal nerves, and in nerves
of motion, whilst fine fibres are found in greater
numbers in their posterior roots, in nerves of sen-
sation, and in branches of the great sympathetic.
These latter also contain a certain proportion of flat,
pale, smooth, or faintly, striated fibres, provided with
well marked oval nuclei, and known as the fibres of
Remak (PI. XII. fig. II.) . It is not as yet fully deter-
mined whether these are really nerve fibres, as
Rernak asserts, or merely a peculiar form of connect-
ing tissue, as Kolliker and some others are disposed
to think. We hold to the latter opinion, and regard
the fibres of Reinak as prolongations of the nucleated
connecting tissue which forms the stroma of the ner-

* Charles Kobin, Prof, agrege d'histoire naturelle medicale a la Faculte
de Medecine de Paris, Prof, d' Anatomic generate, etc., etc. — (Ed.}

ELEMENTS OF NERVOUS TISSUE. 65

vous ganglia (PL XIII. fig. III.). The nerves are not
very rich in blood-vessels ; they form a net-work of
large meshes, the terminal branches from which ra-
mify in the neurileinrna ; they do not come directly
in contact with the naked primitive fibre (Kolliker).

In addition to the nerve cells, which constitute
their most important element, nervous ganglia con-
sist of an intermingling of very delicate connective
fibres with oval nuclei, and a large number of blood-
vessels (PI. XIII. fig. III.). The connective element
is the same which has been already mentioned as
forming the thick nucleated external or second enve-
lope of certain nerve cells, and the sympathetic nerve
fibres of Remak are also derived from it, for their
constituent elements are identical in form, and be-
have similarly under the influence of chemical
reagents.

It is generally conceded that nervous ganglia con-
tain all of the different forms of nerve cells. In those
of the spinal nerves, cells with two branches (bicau-
date) are most numerous, and of these there are two
kinds. The one have their prolongations given off
from diametrically opposite points of their circum-
ference, one being continuous with a nerve fibre from
the spinal marrow, and the other with a peripheral
nerve (PL XII. fig. III.). The other kind of bi-cau-
date cells give off both of their prolongations in the
same direction, and always towards the surface.
Finally, the cells with but one prolongation (uni-
polar) are always continuous with a peripheral fibre.
In the ganglia of the sympathetic system most of the
multi polar nerve cells seem to send off the same

66 ELEMENTS OF NERVOUS TISSUE.

4

number of processes, according to Leydig, as there are
nerves connected with the ganglion (PL XII. fig.
IV.). The study of the relations which exist between
nerve cells and nerve fibres is one of difficulty ; very
thin sections must be made of fresh specimens of
ganglia, and treated with dilute acetic acid, or caustic
potassa, or still better, perhaps, by a solution of car-
mine in liquid ammonia, as recommended by Jacu-
bowitsch.* Similar sections may be made of ganglia
hardened in chromic acid ; and very minute speci-
mens of ganglia are sometimes immersed in potash
and moderately compressed between two slips of
glass.

Nervous centres. The arrangement of the elements of nerve-tissue,

throughout the cerebro-spinal centres, is far from

spinal marrow, being clearly made out. The spinal cord consists of

a central mass of grey matter, surrounded on all sides

by white matter. The latter is made up almost

wwte substance- exclusively of nerve fibres, with some blood-vessels,
supported by scanty and delicate connecting tissue.
By the aid of transverse and longitudinal sections,
we can see that some of the nerve fibres run parallel
with, and others perpendicular to, the axis of the
cord. The former constitute the greater proportion
of the white substance, and are found everywhere ;
whilst the latter are only to be seen where the roots
of the spinal nerves become continuous with the sub-
stance of the cord. It is to be noted also that the

* Jacubowitsch and Owsjannikow are connected with one of the Russian
Universities, and published their researches on the nerves in the Bull, de
1'Acad. de Petersbourg, classe k phys.-^Mathem., torn. xiv. No. 323,
page 173.— (Ed.)

ELEMENTS OF NERVOUS TISSUE. 67

nerve fibres of the spinal cord are of the smaller
varieties.

The grey matter of the cord forms a quadrangular Grey matter,
prism with hollowed sides, or rather, a fluted column.
In its centre is a canal, sometimes closed in the adult,
and of greater diameter at either extremity of the
cord, than in its middle. Its walls are formed by a
layer of connecting tissue of varied thickness, rich in
plasm atic cells, and lined internally by a stratum of
cylindrical ciliated epithelium. Virchow, Kolliker,
and Ley dig* have particularly directed the attention
of microscopists to this cylinder of connecting tissue
which is thus inclosed in the grey matter of the cord,
as the plasmatic cells which it contains are often the
origin of morbid formations which occasionally in-
volve its substance.

The grey matter itself is made up of blood-vessels. Eeiation be-

17 . *• 1 tween nerve cells

fine nerve fibres, and caudate nerve cells, the largest of ™rddfbreB' in the
which are found towards the extremities of the ante-
rior horns. In man the connexions of the caudate
cells have not as yet been clearly demonstrated.
This is not true, however, of some of the lower ani-
mals ; thus, in accordance with the researches of
Owsjannikow, in fishes, each cell has five prolonga-
tions, which are disposed as follows: The most internal
process, after it leaves the cell, enters the white com-
missure of the cord, and traversing it, reaches the
white substance of the opposite side, where it loses
itself in another similar cell (PL XII. fig. V. 7) ; this
is the branch which establishes a route of connexion

Professor of Comparative Anatomy in the University of Wiirzburg.

68 ELEMENTS OF NERVOUS TISSUE.

between the two lateral masses of nerve cells of
either side. The anterior process runs into the ante-
rior, and the posterior, into the posterior root, of each
spinal nerve; and finally, the processes given off
above and below become continuous with the longi-
tudinal fibres of the cord (PL XII. fig. V.). It
remains now to be proved, whether or no a similar
disposition exists in the mammalia and in man.
in the encepha. The facts ascertained in relation to the minute

Ion.

structure of the nervous tissue of the encephalon, are
still more incomplete. Here, as in the spinal marrow,
there is a white substance possessing very little vas-
cularity, and composed entirely of nerve fibres, and a
grey matter consisting of vesicular elements mingled
with nerve fibres, and very numerous blood-capil-
laries. Besides the multipolar or caudate cells, whose
processes anastomose with each other, and become
continuous with nerve fibres, there exist large num-
bers of nuclei and spherical cells — especially in those
portions of the grey matter of the brain and cere-
bellum which lie nearest the surface (PL XIII. fig.
II.). What is the nature and uses of these nuclei ?
Are they germs of future nerve cells, or are they
only the analogues of the oval nuclei which we found
mingled with the connective fibres of the ganglia ?
These are questions which remain to be answered.
As for the arrangement of the nerve fibres of the
encephalon, it is probable that they run from one
mass of grey matter to another, serving as commis-
sures— but this is not positively established.*

* Refer on this subject to the admirable researches " On the Minute
Structure and Functions of the Spinal Cord," by J. L. C. Shroeder van der

ELEMENTS OF NERVOUS TISSUE. 69

The ventricles of the brain and the aqueduct of Epithelium of

the ventricles.

Sylvius, which are properly to be regarded as the
continuation, in the cranium, of the central canal of the
spinal cord, are, like it, lined by a layer of ciliated
epithelium. This epithelium, in some cases, is truly
cjliated only in the fourth ventricle ; at least this is
to be inferred from the researches of Leydig upon
the brain of a criminal. {Gazette hebdomadaire, 1854,.
"p. 687). Beneath the epithelial layer there are some
fibrillse of connecting tissue forming an exceedingly
delicate lamina, in which amyloid corpuscles are
found. (Virchow.)

The membranes by which the cerebro-spinal ner- ^Sbra?dB mai
vous centres are enveloped, are composed of con- cord<
nective and elastic fibres, woven together in layers of
different degrees of density. They have but few
blood-vessels of their own, and still fewer nerves ; as
to lymphatics, their existence has not even been
demonstrated. The external surface of the visceral
layer of the arachnoid is invested with pavement
epithelium, which passes from it upon the free sur-
face of the dura mater, where it alone forms the
parietal layer of this serous membrane.

The corpuscles of Pacchioni, found in the dura corpuscles of

Pacchioni.

mater along the course of its great longitudinal sinus,
consist of very dense connecting tissue, enclosing
sometimes, in its meshes, amyloid corpuscles and cal-
careous concretions.*

Kolk, Professor in the University of Utrecht, published by the Eoyal
Academy of Sciences at ^isterdam, and translated and republished by
the New Sydenham Society, London, 1859.— (Ed.)

* The pineal gland contains pale rounded cells_without any processes,

TO ELEMENTS^OF NERVOUS TISSUE.

Development. Nerve fibres are developed, like the other tissues,
from embryonic cells. These cells unite by their
extremities to form lubes, whilst their contents are
being transformed into nervous marrow and axis-
cylinder. We learn from the investigations of Kol-
liker, made upon the tail of the tadpole, that tl>e
peripheral extremities of nerve fibres take their
origin independently of branching or star-shaped
cells, and thus we have a clue to the mode of forma-
tion of their terminal divisions and loops. As to the
development of nerve cells, it is effected by a simple
change of shape and* volume of primordial cells.

Nerve fibres, when divided, are reproduced, but
the exact mode in which the process is accomplished
is not well ascertained. It is asserted by some that
the peripheral extremity of the injured fibre disap-
pears, and is replaced by a newly formed fibre ;
others again suppose that the medulla alone is the
seat of change, and that the regeneration of the fibre
is effected by the formation of a new medulla in the
original tube. Farther research is obviously required
for the elucidation of this point of histogenesis.

and bnt a few nerve fibres y^-^th to y^ths of a line in diameter ; and,
for the most part, a large quantity of sandy particles.

The pituitary body contains, in its anterior reddish lobe, no nervous
elements, but rather, according to Ecker, the elements of a vascular
gland. The posterior smaller lobe consists of a finely granular substance,
with nuclei and blood-vessels, and possesses, also, fine varicose nerve-
tubes, which, like the vessels, descend to it from the infundibulum. K61-
liker, last edition, p. 233.— (Ed.}

CHAPTEE VI.

Vessels. — Arteries. — Veins. — Capillaries,
and Lymphatics.

VESSELS are of two species : blood-vessels and lyni- classification
phatics. Tlie former are sub-divided into arteries,
capillaries, and veins ; the latter into lymphatics, pro-
perly so called, and lacteals. The structure of arte-
ries, veins, the larger lymphatics, and lacteals, is
almost identical ; the same is true of the capillaries
and smaller lymphatic vessels,

Each one of the tissues which we have studied thus
far has some special or characteristic element; but
this is not the case with the organs now under exa-
mination. No anatomical element of determinate
form belongs exclusively to them ; but that which
serves to distinguish them from other tissues, is the
peculiar arrangement of the several parts of which
they are- composed.

Both recent and dried specimens are required for Preparations.
the examination of their structure. From portions
of dried vessels, very delicate and thin slices are cut
by a razor, and soaked in water before being placed
under the microscope. These sections answer for the
examination of the outer and middle coats, and for
the deeper portions of the internal coat of large ves-
sels ; but when we wish to study the epithelial layer,

72 VESSELS. AETEEIES. VEINS. CAPILLAEIES, ETC.

and vessels of very small size, such as capillaries,
recent specimens are required.

Arteries. SECT. I. AETEEIES. — When a section, either trans-
verse or longitudinal, including the whole thickness
of the wall of an artery, is placed under the micro-
scope, we recognise three distinct strata overlying
each other, which correspond to the three coats of
which the vessel is composed (PL XIV. fig. IV.).
The first, which is the thinnest, and uniformly dark
throughout its whole thickness, represents the in-
ternal coat (Fig. IV. 1). The second stratum, which
is transparent, and much thicker than the first, is the
middle coat (Fig. IV. 2). And, finally, the third
stratum, at least as thick as the second, and darker
in its deeper than in its more superficial portion, cor-
responds to the external coat. By employing a
magnifying power of 300 to 400 diameters it is easy
to make out the nature, as well as the arrangement
of the elements which constitute each of these coats.
The following is a summary of their microscopical
internal coat analysis : the internal tunic is limited, on its free sur-
face, by a layer of simple epithelium, which, exa-
mined in situ, seems to consist of oval nuclei, im-
bedded in a structureless substance ; the walls of its
cells are not distinguishable in consequence of their
extreme paleness (PI. XV. fig. I.). But, by teasing
out this membrane by the aid of needles, some cells
may be detached, which are recognizable as fusiform
in shape, with a very prominent bulge opposite the
situation of their nuclei (PI. XV. fig. II.), and which,
in this respect, resemble certain cells of the spleen.
Beneath this epithelial layer, which is in contact with

VESSELS. ARTERIES. VEIttS. CAPILLARIES, ETC. 73

the blood contained in xthe vessel, there is another
lamella known by the name of fenestrated membrane.
It is amorphous, elastic, traversed by numerous open-
ings which vary both in size and shape, and contains
elastic fibres which are disposed at right angles to
the axis of the vessel (PL XV. fig. III. 1, 2, 3, 4).
The deepest layer of the internal coat is composed of
fine elastic fibres, which run in the direction of the
length of the vessel. This layer is the thickest of the
three laminae which constitute the internal coat, espe-
cially in the larger arterial trunks (PI. XIV. fig. V.
1 ; PI. XV. fig. III. 5 ; fig. IV. 1). The semilunar
valves and the endocardium are formed by the in-
ternal coat.

The middle coat is made up of elastic fibres, and Middle c^t.
those of non-striated muscle. The first are distri-
buted uniformly throughout the thickness of the
layer, but seem to run in no determinate direction ;
this is readily recognised by comparing transverse
and longitudinal sections under the microscope (PL
XIV. fig. V. 2 ; fig. VI. 1 ; PI. XV. fig. IV. 6). The
network formed by these fibres is closer in its meshes
in proportion to the calibre of the artery to which it
belongs, and in these meshes the muscular fibres are
contained. To bring the latter into view it is well
to treat the specimen with dilute acetic acid. In
transverse sections it is difficult to distinguish the
outlines of these fibres on account of their extreme
paleness; but their nuclei, club shaped, and arranged
perpendicularly to the axis of the vessel, are easily
recognised (PL XIV. fig. V. 3). In longitudinal sec-
tions, the outlines of the smooth muscular fibres are

5

Y4 VESSELS. AKTEKIES. VEINS. CAPILLARIES, ETC

much better seen; they form polygons of variable
regularity of outline, in which the central nucleus is
pretty uniformly apparent (PI. XV. fig. IV. 4). It
is to be remarked that these muscular fibres are dis-
tributed with perfect regularity throughout the whole
thickness of the middle coat.

External coat. The external coat is formed by a close interlace-
ment of connective and elastic fibres, resembling felt.
The farther from its outer surface the greater the
amount of elastic fibres, and they generally run
parallel with the axis of the vessel (PL XV. fig. V.
1, 2; fig. VI. 1,2).

In reviewing the structure of the walls of arteries
it is obvious that elastic fibre forms the frame-work
of all their coats ; but also, that in each separate coat
it is associated with another distinct and character-
istic element : in the internal, this is epithelium ; in
the middle coat, muscular, — and in the external, con-
nective, fibre. Just in proportion as we approach
the smaller terminal arterial branches, the elastic
fibres tend to disappear, especially in the middle coat,
which finally becomes entirely muscular (PL XIV.
fig. VII).

In the last and smallest branches of the arterial
tree which we can examine, those, for example, which
measure from T\th to ~th of a line in diameter, we
still recognise the three coats, but each one of them
is constituted by only a single lamella of tissue, com-
prising but a solitary anatomical element. Thus, the
outer coat consists of a very thin layer of connective
fibres mingled with some plasmatic cells (PL XV.
fig. VII. 1). The middle coat shows very short fusi-

VESSELS.— ARTERIES. VEINS. CAPILLARIES, ETC. 75

form fibres of non-striated muscle, indicating that, in
these little arterioles, this tissue remains permanently
in an imperfectly developed condition (PL VII. 2, 3).
As for the inner coat, it is reduced to a mere layer of
epithelial cells (fig. III. 4).

SECT. II. VEINS. — The structure of the veins fol-
lows the same general plan as that of the arteries.
Like them, they have three coats. The epithelial
layer of the internal coat is identical in every respect internal coat
with that of the arteries. In almost all the specimens
which I have examined, a fenestrated membrane has
been present, showing numerous openings, surrounded
by an interlacement of large elastic fibres (PI. XVI.
fig. IV. 1, 2).

Beneath this is a third layer of fine elastic fibres,
forming a somewhat looser web than the correspond-
ing layer of the inner coat of an artery, and pene-
trating, by its deepest fibres, the surface of the middle
coat — so that the dividing line between these two
coats is not so distinct and clear as in the walls of an
artery (PL XVI. fig. II. 2).

The middle tunic presents an intermixture of Middle coat
elastic and muscular fibres, but the latter are not
uniformly distributed (fig. II. 5, 6). Their direction
is generally transverse, but nevertheless, near its
outer surface, there are some which run parallel with
the axis of the vessel (fig. II. 7, 8). May not this
unequal distribution of muscular fibre in the walls of
veins account for the relative weakness of certain
portions of them, and thus explain their tendency to
become varicose ?

The external coat is. similar in every particular to External coat

76 VESSELS. ARTERIES. VEINS. CAPILLARIES, ETC.

that of the arteries ; but it is to be noticed that in
certain veins, principally in those belonging to the
portal system, muscular fibres have been found in its
deeper portion, longitudinal in their direction. The
presence of these muscular fibres, and the direction of
their course, explains the reason why these veins
diminish in length under the influence of the stimulus
of galvanism.

ize. In veins of the smallest size the three tunics are
still distinguishable ; the innermost is a simple epi-
thelial layer ; sometimes, however, there is a fenes-
trated layer outside of it, presenting exceedingly
delicate meshes (PI. XVI. fig. V. 6). The remaining
tunics resemble exactly those of arteries of similar
calibre (fig. V. 1, 3).

valves. The valves of veins are formed by their internal
coat. A lamina of pavement-epithelium constitutes
their surface (PL XVI. fig. III. 1). More deeply, we
encounter wavy and parallel fasciculi of connective
fibres, and a web of delicate elastic fibres intermingled
with plasmatic cells. The latter are rendered visible
by the addition of dilute acetic acid, which dissolves
the connective fibres.

The vasd vcisorum are arterioles and veinules.
According to Kolliker, they are to be found on ves-
sels even of the smallest calibre (of the diameter of
one half a line and less) ; they are distributed mainly
to the outer coat ; in the middle coat there are a few,
but in the inner coat I have never seen them. The

Nerves, nerves which supply the walls of vessels are few in
number, and those which .are encountered are for the
most part destined to the organs supplied by the

VESSELS. AETEEIES. VEINS. — CAPILLAEIES, ETC.

vessels which they accompany, rather than for the
innervation of the vessels themselves. They seem to
terminate by free ends, and it is uncertain whether
or not they reach the internal coat.

SECT. III. CAPILLAEIES. — The capillary vessels, capillaries.
which are the media of communication between the
arteries and veins, are exceedingly simple in their
structure. They are tubules of structureless sub-
stance, studded with oval nuclei. The larger the size
of the capillaries, the thicker are their walls, and the
greater the number of nuclei (PI. XV. fig. VIII ; PL
XVI. fig. I. 1). The smallest of them have such
exceedingly thin walls that they are portrayed by
only a single line. The transition from arteries and
veins to capillaries takes place insensibly, and by the
successive disappearance of the several organized ele-
ments which constitute the three tunics of a vessel.

SECT. IV. LYMPHATIC VESSELS. — After what has
been said concerning the histology of arteries and
veins, a few words only will be required for the
description of the structure of lymphatics.

Their internal membrane consists of a simple layer
of epithelium supported by a web of elastic fibres of
extreme delicacy ; sometimes it appears to be reduced
to epithelium alone. .>;

Their middle coat is composed almost exclusively
of muscular fibres arranged transversely ; elastic
fibres are very few in number (PL XVII. fig. II. 2,
3). Finally, the external coat differs from that, of
arteries and veins, by containing a large amount of
longitudinal muscular fibre in its deepest portion
(fig. II. 5 ; fig. III. 5). Their valves contain also

78 VESSELS. AKTEKIES. VEINS. CAPILLARIES, ETC.

some muscular fibres, and otherwise resemble those of
the veins (PL XVII. fig. IV. 3).

The lymphatics, then, are seen to present the same
general plan of structure as arteries and veins, with
this single feature of difference, that they are richer
in muscular fibre. The lymphatic capillaries, like
those which carry blood, consist of tubes of amor-
phous substance, with oval nuclei set in their walls.
Their characteristic peculiarity consists in the filiform
prolongations which they give off at intervals along
their course, and at their terminal extremities (Kol-
liker). As for the true seat of origin of the lympha-
tics (that of the lacteals being already understood),
it is, according to M. Kiiss,* immediately beneath the
several epithelial membranes — with the functions
of which those of the lymphatics seem to be closely
connected.

0 ^° *he system °f lymphatic vessels are attached
the little gangliform organs known as lymphatic
glands. These glands possess a fibrous envelope, and
consist, internally, of a cortical and a medullary sub-
stance. The cortical substance, which in section pre-
sents a granular aspect, comprises the superficial por-
tion of the parenchyma of the gland. It is a sort of
extremely delicate cavernous body, whose trabeculse,
consisting of imperfectly developed connecting tissue,
serve to support the blood-vessels and lymphatic
trunks which enter it. Its cavities communicate in
every direction with each other, with those of the

* Professor of Pathological Anatomy in the Faculty of Medicine of
Strasbourg, France. — (Ed)

VESSELS. ARTERIES. VEINS. CAPILLARIES, ETC. 9

central medullary portion, and with the terminal
branches of the afferent lymphatics ; they contain an
alkaline liquid, and organized corpuscles, amongst
which we can distinguish little cells, averaging ai^th
of a line in diameter, and spherical granular nuclei of
from 4^oth to ^oth of a line. These elements are
identical with those which exist in lymph and chyle.

The medullary substance, striated in appearance, is
enveloped on all sides of the cortical substance, except
at those points where the afferent vessels enter the
gland. It is made up, mainly, of the terminal radi-
cles of the afferent vessels, which, taking their origin
in the deeper cavities of the cortical substance, anas-
tomose with each other and form a network, whose
branches, becoming gradually larger in size, and
fewer in number, finally terminate in one or two
efferent lymphatic vessels, which make their exit at
the hilus of the gland.

The arteries, most of which terminate in the cor-
tical substance, either arrive there directly, or after
traversing the medullary portion of the organ, to
which they give off a few branches. In the trabeculse
of the cortical substance these vessels form an intri-
cate capillary plexus, which is directly in contact
with the cells of the gland.

The veins, fewer in number and greater in volume
than the arteries, accompany them in their course.
The nerves are not numerous ; they enter the gland
with its vessels, and their mode of termination is
unknown.

The structure of a lymphatic gland may be summed
(up as follows: the essential or secreting portion of

80 VESSELS. AKTEKIES. VEINS. — CAPILLARIES, ETC.

the gland is represented by a large cavity (cortical
substance) filled with globules, which are imbedded
in a vascular network, from which they extract mate-
rial for elaboration. On one side, this cavity is in
communication with the afferent lymphatic vessels,
and on the other, with the efferent vessels, into which
latter it pours the organized products which after-
wards become white, and perhaps, also, red globules
of the blood.

?ee8Iei8pmefit of Arteries, veins, and lymphatic vessels are alike
developed from embryonic cells. They are at first
recognisable in the shape of rows, or columns, of cells.
Of the cells which correspond to the axis of the
column, one portion liquifies, and the remainder
becomes transformed into blood globules. Those
which lie on either side of the axis undergo various
changes, and finally form the three coats which con-
stitute the walls of the vessel.

The development of capillary vessels is accom-
plished in the following manner : cells of oval shape
become united to each other end to end, and then the
partitions which separate them are absorbed and dis-
appear ; so that each series of cells is thus trans-
formed into a minute canal, in the structureless walls
of which nuclei are to be recognised, at regular inter-
vals, as in the fully formed capillaries of the adult.
Anastomoses are effected by means of minute prolon-
gations, like canaliculi, which take their origin from
the walls of the vessel, and, pushing out in different
directions, unite finally with each other.

Kolliker has also demonstrated that branching
plasmatic cells not unfrequently form a connexion, by

VESSELS. ARTERIES. VEINS. — CAPILLARIES, ETC. 81

their prolongations, with the walls of capillaries
already in existence, and thus contribute to the for-
mation of the capillary plexus, or network. Their
prolongations, increasing in diameter, ultimately
become true capillary vessels, and the body of the
cell itself corresponds to the point of confluence of
several vascular canals. The same author asserts that
many large vessels are formed out of capillaries, by
the transformation of the cells which surround them
into their several tunics.

BLOOD AISTD LYMPH. — In a histological point of view j^°pdhand
the composition of blood and lymph is exceedingly
simple. The organized elements of the blood are of
two species, red and white globules. The red glo-
bules are bi-concave discs measuring, on an average,
aajth to 3i<rth of aline in breadth, and Worth to TTO o-th
of a line in thickness. Their external envelope is so
exceedingly delicate that it seems to be continuous
with their contents. They consist internally of an
amorphous substance of some density, very elastic,
and colored yellowish red by hsematine. When
exposed to the air these globules become rapidly
altered in form, and as a common rule, show wrinkles,
or indentations, upon their surfaces (PL I. fig. I. 3).
The red globules, according to Schmidt, constitute
'about one half of the whole mass of the blood.

The white globules of the blood differ from the white giobuiea.
preceding, both in size and shape. They are sphe-
rical corpuscles, with rough or tuberculated surfaces,
and average in diameter from 2¥<rth to rioth of a line
(PI. I. fig. I. 4). Their contents, granular and trans-
parent, include, sometimes, a nucleus so large as to

82 VESSELS. AKTEKIES. VEINS. — CAPILLARIES, ETC.

almost fill the globule, but most frequently it is
represented by several vesicles of brilliant appear-
ance, which are rendered still more apparent by the
addition of acetic acid. Up to the present time dis-
tinctive features between these globules, and those oi
pus, have been sought for in vain. The relative pro-
portion, in the blood, of white to red globules, accord-
ing to Moleschott,* is 1 to 357. In some cases oi
leucocythemia, it is increased to one-third, or even to
two-fifths of the globular element of the blood (Vir-
chow).

The liquid portion, or plasma of the blood, coagu-
lates after escaping from the blood-vessels. One por-
tion remains liquid, and the other assumes the form
of a consistent and elastic mass — the clot. In the
serum, or liquid portion, a few red and white globules
are to be seen floating in the colorless fluid. The
clot, which entangles, and consequently includes, the
great mass of the globular elements of the blood, is
composed, in addition to them, of a substance of a
very finely granular or fibrillated appearance, but not
organized (fibrine).

Lymph giobuies. The solid elements of lymph are globules, whicl
resemble exactly the globules contained in the cor-
tical portion of the lymphatic glands, and the whitt
globules of the blood. These corpuscles, which ave
rage in diameter from 2 srth to T^th of a line, arc
found in considerable quantity in the vessels whicl
emerge from the lymphatic glands, whilst in the affe-
rent lymphatics, or those which enter the gland and

* Professor of Physiology in the University of Zurich. — (Ed.}

VESSELS. ARTERIES. VEINS. CAPILLARIES, ETC.- 83

form its capillary network, there are very few. There
is found also, in the lacteals, a variable quantity of
spherical granules of an oily nature, which are derived
from the food, and which are very early to be seen in
the true lymphatics.

Lymph, also, coagulates when it escapes from its
containing vessel, forming a clot, identical in its com-
position to that of the blood — including, of course,
no red globules. Kolliker asserts that lymph never
contains red globules, and that those occasionally
found in it got there in consequence of the rupture of
a blood-vessel.

The formation of the red blood corpuscles in the F1°™fet£mofred
embryo is effected, as we have already stated, by
transformation of the primordial or embryonic cells
which occupy the centre of the blood-vessels whilst
in process of development. These cells are not at first
distinguishable from the embryonic cells by which
they are surrounded, but they soon become infiltrated
with haematine, flatten out into discs, and their nuclei
tend to disappear. They multiply by the process of
cleavage. In the adult the increase in number of red
corpuscles seems to take place at the expense of the
lymph globules, which become disc-like in shape, and
charged with haematine, whilst at the same time
their nuclei are absorbed. Kolliker, relying upon
what he has observed in the lower animals, asserts
that this is the mode of development of the red cor-
puscles of the blood in man.

•

CHAPTEK VII.
Glands.

