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MANUALS

Students of Medicine

HIS T'©*'®'&«.

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

LECTURER ON GENERAL ANATOMY AND PHYSIOLOGY
AND

J. S. EDKINS, M.A., MB.

JOINT LECTURER AND DEMONSTRATOR OF PHYSIOLOGY IN THE MEDICAL
SCHOOL OF ST. BARTHOLOMEW'S HOSPITAL, LONDON

WITH 296 ILLUSTRATIONS

REVISED AND ENLARGED EDITION

LEA BROTHERS & CO.,

PHILADELPHIA AND NEW YORK,

Co tl&f fHfmorg

SIR WILLIAM BOWMAN, LL.D., F.R.S.,

THIS BOOK IS DEDICATED,

IN ACKNOWLEDGMENT OP HIS MANY AND GREAT DISCOVERIES

IN ANATOMY AND PHYSIOLOGY.

PREFACE TO THE
REVISED AND ENLARGED EDITION.

Since the last edition of this book in 1889, consider-
able additions have been made to the knowledge of
minute structural anatomy. The progress in the
knowledge of the structure and life of the cell and
nucleus, the remarkable discoveries in the structure
of the central nervous system and sense organs
— introduced bv the method of Golo-i, and followed
up by the brilliant work of Ramon y Cajal, Kolliker,
Lenhossek, Retzius, and others — have made it neces-
sary to revise and to make considerable additions
to the chapters dealing with these organs. While
care has been taken to correct and amplify other
jmrts of the book, the chapters on the central nervous
system have been practically rewritten.

The task of rewriting and re-editing the chapters
on the brain and medulhx and on the alimentarv
canal has devolved upon my colleague Dr. Edkins,
who is now associated with me as joint-author.

While a large number of the illustrations of the
former edition have been retained, a considerable
number has been added ; these are either original
photograms prepared by Mr. Norman from Dr.
Edkins's and my own speciiiiens, or they are copied
from Kolliker's " Handbuch," from Ramon y Cajal,
from Schiifer (Quain's " Anatomy "), from Halli-
burton (Kirke's " Physiology "), and from Klein and
Noble Smith's " Atlas of Histoloijv." To our colleague
Dr. Tooth our special thanks are due for the loan of
some of the lantern slides illustrating the medulla.

E. KLEIN.

St, B.uiTHOLOMEw's Hospital,
LONDOX. — 1S98.

COXTENTS.

CHAPTER

I.— Cells . , . . .

II.— Blood

III. — Epithelium ....
IV. — Endothelium ....
V, — Fibrous Connective Tissues

VI. — Cartilage

VII.- Bone

VIII. — Xon-strii:)ed Muscular Tissue .
IX. — fStriped Muscular Tissue .
X.— The Heart and Blood-Vessels .
XI. — The Lymjjhatic Vessels
XII. — Follicles or Simple Lymph Glands
XIII.— Compound Lymphatic Glands .
XIV. — Nerve Fibres ....
XV. — Peripheral Xerve-Endings
XVI.— The Spinal Cord

XVII.— The Medulla Oblongata or Spinal Bulb
XVJII. — Continuation of the Medulla Oblongata throu^
Pons Varolii and the Region of the Crura
XIX. — The Cerebrum and Cerebellum
XX. — The Cerebro-Spinal Ganglia
XXI. — The Sympathetic System
XXII. — General Considerations as to the Anatomical Con
stitution and Nature of the Nervous System

XXIII. -The Teeth

XXIV.— The Salivary Glands

XXV.— The Moutli. Pharynx, and Tongue .
XXVI. — The (Esophagus and Stomach ....

h the

PAGE

10.5

117

126

134

140

155

170

202

216
235
253

2.58

268
275
286
298
307

Elements of Histology.

. " CHAPTJER PAOE

XKVIL— The Small and Large Intestine .... 317

XXTIIL — The Glands of -Brunner andthe Pancreas . . 328

XXIX.— The Liver 333

XXX.— The Organs of Respiration 3.30

XXXI.— The Spleen 3-51

XXXII.— The Kidney. L'reter and Bladder . 356

XXXIIL— The Male Genital Organs 372

XXXIV.— The Female Genital Organs . . . .386

XXXV.— The Mammary Gland 400

XXXVI.— The Skin 404

XXXVII.— The Coniuuctiva and its Glands . . .424

XXXVIII. — Cornea, Sclerotic, Ligamentum Pectinatnrn

and Ciliary Muscle 429

XXXIX. — Iris, Ciliary Processes and Choroid . 436

XL.-— The Lens and Vitreous Body ... 442

XLI. -The Retina 44.5

XLIL— The Outer and Middle Ear .... 4-58

XLIIL— The Internal Ear . . \. . 460

XLIV. — The Xasal Mucous Membrane .... 47-")

XLV.— The Ductless Glands 484

jprnpfrtn o( l\ft

^sjuciaiimi uf i^e ^^lumni of t^e

CoUtgc of I^DS. & iurgs.. gfto fork,

Elements of Histology.

CHAPTER I.

CELLS.

1. The ripe oviiiii (Fig. 1) of man and mammals
is a minute spherical mass of a soft, gelatinous, trans-
parent, granular-looking substance, containing nume-
rous minute particles — yolk
globules. It is invested by
a radially striated delicate
membrane called the zona
pellucida. Inside this mass,
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 shoAv^s distinct
movement, 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 do-
mestic animals varies between ^^^ and y^^ of an
inch. But before it ripens the ovum is considerably

V--^-c

Fig. 1. — Ripe Ovum of Cat.

a, Zona pellucida ; h, gerniinal
vesicle; c, protoplasm.

2 Elements of Histology.

smaller — in fact, its size is in proportion to its
state of develo])ment.

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

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

a Cells foimiui,' ilie ectoderm ; b, cells forming the endoaerm ; c, larue

formative cells ; /, segmentation cavity. {Handooolc.)

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

Fig. 3.— From a Section through the Rudiment of the Embryo Chick,

e, rrimitive groove ; /, dorsal laminae of epihlast : d, raesoblast. The
thin layer of spindle-shaped cells is the hypoblast. (.Handbook.)

has originated two new elements, each of which
consists of protoplasm, of the same substance as that
of the original ovum, and each contains one nucleus
or kernel. ; The investment of the ovum rakes no

Cells,

part ill this process of division. Not long afterwards,
each of the two daughter elements undergoes cleavage

Fig. 4.— Vertical Section tlirough the Ovum of Bufo Cinereiis, in the early
stage of the Embryo Development.

a, Tegmental layer of epiblast ; 6, dorsal groove ; c, rudiiuent of central nervous
system ; d, notochord ; e, deep layer of epiblast ; /, mesoblast ; g, hypoblast ;
ft, cavity of alimentary canal— Rusconi's cavity ; h, central yolk ; A:, remainder
of von Baer's or segmentation cavity. ^Handbook.)

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

4 Elements of Histology.

many generations (Figs. 2, 3, 4), so that after a
few davs we find within the orioinal 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 amceb?e, 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 amoeb?e, grow in size and divide
■ — that is to say, the individuals of a generation grow
in size l^efore each gives rise to two new daughter
individuals.

4. Although for some time during embryonic 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,

Cells. 5

their protoplasm and nucleus disappear, and tliey
give origin to material other than protopLism — e.g.
collagenous, osseous, elastic, and other suljstances.
As develojiment proceeds, and after birth of the
fa3tus, different cells assume different functions, which
for each kind are of a special character and constitute
its specific character or its specific junction.

5. Beginning with the ovum, and ending with the
protoplasmic nucleated elements found constituting
the organs and tissues of the embryo and adult, we
have, then, one uninterrupted series of generations of

Fig. 5. — Amoeboid iiioveinent of a Wliite Blood Corpuscle of Man ; various
phases of nioveiiient. (Handbook.)

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 cellula), but each consists
of the protoplasm of Max Schultze (sarcode of Dujar-
din), 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. A.11 of them in an early stage of
their life-history, and some of them throughout it, show
the phenomenon of contractility, or amoeboid move-
ment (Fig. 5).

In a recent work, and following the procedure of
V. Sachs on the life and activity of vegetable cells, v.
KoUiker systematises and summarises those of animal
cells thus : The protoplasm and nucleus constituting

6 Elements of Histology.

a vegetable cell is called by v. Sachs an energid; in
the animal body it is represented by a nucleated
protoplasmic cell without a cellulose membrane, and
is called by v. Kolliker a protohlast (germinal matter
of Beale). All protoblasts, as also all energids, are
always derived from parent protoblasts ; they always
propagate by division, and in this manner carry on
the race from generation to generation ; they are the
instruments of heredity.

All growth of the protoblasts takes place by
internal processes — that is, by intussusception.

The active work of protoblasts consists in : («)
formation of the typical organs ; (6) special move-
ments of the protoplasDi — e.g. amoeboid movement ;
(c) the formation of alloplasmatic organs (A. Meyer).
These latter are derived from the livmg protoplasm,
are organised, and are participating themselves in the
living functions, but they are not capable of multipli-
cation by division. Such alloplasmatic organs are :
cilia, muscular fibres, nerve cells and nerve tibres, and
the terminal cells in the sense organs, {d) The pro-
duction of passive, partly non-organised, ergastic
structures (A. Meyer), or formed matter (L. Beale) ;
such are the cellulose membranes of vegetable cells,
cuticular formations, fluids, and intercellular and
other substances (collagenous, chondrinous, osseous,
elastic, dental, etc.), cell-juices and granules of all
kinds.

Cells ditfer 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 tt/ou ^^ '"^"^ "^*^^^
to that of a laroe ganglion cell in the anterior horns of

Cells.

the spinal cord of about ^.^o of 'ii^ inch, or to that of
multinucleated cells of the bone marrow — myeloplax —
some of which suri)ass in size even the ganglion cells.
The same holds good of the nucleus. Between the
nucleus of a ganglion cell of about ^\-^ to yaVo ^^ ^^
inch in diameter and the nucleus of a white blood
corpuscle of about -goVo ^^ tit wo ^^ ^^^ inch and less
there are all intermediate sizes.

6. Pi-otoplasiii or cytoplasm is a transparent
homogeneous or granular-looking substance. On very
careful examin-
ation with good
and high powers,
and especially
^vhen examined
with c e r t a i n
reagents, in
many, but not
in all, instances
it shows a more
or less definite
structure (Fig.
6), composed of
fibrils, more or
less regular, and
in some instances grouped into a honeycomhed re-
ticulum, sjyongioplasm, in the meshes of which is
a homogeneous substance, /njaloplasm (Leydig).
The closer the meshes of the reticulum, the less
there is of this interstitial substance, and the
more regularly granular does the reticulum 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 this becomes disintegrated ; so also
act dilute acids and alkalies. All substances that
coagulate proteids have the same effect on protoplasm.

Fig. 6. — Anictboid pale leucocyte of the newt,
showing the nuclei embedded in the cell proto-
Ijlasni— this latter consisting of spongioplasm
and hyaloplasm. (After Scho/er.)

Elements of Histology.

In arrangement of its elements the spongioplasm
ditfers in different cells ; while in some — e.g. spheroidal
or cubical ej^ithelial cells — it is as a rule uniform ; in
columnar cells it is elongated in the direction of the
long axis of the cell, hence the reticulum appears as
an eminently longitudinally fibrillated substance ; in
ganglion cells it is concentrically arranged. In some

Fig. 7. — Cell with radially disposed reticulum from the intestinal epithelium
of a worm. (After Carnoy, from Quain's "Anatomy.")

mc. Cell iiiembraiie ; j)c, cell protoplasm ; mn, nuclear membrane ; pn, nuclear
achromatin surrounding the convoluted chromatin filaments bn.

cells in the outer portion the spongioplasm possesses a
different arrangement from that in the middle portion,
and then a division is made between ectoplasm and
endoplasni (Fig. 7). The hyaloplasm differs in amount
in different cells, and in the same kind of cells it
varies according to different states of cell activity.
Thus in gland cells during activity the amount of
hyaloplasm is increased, containing in these instances
more or less of jjranular matter.

Cells.

In amceboid cells, such as the white corpuscles of
the blood, the hyaloplasm is the substance in which
the spontaneous or amoeboid changes and movement
are principally lodged, as has been shown by instan-
taneous electric illumination by Strieker.

In the protoplasm of many cells are lodged
granules of various kinds, microsomes ; they differ in
size, shape, colour, and chemical nature, and are, as a
rule, the result of cell activity. Such are the zymo-
gen granules in secreting gland cells ; eosinophil e,
basopliile, and neutrophile or amphophile granules
in leucocytes ; glycogen granules in the liver cells,
cartilage cells, and leucocytes ; pigment granules in
various kinds of jDigmented cells ; fat granules and
fat globules in wandering cells, in connective-tissue
cells, in liver cells, in
the epithelial cells of
the milk gland, etc. It
is not justifiable to as-
sume with Altmann that
these microsomes or bio-
blasts are living entities
in the sense that the
whole cell is.

In the cell proto-
plasm of leucocytes, of
epithelial and other cells,
certain granules and
fibrils have been de-
scribed by Flemming,
Boveri, Heidenhain, and
others, which being of
a constant and definite

nature play an important part in the division of the
cell and its nucleus. This is the centrosome, and with
its radiating fibrillse forms the attractionsjyJiere (Fig. 8).
The centrosome is a granule surrounded by a hyaline

Fig. 8.— Leucocyte of Salamandra con-
taining two nuclei, and showing the
attractionsphere : the centrosome is
already divided into two. (After Dr.
Martin Heidenhain.)

