ELEMENTS

OF

HISTOLOGY.

UNIVERSITY

E. KLEIN, M.D., F.R.S.,

, I

JOINT-LECTURER ON GENERAL ANATOMY ANT> PHYSIOLOGY IN THE

MEDICAL SCHOOL OF ST. BARTHOLOMEW'S HOSPITAL,

LONDON.

ILLUSTRATED WITH 181 ENGRAVINGS.

SECOND EDITION.

CASSELL & COMPANY, LIMITED.

LONDON, PARIS $ NEW YORK.

[ALT, EIGHTS RESERVED.]

1883.

• t

STo
WILLIAM BOWMAN, LL.D., F.R.S., &c., &c.,

THIS BOOK IS DEDICATED,

"* pi^.C
IX ACKNOWLEDGMENT OF HIS MANY AND GREAT DISCOVERIES

IN ANATOMY AND PHYSIOLOGY.

PREFACE.

THIS Work is intended as a Manual for Medical
Students. The original plan was to embody in it
only such matter as was absolutely required for the
first year's student in the Medical Schools ; but this
plan was not carried out, since the book would then
have been, in some measure, incomplete as a Manual
of Histology. The work contains a good deal that
will be acceptable to the advanced student, as well
as to the beginner.

My best thanks are due to Mr. Charles Berjeau,
F.L.S., for the readiness and artistic skill with which
he has executed the illustrations on wood. Some of
the figures are copied from the "Atlas of Histology,"
others from the "Handbook for the Physiological
Laboratory." The former are marked "Atlas," the

latter "Handbook."

E. KLEIK

May, 1883.

CONTENTS.

( CHAPTER L

CELTS

CHAPTER IL
BLOOD ............. 10

CHAPTER in.
EPITHELIUM ............ 16

CHAPTER IV.
ENDOTHELIUM ........... 25

CHAPTER V.
FIBROUS CONNECTIVE TISSUES ....... 31

CHAPTER VI.
CARTILAGE ............ 45

CHAPTER Vn.
BONE ...... ........ 50

CHAPTER VIEL
NON-STRIPED MUSCULAR TISSUE ....... 63

CHAPTER IX.
STRIPED MUSCULAR TISSUE ........ 66

CHAPTER X.
THE HEART AND BLOOD-VESSELS ....... 74

CHAPTER XL
THE LYMPHATIC VESSELS ......... 84

x ELEMENTS OF HISTOLOGY.

CHAPTER XII. PAGE
SIMPLE LYMPHATIC GLANDS 92

CHAPTER XIII.
COMPOUND LYMPHATIC GLANDS 98

CHAPTER XIV.
NERVE-FIBRES 103

CHAPTER XV.
PERIPHERAL NERVE-ENDINGS 115

CHAPTER XVI.
THE SPINAL CORD 127

CHAPTER XVH.
THE MEDULLA OBLONGATA 142

CHAPTER XVIII.
THE CEREBRUM AND CEREBELLUM 149

CHAPTER XIX.
THE CEREBRO-SPINAL GANGLIA 163

CHAPTER XX.
THE SYMPATHETIC SYSTEM ... .166

CHAPTER XXI.
TEETH 171

CHAPTER XXII.
THE SALIVARY GLANDS 178

CHAPTER XXIII.
THE MOUTH, PHARYNX, AND TONGUE 187

CHAPTER XXIV.
THE (ESOPHAGUS AND STOMACH 194

CHAPTER XXV.
THE SMALL AND LARGE INTESTINE 201

CONTENTS. xi

CHAPTER XXVI. PAGE

THE GLANDS OF BRUNNER, AND THE PANCREAS . . .208

CHAPTER XXVII.

THE LIVER 210

CHAPTER XXVIII.
THE ORGANS OF RESPIRATION 215

CHAPTER XXIX.
THE SPLEEN 225

CHAPTER XXX.
THE KIDNEY, URETER, AND BLADDER 229

CHAPTER XXXI.
THE MALE GENITAL ORGANS 241

CHAPTER XXXII.
THE FEMALE GENITAL ORGANS 257

CHAPTER XXXin.
THE MAMMARY GLAND 270

CHAPTER XXXIV.
THE SKIN 274

CHAPTER XXXV.
THE CONJUNCTIVA AND ITS GLANDS 291

CHAPTER XXXVI.
THE CORNEA, SCLEROTIC, LIGAMENTUM PECTINATUM, AND

CILIARY MUSCLE 295

CHAPTER XXXVH.
THE IRIS, CILIARY PROCESSES, AND CHOROIDEA . . .300

CHAPTER XXXVIII.
THE LENS AND VITREOUS BODY 305

CHAPTER XXXIX.
THE RETINA 308

xii ELEMENTS OF HISTOLOGY.

CHAPTER XL. PAffB

THE OUTER AND MIDDLE EAR

• • • • Oi/3

CHAPTER XLI.
THE INTERNAL EAR m

CHAPTER XUI.
THE NASAL Mucous MEMBRANE . 333

CHAPTER XLHI.
THE DUCTLESS GLANDS

313

UNIVERSITY]

ELEMENTS OF HISTOLOGY.

CHAPTER I.

CELLS.

1. THE ripe ovum (Fig. 1) of man and mammals is
a minute spherical clump of a soft, gelatinous, trans-
parent, granular-looking substance, containing nume-
rous minute particles — yolk
globules. It is invested
by a vertically-striated deli-
cate membrane, called the
zona pellucida. Inside this
clump, and situated more
or less excentrically, is a
vesicle — the germinal vesicle
— and inside this, one or more
solid spots — the germinal
spot or spots. The gela-
tinous transparent substance
of the ovum, containing a
very large percentage of proteid material, is called
Protoplasm. Before and immediately after fertilisa-
tion, the protoplasm of the ovum shows distinct move-
ment, consisting in contraction and expansion. These
movements are spontaneous — i.e., not caused by any
directly visible external influence.

The diameter of the ripe ovum in man and domestic
animals varies between ^J^ and yi^- of an inch. But
before it ripens the ovum is considerably smaller — in

Fig. 1.— Ripe Ovum of Cat.

a, Zona pellucida ; ft, perminal
vesicle ; c, protoplasm.

2 ELEMENTS OF HISTOLOGY. [chap. i.

fact, its size is in proportion to its state of develop-
ment.

2. Fertilisation causes marked changes in the
contractions of the protoplasm of the ovum ; these

e

Fig. 2. — From a Section through the Blastoderm of Chick, uniucubated.

a. Cells forming the ectoderm ; 6, cells forming the endoderm ; c, large

formative cells ; /, segmentation cavity. (Handbook.)

lead to cleavage or division of its body into two parts,
the germinal vesicle having previously split up into
two bodies or nuclei ; BO that we now find the ovum

Fig. SA.— From a Section through the Eudiment of the Embryo Chick.

e, Primitive groove ; /, doreal laminae of epiblast ; d, mesoblast. The

thin layer of spindle-shaped cells is the hypoblast. (Handbook.)

has originated two new elements, each of which con-
sists of protoplasm, of the same substance as that of
the original ovum, and each contains one nucleus or
kernel. The investment of the ovum takes no part in

Chap. I.]

CELLS.

this process of division. Not long after, each of the
two daughter elements undergoes cleavage or division

Fig. SB. — Vertical Section through the Ovum of Bufo Cinereus, in the

early §tage of the Embryo Development,
a, Tegmental layer of epihlast ; 6, dorsal groove; c, rudiment of central nervous

pyptem ; d, notochord ; e, deep layer of epiblast ;/, niesoblast ; g, hypobla?t ;

h, cavity of alimentary canal— Rusconi's cavity ; H, central yolk ; k, remainder

of von baer's or segmentation cavity. (Handbook.)

into two new elements, the nucleus having previously
divided into two, so that each of the new offspring
possesses its own nucleus. This process of division is
continued in the same manner for many generations

4 ELEMENTS OF HISTOLOGY. [Chap, i

(Figs. 2, 3 A, SB), so that after a few days we find
within the original investment of the ovum a large
number of minute elements, each consisting of
protoplasm, and each containing a nucleus.

3. From these elements, which become smaller as
the process of cleavage progresses, all parts and organs
of the embryo and its membranes are formed. It can
be easily shown that the individual elements possess
the power of contractility. Either spontaneously or
under the influence of moderate heat, electricity,
mechanical or chemical stimulation, they throw out
processes and withdraw them again, their substance
flowing slowly but perceptibly along. Hence they
can change their position. In this respect they com-
pletely resemble those lowest organisms which are
known as amoebse, each of these being likewise a
nucleated mass of protoplasm. Wherefore this move-
ment is termed amoeboid movement. It can be further
shown that they, like amoebae, grow in size and divide
— that is to say, the individuals of a generation grow
in size before each gives rise to two new daughter
individuals.

4. Although for some time during embryonal life
the elements constituting the organs of the embryo are
possessed of these characters, a time arrives when
only a limited number of them retain the power of
contractility in any marked degree. At birth only the
white corpuscles of the blood and lymph, many of the
elements of the lymphatic organs, and the muscular
tissues, possess this power, while the others lose it,
or at any rate do not show it except when dividing
into two new elements. Some of these elements
retain their protoplasmic basis ; as a rule, each con-
tains one nucleus (but some two or more) and is
capable of giving origin by division to a new genera-
tion. Others, however, change their nature altogether,
their protoplasm and nucleus disappear, and they

Chap, i.] CELLS. 5

give origin to material other than protoplasm — e.g.,
collagenous, osseous, elastic, and other substances.

5. Beginning with the ovum, and ending with the
protoplasmic nucleated elements found in the organs
and tissues of the embryo and adult, we have, then,
one uninterrupted series of generations of elements,
which with Schwann we call cells and with Briicke
elementary organisms. Of these it can be said that
not only is each of them derived from a cell (Virchow :
omnis cellula a celhda), but each consists of the
protoplasm of Max Schultze (Sarcode of Dujardin),

Fig. 4.— Amoeboid movement of a White Blood Corpuscle of Man ;
various phases of movement. (Handbook.)

is without any investing membrane, and includes
generally one nucleus, but may contain two or more.
We can further say that each of these cells shows the
phenomenon of growth, which presupposes nutrition,
and reproduction. All of them in an early stage of
their life history , and some of them throughout it,
show the phenomenon of contractility, or amreboid
movement (Fig. 4.)

Cells differ in shape according to kind, locality,
and function, being spherical, irregular, polygonal,
squamous, branched, spindle-shaped, cylindrical, pris-
matic, or conical. These various shapes will be more
fully described when dealing in detail with the various
kinds of cells. Cells in man and mammals differ in
size within considerable limits : from the size of a
small white blood corpuscle of about a^Vo °f an ^nc^
to that of a large ganglion cell in the anterior horns of
the spinal cord of about -^^ of an inch, or to that of a

6 ELEMENTS OF Hisro7.OGY. [Chap, i.

multinucleated cell of the bone marrow — myeloplax —
some of which surpass in size even the ganglion cells.
The same holds good of the nucleus. Between the
nucleus of a ganglion cell of about -gi^ to y^1^ of an
inch in diameter and the nucleus of a white blood
corpuscle of about y^j- to -^^^ of an inch and less
there are all intermediate sizes.

6. Protoplasm is a transparent homogeneous or
granular-looking substance. On very careful examina-
tion with good and high powers, and especially when
examined with certain reagents, in many instances it
shows a more or less definite structure, composed of
fibrils, more or less regular, and in some instances
grouped into a honeycombed or fibrillar reticulum
in the meshes of which is a homogeneous interstitial
substance. The closer the meshes of the reticulum,
the less there is of this interstitial substance, and the
more regularly granular does it appear. In the meshes
of the reticulum, however, may be included larger or
smaller granules of fat, pigment, or other material.
Water makes protoplasm swell up, and ultimately
become disintegrated ; so do dilute acids and alkalies.
All substances that coagulate proteids have the same
effect on protoplasm.

7. The nucleus, the size of which is generally in
proportion to that of the cell, is usually spherical or
oval. It is composed of a more or less distinct invest-
ing cuticle and the nuclear contents, which are in the
ripe state arranged as an irregular or regular network,
the parts of which may be uniform fibrils or septa, or
irregularly-shaped trabeculse. In the life history of
each nucleus there may be stages in which one or more
clumps or nucleoli are present in the nuclear network.
The substance of the nucleus differs chemically from
that of the cell, the former containing nuclein.

Immediately before division the nuclear membrane
disappears, and also immediately after division the

Chap, i.] CELLS. 7

nuclear matter shows no definite boundary. The
nuclear membrane when present is a condensed outer
stratum of the nuclear matter.

In some instances it can be shown that the
nuclear fibrils are in continuity with the fibrils of the
cell substance. In the moving white blood corpuscles
Strieker and linger have seen the nucleus becoming
one with the cell substance, and again afterwards
differentiated by the appearance of a membrane.

8. During division of the cell the nucleus
divides generally before the cell protoplasm. This
division of the nucleus has previously been supposed
to occur in the same manner as that of the cell pro-
toplasm— i.e., by simple cleavage. This mode is called
the direct division, or Remak's mode of division.
In this division the nucleus is supposed to become
constricted, kidney-shaped and hour-glass shaped, and
if the division is into more than two, lobed. Nuclei
of these shapes are not uncommon ; but they need not
necessarily indicate direct division, because, being
very soft structures, pressure exerted from outside, or
the motion of the cell protoplasm, may produce these
shapes ; and, further, the contractility of the nucleus
may and occasionally has been observed to cause
these changes of shape. From the observations of
recent investigators — Biitschli, Hertwig, Strassburger,
Mayzel, van Beneden, Balfour, Eberth, Schleicher,
Peremeschko, Flemming, Klein, Arnold, Pfiitzner,
Retzius, Bizzozero, and many others — it is now known
that in the embryo and adult, in plant and animal,
vertebrates and invertebrates, all kinds of cells, before
their protoplasm undergoes division, show complicated
changes of their nucleus, leading to division. This
manner of division is called the indirect division or
karyokinesis. It has been observed by Mayzel,
Schleicher, and Flemming, that the nuclear fibrils
show movement, hence the name karyokinesis. This

8

ELEM-ENTS OF HISTOLOGY.

[Chap. I.

process of the karyokinesis is represented in the ad-
joining figure, 5, and it consists of the following phases :
(a) The nuclear network become very pronounced,
while the nuclear membrane disappears, and the
fibrils of the nuclear network becomes twisted and
bent into a more or less dense convolution; at the
same time the nucleus, as a whole, is considerably
enlarged, (b) The fibrils unravel into loops, arranged

Fig. 5. — Karyokinesis.

A, Ordinary nucleus of a columnar epithelial cell ; B, c, the same nucleus in the
stage of convolution ; D, the wreath, or rosette form ; E, the aster* or single
star ; p, a nuclear spindle from the Descemet's endothelium of the frog's
cornea; G, H, I, diaster; K, two daughter nuclei.

around the centre as a wreath or rosette, (c) The
peripheral points of the loops become broken, and
we obtain a star-shaped figure of single loops — the
aster, (d) The loops separate into two groups or
new centres : this is the diaster, or double star.
(e) The two groups of threads become further apart,
as if attracted by opposite poles ; but the two groups
remain still connected with one another by fine pale
threads. These latter differ from the others in not
staining with certain dyes, and representing the in-

Chap, i.] CELLS. 9

terstitial substance of the nuclear matter — i.e., the pale
substance contained in the original reticulum of the
nucleus. Flemming calls this substance achromatin,
whereas the threads forming the original network, the
convolution, aster and diaster, he calls chromatin, (5h
account of its readily staining with dyes.

In this stage the whole figure resembles a spindle,
the nuclear spindle of Butschli (Fig. 5, F).

(/) Further, all connection between the two sets
of threads is broken — i.e., between the stars of the
diaster. (g) The threads of each set become greatly
convoluted. (A) A membrane appears for each set.
In this stage we speak of two new or daughter nuclei.
The cell protoplasm may commence to divide at any
stage between the one when the threads aggregate
round two centres, and the one when two distinct
daughter nuclei are present ; or the division of the
nucleus may not be followed by the division of the cell
protoplasm, in which case we have a two-nucleated
cell. In some instances, especially of invertebrates and
lower vertebrates, a peculiar sun-like arrangement of
fibrils of the cell protoplasm towards each of the two
stars of the above nuclear fibrils has been observed.
Martin has noticed, in pathological new growths, a
simultaneous division into three and four daughter
nuclei, after the mode of karyokinesis. Although
this indirect mode of division of the nucleus has been
observed in all kinds of cells in the embryo, and to a
limited degree also in the adult, it is not proved to
be the universal mode of nuclear division. On the
contrary, there is strong evidence that in amoeboid
corpuscles division of the nucleus follows the direct
mode, and it is also probable that other nuclei, under
certain conditions, may undergo the direct mode of
division.

10 [Chap. II.

CHAPTER II.

BLOOD.

9. UNDER the microscope blood appears as a trans-
parent fluid, the liquor sanguinis or plasma, in which
float vast numbers of -formed bodies, the blood cor-
puscles. The great majority of these are coloured;
a few of them are colourless. The latter are called
white or colourless blood corpuscles, or leucocytes.
The former are called red or coloured blood corpuscles,
and appear red only when seen in a thick layer;
when in a single layer they appear of a yellow-
greenish colour, more yellow if of arterial, more
green if of venous blood. The proportions of
plasma and blood corpuscles are sixty-four of the
former and thirty-six of the latter in one hundred
volumes of blood. By measurement it has been found
that there are a little over five millions of blood
corpuscles in each cubic millimetre (g-| -g- of a cubic inch)
of human blood. There appears to be in healthy
human blood one white corpuscle for 600-1200 red
ones. In man and mammals the relative number of
blood corpuscles is greater than in birds, and in birds
greater than in lower vertebrates.

10. The red blood corpuscles (Fig. 6) of man
and mammals are homogeneous bi-concave discs (except
in the camelidse, where they are elliptical), and do not
possess any nucleus. Being bi-concave in shape, they
are thinner and more transparent in the centre than
at the periphery. In other vertebrates they are oval
and more or less flattened from side to side, and each
possesses a central oval nucleus.

The diameter of the human red blood corpuscles is

Chap. II.]

BLOOD.

it

about -j^Vo of an inch on the broad, and ^ov of an

inch on the narrow side. But there are always

corpuscles present which are much smaller by about

one-third to one-half

than the others. In >^ * f\

normal blood these W 0

small red corpuscles

are scarce ; in certain

abnormal conditions,

especially anaemia, or

scarcity of blood, they

are more numerous.

According to Gulliver, Welcker, and others, the
following are the measurements of the sizes of red
blood corpuscles of various vertebrates : — man, ^Vo >
dog, ¥¥Vo ; cat> TWO J sheeP> TtW ; elephant, ^^ ;
horse, ^Vo- ; musk deer> T<mnr ; pigeon, ^Vr '> toad>
newt, ¥i¥ ; proteus, ^ ; pike, ^Vo ; shark>

A B

Fig. 6.— Various kinds of Eed Blood
Corpuscles.

A, Two human, one seen from the broad,
the other from the narrow side ; B, a red
corpuscle of the camel ; c, two red corpus-
cles of the frog, one seen from the broad,
the other from the narrow side.

11. In a microscopic specimen of fresh unaltered blood
(Fig. 7) the red blood corpuscles form peculiar shorter

or longer rolls, like so
many coins, becoming
adherent to one another
by their broad surfaces.
Under various condi-
tions — such as when
isolated, or when blood
is diluted with saline
solution or solutions of
other salts (sulphate of
sodium or magnesium)
— the corpuscles lose
their smooth circular
outline, shrinking and
In a further stage of this

Fig. 7.— Human Blood, fresh.

A, Rouleaux of red corpuscles ; B, isolated
red corpuscle seen in profile ; c, isolated
red corpuscle seen from its broad sur-
face ; D, white corpuscles.

becoming crenate (Fig. 8, A).

process of shrinking they lose their discoid form, and

1 2 ELEMENTS OF HISTOLOGY. [Chap. n.

become smaller and spherical, but beset all over their

surface with minute processes. This shape is called the

horse-chestnut shape (Fig. 8, b, c). It is pro-

Q Q bably due to the corpuscles losing carbonic

acid, as its addition brings back their discoid

shape and smooth circular outline. On ab-

W w stracting the carbonic acid they return to

ft the horse-chestnut shape. Water, acid,

'fed Biood alcohol, ether, the electric current, and

a crenat^T c manv other reagents, produce discoloration

'shSed!h^st"u* °^ *ne red blood corpuscles ; the colouring

matter — generally the combination of

the blood-colouring matter with globulin known as

hcemoglobin — becoming dissolved in the plasma.

What is left of the corpuscles is called the

stroma. In newts' and frogs' blood a separation of

the stroma from the

nucleus plus haemoglobin

can be effected by means

of boracic acid (Fig. 9, B) ;

the former is called by

Briicke the Oikoid, the

-, , , r, . -. mi . Fig. 9. — Bed Blood Corpuscles of

latter Zooid. This stroma Man and Newt;

Contains amongst Other A, Human red corpuscles after the action

• r • j j i £ of tamric acid : n, three red cprpuscles,

tningS a gOOQ Cleal Ot para- from which the haemoglobin is passing

-i » -T rm °ut ; &, Roberta's corpuscles.

globulin. I he Stroma B, Newt's red corpuscles after the action

« , i i £ of boracic acid : a, a corpuscle showing

OI tne COrDUSCleS OI BrUckes' zooid and oikoid ; 6, a corpus-

-i .-, . . cle showing the reticulated stroma;

amplllDiailS IS Seen, c, a corpuscle showing the reticulum

i , . in the nucleus ; d, the nucleus passing

under certain reagents, out.
to be of a reticulated

structure, but in the fresh state appears homo-
geneous and pale. Discoloration of the blood cor-
puscles can be observed to take place also in blood
without the addition of any or with that of per-
fectly harmless fluids, such as humor aqueus of
the eye, hydrocele fluid, &c. The number of cor-
puscles undergoing discoloration is, however, small.

Chap, ii.] BLOOD. 13

The elements of the blood described by Dr. William
Norris, of Birmingham, as the invisible, pale, or third
corpuscle, are simply red blood corpuscles that have
become discoloured by the mode of preparation
(Alice Hart).

1 2. The haemoglobin of the red blood corpuscles
forms crystals (Fig. 10), which differ in shape in the
various mammals.
They are always
of microscopic size,
and of a bright red /j\

colour.

In man and
most mammals
they are of the
shape of prismatic \^£- -j

needles, or rhombic jj^\ ^^^o

plates ; in the p.g 10 _H8emoglobin crystals.

Squirrel they are A Of guinea.pjg ; B> Of squirrel ; c, D, human.

hexagonal plates,

and in the guinea-pig they are tetrahedral or octa-
hedral. The blood pigment itself is an amorphous
dark-brown or black powder — the hcematin ; but it
can be obtained in a crystalline form as hydro-
. chlorate of h£ematin(Fig. 11). These crystals
also are of microscopic size, of a nut-brown
'4 colour, of the shape of narrow rhombic
' plates, and are called hcemin crystals, or
Teichmann's crystals. In extravasated
human blood crystals of a bright yellow
or orange colour are occasionally met with ; they are
called by Virchow, their discoverer, hcematoidin.
They are supposed to be identical with bilirubin,
obtainable from, human J&ile.

13, The white or colourless blood cor-
puscles are' in human blood of about -^ ^Vo to ^wo-
of an inch in diameter, and are spherical in the
\

14 ELEMENTS OF HISTOLOGY. [chap. n.

circulating blood or in blood that has just been
removed from the vessels. Their substance is trans-
parent granular-looking protoplasm, containing larger
or smaller bright granules. These granules are
either of a fatty nature, or, as in some kinds of
blood, notably horses', are of a reddish colour,
and these corpuscles are supposed by some observers
(Semmer and Alexander Schmidt) to be inter-
mediate between red and white corpuscles. The
protoplasm of the colourless corpuscles contains
glycogen (Ranvier, Schafer). In the blood of lower
vertebrates the colourless corpuscles are considerably
larger than in mammals. But in all cases they
consist of protoplasm, include one, two, or more
nuclei, and show amoeboid movement. This may be
observed in corpuscles without any addition to a
fresh microscopic specimen of blood, but it always
becomes much more pronounced on applying artificial
heat of about the degree of mammals' blood. It
is then seen that they throw out longer or shorter
filamentous processes, which may gradually lengthen
or be withdrawn, appearing again at another point of
the periphery. The corpuscle changes its position
either by a flowing movement of its protoplasm as a
whole, thus rapidly creeping along the field of the
microscope, or it may push out a filamentous process
and shift the rest of its body into it. During this
movement the corpuscle may take up granules from
the surrounding fluid.

14. The white corpuscles of the same sample of
blood differ in size and aspect within considerable
limits, sonre being half the size of others, some much
paler than others. The smaller examples generally
possess one nucleus occupying the greater part of the
corpuscle, the larger ones usually include two, three,
or even more nuclei, and show more decided
amoeboid movement than the others. Division by

chap, ii.] BLOOD. 15

cleavage of the white corpuscles of the blood of lower
vertebrates has been directly observed by Klein and
Ranvier.

15. In every microscopic specimen of the blood
of man and mammals are found a variable number
of large granules, more or less angular, singly or in
groups, which have been specially studied by Osier.
According to Bizzozero they are, when

observed in the living and fresh blood, \J a

pale, circular, or slightly oval discs ^ Q

(Fig. 12, b). Their size is only -J- to J VJ
of that of the red blood corpuscles. J>

They are called by him blood plates, and * °

• • .1 i /• ,• i • Fi». 12.— Human

he supposes them to be of essential im- e
portance in the coagulation of the blood,
in fact, the fibrin ferment. Hayem
described them previously as being in-
termediate forms in the development of red blood
corpuscles, and called them hsematoplasts.

16. Development of Blood Corpuscles.—
At an early stage of embryonal life, when blood
makes its appearance it is a colourless fluid, contain-
ing only white corpuscles (each with a nucleus), which
are derived from certain cells of the mesoblast. These
white corpuscles change into red ones, which become
flattened, and their protoplasm gets homogeneous and
of a yellowish colour. All through embryonal life new
white corpuscles are transformed into red ones. In
the embryo of man and mammals these red corpuscles
retain their nuclei for some time, but ultimately lose
them. New nucleated red blood corpuscles are, how-
ever, formed by division of old red corpuscles. Such
division has been observed even in adult blood of
lower vertebrates (Peremeschko) as well as in mammals
(marrow of bone by Bizzozero and Torre).

An important source for the new formation of red
corpuscles in the embryo and adult is the red marrow

1 6 ELEMENTS OF HISTOLOGY. [Chap. in.

of bones (Neumann, Bizzozero, Eindfleisch), in which
numerous nucleated protoplasmic cells (marrow cells)
are converted into nucleated red blood corpuscles. The
protoplasm of the corpuscle becomes homogeneous and
tinged with yellow, the nucleus being ultimately lost.
The spleen is also assumed to be a place for the forma-
tion of red blood corpuscles. Again, it is assumed that
ordinary white blood corpuscles are transformed into
red ones, but of this there is no conclusive evidence.
In all these instances the protoplasm becomes homo-
geneous and filled with haemoglobin, while the cell
grows flattened, discoid, and the nucleus in the end
disappears.

Schafer described intracellular (endogenous) for-
mation of red blood corpuscles at first as small haemo-
globin particles, but soon growing into red blood cor-
puscles, in certain cells of the subcutaneous tissue of
young animals. Malassez describes the red blood cor-
puscles originating by a process of continued budding
from the marrow cells.

The white corpuscles appear essentially to be
derived from the lymphatic organs, whence they are
carried by the lymph into the circulating blood.

CHAPTER III.

EPITHELIUM.

17. Epithelial cells (Fig. 13A) are nucleated proto-
plasmic cells, forming continuous masses on the surface of
the skin, of the lining membrane of the alimentary canal,
the respiratory organs, the urinary and genital organs,
the free surface of the conjunctiva, and the anterior
surface of the cornea. The lining of the tubes and

Chap. III.]

EPITHELIUM.

alveoli of secreting and excreting glands, such as the
kidney, liver, mammary gland, testis and ovary, the
salivary glands, mucous, peptic, and Lieberkiihn's.
glands, the sweat and sebaceous glands, the hair
follicles, &c., consists of epithelial cells. Such is the
case also with the sensory or terminal parts of the
organs of the special senses. And, finally, epithelial
cells occur in other
organs, such as the
thyroid gland, the
pituitary body, &c.

The hairs and
nails, the cuticle of
the skin, certain
parts of the rods
and cones of the
retina, and the rods
of corti of the organ
of hearing, are modi-
fied epithelial struc-
tures.

Epithelial cells

are grouped together Figi 13A>_ Various kinds of Epithelial Cells.

by exceedingly thin
layers of an albu-
minous interstitial
cement substance,
which during life is

of a semi-fluid nature, and belongs to the group of
bodies known as globulins.

18. As regards shape we distinguish two kinds
of epithelial cells — columnar and squamous. The
columnar cells are short or long, cylindrical or pris-
matic, pyramidal, conical, club-shaped, pear-shaped,
or spindle-shaped ; their nucleus is always more or
less oval, their protoplasm more or less longitudinally
striated. On the free surface of the cells — i.e., the

A, Columnar cells of intestine; B, polyhedral
cells of the conjunctiva; C, ciliated conical
cells of the trachea; D, ciliated cell oi frog'l
mouth; E, inverted conical cell of .trachea;
F, siiuamous cell of the cavity of mouth, seen
from its broad surface ; o, squamous cell, seen
from its narrow side.

i8

ELEMENTS OF HISTOLOGY. [Chap. HI.

part facing a cavity, canal, or general surface — in many
instances a bright thinner or thicker cuticular struc-
ture is seen, with more or less distinct vertical striation.
The conical or spindle-shaped, club-shaped, and pear-
shaped cells are drawn out into longer or shorter
single or branched extremities.

The squamous or pavement cells are cubical,
polyhedral or scaly. The nucleus of the former is
almost spherical that of the latter flattened in propor-
tion to the thinness of the scales. In polyhedral
cells it can be occasionally perceived that the granula-
tion is due to the regular honeycombed nature of the
cell protoplasm.

19. As regards size, the epithelial cells differ
considerably from one another in different parts, and
even in the same part. Thus, the columnar cells,

covering the surface of
the villi of the small in-
testine, are considerably
longer than those lining
the mucous membrane of
the uterus ; the columnar
cells lining the larger
ducts of the kidney are
considerably longer than
those lining the small
ducts \ the polyhedral
cells -covering the anterior

surface of the cornea are considerably smaller than
those on the surface of the lining membrane of the
urinary bladder ; the scales lining the ultimate recesses
of the bronchial tubes — the air cells — are considerably
smaller than those on the surface of the membrane
lining the human oral cavity and oesophagus.

20. As regards arrangement, the epithelial cells
are either arranged as a single layer or are stratified,
forming several superimposed layers; in the former case

Fig. 13B.— Three Mucus-secreting
Goblet Cells.

A, From the stomach of newt ; B, from
a raucous gland ; c, from the surface
of the mucous membrane of the in
testiue.

Chap, in.] EPITHELIUM. 19

we have a simple in the latter a stratified epithelium.
The simple epithelium may be composed of squamous
cells — simple squamous or simple pavement epithe-
lium— or it may be composed of columnar cells —
simple columnar epithelium,. The stratified epithelium
may be stratified pavement, or stratified columnar ;
in the former case all or the majority of the layers
consist of squamous or polyhedral cells, in the latter
all cells belong to the ' columnar kind. Simple^
squamous epithelium is that which lines the air *
cells, certain urinary tubules of the kidney (the looped
tubes of Henle, the cortical parts of the collecting
tubes), the acini of the milk-gland, the inner surface
of the iris and choroid membrane of the eyeball.
Simple columnar epithelium is that on the inner
surface of the stomach, small and large intestine,
uterus, small bronchi, ducts and acini of mucous and
salivary glands, of some kidney tubules, ifec. Stratified
pavement epithelium is that on the epidermis, the
epithelium lining the cavity of the mouth, pharynx,
and oesophagus in man and mammals, the anterior i
surface of the cornea, &c. -^

21. The epidermis (Fig. 14) consists of the fol-
lowing layers: — (a) Stratum corneum: this is the super-
ficial stratum, and it consists of several layers of horny
scales, without any nucleus. The layers, which are
separated from one another by narrow clefts contain-
ing air, are then in process of desquamation. • This
stratum is thickest on the palm of the hand and
fingers, and the sole of the foot, (b) The stratum
lucidum, composed of several dense layers of horny
scales, in which traces of an exceedingly flattened
nucleus may be perceived, (c) Then follow many
layers of nucleated cells, forming the stratum or
rete Malpighii or rete mucosum. The most super-
ficial layer or layers of it are flattened scales, which
are characterised by the presence around the nucleus

2O

ELEMENTS OF HISTOLOGY. [Chap. in.

Fig. 14.— From a Vertical Section through the
Epidermis.

a, The stratum Malpighii ; 6, the stratum granulosum ;
c, the stratum lucidum ; d, the stratum corneum.
(Atlas.)

of globular or elliptical granules of the nature inter-
mediate between protoplasm and keratin. Their sub-

^^^^^ .^-.-..---^^^gg^^-gg-^ stance is called

(Ran-
these

eleidin
vier) ;

cells form the
granular layer
(stratum gra-
nulosum) of
Langerhans.
Deeper down
the cells be-
come less flat-
tened and more
polyhedral, and
the deepest
form a layer of
more or less

columnar cells, placed vertically 011 the surface of

the subjacent corium.
The substance of the

hairs, nails, claws, hoofs,

consists of horny scales.

(See chapter on Skin.)
22. The stratified

pavement epithe-
lium (Fig. 15) lining the

cavity of the mouth, the

surface of the tongue, the

pharynx and oesophagus
of man and mammals, and
the anterior surf ace of the

cornea, &c., is, as regards Fig 15_From a Vertical Section

the Style and arrange- through the anterior layers of the

ment of the cells, identi- Cornea'

. .,1,1 «> The stratified pavement epithelium ;

Cal With the Stratum 6, the substantia propria, with the

•» *• i • i • • ^j_i -i corneal corpuscles between its lamelliB.

Malpighii of the epider- (Handbook.)

Chap. 1 1 i.i EPITHELIUM 21

mis. The cell protoplasm is more transparent in the
former, and the granular cells of the stratum granu-
losum are not always present, but they generally are
in the epithelium of the tongue and of the rest of the
oral cavity. The most superficial scales show more or
less horny transformation.

23. Stratified columnar epithelium is met
with on the lining membrane of the respiratory
organs, as larynx, trachea, and large bronchi. It
consists of several layers of columnar cells : a super-
ficial layer of conical or prismatic cells, with a more
or less pointed extremity directed towards the depth ,
between these are inserted spindle-shaped cells, and
finally inverted conical cells.

The epithelium of the ureter and bladder is called
transitional epithelium. It is stratified, and the most
superficial layer consists of squamous cells. Under-
neath this is a layer of club-shaped cells, between
which extend one or more layers of small spindle-
shaped cells.

Amongst the columnar epithelial cells occurring
in man and mammals the ciliated cells and the goblet
cells, and amongst the squamous cells the prickle cells,
deserve special attention.

24. Ciliated cells are characterised by possess-
ing a bundle of very fine longer or shorter hairs or
cilia on their free surface. These cilia are direct pro-
longations of the cell protoplasm. More correctly
speaking, the cilia are continuous with the filaments
or strise of the cell protoplasm. The superficial layer
of conical cells of the epithelium in the respiratory
organs, the columnar cells lining the uterus and ovi-
duct, and the columnar cells lining the tubes of the
epididymis possess such cilia. In lower vertebrates
the ciliated cells are much more frequently observed ;
in Batrachia the epithelial cells lining the mouth,
pharynx, and oesophagus are ciliated.

22 ELEMENTS OF HISTOLOGY. [Chap. in.

While fresh in contact with the membrane which
they line, or even after removal from it, provided
the cells are still alive, the ciliated cells show a rapid
synchronous whip-like movement of their cilia, the
cilia of all cells moving in the same direction. The
movement ceases on the death of the cell, but may
become slower and may cease owing to other causes
than death, such as coagulation of mucus on the
surface, want of sufficient oxygen, presence of car-
bonic acid, low temperature, &c. Under these circum-
stances, removal of the impediment will generally
restore the activity of the cilia. Moderate electric
currents and heat stimulate the movement, strong
electric currents and cold retard it. Reagents fatally
affecting cell protoplasm also stop permanently the
ciliary action.

25. Oofolet or chalice cells (Figs. 13s, 16) are
cells of the shape of a conical chalice. The pointed part
is directed away from the free surface,
and contains a compressed triangular
nucleus, surrounded by a trace
of protoplasm. The body of the
^^ contains mucus. This latter
may be in various states of forma-

*

the large intestine. out of the Cell. Goblet Cells are

most commonly met with amongst
the epithelium lining the respiratory
organs, the surface of the stomach and
intestines, and especially in mucous glands, in whose
secreting portion all cells are goblet cells.

The protoplasm of columnar cells facing a free
surface, no matter whether in simple or stratified
epithelium, ciliated or non-ciliated, may undergo
such alteration as will lead to the transforma-
tion of the cell into a goblet cell. This takes
place during life, and, in fact, represents an im-

Chap, in.] EPITHELIUM. 23

portant function of columnar epithelial cells — viz.,
the formation of mucus. In mucus-secreting
glands all the epithelial cells have this function
permanently, but in ordinary columnar epithelium
only a comparatively small number of the cells,
as a rule, undergo this change, and then only
temporarily ; for a cell subject to it at one time may
shortly afterwards resume the original shape and
aspect of an ordinary protoplasmic, cylindrical, or
conical epithelial cell, and vice versa. If ciliated
cells undergo this change, the cilia are generally first
detached.

It can be shown that in this change of an ordinary
columnar epithelial cell into a goblet cell, the inter-
stitial substance of the cell reticulum increases in
amount, the meshes enlarging and distending the body
of the cell. The interstitial substance probably under-
goes the change into mucin.

26. Prickle Cells (Fig. 14). — Amongst the middle
and deeper layers of the stratified pavement epithelium,
such as is present in the epidermis and on the surface
of the oral cavity and pharynx, we meet with a close,
more or less distinct and regular striation, extending
from the margin of one cell to that of each of its
neighbours, by means of fine transverse short fibrils
which, passing from protoplasm to protoplasm, connect
the surfaces of the cells,

27. Pigmented epithelial cells — i.e., epithelial cells
filled with black pigment particles (crystals) — are found
on the internal surface of the choroid and iris of
the eyeball.

In coloured skins, and in coloured patches of skin
and mucous membrane, such as occur in man and
animals, there is found pigment in the shape of
granules lodged in the protoplasm of the deeper
epithelial cells, as well as in branched cells situated
between the epithelial cells of the deeper layers. Minute

24 ELEMENTS OF HISTOLOGY. rchap. in.

branched non-pigmented nucleated cells are met with
in the interstitial or cement substance of various kinds
of epithelium, simple and stratified, e.g., epidermis,
epithelium of oral cavity, cornea, &c.

28. Epithelial cells undergo division, and by this
means a constant regeneration takes place. In those
parts where the loss of the superficial layers of cells is
conspicuous, such as the epidermis, the stratified epi-
thelium of the tongue and oral cavity, the sebaceous
follicles of hairs, the regeneration goes on more
copiously than at places where 110 such conspicuous loss
occurs — as, for instance, in the stomach and intestines,
the secreting glands, or sense organs.

In the stratified pavement epithelium it is the cells
of the deepest layer which chiefly divide ; the next
layer thereby becomes gradually shifted towards the
surface, and more flattened, and on reaching the surface
dries up owing to rapid loss of water.

29. The interstitial substance between the epi-
thelial cells being soft and semi-fluid, and the proto-
plasm of the epithelial cells themselves being a soft
flexible material, it is possible for the cells to change
their shape and arrangement after pressure and tension,
exerted on them by the contraction or distension of the
membrane on which they are situated. Thus, for in-
stance, the epithelium lining a middle-sized bronchus
may appear at one time as composed of long, thin,
columnar epithelial cells in two layers ; at another, as
a single layer of long columnar cells ; or again as
a single layer of polyhedral or short columnar cells :
the first is the case when the bronchus is contracted,
the second when it is in a medium state of distension,
the third when it is much distended. Similar changes
may be noticed on the epithelium lining the mucous
membrane of the bladder, gland tubes, the epidermis,
and various other epithelial structures.

Chap. IV.] 25

CHAPTER IV.

ENDOTHELIUM.

30. THE free surfaces of the serous and synovia!
membranes, and of those of the brain and spinal
cord, the posterior surface of the cornea and anterior
surface of the iris, the surfaces of tendon and tendon-
sheaths, the lymph sinuses or lymph sacs of amphibian
animals, the cavity of the heart, of blood-vessels
and of lymphatic-vessels are lined with a continuous
endothelial membrane, composed of
a single layer of flattened trans-
parent squamous cells, called endo-
thelial cells (Fig. 17). Each contains
an oval nucleus, situated generally
excentrically. Just as in the case
of epithelium, the endothelial cell
plates are joined by a fluid or semi-
fluid homogeneous interstitial or X™aince8ii°s! 'anthe

7 rt , v , r> nucleus of the latter

cement substance or the nature ot are wen shown,
globulin. When examining any of
the above structures fresh the endothelial cells are
not, as a rule, visible, owing to their great trans-
parency ; but by staining the structures with a
dilute solution of nitrate of silver, and then ex-
posing them to the influence of the light, the cement
substance appears stained black, whereby the shape
and size of the cell plates become evident. By various
dyes also the nucleus of each cell plate may be brought
into view.

On careful examination, and with suitable re-
agents, it can be shown that each endothelial cell
consists of a homogeneous ground-plate. In it

26 ELEMENTS OF HISTOLOGY. [Chap. iv.

lies the nucleus, and around it is a substance which
appears granular, but which is of a fibrillar nature,
the nbrillye being arranged in a network, and extend-

% 18.— Network of Lymphatics in the Central VTendon of the
iaphragm of Babbit, prepared with nitrate of silver, so as to show
the outlines of the Endothelial Cells forming the wall of the
Lymphatics.

a, Big lymphatic wssels ; 6, lymphatic capillaries; c, apparent ends of the
capillaries. (Handbook.)

ing in many places up to the margin of the ground-
plate. The nucleus is limited by a membrane, and
contains a well-developed reticulum. The fibrillse
of the cell substance appear in connection with the
nuclear reticulum.

31. As regards shape, endothelial cells differ
considerably. Those of the pleura, pericardium,
peritoneum, and endocardium of man and mammals

Chap. IV.]

ENDOTHELIUM.

27

are more or less polygonal, or slightly elongated. Their
outlines vary ; in the lining of the lymph sacs of the
frog they are much larger, and of very sinuous out-
line ; while those of the posterior surface of the cornea

Fig. 19.— Omentum of Babbit, stained witli Nitrate of Silver,
a, Ordinary flat endothelial cells ; 6, germinating cells. (Atlas.)

are very regular, pentagonal, or hexagonal, having
straight outlines in the perfectly normal and well-pre-
served condition, but serrated and sinuous after they
have been prepared with various reagents and in the
abnormal state ; the endothelial plates lining the blood-
vessels and lymphatic vessels (Fig. 18) are narrow and
elongated, with more or less sinuous outlines In the
lymphatic capillaries the endothelial plates are poly-
gonal, but their outline serrated.

32. As a rule the endothelial cells are flattened.

28

ELEMENTS OF HISTOLOGY. [Chap. iv.

i.e., scaly — but in some places they are polyhedral,
or even short columnar. Such cells occur isolated or
in small groups, or covering large and small patches,
nodular, villous, or cord-like structures of the pleura

Fig. 20.— Part of Peritoneal Surface of the Central Tendon of Diaphragm
of .Rabbit, prepared with Nitrate of Silver.

s, Stomata ; Z, lymph-channels ; t, tendon bundles. The surface is covered with
endotheiium. The stomata are surrounded by germinating endothelial cells.
(Handbook.)

and omentum, on the synovial membranes, tunica
vaginalis testis, &c. They are especially observable
in considerable numbers in the pleura and omentum
(Fig. 19) of all normal subjects (human, ape, dog, cat,
and rodent animals); their number and frequency of
occurrence are increased in pathological conditions
(chronic inflammations, tuberculosis, cancer, &c.).

These endothelial cells are the germinating endo-
thelial cells, and they can be shown to be in an

Chap. IV.]

EN DO T HELIUM.

active state of division. They thus produce small
spherical lymphoid (amoeboid) cells, which ultimately
are absorbed by the lymphatics, and carried into the
blood system as white blood corpuscles. On the sur-

Fig. 21.— Part of Omentum of Cat, stained with Nitrate of Silver.

a, Fenestrae or holes ; ft, trabeculae covered with endothelium. Only the outlines
(.silver-lines) of the endothelial cells are shown.

face of the serous membranes, especially the diaphragm
(Fig. 20) and pleura, there exist minute openings,
stomata, leading from the serous cavity into a lym-
phatic vessel of the serous membrane. These stomata
are often lined by germinating cells.

33. In the frog, germinating cells occur in great
abundance on the mesogastrium and the part of the
peritoneum which separates the peritoneal cavity
from the cisterna lymphatica magiia. This part of

30 ELEMENTS OF HISTOLOGY. [Chap. TV.

the peritoneum is called the septum cisternse lym-
phaticse magnse, and on it occur numerous holes or
stornata, by which a free communication is established
between the two cavities. On the peritoneal surface
of this septum the stomata are often bordered by-
germinating cells. In the female frog, these and
other germinating endothelial cells of the peritoneum
(mesogastrium, mesenterium, septum cisterns) are
ciliated.

34. The omentum and parts of the pleura are, in
the adult human subject, ape, dog, cat, guinea-pig, rat,
&c., of the nature of a fenestrated membrane (Fig 21),
bands of fibrous tissue of various sizes dividing and
reuniting, and leaving between them larger or smaller
holes, in shape oblong or circular. These holes
or fenestrse are not covered with anything, the endo-
thelial cells adhering only to the surfaces of the
bands without bridging over the fenestrse. On the
peritoneal surface of the diaphragm the endothelial
cells possess a different arrangement from that on
the pleural side ; on the former surface a number of
lymph channels (that is, clefts between the bundles
of tendon and muscle) radiate towards the middle
of the central tendon. The endothelium of the free
surface over these lymph channels is composed of
much smaller cells than at the places between,
so that the endothelium of the peritoneal surface of
the diaphragm shows numbers of radiating streaks
of small endothelial cells. Many of these small cells
are not flattened, but polyhedral, and of the nature
of germinating cells (Fig. 20.) The above-mentioned
stomata occur amongst these small endothelial cells.

Chap.V.]

CHAPTER V.

FIBROUS CONNECTIVE TISSUES.

35. BY the name of " connective tissues " we
designate a variety of tissues which have these things
in common — that they are developed from the same
embryonal elements ; that they all more or less serve
as supporting tissue or framework, or connecting sub-
stance, for nervous, muscular, glandular, and vascular
tissues ; that they are capable of taking one another's
place in the different classes of animals; that in the
embryo and in the growing condition one may be
changed into the other ; and that in the adult they
gradually shade off one into the other.

Connective tissues are divided into the three great
groups of (1) fibrous connective tissue; (2) cartilage;
(3) bone, to which may be added dentine. Each of
these is subdivided into several varieties, as will
appear farther on, but in all instances the ground
substance, or matrix, or intercellular substance, is
to be distinguished from the cells. In the fibrous con-
nective tissue the matrix yields glutin or gelatin, and
the cells are called connective tissue cells, or connective
tissue corpuscles. In the cartilage the ground sub-
stance yields chondrin, and the cells are called carti-
lage cells. In the third group the ground substance
contains inorganic lime salts, intimately connected
with a fibrous matrix, and the cells are called bone
cells.

36. The fibrous connective tissue, or white
fibrous tissue, occurs in the skin and mucous
membranes, in the serous and synovial membranes,
in the membranes of the brain and spinal cord, in

32 ELEMENTS OF HISTOLOGY. [Chap. v.

tendons and tendon sheaths, in fascise and aponeuroses,
in the intermusciilar tissue, and in the tissue con-
necting neighbouring organs, &c. It consists of
microscopic band-like or cylindrical bundles or fasciculi
of exceedingly fine homogeneous fibrils (Fig. 22), which
are known as the elementary connective tissue fibrils.

tr

Fig. 22.— Plexus of Bundles of Fibrous Tissue from the Omentum
of Eat.

a, A capillary blood vessel ; 6, bundles of fibrous tissue ; c, the connective-tissue
corpuscles ; d, plasma cells. (Atlas.)

According to the number of these^ the bundles differ
in size. The bundles, and also their constituent
fibrils, may be of very great length — several inches.
Where the fibrous tissue forms continuous masses —
as in tendon, fascia, aponeurosis, skin, and mucous
membrane — the microscopic bundles are aggregated
into smaller or larger groups, the trabeculce, and these
are again associated into groups. The fibrils are held
together by an albuminous (globulin), semi-fiuid, homo-
geneous cement substance, which is also present between
the bundles forming a trabecula.

On adding an acid or an alkali to a bundle of

Chap, v.] FIBROUS CONNECTIVE TISSUES. 33

fibrous tissue, it is seen to swell up and to become
glassy-looking, homogeneous, and gelatinous. Sub-
jected to boiling in water, or to digestion by dilute
acids, the bundles of fibrous tissue yield glutin or
gelatin.

37. According to the arrangement of the bundles,
the fibrous connective tissue varies in different locali-
ties. (1) In tendons and fasciae the bundles are
arranged parallel to one another. (2) In the true
skin and mucous, serous, and synovia] membranes, in
the dura mater and tendon sheaths, the trabeculae of
bundles divide repeatedly, cross and interlace very
intimately with one another, so that thereby a dense
felt-work is produced. (3) In the subcutaneous, sub-
mucous, or subserous tissue, in the intermuscular tissue,
in the tissue connecting with one another different
organs or the parts of the same organ — i.e., interstitial
connective tissue — the texture of the fibrous tissue is
more or less loose, the trabeculse dividing and re-
uniting and crossing one another, but leaving between
them larger or smaller spaces, cellulae or areolse, so
that the tissue assumes the character of a loose
plexus, which is sometimes called " areolar " or " cel-
lular tissue." Such tissue can be more or less easily
separated into larger or smaller lamellae, or plates of
trabeculae. (4) In the omentum and parts of the
pleura of man, ape, dog, cat, and some rodents, and
in the subarachnoidal tissue of the spinal cord and
brain, the trabeculae form a fenestrated membrane, with
larger or smaller oval or circular holes or fenestrae.

38. The connective tissue cells or corpuscles
occurring in white fibrous tissue are of several varie-
ties, (a) In tendon and fasciae the cells are called
tendon cells or tendon corpuscles; they are flattened
nucleated protoplasmic cells of a square or oblong
shape (Fig. 2 3 A), forming continuous rows (single files),
situated on the surface of groups of bundles of fibrous

34

ELEMENTS OF HISTOLOGY.

[Chap. V.

tissue. Between these groups are wider or narrower
channels — the interfascicular spaces — running parallel
with the long axis of the tendon (Fig. 23B). The cells
in each row are separated from one another by a narrow
line of albuminous cement substance, and the round
nucleus of the cell is generally situated at one end, in

such a way that in two
adjacent cells of the grow-
ing tendon the nuclei
face each other. This
indicates that the indi-
vidual cells undergo divi-
sion. Corresponding to
the margin of each row,
the cells possess minute
processes. The cell plate
is not quite flat, but pos-
sessed of one, two, or even
three membranous projec-
tions, by which it is
wedged in between the
Fig. 23A.-From a Tendon of Tail individual bundles of the

of Mouse, showing the Tend n OTOUD to which the TOW

cells. (The tendon is viewed in /• 11 -i i

the long axis). Ot C611S belongs.

o, The tendon cells seen from their 39. (b) In the SerOUS

broad surface ; 6, the same seen side- i T

ways. (Handbook.) membranes, cornea, subcu-

taneous tissue, and loose

connective tissues, tne cells are flattened transparent
corpuscles, each with an oblong flattened nucleus, and
more or less branched and connected by their processes.
In the cornea they are spoken of as the corneal cor-
puscles, and are very richly branched (Fig. 25). They
are situated between the lamellae of fibrous bundles of
which the ground substance of the cornea consists.

These corpuscles are also situated in the interfasci-
cular spaces, or spaces left between the bundles of the
ground substance, which are cavities in the interstitial

chap, v.] FIBROUS CONNECTIVE TISSUES.

35

substance cementing the bundles and trabeculae together
(von Recklinghausen). In the cornea and serous mem-
branes these spaces
possess the shape
of branched lacu-
nae, each lacuna
being the home
of the body of
the cell, while the
branches or cana-
liculi contain its
processes. These
canaliculi form the
channels by which
neighbouring lacu-
nae anastomose
with one another
(Fig. 26). The cell
and its processes do
not fill up the la-
cuna and its canali-
culi. In loose connective tissue the lacuna may be of
considerable size, and may contain several connective

cells, which make as it
were a lining for it.
These in some places are
very little branched, and
almost form a continuous
endotheloid membrane of
flattened cells. Such is
Fig. 24.-From the Tail of a tne subepithelial endothe-

Tadpole.

Fip. 23s.— From a Transverse Section through
the Tendons of the Tail of a Mouse, stained
with gold chloride.

Several fine tendons are shown here. The dark
branched corpuscles correspond to albuminous
cement substance stained with gold chloride:
they are the channels between the bundles of
fibrous tissue, constituting the tendon, and seen
here as the clear spaces in cross section. In each
of these channels is a row of tendon cells— not
discernible here, the long axis of these rows
being parallel with the long axis of the tendon.
(Handbook.)

c, Branched connective tissue cells: m,
a migratory cell. (Atlas.)

Hum of Debove, occur-
ring underneath the epi-
thelium on the surface

of the mucous membrane of the bronchi, bladder,

and intestines.

40. (c) In the true skin and mucous membranes

ELEMENTS OF HISTOLOGY.

[Chap. V,

the connective tissue cells are also branched flattened
corpuscles, and by their longer
or shorter processes are con-
nected into a network (Fig. 24).
Each cell has a flattened oblong
nucleus. As a rule, some of
the processes are membranous
prolongations coming off under
an angle from the body of the
cell, which is then called the
chief plate, the processes being
the secondary plates. By the
latter the cell is wedged in
between the bundles of the tra-

Networks of theBranched becula to which it belongs.
Corneal Corpuscles. m, . , r , n

•a, The network of their pro- TlllS character of the Cells

cesses; 6, nucleus of the /,,' p of TWUtAWXiTiiy <jp<->nr>rlnrv

corpuscle. (Atlas.) (l'e-> OI possessing secoi.uaiy

plates) is well shown by the
cells of the skin and
mucous membranes, j ^

but only in a very fi .•&*

limited degree by "" \u^

those of the cornea X

and serous mem-
branes, and somewhat
better by some of
those of the subcuta-
neous and other loose
connective tissues.

In the skin and
mucous membranes
also the cells and
their processes are
situated in the in-
terfascicular spaces.
41. The connec-

tive tissue corpuscles

Fig. 26.— From the Cornea of Kitten,
stained with Nitrate of Silver, show-
ing the Lymph-canal System.

a, The lacunas, each containing the nucleated
cell-body, just indicated here ; 6. the
canalicuh for the cell processes. (Atlas.)

Chap, v.] FIBROUS CONNECTIVE TISSUES. 37

hitherto mentioned are fixed corpuscles ; they do not
show movement. Kiihne and Rollett ascribe to the
corneal corpuscles a certain amount of contractility, in-
asmuch as they are said to be capable of withdrawing
their processes on stimulation. When this ceases they
are said again to protrude them. According to Strieker
and Norris, they acquire contractility when the corneal
tissue is the seat of inflammatory irritation. It can
be shown that the connective tissue cells consist, like
the endothelial plates, of a ground plate and a fibrillar
reticulated (granular-looking) substance around the
nucleus, and extending beyond the ground plate into
the processes of the cell. _

42. Pigment Cells. — In the lower vertebrates,
especially fishes, reptiles, and amphibian animals, we
find certain branched nucleated connective tissue cor-
puscles, distinguished by their size and by the proto-
plasm both of the cell-body and processes — but not of
the nucleus — being filled with pigment granules. The
pigment is either white or yellow, or more commonly
dark brown to black. These cells are called pigmented
connective tissue cells, or simply pigment cells. They
are very numerous in the skin of fishes, reptiles, and
amphibian animals, and also around and between the
blood-vessels of the serous membranes. They are also
present in man and mammals, but then they are
chiefly limited to the eye-ball, where they occur in the
proper tissue of the iris of all but albino and bright
blue eyes, and in the tissue of the choroid membrane.
In dark eyes of mammals a large number of these cells
are found in tire tissue between the sclerotic and
choroid, as the lamina fusca, and also, but to a more
limited degree, in the sclerotic. As a rule they appear
to be of various kinds: such as are flattened, large
plates perforated by a number of small and large holes
and minute clefts ; such as possess a more spindle-
shaped body, and long, thin, not very richlv branched

ELEMENTS OF HISTOLOGY.

[Chap V.

processes ; and intermediate forms between the two.
But on careful examination it will be seen that these

Fig. 27.— Pigment Cells of the Tail of Tadpole.

A, B, c, D represent various states ; A being a cell in an un contracted or passive
state, D in a contracted or active state.

appearances are due to different states of contraction
of the same kind of cells (Fig. 27).

43. In lower vertebrates the dark pigment cells
show marked contractility, inasmuch as they are
capable of altogether withdrawing into their body the
pigmented processes. In the passive state these are

chap, v.] FIBROUS CONNECTIVE TISSUES. 39

exceedingly numerous, and form a network so dense
that the whole mass of cells resembles an extremely
close network of pigment. In the maximum of
activity the processes disappear, being withdrawn into
the cell-body, which now looks like a spherical or
oblong mass of black pigment. Between the states
of passiveness and maximum activity there are various
intermediate grades, in which the pigmented processes
are of various numbers and lengths.

44. Owing to the great number of the pigment
cells in the skin of fishes and amphibian animals, the
state of contraction of these cells materially affects
the colour of the skin. If the dark pigment cells
of a particular part contract, the skin of this parti-
cular part will become lighter and brighter, the degree
of lightness and brightness depending on the degree
of contraction of the pigmented processes by the cells.
Briicke has shown that darkness is a stimulus to the
pigmented cells ; they contract, and the skin becomes
light. Sunlight leaves the pigmented cells in the
passive state, i.e., the skin becomes dark. If pre-
viously they have been contracted by darkness, on
being exposed to sunlight they again return to the
passive state. The contraction of the pigment cells
is under the direct influence of the nervous system
(Lister). Pouchet proved that the contractility of the
pigment cells of the skin of certain fishes is influenced
as a reflex action by the stimulation of the retina by
light.

45. Fat Cells— Fat cells in the ripe and fully-
formed state are spherical, relatively large vesicles,
each consisting (a) of a thin protoplasmic membrane,
which at one point includes an oval nucleus flattened
from side to side, and (b) of a substance, which is an
oil globule filling the cavity of the vesicle (Fig. 28).
These fat cells are massed together by fibrous connective
tissue into smaller or larger groups, which in their

ELEMENTS OF HISTOLOGY

[Chap. V.

turn form lobules; these again become lobes, and
these make continuous masses. Each group and
lobule has its afferent arteriole, one or two efferent
veins, and a dense network of capillaries between ;
each mesh of the capillary network holding one,
two or three fat cells. (Fig. 49.) Such are the

...-V

Fig. 28.— From a Preparation of the Omentum of Guinea-pig,
a, An artery ; v, vein ; c, young capillary blood-vessel; d, fat cells. (Atlas.)

nature and arrangement of the fat tissue in the
subcutaneous and submucous tissue, in the serous and
sy no vial membranes, in the intermuscular tissue, in
the loose tissue connecting organs or parts of organs.
It can be shown that fat cells are derived from
ordinary connective tissue cells. In some places —
both in the embryo and adult — the protoplasm of the
connective tissue corpuscles growing in size becomes
filled with small oil globules, which, increasing in
numbers, become fused with one another to larger
globules ; as their size thus increases the cell nucleus
becomes shifted to the periphery; ultimately one

Chap, v.] FIBROUS CONNECTIVE TISSUES. 41

large oil globule fills the cell, and what is left of the
cell protoplasm surrounds this oil globule like a
membrane. The cell as a whole has become in this
process many times its original size.

46. It can also be shown that where at one time
only few isolated connective tissue corpuscles are
present, at another time, in the natural state of
growth, and especially under very favourable condi-
tions of nutrition, the connective tissue cells become
increased by cell-multiplication so as to form groups ;
these continue to increase in size and to be gra-
dually furnished with their own system of blood-
vessels; the individual cells constituting the group
become then converted into fat cells, and their pro-
cesses are thereby lost.

Individual connective tissue cells situated in the
neighbourhood of small blood-vessels are converted
into fat cells under favourable conditions of nutrition.

In starvation the fat cells lose their oil globule,
they become smaller and contain a serous fluid, which
may ultimately also disappear. Finally, the fat cell
may be reduced to a small, solid, protoplasmic, slightly
branched cell.

47. In many places the fibrous connective tissue
includes, besides the fixed cells, others which show
amoeboid movement. These are of two kinds: (1)
migratory or wandering cells. These are identical
with colourless blood corpuscles as regards size, shape,
aspect, and general nature (Fig. 24, m). They wander
about through the spaces of the fibrous tissue. Some
of them are slightly larger, and possess one spherical
relatively large nucleus. The amoeboid movement
of these cells is not so distinct as in the smaller
variety. (2) Plasma cells of Waldeyer. They are
larger than the former, less prone to migrating, being
possessed of only slight amoeboid movement, which
is, however, sufficiently pronounced to be detected.

42 ELEMENTS OF HISTOLOGY. [Chap. v.

They contain always coarse granules, which are com-
posed of a substance which is not fat, but something
between protoplasm and fat. They stain deeply in
dyes, and the corpuscles correspond to similar "gra-
nular" corpuscles of the blood. These " granules"
may change into fat globules, and thus the plasma
cell becomes transformed into a fat cell.

48. The wandering cells occur almost in all loose
fibrous tissues, chiefly around or near blood-vessels ;
they are not numerously met with in the healthy
state, but increase greatly in the state of inflamma-
tion of the part. The larger kinds are met with
in certain localities only; in the sub-lingual gland
of the dog and guinea-pig they occur in numbers
between the gland tubes or acini They are also
found in the mucous membrane of the intestine.
The plasma cells are met with chiefly in the inter-
muscular tissue, in the mucous and sub-mucous tissue
of the intestine, in the trabeculse of the lymphatic
glands, and in the omentum.

49. Development of fibrous tissue. — "Fibrous
connective tissue is developed from embryonal connec-
tive tissue cells, i.e., from spindle-shaped or branched
nucleated protoplasmic cells of the mesoblast. The
former are met with isolated or in bundles, as in the
umbilical cord or embryonal tendon. The latter
form a network, as in the foetal skin and mucous
membrane. In both instances the protoplasm of the
embryonal connective tissue cells becomes gradually
transformed into a bundle of elementary fibrils,
with a granular-looking interstitial substance. The
nucleus of the original cell finally disappears. A
second mode of the formation of fibrous connective
tissue is this : the embryonal connective tissue cell,
while growing in substance, produces the fibrous tissue
at the expense of its peripheral part. A remnant of
the protoplasm persists around the nucleus.

Chap.v.] FIBROUS CONNECTIVE TISSUES.

43

The same modes of formation of connective tissue
may be also observed in the adult under normal and
pathological conditions.

50. Fibrous connective tissue is in most places
associated with elastic fibres or yellow elastic tissue.
These are of bright aspect, of variable thickness and
length, branching

and anastomos-
ing so as to form
networks (Fig.
29). They are
straight or more
or less twisted
and coiled. The
latter condition
may be observed
when the tissue
is shrunk, the
former when it
is stretched.
They do not
swell up in acids
or alkalies, nor
yield glutin or
gelatin on boil-
ing, but contain

a chemically different substance, viz., elastin.
broken their ends generally curl up.

51. Elastic fibres occur in great numbers as net-
works extending between the bundles of fibrous tissue,
in the skin and mucous membranes, in the serous and
synovial membranes, and in the loose interstitial con-
nective tissues. They are not very commonly met
with in tendons and fascia? ; in the former they are
seen as single fibres often twisting round the tendon
bundles.

Elastic fibres forming bundles, but branched and

Fig. 29.— From a Preparation of the Mesentery.

a, Bundles of fibrous tissue; 6, networks of elastic
fibres. (.Atlas.)