Definition. GLANDS are organs which present a great variety
in their size and shape ; they consist essentially of
enclosed cavities, lined or filled with cells, and open-
ing upon the surface of the skin, or of a mucous
membrane, either directly, or by means of special
canals known as their excretory ducts.

Certain organs composed of one or more cavities,
closed on all sides, and filled by cells or globules, are
called blood-glands, and duct-less follicles.

The parenchyma of glands (the essential or secret-
ing portion of the organ) is made up either of tubes,
or of partially closed vesicles, grouped together in
parcels, like clusters of fruit, and opening into a
common canal or outlet. Hence we speak of two
sorts of glands : those composed of clusters of vesi-
cles (racemose), and tubular glands.

General struc- Generally glands are invested externally by an
envelope of connecting tissue, varying in density.
From the deep surface of this external envelope,
processes or trabeculse are given off, which, traversing
the interior of the organ in different directions, divide
up the glandular parenchyma into segments (lobes,
lobules); they also support the vessels and nerves of
the organ. The vesicles and secreting tubes are
formed by a membrane of their own (basement mem-

ture.

GLANDS. 85

brane), which is usually very delicate and structure-
less ; sometimes it is more dense, being strengthened
externally by a layer of fibrillated tissue (as in the
testicles, lungs, etc.). Its internal surface is covered
by a simple layer of epithelial cells, generally many-
sided ; or, these are arranged in strata, so as to fill
completely the cavities of the secreting vesicles, or
tubules. Upon the external surface of their basement
membrane blood-vessels ramify, so as to form a capil-
lary web, or network, with meshes of varying size
in different glands.

Nerves accompany the blood-vessels, but aTe rela-
tively less numerous ; their mode of termination is
not yet fairly known, but it is probably by means of
free extremities.

The excretory canals, or ducts, of glands, have an Ducts,
external coat which is usually formed by the inter-
lacement of connective and elastic fibres, together
with fibres of unstriped muscle ; internally they are
lined by an epithelial layer, the cells of which diifer
from those of the parenchyma of the gland. The
ducts of some glands contain minute clusters of vesi-
cles in the thickness of their walls (liver, pancreas,
lung).

SECT. I. GLANDS CONSISTING OF CLUSTERS OF VESI- Glands formed bj

clust*8 of vesi-

CLES. — The glands of this variety scarcely differ from cles-
each other in structure, except in the minute details
which belong to the disposition and arrangement of
their epithelial element. Therefore, in order to
escape the useless repetitions which a separate de-
scription of each gland would of necessity involve,
we shall study the structure of certain individual

86 GLANDS.

glands, which will then serve as types, around which
those of similar structure will naturally group them-
selves. And let us commence by examining those of
simplest structure, e. g. the salivary glands,
salivary glands, /Salivary Glands. — On placing a very thin section
of the sub-lingual gland under the microscope, we see
that its terminal cul-de-sacs, or ccecal pouches, are
incomplete vesicles, the walls of which are formed by
two layers. The external layer is basement mem-
brane, structureless and exceedingly thin, being only
TeVoth of a line in thickness. Its inner lining con-
sists of a layer of many-sided cells, with extremely
pale outlines, and averaging in diameter aiirth of a
line. Their nuclei are much more distinct, and so
large as to almost fill the cells (PL XVIII. fig. I. 1).
Three or four of these vesicles, connected -together
closely in a group, have an outlet in common, and
constitute thus a microscopic lobule. Several of these
minute excretory canals, each with its corresponding
lobule, meet together in a canal of somewhat larger
size, and by their union form a lobule large enough
to be seen by the naked eye (PL XVII. fig. V).
Finally, the aggregation of a number of lobules, with
a canal of proportionate size, results in the formation
of lobes, and these, in their turn, uniting in a common
excretory duct, make up the gland. The excretory
duct is composed externally of a coat of connecting
tissue, and internally of a layer of cylindrical epithe-
lium. The gland is enveloped .by a membranous
expansion of connecting tissue, from the internal sur-
face of which laminated processes are sent into the
substance of the organ, where they invest the exte-

GLANDS. 87

rior of its lobules and lobes, and convey to them, at
the same time, their blood-vessels and nerves.

The vessels terminate in a rich web of capillaries Jeersv6^8 and
which is spread out upon the external surface of the
vesicles. The nerves ramify with the larger vascular
trunks of the gland, but do not appear to reach their •
terminal secreting pouches. We know little or no-
thing of the sources of distribution of the lymphatics.

To this first type are assimilated the salivary glands
and mucous follicles which belong to the cavities of
the mouth, pharynx, and oesophagus, the glands of
Brunner in the duodenum, the lacrymal glands, the
mucous follicles of the conjunctiva, vagina, and vulva,
the glands of Bartholinus and Cowper, and, finally,
those clusters of vesicles which have been mentioned
as imbedded in the walls of the ducts of the liver,
pancreas, and lung.

The Lungs. — The bronchial tubes, as is well known, Lung*
form a tree, whose principal branches are given off
from their trunks at an acute angle, whilst their ter-
minal ramifications are detached from the penultimate
branches at right angles. On examining the walls of
these little terminal ramifications upon their internal
surface, they are seen to be full of minute openings,
which lead into cavities (primary lobules), measuring
about aVth of an inch in mean diameter, and which
present a somewhat complicated structure. Each of Primary iobuie».
these primary lobules resembles one of the lungs of
the frog ; on its inner surface we recognise large
depressions, or partially formed vesicles (PL XIX.
fig. T. 1), each divided into three or four secondary
vesicles (fig. I. 2), which open by large orifices into

88 GLANDS.

the common cavity. But this latter, instead of being
a large empty space in the centre of the lobule, such
as we see in the frog's lung, forms a sort of corpus
cavernosum, or cavernous sinus, by the anastomosis of
numerous trabeculce which traverse its interior, and
which are given off from the walls of the vesicles.

• I am of opinion, however, that all of the lobules
of the lung are not constructed exactly after this
model; some of them seem to be mere diverticula
from the bronchial walls, presenting vesicular depres-
sions upon their internal surfaces, but without the
trabeculce, resembling, in short, more perfectly, the
lung of the frog. We can often detect lateral open-
ings near the summit of a lobule, by means of which
it communicates with neighboring lobules ; but the
number of these orifices is limited.*

* In a monograph published within the present year (The Anatomy of
the Human Lung, an Essay for which was awarded the Fothergillian
gold medal of the Medical Society of London, by A. T. HOUGHTON WA-
TEES, Lecturer on Anatomy, &c., &c., Liverpool. Lond., 1860), contain-
ing the results of a considerable amount of original research, the true
respiratory structure of the lung is somewhat differently described. The
trabeculce, forming by their anastomoses a species of corpus cavernosum
in the common cavity of the primary lobules, are not recognised. The
following quotations, slightly condensed from the author's own language,
give the result of his investigations. In regard to preparations, he says
(p. 168) : u The plan I have adopted, and which I believe affords the best
means for investigating the lung tissue, consists in the injection of a
colored solution of gelatine into the blood-vessels, inflation of the air-
tubes, and gradual desiccation. In my first attempt I inflated the air-
tubes before injection of the blood-vessels, but I afterwards injected
before inflation. The colors I have used have been red, yellow, and
blue. The red, a finely powdered vermilion ; the yellow, a chromate of
lead, formed, at the time, by the decomposition of acetate of lead by
bichromate of potash ; the blue, a Prussian blue, formed by the decom-
position of ferro-cyanide of potassium and sesquichloride of iron. When

GLANDS. 89

J

The primary lobules, thus described, grouped
together without any intermediate substance, consti-
tute secondary lobules. These latter have the shape
of pyramids, whose bases are directed towards the

a piece of lung is well injected, the walls of the air-sacs become almost
entirely opaque ;• their outline may be distinctly seen when they are
divided ; and, the vessels in their walls being filled with the dried gelatine
and coloring matter, dissections under the microscope can be carried on
with great facility, without which I believe it is impossible to form a
definite notion of the anatomy of these parts." With respect to injection
of the air-tubes, he remarks that, " when gelatine is used as a vehicle for
injecting the blood-vessels with some opaque matter, it usually happens
that the coloring matter is left in the vessels, and a portion of the trans-
parent gelatine exudes into the air-tubes ; and this has appeared to me
as good a way as any, of effecting an injection of this kind. Where such
a preparation is dried, and then soaked in spirit and water, it swells, and
assumes much the shape it has in its normal condition, and much infor-
mation may be derived from an examination of it. When a piece of
lung, in which the blood-vessels are injected, has injected into its air-
tubes a mixture of turpentine and wax, and is left to dry, and then a
slice of it moistened with Canada balsam, as suggested in Adriani's thesis
(Arius Adriani, Dissertatio anatomica inauguralis de subtiliori Pulmo-
num structurd, 1847, p. 41), the substance filling the air-tubes becomes
transparent, and the outline of the air-sacs and ultimate bronchial tubes
is well seen, and a very correct notion of their shape can be formed."
. . . . " If we follow out a bronchial tube on a lung thus injected,
inflated, and dried, and trace it to its termination in the ultimate air-
tubes or cavities, by carefully removing the portions of lung which are
upon it, and then the other half of its wall, so as to lay bare its interior,
we adopt, I believe, the best plan of ascertaining how the tube itself ter-
minates, in what manner the air cavities proceed from it, and what rela-
tion they bear to it. For this purpose, we should expose a bronchial
tube, from its entrance into a lobule, to its termination. We find that
the bronchial tube, having entered its lobule, divides and gives off
branches, and at last terminates in a dilatation, which has opening into
it a number of orifices. These orifices lead to a number of canals, which
have been variously designated : ' intra-lobular bronchial ramifications'
(Addison, PhilosopTiical Transactions, 1842); ' lobular passages' (Todd
and Bowman, v. ii. p. 390); 'intercellular passages' (Rainey on the

6

90 GLANDS.

surface of the lung, whilst their summits are conti-
nuous with the bronchial passages. They are sepa-
rated by a delicate interstitial lamina of connecting
tissue. Their diameter often reaches two-thirds of an

minute structure of the lungs, Med. Chir. Trans., vol. xxviii. 1845) ;
' infundibul urns' (Kossignol, Recherches sur lastructureintim.edu Poumon
de VJiomme, etdes principaux mammiferes, Brussels, 1846) ; ' Halpigliian
vesicles' (Moleschott, de MalpigManis Pulmonum vesiculis, Heidelberg,
1845) ; and * terminal cavities' (Mandl, Anat. Mivroscop. t. ii. cb. vi.).7 "
To all of these terms the author objects, as not expressing clearly the
nature of the structure they are intended to designate ; and after dis-
cussing and rejecting them seriatim, proposes, although unwillingly, a
new term which, he believes, expresses in a "shorter and more exact
manner than any previously used, the particular character and arrange-
ment of the portion of the lungs under consideration :" this term is
" air-sacs" " The air-sacs are those tubes In which the bronchial rami-
fications end ; they are situated at the surface, and throughout all parts
of the lung; they are supported externally by the pleura, and within the
lung they in part rest, by their extremities or their sides, against the
bronchial tubes and branches of the blood-vessels, and they are visible
through the transparent coats of the smaller bronchial tubes, as through
the pleura. The air-sacs consist of somewhat elongated cavities which
communicate with the bronchial ramification by a circular opening, usu-
ally smaller than the cavities into which it leads, and which has some-
times the appearance of a circular hole in a diaphragm, or as if it had
been punched out of a membrane which had originally closed the
entrance to the sac; when this is the case the sac dilates suddenly
beyond the orifice. The sacs are arranged in groups (usually from six to
ten composing a group, p. 144) ; they are placed side by side, and sepa-
rated from each other by their membranous walls ; their shape, when
properly inflated, or when distended by some material which has set in
the sacs, such as gelatine, or a mixture of wax and turpentine, is polygonal ;
they approach very nearly to the circular form, but in consequence of
their mutual pressure, their parietes become somewhat flattened. They
increase somewhat in size as they pass from the bronchial tubes to their
fundus, the latter being usually the broadest part of the sac; but they
are often found to have an almost uniform diameter throughout. All the
sacs pass from the extremity of the bronchial tube towards the circum-
ference of the lobule in which they are placed ; they consequently radiate

GLANDS. 91

inch, or more. In the adult, as a rule, the outline of
the bases of these lobules is marked on the surface of
the lung by a variable amount of black pigmentary
deposit,

from the tip of each terminal bronchial twig. The sacs connected with
one "bronchial termination do not communicate with those of another ;
each set of air-sacs is therefore a little lobule, or lobulette, which, in fact,
represents the entire arrangement of the lung, and is a lung in miniature."
(The resemblance of a lobulette to the entire lung of a frog, is elsewhere
strongly emphasized.) " As the air-nacs pass towards the boundary of
the lobulette, they often bifurcate, and here and there circular orifices
exist, which lead to smaller sacs, sometimes only to a small group of air-
cells or alveoli, so small as scarcely to be considered a sac." The author
adopts the term alveolus from Rossignol as preferable to air-cell, or air-
vesicle, both of which he considers objectionable. " A pulmonary alve-
olus is that portion of an air-sac which exists in its wall, and is circum-
scribed by a slightly raised margin, consisting of thin membrane, and
constituting a cup-like depression. In shape it is more or less polygonal.
The alveoli are found throughout the circumference of the sacs, and at
their fundus, varying in number in each sac from eight to twenty.'"1
u If we trace the sacs from their fundus we may say that, passing from
the periphery of the lobulette, and diminishing somewhat in size, they all
terminate in the dilated extremity of the bronchial tube," by the common
orifice already described. " The sac?, as they pass in this manner, often
join, two and three together, and others terminate in a single mouth."
. . . . " The tube which results from the union of two sacs has a
smaller capacity than that of the two sacs taken together, but a larger
capacity than either of them individually." .... "The shape of
these groups of air-sacs, or lobulettes, is more or less pyriform, the apex
being situated at the termination of the bronchial tube ; the base,
somewhat flattened, especially at the superficies of the lung, at the distal
extremity of the sacs. A most excellent way of examining the air-sacs^
and one which demonstrates most satisfactorily the manner in which those
at the surface of the lungs are arranged with reference to the bronchial
tubes, is the following : a thin slice should be cut off the surface of a
portion of lung which has beerr injected, inflated, and dried, and the
portion itself (not the slice) should then be placed under the dissecting
microscope. The cut orifices of the air-sacs will be observed. Very
fine bristles should then be inserted into these tubes, the largest one being
first chosen. It will be found that several of the bristles, passing into

92 GLANDS.

structure of^the The constituent parts of a pulmonary vesicle, pass-
ing from without inwards, are, 1st, basement mem-
brane; 2d, its epithelial investment. The first is
. formed by an extremely delicate web of elastic fibres ;

different openings, converge to a point a short distance from the surface
of the lung. It will be known that they pass to a common point, as, by
moving one of the bristles gently, it will act upon the others. Having
placed bristles in all the air-sacs which converge to this spot, the bristles
should be left in their position, and the bronchial tube should be laid
bare on its proximal side, down to its termination, i. e. the lung sub-
stance covering it should be removed, care being taken to stop just
before reaching the spot where it communicates with the air-sacs. The
number of bristles communicating with the spot thus exposed, will show
the number of air-sacs belonging to one group. The termination of the
bronchial tube will be seen to be somewhat expanded, and the air-sacs
will be found, many of them, to communicate with it by a circular ori-
fice, which is smaller than the sac itself." . . . . " When the bron-
chial tube has been exposed in the way I have mentioned, and the mode
of communication with the air-sacs observed, a section may be made
longitudinally through one or more of the latter ; it will be then seen
that the sacs lie side by side, and that they occasionally give off smaller
sacs ; the manner also in which they divide, and the mode in which
they terminate, will be observed. It will also be seen, that as each
bronchial tube approaches its termination, it has here and there through-
out its circumference, small circular orifices, which are the commencement
of small canals, leading to groups of air-sacs or lobulettes ; and it will
further be seen that the tube itself, at its termination, has a number of
alveoli in its walls. . .• .

" Another very excellent way of examining the terminal bronchial
tubes, and the commencement of the air-sacs, is to soak a piece of lung
that has been injected, inflated, and dried, in spirits for some time, and
when the piece is well saturated, to dissect it under the microscope. By
imbibition of the spirit the mass of lung swells, and the air tubes and sacs
remaining distended, the parts assume nearly the size and shape they have
in life. When such a piece is examine^, very frequently on opening the
bronchial tubes and following them to their end, their alveoli may be
plainly seen, as well as the orifices leading to the air-sacs, and the band
of elastic fibres which surrounds the opening into each sac becomes
apparent."— pp. 182-14T.— (Ed.}

GLAKDS. 93

these accumulate in the intervesicular partitions, and
form likewise the central portions of the trabeculse
PL XIX. fig. II. 1). The nature of this membrane
explains the great elasticity of the lungs.

The epithelial lining of the pulmonary vesicles is Epithelium.
composed of many-sided cells with very pale outlines,
measuring, in mean diameter, ai^th of a line, and
having no cilia ; their nuclei are very large (2 ijth of
a line) and full of dark granules (PL XIX. fig. II. 2 ;
fig. III.). This epithelial layer is found also upon the
trabeculse. I have reason to believe that fatty dege-
neration of these epithelial cells always constitutes
the initial lesion of pulmonary tuberculosis.*

In tracing the epithelium from the vesicles and ^'nayer epi"
lobules into the bronchial tubes, the single layer of
cells becomes double, and the number of strata con-
tinues to increase as the air-tubes enlarge in calibre ;

* The existence of an epithelial lining toBthe air-cells of the lungs is one
of the most recently established facts of histological science. It is denied
by recent and high authorities, viz. Kainey (Med. CMr. Trans, vol. xxxii.
1849, p. 51 ; and Brit, and For. Med. CMr. Rev. No. xxxii. p. 491), and
Todd and Bowman (Phys. Anat., Lond. 1856, vol. ii. p. 391) ; although
the latter admits the fact in his article on " Mucous Membranes" in the
Cyclopaedia of Anatomy. It is asserted by Carpenter (Human Physio-
logy, p. 513, 4th Ed. Lond.), by Quain and Sharpey, Kolliker, Rossignol,
Adriani, Schroeder van du Kolk, Schultz (Disqumt. de structured et tex-
turd canalium ariferorum, 1850, p. 10) ; Williams (art. Lungs in Cyclo-
pedia of Anatomy, 1855) ; Dr. Radclyffe Hall (Brit, and For. Med. CMr.
Rev. No. xxx. p. 481) ; Mandl (Anat Micros, vol. ii. p. 327) ; Milne
Edwards (Lemons sur la Physiologie, &c., t. ii., p. 326) ; Peaslee (Human
Histology, &c., &c., Philad. 1857, p. 579), and Waters (op. cit., p. 159).
According to the latter authority it is best seen in a perfectly fresh spe-
cimen of lung tissue, and by the aid of acetic acid. According to Kol-
liker it is " an ordinary pavement epithelium without cilia, which forms
a single layer, and rests immediately on the fibrous coat" of the pulmo-
nary vesicles. — (Ed.)

94 GLANDS.

of these, the deeper layers of cells are many-sided, and
present nothing worthy of note ; but those upon the
surface are conical, with their bases directed towards
the axis of the canal, and furnished with vibratile
cilia (PL I. fig. VII.). In the most minute bronchial
tubes the deeper strata of epithelial cells disappear
entirely — the ciliated layer alone remaining.

Underlying the epithelial layer we have the mu-
cous membrane, consisting of a delicate web of inter-
mingled connective and elastic fibres. These latter
have a longitudinal direction, and occupy the outer
aspect of the membrane. In bronchise of some size
they form small whitish longitudinal fasciculi, per-
fectly visible to the naked eye. Outside of the mu-
cous membrane we have a layer of unstriped mus-
cular fibres, circular in their direction. In the tra-
chea, and its larger subdivisions, these fibres are found
only in their posterior aspect, or in the membranous
portion of the canal, and their connexion with the
extremities of the cartilaginous rings has been demon-
strated (Kolliker). Here, also, longitudinal muscular
fasciculi have been recognised, occupying the outer
aspect of the circular layer.

Fibrous coat. Finally, the external or fibrous coat of the bron-
chial tubes is formed by a dense interlacement of
connective and elastic fibres. It contains also carti-
laginous plates of variable shape, which are found
only upon the anterior and lateral regions of the tra-
chea and large bronchi, whilst they are distributed
upon the whole circumference of the smaller canals.
It is to be noticed that these cartilaginous lamellae
become smaller and less frequent in proportion as the

GLANDS. 95

tubes chminish in calibre, and finally, when this has
reached a diameter of one-half of a line, they are no
longer to be found. Tubes of this size, in fact, consist

O I '

simply of an extremely delicate mucous membrane,
lined externally by scattered muscular fibres, and
within, by ciliated epithelium.

Clusters of gland vesicles are found imbedded in Glands.
the thickness of the walls of the trachea and bronchi.
Very numerous in the commencing trunks of the bron-
chial tree, they become less and less frequent as its
branches diminish in size, and, according to Kolliker,
are no longer to be seen in bronchise of from one to
one and a half lines in diameter. These little glands,
which are hardly one-fourth of a line in diameter, are
to be found in the deepest portion of the mucous coat
of the tube, or rather lying upon the inner surface of
its fibrous coat. Their epithelial cells are polygonal,
whilst those lining their ducts, which open into the
bronchial tubes, are cylindrical, but not ciliated.*

The pleura, like the other serous membranes, are Pleur*-
not very complicated in their structure. They are
made up of a somewhat dense interlacement of fibres
— connective and elastic — and, upon the free surface
of the membrane thus formed, a simple layer of pave-
ment epitheliunl. They receive numerous blood-

* Waters (op. cit. p. 122) describes two sets of glands as belonging to
the mucous membrane of the trachea and bronchial tubes : one consisting
of simple mucous follicles, found everywhere on the surface of the mem-
brane ; the other, larger in size and compound in character, found only
in the posterior, or membranous portion of the trachea and larger bron-
chial ramifications. It is these latter which are supposed to furnish the
very tenacious and viscid masses of sputa so characteristic of certain
stages of bronchitis. — (Ed.)

96 GLANDS.

vessels from a variety of sources (the bronchial and
pulmonary arteries, intercostals and internal mam-
maries), which enter at their attached surfaces. Fi-
nally, nervous filaments have been traced into their
substance from the great sympathetic, the nervus
vagus, and the phrenic nerve.

The arteries distributed to the lungs are of two
sorts, bronchial and pulmonary arteries, The latter
accompany the bronchial tubes to their terminal
extremities, and, during their course, subdivide very
frequently, some of their branches going to the small-
est of the bronchise, whilst the rest terminate on the
pulmonary vesicles. Before they finally break up
into a capillary plexus, the smaller arterial branches
are found in the interstices between the lobules of the
lung, where they anastomose with each other in such
a manner as to surround each lobule with a vascular
circle or network, recalling the arrangement of the
branches of the vena portce around the lobules of the
liver. From this arterial circle branches of the small-
est size are given off in great number, which, by
their inosculations, form a capillary network with
exceedingly small meshes (sioth of a line in diameter),
which occupies the deep layer of the walls of the pul-
monary vesicles. Of. these ultimate branches of the
pulmonary artery, some leave the lobules to supply
the visceral layer of the pleura.

veins. The radicles of the pulmonary veins, which take
their origin from the capillary plexus, spread them-
selves upon the surface of the pulmonary vesicles,
forming a stratum more superficial than the capil-
laries ; then they lose themselves in the lobular inter-

GLANDS. 97

slices, where they unite with each other to form
larger branches, which finish their course afterwards,
either alone, or by joining company with branches of
the pulmonary artery.

The bronchial arteries supply the whole bronchial 5™nchial a
tree, and also the pleurae. Some of their terminal
branches, those which supply the smallest of the
bronchial canals, anastomose with branches of the
pulmonary arteries and veins ; others terminate by
corresponding veinules* through which their blood is
ultimately brought back to the vena cava superior. Lymphatics

The lymphatics of lungs form two sets, one of which
is superficial, ramifying upon the pleurae, and the
other deep, and accompanying the bronchi and large
vessels. In the intervals between the lobules nume-
rous anastomoses take place between these two sets
of vessels, both of which ultimately reach the bron-
chial glands at the roots of the lungs. Lymphatic
glands have never as yet been discovered in the
parenchyma of the lungs.

The nerves of the lungs are derived from the pneu- Nerves.

* The existence of bronchial veins within the lungs is denied by Wa-
ters (op. cit.), whose original investigations entitle his opinions to respect.
At p. 405, under the head of bronchial veins, he says, " The only vessels
I have been able to discover to which this name can be applied, are some
small ones situated at the root of each lung, at its posterior aspect. I
have previously mentioned that thgir distribution has always appeared to
me to be confined to the structures about the root of the lung, the bron-
chi, the bronchial glands, &c. ; and that they do not return the blood
from the interior of the lung. I have never seen, either in the lungs of
man, or those of other mammalia I Jiave examined, any veins accompany
the several branches of the bronchial artery along the bronchial tubes''1
Keisseissen (de fab. Pulmonum, Berlin, 1823) appears to hold the same
view.— (Ed.)

98 GLANDS.

mogastric and the great sympathetic. They ramify
in company with the bronchi and branches of the
pulmonary artery, and present, at intervals, minute
enlargements composed of nerve cells ; their mode of
termination is unknown.

Development. According to M. Coste* the first appearance of the
lungs occurs in the shape of a small granulation, in
the median line, projecting from the anterior wall of
the oesophagus. This little mass is hollow within, and
communicates with the oesophagus by means of a
vertical slit which, eventually, by the dilatation of
its walls, forms the larynx and trachea. Soon this
central mass divides into two lateral portions to form
the two lungs. Still later, each lateral mass divides
itself up into an infinite number of vesicular vege-
tations, and is thus transformed into the parenchyma
of the lung. Finally, the process of development is
completed by the various metamorphoses of the em-
bryonic cells by which the several histological ele-
ments which compose the tissue of the respiratory
organs are formed.

According to Bischoff,f and most of the German
embryologists, the lungs are first recognised in the
form of solid sprouting buds, which subsequently
become hollow by the melting down of their central
cells ; the remaining steps of the process being iden-
tical with those already described.

gieabndTU8 Sebaceous Glands. — Sebaceous glands, which are
almost universally associated with the hair follicles,

* Embryogenie Compare'e. Paris, 1837.— (Ed.)
t Professor of Physiology in the t University of Heidelberg, Baden,
Germany. — (Ed.) •

GLANDS. 99

are formed by a duct, which, when traced from its
orifice, is found, most generally, to remain undivided,
and to terminate in a solitary bulb, or coecal pouch,
of considerable size (PL XVIII. fig. II.). The inter- structure.
nal surface of this pouch is covered with depressions,
which represent the vesicles of the glands we have
already described. Sometimes a group of these de-
pressions, becoming deeper, isolate themselves incom-
pletely from the common cavity, by a partially
formed neck, or pedicle, and thus constitute a lobule
(fig. III. 2). The wall proper of the sac, or pouch,
is structureless, and very thin, but it is strengthened
by an external layer of fibrillated tissue (PL XVIII.
fig. II. 5). In contact with its inner surface are one
or two layers of young cells, with finely granular and
transparent contents, and nuclei which are quite dis-
tinct (fig. II. 2). Upon this epithelial layer are
numerous other cells, differing from those just de-
scribed, both in volume, and in their contents. They
increase in size, in fact, exactly in proportion as we
trace them nearer to the centre of the gland cavity ;
and during their growth in size, the nucleus disap-
pears, and their contents are transformed into oil-
globules (fig. II. 1 ; fig, IV. ; fig. V. 2). Finally, near
the orifice of the duct, these cells, having attained the
maximum of their development, and being no longer
able to resist the pressure from all sides of the cavity,
the contents of which are thus constantly increasing,
rupture their cell walls, and give forth a sort of greasy
substance which, in short, is the true secretion of the
sebaceous gland (PL XVIII. fig. II. 4). The excre-
tory canal generally opens into a hair follicle; but

100 GLANDS.

sometimes it gives directly on the surface of the skin,
and when this is the case, that portion of the duct
which traverses the epidermis has no walls of its own
(fig. II 6).

nores and ^e vascular supply of the sebaceous glands pre-
sents nothing peculiar, and as to their nerves we
know nothing of their distribution.

Sebaceous glands are developed from the external
epidermic layer of the hair bulb, or rather from the
rete rmicosum of the epidermis. A small projection
buds forth, on the surface of which others, still small-
er, make their appearance, and these, increasing in
number, constitute the vesicles of the gland ; whilst
the base of the primitive projection, becoming more
elougated and constricted, forms its duct. According
to Valentin, the earliest rudiments of the sebaceous
follicles become perceptible during the last half of
the fourth month of foatal life.