Elements of IIistologv.

spherical space ; through this pass the fibrillse radi-
ating from the former, aod connect it with the
spongioplasm of the cell body. The whole — Le

// ' ' -»— ^-^^-i '— — '^^

Fig. 9. — Blastomeres of Bi-segmented 0\-um of Ascaris megalocephala
{Ajter Boveri,from Kdllik'jr, I.)

A : a, Attractionsphere ; v, nucleus in resting- state ; B : nucleus in stage
of convolution: c, attractionsphere nearly divided; D, attract ionsphere
divided: E. attractionspheres arranged at the poles, chx-omosomes forming
tiiC eauaiorial plate.

centrosome and radiating tibrilhe — represents the
attractionsphere. Preceding the division of the
cell nucleus, the centrosome divides into two,
each daughter centrosome, with its own hyaline
areola and system of radiating fibrillar, forming
by - and - by a separate attractionsphere, which

Cells. i i

migrating towards op})Ositc pules of the cell-
Itody become separate jjoints of attraction for the
divided nuclear mitoma. [See division of nucleus.) So
that the division of the attractionsphere would be
the tirst, the division of the nucleus the second, and
the division of the cell protoplasm the third and final
stage in the division of a cell (Fig. 9).

7. The iiiicleiis, 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 ; the former is
tlie membrane, the latter the nuclear substance, karyo-
plasm, or nucleoplasm. This, again, is composed, in
adult nuclei, of a stroma or network, mitoma, and the
inter-Jibrillar suhsta^ice. The network consists of
tibrils of various thickness, and trabecular or septa
more or less irregular in thickness and length. In-
timately connected with and lodged in the network
are anijular or rounded masses called nucleoli. The
number and size of these vary considerably ; in
young nuclei they may be large and numerous, in
adult or resting nuclei they are few, and in those
about to divide they are altogether absent. Also the
network is subject to great variation : while in adult
or resting nuclei^ and particularly those about to
divide, the network is of great uniformity and well
developed ; it may be very imperfect in young nuclei,
in which it is sometimes represented by a number of
irregular masses joined by short bridges. The more
perfect the nuclear network, the fewer are the nucleoli.
Owing to the ready manner in which the fibrils of the
nuclear network, i.e. the mitoma, take up certain dyes,
their substance is called chromatin, and the fibrils
are the chromosomes ; while the inter-tibrillar sub-
stance not possessed of this character is called
achromatin. Occasionally, also, the achromatin ap-
pears composed of fibrils, and these are then called

1 2 Elements of Histology.

secondary fibrils, as distinct from tlie chromosomes or
})rimary fibrils. Rabl and with him Heidenhain
maintain, however, that the achromatin in typical
adult nuclei is ahvays composed of tine fibrils, and
that both the chromatin and achromatin fibrils possess
a definite unipolar arrangement and convergence,
while Carnoy and van Gehuchten assume a bipolar
arrangement. But this distinction holds good only
for adult nuclei ; in young nuclei the whole nuclear
contents may possess this aflinity for the same dyes,
and in this case the whole nucleus becomes uniformly
stained. The nuclear membrane is a condensed outer
stratum of the nuclear network. At the commence-
ment of the division of the nucleus the membrane
disappears.

In some instances it can be shown that the
nuclear filjrils 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
diti'erentiated by the apjDearance of a membrane.

8. During: division of the cell the nucleus
generally divides before the cell i)rotoplasm. This
division of the nucleus was formerly supj)osed to
occur in the same manner as that of the cell proto-
plasm— i.e. by simple cleavage. This mode is called
the direct or amitotic division, or Remak's mode of
division. In this division the nucleus is supposed to
become constricted, kidney-shaped and hourglass-
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 contrac-
tility of the nucleus may, and occasionally has been
observed to, cause these changes of shape. From the

Cells.

ol>s('r\ations of Schneider, Biitschli, Folil, Strass-
burgor, Mayzel, van Beiieden, Schleicher, Fleniiiiing,
liabl, and others, it is known that in the embryo and
adult, in vertebrates and invertebrates, in all kinds of
cells, both in the noi'nial as well as morbid condition, the
division of the cell protoplasm is preceded by complex
changes of the nuclear mitoma, leading to the division
of the nucleus (Fig. 10). The sum-total of these

Fig. 10. — Karyoinitosis.
A, Ordinary nucleus of a columiiar opitlieli.al cell : b, c, the same nucleus in the
stage of convolution ; D. the wreath, or rosette form; e, the aster, or single
star; F, a nuclear spindle from the Desceiin't's endothelium of the frog's
Cornea; G, H, I, diaster ; k, two daughter nuclei.

changes is called indirect division, karyokinesis
(Schleicher) or karyomitosis "^ (Flemming). Where
this process occurs in its complete and typical form,
the mitoma passes through the following phases
(Flemming, Rabl) : —

i. — Convolution or spireme or shein ; disappearance
of the nucleoli, increase of the fibrils constituting the

* Schleicher noticed that the fibrils duriuo; this process show
movemeut ; hence the name Karyokinesis. Mitosis indicates the
r- . grouping and changes of the fibrils (MtTos = fibril).

14 Elements of Histology.

chromatic substance, at the same time the fibrils
become free, as it were, and bent and twisted at first
into a dense, afterwards into a loose convolution.
The fibrils of the loose convolution are thicker than
before, less twisted, and more like masses of loops.

"> c

^ ^If

^?\r'.4\:^

'^^^ ■- .^^^'r>'

Fig. 11. — Eiiithclium of iiiouth of einbiyo salamander, showing nuclei in
various stages of karyomitosis (Flemming).

These latter Ijy cross division along the periphery of
the mass increase in number, and thereby are con-
verted into simple loops, arranged more or less like a
wreath or rosette. The whole nucleus is larger than
before, its membrane has disappeared, and it is sur-
rounded by a more or less clear halo of cell proto-
plasm (Fig. 11).

ii. — Longitudinal division of the loops, each loop
giving origin to a pair of sister loops; the whole,
viewed from the surface, looks like a star of numerous
fine fibrils, joined centrally so as to form single loops.

Cells.

iii. — The nuclear sjnndle^ a spindle shaped ar-
rangement of tine threads of (possibly) achromatin
extending between two opposite points of the cell
protoplasm ; these points are the poles, and the
transverse line midway between them — i.e. at the

Fig. 12. — Karyomitosis. {Ajter KolUker.)

A, Spireme ; b, diasier; c, ilie nucleus lias divuled, cUe prucoi'lasiu of the cell
In tbe act. of dividing.

broadest part of the spindle — is called the equator.
At each pole the threads of the spindle are connected
with a granule of the cell protoplasm, tlie pole cor-
puscle or centrosome, mentioned on a previous pa^-e ;
from the centrosome radiate numerous fine fibrillar,
connecting the centrosome or pole corpuscle with the
cell protoplasm, thus forming " the suns " or attraction-
spheres, one at each pole (van Beneden).

The above-named sister loops so arrange themselves
about the equator of the spindle as to form a star —
the motJier-star, monaster, or aster. In this arrange-
ment the vertex of the loops is directed inwards, the
open limbs outwards. Seen in profile the aster would
appear like a narrow granular - looking plate of
chromosomes — the nuclear plate.

iv. — Metakinesis : Of each pair of sister loops form-
ing the aster one loop is attracted by — i.e. migrates

1 6 Elements of Histology.

towards one, tLe otlier towards the other pole of the
spindle: that is, towards the attractionspheres, the
vertex of the loops always leading.

V. — Diaster : arrived at tlie pole, the loops form
again an aster or daughter star for each pole (Fig. 12).

\i. — Dispireme : the threads of each star become
convoluted.

ZS^ow follows usually the division of the cell proto-
plasm in the line of the equator of the spindle.

vii. — In the last phase all traces of the spindle are
lost : a membrane appears around each of the two
new nuclei, and the threads of the dispireme become
branched and connected into a network.

From the forecjoin^; it is clear that during division
an intimate fusion Vjetween cell protoplasm and
nucleus takes place : («) by the fusion of the nuclear
interstitial suVjstance with the cell protoplasm after
the disappearance of the nuclear membrane ; and (h)
bv the connection of the nuclear spindle with the
centrosomes and attractionspheres, the fibrils of the
latter being part of the cell protoplasm.

It ought to be mentioned, however, that some
histolo^ists do not rec;ard the fibrils of the nuclear
Spindle as part of and derived from the original
nuclear substance (achromatin). Boveri regards the
fibrils of the spindle as derived from the cell proto-
plasm and as forming part of the attractionspheres
— i.e. those fiVjrils which remain connecting the two
attractionspheres, and which finally, after the nuclear
division has Ijeen completed, by their transverse
division, mark off and initiate the final stage — that is,
the division of the cell body.

While these various details and phases in the
changes and division of the centrosome and attrac-
tionsphere are well enough marked in the ovum, as is
also their relation to the chromosomes of the dividing
ovum nucleus, it is not sufficiently established that

Cells. i 7

the above are of general occurrence in the division of
adult cells; the attractionsphere and its division have
])een observed only in a few such instances — e.g. in
the leucocytes of salamander and man.

In some cases the process of karyomitosis has Vjeen
found to be atypical, inasmuch as some of the above
phases are left out, as it were ; while in other cases
the nuclear division takes place already during the
earlier phases — e.g. in the phase of the spireme.
When the nucleus divides into two or three or more
nuclei without the cell protoplasm also undergoing
division, a cell with two, three, or more nuclei is the
result.

Multiplication of the nucleus by budding and
direct fission has also been observed, but it is quite
possible that this process is only as a sort of imper-
fect and abnormal karyomitosis.

This mode [)robably jDlays a more important part
than the typical karyomitosis, whenever rapid multi-
plication and rei^roduction are necessary. Thus, for
instance, while in the epithelium cells covering the
anterior surface of the normal cornea of the newt and
frog here and there a nucleus can Ije seen which
shows the process of typical karyomitosis, such forms
cannot be found in cases of rapid regeneration of
that epithelium. For example, after removing the
whole thickness of the anterior epithelium from the
middle part of the cornea, rapid multiplication of the
epithelium cells takes place, starting from those
immediately around the defect ; in consequence of
this, in two or three days the defect becomes again
quite covered with the new epithelium. Xow, ex-
amining the epithelium cells at the margin of the
defect, as well as those gradually pushed over and
covering the defect, none of the nuclei are found in
any of the phases of typical karyomitosis ; while a
few days later, after the defect is covered by the new
c

1 8 Elements of Histology.

epithelium, there is no difficulty in finding nuclei in
one or another ])lia.se of the typical kar3"omito.sis.

Paranuclei and cell enclosures, — It was

mentioned above that cells may and do include in
their j^rotoplasm formed substances like granules
of various kinds, fat globules, pigment, etc. ; but in
addition to these, and distinct from the attraction-
spheres mentioned on a former page, occasionally the
cell substance includes corpuscles of an altogether
different nature. These corpuscles, in size and staining
power, resemble the cell nucleus or parts thereof, and
as a matter of fact are derived from the cell nucleus.
Balbiani has called such bodies in the ovum cell
'paranuclei^ and Griitzner has applied the same term
to those that occur in the gland cells of the pancreas.
Now it is a fact that preceding the segmentation
of the ovum, and preceding the fusion of the sperm-
and ovum-pronucleus, part of this latter is eliminated,
and the same occasionally is observed to take place
in other cells prior to the division of the nucleus,
as also under various pathological conditions. The
eliminated body or bodies, known as polar bodies,
are part of the original nuclear substance, principally
the chromatin. The paranucleus is as a rule smaller
than the cell nucleus, lies close to this, and has
similar affinit}'' to the dyes which stain the nucleus
itself.

CHAPTER IT.

BLOOD.

9. Under the microscope blood appears as a
transparent Huid, the liquor sanguinis or plasina, in
which float vast numl^ers of formed bodies, the blood
corpuscles. The great majority of these are coloured ;
a few of them are colourless. The latter are called
ivhite or colourless blood corpuscles, or leucocytes ; the
former are called red or coloured blood coryuscles, or
blood-discs. They 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 cor-
puscles in each cubic millimetre {y-^^o^y of ^ cubic
inch) of human blood. There appears to be in healthy
human blood, on an average, one white corpuscle for
600-1200 red ones. In man and mammals the re-
lative number of blood corpuscles is greater than
in birds, and in birds greater than in lower verte-
brates.

The number of red, and also of white, corpuscles
is subject to variation, both in health and disease.
After profuse haemorrhage, the number of red cor-
puscles is temporarily greatly reduced, but in a short
time, it may be even in twenty-four to forty-eight
hours, they may approach again the normal number ;

2o Elemexts of Histology.

in constitutional chronic diseases the number of red
corpuscles is, as a rale, decreased ; so also in anj^mia,
spontaneous or following acute infectious diseases,
fevers, etc. The number of white corpuscles is always
greater after a copious meal than during fasting.
Certain diseases are associated with a decrease, others
wi.th an increase, of the white corpuscles of the cir-
culating blood ; the decrease when pronounced is
spoken of as leucopenia^ the increase as leucocy-
th(emia^ leucctmia, or leucocytosis.