When

44 ELEMENTS OF HISTOLOGY. [Chap.v.

connected into networks within the bundle, are to be
specially found in considerable numbers in the walls
of the alveoli of the lung, in the ligamenta flava, in
the ligamentum nucha3 of the ox — in which the fibres
are exceedingly thick cylinders, — in yellow elastic car-
tilage (see below), in the endocardium and valves of
the heart, and in the vascular system, particularly the
arterial division. In the latter organs the intima,
and also to a great extent the media, consist of elastic
fibrils densely connected into a network.

52. The following are special morphological modi-
fications of the elastic fibres : (a) elastic fenestrated
membranes of Henle, as met with in the intima
of the big arteries ; these are in reality networks
of fibres with very small meshes, and the fibres
unusually broad and flat. (b) Homogeneous elastic
membranes, which surround, as a delicate sheath, the
connective tissue trabeculse in some localities, e.g.,
subcutaneous tissue, (c) Homogeneous-looking elastic
membranes in the cornea, found behind the anterior
epithelium as Bowman's elastica anterior, and at the
back of the cornea as elastica posterior, or Descemet's
membrane; in this latter bundles of minute fibrils
have been observed, (d) Elastic trabecula3 forming a
network, as in the ligamentum pectinatum iridis.
In the embryonal state the elastic fibres are nucleated,
the nuclei being the last remnants of the cells from
which the fibres develop — one cell generally giving
origin to one fibre. Such nucleated fibres are called
Henle's nucleated fibres.

53. Special varieties of fibrous connective tissue
are these : —

(1) Adenoid reticulum. This is a network of fine
fibrils, or plates, forming the matrix of lymphatic or
adenoid tissue (see Lymphatic Glands). The reticulum
is not fibrous connective tissue nor elastic tissue ; it
contains nuclei in the young state, being derived from

Chap, vi.] CARTILAGE. 45

a network of branched cells ; but in the adult state
the reticulum itself possesses no nuclei. Those found on
it do not form an essential part of it.

(2) The neuroglia of Virchow is a dense network
of very fine homogeneous fibrils forming the support-
ing tissue for the nervous elements in the central
nervous system. These fibrils are supposed to be
elastic fibres (Gerlach). Embedded in the network of
these fibres are found branched nucleated flattened
cell plates, which are the proper connective tissue cells.

(3) Gelatinous tissue. This occurs chiefly in
the embryo, being the unripe state of fibrous
connective tissue. It consists of spindle-shaped or
branched connective tissue cells, separated from one
another by a homogeneous transparent mucoid sub-
stance. It is met with in the umbilical cord of the
embryo, and in the places where fibrous connective
tissue is to be developed. After birth it is found in
the tissue of the pulp of the teeth, and in the cavity
of the middle ear, and in some places as precursor
of fat tissue.

CHAPTER YI.

CARTILAGE.

54. Cartilage consists of a firm ground substance
which yields ckondrin, and of cells embedded in it.
Most cartilages (except on the articulation surface)
are covered on their free surface with a membrane of
fibrous connective tissue with a few elastic fibrils.
This membrane is supplied with blood-vessels, lym-
phatics, and nerves, and is of essential importance for
the life and growth of the cartilagev This is the peri-
chondrium. There are three varieties of cartilage.

46 ELEMENTS OF HISTOLOGY. [chap. vi.

55. (1) Hyaline cartilage (Fig. 30A). This occurs
at the articular surfaces of all bones ; on the borders
of many short bones ; at the sternal part of the ribs,
as costal cartilages ; at the margin of the sternum,
scapula, and os ileum ; in the rings of the trachea, the
cartilages of the bronchi, the septum and lateral carti-
lages of the nose ; and in
the thyroid and cricoid
cartilages of the larynx.
The ground substance is
hyaline, transparent,
ground - glass - like, and
firm. The cells are
spherical or oval proto-
plasmic corpuscles, each
with one or two nuclei.
Eig> 3°A'i;STnreacStilage Cf The7 undergo division,

In the hyaline ground substance are &nd although the two off-

clpsuies6. cartilage a in spring are at first close

together — half-moon-like

— they gradually grow wider apart by the deposit
of hyaline ground substance between them. The
cells are contained in special cavities called the
cartilage lacunce. Each cell generally occupies one
lacuna, but according to the state of division a lacuna
may contain two, four, six, or eight cartilage cells ;
the latter are those cases in which division proceeds
at a more rapid rate than the deposition or formation
of hyaline ground substance between the cells.

The part of the cartilage next to the perichondrium
shows most active growth ; hence the cells are here smaller,
closer together, and there is less ground substance.

Each lacuna is limited by a delicate membrane,
and, according to the state of the cell, is either com-
pletely or partially filled out by it. This membrane
is called the capsule (Fig. 30A). In many cartilages,
especially in growing cartilage, it is thickened by the ad-

Chap. VI .] CAR TIL A GE. 4 7

dition of a layer or layers of hyaline ground substance ;
this is the most recently-formed part of the matrix, but
is still distinct
from the rest of
the ground sub-
stance. -j£.

56. In some

places, especi- ^*& /

ally in articular ^

cartilage (Till-
manns, Baber),

bundles of fine . i |'<£

conne ctive *sp

tissue fibrils
may be noticed
in the hyaline

ground SUb- Fig. 30B. — From a Preparation of Sternal
Stance. Cartilage of Newt.

K*J TV, o/vmp The lacunae, containing the cartilage cells, anastomose
^ ' • -*••*"*• ^^-" l>y fine channels*

cartilages, the

protoplasm of the cell becomes filled with fat globules
(Fig. 30c). This fact may be observed in many normal
cartilages ; sometimes the fat globules
become confluent into one large drop,
and then the cell has the appearance of
a fat cell. In age, disease, and defi-
cient nutrition, lime salts are deposited
in ^the ground substance, beginning
from the circumference of the cells.
The lime matter appears in the shape
j.soc.-Three car- of opaque granules, or irregular or

ilage Cells filled , ^ i 2™ i i

nth Fat Droplets, angular clumps. The ground sub-

From the hyaline , r

cartilage of tho stance thereby loses its transparency,

lineal septum of . •/ •., i i •*;

Guinea-pig. becomes opaque in transmitted, white

in reflected, light, and, of course, very

hard and brittle*. This process is the calcification of

cartilage. It is also met with in cartilage that is to be

48 ELEMENTS OF HISTOLOGY. [Ch*p.vi*

replaced by bone, being the precursor of the formation
of bone, as in the embryo (see below), and at the
growing ends of tubular bones.

58. The multiplication of the cartilage cells has
been observed during life by Schleicher and Flemming.
It takes place after the mode of karyokinesis. The
lacunas of the cartilage are not isolated cavities, but
are connected with one another by fine channels (Fig.
SOe), so that the ground substance is easily permeable
by the current of nutritive fluid. These channels and
lacunae make one intercommunicating system, and are
connected with the lymphatics of the perichondrium
(Budge). Formed matter — like pigment granules, red
and white blood corpuscles, and pus corpuscles — may
also find its way into the channels and lacunae of the
cartilage from the perichondrium.

At the borders of articular cartilage, where it is
joined to the synovial membrane and the articulation-
capsule, the cartilage cells are more or less branched,
and pass insensibly into the branched connective tissue
cells of the membrane. In foetal hyaline cartilage
many of the cells are spindle-shaped or branched.

59. In the cartilage separating the bone of the
apophyses from the end of the diaphysis of tubular
bones, there is a peculiar hyaline cartilage, known as
the intermediary or ossifying. Its cells are arranged in
characteristic vertical rows, owing to the continued
division of the cells in a transverse direction.

Cartilages, or parts of cartilages, in which the cells
are very closely placed, owing to the absence, or im-
perfect deposit and formation, of ground substance,
are called parenchymatous.

60. (2) Fibro-cartilage, or connective tissue
cartilage, occurs as the intervertebral discs, as the
interarticular cartilages, sesamoid cartilages, and as
that forming the margin of a fossa glenoidalis. It is
fibrous connective tissue arranged in bundles, and these

Chap. VI.]

CARTILAGE.

49

again in layers. The ground substance of this carti-
lage is said (?) to
yield chondrin and
not glutin. Be-
tween the strata of
the fibrous bundles
are rows of more or
less flattened oval
protoplasmic nu-
cleated cells, each
invested in a deli-
cate capsule(Fig. 31).
They are less flat-
tened than the cells
of tendon, and the
capsule distinguishes
the two. Where fibro-
cartilage passes into
tendinous tissue,

the two kinds of cells pass insensibly into one another.
.-.^ssEss^^^as^j^. 61. (3) Yellow, or

elastic cartilage. —
This variety is also called
reticular ; it occurs in the
epiglottis, in the ear-lobe,
in the Eustachian tube, in
the cartilages of Wris-
berg and Santorini in the
larynx. In the early
stage this kind is hyaline.
Gradually numbers of
elastic fibrils make their
appearance, growing into

•

-?.

Fig. 31.— Fibro-Cartilage of an Interver-
tebral Ligament.

Showing the bundles of fibrous tissue and rowa
of cartilage cells. (Atlas.)

Fig. 32.— From a Section through
the Epiglottis.

<t, Perichondrinm ; ft, networks of
elastic fibrils surrounding the carti-
lage cells. (Atlas.)

tion, and branching and
E

the cartilage matrix from

the perichondrium in a

more or less vertical direc-

anastomosing with one

50 ELEMENTS GF HISTOLOGY. [Chap. vn.

another. The final stage is reached when the ground
substance is permeated by dense networks of elastic
fibrils (Fig. 32), so arranged that spherical or oblong
spaces are left, each of which contains one or two
cartilage cells, surrounded by a smaller or larger zone
of hyaline cartilage ground substance.

CHAPTER VII.

BONE.

62. BONE, or osseous substance, is associated with
several other soft tissues to form an anatomical
individual.

(a) The periosteum.— Except at the articular
surfaces, and where bones are joined with one another
by ligaments or cartilage, all bones are covered with a
vascular membrane of fibrous connective tissue. This
is the periosteum. It consists in most instances of
an outer fibrous layer, composed of bundles of fibrous
tissue densely aggregated, and an inner, or osteogenetic
layer, which is of loose texture, consisting of a mesh-
work of thin bundles of fibrous tissue, in which
numerous blood-vessels and many protoplasmic cells are
contained. The blood-vessels form by their capillaries
a network. The cells are spheroidal or oblong, each
with one spherical or oval nucleus. They have to
form bone-substance, and are therefore called the osteo-
blasts (Gegenbaur).

(b) The cartilage is hyaline cartilage, and its
distribution on and connection with bone have been
mentioned in §§ 55 and 59.

63. (c) The marrow of bone is a vascular soft
tissue, filling up all spaces and cavities. It consists

chap. vii. j BONE. 51

of a small amount of fibrous tissue as a matrix, and
in it are embedded numerous blood-vessels and cells.
The few afferent arterioles break up into a dense net-
work of capillaries, and these are continued as plexuses
of veins, characterised by their size and exceedingly
thin walls. The cells are of the same size, aspect, and
shape as the osteoblasts of the osteogenetic tissue, and
they are called marrow cells.

In origin and structure, the tissue of the osteo-
genetic layer of the periosteum and the marrow are
identical. In the embryo, the marrow is derived
from an ingrowth of the osteogenetic layer of the
periosteum (see below), and also in the adult the two
tissues remain directly continuous. As will be shown
later, the marrow at the growing ends of the bones
is concerned in the new formation of osseous substance
in the same way as the osteogenetic layer of the peri-
osteum is in that of the surface ; and in both tissues
the highly vascular condition and the cells (osteoblasts
of the osteogenetic layer, and marrow cells of the
marrow) are the important elements in this bone
formation. Marrow is of two kinds, according to
the condition of the cells. If many or most of these
are transformed into fat cells, it has a yellowish aspect,
and is called yellow marrow ; if few or none of them
have undergone this change, it looks red, and is called
red marrow. In the central, or marrow, cavity of the
shaft of tubular bones, and in the spaces of some
spongy bones, the marrow is yellow ; at the ends of the
shaft, in the spongy bone substance in general, and in
young growing bones, it is red.

The cells, especially those of red marrow, are the
elements from which normally vast numbers of red
blood-corpuscles are formed, as has been mentioned on
a former page.

In marrow, particularly in red marrow, we meet
with huge multinucleated cells, called Myeloplaxes of

52

ELEMENTS OF HISTOLOGY. [Chap. vn.

Robin. They are derived by overgrowth from ordinary
marrow cells, and are of importance for the absorption
and formation of bone (see below). According to
Heitzmann, Malassez, and others, they also have to
do with the formation of blood-vessels and blood-
corpuscles.

64. The matrix of osseous substance is dense
fibrous connective tissue, i.e., a tissue yielding gelatin
on boiling. The cement substance between the fibrils
is petrified, owing to a deposit of insoluble inorganic
lime salts, chiefly carbonates and phosphates. These
can be dissolved out by strong acids (hydrochloric)
and are thereby converted into soluble salts. Thus
the organic matrix of osseous substance — called ossein
— may be obtained as a soft flexible material, easily
cut.

The bone substance is in the adult state generally
lamellated, the lamellae being of microscopic thinness.

Between every two
lamellae are num-
bers of isolated,
flattened, oblong
spaces — the bone
lacunae (Fig. 33),
which anastomose
by numerous fine
canals with one
another, and also
with those of the
next lamella above
and below. The
appearances are

very similar to those presented by the lacunas and
canaliculi containing the corneal corpuscles, as des-
cribed in Chapter V.

These bone lacunae and their canaliculi are the lymph-
canalicular system of osseous substance, for they are

t'ig. 33. — Osseous Lamellae ; oblong branched
bone lacuna? and canaliculi between them.
(Atlas.)

Chap, vii.] BONE. 53

V
in open and free communication with lymphatic

vessels of the marrow spaces and Haversian canals.

65. In the bone matrix, each lacuna contains also
a nucleated protoplasmic cell, called the bone cell, which,
however, does not fill it completely. In the young
state, the cell is branched, the branches passing into
the canaliculi of the lacunae ; but in the old state very
few processes can be detected on a bone cell, which,
with its lacuna and canaliculi, is called a bone cor-
puscle.

66. According to the arrangement of the bone
substance, we distinguish compact from spongy sub-
stance. The former occurs in the shaft of tubular
bones and in the outer layer of flat and short bones.
Its lamellse are arranged as : (a) concentric or Haversian
lamellce, directly surrounding the Haversian canals
(Fig. 33A). These are fine canals of varying lengths
pervading the compact substance in a longitudinal direc-
tion, and anastomosing with one another by transverse
or oblique branches. The Haversian canals near the
marrow cavity are larger than those near the perios-
teum. As a matter of fact, those next to the marrow
cavity become gradually enlarged by absorption, until
finally they are fused with the marrow cavity. Each
Haversian canal contains a blood-vessel, one or two
lymphatics, and a variable amount of marrow tissue.
These canals open both into the marrow cavity and on
the outer surface into the osteogenetic layer of the peri-
osteum, and they form the means by which the latter
remains in continuity with the marrow. They are
surrounded by numbers of concentric bone lamellae,
with the bone corpuscles between them, and this is a
system of concentric lamellce. Near the external sur-
face of the compact substance the number of lamella
in each system is smaller than in the deeper parts.
(6) Between these systems of concentric lamella are
the interstitial or ground lamellce; they run in various

54 ELEMENTS OF HISTOLOGY. [Chap.vn.

directions, and in reality fill the interstices between
the systems of the Haversian or concentric lamellse.
Near the external surface of long bones they have pre-
eminently a direction parallel to the surface. These are
the circumferential lamellce of Tomes and de Morgan.

i£^lT&^> UteK-^ s.v?£&U

Fig. 33A.— Compact Bone Substance in Cross Section.

a, Concentric lamellae arranged around the Haversian canals, cut across;
b, interstitial or ground lamellas. The bone lacunas are seen between the
bone lamellae. (Atlas.)

The lamellae of compact bone are perforated by per-
pendicular petrified fibres, the perforating fibres of
Sharpey. They form a continuity with the fibres of
the periosteum, from which they are developed.

Some of these fibres are fine, and of the nature of
elastic fibres.

67. Spongy bone substance occurs in the end of the
shaft, in the apophyses, in short bones, and in the
diploe of flat bones. The cavities or meshes of the
spongy substance are called Haversian spaces; they
intercommunicate with one another, and are filled
with marrow, which in the young and growing state
is generally of the red variety. The firm parts are of
the shape of spicules and septa, called bone trabeculce,

Chap, vii.] BONE* 55

of varying length and thickness, and are composed of
lamellae of bone substance.

According to the arrangement of the trabeculse,
the spongy substance is a uniform honey-combed sub-
stance, or appears longitudinally striated, as in the
end of the shaft. In the latter case the marrow spaces
are elongated and thetrabeculse more or less parallel, but
anastomosing with one another by transverse branches.

68. Development of bone. — Bone is developed
in the embryo, and continues to be formed also after
birth as long as bone grows, either in the cartilage, or
independently of this directly from the osteogenetic
layer of the periosteum. The former mode is called
endochondral, the latter periosteal, or intermembranous
formation.

All bones of the limbs and of the vertebral
column, the sternum, and the ribs, and the bones
forming the base of the skull, are preformed in the
early embryo as solid hyaline cartilage, covered with a
membrane identical in structure and function with
the periosteum, which at a later period it becomes. The
tegmental bones of the skull, the bones of the face,
the lower jaw, except the angle, are not preformed at
all, only a membrane identical with the future perios-
teum being present, and underneath and from it the
bone is gradually being deposited.

69. Endocnondral formation. — The stage
next to the one (1) in which we have solid hyaline
cartilage covered with periosteum is the following
(2) : Starting from the " centre, or point, of ossifica-
tion," and proceeding in all directions, the cartilage
becomes permeated by numbers of channels (cartilage
channels) containing prolongations (periosteal processes
of Virchow) of the osteogenetic layer of the periosteum,
i.e., vessels and osteoblasts, or marrow cells. This is
the stage of the vascularisation of the cartilage. In
the next stage (3) the cartilage bordering on these

ELEMENTS OF HISTOLOGY. [Chap. vii.

channels grows more transparent, the lacunce becoming

enlarged and the
cartilage cells more
transparent. The lat-
ter gradually break
down, while the in-
tercellular trabeculse
become calcified;
the lacuna? them-
selves, by absorp-
tion, fusing with the
cartilage channels.
These latter there-
by become trans-
formed into irregu-
lar cavities, which
are bordered by, and
into which project,
trabeculce of calcified
cartilage. The cavi-
ties are the primary
marrow cavities, and
they are filled with
the primary or car-
tilage marrow, i.e.,
blood - vessels and
osteoblasts, derived,
as stated above, from
the osteogenetic
layer of the perios-
teum. (4) The os-
teoblasts arrange
themselves by active
multiplication as an
epitlteloid layer on
the surface of the

calcined cartilage trabeculse projecting into, and bor-

Fig. 34.— Longitudinal Section through the
entire Foetal Humerus of a Guinea-pig.

T, Periosteum ; J, hyaline cartilage of the epiphysis ;
c, intermediate cartilaere at the end of the shaft ;
tf, zone of calcification ; e.periostealbone.spongy ;
/, endochondral bone, spongy.

Chap, vi i.] BONE. 57

dering the primary marrow cavities. The osteoblasts
form bone s^lbstancet and as this proceeds, the calcified
cartilage trabeculce become gradually ensheathed and
covered with a layer of osseous substance, — the osseous
matrix and branched bone corpuscles. Thus the
original cartilage gradually assumes the appear-
ance of a spongy substance, in which the cavities
(primary marrow cavities) are filled with the primary
marrow, and are of considerable size, while the
trabeculse bordering them are calcified cartilage
covered with layers of new bone. The marrow cells,
or osteoblasts, continue to deposit bone substance on
the free surface of the trabeculse, while the calcified
cartilage in the centre of the trabeculae gradually
becomes absorbed.

70. The nearer the centre of ossification, the
more advanced the process, i.e., the more bone the
less calcified cartilage is found in the trabeculae,
and the thicker the latter. At the "centre of ossifi-
cation," i.e., whence it started, the process is further
advanced ; away from it, it is in an earlier stage.
At this period of embryo life, between the centre of
ossification and a point nearer to the extremity of
the shaft of a tubular bone, all stages described above
may be met with, viz., between the solid unaltered
hyaline cartilage at the end of the shaft, and the
spongy bone with the unabsorbed remains of calcified
cartilage in the middle of the shaft, all intermediate
stages occur (Fig. 34).

71. After birth, and as long as bone grows, we
find in the end of the shaft, and to a further degree
also in the epiphysis, a continuation of the above
process of enclochondral formation. In fact, all
bones preformed in the embryo as cartilage grow in
length before and after birth by endochondral formation
of new bone. The hyaline cartilage at their ex-
tremities (intermediate or ossifying cartilage) is the

58 ELEMENTS OF HISTOLOGY. [Chap. vn.

cartilage at the expense of which the new bone is
formed, by the marrow (blood-vessels and marrow-
cells or osteoblasts) of the spongy substance in con-
tact with the cartilage.

72. Following the development of a tubular bone
after the above-mentioned stage 4, we find that the
spongy bone once formed is not a permanent structure,

Fig. 35.— From a Transverse Section through the Tibia of Foetal Kitten.

a, Fibrous layer of the periosteum ; 6, osteogenetic layer of the periosteum ;
c, periosteal hone: d, calcified cartilage not covered yet by hone; below this
layer the trabeculoa of calcined cartilage covered with plates of hone-
shaded darkly in the figure ; e, boundary between periosteal and endochondral
bone. (Atlas.)

Chap, vi i.i BONE. 59

but becomes gradually absorbed altogether, and this
process also starts from the points of ossification. Thus
a continuous cavity filled with marrow is formed, and
this first appears in the region of the centre of ossifi-
cation, and represents the rudiment of the future
continuous central marrow cavity of the shaft. Simul-
taneously with or somewhat previous to this absorp-
tion of the endochondral bone, new bone — spongy
bone — is deposited directly by the osteogenetic layer
of the periosteum on the outer surface of the en-
dochondral bone. This also commences at the centre of
ossification and proceeds from here gradually to further
points. This is the periosteal bone (Figs. 34, 35). It is
formed without the intervention of cartilage directly
by the osteoblasts of the osteogenetic layer. And as
fresh layers of osteoblasts by multiplication appear on
the surface of the periosteal bone, new layers of bone
trabeculae are formed, and also the old trabeculse become
increased in thickness. In the meshes or Haversian
spaces of this spongy periosteal bone the same tissue
is of course to be found as constitutes the osteo-
genetic layer of the periosteum, being derived from
and continuous with it.

In these Haversian spaces concentric lamellae of
bone substance become formed by the osteoblasts, and
spongy is thus transformed into compact bone, while
at the same time the Haversian spaces, being nar-
rowed in by the deposit in them of the concentric
lamellae, are transformed into the Haversian canals.
When this compact bone is again absorbed — e.g., that
next the central marrow cavity of the shaft of a
tubular bone — the concentric lamellae are first ab-
sorbed, the Haversian canal being in this way again
transformed into a Haversian space.

73. At birth all the primary endochondral bone has
already disappeared by absorption from the centre of
the shaft, while the bone present is all of periosteal

6o

ELEMENTS OF HISTOLOGY. [Chap. vn.

origin.

At the extremity of the shaft, however, the
spongy bone is all
endochondral bone,
and it continues to
S^^§$^3i*< a grow in*° the inter-
S^t^^jjjf ' mediate cartilage as
^.^(^^, stated above, as long
as the bone as a whole
saa^fl grows (Fig. 36).

Of course the parts
of this spongy bone
nearest to the centre
of the shaft are the
oldest, and ulti-
mately disappear by
absorption into the
central marrow
cavity. In the epi-
physis the spongy
bone is also endo-
chondral bone, and
its formation is con-
nected with the deep
layer of the articu-
lar cartilage.

Underneath the

periosteum and on
the surface of the
spongy endochon-

cartilage; c, zone, in which the calcined dral DOne at the
trabeculse of cartilatre become erradually in- o-vfivirm+v rvf \\\(*
vested in osseous substance, shaded light in extremity OI lilt!

shaft, the periosteal
bone is represented
only as a thin layer,
extending as far
to the margin of the

ig.

Femur of Babbit, through the parb in
which the intermediary cartilage joins
the end of the shaft.

a. Intermediary cartilage; 6, zone of calcified
cartilage; c, zone, in which the calcified

,

the figure ; the spaces between the trabecuhe
contain marrow, and the capillary blood-
vessels are seen here to end in loops; d, in
this zone there is more bone formed : the
greater amount the farther away from this
zone. (Atlas.)

as the periosteum reaches, e.g.,
articular cartilage.

Chap. VII.]

BONE.

61

74. I nt or membranous formation. — All

bones not preformed in the embryo as cartilage are
developed directly from the periosteum in the manner
of the periosteal bone just described (Fig. 37). Here also

a

Fig. 37.— A small mass of Bone Substance in the Periosteum of the
Lower Jaw of a Human Foetus.

a, Osteogenetic layer of periosteum ; 6, multinucleated giant cells, myeloplaxes.
The one in the middle of the upper margin corresponds to an osteoclast,
whereas the smaller one at the left upper corner appears concerned in the
formation of bone. Above c the osteoblast cells become surrounded by
osseous substance and thus become converted into bone-cells. (Atlas.)

the new bone is at first spongy bone, which in its inner
layers gradually becomes converted into compact bone.

In all instances during embryo life and after
birth the growth of a bone in thickness takes place
after the manner of periosteal bone ; this is at first
spongy, but is gradually converted into compact bone.

75. All osseous substance is formed in the embryo
and after birth by the osteoblast or marrow cells
(Gegenbaur, Waldeyer) : each osteoblast giving origin
to a zone of osseous matrix, and in the centre of this

62 ELEMENTS OF HISTOLOGY. [Chap. vn.

to a nucleated protoplasmic remnant, which gradually
becomes branched and then represents a bone cell.
The osseous matrix is at first a soft fibrillar tissue,
but is gradually and uniformly impregnated with
lime salts. This impregnation always starts from the
centre of ossification.

76. Wherever absorption of calcified cartilage or of
osseous substance is going on, we meet with the multi-
nucleated huge protoplasmic cells, called the myelo-
plaxes of Robin. Kolliker showed them to be impor-
tant for the absorption of bone matrix, and called
them therefore Osteoclasts (Fig. 37). For cartilage they
may be called Chondroclasts. When concerned in tho
absorption we find these myeloplaxes situated in
smaller or larger pits, which seem to have been pro-
duced by them ; these absorption pits or lacunas on the
surface of bones are called Howship's lacunae. They
invariably contain numbers of osteoclasts. It can,
however, be shown that myeloplaxes are also con-
cerned in the formation of bone, by giving origin to a
number of new osseous zones with their bone cells.
In the earliest stages of development of the foetal jaw
this process is seen with great distinctness (Fig. 37).

77. Dentine forms the chief part of a tooth. It
consists of a petrified matrix, in which are numbers of
perpendicularly-arranged canals — the dentinal tubes —
containing the dentinal fibres. It is in some respects
similar to bone, although differing from it in certain
essentials. It is similar, inasmuch as it is developed
in like manner by some peculiarly transformed
embryonal connective tissue — viz., by the tissue of the
embryo tooth papilla — and inasmuch as cells are con-
cerned in the production both of the petrified matrix
(impregnated with lime salts), and of the processes of
the cells contained in its canals — the dentine fibres.
The details of structure and distribution will be
described in connection with the teeth.

Chap. VIII.]

CHAPTER VIII.

NON-STRIPED MUSCULAR TISSUE.

78. THIS tissue consists of nucleated cells, which,
unlike amceboid cells, are contractile in one definite
direction, becoming shorter and thicker during con-
traction.

The cells are elongated, spindle-shaped, or band-like
(Fig. 3 8 A), and drawn out at each extremity into a longer
or shorter, generally single but occasionally branched,
tapering process. Each cell includes an oval nucleus,

Fig. 38A. — Non-striped Muscular Fibres, isolated.

The cross-markings indicate corrugations of the elastic sheath of the individual
fibres. (Atlas.)

which is flattened if the cell it belongs to is flattened.
The cell-substance is a pale homogeneous-looking or
finally and longitudinally striated substance.

During extreme contraction the nucleus may
become more or less plicated, so that its outline be-
comes wavy or zig-zag.

It has been shown (Klein) in certain preparations —
e.g., the non-striped muscle cells of the mesentery of
the newt — that each muscle cell consists of a delicate

64 ELEMENTS OF HISTOLOGY. [Chap. vin.

elastic sheath, inside of which is a bundle of minute
fibrils, which cause the longitudinal striation of the cell.
These fibrils are the contractile portion ; and they are
contractile towards the nucleus, with whose intranu-
clear reticulum they are intimately connected. When
the cell is contracted its sheath becomes transversely
corrugated (Fig. SSe).

79. The non-striped muscular cells are aggregated
into smaller or larger bundles by an interstitial albu-

Fig. 38B.— A Non-striped Muscular Cell of Mesentery of Newt.

Showing several places where the muscular substance appears contracted,
thickened. At these places the corrugations of the sheath are marked.
<; Atlas.)

minous homogeneous cement substance, the cells being
imbricated with their extremities. The^ bundles may
form a plexus, or they may be aggregated by fibrous
connective tissue into larger or smaller groups, and
these again into continuous masses or membranes. In
the muscular coat of the bladder, in the choroidal
portion of the ciliary muscle, in the arrector pili, in the
muscular tissue of the scrotum, very well marked
plexuses of bundles of non-striped muscular cells may
be met with. In the muscularis mucosae of the
stomach and intestines, in the outer muscular coat of
the same organs, in the uterus, bladder, &c., occur
continuous membranes of non-striped muscular tissue.

When the muscular cells form larger bundles they
are more or less pressed against one another, and,
therefore, in a cross section appear of a polygonal
outline.

80. Non-striped muscular tissue is found in the
following places : in the muscularis mucosse of the
oesophagus, stomach, small and large intestine ; in the

chap, viii.] NON-STRIPED MUSCULAR TISSUE. 65

outer muscular coat of the lower two-thirds or half

of the human resophagus ; in that of the stomach, small

and large intestine ; in the tissue of the pelvis and

outer capsule of the kidney ; in the muscular coat of

the ureter, bladder, and urethra; in the tubules of

the epididymis. in the vas de- ^ .^

ferens, vesicula3 seminalis and _. l

prostate ; in the corpora caver-

nosa, and spongiosa; in the

tissue of the ovary, and in the

ligamentum latum ; in the mus- r

cular coat of the oviduct, the j^fft^ji

uterus and vagina ; in the soft ^'ib/.jf $$?

or posterior part of the wall of % <9 ^

the trachea ; in the large and FJ». 39.— From a Transverse

i-i i i • • ,i i i . Section through Bundles

small bronchi, in the alveolar of Non-striped Muscular

-, , . f ,.., , ,, , Tissue of the Intestine.

ducts and infundibula of the ^ mmcularcell8 Wllg spindle.
lung; in the pleura pulmonalis
(guinea-pig) ; in the peritoneum
of the frog and newt, in the
upper part of the upper eye-lid,

and in the fissura orbitalis ; in the sphincter and
dilatator pupillse, and the ciliary muscle ; in the
capsule and trabeculse of the spleen, and the trabeculse
of some of the lymphatic glands ; in the arrector pili,
and sweat glands of the skin, the tunica dartos of
the scrotum ; in the tissue of the nipple of the breast ;
in the large ducts of the salivary and pancreatic
gland ; and in the muscular coat of the gall bladder,
the hepatic and cystic duct. The aorta and the
arteries have a larger amount of non-striped muscular
tissue, the veins and lymphatics a smaller.

81. As regards length, the muscular cells vary
within considerable limits (from -^ to -J-^ of an inch),
those of the intestine, stomach, respiratory, urinary, and
genital organs being very long, as compared with
those of the blood-vessels, which are sometimes only
F

66 ELEMENTS OF HISTOLOGY. [Chap. ix.

twice or thrice as long as they are broad, and at the
same time branched at their extremities.

Non-striped muscular tissue is richly supplied with
blood-vessels, the capillaries forming oblong meshes,
though their number is not so great as in striped
muscle. The nerves of non-striped muscle are all
derived from the sympathetic ; their distribution and
termination will be described in a future chapter.

CHAPTER IX.

STRIPED MUSCULAR TISSUE.

82. THIS tissue is composed of extremely long (up
to l|-2 inches) more or less cylindrical fibres, of a
diameter varying between ^-^ to -g-^j- of an inch ; they
appear transversely striated. These are the stripefi
muscular fibres. They are held together by delicate
bundles of fibrous connective tissue, with the ordinary
connective tissue cells — endomysium — so as to form
larger or smaller bundles ; these again are aggregated
together by stronger bands and septa of fibrous con-
nective tissue — perimysium — into groups, and these
into the fascicles or divisions of an anatomical muscle.
The fibrous connective tissue, including the perimysium
tissue, is the carrier of the larger vascular and nervous
branches. The endomysium contains the capillaries,
which form very rich networks with elongated meshes,
and are always situated between the individual
muscle fibres. The capillaries and veins appear very
wavy and twisted in the contracted bundles, and
straighter in the uncontracted bundles. The small
vessels are provided here and there with peculiar saccu-
lar dilatations, which act as a sort of safety receptacles

chap, ix.] STRIPED MUSCULAR TISSUE.

for the blood when, during a sudden maximal contrac-
tion, it is pressed out from some of the capillaries.

83. Each muscular fibre during contraction be-
comes shorter and thicker. In the living uninjured
muscular fibres, spontaneously or after the application
of a stimulus, a contraction starts at one point and
passes over the whole muscular fibre like a wave —
contraction wave—the progress of which is noticeable
by the thickening, gradually and rapidly, shifting along
the fibre, the part behind resuming its previous diameter.

84. When looked at in the fresh state, or after the
action of certain re-agents, the muscular fibre shows the
following parts

(Fig. 40) : (1) a
transparent ho-
mogeneous deli-
cate elastic
sheath, the sar-
colemma ; (2)
dark delicate
lines stretching
across the fibre
at regular inter-
vals, so as to
sub-divide the
space within
the sarcolemma
into uniform
transverse com-
partments, the
muscular com-
partments of
Krause. These
dark lines are
the membranes
of Krause. Un-
der a high power they seem permeated or broken up by

- — a

Fig. 40.— Striped Muscular Fibres of the Water-
Beetle (Hydrophilus).

a, Sarcolerama ; &, Krause's mcrahrane. The sarcous
elements are well seen. In A the oblong nuclei of
the muscle-corpuscles are shown. In B the s;m-<>-
leniraa has become unnaturally raised from the mus-
cular contents. The contract ilt> discs arc well shown ;
so also are the sareous elements. (Atlas.)

68 ELEMENTS OF HISTOLOGY. [Chap. ix.

a great number of fine, clear, longitudinal lines (see be-
low), and therefore under these conditions seem to be
made up of one row of granules. The membranes of
Krause appear fixed to the sarcolemma, so that while
a fibre contracts, or while it is contracted or shrunk,
owing to the action of hardening re-agents, or merely
in consequence of being detached from its fixations, its
surface is not smooth, but regularly and transversely
undulating, the valleys being caused by the attachment
of the membranes of Krause to the sarcolemma.
On stretching a fibre beyond its natural passive state,
the surface becomes also uneven and undulating, but
in a reverse manner from the above.

85. These two membranous structures represent,
as it were, the framework. In the muscular com-
partments is contained the muscular substance, which
again consists of (a) the contractile or chief substance
(Rollett), which is a dim, broad, highly refractive,
doubly refractive disc, occupying the greater part of a
compartment, except a thinner or thicker layer at the
side of Krause's membrane. This layer is (b) a trans-
parent homogeneous fluid substance, forming the lateral
disc of Engelmann, or the secondary substance of
Rollett. It is isotropous. In this lateral disc occa-
sionally a transverse row of granules appears present,
but this is by no means of constant occurrence. The
contractile disc seems homogeneous, but is in reality
composed of prismatic or rod-shaped elements, the sar-
cous elements of Bowman, each being as long as the con-
tractile disc. They are very close, and there is left
between them in the fresh and living state an exceed-
ingly minute layer of a homogeneous transparent
interstitial substance, identical with that of the lateral
disc. After death and shrinking of the sarcous
elements, this interstitial substance is more marked,
and is then easily perceived as longitudinal clear
lines separating the sarcous elements in the iiidi-

Chap, ix.] STRIPED MUSCULAR TISSUE. 69

vidual compartments. The total appearance pro-
duced is that of longitudinal striation, the sarcous ele-
ments of successive compartments forming fibrils —
called the primitive fibrils. Sometimes in hardened
muscular fibres the substance of the sarcous elements
shows a middle transparent portion for the whole
contractile disc ; this appears to form a distinct
median transparency, known as the median disc of
Hensen.

86. Of course, each such fibril is a successive row
of sarcous elements, with the corresponding portion of
Krause's membranes, and the adjacent portions of the
lateral discs. Generally, each fibril is thinnest at the
point of Krause's membrane and lateral discs, and
thicker at the part corresponding to the sarcous ele-
ments, so that in reality it is of a moniliform shape
(Haycraft). This varicose condition is the more appa-
rent the shorter and thicker the individual sarcous
elements are (Fig. 4 3 A, B and c).

These differentiations due to structure alone are
sufficient to produce a transverse striation of the mus-
cular fibres; but it must be borne in mind that a fibre
when contracted or shrunk, even in the smallest degree,
would show a transverse striation due to the above-
mentioned undulating surface. Any other fibre with a
moniliform shape would show the same transverse
striation (Haycraft) ; and that usually observed oil
hardened — i.e., shrunk and more or less contracted —
fibres, may be accounted for in this way. Fibres
stretched or prevented from shrinking generally show
pronounced longitudinal striation, but also very faint
cross striae ; these latter are due to the structural
differences.

87. On observing a transverse section through a
fresh and living muscular fibre, the muscular substance
inside the sarcolemma appears as a transparent ground-
glass-like substance, crossed here and there by bright

ELEMENTS OF HISTOLOGY.

[Chap. IX.

lines. These lines gradually increase in number, and
to join that ultimately they form a dense network.
Thus a more or less regular pattern of small polygonal
fields is produced, which are styled Cohnheim's areas or
fields (Fig. 41). Each corre-
sponds to the end-view or
optical section of a sarcous
element prism, and is granu-
lar, as if composed of a
bundle of minute fibrils.
If this be the case, each
sarcous element will have to
be considered as a bundle
of rods. The bright lines
producing the Cohnheim's
fields are the interstitial
substance. When a muscle
fibre shrinks, after death
or after some hardening re-
agents, Cohnheim's fields
shrink into small circular areas, separated by a rela-
tively large amount of the interstitial substance.

88. During contraction the cross striation is much
narrower, the dim disc becoming shorter in the long
diameter of the fibre, but broader in the transverse
direction.

The broader the lateral disc in a fibre, the more
apart from one another are the dim or contractile
discs.

On the surface of the substance of the muscle
fibres, but within the sarcolemma, are seen isolated
oblong nuclei, which belong to small protoplasmic,
more or less branched corpuscles — the muscle cor-
puscles. In the adult fibres these are few and far
between ; in the young and growing fibres they are
numerous and large. Their protoplasm is the sub-
stance which, becoming converted into the muscular

Fig. 41. — Striped Muscular
Fibres in Cross Section.

Each fibre is limited by the sarco-
lemma; the muscular substance
is differentiated into Cohnheim's
areas. (Atlas.)

chap, ix.] STRIPED MUSCULAR TISSUE. 7 1

substance, is the material at the expense of which
new fibres are formed, or fibres already formed
become thickened, as is the case when muscle fibres
are kept at constant work.

In the muscular fibres of man and most verte-
brates (except the fibres of the heart), the muscular
corpuscles are situated on the surface of the muscular
substance ; but in invertebrates (especially insects and
Crustacea) they are often found in the central part
of the fibres, and here they are occasionally seen
forming almost a continuous cylindrical mass of nu-
cleated protoplasmic cells.

89. In the embryo the muscular fibres are de-
veloped from spindle-shaped nucleated cells (Remak,
Weissmann, Kolliker). One spindle-shaped cell with
an oval nucleus grows rapidly in length and thick-
ness, its nucleus divides repeatedly, and the offspring

Fig. 42.— A Striped Muscular Fibre of the Diaphragm of a
Guinea-pig.

The muscle-corpuscles aro much increased in size and numbers; they are
probably used here for the new formation of muscular substance. (Atlas.)

become shifted from one another as the cell con-
tinues to grow in length. The protoplasmic sub-
stance all along one side of the cell gives origin to
the muscular substance — sarcous elements and lateral
disc — while a small rest of protoplasm remains col-
lected around the nucleus as the muscle corpuscle.
This protoplasm continues to increase in amount,

ELEMENTS OF HISTOLOGY. [Chap, ix.

and then the increment again changes into muscular
substance (Fig. 42). In this way the muscular fibre
increases in thickness. Thus one spindle-shaped
embryo cell gives rise to one muscular fibre, which,
at first very slender, continues to grow in thickness
by the active growth of the muscle corpuscles. The

sarcolemma appears to be formed from

cells other than muscle cells.

90. The striped muscular fibres, taken
as a whole, are, as a rule, spindle-shaped,
becoming gradually thinner towards their
ends. They are branched in some excep-
tional cases — e.g., in the tongue ; here
the extremities of the muscle fibres,
passing in a transverse direction into
the mucous membrane, become richly
branched.

91. Muscular fibres terminate in
tendons, either by the whole fibre passing
into a bundle of connective tissue fibrils
(Fig. 43), or by the fibre ending abruptly
with a blunt, conical end, arid becoming
here fixed to a bundle of connective tissue
fibrils. The individual fibres have only,
as mentioned above, a relatively limited
length, so that, following an anatomical

tru>ed~Mui£ fascicle from one point of its insertion to
the other, we find some muscle fibres
terminating, others originating. This
takes place in the following way : the
contents of a fibre suddenly terminate,
while the sarcolemma, as a fine thread,

becomes interwoven with the fine connective tissue

between the muscular fibres.

92. The striped muscular fibres of the heart

(auricles and ventricles) and of the cardiac ends of

the large veins (the pulmonary veins included) differ

cula r Fibres
passing into
Bundles of
Fibrous Tis-
sue.

Termination in
Tendon. (Hand-
book.)

chap, ix.] STRIPED MUSCULAR TISSUE.

73

from other striped muscular fibres in the following
respects: — (1) They possess no distinct sarcolemma.

(2) Their muscle corpuscles are in the centre of the
fibres, and more numerous than in ordinary fibres.

(3) They are very richly branched, each fibre giving off
all along its course short branches, or continually divid-
ing into smaller

fibres and form-
ing a close net-
work (Fig. 43A.) A
transverse section
through a bundle
of such fibres
shows, therefore,
their cross sections
irregular in shape
and size. (4) Each
nucleus of a muscle
corpuscle occupies
the centre of one
prismatic portion \
each fibre and its
branches thus

Fig. 43A.— Striped Muscular Fibres of the
Heart of Mouse.

A, Showing the branching of the fibres and their
anastomosis in networks ; B, part of a thin fibre,
highly ma,«nifled, showing the moniliform
primitive fihrill:c: c, one primitive flbrilla
more highly magnified.

1

appear com

of a single row of

such prismatic

portions, and they

seem separated

from one another

— at any rate in an

early stage — by a septum of a transparent substance.

93. Muscular fibres seem either markedly pale
or markedly red (Ranvier) ; in the former (e.g.,
quaclratus lumborum, or adductor magnus femoris
of rabbit) the transverse striation is more distinct
and the muscular corpuscles less numerous, than
in the latter (e.g., semi-tendinosus of rabbit,

74 ELEMENTS OF HISTOLOGY. [Chap. x.

diaphragm). Here the longitudinal striation ap-
pears very distinct, .but these differences are not
constant in other muscular fibres of other animals
(E. Meyer).

94. Briicke has shown that striped muscular fibres
are doubly refractive, like uniaxial positive crystals
(rock crystal), the optical axis coinciding with the
long axis of the fibres. The lateral disc and inter-
stitial substance are isotropous, the sarcous elements
(Briicke) and Krause's membrane (Engelmann) being
doubly refractive. The sarcous elements are, how-
ever, not the ultimate optical elements, but must be
considered as composed of disdiaclasts, the real doubly
refractive elements (Briicke).

CHAPTER X.

THE HEART AND BLOOD-VESSELS.

95. (A) THE heart consists of an outer serous
covering (the visceral pericardium), an inner lining
(the endocardium], and between the two the muscular
ivall (Fig. 44), Underneath the pericardium and en-
docardium is a loose connective tissue, called the sub-
pericardial and subendocardial tissue respectively.

The free surface of both the pericardium and
endocardium has an endothelial covering, like other
serous membranes — i.e., a single layer of transparent
nucleated cell plates of a more or less polygonal or
irregular shape. The ground- work of these two mem-
branes is fibrous connective tissue, forming a dense
texture, and in addition there are many elastic fibres
composing networks. Capillary blood-vessels, lymphatic

chap, x.] THE HEART AND

vessels, and small branches of nerV^fib'res are met
with everywhere. The subpericardial and subeiido-
cardial tissues consist of loosely connected trabeculse of
fibrous connective tissue, forming a continuity with
the intermuscular connective tissue of the muscular
part of the heart.
The former contains
in many places
groups of fat cells.

96. On the free
surface of the papil-
lary muscles, in some
parts of the surface
of the trabecul?e car-
neae, and at the inser-
tion of the valves,
the endocardium is
thickened by ten-
dinous connective
tissue. The valves
themselves are folds
of the endocardium,
and contain in their

essential parts fibrous Fig. 44.— Transverse Section through the

connective tissue, to Auricle of the Heart of a Child-

which, especially in

the semilunar valves,

numerous elastic

fibres are added. The muscular tissue of the wall

of the auricle penetrates a short way into the auriculo-

ventricular valves.

All the cordse tendinese and the valves are of course
covered on their free surfaces with endothelium.

Special tracts of muscle fibres occur in the sub-
endocardial tissue.

The fibres of Purkinje are peculiar fibres occurring
in the subendocardial tissue in some mammals and

a, Endothelium lining the endocardium ; J, en-
docardium ; c, muscular bundles cut trans-
versely ; d, muscular bundles cut longitu-
dinally ; «, pericardia! covering.

76 ELEMENTS OF HISTOLOGY. [Chap. x.

birds (not in man). They are thin, transversely striped,
muscular fibres, the central part of which is a con-
tinuous mass of protoplasm, with nuclei at regular
intervals, the same as is the case with some skeletal
muscular fibres of insects.

97. The muscular fibres forming the proper wall
of the heart, the structure of which has been described
in the previous chapter, are grouped in bundles
separated by vascular fibrous connective tissue. In the
ventricles the bundles are aggregated into more or less
distinct lamellae.

Like other striped muscular fibres, those of the
wall of the heart are richly supplied with blood-vessels
and lymphatics. The endocardium and valves and the
pericardium possess their own systems of capillaries.

The lymphatics form a pericardial and an endo-
cardial network, the muscular substance of the heart
having numerous lymphatics in the shape of lymph
clefts between the muscular bundles, and also typical
networks of tubular lymphatics.

98. The nerve branches of the plexus cardiacus
form rich plexuses. In connection with some of
them are found numerous collections of ganglion cells
or ganglia. These are very numerous in the nerve
plexus of the auricular septum of the frog's heart (Lud-
wig, Bidder), and in the auriculo-ventricular septum
of the frog (Dogiel). In man and mammals numerous
ganglia are found on the subpericardial nerve branches,
chiefly at the point of junction of the large veins with
the heart, and at the boundary between the auricles
and the ventricles.

99. (B) The arteries (Fig. 45) consist of : (a) an
endothelial layer lining the lumen of the vessel ; (6) an
intima consisting of elastic tissue; (c) a media, con-
taining a large proportion of non-striped muscular cells
arranged chiefly in a transverse, i.e., circular, manner;
and (d) an adventitia composed chiefly of fibrous

chap, x.] THE HEART AND BLOOD-VESSELS.

77

connective tissue, with an admixture of networks of
elastic fibres.

(a) The endothelium is a continuous single layer
of flattened eloii- e

gated cell plates, i

(b) The inti^
ma in the aorta
and large arteries
is a very com-
plex structure, 3
consisting of an
innermost layer
of fibrous con-
nective tissue,
which is the
"inner longitu-
dinal fibrous
layer" of Remak,
outside of which
is a more or less
longitudinally-
arranged elastic

Fig 45<_From a Transverse Section through
the Inferior Mesenteric Artery of the Pig.

membrane. This
is laminated, and

e, Endothelial lining ; l, clastic intima ; TO, mtiprular
media; a, advcntitia with numerous elastic fibrils,
cut in transverse section. (Atlas.)

composed of

fenestrated elastic membranes of Henle (see a former
chapter). The greater the artery the thicker the
intima. In microscopic arteries the intima is a thin
fenestrated membrane, the fibres having distinctly a
longitudinal arrangement.

(c) The media is the chief layer of the wall of the
arteries (Fig. 46). It consists of transversely arranged
elastic lamellae (fenestrated membranes and networks
of elastic fibres), and between them smaller or larger
bundles of circularly arranged muscular cells. The
larger the artery the more is the relation of elastic
and muscular tissue of the media in favour of the

ELEMENTS OF HISTOLOGY.

[Chap. X.

former, in the smaller arteries the reverse is the case.
In microscopic branches of arteries the media consists

almost entirely of

cir-
cular non-striped muscle
cells with only few elas-
tic fibres.

100. In the last
branches of the micro-
scopic arteries, the mus-
cular media becomes dis-
continuous, inasmuch as
the (circular) muscular
cells are arranged not as
a continuous membrane,
but as groups of small
cells (in a single layer)
in a more or less alter-
nate fashion.

"When the media
contracts> tne "itima
is placed in longitudinal
folds.

The aorta has, in the
innermost and in the
outermost parts of the
media, numbers of lon-
gitudinal and oblique
muscle cells. Accord-
ing to Bardelebeii, all
large and middle-sized
arteries have an inner longitudinal muscular coat.

101. Between the media and the next outer layer
there is, in larger and middle-sized arteries, a special
elastic membrane, the elastica externa of Henle.
(d) The adventitia is a relatively thin fibrous con-
nective tissue membrane. In large and middle-sized
arteries there are numbers of elastic fibres present,

Fig. 46. — Transverse Section through,
a Microscopic Artery and Vein in
the Epiglottis of a Child.

A, The artery, showing the nucleated
endothelium, the circular muscular
media, and at a the fibrous-tissue adven-
titia; v, the ran, showing the same
layers ; the media is very much thinner
than in the artery. (Atlas.)

Chap, x.] THE HEART AND BLOOD-VESSELS.

79

especially in the part next to the media ; they form
networks, and have pre-eminently a longitudinal
direction.

The larger the artery the more insignificant is the
adventitia as compared with the thickness of media.

In microscopic arteries (Fig. 47), the jn,i,e
adventitia is represented by thin bundles
of fibrous connective tissue and branched
connective tissue cells.

Large and middle-sized arteries pos-
sess their own system of blood-vessels
(vasa vasorum), situated chiefly in
the adventitia and media ; lymphatic
vessels and lymphatic clefts are also
present in these coats.

102. (c) The veins differ from the
arteries in the greater thinness of their
wall. The intima and media are similar
to those of arteries, only thinner, both
absolutely and relatively. The media
contains in most veins circularly ar-

-, -. „, , ~ *

ranged muscular fibres ; they form a con-
tinuous layer, as in the arteries, and
there is between them generally more

,,, . i -i .

fibrous connective tissue than elastic,

—., , ...

1 h e adventitia is u sual ly the thickest coat,
and it consists chiefly of fibrous connec-
tive tissue (Fig. 46). The smallest veins — i.e., before
passing into the capillaries — are composed of a lining
endothelium, and outside this are delicate bundles of
connective tissue forming an adventitia. The valves
of the veins are folds, consisting of the endothelium
lining the surface, of the whole intima, and of part
of the muscular media.

103. There are many veins that have no muscular
fibres at all, e.g., vena jugularis — interim and externa
— the vena subclavia, the veins of the bones and

ip 47. - Minute

Microscopic

Artery.

ea10*^! 8i««ie

Wer of circular-

ly-ammged nou-

stni>ed muscular

adveutitia-

8o ELEMENTS OF HISTOLOGY. [Chap. x.

retina, and of the membranes of the brain and cord.
Those of the gravid uterus have only longitudinal
muscular fibres. The vena cava, azygos, hepatica,
spermatica interna, renalis and axillaris, possess an
inner circular and an outer longitudinal coat. The vena
iliaca, cruralis, poplitea, mesenterica, and umbilicalis
possess an inner and outer longitudinal and a middle
circular muscular coat. The intima of the venae
pulmonales in man is connective tissue containing
circular bundles of non-striped muscular cells (Stieda).

104. The trunk of the vense pulmonales possesses
striped muscular fibres, these being continuations of
the muscular tissue of the left auricle.

105. Hoyer showed that a direct communication
exists between arteries and veins without the inter-
vention of capillaries — as in the matrix of the nail,
in the tip of the nose and tail of some mammals, in
the tip of the fingers and toes of man, in the margin
of the ear lobe of dog and cat and rabbit.

In the cavernous tissue of the genital organs
veins make large irregular sinuses, the wall of which
is formed by fibrous and non-striped muscular tissue.

106. (D) The capillary blood-vessels are
minute tubes of about -^oV o" to -3 oVo °^ an ^ncn in
diameter. Their wall is a single layer of transparent
elongated endothelial plates, separated by thin lines of
cement substance (Fig. 48) ; each cell has an oval
nucleus. In fact, the wall of the capillaries is merely
a continuation of the endothelial membrane lining
the arteries and veins.

In some places the capillaries possess a special
adventitia made up of branched nucleated connective
tissue cells (hyaloidea of frog, choroidea of mammals),
or of an endothelial membrane (pia mater of brain
and cord, retina and serous membranes), or of adenoid
reticulum (lymphatic glands, His).

The smallest capillaries are found in the central

Chap.x.] THE HEART AND BLOOD-VESSELS.

81

nervous system, the largest in the marrow of bone.
The capillaries form always networks, the richness and

Fig. 48. — From a Preparation of the Peritoneum, stained
with Nitrate of Silver.

a, The endotheltum on the free surface of the membrane ; 6, the capillary blood-
vessels in the membrane ; their wall is a layer of endothelium. (Handbook.)

a

Fig. 49.— Young Fat Tissue of the Omentum, its Blood-vessels injected
a, Artery ; 6, vein ; c, network of capillaries. (Handbook.)

arrangement of which vary in the different organs,
according to the nature and arrangement of the ele-
ments of the tissue (Fig. 49).

82

ELEMENTS OF HISTOLOGY.

[Chap. X.

107. If capillaries are abnormally distended, as
in inflammation, or otherwise injured, the cement sub-
stance between the endothelial plates is liable to give
way in the shape of minute holes, or stigmata, which
may become larger holes, or stomata. The passage
of red blood corpuscles (diapedesis), and the migration
of white corpuscles in inflammation through the
unbroken capillaries and small veins, occur through
these stigmata and stomata.

108. Yoiuig: and Growing Capillaries, both
of normal and pathological tissues, possess solid thread-

Fig. 50. — From a Preparation of Omentum of Babbit, after staining with.
Nitrate of Silver.

», A minute vein ; a, solid protoplasmic prolongations of the wall of a capillary,
connected with connective tissue corpuscles ; c, a solid young sprout. (.Atlas.)

like shorter or longer nucleated protoplasmic processes
(Fig. 50), into which the canal of the capillary is
gradually prolonged, so that the thread becomes con-

Chap.x.] THE HEART AND BLOOD-VESSELS.

verted into a new capillary branch. Such growing
capillaries are capable of contraction (Strieker).

All blood-vessels, arteries, veins, and capillaries,
in their early stages, both in embryonal and adult life,
are of the nature of minute tubes, the wall of
which consists of a simple endothelial membrane.
In the case of the vessel becoming an artery or vein,
cells are added to the outside of the endothelium,
thus forming the elastic, muscular, and fibrous con-
nective tissue elements of the wall.

109. In the first stage, both in the embryo and
in the adult, the
vessel is repre-
sented by a solid
nucleated proto-
plasmic cell, elon-
gated or spindle-
shaped or branch-
ed. Such a cell
may be an isolated
cell of the connec-
tive tissue inde-
pendent of any
pre -existing vessel,
or it may be a
solid protoplasmic
outgrowth of the
endothelial wall of
an existing capil-
lary vessel (Fig. Fig> 61,-Developinj? Capilllry Blood-vessels

51). In both cases f rom the Tail of Tadpole.

it VkP>or»Tnf»a Vir»l "> Capillary vein with clumps of pigment In the wa
11'JJ-~ a, nucleated protoplasmic. sprout ; l, solid anusl

lowed out by a

process of vacuola-

tion; isolated vacuoles appear at first, but they

gradually become confluent, and thus a young vessel is

formed, at first very irregular in outline, but gradually

tnosia between
(Atlas.)

H;

solid anasto-
neig'hbouring capillaries.

84 ELEMENTS OF HISTOLOGY. [Chap. xi.

acquiring more and more of a tubular form. In the
case of an isolated cell, its protoplasmic processes
grow by degrees to the nearest capillary, to the wall
of which they become fixed, and the cavity of the cell
finally opens through such processes into that of the
capillary vessel.

The wall of young capillaries is granular-looking
protoplasm (the original cell substance), and in it
are disposed, in more or less regular fashion, oblong
nuclei, derived by multiplication from the nucleus of
.the original cell. In a later stage, a differentiation
takes place in the protoplasmic wall of the capillary
into cell-plates and cement substance, in such a way
that each of the above nuclei appertains to one cell-
plate, which now represents the final stage in the
formation of the capillary. Both in the embryo and
in the adult a few isolated nucleated protoplasmic cells,
or a few protoplasmic solid processes of an existing
capillary, may by active and continued growth give
origin to a whole set of new capillaries (Strieker,
Affanasieff, Arnold, Klein, Balfour, Ranvier, Leboucq).

CHAPTER XI.

THE LYMPHATIC VESSELS.

110. THE large lymphatic trunks, such as the
thoracic duct, and the lymphatic vessels passing to and
from the lymphatic glands, are thin- walled vessels,
similar in structure to arteries. Their lining endothe-
lium is of the same character as in an artery, and so are
the elastic intima and the media with its circular mus-
cular tissue, only they are very much thinner than in
an artery of the same calibre. The adventitia is an

Chap, xi.] THE LYMPHATIC VESSELS. 85

exceedingly thin connective tissue membrane with a
few elastic fibres. The valves are semi-lunar folds of
the endothelium and intima-.

111. The lymphatics in the tissues and organs
form rich plexuses. They are tubular vessels, the wall
of which is, like that of a capillary blood-vessel, a single
layer of endothelial plates (Fig. 52). The lymphatic
may be, and often is, many times wider than a blood
capillary. The endothelial plates are elongated, but

;U\IB

Fig. 52.— Lymphatic Vessels of the Diaphragm of the Dog, stained with
Nitrate of Silver.

The endothelium forming the wall of the lymphatics is well shown ; v, valves.
(Atlas.)

not so long as in a blood capillary, with more or less
sinuous outlines, but this depends on the amount of
shrinking of the tissue in which the vessel is embedded ;
when there is no shrinking in the tissue or in the vessel,
the outlines of the cells are more or less straight.

The lymphatics are supported by the fibrous con-
nective tissue of the surrounding tissue, which does
not, however, form part of their wall.

86 ELEMENTS OF HISTOLOGY. [Chap. xi.

112. The outline of the vessel is not straight, but
more or less moniliform, owing to the slight dilatations
present below and at the semi-lunar valves ; these are
folds of the endothelial wall, and they are met with in
great numbers. The vessel appears slightly dilated
immediately below the valve, that is, on the side
farthest from the periphery, or rootlet, whence the
current of lymph starts.

113. Tracing the lymphatic vessels in the tissues
and organs towards their rootlets, we come to more or
less irregular-shaped vessels, the wall of which also
consists of a single layer of polygonal endothelial plates ;
the outlines are very sinuous. These are the lym-
phatic capillaries ; in some places they are mere clefts
and irregular sinuses, in others they have more the
character of a tube, but in all instances they have
a complete endothelial lining, and no valves.

Sometimes a blood-vessel, generally arterial, is
ensheathed for a shorter or longer distance in a
lymphatic tube, which has the character of a lym-
phatic capillary j -these are the perivascular lymphatics
of His, Strieker, and others.

114. The rootlets of* the lymphatics are situ-
ated in the connective tissue of the different organs
in the shape of an intercommunicating system of
crevices, clefts, spaces, or canals, existing between the
bundles, or groups of bundles, of the connective tissue.
These rootlets are generally without a complete endo-
thelial lining, but are identical with the spaces in
which the connective tissue corpuscles are situated ;
where these are branched cells anastomosing by their
processes into a network — such as the cornea, or serous
membranes — we find that the rootlets of the lymphatics
are the lacunae and canaliculi of these cells — the typical
lymph-canalicular system of von Recklinghausen. (Fig.
53). • The endothelial cells forming the wall of the
lymphatic capillaries are directly continuous with the

Chap. XI.]

THE LYMPHATIC VESSELS.

connective cells situated in the rootlets. In tendons
and fasciae the minute lymphatics lie between the
bundles, and have the shape of continuous long clefts

Fig. 53.— From a. Silver-stained Preparation of tLe Central Tendon of
the Rabbit's Diaphragm. Showing the direct connection of the
Lymph- canalicular System of the Tissue with the Lymphatic
Capillaries.

a, Lymphatic vessel ; 6, lymphatic capillary lined with ' sinuous ' cndothelium.
(Handbook.)

or channels ; in striped muscular tissue they have the
same character, being situated between the muscular
fibres.

The passage of plasma from the minute arteries
and capillary blood-vessels into the lymph-rootlets
situated in the tissues, and thence into the lymphatic

88

ELEMENTS OF HISTOLOGY.

[Chap. XI.

capillaries and lymphatic vessels, represents the natural
current of lymph irrigating the tissues.

115. Lymph cavities.— In some places the lym-
phatic vessels of a tissue or organ are possessed of, or
connected with, irregularly-shaped large sinuses, much
wider than the vessel itself ; these cavities are the
lymph sinuses, and their wall is also composed of a
single layer of more or less polygonal endothelial
plates with very sinuous outlines. Such sinuses are
found in connection with the subcutaneous and sub-
mucous lymphatics, in the diaphragm, mesentery, liver,
lungs, &c. On the same footing — i.e., as lymph
sinuses — stand the comparatively large lymph cavities
in the body, such as the subdural and subarachnoidal

spaces of the central
nervous system, the
synovial cavities, the
cavities of the tendon-
sheaths, the cavity of
the tunica vaginalis
testis, the pleural,
pericardial, and peri-
toneal cavities. In
batrachian animals,
e.g., frogs, the skin all
over the trunk and
extremities is sepa-
rated from the sub-
jacent fasciae and
muscles by large bags
or sinuses — the sub-
cutaneous lymph sacs.
These sinuses are shut

off from one another by septa. Between the trunk
and the extremities, and on the latter, the septa
generally occur in the region of the joints. In
female frogs in the mesogastrium smaller or larger

Fig. 54.— Stomata, lined with Germi-
.nating Endothelial Cells, as seen
from the Cisternal Surface of the
SeptumCisternse Lymphaticse Magnae
of the Frog. (Handbook.)

Chap. XI.]

THE LYMPHATIC VESSELS.

89

cysts lined with ciliated endothelium are sometimes
found. Behind the peritoneal cavity of the frog,
along and on each side of the vertebral column, exists
a similar large lymph sinus, called the cisterna lympha-
tica magna.

116. In all instances these cavities are in direct
communication with

the lymphatics of the
surrounding parts by
holes or open mouths
(stomata), oiten lined
by a special layer of
polyhedral endothe-
lial cells — germinat-
ing cells (Figs. 54,
55). Such stomata
are numerous on the
peritoneal surface of
the central tendon of
the diaphragm, in
which are found
straight lymph chan-
nels between the
tendon bundles, and these channels communicate here
and there with the free surface by stomata. A
similar arrangement exists on the costal pleura, the
omentum, and the cistern a lymphatica magna of the
frog. (See Chapter IV.)

117. The §erous membranes consist of a
matrix of fibrous connective tissue with networks of
tine elastic fibres; they contain networks of blood
capillaries and numerous lymphatic vessels arranged in
(superficial and deep) plexuses. Those of the pleura
costalis — or rather, intercostalis — and of the diaphragm
and pleura pulmonalis, are most numerous. They are
important in the process of absorption from the pleural
and peritoneal cavity respectively. Lymph and lymph

Fig. 55. — Endothelium and Stomata of
the Peritoneal Surface of the Septum
Cistern Lymphatic Magnae of the
Frog. (Handbook.)