^e Meibomian follicles are an aggregation of
minute sebaceous glands, all opening into a long, com-
mon, excretory duct (PL XXVII. fig. III.).

The mammary gland, which in external appear-
ance resembles the salivary glands, is identical, as
regards its epithelium, with the sebaceous glands, at
least during lactation. It still more closely approxi-
mates to the sebaceous glands by its anatomical posi-
tion, and its mode of development.

The histological elements of milk consist of simple
minute oil-globules, of very brilliant aspect, and dark,
strongly marked outlines, floating in a transparent
fluid (PI. XVIII. fig. VI. 4). During the first few
days of lactation we meet with a certain proportion

GLANDS. 101

of these oil-globules which, instead of being free and
solitary, are aggregated together in little round mass-
es, forming what are known as globules of colostrum
(fig. VI. 2). When the gland is in a state of inflam-
mation, these colostrum globules make their appear-
ance in the milk. The good quality of the milk is
known by the large number and equality in volume
of its globules.

On reviewing and comparing the glands, whose Division of
structure we have thus far studied, reference being
had solely to the character and arrangement of their
epithelium, it is obvious that they can be divided
naturally, into two groups : 1st, glands with simple
epithelium ; 2d, glands with stratified epithelium.
In each of these varieties the process of secretion is
differently accomplished. In the first group, the
plasma of the blood exudes through the epithelial
layer, is modified by its cells, and passes out through
the excretory duct without carrying with it any solid
elements ; this is the process of secretion by -simple
filtration. In the second group, in which the epi-
thelial cells are packed in strata, the blood plasma, in
passing through them, excites in them a higher grade
of vital action ; they increase rapidly both in size and
number, and their contents undergo at the same time
a specific change ; but both the cells and their con-
tents ultimately become disaggregated, melt down, as
it were, and thus form the secretion — which is hence
called secretion by epithelial growth.
;\ The salivary glands, and the numerous family of
mucous follicles, effect their secretion by the mode
first described ; the sebaceous glands, and the mam-

berknhn.

102 GLANDS.

mary gland, alone belong to tlie second class. We
shall see hereafter that these considerations are also
equally applicable to tubular glands.
of Lie- SECTION 2d. TUBULAR GLANDS.— The most simple
form of tubular glands are those of Lieberkuhn,
which, as is well known, are thickly scattered
throughout the whole extent of both the small and
large intestine. They are simple straight tubes, one
end of which opens upon the free surface of the intes-
tinal mucous membrane, whilst the other, slightly
enlarged into a bulbous sac, is imbedded in the
deeper portion of this same membrane (PL XXVI.
fig. X.). Their mean diameter varies from aVth to
aVth of a line. Each follicle is. composed of a struc-
tureless basement membrane, on the outer surface of
which the blood-vessels belonging to the intestinal
glands ramify, whilst within it is lined by a single
layer of cylindrical epithelial cells, which are arranged
very regularly around the cavity of the tube (PL
XXVI. fig. XI. 1, 2). The cavity varies from lioth
to T^rth of a line in diameter.

Development. The development of these glands is effected at the
expense of the epithelial lamina of the intestine,
which is protruded like the finger of a glove in the
form of a tube. They will be hereafter more fully
examined in connexion with the intestinal mucous
membrane.

The glands which secrete pepsin, found near the
cardiac orifice of the stomach, and its mucous follicles,
situated near the pylorus, are nothing more than
compound follicles of Lieberkuhn. They are com-
posed of from two to six single tubes, siinilarlto those

GLANDS. ; 103

described above, which unite to form a common
excretory duct. In the mucous glands the same
variety of epithelium lines the interior of the tubes of
their excretory ducts ; it consists of conical cells simi-
lar to those in the glands of Lieberkuhn, measuring
from -sMla. to ^oth of a line, and their nuclei 4-Joth
of a line in diameter (PI. XXV. fig. VIII). The
epithelium of the ducts of the pepsin glands is similar
to this, but the cells of their tubes are larger (yoo-th
of a line), and. they are polygonal in shape (PL
XXVI. fig. 1.). Sometimes they present minute pro-
jections of the basement membrane of the tubes, so
that they have a mamelonated appearance exter-
nally. According to Kolliker, the epithelium of
these compound glands is liable to fatty infiltration,
a phenomenon which we never observe in Lieber-
kulm's glands. But this is not of constant occur-
rence, and it is probable that the presence or absence
of fatty particles in the epithelium of these glands,
corresponds to periods of activity and rest in the
functions of the gastric mucous membrane.

The glands of the mucous membrane of the uterus uterine glands.
have precisely the same physiognomy as the tubular
gastric glands. Like them, they consist of a solitary
tube, or of two, converging to a common excretory duct,
and their epithelium, of a single layer of conical cells.
As most of them are too long to be accommodated in
the thickness of the mucous membrane, we find that
their local extremities are somewhat curved, or bent
upon themselves.

The glands of the neck of the uterus are not so
long as those of its body. When their orifices be-

104 . GLANDS.

come obliterated, their secretion, accumulating within,
distends them and alters their shape, so that they
become spherical, and thus form what are known as
the Ovula Nabothi.

sweat glands. Sudoriparous Glands. — These tubular glands oc-
cupy the deepest layers of the skin (PL XXIII. fig.
I. 8). The body of the gland, or glomerula, is a little
spheroidal mass, or ball, averaging one-fourth of a line in
diameter. It consists of a tube, rolled and twisted upon
itself, and terminating by a blind extremity, which,
in rare cases, is bifurcated (PL XIX. fig. IV). Its
walls are formed by an extremely thin and structure-
less basement membrane (reVo-th to TaV^th of a line in
diameter), which is strengthened externally by some
fibres of connecting tissue very rich in plasmatic cells
(fig. IV. 4), and which may be regarded as consti-
tuting the fibrous envelope of the gland. The inter-
nal surface of the tube is lined by a single layer of
pavement epithelium, whose cells measure 4<roth of a
line in thickness (fig. VI. 2). Finally, the glomerula
is surrounded by a rich vascular network, which
affords the materials for its secretion. Of the mode
of innervation of these glands we are as yet ignorant.
The excretory duct of a sweat gland, after leaving the
glomerula, runs directly outwards through the sub-
stance of the skin, towards the bottom of one of the
furrows upon its surface, and then, traversing the
epidermis, terminates by an oblique opening upon its
outer surface. During its course through the skin
proper it is perfectly straight ; but, in traversing the
epidermis, it turns upon itself, forming a close spiral
twist (PL XXIII. fig. I. 9). In the epidermis the

GLANDS. 105

duct has no proper coat, this being replaced by the
epidermic cells which form its walls, but, in the thick-
ness of the skin, its walls are formed by two coats :
the outer, dense and fibrillated (2 o oth of a line in
thickness), including non-striated muscular fibres,
which, according to Kolliker, are also found in the
fibrous envelope of the glomerule ; the inner coat thin
(Wo <rth of a line), unorganized, and lined by an epi-
thelium similar to that of the gland (PL XIX. fig. V. ;
fig. VI).

The ceruminous glands, which belong to the exter-

nal ear. are identical in form with the sweat glands :

° .

they differ from them only in the nature and arrange-
ment of their epithelial cells. Thus, instead of being
spread out in a simple layer upon the internal surface
of the secreting tube, their cells form a series of strata
by which its cavity is completely filled (PL XIX. fig.
VII. 2). Moreover they become infiltrated with
yellow pigment, and oil-globules in abundance, cha-
racteristics in which these glomerules, as regards their
secretion, resemble closely the sebaceous glands. The
large sudoriparous glands of the axillae seem to be
absolutely of the same species a# the ceruminous
glands, for their contents are identical.

The sudoriparous glands are developed from the Development
fifth to the eighth month of foetal life. They make
their first appearance in the shape of minute cellular
projections from the deep surface of the epidermis,
which imbed themselves in the true skin. At first
they are nothing more than solid cylinders slightly
bulbous at their dermal extremities. As they grow,
they reach the deepest layer of the skin, but do not

7

106 GLANDS.

pass beyond its limits; as their growth in length,
however, goes on, they curve and twist upon them-
selves, so as to form the glomeruli which we find in the
adult. Whilst these changes are taking place in the
size and external shape of the sweat glands, their inte-
rior is observed to become converted into a canal, and
this is probably effected by the disaggregation and
melting down of the central cells. Finally, the walls
of the gland tubes are perfected by a series of morpho-
logical transformations of the more superficial cells of
the original cylinder.

Preparations. The specimens required for the study of the tubu-
lar glands are very readily prepared. It is simply
necessary to detach, by means of scissors, very deli-
cate little lamellae from the mucous membrane of the
intestine, cutting both parallel with, and at right
angles to, its surface. For those of the skin, a razor
is employed in the same manner, and dilute solutions
of potassa and acetic acid are applied to the speci-
mens in order to render the tissues more trans-
parent.*

Kidneys, struc- Kidneys. — In a longitudinal section of a kidney,
including its Tiilus, the parenchyma of the gland pre-
sents itself in two obviously different aspects ; near
the liilus, and towards the centre of the gland, it is
striated ; elsewhere it is granular in appearance. The
striated portion (cones, medullary substance, pyramids
of Malpighi) consists of sections of cones, of which the

* The spiral twist of the duct of the sweat gland, as it traverses the
epidermis, is best seen by cutting thin slices from the edge of a piece
of dried skin of the palm of the hand or sole of the foot, with a sharp
scalpel.— (Ed.}

tare.

GLANDS. 107

apices (papilla) converge towards the liilus, whilst
their bases are directed outwards, towards the surface
of the organ. The granular portion (cortical substance)
forms not only the peripheral substance or cortex of
the organ, surrounding the bases of the pyramids,
but it dips inwards between them, reaching nearly as
far as their summits. The free surfaces of the papillw
are pierced by numerous small orifices, rVth of a line
in diameter. Each of these orifices leads into a
straight canal, which, in its course, is constantly
dividing and subdividing, always into two branches,
and these are given off invariably at a very acute
angle. Having reached the base of the medullary
cone, all of these subdivisions of the primitive tube,
which thus far have pursued a perfectly straight
course, immediately become exceedingly tortuous,
and by their involutions and twistings, form the cor-
tical substance of the gland, each tubule terminating
at last by a bulbous extremity, which is in intimate
contact with a small tuft of blood-vessels called a
Malpighian body (PL XX. fig. I. 2, 3).

It is noticeable that the line which limits the
base of each pyramid forms a series of indenta-
tions, and that the straight tubes* emerging from
the summit of the intervening projections, are sur-
rounded on all sides by tortuous tubules (fig.

i.i).

In accordance with this description it is obvious
that each primitive straight canal gives origin to a
fasciculus of tubes (pyramid of Ferrein, lobule of the
kidney) which pursue a straight course through the
substance of the medullary cones (tubes of Bellini),

108 GLANDS.

and become tortuous in the cortical substance of the
organ (tubes of Ferrein).

The straight tubes measure, on an average, rVth of a
line, their subdivisions, jVth of a line, the tortuous tu-
bules of the cortical substance aVth of a line, and their
bulbous extremities iVth of a line. A perfectly struc-
tureless basement membrane, scarcely Wo oth of a line
in thickness, forms the outer walls of these secreting
tubules, which is hardly distinguishable except when
denuded of its epithelium (PL XX. fig. II. 4). Its
internal epithelial lining, at least ten times the thick-
ness of the outer wall, is composed of a single layer
of many-sided cells, usually pale in their outlines, and
each containing a large and well-marked nucleus,
which is very clearly recognisable in the midst of its
transparent granular contents (fig. II. 5, 7). Fatty
degeneration of these epithelial cells is the principal
lesion of the urinary tubules in Bright's disease.
These two membranes, alone, constitute the walls of
the urinary tubules, as far as their bulbous or
expanded terminations, where another element makes
its appearance, which we shall proceed to examine.
Arteries. In the hilus of the kidney the renal artery divides
into about a dozen branches, which, arranging them-
selves between the medullary cones, penetrate the
cortical substance, and ultimately reach the surface of
the organ. In their course, which is almost recti-
linear, they give off a great many branches to the
lobes, as they traverse the spaces between them, and
some smaller arterioles, also, to the fibrous envelope
of the gland. The ultimate branches of the renal
artery, having gained the interior of the medullary

GLANDS. 109

pyramids, shortly after their origin, pursue a course
parallel with the straight tubes of which they are
composed, and continue onward through the cortical
substance, towards the periphery of the gland.
Whilst in the pyramids there is nothing peculiar in
their distribution, but, as soon as they reach the cor-
tical substance, they begin to give off small branches,
at regular intervals (afferent vessels), in every direc-
tion, which penetrate the walls of the secreting tubuli,
and occupy the interior of their expanded extre-
mities (PL XX. fig. III. 1 ; fig. IV. 4, 5). Here, each
afferent vessel breaks up into a certain number of
branches, which, becoming exceedingly tortuous, inter-
twine with each other so as to form a little round
ball, or tuft, which is known as the Malpighian body
(glomerula of Malpighi, corpus MalpJiigianwii). bSShian

These little vascular balls completely fill the pouch-
like terminal expansions of the tubuli uriniferi, and it
can be recognised that their surfaces are entirely
covered by a layer of renal epithelium. We have
succeeded in demonstrating this relation between the
Malpighian tufts and the epithelium of the urinary
tubules on several occasions, in the kidneys of the
guinea-pig, and our researches into the structure of
the human kidney have led to the same result (PI.
XXVII. fig. IV. 5).

A solitary vessel, of capillary size (the efferent Efferent vessel,
vessel), leaves the Malpighian tuft, traversing the
wall of its containing cavity, either alone, or in com-
pany with the efferent vessel, near which it is always
found; it immediately divides into a multitude of
ramifications, which anastomose with each other, and

110 GLANDS.

with those of the neighboring efferent vessels. By
this system of anastomosing vessels the capillary
network of the kidney is constituted, and the urinary
tubules are everywhere closely surrounded by it ; in
the cortical substance this network is very fine and
close (PL XX. fig. III. 5), but in the medullary cones,
its meshes grow longer, and the number of the vessels
diminishes (fig. III. 6). They continue to diminish in
number, and to increase in size, forming venous radi-
cles, which, assuming a straight course, ultimately
empty into the renal vein.

Lymphatics. The origin of lymphatics from the kidney is imper-
fectly made out, and the same is true of the termina-
tions of its nerves, which enter the organ at its hilus
in company with its vessels.

We may sum up the structure of the kidney in a
few words, as follows : from a papillary orifice a canal
takes its origin, which, leaving its sub-divisions out of
view, is rectilinear in the medullary cones, becomes
tortuous in the cortical substance, and ends there in a
flask-like pouch, in the interior of which the Malpi-
* ghian tuft is lodged. This takes its origin from one
of the interlobular arterial branches by means of the
afferent vessel, and itself gives off the efferent vessel,
which is the source of the capillary system of the
organ, by which its secreting tubules are enveloped,
and which pours its blood ultimately into the renal
vein. The secreting tubules have two walls : the one
thin and structureless, the other much thicker, and
consisting of a layer of epithelial cells which, at its
expanded extremity, are found covering the entire
surface of the Malpighian tuft. Nothing certain is

GLANDS. Ill

known of its nerves and lymphatics (PL XX.
fig. IV.).

The proper coat of the kidney consists of a dense Fibrous coat
interlacement of connective and elastic fibres ; its
internal surface is united to the cortical substance of
the organ by minute vessels, and delicate trabeculse of
its own tissue ; its outer surface is continuous, by
means of slender fibrous processes, with the mass of
adipose tissue in which the gland is imbedded ; at
the bottom of the hilus it becomes continuous with
the calices.

The secreting duct of the kidney, or ureter, is ureter. -\
expanded above, where it forms the pelvis and calices,
and terminates below at the bladder. On examining
into the structure of its walls, we find, proceeding
from without inwards: 1st, a fibrous tunic; 2d, a
layer of smooth muscular fibres — composed externally
of longitudinal and internally of circular fasciculi ;
3d, a mucous membrane, with its epithelium in strata,
and becoming sensibly thinner where it passes from
the surface of the calices upon the papillae. Of this
epithelium the deep cells are very regularly oval, but
those nearer the surface are variable both in size and
shape, and resemble exactly what are called cancer
cells ; the epithelium of the bladder, which is con-
tinuous with the ureter, presents the same physi-
ognomy; that of the urethra is composed of cylin-
drical and oval cells, of regular form.

In the unmixed urine, as it escapes from a healthy urine.
kidney, histologically, there is nothing to be recog-
nised. It is a liquid in which we find no organized
element, unless it be here and there a cell, acciden-

112 GLANDS.

tally detached from the walls of tlie ureters, bladder,
or urethra, and carried along with the urine in the
act of micturition.

Development. The kidneys are developed behind the "Wolffi an
bodies, and entirely independently of them. They
take their origin from the mucous membrane of the
intestine, but the facts which we possess relative to
the transformations which these organs undergo dur-
ing their development, are not clearly enough esta-
blished to justify their introduction into this work.

Preparations. The most useful preparations for the study of the
structure of the kidneys, are sections made with a
razor of kidneys rendered solid by boiling, and simi-
lar sections of fresh organs, as well as of those previ-
ously injected with fine colors ground in oil and well
rubbed up with pure oil of turpentine.

[The most recent and valuable additions to our knowledge of 'the
minute structure of the kidney are due to the industry and talent of
the late Dr. C. E. Isaacs. His admirable paper, entitled " Researches
into the structure and physiology of the kidney (by C. E. Isaacs,
M.D., Demonstrator of Anatomy in the University of the City of
New York,") was read before the New York Academy of Medicine
in March, 1856, and in its numerous and excellent illustrations the
student will find great assistance in thoroughly comprehending the
minute anatomy of this organ.

In view of the close and searching investigations of Dr. Isaacs
into the doubtful points in the minute structure of the kidney, and
his high character as a conscientious and skilful observer, I feel that
no apology is necessary for stating his conclusions at length, and
describing the ingenious and original methods by which he arrived
at them.

He speaks of the " highly-elastic" nature of the basement mem-
brane forming the outer wall of the urinary tubules, and adds, " the
integrity of the tube being of the highest importance during life,

GLANDS. 113

this membrane has been endowed with the quality of strongly resist-
ing injurious influences, and even powerful chemical reagents. In
virtue of this last-named property, we are enabled to show clearly
the tubes of the kidney, by certain processes hereafter to be de-
scribed."— Trans. N. Y. Acad. of Med., Vol. I. part IX. p. 379.

In relation to the nature of the renal epithelium, it is stated
(p. 380) that "most of the epithelial cells are polygonal, although
many are oval, and others of a rounded or irregularly rounded
shape." . . . " It is extremely difficult to meet with specimens of
the kidney sufficiently healthy to exhibit the perfectly normal
epithelium." ..." The epithelium very soon becomes changed
from decomposition, or by the action of water, which expands the
cells, and sometimes causes them to burst, when the tubes are found
to contain merely nuclei and granular matter. In examining the
epithelium, it is therefore very important to obtain the kidney in as
fresh a condition as possible, and instead of water, to use a solution
of albumen in water, or urine." In conclusion, the opinion is
expressed, that all the appearances presented by the renal cells
differing from the characteristics of pavement, or tesselated epithe-
lium, are the result either of decomposition or disease, (p. 381.)

As to the presence of cilia upon the epithelial cells of the kidney,
it is admitted, in fishes and the amphibia. To determine the ques-
tion as to its existence in the mammalia, he "resorted to the large
establishments, in this city, for killing oxen, sheep, horses, dogs,
rats, etc., and examined the kidneys immediately after the death of
the animal." ..." Some of the scraped substance of the kidney
was gently agitated, in a test tube, containing a solution of albumen,
and a drop of this fluid was then placed under the microscope.
Thin sections were also used. In some animals no motion could be
perceived, but in the dog I observed currents taking place, in the
fluid, and also within the uriniferous tubes. The epithelial cells
would frequently disengage themselves from the sides of the tube,
and pass along for a considerable distance, and after emerging from
the mouth of the tube, would assume a rotatory motion. Sometimes
nearly all the epithelial cells would pass out of a tube, in the space
of fifteen or twenty minutes, leaving it almost denuded of its internal
epithelial lining. I have also seen isolated cells, having a vibratory
or rotatory movement. These appearances I have noticed upon

114 GLANDF.

eight occasions, in the kidneys of dogs. Such motions generally
cease, in these animals, in less than an hour after death. . . .
I have often seen appearances similar to the preceding, in the kid-
neys of the ox and sheep. Nevertheless, it must be stated, that after
very numerous and careful observations, I have never seen the epi-
thelial cells actually provided with cilia, except upon one occasion,
when I observed a single cell apparently fringed with cilia, and in
active rotatory motion. This was in the kidney of the ox." . . .
" What is observed in the kidneys of the dog, sheep, and ox, cer-
tainly seems to be much more powerful than the ciliary motion so
readily seen in the oyster *and clam, and very different in its nature
from molecular motion. Reasoning from the appearances in the
oyster and clam, as well as from analogy in many of the lower
animals, it may be concluded that ciliary motion does exist in those
of a higher grade, although it is, in them, very imperfect, or, as it
might perhaps be said, in a rudimentary condition. In some of the
inferior animals, where the urine is excreted in the semi-fluid state,
a much greater necessity exists that this fluid should be rapidly pro-
pelled in its course through the uriniferous tu^es, and, accordingly,
we here find ciliary motion in its most perfect condition. I have
never seen it in the human kidney, even after many careful exami-
nations. If it does exist, which is probable, it ceases very soon after
death, when it rarely happens that we can obtain an opportunity of
examining it." Kolliker, in the last edition of his Manual of
Human Microscopical Anatomy, Lond. 1860, states (p. 408) that
"it (ciliary motion) is absent in birds and mammalia," and yet he
has the title of Dr. Isaacs' paper, which was translated into Schmidt's
Jahresber. in 185Y, enumerated under the head of literature of the
kidney. So that, as far as this distinguished histologist is concerned,
Dr. Isaacs' observation of the fact of the existence of ciliary motion
in the uriniferous tubes of the kidney in mammalia, is original.

In regard to the presence of epithelium upon the surface of the
Malpighian tufts of the kidney, it is asserted by M. Morel, in the
text, that he has seen it on several occasions in the kidneys of the
guinea-pig, and also in man. This was originally asserted by Ger-
lach, but is doubted by Kolliker (op. cit. p. 408), and denied by
Bowman and Dr. G. Johnson (On Diseases of the Kidney, Lond.
1852, p. 30, note). The observations of Isaacs upon this point are

GLANDS. 115

conclusive, as will appear from the following quotations from his
paper. I will add also that I have myself witnessed several undoubted
demonstrations of the fact at his hands.

" After much reflection as to the best plan of determining this
point, I adopted the following processes : 1. By injecting watery and
etherial solutions into the ureter, I succeeded in bursting the capsule,
the Malphighian tuft, or coil, having been previously only slightly
and, as was intended, imperfectly injected from the artery. Epi-
thelial cells could then be seen upon the uninjected and transparent
edges of the tuft, or coil. Plate 24, fig. 1, exhibits a Malpighian
tuft. Broken fragments of the injected vessels are seen within it.
They had been injected with chrome yellow, and appear black, when
the specimen is viewed by transmitted light. The uriniferous tube
had been distended by the injection from the ureter, and its expanded
extremity or capsule had been burst, and can be perceived lying
in shreds at the sides of the tuft, now uncovered by the capsule.
Nucleated cells can be seen upon the naked and uninjected parts of
the tuft. From the kidney of the black bear, magnified eighty diame-
ters." In another specimen, the capsule had been scratched off with
a needle, and then the naked tuft somewhat torn under the micro-
scope. Some small fragments of the tuft could be seen with nucle-
ated cells on their surface.

Again : " The capsule was torn off from a Malpighian body
with a needle. In doing this, the capsule became reversed, so as to
give a view of its internal surface, upon which small nucleated cells
could be clearly and distinctly seen. The surface of the naked tuft
was covered by cells of much larger size than those upon the interior
of the capsule. Upon the application of dilute nitric acid, the wall
of the cells of the capsule was dissolved, while comparatively little
effect was produced upon those of the tuft, thus showing a difference
in their chemical constitution and organization? This specimen was
taken from the kidney of the racoon, and magnified 400 diameters.

Again : " Fine scrapings of the kidney of a cat were agitated occa-
sionally for two or three days, in a test tube, the water having been
frequently changed. By this method, the epithelial cells within the
capsule were washed out, so that the space thus left between the
tuft and the capsule became filled with water, which had soaked
through the capsule. By slight agitation, while the specimen was

116 GLANDS.

floating in the water, under the microscope, it could be rolled over
and over, so as to show various points of the surface of the tuft,
covered by nucleated cells"

" By the different processes first mentioned," he concludes, " I
consider the existence of nucleated cells upon the surface of the
Malpighian tuft, and, consequently, its analogy with the other
secreting organs, as conclusively demonstrated." These descriptions
are illustrated by several highly satisfactory drawings, pp. 404-407.
The modesty of the author prevented him from emphasising the ori-
ginality of the observation contained in the lines in italics, which were
introduced by the writer. The importance of the anatomical fact,
thus clearly demonstrated, that the Malpighian bodies of the kid-
ney are covered by an epithelium, the cells of which are distinctly
different from the ordinary epithelium of the urinary tubes, can be
estimated by a reference to the fact that the ingenious and almost
universally received theory of the action of the kidney, announced
in 1842 by Mr. Bowman, in his paper in the Philosophical Transac-
tions, is founded mainly on the belief that the surface of the vessels
composing the Malpighian tuft were naked and bare. In a subse-
quent paper " on the function of the Malpighian bodies of the kid-
ney" read before the N. Y. Academy of Med., February 4th, 1857,
its ingenious author, by a series of novel and interesting experiments,
demonstrates, satisfactorily, that the function of the Malpighian tufts
of the kidney is not the mere separation of water from the blood, as
Bowman asserts, and that, on the contrary, it separates from the
blood most of the proximate elements of the urine, any element of the
urine which is not secreted by the Malpighian tuft, being, probably,
afterwards separated by the epithelial lining of the tubes. Trans.
N. Y. Academy of Med., Vol. I., Part IX., p. 452.

Another anatomical point settled by Isaacs is, that the ultimate
ramifications of the renal artery do not all terminate in Malpighian
tufts, although the great majority of them do so. At p. 385, he
gives a wood-cut representing a small branch of the renal artery, as
seen under the microscope, " which divides into two twigs, one of
which supports at its extremity the Malpighian coil or tuft of capil-
laries, whilst the other enters into the venous plexus."

He also confirms, conclusively, the opinion of Bowman as to the
relation existing between the Malpighian tufts and the expanded

GLANDS. 117

extremities of the convoluted tubes of the kidney, demonstrating, in
opposition to the statements of Toynbee, Miiller, Gerlach, Bidder,
and others, "that the convoluted nriniferous tubes terminate by
forming an expanded extremity, or capsule, which embraces the
Malpighian tuft, or coil of capillaries." — (p. 401.)

" This difference of opinion, even among such high authorities,
may probably be accounted for, inasmuch as it is very difficult, by
employing the usual means of examination, to obtain any minute
portion of the organ which will show the tube connected to the
Malpighian body. Moreover, in examining any thin section of the
kidney (as is usually done) for this purpose, it is to be remembered
that the Malpighian body is always embraced in a ring of the fibrous
matrix, and that at the neck of the tube, or its commencement of
expansion into the capsule, is its weakest part, and where it is most
easily, and indeed almost always, torn across, especially when trac-
tion is made upon it, as is usually done, in tearing out the specimen
with needles. On the contrary, by using scrapings of the organ (as
recommended) agitated in water, which softens and removes many
of the adhering portions of the matrix, which last holds and confines
the Malpighian body, this can be washed out, and not unfrequently
with the convoluted tube attached to it." (See plates 15, 16, 19,
20, 21, and 22.) p. 404.

In relation to the 'fibrous matrix ' of the kidney, mentioned in
the last quotation, nothing is said in the text. It is the more impor-
tant to supply the omission, as this histological element of the organ
plays a most important part in many of its diseased conditions. It
was first described by Dr. John Goodsir, Professor of Anatomy,
Univ. of Edinburgh, in the Monthly Journal of Medical Science,
May, 1842 (see also Johnson on Diseases of the Kidney, Lond. ] 852,
pp. 16, 321). Its existence has been doubted by some high authori-
ties, but the demonstrations contained in Dr. Isaacs' paper, and the
numerous views which he gives of appearances presented under the
microscope by his ingeniously prepared specimens, place all doubt at
rest, and constitute him the highest authority on the subject.