10. The red blood corpuscles (Fig. 13) of man
and mammals are homogeneous bi-concave discs (ex-
cept in the camelida?, where they are elliptical), and
do not possess any surroundmg membrane or 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

Fig. 13. — ^arious kiuds of Red Blood i , i i i i

Corpuscles. the human red blood

A, Two human, one seen flat, the other COrpUScle is about

edgeways ; b, a red corpuscle of the ■■ p " 1 '

camel; c, two red corpuscles of the solTo '^^^ mCll 111

frog, one seen from the liroad, the \ ■\,\ ■ i ,

other from the narrow side. DreaCltn, I.e. aOOUt

7 "8 ^. and its thick-
ness about ^ ^QQQ of an inch. But there are always
corpuscles present which are much smaller by about
one-third to one-half than the others — microcytes. In
normal blood these microcytes are scarce : but in
certain abnormal conditions, especially in pernicious
anfemia, they are conspicuous by their number.

According to Gulliver, ^A'elcker, and others, tlie
followinof are the averagfe diameters of the red blood
corpuscles of various vertebrates : Man, -3-2V0 J ^^i

"3 'sou ' ^"^j 4cFo^ y outc|7, 5 0 00^ } v.iv>^jii«.ij.v, :jTi 5" ^

1 • cat, ^ J^ ; sheep, ^^W i elephant,

Blood.

horse, j:^
1

\ .

6 () O '

10 4 3 ; "ewt,
1

1 1 -t 2 •
11

musk deer, y^i^ 5 ; pigeon, ^g^y ; toad,
proteus, yl^ ; pike, ^-qVo ; ^li^^i'k,

S 1 i

In a microscopic specimen of fresh unaltered
blood (Fig. 14) the red blood corpuscles form peculiar
short or long rolls, like
so many coins, from be-
coming adherent to one
another by their broad
surfaces. Under various
conditions — such as
Avhen isolated, or when
blood is diluted with a
7*5-l p.c. saUne solution
or solutions of other salts
(sulphate of sodium or
magnesium) — the cor-
puscles lose their smooth ^•
circular outline, shrink-
ing and becoming crenate
(Fig. 15, a). In a further
lose their discoid form, and become
spherical, but beset all over their sur-
face with minute processes. This shape
is called the liorse-chestnut shaj^e (Fig. 15,
b, c). It is probably due to the cor-
puscles losing carbonic acid, as the
addition of the acid brings back their
discoid shape and smooth circular out-
line. On abstracting the carbonic acid
they return to the horse-chestnut shaj)e. ,
Water, acid, alcohol, ether, the electric
current, and many other reagents,
produce decoloration of the red blood

Fig. 14. — Human Blood, fresh.

Piouleaux of red corpuscles ; b, iso-
lated red fdrpuscle seen in pr<5flle ; c,
isolated red corpuscle seen flat ; D,
•ttliite corpuscles.

stage

of shrinking
smaller

they
and

o o

h ^'

15. — Human
Red Blood
Corpuscles.

Crenate; b, c,
horse-cbestnut-
sliaped.

corpuscles.

the coloured matter — generally the combination of
the blood-colouring matter with globulin, known
as hcenioylohin — becoming dissolved in the plasma.

2 2 Elements of Histology.

What is left of the corpuscles is called the
stroma. In ne^^i;'s and frog's blood a separation
of the stroma from the nucleus and haemoglobin can

be effected by means of
^ ^ a'^ ^c^ boracic acid(Fig. 16, b);

" Ai. ^i \^' ^8 ^F\ c ^^^^ former is called by

O ^ {€^) Briicke the oekoid, the

U^ B

latter zooid. This stroma
contains amongst other

Fig. IG.— Red Blood Corpuscles of things mucll paraf'lobu-
Man and Xewt. t mi j. c J.^

, ^ ^, . im. I he stroma or the

A, Human red corpuscles after the action , i -i •

of tannic acid; a, tbree red corpuscles, COrDUSCles Ot amplllljiaUS
from which the hierauf^loliin is pass- . ■•■ •'•

ing out: 5. Roberts's corpuscles. B, is scen, undcr Certain

^ewt s red corpusdesafter theaction '

of boracic acid; a, corpuscle. show- reao^ents, to be of a re-

mg Briicke s zooid and cekoid ;&,."'

corpuscle showing the reticulated tlCUlated StrUCture, but

stroma ; c, corpuscle showins the • ^ c i

reticulum in the nucleus; d, thenu- ]n the fresh state appears

cleus passing out. ^^

homogeneous and pale.
Decoloration of the blood corpuscles can also be
observed to take place in blood spontaneously without
the addition of any reagents or with that of indifferent
fluids, such as the aqueous humour of the eye, hydro-
cele fluid, etc. The number of corpuscles undergoing
decoloration under these conditions is, however, small,

When blood is dried on a glass in a thin tilm,
the corpuscles, forming a single layer onh", dr}^ on
before they shrink, and thus retain their natural size
and outline ; their strouia can then be easily stained
with aniline dyes.

12. The haeiiioglotoiii of the red blood cor-
puscles forms crystals (Fig. 17), which differ in shape
in various mammals. They are always of microscopic
size, and of a bright red colour. In man and most
mammals they are of the shape of prismatic needles
or rhombic plates ; in the squirrel they are hexagonal
plates, and in the guinea-pig they are tetrahedral or
octahedral.

The blood pigment itself is an amorphous dark-

Blood.

brown or l)l;ick powder — the luematin ; but it can be
obtained in a crystalline form, as liydrochlorate of
hi\iinatin (Fig. 18). These crystals also are of micro-
scopic size, of a
nut-brown colour,
of the shape of
nari'ow rhombic
plates, and are
called lut^rnin cry-
stals, or Teich-
mann^s crystals. In
extravasated hu-
man blood, crystals
of a bright yellow
or orange colour
are occasionally
met with ; they are
coverer, hctmatoidin.
tical with bilirubin
human bile.

13. The white or colourless cor-
puscles, or leucocytes, are in human

blood of about 2-5 00 ^^ 2"5Vo *^^ ^^ ^^^^
in diameter — i e. about 10 fi — and are
spherical in the circulating blood or in
blood that has just been removed from the vessels. Their
substance is transparent granular-looking protoplasm,
some containing larger or smaller distinct granules.
These granules are not all of the same nature, as
will presently appear. In some kinds of blood, notably
horse's, they are of a reddish colour, and these
corpuscles were supposed by some observers (Semmer
and Alexander Schmidt) to be intermediate between
red and white corpuscles. The protoplasm of the
colourless corpuscles contains occasionally glycogen
(Ranvier, Schiifer). In the blood of the lower verte-
brates the colourless corpuscles are much larger than

Fig. 17. — Hitmoglobin crystals.
A, Of guinea-pig ; b, of siiuirrel ; c, D, buiuan.

called by Yirchow, their dis-
They are supposed to be iden-
obtainable from

Fig. IS.— Ha-miii
crystals.

Elements of Histology.

in mammals. But in all cases tliey consist of proto-
plasm (spongioplasm and hyaloplasm), include one,
two, or more nuclei, and show amoeboid movement.
This may he observed in corpuscles without any
addition to a fresh microscopic specimen of blood,
but it always becomes much more jironounced on

Fig. 19. —Phagocyte (with three nuclei) from the iieritoneal fluid of a
guinea-pig, iireviously injected intraperitoneally with cholera culture.
The interior of the phagocyte contains numerous degenerated comma
bacilli. (Photo, highly magnified.)

applying artificial heat of about the degree of
mammals' blood. It is then seen that either they
throw out longer or shorter filamentous processes,
which may gradually lengthen or be withdrawn,
or the corpuscle changes its position either by a
flowing movement, or it pushes out a filamentous pro-
cess and shifts its body into it. During this move-
ment the corpuscle may take up granules from the

Blood. 25

siuToiinding lluicl. Leucocytes, be they in the blood
or in connective tissue or lymph glands {see below),
that can, and in certain circumstances do, take up
granules or similar matter are spoken of as phagocytes
(eating cells) (Figs. 19, 20). Division by simple

Fig. 20. — Hyaline Leucocytes (pus cells) from purulent matter ; the leuco-
cytes contain in their hyaline protoplasm two, three, or more nuclei
two of the cells contain in their protoplasm a number of cocci, these
cells acting as phagocytes. {Photo, highly magnified.)

cleavage of leucocytes of the blood of lower verte-
brates has been directly observed by Klein and
Ranvier.

14. The white corpuscles or leucocytes in the
same sample of blood differ in size and aspect. They
may be classed into three groups : (a) The li/m2)hocyte,

2 6 Elements of Histology.

a small cell possessed of a relatively large single nucleus
surrounded by a narrow zone of protoj^lasm. (6) The
typical leucocyte or liyaline leucocyte is larger than the
former, contains two, three, or even four relatively
small nuclei ; its cell protoplasm appears hyaline,
but includes a spongy network. This leucocyte is

Fig. "21. — Frog's Blood, showing red blood discs and one oxypliile white
cell. (Photo, highly magnified.)

as regards numbers by far the predominating white
corpuscle, and its amceboid movement is very striking,
(c) The gramdar leucocyte forms a small minority, it
contains a single large nucleus, occasionally two, and
its cell })rotoplasm contains conspicuous granules.

The lymphocytes are identical with similar cor-
puscles of the adenoid tissue of lymph glands, from

Blood. 27

Nvliicli ill all probability they are derived. It is highly
probable that they are young forms of the typical
leucocytes. The grnnidar leucocytes — i.e. the white
corpuscles that contain real gi'anules — behave dif-
ferently when subjected to staining with aniline dyes.
In some the granules stain readily with acid aniline
dyes — e.g. eosin — so that they become bright red —
eosinophile (Ehrlich) or o.vi/phile cells (Fig. 21); in
others the granules stain only in basic aniline dyes
— hasopJi He cells ; in still others they stain both with
acid and alkaline aniline dyes — neutrophile or amjjho-
phile. "What the exact relation of these different
granule-cells amongst themselves and to the non-
granular or hyaline cells is, is not definitely established.
But it appears from the researches of Kanthack and
Hardy that in the frog, at any rate, and probably also
in the mammal, the oxyphile or eosinophile leucocyte
does not act as a phagocyte, and that this function is mo-
nopolised by the other or hyaline variety of leucocytes.
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. According to f^
Max Schultze they are derivatives of e^\

broken-up white corpuscles ; but ac- ^S ^^
cording to Bizzozero, they are present ^

al read}' in the living and fresh blood, © o^

as pale, circular, or sliijhtly oval „. ,., „

T-i- ->-» 7\ rr<i • • • FiLT. 22.— Human

discs (Fig. 22, 0). Their size is only ^ Biooti.
1 to i of that of the red blood cor- «. R^d bino.i cor-
puscles. They are called bv him bhod platelets of biz-

■•■ •' "^ zdzero.

platelets^ and he supposes them to be of
essential importance in the coagulation of the blood,
originating the tibrin ferment. Hayem described them
previously as being intermediate forms in the de-
velopment of red blood corpuscles, and called them
hjematoplasts,

2 8 Elements of Histology.

16. Development of blood eorpiii^cles. —

At an early stage of embryonic Jife, when blood makes
its appearance it is a colourless fluid, containing only
white corpuscles (each with a nucleus), which are de-
rived from certain cells of the mesoblast. These white
corpuscles change into red ones ; the protoplasm
becomes homogeneous and yellow ; then it assumes a
flattened shape, and is in reality a coloured blood
corpuscle containing a pale nucleus. All through
embryonic life new white corpuscles are transformed
into red ones. In the embryo of man and mammals
these red corpuscles contain their nuclei for some
time, but ultimately lose them. Xew red blood cor-
puscles may, however, be formed also by division of
nucleated red corpuscles. Such dis'ision has been
observed even in adult blood of lower vertebrates
(Peremeschko) as well as in the foetus of mammals.

The cells of the mesoblast which cHve origin to
vessels (cysts and strands) are capable of producing
by budding and cleavage new white cells, which ulti-
mately change into red corpuscles. (*See formation of
blood-vessels.)

An important source for the new formation of red
corpuscles in the embryo and adult is the red marrow
of bones (Neumann, Bizzozero, E-indfleisch), in whicli
numerous nucleated protoplasmic cells (marrow cells)
are converted into nucleated red blood corpuscles —
erythrohlasts. 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 formation 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 homogeneous and
filled with liEemoglobin, while the cell grows flattened,
discoid, and the nucleus in the end disappears.

Blood. 29

Schiifer described intracellular (endogenous) for-
mation of red blood corpuscles at first as small liH;mo-
i;lobin 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
f I'om the marrow cells.

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

CHAPTER III.

EPITHELIUM.

17. Epitlielial cells (Fig. 23)are nuchated proto-

2)Io.srnic cells for ming co/dinuoas 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 sui'face of the conjunctiva, and the
anterior surface of the cornea. The lining of the
tubes and alveoli of secretin^ and excretinoj slands,
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, etc., 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, the pituitary body, etc.

The bail's and nails, the cuticle of the skin,
certain parts of the rods and cones of the retina, and
the rods of Corti in the organ of hearing, are modified
epithelial structures.

Epithelial cells are grouped together by ex-
ceedingly thin layers of an albuminous interstitial
cement substance, which duiing life is of a semi-
fluid nature, and belongs to the gi'oup of bodies
known as globulins.

18. As rec:ards 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,

Epithelium.

or spindle-shaped ; their nucleus is always more or
less oval, their protoplasm more or less longitudinally^
striated, l)eing a spongy reticulum with predominantly

longitudinal arrange-
ment. On the free
surface of the cells
— i.e. the part facing
or
-in
a
or

f^=f~

a cavity, canal,
general surface -
many instances
Ijright thinner
thicker cuticular
structure is seen,
with more or less
distinct vertical stri-
ation. 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
polyhedral or scalj

Fig. 23.— Various kinds of Epithelial Cells.