QO ELEMENTS OF HISTOLOGY. [Chap. xi.

corpuscles, and other formed matter, are readily taken
up by the stomata (see Fig. 20) and brought into the
lymphatics, and in this the respiratory movement of
the intercostal muscles, of the diaphragm, and of
the lungs respectively, produces the result of the
action of a pump.

118. There is a definite relation between the
lymphatics and the epithelium covering the mucous
membranes and lining the various glands and between
the endothelium covering serous membranes and that
lining vessels and lymph cavities — viz., the albumin-
ous semifluid cement substance (see former chapters)
between the epithelial and endothelial cells is the
path by which fluid and formed matter pass between
the surfaces and the lymph-canalicular system, the
latter being the rootlets of the lymphatics.

119. Lymph taken from the lymphatics of dif-
ferent regions differs in composition and structure.
That from the thoracic duct contains a large
amount of colourless or white corpuscles — lymph cor-
puscles— each of which is a protoplasmic nucleated cell
similar in aspect and nature to a white blood corpuscle.
They are of various sizes, according to the stage of
ripeness. The smaller contain one, some of the larger
contain two and three, nuclei. The latter show more
pronounced amoeboid movement than the small ones.
A few red corpuscles are also met with. Granular
and fatty matter is present in large quantities during
and after digestion.

In the frog (and also in other lower vertebrates,
e.g., reptiles) there exist certain small vesicular lymph
cavities, about an eighth of an inch in diameter,
which show rhythmic pulsation ; they are called lymph
hearts. On each side of the os coccygis and underneath
the skin is a pulsating posterior lymph heart. The
anterior lymph heart is oval, and situated on each
side between the processus transversus of the third

chap, xi.] THE LYMPHATIC VESSELS. 91

and fourth vertebra; it is slightly smaller than the
posterior one. The lymph hearts have an efferent ves-
sel, which is a vein, and from them the venous system

Fig. 56.— Developing Lymph-oapillaries in tne Tail of Tadpole,
a, Solid nucleated protoplasmic branches not yet hollowed out. (Atlas.)

of the neighbourhood can be easily injected, whereas
the reverse is not possible. They are lined with an
endothelium like the lymph sacs, and in their
wall they possess plexuses of striped, branched,
muscular fibres. The nerve fibres terminate in these
striped muscular fibres in the same manner as in those
of other localities. (Ranvier.)

92 ELEMENTS OF HISTOLOGY. [Chap. xn.

120. Lymphatic vessels are developed and newly
formed under normal and pathological conditions in
precisely the same way as blood-vessels. The accom-
panying woodcut (Fig. 56) shows this very well. We
have also here to do with the hollowing out of (con-
nective tissue) cells and their processes previously
solid and protoplasmic.

CHAPTER XII.

SIMPLE LYMPHATIC GLANDS.

121. UNDER this name are to be considered the
blood-glands of His, or the conglobate gland sub-
stance of Henle, or the lymph follicles (Kolliker,
Huxley, Luschka). The ground-substance of all
lymphatic glands, simple as well as compound (see
below), is the lymphatic or adenoid tissue, also called
cytogenous tissue. Like all other gland-tissue, it
is supplied with a rich network of capillaries
derived from an afferent artery, and leading into
efferent veins.

122. The elements constituting this tissue are : —
(a) The- adenoid reticulum (Fig. 57), a network

of fine homogeneous fibrils, v/ith numerous plate-like
enlargements.

(6) Small, transparent, flat, endotheloid cell-plates,^
each with an oval nucleus. These cell-plates are fixed
on the reticulum, of which at first sight they seem
to form part. Their oval nucleus especially appears
to belong to a nodal point — i.e., to one of the
enlargements of the reticulum ; but by continued
shaking of a section of any lymphatic tissue, the oval
nuclei and their cell-plates can be got rid of, so that only
the reticulum is left, without any trace of a nucleus.

Chap, xii.] SIMPLE LYMPHATIC GLANDS.

93

(c) Lymph-corpuscles completely fill the meshes
of the adenoid reticulum. These can be easily
shaken out of the reticulum. They are of dif-
ferent sizes ;
some — the
young ones —
are small cells,
with a com-
paratively
large nucleus ;
others — the
ripe ones — are
larger, have a
distinct pro-
toplasmic cell
body,with one
or two nuclei.
They all show
on a warm
stage amoe-
boid move-
ment, but in
the large ones
it is much more pronounced than in the small ones.

The capillary blood-vessels supplying the adenoid
tissue receive a more or less distinct special investment
from the adenoid reticulum ; this is the capillary
adventitia.

123. The adenoid tissue occurs as :

(1) Diffuse adenoid tissue, without any definite
grouping or arrangement. This is the case in the sub-
epithelial layer of the mucous membrane of the trachea,
in the mucous membrane of the false vocal cords and
the ventricle of the larynx, in the posterior part of
the epiglottis, in the soft palate and tonsils, at the
root of the tongue, in the pharynx, in the mticosa
of the small and large intestine, including the villi

Ficr. 57.— Adenoid Eeticnlum shaken out ; most of
the Lymph-corpuscles are removed. From a
Lymphatic Gland.
a, The reticulum ; c, a capillary blood-vessel. (Atlas.)

94

ELEMENTS OF HISTOLOGY. [Chap. XH.

of the former ; and in the mucous membrane of the
nasal cavity and vagina.

(2) Cords, cylinders, or patches of adenoid tissue ;
as in the omentum and pleura, and in the spleen
(Malpighian corpuscles).

(3) Lymph follicles, i.e., oval or spherical masses
more or less well denned ; as in the tonsils, at the root
of the tongue, in the upper part of the pharynx (pharynx-
tonsil), in the stomach, small and large intestine; in
the nasal mucous membrane, in the large and small
bronchi ; and in the spleen (Malpighian corpuscles).

124. The tonsils (Fig. 58) are masses of lymph folli-
cles and diffuse adenoid tissue covered with a thin mucous
membrane, which penetrates in the shape of longer or

7T?

Tig. 58.— Vertical Section through part of the Tonsil of Dog.

«, Stratified pavement epithelium covering the free surface of the mucous
membrane. The tissue of the mucous membrane is infiltrated with adenoid
tissue. /, lymph follicles ; m,, mucous gland of the submucous tissue. (Atlas.)

Chap, xii.] SIMPLE LYMPHATIC VESSELS. 95

shorter folds into the substance within. Numbers of
mucus-secreting glands situated outside the layer of
lymph follicles discharge their secretion into the pits —
the crypts — between the folds. The free surface of the
tonsils and the crypts is covered or lined respectively
with the same stratified epithelium that lines the oral
cavity. Numbers of lymph corpuscles constantly, in
the perfectly normal condition, migrate through the
epithelium on to the free surface, and are mixed with
the secretions (mucus and saliva) of the oral cavity.
The so-called mucous or salivary corpuscles of the
saliva, taken from the oral cavity, are such discharged
lymph corpuscles. They become swollen up by the
water of the saliva, and assume a spherical shape.
They finally disintegrate.

Similar relations, only on a smaller scale, obtain
at the root of the tongue.

The pharynx tonsil of Luschka, occurring in the
upper part of the pharynx, is in all essential respects
the same as the palatine tonsil. Owing to large parts
of the mucous membrane of the upper portion of the
pharynx being covered with ciliated columnar epithe-
lium, some of the crypts in the pharynx tonsil are also
lined with it.

125. The lenticular glands of the stomach are
single lymph follicles.

The solitary glands of the small and especially
the large intestine are single lymph follicles.

The agminated glands of the ileum are groups
of lymph follicles. The mucous membrane containing
them is much thickened by their presence, and repre-
sents a Peyer's patch or a Peyer's gland.

126. In most instances the capillary blood-vessels
form in the lymph follicles meshes, arranged in a more
or less radiating manner from the periphery towards
the centre ; around the periphery there is a network
of small veins. A larger or smaller portion of the

96 ELEMENTS OF HISTOLOGY. [Chap. XH.

circumference of the follicles of the tonsils, pharynx,
intestine, bronchi, &c., is surrounded by a lymph
sinus leading into a lymphatic vessel. The lymphatic
vessels and lymph sinuses in the neighbourhood of lym-
phatic follicles or of diffuse adenoid tissue are almost
always found to contain numerous lymph corpuscles,
thus indicating that these are produced by the adenoid
tissue and absorbed by the lymphatics.

127. The Tliymus gland consists of a frame-
work and the gland substance. The former is fibrous
connective tissue arranged as an outer capsule, and
in connection with it are septa and trabeculae passing
into the gland and subdividing it into lobes and
lobules, which latter are again subdivided into the
follicles (Fig. 5 9 A). The follicles are very irregular
in shape, most of them being oblong or cylindrical
streaks of adenoid tissue. Near the capsule they are
well denned from one another, and present a poly-
gonal outline ; farther inwards they are more or less
fused. Each shows a central transparent medulla
and a peripheral less transparent cortex (Watney).
At the places where two follicles are fused with one
another the medulla of both is continuous. The matrix
is adenoid reticulum, the fibres of the medullary part
being coarser and shorter, those of the cortical portion
of the follicle finer and longer. The meshes of the
of the reticulum in the cortical part of the follicles are
filled with the same lymph-corpuscles as occur in the
adenoid tissue of other organs, but in the medullary
part they are fewer, and the meshes are more or less
completely occupied by the enlarged but transparent
endotheloid plates. These conditions cause the greater
transparency of the medulla. In some places the
endotheloid cells are granular, and include more than
one nucleus ; some are even multinucleated giant cells.

128. There occur in the medulla of the follicles,
larger or smaller, more or less concentrically-arranged

Chap. xii.] SIMPLE LYMPHATIC GLANDS.

97

nucleated protoplasmic cells, which are the concentric
bodies of Hassall (Fig. 5 OB). They are met with al-

Fig-. 59A.— Section through the Thymus Gland of a Foetus.

a, Fibrous tissue between the follicles ; b, the cortical portion of the follicles ;
c, the medullary portion.

ready in the early stages of the life of the thymus, and
cannot therefore be connected with the involution of
the gland, as maintained by Afanassief, according to
whom the concentric cor-
puscles are formed in
blood-vessels which there-
by become obliterated.
According to Watney
they are concerned in the
formation of blood- vessels
and connective tissue.

The lymphatics of the
interfollicular septa and

Fig. 59B. — Two Concentric or Has-
sall's Corpuscles of the Tbymus.
Foetal Gland.

trabeculse always contain

numbers of lymph corpuscles. The blood capillaries
of the follicles are more richly distributed in the

98 ELEMENTS OF HISTOLOGY. [Chap. xin.

cortex than in the medulla, and they radiate from the
periphery towards the central parts.

129. After birth, the thymus gland commences to
undergo degeneration, leading to the gradual dis-
appearance of the greater portion of the gland, its
place being taken by connective tissue and fat. But
the time when the involution is completed varies
within very broad limits.

It is not unusual to find in individuals of fifteen
to twenty y ^ars of age still an appreciable amount of
thymus gland tissue. In some animals — e.g., guinea-
pigs — the involution of the gland even in the adult has
not made much progress. In the thymus of the dog
Watney found cysts lined with ciliated epithelial cells.

CHAPTER XIII.

COMPOUND LYMPHATIC GLANDS.

1 30. THE compound or true lymphatic glands are
directly interpolated in the course of lymphatic vessels.
Such are the mesenteric, portal, bronchial, splenic,
sternal, cervical, cubital, popliteal, inguinal, lumbar,
&c., glands. Afferent lymphatic vessels anastomosing
into a plexus open at one side (in the outer capsule)
into the lymphatic gland, and at the other (the hilum)
emerge from it as a plexus of efferent lymphatic tubes.

131. Each true lymphatic gland is enveloped in a
fibrous capsule which is connected with the interior
and the hilum by connective tissue trabeculce and septa.
The trabeculse having advanced a certain distance,
about one-third or one-fourth, in a manner more or
less radiating towards the centre, branch into minor
trabeculae, which in the middle part of the gland anasto-
mose with one another so as to form a plexus with small

Chap, xii i.i COMPOUND LYMPHATIC GLANDS.

99

meshes. Thus the peripheral third or fourth of the
gland is subdivided by the septa and trabeculae, into
relatively large spherical or oblong compartments, while
the middle portion is made up of relatively small cylin-
drical or irregularly-shaped compartments (Fig. 60).
The former region is the cortex, the latter the medulla of
the gland. The compartments of the cortex anastomose
with one another and with those of the medulla, and
these latter also form one intercommunicating system.
The fibrous capsule, the septa and trabeculse are
the carriers of the vascular trunks ; the trabeculse
consist of fibrous connective tissue and of a certain

Fig. 60.— From a Vertical Section through a Lymphatic Gland, the
Lymphatics of which had been injected.

c, The outer capsule, with lymphatic vessels in section : a, the cortical lymph
follicles; around them are the cortical lymph sinuses; 6, the medullary ;
injected lymph sinuses between the masses of adenoid tissue. (Atlas.)

amount of non-striped muscular tissue, which is con-
spicuous in some animals — e.g., pig, calf, rabbit,
guinea-pig — but is scarce in man.

Sometimes coarsely granular connective tissue cells

TOO

ELEMENTS OF HISTOLOGY. [Chap. xiu.

(plasma cells) are present in considerable numbers in
the trabeculse.

132. The compartments contain masses of adenoid
tissue, without being completely filled with it ; those
of the cortex contain oval or spherical masses — the
lymph follicles of the cortex ; those of the medulla
cylindrical or irregularly-shaped masses — the medullary
cylinders. The former anastomose with one another
and with the latter, and the latter amongst them-
selves, a condition easily understood from what has
been said above of the nature of the compartments
containing these lymphatic structures. The follicles

and medullary
cylinders consist
of adenoid tissue
of exactly the
same character as
that described in
the previous chap-
ter. And this
tissue also con-
tains the last rami-
fications of the
blood-vessels, i.e.,
the last branches
of the arteries, a
rich network of
capillary blood-
vessels, and the
first or smaller
branches of the
veins. The

capillaries and
other vessels re-
ceive also here
an adventitious envelope from the adenoid reticulura.

133. The cortical follicles and the medullary

Fig. 61. — From a Section through a
Lymphatic Gland.

c, The outer capsule; *, cortical lymph sinus;
a, adenoid tissue of cortical follicle. Numerous
nuclei, indicating lymph corpuscles. (Atlas.)

chap, xin.] COMPOUND LYMPHATIC GLANDS. 101

cylinders do not completely fill out the compartments
made for them by the capsule and trabeculse respec-
tively, but a small peripheral zone of each compart-
ment is left free ; this is a lymphatic sinus. In the
cortex it is spoken of as a cortical (Fig. 61), in the
medulla as a medullary, lymph sinus (Fig. 62). The

Fig. 62.— From a Section through the Medulla of a Lymphatic Gland.

a, Transition of the medullary cylinders of adenoid tissue into the cortical
follicles : 6, the lymph sinuses occupied by a reticulum ; c, the fibrous tissue
trabeculae ; rf, the medullary cylinders. (Atlas.)

former is a space between the outer surface of the
cortical lymph follicle and the corresponding part of
the capsule or cortical septum, the latter between the
surface of a medullary cylinder and the trabeculse.
From wha.t has been said of the relation of the com-
partments, it follows that the cortical and medullary
lymph sinuses form one intercommunicating system.

io2 ELEMENTS OF HISTOLOGY. [Chap. xin.

These are not empty free spaces, but are filled with a
coarse reticulum of fibres, much coarser than the ade-
noid reticulum ; to it are attached large transparent
cell plates — endotheloid plates. In some instances (as
in the calf) these cell-plates of the medullary sinuses
contain brownish pigment granules, which give to the
medulla of the gland a dark brown aspect. In the
meshes of the reticulum of the sinuses are contained
lymph corpuscles, the majority of which consist of a
relatively large protoplasmic body, and one or two
nuclei ; they show lively amoeboid movement; a few
small lymph corpuscles are also amongst them.

The surface of the trabecula3 facing the lymph
sinuses is covered with a continuous layer of endothe-
lium (von Recklinghausen), and a similar endothelial
membrane, but not so complete, can be made out on
the surface of the cortical follicles and the medullary
cylinders. The endotheloid plates, as applied to the
reticulum of the sinuses, are stretched out, as it were,
between the endothelial membrane covering the sur-
face of the trabeculse on the one hand and that
covering the surface of the follicles and cylinders on
the other.

In the mesenteric gland of the pig the distribution
of cortical follicles and medullary cylinders is almost
the reverse from that of other glands or in other
animals.

134. The afferent lymphatic vessels having entered
the outer capsule of the gland, and having formed
there a dense plexus, open directly into the cortical
lymph sinuses. The medullary lymph sinuses lead
into lymphatic vessels, which leave the" gland per
hilum as the efferent vessels.

Both afferent and efferent vessels are supplied
with valves.

135. The course of the lymph through a lymphatic
gland is then simply this — from the afferent vessels,

Chap, xiv.] NERVE-FIBRES. 103

situated in the capsule, into the cortical lymph sinuses,
from these into the medullary sinuses, and from these
into the efferent lymphatics. Owing to the presence
of the reticulum in the sinuses the current of the
lymph will proceed only very slowly and with diffi-
culty, as if it were passed through a spongy filter.
Hence a large number of formed corpuscles, pigment,
inflammatory or other elements, passing into the gland
by the afferent vessels are easily arrested and de-
posited in the sinuses, and there readily swallowed by
the amoeboid corpuscles lying in the meshes.

Passing a stream of water through the gland, the
contents of the meshes of the reticulum of the sinuses —
i.e., the lymph corpuscles — are of course the first things
washed out (von Recklinghausen), and on continuing
the stream some of the lymph corpuscles of the
follicles and cylinders are also washed out. Hence it
is probable also that by the normal stream of lymph
passing through the gland, lymph corpuscles are
drained, as it were, from the follicles and cylinders
into the sinuses. The amoeboid movement of the lymph
corpuscles, especially of the large and ripe ones, will
greatly facilitate their passage from the follicles and
cylinders into the lymph sinuses.

CHAPTER XIV.

NERVE-FIBRES.

136. THE nerve-fibres conduct impulses to or from
the tissues and organs on the one hand, and the nerve-
centres on the other, and accordingly we have to con-
sider in each nerve-fibre the peripheral and central
termination and the conducting part. The latter, i.e..

104

ELEMENTS OF HISTOLOGY. [Chap. xiv.

the nerve-fibres proper, in the cerebro-spinal nerves are
grouped into bundles, and these again into anatomical
nerve-branches and nerve-trunks. Each anatomical
cerebro-spinal nerve consists, therefore, of bundles of
nerve-fibres (Fig. 63). The general matrix by which
these bundles are held together is fibrous connective
tissue called the Epineurium (Key and Retzius) ; this
epineurium is the carrier of the larger and smaller
blood-vessels with which the nerve-trunk is supplied,
of a plexus of lymphatics, of groups of fat-cells, and
sometimes of numerous plasma cells.

137. The nerve-bundles (Fig. 64) are of various sizes,
according to the number and size of the nerve-fibres they
contain. They are well-defined by a sheath of their

P

Fig. 63. — From a Transverse Section through the Sciatic Nerve of
the Dog.

ep, Epineurium ; p, perineurhun ; n, nerve fibres constituting a nerve-bundle in
cross section ; /, fat tissue surrounding the nerve. (Atlas.)

own, called perineurium (Key and Ketzius). This peri-
neurium consists of bundles of fibrous connective tissue
arranged in lamellae, every two lamellae being separated
from one another by smaller or larger lymph spaces,

chap, xiv.] NERVE-FIBRES. 105

which form an intercommunicating system, and
anastomose with the lymphatics of the epineurium
whence they can be injected. Between the lamellae,
and in the spaces, are situated flattened endotheloid
connective tissue corpuscles.

The nerve-bundles are either single or compound.
In the former the nerve-fibres contained in a bundle
are not sub-divided into groups, in the latter the
bundles are sub-divided by thicker and thinner septa
of fibrous connective tissue connected with the peri-
neurium. When a nerve-bundle divides — as when a
trunk repeatedly branches, or when it enters on its peri-
pheral distribution — each branch of the bundle receives
a continuation of the lamellar perineurium. The more
branches the perineurium has to supply, the more re-
duced it becomes in thickness. In some of these minute
branches the perineurium is reduced to a single layer
of endothelial cells. When one of these small bundles
breaks up into the single nerve-fibres, or into small
groups of them, each of these has also a continuation
of the fibrous tissue of the perineurium. In some
places this perineural continuation is only a very
delicate endothelial membrane, at others it is of
considerable thickness, and still shows the laminated
nature. Such thick sheaths of single nerve-fibres,
or of small groups of them, represent what is called
Henle's sheath.

138. The nerve-fibres are held together within the
bundle by connective tissue, called the Endoneurium
(Fig. 64). This is a homogeneous ground substance in
which are embedded fine bundles of fibrous connective
tissue, and connective tissue corpuscles, and capillary
blood-vessels arranged so as to form a network with
elongated meshes. Between the perineurium and the
nerve-fibres are found here and there lymph spaces ;
similar spaces separate the individual nerve-fibres, and
have been injected by Key and Retzius.

io6 ELEMENTS OF HISTOLOGY. LChap. xiv.

When nerve-trunks anastomose so as to form a
plexus — e.g., in the brachial, or sacral plexus— there
occurs an exchange and re- arrangement of nerve-
bundles in the branches. A similar condition obtains
in the ganglia of the cerebro-spinal nerves. Nerve-

64. — Transv'erse Section through a Nerve-bundle
in the Tail of Mouse.

P, The perineuriuni ; «, the endoneurium separating the medullated nerve-fibres
seen in cross section ; 7, lymph spaces in the perineurium ; V, lymph spaces
in the endoneurium. (Atlas.)

trunks and nerve-branches passing through a lymph
cavity, such as the subdural spaces, or the sub-
cutaneous lymph sacs, or the cisterna lymphatica
magna in the frog, receive from the serous membrane
an outer endothelial covering.

139. The nerve-fibres in the nerve-bundles of the
cerebro-spinal nerves, with the exception of the
olfactory nerve, are medullated nerve-fibres. These are
doubly or darkly contoured smooth cylindrical fibres,
varying in diameter between ^TrW and y^^u of an
inch. Within the same bundle of a nerve — e.g., of
the brachial or sacral plexus — there occur fibres which
are several times thicker than others, and it is pro-
bable that they are derived from different sources.
Schwalbe has shown that the thickness of the nerve-

Chap, xiv.] NERVE-FIBRES. 107

fibre stands in a certain relation to the distance of its
periphery from the nerve-centre and to functional
activity.

A medullated nerve-fibre in the fresh condition
is a bright glistening cylinder, showing a dark
double contour. Either spontaneously after death,
or after re-agents — as water, salt solution, dilute
acids — or after pressure and mechanical injury, the
outline of the nerve-fibre becomes irregular ; smaller,
or larger, glistening dark -bordered droplets and masses
appear and gradually become detached. These
droplets and masses are derived from the fatty sub-
stance constituting the medullary sheath or white
substance of Schwann (see below). When a nerve-
fibre within the bundle undergoes degeneration during
life, either after section of the nerve or after other
pathological changes, or in the natural course of its
existence (S. Mayer), the medullary sheath breaks up
into similar smaller or larger globules or particles,
which gradually become absorbed.

140. Each medullated nerve-fibre (Figs. 64A, 66)
consists of the following parts : (a) the central axis
cylinder. This is the essential part of the fibre, and is
a cylindrical or bandlike, pale, transparent structure,
which in certain localities (near the terminal distribu-
tion, in the olfactory nerves, in the central nervous
system), and especially after certain re-agents, shows
itself composed of very fine homogeneous or more or
less beaded fibrillae — the elementary or primitive fibrill-ce
(Max Schultze) — held together by a small amount of a
faintly granular interstitial substance. The longitu-
dinal striation of the axis cylinder is due to its being
composed of primitive fibrillse. The thickness of the
axis cylinder is in direct proportion to the thickness
of the whole nerve-fibre. The axis - cylinder is said
to be enveloped in its own hyaline more or less elastic
sheath, composed of neurokeratin.

io8

ELEMENTS OF HISTOLOGY. [Chap. xiv.

141. (b) The medullary sheath or white substance
of Sch warm, also called the medulla of the nerve-fibre.
This is a glistening bright fatty substance surrounding
the axis cylinder, as an insulating hollow cylinder
surrounds an electric wire. The medullary sheath
gives to the nerve-fibre its double or dark contour.
Between the axis cylinder and the medullary sheath
there is a small amount of albuminous fluid
which appears greatly increased
when the former, owing to shrink-
ing, stands farther apart from the
latter.

142. (c) The sheath of Schwann,
or the neurilemma, surrounds closely
the medullary sheath, and forms
the outer boundary of the nerve-
fibre. It is a hyaline delicate
membrane. From place to place
there is present between the neuri-
lemma and the medullary sheath, and
situated in a depression of the latter,
an oblong nucleus, surrounded by a
thin zone of protoplasm. These
nucleated corpuscles are the nerve
corpuscles (Fig. 6 4 A), and are analo-
gous to the muscle corpuscles, situated
between the sarcolemma and the
striated muscular substance. They
are not nearly so numerous as the
muscle corpuscles.

143. The neurilemma produces
at certain definite intervals annular

constrictions, the nodes or constrictions of Janvier (Figs.
64A, 65, 66), and at these nodes of Ranvier the medullary
sheath, but not the axis cylinder and its special sheath,
suffers a discontinuity and sharply terminates. The
portion of the nerve-fibre situated between two nodes is

v

rig. 64A.— Two Nerve
Fibres, showing the
nodes or constric-
tions of Ranvier and
the axis cylinder.
The medullary
sheath has been dis-
solved away. The
deeply - stained ob-
long nuclei indicate
the nerve corpuscles
within the neuri-
lemma. (Atlas.)

Chap. XIV.]

NER VE-FIBRES.

the internodal segment. Each internodal segment has
generally one, occasionally more than one, nerve
corpuscle. The medul-
lary cylinder of each in-

ternodal segment is made fffWM /M II UK 6

up of a number of coni-
cal sections (Fig. 6 6 A)
imbricated at their ends
(Schmidt, Lantermann)
(Fig. 66), and each such

Fig. 66.— Medullated Nerve-

L, A medullated nerve - fibre,
showing the subdivision of the
medullary sheath into cylin-
drical sections imbricated with
their ends ; a nerve corpuscle
with an oval nucleus is seen
between the neurtlemina and
the medullary sheath ; B, a
meduliated nerve fibre at a
node or constriction of Ranvier;
the axis cylinder passes unin-
terruptedly from one segment
into the other, but the medul-
lary sheath is interrupted.
(Key and Retzius.)

Fig. 65. — Medullated Nerve -fibres,
after staining with Nitrate of Silver.

a, The axis cylinder ; 6, Ranvier's constric-
tion. (Key and Retzius.)

section is again made up of
a large number of rod-like
structures (Fig. 67) placed
vertically on the axis cylin-
der.

These rods are, how-
ever, connected into a net-
work. The network itself
is very likely the neuro-
keratin of Ewald and Kiihne,
whereas the interstitial sub-
stance of the network is
probably the fatty sub-
stance leaving the nerve-
fibre in the shape of droplets

no

ELEMENTS OF HISTOLOGY. [Chap. xiv.

when pressure or reagents are applied to the fresh
nerve-fibre.

144. Medullated nerve-fibres without any neuri-
lemma, and consequently without any nodes of Ranvier,
with a thick more or less distinctly laminated medul-
lary sheath, form the
white substance of the
brain and spinal cord.
In these organs, in the
hardened and fresh state,
numerous nerve - fibres
may be noticed, which
show more or less regu-
lar varroosities, owing to
local accumulations of
fluid between the axis
cylinder and medullary
sheath. These are called
varicose nerve-fibres.
They occur also in the
branches of the sympa-
thetic nerve.

The nerve-fibres of
the optic and acoustic
nerve are medullated,
but without any neuri-
lemma ; varicose fibres
are common in them.

145. Medullated
nerve-fibres occasionally

in their course divide into two medullated fibres. Such
division is very common in medullated nerve-fibres
supplying striped muscular fibres, especially at or near
thepointof entrance into the muscular fibres (see below).
But also in other localities division of nerve-fibres
may be met with. The electric nerve of the electric
fishes (malapterurus, gymnotus, silurus, etc., elec-

Fig. 67.-Medullated Nerve-fibres.

A, B, showing on a surface view tbe
reticulated nature of the medullary
sheath ; c, two nerve-fibres showing
the axis cylinder, the medullary sheath
with their vertically-arranged minute
rods, and the delicate neurilemma or
outer hyaline eheath. (Atlas.)

Chap, xiv.] NERVE-FIBRES. • in

tricus) shows such divisions to an extraordinary degree,
one huge nerve-fibre dividing at once into a bundle of
minor fibres. Division of a medullated fibre takes
place generally at a node of Ranvier. The branches
taken together are generally thicker than the un-
divided part of the fibre, but in structure they are iden-
tical with the latter.

146. When medullated nerve-fibres approach their
peripheral termination, they change sooner or later, in
so far as their medullary sheath suddenly ceases ; and
now we have a non-medullated, or Remak's nerve-
fibre. Each of these consists of an axis cylinder, a
neurilemma, and between the two a nucleated nerve
corpuscle from place to place. Non-medullated nerve-
fibres always show the fibrillar nature of their
axis cylinder. The olfactory nerve-branches are
entirely made up of non-medullated nerve fibres. In
the branches of the sympathetic most fibres are non-
medullated.

The non-medullated fibres undergo always repeated
divisions. They form plexuses, large fibres branching
into smaller ones, and these again joining (Fig. 68).
Generally at the nodal points of these plexuses there are
triangular nuclei, indicating the corpuscles of the
neurilemma.

147. Finally the non-medullated nerve-fibres lose
their neurilemma, and then we have simple axis
cylinders. These branch and ultimately break up
into the constituent primitive nerve-fibrillce, which
occasionally show regular varicosities (Fig. 69).
Of course, of a neurilemma or the nuclei of the
nerve corpuscles there is nothing left. These
primitive fibrillse branch and anastomose with one
another, and thus form a network. The density
of this network depends on the number of primitive
fibrils and the richness of their branching. These
primitive fibrils and their networks represent the

ii2 ELEMENTS OF HISTOLOGY. [Chap. xiv.

peripheral termination, and this mode of termination
occurs in the nerve-fibres of common sensation, as in
many of the nerve-fibres of the skin, cornea, and

Fig. 68. — Plexus of Fine Non-medullated Nerve-fibres of the Cornea.

a, A thick non-medullated nerve-fibre : 6, a fine one ; c, d, elementary fibrils,
anastomosing into a network.

mucous membranes. In all these cases the peripheral
termination, i.e., the primitive fibrils and their net-
works are found intra-epithelial (Fig. 70), i.e. situated
in the stratum Malphigii of the epidermis, in the epithe-
lial parts of the hair follicle, in the anterior epithelium
of the cornea, and in the epithelium of the mucous

Chap. XIV.-]

NERVE-FIBRES.

membranes. The primitive nerve-fibrils lie in the
interstitial substance between the epithelial cells, as

Fig. 69.— Nerve-fibres of the Cornea.

a, An a,xis cylinder splitting up into its constituent primitive flbrilte near the
anterior epithelium of the cornea; 6, primitive flbrillae.

intra-epithelial networks and as primitive fibrils which
appear to terminate with free ends.

148. Tracing then a nerve-fibre, say one of common
sensation, from the periphery towards the centre, we
have isolated primitive fibrils or networks of them ;
I

ii4 ELEMENTS OF HISTOLOGY. [Chap. xiv.

they form by association simple axis cylinders, which
vary in thickness according to the number of their
constituent primitive fibrils. These simple axis cylin-

Fig. 70.-

Intra-epithelial Nerve-termination in the Anterior Epith
of the Cornea, as seen in an oblique section.

elium

a, An axis cylinder ; b, sub-epithelial nerve-flbrillas ; c, intra-epithelial network ;
d, epithelial cells. (Handbook.)

ders form plexuses. By association they make larger
axis cylinders, and these becoming invested with a
neurilemma, and with the nuclei of nerve corpuscles,
form non-medullated nerve-fibres. These also form
plexuses. A medullary sheath makes its appearance
between the neurilemma and the axis cylinder, and
thus forms a medullated nerve-fibre.

Chap. XV.] 115

CHAPTER XV.

PERIPHERAL NERVE-ENDINGS.

149. IN the preceding chapter the termination of
the nerves of common sensation, as isolated primitive
fibrillse, and as networks of these, has been described
in the epithelium of the skin and mucous mem-
branes, and in the anterior epithelium of the cornea.
Besides these there are other special terminal organs
of sensory nerves, probably concerned in the per-
ception of some special quality or quantity of sensory
impulses. They are all connected with a medullated
nerve-fibre, and are situated, not in the epithelium
of the surface, but in the tissue, at greater or
lesser depth. Such are the Pacinian corpuscles, the
Herbst corpuscles, the end-bulbs of Krause in the
tongue and conjunctiva, the genital end-corpuscles or
end-bulbs in the external genital organs, the corpuscles
of Meissner, or tactile corpuscles, in the papillae of
the skin of the volar side of the fingers, the touch-cells
of Merkel in the beak and tongue of duck, &c.

150. The Pacinian corpuscles. — These are
also called Yater's corpuscles. They occur in large
numbers on the subcutaneous nerve-fibres of the palm
of the hand and foot of man, in the mesentery of the
cat, along the tibia of the rabbit, on the genital organs
of man (corpora cavernosa, prostate). Each corpuscle
is oval, more or less pointed, and in some places
easily perceptible to the unaided eye (palm of
the human hand, mesentery of the cat), the largest
being about -j^th of an inch long and -^th of an inch
broad; in other places they are of microscopic size
only. Each possesses a stalk, to which it is attached,

n6

ELEMENTS OF HISTOLOGY. [Chap. xv.

and which is a single efferent medullated nerve-fibre
(Fig. 71), differing from an ordinary medullated nerve-
fibre merely in the fact that outside the neurilemma of

the nerve-fibre there is
present a thick laminated
connective tissue sheath,
which is the sheath of
Henle — continuous with
the perineural sheath of
the nerve branch with
which the nerve-fibre is in
connection. This medul-
lated nerve-fibre within its
sheath possesses generally
a very wavy outline. The
corpuscle itself is com-
posed of a large number of
lamellee, or capsules, more
or less concentrically ar-
ranged around a central
elongated or cylindrical
clear space. This space
contains in its axis from
the proximal end, i.e., the
one nearest to the stalk , to
near the opposite or distal

end, a continuation of the nerve-fibre in'the shape of a
simple axis cylinder. But this axis cylinder does not
fill out the central space, since there is, all round the
faintly and longitudinally striated axis cylinder, a good
deal of space left filled with a transparent substance, in
which, in some instances, rows of spherical nuclei may
be perceived along the margin of the axis cylinder.
At or near the distal end of the central space the
axis cylinder divides in two or more branches, and
these terminate in pear-shaped, oblong, spherical, or
irregularly-shaped granular-looking enlargements.

Fig. 71.— A Paciniaii Corpuscle,
from the Mesentery of the Cat.

a, The medullated nerve-flbre ; b, the
concentric capsules.

Chap, xv.] PERIPHERAL NERVE-EN^Y^GS. 117

Y^GS. 1

151. The concentric capsules forming

itself are disposed in a different manner at the periphery
and near the central space from that in which they
are disposed in the middle parts, viz., in the former
localities they are much closer together, being thinner
than in the latter. On looking, therefore, at a
Pacinian corpuscle in its longitudinal axis, or in cross
section, we always notice the striation (indicating the
capsules) to be closer in the former than in the latter
places. Each capsule consists of — (a) a hyaline, pro-
bably elastic, ground substance, in which are embedded
here and there (&) fine bundles of connective tissue
fibres; (c) on the inner surface of each capsule, i.e.,
the one directed to the central axis of the Pacinian
corpuscle, is a single layer of nucleated endothelial
plates. The oblong nuclei visible on the capsules at
ordinary inspection are the nuclei of these endothelial
plates. There is no fluid between the capsules, but
these are in contact with one another (Huxley).
Neighbouring capsules are occasionally connected with
one another by thin fibres.

152. In order to reach the central space of the
corpuscle, the medullated nerve-fibre has to perforate
the capsule at one pole; thus a canal is formed
in which is situated the medullated nerve-fibre,
and as such, and in a very wavy condition, it reaches
the proximal end of the central space. This
part of the nerve-fibre may be called the interme-
diary part. The lamellae of the sheath of Henle
pass directly into the peripheral capsules of the
corpuscle.

Immediately before entering the central space, the
nerve-fibre divests itself of all parts except the axis
cylinder, which, as stated above, passes into the central
space of the Pacinian corpuscle. In some cases a
minute artery enters the corpuscle at the pole, opposite
to the one for the nerve-fibre; it penetrates the

u8

ELEMENTS OF HISTOLOGY. [Chap. xv.

peripheral capsules, and supplies them with a few
capillary vessels.

153. The corpuscles of Herbst are similar to
the Pacinian corpuscles, with this difference, that they
are smaller and more elongated, that the axis cylinder
of the central space is bordered by
a continuous row of nuclei, and
that the capsules are thinner and
more closely placed (Fig. 72).
This applies especially to those
near the central space, and here
between these central capsules we
miss the nuclei indicating the en-
dothelial plates. Such is the nature
of Herbst's corpuscles in the mucous
membrane of the tongue of the
duck, and to a certain degree also
in those of the rabbit, and in
tendons.

154. The tactile corpus-
cles, or corpuscles of Meiss-
ner, occur in the papillae of the
corium of the volar side of the
fingers and toes in man and ape ;
they are oblong, straight, or
slightly folded. In man they are
about ^i-Q to 3^-5- of an inch long,
and -^ to ^IJo of an inch
broad. They are connected
with a medullated nerve fibre — generally one, occa-
sionally, but rarely, two — with a sheath of Henle.
The nerve-fibre enters the corpuscle, but usually
before doing so it winds round the corpuscle as a
medullated fibre once or twice or oftener, and its
Henle's sheath becomes fused with the fibrous capsule
or sheath of the tactile corpuscle. The nerve-fibre
ultimately loses its medullary sheath and penetrates

Fig. 72. — A Herbst's
Corpuscle, from the
Tongue of Duck.

a, The medullated nerve-
fibre cut away.

Chap, xv.] PERIPHERAL NERVE-ENDINGS.

119

into the interior of the corpuscle, where the axis
cylinder branches ; its branches re-
tain a coiled course all along the
tactile corpuscle (Fig. 73), anastomose
with one another, and terminate in
slight enlargements, pear-shaped or
cylindrical. These enlargements, ac-
cording to Merkel, are touch cells.
The matrix, or main part of the
tactile corpuscle consists, besides the
fibrous sheath with nuclei and numer-
ous elastic fibres, of fine bundles of
connective tissue, and of a number
of nucleated small cells.

155. The end- bulbs of
Krause. — These occur in the con-

/••.,. -, j Showing the convolu-

lunctiva of call and man, and are tions of the nerve-

•* , , T j • i • fibre. (E. Fischer and

oblong or cylindrical minute corpus- w. Fiemming.)
cles situated in the deeper layers of

the conjunctiva,

the

Pig. 73.— A Tactile
Corpuscle of Meiss-
ner from the Skin of
the Human Hand.

near
margin

Fig. 74.— An End-bulb of Krause.
a, Medullated nerve-flbre ; b, the capsule of the

corneal
A medul-

lated nerve - fibre,
with Henle's sheath,
enters the corpuscle
(Fig. 74). This
possesses a nu-
cleated capsule, and
is a more or less
laminated (in man
more granular-
looking) structure,
numerous nuclei be-
ing scattered be-
tween the laminse.
Of the nerve-fibre,
as a rule, only the

120

ELEMENTS OF HISTOLOGY. [Chap. xv.

axis cylinder is prolonged into the interior of the
corpuscle. Occasionally the medullated nerve-fibre
passes, as such, into the corpuscle, being at the
same time more or less convoluted. Having passed
to near the distal extremity, it branches, and termi-
nates with small enlargements (Krause, Longworth,
Merkel, Key and Retzius).

The end-bulbs in the genital organs, or the genital
corpuscles of Krause, are similar in structure to the
simple end-bulbs. They occur in the tissue of the
cutis and mucous membrane of the penis, clitoris, and
vagina.

156. The corpuscles of Orandry or touch-
corpuscles of Merkel, in the tissue of the papillae in the
beak and tongue of birds, are oval or spherical cor-
puscles of minute size, possessed of a very delicate

Fig. 75. — Corpuscles of Grandry in the Tongue of Duck.

A, Composed of three cells ; B, composed of two cells; c, showing the develop-
ment of a Grandry's corpuscle from the epithelium covering the papilla;
e, epithelium ; n, nerve-nbre. (Izquierdo.)

nucleated membrane as a capsule, and consisting of a
series (two, three, four, or more) of large, slightly-
flattened, granular-looking, transparent cells, each with
a spherical nucleus, and arranged in a vertical row (Fig.
75). A medullated nerve-fibre enters the corpuscle from
one side, and losing its medullary sheath, the axis cy-
linder branches, and its branchlets terminate, according
to some (Merkel, Henle), in the ceils of the corpuscle

chap, xv.] PERIPHERAL NERVE-ENDINGS. 121

(touch-cells of Merkel) ; according to others (Key and
Retzius, Ranvier, Hesse, Izquierdo), in the trans-
parent substance between the touch-cells, thus form-
ing the * disc tactil ' of R,anvier or the Tastplatte of
Hesse. Neither theory seems to me to answer to the
facts of the case, since I find that the branchlets of
the axis cylinder terminate, not in the touch-cells, nor
as the disc tactil, but with minute swellings in the
interstitial substance between the touch-cells, in a
manner very similar to what is the case in the con-
junctival end bulbs. According to Merkel, single or
small groups of touch-cells occur in the tissue of the
papillae, and also in the epithelium, in the skin of
man and mammals.

157. In articulations — e.g., the knee-joint of the
rabbit — Nicoladoni described numerous nerve branches,
from which fine nerve-fibres are given off. Some of
these terminate in a network, others on blood-vessels,
and a third group enter Pacinian corpuscles. Krause
described in the sy no vial membranes of the joints of
the human fingers medullated nerve-fibres which end
in peculiar tactile corpuscles, called by him " articula-
tion-nerve corpuscles."

158. The nerve branches supplying non-
striped muscular tissue are derived from the
sympathetic system. They are composed of non-
medullated fibres, and the branches are invested in
an endothelial sheath, — perineurium. The branches
divide into single or small groups of axis cylinders,
which reunite into a plexus — the ground plexus of
Arnold. Small fibres coming off from the plexus
supply the individual bundles of non-striped muscle
cells, and they form a plexus called the intermediary
plexus (Fig. 76). The fibres joining this plexus are
smaller or larger bundles of primitive fibrillae ; in
the nodes — i.e., the points, of meeting of these fibres
are found angular nuclei. From the intermediary

122

ELEMENTS OF HISTOLOGY. [Chap. xv.

plexus pass off isolated or small groups of primitive
fibrillse, which pursue their course in the interstitial

Fig. 76.— Bundles of Non-striped Muscular Tissue surrounded by
Plexuses of Fine Nerve-fibres. (Handbook.)

substance be-
t wee n the
muscle cells;
these are the
inter muscular
fibrils (Fig. 76A).
According to
Frankenhaiiser
and Arnold,
they give off
finer fibrils,
ending in the
nucleus (or
nucleolus). Ac-
cording to
Elischer, the
primitive fibrils
terminate on the
surface of the
nucleus with a
minute swelling.

Fig. 76A. — Termination of Nerves in Non-
striped Muscular Tissue.

a, Non-medullated fibre of the intermediary plexus ;
b, fine intermuscular fibrils ; c, nuclei of muscular
cells. (Atlas.)

Chap, xv.] PERIPHERAL NERVE-ENDINGS.

123

In many localities there are isolated ganglion cells
in connection with the intermuscular fibres.

159. The nerves of blood-vessels are derived
from the sympathetic, and they terminate in arteries
and' veins in essentially the same way as in non-
striped muscular tissue, being chiefly present in those

Tig. 77.— Plexus of Fine Non-medullated Nerve-fibres surrounding
Capillary Arteries in the Tongue of Frog, after staining with
Chloride of Gold.

a Blood-vessel; 6, connective tissue corpuscles ; c, thick non-medullated fibres ;
d, plexus of flue nerve-flbres. (.Handbook.)

parts (media) which contain the non-striped muscular
tissue. But there are also fine non-medullated nerve
fibres, which accompany capillary vessels — capillary
arteries and capillary veins — and in some places they
give off elementary fibrils, which forma network around
the vessel (Fig. 77). In some localities the vascular
nerve branches are provided with small groups of
ganglion cells.

160. In striped muscle of man and mammals,
reptiles, and insects, the termination of nerve fibres
takes place, according to the commonly accepted view
of Klihne, in the following manner : — A medullated

I24

ELEMENTS OF HISTOLOGY. [chap.

nerve-fibre, generally derived from one that has
divided, enters at almost a right angle a striped
muscular fibre, the neurilemma becoming fused with

Fig. 78. — From a Preparation of Striped Muscular Fibres of the Snake,
showing the termination of the Medullated Nerve-fibres. (After
a preparation of Mr. A. Lingard.)

a, The nerve endplate seen from the broad side ; 6, the same seen from the
narrow side. Each endplate is a network connected with the axis cylinder
of a medullated nerve-fibre, and contains numerous nuclei of various sizes
and shapes.

the sarcolemma, and the nerve-fibre, either at the
point of entrance or soon after loses its medullary
sheath, so that only the axis cylinder passes on.
This latter divides simultaneously into a number of
smaller fibres, which soon break up into a network of
fine fibrils, this ultimate network being embedded in a
more or less granular-looking plate, provided with

Chap, xv.] PERIPHERAL NERVE-ENDINGS.

I25

a number of oblong nuclei (Fig. 78). The whole struc-
ture represents the nerve endplate. When the muscular
fibre contracts, this endplate naturally assumes the
shape of a prominence — Doyere's nerve-mount. Each
muscular fibre has at least one nerve endplate, but
occasionally has several in near proximity. An
endplate is generally supplied by one, sometimes,
however, by two, nerve-fibres. The contraction
wave generally starts from the endplate. In
Batrachia the nerve-fibre does not, as a rule, termi-
nate in the shape of a granular endplate, but
having penetrated the sarcolemma ramifies into
several axis cylinders, each of which again branches ;
all branches have a more or less longitudinal
direction, and are provided, either terminally or in

*>^.:v

Fig. 79. — Termination of Medullated Nerve-fibres in Tendon, near the
Insertion of the Striped Muscular Fibres.

The nerve-fibres terminate in peculiar reticulated endplates of primitive
flbrillae. (Golgi.)

their course, with oblong nuclei. Arndt has
shown that both kinds of terminations occur in
Batrachia. These two sorts of nerve endings lie

126

ELEMENTS OF HISTOLOGY. [Chap. xv.

underneath the sarcolemma and on the surface of the
muscular substance proper. But besides this intra-
muscular termination, there is a plexus of nerve-fibres,
which is situated outside the sarcolemma — i.e., inter-
muscular ; this
has been seen by
Beale, Kolliker,
Krause, and
others. Arndt
considers these in-
•a termuscular fibres
as sensory nerves.
161. Tendons
are supplied with
special nerve end-
ings, studied by
Sachs, Rollett,
Gempt, Rauber,
and particularly
Golgi, whose work
on this subject is very minute. These terminations are
especially numerous near the muscular insertion. They

Fig. 80.— One of the Eeticulated Endplates
of the previous figure, more highly
magnified.

«, The medullated nerve fibre ; 6, the reticulated
endplate. (Golgi.)

Fig. 81.— Termination of Medullated Nerve-fibi-es in Tendon.

a, End-bulbs with convoluted medullated nerve-fibre ; 6, end-bulb similar to a
Herbst's corpuscle. (Golgi.)

are of the following kinds : — (a) A medullated nerve
fibre branches repeatedly, and the axis cylinder breaks
up into a small plate composed of a network of fine
primitive nerve-fibrils (Fig. 79). (b) This network is

chap, xvi.] THE SPINAL CORD. 127

occasionally embedded in a granular-looking material,
and thereby a similar organ as the nerve endplate of
muscular fibres is produced (Fig. 80). (c) A medul-
lated nerve-fibre terminates in an end-bulb (Fig. 81),
similar to those of the conjunctiva, or of a Herbst's
corpuscle.

CHAPTER XVI.

THE SPINAL CORD.

162. THE spinal cord is enveloped in three distinct
membranes. The outermost one is the dura mater.
This is composed of more or less distinct lamellae of
fibrous connective tissue with the flattened connective
tissue cells and networks of elastic fibres. The outer
and inner surface of the dura mater is covered with
a layer of endothelial plates.

163. Next to the dura mater is the arachnoid
membrane. This also consists of bundles of fibrous
connective tissue. The outer surface is smooth and
covered with an endothelial membrane facing the
space existing between it and the inner surface of the
dura mater ; this space is the sub-dural lymph space.
The inner surface of the arachnoidea is a fenestrated
membrane of trabeculse of fibrous connective tissue,
covered on its free surface — i.e., the one facing the
sub-arachnoidal lymph space — with an endothelium.

164. The innermost membrane is the pia mater.
Its matrix is fibrous connective tissue, and it is lined
on both surfaces with an endothelial membrane.
Between the arachnoid and pia mater extends, from
the fenestrated portion of the former, a spongy plexus
of trabeculse of fibrous tissue, the surfaces of the
trabeculse being covered with endothelium. By this

128 ELEMENTS OF HISTOLOGY. . [c-ap. xvi.

spongy tissue — the sub-arachnoidal tissue (Key and
Retzius) — the sub-arachnoidal space is subdivided into
a labyrinth of lacunae. On each side of the cord,
between the anterior and posterior nerve roots,
extends a spongy fibrous tissue, called lig amentum
denticulatum, between the arachnoidea and pia.
By it the sub-arachnoid al space is subdivided into
an anterior and posterior division.

165. The sub-dural and sub-arachnoidal spaces do
not communicate with one another. (Luschka, Key
and Retzius.)

The dura mater, as well as the arachnoidea, sends
prolongations on to the nerve roots; and the sub-
dural and sub-arachnoidal spaces are continued into
lymphatics of the peripheral nerves.

All three membranes contain their own system of
blood-vessels and nerve-fibres.

166. The cord itself (Fig. 82) consists of an outer
or cortical part composed of medullated nerve-fibres ;
this is the white matter, and an inner core of grey
matter. On a transverse section through the cord
the contrast of colour between the white mantle and
the grey core is very conspicuous. The relation
between the white and grey matter differs in diffe-
rent parts ; it gradually increases in favour of the
former as we ascend from the lumbar to the upper
cervical portion. The grey matter presents in every
transverse section through the cord more or less the
shape of a capital H; the projections being the
anterior and posterior horns or cornua of grey
matter, and the transverse stroke being the grey
commissure. In the centre of this grey commissure
is a cylindrical canal lined with a layer of columnar
epithelial cells ; this is the central canal ; the part
of the grey commissure in front of this canal is
the anterior, the rest the posterior, grey commissure.
The shape of the whole figure of the grey matter

Chap. XVI.]

THE SPINAL CORD.

129

differs in the different regions, and this difference
is chiefly brought about by the length and thickness
of the grey commissure. In a section through the
cervical region the grey commissure is thick and
short; in the dorsal region it becomes thinner and

a

Fig. 82.— Transverse Section through the Spinal Cord of Calf.

a, Pia mater ; 5, prolongation of pia mater into the anterior longitudinal fissure ;
c. posterior longitudinal fissure; d, anterior column of white matter; e,
lateral column of same ; /, posterior column of same : g, anterior white
commissure ; h, central canal ; i, anterior horn of grey matter ; j, posterior
horn of grey matter ; k, anterior nerve roots ; I, posterior nerve roots.

longer ; and in the lumbar region it is comparatively
very thin and long. Besides this, of course the relative
proportions of grey and white matter, as mentioned
before, indicate the region from which the particular
part of the cord has been obtained. In the lower
J

130 ELEMENTS OF HISTOLOGY. [Chap. xvi.

cervical and lumbar region where the nerves of the
brachial and sacral plexus respectively join the cord,
this latter possesses a swelling, and the grey matter
is there increased in amount, the swelling being in
fact due to an accumulation of grey matter, in which
an additional number of nerve-fibres originates ; but
the general shape of the grey matter is there retained.

167. The cornua of the grey matter are generally
thicker near the grey commissure; they become thinned
out into anterior and posterior edges respectively,
which are so placed that they point towards the
antero-lateral and postero-lateral fissures. The an-
terior horns are generally thicker and shorter than
the posterior ones, and, therefore, the latter reach
nearer to the suface than the former.

168. The white matter is composed chiefly of
rnedullated nerve fibres running a longitudinal course.
They are arranged into columns, one anterior, one
lateral, and one posterior column for each lateral
half of the cord ; the two halves being indicated by
the anterior and posterior median longitudinal
fissure. The anterior median fissure is a real fissure

extending in a vertical direction from the surface of
the cord to near the anterior grey commissure. It
contains a prolongation of the pia mater and in it
large vascular trunks. The posterior fissure is not
in reality a space, but is filled up by neuroglia. It
extends as a continuous mass of neuroglia in a vertical
direction from the posterior surface of the cord to the
posterior grey commissure. The exit of the anterior
or motor nerve roots, and the entrance of the posterior
or sensitive nerve roots are indicated by the anterior
lateral and posterior lateral fissures respectively.
These are not real fissures in the same sense as the
anterior median fissure, but correspond more to the
posterior median fissure, being in reality filled up with
neuroglia tissue, into which extends a continuation

Chap. XVI.]

THE SPINAL CORD.

from the pia mater with large vascular trunks. The
white matter between the anterior median and ante-
rior lateral fissure is the anterior column, that between
the anterior lateral and posterior lateral fissure is the
lateral column, and that between the posterior lateral
and posterior median fissure is the posterior column.
169. Besides the septa situated in the two lateral

Fig. 83.— Diagram of a Transverse Section through the Cord in the
region of the Cervical Swelling.

a, Anterior longitudinal fissure ; 6, posterior longitudinal fissure : the part of the
white matter next to it is the fasciculus of Goll ; c, central canal; d, direct
pyramidal fasciculus ; e, roots of anterior or motor nerves ; /, lateral bundle
of posterior nerve roots ; g, median bundle of same; h. the emirate fasci-
culus : i, the crossed pyramidal fasciculus or the fasciculus of Tiirk ; A-, the
anterior radicular zone of the lateral column of white matter; ?, the direct
cerebellar fasciculus; m, the anterior horn of grey matter; n, the posterior
horn of same.

fissures respectively, there are other smaller septa,
neuroglia tissue and prolongations of the pia mater,

132 ELEMENTS OF HISTOLOGY. [Chap. xvi.

which pass in a vertical and radiating direction into
the white matter of the columns, and they are thus
subdivided into a number of smaller portions ; one
such big septum is sometimes found corresponding to
the middle of the circumference of one half of the
cord. This is the median lateral fissure, and the
lateral column is subdivided by it into an anterior
and posterior division.

Similarly, the anterior and posterior columns
may be subdivided into a median and lateral division
(Fig. 83).

170. Some of these various subdivisions bear
definite names (Turk, Charcot, Flechsig) : —

(a) The median division of the anterior column is
called the direct or uncrossed pyramidal fasciculus,
being a ^continuation of that part of the anterior
pyramidal tract of the medulla oblongata (see below)
that does not decussate.

(b) The anterior division of the lateral column is
called the anterior radicular zone.

(c) The direct cerebellar fasciculus corresponds to
the peripheral portion of the postero-lateral column ;
it is a direct continuation of the white matter of the
cerebellum.

(d) The posterior division of the lateral column
inside the cerebellar fasciculus is called the fasciculus
of Turk, or the crossed portion of the pyramidal fasci-
culus, it being a continuation of the decussated part of
the anterior pyramidal tract of the medulla oblongata.

(e) The lateral division of the posterior column,
with the exception of a small peripheral zone, is the
cuneiform or cuneate fasciculus, or posterior radicular
zone.

(/) The median division of the posterior column is
called the fasciculus of Goll.

This part is connected directly with the median
bundle of the posterior nerve roots. (See below.)

Chap. XVI.]

THE SPINAL CORD.

133

These various divisions can be traced from the
medullata oblongata into the cervical, and a greater
or smaller portion of the dorsal part of the cord, but
farther down most of them are lost as separate tracts,
except the fasciculus of Turk.

171. The ground substance (Fig. 84) of both
the white and grey matter — i.e., the substance in
which nerve-fibres,
nerve cells, and blood-
vessels are embedded-^-
is a peculiar kind of con-
nective tissue, which
is called by Virchow
neuroglia and by Kol-
liker supporting tissue.
It consists of three dif-
ferent kinds of ele-
ments : (a) a homoge-
neous transparent semi-

A special peripheral' condensation of
neurogliA; ;<>, white matter with the
inedullatect nerve-Iihres shown in
cross section, and neuroglia between
them. (Atlas.)

Fig. 84.— From a Transverse Sectiou
through a most Peripheral Part of
the White Matter of the Cord.

fluid matrix, which in
hardened sections ap-
pears more or less gran-
ular; (b) a network of

very delicate fibrils — neuroglia fibrils — which are
similar in some respects, but not quite identical with
elastic fibres.

In the columns of the white matter the fibrils extend
pre-eminently in a longitudinal direction, in the grey
matter they extend uniformly in all directions, and in
the septa between the columns they extend chiefly in
the direction vertical to the long axis of the cord.

(c) Small branched nucleated cells intimately
woven into the network of neuroglia fibrils. These
cells are the neuroglia cells. The greater the amount
of neuroglia in a particular part of the white or grey
matter the more numerous are these three elements.

172. In both the white and grey matter the

134 ELEMENTS OF HISTOLOGY. [Chap. xvi.

neuroglia lias a very unequal distribution ; but there
are certain definite places in which there is always a
considerable amount— a condensation, as it were, of
neuroglia tissue. These places are : underneath the
pia mater — i.e., on the outer surface of the white
matter — there most of the neuroglia fibrils have a
horizontal direction ; near the grey matter there is
a greater amount of neuroglia between the nerve-
fibres of the white matter than in the middle parts of
this latter ; in the septa between the columns and
between the divisions, of columns of white matter ; at
the exit of the anterior and the entrance of the
posterior nerve roots.

A considerable accumulation of neuroglia is
present immediately around the epithelium lining the
central canal j this mass is cylindrical, and is called
the central grey nucleus of Kolliker. The epithelial
cells lining the central canal are conical, their bases
facing the canal, their pointed extremity being drawn
out into a fine filament intimately interwoven with
the network of neuroglia fibrils. In the embryo and
young state, the free base of the epithelial cells has a
bundle of cilia, but in the adult they are lost.

Another considerable accumulation of neuroglia
exists in the posterior portion of the posterior grey
horns, as the substantia gelatinosa of Rolando.

173. The white matter (Fig. 85) is composed,
besides neuroglia, of medullated nerve-fibres varying
very much in diameter, and forming the essential and
chief part of it. They possess an axis cylinder and
a thick medullary sheath more or less laminated, but
are devoid of a neurilemma and its nerve corpuscles.
Of course, no nodes of Hanvier are observable. In
specimens of white matter of the posterior columns,
where the nerve-fibres have been isolated by teasing
or otherwise, many fine medullated fibres are met
with which show the varicose appearance mentioned

Chap. XVI.]

THE SPINAL CORD.

'35

Fig. 85.— From a Transverse Section
through the White Matter of the Cord.

Showingthe transversely-cut medullated nerve-
fibres, the neuroglia between them with two
branched neuroglia cells. (Atlas.)

in a former chapter. The medullated nerve-fibres,
or rather the matrix of their medullary sheath, con-
tains neurokeratin. The nerve-fibres of the white
matter run chiefly
in a longitudinal
direction, and they
are separated from
one another by the
neuroglia. Here and
there in the columns
of white matter are
seen connective tis-
sue septa with ves-
sels, by which the
nerve - fibres are
grouped more or
less distinctly in
divisions.

174. Although

most of the nerve-fibres constituting the columns of
white matter are of a longitudinal direction — i.e.,
passing upwards or downwards between the grey
matter of the cord on the one hand, and the brain and
medulla oblongata on the other — there are nevertheless
a good many nerve-fibres and gro.ups of nerve-fibres
which have an oblique or even horizontal course.

(1) The anterior median fissure does not reach
the anterior grey commissure, for between its bottom
and the latter there is the white commissure. This
consists of bundles of medullated nerve-fibres passing
in a horizontal or slightly oblique manner between the
grey matter of the anterior horn of one side, and the
anterior white column of the opposite side (Fig. 82,^).

(2) Numerous medullated fibres are derived from
the grey matter, and they pass in a horizontal or
oblique direction into the white matter, especially in
considerable numbers into that of the lateral columns.

136 ELEMENTS OF HISTOLOGY. [chap. xvi.

Having entered the white matter, they take a longitu-
dinal direction. Most of these fibres enter the white
matter in the septa and septula, by which the nerve-
fibres of the white matter of the columns are sub-
divided, and having passed in a horizontal direction
in the septa and septula, some for a shorter, others
for a longer distance, they enter the columns and
pursue a longitudinal course.

175. (3) The medullated nerve-fibres which leave
the cord by the anterior nerve roots are comparatively
thick fibres, which pass out of the anterior portion of
the grey matter of the anterior horns in bundles ;
they pass through the white matter in an oblique
direction by septa, and emerge in the anterior lateral
fissure above mentioned.

(4) The medullated nerve-fibres entering the cord
by the posterior nerve roots are thinner than those of
the anterior nerve roots ; they pass into the cord by
the posterior lateral fissure. Having entered, they
divide into two bundles, one median and another
lateral. The fibres of the former pass in an oblique
direction into the white matter of the posterior
columns — the cuneiform fasciculus (see above) ; — and,
having run in these in a longitudinal direction, again
leave them, sooner or later, and enter, in a horizontal
or slightly oblique direction, the grey matter of the
posterior horns. The fibres of the lateral bundle,
on the other hand, pass directly from the posterior
nerve root into the hindmost portion of the grey
matter of the posterior horn. The nerve-fibres of
the posterior roots entering the grey matter divide
repeatedly, and show very markedly the varicose
appearance.

176. The grey matter consists, besides the
uniform network of neuroglia fibres and neuroglia
cells, of nerve-jibres and of nerve-cells, or ganglion cells.

The nerve-fibres are of three kinds — medullated

chap, xvi.] THE SPINAL CORD. 137

fibres, simple axis cylinders of various sizes, and primi-
tive nerve-fibrillse.

The medullated nerve-fibres run a more or less
horizontal course, and they belong to different
sources : —

(1) Medullated nerve-fibres connected directly —
i.e., by the axis cylinder process (see below) — with
ganglion cells of the anterior horns; they leave the
anterior horns by the septa and septula, and they
form the anterior nerve roots.

(2) Medullated nerve-fibres which form the an-
terior white commissure ; they are traceable from the
anterior column of one side into the grey matter of
the anterior horns of the opposite side, as has been
mentioned above; some of these, at any rate, are
distinctly and directly traceable to ganglion cells.

(3) Medullated nerve -fibres derived indirectly
from the median bundle of the posterior nerve root —
i.e., coming out of the cuneiform fasciculus of the
posterior column and medullated nerve-fibres derived
directly from the lateral bundle of the posterior nerve-
root. Both these kinds of nerve-fibres can be traced
for longer or shorter distances in the grey matter of
the posterior horns ; on their way they undergo
numerous divisions into very fine medullated fibres.

(4) Medullated nerve-fibres passing from, the grey
matter into the white matter of the lateral column. Some
of these are nerve-fibres that pass simply through the
grey matter of the anterior horns from an anterior
nerve root ; others are derived directly from ganglion
cells forming the columns of Clarke in the dorsal
region (see below). But the majority are derived from
that part of the grey matter intermediate between the
anterior and posterior horn.

177. The simple axis cylinders are found very
numerously in the grey matter of all parts ; they are
of many various sizes, and run in all directions, many

138 ELEMENTS OF HISTOLOGY. [Chap. xvi.

of them, especially the larger ones, are only the first
part of the medullated nerve-fibres, being the axis
cylinder process of a ganglion cell, which process,
after a shorter or longer course in the grey matter,
becomes ensheathed in a medullary sheath, and re-
presents one of the above medullated fibres. But
there are also numerous fine axis cylinders, which are
the last outrunners of the nerve-fibres entering the
grey matter by the posterior roots. They are seen
everywhere, isolated and running in smaller or larger
bundles.