The following quotations contain the essential points which he
has demonstrated ; but for a thorough knowledge of the subject, a
perusal of his paper with its admirable illustrations is necessary.
" I have never satisfactorily succeeded in exhibiting it (the matrix)

118 GLANDS.

by following the directions usually given for this purpose. It can,
however, be always easily and distinctly shown by the following
process: "Very thin slices of the kidney are to be made with
Valentin's knife, put into a long test tube about one third full of
water, and agitated from time to time for two or three hours. Pre-
pared in this manner, a thin section exhibits under the microscope a
kind of mesh, network, or honeycomb arrangement — the cells of the
honeycomb, however, having no bottom. In the natural condition
of the kidney, the smaller cells or openings transmitted the tubes ;
the large cells or openings were occupied by the Malpighian bodies;
which last, together with the tubes, have now been washed out of
the cells, although a few are often seen still remaining in situ, pi.
28." Here follow representations of similar preparations from the
kidney of the rat, dog, rabbit, raccoon, hog, sheep, ox, horse, elk,
moose, black bear, and finally of the human kidney. " According
to my experience," he continues, " it is rare to find a human kidney
which is perfectly healthy. This is particularly the case in subjects
in the dissecting room, and in those who have died in large hospi-
tals. Out of more than 500 subjects which I have examined in this
city, I have seen but very few in which the kidney could be regarded
as in an entirely healthy condition. Being very anxious to procure
a perfectly healthy specimen of the organ, I obtained a considerable
number of kidneys from the bodies of persons killed by violence and
accidents, but these were also found to be diseased, most probably
from intemperance, etc. I at length procured the healthy organs
from which the present view of the matrix is here given."

"From what has now been said and exhibited, it is evident that
the fibrous matrix is really the skeleton, or frame-work of the kid-
ney. It consists of myriads of septa, or partitions, crossing each
other in various directions, so as to form elongated spaces for the
straight tubes, or rounded spaces, cells, or rings, for the Malpighian
bodies and convoluted tubes." " In certain pathological conditions
of the kidney, it becomes diminished in size, and indurated ; its sur-
face is irregular and covered with small projecting points, like vari-
ously sized shot. This condition is not unfrequently seen in old
drunkards, and would seem to be analogous to cirrhosis of the liver,
and probably induced in a similar manner ; the alcoholic fluid passing
through the tubes of the kidney, and by continued irritation pro-

GLANDS. 119

ducing crisping, or irregular contraction of the meshes of the matrix,
which consequently constrict the tubes and the Malpighian bodies."

" Thickening and induration of the matrix may produce injurious
effects otherwise than by constriction of the tubes and Malpighian
bodies. The minute vessels and capillaries pass through the sub-
stance of the fibrous rings. Consequently, induration and contrac-
tion of the matrix, by direct pressure on the vessels, must greatly
interfere with the circulation, nutrition, and secretion of the kidney,
and thus various morbid products, as blood, albumen, pus, tubular
casts, etc., may be found in the urine." Pp. 418-429. By isolation
of portions of the matrix by repeated washings, and the subsequent
application of dilute acetic acid and other reagents, it was found to
consist entirely of fibres, containing elongated fusiform nuclei ; in
other words, to be pure connective, or white fibrous tissue — the
yellow elastic element being invariably absent.

"From the foregoing remarks, it is evident that a correct know-
ledge of the fibrous matrix is of great importance, and that its
microscopical and chemical investigation, in all cases of diseased
kidney, would probably furnish interesting and valuable results."
P. 431.

It remains to notice the original and very ingenious methods of
preparing the specimens by means of which Dr. Isaacs succeeded in
attaining such successful results. His aim was to render the sub-
stance of the kidney transparent under the microscope, and to effect
this he instituted numerous experiments with chemical reagents, and
"at length arrived at the knowledge of certain processes, which
have not only been useful by giving transparency to small portions
and thin sections of the organ, but have often enabled them to be
viewed both as opaque and as transparent objects." With these
processes, all the usual means, such as injections, etc., were also
employed. The following, in addition to those already indicated,
are the modes of preparing microscopical objects which he praises
most highly.

To show the epithelium of the urinary tubes; their sections, or
scrapings of the kidney, should be kept in a solution of albumen in
fresh urine. "To view the tubes of the kidney in their normal con-
dition very thin sections, or scrapings of the cut surface of the organ,
may be put into a test-tube with water, agitated for a few minutes,

120 GLANDS.

placed on a slide of glass, covered by a thin slip, and then examined
under the microscope." Or, to render the object transparent, scrap-
ings are put into a test-tube with about half an ounce of water, to
which three drops of pure sulphuric acid are added, and the whole
boiled for one or two minutes. " If too much acid be used, it will
dissolve all the minute vessels and capillaries, but not the Malpighian
coil, or tuft. This is worthy of notice, as showing a great difference
in the chemical constitution, and consequently in the organization,
of these different parts."

The addition of chloroform, under similar circumstances, also has
the effect of rendering objects transparent. " I have succeeded in
exhibiting the tubes of the kidney very distinctly, by boiling small
pieces of the organ in diluted chloroform, and also in solution of
chlorate of potassa, which latter is useful in giving a clear view of
the surface of the kidney when congested, as it shows the venous
plexus and the tubes, and acts but slowly upon the blood-globules."
To show the vessels in connexion with the Malpighian bodies, and
at the same time to exhibit the tubes : — after injecting the vessels
with white lead finely ground in oil (artists' tubes), and well agitated
with sulphuric ether, small pieces of the organ were boiled in very
diluted chloroform, and some thin sections were made with Valen-
tin's knife ; other sections were first dried, then immersed in spirits
of turpentine, and finally placed on a glass slide, in a drop of water,
under the microscope. " Muriatic, acetic, and nitric acids, also ex-
hibit the tubuli with considerable distinctness; the last, however, is
apt to discolor the tubes. I have also tried the effect of many other
chemical reagents; among others, the phosphoric, chromic, boracic,
tartaric, and citric acids, the alkalies and their carbonates, various
salts, etc."

In conclusion, I must again urge the student who wishes to fully
comprehend the anatomy of the kidney, to consult this admirable
paper, and study its graphic illustrations ; it is the ablest anatomical
monograph that our country has as yet produced, and a fit contribu-
tion, by its lamented author, to the science to which he devoted his
life.]— (Ed.)

Testicle. Testicle. — The proper coat of the testicle (tunica
albuginea) is of the same structure as that of the

GLANDS. 121

kidney — but somewhat more dense. Its external
surface, excluding that portion corresponding to the
hilus of the organ, is clothed with a simple layer of
the epithelium, which constitutes the visceral ]amina
of the serous membrane of the testis (tunica vagina- structure.
li$) ; its internal surface is in immediate relation with
the secreting tubules of the gland. Along the line
where its vessels enter and leave the organ (hilus)*
the tunica alkuginea presents a very considerable
thickening (corpus HigJimorianutri), which, in the
form of a ridge, buries itself in the parenchyma of
the gland, and from its surface the interlobular
fibrous septa take their origin. In the interior of the
corpus Highmorianum is a tubular network (rete tes~
tis), from which the secreting tubules are given off on
one side, and from the other, the efferent canals which
terminate in the excretory duct.

From the interior of the rete testis twenty to thirty vasa recta,
straight tubes, rVth of a line in their mean diameter,
take their origin (vasa recta), and, after a short
course, divide into several branches. Each one of
them becomes exceedingly tortuous (PI. XXL fig. I),
and again gives off several subdivisions, which anasto-
mose with each other, and terminate either by loops,
or by blind extremities. Sometimes one of these
branches, but more frequently two or three of them
closely united, form a lobule of a conical shape, the
apex of which is in relation with the rasa recta, whilst
its base looks towards the periphery of the organ.
Not unfrequently canals of communication exist be-
tween these lobules.

The upper extremity of the rete: testis gives off a Efferent tubes.

8

122 GLANDS.

dozen tubuli (vasa efferentid) which, by their union,
constitute the head of the epidydimis (cjlobus major).
Immediately after emerging from the corpus HigJimo-
rianum these tubes become exceedingly convoluted,
and proceed in succession to the globus major of the
epidydimis ; each of them takes the shape of a cone
(coni vasculosi), the apex of which is continuous with
the rete testis. Finally, the canal of the epidydimis,
after having by its convolutions formed the body of
the epidydimis and its lower extremity (c/lobus mi-
nor), and after giving off the vasculum aberrant, be-
comes the vas deferens, or excretory duct of the
gland.

Tubuii testis. The spermatic tubules (tubuli testis) and the vasa
recta, which are directly continuous with them, have
very thick walls, consisting of several distinct layers.
The external, which is the thickest (zioth of a line),
is fibrous and very rich in plasniatic cells (PL XXI.
fig. II. 1) ; the internal, exceedingly thin and struc-
tureless (fig. II. 2), is in relation, by its inner surface,
with the stratified epithelium by which the cavity of
the tubule is completely filled (fig. IL 3). The cells
of this epithelium are of considerable size, polyhe-
dral, and, in the adult, most of them contain oil-
globules. In the rete testis the tubuli have no pro-
per walls ; they are simply tunnels through the fibrous
substance of which the corpus Highrnorianum is com-
posed.

^id/eferen8.and ^n the epidydimis the non-striated muscular ele-
ment is added to those already recognised in the
walls of the tube, and its epithelium is cylindrical
(PI. XXI. fig. III.). The vas deferens, proceeding from

GLANDS. 123

without inwardly, is composed : 1st. of a fibrous coat ;
2d. of a muscular coat, with both longitudinal and
circular fibres ; 3d. of a mucous coat, lined by simple
pavement epithelium. The vesiculce seminales, with
the exception that their walls are thinner, possess the
same structure as the vas deferens.

The arteries of the testes, ramifying in the inter- ^8aiMi
lobular septa, terminate in a capillary plexus which
surrounds the tubuli seininiferi. The veins follow
the course of the* arteries. The lymphatics are very
numerous ; they accompany the vessels of the cord,
and run into the lumbar glands. The nerves, few in
number, follow its arteries into the parenchyma of the
gland, but how they terminate there is not known.

The -semen is an alkaline liquid, destitute of color, seminal fluid.
in which certain accessory elements are encountered,
such as cells and the debris of cells, and also certain
essential and characteristic elements — the filiform cor-
puscles endowed with the power of motion, and
known under the name of spermatozoa. These
curious corpuscles consist of exceedingly delicate fila-
ments with an almond-shaped enlargement at one
extremity, constituting its head, whilst the remainder
of the filament, tapering off to an extremely fine
point, represents the tail. A delicate linear depres-
sion, or species of collar, marks the line of junction
of these two portions, on the borders of which a
minute tubercular projection is sometimes to be seen
(PL XXI. fig. IV.). No trace of organization can
be detected, on the closest examination, in any part
of the spermatozoa ; the substance of which it is
composed being homogeneous, transparent, and amor-

124 GLANDS.

phous. The movements of the spermatozoa con-
tinue a long time after death (10 to 24 hours) ;
water and acids arrest them, but they are renewed
again by the application of slightly alkaline liquids.
of These elements, which constitute the essential por-
tion of the seminal secretion, are developed in the
following manner : On examining the epithelium of
the tubuli seminiferi it is observed that its central
cells are generally more voluminous than the rest,
and give evidence of a more or less active process of
endogenous vegetation (PL XXL fig. V.) ; thus, some
cells are to be seen enclosing as many as ten nuclei.
In addition to the nucleolus, which is visible in each
nucleus, in the shape of a brilliant spherical vesicle,
there is also observable upon one point of. its peri-
phery an elongated spot (fig. V. 3), from which shortly
a long and delicate filament takes its origin, which
coils, upon itself as it increases in size, occupying
always the periphery of the nucleus (fig. V. 7). As
soon as the nuclei have attained their full develop-
ment, the parent cell, being no longer able to contain
them, bursts, and they thus become free. Its ele-
ments subsequently become disintegrated and disap-
pear. The tail of the spermatozoon then uncoils itself
(fig. V. 8), afterwards its head becomes disentangled,
and its development is accomplished.

In the testes of the guinea-pig, we have, on several
occasions, traced the successive transformations which
the epithelial cell undergoes in giving origin to sperma-
tozoa, and have always witnessed the occurrence of the
phenomena taking place as above described ; that is,
each nucleus distinctly gives origin to a spermatozoon.

GLANDS. 125

In the human testis the same process has been demon-
strated.

The testicle is developed from the internal sub-
stance of the Wolffian body, whilst its excretory duct
is formed by the external canal of the same organ
The vas aberrant takes its origin from the centre of
the Wolffian body, from which, according to some
authorities, the epidydimis also is formed. The his-
tological changes which take place during the deve-
lopment of the testicle are not demonstrable with
sufficient certainty to justify their formal description.

What has been said already in reference to the
epithelium, and mode of secretion, of glands composed
of clusters of follicles, applies with equal force to
those composed of tubes. Those which possess a
single layer of epithelium, and in which secretion is
effected by simple filtration, are : the glands of the
intestinal canal, those of the uterus, the sweat glands,
the kidneys, and the liver.

The glands which have a stratified epithelium, and
in which secretion is effected by vegetation of its
cells, are the ceruminous glands, and the testicles.

SECT. III. MIXED GLANDS. — The ovary in some
respects resembles the blood-glands, but differs from
them by possessing an excretory canal, and by the
peculiar character of its follicles ; the liver, with its
double apparatus for the secretion of bile and sugar,
is both a tubular and a blood-gland. The structure
of these two organs makes it necessary, therefore, to
associate them together in a separate group, which
constitutes naturally a connecting link between the
true and blood-glands.

126 GLANDS.

ovary structure. The Ovary. The envelope of the ovary (tunica
albugined) is of the same nature as that of the testi-
cle, and like it, is covered everywhere, except at its
lower border (hilus), by a serous membrane. Its
inner surface is intimately adherent to, and continu-
ous with the parenchyma of the organ. This is com-
posed of an obscurely fibrous substance, traversed by
numerous blood-vessels, in the meshes of which the
ovisacs, or Graafian vesicles are found. At the lower
border of the ovary its fibrous element is denser than
elsewhere, and forms, with the tunica albuginea, a
sort of corpus Highmorianum, in which there are no
ovisacs ; but just outside of it, and throughout the
whole parenchyma to its outer surface, large numbers
of them exist, and of all dimensions — the larger ones
always lying nearest to the surface of the organ.

The outer envelope of the ovisac is a fibro-vascular
membrane consisting of the same material as the
parenchyma in which it is embedded, only more con-
densed. The external portion of this membrane,
which is loosely adherent to the surrounding tissue,
is less vascular than its deeper surface. In contact
with this is a stratified epithelium (inenibrana granu-
losa), which increases considerably in thickness near
the point which looks towards the surface of the
ovary, and constitutes the proligerous disc, in the
interior of which the ovule or egg is contained (PL
XXI. fig. VI. 2, 3, 4). The remaining cavity of the
ovisac is filled by an albuminous fluid which contains
cells, or the debris of cells, detached from the mem-
brana granulosa.

The proper tunic of the ovule (vitelline membrane,

GLANDS. 127

zona pellucida) is about ^th of a line in thickness,
transparent, and entirely structureless. Its contents,
the vitellus or yelk, scarcely liquid in consistence,
contains a great number of very fine granules, pro-
bably fatty in their nature. At one point of the
periphery of the vitellus there is a brilliant spherical
nucleus, the germinal vehicle, or vesicle of Purkinje.*
Finally, the nucleus itself contains a nucleolus, called
the germinal spot ( Wagner). f

Generally, as is well known, the ovisac contains but
one ovule ; nevertheless, it may contain two, as we
have seen in one instance, in the ovary of an adult (PL
XXI. fig. VII. 1, 2). We have also observed an
example of segmentation of the vitellus in another
ovum of the same female, which proves that this phe-
nomenon may take place in the interior of the ovary
without previous fecundation (fig. VIII).

The Fallopian tube, or oviduct, which serves as the raiiopian tube.
excretory duet of the ovary after the detachment of
the ovum, has three layers of tissue in its walls ; the
first is serous, and belongs to the peritonaeum; the
next is composed of smooth muscular fibres and
blood-vessels ; the third is mucous membrane, the
surface of which presents longitudinal plaits, and is
covered by a single layer of cylindrical ciliated epi-
thelium. The vibratory motion of the cilia tends to
carry the contents of the tube onwards from without
inwards, and consequently facilitates the descent of
the ovum towards the cavity of the uterus.

* Purkinje, Professor of Physiology in the University of Prague. — (Ed.)
t Rudolf Wagner lately resigned the Chair of Physiology at the Uni-
versity of Gottingen, and was succeeded by Meissner. — (Ed)

128

GLANDS.

The uterus, into which the ovum passes from the
Fallopian tube, possesses the same tissues in its walls,
only the second, or muscular coat, is much more
developed than in the oviduct, especially during ges-
tation. Its third, or mucous lining, is also more com-
plicated in its structure ; the portion of it which
belongs to the body of the organ resembles that of
the Fallopian tube, but that which lines its neck is
studded with filiform papillae which overlap each
other ; they are found near its inferior orifice ; in
addition, we have, in the mucous lining of the uterus,
large numbers of tubular glands, which have already
been described.

The vagina has also three coats : the outer, fibrous ;
the middle, musculo-vascular ; and internal, mucous.
On the latter we find numerous deep rugae, especially
towards its orifice, and a large number of conical
papillae. Its epithelium is thick and stratified. Thus
far no glands have been found in the thickness of its
walls.

and The arteries of the ovary enter that organ at its
lower border, and break up into a great many very
tortuous branches, of which some are distributed to
its parenchyma and fibrous envelope, whilst the rest
go to form a close capillary plexus in the walls of the
ovisacs. Its veins follow the track of the arteries,
and terminate in the ovarian and uterine veins. Its
lymphatics, whose origin is not fairly made out,
accompany the blood-vessels, and finally communicate
with the pelvic and lumbar glands. As to its nerves,
they run with its arteries into the secreting portion
of the organ, but their distribution and mode of ter-
mination are unknown.

GLANDS. 129

The ovary is developed at the expense of the inte- Development,
rior substance of the Wolffian body, and is distin-
guishable -from a testicle, by not being continuous
with its excretory duct. It consists, at first, exclu-
sively of embryonic cells, the greater part of which
are transformed into the ovisacs ; the remainder form
the parenchyma and envelope of the organ. In the
ovaries of the foetus, or newly born infant, the ovi-
sacs are readily recognised as a series of pockets lined
internally by a layer of epithelial cells which sur-
round another larger central cell; this eventually
becomes the ovula, whilst those which surround it,
increasing in number, form the membrana granulosa,
and proligerous disc.

The body of Rosenmuller, or parovarium, situated
between the layers of peritonaeum which connect the
ovary and fimbriated extremity of the Fallopian tube,
and consisting of a number of blind canals, represents
the remains of the central portion of the Wolffian
body, and corresponds to the vasculum dberrans in
the male.

The liver is covered externally, on all sides, by a LlTer-
layer of connecting tissue which, at its transverse fis-
sure, applies itself to the vessels of the organ, and
following them into its parenchyma, accompanies
them in their ramifications, forming a common invest-
ment for them, and the whole organ, which is known
as the capsule of Glisson.

The outer surface of this proper coat of the liver is
very closely united to the peritonaeum throughout its
whole extent, except at its posterior border, its trans-
verse fissure, and at the fissure for the gall-bladder.

130 GLANDS.

Its internal surface sends innumerable delicate pro-
cesses, or trabeculse, into the interior of the organ,
which traverse its parenchyma, ' and become ulti-
mately continuous with the connecting tissue which
accompanies its vessels to their extreme ramifications.

The parenchyma of the gland consists of an aggre-
gation of little granules, one-fourth to one- half of a
line in diameter, of a yellowish-brown color, and
darker centrally than on the surface. This color
varies considerably, for it depends upon the amount
of blood in the ramifications of the portal vein, and
in those of the hepatic vein, and also upon the degree
of fatty infiltration which exists in the hepatic cells.
In the human liver the outlines of these granules,
called also acini or lobules, are rather indistinct ;
but in the hog it is different ; here each lobule forms
a little polygon, entirely independent of its neighbors,
and presenting a very distinct outline.

Each lobule of the liver represents, in its structure,
a miniature of the whole organ ; it will suffice there-
fore to study one of them thoroughly, in order to get
an exact idea of the histology of the gland. In each
lobule we find : 1st, a mass of hepatic cells ; 2d, the
terminal ramifications of the venae portae and of the
hepatic veins ; 3d, the biliary apparatus, consisting of
the radicles of the hepatic duct, and the terminal
branches of the hepatic artery.

The cells are of two sorts : the one, which consti-
tutes pretty much the whole epithelial mass, are large
and irregular polygons, jVth of a line in diameter,
with nuclei almost always infiltrated with fat, and
contents consisting of free oil-globules, and a large

GLAWDS. 1 31

quantity of minute pale granules, which Sehiff*
regards as a species of animal starch (PL XXII. fig.
IV. 1). The other cells, much smaller (^th of a
line) and less numerous, have a regular polygonal
form, and finely granular contents, generally free from
fat (fig. IV. 2). In the interlobular spaces, which in
the hog's liver are very 'distinct, we find minute
branches of the venae portee (interlobular veins), by
which the lobules between which they are situated
are supplied with blood (PL XXII. fig. I. 2, 3). If
we examine closely the relations between the inter-
lobular veins and a single lobule, we find them form-
ing around it a vascular network, from the concavity
of which a multitude of minute ramusculi take their
origin, which penetrate the substance of the lobule,
and immediately break up into capillaries (fig. I. 4 ;
fig. II. 2). They anastomose freely with each other,
and thus form a network with very close meshes
(^oth of a line), which empties, finally, at the centre
of the lobule, into a minute veinule, which is a radi-
cle of the sub-lobular hepatic vein (fig. III. 2). In
man, the lobules not being clearly limited in their
outlines, the vascular circle thus formed by the penul-
timate branches of the portal vein is not readily dis-
tinguished, but the capillary network in their interior
has the same appearance and arrangement as that
described (fig. IL).

The large hepatic cells, usually connected to each
other in pairs, fill up the meshes of the capillary
plexus of the lobule, and in their aggregate mas& con-

* Professor of Physiology in the University of Zurich. — (Ed.)

132 GLANDS.

stitute an epithelial network, which is interwoven thus
with the web of capillary vessels. The elements of
the liver which we have studied thus far constitute
its glycogenous apparatus.

Hepatic duct. The hepatic duct enters the liver at its transverse
fissure along with the hepatic artery and portal vein,
and accompanies these vessels to the lobules. In its
course it gives off a great many arborescent branches,
of which the larger anastomose frequently with each
other, whilst the smaller ones remain solitary and
continue on to the surfaces of the lobules. From
these minute perilobular ramifications arises a set of
capillary tubes which enter the substance of the
lobules — not very deeply — and there terminate in
blind extremities ; they are lined within by a simple
epithelial layer, made up of the smaller cells which
have been described above (PL XXII. fig. VI. 5, 6,
7). In the biliary ducts which possess a diameter
beyond sVth of a line, according to Kolliker, their
pavement epithelium is replaced by a cylindrical epi-
thelium. Finally, the hepatic ducts proper, together
with the cystic duct and the ductu-s communis chole-
doclius have muscular fibres in their walls, and also a
considerable number of minute racemose glands. The
hepatic artery accompanies the hepatic ducts to the
lobules, supplies them with very numerous branches,
and finally terminates in the capillary plexus of the
portal vein. This second apparatus, composed of the
biliary ducts and the hepatic artery, constitutes a
tubular gland. The liver then is made up of two
glands, which are intimately intermingled with each
other ; one of these (a blood-gland) is concerned in

GLANDS. 133

the secretion of sugar, and the other (a tubular gland)
in the secretion of bile. The physiology of the liver,
so well established by M. Claude Bernard, as well as
its comparative anatomy, entirely justify this view.

The mode of origin of the radicles of the hepatic
duct has been the object of varied researches,, and the
number of theories which have been proposed in
explanation of it are evidence of the uncertainty
which surrounds the subject. We have admitted
that the liver is made up of two distinct glands,
because, as we have already said, both physiology and
comparative anatomy unite to prove it, and we have
described the radicles of the hepatic ducts as tubes
terminating in blind extremities, because we have
witnessed this fact twice in a cirrhotic liver, and we
know that Professor Kiiss* had already observed the
same several years since in a syphilitic liver.f

* Professor of Pathological Anatomy in the Faculty of Strasbourg,
France.—^.)

t It will be observed that our author, in his very succinct account of
the minute anatomy of the liver, makes no allusion to the labors of Kier-
nan, Lereboullet, or Beale, an omission which cannot be fairly over-
looked. These authors throw too much light upon the mueh-debated
question of the mode of origin of the radicles of the hepatic duct to be
passed over in silence. The best supported opinion on this subject at the
present day is not that the radicles of the hepatic ducts are merely tubes
terminating in blind extremities, as stated in the text, but that these
radicles take their origin from a Mliary plexus or network of tubes, ana-
logous to the network of blood-vessels in the interior of the hepatic
lobule, and occupying its interstices. Kiernan first described and figured
this " biliary plexus" in his admirable paper on u the Anatomy and Phy-
siology of the Liver," in the Philosophical Transactions, London, 1843,
(part 1st, p. 741, and PI. XXIII. fig. III). His figure, however, is dia-
grammatic, and not taken from nature. It has been reproduced in most
of the works on Descriptive Anatomy of the present day.

I* 1853, M. Lereboullet published a prize essay, in Paris, u on the Mi-

134 GLANDS.

The walls of the gall-bladder are composed of the
same elements as those of the larger biliary ducts.
Its mucous membrane has numerous folds and rugse

nute Structure of the Liver" in which, after very thorough investigation
of the subject, he arrives at the conclusion that Kiernan's hypothesis is
correct, and that the biliary plexus is truly demonstrable, although, after
long and laborious research, he was not able to demonstrate the existence
of the membrane forming the Avails of the tubes composing it. He
speaks, however, with confidence, of the network of tubes, or biliary
plexus, containing the secreting cells of the liver (hepatic cells), as occu-
pying the interstices of the vascular plexus of the lobule — so that the two
sets of tubes, biliary and vascular, interlace with each other accurately,
the walls of the bile-tubes being everywhere so closely adherent to the
external surfaces of the blood capillaries that the former were riot sus-
ceptible of separate demonstration (p. 59 et seq.).

In a Monograph by Dr. Lionel S. Beale (on some points in the Ana-
tomy of the Liver of Man and Vertebrate Animals, London, 1856), the
following passage occurs in the summary of his able and interesting
investigations on this subject :

" The liver cells lie within a tubular network of basement membrane,
which separates them from the walls of the capillaries. In many cases,
however, these thin membranous tubes cannot be separated, and are, no
doubt, incorporated with each other."

" The cell-containing network is directly continuous with the most
minute ducts, which ramify at the circumference of the lobule, and it
. terminates in the centre by loops, which lie close to the intralobular
vein.'1 (p. 74.)

Both Lereboullet and Beale describe the tubes composing the " cell-
containing network" as larger in diameter than the " minute ducts,"
which are the radicles of the hepatic duct. " The tubes of the cell-con-
taining network are about ToV^tn of an inch in diameter, or more, but
the finest ducts are commonly not more that 3 oVotn? an<^ tnev are °ften
seen even less." . . . "The smallest ducts are lined with a very delicate
layer of epithelium, composed of flattened cells of a circular form, con-
trasting remarkably with the large secreting cells" — the hepatic cells
proper, which occupy the cell- containing network, or biliary plexus.
(Beale, p. 74.)

In addition to the evidence we have quoted, which sets forth what we
believe to be the true anatomy of the liver in relation to the point in
question, the monographs of Lereboullet and Beale may be advanta-

GLANDS. 135

upon its surface, the intersection of which gives it a
honey-combed appearance ; it is lined by a cylindrical
epithelium, composed of yellowish colored cells, which
are very pale and often destitute of nuclei (PL XXII.
fig. V.).

The liver has two sets of lymphatics : one super- Lymphatics.
ficial, ramifying in the thickness of its proper coat ;
the other deep, and following the subdivisions of the
portal vein ; they anastomose freely with each other,
and terminate, those from the convex surface of the
organ, by passing upwards through the thoracic
cavity, and those from its inferior surface, by running
into the lymphatic glands of the abdomen.