A, Columnar cells of intestine; b. polyhedral
cells of the conjunctiva; c, ciliated conical
cells of the trachea ; d, ciliated cell of
frog's mouth ; E. inverted conical cell of
trachea; f, squainous cell of the cavity of
inouth, seen from its broad surface ; G,
squamous cell, seen edgeways.

pavement cells are cubical.
The nucleus of the former is
almost spherical, that of the latter flattened in pro-
portion to the thinness of the scales. In polyhedral
cells it can be shown that the uniform granulation is
due to the regular honeycombed nature of the cell
protoplasm.

19. As regards size, the epithelial cells dilfer
considerably from one another in different parts, and
even in the same part. Thus, the columnar cells,
covering the surface of the ^^Ili of the small intestine,
are consideraljly longer than tho.se lining the mucous
membrane of the uterus : the columnar cells lining
the larger ducts of the kidney are considerably longer

Elements of Histology.

- Three Mucus-secreting
Goblet Cells.

A, From the jitomach of newt ; B, from
a mucous glaml; c, from tbe sur-
face of the mucous membrane of
the intestine.

regards ar-

than tliose 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 con-
siderably smaller than
those on the surface of
the membrane lining the
human oral cavity and
oesophagus (Fig, 24).

20. As
raiig:eiiieiit, the epithe-
lial cells are arranged
as a sinfjle layer or are
stratified, forming several
superposed layers ; in the
former case we have a sin^le-lavered, in the latter a
stratified epithelium. The simple epithelium may be
composed of squamous cells, simjyle squamous or simple
jjavement epitJiellum ; or it may be composed of columnar
cells, siinple coliLinnar epithelium. The stratified epithe-
lium 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 whicli 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, etc. Stratified
pavement epnthelium is that on the epidermis, the
epithelium lining the cavity of the mouth, pharynx,

Epithelium. 33

and oesophagus in man and mammals, the anterior
surface of tlie cornea, etc.

Functionally, epithelium can be classified as : (a)
tegmental — p.y. tlie epidermis of the skin, the epithe-
lium of mucous membrane ; (6) as secretory — e.g. the
epithelium lining tlie alveoli and tubes of secreting
glands, the liver, the kidney, etc.; (c) sensory — e.g. the
epithelial-like cells forming the terminal organs of
nerve fibres — e.g. in the retina, in the organ of hearing
(cochlea, vestibule, and semicircular canals of the
internal ear), in the taste buds, in the olfactory
membrane, and in the skin; (':/) forming special horny
organs — e.g. hairs, nails, the horny papillae on the tongue
of feline animals ; [e) some specific, not well-understood
function — e.g. the epithelium covering the glomeruli
of the Malpighian corpuscles of the kidney, the
epithelium (or endothelium) forming the wall of blood-
capillaries and lymph vessels.

•Jl. The epidermis (Fig. 25) consists of the
following layers : — («) Stratum corneum : this is the
superficial horny layer, and it consists of several
layers of horny scales, without any nucleus. Its
layers are separated from one another by narrow
clefts containing air, and they are in process of des-
quamation. This stratum is thickest on the palm
of the hand and fingers and the sole of the foot.
(6) The stratum lucidum, composed of several dense
layers of horny scales, in which traces of an ex-
ceedingly flattened nucleus may be perceived,
(c) Then follow many layers of nucleated cells,
forming the stratum or rete Malpighii or rete
mucosum. The most superficial layer or layers of it
are flattened scales, which are characterised by the
presence around the nucleus of globular or elliptical
granules of the nature intermediate between pro-
toplasm and keratin. Their substance is called
eleidin by Ranvier, keratohyalin by Waldeyer ; these

Elements of Histology,

cells
bans.

form the stratura granulosum of ^cv^.^

DeejDer down, the cells are

Fi-. 25.

a. The st
c, the

— From a Vertical Section tlirougli the
Epidermis. {Atlas.)

ratum Malpiirhii ; h. tlie Ptratuiu ,trranulo>iiiii ;
stratum luciduiii ; d, the stratum corneum.

Laiiger-
less flattened
and more
polyhed r al ,
and the deepest
form a layer of
more or less
columnar cells,
placed verti-
cally on the
surface of the
subjacent co-
rium.

The sub-
stance of the
hairs, nails,
claws, hoofs,
consists of

horny scales.

{See chapter on Skin.)
22. The
pavement
liiiiii (Fig.

Fig. 26. — From a Vertical Section
tliroiigh the anterior layers of tlie
Cornea. (Handbook.)

a. The stratified pavement eiiithelium;
b, the substantia propria, with the
corneal corpuscles between its la-
melht.

Stratified
epitlie-

26) lining
the cavity of the mouth,
the surface of the tongue,
the pharynx and oeso-
phagus of man and mam-
mals, and the anterior
surface of the cornea,
etc., is, as regards tlie
style and arrangement
of the cells, identical
with the stratum Mal-
pighii of the epidermis.
The cell protoplasm is
more transparent in the
former, and the granular
cells of the stratum

Epithelium.

granulosum are not always present, but they generally
are in the e})itheliiini of the tongue and of the rest
of the oral ca^•ity. The most superficial scales show
more or less horny transformation.

23. Stratified roliiiiiiiai' €>|>itiic'iiiini is met
with on the lining Hi('iiil)iane of the respiratory
organs : in the larynx, trachea, and large bronchi.
It consists of several layers of columnar cells ; a
superficial 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 epitheUum. It is stratified, and the most
superficial layer consists of j^olyhedral 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 gohlet
cells, and amongst the squamous cells the jirickle cells,
deserve special notice.

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
prolongations of the cell protoplasm. More correctly
speaking, the cilia are continuous with the filaments
or striye of the cell protoplasm. The superficial
layer of conical cells of the epithelium in the respira-
tory organs, the columnar cells lining the uterur, and
oviduct, and the columnar cells lining the tubes of
the epididymis, possess such cilia. In lower verte-
brates the ciliated cells are much more frequently
observed ; in Batrachia the epithelial cells lining the
mouth, pharynx, and (esophagus are ciliated.

While fresh in contact with the membrane which
they line, or even after removal from it, provided the

36 Elements of Histology.

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, etc. In these circum-
stances, removal of the impediment, as by dilute
alkalies, wdll generall}^ restore the activity of the
cilia. Moderate electric currents and heat stimu-
late the movement, strong electric currents and cold
retard it. Reagents fatally affecting cell protoplasm
also stop permanently the ciliary action.

25. CjJoblet or clialice cells (Figs. 24, 27) are

cells of the shape of a conical cup. 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

=^="^-='^-%nn goblet contains mucus. This latter

P|'| -P< £' ^ -^' - J ^i"*^! ^^ ^^ various states of for-

^llim^^^ mation, and may at any time be

Fig. 27.— From a Ver- poured out of the cell. Goblet

tical Section throucrh n , i j. •-!

the Epithelium on cclls are most commonlv met with
the surface of the amon^jst the epithelium lining the

mucous membrane . ^ ^ , , ^ ^

of the large intes- respiratory Organs, the surface 01
^'"^* the stomach and intestines, and

Three goblet cells are • n • i t •

seenpourin^'oiit their especiallv HI mucous glands, m

luucus. TliG r6st urt* "^ . .

ordinary coiiuunar whose secretiuo- portion all cells

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 transformation of
the cell into a mucus-secretinfj goblet cell. This
takes place during life, and corresjDonds to an im-
portant function of columnar ejDithelial cells — viz.

Epithelium. 37

the formation of iniicus. In mucus-secreting glands
all the epithelial cells have this function permanently,
but in ordinary columnar epithelium only a compara-
tively 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 shorth^ afterwards
resume the original shape and aspect of an ordinary
protoplasmic, cylindrical, or conical epithelial cell,
and vice versa. If ciliyted 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 interstitial substance of the cell reticulum swells
up and increases in amount, the meshes enlarging and
distending the body of the cell. The middle and
upper part of the cells then change, tirst into
mucigen, and hnally into mucin, which is eventually
discharged, leaving in the deeper part the compressed
nucleus surrounded by a trace of protoplasm behind
(see Fig. 34).

2G. Prickle cells (Fig. 25). — Amongst the
middle and deeper la3^ers 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 proto-
plasm to ])rotoplasm, connect the surfaces of the cells.

27. Pigmented epithelial cells — i.e. epithelial cells
filled with black pigment pai'ticles (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, pigment in the shape of dark granules is found
in the protoplasm of the deeper epithelial cells, as well

38 Elements of Histology.

as in branched cells situated between the epithelial
cells of the deeper layers. Minute branched non-
pig mented 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 cavit}', cornea, etc.

28. Epitlielial 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 no such conspicuous
loss occurs — as, for instance, in the stomach and in-
testines, the secreting glands, or sense organs.

In the stratified pavement epithelium it is the
cells of the deepest layers which chiefly divide. As
a rule, this division takes place transversely in the
cylindrical cells, but may also occur longitudinally (A.
Kollmann). The epithelial cells next to the deepest
layer of columnar cells are to a great extent the result
of the division of the latter, and as this proceeds there
is a orradual shiftino; of the older cells towards the
surface and a simultaneous flattening of the cell
protoplasm as well as the nucleus.

29. The interstitial substance between, and the
protoplasm of, the epithelial cells being a soft flexible
material, the cells can change their shape and arrange-
ment owing to pressure exerted on them by the con-
traction or distension of the subjacent membrane.
Thus the epithelium lining a middle-sized bronchus
at one time apjDears composed of thin columnar cells
in two layers ; at another, as a single layer ; or again,
as a single layer of short columnar cells : in the first
case the bronchus ig contracted, in the second in a
medium state of distension, in the third much dis-
tended. Similar changes may be noticed in the

Epithelium. 39

epithelium lining tlu^ bladder and the, stratum
Malpighii.

The interstitial substance, being a soft, semi-fluid
substance, represents the paths through whicli granules
and formed particles may find their way from the free
surface into the membrane beneath, or vice versa.
Also leucocytes pass out in certain localities from the
membrane underneath, between and into the sul)stance
of epithelial cells, and may Anally be discharged on to
the free surface — e.g. in the tonsils, in the fauces and
pharynx and larynx. Epithelial cells may in this way
include in tlieir substance various formed particles :
granules, fat globules, leucocytes, nuclei of leucocytes,
etc. Besides these cell enclosures and the paranuclei
and chromatin granules mentioned in a former para-
graph, in some localities [e.g. stratum Malpighii of the
ef)idermis, epithelium of the oral cavity, pharynx and
oesophagus) the epithelial cell substance undergoes
a partial or total change into keratinous substance,
keratohyalin, forming a mantle around the unchanged
cell j)rotoplasm like a capsule.

CHAPTER lY

ENDOTHELIUM.

30. The free surfaces of the serous and synovial
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-
jjarent squamous cells, called endo-
thelial cells (Fig. 28). Each
contains an oval nucleus, situated
as a rule excentrically. Just as in
Fig 28 -Endothelium the case of epithelium, " the endo-

of the Mesentery of ■,■,•■> n i ■ •

Cat. thelial cell plates are joined by a

The outlines of the endo- fluid or semi-fluid liomoifeneous in-

thehal cells and tlie • • 7 7

nucleus of the latter terstitiat or Cement substance or the

are well shown. „ , , , .

nature oi globulin. \\ hen examin-
ing any of the above structures fresh, the endothelial
cells are not, as a rule, visible, owing to their great
transparency; but by staining the structures with a
dilute solution of nitrate of silver, and then exposing
them to the influence of the light, the cement sub-
stance appears stained black, whereby the shape and
size of the cell plates become e^■ident. 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

En DO THELIUM.

consists of a homogeneous ground 'plate. Tii it lies
tlie nucleus, and around it is a sul)staiicf* which ap-
pears granular, but ^vhich is of a fibrillar nature, the
fibril he being arranged in a network, and extending

Fig. 20.— Network of Lymphatics in the Central Teudon of the Diaphragm
of Rabbit, prepared with nitrate of silver, so as to show the outlines of
the Endothelial Cells formiug the wall of the Lymphatics. {Handbook.)

a. Large I^-mphatic vessels; b, Ivinphatic capillaries ; c, apparent ends of the

capillaries.

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 tibrillje of
the cell substance appear to be connected with the
nuclear reticulum.

31. As regards shape, endothelial cells differ
considerably. Those of the pleura, pericardium, peri-
toneum, and endocardium of man and mammals are

Elemexts of Histology.

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. 30. — Onientum of Rabbit, stained with Nitrate of Silver. {Atlo.s.)
(I. Ordiuaiy flat endothelial cells ; b, germinating cells.

are very regular, pentagonal, or hexagonal, ha^^Ilg
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. 29) are narrow
and elongated, with more or less sinuous outlines. In
the lymphatic capillaries the endothelial plates are
polygonal, but their outline is serrated.

32. As a rule, the endothelial cells are flattened — -

Endothelium.

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

Fig. 31.— Part of Peritoneal Surface of the Central Tendon of Diaphragm of
Rabbit, prepared with Nitrate of Silver. (Handbook.)

s, StoniRta; Z, lymph-channe!s ; f, tendon Inindles. The surface is covered witli
endothelium.' The stomata are surrounded by geruunatiug endi)thelial cells.

and omentum, on the synovial membranes, tunica
vaginalis, testis, etc. They are especially observable
in considerable numbers in the pleura and omentum
(Fig. 30) of all normal subjects (in man, ape, dog, cat,
and rodent animals) ; their number and frequency of
occurrence are increased in pathological conditions
(chronic inflammations, tuberculosis, cancer, etc.).