178. The primitive nerve fibrillce form the greater
part of the grey matter, in fact the matrix of the
grey matter of all parts being composed, besides the
network of neuroglia fibrils, of an exceedingly fine
and dense network of primitive fibrillce (Gerlach).
These are the nervous groundwork into which pass,
and from which originate, nerve-fibres. The nerve-
fibres which are derived from the posterior roots
having entered the grey matter of the posterior
horn undergo repeated divisions, and ultimately be-
come connected with this network of primitive
fibrillse. Numerous nerve-fibres take their origin in
the network of primitive fibrillae, and leave the grey
matter as medullated nerve-fibres, which pursue a
longitudinal course in the anterior and especially in
the lateral column of the white matter.

179. The g-ataglion cells (Fig. 86) of the grey
matter are of various sizes and shapes, the branched, or
stellate, or multipolar shape being predominant ; some
have a more or less spindle-shaped or bipolar body, but
each extremity may be richly branched. Each has a
relatively large nucleus bordered by a membrane, and
in it is a reticulum with one or two nucleoli. The
largest ganglion cells occur in the anterior horns,
likewise in the Clarke's column of the dorsal region ;
the smallest in the posterior horns. The ganglion cells

Chap. XVI.]

THE SPINAL CORD.

139

are much more numerous in the anterior horn than in
the posterior, where they are relatively scarce.

In the former they are all stellate or multipolar,
and form definite groups : (a) an anterior group,

Fig. 86,— An Isolated Ganglion Cell of the Anterior Horn of the

Human Cord.

«, Axis cylinder process : 6, pigment. The branched processes of the ganglion
o"ll break up into the fine nerve network shown in the upper part of the
figure. (Gerlach. in Strieker's " Manual of Histology.")

(b) a median or inner group, and (c) a lateral group.
The cells of the lateral group are the largest, those of
the inner or median group are the smallest of the
three. The lateral group of ganglion cells extends in
the cervical region for a longer or shorter distance
into the white matter of the lateral column.

1 4o

ELEMENTS OF HISTOLOGY. [Chap. xvi.

180. In the dorsal region of the cord there exists
near the grey commissure
a special cylindrical group
of large multipolar gan-
glion cells, which form the
column of Lockhart Clarke.

In the posterior horns
the ganglion cells are few
and far between. Most of
them belong to the portion
of the posterior horn near
the posterior commissure.

The substance of the
ganglion cells is fibril lated,
but there exists a granular
interstitial material, which
is especially well developed
near the nucleus. Some-
times smaller or larger
masses of yellowish pig-
ment granules are present
in this part of the cell
substance — i.e., near the
nucleus.

181. The fibrillated sub-
stance of the ganglion cells
is prolonged on to the pro-
cesses. There are always
one or two that are thicker
than the others. At a
longer or shorter distance
fromtne cel1 *he processes
branch dendritically into

a loro-p rmrnVipr nf fihrps;
a Aaige numoer CS,

-wliinh mTa-nf -nailer Impair nr»
WlllCll e\ eilt'Ually break Up

into the fine network of
primitive fibrillse, forming the nervous groundwork of

Fi£f. 87.-An Isolated Multipolar

Sathe°CordlloftlieGreyMatter
The dendritTcaiiy-branched processes

break up into the fine nerve network
into which is seen to pass a fine nerve-
fibre derived from a posterior nerve
root. (Gerlacb, in Strieker's Manual.)

Chap, xvi.] THE SPINAL CORD. 141

the grey matter (Fig. 87). The ganglion cells of the
anterior horn and the cells of Clarke's column have,
in addition to these branched processes, generally one
unbranched pale process (occasionally, but rarely, this
is double), which takes its origin in the cell substance
with a thin neck. This is the axis cylinder process of
Deiters ; it becomes invested sooner or later in a
medullary sheath, and then represents a medullated
nerve-fibre, as mentioned on a former page. The
ganglion cells of the posterior horns have no axis
cylinder process, all processes being branched and
connected with the ground nerve network in the same
way as the branched processes of the ganglion cells of
the anterior horns.

Anastomoses between the processes of the ganglion
cells of the anterior horns have been observed in a
few instances (Carriere).

182. The ganglion cells of the anterior horns and
those forming Clarke's column — i.e., the ganglion
cells with axis cylinder process — are considered as
motor, the others as sensory ganglion cells ; that is to
say, the former are connected with a motor nerve-fibre,
the latter with a sensory fibre ; but it would be quite
incorrect to say that all motor fibres are connected
with the former, all sensory fibres with the latter.

183. The white and grey matter is supplied with a
large number of blood-vessels, the capillaries being
more abundant and forming a more uniform network
in the grey than in the white matter ; in the latter,
most of them have a course parallel with the long
axis. The blood-vessels are ensheathed in lymph
spaces (perivascular spaces of His), and the ganglion
cells are each surrounded by a lymph space (peri-
cellular space).

142 [Chap. XVII.

CHAPTER XVII.

THE MEDULLA OBLONGATA.

184. As the cervical portion of the cord passes
into the medulla oblongata, its parts alter position,
arrangement, and name in the following manner : —

(a) The anterior median fissure is continued as
far as the medulla extends. The posterior fissure of
the cord is also continued on the medulla, but in the
upper portion is lost, owing to the fact that the
central canal, which in the cord is situated in about
the middle, shifts in the medulla towards the posterior
surface, and soon altogether opens into the fourth
ventricle.

185. (6) The tracts of white matter bordering the
anterior median fissure of the medulla, and separated
from the other tracts by a distinct fissure on the
surface, are the pyramidal tracts. As was mentioned
on a former page, the median portion of the anterior
columns of white matter of the cord — i.e., the un-
crossed or direct anterior fasciculus — is a direct pro-
longation of the pyramidal tract, and can be followed
in this upwards into the pyramids — i.e., the oblong
prominences in the upper part of the medulla next
to the anterior median fissure — and from there to
the pons Yarolii and farther into the crus cerebri
A major portion of the pyramidal tract crosses in
the lower portion of the medulla, in the anterior
median fissure — this forms the pyramidal decussation
(Fig. 88). These crossed bundles enter the postero-
lateral column of the cord, that part of it which has
been mentioned above as the fasciculus of Turk. The
crossed portion of the pyramidal tract passes into

chap, xvn.] THE MEDULLA OBLONGATA.

the pyramids and farther on into the pons Varolii and
eras cerebri.

186. The greater portion, of the anterior column.

Fig. 88.— Transverse Section through the Medulla Oblongata in the
Eegion of the Pyramidal Decussation.

y matter ; fa, part of
gelatinous nucleus

erior pyramidal tract; ct/a, lateral nucleus of grey
aerior column not decussating' ; ng, nucleus gracilis; g,
of posterior born ; 11, spinal accessory nerve. (.Henle.)

fpy, Anterior
anteri

of white matter of the cord is situated deeper in the
medulla than the pyramidal tracts.

(c) The lateral column of white matter of the
cord can be traced into the medulla as the lateral
tract. In the upper part of the medulla it becomes
hidden from view by the olivary bodies and the
transversely arranged white tracts. The lateral tract

144 ELEMENTS OF HISTOLOGY. [Chap. xvn.

of the medulla comprises all parts of the lateral
column of the cord including that portion which was
mentioned as the anterior radicular zone and the direct
cerebellar fasciculus, but not that posterior division
of it which was mentioned previously as the fasciculus
of Turk, or the crossed pyramidal fasciculus.

(c?) The posterior column of the white matter of the
cord is continuous with the same column of the medulla.
That portion of it which lies next to the posterior
median fissure, and which is called in the cord the
fasciculus of Goll, is in the medulla called the fasciculus
(or funiculus) gracilis. In the upper part of the
medulla, as the central canal opens into the fourth ven-
tricle, the fasciculus gracilis turns in an oblique manner
outside, and forms the lateral boundary of the ventricle.

187. (e) The lateral part of the posterior column of the
cord, which was mentioned as the fasciculus cuneatus, is
prolonged into the medulla under the same name. But
between the two — i.e., the fasciculus gracilis and fasci-
culus cuneatus — there exists another tract, which is
called by Schwalbe funiculus of fiolando. In the
upper part of the medulla the fasciculus cuneatus
becomes covered by transverse bundles of medullated
nerve-fibres ; these pass from - the anterior median
fissure across the surface of the pyramids and olivary
body in a transverse direction towards the posterior
fissure, but before reaching this take an upward
direction. These bundles are the external arcuate
fibres. In the upper part of the medulla the ex-
ternal arcuate fibres, part of the funiculus cuneatus
and funiculus of Rolando, as well as the direct cere-
bellar fasciculus of the lateral column, all join to form
a prominent tract of white matter — the corpus resti-
forme — which enters the white matter of the cerebellar
hemisphere on the same side ; this is the pedunculus
cerebelli ad medullam oblongatam, or the lower cere-
bellar peduncle.

Chap, xvi i.j THE MEDULLA OBLONGATA. 145

188. (/) In the region of the pyramidal decussation
— i.e., the lower part of the medulla immediately fol-
lowing the cervical portion of the cord — the grey
matter of the cord is changed in its disposition by
the fasciculus of Tiirk or the crossed pyramidal
fasciculus passing en masse from the lateral column
of white matter through the anterior horns of the
grey matter. Hereby the anterior portion of the
grey matter of the cord is shut off from the rest of
the grey matter, and is found lying near the surface of
the lateral column of the lower portion of the medulla
as the lateral nucleus of grey matter (Fig. 88). The
main part of the anterior horn, however, is repre-
sented by the reticular formation of grey matter.
This contains in its lateral portion, at any rate, the
same large multipolar motor ganglion cells with axis
cylinder processes of Deiters and nervous ground-
network as the anterior horn of the cord ; but in
addition there are the numerous bundles of medul-
lated nerve-fibres passing through it in transverse,
oblique, and longitudinal directions. Some of these
fibres belong to the continuation of the anterior
columns of white matter of the cord, others join the
fasciculus gracilis and cuneatus, and a third kind pass
out from the middle line of the medulla.

189. (g) The grey matter of the posterior horns of
the cord undergoes a change of disposition when passing
into the medulla. Its hindmost portion is gradually
shifted outwards by the development of the reticular
formation of grey matter, and in about the middle of
the medulla it is found lying near the surface of the
lateral column as the tubercle of Rolando. The rest
of the posterior horn remains at first collected around
the central canal; but as this gradually approaches
the posterior fissure, in order to open as the fourth
ventricle above, the grey matter gradually expands
laterally into the funiculus gracilis and cuneatus of

146

ELEMENTS OF HISTOLOGY. [Chap.xvn.

Fig. 89.— Transverse Section through the Medulla Oblongata in the

Region of the Fourth Ventricle.
fpy, Anterior pyramidal tract ; /r, restiforra bodies; np, nucleus of pyramids;

no olivary nucleus ; n°a, accessory olivary nucleus; nh, nucleus of liypo-

glossal nerve: nv, nucleus of vagus; ngl, nucleus of glosso-pbaryugeus;

r.raphe; 9, «lossdplaaryugeal nerve; 12, hypogiossal nerve; y, horizontal

fibres. (.Henle.)

Chap, xvii.] THE MEDULLA OBLONGATA. 147

the white matter, and forms one distinct accumulation
of grey matter in each of these funiculi ; they are
respectively the nucleus gracilis and the nucleus
cuneatus. The former is the 'grey matter, in the
axis cylinder process of whose ganglion cells the nerve-
fibres of the f uniculus gracilis originate ; but in the
latter only a portion of the nerve-fibres of the
funiculus cuneatus take their origin ; since another
part of it joins the restiform body, and with this
passes into the cerebellum.

190. In the upper part of the medulla — i.e., in the
region of the fourth ventricle- — the grey matter forms a
continuous mass, thejloor of the fourth ventricle (Fig.
89). In this region there is a distinct median septum,
by which the medulla is divided into two halves ; this
is the raphe. It represents a thin membrane of nerve
substance, extending from the anterior longitudinal
iissure to near the middle line of the floor of the fourth
ventricle. This membrane consists of white matter
in the shape of bundles of medullated nerve-fibres
passing longitudinally, transversely, and obliquely ;
and of small masses of grey matter interspersed
between the nerve-bundles, and especially at the side
of the raphe, where nerve-fibre bundles pass out of
it. The grey matter contains multipolar ganglion
cells.

191. In a transverse section through the upper
part of the medulla, we find at the side of the
pyramid, and a little behind it, but covered on the
outer surface by white matter — i.e., the bundles of
nerve-fibres constituting the fibrse arcuatae externse — •
a plicated lamina of grey matter which constitutes the
olivary nucleus, or nucleus dentatus of the olivary
body. It extends with its posterior portion into the
reticular formation. Continuous with the olivary
nucleus, but situated nearer the raphe, is a small
lamina of similar grey matter ; this is the accessory

148 ELEMENTS OF HISTOLOGY. [Chap. xvn.

olivary nucleus. In both nuclei are found numerous
multipolar ganglion cells, each with an axis cylinder
process.

192. The grey matter at the floor of the

fourth ventricle is that from which the nerve roots
of the cerebral nerves (facial auditory, glossopharyn-
geal, pneumogastric, accessory, and hypoglossal) origi-
nate. The ganglion cells in it are of various sizes,
and are aggregated into groups which represent the
"nuclei" — i.e., the origin of the above nerves. The
thin layer of grey matter forming the floor of the
ventricle, in the strict sense, is neuroglia only, a con-
tinuation of the central grey nucleus of the cord.

The nerve cells in the hypoglossal nucleus are
the largest ; they are as large as the large cells
of the anterior horns of the cord. The cells of
the glossopharyngeal nerves are considerably smaller.
The motor nerve-fibres (e.g., those of the hypoglossal
and pnoumogastric) originate, as the axis cylinder
process of the multipolar ganglion cells, in exactly
the same manner as was mentioned in the cord,
but the sensory nerve- fibres of these nerves originate
from the nerve ground network, into which the
processes of the ganglion cells of these nuclei break up.

193. In the lower part of the medulla, as long as
there is still a closed central canal, we find next to
this the last outrunners of the groups of ganglion
cells representing the nucleus of the spinal accessory
and hypoglossal.

As we pass upwards, and as the central canal
opens as the fourth ventricle, the groups of ganglion
cells below the floor of the ventricle are so arranged
that we find near the median line the group repre-
senting the hypoglossal nucleus; then, farther out-
wards, several groups representing several sub-divisions
of the pneumogastric nucleus ; still farther upwards,
but more in the anterior part of the medulla, the nucleus

Chap, xviii.] CEREBRUM AND CEREBELLUM. 149

of the glossopharyngeal nerve ; and, lastly, but more
outwards and upwards, several divisions of the nucleus
of the auditory nerve. The nerve-fibres, originating
in these nuclei, pass in bundles through the substance
of the medulla oblongata, so as to appear on the
antero-lateral surface. Of course these nerves, the
nuclei of which are situated nearer to the middle line —
e.g.., the hypoglossal and spinal accessory — have to pass
through the reticular formation, whereas those whose
nuclei are situated more laterally pass only through
the lateral part of the medulla.

CHAPTER XVIII.

THE CEREBRUM AND CEREBELLUM.

194. THE structure of the dura mater, arachnoidea,
and pia mater of the brain is similar to that of the
same membranes of the cord.

As has been shown by Boehm, Key and Retzius,
and others, the deeper part of the dura contains peculiar
ampullated dilatations connected with the capillary
blood-vessels, and representing in fact the roots of the
veins.

The glandulce, Pacchioni, or arachnoidal villi of
Luschka, are composed of a spongy connective tissue,
prolonged from the sub-arachnoidal tissue and covered
with the arachnoidal membrane. These prolongations
are pear-shaped or spindle-shaped, with a thin stalk.
They are pushed through holes of the inner part of
the dura mater into the venous sinuses of this latter,
but are covered with endothelium. Injection matter
passes from the sub-arachnoidal spaces through these
stalks into the villi. The. spaces of their spongy

150 ELEMENTS OF HISTOLOGY. [Chap. xvm.

substance become thereby filled and enlarged, and
finally the injection matter enters the venous sinus
itself. The pia cerebralis is very rich in blood-vessels,
like that of the cord, which pass to and from the
brain substance. The capillaries of the pia mater
possess an outer endothelial sheath. The plexus
choroideus is covered with a layer of polyhedral
epithelial cells, which are ciliated in the embryo and
young.

1 95. As was mentioned of the cord, so also in the
brain the sub-dural lymph space does not communicate
with the sub-arachnoidal spaces or with the ventri-
cles (Luschka, Key and Ketzius). Nor is there a
communication between the sub-arachnoidal space and
the epicerebral space — i.e., a space described by His to
exist between pia mater and brain surface, but doubted
by others. The relations between the cerebral nerves
and the membranes of the brain, and the lymph-
spaces of both, are the same as those described of
the cord and the spinal nerves on a previous page.

196. The pia mater passes with the larger blood-
vessels into the brain substance by the sulci of the
cerebrum and cerebellum.

In the white and grey matter of the brain we
find the same kind of supporting tissue that we
described in the cord as neuroglia. It is also in
the brain composed of a homogeneous matrix, of a
network of neuroglia fibrils, and of branched, flat-
tened neuroglia cells, called Deiters' cells.

In the white matter of the brain the neuroglia
contains between the bundles of the nerve-fibres rows
of small nucleated cells ; these form special accumula-
tions in the bulbi olfactorii, and in the cerebellum.
Lymph corpuscles may be met with in the neuroglia,
especially around the blood-vessels and ganglion cells.

All the ventricles, including the aqueductus Sylvii,
are lined with a layer of neuroglia, being a direct

chap, xviii.] CEREBR UM A ND CEREBELL UM. 151

continuation of the one lining the fourth ventricle,
and this again being a direct continuation of the
central grey nucleus of the cord. Like the central
canal of the cord, also, the ventricles are lined with a
layer of ciliated columnar, or short columnar epithelial
cells.

197. The blood-vessels form a denser capillary
network in the grey than in the white matter ; in the
latter the network is pre-eminently of a longitudinal
arrangement, i.e., parallel to the long axis of the
bundles of the nerve-fibres. In the grey cortex of
the hemispheres of the cerebrum and cerebellum, many
of the capillary blood-vessels have an arrangement
vertical to the surface, but are connected with one
another by numerous transverse branches.

The blood-vessels of the brain are situated in
spaces, perivascular lymph-spaces, traversed by fibres
passing between the adventitia of the vessels, and
the neuroglia forming the boundary of the space.
There are no real lymphatic vessels in the grey or
white substance.

198. The white matter consists of medullated
nerve-fibres, which like those of the cord possess no
neurilemma or nuclei of nerve corpuscles, and no
constrictions of Ranvier. The nerve-fibres are of
very various sizes, according to the locality. Divisions
occur very often. When isolated they show the
varicosities mentioned in the cord.

The grey matter consists, like that of -the cord
and medulla, besides the neuroglia, of a very fine net-
work of elementary nerve-fibrils (Rindfleisch, Gerlach),
into which pass, on the one hand, nerve-fibres, and,
on the other, the branched processes of ganglion cells.

With regard to the structure of the ganglion cells
of the brain and medulla, what has been mentioned
of the ganglion cells of the cord holds good as to
them. Like the former, those of the medulla and

152 ELEMENTS OF HISTOLOGY. [Chap. xvm.

brain are situated in lymph spaces or the pericellular
spaces (Obersteiner).

199. We now follow the above description of
the structure of the medulla with that of the cere-
bellum and pons Varolii.

I. The cerebellum is composed of laminae,
folds, or convolutions, composed of secondary folds,
each of which consists of a central tract of white
matter covered with grey matter. The tracts of white
matter of neighbouring convolutions of one lobe or
division join, and thus form the principal tracts of
white matter.

The white matter of the cerebellar hemisphere is
connected (a) with the medulla oblongata by the
corpus restiforme, this forming the inferior peduncle
of the cerebellum ; (6) with the cerebrum by the
pedunculus cerebelli ad cerebrum, this forming the
superior pedunculus ; and (c) with the other cerebellar
hemisphere by the commissure passing through the
pons Varolii ; this is the pedunculus cerebelli ad
pontem, or the middle pedunculus.

200. On a vertical section, through a lamina of the
cerebellum (Fig. 90), the following layers are seen : (a)
the pia mater covering the general surface, and pene-
trating with the larger blood-vessels into the peripheral
substance of the lamina ; (6) a thick layer of cortical
grey matter ; (c) the layer of Purkinje's ganglion
cells ; (d) the nuclear layer, and (e) the central white
matter.

201. The layer of ganglion cells of Purkinje is the
most interesting layer ; it consists of a single row of
large multipolar ganglion cells, each with a large
vesicular nucleus. Each possesses also a thin axis
cylinder process, directed towards the depth, the
cell sending out in the opposite direction — i.e., towards
the surface — a thick process which soon branches
like the antlers of a deer, the processes being all very

Fig. 90.— From a Vertical Section through the Grey Matter of the

Cerebellum of the Dog.

pm, Pia mater ; p, the ganglion cells of Purkinjc ; g, the nuclear layer ; /, the
layer of nerve-fibres (white matter). (Atlas.)

154 ELEMENTS OF HISTOLOGY. [Chap. xvm.

long-branched and pursuing a vertical course towards
the surface ; sooner or later they all break up into the
fine nerve-ground network of the grey cortex. The
longest processes reach near to the surface. The
layer (b) above mentioned — i.e., the cortical grey
matter — is in reality the terminal nerve network for
the branched processes of the ganglion cells of
Purkinje. Sankey maintains that in the human cere-
bellum there are also other smaller multipolar gang-
lion cells connected with the processes of the cells of
Purkinje.

202. The nuclear layer contains a large number of
spherical or slightly oval relatively small nuclei em-
bedded in a network of fine fibrils, the nature of
which is not definitely ascertained — i.e., whether it
consists of neuroglia only, or whether it contains,
in addition, also a network of nerve fibrils. The latter
is exceedingly probable. The nuclei are nuclei of
neuroglia cells, of lymph corpuscles and of small gang-
lion cells.

The axis cylinder process of the ganglion cell of
Purkinje passes through the nuclear layer, and be-
coming invested with a medullary sheath, enters as
a medullated nerve-fibre the central white matter.
There are, however, medullated nerve- fibres of the
central white matter, which are not connected with an
axis cylinder process of a Purkinje's cell, but enter
the nuclear layer and probably terminate there in the
nerve network, or pass through it and terminate in the
nerve network of the grey matter of the cortex.

203. II. The pons Varolii (Fig. 91) is a pro-
longation partly of the medulla and partly of the
cerebellum. Of the latter only white matter passes
transversely into the anterior portion of the pons,
and forms there the transverse bundles of nerve-fibres,
which give to the pons the horizontal striation.

As we pass upwards — i.e., farther away from the

Chap, xvi 1 1 .] CEREBR UM A ND CEREBELLUM.

155

medulla, this part of the pons — i.e., that composed of
horizontal fibres — increases in thickness.

204. Of the medulla there is a greater portion

Fig. 91.— Transverse Section through the Lower Corpus Quadrigeminum
and the Pons Varolii.

a, AqscductuB sylvii ; 5. crossing of the brachia of the lower corp. Quadrip.: q,
ganglion of toe lower corp. quadri p.; i ,pedunculus of the lower corp. quadrlg.;
ba, tegmentura : 5, the descending root of the fifth ; p. bundles of tho
anterior pyramidal tracts in cross section ; trp, deep transverse bundles
of the pons; trs, superficial transverse bundles of the pons. (Mcynert. in
Strieker's Manual.)

continued into the pons than of the cerebellum.
(1) There are the pyramidal tracts ; they do not lie on
the surface as in the medulla, but are hidden by some

156 ELEMENTS OF HISTOLOGY. [Chap. xvm.

— the most anterior bundles — of the transverse fibres.
The bundles of the pyramidal tract pass as longitudinal
fibres merely through the anterior half of the pons,
and enter the crura cerebri where they form the
crusta. (2) The raphe. (3) The reticular formation ;
but this is limited to the posterior part. Small masses
of grey matter arid ganglion cells are scattered every-
where between the transverse bundles of the nerve-
fibres of this formation. (4) The grey matter at the
floor of the fourth ventricle. This grey matter con-
tains also on the posterior surface of the pons groups
of multipolar ganglion cells.

Near the middle line there is a group of large
multipolar ganglion cells, each with an axis cylinder
process. This is the nucleus for the sixth nerve, and
of part of the seventh, the former lying more median
than the latter. There is another nucleus of the
seventh situated more deeply — i.e., in the reticular
formation. More outwards we meet with the superior
nucleus of one of the roots of the auditory nerve,
Farther upwards we meet with the nucleus of the
motor roots of the fifth.

(5) In the lower part of the pons there exists also
a continuation of the grey matter of the corpus den-
tatum of the olivary body.

205. The pons is connected with the cerebrum by
the crusta of the crus cerebri, which, as mentioned
above, are bundles of medullated nerve-fibres passing
merely through the pons but being continuations of
the anterior pyramidal tracts of the medulla.

206. III. The hemispheres of the cere-
brum.— On a vertical section each convolution shows
a white centre and a grey cortex. The former is com-
posed of medullated nerve-fibres. The white matter
of the convolutions of the cerebral hemispheres is ar-
ranged as (a) the centrum ovale — i.e., the central mass
of white matter from which the lamina of white matter

chap, xviii.] CEREBRUM AND CEREBELLUM.

'57

for each convolution
branches off, and, (6),
the commissure of white
matter between the two
hemispheres, i.e., the
corpus callosum and
anterior commissure.
The centrum ovale again
consists of tracts of
medullated nerve-fibre,
which connect (a) the
convolutions of the same
hemisphere with one
another, and (b) such as
pass between the con-
volutions on the one
hand, and the thalamus
opticus, the pons, and
medulla on the other.
These tracts pass by the
internal capsule (see
below) to the thalamus
opticus, and to the crus
cerebri.

The grey cortex con-
sists, according to Mey-
nert, of the following
layers (Fig. 92) :— (1) a
superficial layer of grey

Fig. 92. — Vertical Section
through the Grey Matter of a
Cerebral Convolution.

a, Superficial layer; 6, closely-
packed small ganglion cells ; c, the
layer of the cornu Ammonia, this
being the principal layer; d, the
" granular formation," small
niultipolar ganglion cells; «, the
layer of spindle-shaped ganglion
cells. (Meynert, in Strieker's
Manual.)

158

ELEMENTS OF HISTOLOGY. [Chap. XVIIL

matter (neuroglia and nerve ground network), with
few and small ganglion cells.
(2) A layer of small more or
less pyramidal ganglion cells
densely aggregated. (3) The
formation of the cornu Am-
monis. This is the principal
or broadest stratum of the
cortex ; it is composed of
several layers of large, pyra-
midal ganglion cells, increas-
ing in size as a deeper layer
is reached.

The pyramidal cells of
this third and of the previous
second stratum consist of a
pyramidal body including an
oval vesicular nucleus (Fig.
93). From the body pass out
the following principal pro-
cesses : — (a) the process of the

apex,

directed towards the

Fig. 93.— A large Pyramidal Ganglion
Cell of the Grey Cortex of the Human
Cerebrum.

The process of theapex and the other processes
branch and break up into the fine nerve net-
work. The median process of the base of the
pyramid remains unbranohcd, and becomes
an axis cylinder of a nerve-fibre. (Atlas.)

surface of the convolution ;
it can be traced for
a longer or shorter
distance. (6) The
lateral basilar pro-
cesses, and finally
the median basilar
process. This latter
is fine, remains un-
branched, and is an
axis cylinder process,
i.e., becoming in-
vested with a medul-
lary sheath is a nerve-
fibre of the central

Chap, xviii.] CEREBRUM ANL CEREBELLUM. 159

white matter. The other processes, sooner or later in
their course, branch and break up finally into tte
nerve ground network of the grey matter. (4) A thin
stratum of small irregular branched ganglion cells, the
granular formation of Meynert. (5) A last stratum
of spindle-shaped and branched ganglion cells, ex-
tending parallel to the surface.

207. According to Meynert, the grey cortex of the
posterior portion of the occipital lobe about the sulcus
hippocampi consists of eight layers, the granular for-
mation being the principal one. In the grey cortex of
the cornu Ammonis, on the other hand, the third
layer is the principal layer, the fourth being wanting.
In the claustrum (part of the wall of the fossa Sylvii),
the spindle-shaped cells of the fourth layer form the
principal stratum.

208. The tmlbus olfactorius contains in most
mammals, but not in man, a small central cavity
lined with columnar ciliated epithelial cells. The sub-
stance of the bulb around this cavity consists of an
upper part, which is white matter, and is a continua-
tion of the tractus olfactorius. The lower part is
grey matter, and contains the following layers, count-
ing from below upwards : (1) a layer of non-medul-
lated nerve-fibres, each with a neurileinma ; this layer
forms farther on the olfactory nerve going to the
olfactory organ ; (2) the stratum glomerulosum, com-
posed of a number of glomeruli or convolutions,
each of which consists of an olfactory nerve-fibre, and
in addition to it numerous small neuroglia cells ; (3)
stratum gelatinosum of Lockhart Clarke, composed
of a fine nerve network, and embedded in it multi-
polar ganglion cells ; (4) a last and thickest layer of
nuclei embedded in a network of fibrils, and similar in
structure with the " nuclear layer."

209. IV. The mesenceplmlon.— The fourth
ventricle above the upper part of the pons Varolii

160 ELEMENTS OF HISTOLOGY. [cup. xvm.

closes again into a small canal — the aqueductus
Sylvii — which having passed in front out of the region
of the corpora quadrigemina opens out again as the
third ventricle. The parts around the aqueductus
Sylvii represent the mesencephalon (Fig. 91), developed
from the middlfe brain vesicle in the embryo. They
include the wall of the aqueductus Sylvii, the corpora
quadrigemina, and the crura cerebri.

The aqueductus Sylvii is lined with epithelium
and a layer of neuroglia continued from the fourth
ventricle. The raphe of the medulla and of the pons
are continued into the lower wall of the aqueductus.
The lining layer of neuroglia is on its frontal aspect
surrounded by a layer of grey substance continued
from the grey substance of the floor of the fourth
ventricle. It contains in a nerve network numerous
multipolar ganglion cells grouped into nerve nuclei,
connected with the third, fourth, and part of the fifth
pair of nerves. In front of this layer is one of con-
siderable thickness representing the tegmentum, which
is the dorsal or posterior portion of the crus cerebri.

210. The corpora quadrigemina. — Each of
the two inferior prominences consists of a superficial
layer of white matter, and a deep grey portion, con-
taining multipolar ganglion cells of various sizes
embedded in a fine nerve network. Between this and
the grey substance of the wall of the aqueductus Sylvii
are tracts of white matter, forming part of thejillet.
In each of the two superior prominences there is also
a superficial layer of white matter, beneath which
is a layer of grey matter (stratum cinereum) ; under-
neath this is the main portion — the stratum opticum —
consisting of longitudinal tracts of nerve-fibres, be-
tween which are small masses of grey substance.
Between this stratum opticum and the grey matter
forming the wall of the aqueductus Sylvii is a layer
of white matter, part of the fillet.

Chap, xviii.] CEREBRUM AND CEREBELLUM. 161

211. The cms cerefori of each side consists of an
anterior, middle, and posterior portion. The anterior
or ventral portion is the crusta, or pes , the
posterior or dorsal portion is the tegmentum. Be-
tween the two is the substaiitia nigra. The crusta is
composed of longitudinal tracts of medullated nerve-
fibres passing from the margin of the pons Varolii
to the internal capsule of the thalamencephalon, and
farther into the white matter of the hemisphere.

212. The tcgmcntum has been mentioned above
as being situated in front of the grey matter forming
the anterior wall of the aqueductus Sylvii. The
tegmentum is a prolongation of the reticular formation
of the pons Yarolii and medulla (see above), i.e., small
masses of grey substance separated by tracts of nerve-
fibres, most of which run in a longitudinal or transverse
direction. The longitudinal bundles include a con-
tinuation of the white matter of the cerebellum,
mentioned in a previous page as the superior
peduncle of the cerebellum, or the pedunculus cere-
belli ad cerebrum. These undergo total decussation in
the upper part of the mesencephalon, and ultimately
enter the thalamus opticus.

213. The substaiitia nigra is grey matter
situated between the two above ; it has received its
name from the numerous dark pigment granules
lodged in the substance of its ganglion cells. These
are small and multipolar.

214. V. The ttialamencephalon and corpus
striatum. — The former comprises the parts of the
brain situated round the third ventricle, the most im-
portant being the thalamus opticus, the pineal gland,
the corpora albicautia, the infundibulum and tuber
cinereum, and the hypophysis cerebri. The corpus
striatum is the ganglion of the cerebral hemisphere,
with which it originates from the same part — i.e., the
frontal part of the first cerebral vesicle of the embryo.

L

1 62 ELEMENTS OF HISTOLOGY. [Chap. xvm.

215. The tlialaimis options consists of a super-
ficial layer of white, and a centre of grey matter.
In this numerous multipolar ganglion cells are noticed.
The white matter in the outer portion is very con-
siderable, and of great importance from its connec-
tions. From it radiate tracts of medullated nerve-
fibres, which join the tracts of the internal capsule on
their way to and from the different parts of the
cerebral hemisphere.

The superior pedunculus cerebelli, after its
decussation with that of the opposite side, passes
into the white matter of the thalamus. The trac-
tus opticus is connected with the outer white matter
of the posterior portion of the thalamus — i.e., the
pulvinar.

216. The corpus stria t mil, as stated before,
is considered as the ganglion of the cerebral hemi-
sphere. It consists of the nucleus caudatus and the
nucleus lenticular is. The former projects into the
lateral ventricle, the latter is the outer portion of
the corpus striatum. The nucleus lenticularis is
separated from the nucleus caudatus and from the
anterior portion of the thalamus opticus by tracts of
medullated nerve-fibres, known as the internal capsule.
On the outer surface of the nucleus lenticularis is a
thin lamina of white matter which is the external
capsule. This is separated from the white matter
of the cerebral convolutions at this part — i.e., the
island of Eeil — by a thin lamina of grey matter, called
the claustrum. The nucleus caudatus and lenti-
cularis consist of grey matter with larger and smaller
groups of multipolar ganglion cells, permeated by
tracts of medullated nerve-fibres, which originate in
the grey matter. These tracts of white matter pass
transversely and obliquely into the internal capsule,
and. are to be traced on the one hand to the white
matter of the convolutions of the cerebral hemisphere,

Chap, xix.] THE CEREBRO-SPINAL GANGLIA. 163

which is, however, doubted by many observers, and
on the other into the crusta of the cms cerebri.

217. The internal capsule is one of the most
important masses of white matter ; it contains the
tracts of medullated nerve-fibres which pass between
the white matter of the cerebral hemisphere and the
crus cerebri — i.e., the corona radiata of Reil ; further,
it contains tracts of medullated nerve-fibres passing
between the thalamus opticus and the white matter
of the cerebral hemispheres ; and, finally, it contains
tracts of nerve-fibres passing between the corpus
sfcriatum and the crus cerebri.

218. The pineal fland, or conarium, and the
anterior lobe of the hypophisis cerebri, are epithelial
in structure and origin, and will be described in a
future chapter. The pineal gland contains a large
amount of calcareous matter — brainsand.

The corpora albicantia are masses of white
matter — i.e., medullated nerve-fibres; each corpus
albicans includes a centre of grey substance.

The infundibulum and tuber cinereum at the floor
of the third ventricle are composed of grey matter ;
the latter extends between the corpora albicantia
to the optic commissure, while the former is connected
with the posterior or minor lobe of the hypophisis.

CHAPTER XIX.

THE CEREBRO-SPINAL GANGLIA.

219. THE ganglia connected with the posterior
roots of the spinal nerves, and with some of the
roots of the cerebral nerves — e.g., Gasserian, otic,
geniculate, ciliary, Meckel's ganglion, the ganglia of

164

ELEMENTS OF HISTOLOGY. [Chap. xix.

the branches of the acoustic nerve, the sub maxillary
ganglion, &c. — possess a capsule of fibrous connective
tissue continuous with the epineurium of the afferent
and efferent nerve trunks. The interior of the ganglion
is subdivided into smaller or larger divisions, contain-
ing nerve bundles with their perineurium, or larger
and smaller groups of ganglion
cells. In the spinal ganglia
these latter are generally dis-
posed about the cortical part,
whereas the centre of the
ganglia is chiefly occupied by
bundles of nerve-fibres.

220. The ganglion cells differ
very greatly in size, some being
as big, and bigger, than a large
multipolar ganglion cell of the
anterior horn of the cord, others
much smaller. Each cell has
a large oval nucleus, including
a network, with one or two
large nucleoli. Its substance
shows a distinct fibrillation.
Each cell of the ganglia in man
and mammals is unipolar (Fig.
94), flask or pear-shaped, and
invested in a hyaline capsule,
lined with a more or less con-
tinuous layer of nucleated endo-
thelial cell-plates. The single
process of the ganglion cell is
finely and longitudinally stri-
ated, and is an axis cylinder
process. Immediately after
leaving the cell body it is much
convoluted (Retzius) ; then it gets invested in a
medullary sheath — i.e., it becomes a medullatod nerve-

94.— A large and small
Ganglion Cell of the Gang-
lion Gassed of the Rabbit.

The axis cylinder, alter leaving
the cell, becomes convoluted
and transformed into a medul-
lated nerve-fibre, which divides
into two medullated fibres.
(Key and Eetzius.)

Chap, xix.] THE CEREBRO-SPINAL GANGLIA. 165

fibre. The capsule of the ganglion cell is continued
011 the axis cylinder process, and, farther on, on the
medullated nerve-fibre, as the neurilemma ; while the
endothelial plates of the capsule pass into the nerve
corpuscles lining the neurilemma, their
number greatly diminishing (Fig. 95).

221. In the rabbit this medullated
nerve-fibre at its first node of Ranvier,
which is not at a great distance from
the ganglion cell, divides into two me-
dullated nerve-fibres in the shape of a
T ; one branch is supposed by Ranvier
to pass to the cord, the other to the
periphery. In man, this T-shaped
division has also been observed by
Retzius, but it cannot be said with
certainty that in rabbit or man
every axis cylinder process shows this
T-shaped division. Retzius observed
this T-shaped division also in the
Gasserian, geiiiculate, and vagus gan-
glia in man.

The ganglion cells are not unipolar
in all cerebral ganglia ; in the ciliary
and otic ganglia there are a good many
ganglion cells which are multipolar.

222. Numerous ganglia of micro-
scopic sizes are to be found in the
sub-maxillary (salivary) gland ; they
are of different sizes, and are in
reality ganglionic enlargements of
larger or smaller nerve-bundles. Each
ganglion is invested in connective
tissue continuous with the perineu-

rium, and the ganglion cells are unipolar, and of the
same nature as those described above, each being
possessed of an axis cylinder process, which becomes

Pip. 95.-An iso-
lated Ganglion
Cell of a Spinal
Ganglion of
Toad.

The axis cylinder
process becomes
triinsfurined into a
medullated nerve-
fibre. The capsule
of the cell is pro-
longed as the neu-
rilemma of the
nerve-fibre. (Key
and Retzius. )

i66

ELEMENTS OF HISTOLOGY. [chap. xx.

soon connected with a nerve-fibre. At the back
of the tongue there are similar small microscopic
ganglia.

CHAPTER XX.

THE SYMPATHETIC SYSTEM.

223. THE sympathetic nerve-branches are of exactly
the same nature in their connective tissue investments
(epi- peri- and endo-neurium), and in the arrangement

—Sympathetic Nerves.

A, A small bundle invested in an endothelial sheath perineuriuni ; B, one
medullated and three non-medullated nerve-flbres of various sizes; the
largest shows division ; c, two varicose nerve-fibres. (Atlas.)

of the fibres in bundles (Fig. 96, A), as the cerebro-
spinal nerves. Most of the nerve-fibres in the bundles
are noii-medullated or Remak's fibres (Fig. 96, B), each

chap, xx.] THE SYMPATHETIC SYSTEM. 167

being an axis cylinder invested in a neurilerama, with
oblong nuclei indicative of nerve corpuscles. But there
are some medullated nerve-fibres to be met with in

Fig. 97. — A croup of Ganglion Cells interposed in a bundle of Sympa-
thetic Nerve-fibres ; from the Bladder of a Eabbit. (Handbook.)

each bundle, at least, of the larger nerve-trunks.
These in some cases show the medullary sheath more
or less discontinuous, and with a varicose outline

Fig. 98.— A small collection of Ganglion Cells along a smnll Bundle of
Sympathetic Nerve-fibres in the Bladder of the Eabbit.

Each ganglion cell possesses a capsule. The substanre of the ganglion cell is
prolonged as the axis cylinder of a nerve-fibre. (Atlas.)

(Fig. 96, c), owing to a uniform local accumulation of
fluid between it and the axis cylinder. The small or
microscopic bundles of nerve-fibres have an endothelial

i68

ELEMENTS OF HISTOLOGY. [Chap. xx.

(perineural) sheath. The small and large branches
form always rich plexuses.

224. In connection with the macroscopic and
microscopic sympathetic nerve-branches, are gang-
1 ionic enlargements. They occur in some organs very
numerously — e.g., alimentary canal, urinary bladder

(Fig. 97 and Fig.
98), respiratory or-
gans— and are of
all sizes, from a
few ganglion cells
placed between, or
laterally to, the
nerve-fibres of a
small bundle, to
huge oval, spheri-
cal, or irregularly-
shaped masses of
ganglion cells placed
in the course of a
large nerve-bundle,
or situated at the
point of anastomo-
sis of two or more
nerve-branches.

The ganglion
cells (Fig. 99) are
of very different
sizes, each possess-
ing a large oval or
spherical nucleus
with one or two
nucleoli. Their
shape is spherical
or oval, flask-
shaped, club-shaped, or pear-shaped ; they possess
either one, two, or more processes, being uni-, bi-,

Fig. 99. — Sympathetic Ganglion Cell of Man.

The ganglion cell is raultipolar ; each process re-
ceiving a neurilemma from the capsule of the
cell becomes a non-inedullated nerve-fibre.

chap. xx.] THE SYMPATHETIC SYSTEM.

169

or multi-polar. The cell is invested in a capsule lined
with nucleated cells, both being continued on the pro-
cesses as neurilemma and nerve corpuscles respectively.
The processes of the ganglion cells are all axis
cylinder processes, and invested in the neurilemma,
thus representing non-medul-
lated nerve-fibres. They do not
become as a rule medullated.

225. In the frog (Beale,
Arnold) and also in some few
instances in the mammal, the
sympathetic ganglion cell gives
off one straight axis cylinder
process, into which the sub-
stance of the ganglion cell is
prolonged. This is entwined
by a thin spiral fibre (Fig. 100),
taking its origin by two or
more rootlets from the ganglion
cell substance, and circling
round the (thicker) straight
axis cylinder process. A single
neurilemma ensheathes them
both. Soon the spiral fibre
leaves the axis cylinder process,
becoming invested with a
medullary sheath and its own
neurilemma, thus forming a
medullated fibre, whereas the
straight axis cylinder continues
its course as a non-medullated
nerve-fibre (Key and Retzius).

226. The ganglia in connec-
tion with the plexuses of nerve
branches of the heart, the

ganglia in the plexus of non-medullated nerve-fibres
existing between the longitudinal and circular coat

100.— A Sympathetic
Ganglion Cell of the Frog,
showing the straight pro-
cess and the spiral fibre ;
the latter becomes a me-
dullated fibre. (Key and
Eetzius.)

1 70 ELEMENTS OF HISTOLOGY. [chap. xx.

of the external muscular coat in the alimentary canal,
known as the plexus myentericus of Auerbach, the
ganglia in the plexus of nerve branches of the sub-

-a

r

Fig. 101. — Plexus of fine Sympathetic Nerve-fibres, with Ganglionic
Enlargements in the Nodal Points. From the Plexus of Meissner
in the Submucous Tissue of the Intestine.

a, Fine nerve-fibres ; b, groups of ganglion cells interposed between the
nerve-fibres.

mucous tissue in the alimentary canal, and known as
Meissner's plexus (Fig. 101), the ganglia in the plexuses
of nerve branches in the outer wall of the bladder, in
the bronchial wall, in the trachea, the ganglia in con-
nection with the nerves supplying the ciliary muscle
of the eye, <fcc., belong to the sympathetic system.

Chap. XXI.]

171

CHAPTER XXI.

TEETH.

227. A HUMAN tooth, adult and milk-tooth, consists
(Fig. 102)-of (a) the enamel covering the crown, (6) the
dentine forming the real

matrix of the whole
tooth, and surrounding
the pulp cavity both of
the crown and fangs,
and (c) the cement, or
crusta petrosa, or sub-
stantia osteoidea. This
cement covers the outside
of the dentine of the
fang or fangs, in the
same way as the enamel
covers the dentine of the
crown. The crusta pe-
trosa is covered on its
outside by a dense fibrous
tissue acting as a perios-
teum to it, and is fixed
by it to the inner surface
of the bone forming the
wall of the alveolar
cavity.

228. The enamel
(Fig. 103) consists of

thin microscopic pris- Fig. m-Longitudiuai Section

matic elements, the through the Preemolar Tooth of

enamel prisms placed Jfa'niel: 6> dentine crustfi
closely, and extending in

172 ELEMENTS OF HISTOLOGY. [Chap. xxi.

a vertical direction from the surface to the dentine.
When viewed in transverse section, the enamel prisms
appear of an hexagonal outline, and separated by a very
fine interstitial cement substance. The outline of the
enamel prisms is not straight, but wavy, so that the
prisms appear varicose. The prisms are aggregated
into bundles, which are not quite parallel, but more
or less slightly cover one another. On a longitudinal
section through a tooth, the appearance of alternate

Pig. 103.— Enamel Prisms.
A, In longitudinal view ; B, in cross section. (Kollikor.)

light and dark stripes in the enamel is thus produced.
Besides this there are seen in the enamel dark hori-
zontal curved lines, the brown parallel stripes of
Retzius, probably due to inequalities in the density of
the enamel prisms produced by the successive forma-
tion of layers of the enamel. The enamel consists
chiefly of lime-salts : phosphate, carbonate, and fluorate
of calcium.

In young teeth the free surface of the enamel
is covered with a delicate cuticle (the cuticle of
Nasniyth), being a single layer of non-nucleated
scales. In adult teeth this cuticle is wanting, hav-
ing been rubbed off.

229. The dentine is the essential part of the hard

Chap. XXI.]

TEETH.

substances of the tooth. It forms a complete invest-
ment of the pulp cavity of the crown and fang, being
slightly thicker in the

former than in the latter U=^^^=^ — —

region. The dentine is El^^SS^

composed of (Fig. 104) :

(1) a homogeneous ma-
trix; this is a reticular
tissue of fine fibrils im-
pregnated with lime-
salts, and thus resem-
bles the matrix of bone ;

(2) long fine canals, the
dentinal canals or tubes
passing in a more or less
spiral manner, and ver-
tically from the inner
to the outer surface of
the dentine. These tubes
are branched; they open
in the pulp cavity with
their broadest part, and
become finer as they
approach the outer sur-
face of the dentine.
Each canal is lined with
a delicate sheath — the
dentinal sheath. Inside
the tube is a fibre, the
dentinal fibre, a solid
elastic fibre originating
with its thickest part
at the pulp side of the
dentine from cells lining

the outer surface of the pulp, and called odontoblasts.

On the outer surface of the dentine, both in the

region of the enamel and crusta petrosa, the dentinal

Fig. 104.— From a Section through
a Canine Tooth of Man.

a, Crusta petrosa, with large bone cor-
puscles ; b, interglobular substance;
c, dentinal tubules. (Waldeyer, in
Strieker's Manual.)

174 ELEMENTS OF HISTOLOGY. [Chap. xxi.

tubes pass into a layer of intercommunicating irregular
branched spaces, the interglobular spaces of Czerniak,
or the granular layer of Purkinje. These communicate
with spaces existing between the bundles of enamel
prisms of the crown, as well as with the bone laminae
of the crusta petrosa of the fang. The interglobular
spaces contain each a branched nucleated cell. The
dentinal fibres anastomose with the processes of these
cells. The incremental lines of Salter are lines more
or less parallel to the surface, owing to imperfectly cal-
cined dentine — the interglobular substance of Czermak.
The lines of Schreger are curved lines parallel to the
surface, and due to the optical effect of simultaneous
curvatures of dentinal fibres.

230. The cement is osseous substance, being
lamellated bone matrix with bone corpuscles. These
latter are larger than in ordinary bone.

231. The pulp is richly supplied with blood-vessels,
forming networks, and extending chiefly in a direction
parallel to the long axis of the tooth. Numerous
medullated nerve-fibres forming plexuses are met
with in the pulp tissue ; on the outer surface of the
pulp they become non-medullated fibres, and probably
ascend in the dentinal tubes. The matrix of the
pulp is formed by a transparent network of richly
branched cells, similar to the network of cells forming
the matrix of gelatinous connective tissue.

232. On the outer surface of the pulp — i.e., the
one in contact with the inner surface of the dentine —
is a layer of nucleated cells, which are elongated,
more or less columnar. These are the odontoblasts
proper. Between them are wedged in more or less
spindle-shaped nucleated cells, the outer or distal pro-
cess of which passes into a dentinal fibre. The odonto-
blasts proper are concerned in the production of the
dentinal matrix, according to some by a continuous
growth of the distal or outer part of the cell and

Chap, xx i.] TEETH. 175

a petrification of this increment, according to others
by a secretion by the cell of the dentinal matrix.
Waldeyer, Tomes, and others, consider the odontoblasts
proper concerned in the production both of the dentinal
matrix and dentinal fibres. The odontoblasts proper
and the spindle-shaped cells are continuous with the
branched cells of the pulp matrix.

2 3 3. Development of teeth. — The first rudi-
ment of a tooth in the embryo appears as early as the
second month. It is a solid cylindrical prolongation of
the stratified epithelium of the surface into the depth
of the embryonal mucous membrane. Along the
border of the jaws the epithelium appears thickened,
and the subjacent mucous membrane forms there a
depression — the primitive dental groove. Into this
groove the solid cylindrical prolongation of the surface
epithelium takes place. This prolongation represents
the rudiment of the enamel organ. While con-
tinuing to grow in the depth, it soon broadens at its
deepest part, and the surrounding vascular mucous
membrane condenses at the bottom of the prolongation
as the rudiment of the tooth papilla. While the distal
part of the enamel organ continues to grow towards the
depth, it gradually embraces the tooth papilla in the
shape of a cap — the enamel cap. During this time the
connection between the surface epithelium and the
enamel cap becomes greatly thinned out and pushed
to one side, owing to the growth of the enamel cap and
papilla taking place chiefly to one side of the original
dental groove.

234. The enamel cap (Fig. 105) is composed of
three strata — an inner, middle, and outer stratum.
The inner stratum is the layer of the enamel cells ; it
is a layer of beautiful columnar epithelial cells ; they
were originally continuous with the deep layer or the
columnar cells of the surface epithelium. The middle
stratum is the thickest and is of great transparency,

176 ELEMENTS OF HISTOLOGY. [chap. xxi.

owing to a transformation of the middle layer of the
epithelial cells into a spongy gelatinous tissue, due to
accumulation of fluid between the epithelial cells
of this layer, and to a reduction of its substance
to thin nucleated plates, apparently branched. The

Fig. 105.— From a Section through the Tooth and Lower Jaw
of Fo3tal Batten.

a, Epithelium of the free surface of the gum.: 6, the mucous membrane of same ;
c, spongy bone of jaw; d, papilla of tooth; e, odontoblasts ; /, dentine: g,
enamel ; h, membrane of Nasmyth ; i, enamel cells ; j, middle layer of enamel
organ ; k, outer layer of enamel organ.

outer stratum consists of one or more layers of
polyhedral cells, continuous with the deep layers of
cells of the epithelium of the surface of the gum.
Outside the enamel cap is the gelatinous vascular
tissue of the mucous membrane of the gum.

235. The foetal tooth papilla is a vascular embryo-
nal or gelatinous tissue ; on its outer surface a con-

chap, xxi.] TEETH. 177

densation of its cells is soon noticeable into a more or
less continuous stratum of elongated or columnar cells,
the odontoblasts.

236. The dentine is formed in connection with
the odontoblasts (Fig. 105); on its outside appears the
enamel formed by the enamel cells, i.e., the inner
layer of the enamel organ. The dentine and enamel
are deposited gradually, and in layers. At first they
are soft tissues, showing a vertical differentiation
corresponding to the individual cells of the enamel
cells and odontoblasts respectively. Soon lime salts
are deposited in it, at first imperfectly, but afterwards
a perfect petrifaction takes place. The layer of most
recently formed enamel and dentine is more or less
distinctly marked off from the more advanced layer,
the most recently formed layer of the enamel being
situated next to the enamel cells, that of the dentine
next to the odontoblasts.

The milk tooth remains buried in the mucous
membrane of the gum. When it breaks through, the
enamel remains covered with — i.e., carries with it —
the inner stratum of the enamel organ only, i.e., the
enamel cells (Fig. 105, h) \ these at the same time as
the surface of the enamel increases become much
flattened, and, finally losing their nuclei, are con-
verted into a layer of transparent scales, the membrane
or cuticle of Nasmyth.

237. Long before the milk tooth breaks through
the gum, there appears a solid cylindrical mass of
epithelial cells extending into the depth from the
connection between the enamel organ and the epithe-
lium of the surface of the gum mentioned above.
This epithelial outgrowth represents the germ for
the enamel organ of the permanent tooth ; but it
remains stationary in its growth till the time arrives
for the milk tooth to be supplanted by a permanent
tooth. Then that rudiment undergoes exactly the

i78

ELEMENTS OF HISTOLOGY, [chap. xxn.

same changes of growth as the enamel organ of the
milk tooth did in the first period of foetal life. A
new tooth is thus formed in the depth of the alveolar
cavity of a milk tooth, and the growth of the former
in size and towards the surface gradually lifts the
latter out of its socket.

CHAPTER XXII.

THE SALIVARY GLANDS.

238. THE salivary glands, according to their

structure and secretion, are of the following kinds : —

(1) True salivary (Fig. 106), serous, or albuminous

Fig. 106.— From a Section through a Serous or True Salivary Gland ;
part of the Human Sub-maxillary.

a, The gland alveoli, lined with the albuminous " salivary cells ; " 6, intralobular
duct cut transversely. (Atlas.)

chap, xxii.] THE SALIVARY GLANDS.

179

glands, such as the parotid of man and mammals,
the sub-maxillary and orbital of rabbit, the sub-
maxillary of the guinea-pig. They secrete true, thin,
watery saliva.

(2) Mucous glands, such as the sub-maxillary and
orbital of cat and dog (Fig. 107), the sub-lingual

Fig. 107. — From a Section through the Orbital (mucous) Gland
of Dog. Quiescent state.

The alveoli are lined with transparent " raucous cells," and outside
these are the demilunes of Heidenhain. (Heidenhain.)

of cat, dog, rabbit, and guinea-pig. They secrete
thickish, less watery mucus.

(3) Mixed salivary, or muco -salivary glands, such as
the sub-maxillary and sub-lingual of man and ape.

In addition to the three salivary glands — parotid,
sub-maxillary, and sub-lingual — there are in some
cases, as in the rabbit and the guinea-pig, two minute
additional glands, one intimately annexed to the
parotid and the other to the sub-maxillary, and of the
nature of a mucous gland. These are the superior and
inferior admaxillary glands.

180 ELEMENTS OF HISTOLOGY. [Chap. xxn.

239. The framework.— Each salivary gland
is enveloped in a fibrous connective tissue capsule,
in connection with which are fibrous trabeculse and
septa in the interior of the gland, by which the sub-
stance of the latter is subdivided into lobes, these
again into lobules, and these finally into the alveoli
or acini The duct, large vessels and nerves pass
to and from the gland by the hilum. The con-
nective tissue is of loose texture, contains elastic
fibres, and, in some instances more, in others less,
numerous lymphoid cells. In the sub-lingual gland
they are so numerous that they form continuous rows
between the alveoli. The connective tissue matrix
between the alveoli is chiefly represented by fine
bundles of fibrous tissue, and branched connective
tissue corpuscles.

240. The ducts. — Following the chief duct of
the gland through the hilum into the interior, we see
that it divides into several great branches, according
to the number of lobes; each of these breaks off
into several branches, one for each lobule. Entering
the lobule the duct has become very minute, and
passing along it gives off" laterally several minute ducts,
all within the lobule being the intralobular ducts,
or the salivary tubes of Pfliiger, the bigger ducts
being the interlobular, and, further, the interlobar
ducts. Each of the latter consists of a limiting
membrana propria, strengthened, according to the
size of the duct, by thicker or thinner trabeculse of
connective tissue. In the chief branches there is pre-
sent in addition non-striped muscular tissue. The
interior of the duct is a cavity lined with a layer of
columnar epithelial cells. In the largest branches there
is, outside this layer and inside the membrana propria,
a layer of small polyhedral cells.

241. The intralobular ducts, or the salivary
tubes of Pfliiger, consist of a limiting membrana

Chap, xxii.] THE SALIVARY GLANDS. 181

propria, with a single layer of columnar epithelial cells.
Each of these has a spherical nucleus in about the
middle ; the outer half of the cell substance shows very
marked longitudinal striation, due to more or less coarse
fibrillae (see Fig. 106). The inner half, i.e., the one
bordering the lumen of the duct, is only very faintly
striated. The outline of these salivary tubes is never
smooth, but irregular, hence the diameter of the tube
varies from place to place.

Not in all salivary glands do the epithelial cells
of the intralobular ducts show this coarse fibrillation
in the outer part of their substance; e.g., it is not
present in the sub-lingual gland of the dog and guinea-

Pig-

242. The ends of the branches of the salivary
tubes are connected with the secreting parts of the
lobule, i.e., the acini or alveoli. These always very
conspicuously differ in structure from the salivary
tubes, and, as a rule, are larger in diameter. That
part of the duct which is in immediate connection with
the alveoli is the intermediary part, this being inter-
posed, as it were, between the alveoli and the salivary
tube with fibrillated epithelium. The intermediary part
is much narrower than the salivary tube, and is lined
with a single layer of very flattened epithelial cells,
each with a single oval nucleus ; the boundary is
formed by the membrana propria, continued from the
salivary tube. The lumen of the intermediary part is
much smaller than that of the salivary tube, and is
generally lined with a fine hyaline membrane, with
here and there an oblong nucleus in it.

At the point of transition of the salivary tube
into the intermediary part there is generally a sudden
diminution in size of the former, and the columnar
cells of the salivary tube are replaced by polyhedral
cells ; this is the .neck of the intermediary part. In
some salivary glands, especially in the mucous, this

1 82 ELEMENTS OF HISTOLOGY, [chap. xxn.

neck is the only portion of the intermediary part
present, 'e.g., in the sub-maxillary and orbital glands
of dog and cat, and in the sub-lingual of the rabbit.
In others, especially in the serous salivary glands, as
in the parotid of man and mammals, sub-maxillary of
rabbit and guinea-pig, and in the mixed salivary —
e.g., sub-maxillary and sub-lingual of man and ape —
there exists after the neck a long intermediary part,
which gives off several shorter or longer branches of
the same kind, all of which terminate in alveoli.

243. The alveoli or acini are the essential
or secreting part of the gland ; they are flask-shaped,
club-shaped, shorter or longer cylindrical tubes, more
or less wavy, or if long, more or less convoluted;
many of them are branched. Generally several open
into the same intermediary part of a salivary tube.
The alveoli are much larger in diameter than the
intermediary part, and slightly larger, or about as
large, as the intralobular ducts. But there is a
difference in this respect between the alveoli of a
serous and a mucous salivary gland ; in the former
the alveoli are smaller than in the latter.

The membrana propria of the intermediary duct
is continued as the membrana propria of the alveoli.
This is a reticulated structure, being in reality a basket-
shaped network of hyaline branched nucleated cells
(Boll). The lumen of the alveoli is very minute in
the serous, but is considerably larger in the mucous
glands ; it is in both glands smaller during secretion
than during rest.

244. The epithelial cells lining the alveoli are
called the salivary cells — they are of different
characters in the different salivary glands, and chiefly
determine the nature of the gland. The cells are
separated from one another by a fluid albuminous
cement substance. (1) In the serous or true salivary
glands, as parotid of man and mammals, sub-maxillary

Chap, xxii.] THE SALIVARY GLANDS. 183

of rabbit and guinea-pig, the salivary cells form a
single layer of shorter or longer columnar or pyra-
midal albuminous cells, composed of a densely reticu-
lated protoplasm, and containing a spherical nucleus in
the outer part of the cell. (2) In the mucous glands,
such as the sub-lingual of the guinea-pig, or the
admaxillary of the same animal, the cells lining the
alveoli form a single layer of goblet-shaped mucous
cells, such as have been described in par. 25. Each
cell consists of an inner principal part, composed of a
transparent rnucoid substance (contained in a wide-
meshed reticulum of the protoplasm), and an outer
small, more opaque part, containing a compressed and
flattened nucleus. This part is drawn out in a fine
extremity, which, being curved in a direction parallel
to the surface of the alveolus, is imbricated on its
neighbours.

245. In the case of the sub-maxillary and orbital
glands of the dog, the sub-lingual of rabbit, there exist,
in addition to, and outside of the mucous cells lining
the alveoli, but within the meinbrana propria, from
place to place crescentic masses, being the demilunes
of Heidenhain, or the crescents of Gianuzzi (see Fig.
107). Each is composed of several polyhedral granu-
lar-looking cells, each with a spherical nucleus ; the
cells at the margin of the crescent are of course
thinner than those forming the middle. Heiden-
hain and his pupils, Lavdovski and others, have
shown that, during prolonged exhausting stimula-
tion of the sub-maxillary and orbital of the dog,
all the lining cylindrical mucous cells become re-
placed by small polyhedral cells, similar to those
constituting the crescents, while at the same time
the alveoli become smaller (Fig. 108). These ob-
servers maintain that this change is due to a total
destruction of the mucous cells, and a replacement
of them by new ones, derived by multiplication

1 84

ELEMENTS OF HISTOLOGY. [Chap. xxn.

from the crescent cells. This is improbable, since,
during ordinary conditions of secretions, there is no
disappearance of the mucous cells as such ; they change

in size, be-
coming
during

larger
secre-

tion, and their
contents are
converted into
perfect mucus.
It is probable
that, on pro-
longed exhaus-
tive stimula-
tion, the mucous
cells collapse
into the small
cells, seen by
I03.-From a Section through the Orbital Heidenhainand

land of Dog, after prolonged electrical his pupils.

^

alveoli of the
sub -lingual of

the dog are again different in structure both from those
of the sub-maxillary of the dog and of the sub-lingual
of guinea-pig, for the alveoli are there lined either
with mucous cells or with columnar albuminous
cells, or the two kinds of cells follow one another
in the same alveolus.

This gland is a sort of intermediate form be-
tween the sub-lingual of man and the sub-maxillary
of man and ape, i.e., the mixed or muco-salivary
glands. In these the great number of alveoli are
serous, i.e., small, with small lumen, and lined witli
albuminous cells, whereas there are always present
a few alveoli exactly like those of a mucous gland.
The two kinds of alveoli are in direct continuity with

stimulation.
The alveoli are lined with small granular cells.

Chap, xxii.] THE SALIVARY GLANDS. 185

one another. In some conditions there are only very
few mucous alveoli to be met with within the lobule,
so few sometimes that they seem to be altogether
absent ; in others they are numerous, but even under
most favourable conditions form only a fraction of the
number of the serous alveoli. In the sub- lingual of
man they are much more frequent, and for this reason
this gland possesses a great resemblance to the sub-
lingual of the dog.

What appear to be crescents in the mucous alveoli

Fig. 109.— Alveoli of Serous Gland.
A, At rest ; B, first stage of secretion ; c, prolonged secretion. (Langley.)

of the human gland are an oblique view of albuminous
cells lining the alveoli at the transition between the
mucous and serous part of the same gland-tube.

247. The columnar salivary cells lining the alveoli
of the sub-maxillary of the guinea-pig in some condi-
tions show two distinct portions, an outer homogeneous
or slightly and longitudinally striated substance, and
an inner, more transparent, granular-looking part, and
in this respect the cells resemble those of the pancreas.
(See a future chapter.)

Langley has shown (Fig. 109) that during the
period preparatory to secretion the cells lining the
alveoli of the serous salivary glands become enlarged

1 86 ELEMENTS OF HISTOLOGY. [Chap. xxn.

and filled with coarse granules ; during secretion
these granules become used up, so that the cell-
substance grows more transparent, beginning from the
outer part of the cell and gradually progressing to-
wards the lumen of the alveolus.