The nerves of the liver, which are derived from the
pne in no-gas trie and great sympathetic, join the hepa-
tic artery and follow its ramifications ; but their mode
of termination in the interior of the lobules is un-
known.

The first traces of the liver make their appearance Development.
in the shape of two little masses of cells, one upon
the outer, the other upon the inner or epithelial layer
of the intestinal wall. As to their subsequent meta-
morphoses, what has been ascertained by the most
reliable einbryologists may be stated as follows:
Whilst the more external of the two cellular masses
enlarges and surrounds the common trunk formed by
the umbilical and portal veins, constituting thus a
parenchymatous mass enclosing the portal system of
veins which are closely enveloped by large sized

geously consulted by the student ; they contain much valuable informa-
tion as to injecting and preparing specimens of the liver for micro-
scopical study.— (Ed)

136 GLANDS.

hepatic cells, the internal mass sprouts into numerous
tubular branches which, penetrating the substance of
the outer mass, constitute the system of biliary
ducts. Whilst these changes are taking place, the
original primordial cells, of which the masses were
composed, undergo various metamorphoses which
result in the formation of the several tissues consti-
tuting the substance of the gland.

preparations. The preparations on which the structure of the

liver is best studied are very delicate sections of the
fresh liver, and also of livers injected with colors
ground in oil and diluted- with essence of turpentine.

3Utfeeinteft?ned88 SECT. IV. DUCTLESS FOLLICLES AND BLOOD GLANDS.

— The most simple in their structure of this class of
organs are the solitary glands of the intestinal canal.
These are little spherical bodies, situated deeply in
its mucous membrane, and varying from half a line
•to one line in diameter. Their walls consist of fibroid
membrane studded thickly with plasmatic ceils. Their
contents, greyish in color, and of a solid consistence,
are made up of a quantity of rounded globules, from
aFifth to T^jth of a line in diameter, and bearing a
very close resemblance to the cells contained in the
interior of the lymphatic glands. Numerous blood-
vessels ramify upon their exterior, and then, penetrat-
ing their walls, converge towards the centre of each
follicle. Externally to the follicle they anastomose
freely, but towards its centre they form a great number
of loops, which, when filled by injection, present a very
beautiful appearance (PL XXVI. fig. XIII. 2). Kol-
liker has found nerves in the follicles of the tongue,
, according to this author, E. Weber has also

GLANDS.

recognised in them radicles of lymphatics. No exter-
nal outlet has been discovered, after the most rigor-
ous examination of the external surfaces of these
glands. Reasoning from the structure of these
organs, and also from certain pathological relations
existing between them and the mesenteric glands, the
conclusion seems to us legitimate that they are iden-
tical in their nature with lymphatic glands. This
opinion is sustained, also, by the most distinguished
histologists of Germany. These ductless glands are
what are known as the solitary glands of the intes-
tine ; they constitute the essential portion of Peyer's
glands, of the tonsils, the follicles of the tongue, and
the pharynx. The structure of the vesicles of the
thymus gland warrants us also in including it in the
same category.

Thyroid body. — The fibrous envelop of the thyroid Thyroid body
body gives off from its internal surface a great num-
ber of delicate trabeculse of connecting tissue by which
its interior is divided up into spaces, or cavities, in
which the vesicles, of the gland are contained (PL
XXII. fig. VIII.) . Each vesicle is thus enclosed by
a delicate partition of connective fibres, in the sub-
stance of which a considerable number of plasmatic
cells are found, together with an abundance of ves-
sels (fig. VIII. 2, 3). A single layer of polygonal
epithelium lines the interior of the vesicle, and its
cavity is filled with an albuminous fluid. In the
foetus, and young child, the epithelial layer consists
of cells Troth of a line in diameter, with finely granu-
lar contents, and a nucleus measuring about zieth of
a line. But in the adult, and in old age, it is very

9

138 GLANDS.

difficult to find the epithelium well marked and dis-
tinctly separate from the liquid contents of the vesi-
cle; most frequently its cells are found infiltrated
with fat, and a large number of free oil globules and
nuclei are contained in the liquid which fills the vesi-
cle, which is evidence of the disintegration and break-
ing down of its elements (fig. VIII. 4). It is doubtless
in these vesicles, or follicles, of the thyroid, that most
of the morbid growths to which the gland is liable,
take their origin. The lobulated shape of the thyroid
body depends upon the aggregation of its follicles
into little masses, or lobules, which remain to a cer-
tain extent independent of each other.
vessels. The blood-vessels of the thyroid are remarkable
for their size and number, and the rich and delicate
plexuses of capillaries which they form around the
walls of each follicle. Its nerves come from the
sympathetic ; with regard to their mode of termina-
tion, as well as to the distribution of its lymphatics,
nothing is certainly known.

Development. The facts ascertained thus far in relation to the
development of the thyroid gland are not sufficiently
accurate and positive to justify their record in this
work.

spleen. Spleen. — The spleen is an organ in regard to the
structure of which much remains yet to be elucidated ;
the following account includes all that the labors of
the most eminent microscopic anatomists have thus
far established as certain.

The envelop of this vascular gland is similar to
that of the liver, and is intimately adherent, exter-
nally, to the peritonaeum, and internally, to its paren-

GLANDS. 139

ch yma ; at the hilus of the organ it is reflected upon
its vessels, and accompanying them into its interior,
forms a sort of capsule of Glisson.

Its parenchyma consists of a sort of coi^pus caver- p*«mchyma.
no-sum, the trabeculse of which, fibrous in their nature,
are continuous by their extremities with the inner
surface of the proper coat of the organ, and in their
interspaces is a soft material very closely resembling
blood-clot, called the pulp of the spleen. There are
also certain spherical bodies connected with its arte-
ries, and called corpuscles of Malpighi, which form a
portion of the parenchyma of the organ.

We have said that the fibrous coat of the spleen
was reflected upon its vessels, and constituted for
them a sheath or capsule, continuous, in its interior,
with the trabeculse. The splenic artery gives off
near its hilus, a certain number of branches, which,
as they penetrate the substance of the gland, con-
tinue independent of each other, and form, each one
of them, by its subdivisions, a sort of vascular brush.
Situated upon arterioles of from eVth to *Vth of a line
in diameter are the little rounded whitish colored
bodies already mentioned as the corpuscles of Mal-
pighi ; they measure from one-eighth to one-fourth
of a line in diameter. Their structure is identical
with that of the solitary glands of the intestinal
canal. They have a very delicate outer coat of con-
necting tissue, which is continuous with the sheath of
the artery upon which each corpuscle is situated, and
its contents are made up of the same elements that we
find in the interior of a lymphatic gland, viz., spheri-
cal cells of from 3 loth to rioth of a line in diameter,

140 GLANDS.

and free nuclei ; Kolliker mentions also the presence
of blood globules, both normal in appearance, and
in various stages of alteration. Leydig has described
a vascular network which penetrates the interior of
the corpuscle, and thus completes its resemblance to
a ductless gland ; this author, in fact, does not hesitate
to consider the Malpighian corpuscle of the spleen as
a minute lymphatic gland.

spiemc puip. The splenic pulp, the substance of which is tra-
versed by the finest vessels, and the most delicate
trabeculse, includes elements of different kinds. Its
principal bulk consists of cells similar to those of the
Malpighian corpuscles (PI. XXII. fig. VII. 1) ; debris
of red blood globules, blood pigment, and larger
cells with many nuclei, joth of a line in diameter,
make up the remainder. In some of these latter
elements the formation of red globules seems to take
place by endogenous vegetation ; at least this is to be
inferred from the drawing by Otto Funke,* in his
Atlas of Physiological Chemistry. But Kolliker
asserts, on the contrary, that these cells are at first
nothing more than aggregations of red globules,
around which a membrane has formed, thus consti-
tuting a cell, of which these old blood globules
become the nuclei, and that they are about to undergo
still farther metamorphoses in a retrograde direction,
of which he gives drawings confirmatory of his
opinion. Are we to conclude then, with Otto Funke,
that red globules of the blood are formed in the

* Formerly Professor of Physiology in the University of Leipzig ; at
present occupies the same chair at Freiburg, Grand Duchy of Baden,
Germany. — (Ed.)

GLANDS. 141

spleen, or, with Kolliker, that it is an organ whose
function is to destroy them ?

Amongst the elements of the spleen there remain
to be noticed some cells of a fusiform shape, very
much enlarged around their nuclei (fig. VII. 2). In
comparing these corpuscles with the epithelial cells
of the vessels, it is difficult, from their similarity of
shape, not to regard them as identical in nature
Nevertheless, Fiihrer* (Gazette hebd., 1855, p. 314),
takes a different view of them, and assigns to them
an important physiological function. According to
his view, these fusiform cells, swelled out like so
many aneurisms, are nothing more than tubes con-
nected to each other, end to end, and communicating
with the capillaries of the spleen, whilst their nuclei
are the future red blood globules. Fiihrer has doubt-
less allowed himself to be carried away by the desire
to establish an analogy between these fusiform bodies
and the arterial dilatations which exist in fishes, and
he has overlooked their epithelial character.

The smallest of the veins spring from the capil- veins, etc.
laries, run alone for a short distance, and then join
the arteries. The lymphatics, superficial and deep,
meet and unite at the hilus, whence they are trans-
mitted directly to the thoracic duct. The nerves of
the spleen are numerous ; they are distributed with
its arterial branches, and seem to terminate by free
extremities.

It is a matter of extreme difficulty to determine
the relations which exist between the splenic pulp,

*• A practising physician at Hamburgh, author of a popular work on
Surgical Anatomy. — (Ed.)

142 GLANDS.

and the larger veins of the organ. Is the pulp
entirely outside of the vessels, as asserted by some
authorities, or are the spaces in which it is contained
simply dilatations of the veins, and if this be true,
does it form a part of the general circulation ? The
researches which seem to us most conclusive tend
rather to establish the entire independence of the
cavities which contain the splenic pulp ; yet the fact
is not to be accepted as demonstrated.

Development It is not agreed at what point exactly the spleen
takes Us origin, Arnold asserts that at first (from
the seventh to the eighth week), it is confounded
with the pancreas. BischofP says that, in the fcetal
calf, he has seen it spring from the greater curvature
of the stomach ; and according to other observers, it
is developed from a blastema, at first isolated, but
which shortly becomes attached to the great cul-de-
sac of the stomach. As to the histological transfor-
mations which the organ undergoes during its increase
of size> they have not been accurately demonstrated.
*H>" Supra-renal Capsules. — The nature and physio-
logical function of these organs are as yet unknown.
Nevertheless it seems probable, from the nature of
certain elements which enter into their composition,
and which form, in fact, almost the whole of their
central portion, that they belong rather to the ner-
vous system than to the class of glands under consi-
deration.

structure. The supra-renal capsule possesses a thin envelop,
fibrous in its structure, and intimately connected with

* Professor of Physiology at Heidelberg, Baden, Germany. — (Ed.)

GLANDS. 143

the parenchyma of the organ by delicate processes, or
trabeculse, given off from its internal surface.

On making a section completely through the body £°8rtical 8Ubfitafl'
of the organ it is found to consist of two distinct sub-
stances, of which one forms its cortical portion, and
the other its centre. The first, or cortical substance,
one-half a line to a line in thickness, is of a soft, solid
consistence and brownish color, being of a somewhat
deeper tint externally than internally. In the fibril-
lated tissue which forms its basis are a number of
elongated cavities filled with large cells (from y£oth
to irVth of a line in diameter) and very much infil-
trated with fat.

The fibrillated element of its central or medullary
substance is more delicate than that of its outer por-
tion, and the cells which it contains resemble exactly
the multipolar or caudate cells of the nervous gan-
glia. The numerous nerves with which the supra-
renal capsule is supplied penetrate this substance, and
unite, as Leydig has demonstrated, with the prolon-
gations of these nerve cells. We haye'a right, then,
in accordance with these facts, to regard this organ
as a nervous centre, and to consider its cortical layer
as simply a protecting membrane, for the very con-
siderable amount of fatty infiltration of its cellular
element seems to indicate an arrest of its functional
activity.*

* In one of the most aggravated instances of hysterical temperament
that I have ever encountered, the patient, a maiden lady, died, at the age
of 84, of cancer. The cancerous deposit involved both supra-renal cap-
sules, which were each as large as the closed fist; the right, which was
somewhat the larger, having imbedded itself firmly in the under surface
of the liver. There was also a cancerous mass in the posterior wall of

144 GLANDS.

vessels. Its arteries and veins are numerous ; in their mode
of distribution they present no peculiarities worthy
of note. The lymphatics are few in number, and
seem to belong to the cortical substance alone. The
development of the supra-renal capsule takes place at
the same time with that of the kidney, but entirely
independently of that organ. Of the histological
transformations which it undergoes during foetal life
little is known.

the transverse colon, and another in the root of the right lung. This
latter, by its pressure upon the pulmonary veins, the interior of which it
had also invaded, gave rise first to haemoptysis, and afterwards to exten-
sive pleuritic effusion— from the immediate effects of which death took
place. The most prominent abnormal nervous phenomenon manifested
by this patient, which continued during her whole life, and included most
of her multifarious ailments, was excessive general hyper-sesthesia with
great mobility of the nervous system.— (Ed.)

CHAPTER VIII.
Skin and its Appendages.

SECT. I. SKIN. — The skin consists of two distinct Epidermis,
layers : the first, superficial, and composed entirely of
cells, is the epidermis, or cuticle ; the second, beneath
this, which has for its basis a dense interlacement of
fibres of connecting tissue, containing in its meshes a
quantity of nerves, blood-vessels, glands, and masses
of adipose cells, is the derma, or true skin.

In the epidermis there are three distinct strata.
The first, in contact with the true skin, consists of a
single layer of cylindrical cells with well marked
nuclei, and with their long diameters at right angles
to its surface (PL XXIII. fig. II. 3 ; fig. III. 1 ; fig. IV.
3). It is principally in this layer that the deposit of
black pigment is found which causes the dark color
of the negro, and in certain regions of the skin in the
white, as, for example, the nipple and the scrotum
(fig. III. 1), Upon this stratum of cylindrical cells
is another, five or six times the thickness of the first,
and likewise consisting of nucleated cells (fig. I. 3 ;
fig. II. 2). The deepest cells of this layer are oval,
the next in order, round, or regularly polygonal, and
the most superficial again oval ; but their long dia-
meters have a different direction from those of the
deep cells ; that is, they are parallel to the cutaneous
surface. It is these two united layers which form the

146 SKIN AND ITS APPENDAGES.

rete mucosum of Malpighi. Finally, the third stratum
or horny layer, very variable in its thickness, is com-
posed entirely of scale-like cells, which overlie each
other regularly (fig. I. 2; fig. II. 1), and which differ
from the cells of the rete mucosum, not only in their
form, but also in the absence of their nuclei, and in
their contents, which are more or less opaque, and
coarsely granular. They resist also for -a longer time
the action of acetic acid, and caustic potash.

The epidermis, like the other epithelial membranes,
has neither vessels nor nerves, but it does not, on this
account, possess in any less degree true organization
and indubitable vitality.

Derma. The true skin is naturally divisible into two strata,
which insensibly mingle with each other along their
line of contact. The deep, or reticulated layer is
made up of a loose interlacement of connective and
elastic fibres which, on its internal surface, become
continuous with those which go to form the super-
ficial fascia. It is in this reticulated stratum of the
derma that we find its glands, the hair follicles, and
fat cells, grouped together in little rounded masses.
(PL XXIII. fig. I. 8, 10.) It is here also that its
blood-vessels ramify and give off their ultimate
branches, which are distributed to the superficial
layer.

The surface of the superficial or papillary layer of
the true skin is studded with minute projections
known as its papillae. These papillae are not every-
where uniformly distributed, nor do they present
everywhere the same volume ; they are most numerous
and largely developed on the extremities of the fin-

SKIN AND ITS APPENDAGES.

gers and toes, and upon the palms of the hands and
soles of the feet ; some of them, in these localities, are
even surmounted by secondary papillae.

The papillae, as well as the portion of the derma
from which they project, are composed of very deli-
cate fibrous tissue, containing a large number of plas-
matic cells (fig. II. 5), and tunnelled by the terminal
branches of the vascular and nervous systems. The
papillary surface of the true skin is limited by a very
delicate structureless membrane (reVoth of a line in
thickness), which separates it from the epidermis
(fig. II. 4).

The blood-vessels of the skin form two sets : one vessels.
occupies the deep stratum, and supplies the glands,
hair follicles, and pellets of fat; the other, in the
shape of a close network, is found spread out in the
superficial layer, where it gives off the terminal
loops which penetrate the interior of most of the
papillae.

The nervous filaments of the deep layer, few in -servef.
number, are destined for the supply of the organs
which it contains, whilst those of the papillary layer are
very numerous, forming a plexiform network which
seems to terminate, after previous sub-divisions, by
free extremities. A large number of these ultimate
nervous filaments enter the bases of a certain propor-
tion of the papillae (nervous papillae), and terminate
there either by free extremities, more rarely by form-
ing loops, or lastly by olive-shaped extremities, which
constitute the tactile corpuscles already described
(PL XXIII. fig. II. 6). It will be recollected, also,
that the Paccinian corpuscles constitute another mode

148 SKIN AND ITS APPENDAGES.

of termination of the cutaneous nerves (PL XIV

%. ii).

lymphatics. The lymphatics of the skin form a very close web in
the papillary layer, communicating by larger branches
with the subcutaneous vessels of the same system.
We possess no positive information as to their mode
of origin. M. Kiiss asserts that they are in direct
communication with the deep stratum of the epi-
dermis.

The cutaneous glands have been already described.
Development. According to Bischoff, the skin can be distinguished
as a distinct membrane as early as the commence-
ment of the second month of foetal life. The true
skin, as yet consisting entirely of embryonic cells,
very soon acquires an increased degree of density,
and becomes distinct from the epidermis ; later, the
cells are metamorphosed, some of them into connec-
tive and elastic fibres, and others into vessels, etc.
Finally, a certain proportion of them seem to undergo
a temporary arrest in their development, and consti-
tute what have been denominated plasrnatic cells.
As for the epidermis, it is developed by the multi-
plication and increase in volume of its globular ele-
ments. Although the fact has not as yet been
demonstrated, it is probable that this multiplication
of cells is effected, both in the embryo, and through-
out life, by the endogenous generation of new nuclei,
and subsequent cleavage of the parent cell.

Preparation. To study its structure, very thin sections both of
recent and dried skin, must be made by a razor.
Acetic acid renders these sections more transparent,
and caustic potash has the same effect, but breaks

SKIN AND ITS APPENDAGES. 149

down their tissue ; these reagents, therefore, are useful
in bringing out their details of structure. Tactile
corpuscles are best found in sections of the skin of the
palmar surface of the third phalanges of the fingers,
and in the corresponding portions of the toes.

SECT. II. NAILS. — The substance of the nails is
nothing more than a peculiar form of hypertrophy
of the epidermis. The deep surface of this horny
plate rests directly upon the true skin ; its anterior
margin is free, whilst its posterior and lateral borders
are received into a groove formed by a fold of the
true skin (PL XXIV. fig. I. II. IIL). '

On the surface of the derma, in contact with the Matrix.
deep surface of the nail, known as its matrix, we
find numerous delicate ridges which run parallel with
each other and with the axis of the limb, converging
at the root of the nail towards a common centre, and
usually possessing no papillae. With these exceptions
the structure of the matrix of the nail is the same as
that of the true skin elsewhere ; its two strata exist
as usual ; it is to be noticed, however, that its vascu-
lar network is less rich towards the root of the nail,
causing a dead white surface of the semilunar shape
(the lumda) partly covered by the margin of the
fold of the skin, into which the posterior border of
the nail is received.

It consists of both of the layers of which the skin
is formed, but the dermal layer is destitute of papil-
Ise (fig. I. 5).

In the nail we find a repetition of the three strata structure of
of cells which we have seen forming the epidermis.
The middle and deep layers are identical with those

150 SKIN AND ITS APPENDAGES.

of the epidermis, and continuous with them without
any line of demarcation (fig. II. 2, 7). In the
superficial stratum, the distinctive characteristics in
which it differs from the corresponding layer of the
cuticle are : the persistence of the nuclei of its cells,
the greater transparency of their contents, and a
firmer cohesion of the cells to each other.

The epidermis of the fold at the root of the nail
adheres closely to its surface (fig. II. 10), but as its
component cells are not exactly identical with those
of the surface of the nail, there results a very distinct
line of demarcation between the two otherwise con-
tinuous layers (fig. II. 4).

Development. As early as the third month, the groove which
receives the root and sides of the nail is apparent.
Both the true skin and epiderm become slightly
hypertrophied, and by the fifth month, the laminated
ridges of the derma have become visible, and" the nail
is distinguishable from the surrounding cuticle — with
which it. is continuous.

Growth. The growth of the nail takes place at the expense
of the rete mucosum, the more superficial cells of
which become successively transformed into scales of
horn. Its increase in length is effected by the active
vegetation of the cells at the bottom of the groove
which lodges its root, they becoming continuous with
its substance. Whilst it is thus pushed forwards, the
deep surface of the nail appropriates a portion of the
cells generated from the surface of its matrix, and it
thus grows in thickness ; but the growth in length is
by far the more rapid of the two processes.

In the study of its structure, similar preparations

SKIN AND ITS APPETOAGES. 151

are required to those of the skin ; the use of dilute
solution of potassa is required to separate the cells
of the horny lamina.

SECT. III. HAIR, — The hairs, like the nails, are Hair,
composed of epithelium. A hair is a delicate cylin-
der, generally more or less flattened, variable in its
dimensions, and consisting of two distinct portions:
the shaft, which projects beyond the surface of the
skin, and the root which'is imbedded in a sheath,* or
follicle, furnished by the skin. This latter terminates
by a bulbous enlargement, at the extremity of which
is a deep excavation, which is occupied by one of the
papillae of the skin (germ, pulp, papilla of the hair,
PL XXIV. fig. IV. 3, 7).

The surface of the hair is formed by a single layer structure.
of epithelium, called the epidermis of the hair (PI.
XXIV. fig. VII. 1) ; immediately beneath this is
found a material arranged in longitudinal striae which
constitutes almost the entire bulk of the hair, and
which is known as its cortical substance (fig. VII. 2) ;
finally, in the centre of the shaft there is generally,
but not always, a canal filled by cells of a peculiar
shape, which forms its medullary substance (fig.
VIL 3).

The epidermis is composed of a single layer of scaly Epidermis,
cells, presenting an imbricated arrangement, so that
their superior margins are free (PL XXIV. fig. V.).
On treating this layer with acetic acid, or caustic
potash, its -cells swell out and become more trans-
parent, so that it can be seen that their contents
consist of fine granules, and that their nuclei have
disappeared (fig. VI.). The epidermis is found only

152 SKIN AND ITS APPENDAGES.

upon the shaft of the hair, it ceases abruptly at
the commencement of its root. Leydig has repre-
sented, as the epidermis of the root of the hair, a
layer of cylindrical cells, which are arranged perpen-
dicularly to its surface, but their existence is by no
means constant.

?tenceal sub" The cortical substance, the color of which varies
with the hair, is marked by longitudinal striae and
linear spots, which run in • the same direction (PL
XXIV. fig. VII. 2). The elements of which it is
composed cohere very closely, but, by the aid of
caustic potassa, they can be readily separated and
recognised as long fusiform bodies, homogeneous in
their structure, without trace of nuclei, and contain-
ing, sometimes, pigmentary granules. The dark
linear spots seem to be simply cavities filled with air,
for they are found in white, as well as in colored
hairs (PI. XXV. fig. I).

In the root of the hair the cortical substance pre-
sents again a different appearance ; in the bulb we
find regular polygonal cells with clearly defined
nuclei, and granular contents sometimes transparent
and at others charged with pigment (PL XXV. fig.
II. 6). A little higher up, these cells, and their
nuclei also, become elongated, and the outlines of the
cells gradually grow pale and disappear, whilst their
nuclei continue to elongate, and remain visible. They
finally, however, become pale and disappear also, or,
perhaps, they are converted into the fusiform bodies
of the cortical substance after their cell walls are
absorbed ?
sub- r me(jnnary canai <joeQ not always exist, and,

SKIN AND ITS APPENDAGES. 153

when present, it varies in shape and length. Thus,
sometimes it occupies the whole length of the hair ;
at others, it ceases at the root ; and again, it fre-
quently presents constricted portions, and even entire
interruptions (PL XXIV. fig. IV. 6, fig. VII. 3 ; PL
XXV. fig. II. 8). The cells by which it is filled con-
stitute the medullary substance ; they contain, usu-
ally, a very pale nucleus, and fatty looking granules ;
according to Kolliker they contain also air bubbles.

The hair follicle, or sheath, which envelops its root,
recalls in its structure that of the skin ; in fact we
find, on section of its walls, two layers of connecting
tissue similar to those of the skin, and two other
strata of cells representing the epidermis. This
structure suggests the idea, although the mode of
development of the hair proves the contrary, that the
hair follicle is formed by an indentation, or an invo-
lution, of the skin. The following, however, is its
structure :

Proceeding from without inwards, we recognise : structur
1st, a stratum of very loose* connecting tissue, which
is continuous with the deep layer of the true skin
(PL XXV. fig. II. 1) ; 2d, another stratum, very dis-
tinct from the preceding, and similar in structure to
the papillary layer of the true skin, with which it is
also continuous ; internally this layer is limited by a
delicate and structureless basement membrane, as in
the skin (fig. II. 2, 3) ; 3d, reposing upon this deli-
cate line is the deep epidermic layer, made up of cells
whose shape and mode of stratification resemble those
of the rete muoosum (fig. II. 4, PL XXVII. fig. V. 4);
4th, the internal epidermic layer, which, with its

10

154 SKIN AND ITS APPENDAGES,

scale-like cells, destitute of nuclei, is exactly similar
to the horny surface of the epiderm ; it terminates by
growing generally thinner in the upper third of the
follicle, about where the excretory duct of the seba-
ceous glands appended to the hair pours out its secre-
tion (PI. XXIV, fig. IV. 10; PL XXV. fig. II. 5) ;
P. XXVII. fig. V. 3). A very small fasciculus of
unstriped muscular fibres is attached to the bottom
of the hair follicle externally, on the side towards
which the hair inclines ; it passes obliquely upwards
to the surface of the true skin, where it is inserted ;
this is the muscle, by the contraction of which the
hair is made to straighten up at right angles to the
surface of the skin, or, as the phrase is, to " stand on
end."

The papilla which occupies the excavation at the
bottom of the bulb belongs to the true skin, and is
more delicate in its structure than its other papillae.
It contains several vessels which form loops in its
interior, but its connexion with the nervous system is
as yet unknown (PL XXV. fig. II. 7).

Development. The hair and the two epidermic layers of its fol-
licle, are developed from a minute mass, or granula-
tion of the rete mucosum which imbeds itself in the
surface of the cutis, whilst the two outer strata of the
walls of the follicle are derived from the formative
cells of the true skin. The hair is developed all in
one mass, from the little germ at the bottom of its
follicle ; the cells composing which, by their various
transformations, produce the several elements of
which it consists, as well as the two epidermic layers
by which the follicle itself is lined.

oj CHAPTER IX.

••{isiu/;* \q '>rfl

Intestinal Mucous Membrane.

THE mucous rfnembrane of the alimentary canal is ^eral struc-
continuous with the skin, and, in its essential consti-
tuents, possesses a similar structure ; thus, it consists
of two layers, one of which corresponds to, and resem-
bles closely, the superficial stratum of the true-skin —
the mucous membrane proper ; the other, the ana-
logue of the cuticle, and like it composed of cells, is
the epithelium. Nevertheless, the varying shape and
disposition of its epithelial cells, and the peculiar
modes of distribution of its blood-vessels, as well as
Its glands, constitute a membrane $ui generis which
requires a description in detail.

A general examination of this membrane shows at
once that its appearance and structure are not the same
throughout. There is evidently a considerable differ-
ence existing between the several segments of the
intestinal tube; and in view of this fact, and to faci-
litate our examination of the membrane, we shall
study its structure successively : 1st, in the mouth ; 2d,
in the pharynx and oesophagus ; 3d, in the stomach ;
4th, in the small, and lastly in the large, intestine.