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

Elements of Histology.

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 1)1 ood corjiuscles. On the

Fi.£

-Part of Omentum of Cat, stained with Nitrate of Silver.

a, Feuestraj or holes ; />, tianecultB covert-a witli emloilielium. Ouiy tiie outliues
(silver lines) of the endothelial cells are shown.

surface of the serous membranes, especially the
diaphragm (Fig. 31) and pleura, there exist minute
openings, stomata, leading from the serous cavity into
a lymphatic 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 ])eritoneal cavity
from the cisterna lymphatica magna. This part of

Endothelium. 45

the peritoneum is called the septum cisternae lym-
phaticji? magnsB, and on it occur numerous holes or
stomata, 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 th(^ female frog, these and
other germinating endothelial cells of the peritoneum
(mesogastrium, mesenterium, septum cisternee) are
ciliated.

34. The omentum and parts of the pleura are, in
the adult human subject, ape, dog, cat, guinea-pig, rat,
etc., of the nature of di. fenestrated membrane {¥\g. 32),
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
fenestras 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. 31). The above-mentioned
stomata occur amongst these small endothelial cells.

CHAPTER Y.

FIBROUS CONNECTIVE TISSUES.

35. By the name of " connective tissues " we
designate a variety of tissues which have in common
with one another, that they are developed from the
same embryonic elements ; that they all serve as sup-
porting tissue or connecting substance, 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 normal and morbid condition one may
be changed into the other ; that in the adult they
gradually shade off one into the other ; and that they
yield allied chemical products.

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 tJie cells. In the fibrous con-
nective tissue the matrix yields collagen or gelatin,
and the cells are called connective-tissue cells, or con-
nective-tissue corpuscles. In the cartilage the ground
substance yields chonclrin, and the cells are called
cartilage cells. In the third group the ground sub-
stance contains inorganic lime salts, intimately con-
nected with a fibrous matrix, and the cells are called
hone cells.

36. The fibrous coiiiiertivc tissue, or white
fibrous tissue, occurs in the skin and mucous

Fibrous Connective Tissues.

membranes, in tlie serous and synovial membranes,
in tlie membranes of the brain and spinal cord, in
tendons and tendon sheaths, in fascite and aponeuroses,
in the intermuscuhir tissue, and in the tissue con-
nectino; neiirhbourim'- organs, etc. It consists of
microscopic band-like or cylindrical bundles or fasciculi
of exceedingly tine homogeiuous tinrils (Fig. 33), which

Fig. 33. — Plexus of Bundles of Fibrous Tissue from the Oiuentuiu of Rat.

«, Capillary blood-v'cSi'cl ; ^, lumiilc:^ nr Hijidhs tissue ; c tue oouuectivc-tiiiu.:
foi'iuiscles; c/, i)lasiii i ceils. {Atlas.)

are known as the elementary connective-tissue fibrils.
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 microscoj)ic bundles are aggregated
into smaller or larger groups, the trabeciilce., and these
are again associated into groups. The fibrils are held
together by an albuminous (globulin), semi-fluid,
homogeneous cement substance^ which is also present
between the bundles forming a trabecula.

48 Elements of Histology.

The groups of bundles, and even the individual
bundles, are in some localities invested with an elastic
sheath — e.g. in the trabeculae of bundles in the
subcutaneous tissue.

On addincj an acid or an alkali to a bundle of
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 tibrous tissue vield collacjen or
gelatin.

37. According to the arrangement of the bundles,
the fibrous connective tissue varies in ditierent locali-
ties. (1) In tendons and fasciae the bundles are
arranged j^arallel to one another. (2) In the true
skin and mucous, serous, and synovial membranes, in
the dura mater and tendon sheaths, the trabeculse 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 parts of the same organ — i.e. inter-
stitial connective tissue— the texture of the tibrous
tissue is more or less loose, the trabecul^e dividing and
reuniting and crossing one another, but leaving between
them larger or smaller spaces, celluhe or areola?, 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 lamelhie, or plates of
trabecul^e. (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 trabecule form a fenestrated membrane, with
larger or smaller oval or circular holes or fenestra?.

38. The eoiiiiective -tissue cells or corpuscles
occurring in white fibrous tissue are of several

F/niwus C(hxXECTn'E T/ssu/:s.

varieties, {a) lii teiulon and faseiie tlie cells ai<' called
tendon cells or tendon corpuscles ; they are flattened

^-3^^

Fig. 34.— Tendon of Mouses Tail. (£. A. Schu/er.)
a, Chains of tendon-celJ!? seen broadways ; b, the same in profile.

nucleated protoplasmic cells of a square or oblong
shape (Fig. 34), forming continuous rows (single files),
situated on the
surface of groups
of bundles of
fibrous tissue.
Between these
groups are wider
or narrower
channels, the in-
t erf CISC i culn r
lymph spaces,
running parallel
with the long
axis of the ten-
don (Fig. 35).
The cells in each
row are separ-
ated from one
another by a nar-
row line of allju-

minous cement substance, and the round nucleus of
the cell is generally situated at one end, in such a

Fig. 3.J. — From a Transveix- Section through the
Tendons of tlie Tail of a Mouse, stained with
gold chloride. {Handbook.)

Several fine tendons are shown here. The darfe
branched corpnseies correspond to albuminous
cement substance stained with srold 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 Ion? axis of these rows
beins parallel with the long axis of the tendon.

Elemexts of Histology.

Fig. 36.— From the Tail of a Tadpole.

c. Branched coDnective tissue cells ; m,
a migratory cell. (Atlas^

way that in two adjacent cells of the growing tendon
the nuclei face each other. This indicates that the
individual cells undergo division. Corresponding to

the martjin of each
row, the cells j;>ossess
minute processes. The
cell plate is not quite
riat, Ijut possessed of
one, two, or even
three membranous pro-
jections l)y which it
is wedged in between
the individual bundles
of the group to which the row of cells belongs.

39, (fe) In the serous meuibranes, cornea, subcu-
taneous tissue, and loose connective tissues, the cells

are flattened transparent cor-
puscles, eac-li witli an oblong
flattened nucleus, and more or
less branched and connected by
tlifir processes. In the cornea
they are spoken of as the
corneal corpuscles, and are ver}'
richly branched (Fig. 37). 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 interfascicular
lymph spaces, or spaces left
between the bundles of the
fibrous matrix, which are cavi-
ties in the interstitial cement,
cementing tlie Imndles and trabecuke together (von
Recklinghausen). In the cornea and serous mem-
branes these spaces possess the shape of branched

Fig. 37. — Fi-om the Cornea
of Kitten, showing the
Networks of the Branched
Corneal Corpuscles.

a. The network of their pro-
cesses ; b, nucleus of the
corpuscle. (Atla^.')

Fibrous Conxecth'e Tissues.

lymph

laciinne, eacli lacuna being the home of the body of
the cell, while the branches or canaliculi contain
its processes. These canaliculi form the channels
by which neighbouring lacuna? anastomose with one
another (Fig. 38). The cell and its processes do not
fill up the lacuna and its canaliculi, but are bathed
in the paraplasma or fluid contained in the
canal system. In

loose connective tis- v^^':m^'''"'^'m
sue the lacuna may " ^ '^

be of considerable 7

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 mem-
brane of flattened
cells. Such is the
subepithelial endotJie-
lium ofDehove, occur-
ring underneath the
epithelium on the
surface of the mucous

membrane of the bronchi, bladder, and intestines.
40. (c) In the true skin and mucous membranes
the connecti^'e-tissue cells are also branched flattened
corpuscles, and by their longer or shorter processes
are connected into a network (Fig. 36). Each
cell has a flattened oblong nucleus. As a rule,
some of the processes are membranous prolongations
coming ofl" under an angle from the body of the cell,
which is then called the chief plate, the processes
being the secondarv plates. By the latter the cell is

g. 38.— From the Cornea of Kitten,
stained with Nitrate of Silver, show-
ing the Lymph-canal System.

fl. The lacuna?, each containiugthe nucleated
cell-body just indicated here; b, the
canaliculi for the cell procer^ses. (Atlas.')

52 Klemexts of Histology.

wedged in between the bundles of the trabecula to
which it belongs.

This character of the cells (i.e. possession of
secondary j)lates) is well shown Ijy the cells of the
skin and mucous membranes, but only in a very
limited degree by those of the cornea and serous mem-
branes, and somewhat better by some of those of the
subcutaneous and other loose connective tissues.

In the skin and mucous membranes also the cells
and their processes are bathed in the paraplasma
contained in the interfascicular lymph spaces.

41. The connective - tissue corpuscles hitherto
mentioned are fixed corpuscles : they do not show
movement. Kiihne and Rollett ascriVje to the corneal
corpuscles a certain amount of contractility, inasmuch
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 proces.ses of the
cell.

42. Pigment cells. — In the cold-blooded verte-
brates, 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 grey or yellow, or more commonly
dark brown, or even black. These cells are called pig-
mented connective-tissue cells, or simply inijinent cells.
They are very numerous in the skin of fishes, reptiles,
and amphibian animals, and also around and between

Fibrous Connective Tissues.

the blood-vessels of the serous membranes. They are
also present in man and mammals, but then they are
chieriy linuted to the eye-ball, where they occur in the

Fig. 89,— Pigment Cells of the Tail of Tadpole.

A, B, c, D represent variims states ; a heinar a cell in an uncontracted or passive
stati'. D in a contracied or active state.

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 the tissue between the sclerotic and
choroid, as the lamina fusca, and also, but to a more

54 Elemexts of Histology.

limited degree, in the sclerotic. As a rule, they appear
to be of various kinds : sucli as are flattened, large
plates perforated l>y a number of small and large holes
and minute clefts : such as possess a more spindle-
shaped liudy. and loni'. thin, not very richly branched
processes : and intermediate forms between the two.
But on careful examination it will be seen that these
appearances are due to different .states of contraction
of the same kind of cells (Fig. 39).

43. In the lower vertebrates the dark pigment
cells show marked contractility, ina^mucli as they are
capable of altogether withdrawing into their body the
pigmented processes. Tn the passive state these are
exceedino'lv numerous, anrl form a network so dense
that the whole mass of the cells and their paraplasma
resembles an extremely close network of pigment.
In tlie maximum of activity the pigmented 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.

41. Owing to the great number of the pigment
cells in the skin of fishes and amphibians, 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 jiarticular
part will 1)ecome lighter and brighter, the degree of
liijhtness and brightness depending on the degree of
contraction of the pigmented processes by the cells.
Briicke has shown that darkne.ss is a stimulus to the
pigmented cells : they contract and the skin becomes
lifdit. Sunlidit leaves the piomented cells in the
pas.sive state, their pigmented processes numerous
and well branched, and the skin appears therefore
of a darker colour. If previously they have been

Fibrous Coxnective Tissues.

contracted by darkness, on being exposed to sunlight
they again return to tlie passive state. Tlie contrac-
tion 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 intiuenced 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, large vesicles, each

Fig. 40. — From a Preparation of the Omentum of Guiuea-pig. {Atlas.)
a, Artery ; v, vein ; c, young capillary lilooil-vesriel ; d, fat ceils?.

consisting {a) of a thin protoplasmic membrane, which
at one point includes an oval nucleus flattened from side
to side, and (/>) of a substance, which is a fat globule
filling the cavity of the vesicle (Fig. 40). These fat
cells are collected together by fibrous connective
tissue into smaller or larger groups, which in their
turn form lobules ; these again form by means of
thicker masses of fibrous connective-tissue lohes, and
these are finally arranged as continuous masses. Each
group and lobule has its afferent arteriole, one or two

56 Elemexts of Histology.

efferent veins, and a dense network of capillaries
between ; each mesh of the capillary network holding
one, two. or three fat cells [see below). Such are the
nature and arrangement of fat or adipose tissue in
the subcutaneous and sul)mucous tissue, in the serous

Fig. 41. — From a Section through the adipose layer of the Skin ; showing
Lobules of Fat-cells. Magnifying jiower, 40. {From a Photograph by
Mr. A. Pringle.)

and synovial 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

Fibrous Connective Tissues.

tilled with small fat globules, wliicb, increasing in
number, become fused with one another to larger
globules ; as their size thus increases the cell nucleus
becomes shifted to the periphery ; ultimately one
larijje fat globule tills the cell, and what is left of the

Fig. 42. — From a Section of Lobules of Fretal Fat, showing connective-tissue
septa with vessels (surrounding the lobules) ; the spheroidal young
cells, many of them containing globules of fat. {Photograph, moderately
magnified.)

cell protoplasm surrounds this fat globule like a mem-
branous envelope. The cell as a whole has become in
this process many times its original size (Fig. 41).

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

58 Elemexts of Histology.

growth, and especially under very fav-ourable con-
ditions of nutrition, the connective-tissue cells become
increased by cell-multiplication so as to form groups ;
these groups continue to increase in size and to be
srraduallv furnished with their own svstem of blood-
vessels ; the individual cells constituting the group
become then converted into fat cells, and their pro-
cesses are thereby lost (Fig. 42).