248. Blood-vessels and lymphatics. — The
lobules are richly supplied with blood-vessels. The
arteries break up into numerous capillaries, which
with their dense networks surround and entwine the
alveoli. Between the interalveolar connective tissue
carrying the capillary blood-vessels and the inembrana
propria of the alveoli exist lymph spaces surrounding
the greater part of the circumference of the alveoli
and forming an intercommunicating system of spaces.
They open into lymphatic vessels accompanying the
intralobular ducts, or at the margin of the lobule
directly empty themselves into the interlobular
lymphatics. The connective tissue between the lobes
contains rich plexuses of lymphatics.

249. The nerve-branches form plexuses in
the interlobular tissue. In connection with them are
larger or smaller ganglia. They are very numerously
met with in the sub-maxillary, but are absent in the
parotid. Some ganglia are present in connection with
the nerve-branches surrounding the chief duct of the
sub-lingual gland.

Pfliiger maintains that the ultimate nerve-fibres
are connected with the salivary cells of the alveoli
in man and mammals, but this remains to be proved.

Chap. XXIII.] 187

CHAPTER XXIII.

THE MOUTH, PHARYNX, AND TONGUE.

250. The glaiids. — Into the cavity of the
mouth and pharynx open very numerous minute
glands, which, as regards structure and secretion, are
either serous or mucous. The latter occur in the
depth of the mucous membrane covering the lips of the
mouth, in the buccal mucous membrane, in that of the
hard palate, and especially in that of the soft palate
and the uvula, in the depth of the mucous membrane
of the tonsils, at the back of the tongue, and in the
mucous membrane of the pharynx. The serous glands
are found in the back of the tongue, in close proximity
to the parts containing the special organs for the
perception of taste — the taste goblets or buds (see
below.) All glands are of very minute size, but
when isolated they are perceptible to the unaided eye
as minute whitish specks, as big as a pin's head, or
bigger. The largest are in the lips, at the back of
the tongue and soft palate, where there is something
like a grouping of the alveoli around the small branches
of the duct, so as to form little lobules.

251. The chief duct generally opens with a narrow
mouth on the free surface of the oral cavity ; it
passes in a vertical or oblique direction through the
superficial part of the mucous membrane. In the
deeper, looser part (submucous tissue) it branches
in two or more small ducts, which take up a number
of alveoli. Of course, on the number of minute ducts
and alveoli depends the size of the gland.

In man, all ducts are lined with a single layer of
columnar epithelial cells, longer in the larger than

i88

ELEMENTS OF HISTOLOGY. [Chap. xxm.

in the smaller ducts ; in mammals, the epithelium
is a single layer of polyhedral cells. No fibrillation
is noticeable in the epithelial cells. At the transition
of the terminal ducts into the alveoli there is occasion-
ally a slight enlargement, called the infundibulum ;

here the granular-
looking epithelial
cells of the duct
change into the
columnar transparent
mucous cells lining
the alveoli.

252. The alveoli
of these glands are
identical with those
of the mucous glands
described above (Fig.
110)— e.g., the sub-
lingual gland, as re-
gards size, tubular
branched nature, the
lining epithelium, and
lumen.

In some instances
(as in the soft palate
and tongue) the duct
near the opening is
lined with ciliated
columnar epithelium.
The stratified epithe-
lium of the surface is generally continued a short dis-
tance into the mouth of the duct.

253. The serous glands at the root of the
tongue (von Ebner) differ from the mucous chiefly
in the size, epithelium, and lumen of the alveoli.
These are of exactly the same nature and structure
as those of the serous or true salivary glands.

Fig. 110.— Part of a Lobule of a Mucous
Gland in the Tongue of Dog.

o, Gland tubes (alveoli) viewed in various
directions ; they are lined with transparent
•' mucous cells;" d, duct, lined with small
polyhedral cells. (Atlas.)

Chap, xxiii.] MOUTH, PHARYNX, AND TONGUE. 189

Saliva, obtained from the mouth contains num-
bers of epithelial scales, detached from the surface
of the mucous membrane, groups of bacteria and
micrococci, and lymph corpuscles. Some of these are
in a state of disintegration, while others are swollen
up by the water of the saliva. In these there are
contained numbers of granules in rapid oscillation,
called Brownian molecular movement.

254. The mucous membrane lining the cavity
of the mouth is a thin membrane covered on its free
surface with a thick stratified pavement epithelium,
the most superficial cells being scales, more or less
hornified.

Underneath the epithelium is a somewhat dense
feltwork of fibrous connective tissue, with numerous
elastic fibrils in networks. This part is the mucosa,
and it projects into the epithelium in the shape of
cylindrical or conical papillae.

According to the thickness of the epithelium, the
papillae differ in length. The longest are found where
the epithelium is thickest — e.g., in the mucosa of the
lips, soft palate, and uvula.

Numerous lymph corpuscles are found in the
mucosa of the palate and uvula. Sometimes they
amount to diffuse adenoid tissue. The deeper part of
the mucous membrane is the submucosa. It is looser in
its texture, but it is also composed of fibrous connec-
tive tissue with elastic fibrils. The glands are- here
embedded ; fat tissue in the shape of groups of fat
cells up to continuous lobules of fat cells are here to
be met with. The large vascular and nervous trunks
pass to and from the submucosa.

255. Striped muscular tissue is found in the
submucosa. Of the lips, soft palate, uvula, and pala-
tine arches, it forms a very conspicuous portion —
e.g., musculus sphincter orbicularis, with its outrunners
into the mucous membrane of the lip, the muscles of

190 ELEMENTS OF HISTOLOGY. [Chap. xxm.

the palate, uvula (levator and tensor palati), and the
arcus, palato-pharyngeus, and palato-glossus.

256. The last branches of the arteries break up in
a dense capillary network on the surface of the mucosa,
and from it loops ascend into the papillae. Of
course, fat tissue, glands, and muscular tissue re-
ceive their own supply. There is a very rich plexus
of veins in the superficial part of the mucosa. They are
conspicuous by their size and the thinness of their wall.

The lymphatics form networks in all layers of the
mucosa, including the papillae. The large efferent
trunks are situated in the submucosa. The last
outrunners of the nerve branches form a plexus of non-
medullated fibres in the superficial layer of the mucosa,
whence numerous primitive fibrillce ascend into the
epithelium to form networks. Meissner's tactile cor-
puscles have been found in the papillae of the lips and
in those of the tongue.

257. In the pharynx the relations remain the
same, except in the upper or nasal part, where
we find numerous places covered with columnar
ciliated epithelium. As in the palatine tonsils so
also here, the mucosa is infiltrated with diffuse
adenoid tissue, and with lymph follicles in great
numbers. This forms the pliarynx tonsil of Luschka.

In the palatine tonsil and in the pharynx tonsil
there are numerous crypts leading from the sur-
face into the depth. This is due to the folding of
the infiltrated mucosa. Such crypts are, in the
pharynx, sometimes lined all through with ciliated epi-
thelium, although the parts of the free surface around
them are covered with stratified pavement epithelium.

258. The tongue is a fold of the mucous
membrane. Its bulk is made up of striped muscular
tissue (genio-, hyo-, 'and stylo-glossus ; according to
direction : longitudinalis superior and inferior, and
transversus linguae). The lower surface is covered

chap, xxiii.] MOUTH, PHARYNX, AND TONGUE. 191

with a delicate mucous membrane, identical in struc-
ture with that lining the rest of the oral cavity,
whereas the upper part is covered with a mem-
brane, of which the mucosa projects over the free
surface as exceedingly numerous fine and short hair-
like processes, the papillae filif or mes, or as less nume-
rous isolated somewhat longer and broader mushroom-
shaped papillae fungiformes. The papillae, as well as
the pits between them, are covered with stratified
pavement epithelium. Each has numbers of minute
secondary papillae. Their substance, like the mucous
membrane of the tongue, is made up of fibrous
connective tissue. This is firmly and intimately
connected with the fibrous tissue forming the septa
between the muscular bundles of the deeper tissue.
The mucous membrane is on the whole thin. It
contains large vascular trunks, amongst which the
plexus of veins is very conspicuous. On the surface
of the mucosa is a rich network of capillary blood-
vessels, extending as complex loops into the papillae.
Lymphatics form rich plexuses in the mucosa and
in the deep muscular tissue. Fat tissue is common
between the muscular bundles, especially at the back
of the tongue.

259. There are two varieties of glands present
in the tongue, the mucous and serous. The latter
occur only at the back, and in the immediate
neighbourhood of the taste organs ; the mucous
glands are chiefly present at the back ; but in
the human tongue there are small mucous glands
(glands of Nuhn) in the tip. All the glands at
the back are embedded between the bundles of
striped muscular tissue, and thus the movements
of the tongue have the effect of squeezing out the
secretion of the glands. Near and about the glands
numerous nerve bundles are found connected with
minute ganglia.

192

ELEMENTS OF HISTOLOGY. [Chap, xxm.

At the root of the tongue the mucous membrane
is much thicker, and contains in its mucosa numerous
lymph follicles and diffuse adenoid tissue. Thus

a

Fig. 111.— From a Vertical Section through a Circumvallate Papilla
of the Tongue of a Child.

a, The stratified pavement epithelium covering the fold around the papilla;
6, the mucous membrane ; *, the serous glands ; g, the pit between the fold
and the papilla ; in the epithelium of this latter are seen the "taste gublete."
(Atlas.)

numerous knob-like or fold- like prominences of the
mucosa are produced. There are also minute pits or
crypts leading into the depth of these prominences.

260. The papillae circiimvallatae (Fig. Ill)
are large papillae fungiformes, each surrounded by a fold
of the mucosa. They contain taste goblets or buds —

Chap, xxiii.] MOUTH, PHARYNX, AN

of the

i.e., the terminal taste organs. At tne innrcrin ot Tiio
tongue, in the region of the circumvallato papilla,
there are always a few perriianent folds, which also
contain taste goblets. In some domestic animals
these folds assume a definite organisation — e.g., in the
rabbit there is an oval or circular organ composed of
numbers of parallel and permanent folds, papillce
foliatce. The papillae fungiformes of the rest of the
tongue also contain in some places a taste goblet. But
most of the taste goblets are found on the papillae cir-
cumvallatae and foliatae. In both kinds of structures
the taste goblets are placed in several rows close round
the bottom of the pit, separating, in the papillae
circumvallatae, the papillae fungiformes from the fold
of the mucosa surrounding
it : in the papillae foliatae
the pits are represented by
groves separating the indi-
vidual folds from one
another.

261. The taste gob-
lets or taste buds are
barrel-shaped structures
(Fig. 112,), extending in a
vertical direction through
the epithelium, from the
free surface to the mucosa.
Each is composed of a
layer of flattened epithelial
cells, elongated in the
direction of the goblet, and
forming its cover; these
are the tegmental cells.
The interior of the goblet

is made up of a bundle of spindle-shaped or staff-
shaped taste cells. Each includes an oval nucleus,
and is drawn out into an outer and an inner fine

N

g, The base of the goblet next the
muros.a; ft, the free surface; e, the
epithelium of the surface. (Atlas.)'

194 ELEMENTS OF HISTOLOGY. [Chap. xxiv.

extremity. The former extends to the free surface,
projecting just through an opening of the goblet,
and resembles a fine hair; the latter is generally
branched, and passes towards the rnucosa ; there,
probably, it becomes connected with a nerve-fibre, the
mucosa of these parts containing rich plexuses of
nerve-fibres.

Into the pits surrounded by taste goblets open the
ducts of the serous glands only (von Ebner).

CHAPTER XXIV.

THE (ESOPHAGUS AND STOMACH.

262. I. THE oesophagus.— Beginning with the
oesophagus, and ending with the rectum of the large
intestine, the wall of the alimentary canal consists of
an inner coat or mucous membrane, an outer or mus-
cular coat, and outside this a thin fibrous coat, which,
commencing with the cardia of the stomach, is the
serous covering, or the visceral peritoneum.

The epithelium lining the inner or free surface of
the mucous membrane of the oesophagus is a thick,
stratified, pavement epithelium.

In Batrachia, not only the oral cavity and
pharynx, but also the oesophagus, are lined with
ciliated columnar epithelium.

The mucous membrane is a fibrous connective
tissue membrane, the superficial part of which is
dense — the mucosa; this projects, in the shape of
small papillae, into the epithelium. •

The deeper, looser portion of the mucous membrane
is the submucosa ; in it lie small mucous glands, the
ducts of which pass in a vertical or oblique direction

chap, xxiv.] (ESOPHAGUS AND STOMACH.

195

through the mucosa, in order to open on the free sur-
face. In man, these glands are relatively scarce ; in
carnivorous animals (dog, cat) they form an almost
continuous layer (Fig. 113).

263. Between the mucosa and submucosa are
longitudinal bundles of non-striped muscular tissue.

Fig. 113. — From a Longitudinal Section through the Mucous Membrane
of the (Esophagus of Dog.

«, The stratified pavement epithelium of the surface ; m, the muscularis mucosiB :
between the two Is the mucosa; g, the mucous glands ; d, ducts of same.
(Atlas.)

At the beginning of the oesophagus they are absent,
but soon make their appearance — at first as small
bundles separated from one another by masses of con-
nective tissue; but lower down, about the middle,
they form a continuous stratum of longitudinal
bundles. This is the muscularis mucosce.

ig6 ELEMENTS OF HISTOLOGY. [Chap, xxiv,

Outside the submucosa is the muscularis externa.
This consists of a thicker inner circular and an outer
thinner longitudinal coat. And outside .this is the outer,
or limiting, fibrous coat of the oesophagus. In man,
the outer muscular coat consists of non-striped muscu-
lar tissue, except at the beginning (about the upper
third, or less) of the oesophagus, which is composed
of the striped variety ; but in many mammals almost
the whole of the external muscular coat, except the
part nearest the cardia, is made up of striped fibres.

264. The large vessels pass into the submucosa,
whence their finer branches pass to the surface parts.
The superficial part of the mucosa and the papillae
contain the capillary networks. The outer muscular
coat and the muscularis mucosse have their own
vascular supply.

There is a rich plexus of lymphatics in the mucosa,
and this leads to a plexus of larger vessels in the sub-
mucosa (Teichmaiin). The nerves form rich plexuses
in the outer fibrous coat ; these plexuses include
numerous ganglia. A second plexus of non-medullated
fibres lies between the longitudinal and circular mus-
cular coat ; a few ganglia are connected with this
plexus. In the submucosa are also plexuses of non-
medullated fibres. Now and then a small ganglion is
connected also with this plexus.

265. II. The stomach. — Beginning with the
cardia, the mucous membrane of the stomach is covered
with a single layer of beautiful thin columnar epithelial
cells, most of which are mucus-secreting goblet cells.
On the surface of the mucous membrane of the stomach
open numerous fine ducts of glands, placed very closely
side by side. These extend, more or less vertically, as
minute tubes, into the depth of the mucous membrane.
In the pyloric end, where the mucous membrane
presents a pale aspect, the glands are called the pyloric
glands; in the rest of the stomach, whose mucous

Chap. xxiv.] (ESOPHAGUS AND STOMACH. 197

membrane presents a reddish or red-brown appear-
ance, they are called the peptic glands. Owing
to the very numerous fine ducts opening on the
surface of the mucous membrane, the tissue of this
latter appears on a vertical section to be made up
of thinner or thicker folds, or villi — plicae villosae.
But they are not real villi.

The part of the mucous membrane containing
the glands is the mucosa ; outside this is a loose con-
nective tissue containing the large vessels — this is
the submucosa. Between the two, but belonging
to the mucosa, is the muscularis mucosce, a thick
stratum of bundles of non-striped muscular tissue,
arranged in most parts of the stomach as an inner
circular and an outer longitudinal layer. The tissue
of the mucosa is dense, owing to its containing,
placed closely side by side, the gland tubes. Be-
tween them is a delicate connective tissue, in which
the minute capillary blood-vessels pass in a direction
vertical to the surface. Numerous small bundles
of non-striped muscular fibres pass from the mus-
cularis mucosEe towards the surface — up to near the
epithelium of the surface — forming longitudinal mus-
cular sheaths, as it were, around the gland tubes.

The plicae villosse of the superficial part of the
mucosa contain fibrous connective tissue and numerous
lymphoid cells.

266. The peptic glands (Fig. 114) are more or less
wavy tubes, extending down to the muscularis mucosse.
The deep part is broader than the rest, and is more
or less curved, seldom branched. This is the fundus of
the gland ; near the surface of the mucosa is the
thinnest part of the tube ; this is the neck. Two
or three neighbouring glands join, and open into
the short cylindrical duct mentioned above. The
duct is lined with a layer of columnar epithe-
lial cells, continuous and identical with those of the

198

ELEMENTS OF HISTOLOGY. [Chap. xxiv.

free surface of the mucous membrane. The cavity of
the duct is continued as a very fine canal into the
neck and through the rest of the gland tube. Next

Pig. 114— Peptic Glands.

A, Under a low power ; d, duct ; n, neck ; B, part of the f undns of a gland
tube under a high power; p, parietal cells; c, chief cells.

to the lumen is a continuous single layer of more or
less transparent, granular-looking, epithelial cells,
each with a reticulated protoplasm and a spherical or
slightly oval nucleus. In the neck these cells are

Chap, xxiv.] (ESOPHAGUS AND STOMACH.

199

polyhedral, but farther downwards increase to cylin-
drical cells, and in the fundus of the gland tube they
are long columnar. This layer of cells bordering the
lumen is the layer of chief
cells (Heiderihain.) Outside
them is the limiting mem-
brana propria of the gland
tube. But from place to
place, between the mem-
brana propria and the chief
cells, are single oval sphe-
rical or angular large
granular and opaque-look-
ing cells, called the parietal
cells (Heidenhain). These
are more numerous in the
neck than in any other
part of the gland ; at the
fundus they are few and
far between, whereas at
the neck they form almost
a continuous layer. Their
protoplasm is densely reti-
culated.

267. The pyloric
glands (Fig. 115).— The
duct of each pyloric gland
is several times longer than
in the peptic. The duct of
the former occupies in
some places as much as
half of the thickness of the
mucosa, whereas that of the latter does not exceed
in the fundus of the stomach or in the cardia, more
than one-fourth or one-fifth of the thickness.

The epithelium lining the duct of the pyloric
glands is the same as in that of the peptic. Each

Fig. 115.— From a Vertical Section
through, the Mucous Membrane
at the Pyloric End of the
Stomach.

«, Free surface,- rf, ducts of pyloric
glands ; n, neck of same : m, the gland
alveoli; mm, muscularis niucosae.
(Atlas.)

200 ELEMENTS OF HISTOLOGY. [Chap. xxiv.

duct takes up two or three tubes by their short,
narrow, thin neck. The main part of each gland tube
is convoluted and slightly branched. The neck is lined
with a layer of polyhedral cells, whereas the gland
tube has a lining of columnar transparent cells, and
its lumen is very conspicuous.

During exhaustion these cells are smaller and less
transparent than during secretion. Their protoplasm
in the former state is a denser reticulum than in the
latter, the transparent interstitial substance in the
meshes of the cell reticulum being increased in amount
during secretion.

The cells are serous, not mucous, and the se-
cretion of the glands cannot therefore be mucous.
According to Ebstein the secretion is pepsin, and
so he and Heidenhain consider the pyloric glands
as simple peptic glands. But this view is not generally
accepted.

Between the mucous membrane with peptic
glands and the pyloric end of the stomach with
pyloric glands there is a narrow intermediary zone,
in which the peptic glands appear by degrees to
merge into the pyloric glands. That is, the short duct
of the former gradually elongates, the gland tubes
get shorter in proportion and convoluted, their
lumen gradually enlarges, and the parietal cells
become fewer and ultimately disappear.

268. The mucosa contains isolated lymph follicles,
glandulse lenticulares, and in the pyloric part also
groups of these — glandulse agminatse.

The submucosa is of very loose texture, and enables
the mucosa to become easily folded in all directions.

The muscular coat is very thick, and consists of
an outer longitudinal and an inner thicker circular
stratum of non-striped muscular tissue. Numerous
oblique bundles are found in the inner section of the
circular stratum.

Chap, xxv.] SMALL AND LARGE INTESTINE. 201

The gland tubes are enslieatlied in a longitudinal
network of capillary blood-vessels derived from arteries
of the submucosa. This network forms on the surface
a special dense horizontal layer, from which the venous
branches are derived. The outer muscular coat and the
muscularis mucosse possess their own vascular supply.

269. The lymphatics form a network in the
rnucosa near the fundus of the glands. Into this
plexus lead lymphatics running longitudinally between
the glands anastomosing with one another freely, and
extending to near the surface (Loven). Another
plexus belongs to the submucosa.

Between the longitudinal and circular stratum of
the outer muscular coat, and extending parallel to the
surface, is a plexus of non-medullated nerve-branches
with a few ganglia in its nodes. This corresponds to the
plexus of Auerbach of the intestine, and is destined
for the outer muscular coat. A second plexus of non-
medullated nerve-branches with ganglia also extending
parallel to the surface lies in the submucosa. This cor-
responds to the plexus ofMeissner of the intestine, and
is destined for the muscularis mucosae and the mucosa. /

According to Rabe, the gastric gland tubes in the
horse are surrounded by a rich plexus of nerve-fibres,
terminating in peculiar spindle-shaped cells.

CHAPTER XXV.

THE SMALL AND LARGE INTESTINE.

270. THE epithelium covering the inner or free
surface of the mucous membrane of the small and
large intestine is a single layer of columnar cells, their
protoplasm more or less distinctly longitudinally fibril-
lated ; their free surface appears covered with a

202

ELEMENTS OF HISTOLOGY. [Chap. xxv.

Fig. 116.— From a Longitudinal Section through
a Villus of the Small Intestine.

a. The epithelium of the surface; 6, non-striped
muscular fibres. Immediately underneath the
epithelium is a basement membrane with oblong
nuclei; the tissue of the villus is made up of a

reticulum of cells; in its meshes are

corpuscles.

mph

vertically and
finely striated
basilar border.
Many cells are
goblet cells.
Underneath the
epithelium is a

basement
, ,

brane> tne

eDlthelial
CP1U

thelium OI JJe-
]

bove (see par. 39).

,

As in the stomach, so also
in the small and large intes-
tine, the mucosa is connected
with the outer muscular coat
by a loose-textured fibrous sub-
mucosa, in which lie the large
vascular trunks, and in many
places larger or smaller groups
of fat cells and lymph cor-
puscles. Between the mucosa
and submucosa, but belonging
to the former, is a layer of
non-striped muscular tissue,
the muscularis mucosce. This
is in many places composed of
inner circular and outer longi-
tudinal bundles, but there are
a good many places, especially
in the small intestine, where
only a layer of longitudinal rJTli7.— From
bundles can be made out.

The tissue of the mucosa is

-i-n of vnr>f iivc* +r\ arlonrnrl

in structure to aaenoia

/TTirr 1 1 (\\ nrmcicfino- r*f
(fig. HO/, Consisting OI

a iwHrvnlav rntifviY with flat

a leticuiar matux wren nat-

a vertical

intestine of Dog.

m> The mucosa containing the

crJTts of Lieberkuhn, cioseiy

placed side by side ; each crypt
fsii

ned with a layer of columnar
epithelium; mm, muscularis

mucosse ;«, submucosa. (Atias.)

chap, xxv.] SMALL AND LARGE INTESTINE.

203

tened large nucleated endotheloid cells and numerous
smaller lymph corpuscles. The mucosa of the small
and large intestine contains simple gland tubes, the
crypts or follicles of Lieberkuhn (Fig. 117); they
are placed vertically and closely side by side, extend-

Fig. 118.— From a Vertical Section through a Fold of the
Mucous Membrane of the Jejunum of Dog.

c. The mucosa, containing the crypts of Lieberktihn, and projecting
as the villi ; m, muscularis mucogse ; «, submucosa. (Atlas.)

ing from the free surface, where they open, to the
muscularis mucosse. These glands possess a large
lumen, and are lined with a single layer of columnar
epithelial cells, many of them goblet cells.

271. In the small intestine the tissue of the
mucosa projects beyond the general surface in the
shape of very numerous fine, longer or shorter, cylin-
drical, conical or leaf-shaped villi (Fig. 118). These
are, of course, covered with the columnar epithelium

204

ELEMENTS OF HISTOLOGY. [Chap. xxv.

of the general surface, and their tissue is the same as
that of the mucosa — i.e., adenoid tissue — with the
addition of : (a) One or two central wide chyle (lymph)
vessels (see Fig. 120), their wall being a single layer
of endothelial plates, (b) Along these chyle vessels
are longitudinal bundles of non-striped muscular tissue,
extending from the base to the apex of the villus,
terminating in connection with the cells of the base-
ment membrane— i.e., the subepithelial endotheliuni.

(c) A network of
capillary blood-
vessels extending
over the whole of
the villus close to
the epithelium of
the surface (Fig.
119). This capil-
lary network de-
rives its blood
from an artery in
about the middle

?£ "PP61 gf1* °f
thevillus. iwove-

iious vessels carry
away the blood
from the villus.

The Lieberkiihn's crypts open between the bases of
the villi.

At the sides of the villi of the small intestine,
and at the sides of the plicse villosse of the stomach
(see a former chapter), there exist amongst the epithe-
lium of the surface peculiar goblet-shaped groups of
epithelial cells, which, as Watney has shown, are due
to local multiplication of the epithelial cells.

272. Lymph follicles occur singly in the submucosa,
and extend 'with their inner part or summit through
the muscularis mucosse into the mucosa to near the

Fig. 119. — From a Vertical Section through,
the Small Intestine of Mouse; the Blood-
vessels are injected.

The networks of the capillaries of the villi are
well shown. (Atlas.)

Chap. xxv. j SMALL AND LARGE INTESTINE. 205

internal free surface of the latter (Fig. 120). These
are the solitary lymph follicles of the small and large
intestine ; in the latter they are larger than in the
former.

Agminated glands, or Peyer's glands, are larger or
smaller groups of lymph follicles, more or less fused

Fig. 120.— From a Section through a part of a Human Peyer's Patch,
showing the distribution of the Lymphatic Vessels in the Mucosa
and Submucosa.

a, Vi Hi, with central chyle vessel ; 6, Lieberkiihn's crypts ; c, region of rauscularia
mucosiu; /, lympta follicle; g, network of lymphatics around the lymph
follicle; I, lymphatic network of the submucosa; *, an efferent lymphatic
trunk. IFrejM

with one another, and situated with their main part
in the submucosa, but extending with their summit
to the epithelium of the free surface of the mucosa.
In the lower part of the ileum these Peyer's glands
are very numerous. The epithelium covering the
summits of these lymph follicles is invaded by, and
more or less replaced by, the lymph corpuscles of the

206 ELEMENTS OF HISTOLOGY. [Chap. xxv.

adenoid tissue of the follicles (Watney), similar to
what is the case in the tonsils (see par. 124).

The outer muscular coat consists of an inner thicker
circular and an outer thinner longitudinal stratum of
non-striped muscular tissue.

In the large intestine, in the "ligamenta," only
the longitudinal layer is present, and is much thickened

273. The blood-vessels form separate systems of
capillaries for the serous covering, for the outer mus-
cular coat, for the muscularis mucosse, and the richest
of all for the mucosa with its Lieberkiihn's crypts.
The capillary network of the villi is connected with
that of the rest of the mucosse.

The chyle vessel, or vessels of the villi, commence
with a blind extremity near the apex of the villi.
At the base the chyle vessel becomes narrower, and
empties itself into a plexus of lymphatic vessels and
sinuses belonging to the mucosa, and situated between
the crypts of Lieberkiihn (Fig. 120). This network is
the same both in the small and large intestine, as
is also that of the lymphatics of the submucosa with
which the former communicates. The lymph follicles
are generally surrounded with sinuous vessels of this
plexus. The efferent trunks of the submucous plexus,
while passing through the outer muscular coat in order
to reach the mesentery, take up the efferent vessels of
the plexus of the lymphatics of the muscular coat.

The chyle, composed of granules and globules
of different but minute sizes, passes from the inner
free surface of the mucous membrane of the small
intestine through the epithelium (probably through its
fluid interstitial cement substance) into the reticulum
of the villus matrix, and from thence the central
chyle vessel, and farther into the plexus of vessels
of the mucosa and submucosa.

Owing to the peripheral disposition of the
capillaries in the villi, and owing to the greater

chap, xxv.] SMALL AND LARGE INTESTINE 207

filling with blood of the capillaries during digestion,
the villi are thrown into a state of turgescence during
this period, in consequence of which the central chyle
vessels are kept distended. Absorption is thus
greatly supported. The contraction of the muscular
tissue of the villi and of the muscular coat of the in-

Fig. 120A.— Plexus Myentericus of Auerbach of the Small Intestine

of a new-born Child.
The minute circles and ovals indicate ganglion cells. (Atlas.)

testine greatly facilitates the absorption and discharge
of the chyle.

274. The non-medullated nerves form a rich
plexus, called the the plexus tnyentericus of Auerbach
(Fig. 120A), with groups of ganglion cells in the
nodes ; this plexus lies between the longitudinal and
circular muscular coat. Another plexus connected
with the former lies in the submucous tissue ; this
is the plexus of Meissner, with ganglia. In both

208

ELEMENTS OF HISTOLOGY. [Chap. xxvr.

plexuses the branches are of a very variable thickness ;
they are groups of simple axis cylinders, held together
by a delicate endothelial sheath.

CHAPTER XXVI.

THE GLANDS OF BRUNNER, AND THE PANCREAS.

275. AT the passage of the pyloric end of the
stomach into the duodenum (Fig. 121), and in the first

Fig. 121. — Vertical Section through the Mitcous Membrane of the
end of Stomach and commencement of Duodenum.

», Villi of duodenum; 6, a lymph follicle; c, Lieberkuhn's crypts: d, mucosa of
pyloric end of stomach : g, the alveoli of the pyloric. glands; t, the fame in
the submucosa: they are continued into the duodenum as— ». the Brunner'8
glands ; m, the muscularis mucoeaB. (Atlas.)

Chap. XXVI.]

THE PANCREAS.

209

part of the latter, is a continuous layer of gland tissue
in the submucosa, composed of convoluted, more or less
branched tubes grouped into lobules, and permeated
by bundles of non-striped muscular tissue, outrunners
of the muscularis mucosae. These are the glands of
Brunner. Numerous thin ducts lined with a single
layer of columnar epithelial cells pass through the
mucosa, and open into the crypts of Lieberkiihii be-
tween the bases of the villi. The gland tubes of
Brunner's glands are identical in structure with the
pyloric glands, with which they form a direct ana-
tomical continuity.

276. The pancreas (Fig. 122) is in most respects
identical in struc-
ture with a serous
or true salivary
gland. The connec-
tive tissue frame-
work, the distribu-
tion of the blood-
vessels and lym-
phatics, and of the
gland tissue in lobes
and lobules, with the
corresponding inter-
and intra - lobular
ducts, is similar in
both cases. The
epithelium lining
the latter ducts is

Only faintly striated, Fig. 122.— From a Section through the

not by any means Pancreas of Dog.

j. ,. ,1 . a, The alveoli (tubes) of the gland; the lining

SO CtlStinCtly as in cells show an outer honiosreneous and an inner
.1 . „„!• , 4. -U granular-looking portion; d, a minute duct.

the salivary tubes. (Atias.)
The alveoli or acini

are club-shaped, flask-shaped, shorter or longer cylin-
drical, and convoluted.

210 ELEMENTS OF HISTOLOGY. [Chap. xxvu.

277. The intermediary part of the duct and its
passage into the alveoli is the same as in the
salivary glands. The cells lining the alveoli are
columnar or pyramidal, and show an outer homo-
geneous, or faintly and longitudinally striated zone
(Langerhans, Heidenhain), and an inner more tran-
sparent granular-looking zone. The nucleus of the
cell is spherical, and lies in about the middle. According
'to the state of secretion the two zones vary in amount,
one at the expense of the other.

The lumen of the alveoli is very minute, and
in the beginning of the alveoli, i.e., next to the
intermediary part of the duct, are seen spindle-shaped
cells occupying the lumen, the centroacinous cells of
Langerhans.

In the rabbit's pancreas Kiihne and Lea have
shown that there are peculiar accumulations of cells
between the alveoli, which are supplied with veritable
glomeruli of capillary blood-vessels.

CHAPTER XXVII.

THE LIVER.

278. THE outer surface of the liver is covered with
a delicate serous membrane, the peritoneum, which,
like that of other abdominal organs, has on its free
surface a layer of endothelium. It consists chiefly of
fibrous connective tissue.

At the hilum or porta hepatis this connective
tissue is continued into the interior, and becomes one
with the connective tissue of the Glisson's capsule, or
the interlobular connective tissue (connective tissue
of the portal canals). This tissue is fibrous, and

Chap. XXVII.]

THE LIVER.

211

more or less lamellated ; by it the substance of
the liver is subdivided into numerous, more or less
polyhedral, solid lobules or acini (Fig. 12 3), each about
•gJgth of an inch in diameter. According to whether
the interlobular
tissue forms com-
plete boundaries
or not, the acini
appear well de-
fined from one
another (pig, ice-
bear), or more or
less fused (man
and carnivorous
animals and ro-
dents).

Within each W$ Nf

acinus there is
only very scanty

Connective tissue, Fig. 123.— From a Section through the Liver

in +ViA eVmnn nf °* ¥*%• Five lobules are shown. They are

well separated from one another by the

extremely delicate
bundles and flat-
tened connective-
tissue cells. Occa-
sionally, especially in the young liver, migratory
cells are to be met with in the acini and in the tissue
between them.

279. The vena portse having entered the hilum
gives off rapidly numerous branches, which follow the
interlobular tissue in which they are situated, and
they form rich plexuses around each acinus ; these are
the interlobular veins (Fig. 124). Numerous capillary
blood-vessels are derived from these veins. These
capillaries pass in a radiating direction to the centre
of the acinus, at the same time anastomosing with
one another by numerous transverse branches. In the

interlobular tissue.

Interlobular connective tissue, containing the
interlobular blood-vessels, i.e., the branches of the
hepatic artery and portal vein, and the interlobular
bile ducts; i, intralobular or central vein. (Atlas.)

212 ELEMENTS OF HISTOLOGY. [Chap. xxvu.

centre of the acinus the capillaries become con-
fluent into one large vein, the central or intralobular
vein. The intralobular veins of several neighbouring
acini join so as to form the sublobular veins, and
these lead into the efferent veins of the liver, or

Fig. 124.— From a Vertical Section through the Liver of Rabbit ; the
Blood-vessels and Bile-vessels injected.

a, Intcrlobular veins surrounded by interlolnilar bile-ducts ; these latter take up
the network of fine intralobular bile capillaries; the meshes of this net-
work correspond to the liver cells; b, the intralobular or central vein.
(Atlas.)

the hepatic veins, which finally pass into the vena
cava inferior.

280. The substance of each acinus — i.e., the
tissue between the capillary blood-vessels — is com-
posed of uniform polygonal protoplasmic epithelial
cells, of about T^Vo^h of an inch in diameter ; these
are the liver cells. Owing to the peculiar, more or
less radiating, arrangement of the capillaries, the liver
cells appear to form columns or cylinders, also more
or less radiating from the periphery towards the

Chap. XXVII.]

THE LIVER.

213

centre of the acinus. Sometimes the liver cells contain
minute pigment granules.

Each liver cell shows a more or less fibrillated and
reticulated protoplasm (Kupfer), and in the centre a
spherical nucleus with its reticulum, generally with
one or more nucleoli.
During activity the
liver cells are larger
and look more gran-
ular than after
action.

The liver cells
are 'joined with one
another by an albu-
minous cement sub-
stance, in which are
left fine channels ;
these are the bile

rriwllavipfi nr intvn
Capillaries, Or llltra-

lobular bile Vessels

(Fig. 125) In a

c ii • •

BUCCeSSlUllv iniected
. J J .

preparation, the

125.— From a Lobule of the Liver of
Rabbit, in which Blood and Bile Vessels
had been injected, more highly magnified

6, Bile capillaries between the liver cells; these
!"'(' wll shown as nucleated polygonal cells,
each with a distinct reticulum; c, capillary

biood-vesseis,

liver cells appear
separated everywhere from one another by a bile
capillary, and these form for the whole acinus a con-
tinuous intercommunicating network of minute
channels. Where the liver cells are in contact witli
a capillary blood-vessel, there, of course, are no bile
capillaries, since these exist only between liver celh.

281. At the margin of the acinus the bile capil-
laries are connected with the lumen of minute tubes;
these possess a membrana propria and a lumen lined
with a single layer of transparent polyhedral epithelial
cells. These are the small interlobular bile ducts
(Fig. 124). Their epithelial cells are in reality con-
tinuous with the liver cells. They join so as to form

2i4 ELEMENTS OF HISTOLOGY. [Chap. xxvu.

the larger interlobular bile ducts, lined with more or less
columnar epithelium. The first part of the bile duct
lined with polyhedral cells corresponds to the inter-
mediary part of the ducts of the salivary glands.
The interlobular bile ducts form networks in the inter-
lobular tissue. Towards the hilum they become of
great diameter, and their wall is made up of fibrous
tissue, with non-striped muscular tissue. Small
mucus-secreting glands are in their wall, and open
into their lumen.

The wall of the hepatic duct, and of the gall
bladder, are merely exaggerations of this structure.

282. The hepatic artery follows in its ramification
the interlobular veins. The arterial branches form
plexuses in the interlobular tissue, and they supply
the capillary blood-vessels of the interlobular con-
nective tissue, and especially of the bile ducts. The
capillary blood-vessels of the bile ducts join so as
to form small veins which finally empty themselves
into the interlobular veins. The anastomoses of the
capillary blood-vessels, derived from the arterial
branches, directly with the capillary blood-vessels of
the acini, are insignificant (Cohnheim and Litten).
The serous covering of the liver contains special
arterial branches — rami capsulares. Networks of lym-
phatics— deep lymphatics — are present in the inter-
lobular connective tissue, forming plexuses around
the interlobular blood-vessels and bile ducts, and
occasionally forming a perivascular lymphatic around
a branch of the hepatic vein. Within the acinus,
the lymphatics are represented only by spaces and
clefts existing between the liver cells and capillary
blood-vessels ; these are the intralobular lymphatics
(Macgillivry, Frey, and others). They anastomose
at the margin of the acinus with the interlobular
lymphatics.

In the capsule of the liver is a special network

Chap. xxvi 1 1.] ORGANS OF RESPIRATION. 215

of lymphatics, called the superficial lymphatics.
Numerous branches pass between this network and
those of the interlobular lymphatics.

CHAPTER XXVIII.

THE ORGANS OF RESPIRATION.

283. I. The larynx. — The supporting frame-
work of the larynx is formed by cartilage. In the
epiglottis the cartilage is elastic and reticulated,
i.e., the cartilage plate is perforated by numerous
smaller and larger holes. The cartilages of Santorini
and Wrisbergii, the former attached to the top of
the arytenoid cartilage, the latter enclosed in the
aryteno-epiglottidean fold, are also elastic. The
thyroid, cricoid, and arytenoid cartilages are hyaline.
All these are covered with the usual perichondrium.

A small nodule of elastic cartilage is enclosed in
the front part of the true vocal cord. This is the
cartilage of Luschka.

The mucous membrane lining the cavity of the
larynx (Fig. 126) has the following structure : —

The epithelium covering the free surface is
strati/ied columnar ciliated, i.e., the most superficial
layer is made up of conical cells with cilia on their
surface ; then between the extremities of these cells
are wedged in spindle-shaped and inverted conical cells.
Numerous goblet cells are found amongst the superficial
cells. The two surfaces of the epiglottis and the
true vocal cord are covered with strati/ied pavement
epithelium.

Underneath the epithelium is a basement mem-
brane separating the former from the mucous mem«
brane proper.

2l6

ELEMENTS OF HISTOLOGY. [Chap.xxvm.

284. The mucous membrane is delicate connective
tissue with numerous lymph corpuscles. In the pos-
terior surface of the epiglottis, in the false vocal cord,

Fig. 126.— From a Longitudinal Section through the Ventricle
of the Larynx of a Child.

a, True vocal cord ; 6, false vocal cord ; c, a nodule of elastic cartilage (cartilage
of Liiisrlika) ; d, ventricle; I, lymphatic tissue; m, bundles of the tliyro-
arytenoid muscle in transverse section. (Atlas.)

and in the lower parts of the larynx, but especially in
the ventricle, this infiltration amounts to diffuse
adenoid tissue, and even to the localisation of this
as lymph follicles. In both surfaces of the epiglottis,
and in the true vocal cords, the mucosa extends into
the stratified pavement epithelium in the shape of
minute papillae.

Chap.xxvin.] ORGANS OF RESPIRATION. 217

In the lower part of the larynx the mucous mem-
brane contains bundles of elastic fibres connected into
networks, and running in a longitudinal direction
These elastic fibres are found chiefly in the superficial
parts of the mucous membrane. In the true vocal
cord the mucosa is entirely made up of elastic fibres
extending in the direction of the vocal cord.

285. The deeper part of the mucous" membrane is
of loose texture, and corresponds to the sub-mucosa ;
in it are embedded numerous mucous glands, the ducts
of which pass through the mucosa and open on the
free surface. The alveoli of the glands are of the
nature of mucous alveoli, i.e., a considerable lumen
lined with a layer of mucous goblet cells. There are,
however, also alveoli lined with columnar albuminous
cells, and such as have both side by side, as in the
case of the sub-lingual gland of the dog. The ciliated
epithelium of the surface in some places extends also
for a short distance into the duct. The true vocal
cords have no mucous glands.

The blood-vessels terminate as the capillary net-
work in the superficial — i.e., sub-epithelial — layer of the
mucosa; where there are papillae — i.e., in the epiglottis
and true vocal cord — these receive a loop of capillary
blood-vessels. The lymphatics form superficial networks
of fine vessels, and deep submucous networks of large
vessels. These are of enormous width and size in the
membrane of the anterior surface of the epiglottis.
The finer nerves form superficial plexuses of non-
medullated fibres. Here, according to Luschka and
Boldyrew, there are end bulbs. Taste-buds have
been found in the posterior surface of the epiglottis
(Verson, Schofield, Davis), and also in the deeper
parts of the larynx (Davis).

286. II. The trachea. — The trachea is very
similar in structure to the lower part of the larynx,
from which it differs merely in possessing the rings

2l8

ELEMENTS OF HISTOLOGY. [Chap.xxvm.

of hyaline cartilage, and in possessing, in the posterior
or membranous portion, circular bundles of non-

-I

Fig. 127.— Prom a Longitudinal Section through the Trachea of a Child.

a, The stratified columnar ciliated epithelium of the internal free surface; 6.
the basement membrane; c, the mucnsa; d, the networks of longitudinal
elastic fibres; the oval nuclei between them indicate connective tissue
corpuscles; e, the submucous tissue containing mucous glands;/, large
blood-vessels; g, fat cells; ft, hyaline cartilage of the tracheal rings.
(Atlas.)

striped muscular tissue, extending, as it were, between
the ends of the rings. Its component parts are (Fig.
127) :—

(a) A stratified columnar ciliated epithelium.

(b) A basement membrane.

Chap.xxvur.] ORGANS OF RESPIRATION. 219

(c) A inucosa, with the terminal networks of
capillary blood-vessels, and infiltrated with adenoid
tissue.

(d) A layer of longitudinal elastic fibres.

(e) A loosely-textured submucous tissue, contain-
ing the large vessels and nerves and small mucous
glands. Occasionally the gland or its duct is embedded
in a lymph follicle.

287. III. The bronchi and the lungr.—
The bronchi branch within the lung dendritically
into finer and finer tubes. The finest branches
are the terminal bronchi. In the bronchi we find,
instead of rings of hyaline cartilage, as in the trachea,
larger and smaller oblong or irregularly-shaped plates
of hyaline cartilage distributed more or less uniformly
in the circumference of the wall. Towards the small
microscopic bronchi, these cartilage plates gradually
diminish in size and number. The epithelium, the
basement membrane, the sub-epithelial mucosa, and
the layer of longitudinal elastic fibres, remain the same
as in the trachea. The submucous tissue contains
small mucous glands.

288. Between the sub-epithelial mucosa and sub-
mucosa is a continuous layer of circular non-striped
muscular tissue. In the smaller microscopic bronchi
this layer is one of the most conspicuous. By the
contraction of the circular muscular coat the mucosa
is placed in longitudinal folds.

The state of contraction and distension of the
small bronchi bears an important relation to the aspect
of the epithelium, which appears as a single layer of
columnar cells in the distended bronchiole, and strati-
fied when the bronchiole is contracted.

The distribution of the blood-vessels is the same
as in the trachea. Lymph follicles are met with in
the submucous tissue of the bronchial wall in animals
and man.

220 ELEMENTS OF HISTOLOGY. [Chap.xxvm.

Tlie lymphatic networks of the bronchial mucous
membrane are very conspicuous. Those of the sub-
mucous tissue, i.e., the peribronchial lymphatics, anas-
tomose with those surrounding the pulmonary blood-
vessels.

Pigment and small particles can be easily absorbed
through the cement substance of the epithelium
into the radicles of the superficial lymphatics, whence
they pass readily into the (larger) peribronchial lym-
phatics.

In connection with the nerve branches in the
bronchial wall are minute ganglia.

289. Each terminal bronchiole branches into
several wider tubes called the alveolar ducts, or infundi-
bula ; each of these branches again into several similar
ducts. All ducts, or infundibula, are closely beset in
their whole extent with spherical, or, being pressed
against one another, with polygonal, vesicles — the air-
cells or alveoli — opening by a wide aperture into the
alveolar duct or infundibulum, but not communicating
with each other. The infundibula are much wider
than the terminal bronchioles, and also wider than
the alveoli.

290. All infundibula with their air-cells, belonging
to one terminal bronchiole, represent a conical struc-
ture, the apex of which is formed by the terminal
bronchus. Such a conical mass is a lobule of the lung,
and the whole tissue of the lung is made up of such
lobules closely aggregated, and arranged as lobes.
The lobules are separated from one another by delicate
fibrous connective tissue ; this forms a continuity
with the connective tissue accompanying the bron-
chial tubes and large vascular trunks, and with these
is traceable to the hilum. On the other hand, the
inteiiobular connective tissue of the superficial parts
of the lung is continuous with the fibrous tissue
of the surface called the pleura pulmonalis. This

chap. xxvui.] ORGANS OF RESPIRATION.

221

membrane contains numerous elastic fibres, and
on the free surface is covered with a layer of endo-
thelium.

In some instances (guinea-pig) the pleura pulmo-
nalis contains bundles of non-striped muscular tissue.

P'g. 128.— From a Section through the Lung of Gat, stained with Nitrate
of Silver.

a, An infundibulum or alveolar duct in cross section ; 5, groups of polyhedral
cells lining one part of the infundibulum, the rest being lined with flattened
transparent epithelial scales; c, the alveoli lined with flattened epithelial
scales ; here and there between them is seen a polyhedral granular epithelial

The lobes of the lung are separated from one
another by large septa of connective tissue — the liga-
menta pulmonis.

291. The terminal bronchi contain no cartilage

222 ELEMENTS OF HISTOLOGY. [Chap.xxvm.

or mucous glands in their wall. This is made up of
three coats : (a) a tiny epithelium — a single layer of
small polyhedral granular-looking cells ; (b) a circular-
muscular coat of non-striped muscular tissue ; and
(c) a fine adventitia of elastic fibres, arranged chiefly
as longitudinal networks.

292. Tracing the elements constituting the wall
of a terminal bronchiole into the infundibula and air-
cells (Fig. 128), we find the following changes : (a) the
polyhedral granular-looking epithelial cells forming a
continuous lining in the terminal bronchiole, are trace-
able into the infundibulum only as larger or smaller
groups ; between these groups of small polyhedral
granular-looking cells large, flat, transparent, homo-
geneous, nucleated, epithelial scales make their ap-
pearance. The farther away from the terminal
bronchiole, the fewer are the groups of polyhedral
granular-looking cells. In all infundibula, however,
the transparent scales form the chief lining. This
becomes still more marked in the air-cells. There
the small polyhedral granular-looking cells are trace-
able only singly, or in groups of two or three (Elens),
the rest of the cavity of the air-cells being lined with
the large transparent scales.

In the fatal state all cells lining the infundibula
and air-cells are of the small polyhedral granular-
looking variety (Kiittner). With the expansion of
the lungs during the first inspiration many of these
cells change into the large transparent scales, in order
to make up for the increment of surface. A lung
expanded ad maximum shows much fewer or none of
the small polyhedral cells ; while a lung that is col-
lapsed shows them in groups in the infnndibula,
and isolated or in twos or threes in the alveoli.

293. (b) The circular coat of non-striped muscular
tissue of the terminal bronchiole is continued as a con-
tinuous circular coat — but slightly thinner — on the

chap. xx vi ii.] ORGANS OF RESPIRATION'.

223

alveolar ducts or infundibula, in their whole extent,
but not beyond them, i.e., not on the air-cells.

(c) The adventitia of elastic networks is con-
tinued on the infundibula, and thence on the air-
cells, where they form an essential part of the wall
of the alveoli, being its framework.

Amongst the network of elastic fibres forming
the wall of the alveoli is a network of branched con-
nective tissue cells, contained as usual in similarly
shaped branched lacunae, which are the radicles of
the lymphatic vessels.

294. The blood-vessels and lymphatics.—
The branches of the pulmonary artery and veins
are contained within the connective tissue separat-
ing the lobes and lobules, whence they can be
traced into
their finer
ramifications
towards the in-
fundibula and
air-cells. Each
of these latter
is surrounded
by a sort of
basket - shaped
dense network
of capillary
blood - vessels
(Fig. 129). The
capillary net-
works of adja- Fig. 129.— Networks of Capillary Blood-vessels

cent alveoli are 8§S££)* the Alveoli of the Human Lung<

continuous

with one another, and stand in communication on the

one hand with a branch of the pulmonary artery, and

on the other with branches of the pulmonary vein.

The branches of the bronchial artery belong to the

224 ELEMENTS OF HISTOLOGY. [Chap.xxviu.

bronchial walls, which are supplied by them with
capillary networks.

The lacunae and canaliculi in the wall of the alveoli,
mentioned above, are the rootlets of lymphatic vessels,
which accompany the pulmonary vessels, and form a
network around them ; these are the deep lymphatics,
or the perivascular lymphatics. They are connected
also with the networks of lymphatics surrounding the
bronchi, -i.e., the peribronchial lymphatics. The root-
lets of the superficial air-cells empty themselves into
the sub-pleural plexus of lymphatics, a rich plexus of
large lymphatics with valves. All these lymphatics
lead by large trunks into the bronchial lymph glands.

295. Between the flattened transparent epithelial
cells lining the alveoli are minute openings, stomata
(Fig. 128), leading from the cavity of the air-cells into
the lymph lacunae of the alveolar wall. These stomata
are more distinct during expansion, i.e., inspiration,
than in the collapsed state. Inspiration, by its ex-
panding the lungs, and consequently also the lym-
phatics, favours greatly absorption. Through these
stomata, and also through the interstitial cement
substance of the lining epithelium, formed particles
— such as soot particles of a smoky atmosphere,
pigment artificially inhaled, cellular elements, such
as mucus or pus corpuscles, that have been car-
ried into the alveoli from the bronchi by natural
inspiration, germ-particles, <fec., find their way into
the radicles of the lymphatics ; thence into the peri-
vascular and sub-pleural lymphatics, and finally into
the bronchial glands.

Chap. XXI X.J

225

CHAPTER XXIX.

THE SPLEEN.

296, THE capsule enveloping the spleen is a
serous membrane — the peritoneum. It is a connective

' '

S Qa ".i o o • * •

Fig. 130.— From a Vertical Section through the Spleen of Ape.

a, The capsule ; 6, the trabeculaa ; c, Malpighian cof imscle ; d, artery ensheathed
in a Malpighian corpuscle ; e, pulp tissue. (Atlas.)

tissue membrane with networks of elastic fibres, and
covered 011 its free surface with an endothelium. The
p

226

ELEMENTS OF HISTOLOGY. [Chap. xxix.

deep part of the capsule contains bundles of non-striped
muscular tissue forming plexuses. In man the bundles
are relatively thin, but in some mammals — e.g.,
dog, pig, horse — they are continuous masses arranged
sometimes as a deep longitudinal and a superficial
circular layer.

In connection with the capsule are the trabeculce
(Fig. 130). These are microscopical, thicker or thinner
cylindrical bands branching and anastomosing, and
thus making a framework in which the tissue of
the spleen is contained. Towards the hilum the
trabeculse are larger, and they form there a continuity
with the connective tissue of the hilum. They are
the carriers of the large vascular branches. The
trabeculse in the human spleen consist chiefly of
fibrous tissue with an admixture of longitudinal non-
striped muscular
tissue. This is
more pronounced
in the dog, horse,
pig, guinea-pig, in
which the trabe-
culse are chiefly
composed of non-
striped muscular
tissue. Following
a small trabecula

JFig. 131.— From a Section through the after it IS given
Pulp of the Spleen of the Pig. ,&

a, Last outrunners of the muscular trabeculas ; Ott trOm a larger

6, the flattened cells forming the honeycombed nnp WP finrl it,

matrix of the pulp: in the meshes of this One> We Dn(\ 1T}

rnatrix are contained lymphoid cells of various branching into

still smaller ones,

which ultimately lose themselves amongst the elements
of that part of the spleen tissue called spleen pulp
(Fig. 131).

The meshes of the network of the trabeculas are
filled up with the parenchyma. This consists of two

chap, xxix.] THE SPLEEN. 227

kinds of tissues : (a) the Malpighian corpuscles ; and
(b) the pulp tissue.

297. The Malpighian corpuscles are masses
of adenoid tissue connected with the branches of the
splenic artery. Following the chief arterial trunks as
they pass in the big trabeculse towards the interior
of the spleen, they are seen to give off numerous
smaller branches to the spleen parenchyma ; these are
ensheathed in masses of adenoid tissue which are
either cylindrical or irregularly-shaped, and in some
places form oval or spherical enlargements. These
sheaths of adenoid tissue are traceable to the end of
an arterial branch ; and in the whole extent the
adenoid tissue or Malpighian corpuscle is supplied by
its artery with a network of capillary blood-vessels.

298. The rest of the spleen parenchyma is made up
of the pulp. The matrix of this is a honeycombed,
spongy network of fibres and septa, which are the
processes and bodies of large, flattened, endotheloid
cells, each with an oval nucleus. In some, especially
young, animals, some of these cells are huge and
multinucleated. The spaces of the honeycombed tissue
are of different diameters, some not larger than a blood
corpuscle, others large enough to hold several. All
spaces form an intercommunicating system. The
spaces contain nucleated lymph corpuscles, more or
less connected with and derived from the cell plates
of the matrix. But they do not fill the spaces, so
that some room is left, large enough to allow blood
corpuscles to pass.

The spaces of the honeycombed pulp matrix are in
communication, on the one hand, with the ends of the
capillary blood-vessels of the Malpighian corpuscles,
and, on the other, they open into the venous radicles
or sinuses (Fig. 132), which are oblong spaces lined
with a layer of more or less polyhedral endothelial cells.
These sinuses form networks, and lead into the large

228

ELEMENTS OF HISTOLOGY. [Chap. xxix.

venous branches passing in the big trabeeulae to the
hilum. The venous sinuses in man and ape possess a
special adventitia formed of circular elastic fibrils.
Not all arterial branches are ensheathed in

Fig. 132.— From a Section through the Spleen of a Guinea-pig ; the
Blood-vessels had been injected (not shown in the figure).

a, Artery of Malpighian corpuscle ; 6, pulp ; between its cells are the minute
blood-channels opening mtoc, the radicles of the veins. (Atlas.)

Malpighian corpuscles ; some few fine arterial branches
open directly into the spaces of the pulp matrix, being
invested in a peculiar reticular or concentrically ar-
ranged cellular tissue (not adenoid). These are the
capillary sheaths of Schweigger Seidel.

299. The blood passes then from the arterial
branches through the capillaries of the Malpighian

Chap, xxx.] KIDNEY, URETER, AND BLADDER. 229

corpuscles, whence it travels into the labyrinth of
minute spaces in the honeycombed pulp matrix ;
thence it passes into the venous sinuses, and finally
into the venous trunks. The current of blood on its
passage through the pulp tissue becomes, therefore,
greatly retarded. Under 'these conditions numerous
red blood-corpuscles appear to be taken up by the
cells of the pulp, some of which contain several
in their interior. In these corpuscles the blood-discs
become gradually broken up, so that, finally, only
granules and small clumps of blood-pigment are left
in them. The presence of blood-pigment in the cor-
puscles of the pulp is explained in this way ; and it is
therefore said that the pulp tissue is a destroyer of
red blood-corpuscles.

The pulp tissue is most probably the birthplace of
colourless blood-corpuscles ; and according to Bizzozero
and Salvioli it is also the birthplace of red blood-
corpuscles.

The lymphatics form plexuses in the capsule
(Tomsa, Kyber). These are continuous with the plexus
of lymphatics of the trabeculse j and these again with
the plexus of lymphatics in the adventitia of the
arterial trunks.

Non-medullated nerve-Jlbres have been traced along
the arterial branches.

CHAPTER XXX.

THE KIDNEY, URETER, AND BLADDER.

300. A. The framework.

The kidney possesses a thin investing capsule com-
posed of fibrous tissue, more or less of a lamellar
arrangement. Bundles of fibrous tissue pass with

230 ELEMENTS OF HISTOLOGY. [Chap. xxx.

blood-vessels between the deeper part of the capsule
and the parenchyma of the periphery. According
to Eberth, a plexus of non-striped muscle cells is
situated underneath the capsule.

The ureter entering the hilum enlarges into the
pelvis of the kidney, and with its minor recesses or
prolongations forms the calices. Both the pelvis and
the calices are limited by a wall which is a direct con-
tinuation of the ureter. The internal free surface is
lined with stratified transitional epithelium. Under-
neath the epithelium is a fibrous connective tissue
membrane (the mucosa), containing the networks of
capillary blood-vessels and fine nerve-fibres. Outside
the mucosa and insensibly passing into it is the
loose-textured submucosa, with groups of fat cells.
There are present in the sub-mucosa bundles of
non-striped muscular tissue, continued from the
ureter, in the shape of longitudinal and circular
bundles.

In the pelvis of the kidney of the horse small
glands (simple or branched tubes), lined with a single
layer of columnar epithelial cells, have been observed
by Paladino, Sertoli, and Egli. The last-named
mentions also that in the pelvis of the human kidney
there are gland-tubes similar in structure to sebaceous
follicles.

301. The large vascular trunks enter, or pass from
the tissue of the calices into the parenchyma of the
kidney between the cortex and medulla, and they are
accompanied by bundles of fibrous connective tissue
and here and there a few longitudinal bundles of non-
striped muscular tissue.

In the parenchyma there is a very scanty
fibrous connective tissue, chiefly around the Mal-
pighian corpuscles and around the arterial vessels,
especially in the young kidney. In the papillae there
is relatively a great amount pf fibrous tissue. On

Chap, xxx.] KIDNEY, URETER, AND BLADDER. 231

the surface of the papillae (facing the calices) there
is a continuous layer of fibrous tissue, and this on
its free surface is covered with stratified transitional
epithelium.

The parenchyma of the kidney consists entirely of
the urinary tubules and the intertubular blood-vessels,
and there is an interstitial or intertubular connective
tissue framework in the shape of honeycombed hyaline
membranes with flattened nucleated branched or
spindle-shaped cells. The meshes of the honeycomb
are the spaces for the urinary tubules and blood-
vessels.

302. B. The parenchyma. — I. The urinary
tubules (Fig. 133). — In a transverse or longitudinal
section through the kidney we notice the cortex, the
boundary layer of Ludwig and the papillary portions,
the last terminating in the conical papUlce in the cavity
of the calices.

The boundary layer and the papillary portion
form the medulla. A papilla with the papillary
portion and boundary layer, continuous with it, con-
stitute a Malpighian pyramid. The relative propor-
tion of the thickness of the three parts is about 3 -5
cortex, 25 boundary layer, and 4 papillary portion.

303. The cortex consists of vast numbers of con-
voluted tubules with their csecal origin, the Mal-
pighian corpuscle ; this is the labyrinth separated into
vertical divisions of equal breadth by regularly disposed
vertical straight striae originating a short distance from
the outer capsule, and radiating towards the boundary
layer which they enter. Each of these striae is a bundle
of straight tubules, and represents a medullary ray.
The boundary layer shows a uniform longitudinal stria-
tion, in which opaque and transparent striae alternate
with one another. The opaque striae are continuations
of the medullary rays, the transparent striae are
bundles of blood-vessels.

Fig. 133. — Diagram showing the course of the Uriniferous Tubules in
the different parts of the Cortex and Medulla.
(For description of Fig. 133, see foot of next page.)

chap, xxx.] KIDNEY, URETER, AND BLADDER. 233

The papillary portion is uniformly and longi-
tudinally striated.

Tracing a medullary ray from the boundary layer
into the cortex, it is seen that its breadth gradually
diminishes, and it altogether ceases at a short distance
from the outer capsule. A medullary ray is, con-
sequently, of a conical shape, its apex being situated
at the periphery of the cortex, its base in the
boundary layer. Such a pyramid is called a pyramid
of Ferrein.

304. All urinary tubules commence as convoluted
tubules in the part of the cortex named the
labyrinth, but not in the medullary rays, with a
csecal enlargement called a Malpighian corpuscle, and
terminate — having previously joined with many other
tubules into larger and larger ducts — at one of the
many minute openings or mouths at the apex of a
papilla. On their way the tubes several times alter
their size and nature.

From its start to its end there is a continuous
fine membrana propria forming the boundary wall
of the urinary tubule, and this membrana propria is
lined with a single layer of epithelial cells differing in
size, shape, and structure from place to place; in
the centre of the tubule is a lumen, differing in size
according to the size of the tubule.

305. (1) Each Malpighian corpuscle (Fig. 134)
is composed of the capsule — the capsule of Bowman —
and the glomerulus, or Malpighian tuft of capillary
blood-vessels.

A, Cortex limited on its free surface by the capsule ; a, subcapsular layer not
containing Malpighian corpuscles; a', inner stratum of cortex without
Malpighian corpuscles; B, boundary layer; c, papillary part next the
boundary layer; 1, Bowman's capsule : 2, neck of capsule : 3, proximal con-
voluted tube ; 4, spiral part ; 5, descending limb of Henle's loop-tube ; 6,
the loop itself ; 7, 8, and ». the ascending limb of Henle's loop-tube ; 10, the
irregular tubule ; 11, the distal convoluted tubule; 12, the first part of the
collecting tube ; 13 and 14, larger collecting tube ; in the papilla itself, not
represented here, the collecting tube joins others, and forms the duct.
(Atlas.)

234 ELEMENTS OF HISTOLOGY, [chap. xxx.

The capsule of Bowman is a hyaline membrana
propria, supported, as mentioned above, by a small
amount of connective tissue. On its inner surface
there is a continuous layer of nucleated epithelial

Fig. 134. — From a Section through the Cortical Substance of the
Kidney of a Human Foetus, showing a Malpighian corpuscle.

a, Glomerulus ; 6, tissue of the glonierulus; e, epithelium covering the
glomerulus ; d, flattened epithelium lining Bowman's capsule ; e, the
capsule itself; /, uriniferous tubules in cross section. (Handbook.)

cells, in the young state of polyhedral shape, in the
adult state squamous.

The glomerulus is a network of convoluted
capillary blood-vessels, separated from one another
by scanty connective tissue, chiefly in the shape
of a few connective tissue corpuscles. The capil-
laries are grouped together in two to five lobules.
The whole surface of the glomerulus is lined with
a delicate membrana propria, and a continuous layer

MW4

chap, xxx.] KIDNEY, URETER, AND BLADDER. 235

of nucleated epithelial cells, polyhedral, or even
columnar in the young, squamous in the adult state.
The membrana propria and epithelium dip in, of
course, between the lobules of the glomerulus, and
represent in reality the visceral layer of the capsule
of the Malpighian corpuscle, the capsule of Bowman
being the parietal layer. The glomerulus is connected
at one pole with an afferent and efferent arterial
vessel, the former being the larger.

Between Bowman's capsule and the glomerulus
there is a space, the size of which differs according
to the state of secretion, being chiefly dependent on
the amount of fluid present.

The Malpighian corpuscles are distributed in the
labyrinth of the cortex only, with the exception of a
thin peripheral layer near the outer capsule, and a
still thinner layer near the boundary layer. The
Malpighian corpuscles near the boundary layer are the
largest, those near the periphery the smallest; in
the human kidney their mean diameter is about yi^
of an inch.

306. On the side opposite to that where the
afferent and efferent arterioles join the glomerulus,
the capsule of Bowman passes through a narrow neck
into the cylindrical urinary tubule in such a way,
that the membrana propria and epithelium, of the
capsule are continued as the membrana propria and
lining epithelium of the tubule respectively, and
the space between the capsule of Bowman and
the glomerulus becomes the cavity or lumen of the
urinary tubule.