The mucous membrane of the lips, cheeks, palate, MUCOUS mem-

braneof the

and gums, resembles exactly the superficial stratum mouth-
of the true skin. It consists of a layer furnished with
papillae at least as numerous, and of the same shape,

156 INTESTINAL MUCOUS MEMBRANE.

as those of the cutis, and presenting a structure,
which, though perhaps a little more delicate, contains
the same elements. There is a striking analogy also
in the distribution of its vessels and nerves, but up to.
the present time no tactile corpuscles have been
observed, except in the papillae of the lips. On the
hard palate and the gums the mucous layer is strongly
adherent to the periosteum, with which, in fact, it is
continuous ; but on the cheeks and lips, it is rein-
forced by a delicate fibrous layer, by which it is
loosely connected with the subjacent muscles.
Epithelium. Its epithelial investment presents the same general
physiognomy as the epidermis ; the two deeper strata,
corresponding to the rete mucosum of the cuticle, are
absolutely identical with it, both in the shape of their
cells, and in the order of their superposition. The
superficial layer is likewise composed of scaly cells,
but differing from those of the skin in the persistence
of their nuclei.

Glands. The glands of this portion of the alimentary mu-
cous membrane are all of the clustered variety ; they
occupy the sub-mucous stratum, sometimes even, as in
the cheeks, being imbedded in the muscular layer ; on
the hard palate and gums they are absent.
MUCOUS mem- The mucous coat of the inferior surface of the

brane of the

tongue is similar to that of the lips, but on its dorsal
aspect it is very different, both in its external appear-
ance, and in certain structural details.

On the base of the organ its mucous membrane is
almost smooth, and sparsely studded with little len-
ticular prominences, with a hole in the centre of each,
formed by the projection of small masses of subjacent

INTESTINAL MUCOUS MEMBRANE.

ductless follicles. The rest of its dorsal surface is Ductless.
thickly covered with very prominent papillae, which
from their variety in form, are divided into three sets,
viz : circumvallate,fungiform, and conical, or filiform,
papillae.

The papillae of the first set are found immediately
in front of the base of the tongue, where they are
arranged in the shape of the letter V. They have
the shape of an inverted cone, with the apex conti-
nuous with the membrane below, and its base looking
upwards and free, and are moreover surrounded by
an elevated circle formed by the mucous membrane,
which constitutes a sort of imperfect capsule, in
which they are almost concealed (PL XXV. fig.
III. 1).

IL\\Q fungiform papillae have the same shape as the
last, but are smaller, and project farther from the
surface of the membrane. They are pretty uniformly
distributed over the whole surface of the tongue,
being somewhat more numerous at its border and
tip.

The filiform papillae, whose shape is very well riiiform papiiiae.
indicated by their name, although found everywhere
on the upper surface of the tongue, are more nume-
rous in the neighborhood of its median line than its
edges, where they lose their characteristic appear-
ance (PL XXV. fig. IV.). Their direction is obliquely
upwards and backwards.

Each papilla, whatever may be its shape, is com- structure,
posed of the mucous membrane proper, of the sub-
stance of which it is a projection, and covered
externally by epithelium. In each of the three

158 INTESTINAL MUCOUS MEMBRANE.

varieties, the inner or proper surface of the papilla
is studded with secondary papillae, in the shape of
slender processes of variable length (PL XXV. fig. III.
2 ; fig. IV. 2). As for the epithelium, it adapts itself
accurately to the subjacent membrane, presenting a
free surface which differs in appearance according as it
corresponds to the localities occupied by the circurn-
vallate and fungiform papillae, or to those of the fili-
form variety ; in the first case it is perfectly smooth
(fig. III. 3), but in the latter it presents long and
delicate filaments, variable in length, and identical in
shape with the secondary papillae, the surface of
which they cover (fig. IV. 3, 4). It is this epithe-
lium of the filiform papillae which in some animals
assumes a horny character, and thus constitutes a
prehensile organ ; in the pike its structure is identi-
cal with that of its teeth. The epithelium of the
tongue is identical with that of the lips and cheeks,
both as regards the form and disposition of its cells.

The filiform papillae differ from both of the other
varieties, not only in their epithelial aspect, but also
in their relations to the nervous system ; thus the
nervous filaments which penetrate them are few in
number, and they do not reach their secondary
papillae. The circum vail ate and fungiform papillae,
on the contrary, are relatively rich in nerve fibres,
and they can be traced readily into their secondary
papillae, where they seem to terminate by free extre-
mities ; Kolliker has even demonstrated the presence
of tactile corpuscles in the fungiform papillae of the
tip of the tongue.

The blood-vessels which they receive are distri-

INTESTINAL MUCOUS MEMBRANE. 159

buted similarly to those of the other papillae of the
buccal cavity.

The glands of the mucous membrane of the tongue Glands.
are of two sorts : clusters of follicles, and ductless
follicles. The former, strictly speaking, do not belong
to the membrane, for they are imbedded in the sur-
face of the muscular tissue of the organ. They are
very numerous at its base, where they form a con-
tinuous layer which extends, on either side, to the
pillars of the fauces, and, in front, encroaches upon
its papillary surface. Those which are situated pos-
teriorly upon the edges of the tongue, and upon the
under surface of its tip, are also concealed amongst
the superficial muscular fibres of the organ, and are
connected with its mucous membrane by their excre-
tory ducts only, which pierce it, and open either at
the bottom of the sulti on its edges, or on either
side of the frcenum.

The ductless follicles at the base of the tongue Ductless glands,
constitute the little lenticular eminences which are
found in that region. Upon the summit of each lit-
tle projection is an orifice, visible to the naked eye,
which leads into a flask-shaped cul-de-sac, the walls of
which are continuous, and identical in structure, with
the mucous lining of the organ. The network of
vessels which immediately surrounds this orifice
is closer and richer than elsewhere in its vicinity
(PL XXV. fig. V.). The walls of the cavity are
reinforced by a dense lamina of connecting tissue, in
the substance of which are imbedded about twenty
minute spherical bodies, of the same size as the soli-
tary glands of the intestine, and identical with them

160 , INTESTINAL MUCOUS MEMBKANE.

in structure (vide ut supra}. These follicles present
no trace of an excretory duct, or any visible external
opening ; the existence of the central orifice on the
surface of the mucous covering of the eminence
which they form, has led to mistakes on this point,
but, as we have already seen, this opens only into a
cul-de-sac.

Tonsils. The tonsils are composed of an aggregation of
ductless follicles identical with those just described ;
they are therefore compound ductless glands. The
excavations which we see upon their free convex sur-
faces are simple blind cavities, sometimes containing
masses of whitish material of a disagreeable odor,
and consisting of debris of epithelium in a state of
partial fatty degeneration.

The lymphatics of the cavity of the mouth are
very numerous, especially those of the mucous mem-
brane of the tongue. They appear to take their
origin immediately beneath its epithelial layer, and
communicate with the cervical lymphatic glands.

The papillae of the mucous membrane of the pha-
rynx are smaller, and less numerous, than those of
the mouth. Its epithelium, in strata, resembles that
of the buccal cavity, only it is to be noticed that in
the upper portion, or vault, of the pharynx, it is pro-
vided with ciliated cells, In the deeper layers of the
membrane proper are numerous ductless glands, and
clusters of follicles ; the first are found only in the
upper part of the pharynx, whilst the mucous folli-
cles exist in all parts of the membrane. Its blood-
vessels are numerous, and are similarly distributed to
those of the walls of the cavity of the mouth. Its

s

INTESTINAL MUCOUS MEMBRANE. 161

lymphatics run into the deeper cervical glands. The
nerves are very numerous, and seern to terminate by
free extremities.

In the mucous membrane of the oesophagus there
are a great many conical papillae, but otherwise its
structure is the same as that of the pharynx. It has
no ductless glands, and its mucous follicles are not
very numerous. Its blood-vessels, by no means so
abundant as those of the pharynx, have no peculi-
arities in regard to their distribution. Its lymphatics
communicate with the deep glands of the lower -part
of the neck, and with those of the posterior medi-
astinum. It is freely supplied with nerves, but their
mode of termination is as yet undetermined.

The mucous membrane of the pharynx and ceso-
phagus is everywhere connected by its attached sur-
face to a thick stratum of muscular tissue ; in the
pharynx this is formed by its constrictor muscles, and
in the cesophagus by two layers, of which the fibres
of the inner are circular, and the outer, longitudinal.
The muscular walls of the pharynx are composed
exclusively of striped fibres, but in the cesophagus
this is true only of its upper part ; below, its mus-
cular fibres are non-striated.*

The mucous membrane of the stomach is softer and Gasti:ic mucous

membrane.

* According to Todd and Bowman (Physiological Anatomy, Lond.
1856, vol. II. p. 188), striped muscular fibres can be traced as far as the
diaphragm, in the muscular coat of the oesophagus ; and according to
Sharpey and Quain (Elements of Anatomy, 5th Ed., Lond., 1848, vol.
II. p. 1015), "they have been traced throughout its whole length, and
even, it is said (Ficinus), upon the cardiac end of the stomach." This is
also stated by Cruveilhier, on the authority of Valentin and Ficinus (Ana-
tomy, 1st Am. ed. New York, 1844, foot note, p. 323. — (Ed.)

162 INTESTINAL MUCOUS MEMBRANE.

thicker than that of the oesophagus ; it is of a pale
rose color whilst the organ is empty, but becomes
red during digestion. When relaxed, it is thrown
into a great number of wrinkles (rug of), which are
effaced when the stomach is distended. Its surface
is smooth : throughout its whole extent, except near
the cardiac orifice, where there are papillae similar to
those of the oesophagus (Berres*), and at the pylorus,
where flattened villi are found (Krausef ). Its epi-
thelium consists of a single layer of cylindrical cells,
similar to those of the intestine. The reddish tint,
which it derives from the subjacent layers of mus-
cular tissue, contrasts strongly with the whiter color
of the epithelium of the oesophagus ; the serrated
line, at the cardiac orifice of the stomach, which
marks the union of these two layers of epithelium, is
very distinct.

Glands. The surface of the gastric mucous membrane is
pierced by an infinite number of minute holes, from
iio-th to Voth of a line in diameter ; these are the ori-
fices of the gastric glands (PL XXV. fig. VII. 1).
These glands all belong to the tubular variety, but
some of them are single, and others compound. The
former (the glands which secrete gastric juice) occupy
nearly the whole extent of the membrane, and are
the same in form and structure as the follicles of Lie-
berkuhn already described. As for the compound

* Joseph Berres, Professor of Anatomy in the University of Vienna,
predecessor and preceptor of Hyrtl, the present occupant of the same
chair. Berres died in 1846, leaving an unfinished work on Microsco-
pical Anatomy. — (Ed.}

t C. F. J. Krause, Professor of Anatomy at Hanover. — (Ed.)

INTESTINAL MUCOUS MEMBRANE. 163

gastric follicles, one portion of them occupies the
vicinity of the cardiac orifice (those secreting pepsin),
whilst the other (consisting of mucous glands) is
found near the pylorus ; both have been already
described (PL XXV. fig. VIII. ; PL XXVI. fig. I).

The mucous coat of the stomach is rich in blood-
vessels which, first supplying its glands, terminate
nearer its surface in a very regular capillary network,
the largest meshes of which surround their orifices.
Its Jyinphatic vessels communicate with the little
glands which lie along the greater or lesser curvatures
of the organ. The mode of distribution and ultimate
termination of the very numerous nervous branches
which it receives from the great sympathetic and
pneumogastric, are not clearly demonstrated.

The mucous membrane of the small intestine, which smaii intestine.
in all the essential points of its structure resembles
that of the stomach, differs, from it, nevertheless, both
in the appearance of its surface, and in the character
of certain of its glands. Upon its free surface two
species of prominences are noticeable — valvulce con-
niventes and villi. The former are long semilunar
folds, formed by the plaiting of the membrane upon
itself; their direction is perpendicular to the axis of
the canal, and each occupies the half or two-thirds of
its circumference ; they slope . off to a point at either
extremity, and are_ connected to each other by little
oblique folds. They are very large and numerous in
the duodenum, where they overlap each other like
shingles on the roof of a house, and in such a manner
that their free edges look downwards. As we trace
them downwards, following the surface of the bowel,

164 INTESTINAL MUCOUS MEMBRANE.

they gradually and regularly diminish both in num-
ber and in size, until, in the lower part of the ileum,
they are recognisable only by a faint thickened line.
The villi of the small intestine are minute pro-
cesses, analogous to the papillae of the tongue, but
more delicate in their proportions. The* best idea of
their shape, number, and mode of arrangement, is to
be got by placing a piece of the mucous membrane
under water, and examining it with a magnifying
glass, or a microscope with a low power. They are

> seen to occupy the whole extent of the surface of the

membrane, and to be more numerous in the duo-
denum and jejunum, than in the ileum / they are seen
also to assume two principal forms — the flat, or val-
vular, and the conical. The flat villi are principally
found in the upper portion of the small intestine;
they are simple and solitary, or, by running into each
other, become compound, in which case they resemble
minute valvulce conniventes (PL XXVI. fig. II. 2, 3).
The conical villi are found everywhere throughout
the small intestine, but they exist in larger proportion
in the ileum (fig. III. 1). In some instances, instead
of terminating in a point, their apices are slightly
bulbous (PL XXVI. fig. XII.) ; their average height
is from one-fourth to one-half a line, and their dia-
meter from one-sixteenth to one-fourth of a line.

structure of the Whatever may be the form of a villus its structure

villi. . J

is always the same, and, in examining it from its surface
inwards we find, first : a single lamina of epithelium
which, on a perfectly fresh specimen which has not
been roughly handled, presents the appearance of a
mosaic, upon the surface of which an unbroken layer

INTESTINAL MUCOUS MEMBKANE. 165

of amorphous material has been applied (PL XXVI.
fig. TV. 1, 2, 3 ; fig. V.). By breaking up this layer
of epithelium we recognise the elements of which it
is composed, viz. conical cells, the summits of which
rest upon the surface of mucous membrane, whilst
their bases are directed outwards and free, or rather
covered by the amorphous substance already men-
tioned, which adheres to them very closely (fig. VI.).
It is only in perfectly fresh and recent specimens that
the cells are found covered by this amorphous coat-
ing; it disappears entirely in from twelve to twenty-
four hours after death (PL I. fig. VI.). The contents
of a- cell consist of fine granules, and its nucleus, which
is oval in shape, is usually nearer to its apex than its
base ; their mean length is Toth of aline, their breadth
232<l of a line, and the diameter of their nuclei a^th
of a line. The epithelium which covers the mucous
membrane in the intervals between the villi has also
the appearance and structure of that first described.
Immediately beneath the layer of epithelium is the
surface of the naked villus, or papilla, and this is
formed by a structureless basement membrane similar
to that already noticed upon the surface of the papil-
lary layer of the true skin.

Beneath this simple membrane is a close network of
capillary vessels formiDg a sort of hollow bulb which
encloses the remainder of the villus (PL XXVI. fig.
VIII.) ; this capillary plexus seems to communicate
more freely with the venous than with the arterial sys-
tem, for it is much easier to fill -it with fine injection
from the venaportce than from the abdominal aorta.
In the centre of the villus is a large hollow canal (T<T o th

166 INTESTINAL MUCOUS MEMBKANE.

to Tsad of a line in diameter) ending by a blind and
somewhat bulbous extremity; this is the origin of a
lacteal vessel (PL XXVII. fig. VI. 2). The situation
of this solitary vessel in the centre of the villus,
compared with the position, on its surface, of the
capillary plexus, so rich in blood-vessels, should teach
us that the activity of its function as an absorbent is
subordinate to that of the elements by which it is
surrounded. The remainder of the villus consists of
a material faintly fibrillated rather than amorphous,
which encloses a number of oval nuclei, the meaning
of which is unknown (PL XXVI. fig. VII. 3).
Around the outer surface of the lacteal, non-striated
fibres of muscular tissue are sometimes found, running
parallel with the axis of the villus. We know nothing
of the connexion of the nervous system with the villi.
The glandular apparatus of the small intestine is
composed of clusters of follicles, tubular glands, and
ductless follicles.

Glands of Brun- Brunue^ s glands are clusters of follicles, situated
deeply in the mucous membrane, or rather in the sub-
mucous layer of connecting tissue. They are little
yellowish-white granules, averaging one-half a line in
diameter, and precisely similar in structure to the
salivary glands ; they are provided with a single
layer of polygonal epithelium, and they secrete an
alkaline fluid in which no organic element is disco-
verable (PL XXVI. fig. IX.). These glands are only
found in the duodenum.

Glands of Lieber- ^he tubular glands, or follicles of Lielerlvuhn,
placed side by side like quills in a bundle, constitute
a secretory apparatus which occupies the whole

INTESTINAL MUCOUS MEMBRANE. 167

extent of the small intestine. On examining the sur-
face of a piece of mucous membrane under water,
with a low magnifying power, we recognise a great
number of minute holes, which are nothing more than
the orifices of these glands (PL XXVI. fig. II. 4 ; fig.
III. 2 ; fig. XII. 3). Their structure has been already
studied.

The ductless follicles, with the structure of which Ductless glands
we are already familiar, are either solitary or aggre-
gated in groups, and in either case are imbedded in
the sub-mucous tissue. As solitary glands, they are
scattered throughout the whole extent of the mucous
coat of the jejunum and ileum. It is only in excep-
tional cases that they are found in the duodenum.
When collected in groups they constitute the essen-
tial element of the patches of Peyer. These latter,
very variable in number, are usually seated in the
ileum and lower half of \\\e jejunum y sometimes, but
very rarely, they are found higher up, and even in
the duodenum. They are oval in shape, with their
Long diameters parallel with the axis of the intestinal
canal, and are seated opposite to the attachment of
the mesentery. The surface of a patch of Peyer is
studded with villi, and also with the minute orifices
of Lieberkuhn's follicles, as elsewhere on the surface
of the intestinal mucous membrane ; but besides these
it presents a number of larger depressions (one-half a
line in measurement), at the bottom of each of which
is a little prominence which corresponds to the posi-
tion of a ductless gland. These are perfectly blind
depressions, situated just over the glands, and this
relation between the two has given rise to the false

168 INTESTINAL MUCOUS MEMBKANE,

impression that these glands possess outlets. The
solitary glands, instead of underlying a depression, on
the contrary cause a slight projection of the membrane
which covers them, which, with this exception, pre-
sents the same appearance as elsewhere (PL XXVI.
fig. XII. 1).
MUCOUS mem- The mucous membrane of the large intestine is

brane of large in- ....

smooth and destitute of villi, and in this respect
resembles that of the stomach. Its glandular appa-
ratus comprises follicles . of Lieberkuhn and solitary
glands, identical with those of the small intestine,
only it is to be noticed that its solitary glands corres-
pond in situation always with a depression on the
surface of the membrane, as we have seen in the
patches of Peyer (PL XXVI. fig. XV.). Its vessels
present the same appearance and distribution as those
of the stomach ; in relation to its nerves nothing pre-
cisely is known.

The intestinal mucous membrane of the abdomen
is connected to the muscular coat of the canal by a
rather lax stratum of connecting tissue (sub-mucous
layer, fibrous coat, nervous coat) in which are im-
bedded the glands of Brunner, the ductless follicles —
solitary and aggregated, and the sub-mucous network
of blood-vessels.

The development of the glands of the intestine
takes place by means of minute granulations which
spring from its epithelial layer, and in this respect
presents a close analogy with the mode of develop-
ment of the glands of the skin.

The mode in which the epithelium of the intestine
is reproduced is unknown at the present time ; it is

*

INTESTINAL MUCOUS MEMBRANE. 169

probably accomplished by endogenous vegetation and
subsequent cleavage of its cells; the presence of
nuclei in a large proportion of these elements renders
it probable that the process is thus effected.

CHAPTER X.
Organs of Sense.

SECT. I. THE EYE. — The apparatus of vision com-
prises the globe of the eye, or the organ of sight pro-
perly so called ; its organ of protection, the eyelids ;
and its motor and lachrymal apparatus. As the two
latter present no features of special histological
interest, we shall omit their consideration.
Eyelids The several layers of tissue which enter into the
composition of the eyelids, proceeding from without
inwards, are : the skin, the orbicular muscle, the
fibrous stratum, and finally, the mucous membrane.

The skin is exceedingly delicate, but otherwise it
presents the same structure as elsewhere. Situated
deeply in its substance, and near the free edges of the
eyelids, we find the hair-follicles of the cilia or eye-
lashes, surrounded by their sebaceous glands (PL
XXVII. fig. V.). The orbicular muscle of the eye-
lids belongs to the class of striped muscles (PL
XXVII. fig. II.). The fibrous stratum, very thin at
the bases of the eyelids, becomes more dense towards
their free edges, where it forms the tarsal cartilages.
These are composed of connecting tissue very much
condensed, and studded with plaematic cells. We
search in vain in this stratum of fibrous tissue for car-
tilage cells, or at least, they are so rarely encountered
that they cannot be regarded as constituting one of

OKGATCS OF SENSE.

Ill

its normal elements. "We must give up the idea
therefore that these dense laminae consist of fibro-
cartilage, for they have only its appearance, without
possessing its structure. On their deep surfaces there
are from twenty to thirty parallel grooves, which
accommodate the Meibomian glands (PL XXVII.

%. in.).

The mucous membrane, or conjunctiva, consists of
quite a dense layer of connecting tissue, the ocular
surface of which is studded with numerous papillae
analogous to those of the skin ; its epithelium, which
is stratified, resembles that of the skin and mucous
membrane of the mouth (Pi. XXVIII. fig. II. 5).
This membrane, as is well known, is reflected from
the eyelids upon the globe of the eye, to which it
becomes intimately attached ; tracing it here to the
circumference of the cornea, it is to be remarked that
its deep layer becomes gradually thinner, and ceases
suddenly by becoming inserted into the amorphous
border which surrounds the anterior margin of the
cornea (PL XXVIII. fig. II. 4), whilst its epithelial
layer continues its course and covers the whole ante-
rior surface of the cornea (fig. I. 7 ; fig. II. 5). The
vessels and nerves of the cornea present no peculia-
rities worthy of note.

Globe of the Eye. — The first proper coat of the eye-
ball is formed posteriorly by the scierotica, and in
front, by the cornea. The scierotica is an exceeding-
ly dense membrane, thicker anteriorly and posteriorly
than around the centre of the eye-ball, and consisting
of a close tissue of connective and elastic fibres. An-
teriorly this membrane adheres very intimately to

172 OKGANS OF SENSE.

the conjunctiva, which is distinguishable from it by
the greater looseness of its texture, and by the larger
number of plasmatic cells which it contains (PL
XXVIII. fig. II.). Its deep surface is closely attached
to the dioroid membrane only at its anterior limits,
where it gives insertion to the ciliary muscle (fig.
IV. 1). The canal of Schlemm is also found along
the line which limits the sclerotica in front, forming
a tunnel near the deep surface of the membrane (fig.
IV. 2).

The cornea is composed of an amorphous funda-
mental substance, which contains a great quantity of
plasmatic cells (fig. I. 2 ; fig. III. 2). These are dis-
posed very regularly in concentric lines running
parallel with the two surfaces of the cornea. When
very dilute acetic acid is applied to prepared speci-
mens of the cornea, the stellate shape of these cells,
and the numerous anastomoses between their prolon-
gations, are rendered perfectly visible, and their
appearance recalls vividly the structure of bone.
But if the acid should be too much concentrated the
prolongations of the cells become pale, and their
bodies alone remain visible (PL II. fig. V.). The
front surface of the cornea is limited by a thin edge
which, in a section, forms an amorphous border from
aloth to aioth of a line in thickness, the anterior mar-
gin being in contact with the epithelium of the con-
junctiva (PL XXVIII. fig. II. 3). Its posterior sur-
face also forms an amorphous border, of the same
thickness as the latter ; it is continuous, by means of
fibrous tissue, with the anterior margin of the scle-
rotica and the ciliary muscle (fig. III. 4 ; fig. IV.).

OEGANS OF SENSE. 173

It is invested by a single layer of pavement cells,
which is reflected upon the anterior surface of the
iris, and ceases at the margin of the ptfpil (membrane
of Demoins, of Descemet, fig. III. 4, 5).

There is no distinct line of demarcation, as inspec-
tion by the unassisted eye would lead us to suppose,
between the cornea and sclerotica. The two mem-
branes blend insensibly with each other (fig. I. 3).
The fibres of the sclerotica become rarified as they
approximate the corneal margin, and they can be
clearly seen to be continuous with the branches of its
plasmatic cells (fig. II. 1, 2).

The sclerotica has but few vessels,- and hardly any vessels and

' J J nerves.

nerves. There are no blood-vessels in the cornea;
its network of plasmatic cells affords ample circulation
for the nutritive fluid. Its nerves are very numerous,
and form a rich web of filaments which are found
chiefly near its anterior surface (Kolliker) ; according
to some authorities they terminate by free extre-
mities.

The second tunic of the eye-ball is formed poste-
riorly by the choroid, and in front by the iris. The
choroid coat lines the internal surface of the sclero-
tica, very accurately, and is continuous in part with
the iris, without any line of demarcation (PL XXVIII.
fig. I. 11, 12). It is loosely .connected by its external
surface to the sclerotica, by means of the ciliary ves-
sels and nerves, and an occasional very delicate fasci-
culus of fibrous tissue ; its brownish-black color is
explained by the presence of a layer of irregularly
branching cells filled with pigment granules (PL II.
fig. II. 1, 2, 3). Its internal surface is likewise covered

174 OEGANS OF SENSE.

by a layer of pigment cells, but these are regular
polygons, more numerous, and containing a larger
quantity of pigment, than those last mentioned (PL
II. fig. I.) ; this layer has no connexion with the
retina, with which it is in contact. Between these
two layers of pigment cells is the proper substance of
the choroid membrane.

cmary muscles. The greyish thickened ring of tissue which forms
the limit, anteriorly, of the choroid, and by which it
is firmly united to the sclerotica, is muscular in its
nature, and constitutes the principal bulk, or body, of
the ciliary muscle ; it is also described as the ciliary
circle or ring, ciliary ligament, and ciliary ganglion.
On its surface it appears to consist of non-striated
muscular fibres, parallel in their direction with the
antero-posterior axis of the globe of the eye. Ante-
riorly it grows thin (jVd of a line in thickness), and
is inserted, at first, into the inferior wall of the canal
of Schlemm, and, a little farther on, into the posterior
extremity of a fasciculus of fibres which is continuous
with the amorphous border of the cornea, and adhe-
rent also to the circumference of the iris, called the
pectiniform ligament (PL XXVIII. fig. IV. 3). The
deeper portions of the ciliary muscle, which are in
relation with the ciliary processes, consist of inter-
laced muscular fibres; at. least this is the inference to
be drawn from the variable aspect presented by the
muscular nuclei of the part in a section (fig. IV. 5, 6).
Posteriorly, the muscle gives off longitudinal fasciculi
which extend as far as the middle of the choroid, and
anteriorly, it presents similar fasciculi of fibres which
penetrate the iris, and converge towards the pupil.

ORGANS OF SENSE. 175

The ciliary vessels which traverse the muscle become
intimately amalgamated, so to speak, with its sub-
stance, and thus constitute an erectile apparatus
(Kouget). The posterior half of the choroid is com-
posed of vessels united together by very delicate con-
necting tissue, which contains some plasmatic cells.

Each of the surfaces of the iris is covered by a
simple layer of epithelium. That upon its anterior
aspect has been already examined (fig. III. 5) ; the
epithelium upon its posterior surface (uvea) is com-
posed of polygonal pigment cells similar to those of
the choroid. In addition to the blood-vessels con-
tained in the iris, we find also, in the substance of
this membrane, a ring of muscular fibres surrounding
the pupil and connected, by its circumference with
the converging fibres of the ciliary muscle, and finally
a web of connecting tissue full of plasmatic cells. In
most eyes, but especially in those of dark color, the
majority of these cells contain pigment granules.

The nerves of the choroid coat and iris (ciliary
nerves) are very numerous, and seem intended for
the supply of the muscular apparatus belonging to
these membranes.

The retina, which constitutes the third coat of the
eye-ball, is coextensive with the choroid coat, beneath
which it lies. At the entrance of the optic nerve it
is thicker than elsewhere ; in fact a slight prominence
is perceptible at this point, which has been designated
as the papilla of the retina. At the posterior extre-
mity of the antero-posterior axis of the globe, and
consequently to the outer side of the pupil, there is,
upon the surface of the retina, an elongated depres-

176 OEGAJTS OF SENSE.

sion of a light yellowish color — the yellow spot of
Scemmering. As we trace it forwards, the retina grows
thinner, and its anterior border corresponds with the
outer circumference of the iris ; its nervous matter,
however, can be traced no farther than the com-
mencement of the ciliary processes, where it ter-
minates abruptly, by a serrated margin (or a serrata).