Isolated 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 fat globule,
tliey 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, u-andering cells. These are of
various kinds, like tliose of the blood : (1) A majority
are identical with the typical hyaline leucocytes of
thf- blood, as regards size, shape, aspect, and
general nature (Fig. 36, m). They wander about
through the spaces of the fibrous tissue. They con-
tain two or tViree nuclei. (2) Those of the second
varietv possess a small amount of protoplasm, and one
comparatively large nucleus : they correspond to the
lymplwcytes mentioned in connection with the white
blood corpuscles. The amoeboid movement of these
cells is not so distinct as in the first variety. (3)
Plasma cells of Waldeyer. They are larger than the
former, less prone to migrating, being possessed of
only slight amceboid movement, which is, however,
sutiiiciently pronounced to be detected. They always
contain granules, and correspond to the granular cells
mentioned of the blood : also in regard to their predi-
lection for acid and basic aniline dyes they may be

Fibrous Connective Tissues. 59

distinguished as eosinopliile or oxypliile, basophile
or neutropliile cells. The "grnnules" in some of
the plasma cells may change into fat globules, and
thus the plasma cell becomes convei-ted 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. Those of the larger kind — e.g. the
granular wandering cells or plasma cells, are met with
in certain localities onlv ; in the sub-linijual orland 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, in the trabecular
of the lymphatic glands, and in the omentum. The
" granules " of these cells under many conditions
change into fat globules. Just like the hyaline
leucocytes of the blood so also those of the connective
tissues are capable of swallowing minute particles of
extraneous matter — granules of living (bacteria) and
non-living matter that accidentally find entrance into
the connective tissue. These cells, when acting in
this capacity, are called pliagocytes.

49. Development of fibrous tissue. — Fibrous
connective tissue is developed from embryonic connec-
tive-tissue cells — i.e. from spindle-shaped or branched
nucleated protoplasmic cells of the mesoblast. The
spindle-shaped cells are met with isolated or in
bundles, as in the umbilical cord or embryonic tendon.
The branched cells form a network, as in the foetal
skin and mucous membrane. In both instances the
p)'otoplasm of the embryonic connective-tissue cells
increases rapidly in amount, and becomes gradually
transformed into a bundle of elementary fibrils, with
a granular-looking: interstitial substance. The nucleus
of the original cell finally disappears, A modification

Elements of Histology.

of this is when only part — generally unilateral — of
the cell substance is converted into a bundle of con-
nective tissue tibrils and inter-fibrillar cement sub-
stance. A remnant of the protoplasm persists with
the nucleus as a connective-tissue cell.

The same modes of formation of connective tissue
may be also observed in the achilt 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 vari-
able thickness
and length,
branching and
anastomosing so
as to form net-
works (Fig. 43).
They are some-
times straight,
but more often
twisted and
coiled. The
latter condition
maybe observed
when the tissue
is shrunk, the former when it is stretched. They do
not swell up in acids or alkalies, nor yield gelatin
on boiling, but contain a chemically ditferent sub-
stance— viz. elastin. When broken their ends
generally curl up.

51. Elastic fibres occur in great numbers as net-
works extending on and between the bundles of tibrous
tissue in the skin and mucous membranes, in the

-From a Prei>aration of the Mesentery.

of fibrim-; tissue; h, networks of elastic
fibres. {Atlas.')

F/BKOus Connect I \'E Tissues. 6i

serous and synovial membranes, and in tlie loose in-
terstitial connective tissues. They are not very com-
monly met with in tendons and fasciae ; in the former
they are seen as single fibres often twisting round the
tendon bundles.

Elastic fibres forming bundles, l)ut branched and
connected into networks within the bundle, are to be
found in large numbers in the walls of the trachea,
l)ronchi, infundibula, and alveoli of the lung, in the
ligamenta flava, in the ligamentum nucha? of the ox
(in which the fibres are exceedingly thick cylinders),
in yellow elastic cartilage {see below), in tlie mem-
brane lining the cavity of the heart, and in the
vascular system, particularly the arterial division.
In the latter organs the intinia, 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 : (o) 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 Hat. {h) Homogeneous elastic membranes,
which surround, as a delicate sheath, the connective-
tissue trabecules in some localities — e.^. subcutaneous
tissue, (c) Homogeneous-looking elastic membranes
iu the cornea, behind the anterior epithelium as Botv-
'nianHs anterior elastic membrane, and at the back of
the cornea as elastica posterior, or Descemet's mem-
brane; in the latter bundles of minute fibrils haA'e
been observed. Between the mucosa and submucosa
of the stomach of the cat occurs an elastic membrane
of considerable thickness, (d) Elastic trabeculae form-
ing a network, as in the ligamentum pectinatum iridis.
In the embryonic state the elastic fibres are nucleated,
the nuclei beincj the last remnants of the cells from
which the fibres develop, one cell generally giving

0 2 Elements of Histology.

oricjiii to one fibre. These nucleated fibres are called
Henle's nucleated fibres.

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

(1) Adenoid retlcidum. This is a network of fine
fibrils, or plates, forming the matrix of lymphatic or
adenoid tissue. {!See Lymphatic glands.) The reti-
culum is not fibrous connective tissue nor elastic
tissue ; it contains nuclei in the young state, and is
derived from 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 iiearogUa of Virchow is a dense network
of very fine homogeneous fibrils which form the sup-
porting tissue for the nervous elements in the central
nervous system. These fibrils are supposed to be
elastic fibres (Gerlach). Embedded in, and inti-
mately connected with, the network of these fibres
are found branched, nucleated, flattened cell plates,
which correspond to the fixed connective-tissue cells.

(3) Gelatinous tissue. This occurs chiefly in the
embiTO, being the unripe state of fibrous connective
tissue (see above). 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 and
ill tlie cavity of the middle ear of the embryo, and in
all places Avhere fibrous connective tissue is to be
developed. After birth it is found in the tissue of
the pulp of the teeth, where it persists through life ;
in some places it is the precursor of fat tissue, its cells
becoming: transformed into fat cells.

CHAPTER YI.

CARTILACiE.

54. Cartilage consists of a firm ground sub-
stance which yields diondrin, and of cells embedded
in it. Most cartilages (except on the articulating
surface) are covered on their free surface with a
membrane of tibrous connective tissue with a few
elastic fibrils. This membrane is supplied with
blood-vessels, lymphatics, and nerves, and is of
essential imjiortance for the life and growth of the
cartihige. This is the perichondriiun. There are
three varieties of cartila^je.

55. (1) Hyaline cartila§:e(Fig. 44).— This occurs
on the articular surfaces of all bones ; on the borders
of many short bones ; in 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
cartilages of the nose ; and in the thyroid and cricoid
cartilages of the larynx. The ground substance is
hyaline — i.e. transparent, like ground glass, and firm.
The cells are spherical or oval proto^^lasmic corpuscles,
each with one or two nuclei. They undergo division,
and although the two offsprings are at first close
together (half moon-like in optical section), they
gradually grow wider apart by the deposit of hyaline
ground substance between them. The cells are con-
tained in cavities, called the cartilage lacunce. Each
cell generally occupies one lacuna, but, according to
the progress of division, a lacuna may contain two.

Elemexts of Histology.

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 ot hyaline ground
substance between the cells.

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

Each lacuna is liner] liy a delicate membrane, and,
according to the state of the cell, is either completely

or partially filled out bv
it. This membrane is
called the capsiiIe(Fig. 44).
In many cartilages, espe-
cially in growing cartilage,
it is thickened by the ad-
dition of a layer or layers
of hyaline ground sub-
stance. This is the most
recently-formed j^art of
the matrix; it stains differ-
ently with dyes, and is dis-
tinct from the older part
of the ground substance.

56. In some places, especially in articular carti-
lage (Tillmanns Baber), bundles of fine connective-
tissue lil>rils may Ije noticed in the hyaline ground
substance.

57. In some cartilages the protoplasm of the cell
becomes filled with fat globules (Fig. 46). This fact
may be observed in many normal cartilages ; some-
times the fat globules become c(mfluent into one larjje
drop, and then the cell has the appearance of a fat
cell. In old age, disease, and deficient nutrition lime
salts are deposited in the ground sul)stance, beginning
from the circumference of the cell. The earthy matter
a])})ears in the shape of opaque granules, or irregular

Fig. 44.— Hyaline Cartilage of
Hixiiian Trachea.

In the hyaline ground substance are
seen the cartilage cells enclosed in
capsules.

Cartilage.

or anujular granult's. Tlie groiincl suljstance thereby
loses its transparency, becomes o})H<jue in transmitted,
white in re-
flected, light,

and, of course, /

ver}^ hard and
brittle. This
process is the
calcification of
cartilage. It is
also met with
in cartilage
that is to be
replaced by
bone, being the
precursor of the
formation of
bone, as in the
€mbr3'0 {see be-
low), and at the

Fit

45. — From a Preparation of the Sterna
Cartilage of a Newt.

growing ends of

The lacunae containing the cartilage cells anastomose
by tine channels.

I. •',•-•5

long bones.

58. The division of the nucleus of the cartilage
cells has been observed during life by Schleicher and
Flemming. It takes place after the
mode of karyokinesis. The lacunie _<«U.,/ ,

of the cartilage are not isolated
cavities, but are connected with one
another by fine channels (Fig. 45),
so that the ground substance is
easily permeable by the current of
nutritive fluid. These channels and
lacunae form an intercommunicating
system, and are connected with the
lymphatics of the perichondrium
(Budge). Formed matter, as pig-
ment granules, red and white blood

Fig. 40.— Three Car-
tilage Cells filled
with Fat Droplets.
From the hyaline
cartilage of the
nasal septum of
Guinea-pig.

Elements of Histology.

a, o" o::S,

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 this
is joined to the synovial meml)rane and to the capsule
of the joint, the cartilage cells are more or less branched,
and pass insensibly into the branched connective tissue
cells of the membrane. In fcetal hvaline cartilacre
many of the cells are spindle-shaped or branched.

59. Ju the cartilage separating the bone of the
apophyses from the end of the diapbysis of tubular
bones there is a peculiar hyaline cartilage, known as
the intermediate or ossifying cartilage. Its cells are
arranged in characteristic vertical rows, owing to

the continued division
^11 ,jg of the cells in a trans-

verse direction.

Cartilages, or parts
of cartilages, in which
the cells are very
closely placed, owing
to tlie absence, or
scanty deposit and
formation, of ground
substance, are called
jKi.rencliyiiiatous or cel-
hdar cartilacje.

60. (2iFibro-car-
tilagre. or connective-
tissue cartilage, occui-s
as the intervertebi-al
discs, as the inter-
articular cartilages, sesamoid cartilages, and as the
cartilat{e forminc( the marmn of a fossa »lenoidalis.
It consists of fibrous connective tissue arranged in
hundles, and these again in layers. The ground sub-
stance of this cartilage is said to yield chondrin and

■O

^ <S Q ^

€/^

• Fig. 47. — Fibro-Cartilage of an Inter-
vertebral Ligament. {Atlas.)

Showing the bundles of fibrous tissue and
rows of cartilage cells.

Cartilage. 67

not gelatin. Between the strata of the fibrous bundles
are rows of more or less flattened oval protoi)lasmic
nucleated cells, each invested in a deticate capsule
(Fig. 47). They are less flattened than the cells of
tendon, and the capsule dis-
tinguishes the two. Where

fibro-cartilage passes into %^^ ^^ ^ ; -«»^5-C7
tendinous tissue the two WC
kinds of cells pass insen- if^
sibly into one another. 5^^^^M_

61. (3) Yellow, or ^iS^^K^i?)
ela«>tic cai'tilag:e. this ^ji^?^?r^i^K:''^ii^^^o
variety is also called reti- ^p ''^-^^^^^^i
cular ; it occurs in the epi- •^, ^^.;''®^^ TO
glottis, in the pinna of the ^ -■--«--—. ^
external ear, in the Eus-
tachian tube, in the car-

tilacrps of AVn\bp7-rr and ^ig. 4S.— From a Section through

iiiages or » iisueig ana the Epiglottis. {AtUs.)

Santorini in the larynx. «^ perichondrium; &, networks of

In the early stages this eig^c^fltois sun-ounding the car-
kind is hyaline. Gradually

numbers of elastic tibrils make their appearance,
growing into the cartilage matrix from the peri-
chondrium in a more or less vertical direction, and
branching and anastomosin^r with one another. The
final stage is reached when the ground substance is
permeated by f/^e/ise neiicorJxs of elastic Jibrils (Fig. 48),
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
ground substance.

CHAPTER VII.

BONE.

62. BoxE, or osseous substance, is associated with
several other soft tissues to form a bone in the ana-
tomical sense of the word.

(a) The periosteiiiii. — Except at the articular
surfaces, and where bones are joined with one another
bv liiraments or cartilao;e, 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 l^undles of fibrous tissue, in which
numerous hlood-vessels and many protoplasmic cells
are contained. The blood-vessels form hj their capil-
laries 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
osteoblasts (Gegenbaur).

(b) Tlie carlilag-e is hyaline cartilage, and its
distribution on and connection with bone have been
mentioned on pp. 63 and 64.

63. (c) The marrow of l>oiie is a soft \'ascular
tissue, filling up all spaces and cavities. It consists
of a very small amount of fibrous tissue as a matrix,
and in it are embedded numerous blood-vessels and
cells. The few afierent arterioles break up into a
dense network of capillaries, and these are continued
as plexuses of veins, characterised by their compara-

Bone. 69

lively large 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 tlie periosteum and tlie 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 (osteo-
blasts 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 marroio ; if few or none of them
have undergone this change, it looks red, and is called
red marroiD. 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.