307. (2) After it has passed the neck, the urinary
tubule becomes convoluted ; this is the proximal con-
voluted tubule (Fig. 135). It is of considerable length
and is situated in the labyrinth. It has a distinct
lumen, and its epithelium is a single layer of polyhedral
or short, columnar, angular, or club-shaped cells, each

236

ELEMENTS OF HISTOLOGY, [chap. xxx.

with a spherical nucleus. These cells commence gene-
rally at the neck, but in some animals — e.g., in the

Fig. 135.— From a Vertical Section through the Kidney of Dog, showing
part of the Labyrinth and the adjoining Medullary Eay.

a, The capsule of Bowman; the capillaries of the glomerulus are arranged in
lobules ; n, neck of capsule ; 6, irregular tubule ; c, proximal convoluted
tubules ; d, a collecting tube ; e, part of the spiral tubule ; /, portion of the
ascending limb of Henle's loop-tube ; d, e, f form the medullary ray.
(Atlas.)

mouse — they already have begun in the Malpighian
corpuscle. The outer part of the cell protoplasm — i.e.,

Chap, xxx.] KIDNEY, URETER, AND BLADDER. 237

next the membrana -propria — is distinctly striated,
owing to the presence of rod-shaped fibrils (Heiden-
hain) vertically arranged. The inner part of the cell
substance — i.e., between the nucleus and the inner
free margin — appears granular. Epithelial cells the
protoplasm of which possesses the above rod-shaped
fibrils, will in the following paragraphs be spoken of
as fibrillated ceils.

The proximal convoluted tube appears sometimes
thicker than at other times ; in the first case, its
lumen is smaller, but its lining epithelial cells are
distinctly more columnar. This state is probably con-
nected with the state of secretion.

308. (3) The convoluted tube passes into the
spiral tubule (Schachowa). This differs from the
former in being situated not in the labyrinth, but in
a medullary ray, in which it forms one conspicuous
element, and in not being convoluted, but more or
less straight, slightly wavy, and spiral. Its thickness
and lumen are the same as in the former ; its
epithelium is a single layer of polyhedral cells, with
distinct indication of fibrillation.

309. (4) Precisely at the line where the cortex
joins the boundary layer, the spiral tube becomes
suddenly greatly reduced in thickness ; it becomes at
the same time very transparent; its lumen is distinct;
its membrana propria is now lined with a single
layer of scales, each with an oval flattened nucleus.
This altered tubule is the descending loop-tube of
Henle, and it pursues its course in the boundary
layer as a straight tubule, in the continuation of the
medullary ray.

In aspect and size this part of the urinary
tubule resembles a capillary blood-vessel, but differs
from it inasmuch as, in addition to the lining layer
of flattened epithelial cells, it possesses a membrana
propria.

238 ELEMENTS OF HISTOLOGY. [Chap. xxx.

310. (5) The so formed descending Henle's loop-
tube passes the line between the boundary layer
and. papillary portion, and having entered this
latter pursues its course for a short distance, when
it sharply bends backwards as the loop of Henle's
tube ; it now runs back towards the boundary layer,
and precisely at the point of entering this becomes
suddenly enlarged. Up to -this point the structure
and size of the loop are exactly the same as those of
the descending limb.

311. (6) Having entered the boundary layer it
pursues its course in this latter to the cortex in a
more or less straight direction within the medullary
ray as the ascending loop-tube. Besides being bigger
than the descending limb and the loop, its lumen
is comparatively smaller, and its lining epithelium
is a layer of polyhedral, distinctly fibrillated
epithelial cells. The tube is not quite of the same
thickness all along the boundary layer, but is broader
in the inner than in the outer half; besides, the tube
is not quite straight, but slightly wavy or even
spiral.

(7) Having reached the cortex, it enters this as the
cortical part of the ascending loop-tube, forming one
of the tubes of a medullary ray ; it is at the same
time narrower than in the boundary layer, and is
more or less straight or wavy. Its lumen is very
minute, its lining cells are flat polyhedral with a
small flattened nucleus, and there is an indication of
fibrillation (Fig. 135).

(8) Sooner or later on its way in the cortex in
a medullary ray it leaves this latter to enter the
labyrinth, where it winds between the convoluted
tubes as an angular irregular tubule (Fig. 135). Its
shape is very irregular, its size alters from place
to place, its lumen is very minute, its epithelium a
layer of polyhedral, pyramidal, or short columnar cells

Chap, xxx.i KIDNEY, URETER, AND BLADDER. 239

— according to the thickness of the tube; each cell
possesses a flattened oval nucleus next to the lumen,
and a very coarsely and conspicuously fibrillated pro-
toplasm.

312. (9) This irregular tubule passes into the
distal convoluted tubule or intercalated tubule of
Schweigger Seidel. This forms one of the convoluted
tubes of the labyrinth, and in size, aspect, and
structure, is identical with the proximal convoluted
tubule.

(10) The distal convoluted tube passes into a
short, thin, more or less curved or wavy collecting
tubule, lined with a layer of transparent, flattened,
polyhedral cells ; this is still contained in the laby-
rinth.

(11) This leads into a somewhat larger straight
collecting tube, lined with a layer of transparent poly-
hedral cells and with distinct lumen. This tube
forms part of a medullary ray, and on its way to the
boundary layer takes up from the labyrinth numerous
curved collecting tubules.

(12) It then passes unaltered as a straight collect-
ing tube through the boundary layer into the papillary
portion.

313. (13) In this part these tubes join under acute
angles, thereby gradually enlarging. They run in a
straight direction towards the apex of the papilla,
and the nearer to this the fewer and the bigger they
become. These are the ducts or tubes of Bellini.
They finally open on the apex into a calix. The lumen
and the size of the lining epithelial cells — viz., whether
more or less columnar — are in direct relation to the size
of the collecting tube. The substance of the epi-
thelial cells is a transparent protoplasm, and the
nucleus is more or less oval.

314. In many places nucleated cells, spindle-
shaped or branched, can be traced from the membrana

240 ELEMENTS OF HISTOLOGY. [Chap. xxx.

propria of the tubule between the lining epithelium ;
and, in some cases, even a delicate nucleated membrane
can be seen lining the surface of the epithelium next
the lumen. In the frog, the epithelium lining, the
Malpighian corpuscles, and the exceedingly long neck
of the urinary tubule, are possessed of long filamentous
cilia, rapidly moving during life. In the neck of
some of the urinary tubules in mammals there is
also an indication of cilia to be noticed.

Heidenhain has shown that indigo- sulphate of
sodium, injected into the circulating blood of the dog
and rabbit, is excreted through certain parts of the
urinary tubules only — viz., those which are lined
with " fibrillated" epithelium. He maintains that
this excretion is effected through the cell sub-
stance ; but, in the case of carmine being used as
pigment, I have not found the excretion to take place
through the substance of the epithelial cells, but
through the homogeneous interstitial or cement sub-
stance between the epithelial cells.

315. II. Tlie blood-vessels (Fig. 136).

The large branches of the renal artery and vein
are situated in the submucous tissue of the pelvis,
and they enter, or pass out respectively from, the part
of the parenchyma corresponding to the junction of
the cortex and boundary layer, where they follow a
more or less horizontal course, and give off, or take up
respectively, smaller branches to or from the cortex
and medulla.

(1) In the cortex the arterial trunks give off to
the cortex small branches, which singly enter the
labyrinth in a direction vertical to the surface of the
kidney. These are the interlobular arteries. Each of
these, on its way towards the external capsule of the
kidney, gives off, on all sides of its circumference,
shorter or longer lateral branches; these are the
afferent arterioles for the Malpighian corpuscles, each

chap, xxx.] KIDNEY, URETER, AND BLADDER. 241

one entering a Malpighian
corpuscle and breaking up
into the capillaries of the
glomerulus.

On its way towards
the external capsule, the
interlobular arteries be-
come greatly reduced, and
finally enter the capillary
network of the most peri-
pheral part of the cortex ;
but some of these arterioles
may be also traced into the
outer capsule, where they
become connected with the
capillary networks of this
latter. The efferent vessel
of a Malpighian glome-
rulus at once breaks up
into a dense network of
capillary blood - vessels,
which entwine in all pos-
sible directions the urinary
tubules of the labyrinth.
This network is continued
with that of capillaries of
the medullary rays, the
meshes being there elon-
gated, and the capillary
blood-vessels, for obvious
reasons, more of a straight

Intertobular artery ; vi, intcrlobular
vein ; g, glomerulus of Malpighian
corpuscle; r«, vena stellata; ar,
arterite rectse ; vr, vense rectse ; ab,
bundle of arterias rectae ; »>&, bundle
of vena) rectos ; «•?>, network of vessels
around the mouth of the ducts
at the apex of the papillae. (Ludwig,
in Strieker's Manual.)

vs-'

Fig. 136.— Diagram of the Vessels
of the Kidney.

242 ELEMENTS OF HISTOLOGY. [Chap. xxx.

arrangement. The capillaries of the whole cortex
form one continuous network.

316. The veins which take up the blood from this
network are arranged in this manner : — There are
formed venous vessels underneath the external
capsule, taking up like rays on all sides, minute
radicles connected with the capillaries of the most
peripheral part of the cortex. These are the vence
stellate?,; they pass into the labyrinth of the
cortex, where they follow a vertical course in
company with the interlobular arteries. On the
way they communicate with the capillaries of the
labyrinth, and ultimately open into the large
venous branches situated between cortex and boun-
dary layer.

317. (2) In the medulla. From the large arterial
trunks short branches come off, which enter the
boundary layer, and there split up into a bundle
of minute arterioles, which pass in a straight direc-
tion vertically through the boundary layer into the
papillary portion. These are the arterice rectce
(Fig. 136). The number of vessels of each bundle
is at the outset increased by the efferent vessel of
the Malpighian corpuscles nearest to the boundary
layer.

On their way through the boundary layer, and
through the papillary portion of the medulla,
these arterioles give off the capillary network for
the urinary tubules of these parts, the network,
for obvious reasons, possessing an elongated arrange-
ment.

From this network originate everywhere minute
veins, which on their way towards the cortical margin
increase in size and number ; they form also bundles
of straight vessels — vence rectce — and ultimately enter
the venous trunks situated between the boundary
layer and cortex.

Chap, xxx.] KIDNEY, URETER, AND BLADDERS

The bundles of the arteriae rectae an<
rectae form severally, in the boundary lay, , ^^
transparent striae mentioned on a previous page as
alternating with the opaque striae, these latter being
bundles of urinary tubules,

At the apex of each papilla there is a network
of capillaries around the mouth of each duct.

318. The outer capsule of the kidney contains a
network of capillary blood-vessels ; the arterial
branches leading into them are derived from two
sources : (a) from the outrunners of the interlobular
arteries of the cortex, and (£) from extrarenal arteries.
The veins lead (a) into the venae stellatae, and (6) the
extrarenal veins.

The lymphatic vessels form a plexus in the capsule
of the kidney. They are connected with lymph
spaces between the urinary tubes of the cortex.
The large blood-vessels are surrounded by a plexus of
lymphatics, which take up lymph spaces between the
urinary tubules, both in the cortex and the boundary
layer.

319. The ureter is lined with stratified transi-
tional epithelium. Underneath this is the mucosa,
a connective tissue membrane with capillary blood-
vessels. The submucosa is a loose connective tissue
Then, follows a muscular coat composed of non-
striped muscular tissue, arranged as an inner and
outer longitudinal and a middle circular coat. Then
follows an outer limiting thin fibrous coat or adventitia.
In this last have been observed minute ganglia in
connection with the nerve branches.

320. The bladder is similar in structure, but the
mucous membrane and muscular coat are very much
thicker. In the latter, which consists of non-striped
fibres, are distinguished an inner circular, a middle
oblique, and an outer longitudinal stratum. The
last is best developed in the fundus.

244 ELEMENTS OF HISTOLOGY. [Chap. xxxi.

Numerous sympathetic ganglia, of various sizes,
are found in connection with the nerve branches un-
derneath the adventitia (peritoneal covering), and in
the muscular coat (F. Darwin). The epithelium lining
the bladder is stratified transitional, and it greatly
varies in the shape of its cells and their stratification,
according to the state of expansion of the bladder.

CHAPTER XXXI.

THE MALE GENITAL ORGANS.

321. (1) THE testis of man and mammals is en-
veloped in a capsule of white fibrous tissue, the tunica
adnata. This is the visceral layer of the tunica
vaginalis. Like the parietal layer, it is a serous
membrane, and is therefore covered with endo-
thelium. Minute villi are occasionally seen pro-
jecting from this membrane into the cavity of
the tunica vaginalis. These villi are generally
covered with germinating endothelium (see par. 33).
Inside the tunica adnata, and firmly attached to
it, is the tunica albuginea, a fibrous connective
tissue membrane of lamellar structure. Towards
the posterior margin of the human testis its thick-
ness increases, and forms there a special accumu-
lation— in cross section more or less conical, with
posterior basis — the mediastinum testis, or corpus
Highmori.

Between the tunica adnata and tunica albuginea
is a rich plexus of lymphatics, which, on the one hand,
takes up the lymphatics of the interior, and on the

Chap, xxxi.] THE MALE GENITAL ORGANS. 245

other leads into the efferent vessels that accompany
the vas deferens.

The testis of the dog, cat, bull, pig, rabbit, &c.,
have a central corpus Highmori ; that of the mole,
hedgehog, and bat a peripheral one ; while that of the
rat and mouse have none (Messing).

322. The framework. — From the anterior
margin of the corpus Highmori spring numerous
septa of connective tissue, which, passing in a radiat-
ing direction towards the albuginea, with which they
form a continuity, subdivide the testis into a large
number of long, conical compartments, or lobules,
the basis of which is situated at the tunica albu-
ginea, the apex at the corpus Highmori. Kolliker
mentions that non-striped muscular tissue occurs in
these septa.

From these septa thin connective tissue lamellae
pass into the compartments, and they form the sup-
porting tissue for the blood-vessels and also represent
the interstitial connective tissue between the seminal
tubules.

This intertubular or interstitial tissue is distinctly
lamellated, the lamellae being of different thicknesses,
and consisting of thin bundles of fibrous connective
tissue — arranged more or less as fenestrated mem-
branes— and endotheloid connective plates on their
surface. Between the lamellae are left spaces, and
these form, through the fenestne or holes of the
lamellae, an intercommunicating system of lymph
spaces — being, in fact, the rootlets of the lymphatics
(Ludwig and Tomsa).

"Within the lamellae are found peculiar cells,
which are much larger than lymph-cells, and which, in
some instances (e.g., guinea-pig), include pigment
granules. They contain a spherical nucleus. In man,
in dog, cat, sheep, especially boar, these cells form
large, continuous groups — plates and cylinders — and

246 ELEMENTS OF HISTOLOGY. [Chap.xxxi.

the cells are polyhedral, and exactly similar to epithe-
lial cells. They are separated from one another within
the group by a thin interstitial cement-substance.
Their resemblance with epithelium is complete. They
are remnants of the epithelial masses of the Wolffian
body of the foetus.

323. The seminal tubules (Fig. 137). -
Within each compartment, above mentioned, lie

Fig. 137.— From a Section through the Testis of Dog.

Showing three seminal tubules in cross section. In two of these the lining
epithelium— seminal cells— is shown, and bundles of spermatozoa projecting
into the lumen of the tubules. Between the tubules is connective tissue
containing groups of polyhedral epithelial-like cells.

numerous seminal tubules, twisted and convoluted
in many ways, and extending from the periphery to
near the corpus Highmori. The tubules, as a rule,
are rarely branched ; *but in the young state, and
especially towards the periphery, branching is not un-
common.

Each seminal tubule consists of a membrana pro-
pria, a lining epithelium, and a lumen. The mem-
brana propria is a hyaline membrane, with oval nuclei
at regular intervals. In man it is thick and lamel-
lated, several such nucleated membranes being super-

Chap, xxxi.] THE MALE GENITAL ORGANS. 247

imposed over one another. The lumen is in all tubes
distinct and relatively large. The lining epithelium,
or the seminal cells, differ in the adult in different
tubules, and even in different parts of the same tubule,
being dependent on the state of secretion.

324. Before puberty all tubules are uniform in
this respect, being lined with two or three layers of
polyhedral epithelial cells, each with a spherical
nucleus. After puberty, however, the following
different types can be distinguished : —

(a) Tubules or parts of tubules similar to those
of the young state — viz., several layers of polyhedral
epithelial cells lining the membrana propria. These
are considered as (a) the outer and (6) the inner
seminal cells. The former are next to the membrana
propria; they are polyhedral in shape, transparent,
and the nucleus of some of them is in the process
of karyokinesis or indirect division (see par. 8) ;
others include an oval transparent nucleus. The
inner seminal cells generally form two or three layers,
and are more loosely connected with one another than
the outer seminal cells, and therefore possess a more
rounded appearance. Between these a nucleated reti-
culum of fine fibres is sometimes noticed, the germ
reticulum of von Ebner. But this is merely a support-
ing tissue, and has nothing to do with the germina-
tion of the cells or the spermatozoa (Merkel). The
inner seminal cells show very abundantly the process
of indirect division or karyokinesis, almost all being
seen in one or other phase of it.

325. In consequence of this, numerous small
spherical daughter-cells are formed ; these lie nearest
the lumen, and are very loosely connected with one
another. It is these which are transformed into sper-
matozoa, and hence are appropriately called spermato-
Uasts (Fig. 137).

Amongst the seminal cells, especially of cat and

248

ELEMENTS OF HISTOLOGY. [Chap.xxxi.

dog, are found occasionally, but not very commonly,
large multinuclear cells, the nuclei of which are also
in one or the other stage of karyokinesis.

(b) The innermost cells, i.e., the spermatoblasts,
become pear-shaped, the nucleus being situated at the

Fig. 138.— From a Section through the Testis of Dog, showing
portions of three Seminal Tubules.

A., Seminal epithelial cells and numerous small cells loosely arranged; B, the
small cells or sp-Tinatoblnsts converted into spermatozoa: c, groups of
these in a further stage of development. (Atlas.)

thinner extremity, becoming at the same time flattened
and homogeneous (Fig. 138). The elongation of the
spermatoblasts gradually proceeds, and in consequence
of this we find numerous elongated, club-shaped sper-
matoblasts, each with a flattened nucleus at the thin
end. These are the young spermatozoa, the nucleated
extremity being the head.

(c) At the same time these young spermatozoa
become grouped together by an interstitial granular
substance, in peculiar fan-shaped groups; in these

Chap, xxxi.] THE MALE GENITAL ORGANS. 249

groups the head, — i.e., the thin end containing the
flattened homogeneous nucleus, — is directed towards
the inner seminal cells, while the opposite extremity
is directed into the lumen of the tube. Meanwhile
the inner seminal cells continue to divide, and thus
the groups of young spermatozoa get more and more
buried, as it were, between them.

326. The original cell-body of the spermatoblasts
goes on elongating until its protoplasm is almost, but
not quite, used to form the rod-shaped middle piece
(Schweigger Seidel) of the spermatozoa; from the
distal end of this, a thin long hair-like filament, called
the tail, grows out. Where this joins the end of the
middle piece, there is, even for some time afterwards,
a last remnant of the granular cell-body of the original
spermatoblast to be noticed.

When the granular interstitial substance holding
together the spermatozoa of a group has become dis-
integrated, the spermatozoa are isolated. While this
development of the spermatozoa goes on, the inner
seminal cells continue to produce spermatoblasts,
which in their turn are converted into spermatozoa.

327. Spermatozoa (Fig. 139).— Fully formed
spermatozoa of man and mammals consist of a homo-
geneous flattened and slightly convex-concave head (the
nucleus of the original spermatoblast), a rod-shaped
middle piece (derived directly from the cell body of
the spermatoblast), and a long hair-like tail. While
living, the spermatozoa show very rapid oscillatory and
propelling movement, the tail acting as a flagellum or
cilium ; its movements are spiral.

In the newt there is a fine spiral thread
attached to the end of the long, curved, spike-like
head, and by a hyaline membrane it is fixed to the
middle piece ; it extends beyond this as the long thin
tail. Also in the mammalian and human sperma-
tozoa, a similar spiral thread, closely attached to the

25°

ELEMENTS OF HISTOLOGY. [Chap.xxxi.

middle piece, and terminating as the tail, has been ob-
served (H. Gibbes).

328. The seminal tubules of each compartment
or lobule empty themselves into a short, more or less
straight, tubule — the vas rectum. -- This is narrower

Fig. 139.— Various kinds of Spermatozoa.

A, Spermatozoon of guinea-pig not yet completely ripe ; B, the same seen side-
"ways, the head of the spermatozoon is flattened from side to side ; c, a
spermatozoon of the horse ; D, a spermatozoon of the newt.

than the seminal tubule, and is lined with a single
layer of polyhedral or short columnar epithelial cells.
The vasa recta form, in the corpus Highmori, a dense
network of tubular channels, which are irregular in
diameter, being at one place narrow clefts, at another
wide tubes, but never so wide as the seminal tubules ;
this network of channels is the rete testis.

329. (2) The epididymis.— From the rete testis
we pass into the vasa ejferentia, each being a tube

Chap, xxxi.] THE MALE GENITAL ORGANS.

251

wider than those of the rete testis, and each leading into
a conical network of coiled tubes. These are the coni
vasculosi. The sum total of all the coni vasculosi
forms the globus major or head of the epididymis.

330. The vasa effereiitia and the tubes of the
coni vasculosi are about the size of the seminal
tubules, but, unlike them, are lined with a layer of
beautiful columnar epithelial cells, with a bundle of
cilia (Fig. 140). Outside
these is generally a layer,
more or less continuous, of
small polyhedral cells. The
substance of the columnar
cells is distinctly longitudi-
nally fibrillated. The mem-
brana propria is thickened
by the presence of a cir-
cular layer of non-striped
muscular fibres. The rest,
i.e., the globus minor, or
tail of the epididymis, is

-.r.^1^ i ^f 4-i-^ ri+i^-i-, The wall of the tubule is made up of

made Up OI a Continuation a thick layer of concentrically ar-

of the tubes of the globus
major, the tubes diminish-
ing gradually in number by
fusion, and at the same time thereby becoming larger.
The columnar epithelial cells, facing the lumen of the
tubes of the globus minor, are possessed of cilia of
unusual length.

The tubes of the epididymis are separated from
one another by a larger amount of connective tissue
than those of the testis.

The tubes of the organ of Giralde, situated in
the beginning of the funiculus spermaticus, are lined
with columnar ciliated epithelium. So is also the
pedunculated hydatid of Morgagni attached to the
globus major.

Fig. 140.— A tubule of the epi-
didymis in cross section.

ran wed non-striped muscular tissue,
a layer of columnar epithelial cells
y'itli extraordinarily long cilia pro-
jecting into the lumen of the tube.

252 ELEMENTS OF HISTOLOGY. [Chap. xxxi.

331. The seminal tubules and the tubes of the
epididymis are entwined by a rich network of
capillary blood-vessels. Between the tubes of the
testis and epididymis are lymph spaces, forming an
intercommunicating system, and emptying themselves
into the superficial networks of lymphatics, i.e., those
of the albuginea ; the arrangement of these networks
is somewhat different in the testis and epididymis.

332. (3) Vas deferens mid vc si cruise semi-
nales. — The tubes of the globus minor open into the
vas deferens. This is of course much larger than
the former, and is lined with stratified columnar
epithelium. Underneath this is a dense connective
tissue mucosa, containing a rich network of capillary
blood-vessels. Beneath this mucosa is a thin sub-
mucous tissue, which in the Ampulla is better de-
veloped than in other parts, and therefore allows the
mucous membrane to become folded. Outside the sub-
mucous tissue is the muscular coat, which consists of
non-striped muscular tissue, arranged as an inner
circular and an outer longitudinal stratum. At the
commencement of the vas deferens there is in addition
an inner longitudinal layer. There is finally a fibrous
tissue adventitia. This contains longitudinal bundles
of non-striped muscular tissue, known as the cremaster
internus (Heiile). A rich plexus of veins — plexus
pampiniformis — and a rich plexus of lymphatic trunks,
are situated in the connective tissue of the spermatic
cord. The plexus spermaticus consists of larger and
smaller nerve-trunks, with which are connected small
groups of ganglion cells and also large ganglionic
swellings.

333. In the vesiculce seminales we meet with
exactly the same layers as constitute the wall of the
vas deferens, but they are thinner. This refers espe-
cially to the mucosa and the muscular coat. The
former is placed in numerous folds. The latter con-

Chap, xxxi.] THE MALE GENITAL ORGANS. 253

sists of an inner and outer longitudinal and a middle
circular stratum. The ganglia in connection with the
nerve-trunks of the adventitia are very numerous.

334. In the ductus ejaculatorii we find a lining of
columnar epithelial cells ; outside of this is a delicate
inucosa and a muscular coat, the latter consisting of
an inner thicker longitudinal and an outer thinner
circular stratum of non-striped muscular tissue.

When passing into the vesicula prostatica the
columnar epithelium is gradually replaced by stratified
pavement epithelium.

335. (4) The prostate gland. — Like other
glands, the prostate consists of a framework and the
gland tissue proper or the parenchyma.

The framework, unlike that of other glands, is
essentially muscular, being composed of bundles of
non-striped muscular tissue, with a relatively small
admixture of fibrous connective tissue. The latter
is chiefly limited to the outer capsule and the thin
septa passing inwards, whereas the non-striped mus-
cular tissue surrounds and separates the individual
gland alveoli.

336. The parenchyma consists of the chief ducts,
which open at the base of and near the colliculus
seminalis, and of the secondary ducts, minor branches
of the former, which ultimately lead into the alveoli.
These are longer or shorter, wavy or convoluted
branched tubes with numerous saccular or club-shaped
branches. The alveoli and ducts are limited by a
membrana propria, have a distinct lumen, and are
lined with columnar epithelium. In the alveoli there
is only a single layer of beautiful columnar epithelial
cells, the substance of which is distinctly and longi-
tudinally striated. In the ducts there is an inner
layer of short columnar cells, and an outer one of
small cubical, polyhedral or spindle-shaped cells.

At the mouth of the ducts the stratified pavement

254 ELEMENTS OF HISTOLOGY. [Chap. xxxi.

epithelium of the pars prostatica of the urethra
passes a short distance into the duct.

The alveoli are surrounded by dense networks of
capillary blood-vessels.

In the peripheral portion of the gland numerous
ganglia are interposed in the rich plexus of nerves.
Also Pacinian corpuscles are to be met with.

337. (5) The urethra.. — The mucous membrane
of the male urethra is lined with simple columnar
epithelium, except at the commencement — the pars
prostatica — and at the end — the fossa navicularis —
where it is stratified pavement epithelium.

The mucous membrane is fibrous tissue with very
numerous elastic fibres. Outside of it is a muscular coat
composed of non-striped muscular tissue, and arranged
as an inner circular and an outer longitudinal stratum,
except in the pars prostatica and pars membranacea,
where it is chiefly longitudinal. In the latter portion
the muscular bundles pass also into the mucous mem-
brane, where they follow a longitudinal course between
large veins arranged in a longitudinal plexus. These
veins empty themselves into small veins outside. This
plexus of large veins with the muscular tissue between
represents a rudiment of a cavernous tissue (Henle).

The mucous membrane forms peculiar folds sur-
rounding the lacunse Morgagni. There are small mucous
glands, lined with columnar epithelium, embedded in
the mucous membrane ; they open into the cavity of
the urethra and are known as Littre's glands.

338. (6) The glands of Cowper. — Each gland
of Cowper is a large compound tubular gland, which,
as regards structure of ducts and alveoli, resembles a
mucous gland. The wall of the chief ducts possesses
a large amount of longitudinally-arranged non-striped
muscular tissue. The epithelium lining the ducts is
composed of columnar cells. The alveoli possess a
large lumen and are lined with columnar mucous

Chap, xxxi.] THE MALE GENITAL ORGANS. 255

cells, the outer portion of the cell being distinctly
striated (Langerhans). In the cell the reticulum is
also distinct. In this respect the alveoli completely
resemble those of the sub-maxillary of the dog, but
there are no real crescents in the alveoli of Cowper's
gland.

339. (7) The corpus spongiosum. — The cor-
pus spongiosum of the urethra is a continuation of
the rudimentary corpus cavernosum above-mentioned
in connection with the pars membranacea of the
urethra. It is essentially a plexus of large veins
arranged chiefly longitudinally and leading into small
efferent veins. Between the large veins are bundles
of non-striped muscular tissue. The capillary blood-
vessels of the mucous membrane of the urethra open
into the veins of the plexus. The outer portion of
the corpus spongiosum, including the bulbus urethrae,
shows, however,. numerous venous sinuses, real caver-
nse, into which open capillary blood-vessels.

340. The glans penis is of exactly the same
structure as the corpus spongiosum. The outer surface
is covered with a delicate fibrous tissue membrane,
which on its free surface bears minute papillae,
extending into the stratified pavement epithelium. At
the corona glandis exist small sebaceous follicles, the
glands of Tyson; they are continued from the inner
lamella of the prepuce, where they abound. The
papillae of the glans contain loops of capillary blood-
vessels. Plexuses of non-medullated nerve-fibres are
found underneath the epithelium of the surface of
the glans. With these are connected the end bulbs
described in a former chapter as the genital nerve-end
corpuscles.

341. (8) The corpora oavernosa penis. — Each
corpus cavernosum is enveloped in a fibrous capsule,
the albuginea, made up of lamellae of fibrous con-
nective tissue. Numerous Pacinian corpuscles are

256 ELEMENTS OF HISTOLOGY. [Chap. xxxi.

met with around it. The matrix of the corpus
cavernosum consists of trabeculse of fibrous tissue,
between which pass bundles of non-striped muscular
tissue all in different directions. Innumerable
cavernse or sinuses, intercommunicating with one
another, are present in this matrix, capable of such
considerable repletion, that in the maximum degree
of this state the sinuses are almost in contact,
and the trabeculas compressed into very delicate
septa. The sinuses are lined with a single layer of
flattened endothelial plates, and their wall in many
places is strengthened by the bundles of non-striped
muscular tissue. The sinuses during erection become
filled with blood, being directly continuous with capil-
lary blood-vessels. These are derived from the arte-
rial branches which take their course in the above
trabeculae of the matrix. The blood passes from the
sinuses into small efferent veins. But the blood
passes also directly from the capillaries into the
efferent veins, and this is the course the blood takes
under passive conditions, while during erection it
passes chiefly into the above sinuses.

342. In the peripheral part of the corpus caver-
nosum there exists a direct communication between the
sinuses and minute arteries (Langer), but in the rest
the arteries do not directly communicate with the
sinuses except through the capillary blood-vessels.
In the passive state of the corpus cavernosum, the
muscular trabeculse forming part of the matrix are
contracted, and the minute arterial branches embedded
in them are therefore much coiled up ; these are the
arterise helicinse.

Chap. XXXII.]

257

CHAPTER XXXII.

THE FEMALE GENITAL ORGANS.

343. (1) THE ovary (Fig. 141.)— In the ovary, as
in other glands, the framework is to be distinguished
from the paren-
chyma. In the part
of the ovary next
to the hilum there
are numerous blood-
vessels, in a loose
fibrous connective
tissue, with nu-
merous longitudinal
bundles of non-
striped muscular
tissue directly con-
tinuous with the
same tissues of the
ligamentum latum.
This portion of the
ovary is the zona
vasculosa (Wal-
deyer). All parts of
the zona vasculosa
— i.e., the bundles
of fibrous connec-
tive tissue, the
blood-vessels, and
the bundles of non-
striped muscular
tissue — are traceable into the parenchyma. The stroma
of this latter, however, is made up of bundles of shorter

Fig. 141.— Vertical Section through the
Ovary of half -grown Cat.

a, The alhuginea ; tbe germinal epithelium is not
distinguishable owing to the low power under
which the section is supposed to be viewed;
6, the layer of smallest Graaflan follicles and
ova ; c, the medium-sized follicles : d, the layer
of large follicles ; e, the zona vasculosa. (Atlas.)

258 ELEMENTS OF HISTOLOGY. [Chap. xxxn.

or longer transparent spindle-shaped cells, each with an
oval nucleus. These bundles of spindle-shaped cells
form, by crossing and interlacing, a tolerably dense
tissue, in which lie embedded in special arrangements
the Graafian follicles. Around the larger examples of
the latter the spindle-shaped cells form more or less
concentric layers. In the human ovary bundles of
fibrous tissue are also met with.

The spindle-shaped cells are most probably a
young state of connective tissue.

Between these bundles of spindle-shaped cells
occur cylindrical or irregular streaks or groups of
polyhedral cells, each with a spherical nucleus ; they
correspond to the interstitial epithelial cells men-
tioned in the testis, and they are also derived from
the foetal Wolffian body.

344. According to the distribution of the Graafian
follicles, the following layers can be distinguished in
the ovary : —

(a) The albuginea. This is the most peripheral
layer not containing any Graafian follicles. It is
composed of the bundles of spindle-shaped cells, inti-
mately interwoven. In man, an outer and inner
longitudinal, and a middle circular, layer can be made
out (Henle). In some mammals an outer longitudinal,
an inner circular, or slightly oblique layer can be
distinguished in the albuginea.

The free surface of the albuginea is covered with
a single layer of polyhedral, or short columnar granu-
lar-looking epithelial cells, the germinal epithelium
(Waldeyer). This epithelium, in its shape and aspect,
forms a marked contrast to the transparent, flattened,
endothelial plates covering the ligamentum latum.

345. (6) The cortical layer (Schron). This is a
layer containing the smallest Graafian follicles, either
aggregated as a more or less continuous layer (cat and
rabbit), or in small groups (human), separated by the

Chap, xxxii.] FEMALE GENITAL ORGANS, 259

stroma. These follicles are spherical or slightly oval,
of about T^\) y- inch in diameter, and each of them is limi-
ted by a delicate membrana propria. Inside of this is
a layer of flattened, transparent, epithelial cells, each
with an oval, flattened nucleus; this is the mem-
brana granulosa. The space within the follicle is
occupied by, and filled up with, a spherical cell — the
ovum cell, or ovum. This is composed of a granular-
looking protoplasm, and in this is a big spherical, or
slightly oval, nucleus— the germinal vesicle. The
substance of this is either a fine reticulum, limited
by a delicate membrane, with one or more nucleoli
or germinal spots, or it is in one of the phases of
indirect division or karyokinesis, thus indicating
division of the ovum.

346. (c) From this cortical layer to the zona
vasculosa we find embedded in the stroma isolated
Graafian follicles, of various sizes, increasing from the
former to the latter. The biggest
follicles measure in diameter about
~^ inch. Those of the middle layers
are of medium size (Fig. 142). In them
we find inside the membrana propria
the membrana granulosa, made up of a
single layer of transparent, columnar,
epithelial cells. The ovum, larger than F&aafl2an~ Af o
in the small cortical follicles, fills out catuth<
the cavity of the follicle, and is T^H
limited by a thin hyaline cuticle — the S
zona pellucida. This appears as an SSft
excretion of the cells of the membrana JS& \V • *
granulosa. The protoplasm of the tSfJSTfeSSSi!

OVUm is fibrillated. The Part Slir- with tlie intranuclear
j. ,, . . , f » reticulum. (Atlas.)

rounding tne germinal vesicle is more
transparent, and stains differently in osmic acid than
the peripheral part. The big nucleus, or germinal
vesicle, is limited by a distinct membrane, and inside

260

ELEMENTS OF HISTOLOGY. [Chap. xxxn.

this membrane is a reticulum with generally one big
nucleolus or germinal spot.

Between these medium-sized follicles and the
small follicles of the cortical layer we find all inter-
mediate degrees as regards size of the follicle and the
ovum, and especially as regards the shape of the cells
of the membrana granulosa, the intermediate sizes of

follicles being
lined by a gran-
ulosa made up
of a layer of
polyhedral epi-
thelial cells.

347. The
deeper Graafian
follicles, i.e.,
those that are
to be regarded
as big follicles,
contain an
o v u m — o c c a -
sionally, two or
even three ova
of the — which is simi-
lar to that of
the previous fol-
except

that it is larger,
and its zona pel-

lucida thicker. The ovum does not fill out the whole
cavity of the follicle, since at one side, between it and
the membrana granulosa, there is an albuminous fluid,
the rudiment of the liquor folliculi.

348. The biggest or most advanced follicles are of
great size, easily visible by the naked eye, and con-
tain a large quantity of this liquor folliculi (Fig. 143).
In fact, the ovum occupies only a small part of the

Fig. 143.— A large Graafian ' Follicle
Ovary of Cat.

The follicle is limited by a capsule, the theca folliculi ;
the membrana Rranulosa is composed of several

layers of epithelial cells. The ovum with its distinct
hyaline zona pelludda is embedded in the epithelial
cells of the discus proligerus. The cavity of the
follicle is filled with fluid, the liquor folliculi.

chap, xxxii.] FEMALE GENITAL ORGANS. 261

cavity of the follicle. The ovum is big, surrounded by
a thick zona pellucida, is situated at one side, sur
rounded by the discus proligerus. This~ consists of
layers of polyhedral cells, except the cells immediately
around the zona pellucida, which are columnar. The
ovum with its discus proligerus is connected with the
membrana granulosa. This latter consists of stratified
pavement epithelium forming the entire lining of the
follicle. The outermost layer of cells is columnar.
The membrana propria of these big follicles is strength-
ened by concentric layers of the stroma cells, and this
represents the tunica fibrosa (Henle) or outer coat of
the follicle — -theca folliculi externa. Numerous blood
capillaries connected into a network surround the big
follicles.

In those follicles that contain a greater or smaller
amount of the liquor folliculi, we notice in the fluid a
variable number of detached granulosa cells in various
stages of vacuolation, maceration, and disintegration.

349. In connection with the medium-sized and
large Graafian follicles are seen occasionally smaller
or larger solid cylindrical or irregularly-shaped out-
growths of the membrana granulosa and membrana
propria ; they indicate a new formation of Graafian
follicles, some containing a new ovum. When these
side branches become by active growth converted into
larger follicles, they may remain in continuity with the
parent follicle, or may be constricted off altogether.
In the first case, we have one large follicle with two
or three ova, according as a parent follicle has given
origin to one or two new outgrowths.

Amongst the epithelial cells constituting the strati-
fied membrana granulosa of the ripe follicles we notice
a nucleated reticulum.

Many follicles reach ripeness, as far as size and
constituent elements are concerned, long before
puberty, and they are subject to degeneration ; but

262 ELEMENTS OF HISTOLOGY. [Chap. xxxn.

this process of degeneration involves also follicles of
smaller sizes.

350. Before menstruation, generally one, occasion-
ally two or more, of the ripe follicles become very
hypersemic. They grow, in consequence, very rapidly
in size ; their liquor folliculi increases to such a degree
that they reach the surface of the ovary ; finally —
i.e., during menstruation — they burst at a superficial
point ; the ovum, with its discus proligerus, is ejected,
and brought into the abdominal ostium of the oviduct.
The cavity of the follicle collapses, and a certain
amount of blood, derived from the broken capillaries
of the wall of the follicle, is effused into it. The follicle
is converted into a corpus luteum, by an active multi-
plication of the cells of the granulosa. New capilla-
ries with connective tissue cells derived from the theca
folliculi externa gradually grow into the interior, i.e.,
between the cells of the granulosa. This growth
gradually fills the follicle, except the centre; this
contains blood-pigment in the shape of granules,
chiefly contained in large cells, and a few new
blood-vessels, the blood-pigment being the remains
of the original blood effused into the follicle.
But, ultimately, the pigment all disappears, and a
sort of gelatinous tissue occupies the centre, while
the periphery — i.e., the greater part of the follicle
— is made up of the hypertrophied granulosa, with
young capillary vessels between its cells. . The
granulosa cells undergo fatty degeneration, becoming
filled with several small fat globules, which gradually
become confluent into a big globule. In this state the
corpus luteum is complete, and has reached the height
of its progressive growth. The tissue is then gradually
absorbed, and cicatrical tissue is left. When this
shrinks it produces a shrinking of the corpus luteum.
This represents the last stage in the life of a
Graafian follicle. The corpus luteum of Graafian

chap, xxxii.] FEMALE GENITAL ORGANS. 263

follicles, of which the ovum has been impregnated,
grows to a much larger size than under other condi-
tions, the granulosa becoming by overgrowth much
folded.

351. Development of the ovary and Graa-
fhiii follicles* — The germinal epithelium of the
surface of the foetal ovary at an early stage undergoes
rapid multiplication, in consequence of which the epi-
thelium becomes greatly thickened. The vascular
stroma of the ovary at the same time increases, and
permeates the thickened germinal epithelium. The
two tissues in fact undergo mutual ingrowth, as is the
case in the development of all glands — viz., the epithe-
lial or glandular part suffers mutual ingrowth with
the vascular connective tissue stroma.

In the case of the ovary, larger and smaller
islands or nests (Balfour) of epithelial cells are thus
gradually differentiated off from the superficial epithe-
lium. These nests are largest in the depth, and smallest
near the surface. They remain in connection with
one another and with the surface for a considerable
period. Even some time after birth some of the
superficial nests are still connected with the surface
epithelium, and with one another (Fig. 143A). These
correspond to the ovarial tubes (Pfliiger). While in
the rabbit these nests are solid collections, in the dog
they soon assume the character of tubular structures
(Pfliiger, Schafer). The cells constituting the nests
undergo multiplication (by karyokinesis), in conse-
quence of which the nests increase in size, and even
new nests may be constricted off from old ones (see
also above).

352. At the earliest stages we notice in the
germinal epithelium some of the cells becoming en-
larged in their cell-body, and especially their nu-
cleus ; these represent the primitive ova. When the
germinal epithelium undergoes the thickening above

264

ELEMENTS OF HISTOLOGY. [Chap. xxxn.

mentioned, and when this thickened epithelium sepa-
rates into the nests and ovarial tubes, there is a
continued formation of primitive ova — i.e., cells of
the nests undergo the enlargement of cell-body and

Fig. 143A..— From a Vertical Section through the Ovary of a
new-born Child.

a, Germinal epithelium; &, ovarian tube: c, primitive ova; d, longer tubes be-
coming constricted off into several Graaflsin follicles; e, larwe nests; /.
isolated finished Graaflan follicles; g, blood-vessels. (Waldeyer, in Strieker's
Manual.)

nucleus, by which they are converted into primitive
ova. Like the other epithelial cells, the primitive
ova of the nests and ovarial tubes undergo division
into two or even more primitive ova after the mode
of karyokinesis (Balfour). Thus each nest contains
a series of ova.

353. The ordinary small epithelial cells of the
nests and ovarial tubes serve to form the membrana
granulosa of the Graafian follicles. According to

chap, xxxii.] FEMALE GENITAL ORGANS. 265

the number of ova in a nest or in an ovarial tube
a subdivision takes place in so many Graafian follicles,
each consisting of one ovum with a more or less
complete investment of small epithelial cells — i.e., a
membrana granulosa. This subdivision is brought
about by the ingrowth of the stroma into the nests.

The superficial nests being the smallest, as above
stated, form the cortical layer of the small Graatian
follicles ; the deeper ones give origin to larger follicles.
Thus we see that the ovum and the cells of the
membrana granulosa are derived from the primary
germinal epithelium; all other parts — membrana
propria, theca externa, stroma, and vessels — are
derived from the foetal stroma.

There is a good deal of evidence to show that
ova and Graafian follicles are, as a rule, reproduced
after birth (Pfliiger, Kolliker), although other ob-
servers (Bischoff, Waldeyer) hold the opposite view.

354. (2) The oviduct. — The oviduct consists of
a lining epithelium, a mucous membrane, a muscular
coat, and an outer fibrous coat — the serous covering,
or peritoneum. The epithelium is columnar and
ciliated. The mucous membrane is much folded ; it
is a connective tissue membrane with networks of
capillary blood-vessels. In man and mammals there
are no proper glands present, although there are seen
appearances in sections which seem to indicate the
existence of short gland tubes ; but these appear-
ances are explained by the folds of the mucous
membrane. The muscular coat is composed of non-
striped muscular tissue of a pre-eminently circular
arrangement; in the outer part there are a few
oblique and longitudinal bundles. The serous cover-
ing contains numerous elastic fibrils in a connective
tissue matrix.

355. (3) The uterus. — The epithelium lining
the cavity of the uterus is a single layer of columnai

266 ELEMENTS OF HISTOLOGY. [Chap. xxxn.

cells, each with a bundle of cilia on their free surface.
These are very easily detached, and therefore difficult
to find in a hardened and preserved specimen. But
in the fresh and well-preserved human uterus (Fried-
lander), as well as in that of mammals, the cells are
distinctly ciliated. The whole canal of the cervix is
also lined with ciliated epithelium, but in children,
according to Lott, only beginning from the middle.
The surface of the portio vaginalis uteri is, like that
of the vagina, covered with stratified pavement epithe-
lium.

356. The mucous membrane of the cervix is
different from that of the fund us. In the former it is
a fibrous tissue possessed of permanent folds — the
palmse plicatae. Few thin bundles of non-striped mus-
cular tissue penetrate from the outer muscular coat
into the mucous membrane. Between the palmse
plicatse are the openings of minute gland-tubes, more
or less cylindrical in shape. They possess a mera-
brana propria and a distinct lumen lined with a single
layer of columnar epithelial cells, which, according
to some, are ciliated in the new-born child, but, ac-
cording to Friedlander, non-ciliated. Goblet-cells are
met with amongst the lining epithelium. Several
observers (Kolliker, Hennig, Tyler Smith, and others)
maintain the existence of minute, thin, and long
vascular papillae projecting above the general surface
of the mucous membrane in the lower part of the
cervix ; these apparent papillse are, however, only due
to sections through the folds of the mucous membrane.
The mucous membrane of the fundus is a spongy
plexus of fine bundles of fibrous tissue, covered or
lined respectively with numerous small endothelial
plates, each with an oval flattened nucleus. The
spaces of this spongy substance are lymph-spaces, and
contain the glands and the blood-vessels (Leopold).

357. The glands — glandulae tit crime — are

chap, xxxii.] FEMALE GENITAL ORGANS. 267

short tubular glands. They occur in the new-born
child chiefly at the sides ; during puberty their number
and their size increase considerably, new glands being
formed by the ingrowth of the surface epithelium into
the mucous membrane (Kundrat and Engelmann).
During menstruation, and especially during pregnancy,
they greatly increase in length. They are more or
less wavy and branched at the bottom. A delicate
membrana propria forms the boundary of the tube ; a
distinct lumen is seen in the middle, and this is lined
with a single layer of ciliated columnar epithelium
(Allen Thomson, Nylander, Friedlander, and others).

358. During menstruation the thickness of the
mucous membrane increases, the epithelium of the
surface and of the greater part of the glands being
destroyed by fatty degeneration, and finally alto-
gether detached. Afterwards its restitution takes
place from the remnant in the depth of the glands.
But according to J. Williams and also Wyder, the
greater part of the mucous membrane, in addition to
the epithelium, is destroyed during menstruation.

The muscular coat forms the thickest part of the
wall of the uterus ; it is composed entirely of the non-
striped variety.

In the cornua uteri of mammals the muscular
coat is generally composed of an inner .thicker circular
and an outer thinner longitudinal stratum, a few
oblique bundles passing from the latter into the
former. In the human uterus the muscular coat is
composed of an outer thin longitudinal, a middle
thick layer of circular bundles, and an inner thick
one of oblique and circular bundles. Within these
layers the bundles form plexuses.

359. The arterioles in the cervix and their capil-
laries are distinguished by the great thickness of their
wall. The mucous membrane contains the capillary
networks. These discharge their blood into veins

268 ELEMENTS OF HISTOLOGY. [Chap, xxxn,

situated in the muscular coat. There the veins are
very numerous, and arranged in dense plexuses, those of
the outer and inner stratum being smaller than those
of the middle stratum, where they correspond to huge
irregular sinuses, the bundles of muscular tissue of
the muscular coat giving special support to these
sinuses. Hence the plexus of venous sinuses of the
middle stratum represents a sort of cavernous tissue.

360. The lymphatics are very numerous ; in
the intermuscular connective tissue of the muscular
coat are lymph sinuses and lymph clefts forming an
intercommunicating system ; they take up the lymph
sinuses of the mucous membrane above mentioned,
and on the other hand lead into a plexus of lymphatic
vessels with valves, situated in the subserous connec-
tive tissue.

The nerves entering the mucous membrane are
connected with ganglia. According to Lindgren, there
is in the mucous membrane a plexus of non-medu Hated
nerve-fibres, which, near the epithelium, break up
into their constituent primitive fibrillae.

361. (4) The vagina — The epithelium lining
the mucous membrane is a thick, stratified, pavement
epithelium. The superficial part of the mucous mem-
brane— i.e., the mucosa — is a dense, fibrous, connective
tissue with numerous networks of elastic fibres ; it
projects into the epithelium in the shape of numerous
long, single or divided papillae, each with a simple or
complex loop of capillary blood-vessels. The mucosa
with the covering epithelium projects above the gene-
ral surface in the shape of longer or shorter, conical
or irregular, pointed or blunt, permanent folds — the
rugae. These contain a plexus of large veins, between
which are bundles of non-striped muscular tissue j
hence they resemble a sort of cavernous tissue.

Outside of the mucosa is the loose submucosa
containing a second venous plexus ; its meshes are

chap, xxxii.] FEMALE GENITAL ORGANS. 269

elongated and parallel to the long axis of the vagina.
Outside of the submucous tissue is the muscular coat,
consisting of an inner circular and an outer longitu-
dinal stratum of non-striped muscular tissue. Oblique
bundles pass from one stratum into the other. From
the circular stratum bundles may be traced into the
submucosa and mucosa. A layer of fibrous tissue
forms the outer boundary of the wall of the vagina,
and in it is the most conspicuous plexus of veins, the
plexus venosus vaginalis. This plexus also contains
bundles of non-striped muscular tissue, and therefore
resembles a cavernous tissue (Gussenbaur.) It is
not quite definitely ascertained whether or not there are
secreting glands in the mucous membrane of the
vagina. Von Preuschen and also Hennig described
tubular glands in the upper part of the fornix and in
the introitus.

The lymphatics form plexuses in the mucosa, sub-
mucosa, and the muscular coat. The first are small
vessels, the second are larger than the third and possess
valves. The efferent vessels form a rich plexus .of
large trunks with saccular dilatations in the outer
fibrous coat.

There are in the mucous membrane solitary lymph
follicles and diffuse adenoid tissue (Loevenstein).

Numerous ganglia are contained in the nerve
plexus belonging to the muscular coat.

End bulbs in connection with the nerve-fibres of
the mucosa have been mentioned in Chapter XY.

362. (5) The urethra. — The structure of the
female urethra is similar to that of the male, except
that the lining epithelium is a sort of stratified tran-
sitional epithelium, the superficial cells being short,
columnar, or club-shaped ; underneath this layer are
several layers of polyhedral, or cubical cells. Near
the orificium externum the epithelium is stratified
pavement epithelium.

270 ELEMENTS OF HISTOLOGY. [Chap. xxxm.

The muscular coat is composed of an inner longi-
tudinal, and an outer circular, layer of non-striped
muscular tissue.

363. (6) The nymphae, clitoris, and vesti-

biilum. — These are lined with thick stratified epi-
thelium, underneath is a fibrous connective tissue
mucous membrane, extending into the epithelium in
the shape of cylindrical papilla with capillary loops
and nerve-endings (end bulbs). The nymphse contain
large sebaceous follicles, but no hairs.

The nymphse contain a plexus of large veins with
bundles of non-striped muscular tissue; hence it re-
sembles a cavernous tissue (Gassenbaur). The corpora
caveriiosa of the clitoris, the glans clitoridis, and the
bulbi vestibuli, correspond to the analogous parts in
the penis of the male. The glands of Bartholin corre-
spond in structure to the glands of Cowper in the
mala

CHAPTER XXXIII.

THE MAMMARY GLAND.

364. THIS, like other glands, consists of a frame-
work and parenchyma. The former is lamellar fibrous
connective tissue subdividing the latter into lobes and
lobules and containing a certain amount of elastic
fibres. In some animals (rabbit, guinea-pig) there are
also small bundles of non-striped muscular tissue.
From the interlobular septa fine bundles of fibrous
tissue with branched connective tissue corpuscles pass
between the alveoli of the gland substance. The
amount of this iiiteralveolar tissue varies in different
places, but in the active gland is always relatively
scanty.

Chap, xxxiii.] THE MAMMARY GLAND. 271

Migratory or lympli corpuscles are to be met with
in the interalveolar connective tissue of both active
and resting glands. In the latter they are more
numerous than in the former. According to Creighton,
they are derived, in the resting gland, from the epi-
thelium of the gland alveoli. Granular large yellow
(pigmented) nucleated cells occur in the connec-
tive tissue, and also in the alveoli of the resting
gland, and Creighton considers them both identical,
and derived from the alveolar epithelium. And
according to this author, the production of these cells,
would constitute the principal function of the resting
gland.

The large ducts as they pass from the gland to
the nipple, acquire a thick sheath, containing bundles
of non-striped muscular tissue. These latter are de-
rived from the bundles of non-striped muscular tissue
present in the skin of the nipple of the breast.

The small ducts in the lobules of the gland tissue
possess a membrana propria, and a lining — a single
layer of longer or shorter columnar epithelial cells.

The terminal branches of the ducts, i.e., just before
these latter pass into the alveoli, are lined with a
single layer of flattened pavement epithelium cells ;
they are analogous to the intermediary portion of the
ducts of the salivary glands (see Chap. XXII.).

365. Each of these terminal branches divides and
takes up several alveoli (Fig. 144). These are wavy
tubes, saccular or flask-shaped. The alveoli are
larger in diameter than the intralobular ducts. Each
alveolus in the active gland has a relatively large
cavity, varying in different alveoli ; it is lined with a
single layer of polyhedral, granular-looking, or short
columnar epithelial cells, each with a spherical nucleus ;
a membrana propria forms the outer limit. This mem-
brana propria, like that of the salivary, lachrymal and
other glands, is a basket-work of branched cells.

272

ELEMENTS OF HISTOLOGY. [Chap, xxxin.

In the active gland each epithelial cell is capable
of forming in its interior one or more smaller or larger
oil globules. These may, and generally do, become
confluent, and, pressing the nucleus towards one side
of the cell, give to the latter the resemblance of a fat-
cell. The oil globules are finally ejected by the cell-
protoplasm into the lumen of the alveolus, and repre-

Fig. 144.— From a Section through the Mammary Gland of Cat in a
late stage of Pregnancy.

a, The epithelial cells lining the gland-alveoli, seen in profile ; 6, the same, seen
from the surface. Many epithelial rells contain an oil globule. In the cavity
of some of the alveoli are milk globules and granular matter. (Atlas.)

sent now the milk globules. The cell resumes its
former solid character, and commences again to form
oil globules in its protoplasm. The epithelial cells,
as long as the secretion of milk lasts, go on again
and again forming oil globules in the above manner
without being themselves destroyed (Langer). These
milk globules, when in the lumen of the alveoli, are

chap, xxxiii.] THE MAMMARY GLAND. 273

enveloped in a delicate cuticle — the albumin mem-
brane of Ascherson. This membrane they receive
from the cell protoplasm.

According to the state of secretion, most epithelial
cells lining an alveolus may be in the condition of
forming oil globules, or only some of them ; and
according to the rate in which milk globules are formed
and carried away, the alveoli differ in the number of
milk globules they contain.

According to Schmid, the epithelial cells, after
having secreted milk globules for some time, finally
break up, and are replaced by new epithelial cells
derived by the division of the other still active
epithelial cells.

366. The resting gland, i.e., the gland of a non-
pregnant or non-suckling individual, contains, compara-
tively speaking, few alveoli, but a great deal of fibrous
connective tissue ; the alveoli are all solid cylinders,
containing within the limiting membrana propria
masses of polyhedral granular-looking epithelial cells.
During pregnancy these solid alveoli undergo rapid
multiplication, elongation, and thickening, owing to
the rapid division of the epithelial cells.

Finally, when milk secretion commences, the cells
occupying the central part of the alveolus undergo the
fatty degeneration just like the peripheral cells, but
they, i.e.) the central cells, are eliminated, while the
peripheral ones remain. These central cells are the
colostrum corpuscles, and consequently they are found
in the milk of the first few days only.

367. Ordinary milk contains no colostrum corpus-
cles, but only milk globules of many various sizes, from
the size of a granule to that of a globule several times
as big as an epithelial cell of an alveolus of the milk
gland. These large drops are produced by fusion of
small globules after having passed out of the alveoli.
Each milk globule is an oil globule surrounded, as

274 ELEMENTS OF HISTOLOGY, [chap, xxxiv.

stated above, by a thin albuminous envelope — Ascher-
son's membrane. The small bits of granular substance
met with here and there, are probably the remains of
broken-down* protoplasm of epithelial cells.

368. Each gland alveolus is surrounded by a dense
network of capillary blood-vessels. The alveoli are
surrounded by lymph spaces like those in the salivary
glands (Coyne) and these spaces lead into networks of
lymphatic vessels of the interlobular connective tissue.

CHAPTER XXXIV.

THE SKIX.

369. THE skin consists of the following layers
(Fig. 145): — (1) the epidermis; (2) the corium, or
cutis vera, with the papillae; (3) the subcutaneous
tissue, with the adipose layer or the adipose tissue.

370. (1) The epidermis (Fig. 14), in all its
constituent elements, has been minutely described in
Chapter III. Its thickness varies in different parts,
and is chiefly dependent on the variable thickness of
the stratum corneum. This is of great thickness in
the palm of the hand and the sole of the foot. The
stratum Malpighii fits into the depressions between
the papillae of the corium as the interpapillary pro-
cesses. The presence of prickle cells, of pigment
granules, and of branched interstitial nucleated cells,
&c., has been mentioned in Chapter III.

There occur in the stratum Malpighii migratory
cells of granular aspect ; they appear to migrate from
the papillary layer of the corium into the stratum
Malpighii (Biesiadecki).

371. (2) The corium is a dense feltwork of
bundles of fibrous connective tissue, with a large

Chap. XXXIV.]

THE SKIN.

275

admixture of networks of elastic fibres. From the
surface of the coriura project small conical or cylin-
drical pajrillce. These are best developed in those
parts where the skin is thick, e.g., volar side of
hand and foot, scalp, lips of mouth, &c. Between
the surface of the coriuni and the epidermis there
is a basement membrane. Migratory cells, with and

Fig. 145.— Vertical Section through the Skin of Human Finger.

a, Stratum corneum : 8, stratum luridnm : c, stratum Malpipbii : d, Meissner's,
or tactile corpuscles ; «. blood-vessels cut across;/, a sudoriferous canal or
duct.

without pigment granules in their interior, are 'met
with, especially in the superficial part of the corium ;
they, as well as the fixed or branched connective
tissue corpuscles (see par. 40), and other structures, as
vessels and nerves, lie in the interfascicular spaces.

372. (3) The superficial part of the subcuta-
neous tissue insensibly merges into the deep part of
the corium ; it consists of bundles of fibrous connective
tissue aggregated into trabeculse crossing one another

276 ELEMENTS OF HISTOLOGY. [Chap, xxxiv.

and interlacing in a complex manner. Numerous
elastic fibres are attached to these trabeculse. It con-
tains groups of fat cells, in many places arranged as
more or less continuous lobules of fat tissue, forming
the stratum adiposum. These lobules are separated
by septa of fibrous connective tissue ; their structure
and development, and the distribution of the blood-
vessels amongst the fat cells, have been described
in par. 45. The deep part of the subcutaneous tissue
is loose in texture, and contains the large vascular
trunks and the big nerve branches.

373. The superficial part of the subcutaneous
tissue, or, as some have it, the deep part of the
corium, contains the sudoriparous or sweat glands.
I^ach gland is a single tube coiled up into a dense
clump of about -^ of an inch in diameter — in some
places, as in the axilla, reaching as much as six times
this size. From each gland a duct — the sudori-
ferous canal — passes through the corium in a slightly
wavy and vertical direction towards the epidermis ;
it penetrates more or less spirally through the inter-
papillary process of the stratum Malpighii and the
rest of the epidermis, and appears with an open mouth
on the free surface of the skin.

The total number of sweat glands in the human
skin has been computed by Krause to be over two
millions ; but it varies greatly in different parts of the
body, the largest number occurring in the palm of
the hand, the next in the sole of the foot, the next
on the dorsum of the hand and foot, and the smallest
in the skin of the dorsum of the trunk.

374. The sudoriferous canal and the coiled tube
possess a distinct lumen \ this is lined with a delicate
cuticle, especially marked in the sudoriferous canal
and in the commencement of the coiled tube. In the
epidermis the lumen bordered by this cuticle is all
that is present of the sudoriferous canal. It receives

Chap, xxxiv.] THE SKIN. 277

a continuation from the middle layer of the stratum
Malpighii and from the basement membrane ; the
former is the lining epithelium, the latter the limiting
membrana propria of the sudoriferous canal. The
epithelium consists of two or three layers of small
polyhedral cells, each with a spherical or oval nucleus.

"I

Fig. 146.— From a Section through Human Skin, showing the Sweat
gland tubes cut in various directions.

a, First part of the coiled tube seen in longitudinal section : 6, the same seen in
cross section , c, the distal part seen in longitudinal section ; d, the same seen
in cross section. (Atlas.)

375. The structure of the sudoriferous canal is
then — a limiting membrana propria, an epithelium
composed of two or three layers of polyhedral cells, an
internal delicate membrane, and, finally, the central
cavity, or lumen.

The first part — about one-third or one-fourth —
of the coiled tube (Fig. 146) is of the same struc-
ture, and is directly continuous with the sudoriferous
canal, with which it is identical, not only in structure,
but in size. The remainder of the coiled tube — i.e.,
the distal part — is larger in diameter, and differs in

278 ELEMENTS OF HISTOLOGY. [Chap, xxxiv.

these essential respects, that its epithelium is a single
layer of transparent columnar cells, and that there
is between this and the limiting membrana propria
a layer of non-striped muscle cells (Kolliker) arranged
parallel with the long axis of the tube. In some
places, as in the palm of the hand and foot, in the
scrotum, the nipple of the breast, the scalp, but
especially in the axilla, this distal portion of the coiled
tube is of very great length and breadth, and its
epithelial cells contain a variable amount of granules.
It appears to me that the cells resemble in this
respect those of the serous salivary glands and the
chief cells of the gastric glands (Langley), inasmuch
as they produce in their interior larger or smaller
granules which are used up during secretion, from the
peripheiy towards the lumen.

376. The cenimmoiis glands of the meatus
auditorius externus are of the same structure as the
distal portion just described, except that the inner
part of the cell protoplasm of the epithelium contains
yellowish or brownish pigment, found also in their
secretion, i.e., in the wax of the ear.

Around the anus there is an elliptical zone, in the
skin of which are found large coiled gland tubes — the
circumanal glands of A. Gay — which are identical in
structure with the distal portion of the sweat gland
tubes.

377. The sweat glands develop as a solid cylin-
drical outgrowth of the stratum Malpighii of the
epidermis, which gradually elongates till it reaches
the superficial part of the subcutaneous tissue, where it
commences to coil. The lumen of the tube is of
later appearance. The membrana propria is derived
from the tissue of the cutis, but the epithelium and
muscular layer are both derived from the original
outgrowth of the epidermis.

378. The hair-follicles (Fig. 147).— The skin

Chap. XXXIV.j

THE SKIN.

279

almost everywhere contains cylindricaiyb^Wes, planted
more or less near to one another, and in groups. In
each of them is fixed the root of a hair ; that part

Fig. 147. —Longitudinal Section through a Human Hair.

1, Epidermis; 2, mouth of hair follicle1; 3, sebaceous follicle; 4, musculua
arrector plu ; 5, papilla of hair ; 6, adipose tissue. (Atlas.)

of the hair which projects beyond the general surface
of the skin is the shaft.

A very few places contain no hair-follicles, such,
for instance, as the volar side of the hand and foot,
and the skin of the penis.

In size, the hairs and hair-follicles differ in diffe-
rent parts. Those of the scalp, the cilia of the eyelids,

280 ELEMENTS OF HISTOLOGY. [Chap, xxxiv.

the hairs of the axilla and pubic region, those of
the male whiskers and moustache, are coarse and
thick, while the hairs of other places — e.g., the skin-
surface of the eyelids, the middle of the arm and
forearm, &c. — are very minute : but, as regards struc-
ture, they are all very much alike.