The researches of H. Muller* demonstrate the
structure of the retina to be as follows :

Its outer layer is made up of little " club-shaped
rods" arranged closely side by side so as to form an
uninterrupted lamina — the membrana Jacolri. Their
direction is perpendicular to the surface of the retina,
and their shape, as their name indicates, is cylindri-
cal; but some of them enlarge at their outer extremi-
ties, so as to assume a conical form. These latter are
fewer in number than the club-shaped bodies first
mentioned, and are quite uniform in their distribu-
tion, with this exception, that they alone constitute
the whole thickness of Jacob's membrane where it
passes over the yellow spot of Soemmering. The
internal extremities of these club-shaped bodies taper
off, and each one of them, becomes continuous with a
fibre (fibre of Muller), which traverses the whole
thickness of the retina. In its course this fibre pre-
sents three distinct enlargements : the first is situated
at its outer extremity, just where it is joined by the
corresponding club-shaped body; the second at its
middle, and the third at its internal extremity. The
first corresponds to the external granular layer, which

* Professor, or Lecturer, on Anatomy in the University of "Wurz-
burg, Bavaria. — (Ed.)

OEGANS OF SENSE.

is made up entirely by these external enlargements
or granules, the second to the internal granular layer,
and the third series of enlargements is intimately
mingled with the fibres of the optic nerve, and with
them constitutes the fibrous stratum of the retina.
The external and middle enlargement of the fibres of
Miiller are composed of cells ; the internal enlarge-
ment consists of a homogeneous mass, with a depres-
sion upon its inner surface, by which it rests upon a
very delicate structureless lamella (2 oVo-th of a line in
thickness) which constitutes the limitary membrane
of the retina within.

On the internal surface of the internal granular
layer, and consequently between it and the fibrous
layer, is a stratum composed of multipolar or caudate
nerve cells (nervous layer) ; and the fibrous layer, as
already stated, consists of an expansion of the fibres
of the optic nerve.* These latter, as they run for-
wards towards the anterior border of the retina,
curve outwards to unite themselves with the pro-
longations of the nerve-cells, which, in their turn,
send an anastomosing fibre to each of the middle
enlargements on the fibres of Miiller. In the centre
of the yellow spot of Scenamering we find nothing but
nerve-cells within the meinbrana Jacobi.

In reviewing what has just been said in relation to
the arrangement of the diverse elements composing
the retina, it is obvious that this membrane presents

* The superposition of a layer of nerve cells upon a layer of nerve
fibres recalls the structure of the convolutions of the cerebrum and cere-
bellum. The capillary layer of the retina formed by the branches of the
arteria centralis retinae occupies the stratum of nerve cells.— (Ed.) j

178 OKGAtfS OF SENSE.

\

a series of distinct strata, which, proceeding from
without inwards, are as follows : 1st, the membrana
Jacobi, composed of club-shaped bodies; 2d, the
external granular layer, corresponding with the exter-
nal enlargements upon the fibres of Muller ; 3d, the
internal granular layer, corresponding to the middle
enlargements of the same fibres ; 4th, the nervous
layer, consisting of nerve cells; 5th, the fibrous
layer formed by the fibres of the optic nerve ; 6th,
and last, the limitary membrane.*
Arteria centraiis The central artery of the retina traverses the

retinae. *

papilla of the optic nerve, and is distributed in the
more internal layers of the retina. It forms a vas-
cular circle around the " yellow spot," and terminates,
by a second circular plexus, at the ora serrata. The
vein has the same distribution as the artery.
vitreous ha- Interior of the eye. — Vitreous humor. — The vitre-
ous humor of the eye occupies the cavity of the
retina, and is adherent to that membrane only in
the interval between the ora serrata and its anterior
margin ; in front it presents a cup-shaped depression
which receives the crystalline lens. Its envelope, the
hyaloid membrane, is very delicate, structureless, and
transparent; interiorly it is somewhat thicker than
elsewhere, and gives off two laminae, which invest,
respectively, the anterior and posterior surfaces of

* To obviate any obscurity in the text, arising from the very compen-
dious and precise style of the author, who always assumes that his reader
is a good descriptive anatomist and possesses alfair knowledge of general
structure, it would be well for the student to refer to the admirable work
of TODD and BOWMAN, " The Physiological Anatomy and Physiology of
Man,'"1 where fuller details, up to the period of its publication, will be
found. Vide Vol. IT., p. 27. London, 1856.—

mor.

OEGANS OF SENSE. 1*79

the crystalline lens, enclosing, at their angle of sepa-
ration, the canal of Petit, which surrounds the peri-
pheral border of the lens. The vitreous humor,
which is adherent to the internal face of this mem-
brane, is an amorphous hyaline substance which, in
the fo3tus, contains oxal nuclei and stellate cells ; but
in the adult these cellular elements are no longer
visible, and nothing remains beyond an amorphous
jelly-like mass.

The vitreous humor contains neither nerves nor
vessels. During foetal life its antero-posterior axis is
occupied by a tubular canal, containing a delicate
branch of the arteria centralis retinae sent forward to
the capsule of the lens ; after birth this canal becomes
obliterated.

The crystalline lens is a solid body, surrounded by crystalline ie
a membranous envelope. This containing membrane,
or capsule, of the lens is highly transparent and
entirely destitute of structure, resembling a delicate
lamina of the purest glass. It possesses great elasti-
city, but is readily torn ; on the anterior surface of
the lens its thickness is ri <rth of a line, and posteriorly
but T loth of a line. It resists perfectly the action of
boiling water, a solution of potassa, and the acids.
Its external surface is continuous posteriorly with the
hyaloid membrane of the vitreous humor ; anteriorly
it is free ; its internal surface is lined by a layer of
exceedingly delicate polygonal cells, which, liquefy-
ing shortly after death, form the liquid of Morgagni.*

* John Baptist Morgagni, the celebrated professor of anatomy at the
University of Bologna in Italy, and the preceptor of Scarpa, was born in
1682, and died in 1771.— (Ed.)

180 OEGANS OF SENSE.

This liquid has been supposed by "some2 to be derived
from a different source, viz. from a layer of globules
underlying the capsular epithelium, and distinguish-
able from it by their spherical shape, and by the
absence of nuclei in their contents (Warlomont).*

Beneath the epithelium of -the capsule, and the
globules of Morgagni, is the proper substance of the
crystalline lens, which consists of a central portion or
nucleus, and a peripheral or cortical portion. The
central nucleus is a little star-shaped mass, made up
entirely of very minute granules. The cortical por-
tion of the lens is composed of concentric lamellae,
and each lamella, of hexagonal prisms in close appo-
sition and flattened antero-posteriorly. These pris-
matic bodies are more numerous and delicate in their
proportions as we trace them more deeply into the
substance of the lens, and they adhere to each other
more closely by their edges than by their faces, which
explains, on one hand, why the substance of the lens
increases in density from its surface towards its cen-
tre, and on the other, why it disintegrates more
readily into laminae than into fibres. They consist
of a very delicate and structureless containing mem-
brane, with contents of a semi-fluid consistence,
equally destitute of structure, and albuminous in
their nature ; their edges are serrated, and the inter-
digitation of these serrations adds to the solidity of
their union.

Each prism, taking its origin from one of the pro-
longations of the central nucleus of the 'lens, passes

* Dr. E. Warlomont, chief editor of the * Annales d'Oculistique,' pub-
lished at Brussels, Belgium.— (Ed.}

ORGANS OF SENSE. 181

outwards towards its border wliicli it doubles, and
returns upon its opposite surface, where it terminates ;
its two faces do not give the same measurement in
length, which is explained by the fact that its extre-
mities are both beveled, and in opposite directions.

Neither the crystalline lens nor its capsule possesses
vessels or nerves, at least in the" adult. During foetal
life, the branch of the central artery of the retina,
which traverses the tubular canal in the vitreous
humor, furnishes branches which encircle the capsule,
and afterwards lose themselves in the pupillary mem-
brane, where they anastomose with the^ciliary arte-
ries.

The histological development of the eye follows Development.
the universal law; all of its component parts take
their origin from embryonic cells which take on
determinate metamorphoses in order to form each of
its individual tissues. Each of the prismatic fibres of
the crystalline lens is the result, apparently, of the
.elongation of a single cell, and not of the fusion
together of an indefinite number of cells.

SECT. II. THE EAE. — The skeleton of the external External ear.
ear is osseous in the deep portion of the meatus, but
elsewhere it is fibro-cartilaginous. The integument
by which it is invested contains glands of different
kinds in its several regions. In the concha we find
a great many sebaceous glands ; we encounter these
organs again in the external meatus, but here they
are in company with ceruminous glands ; finally,
sudoriparous glands are found everywhere, but prin-
cipally upon the internal surface of the concha.

There is nothing especially worthy of notice in the

182 OKGANS OF SENSE.

mode of distribution of the vessels and nerves of the
external ear.

Middle ear. The mucous membrane of the middle ear is very
thin ; in the Eustachian tube only it is somewhat
thicker. From the bony walls of the cavity it is
reflected upon the inner surface of the membrana
tympani to which it is closely adherent, and upon
the muscles and ossicula, for which it forms a perios-
teal investment. Its epithelium is everywhere cili-
ated, except upon the internal surface of the mem-
l)rana tympani, where, according to Kolliker, it' forms
a simple tessellated layer.

The membrana tympani consists of a fibrous ex-
pansion made up of radiating and circular fasciculi,
and inserted by its circumference into the groove of
the temporal bone like a watch crystal into its case ;
we are familiar with the relation of its internal sur-
face to the mucous lining of the tympanum ; its ex-
ternal surface receives a layer of epidermis from the
walls of the meatus auditorius externus.

The blood-vessels of the middle ear are numerous ;
they form a rich network in the substance of its mu-
cous membrane, and in the membrana tympani. The
lymphatic vessels probably accompany its arteries
and veins.

The nerves of the middle ear come from the fifth,
seventh, and ninth* pairs of cranial nerves; their
mode of termination is unknown ; Kolliker describes
masses of ganglionic cells as existing in the substance
of the tympanic nerve.
internal ear. The bony walls of the semicircular canals, vesti-

* According to the classification of Scemmering.

ORGANS OF SENSE. 183

bula, and cochlea, are covered by a layer of connect-
ing tissue, with pavement epithelium upon its surface.

The walls of the membranous labyrinth consist of
a lamina of extremely delicate connecting tissue, the
fibrillated character of which is with difficulty recog-
nizable, but it contains a large quantity of oval (fibro-
plastic) nuclei, and is covered by a very thin amor-
phous layer, on the internal surface of which we find
a stratum of pavement epithelium.

The white specks which are observed upon the
inner surfaces of the sacculus communis and sacculus
proprius (otoliths, otoconites) are composed of cal-
careous granules, which sometimes present a crystal-
line aspect. Both outside and inside of the tubes
and cavities forming the membranous labyrinth, is a
pellucid fluid (pe.rilymph, endolymph), the chemical
nature of which is not as yet clearly determined.

The nerves which reach the ampullae of the semi-
circular canals and the sacculi appear to terminate
by free extremities, after having undergone frequent
division and subdivision ; beyond these localities it
has been found impossible to trace them.

The vessels form a close network which principally
occupies the fibrous coat of the semicircular canals,
and the two vestibular sacculi.

The labors of Corti* and Kolliker tend to prove
that the nervous fibres of the cochlea terminate by
free extremities in the substance of the membranous
portion of the lamina spiralis. These authors have
also demonstrated that there are cellular enlarge-

* Corti wrote on the structure of the retina in Miiller's Archiv, 1850,
p. 274.— (Ed.}

184 ORGANS OF SENSE.

ments in the course of these fibres, analogous to those
of the nerve fibres of the retina.

The capillary network formed by the blood-vessels
of the cochlea is equally rich with that of the vesti-
bule and semicircular canals.

SECT. III. OLFACTORY Mucous MEMBRANE. — The
mucous lining of the nasal cavities is thick, soft,
tomentose, and reddish in color, especially in its in-
ferior two-thirds. Its texture is composed of inter-
woven fibres — connective and elastic — but the pro-
portion of the latter is small ; it contains likewise
an abundance of plasmatic cells. Its deeper surface is
intimately adherent to the periosteum, and contains
a great number of mucous follicles, in clusters. Its
free surface is covered by stratified epithelium, and
its superficial layer of conical cells is provided with
cilia. Its vessels are exceedingly numerous, and form
a web of unusual thickness. The nervous filaments
furnished by the fifth pair are distributed throughout
its whole extent, and present nothing worthy of note,
but those which come from the olfactory nerve are
distributed only to the mucous membrane covering
the superior turbinated bone, and the upper third of
the septum between the nostrils; moreover, they
apparently end by free extremities. According to
some authors they present globular enlargements at
their extremities, similar to those of the retina.

THE END.

EXPLANATION OF THE PLATES.

PLATE I.

VARIOUS FORMS OF CELLS.

FIG. L* Blood of the adult. — 1, Red globules, front view;
2, same in profile ; 3, same altered ; 4, white globule.

FIG. II. Epithelial cells of the bladder.— 1, Cell with
granular contents ; 2, its nucleus, also containing granules, one
of which (3) larger than the rest forms the nucleolus ; 4, cell
with two nuclei ; 5, group of cells retaining their original rela-
tion to each other.

FIG. III. Hepatic cells. — They are polygonal in shape, and
scattered amongst their granular contents free fat is to be seen
in the form of brilliant little pearl-like globules.

FIG. IV. Epidermic cells. — 1, Cells of the rete mucosum /
2, cells of the middle stratum ; 3, cells of the surface, in the
shape of granular scales without nuclei ; 4, other cells from the
superficial layer, detached and swelled by very dilute acid.

FIG. V. Adipose cells from beneath the integument. Their
fluid contents are so transparent that the outlines of the. cells
alone are visible.

! * "(i't • ••' ': •' •'• ' •' ' • Fil'J-J ii-'». >'•!/<"' iI>'G

FIG. VI. Epithelial cells from the small intestine, exa-
mined thirty hours after death.

FIG. VII. Epithelial cells of the trachea.— 1, Body of

* All of the figures contained in the following plates, unless otherwise
stated, were drawn from preparations taken from the adult male subject,
and magnified 400 diameters by a Nachet's microscope.

12

186 EXPLANATION OF THE PLATES.

a ciliated cell with its nucleus ; 2, outline of the layer of amor-
phous material at its base ; 3, cilia ; 4, deeper cells of the same
layer ; 5, normal relation of these cells. The ciliated cells con-
stitute the free surface of the epithelial membrane.

PLATE H.

CELLS, continued; CONNECTING TISSUE.

FIG. I. Pigment cells from the deep surface of the choroid.
They are very regular polygons filled with granules of pigment,

except in the centre, where the bright spot corresponds with

•• .1 .•:;.-:
the nucleus.

FIG. II. Branching pigment cells from the outer surface
of the choroid; 1, cell; 2, nucleus; 3, anastomosing branch;
4, nucleus of oval or fusiform cells, scattered amongst very pale
connective fibres.

FIG. III. Fusiform cells (fibro-plastic).

FIG. IV. Adipose cells containing acicular crystals of mar-
garine in tufts, or solitary.

FIG. V. Plasmatic cells, or nuclei of the cornea. Their
anastomoses are perceptible.

FIG. VI. Cells from a cancer of the heart, in which endo-
genous multiplication of the nuclei, by cleavage, is seen.

FIG. VII. Another type of cancer cell, showing process
of endogenous multiplication of nuclei by cleavage. — 1, Nucleus
in process of cleavage ; 2, separate nuclei.

FIG. VIII. Multiplication of cells. — 1, Process of endo-
genous formation as observed in fo3tal marrow ; 2, multiplica-
tion by cleavage in the cartilage cell.

FIG. IX. Superficial fascia of the forearm. It is com-
posed of fasciculi of connective fibres : 1, wavy and crossing in
all directions so as to form an interlacement varying in density.
Amongst these fasciculi a number of elastic fibres (2) are to be
seen.

EXPLANATION OF THE PLATES.

PLATE HI.

CONNECTING TISSUE, continued.

FIG. I. Connective fibres in wavy and parallel bundles.
On the right of the preparation they have been slightly teased
out (tendo Achillis).

FIG. II. Longitudinal section of tendon (tendo Achillis),
treated by acetic acid. The fasciculi of connective fibres have
grown pale and disappeared. 1, Plasmatic cells in longitudinal
rows between the fasciculi of fibres ; 2, anastomoses between
them (from the fetus).

FIG. III. Longitudinal section of tendon (Peronceus
longus). — 1, Bundles of connective fibres ; 2, plasmatic cells.

FIG. IV. Transverse section of the tendon of the
Peronseus longus. — 1, Granular basis indicating the section of
the connective fibres; 2, irregular wavy lines marking the
intervals between the fasciculi ; 3, plasmatic cells.

FIG. V. Elastic fibres from a yellow ligament. — 1, The
fibres in their normal relation ; 2, separate fibres.

PLATE IV.

CONNECTING TISSUE, continued.

FIG. I. Longitudinal section of the superior extremity
of the tendo Achillis (of an old man). — 1, Fasciculus of con-
nective fibres ; 2, plasmatic cells in parallel rows.

FIG. II. Similar section of inferior extremity of same
tendon. 1, Connective fibres, slightly wavy ; 2, cartilage cells
which have taken their origin from plasmatic cells.

The following figures show the different modes of develop-
ment of connective fibres.

FIG. III. — 1, Embryonic cell; 2, same cell elongated, its
contents already divided into fibrilla? ; 3, two cells united at
their extremities, about to form a bundle of connective fibres.

188 EXPLANATION OF THE PLATES.

FIG. IV. Fibrous tumor of the dura-mater. — 1, Free
fusiform cells ; 2, fasciculi of same cells united at their extremi-
ties ; 3, fasciculi of fibres formed by the elongation of the same
cells and the disappearance of their nuclei. In this case each
row of cells forms but one solitary fibre.

FIG. V. Fibrous tumor of the uterus in which the for-
mation of a fibre by metamorphosis of a nucleus can be traced.
1, Finely granular substance ; 2, nuclei.

FIG. YI. Another portion of same tumor. The nuclei
somewhat elongated in shape already show a disposition to
assume the form of fibres.

FIG. VII. Same tumor. The nuclei are still more elon-
gated ; at some points they can be seen with their extremities
united together so as to form fibres.

PLATE V.

CAETILAGE AND BONE.

FIG. I. Section involving the centre of a costal carti-
lage. 1, Fundamental substance, slightly granular and trans-
parent ; 2, cartilaginous capsule ; 3, primordial cell, or utricu-
lus ; 4, nucleus — made up of fatty granules ; 5, capsule contain-
ing four cells, two of which have no nuclei.

FIG. II. Costal cartilage with its perichondrium, taken
from a subject eighteen years of age. 1, Perichondrium formed
by a dense interlacement of connective and elastic fibres, and
studded with plasmatic cells. 2, There is no clear and distinct
line of demarcation between the deepest portion of the peri-
chondrium and the substance of the cartilage ; it is also almost
impossible to make out a distinct difference in the character of
the superficial cells of the cartilage and the plasmatic cells of
the deepest layer of the perichondrium.

FIG. III. Fibro-cartilage from the ear. 1, Fibrous fun-
damental substance or basis ; 2, capsule inclosing these cells.

FIG. IV. Transverse section of the ulna. In the midst

EXPLANATION OF THE PLATES. 189

of the amorphous fundamental substance of the line are to be
seen: 1, the stellate or branching bone-cells (lacunae); their
branches or prolongations (2) in the shape of canaliculi, anasto-
mosing with each other so as to form a network by which a
communication is established between the corpuscles themselves,
and also with the Haversian canals 3, or with the interior cavi-
ties of the bone.

FIG. V. Same section seen with a magnifying power of
eighty diameters. The bone-corpuscles (lacunae), in the shape
of minute elongated black spots, are seen to be grouped in con-
centric circles around the Haversian canals (1).

,' rl ; (L'o

PLATE VI.

BONE, continued.

FIG. I. Longitudinal section of the shaft of the femur

(80 diameters). 1, Longitudinal Haversian canals; 2, trans-
verse anastomotic canal ; 3, confluence of several canals.

FIG. II. Longitudinal section of the condyles of the
femur (in a newly born infant. Magnifying power of 180
diameters). 1, Line of junction of the cartilage with the bone.
Above this line the cells of the cartilage are seen grouped in
parallel rows. Their nuclei (2) deeply shaded and presenting
jagged edges. Below this same line the cartilage is seen, infil-
trated with earthy salts and in process of ossification.

FIG. III. Section of cartilage taken from same femur y^th
of an inch beyond the newly ossified portion. 1, Fundamental
substance, entirely transparent ; 2, limit of the capsule ; 3, limit
of the cell ; 4, nucleus assuming a branching character.

FIG. IV. Formation of marrow and of medullary cavi-
ties in newly ossified bone (from same femur). 1, Fundamen-
tal substance infiltrated at certain points with free fat 2 ; 3,
capsule of cartilage cells ; 4, a parent cell full of young cells ;
5, unbroken partition between two capsules ; 6, cavity resulting
from the fusion of several cells ; it contains young cells (cells of

190 EXPLANATION OF THE PLATES.

foetal marrow) and a great deal of free fat ; 7, angle correspond-
ing to position of a partition which has disappeared.

FIG. V. Ossification "by periosteum (femur of a. newly
born infant). 1, Completely formed bone; 2, deepest portion
of the periosteum, in which some connective fibres and a large
number of plasmatic cells can be still distinguished ; of the lat-
ter, those nearest the bone begin to resemble bone corpuscles
in shape ; 3, superficial portion of periosteum, show few plas-
matic cells and numerous connective fibres ; 4, plasmatic cells.

PLATE VII.
BONE, continued ; TEETH.

FIG. I. Ossification of the os frontis at the margin of the
anterior fontanelle (from an infant four months old) ; 1, recently
formed bone ; 2, deepest portion of the periosteum ; 3, super-
ficial portion of the periosteum. The plasmatic cells, in this
specimen, give off distinctly marked branches.

FIG. II. Ossification of cartilage, according to the most
generally received theory. — 1, Capsule and cells, unaltered;
first appearance of the corrugation of the cell-wall ; 3, corru-
gation more marked ; 4 and 5, corrugation still farther advanced
and completed, resulting in formation of a bone-corpuscle.

FIG. III. Transverse section of the canalieuli of the
ivory of a tooth. — 1, Canalieuli; 2, their anastoniotic
branches ; 3, canaliculi divided a little obliquely.

PLATE VIII.

TEETH, continued.

FIG. I. Incisor tooth of a child nine years old — magnified
thirteen diameters. — 1, Dental cavity ; 2, ivory ; 3, cementum
investing its root ; 4, enamel covering its crown.

EXPLANATION OF THE PLATES. 191

FIG. II. Ivory and cementum. — 1, Amorphous substance ;
canaliculi of the ivory, with their lateral anastomotic branches ;
3, dilatations in the course of the canaliculi ; 4, confluence of
several canaliculi ; 5, inter-globular spaces ; 6, cementum with
very large bone-corpuscles. Some of these latter communicate
with the cavities of the inter-globular spaces.

FIG. III. Transverse section of the crown of a large
molar tooth. — 1, Ivory, and terminations of its canaliculi ; some
of these canaliculi enlarge in diameter (2) and penetrate the
substance of the enamel ; 3, enamel, consisting of wavy and
parallel prisms ; they are seen in groups slightly diverging from
each other ; 4, lines of separation between the prisms.

FIG. IV. Transverse section of enamel. — 1, Prisms seen
in transverse section ; prisms divided a little obliquely. The
white lines are the intervals between the prisms.

PLATE IX.

MUSCLE.

FIG. I. Muscular coat of the stomach treated by acetic
acid. — 1, Finely granulated muscular fibre, with very pale out-
lines, often indistinctly visible ; 2, nuclei ; 3, lines of separation
between the muscular fibres ; 4, elastic fibres.

FIG. II. Same coat in transverse section, and hardened by
moderate boiling. — 1, Muscular fibres; 2, nuclei; 3, line of
separation between the fibres; 4, outline of a fasciculus of mus-
cular fibres.

FIG. III. Dartos treated by acetic acid. — 1, Very pale finely
granulated substance, corresponding to the muscular fibres ; 2,
elongated nuclei.

FIG. IV. Embryonic fibres of striped muscle. — 1, Two
varicose fibres formed by the union of embryonic cells; 2,
nuclei of these cells ; 3, two other fibres, a little longer and less
varicose ; 4, division of the contents of the cells into granules
and transverse striae ; 5, fibres showing the commencement of

192 EXPLANATION OF THE PLATES.

striation in the direction of their length ; 6, another fibre, in
which this appearance is more strongly marked.

FIG. V. G-emellus muscle hardened by cooking (from a
newly born infant). — 1, Myolemma ; 2, its contents, showing
transverse striae ; 3, nucleus ; 4, a broken fibre, with its con-
tents divided into discs ; 5, a fibre in which the division of its
contents into discs is very well marked.

PLATE X.

MUSCLE, continued.

FIG. I. Antero-posterior section of the tongue (in a

newly-born infant). — 1, Muscular fasciculi seen in the direction
of their length; 2, same, in transverse section.

FIG. II. Different views of striped muscular fibre. —
1, A fibre, the contents of which are crushed in two places ; at
its left extremity its myolemma is very well seen, corrugated
and contracted upon itself; 2, a fibre with transverse striae,
showing a nucleus (3) ; 4, a fibre in which both longitudinal
and transverse stripes are visible ; 5, another fibre broken off at
its upper -extremity ; each fib rill a is seen to be composed of a
series of slightly flattened granules superimposed upon each
other. All of these muscular fibres were procured from the
perfectly fresh biceps muscle of a suicide.

FIG. III. Fibres of the heart. — 1, A common trunk giving
off several brandies ; 2, divisions of the trunk.

PLATE XI.

Distribution of the nerves as seen in the subcutaneous pec-
toral muscle of a frog. The parallel lines indicate the outlines
of the muscular fibres.

EXPLANATION OF THE PLATES. 193

PLATE XII.

ELEMENTS OP NERVE TISSUE.

FIG. I. Nerve fibres. — 1, Nerve fibres of the large variety ;
2, envelope of the fibres ; 3, its contents ; 4, another fibre
treated by chromic acid ; 5, envelope ; 6, medulla ; 7, axis
cylinder ; 8, fine nerve fibres with a single outline, taken from
the spinal marrow.

FIG. H. Fibres of Remak taken from a sympathetic gan:
glion from the lumbar region.

FIG. III. and IV. Connexion between nerve-fibres and
ganglionic cells (after Leydig).

FIG. Y. Connexion between nerve-fibres and cells of
the spinal marrow. 1, Central canal of the medulla spinalis ;
2, nerve-cells ; 3, superior prolongation ; 4, inferior prolonga-
tion ; 5, anterior root ; 6, posterior root ; 7, transverse pro-
longation forming the anterior commissure and establishing anas-
tomoses between the cells of the two halves of the spinal mar-
row (after Owsjauikow).

FIG. VI. Nerve-cells. — 1, Cells with one prolongation
(unipolar) from a dorsal ganglion of the sympathetic ; 2, ano-
ther cell from the ganglion of Gasser (on the fifth cranial
nerve) ; 3, mass of pigment.

PLATE XIII.

ELEMENTS OF NERVE TISSUE.

FIG. I. Nerve cells. — 1, Simple (apolar) cells from the grey
matter of the brain ; 2, multipolar cells from the grey matter
of the cerebellum ; 3, cell from the floor of the fourth ventricle ;
4, another cell from the grey matter of the cord in the cervical
region; 5, nucleus; 6, mass of pigment surrounding the
nucleus ; 7, two cells from the ganglion of Gasser ; one of them
has a nucleated envelope (8).

194 EXPLANATION OF THE PLATES.

FIG. II. Grey matter from the cerebellum.— 1, Apolar
cells ; 2, mass of nuclei grouped around the cells ; 3, fine nerve
fibres — varicose.

FIG. III. Superior cervical ganglion. — 1, Nerve cells
imbedded in a faintly fibrillated substance containing nuclei
similar to those represented on the cell at (8).

PLATE XIY.

TERMINATION OF NERVE-FIBKES. AKTEKIES.

FIG. L Nerve-fibre from the subcutaneous pectoral mus-
cle of the frog ; 1, muscular fibre ; 2, nerve fibre; 3, terminal
ramifications.

FIG. II. Pacinian corpuscle. — 1, Its pedicle ; 2, its cor-
tical substance divided into lamellae by concentric lines, on the
concave surface of which numerous little nuclei are seen pro-
jecting ; 3, its central cavity filled with finely granular matter,
and a considerable number of nuclei with pale outlines ; 4, the
nerve fibre which forms the axis of its pedicle, running into its
central cavity, where it ends in a slight enlargement.