Some of the cells, especially those of red marrow,
the erythrohlasts, are the elements from which nor-
mally 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 large multinucleated cells, called inyeloplaxes of
Robin. They are derived by overgrowth from ordin-
ary marrow cells, and are of importance both for
the absorption as also for the formation of bone
[see below). According to Heitzmann, Malassez, and

Elements of HistoloCjY.

others, they also have to do witli the formation of
blood-vessels and blood corpuscles. NuQierous eosino-
phile cells are present in the marrow,

64. The matrix of osseous substance is dense
plexiform fil^rous connective tissue, i.e. a tissue yield-
ing- 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 (hydro-
chloric) and are thereby converted into soluble salts.
Thus the orijanic matrix of osseous substance — called
ossein — may be obtained as a soft flexible material,
easily cut.

In young bone the matrix or ossein is a plexus of
trabecuLe of fibrous tissue (v. Ebner), and in it are
also a few elastic fibres to be noticed.

The bone substance is in the adult state generally
lainellated, the lamellse being of microscopic thinness.
Between every two lamellae are numbers of isolated,
flattened, oblong spaces — the hone lacnnce (Fig. 49),

which anastomose
by numerous fine
canals with one
another, and also
with those of the
next lamella above
and below (Fig. 50).
The appearances are
very similar to those
presented by the
lacunse and canali-
culi containing the
corneal corpuscles
as described in
Chapter V.

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

Fig. 49. — Osseous Lanieihe ; oblong branched
bone lacun;e and canaliculi between them.
{Atlas.)

Bone. 7 1

are in open and free communication with the lymphatic
vessels of the marrow spaces and of the Haversian
canals.

65. In the bone matrix, each lacuna contains also
a nucleated protoplasmic cell, called the hone celi,
which, however, does not fill it completely. In the

Fig. 50. — From a Transverse Section through Compact Bone, showing
systems of concentric lamelliB (with bone corpuscles between) around
Haversian canals. (From a photogram by Mr. Pearce.)

young state the cell is branched, the branches passing
into the canaliculi of the lacunae ; but in the old state
only traces of the original nucleated cell and very few
processes can be detected ; this with its lacuna and
canaliculi is called a bone corpuscle.

66. Accordinsf to the arrano^ement of the bone
substance, we distinguish compact from spongy sub-
stance. The former occurs in the shaft of tubular

72 Elemexts of Histology.

bones and in the outer layer of flat and short bones.
Its lamell?e are arranged as : («) concentric or Haversian
lamella ., directly surrounding the Haversian canals
(Fig. 51). These are narrow canals of varying lengths
pervading the compact substance in a longitudinal

P'ig. 51.— Compact Bone Substance in Cross-section. (Atlas.)

a. Concentric lamellae arranged around the Haversian canals, cut across; 6, in-
termediate or ground lamellia The bone lacuna? are seen between the bone
lamellas.

direction, and anastomosing with one another by
transverse or oblique branches. The Haversian canals
near the marrow cavity are larger than those near
the periosteum. In fact, those next to the marrow
cavity become gradually enlarged by absorption of
the concentric lamellse, until finally they are fused
with the marrow cavity. Each Haversian canal con-
tains 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 periosteum, and
they form the means by which the latter remains in
continuity with the marrow. Each canal is surrounded

Bone. 73

by a series of concentric bone la?7iellcf, tvith the bone
corpuscles between thein, and this is a system of con-
centric lanielhe. Near the external surface of the
compact substance the number of lamellae in each
system is smaller than in the deeper parts, {b)

^'^^^mm^g

Fig. 51a. — Sharjipy's fibres amongst the iiisterstitial lamella; of a transverse
section of the human humerus ; the fibres run in a vertical direction,
and surround spaces wliicli contain the bone-cells. {After KolUker, I.)

Between these systems of concentric lamellae are the
intermediate or ground lamelhe ; they run in various
directions, and in reality fill the interstices between
the systems of the Haversian or concentric lamellae.
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,
The ground lamellae are the earliest to be developed,
being the matrix of the first-formed spongy bone,
and they are the last to disappear where bone is

74 Elements of Histology.

melted clown in the marrow cavity. The concentric
lamellfe, on the other hand, are the last to be formed
where spongy bone is converted into compact bone,
and they are the tirst to become absorbed where com-
pact bone is reduced again to spongy bone, as near
the central marrow cavity. The lamellae of compact
bone are perforated by perpendicular petrified fibres,
the perforating fibres of Sharpey. They form a con-
tinuity with the fibres of the periosteum, from which
they are developed, through the lamellae of osseous
substance deposited by the osteogenetic layer of the
periosteum (Fig. 51a).

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 or can-
celli ; they intercommunicate with one another, and
are filled with marrow, which in the vouncf and grow-
inij state is fjenerallv of the red varietv. The firm
parts form spicules and septa, called hone trahecuUt,
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 honeycombed sub-
stance, or appears longitudinally striated, as in the
end of the shaft. In the latter case the marrow
spacas are elongated and the trabeculse more or less
parallel, but anastomosing with one another by
transverse Ijranches.

68. Development of bone.— Bone is developed
in the embryo, and continues to be fonned also after
birth as long as bone grows, either in the cartilage
or, independently of this, directly from the osteo-
genetic layer of the periosteum. The former mode
is called endodiondral, or intracartilagino^is: the latter
periosteal^ or inter me mhranous formation.

All the bones of the limbs and of the vertebral

Bone. 7 5

column, the sternum, and the ribs, and the bones
forming the base of the skull, are preformed in the
early em])ryo as solid hyaline cartilage, covered with
a membrane identical in structure and function with
the periosteum, which at a later period it represents.
This cartilage is eventually replaced by bone —
endochondral hone. The tegmental bones of the
skull, the bones of the face with the lower jaw,
except the angle, are not preformed as cartilage at
all. Only a membrane identical with the future
periosteum is present, and underneath and from it
the bone is gravlually deposited — i-)eriosteal hone. The
same deposit of periosteal bone takes place on all
bones, no matter what their origin, and this deposi-
tion of layer after layer of bone by the osteogenetic
layer of the periosteum represents the groivtli of the
hone in thickness.

69. EiKlochoiiclral foriiiatioii. — 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
l)ecomes permeated by numbers of channels (cartilage
channels) containing prolongations (periosteal pro-
cesses of Virchow) of the osteogenetic layer of the
periosteum — i.e. vessels and osteoblasts, or marrow
cells. This is the stage of the vascidarisation of the
cartilage. In the next stage (3) the cartilage border-
ing on these channels grows more transparent, the
lacun{3e becoming enlarged and the cartilage cells
more transparent. The latter gradually break down,
while the intercellular trabeculse become calcified;
the lacume, by absorption of the calcified trabeculfe,
fusiuff witli the cartilaoje channels. These latter
thereb}^ become transformed into irregidar cavities,
which are bordered by trahecuhe of calcified cartilage.
The cavities are the primary marroiv cavities, and

Elements of Histology.

they are filled witli \\\^ jjrimary or

j\4 '^'-^-f'^/'i',--, ^-- ■

Fig. 52. — Longitudinal Section through the entire
Foetal Humerus of a Guinea-];)ig.

fl, Periosteum ; 6, hyaline cartilage of the epiphysis ;

c, intennediate cartilage at the end of the shaft ;

d, zone of calcification ; t, i>eriostealbone, spongy ;
/, endochondral bone, spongy.

tilage gradually assumes the appear

cartilage marroiv
— i.e. blood-ves-
sels and osteo-
blasts, derived,
as stated above,
from the osteo-
genetic layer of
the periosteum.
(4) The osteo-
blasts arrange
themselves by
active multipli-
cation in a special
layer on the sur-
face of the calci-
fied cartilajje
trabeculse pro-
jecting into and
bordering the
primary marrow
cavities. The

osteoblasts form
hone substance —
osseous matrix
and branclied
bone corpuscles
— and as this
proceeds, the cal-
cified cartilage
trabecules become
gradually en-
sheathed and
covered icitli a
layer of osseous
substance. Thus
the original car-
ance of a spongy

Bone. 7 7

substance, in wliicli the cavities (primary marrow
cavities) arc tilled with the primary marrow, and
are of considerable size, while the trabecuhe bor-
dering them are calcified cartilage covered with
layers of new bone. The marrow cells, or osteo-
blasts, continue to deposit bone substance on tlie
free surface of the trabecul?e, while the calcified
cartilage in the centre of the trabeculte gradually
becomes absorbed.

70. The nearer to the centre of ossification, the
more advanced is the process — i.e. the more bone and
the less calcified cartilage is found constituting the
trabecuhe, and the thicker the latter. At the " centre
of ossification," i.e. whence it started, the process is
farthest 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 ex-
tremity of the shaft of a long 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. 52).

71. After birth, and as long as bone grows, we
find in the end of the shaft, and also in the epiphysis,
a continuation of the process of endochondral forma-
tion described above. In fact, all bones preformed
in the embryo as cartilage grom) in length before and
after birth by endochondral formation of new bone.
The hyaline cartilages at their extremities, the carti-
lage of the epiphysis, the intermediate cartilai^e at
the end of the shaft, are the cartilages at the expense
of which the new bone of the epiphysis and of the
end of the shaft respectively are formed by the marrow
(blood-vessels and marrow cells or osteoblasts) in
contact with the cartilage. As long as this cartilage
continues to grow, so long is there new formation of

Elemexts of Histology.

bone by the marrow encroaching on it, or, in other
words, so long is there growth in length of the shaft.
When at a certain period of adidt life the growth
of the intermediate cartilage has come to an end, the
cartilage is completely replaced by the spongy bone

y^^M

m:\\b « i (f^,^m rt^ Q)% /fiT

■* \i* it)

Fig. 53. — From a Transverse Section tlirough the Tibia of Foetal Kitten.

a. Fibrous layer of the periosteum; b, osteogenetic Inyer of the periosteum;
c. periosteal bone; d, calcifled cartilage not covered yet by bone; below this
layer the tralieculte of calcified cartilage covered with plates of bone —
sbaded darkly in the figure ; e, boundary between periosteal and endochondral
bone. iAtlas.)

Bone.

of the end of the shaft, and this is not capable of
further lengthening.

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. 54.— From a Section through the Intermediate Cartilage of Femur of a
Foetus. Low magnifjing power. {From a photogrcqjh by Mr. A.
Pringle.)

a, intermediate cartilajsre ; b, cartilage of the eiiiiihysis ; c, spongy bone of
epiphysFs ; d, spongy bi>ne at the end of the shaft.

but becomes gradually absorbed altogether, and this
process also starts from the points of ossification.
Thus a f;rc\dual enlargement and ultimate fusion of
the marrow cavities of the spongy endochondral bone

8o Elements of Histology.

into one continuous cavity takes place. This repre-
sents the rudiment of the future central marrow
cavity of the shaft. Simultaneously with, or some-
what previous to, this absorption of the endochondral
bone, new bone of the nature of spongy hone is
deposited directly hy tlie osteogenetic layer of the
periosteum on the outer surface of the endochondral
hone. This also commences at the centre of ossifica-
tion, and proceeds from here gradually to further
l^oints. This is the tirst rudiment of the periosteal
hone of the shaft (Figs. 52, 53). It is formed without
the intervention of cartilage directly by the osteo-
blasts of the osteogenetic layer. And as fresh masses
of osteoblasts become developed l)y division, new
layers of spongy bone are formed by the change of
the former into bone matrix and bone cells, and the
old trabecular become increased in thickness. In the
meshes or Haversian spaces of this new spongy
periosteal bone the same tissue is to be found that
constitutes the osteogenetic layer of the periosteum,
the one being derived from, and continuous with, the
other.

In these Haversian spaces concentric lamellai of
bone substance become subsequently formed by the
osteoblasts, while at the same time the Haversian
spaces, being narrowed in by the deposit of the con-
centric lamellae, are transformed into the Haversian
canals. The original spongy bone represents, there-
fore, the ground substance (primary, or ground lamella?),
in which, or rather in the spaces of which, the secondary
deposit of the concentric lamella} or Haversian
systems of bone lamellae takes place, by which deposit
the spongy bone becomes transformed into compact
bone. This process is farthest advanced in the
middle of the thickness of the shaft, and least near
the periosteum. When this compact bone is again
absorbed — e.g. that next the medullary cavity of the

Bone.

sliaft of a long bone— tlie concentric lamella? are first
absorbed, the Ha-

be-
way
and

versian canal
ing in this
widened out
again transformed
into a Haversian
space.

While, then,
the bone first de-
posited by the peri-
osteum is of a
spongy character,
and gradually be-
comes transformed
into comi3act_, the
reverse is ""oing on
at the same time
near the marrow
cavity, inasmuch
as compact bone is
here changed into
spongy bone, and
this ultimately dis-
a23pears and be-
comes absorbed by
the mari'ow.

73. At birth
all the primary en-
dochondral bone «.
has already disap-
peared by absorp-
tion from the centre
of the shaft, and
the bone present is
all of periosteal origin
shaft

Fig. 55. — From a Longitudinal Section
Femur of Rabbit, through the part in
which the intermediate cartiLige joins
the end of the shaft. {Atlas.)

a, Intermediate cartilage; 6, zone of calcified
cartilage ; c, zone in which the calcified tra-
heculEB of cartilage become gradiiRlly in-
vested in osseous substance, shaded light in
the figure; the spaces between the tral>e-
cula3 contain marrow, and the cai>illar.v
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.