379. A complete hair and hair-follicle — that is, the
papillary hair of Unna — shows the following struc-
ture : —

The hair-follicle. Each hair-follicle commences
on the free surface of the skin with a funnel-
shaped opening or mouth; it passes in an oblique
direction through the corium into the subcutaneous
tissue, in whose middle strata — i.e., in the stratum
adiposum — it terminates with a slightly enlarged
extremity, with which it is invaginated over a rela-
tively small fungus-shaped papilla. This latter is of
fibrous tissue, containing numerous cells and a loop of
capillary blood-vessels.

Minute hairs do not reach with their follicles to
such a depth as the large coarse hairs, the former not
extending generally much farther than the deep part
of the corium. Degenerating and imperfect hairs
(see below) also do not reach to such a depth as the
perfect large hair-follicles. In individuals with
"woolly" hair — e.g., the negro race (C. Stewart), and
in animals with " woolly " hair, such as the fleece of
sheep — the deep extremity of the hair-follicle is
curved, sometimes even slightly upwards.

380. The structure of a hair-follicle is as follows
(Fig. 148) : There is an outer coat composed of
fibrous tissue; this is the fibrous coat of the hair-
sac. It is merely a condensation of the surround-
ing fibrous tissue, and is continuous with the
papilla at the extremity of the hair-follicle. About
the end of the hair-follicle, or sometimes as much
as in the lower fourth, there is inside of this

Chap. XXXIV.]

THE SKIN.

281

I'.

fibrous layer of the hair-sac a single continuous
layer of transversely or circularly-arranged spindle-
shaped cells, each with an oval flattened or staff-
shaped nucleus, completely resembling, and generally
considered to be,
non-striped mus-
cle cells. Inside
of this layer of
the hair-sac is
a glassy-looking, /,j
hyaline,basement
membrane, which
is not very dis-
tinct in minute
hairs, but is suffi-
ciently conspicu-
ous in large adult
hair - follicles.
This glassy mem-
brane, as it is
called, is a direct
continuation of

,i -i sheath ; g, glassy membrane ; h, fibrous coat of hair

tne Oasement sac ; i, lymph spaces in the same.

membrane of the

surface of the corium, and it can be traced as a delicate

membrane also over the surface of the hair-papilla.

381. Next to the glassy membrane is the outer
root-sheath, the most conspicuous part of the hair-fol-
licle. It consists of a thick stratified epithelium of
exactly the same nature as the stratum Malpighii of
the epidermis, with which it is directly continuous,
and from which it is developed. In the outer root-
sheath the layer of cells next to the glassy membrane
is columnar, just like the deepest layer of cells in the
stratum Malpighii ; then follow inwards several layers
of polyhedral cells ; and, finally, flattened nucleated
scales form the innermost boundary of the outer root-

Fig. 148.— Cross Section through a Human Hair
and Hair Follicle.

a. Marrow of hair ; 6, cortex of hair ; c, cuticle of
hair; d, Huxley's layer of inner root -sheath;
e, Hcnle's layer of inner root-sheath ; /, outer root-

282 ELEMENTS OF HISTOLOGY. [Chap, xxxiv.

sheath. The stratum granulosum of the stratum
Malpighii is not continued beyond the mouth of the
hair-follicle, but there it is generally very marked.
The outer root-sheath becomes greatly attenuated at
the papilla — -in fact, is there continuous with the cells
constituting the hair-bulb.

382. The centre of the hair-follicle is occupied by
the root of ike, hair, which terminates with an en-
larged extremity — the hair-bulb; this grasps the
whole papilla. The hair-bulb is composed of poly-
hedral epithelial cells, separated from one another
by cement substance, and continuous with the cells
of the extremity of the outer root-sheath, from
which they originate in the first instance ; just over
the papilla there is a special row of short columnar
cells, which are in an active state of multiplication,
and by which continuously new cells are formed.
Thus a gradual shifting of the cells of the hair-
bulb upwards into the cavity of the hair-follicle —
i.e., the hair — takes place ; but at the same time
these progressing cells become elongated, spindle-
shaped, and constitute the cells of the hair substance,
except in the very centre, where they remain poly-
liedral, so as to represent the cells of the marrow of
the hair, and in the periphery, where they remain
more or less polyhedral, so as to form the inner root-
sheath.

383. The root of the hair, except at the hair-
bulb, shows the following parts : The substance of the
hair, the cuticle, and the inner root-sheath. The
substance of the hair is composed of the hair fibres,
i.e., long thin fibres, or narrow long scales, each com-
posed of hyaline horny substance, and possessed of
a thin staff-shaped remnant of a nucleus. These
are held together by a certain amount of interstitial
cement substance. Towards the bulb they gradually
change into the spindle-shaped cells above men-

Chap. XXXIV.]

THE SKIN.

283

tioned. They can be isolated by strong acids and
alkalies. In pigmented hairs there occur numerous
pigment granules between the hair fibres, but also
diffused pigment in their substance. The same is
noticed with reference to the hair-bulb — viz., pigment
granules being present in the intercellular cement,
and pigment also in the cell substance. In the centre
of many hairs is a cylindrical space, containing gene-
rally one row of polyhedral cells, which are, to a great
extent, filled with air, and, in pigmented hair, also
with pigment granules.

384. On the surface of the hair substance is a thin
cuticle, a single layer of horny non-nucleated hyaline
scales arranged more or less transversely ; they are
imbricated, and, according to the degree of imbrica-
tion, the cuticle shows more or less

marked projections, which give to the
circumference of the hair the appear-
ance of minute teeth, like those of a saw.

385. The inner root-sheath in well-
formed, thick hairs, is very distinct,
and consists of a delicate cuticle next
to the cuticle of the hair ; then an
inner, or Huxley's, layer, which is a
single, or sometimes double, layer of
horny cubical cells, each with a rem-
nant of a nucleus ; and, finally, an
outer, or Ilenle's, layer — a single layer
of non-nucleated horny cubical cells.

The shaft of the hair (Fig.
149), or the part projecting over
the free surface of the skin, is of
exactly the same structure as the root, except that it
possesses no inner root-sheath.

386. As mentioned above, at the hair-bulb the
polyhedral cells constituting this latter gradually pass
into the different parts of the hair — i.e., marrow-sub-

149. — Longitu-
dinal View of the
Shaft of a Pi fo-
mented Human
Hair.

a, Marrow of hair ;
6, nbres of hair sub-
stance ; c, cuticle.

284

ELEMENTS OF HISTOLOGY, [chap, xxxiv.

stance, cuticle, and inner root-sheath — and the con-
tinual new production of cells over the papilla causes a
gradual progression and con-
version of the cells, and a
corresponding growth in
length of the hair shaft.

Pigmented hairs, as men-
tioned above, contain pig-
ment gran ules between — i. e. ,
in the interstitial substance
cementing together — the
hair fibres, and diffuse pig-
ment in their substance.
According to the amount
of these pigments, but es-
pecially of the interstitial
pigment granules (Pincus),
the colour of the hair is of
a greater or lesser dark
tint. In red hairs there is
chiefly diffuse pigment. In
white or fair hairs neither
the one nor the other
pigment is present ; in grey
there is air at least in
the superficial layers of the
hair substance, besides ab-
sence of pigment.

Sleek hairs are circu-
lar, curly oval, in cross-sec-
tion.

387. New formation
of hair (Fig. 150). -

TPtTciv-iT Vioiy V»o if -fino anrl

-^veiy hair, be it Due and

cnrkT.f r»r> fninV anrl Inner
Snort Or ttllCK ana long,

i1Tlr|/}v nnrrnnl nrmrlifirvn«
Under normal Conditions,

a liTrntprl
• limited

Fig. 150.— From a Section

through Human Scalp, showing

a degenerating Hair.

o. The epidermis ; 6, the hair ; c, the
outer root-sheath of the hair folli-
cle ; d, the sebaceous follicle ; e, the
arrector pili ; /, a cyst grown out
of the outer root-sheath ; g, the
hair-knoh ; h, the new outgrowth
of the outer root -sheath; *, the
new papilla. (Atlas.)

Chap, xxxiv.] THE SKIN. 285

tence, for its hair-follicle, including the papilla, sooner
or later undergoes degeneration, and subsequent to
this a new papilla and a new hair are formed in its
place. What happens is this — the lower part of
the hair-follicle, including the papilla and hair-bulb,
degenerates and is gradually absorbed. Then there
is left only the upper part of the follicle, and in
the centre of this is the remainder — i.e., non-degene-
rated portion — of the hair root. The fibres of this are
at the extremity fringed out and lost amongst the
cells of the outer root-sheath of the follicle. This
represents the hair-knob (Henle). Now, from the
outer root-sheath a cylindrical outgrowth of epithe-
lial cells into the depth takes place; against the
extremity of this a new papilla is made. In con-
nection with this new papilla, and in the centre of
that cylindrical outgrowth, a new hair and hair-bulb
are formed, and as these gradually grow outwards
towards the surface they lift, or rather push, the old
hair — i.e., the hair-knob — out of the follicle. The
outer part of the follicle of the old hair persists.

Thus we find in all parts of the skin where hairs
occur, complete or papillary hairs side by side with
degenerating hairs, or hair-knobs.

388. Development of hair.— In the human
foetus the hair-follicles make their first appearance about
the end of the third month, as solid cylindrical out-
growths from the stratum Malpighii. This is the rudi-
ment of the outer root-sheath. After having pene-
trated a short distance into the corium, this latter be-
comes condensed around it as the rudiment of the hair-
sac, and at the distal extremity forms the papilla
growing against the outer root-sheath and inva-
ginating it. In connection with the papilla a rapid
multiplication of the epithelial cells of this extremity
of the outer root-sheath takes place, and this forms the
hair-bulb, by the multiplication of whose cells the hair

286 ELEMENTS OF HISTOLOGY, [chap, xxxiv.

and the inner root-sheath are formed. As growth
and multiplication proceed at the hair-bulb, so the
new hair, with its distal-pointed end, gradually reaches
the outer surface. It does not at once penetrate the
epidermis, but remains growing and burrowing its
way for some time in the stratum corneum of the
epidermis in a more or less horizontal direction.

389. In many mammals occur, amongst ordinary
hairs, special large hairs, with huge hair-follicles
planted deeply into the subcutaneous tissue ; such
are the big hairs in the skin about the lips of the mouth
in the dog, cat, rabbit, guinea-pig, mouse and rat, <fec.
These are the tactile hairs. Their hair-follicle pos-
sesses a thick hair-sac, in which are contained large
sinuses intercommunicating with one another and
with the blood system ; these sinuses are separated by
trabeculse of non-striped muscular tissue, and repre-
sent, therefore, a cavernous tissue. The papilla is
very huge, and so is the outer root-sheath and the
hair-root in all its parts. There are vast numbers of
nerve-fibres, distributed and terminating amongst the
cells of the outer root-sheath (Arnstein).

390. With each hair-follicle is connected one or
two sebaceous follicles. These consist of several flask-
shaped or oblong alveoli, joining into a common short
duct opening into the hair-follicle near the surface —
i.e., that part called the neck of the hair-follicle.

The alveoli have a limiting membrana propria;
next to this is a layer of small polyhedral, granular-
looking, epithelial cells, each with a spherical or oval
nucleus ; next to this, and filling the entire space of
the alveolus, are large polyhedral cells, each with a
spherical nucleus \ the cell- substance is filled with
minute oil-globules, between which is left a sort of
honeycombed reticulated stroma. The cells nearer to
the centre of the alveolus are the largest. To-
wards the duct they become shrivelled up into an

chap, xxxiv.] THE SKIN. 287

amorphous mass. The duct itself is a continuation of
the outer root- sheath.

As multiplication goes on in the marginal layer of
epithelial cells — i.e.. those next the membrana propria
— the products of this multiplication are gradually
shifted forward towards the duct, and through this
into the neck and mouth of the hair-follicle, where
they constitute the elements of sebum.

There is a very characteristic misproportion be-
tween the size of the hair-follicle and that of the
sebaceous gland in the embryo and new-born, the
sebaceous gland being there so large that it forms the
most conspicuous part, the minute hairs (lanugo) being
situated, as it were, in the duct of the sebaceous
follicle.

391. In connection with each hair-follicle, espe-
cially where they are of good size — as in the scalp — •
there is a bundle, or rather group of bundles, of non-
striped muscular tissue ; this is the arrector pili. It is
inserted in the hair-sac near the bulbous portion of the
hair-follicle, and passes in an oblique direction towards
the surface of the corium, grasping, as it were, on its
way the sebaceous follicle, and terminating near the
papillary layer of the surface of the coriura. The
arrector pili forms with the hair-follicle an acute
angle — this latter being planted into the skin in an
oblique direction, as mentioned above — and conse-
quently, when the arrector contracts, it has the effect
of raising the hair follicle and hair (cutis anserina —
"goose's skin"), and of making the hair assume a
more upright position (causes it, as we say, to " stand
on end"). At the same time, it compresses the
sebaceous follicle, and thus facilitates the discharge of
the sebum.

392. The corium of the scrotum, of the nipple of
the breast, of the labia pudendi majora, and of the
penis, contains numbers of bundles of non-striped

288

ELEMENTS OF HISTOLOGY. [Chap, xxxiv.

muscular tissue (Kb'lliker), independent of the hairs ;
these run in an oblique and horizontal direction, and
form plexuses.

393. The nails (Fig. 151).— We distinguish the
body of the nail from the free margin and from the

Fig. 151.— Vertical Section through the Human Nail and Nail-bed.

a, Stratum Halpighii of nail-bed; 6, stratum granulosum of nail-bed; c, the
deep layers of the nail substance ; d, the superficial layers of same.

root ; the body is the nail proper, and is fixed on to
the nail-bed, while the nail-root is fixed on the nail-
matrix — i.e., the posterior part of the nail-bed. The
nail is inserted, with the greater part of its lateral
and the posterior margin, in the nail-groove, a fold

Chap, xxxiv.] THE SKIN. 289

by which the nail-matrix passes into the surrounding
skin.

394. The substance of the nail is made up of a
large number of strata of homogeneous horny scales —
the nail-cells — each with a staff-shaped remnant of a
nucleus.

The coriutn of the nail-bed is highly vascular ; it
is firmly fixed by stiff bands of fibrous tissue on the
subjacent periosteum ; it is covered with a stratum
Malpighii of the usual description, except that the
stratum granulosum is absent in the nail- matrix, but
is present in a rudimentary state in the rest of the
nail-bed. The nail itself represents the stratum
lucidum, of course of exaggerated thickness, situated
over the stratum Malpighii of the nail-bed. There
is no stratum corneum over the nail.

The stratum Malpighii and corium of the nail-bed
are placed into permanent minute folds, and the nail
possesses on its lower surface corresponding linear
indentations.

395. In the foetal nail-bed the stratum Malpighii
is covered with the usual stratum lucidum and stratum
corneum, but the former is the larger; by a rapid
multiplication of the cells of the stratum Malpighii,
and a conversion of its superficial cells into the scales
of the stratum lucidum, the foetal nail is produced.
At this early stage the nail is covered by stratum
corneum. By the end of the fifth month the margin
breaks through this stratum corneum, and by the
seventh month the greater part has become clear
of it.

396. The blood-vessels of the skin.— The
blood-vessels are arranged in different systems for the
different parts of the skin (Tomsa) : —

(a) There is, first, the vascular system of the
adipose tissue, differing in no way from the dis-
tribution of blood-vessels in fat tissue of other places.

290 ELEMENTS OF HISTOLOGY. [Chap, xxxiv.

(b) Then there is the vascular system of the hair-
follicles. The papilla has a capillary loop, or rather
a minute arteriole, a capillary loop, and a descending
vein, and the fibrous tissue of the hair-sac possesses
capillaries arranged as a network with elongated
meshes, with its afferent arteriole and efferent vein.

(c) The sebaceous follicle has its afferent arteriole
and efferent vein, and capillary networks surrounding
the alveoli of the gland. The arrector pili and other
bundles of non-striped muscular tissue possess capil-
lary networks with elongated meshes.

(d) The sweat-glands have an afferent arteriole,
from which proceeds a very rich network of capil-
laries, twining and twisting round the gland-tube.
The duct possesses its separate afferent arteriole and
capillaries, forming elongated meshes.

(e) The last arterial branches are those that reach
the surface of the corium, and there break up into a
dense capillary network with loops for the papillae.
In connection with these capillaries is a rich plexus of
veins in the superficial layer of the corium.

(jQ In the na,il-bed are dense networks of capil-
laries, with loops for the above-named folds.

397. The lymphatics. — There are networks of
lymphatic vessels in all strata of the skin ; they are,
more or less, of horizontal expansion, with oblique
branches passing between them. Their wall is a
single layer of endothelial cells, and some of them
possess valves. Those of the surface of the corium
take up lymphatics of the papillae. The subcutaneous
lymphatics are the biggest. The fat tissue, the sweat-
glands, and the hair-follicles possess their own lym-
phatic clefts and sinuses. The interfascicular spaces
of the corium and subcutaneous tissue are directly
continuous with the lymphatic vessels in these
parts.

398. The nerves. — The nerve-branches break up

Chap, xxxv.] CONJUNCTIVA AND ITS GLANDS. 291

into a dense plexus of fine nerve-fibres in the super-
ficial layer of the coriuin. This plexus extends hori-
zontally, and gives off numerous elementary fibrils
to the stratum Malpighii, in which they ascend verti-
cally and in a more or less wavy fashion towards the
stratum lucidum (Langerhans, Podkopaeff, Eberth,
Eimer, Ranvier, and others). According to some, they
terminate with a minute swelling ; according to others,
they form networks ; but they always remain between
the epithelial cells.

The subcutaneous nerve-branches of some places
— palm of hand and foot and skin of penis — give
off' single medullated nerve-fibres, terminating in a
Pacinian corpuscle, mentioned in a former chapter.
In the volar side of the fingers and toes there occur
iu some of the papillae of the coriuin the tactile or
Meissner's corpuscles, each connected with one or two
medullated nerve-fibres, as described in a previous
chapter. The outer root-sheath of the hair-follicles
contains the terminations of fine nerve-fibres, in the
shape of primitive fibrillse (Jobert, Bonnet, and
Arnstein). According to Jobert, the nerve-fibres
entwine the hair-follicle in circular turns. The tactile
hairs possess a greater supply of nerves than the
ordinary hair-follicles.

CHAPTEK XXXV.

THE CONJUNCTIVA AND ITS GLANDS.

399. (1) THE eyelids — The outer layer of the
eyelids is skin of ordinary description ; the inner is a
delicate, highly vascular membrane — the conjunctiva
palpebrce. This includes a firm plate — the tarsal-plate

292 ELEMENTS OF HISTOLOGY. [Chap, xxxv

— which is not cartilage, but very dense, white, fibrous
tissue. In it lie embedded the Meibomian glands.
These extend in each eyelid in a vertical direction
from the distal margin of the tarsal-plate to the free
margin of the eyelid ; in the posterior angle of this
margin lies the opening or mouth of each of the
Meibomian glands.

The duct of a Meibomian gland is lined with a
continuation of the stratified pavement epithelium,
lining the free margin of the lid ; it passes in the
tarsal-plate toward its distal margin, and takes up on
all sides short minute ducts, each of which becomes
enlarged into a spherical, saccular, or flask-shaped
alveolus. This is identical in structure and secretion
with the alveoli of the sebaceous follicles of the
skin.

400. The conjunctival layer is separated from the
subcutaneous tissue of the skin-layer of the eyelid by
the bundles of the sphincter orbicularis — striped mus-
cular tissue. Some bundles of this extend near the
free margin of the lid, and represent what is known
as the musculus ciliaris Biolani. This sends bundles
around the mouth of the Meibomian ducts.

401. At the anterior angle of the free margin of
the lid are the eyelashes or cilia, remarkable for their
thickness and rapid reproduction. Near the cilia, but
towards the Meibomian ducts, open the ducts of pecu-
liar large glands — the glands of Mohl. Each of these
is a wavy or spiral tube, passing in a vertical direction
from the margin of the lid towards its distal part ; it
completely coincides in structure to the large portion
of a sweat gland — i.e., that part containing a columnar
epithelial lining, and between this and the membrana
propria a longitudinal layer of non-striped muscular
cells.

The free margin is covered, as mentioned above,
with stratified pavement epithelium, into which the

chap, xxxv.] CONJUNCTIVA AND ITS GLANDS. 293

mucous membrane extends in the shape of minute
papillae. In the conjunctiva palpebrse the epithelium
is thin, but stratified pavement epithelium; there are
no papillsG, but the sub-epithelial mucosa — that is, the
layer situated between the epithelium of the surface
and the tarsal-plate — contains a dense network of
capillary blood-vessels.

402. Passing from the eyelids on to the eyeball,
we have the continuation of the conjunctiva palpebrae
— i.e., the fornix conjunctive — and, further, the con-
junctiva fixed to the sclerotic, and terminating at the
margin of the cornea — the conjunctiva bulbi. The
epithelium covering the conjunctiva fornicis and con-
junctiva bulbi is stratified epithelium, the superficial
cells being short columnar; next to the fornix the
superficial cells are beautiful columnar, and the
mucosa underneath the epithelium is placed in regular
folds (Stieda, Waldeyer). Towards the cornea the
epithelium of the conjunctiva assumes the character
of stratified pavement epithelium, and minute papillaB
extend into it from the mucosa.

403. The mucous membrane is fibrous tissue^
containing the networks of capillary blood-vessels.

Into the fornix lead minute mucous glands, em-
bedded in the conjunctiva fornicis ; they are the glands
of Krause. Similar glands exist in the distal portion
of the tarsal-plate.

404. The blood-vessels of the conjunctiva ter-
minate as the capillary network of the superficial
layer of the mucosa, and as capillary networks for the
Meibomian glands, Krause's gland, &c. Around the
corneal margin the conjunctival vessels are particu-
larly dense, and loops of capillaries extend from it
into the very margin of the cornea.

405. The lymphatics form a superficial and
deep network. Both are connected by short branches.
The deep vessels are possessed of valves. The super-

294 ELEMENTS OF HISTOLOGY. [Chap. xxxv.

ficial plexus is densest at the limbus cornese, and they
are in direct connection with the interfascicular
lymph clefts, both of the sclerotic and cornea. In
the margin of the lid the superficial lymphatics of
the skin anastomose with those of the conjunc-
tiva.

Lymph follicles occur in groups in the conjunctiva
of many mammals about the inner angle of the eye.
In the lower eyelid of cattle they are very con-
spicuous, and known as the glands of Bruch. They
are also well-marked in the third lid of many
mammals.

According to Stieda and Morano, isolated lymph
follicles occur also in the human conjunctiva.

406. The nerves are very numerous in the con-
junctiva • they form plexuses of non-medullated fibres
underneath the epithelium. From these plexuses fine
fibrils pass into the epithelium of the surface, between
whose cells they terminate as a network (Helfreich,
Morano). End bulbs of Krause occur in great num-
bers in man and calf. They have been mentioned in
a former chapter.

407. (2) The lachrymal glands are identical
in structure with the serous or true salivary
glands. The arrangement of the connective tissue
stroma, the nature and structure of the ducts — espe-
cially of the intralobular ducts — and alveoli, the dis-
tribution of blood-vessels and lymphatics, are exactly
the same as in the true salivary glands. Reichel
has found that the epithelial cells lining the
alveoli are well defined, conical or cylindrical, trans-
parent and slightly granular during rest ; but
during secretion they grow smaller, more opaque
and granular, their outlines not well defined, and
the nucleus becomes more spherical and placed more
centrally.

408. In most mammals there is in the inner

Chap, xxxvi.] THE CORNEA. 295

angle of the eye, and closely placed against the sur-
face of the eyeball, a gland, called Hardens gland.
According to Wendt, this is either a true serous
gland, like the lachrymal — as in the ox, sheep, and
pig — or it is identical in structure with a sebaceous
gland, as in the mouse, rat, and guinea-pig ; or it
consists of two portions, one of which (white) is
identical with a sebaceous, while the other (rose-
coloured ) is a true serous gland ; such is the case in
the rabbit and hare. According to Giacomini, a
rudiment of Harder's gland exists also in the ape
and man.

CHAPTER XXXYI.

THE CORNEA, SCLEROTIC, LIGAMENTUM PECTINATUM,
AND CILIARY MUSCLE.

409. I. THE cornea (Fig. 152) of man and many
mammals consists of the following layers, counting
from front to back : —

(1) The epithelium of the anterior surface (see
Fig. 15) ; this is a very transparent, stratified, pave-
ment epithelium, such as has been described in par.
22. It is directly continuous with the epithelium of
the conjunctiva, but it is more transparent ; in dark
pigmented eyes of mammals the epithelium of the
conjunctiva is also pigmented. In these cases the
pigment, as a rule, does not pass beyond the margin
of the cornea.

410. (2) Next follows a homogeneous elastic mem-
brane, Bowman 's membrane, or elastica anterior. It
is best shown in the human eye, but is present, even
though only rudimentary, in the eye of mammals.

296

ELEMENTS OF HISTOLOGY. [Chap, xxxvi.

(3) Then follows the ground substance, or sub-
stantia propria, of the cornea. This is composed of

lamellae of bundles
of fibrous connective
tissue. Neighbouring
lamellae are connected
with one another by
oblique bundles.

The fibre bundles
within each lamella
run parallel to the sur-
face of the cornea, but
may cross one another
under various angles.

In the anterior
layer of the ground
substance some of the
bundles pass through
several lamellae in an
oblique manner ; they
represent the fibrae
arcuatae.

The fibrils within
the bundles, and the
bundles, and the la-
mellae of bundles are
held together by an
interstitial, albumin-
ous, semi-fluid, cement
substance, which, like
other similar intersti-
tial substances, be-

Fig. 152.— From a Vertical Section , ., , , ' ,.

through the Membranes of the Eye longs to the globulins,

°f * Child, and is soluble in 10

a, Cornea; 6, sclerotic: c, iris; d, processus -r.p.-r
cilinris; e, ligamentum pectinatum ; /, Per

tsnlinp
SailllC

ciliary muscle, its meridional bundles iff, firm /^«lr>lT\x7-e>irrri>c>T> ^im
choroid membrane ; A, the retina of the ora tlOn (bcliweigger bei-

Spbincter pupillae in cross A few elastic

Atia)

del).

chap, xxxvi.] THE CORNEA. 297

fibrils are seen here and there. Between the lamellae
are left the lacunae and canaliculi for the branched,
flattened, nucleated corneal corpuscles, described in
a previous chapter (Figs. 25, 26). They anasto-
mose with one another within the same plane, and
also, to a limited degree, with those of neighbouring
planes.

411. (4) The membrana Descemcti, or elastica
posterior, is a resistent elastic membrane, conspicuous
by its thickness in all cornese.

(5) The posterior surface of this membrane is
covered with a mosaic of beautiful polygonal endo-
thelial cells, each with an oval nucleus — the en-
dothelium of Descemet's membrane. Under stimu-
lation these cells contract. At first they appear
slightly and numerously branched, but gradually
their processes become longer and fewer, and
ultimately they are reduced to minute clumps
of nucleated protoplasm, each with a few long pro-
cesses.

There are no blood-vessels in the normal cornea,
except in fcetal life, when there is underneath the
anterior epithelium a plexus of capillaries.

The lymphatics are represented as the inter-
communicating lymph-canalicular system — i.e., the
lacunae and canaliculi of the corneal corpuscles ; and
in connection with these are lymph channels lined
with a continuous endothelium and containing the
nerve bundles.

412. The nerves (Figs. 68, 69, 70) are distri-
buted as the nerves of the anterior layers, and as
those of the Descemet's membrane. The first form
rich plexuses of fibrillated axis cylinders, with trian-
gular nodal points (Cohnheim), in the anterior layers of
the ground substance ; from this plexus pass obliquely
through Bowman's membrane short branches — the
rami perforantes (Kolliker) — and these immediately

298 ELEMENTS OF HISTOLOGY. [Chap, xxxvi.

underneath the epithelium break up into their con-
stituent primitive fibrils, the latter coming off the
former brush-like (Cohnheim). These primitive
fibrillse ultimately ascend into the anterior epithelium
(Hoyer, Cohnheim, and others), where they branch,
and nearly reach the surface. They always run
between the epithelial cells, and are connected into
a network. According to some observers, they termi-
nate with free ends, pointed or knobbed ; but according
to others, with whom I agree, these apparent free ends
are not in reality free endings.

413. The nerves of Descemet's membrane form
also a plexus of non-medullated fibres in the posterior
layers of the ground substance; from them come
off vast numbers of primitive fibrillae, running a more
or less straight and long course, crossing one another
often under right angles ; they give off very fine
fibrils, which are closely associated with the corneal
corpuscles, without, however, really becoming con-
tinuous with their protoplasm.

414. II. The sclerotic consists of lamellae of
tendinous tissue. The bundles of fibrous tissue are
opaque as compared with those of the cornea, although
they pass insensibly into them. There are lymph
clefts between the lamellae and trabeculas, and in
them lie the flattened connective tissue corpuscles,
which, in the dark eyes of some mammals only, contain
pigment granules. Numerous elastic fibrils are met
with in the inner layers of the sclerotic.

415. Between the sclerotic and choroid membrane
is a loose fibrous tissue, which acts also as the sup-
porting tissue for the blcod-vessels passing to and from
the choroid. The part of this loose tissue next
to the sclerotic, and forming part, as it were, of
the sclerotic, contains, in dark eyes of mammals,
numerous pigmented connective tissue corpuscles ; it
is then called lamina ftisca. The rest— -i.e., next

Chap. XXXVI.] LlGAMENTUM ^ECTINATUM. 299

to the choroid membrane — is the supra-choroidal
tissue.

416. There are blood-vessels in the sclerotic, which
belong to it : they are arterioles, capillaries, and
veins ; in addition to these are the vascular branches
passing to and from the choroid.

417. III. The ligamentum pectinatum
iridis (see Fig. 152) is a conical mass of spongy tissue,
joining firmly the cornea and sclerotic to the iris and
ciliary processes. It forms an intimate connection, on
the one hand, with the junction of cornea and sclerotic,
and on the other, with that of the iris and ciliary pro-
cesses. This ligament is composed of trabeculae and
lamellae of stiff elastic fibres, forming a continuity, on
the one hand, with the lamina Descemeti of the cornea
and the elastic fibres of the sclerotic, and on the other,
with the tissue of the ciliary border of the iris. The
trabeculse anastomose, so as to form a honeycombed
plexus, and the spaces in this plexus are lined
with a layer of flattened endothelial cells, directly
continued from the endotheliurn of Descemet's mem-
brane, on the one hand, and with the layer of endo-
thelial cells covering the anterior surface of the iris,
on the other hand. In some mammals, the spaces
in the ligamentum pectinatum at the iris end are
very considerable, and are called the spaces of
Fontana.

The interlamellar and interfascicular lymph-
spaces of the sclerotic form an intercommunicating
system.

The nerves form a dense plexus of non-medullated
fibres in the tissue of the sclerotic (Helfreich).

At the point of junction of the cornea and sclerotic,
but belonging to the latter, and in the immediate
neighbourhood of the ligamentum pectinatum iridis,
is a circular canal — the canal of Scldemm; this is
lined with endothelium, and is considered by some

300 ELEMENTS OF HISTOLOGY. [Chap, xxxvn.

(Schwalbe) as a lymphatic canal; by others (Leber)
as a venous vessel.

418. IY. The ciliary muscle (Fig. 152) or
tensor choroidese, is fixed to this ligamentum pecti-
natum ; it is composed of bundles of non-striped
muscular tissue. This muscle consists of two parts :
(a) one of circular bundles nearest to the iris — this
is the portio Miilleri ; (b) the greater part is composed
of radiating bundles, passing from the ligamentum
pectinatum in a meridional direction for a consider-
able distance backwards into the tissue of the choroid
membrane. It occupies the space between the liga-
mentum pectinatum, sclerotic, ciliary processes, and
the adjoining portion of the choroid membrane.
The bundles of the muscle are arranged more
or less in lamellae; within each lamella they form
plexuses.

A rich plexus of non-medullated nerve-fibres, with
groups of ganglion cells, belongs to the ciliary muscle.

CHAPTER XXXVII.

THE IRIS, CILIARY PROCESSES, AND CHOROIDEA.

419. I. THE iris consists of the following layers : —

(1) The endothelium of the anterior surface : trans-
parent, flattened, or polyhedral cells, each with a
spherical or slightly oval nucleus ; in dark-coloured
eyes of man and mammals brown pigment granules
are contained in the cell-substance.

(2) A delicate hyaline basement membrane : it is
continuous through the trabeculse of the ligamentum
pectinatum, with the meinbrana Descemeti of the
cornea.

Chap, xxxvii.] THE IRIS. 301

(3) The substantia propria : this is the ground-
substance ; it consists of fibrous connective tissue in
bundles, accompanying the blood-vessels, which are
very numerous in the tissue of the iris. Many
connective tissue corpuscles are found in the sub-
stantia propria ; they are more or less branched, and
many of them contain, in all but albino and blue
eyes, yellowish-brown pigment granules. The colour
of the iris varies according to the number of these
pigmented connective tissue cells, and to the amount
of the pigment granules present in them.

(4) A hyaline delicate basement membrane limits
the substantia propria at the posterior surface ; this
is an elastic membrane, and is continued over the
ciliary processes and choroid as the lamina vitrea.

420. (5) The last layer is the epithelium of the
posterior surface : this is a layer of polyhedral cells,
filled with dark pigment granules, except in albinos,
where there are no pigment granules. This endo-
thelium is called the uvea, or tapetum nigrum. The
interstitial cement substance between the cells is not
pigmented, but transparent.

The name " uvea " is sometimes applied to the
whole of the iris, ciliary processes, and choroid mem-
brane.

In blue eyes the posterior epithelium is the only
pigmented part of the iris, and so it is also in the
iris of new-born children ; hence, their eyes are blue.
Such iris appears blue because its dull tissue is viewed
on dark ground — i.e., on the pigmented epithelium of
the posterior surface.

421. Near the pupillary border the posterior sec-
tion of the substantia propria contains a broad layer
of circular bundles of non-striped muscular tissue :
this is the sphincter pupillce. In connection with this
are bundles of non-striped muscular fibres, passing in
a radiating direction towards the ciliary margin of the

302

ELEMENTS OF HISTOLOGY. [Chap, xxxvn.

-f

iris : these are the bundles of the dilatator pupillce,
forming a sort of thin membrane near the posterior
surface of the iris (Henle and others). At the ciliary
margin the bundles take a
circular direction, and form a
plexus (Ivaiioff).

422. The blood-vessels
(Fig. 153) of the iris are
very numerous. The arteries
are derived from the circulus
arteriosus iridis major, situated
at the ciliary margin of the
iris, and from the arteries of
the ciliary processes. These
arteries run in a radiating
direction towards the pupillary
margin, where they terminate
in a dense network of capillaries
for the sphincter pupillse. But
there are also numerous capil-
lary blood-vessels of a moie or
less longitudinal direction near
the posterior surface of the iris.
The veins accompany the arte-
ries, and both are situated in
the middle stratum of the
substantia propria.

In the sheath of the blood-
vessels are lymph clefts and
lymph sinuses ; there appear to
be no other lymphatics.

423. The nerve -fibres
are very numerous (Arnold,
Formad), and in the outer or

ciliary portion of the iris form a rich plexus, from
which are derived, (a) networks of non-medullated
fibres for the dilator pupillse; (b) a network of fine

Fig. 153. — Blood-vessels
(injected) of the Iris
and Choroid Membrane
of the Eye of a Child.

a. Capillaries of the choroid ;
6, ora serrnta ; c, blood-
vessels derived from d,
those of the ciliary pro-
cesses, and from e, those
of the iris ; /, capillary net-
work of the pupillary bor-
der. (.Kb'lliker, after Arnoid.\

Chap. XXXVIL] THE ClLIARY PROCESS. 303

non-medullated fibres for the anterior surface ; and
(c) a network of non-medullated fibres for the
sphincter pupillse.

The capillary blood-vessels are also accompanied
by fine nerve-fibres (A. Meyer), and, according to
Fa her, there exist ganglion cells in these nerve net-
works.

424. II. The ciliary processes are similar in
structure to the iris, except, of course, that they do
not possess an anterior endothelium or an anterior
basement membrane. The substantia propria is
fibrous tissue with elastic fibres and numerous
branched cells, pigmented in dark (but not in blue)
eyes. The posterior basement membrane is very
thick, and is called the lamina vitrea ; in it may be
detected bundles of fine fibrils. It possesses perma-
nent folds arranged in a network (H. Miiller). The
inside of it is covered with a layer of pigmented poly-
hedral epithelium, the tapetum nigrum : the cells are
polygonal when viewed from the surface. The in-
dividual cells are separated by thin lines of a trans-
parent cement substance. This pigmented epithelium
is covered with a layer of transparent columnar
epitheloid cells, each with an oval nucleus. These are
closely fixed on the tapetum nigrum, and represent a
continuation of the retina over the ciliary processes :
this is the pars ciliaris retinae, (Fig. 154).

425. The arterial branches for the ciliary processes
and muscle are chiefly derived from the circulus arte-
riosus iridis major, and form a dense network of
capillaries for the former; to each of these corre-
sponds a conical group of capillaries (Fig. 153).

426. III. The choroid membrane consists —
counting from outwards, i.e.. from the sclerotic, inwards,
i.e., towards the retina — of the following layers : —

(1) The membrana supra-choroidea. This is a
continuation of the sclerotic, with which it is identical

304 ELEMENTS OF HISTOLOGY. [Chap, xxxvu.

in structure ; the spaces between its lamellae are
lined with endothelium, and represent lymph spaces
(Schwalbe).

(2) Next follows an elastic layer which contains
networks of elastic fibres, the branches of the arteries

Fig. 154.— From a Vertical Section through the Ciliary Processes of
the Ox's Eye.

a, Fibrous tissue with picrmented cells ; 6, loose fibrous tissue forming the
proper membrane of the ciliary process ; c, the pigmented epithelium covering
the posterior surface of the ciliary process; d, the epitheloid cells, forming
the pars ciliaris retinae covering the back of the ciliary processes ; e, Zonula
Zinnii, with bundles of fibres. (Atlas.)

and veins, and, in its outer portion, pigmented cells
(Fig. 155).

427. (3) Then follows the membrana chorio-
capillaris, a dense network of capillary blood-vessels
embedded in a tissue containing numerous branched

Chap. XXXVIII.]

THE LENS.

3°5

and unbranched pigmented and unpigmented connec-
tive-tissue cells.

(4) The lamina vitrea ; and, finally,

(5) The tapetum nigrum, or the pigmented epithe-
lium, which, however, is considered part of the
retina. In the region of the ora serrata of the
retina also — i.e., next

to the ciliary processes
— this zone of the
choroidea is lined
with a layer of trans-
parent, columnar,
epitheloid cells, re-
presenting the pars
ciliaris retinae.

428. The arterise
ciliares breves and recurrentes, situated in the outer
part of the choroidal tissue, form ultimately the dense
networks of capillaries for the chorio- capillaries. The
veins derived from this pass into the outer part of
the choroid, where they anastomose so as to form the
peculiar large veins, which are called the venaj
vorticosse.

Fis

. 155.— Pigmented Connective Tissue
ells of the Choroid Coat. (Atlas.)

CHAPTER XXXVIII.

THE LENS AND VITREOUS BODY.

429. (1) THE lens consists of a thick, firm, elastic
capsule and of the lens substance. The former shows
fine longitudinal striae, and diminishes in thickness
towards the posterior pole of the lens. The surface
of the capsule facing the anterior surface of the lens-
substance is lined with a single layer of polyhedral,
granular-looking, epithelial cells, each with a spherical
or oval nucleus. This epithelium stops as such at the

3°6

ELEMENTS OF HISTOLOGY, [ciiap. xxxvin.

margin of the lens, where its cells, gradually elonga-
ting, pass into the lens-fibres. The nuclei of these
lie in a curved plane belonging to the anterior half of
the lens : this is the nuclear zone. The lens-substance
consists of the lens-fibres. These are band-like, hexa-
gonal in transverse section ; their outline is beset
with numerous fine ridges and furrows, which in
neighbouring fibres, fitting the one into the other,
form a firm connection between the fibres (Valentin,
Henle, Kolliker, and others). The fibres of the
peripheral portion are broader and thicker, and their
substance less firm than those of the centre — i.e., of
the lens-nucleus. The substance of the lens-fibres is
finely granular and delicately and longitudinally
striated.

430. The lens fibres (Fig. 156) are arranged in
concentric lamellae, each consisting of a single layer of
fibres joined by their broad
surfaces. Each fibre is slightly
enlarged at the extremities ;
and in each lamella the fibres
extend from the anterior to the
posterior surface. Their ex-
tremities are in contact with
the ends of the fibres of the
same lamella in the sutures, or
the rays of the so-called lens
stars. In the lens of the new-
born child, the stars of both
anterior and posterior lamellae
possess three such rays, while
in the adult each of these rays
has secondary rays. In these
rays there is a homogeneous thin layer of an albu-
minous cement substance ; a similar substance in
minute quantity is also present between the lamellae,
and in it occur smaller or larger clefts and channels,

Fig. 156.— From a Section
through the Lens of
Dog.

Showing four lamellae ; in
each the component lens-
fibres are cut across ; they
appear as flattened hexa-
gons. (Atlas.)

Chap, xxxviii.] THE VITREOUS BODY. 307

which evidently carry the nutritious fluid for the lens-
fibres.

431. (2) The vitreous body is a fluid substance
enclosed in a delicate hyaline capsule — the membrana
hyaloidea. This membrane, at the margin of the
fossa patellaris of the vitreous body — i.e., the fossa in
which the lens is lodged — but without covering it,
passes as the zonula ciliaris, or zonula Zinnii, or
suspensory ligament of the lens, to the margin of the
latter, to which it is firmly adhering. So it adheres
also to the surface of the ciliary processes. The
zonula Zinnii is hyaline and firm, and is strengthened
by numbers of bundles of minute stifl' fibrils.

Between the suspensory ligament of the lens, the
margin of the lens and of the fossa patellaris is a
circular lymph space, called the canalis Petiti.

Beneath the membrana hyaloidea are found iso-
lated nucleated granular-looking cells (the subhyaloid
cells of Ciaccio), possessed of amoeboid movement
(Ivanoff).

432. The substance of the corpus vitreum appears
differentiated by clefts, concentric in the peripheral,
radiating in the central, part (Brticke, Hannover,
Bowman, Ivanoff, Schwalbe). But these do not
contain any distinct membranous structures (Stilling,
Ivanoff, Schwalbe).

The canalis hyaloideus, or canal of Stilling, extends
from the papilla nervi optici to the posterior capsule
of the lens, and is lined with a continuation of the
membrana hyaloidea.

433. In the substance of the corpus vitreum occur
isolated nucleated cells ; they have amoeboid move-
ments, and some contain vacuoles, from commencing
degeneration. They are all identical with white
blood-corpuscles (Lieberkiihn, Schwalbe).

Fine bundles of fibrils are occasionally seen in the
substance of the vitreous body.

3o8

[Chap. XXXIX.

— a.

CHAPTER XXXIX.

THE RETINA.

434. THE retina (Fig. 157) consists of the following
layers, counting from inwards towards the choroid mem-
brane:— (1) The
membrana limitans
interna, which is
next to the mem-
brana hyaloidea of
the vitreous body ;
(2) the nerve-fibre
layer; (3) the layer
of. ganglion cells;
(4) the inner gran-
ular or inner mole-
cular layer; (5) the
layer of inner
nuclei ; (6) the
outer granular, or
outer molecular, or
internuclear layer ;
(7) the layer of
outer nuclei ; (8)
the membrana
limitans externa ;
(9) the layer of
rods and cones ;
and (10) the pig-
mented epithelium
of the retina, or the tapetum nigrum mentioned above,
which forms, at the same time, the inner lining epithe^
Uum of the choroid membrane.

Tig. 157.— Irom a Transverse Section
through the Eye of Sheep; Peripheral
Portion of Eetina.

a, The inner part of the sclerotic 6, the supra-
rhoroidal 'piemen ted) lamellae ; !, d, the layers
" choroid coat ; e, the pigmented epithe-

of the

lium of the retina ; f, the layer of rods ; ~g, the
cones ; h, the layer of outer nuclei ; i, the outer
molecular layer; j, the layer of inner nuclei;
k, the inner molecular layer ; i, the layer of
panglion cells, with the radial or Muller's
fibres between ; m, the layer of nerve-fibres.
(Atlas.)

Chap. XXXIX.]

THE RETINA.

309

435. From this arrangement is excepted — (a) the
papilla nervi optici, (6) the macula lutea and fovea
centralis retinae, and (c) the ora serrata of the retina.

(a) The papilla nervi optici, or the blind spot of

Fig. 158.— Diagram of the Ner- Fig. 159.— Diagram of the Connective
vons Elements of the Retina. Tissue Substance of the same.

2, Nerve.flbres ; 3, ganglion cells; 4, inner molecular layer ; 5, inner nuclear

layer; 6, outer molecular layer; 7, outer nuclear layer: 8, the membrana

limitans externa ; 9, the rods and cones. (Max Schultze.)

the retina, represents the entrance of the optic nerve-
fibres into the retina; thence, as from a centre,
they spread out in a radiating direction into the
saucer-shaped retina, of which they form the internal

310 ELEMENTS OF HISTOLOGY, [chap, xxxix.

layer. No other elements of the retina are present at
the papilla, except a continuation of the limitans
interna. At the papilla nervi optici the arteria and
vena centralis nervi optici also enter, and spread
out with their branches in the inner layers of the
retina. A large lymph space is also found there.

(6) The macula lutea and fovea centralis will be
considered after the various layers of the retina have
been described.

(c) At the ora serrata all cellular and nuclear
elements of the retina — except the pigmented epithe-
lium— and the nerve-fibres, come to an end ; but the
limitans interna, with its peculiar radial or M filler's
fibres, is continued over the ciliary processes in the
shape of columnar epibheloid nucleated cells men-
tioned above : this is the pars ciliaris retinae.

436. Structure of the layers of the retina (Figs.
158, 159).

(1) The membra BISI limitans interna is
composed of more or less polygonal areas, which are
the ends or bases of pyramidal, finely-striated fibres
— the radial fibres of Muller. Each radial fibre passes
from the limitans interna in a vertical direction
through all layers to the limitans externa, and on its
way gives off numerous lateral branchlets, fibrils, and
membranes, which anastomose with one another so as
to form a honeycombed stroma or matrix for all
cellular and nuclear elements of the retinal layers.
In the nerve-fibre layer the radial fibres are thickest,
this being, in fact, the pyramidal basis ; in the inner
nuclear layer each possesses an oval nucleus.

437. (2) The layer of nerve- fibres.— The
optic nerve-fibres at their entrance into the eyeball
lose their medullary sheath, and only the transparent
axis cylinder is prolonged into the retina. In man,
medullated nerve-fibres in the retina are very excep-
tional ; in the rabbit there are two bundles, whose

&t !

Chap, xxxix.] THE RETINA.^ N I V E BI$ I 1

fibres retain their medullary sheath in the retina
(Bowman). The nerve-fibres remain grouped in
bundles in the retina, and even form plexuses. For
obvious reasons, the number of nerve-fibres in the
nerve-fibre layer diminishes towards the ora serrata.

438. (3) The layer of ganglion cells. — There
is one stratum of these cells only, except in the
macula lutea, where they form several strata. Each
cell is multipolar, and possessed of a large nucleus.
One process is directed inwards and becomes con-
nected with a fibre of the nerve-fibre layer. Several
processes pass from the opposite side of the cell, and
enter the next outer layer, i.e., the inner molecular
layer.

According to Max Schultze and others, they break
up there into a reticulum of fibrils which is part of
this molecular layer ; but according to Retzius, Mans,
and Schwalbe, they simply pass through the inner
molecular layer.

The ganglion cells are separated from one another
by the radial fibres of Miiller.

439. (4) The inner molecular layer is a
fine and dense reticulum of fibrils, with a small
amount of granular matter between. The fibrils are
connected with lateral branchlets of the radial fibres
of Miiller. This layer is, on account of its thickness,
a conspicuous part of the retina. In lower vertebrates
it appears stratified.

440. (5) The inner nuclear layer contains in
a honeycombed matrix of a hyaline stroma numerous
nuclei, in two, three, or four layers. In the am-
phibian retina these form a larger number of layers.
Some oblong nuclei of this layer belong, as has been
mentioned above, to the radial fibres of Miiller.
Next to the molecular layer are small nuclei belonging
to flattened branched cells (Vintschgau). But the
great majority of the nuclei of this layer are slightly

312 ELEMENTS OF HISTOLOGY. [Chap, xxxix.

oval, with a reticulum in their interior. Each belongs
to a spindle-shaped cell, with a small amount of proto-
plasm around the nucleus ; it is, in fact, a bipolar gang-
lion cell (Max Schultze), of which one process (the
inner) passes as a fine varicose fibre into and through
the inner molecular layer, to become connected with
the outer processes of the ganglion cells (Retzius,
Schwalbe), while the other or outer process passes into
and through the next outer layer of the retina,

(6) Tlie outer molecular layer is of exactly
the same structure as the inner molecular layer — i.e.,
a fine reticulum of fibrils — but is considerably thinner
than the latter.

441. (7) The outer nuclear layer contains, in
a honeycombed matrix, a large number of oval nuclei.
In the retina of man and mammals these nuclei are
always present in considerably greater numbers or
layers than those of the inner nuclear layer, but in
the amphibian animals the reverse is the case. They
are smaller than the nuclei of the inner nuclear layer,
and show often a peculiar transversely-ribbed differ-
entiation of their contents (Henle, Krause). The
honeycombed matrix of this layer is in connection
with lateral branch! ets of the radial fibres of Muller,
with which it forms a sort of limiting delicate mem-
brana propria at the outer surface of the layer ;
this is

442. (8) The limitaus externa. — The nuclei of
the outer nuclear layer next to this limitans externa are
connected, in the retina of man and mammals, with
the cones, while the nuclei farther inwards from the
limitans externa are connected with the rods. In
both instances the connection is established through
holes in the limitans externa. Each nucleus of
the outer nuclear layer is, in reality, that of a
spindle-shaped cell with a minute amount of proto-
plasm ; this is prolonged outwards, as the outer part

Chap, xxxix.] THE RETINA. 313

of the rod- or cone-fibre, to become connected with a
rod or cone respectively, while inwards it passes into
a longer, more conspicuous fibre, the inner part of the
rod- or cone-fibre. This branches, and penetrating
into the outer molecular layer, is lost with its
branchlets among the fibrils of this layer.

443. (9) The rods and cones. — Each rod is
of cylindrical shape, with rounded or conical outer
extremity ; it consists of an outer and inner member,
joined by linear cement. Its substance is bright and
glistening, and that of the outer member is composed
of the neurokeratin of Kiilme and Ewald. In
the fresh state the outer member shows a more or
less fine and longitudinal striation, due to longitudinal
fine ridges and furrows (Hensen, Max Schultze).
After certain reagents, such as serum, liquor potassae,
the outer rod-member disintegrates into numerous
transverse, thin, homogeneous-looking discs (Hannover).
The inner member in the human rods is slightly
broader than the outer ; it is pale or finely and longi-
tudinally striated, and contains in many instances a
peculiar lenticular structure ; in the human and
mammalian retina this is absent, but in its stead is a
mass of longitudinal fibrils (Max Schultze). The
inner member passes through a hole in the limitans
externa, and becoming thinner, represents the outer
part of the rod-fibre.

444. Each cone is composed of an outer, short,
pointed, conical member, and an inner larger member
with convex surface: this is the body of the cone.
The outer member of the cone separates under certain
conditions also into thin transverse discs. The body
of the cone is longitudinally and finely striated.
The outer extremity of the body of the cones in
many birds, reptiles, and amphibia contains a spheri-
cal corpuscle of red, orange, yellow, green, or even
blue colouration.

3*4

ELEMENTS OF HISTOLOGY. [Chap, xxxix.

The cones are shorter than the rods, the pointed
end of the former not reaching
much farther than the junction
between the outer and inner
members of the rods.

In the macula lutea and
fovea centralis of man and
most mammals there are pre-
sent cones only, and towards
the peripheral portion of the
retina they gradually de-
crease in numbers; in the
peripheral part there are only
rods. But in birds the cones
exceed the rods everywhere.

In the bat and mole the
macula lutea possesses no
cones, and in the owl, rat,
mouse, guinea-pig, and rabbit,
they are few and small.

445. The outer members
of the rods (only) contain in
the fresh and living state a
peculiar diffuse purplish colour
(Leydig, Boll, Kiihne) : -this
is the visual purple or Hhod-
opsin of Kiihne. When
exposed to sunlight it
passes through red, orange,
and yellow, and finally
disappears altogether — be-
comes bleached. There is
no visual purple in the rods
of Rhinolophus hipposideros,
fowl and pigeon ; in those
retinue in which the cones
contain coloured globules (see

Fig. 160.— Vertical Section
through the Frog's Eetina.

•i, The pigiuented epithelium
of the retina or tapetum
nigrum ; 6, the outer mem-
bers of the rods, those of
cones between them ; c, the
inner members of the rods
and cones; d, hnritans ex-
terna ; e, the outer nuclei ; /,
the outer molecular layer; g,
the inner nuclei ; h, the inner
molecular layer ;i. the nuclei

of the ganglion cells ; j, the

Ibres; the py
extremities of the radial

nerve-fibres"; the pyramidal
extremities of the radial
fibres are well shown. (Atlas.)

Chap. XXXIX.] THE R-ETINA. 315

above) the surrounding rods are wanting in the visual
purple.

The visual purple stands in an intimate relation to
the pigmented epithelium of the retina, since a
retina regains its visual purple after bleaching, when
replaced on the pigmented epithelium (Kiihne). This
holds good, of course, only within certain limits.

446. (10) The pigmented epithelium (Fig.
160), or tapetum nigrum, is composed of polygonal pro-
toplasmic cells, which, when viewed from the surface,
appear as a mosaic, in which they are separated from
one another by a thin layer of cement substance. Each
cell shows an outer non-pigmented part, containing the
slightly-flattened oval nucleus, and an inner part next to
the rods and cones, which is full of pigmented crystalline
rods (Frisch). This part is prolonged into numerous
fine fibrils, each containing a row of the pigmented
particles, and these fibrils pass between the outer
members of the rods, to which they closely adhere, and
which in reality become almost entirely ensheathed
in them (M. Schultze). Each cell supplies a number
of rods with these fibrils. Sunlight causes a protru-
sion of these fibrils from the cell body, whereas in
the dark they are retracted (Kiihne), in a manner
similar to what takes place in pigmented connective
tissue cells. (See par. 43.) The tint of this pigment
is darker in dark than in light eyes. It is bleached
by the light in the presence of oxygen (Kiihne), but
it persists in the absence of oxygen (Mays).

447. The macula lutea (Fig. 161) of man and
ape contains a diffuse yellow pigment, between the ele-
ments of the retina (M. Schultze). In man and most
mammals, as mentioned above, there are hardly any
rods here, but cones only ; these are longer than in
other parts, and in the fovea centralis they are
longest, and, at the same time, very thin. Since
there are few rods here, the nuclei of the outer nuclear

ELEMENTS of HISTOLOGY. [Chap, xxxix.

layer are limited to a very few layers (generally about
two) next to the membrana limitans externa. For
this reason, the rest of the outer nuclear layer is
occupied by the cone-fibres only, which in the fovea
centralis pass in a slanting, or almost horizontal,

Fig. 161. — Prom a Vertical Section through the Macula Lutea and
Fovea Centralis,

a, Nerve-fibres ; 6, ganglion cells : c, inner molecular layer ; d, inner nuclei ;
e, outer molecular layer ; /, cone-fibres ; g, cones. (Diagram by Max Scbultze.)

direction sideways into the outer molecular layer.
The ganglion cells form several strata in the macula
lutea. In the fovea centralis are present the cones
(very long and thin), the limitans externa, the few
nuclei representing the outer nuclear layer, a thin
continuation of the inner molecular layer, and the
limitans interna.

448. In the embryo, the primary optic vesicle
becomes invaginated so as to form the optic cup,
which consists of two layers — an outer, giving origin
fco the pigmented epithelium ; and an inner, the retina

Chap, xxxix.] THE RETINA. 317

proper. In this the rods and cones, with their fibres
and the nuclei of the outer nuclear layer, corre-
spond to columnar epithelial cells (the sensory epithe-
lium), while all the other layers — i.e., the outer mole-
cular, inner nuclear, inner molecular layer, ganglion
cells, nerve-fibres, and limitans interna — represent
Briicke's tunica nervea or Henle's stratum nerveum.

449. The blood-vessels of the retina. The
branches of the arteria and vena centralis of the optic
nerve can be traced into the retina in the layer of
nerve-fibres and ganglion-cells, while the capillaries
connecting the arteries with the veins extend through
the layers up to the outer molecular layer.

The lymphatics of the retina exist as perivascular
lymphatics of the retinal veins and capillaries (His).
Lymph channels are present in the nerve-fibre layer.

450. The lamina criforosa is the part of the
sclerotic and choroid membrane through which the optic
nerve-fibres have to pass in order to reach the papilla
nervi optici. In the optic nerve the fibres are grouped
in larger or smaller groups — not bundles, in the sense
of those present in other nerves and surrounded by
perineurium (see a former chapter) — but surrounded
by septa of connective tissue, and these groups pass
through corresponding holes of the sclerotic and choroid.

451. The optic nerve possesses three sheaths,
composed of fibrous connective tissue — (a) an outer,
or the dural ; (b) a middle, or arachnoidal ; and (c) an
inner, or pial, sheath — which are continuations of the
respective membranes of the brain. The pial sheath
is, in reality, the perineurium, the whole optic nerve
being comparable to a compound nerve-bundle as de-
scribed in a former chapter. The dural sheath of the
optic nerve, at its entrance into the lamina cribrosa,
passes into the outer strata of the sclerotic, while the
arachnoidal and pial sheaths pass into the inner strata
of the sclerotic. Outside the dural sheath is a lymph

318 ELEMENTS OF HISTOLOGY. [Chap. XL.

space — the supra vaginal space ; and also between these
various sheaths are lymph spaces — the subdural or
subvaginal space of Schwalbe, and the subarachnoidal
space. The supravaginal and subvaginal spaces anas-
tomose with one another (Michel).

452. Around the sclerotic is a lymph space limited
by a fibrous membrane — the Tenonian capsule : the
space is called the Tenonian space. The supravaginal
space anastomoses with this Tenonian space, and into
it pass also the lymph clefts in the suprachoroidal
tissue (Schwalbe), by means of the lymph canalicular
system of the sclerotic (Waldeyer). The supracho-
roidal lymph spaces communicate also with the sub-
arachnoidal space of the optic nerve.

CHAPTER XL.

THE OUTER AND MIDDLE EAR.

453. THE meatus auditorius externus is lined with
a delicate skin, in structure identical with, but thinner
than, the skin of other parts. The ceruminous
glands have been mentioned and described before.
The cartilage of the auricula and its continuation into
the meatus auditorius externus is elastic cartilage.

454. The membrana tympaiii separating the
outer from the middle ear has for its matrix a firm
stratum of stiff trabeculae of fibrous connective tissue,
with numerous elastic fibrils and elastic membranes.
This is the middle and chief stratum of the membrane :
outwards it is covered with a delicate continuation of
the skin of the meatus auditorius externus, and inwards
with a continuation of the delicate mucous membrane
lining the cavum tympani. In the middle stratum of
the membrana tympani the trabeculse radiate more or
less from the junction of the manubrium mallei with
the membrane ; but towards the periphery many are

chap. XL.] THE OUTER AND MIDDLE EAR. 319

also arranged in a circular direction. The former
belong to the outer, the latter to the inner, portion of
the middle stratum.

The mucous membrane lining the tympanic surface
of the membrane is delicate connective tissue, covered
with a single layer of polyhedral epithelial cells.

The blood-vessels form capillary networks for all
three layers — i.t., a special network for the skin
layer, a second for the middle stratum, and a third one
for the mucous layer ; the lymphatics are also arranged
in this way. An intercommunicating system of lym-
phatic sinuses and clefts (Kessel) is left between the
trabeculse. The non-medullated nerve-fibres form
plexuses for the skin and mucous layer ; from these
pass off fine fibrils, which form a sub-epithelial net-
work, and from this the fibrils pass into the epithelium.

455. The tuba distachii is lined with a
mucous membrane, which is a continuation of that
lining the upper part of the pharynx, and therefore,
like it, is covered on its inner or free surface with
columnar ciliated epithelium. As in the pharynx, so
also here, we find a good deal of adenoid tissue in the
mucous membrane.

The cartilage of the tuba Eustachii in the adult ap-
proaches in structure the elastic cartilages of other parts.

456. The cavuni tympani, including the cellulae
mastoidese and the surface of the ossicula auditus, is
lined with a delicate connective tissue membrane. Its
free surface is covered with a single layer of poly-
hedral epithelial cells in the following regions : on
the promontory of the inner wall of the cavity, on the
ossicula auditus, on the roof of the cavity, and in the
cellulse mastoidese ; in all other parts it is columnar cili-
ated epithelium, like that lining the tuba Eustachii.

457. The three ossicula auditus are osseous
substance covered with periosteum, which is covered
with the delicate mucosa just described. The liga-

320 ELEMENTS OF HISTOLOGY. [Chap. XLI.

ments of the bones are, like other ligaments, made up
of straight and parallel bundles of fibrous connective
tissue. The articulation surface of the head of the
malleus, of the incus, of the extremity of the long
process of the incus, and of the stapes, are covered
with hyaline (articular) cartilage.

CHAPTER XLI.

THE INTERNAL EAR.

458. THE osseous labyrinth consists of the vesti-
bule, prolonged on one side into the cochlea, and on
the other into the three semicircular canals, each of
which possesses an ampulla at one extremity. The
vestibule shows two divisions — the fovea hemispherica
next to the cochlea, and the fovea hemielliptica next
to the semicircular canals. The cochlea consists of
two and half turnings twisted round a bony axis — the
modiolus. From this a bony lamina extends towards
the outer wall for each turn, but does not reach it :
this is the lamina spiralis ossea. It extends through
all turns, and it subdivides the cavity of each turn
into an upper passage, or scala vestibuli, and a lower,
or scala tynipani. At the top of the cochlea the two
scalse pass into one another by the helicotrema. The
scala vestibuli opens into the fovea hemispherica,
while the scala tympani at its commencement — i.e.,
at the proximal end of the first turn — would be in
communication, by the fenestra rotunda, with the
cavum tympani, were it not that this fenestra rotunda
is closed by a membrane — the secondary membrane.

459. The semicircular canals start from, and return
to, the fovea hemielliptica of the vestibule.

The fenestra ovalis leads from the cavum tympani
into the vestibule — its hemispheric division ; and this

Chap, x LI.] THE INTERNAL EAR. 321

fenestra ovalis is, in the fresli condition, filled out by a
membrane, in which the basis of the stapes is fixed,
the circumference of this being nearly as great as that
of the fenestra.

460. The osseous labyrinth in all parts consists of
ordinary osseous substance, with the usual periosteum
lining its outer surface and its inner cavities. These
cavities contain the albuminous fluid called perilyinph.
But they are not filled out by this, since, in each of
the two divisions of the vestibule, in each of the
semicircular canals, and in the cochlea, is a mem-
branous structure, analogous in shape to the corre-
sponding division of the labyrinth. These membranous
structures possess a cavity filled with the same albu-
minous fluid as above, called the endolymph. These
structures are disposed thus — in the fovea hemispherica
is a spherical sac, called the saccule ; in the fovea
hemielliptica is an elliptical sac, the utricle; in each of
the three semicircular canals is a membranous semi-
circular tube, which possesses also an ampulla corre-
sponding to the ampulla of the bony canal.

461. In the cochlea is a membranous canal, tri-
angular in cross-section — the scala media or cochlear
duct — which also twists two and half times from the
basis to the apex of the cochlea, and is placed against
the end of the lamina spiralis ossea so as to occupy a
position between the peripheral part of the scala vesti-
buli and scala tympani.

462. The different divisions of the membranous
labyrinth are connected with one another in this
manner : the three semicircular (membranous) canals ,
open into the utricle ; this does not form a direct con-
tinuity with the saccule, but a narrow canal comes off
both from the saccule and utricle; the two canals
join into one minute membranous tube situated in the
aqueductus vestibuli. At its distal end it enlarges
into the saccus endolyrnphaticus, situated in a cleft of

V

322 ELEMENTS OF HISTOLOGY. [Chap. XLI.

the dura mater, covering the posterior surface of the
petrous bone. The saccule is in communication with
the cochlear canal or scala media, by a short narrow
tube — the canalis reunions of Reichert. Thus the
cavity of the whole membranous labyrinth is in
direct communication throughout all divisions, and it
represents the inner lymphatic space of the labyrinth.
There is no communication between the perilymph
and endolymph, and the cavity of the membranous
labyrinth stands in no direct relation to the cavuin
tympani, since the fenestra ovalis and fenestra rotxmda
both separate the perilymphatic space, or the cavity
of the bony labyrinth, from the cavum tympani. The
vibrations of the membrana tympani, transferred by
the ossicula auditus to the fenestra ovalis, directly
affect, therefore, only the perilymph. The fluctuations
of this pass from the vestibule, on the one side,
towards and into the perilymph of the semicircular
canals ; and on the other side, through the scala
vestibuli, to the top of the cochlea, then by the heli-
cotrerna into the scala tympani, and find their conclu-
sion on the membrana secundaria closing the fenestra
rotunda. On their way they affect, of course, the
membrane of Reissner (see below) separating the scala
media from the scala vestibuli ; and the vibrations of
this membrane naturally affect the endolyrnph of the
scala media and the terminations of the auditory
nerve-fibres (see below).