FIG. III. Termination of a nerve fibre of the retina
(after H. Muller). — 1, Nerve-cells ; 2, fibres from the optic
nerve ; 3, another fibre on its way to rejoin the club-shaped
bodies of the external layer of the retina.

FIG. IV. Transverse section of the primitive carotid
artery of a child 15 years of age — magnified 120 diameters. —
1, Internal coat ; 2, middle coat ; 3, external coat.

FIG. V. The same section treated by acetic acid and exa-
mined with a magnifying power of 400 diameters. — 1, Internal
coat ; the transverse section of the elastic fibres of which it is
composed are visible ; 2, middle coat ; 3, nuclei of muscular
fibres ; there is a pale line (4) on each side of the nuclei, indi-
cating the limits of the muscular fibres ; 5, elastic fibres ; 6,
same, in transverse section.

FIG. VI. The same artery. — 1, Middle coat ; 2, external
coat, composed of elastic fibres, most of which run longitudi-

EXPLANATION OF THE PLATES. 195

nally, and which are more numerous and closer together towards
its internal limit. Between these elastic fibres are connective
fibres which grow pale and break down under the action of
acetic acid, leaving a hyaline mass (3).

FIG. VII. Middle coat of a branch of the artery occupying
the fissure of Sylvius ; it is composed entirely of muscular fibres,
no traces of elastic fibres being visible.

FIG. VIII. Four muscular fibres from the basilar artery.
The two on the right have been subjected to the action of acetic
acid, by which they are rendered pale, and their nuclei much
more distinct.

PLATE XV.

ARTERIES, continued.

FIG. I. Epithelial layer of the internal coat (from the
radial artery). — 1, Nucleus ; 2, internuclear substance composed
of cells the outlines of which are not visible.

FIG. II. Epithelial cells, isolated (from the radial artery).

FIG. III. Fenestrated layer. — 1, Amorphous material
through which the fibres of the subjacent coat are visible ; 2,
elastic fibres imbedded in the amorphous substance ; 3, openings
or fenestra, of various shapes and sizes ; 4, irregular line show-
ing where the layer has torn or ruptured ; 5, the subjacent layer
consisting of longitudinal elastic fibres (from the radial artery).

FIG. IV. Longitudinal section of the primitive carotid
artery of a young subject (15 years of age) ; 1-2, internal
coat ; 2-3, middle coat ; 4, muscular fibres of the middle coat ;
5, their nuclei ; 6, network of elastic fibres ; 7, transverse sec-
tion of these same fibres.

FIG. V. Same artery, dried like the preceding, and
treated by acetic acid. — 1, Line of junction of its middle and
external coats. The latter (2) consists of a web of elastic fibres,
which run mostly parallel with the axis of the vessel, and are
crossed by connective fibres ; these have been rendered invisible
by the acetic acid.

196 ^ EXPLANATION OF THE PLATES.

FIG. VI. A recent specimen of the external coat of an
artery simply spread out upon the glass. — 1, Elastic fibres ; 2,
fasciculi of connective fibres.

FIG. VII. A small artery of the brain, measuring J¥ th Of
a line in diameter, treated by very dilute acetic acid. — 1, Ex-
ternal coat consisting of connective fibres ; 2, transverse mus-
cular cells ; 3, their nuclei ; they form the middle coat. Beneath
this, oval nuclei can be distinguished (4) with their long dia-
meters in the direction of the axis of the vessel. They are
imbedded in a thin layer of amorphous substance, and constitute
the internal coat.

FIG. VIII. Two capillaries from the brain, the upper
measuring al^th and the lower 2^otn OI> a ^me *n diameter. —
1, Structureless wall; 2, nuclei contained in the thickness of
this wall ; 3, cavity of the vessel.

PLATE XVI.

VEINS.

FIG. I. Capillary, measuring T£¥ of a line in diameter ; 2,
minute vein, measuring ¥£^th ; their walls are formed by con-
nective fibres running lengthwise of the vessel and studded
with numerous plasmatic cells (3).

FIG. II. Transverse section of the femoral vein — first
dried and then treated by acetie acid. — 1-2, Internal coat; 2-3,
middle coat ; 3-4, external coat. In the internal coat some of
the elastic fibres, of which it is constituted, are seen in longi-
tudinal, and others in transverse section ; 5, strata of muscular
fibres very well characterized by their club-shaped nuclei (6),
the outlines of which are clear and distinct ; 7, other muscular
fibres, seen in transverse section, most of them having a nucleus
(8) ; 9, strata of elastic and connective fibres alternating with
the strata of muscular fibres. The external coat is similar to
that of the arteries.

FIG. III. Valve from the internal Saphoena vein. —

EXPLANATION OF THE PLATES. 197

1, Epithelium ; the oval nuclei of its cells only are visible, the
outlines of the cells themselves being too pale ; 2, subjacent
layer, formed exclusively of regularly undulating connective
fibres.

FIG. IV. Elastic sub-epithelial membrane from a small
mesenteric vein, treated by acetic acid. — 1, Web of elastic fibres ;

2, openings of different dimensions, giving this layer the same
appearance as the fenestrated coat of an artery ; 3, nuclei of its
muscular coat, seen by transmitted light.

FIG. Y. A mesenteric vein of yL-th of a line in diameter. —
1, Its external coat, made up of elastic fibres, connective fibres,
and plasmatic cells (2) ; 3, middle coat, entirely muscular ; 4,
the cells which form its muscular fibres in transverse section,
containing nuclei ; 5, nuclei of same cells, seen in the direction of
their length ; 6, elastic membrane of the internal coat, rendered
visible by the transparency of the specimen.

PLATE XVH.

VEINS. LYMPHATIC VESSELS. GLANDS COMPOSED OF CLUSTERED

FOLLICLES.

FIG. I. Longitudinal section of the femoral vein, dried
and then treated by dilute acetic acid. — 1, Internal coat — its
elastic fibres almost all running parallel with the axis of the
vessel ; 2, middle coat ; 3, longitudinal elastic fibres ; 4, trans-
verse elastic fibres ; 5, muscular fibres irregularly distributed ;
6, their nuclei ; *7, external coat, made up of mingled elastic
and connective fibres ; these latter, in consequence of the action
of acetic acid, present the appearance of a homogeneous gra-
nular mass (8).

FIG. II. Transverse section of a lymphatic vessel of
the thigh, treated by dilute acetic acid. Its internal coat seems
to be composed of but a single layer of epithelial cells. — 1,
Middle coat, formed entirely of muscular fibres, the nuclei of
which are very well seen (2) ; 3, elastic fibres — of which there

198 EXPLANATION OF THE PLATES.

are very few ; 4, external coat, made up of connective, elastic,
and muscular fibres ; the latter (5) run parallel with the axis of
the vessel.

FIG. III. A longitudinal section of the same lymphatic. —
1, Middle coat ; 2, muscular fibres seen in transverse section ;
3, nuclei ; 4, external coat ; 5, nuclei of muscular fibres encircling
the vessel.

FIG. IV. Recent specimen of a valve treated by acetic
acid. — 1, Nuclei of epithelial cells; 2, elastic fibres; 3, nuclei of
muscular fibres.

FIG. Y. Section of a lobe of the sub-lingual gland —
magnified 80 diameters. — 1, Excretory duct; 2, its radicles, one
of which belongs to each lobule ; 3, cavity of one of the coecal
pouches of which the gland is composed ; 4, connective tissue
surrounding its walls.

PLATE XVIII.

GLANDS COMPOSED OF CLUSTERED FOLLICLES.

FIG. I. Three co3cal pouches of the sub-lingual gland,
lined by thin epithelium. The nucleus (1) almost fills each of
the epithelial cells.

FIG. II. Sebaceous follicle from the scrotum. — 1, Cavity
of the follicle filled with cells ; 2, young cells containing nuclei,
and immediately in contact with the walls of the cavity; 3,
other cells, of greater age, in process of fatty transformation ;
4, excretory duct filled with minute globules of fat; 5, con-
nective fibres enveloping the follicle ; 6, epidermis.

FIG. III. Sebaceous gland from the external auditory
canal. — 1, Body of the gland presenting irregular pouched pro-
jections (2) ; 3, excretory duct.

FIG. IV. Cells from a sebaceous gland showing different
stages of fatty infiltration.

FIG. V. Epithelium from a Meibomian gland— 1,
Young cells ; 2, older cells, filled with oil globules.

EXPLANATION OF THE PLATES. 199

FIG. VI. Milk from the human female. — 1, Milk of the

first day ; 2, colostrum corpuscles ; 3, free oil globules ; 4, milk
on the sixteenth day after delivery — from the same woman.

PLATE XIX.

CLUSTERED GLANDS, Continued. TUBULAR GLANDS.

FIG. 1. Portion of dried and inflated lung, seen with a
magnifying power of 25 diameters.

FIG. II. Pulmonary vesicles from a fresh lung. — 1, Walls
of the vesicles ; 2, layer of epithelium lining the walls of the
vesicles.

Fig. III. Pulmonary epithelium from a foetus at the third
month. — 1, Cells in their normal relation ; 2, detached cells.

FIG. IV. A sweat gland, seen under a magnifying power
of 165 diameters (from the palmar surface of the middle finger).
1, Excretory duct lined by its epithelium ; 2, nuclei of the epi-
thelium ; 3, commencement of the excretory duct ; 4, fibrous
stroma (connective) of the gland, showing numerous plasmatic
cells (5).

FIG. V. Excretory duct of the same gland. — 1, Its external
layer consisting of connecting tissue ; 2, its internal layer —
structureless basement membrane ; 3, polygonal epithelium.

FIG. VI. Same duct seen in transverse section. — 1,
Wall of the duct; 2, its epithelium; 3, its cavity.

FIG. VII. Transverse section of the excretory duct
of a ceruminous gland. — 1, Its walls, showing plasmatic
cells ; 2, its contents; 3, young cells, such as line the walls of
the gland ; 4, cells a little more advanced in age.

200 EXPLANATION OF THE PLATES.

PLATE XX.

TUBULAR GLANDS, Continued. KIDNEYS.

FIG. I. Portion of the kidney of a cat— magnified 50
diameters. — 1, Straight tubes of the medullary substance; 2,
tortuous tubes of the cortical substance ; 3, Malpighian tufts.

'FiG. II. 1 and 2, Fresh tubes showing their internal epithe-
lial lining ; 3, a tube, throughout the greater portion of which
(4) its external wall only is visible — contracted and slightly
wrinkled ; 5, detached epithelial cells ; 6, transverse section of
an urinary tubule ; 7, its epithelium ; 8, its cavity.

FIG. III. Portion of an injected kidney (from Dr.
Boeckel), magnified 60 diameters. — 1, Arteries; 2, Malpighian
tufts ; 3, afferent vessel ; 4, efferent vessel ; 5, vascular plexus
of the cortical substance; 6, same, of the medullary substance.

FIG. IV. Diagrammatic representation of the structure
of the kidney. — 1, A straight tube of the medullary sub-
stance ; 2, tortuous tube of the cortical substance ; 3, its ter-
mination in a bulbous expansion ; 4, an artery ; 5, Malpighian
tuft; 6, the efferent vessel; 7, capillary plexus; 8, veins in
which the vascular plexus pours its blood ; 9, relation between
the vascular portion of the Malpighian tuft, and the terminal
bulbous expansion of a tube; 10, epithelium covering the sur-
face of the Malpighian tuft, and lining the interior of the uri-
nary tube by the terminal bulb of which it is enveloped.

PLATE XXI.

^ ; ; /»•£;; f.rj j>byH&7.ifft 9t<>ill iii.UU ft tfiv'Jfj. ,*• \\*''--'

TUBULAR GLANDS, Continued. — OVAEY.

FIG. I. Section of a testicle rendered hard by boiling,
magnified 50 diameters.— 1, External wall of a secreting tubule ;
2, its internal tunic ; 3, its cavity and epithelium.

FIG. II. A fresh tubule of the testicle. — 1, Outer coat of
its wall ; 2, inner coat ; 3, polygonal epithelium.

EXPLANATION OF THE PLATES. 201

FIG. III. Epithelial cells from the epididymis.

FIG. IV. Human spermatozoa. — 1, Head of a spermato-
zoon ; 2, its caudal prolongation.

FIG. V. Development of spermatozoa, as observed in
the Guinea pig. — 1, Epithelial cell with a solitary nucleus; 2,
epithelial cell with two nuclei ; 3, the head of the spermatozoon
making its appearance in the periphery of a nucleus ; 4 and 5,
two other cells inclosing a larger number of nuclei in the same
stage of development ; 6, nuclei in which the caudal prolonga-
tion (7) of the spermatozoon is visible ; 8, a nucleus with its
spermatozoon uncoiled ; 9, free spermatozoa.

FIG. VI. Ovisac. — 1, stroma of the ovisac ; 2, membrana
granulosa of the ovisac ; 3, its proligerous disc ; 4, zona pellu-
cida of the ovule ; 5, yelk ; 6, germinal vesicle ; 7, germinal
spot.

FIG. VII. Ovisac containing two ovules, 1 and 2.

FIG. VIII. An ovule in which the process of segmen-
tation has taken place. — 1, Zona pellucida ; 2, segmenta-
tion of the vitellus.

PLATE XXII.

LIVER. SPLEEN. TPIYKOID GLAND.

FIG. I. Vena portse of the hog — magnified 50 diameters. —

1, A lobule of the liver; 2, interlobular branches of the vena
portce / 3, their subdivisions ; 4, capillary network.

FIG. II. Human vena portse (from a child three years of
age)', magnified 50 diameters. — 1, Branches of the vena portce /

2, their termination in the capillary plexus.

FIG. III. Intra-lobular vein of the rabbit — magnified 50
diameters. — 1, Boundary of a lobule ; 2, trunk of the vein ; 3,
capillary network.

FIG. IV. Hepatic cells. — 1, Large cells; 2, small cells.

FIG. V. Epithelial cells from the mucous membrane of the
gall-bladder.

13

202 EXPLANATION OF THE PLATES.

FIG. VI. Diagrammatic representation of the minute
structure of a lobule of the liver. — 1, Vena portse ; 2,
interlobular vein ; 3, capillary network (portal plexus) ; 4,
meshes of this network filled with large hepatic cells ; 5, biliary
duct; 6, prolongations from this duct terminating in blind
extremities ; 7, epithelium of the biliary duct.

FIG. VII. Cellular elements of the spleen. — Splenic
cells ; 2, epithelial cells from its blood-vessels.

Fig. VIII. Thyroid "body (adult). — 1, One of its cavities ;
2, walls of the cavity composed of connective fibres ; 3, plas-
matic cells ; 4, epithelium which has already undergone change.

PLATE XXIII.

THE SKIN.

FIG. I. Section of the skin from the palmar aspect of the
last phalanx of the index finger — magnified 60 diam. — 1, Epi-
dermis ; 2, its external or horny layer ; 3, internal layer, or rete
mucosum of Malpighi. Beneath the epidermis the true skin, or
derma, is represented, also in two layers ; 4, its superficial, 5, its
deep layer ; 6, papillae of the derma ; 7, a tactile corpuscle ;
8, sweat glands ; 9, excretory duct of sweat glands; 10, adi-
pose cells.

FIG. II. Section of the skin from the palmar surface of
the last phalanx of the middle finger. — 1, Cells of the horny
layer of epidermis destitute of nuclei; 2, polygonal cells of the
rete mucosum: 3, oval cells, which always form the deepest
layer of the epidermis ; 4, structureless and transparent boun-
dary line between epidermis and cutis vera ; 5, plasmatic cells
of derma, mingled with connective and elastic fibres ; 6, tactile
corpuscle in the interior of a papilla ; 7, the nerve fibre with
which it is connected ; 8, branches of this nerve fibre; 9, plas-
matic nuclei enveloped by amorphous material.

FIG. III. Section of the skin from the scrotum. — 1,
Deep epidermic cells loaded with pigment.

EXPLANATION OF THE PLATES. 203

FIG. IV. Transverse section of a papilla of the true
skin. — 1, True skin ; 2, its limitary border ; 3, epidermis.

PLATE XXIV.

NAILS AND HAIK.

FIG. I. Transverse section of a nail near its root —

magnified 6 diam. — 1, The true skin, forming the matrix of the
nail ; 2, rete mucosum / 3, epidermic structure of the nail ; 4,
fold of true skin in which the root and sides of the nail are
received ; 5, surface of this fold continuous with the matrix ;
6, rete mucosum of neighboring skin, continuous with that of
the nail ; 7, line of junction of the epidermis of the neighbor-
ing integument with the epidermic layer of the nail.

FIG. II. The same section — magnified 25 diam. — 1, Papillae
of true skin forming matrix of the nail ; 2, rete mucosum of
nail; 3, its epidermic layer; 4, line of junction of epidermis
of neighboring skin with that forming the nail ; 5, the only
locality at which they are truly continuous : 6, true skin, with
its papillae, of the fold, or groove, lodging the roots and sides
of the nail ; 7, rete mucosum ; 8, papillae of the derma in trans-
verse section ; 9, sweat duct ; 10, epidermis.

FIG. III. Longitudinal section of a nail — magnified 6
diam. — 1, Nail ; 2, derma ; 3, epidermis.

FIG. IV. A hair from the scrotum in its follicle, with a
sebaceous gland — magnified 50 diam. — 1, lower part of the
shaft of the hair ; 2, its root ; 3, its bulb ; 4, epidermis of the hair;
5, its cortical substance ; 6, its medullary canal ; 7, papilla of the
bulb ; 8, true skin forming wall of the hair follicle; 9, exterior
epidermic layer; 10, interior epidermic layer; 11, sebaceous
gland; 12, its excretory duct.

FIG. V. Imbrication of the cells forming the epidermic
layer of the hair.

FIG. VI. Cells from the same layer detached and treated
by acetic acid.

204 EXPLANATION OF THE PLATES.

FIG. VII. Portion of the shaft of a hair.—], Epidermis;
2, cortical substance ; 3, medullary canal filled with cells.

[PLATE XXV.

HAIES, continued. — MUCOUS MEMBEANE OF THE ALIMENTAEY

CANAL.

FIG. I. Cortical substance of a hair subjected to the
action of caustic potash. It is seen to be made up of fusiform
bodies, the result, apparently, of metamorphosis of the nuclei of
epidermic cells.

FIG. II. Hair follicle — magnified 200 diam. — 1, External
layer ; 2, internal layer, and 3, amorphous limitary border of
the involuted portion of true skin forming the follicle ; 4, exter-
nal epidermic layer, corresponding to the corpus mucosum of
Malpighi ; 5, internal epidermic layer, corresponding to the
external or horny layer of the epidermis ; 6, bulb ; 7, vascular
papilla ; 8, medullary substance.

FIG. II. One of the papillae circumvallatse of the tongue
— magnified 25 diam. — 1, Section of the principal papilla sur-
mounted by secondary papillae, 2 ; 3, epithelium, presenting a
smooth surface.

FIG. IV. A filiform papilla — magnified 25 diam. — 1, Body
of the papilla, surmounted by secondary papillae, 2 ; 3, epithe-
lium presenting also secondary papillae, 4.

FIG. V. A lenticular papilla — magnified 50 diam. —
1, Central orifice leading into a cul-de-sac ; around this the
capillaries of the mucous membrane are shown.

FIG. VI. Epithelium of the O3sophagus. — 1, Two of its
cells, detached.

FIG. VII. Surface of the mucous membrane of the
stomach — magnified 25 diam. — 1, Orifice of a gastric gland.

FIG. VIII. Compound pyloric gland of an infant — magni-
fied 250 diam. — 1, 1, Its two terminal cul-de-sacs opening into
a common outlet.

EXPLANATION OF THE PLATES. 205

PLATE XXVI.

-.flOfcO lo SilfiV
MUCOUS MEHBKAUE OF THE ALIMENTARY CAXAL, continued.

FIG. I. Cul-de-sac of a compound cardiac gland. Its

epithelial cells are larger than those of the simple and pyloric
glands, and possess a different shape.

FIG. II. Mucous membrane of the duodenum — mag-
nified 25 diam. — 1, A conical villus ; 2, same, valvular in
shape ; 3, a compound valve-shaped villus ; 4, orifice of Lieber-
kuhn's glands.

. FIG. III. Mucous membrane of the ileum — magnified
25 diam. — 1, A villus ; 2, orifice of Lieberkuhn's glands.

FIG. IV. A villus covered by its epithelium — magni-
fied 250 diam. — 1, Cells seen with their bases presenting ; 2,
cells seen obliquely ; 3, amorphous coating.

FIG. V. Epithelium seen on its superficial aspect —
magnified 400 diam.

FIG. VI. Cells seen in tjieir whole length ; their bases

still covered by the amorphous investment. — 1, A cell with two

, .
nuclei.

FIG. VII. A villus deprived of its epithelium. — 1, Amor-
phous or slightly fibrillated substance ; 2, a vascular loop ;
3, nuclei, most of which seem to belong to capillary vessels.

FIG. VIII. Villi, injected— magnified 50 diam.

FIG. IX. A Brunner's gland — magnified 50 diam.

FIG. X. A Lieberkuhn's gland — magnified 125 diam. —
1, Its wall; 2, its epithelium.

FIG. XI. Orifice of a Lieberkuhn's gland — magnified 125
diam. — 1, Epithelium of the gland forming a radiating crown
around the central open space, 2.

FIG. XII. A solitary gland of the ileum — magnified 25
diam. — 1, Projection of the gland; 2, villi; 3, orifices of Lie-
berkuhn's glands.

FIG. XIII. Two solitary ductless glands injected — mag-
nified 50 diam. — 1, Radicles of the meseraic vein; 2, capillaries
•urmounting the glands.

206 EXPLANATION OF THE PLATES.

FIG. XIV. Mucous membrane of the colon, showing
orifices of Lieberkuhn's glands.

FIG. XV. Mucous membrane of colon. — 1, Lieberkuhn's
glands ; 2, orifice situated over the position of a solitary gland.

SUPPLEMENTARY PLATES.
PLATE XXVII.

FIG. I. Ossification in a medullary canal. — 1, Newly
formed bone; 2, oval nuclei ; 3, nuclei with radiating processes;
4, line of junction of the blastema and bone.

FIG. II. Transverse section of the orbicularis palpe-
brarum muscle.

FIG. III. Meibomian gland. — 1, Common excretory duct ;
2, lobules. Magnified 25 diam.

FIG. IV. Kidney of guinea-pig. — 1, Urinary tubule ; 2, its
terminal enlargement ; 3, Malpighian tuft ; 4, aiferent and effe-
rent vessels ; 5, epithelium covering surface of the tuft. Mag-
nified 240 diam.

FIG. V. Transverse section of an eye-lash at its base. —
1, Medullary substance; 2, cortical substance of the hair; 3,
internal epidermic layer of the hair follicle ; 4, external epider-
mic layer ; 5, internal zone of the derma of the hair follicle ;
6, external zone; 7, sebaceous glands. Magnified 220 diam.

FIG. VI. An internal villus bare of epithelium, taken from
a portion of intestine during the progress of digestion. — 1, Body
of the villus infiltrated with oil-globules ; 2, lacteal occupying
the central axis of the villus and ending by a closed extremity.
Magnified 220 diam.

EXPLANATION OF THE PLATES. 207

PLATE XXVHI.

THE EYE.

FIG. I. Section of the two external tunics of the eye-
ball at the junction of the cornea and sclerotica. — 1, Sclerotica ;
2, cornea; 3, line of junction of these two parts; 4, canal of
Sehlemm; 6, conjunctiva; 7, corneal and conjunctival epithe-
lium ; 8, line of junction of conjunctiva and sclerotica ; 9, amor-
phous layer on the front of the cornea; 10, same layer on
posterior surface of cornea ; 11, iris ; 12, choroid ; 13, a ciliary
process. Magnified 25 diarn.

FIG. II. Cornea, sclerotica, and conjunctiva. — 1, Scle-
rotica ; 2, cornea ; 3, amorphous layer on front surface of
cornea; 4, junction of this layer with the conjunctiva; strati-
fied epithelium of the conjunctiva and anterior surface of cor-
nea. Magnified 300 diam.

FIG. III. Section of cornea and iris. — 1, Cornea ; 2,
anastomosing plasmatic cells ; 3, its posterior amorphous layer ;
4, junction of this layer with the sclerotica ; 5, its epithelial
investment which, reflected upon the anterior surface of the
iris, constitutes the membrane of Demours. Magnified 360
diam.

FIG. IV. Ciliary muscle. — 1, Sclerotica; 2, canal of
Schlemm ; 3, ciliary ring ; 4, ciliary processes in which nuclei
of muscular fibres are seen in the direction of their length at 5,
and in transverse section at 6 ; 7, external circumference of the
iris.. Magnified 120 diam.

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Influences of Physical and Moral Agencies on the different Tribes of the Human
Family. By JAMES COWLES PKICHAKD, M.D., F.R.8., M.E.I.A., Corresponding Member
of the National Institute, of the Koyal Academy of Medicine, and of the Statistical
Society, etc. 4th edition, revised and enlarged. By EDWIN NOKBIS, of the Eoyal
Asiatic Society, London. With 62 plates, colored, engraved on steel, and 100 engrav-
ings on wood. 2 vols. royal 8vo. elegantly bound in cloth. London, 1855 . . 10 00

Six Ethnographical Maps. Supplement to the Natural History of Man, and to

the Eesearches into the Physical History of Mankind. Folio, colored, and one sheet

of letter-press, in cloth boards. 2nd edition. London, 1850 . . . .600

QUEKETT (J.) A Practical Treatise on the Use of the Microscope, including the Dif-
ferent Methods of Preparing and Examining Animal, Vegetable, and Mineral Struc-
tures. 8vo. 3rd edition. London . . .,#«,;,, • • . - . -5 00

Lectures on Histology, delivered at the Royal College of Surgeons of England.

VoL I. Elementary Tissues of Plants and Animals. Vol. II. On the Structure of the
Skeletons of Plants and Animals. 2 vols. 8vo. Illustrated with 340 wood-cuts. Lond. 5 75

Descriptive and Illustrated Catalogue of the Histological Series contained in

the Museum of the Eoyal College of Surgeons of England, prepared for the Micro-
scope. Vol. I. Elementary Tissues of Vegetables and Animals. Vol. II. Structure of

the Skeletons of Vertebrate Animals. 2 vols. 4to. illustrated. London . . . 17 50

RECORDS OF DAILY PRACTICE: a Scientific Visiting List for Physicians and
Surgeons. This little book is not intended to supersede the use of a regular visiting
list ; its aim, as its title indicates, is to supply a medium for taking notes of the state of
a patient, as soon after the visit as it is possible, and whilst the facts are still fresh in
the memory. In hospital practice, we believe it will be found invaluable. Price, in
cloth, 50 cents, with tucks . . . . . . . . . 00 75

ROBIN (CH.) Du Microscope et des injections dans leurs applications a 1'anatomie et a

la pathologie. 8vo. Parisu1849 1 75

— * ; — Histoire Naturelle dea vegetaux Parasites qui croissent sur Thomme et les ani-
maux vivants. 1 vol. 8vo. et Atlas de 15 planches. Paris, 1853 . . . . 4 00

SICH EL- Iconographie Ophthalmologique, ou Description et figures coloriees des maladies
de 1'organe de la vue, comprenant Tanatomie pathologique, la pathologie et la thera-
peutique, medico-chirurgicales, par le docteur J. SICHEL, professeur d'ophthalmologie,
medecin-oculiste des maisons d'education de la Legion d'honneur, etc., 1852-1859.
Ouvrage complet, 2 vol. grand in 4to. dont 1 volume de 840 pages de texte, et 1 volume
de 80 planches dessinnees d'apres nature, gravees et coloriees avec le plus grand soin,
accompagnees d'un text descriptif . . . . . . . 44 00

Le text se compose d'une exposition theorique et pratique de la science, dans laquello
viennent se grouper les observations cliniques, mises en concordance entre elles, et
dont I'ensemble forme un Traite clinique des maladies de Vorgane de la vue, com-
mente et complete par une nombreuse serie de figures.

THE LONDON MEDICAL REVIEW (monthly) 360

VOGEL AND DAY- The Pathological Anatomy of the Human Body. By JULIUS Vo-
GEL, M.D., Translated from the German, with Additions, by GEORGE E DAY, M.D.,
Professor to the University of St. Andrew's. Illustrated with 100 plain and colored
engravings. 8vo. London, 1847 . . . . . . . . 4 50

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