463. Structure of semicircular canals
utricle and saccule. — The membranous semi-
circular canals are fixed by stiff bands of fibrous
tissue to the inner periosteum of the one (convex)
side of the osseous canal, so that towards the concave
side there is left the space for the perilymph. A
similar condition obtains with regard to the saccule
and utricle, which are fixed by the inner periosteum
to one side of the bony part.

Chap.XLI.]

THE INTERNAL EAR.

323

The structure of the wall is the same in the semi-
circular canals, utricle and saccule. The above-men-
tioned fibrous ligaments of the periosteum form an
outer coat; inside this is a glassy- looking tunica
propria. At one side (the one away from the bone)
this tunica propria forms numerous papillary projec-
tions. The internal
surface of the mem-
brane is covered with a
single layer of poly-
hedral epithelial cells.

464. Each of the
branches of the nervus
vestibuli — i.e., one for
the saccule, one for the
utricle, and three for
the three ampullae—
possesses a ganglionic
swelling. The nerve-
branch, having passed
through the membra-
nous wall, enters
special thickenings of

the tunica propria, on pig> 162._From a Transverse Section
that part of the mem- through the Macula Acustica of the
brailOUS wall next to Utricle of the Labyrinth of a Guinea.

the bone ; in the sac-
cule and utricle the
thickening is called
macula acustica, in the
ampullae crista acustica

(Fig. 162) (M. Schultze). This thickening is a large
villous or fold-like projection of the tunica propria,
into which pass the nerve fibres of the several
branches. These fibres are all medullated nerve-
fibres, and, ascending towards the internal or
free surface of that projection, form a plexus. In

:, Medullated nerve fibres, forming plex-
uses; b, nuclei of the membrane; e,
the sensory epithelium (diagrammatic) ;
the spindle-shape^ sensory-cells possess
long auditory hairs projecting between
the conical epithelial cells beyond the
free surface. (Atlas.)

324 ELEMENTS OF HISTOLOGY. [chap. XLI.

this plexus are interspersed numerous nuclei. From
the meclullated fibres pass off minute bundles of
primitive fibrillse, which enter the epithelium that
covers the free surface of the projection.

465. This epithelium is composed of a layer of
columnar or conical cells, between Avhich are wedged
in spindle-shaped cells ; both kinds possess an oval
nucleus. According to Max Schultze and others, each
of the spindle-shaped cells is connected by its inner
process with the nerve-fibrillge coming from under-
neath ; whereas, towards and beyond the free surface,
its outer process is prolonged into a long, thin, stiff,
auditory hair. Max Schultze, therefore, calls the
columnar cells epithelial; the spindle-shaped ones,
sensory.

Retzius, on the other hand, maintains that, in the
case of fishes at any rate, the epithelial cells are those
which are connected each with a bundle of nerve-
fibrillae, and that each sends out over the internal free
surface a bundle of fine stiff hairs — the auditory hairs.
The spindle-shaped cells of Max Schultze, according
to this theory, are only supporting cells. The free
surface of the epithelium is covered with a homo-
geneous cuticle, perforated by holes which correspond
to the epithelial cells and the auditory hairs.

On the internal surface of the macula and crista
acustica are found the otoliths, rhombic crystalSj and
amorphous masses, chiefly of carbonate of lime, em-
bedded in a gelatinous or granular-looking basis.

466. The cochlea (Fig. 163), as has been men-
tioned above, consists also of a bony shell and a
membranous canal, the former surrounding the latter
in the same way as the bony semicircular canal does
the membranous — i.e., the latter is fixed to the outer
or convex side of the former. The difference between
the cochlea and the semicircular canals is this, that in
the cochlea there is a division of the perilymphatic

Chap. XLL]

Fig. 163. — From a Vertical Section through the Cochlea of a Guinea-
pig's Ear, seen in the long axis of the Modiolus.

<f., The scala vestibuli : 6, the scala tympani ; c, the scala media; d, the membrana
tectoria ; e, the cells of Claudius : /, the upper outer angle- of the scala media :
ff, the region of the outer hair cells on the membrana basilaris ; A, the mera-
l)rane of Ileissner ; i. the epithelium lininp the sulcus BpiraliB (internus) \j, the
tunnel of Corti's arch; k the stria vascularis; I, the lipnmentura spirale;
?)?„ the cripta spiralis: n, the nerve-fib ree in the lamina spiralis ossea ; o, the
ganBlion spirale ; p, the nerve-fibres in the niodioliis ; q, channels in bone con-
taining Ijlood-vessels ; r, masses of bone in the uiodlolua ; «, the bony capsule.
(Atlas.)

326 ELEMENTS OF HISTOLOGY. [Chap. XLI.

space by an osseous projection — the lamina spiralis
ossea — and by the scala media into two scalse, viz., the
(upper) scala vestibuli, and the (lower) scala lympani.

467. In the osseous modiolus are numerous paral-
lel canals for bundles or groups of the fibres of the
cochlear branch of the auditory nerve ; these canals
open into the porus internus, in which lies a large
ganglion connected with the nerve.

The nerve bundles situated in the canals of the
modiolus, corresponding to the lamina spiralis ossea,
are connected with ganglionic masses — composed of
bipolar ganglion cells — called the ganglion spirale of
Corti. From this ganglionic mass the nerve-fibres (all
medullated) can be traced into the lamina spiralis
ossea, in which they form rich plexuses extending to
the margin of this lamina — i.e., to the membrana
basilaris of the scala media (see below).

468. From the margin of the lamina spiralis ossea
to the external bony shell extends the membrana basi-
laris (Fig. 163), forming the lower and chief wall of
the scala media, while the upper wall of the canal is
formed by the membrane of Reissner, extending
under an acute angle from near the margin of the
lamina spiralis ossea to the outer bony shell.

On a transverse section through the scala media
we see the following structures : —

469. (1) Its outer wall is placed close against
the periosteum lining the internal surface of the bony
shell ; it consists of lamellar fibrous tissue, with
numerous stiff elastic bands, and is the vestibular
part of a peculiar ligament — the ligamentum spirale
(Kolliker) — semi-lunar in cross section, and with its
middle angular projection fixed to the outer end of
the membrana basilaris.

470. (2) Its inner wall is represented by an
exceedingly delicate membrane — the membrane of
Reissner ; this is also its upper wall, extending under

chap. XLI.] THE INTERNAL EAR. 327

an acute angle from the upper outer angle of the scala
media to the lamina spiralis ossea. But there it is not
fixed on the osseous substance, but on a peculiar pro-
jection on this latter — the crista spiralis (Fig. 163, m),
which is a sort of tissue intermediate between fibrous
and osseous tissue, and added to the vestibular surface
of the lamina spiralis ossea. This crista spiralis has
on its inner surface — i.e., that directed towards the
scala media — a deep sulcus, called the vulcus spiralis, or
snlcus spiralis internus ; so that of the crista spiralis
there are two labia to be distinguished — the labium
vestibulare and the labium tympanicum; the former
being the upper, the latter the lower, boundary of the
sulcus spiralis.

471. (3) Between the labium tympanicum of the
crista spiralis and the above-mentioned projection
of the ligamentum spirale extends, in a straight
direction, the membrana basilaris, forming the lower
wall of the scala media. The scala media is lined on
its whole internal surface with epithelium, this only
being derived from the epithelium forming the wall of
the auditory vesicle of the embryo, peculiarly modified
in certain places. The scala tympani and scala vesti-
buli are likewise lined with a continuous layer of
flattened cells — an endothelium, which only on the
lower (tympanic) surface of the membrana basilaris
is somewhat modified, being composed of granular
looking irregular cells.

472. As regards the scala media, the epithelium
lining its internal surface is of the folllowing aspect :
Starting with the lower outer angle — i.e., where the
membrana basilaris is fixed to the ligamentum
pirale — we find it a single layer of polyhedral or
short columnar transparent cells, lining this outer
angle — the cells of Claudius ; ascending on the liga-
mentum spirale, the cells become shorter, more squa-
mous ; such are found over a slight projection on

328 ELEMENTS OF HISTOLOGY. [Chap. xu.

the outer wall — i.e., the ligamentum spirale accesso-
rium — caused by a small blood-vessel, the vas pro-
minens.

473. Then we come to the stria vascularis,

lining nearly the upper two-thirds of the outer
wall of the scala media. It consists of a layer of
columnar and spindle-shaped epithelial cells, between '
which extend capillary blood-vessels from the ligamen-
tum spirale, and in some animals (guinea-pig) clumps
of pigment granules are found between them.

474. Then we pass from the upper angle of the scala
on to the membrane of Reissner. This consists of a
homogeneous thin membrana propria, covered on its
outer vestibular surface with a layer of flattened
endothelium, and on its inner surface — i.e., that facing
the scala media — with a layer of less flattened, smaller,
polyhedral, epithelial cells.

475. We come next to the vestibular labium of
the crista spiralis, on which peculiar cylindrical
horizontal projections anastomose with one another :
these are the auditory teeth (Huschke). The epi-
thelium of Reissner's membrane is continued as small
polyhedral cells into the grooves and pits between the
auditory teeth, but over the teeth as large, flattened,
squamous cells, which pass on, lining the sulcus
spiralis, and, as such, cover also the tympanic labium
of the crista spiralis. Now we arrive at the mem-
brana basilaris, on which the epithelium becomes
modified into the organ of Corti.

476. The memforana basilaris consists of a
hyaline basement membrane, on which the organ of
Corti is fixed ; underneath this is i/lie tunica propria,
a continuation of the tissue of the ligamentum spirale,
composed of fine parallel stiff fibrils (Hannover,
Henle) stretched in a very regular and beautiful
manner in the direction from the ligamentum spirale
to the crista spiralis (Nuel). On the tympanic side

Chap. XLI.] THE INTERNAL EAR. 329

there is also a hyaline basement membrane. The
endothelial cells covering this on the tympanic surface
have been mentioned above.

477. The organ of Corti (Fig. 164). — Passing
outwards from the epithelium lining the sulcus spiralis,
we meet with small polyhedral epithelial cells in the
region of the termination of the lamina spiralis ossea,
next which are columnar-looking cells — the inner
supporting cells; next to these is the inner hair-cell —

Fig. 164.— Organ of Corti of the Cochlea of a Guinea-pig.

o, Outer rod or pillar of Corti ; 6, inner rod or pillar of Corti ; c, tunnel of Corti'8
arch ; d, outer hair-cells ; e, inner hair-cell ; /, outer supporting cells contain-
ing fat globules ; Dinner supporting cells; h, cells of Claudius; i, epithelial
cells lining the sulcus spiralis internus;/, ncrvc-flbres; *, part of crista
spiralis. (Atlas.)

a columnar, or conical, epithelial cell, with a bundle
of stiff hairs, or rods, extending beyond the surface.
The inner hair-cells form a single file along the whole
extent of the two and a half turns of the scala media.
478. Next to the inner hair-cell is the inner rod, or
inner pillar, of Corti, and next to this the outer rod,
or older pillar, of Corti. Each forms a single file for
the whole extent of the tw£> and a half turns of the
scala "media. The two fods are inclined towards one
another, and "in contact wifch-their" upper extremity, or
hea^ ; whe*reas their opposite extremj^;, the^ .fodt,
rests under an acute angle on the membrana basilaris,
on which it is firmly fixed The rest of the rod is a
slender, more or tefes cylindrical, piece — the body. The

330 ELEMENTS OF HISTOLOGY. [Chap. XLI.

outer rod is larger and longer than the inner, the
latter being slightly bent in the middle. Owing to
the position of the rods, the two files form an arch —
the arch of Corti. Between it and the corresponding
part of the basilar membrane is a space — the tunnel of
the arch, triangular in cross section.

479. The substance of the rods, or pillars, of Corti
is bright, highly refractive, and slightly and longitu-
dinally striated.

The head of the inner rod is triangular, a short
process extending inwards towards the inner hair-cell,
a long process extending outwards over the head of
the outer pillar. Outwards, the triangular head pos-
sesses a concave surface grasping the convex surface of
the head of the outer rod. This latter possesses a
process directed outwards, and firmly applied to the
outer process of the head of the inner rod, the two
together forming part of the membrana reticularis (see
below).

The relation between the outer and inner rods is
such that the head of one outer rod fits into those of
about two inner rods.

480. At the foot, each rod has, on the side directed
towards the tunnel, a granular, nucleated, lump of
protoplasm, probably the remnant of the epithelial
cell from which the lower half of the rod is derived ;
the upper part sometimes possesses a similar remnant,
proving that this also has been formed by an epithelial
cell, so that each rod is in reality derived from two
epithelial cells (Waldeyer).

481. Next follow three or four rows of outer hair-
cells, similar in size and structure to the inner hair-
cells. Each of the outer hair-cells represents a file
of hair-cells, extending on the membrana basilaris
along the whole extent — i.e., two and a-half turns —
of the scala media. Each hair-cell possesses an oval
nucleus and a number of stiff rods, or hairs, disposed

Chap. XLI.] THE INTERNAL EAR. 331

in the shape of a horseshoe in the outer part of the
free surface of the cell.

Four, and even five, rows of hair-cells (Waldeyer),
arranged in an alternating manner, are found in
man.

The outer hair-cells are also called the cells of
Corti ; they are conical, and more or less firmly con-
nected with a nucleated spindle-shaped cell — the cell
of Deiters. The two cells are more or less fused
together in their middle part (Nuel). The cell of
Corti is fixed by a branched process to the membrana
basilaris, while the cell of Deiters sends a process
towards the surface, where it joins the membrana
reticularis (see below).

482. Farther outwards from the last row of outer
hair-cells are columnar epithelial cells, called the outer
supporting cells of Hensen ; they form the transition
to the epithelium lining the outer angle of the scala
media, i.e., to the cells of Claudius.

In the guinea-pig, the outer supporting cells in-
clude fat globules.

483. The medwllated nerve-fibres, which we
traced in a former page to the margin of the lamina
spiralis ossea, make rich plexuses in this, and pass
tli rough holes in it, in order to reach the organ of
Corti on the membrana basilaris. Looking from the
surface on this part, we notice a row of holes — the
Jiabenula perforata of K olliker — a little to the inside
of the region of the inner hair-cells. Numerous
primitive fibrillse pass there among small nucleated
cells situated underneath the inner hair-cells : these
are the granular cells. Some of these nerve-fibrillsB
— the inner bundle of spiral nerve-fibres — become con-
nected with the inner hair-cells ; while others — the
three outer bundles of spiral fibrils (Waldeyer) — pass,
between the inner rods of Corti, right through the
tunnel ; and, further, penetrating between the outer

332 ELEMENTS OF HISTOLOGY. [Chap. XLI.

rods of Corti, they reach the outer hair-cells, with
which they become connected (Gottstein, Waldeyer).

484. In connection with the outer process of the
head of the inner and outer rods of Corti, mentioned
above, is an elastic hyaline membrane — the lamina
or membrana reticularis. It extends outwards over
the organ of Corti to the supporting cells of Hensen,
and possesses holes for the tops of the outer hair-cells
and their hairs. The parts between the rods of Corti
and between the outer hair-cells appear of the shape of
phalanges — phalanges of Deiters. A short cuticular
membrane extends from the head of the inner rod of
Corti inwards to the inner supporting cells : it possesses
holes for the tops of the inner hair-cells.

485. From the vestibular labium of the crista
spiralis to the outer hair-cells of the organ of Corti
extends a peculiar fibrillated membrane — the mem-
brana tectoria. By means of it the sulcus spiralis
internus is bridged over, and so converted into a
canal.

486. As we ascend towards the top of the cochlea,
all parts in the scala media decrease gradually in size.
The organ of Corti, being of an epithelial nature,
possesses no blood-vessels. From the anatomical
relations of the organ of Corti, it appears most pro-
bable that the pillars, or rods, of Corti act as the
supporting tissue, or framework, around which the
other elements are grouped ; and it seems likely
that the hair-cells, with their rod-like hairs projecting
freely into the endolymph, are the real sound-perceiving
elements of the organ of Corti. Their connection
with the terminal tibrillte of the nerves points in the
same direction.

Chap. XL1I.] 333

CHAPTER XLII.

THE NASAL MUCOUS MEMBRANE.

487. THE lower part of the nasal cavity is lined
with a mucous membrane, which has no relation to
the olfactory nerve, and therefore is not connected
with the organ of smell. It is covered with a strati-
fied, columnar, ciliated epithelium of exactly the same
nature as that of the respiratory passages — e.g., the
larynx and trachea. Large numbers of mucous secret-
ing" goblet-cells are met with in it. Below the epi-
thelium is a thick hyaline basement membrane, and
underneath this is a mucosa of fibrous tissue, with
numerous lymph corpuscles in it. In many places this
infiltration with lymph corpuscles amounts to diffuse
adenoid tissue, or to perfect lymph follicles.

488. The mucosa contains in its most superficial
layer the network of capillaries, but in the rest it
includes a rich and conspicuous plexus of venous
vessels.

In the deeper parts of the mucous membrane —
i.e., in the submucosa — are embedded smaller and
larger glands, the ducts of which pass through the
mucosa, and open on the free surface. Some of the
glands are mucous ; others are serous. In some cases
(e.g., guinea-pig) almost all glands are serous, and
of exactly the same nature as those of the back of
the tongue. In some places the mucous membrane is
much thicker than in others, and then it contains
larger glands, and between them bundles of non-striped
muscular tissue.

489. In the upper or olfactory region (Fig. 165)
of the nasal cavity, the mucous membrane is of a

334

ELEMENTS OF HISTOLOGY. [Chap. XLTI.

different tint, being more of a brownish colour; it
contains the ramifications of the olfactory nerve, and
is the seat of tit e organ of smell.

490. The free surface is covered with a columnar

Pig. 165.— From a Section through the Olfactory Region of the

Guinea-pig.

a. Thick olfactory epithelium; 6, thin olfactory epithelium; c. Ciliated non-
olfactory epithelium; rf, hone. The transverse sections or the olfactory
nerve bundles and the tubular glands of Bowman are well seen. (Atlas.)

epithelium, composed of the following kinds of cells
(Fig. 166):—

(a) A. superficial layer of long columnar, or rather

Chap. XLII.] NASAL Mucous MEMBRANE.

335

conical, epithelial cells, each with an oval nucleus. In
some places the free surface of these cells is covered
with a bundle of cilia, similar to the superficial cells

Fig. 166.— From a Vertical Section through the Olfactory Mucous

Membrane of the Guinea-pig.

a. The epithelial cells; 6, the sensory or olfactory colls; o, the deep epithelial
cells ; d, the bundles of olfactory nerve-fibres ; e, the alveoli of serous
(Bowman's) glands. (Atlas.)

of the respiratory part of the nasal cavity ; in most
places, however, the cilia are absent ; the former
condition obtains in those places which are in close
proximity to the respiratory region.

(b) Between the epithelial cells extend spindle-
shaped cells, each with a spherical, or very slightly

336 ELEMENTS OF HISTOLOGY. [Chap. XLII.

oval, nucleus — the sensory cells (Max Schultze).
Each cell sends one broad process towards the free
surface, over which it projects in the shape of a small
bundle of shorter or longer rods ; whereas a fine
varicose filament passes from the cell body towards
the nmcosa, and, as shown first by M. Schultze, be-
comes connected with a fibrilla of the network of the
olfactory nerve-fibres.

(c) In some places there is a deep layer of epithe-
lial cells, each with a spherical nucleus, of an inverted
cone in shape, their pointed extremity passing be
tween the other cells just mentioned and their broad
basis resting on the basement membrane. Von
Brunn has shown that there is on the free surface of
the epithelium a sort of cuticle — a delicate limitans
externa.

491. The mucous membrane is of loose texture,
and contains a rich plexus of bundles of olfactory
nerve-fibres, extending chiefly in a direction parallel
to the surface. Each olfactory nerve-fibre is non-
medullated, i.e., is an axis cylinder composed of minute
or primitive fibrillse, and invested in a neurilemma with
the nuclei of the nerve corpuscles. Near the surface
the fibres of the plexus are thin, and they split up
into the constituent fibrils which form a network ; into
this pass the fine varicose processes of the sensory
cells above named.

492. The blood-vessels supply with capillary net-
works the superficial part of the mucous membrane
and the numerous glands. These are the glands of
Bowman, extending through the thickness of the
mucous membrane. They are tubes, slightly branched,
and gradually enlarging towards their distal end ; in
some parts they are more or less straight. In struc-
ture they are identical with serous glands, possessing
a minute lumen, and being lined with a layer of
columnar albuminous cells. The duct is a very fine

Chap.XLii.] NASAL Mucous MEMBRANE. 337

canal ; it is that part of the gland that is situated
in the epithelium of the free surface ; it passes verti-
cally through this, and consists of a tine limiting
membrane, the continuation of the membrana propria
of the gland-tube, and a layer of very flattened epi-
thelial cells.

493. There is a definite relation between the
size and number of the bundles of the olfactory iierve-
libres, the thickness of the olfactory epithelium, and
the length of the gland-tubes. The size and number
of the bundles of the nerve-fibres are determined
by the thickness of the epithelium — i.e., by the
number of the sensory cells ; the number and thick-
ness of the olfactory nerve bundles determine the
thickness of the mucous membrane, and the thicker
it is, the longer are the glands of Bowman.

494. The organ of Jacobson is a minute
tubular organ present in all mammals, and, as has
been shown by Dursy and Kblliker, also in man. In
mammals it is a bilateral tube, compressed from side
to side, and situated in the anterior lower part of
the nasal septum. Each tube is supported by a
hyaline cartilage, in the shape of a more or less
plough-shaped capsule — the cartilage of Jacobson
— and opens in front directly into the nasal furrow
(guinea-pig, rabbit, rat, <fec.) ; or it leads into the canal
of Stenson (dog), which passes through the canalis
naso-palatinus, and opens immediately behind the
incisor teeth on the palate. In all instances, how-
ever, it terminates posteriorly with a blind ex-
tremity.

495. The cavity of the tube is lined with stratified
columnar epithelium, which on the lateral wall is
ciliated in the guinea-pig and dog, and non-ciliated in
the rabbit. The median wall — i.e., the one next to
the middle line — is lined with olfactory epithelium,
:dentical with that of the olfactory region of the nasal

w

338 ELEMENTS OF HISTOLOGY. [Chap. XLIII.

cavity. Branches of olfactory nerve-fibres also pass
into the median wall, and behave in exactly the same
manner as in the olfactory region. Numerous serous
glands — belonging chiefly to the upper and lower
wall — open into the cavity of the organ of Jacobson.

In the lateral wall there is in many instances a
plexus of veins, extending in a longitudinal direction,
and between the vessels are bundles of non-striped
muscular tissue, thus constituting a sort of cavernous
tissue.

CHAPTER XLIII.

THE DUCTLESS GLANDS.

496. I. The hypophysis cerebri. — The upper
or smaller lobe belongs to the central nervous system.
The lower or larger lobe is surrounded by a fibrous
capsule, which sends numerous minute septa into the
interior. These split up into numerous trabeculse of
fibrous tissue, which, by dividing and re-uniting, form
a dense plexus, with smaller and larger, spherical or ob-
long, or even cylindrical spaces — the alveoli. In these
lie spherical or oblong masses of epithelial cells. These
epithelial cells are columnar, pyramidal, or polyhedral,
each with an oval or spherical nucleus. Between the
epithelial cells of the same group are found here and
there small branched or spindle-shaped cells, with a
small flattened nucleus. In some of the groups or
alveoli of epithelial cells is a cavity, a sort of lumen,
filled with a homogeneous gelatinous substance.

The interalveolar connective tissue contains a
network of capillaries. Between the alveoli and the
interalveolar tissue there are lymph sinuses, like those
around the alveoli of other glands — e.g., the salivary
glands.

chap. XLIII.] THE DUCTLESS GLANDS.

339

m

497. II. The thyroid gland (Fig. 167).— The
framework of this gland is in many respects similar
to that of other glands, there being an outer fibrous
capsule, thicker and thinner septa, and finally the fine
trabeculae forming the septa between the gland alveoli.
These are closed vesicles of a spherical or oval shape,
and of various sizes. Each vesicle is lined with a single
layer of polyhedral or

columnar epithelial cells,
each with a spherical or
oval nucleus. There is a
cavity, which differs in size
according to the size of the
vesicle. It contains, and
is more or less filled with,
a homogeneous, viscid, albu-
minous fluid — the so-called
colloid. In this often oc-
cur degenerating nucleated
lymph - corpuscles and
coloured blood - corpuscles
(Baber).

498. The vesicles are
surrounded by networks of
blood capillaries. In the

connective tissue framework lie networks of lym-
phatics; between the framework and the surface of the
vesicles are lymph sinuses lined with endothelium
(Baber). The large and small lymphatics are often
filled with the same colloid material as the vesicles,
and it is probable that this colloid material is produced
in the vesicles, and carried away by the lymphatics,
to be finally discharged into the circulating blood.

499. Its formation in the vesicles is probably due
to an active secretion by the epithelial cells of the
vesicles, and to a mixture with it, or maceration by
itj of the effused blood mentioned above. In some

Fig. 167. — From a Section
through the Thyroid Gland
of Dog.

a, The epithelium lining the vesi-
cles : b, the " colloid" contents of
the vesicles ; c, a lymphatic filled
with the same material as the
vesicles: d, the fibrous tissue be-
tween the gland vesicles.

340

ELEMENTS OF HISTOLOGY. [Chap. XLIII.

instances Baber found the

Fig. 168.— From a Vertical Section through
the Suprarenal Body of Man.

1, Cortical substance : 2, medullary part ; a, outer
capsule ; 6, zona glomerulosa ; c, zona fascicu-
lata; d, zona reticularis ; e, medulla ; /, a large
vein. (Elberth, in Strieker's Manual.)

glomerulosa ; it contains

amount of blood effused
into the cavity of
the vesicles very
considerable, and
hence it is justifi-
able to assume that
the destruction of
red blood-corpus-
cles forms one of
the functions of the
thyroid gland.

500. III. The
s 11 p r ar enal
bodies (Fig. 168).
— The suprarenal
body is enveloped
in a fibrous cap-
sule ; in connection
with this are septa
and trabeculse pass-
ing inwards, and
they are arranged
differently in the
cortex and in the
medulla of the
gland, as will be
seen presently.

The cortex of
the gland consists
of an outer, mid-
dle, and inner
zone, all three be-
ing directly con-
tinuous with one
another. The outer
one is the zona

numerous spherical, or,

Chap. XLIII.] THE DUCTLESS GLANDS. 341

more commonly, elongated, masses of epithelial cells.
The cells are polyhedral or cylindrical, each with a
spherical or oval nucleus. In some animals — as the
dog, horse — the cells are thin and columnar, and
arranged in a transverse manner. Occasionally a sorfc
of lumen can be discerned in some of these cell masses.

501. Next follows the middle zone, or zona
fasciculata. This is the most conspicuous and
broadest part of the whole gland. It consists of
vertical columns of polygonal epithelial cells, each
with a spherical nucleus. The cell substance is trans-
parent, and often contains an oil globule. The columns
anastomose with their neighbours. Between the
columns are fine septa of connective tissue carrying
blood capillaries.

Between the cell columns and the connective septa
are seen here and there lymph spaces, into which lead
fine channels, grooved out between some of the cells of
the columns.

502. Next follows the inner zona, or zona reticu-
laris, composed of smaller or larger groups of poly-
hedral cells, with more or less rounded edges. These
cell-groups anastomose with one another. The indi-
vidual cells are slightly larger, and their substance is
less transparent than those of the zona fasciculata. In
the human subject they are slightly pigmented.

503. In the medulla we find cylindrical streaks
of very transparent cells ; the streaks are separated by
vascular connective tissue. The cells are polyhedral,
columnar, or branched. These cell-streaks anasto-
mose with one another, and are directly continuous
with the cell-groups of the zona reticularis of the
cortex.

504. The cortex is richly supplied with dense
networks of capillary blood-vessels ; their meshes are
polyhedral in the outer and inner zone, elongated in
the middle zone, or zona fasciculata. In the medulla

342 ELEMENTS OF HISTOLOGY. [Chap. XLIII.

numerous plexuses of veins are met with. In. tbe
centre of the suprarenal body lie the large efferent
venous trunks. In the capsule (Kolliker, Arnold),
and in the connective tissue around the central veins,
are plexuses of lymphatic tubes with valves. The
nerves are very numerous, and composed of non-
medullated fibres ; in the medulla they form rich
plexuses. In connection with these and with those of
the outer capsule are small ganglia (Holm, Eberth).

505. IV. The glandula coecygea and iii-
tercarotica. — The first of these is a minute corpuscle
situated in front of the apex of the os coccygis, and
was discovered by Luschka. The gland ula carotica
of Luschka (ganglion intercaroticum) is of exactly the
same structure as the glandula coccygea.

506. Its framework is of about the same nature as
that of other glands — a fibrous capsule and inner
fibrous septa and trabeculse. The septa and trabeculre
contain in some places bundles of non-striped muscular
tissue (Sertoli).

507. The spaces of the framework are occupied by
the parenchyma. This consists of spherical or cylin-
drical masses of cells connected into networks. The
individual cells are polyhedral epithelial cells, each
with a spherical nucleus. According to Luschka, in
the new-born child they are ciliated. In the centre
of each of the cell-masses lies a capillary blood-vessel,
much convoluted and wavy.

Numerous non-niedullated nerve-fibres forming a
plexus are situated in the framework of the gland.

INDEX.

Absorption (see Lymphatics).

Achromatin, 9.

Acini of glands, 180, 182.

of liver, 211.

of pancreas, 209.

Adenoid reticulum, 44, 80, 92.

tissue, 92.

Admaxillary glands, 179.
Adventitia of arteries, 76, 78.

of capillaries, 80, 93.

of veins, 79.

lymphatic vessels, 102.

Agminated glands, 95.
Air cells, 220.
Alae nasi, 46.
Albuginea of ovary, 258.
Albumin membrane of Aschcrson,

273.

Albuminous cells, 183.
Alveolar cavity, 171, 178.

ducts, 65, 220.

Alveoli of glands, 180, 182.

of lung, 220.

of pancreas, 209.

Amoeboid corpuscles, 9.

movement, 4, 5, 14, 41, 90, 93.

Ampulla, 320, 323.
Anterior commissure, 157.

nerve-roots from cord, 136.

Aorta, 65, 78.
Apoueurosis, 32.
Aqueductus cochleae, 321

Sylvii, 150, 160.

vestibuli, 321.

Arachnoid membrane of spinal

cord, 127.
— — of brain, 149.
Arachnoidal villi, 149.
Areolar tissue, 33.
Arrector pili, 64, 287.
Arterise ciliares breves, 305.

recurrentes, 305.

helicinae, 256.

jvctffi, 242.

Arteries, 65, 76.
Arterioles, Afferent, 40, 51.

Arterioles of ovary, 267.
Articular cartilage, 47, 60.
Articulation nerve-corpuscles,121.
Arytenoid caitilage, 215.
Ascending loop-tube, 238.
Astf r stage in nucleus, 8.
Auditory hairs, 324.

nerve, Origin of, 149.

, Division of, 148.

teeth, 328.

Auerbach's plexus, 170, 201, 207.
Auricle of heart, 75.
Auriculo-ventricular valves, 75.
Axis cylinder, 107.

process of sympathetic

ganglion cell, 169.

Bartholin's glands, 270.
Basement membranes of skin, 277.
Basilar membrane of cochlea, 327,

328.

Bellini's ducts, 239.
Bile-duct, 213, 214.
Bile capillaries, 213.
Bilirubin, 13.
Bladder, 64, 243.
Blastoderm of chick, 2.
Blood, 10.

— corpuscles, 10, 13.

, their origin, 15.

glamls of His, 92.

-plates of Bizzozero, 15.

vessels in grey matter, 151.

Bone, 50.

, Development of, 55.

cartilage, 50.

cells, 31, 53.

trabeculae, 54.

— corpuscles, 53.
Bowman's capsule, 234.

elastica anterior, 44.

glands, 336.

membrane, 295.

sarcous elements, OS.

Hrain membranes, 149.
Brainsand, 163.

344

ELEMENTS OF HISTOLOGY.

Bronchi, 65, 219.

Browjiian molecular movement,

189.

Bruch, Glands of, 294.
Briicke's elementary organisms, 5.

oikoid and zooid, 12.

tunica nervea, 317.

Brunner's glands, 2*. 8, 209.
Buccal glands, 187.
bnlbus olfactorius, 159.
Biitschli s nuclear spindle, 9.

Calcification of tone, 55.

• of cartilage, 47.

of dentine, 62.

Calices of kidney, 230.
Canal of Schlernm, 299.

of Stenson, 337.

of Stilling, 307.

Canal is hyaloideus, 307.

Petiti, 307.

reuniens, 322.

Canaliculi in bone, 52.

in cartilage, 48.

Capillaries of marrow-bone, 81.

of nerve system, 80.

Capillary bile-ducts, 213.

blood-vessels, 80, 201.

lymphatics, 86.

network in mucosa, 190.

sheaths, 228.

Capsule, External, of brain, 162.

, Internal, of brain, 162, 163.

of Glissou, 210.

of kidney, 65.

of the spleen, 65, 225.

Cartilage, 45.

, Articular, 47, 60.

cells, 31, 48.

• , Elastic, 49.

, Fibrous, 48.

, Hyaline, 46.

, Lacunae, 46.

of Jacobson, 337.

of Luschka, 215.

Cavernous tissues in genital

organs, 255.

Cavities of tendon sheaths, 88.
Cavum tympani, 319.
Cells, 5.
, Muscular, of blood-vessels,

65.

, of intestine, 65.

, of respiratory organs, 65.

, of stomach, 65.

, of urinary organs, 65.

in tadpole's tail, 35.

of Claudius, 327, 331.

Cellulse mastoideae, 319.

Cellular tissue, 33.
Cement of teeth, 174.

- substance, 80, 82, 90.
-- of endoth(4ium, 25.
--- of epithelium, 17.
-- of fibrous tissue, 32.
Central canal, 128.

- grey nucleus, 134.
Centroacinous cells, 210.
Centrum ovale, 156, 157.
Cerebellum, 149, 152.
Cerebrum, 149, 1.56, 157.
Cerumirious glands, 278, 318.
Cervix of uterus, 266.
Chalice cells, 22.
Chondrin, 31, 45.
Chondroclasts, 62.

Choroidal portion of ciliary

muscle, 64.

Choroid membrane, 303.
Chromatin, 9.
Chyle, 206. -—

yCiliary muscle, 65, 300.
' - nerve, 163.

processes, 303.

Ciliated cells, 21.
ci

^-<

iris, 302.

irculus arteriosus in i
Circumanal glands, 278.
Cisterna lymph atica magna, 89.
Clarke's columns, 137, 140.
Claustrum, 159, 162.
Cleavage of ovum, 2.

- of wbite blood corpuscles, 15.
Clitoris, 270.

Cochlea, 320, 324.
Cohnheim's areas, 70.
Colloid, 339.

Colostrum corpuscles, 273.
Coloured blood corpuscles, 10.
Colourless blood corpuscles, 13.
Columnar epithelial cells, 17.
Commissure, Grey, of spinal cord,
128.

- , White, of spinal cord, 135.
Compound lymphatic glands, 98.
Conarium, 163.

Concentric bodies of Hassall, 97.

- lamellse, 53.
Cone fibre, 316.
Cones of retina, 313.
Coni vasculosi, 250.
Conjunctiva, 291.

- blood-vessels, 293.

- bulbi, 293.

- lymphatics, 293.

- nerves, 294.

- palpebrse, 291, 293.
Connective tissue, 31.
Contraction wave, 67.

INDEX.

345

Contractility of corneal cor-
puscles, 37.

of pigment cells, 28.

Convolution in brain, 157.

in nucleus, 8.

Cordae tendinese, 75.
Cords of adenoid tissue, 94.
Corium, 274.
Cornea, 20, 295.

nerves in, 297.

Corneal cells, 36.

corpuscles, 34, 297.

Cornu Ammouis, 158, 159.
Cornna uteri, 267.
Corona rariiata, 163.
Corpora albicantia, 161, 1G3.

cavernosa, 65, 2^5.

quadrigemina, 16).

• striata, 161, 162.

Corpus callosum, 157.

Highmori, 244.

luteurn, 262.

restiforme, 144, 142.

spongiosum, 255.

Corpuscles, Malphigian, 227, 233.

of blood, 10, 13.

of bone, 53.

of connective tissue, 36.

of Grandry, 120.

of Herbst, 115, 118.

of lymph, 90, 93.

of Meissner, 115, 118.

of muscle, 70.

of nerve, 108.

of Pacini, 115, 121, 291.

of Vater, 115.

, Tactile, 115, 118.

Corti's arch, 330.

cells, 331.

ganglion, 326.

rods, 329.

Cortical layer of ovnry, 258.

lymph-sinus, 101.

Costal cartilages, 46.

pleura, 89.

Cowper's glands, 254. 270.
Creuiaster internus, 252.
Crescents of Gianuz/.i, 183.
Cricoid cartilage, 46.
Crista acustica, 323.

spiralis, 327, 332.

Crus cerebri, 142, 161.

, Crusta of, 163.

Crusta petrosa, 171.
Crypts, 95.

of Lieberkiihn, 203, 200.

Cuticle of Nasmyth, 172, 177.
Cutis anserina, 287.
vera, 274.

Cystic duct, 65.
Cytogenous tissue, 92.

Deiters' cells, 150, 331.

phalanges, 332.

processes, 141, 145.

Demilunes of Heidenhain, 183.
Dentinal canals, 173.

fibres, 62, 173.

sheaths, 173.

tubes, 62.

Dentine, 62, 172, 173.
Descemet's membrane, 44.
Diapedesis, 82.
Diaphragm, 73, 88.
Diaster stage in nucleus, 8.
Diffuse adenoid tissue, 93.
Dilatator, 65.

pupillse, 302.

Direct division, 7, 9.

" Disc tactil," 121.

Discus proligerus, 261.

Disdiaclasts, 74.

Distal convoluted tubes, 238.

Division, Remak's mode of, 7.

Doyere's nerve-monnt, 125.

Ductless glands, 338.

Ducts of pancreatic gland, 65.

of salivary gland, 65.

Ductus ejaculatorii, 253.
Dura mater, 127.
Dural sheath, 317.

Ear, External, 318.
— , Internal, 320.
Efferent lymphatics, 102.

medullated nerve-fibres, 116.

veins, 40.

Elastic fenestrated membrane of

Henle, 44.
Elastin, 43.
Electric nerve, 111.
Eleidin, 20.
Momentary fibrillse, 107.

fibrils, 32.

organisms, 4.

Enamel, 171.

cap, 175.

cells, 175, 177.

organ, 175, 177.

prisms, 171.

End-bulbs of Zrause, 115, 119,

294.

Endocardium, 74, 76.
Endochondral formation of bone,

55.

Fndolymph, 321.
Eudomysium, 66.

346

ELEMENTS OF HISTOLOGY.

Endoneurium, 105.
Endothelial cells, structure, 25.

membrane, 25.

Endothelium, 25.
Endotheloid cell-plates, 92.
Kngelmann's lateral disc, 68.
Epicerebral space, 150.
Epidermis, 19, 274.
Epididymis, 65, 250.
Epiglottis, 49, 93.
Epineurium, 104.
Epithelial cells, 16.

division of, 24.

regeneration of, 24.

Epithelium, 19.
Epitheloid layer, 56.
Eustacbian tube, 319.
External arcuate fibres, 144, 147.

capsule of brain, 162.

Eye, 290.

lashes, 292.

lids, 291.

Fascise, 87.
Fascicles, 66.
Fasciculus cuneatus, 144.

gracilis, 144.

of Goll, 132, 144.

of Turk, 132, 142, 145.

pyramidal direct, 132,

Fat cells, 39.

and starvation, 41 .

Femur, 60.
Fenestra ovalis, 320.

rotunda, 320.

Fenestrated membrane, 30, 33,
127.

9f Henle, 77.

Fertilisation of ovum, 2.

Fibne arcuatse, 296.

Fibres, Connective tissue, 31.

, Elastic tissue, 50.

of muscle, 63, 66, 72.

of nerves, 103.

of Purkinje, 75.

Fibrillse of connective tissue, 32.

of muscle, 64.

- — of nerve, 107,

Fibro-cartilage, 48.

Fibrous tissue development, 42.

Fillet, 160.

Fissura orbitalis, 65.

Fissures of spinal cord, 130.

Foetal tooth papilla, 176.

Follicles, Lieberkiihn's, 203.

, Lymph, 92, 94, 100.

- — , Sebaceous, 286.

, Thymus, 93.

Foruix coivjunctivse, 293.

Fornix vaginal, 269.
Fossa gleuoidalis, 48.

navicularis, 254.

patillaris, 307.

Sylvii, 159.

Fovea centralis, 310, 314, 315

hemielliptica, 320.

hemispherica, 320.

Fundus, 266.

Funiculus of Rolando, 144.

Gall-bladder, 65.

Ganglia, Cerebro-spinal, 138, 141.

, Sympathetic, 168.

Ganglion cells, 138, 164.
Gasserian ganglion, 163.
Gelatinous tissue, 45.
Geniculate ganglion, 163.
Genital corpuscles of Krause, 120.

end-corpuscles, 115.

organs (male), 244.

(female), 257.

Germ reticulum of von Ebner, 247.
Germinal endothelial cells, 28.

epithelium, 258.

spots, 1, 259.

vesicle, 1, 259.

Germinating cells, 29.
Giralde"'s organ, 251.
Gland, Prostate, 253.
Glands, Bartholini, 270.

, Brunner, 208, 209.

, Bucoal, 187.

, Carotic, 342.

— — , Ceruminous, 278, 318.

, Cocc.vgeal, 342.

, Harder, 295.

, Krause, 293.

, Lachrymal, 294.

, Lieberkiihn's, 17.

, Littre", 254.

, Lymphatic, 80, 84, 100.

, Meibomian, 292.

, Mohl, 292.

, Mucous, 179, 101.

, Peptic, 197.

, Peyer, 95, 205.

, P.vloric, 199.

, Salivary, 178.

, Sebaceous, 287.

, Solitary, 95.

, Submaxillary, 179.

— j Sweat, 276.
Glaudulse agmmatse, 200.

lenticulares, 200.

Pacchioni, 149.

uterinse, 266.

Glans clitoridis, 270.
penis, 255.

INDEX.

347

Glassy membrane, 231.
Glisson's capsule, 210.
Globulin, 12.
Glomerule, 159.
Glutin, 31, 33.
Glycogen, 14.
Goblet cells, 18, 22.
Graafian follicles, 258, 263.
Grandry's corpuscles, 120.
Granular formation of Meynert,
159

layer of Purkinje, 174.

Granules in blood, 15.
Granuloea membrana, 259.
Grey commissure, 128.
Ground lamellae, 53.

plexus of Arnold, 121.

substance, 117.

Growing capillaries, 82.

Habenula perforata, 331.
Haematiu, 13.
Haematoidin, 13.
HsBmatoplasts, 15.
Hsemin crystals, 13.
Haemoglobin, 12.

crystals, 13.

Hair, 278.

bulb, 282, 285.

, Development of, 285.

fibres, 282.

follicles, 278, 280.

knob, 285.

, Marrow of, 282.

f New formation of, 284.

papilla, 285.

, Eoot of, 2»2.

sheath of, 281.

sac, 280.

, Shaft of, 279, 283.

Harder' s gland, 295.
Haversian canals, 53.

lamellae, 53.

spaces, 54.

Heart and blood-vessels, 74.
Helicotrema, 320.
Hemisphere of brain, 152.
Heule, Fenestrated membranes
of 44, 77.

Fibres of, 44.

Sheath of, 105.

Stratum nerveum of, 317.

Tubes of, 237

Hensen's cells, 331.
Hepatic cells, 212.

duct, 65.

lobules, 211.

veins, 211.

Herbst, Corpuscles of, 115, 118.

Hilum of glands, 98.

of salivary glands, 180.

of spleen, 226.

Hippocampus, 159.
Homogeneous elastic membranes,

44.

Howship's lacunae, 62.
Hyaline cartilage, 46.
Hyaloid membrane, 307.
Hypophysis, 161, 338.

Ileum, 205.

Incremental lines of Salter, 174.

Incus, 320.

Indirect division, 7.

Infundibula, 65, 161, 163.

of bronchiole, 220.

of gland, 188.

Inner molecular layer, 311.

nuclear layer, 311.

Interarticular cartilages, 48.
Jnterfascicular spaces, 34, 36.
Interglobular spaces of Czermak,

174.

Interlobar ducta, 180.
Interlobular bile-ducts, 213, 214.

connective tissue of liver,

210.

ducts, 180.

Intermediary cartilage, 48.

plexus, 121.

zone, 200.

Interrnembranous formation of
bone, 55, 61.

Intermuscular fibrils, 122.

Internal capsule of brain, 163.

Interstitial lamellae, 53.

Intervertebral discs, 48.

Intestine, Large, 201
— , Small, 201.

Intima of arteries, 76, 77.

Intralobular bile-vessels, 213.

ducts, 180.

Intranuclear network,

Iris, 300.

, Blood-vessels of, 302.

, Lymph-clefts of, 302.

, Lymph-sinuses of, 302.

, Nerve-fibres of, 302.

Island of Eeil, 162.

Jacobsou's organ, 337, 338.

Karyokinesis, 7, 48, 247.
Kidney, 229.

Afferent arterioles of, 240.

blood-vessels, 240.

glomerulus, 234.

348

ELEMENTS OF HISTOLOGY.

Kidney lymphatics, 214, 215, 243.

parenchyma, 231.

vessels, 241.

Kolliker's osteoclasts, 62.

Labia pudendi majora, 287.
Labium tympanicum, 327.

vestibulare, 327.

Labyrinth, Osseous, 320.
Lachrymal glands, 294.
Lacunae Morgagni, 254.

of bone, 52, 53.

of cartilage, 46.

of lymphatics, 86.

Lamellae of bone, 54.

of cornea, 296.

of lens, 306.

Lamina cribosa, 317.

elastica of cornea, 295.

fusca, 299.

reticularis, 332.

spiralis ossea, 320.

vitrea, 301, 305.

Langerhans' granular layer, 20.

Larynx, 215.

Lateral basilar process, 158.

nucleus, 145.

tract, 143.

Lens, 305.

fibres, 306.

stars, 306.

Lenticular glands, 95.
Ligamentum denticulatum, 128.

latum, 65.

pectinatum, 299.

pulmonis, 221.

spirale accessorium, 326, 328.

suspensory of lens, 307.

Limitans externa, 312.

interna, 310.

Lines of Schreger, 174.
Liquor folliculi, 260.

• sanguinis, 10.

Littrd's glands, 254.
Liver, 88, 210.

vessels of, 211, 212.

Lobes of pancreas, 209.

of salivary gland, 180.

of thymus gland, 96.

of lung, 220.

Lobules of liver, 211.

of lung, 220.

of salivary glands, 180.

of thymus gland, 96.

Lung, 88, 219.

blood-vessels, 223.

lymphatics, 223.

Lymph, 90.

Lymphatic capillaries, 86.

Lymphatic clefts, 7D. 86.

glands, 80, 84, 10 J.

rootlets, 86.

sinuses, 88, 101.

tissue, 85.

vessels, 79, 84. 92.

Lymphatics, 65, 201.

in mucosa, 190.

Lymph-canal system hi cornea, 3*3.

canalicular systern,86, 90, 297.

cavities, 88.

corpuscles, 90, 93.

follicles, 92, 94.

hearts, 90.

Lymphoid cells, 29.

Macula acustica, 323.

lutea, 310, 311, 314, 315.

Malleus, 320.

Malpighian corpuscles of kidney,

of spleen, 227.

pyramids of kidney, 231.

stratum of skin, 19.

Mammary glajid, 270.
Manubrium mallei, 318.
Marrow of bone, 50.
Matrix of osseous substance, 52.
Meatus auditorius externus, 318.
Meckel's ganglion, 163.
Media of arteries, 76.
Median lateral fissure, 132.
Mediastinum testis, 2 14.
Medulla oblongata, 142.

of gland, 99.

Medullary cylinders, 100.

lymph-sinus, 101.

ray, 231.

sheath of nerve-fibres, 107,

108.
Medullated nerve-fibres, 106, 114,

137.

Meibomian glands, 292.
Meissner's corpuscles, 191, 291.

plexus, 170, 201, 207.

Membrana basilari*, 327, 328.

chorio-capillaris, 304.

Descemeti, 297.

granulosa, 259.

hyaloidea, 307.

secundaria, 322.

supra-choroidea, 303.

tectoria, 332.

tympani, 318.

Membranes of Krause, 67, 74.
Mesencephalon, 159.
Mesentery, 88.
Mesogastrium, 30.
Migratory cells, 41.

INDEX.

349

Milk, 273.

globules, 272.,

tooth, 177.

Modiolus, 320, 326.
Motor ganglion cells, 141.
Movement of cilia, 22.
Mucin, 23.
Mucosa, 189.

, Lymph follicles of, 200.

Mucous cells, 183.

glands, 179, 191.

membrane, 189.

Muco-salivary plands, 179.
Mucus, formation of, 23.
Miiller's fibres, 310.

muscle, 300.

Muscle bundles, 64.

cells, 64.

corpuscles, 70.

fibres, 63, 72.

tissue, striped, 66, 189.

, Non-striped, 63, 65.

Muscular compartments, 67.
Muscularis exterua, 196.

mucosae, 64, 195.

Musculus ciliaris Biolani, 292.

Myeloplax, 6.

Myeloplaxes of Eobin, 51, 62.

Nail, 288.

cells, 289.

groove, 288.

substance, 289.

Nasal mucous membrane, 333.

septum, 46.

Nerve bundles, 104.

corpuscles, 108.

end plate, 124.

endings, 112, 115.

fibres, 103.

plexus, 106, 111, 114.

Network of fibrillaj, 111.
Neurilemma, 108.
Neuroglia, 133.
— cells, 133.

fibrils, 133, 150.

of Virchow, 45.

tissue, 130.

Neurokeratin, 107, 109, 135, 313.

Nipple, 65.

Nou-medullated nerve-fibres, 111,

114.

Norris's blood corpuscles, 13.
Nuclear layer in bulbus olfac-

torius, 159.

zone, 306.

Nuclein, 6.
Nucleoli, 6.
N ucleus, Structure of, 6.

Nucleus caudatus, 162.

cuneatus, 147.

deutatus, 147.

gracilis, 147.

lenticularis, 162.

Nuclei, Inner, of retina, 311.

, Outer, of retina, 312.

Nj-inphse, 270.

Odontoblasts, 173, 174, 177.
(Esophagus, 194.
Oil-globule, 39, 40.
Olfactory cells, 336.

nerves, 111, 159.

Olivary bodies, 143.

nucleus, 147.

Omentum of cat, 29.

of frog, 89.

of guinea-pig, 40.

of rat, 32.

, Structure of, 83.

Optic nerve, 317.

nerve-fibres, 310.

tract, 162.

vesicle, 316.

Ora serrata, 310.

Organ of Corti, 328, 329, 332.

of Giralde, 251.

of Jacobson, 337, 338.

Ossein, 52.

Osseous labyrinth of ear, 321.

lamellae, 52.

substance from osteoblasts.-

61.

Ossicula auditus, 319.
Ossifying cartilage, 48.
Osteoblasts forming bone, 50, 57,

61.

Osteoclasts, 62.
Osteogenetic layer, 49.
Otoliths, 324.
Oval nucleus, 39.
Ovary, 65, 257.

, Development of, 263.

, Lymphatics of, 268.

, Nerves of, 268.

Oviduct, 65, 265.
Ovum, 1, 259.

Pacinian corpuscles, 115, 121, 291.

Palate, 187.

Palmae plicatee, 266.

Palpebraj, 293.

Pancreas, 208, 209.

Papilla circunivallata, 192.

filiformis, 191.

foliata, 193.

fungiformis, 191.

nervi optici, 303.

35°

ELEMENTS OF HISTOLOGY.

Papillary hair of Unna, 280.

muscle, 75.

Paraglobulin, 12.
Parenchyma of testis, 253.
Parenchymatous cartilage, 48.
Parietal cells, 199.
Pars ciliaris retinae, 303, 305, 310.

membranacea, 254.

prostatica, 254.

Pedunculated hydatid of Mor-

gagni, 251.

Pedunculus cerebelli, 144, 152.
Penis, 255.

corpora cavernosa, 255.

nerve endings, 120.

Peptic glands, 197.
Peribronchial lymphatics, 220, 224.
Pericardial cavities, 88.
Pericellular space, 141.
Perichondrium, 45, 46.
Perilymph, 321.
Perimysium, 66.
Perineurium, 104, 121.
Periosteal bone, 59, 61.
formation, 55.

— processes of Virchow, 55.
Periosteum, 50.

Peripheral nerve-endings, 112, 115.
Peritoneal cavities, 88.
Peritoneum, 65.
Perivascular lymphatics, 89, 224.

— lymph-spaces, 151.

spaces of His, 141.

Pes, 161.

Peyer's glands, 95, 205.

patch, 95.

Pharynx, 190.

tonsil, 94, 190.

Pia mater, 80, 127.
Pial sheath, 317.
Pigment cells, 23, 37.
Plasma, 10.

— cells, 41, 100.
Pleura pulmonalis, 65, 220.
Pleural cavities, 88.
Plexus choroideus, 150.

myentericus, 173, 201, 217.

of Meissner, 201, 207.

venosus vaginalls, 269.

Plicae villosje, 197, 204.
Pons Varolii, 142, 152, 154, 159.
Porta hepatis, 210.
Portio Miilleri, 300.

— vaginalis uteri, 266.
Posterior nerve roots from spinal

cord, 136.
Prickle cells, 23.
Primitive dental groove, 175.
fibrillge, 107, 111, 138.

Primitive fibrils, 69, 113.

ora, 263.

Prostate, 253.
Protoplasm, 1.

, Structure of, 6.

Protoplasmic membrane, 39.
Proximal convoluted tubule, 235.
Pulp tissue, 227.
Pulvinar, 162.

Purkinje's ganglion cells, 152, 154.
Pyloric glands, 196, 199.
Pvramid of Ferrein, 233.
Pyramidal decussation, 142.
tracts, 142.

Rami capsulares, 214.
Ranvier's constrictions, 108.

nodes, 108.

Raphe, 147, 156.
Red blood corpuscles, 10, 12.
Reissner's membrane, 326, 328.
Remak's fibrous layer, 77.

nerve-fibre, 111.

Rete Malpighii, 19.

mucosum, 19.

testis, 250.

Reticular cartilage, 49.

formation, 156.

Retina, 308.

, Blind spot of, 309.

, Blood-vessels of. 317.

, Ganglion cells of, 311.

, Lymphatics of, 317.

Rhodopsin of Kuhne, 314.
Rods and cones, 313.
Reliefs secondary substance, 68.
Rosette stage in nucleus, 8.
Rugse, 268.

Saccules, 321, 322.

Saccus endolymphaticus, 321.

Saliva, 189.

Salivary cells, 182.

glands, 178.

Blood-vessels of, 186.

Ducts of, 180.

Lobes of, 180.

Lobules of, 180.

Lymphatics of, 186.

Nerves of, 186.

Sarcode of Dujardin, 5.
Sarcolemma, 67, 68, 72.
Scala tympani, 320.

vestibuli, 320.

Schultze's protoplasm, 5.
Schwann's cells, 5.
Sclerotic, 298.
Scrotum, 64.
Sebaceous follicles, 236.

INDEX.

351

Semicircular canals, 320, 322.
Semilnnar valves, 75, 86.
Seminal cells, 247.

— tubules, 246, 252.
Sensory ganglion cells. 141.
Septum cisternae lymphaticae, 30.
Serous glands, 178, 188.

membranes, 89.

Sesamoid cartilages, 48.
Sharpey's perforating fibres, 54.
Sheath of Henle, 116, 119.

of Schwann, 108.

Simple axis cylinders, 111, 114.

lymphatic glands, 92.

Skin, 274.

blood-vessels of, 289.

lymphatics of, 290.

nerves of, 290.

Solitary glands, 95.

lymph follicles, 205.

Spaces of Fontana, 299.
Spermatoblasts, 247.
Spermatozoa, 249.
Sphincter papillae, 301.
Sphincters, 65.
Spinal cord, 127.

grey matter, 128, 136.

white matter, 128, 130.

Spiral tubule, 237.
Spleen, 225.

, Capsule of, 225.

, Lymphatics of, 229.

, Nerve-fibres of, 229.

, Parenchyma of, 226.

, Pulp of, 226.

, Eed blood corpuscles of, 16.

, Trabeculoe of, 226.

Spongy bone substance, 54.
Squamous epithelial cells, 18.
Sternal cartilage, 47.
Stigmata, 82.
Stomach, 196.
Stomata, 29, 82, 89, 224.
Stratified columnar epithelium,
21.

— pavement epithelium, 20.
Stratum adiposum, 276.

cinereurn, 160.

corneum, 19, 274.

gelatinosum, 159.

glomerulosum, 159.

lucidum, 19.

Malpighii, 274.

— opticum, 160.
Stria vascularis, 328.
Stroma, 12.
Subarachiioidal spaces, 88, 127,

150, 318.
tissue, 128.

Subcutaneous lymphatics, 88.
Subcutaneous tissue, 275.
Subdural spaces, 88, 127, 150.
Subendocardial tissue, 74, 75.
Subepitbelial endothelium of De-

bove, 35.

Subhyalpid cells, 307.
Submaxillary ganglion, 163.
Submucosa, 189.
Submucous lymphatics, 88.
SuLpericardial nerve branches,

76.

tissue, 74.

Substantia gelatinosa, 134.

nigra, 161.

Subvaginal space, 318.
Sudoriferous canal, 276, 277.
Sulcus hippocampi, 159.

— spiralis, 327, 328.
Superior pedunculus cerebelli,

162.

Suprachoroidal tissue, 300.
Suprarenal bodies, 340.
Supravaginal space, 318.
Sweat glands, 65, 276, 290.
Sympathetic system, 166.
Synovial cavities, 88.

Tactile corpuscles, 115, 118.

hairs, 286.

Tapetum nigrum, 301, 303, 305,

315.

Tarsal plate, 292, 293.
Taste buds, 193.

cells, 193.

goblets, 193.

Teeth, 171.

cement, 174.

development, 175.

pulp, 174.

Tegmental cells, 193.
Tegmentum, 160, 161.
Teichmann's crystals, 13.
Tendon cells, 33.
Tendons, 87.
Tenouian cnpsule, 318.

spa.ce, 318.

Tensor choroidese, 300.
Terminal bronchi, 221.
Testis, 244.

Thalamencephalon, 161.
Thalamus opticus, 157, 161, 162.
Thoracic duct, 84.
Thymus follicles, 96.

gland, 96.

Thyroid cartilage, 46.

gland, 339, 340.

Tongue, 190.

serous glands of, 191.

352

ELEMENTS OF HISTOLOGY.

Tonsils, 95.

Touch-cells of Merkel, 115, 119.

corpuscles of Merkel, 120.

Trabeculse carnese, 75.

• of lymphatics, 65.

of spleen, 65.

Trachea, 46, 65, 217.
Tractus olfactorius, 159.

opticus, 162.

Transitional epithelium, 21.
Tuba Eustacliii, 319.
Tuber cinereum, 161, 163.
Tubercle of Rolando, 145.
Tubes of epididymis, 252.
Tunica adnata, 244.

albuginea, 244.

dartos, 65.

fibrosa, 261.

propria, 328.

vaginalis, 244.

Tyson's glands, 255.

Ureter, 230, 243.
Urethra, Female, 269.

, Male, 254.

Urinary tubules, 231.
Uterus, 64, 265.
Utricle, 321.

Vagina, 65, 268.
Varicose nerve-fibres, 110.
Vas defereus, 65, 252.

• rectum, 250.

Vasa eff erentia, 250.
Vascularisation of cartilage, 55.
Vater's corpuscles, 115.
Veins, 65.

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, Media of, 79.

of the bones, 78.

Veins of the bra.in, cord, gravid
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— , Valves of, 79.

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jugularis, and subclavia, 79.

Venae rectse, 242.

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vorticosae, 305.

Venous radicles, 227.

sinuses, 227.

Ventricle, Fourth, 148.

Ventricles, 76.

Vesiculse seminales, 65, 252.

Vestibulum, 270.

Virchow's crystals, 13.

Visceral pericardium, 74.

peritoneum, 194.

Vitreous body, 307.

White blood corpuscles, 13, 16.

commissure, 135.

fibrous tissue, 30, 31.

substance of brain, 151.

of cord, 110.

of Schwann, 107, 108.

Wolffian body, 258.

Wreath arrangement of nucleus, b.

Yellow elastic cartilage, 49.
tissue, 43.

Zona fasciculata, 341.

glomerulosa, 340.

pellucida, 259.

reticularis, 34L

vasculosa, 257.

Zonula ciliaris, 307.

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particulars of several Hundred Volumes, including Bibles and
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Books, Dictionaries, Educational Works, History, Natural
History, Household and Domestic Treatises, Science, Travels,
&c., together with a Synopsis of their numeroiis Illustrated
Serial Publications, sent post free on application.

Cassell & Company, Limited, London; and all Booksellers.

CLINICAL MANUALS

For Practitioners and Students
of Medicine.

Complete Monographs on Special Subjects.

rPHE object of this series is to present to
•*• the Practitioner and Student of Medicine
original, concise, and complete monographs
on all the principal subjects of Medicine and
Surgery, both general and special.

It is hoped that the series will enable
the Practitioner to keep abreast of the rapid
advances .at present made in medical know-
ledge, and that it will supplement for the
Student the comparatively scanty information
contained in the general text-books.

The Series will form a complete Ency-
clopaedia of Medical and Surgical Science
in separate volumes.

The Manuals will be written by leading
Hospital Physicians and Surgeons, whose
work on each special subject may be con-
sidered to be authoritative,

[P.T.O..

The following are among the Subjects that will be

dealt with in the earlier Volumes: —

THE PULSE — HEART DISEASES- INSANITY — SYPHILIS
— LUNG DISEASES — KIDNEY DISEASES - GOUT
AND RHEUMATISM— AFFECTIONS OF THE TONGUE
AND TESTICLE — INTESTINAL OBSTRUCTION —
DISEASES OF JOINTS — FRACTURES AND DISLO-
CATIONS, SURGICAL AND MEDICAL DISEASES
OF CHILDREN — CONTINUED FEVERS — AFFEC-
TIONS OF THE UTERUS AND OVARIES — MID-
WIFERY—SURGICAL DISEASES OF THE KIDNEY-
ORTHOPAEDIC SURGERY— TREATMENT OF WOUNDS
—DISEASES OF THE EYE, EAR, SKIN, AND THROAT.

Each Manual will be printed in clear
type upon good paper. They will be of a
size convenient for the pocket, substantially
bound in blue cloth limp, with blue edges.
They will contain from 270 to 540 pages,
and will be freely Illustrated by Original
Chromo-Lithographs and Woodcuts, when
required, and will be published at prices
varying from 5s. to 8s. 6d.

IN ACTIVE PREPARATION.

I.— SYPHILIS. By JONATHAN HUTCHINSON,

F.R.S., Consulting Surgeon to the London Hospital, &c.

II.— INSANITY, including HYSTERIA.

By G. H. SAVAGE, M.D., Medical Superintendent, Bethlem
Royal Hospital, and Lecturer on Mental Diseases at Guy's
Hospital.

III.— THE PULSE. By W. H. BROADBENT, M.D.,

F.R.C.P., Physician to St. Mary's Hospital.
Other Volumes will be announced in due course.
CASSELL & COMPANY, Limited, Ludgate Hill, London.

UNIVERSITY OF CALIFORNIA LIBRARY

THIS BOOK IS DUE ON THE LAST DATE
STAMPED BELOW

OCT 9 1916
OCT 29 1917

AUG241920
OCT 17 18*1

OCT 3

4 1930

THE UNIVERSITY OF CALIFORNIA LIBRARY