At the extremity of the
however, tlie spongy bone is all endochondral

82 Elements of Histology.

bone, and it continues to grow into the interme-
diate cartilage as stated above, so long as the
bone grows as a whole (Fig. 55). Of course the
parts of this spongy bone nearest to the centre

'^'

^^§)^

Fig. 5(3. — Small mass of Boiie Substance in the Periosteum of the Lower
Jaw of a Human Foetus. [Atlas.)

tt, Osteou'enetic liiyer of periosteum ; l>. luuliiuiicle.ired giuiit cells, inyeloiil.ixes.
Tbe one in the midcile of the upper margin is an osteoclast, whereas the
smaller one at the left upper corner appears concerned in the fornntion of
bone. Above c the osteoiihist cells become surrounded by osseous substance
and thus become converted into bone cells.

of the shaft are the oldest, and ultimately dis-
appear by absorption into the central medullary
cavity. In the epiphysis the spongy bone is also
endochondral bone, and its formation is connected
with the deep layer of the articular cartilage, but
more so with the hyaline cartilage separating the
epiphysial spongy bone from the intermediate carti-
lao-e (see c of Fisj. oi).

Underneath the periosteum and on the surface of
the spongy endochondral bone at the extremity of the
shaft, the periosteal bone is represented only by a

Bone.

thill liiyer, extending as far as the periosteum reaches
— e.g. to tlie margin of the articular cartilage.

74. liiteriuoiiibrsiiioiis format ion. — All

Fig. 57.— From a Longitudinal Section through the Spongy Bone of Shaft,

near the intermediaiy cartilage, of Foetal Kitten, showing the formation

of osseous substance on tlie calcilied cartilage. {Atlas.)

a, Mhitow space, with bluud-vcssei ; 6, caicifled cartilage, covered with isolated

or confluent zoues of new osseous substance, consisting of fibrillated bone

matrix, bone lacuna, and in it a bone cell.

Elements of Hjstologv.

Fig. 58. — From a Lolly itudiual Section
of Femur of Rabbit, close to the
intermecliate cartilage.

a, Calcified cartilage, next to the inter-
mediate cartilage; 6, calcified carti-
lage covered with thin layer of
bone ; c, uiari'ow spaces containing
osteoblasts, forming bone on the
calcified cartilage; d, niyeloplaxes
(chondroclastsj.

bones not preformed in
the embryo as cartilage
are developed directly
from the osteogenetic
layer of the periostemii in
the manner of the i^eri-
osteal bone described on
p. 80. Here also the new
l)one is at first spongy
bone, which in its deeper
or older layers gradually
becomes converted into
compact bone.

In all instances dm'ing
embryonic life and after
birth the growth of a
bone in thickness takes
place after the manner of
periosteal or intermem-
hranous hone ; this is at
first spongy, but is gra-
dually converted into
compact bone.

75. All osseous sub-
stance is formed in the
embryo and after bii th by
the osteoblasts, or marrow
cells (Gegenbaur, Wal-
deyer) : each osteoblast
oivino: orioin to a zone
of osseous matrix, and re-
maininof in the centre of
this as a nucleated ^yo-
toplasmic remnant, which
gradually becomes
branched and transformed
into a bone cell. The

Bone. 85

osseous matrix is at first a soft fil)nllar tissue, but is
gradually and uuiformh^ impregnated with lime salts.
This impregnation always starts from the centre of
ossification (Fig. 57).

76. Wherever in the embryo or adult, in health
or disease, absorption of calcified cartilage or of osseous
substance is going on, we meet witli the multi-
nucleated large protoplasmic cells called the myelo-
plaxes of Robin. K()lliker showed them to be import-
ant for the absorption of bone matrix, and called
them therefore osteoclasts (Fig. 5Q). For cartilage they
ma}" be called chondroclasts ( Fig. 58). When concerned
in the absorption we find these myeloplaxes situated
in smaller or larger pits, which seem to have been
produced by them; these absorption pits or lacunae on
the surface of l)ones are called Howships lacunce.
They invariably contain numbers of osteoclasts. It
can, however, be shown that myeloplaxes are also
concerned 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
ftetal jaw" this process is seen with great distinctness
(Fig. 56).

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 diftering from it in certain
essentials. It is similar inasmuch as it is developed
in like manner by some peculiarly transformed
embryonic connective tissue — viz. by the tissue of the
embryonic tooth papilla — and inasmuch as cells are
concerned in the production both of the petrified
matrix (impregnated with lime salts) and of the
processes of the cells contained in its canals — the
dentinal fibres. The details of structure and distri-
bution will be described in connection with the teeth.

CHAPTER V]II.

XOX-STRIPED MUSCULAR TISSUE.

78. This tissue consists of nucleated cells, which,
unlike amoeboid cells, are contractile in one definite
direction, becoming' shorter and thicker diirinc; con-
traction.

The cells are elongated^ spindle-shaped, or band-like
(Fig. 59), and drawn out at eacli extremity into a
lonuer or shorter, sfenerallv single, but occasionally

Fig. 59.— Xon-striped Muscular Fibres, isolated. (Atlas.)

The cross-markings indicate corrugations of the elastic sheath of the individual

fibres.

branched, tapering process. Each cell includes an
oval nucUAis, which is flattened if the cell it belongs
to is flattened. The cell substance is a pale, homo-
geneous-looking or longitudinally striated substance.

During extreme contraction the nucleus may be-
come more or less plicated, so that its outline becomes
wavv or zicj-zag.

It lias been shown by Klein in certain preparations

Non-striped Muscular Tjssue. 87

— e.y. the non-striped muscle cells of the mesentery of
tlie newt — that each muscle cell consists of a delicate
elastic shentJi, 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 intra-
nuclear reticulum they are intimately connected.
AVhen the cell is contracted its sheath becomes trans-
versely corrugated (Fig. GO).

79. The non-striped muscular cells are aggregated
into smaller or larger bundh>^ by an interstitial alV)U-

Fig. 60.— Xon-stiipL'<l Muscular Cell of Mesenteiy of Xewt. {Atlo.s.)

Sliowin:,' several places whei'e the muscular substance appears cuntracted,
thickened. At these places the corrugations of the sheath are mariced.

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 of the frog, 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 l)e met with. In the muscularis mucosae of the
stomach and intestines, in the outer muscular coat of
the same organs, in the uterus, bladder, etc., occur
continuous membranes of non-stri})ed 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 polvgonal
outline.

80. Non-striped muscular tissue is found in the

88 Elements of Histology.

following places : In the muscularis mucosae of the

oesophagus, stomach, small and large intestine ; in the

outer muscular coat of the lower two-thirds or half

of the human oesophagus ; 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 ;

a *^ in the tubules of the epididymis,

f%^*^-^ in the vas deferens, vesiculfe

^ ^ ., ^ ^ >eminalis and j^rostate ; in the

^. , , 9 ^ - corj^ora cavernosa and spongiosa ;

■"''" ' ' .^ , _ ill the tissue of the ovary and in

' . . the broad ligament : in the mus-

x^ -^ cular coat of the oviduct, the

uterus and vagina ; in the pos-

Fig.61.-From a Transverse terior part of the Wall of the
Section through Bundles \y^r.\^r.^ . infhp Inrcrp and cimnll

of Non-striped Muscular ^racnea , mine large ana small

Tissue of the Intestine, bronchi, in the alveolar ducts

'^%^l^l^Jt'. c'uT^, and infundibula of the lung ; in

cor^cie"^of%=he'flga?l the pleura pulmonalis (guinea-

?{:^''irinre.^'^ril!e''et pig) ; in the peritoneum of the

ceii"""(4itol)"'^ """'"^^ frog and newt, in the upper part

of the upper eyelid, and in the

fissura orbitalis ; in the sphincter and dilator

pupilliTe, and the ciliary muscle ; in the capsule

and trabecular of the spleen, and the trabecular of

some of the lymphatic glands ; in the arrectores

pilorum, and sweat glands of the skin, the tunica

dartos of the scrotum ; in the tissue of the nipple of

the breast ; in the larcfe ducts of the sali^'arv and

pancreatic glands ; and in the muscular coat of the

gall bladder, the hepatic and cystic duct. The aorta

and the arteries have a large amount of non-striped

muscular tissue, the veins and lymphatics less.

81. As regards length, the muscular cells vary
within considerable limits (from ^\-^ to 0-5 millimeter),
those of the intestine, stomach, respiratory, urinary.

NoN-STKiPED Muscular Tissu/-:. 89

and genital organs being very long as compared with
those of the blood-vessels, which are sometimes only
twice or thrice as long as they are broad, and at tlie
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. The striped muscular tissue is composed of
long cylindrical fibres, some measuring in length as

Fig. 02.— Striped Muscular Fibres of the Tongue of a Guinea-pig, of which
the blood-vessels have been injected with carmine gelatine. Owing to
the contracted state of the niuscular tibres the capillaries are much
twisted and wavy ; in several places tlie " safety receptacles " are well
show n. (From a microplwto. , moderatehi magnified.)

mucli as 1.^-2 inches, others are much shorter; their
thickness varies between ^-^o ^^ e^o ^^ ^^^ inch. The

Striped Muscular Tissue. 91

til:) res are regularly transversely striated, and are
therefore called the striped oi' striated muscular fil)res
By fibrous connective tissue they are grouped together
so as to form larijer or smaller bundles — muscular
fasciculi ; the connective tissue surrounding the
bundles is called the perimT/sium ; while the delicate
connective tissue passing from the perimysium into
the bundle, and separating the individual muscular
fibres from one another, is called the endomysium.
The perimysium is the carrier of the larger vascular
and nervous branches, while the endomysium contains
the capillaries and the terminal nerves. The capil-
laries form very rich networks with elongated meshes,
and are always situated between the individual
muscle fibres. The capillaries and veins appear very
wav^y and twisted in the contracted bundles, and
straighter in the uncontracted bundles (Fig. 62). The
small vessels are provided here and there with j)eculiar
saccular dilatations, which act as a sort of safety
receptacle for the blood when, during a sudden
intense contraction, 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 tibres, sjDontaneously or after the application
of a stimulus, a contraction starts at one point and
passes over the whole muscular fibre like a wave —
contraction vxive — the progress of which is noticeable
by the thickening rapidly shifting along the fibre, the
part behind resuming its previous diameter.

84. A striped muscular fibre consists of (1) a
delicate hyaline elastic sheath, the sarcolenima, and
(2) the rnuscniar contents. It is the structure of the
latter which has given origin to a variety of theories,
owing to optical difficulties in examining fresh and
living fibres, and owing to the varied changes it is
liable to undergo when acted upon by many reagents.

Elemexts of Histology.

jMJS8S»i»i*9f^^§i^f/

;i^6siJ^aS

1; .

»S24? ji ;t5J

t " vC^S

In the following we shall adopt the view enunciated
by Rollett during recent years ; we think that his
conclusions are based on extensive observations and
study of muscular fibres in vertebrates and inverte-
brates under the best conditions, and his conclusions
harmonise best with the classical observations of
Bowman, Briicke, Cohnheira, and Engelmann, and

with observations which can
g ---.,„.,,,,.,,.,,, 3 be verified by careful study
f of fresh muscular fibres.

S5. The contents of a mus-
cular fibre consist of two prin-
cipal parts (Figs. 63, G4) : {a)
the fihrillce, or rhabdia of
Kiihne ; and (h) the sarco-
plas'/ii or intertibrillar sub-
stance, a hyaline or faintly
granular substance, having
resemblances to protoplasm,
and acting as the matrix for
the tibrilhe. The fibrillar ex-
tend in a longitudinal direc-
tion parallel to the long axis
of the muscular fibre, and they
are grouped together into
bands, strands, or tubes, called
the muscle columns ; the latter
larger groups. The sarco-
plasm fills up all interstices between the groups of
the muscle columns, between the columns of each
group, and between the fibrillfe of each column. The
amount of sarcoplasm between the groups of columns
is generally greater than between the columns of each
group. During growth and regeneration of mus-
cular fibres in the adult the collections of nucleated
sarcoplasm on the surface —i.e. underneath the sarco-
lemma — become conspicuously increased in vertebrate

Fig. 63. — Part of a Muscular
Fibre of Geotruxjes sylva-
ticus, showing its compo-
sition of fibrillit. {Rollett.)

I, Intermediate disc (Krause's
membrane) ; s, sarcous ele-
ments.

are aorgresfated

into

Striped Muscular Tissue.

muscular tibres, both in number and size ; and they are

the material from which muscular fil^rilhe are formed.

Special collections of nucleated

sarcoplasm are found at the

termination of the motor nerve

tiljre in the muscular fibre [see

below).

On observing a cross section
through fresh or well-preserved
muscular fibres, the sarcoplasm
is seen as transparent lines sub-
dividing the muscular contents,
which appear dim like ground
glass, into small more or less
polyhedral areas, the areas of
Cohnheim. These areas are the
cross-sections of the muscular
columns, and are therefore made
up of a number of granules,
the optical cross-sections of the
constituent fibrillae. The mus-
cular columns appear aggre-
gated by larger accumulations
of sarcoplasm into larger or
smaller groups ; and between
the groups the sarcoplasm is
again greater than between the
fibrillae of each column, and in
this respect there exists the
greatest variety between the
different animals. In the per-
fectly fresh condition tlie
amount of sarcoplasm between
the fibrilhe of a column is
in some cases insignificant,
and almost appears absent from place to place.

Tlie sarco[)lasm shows also other differences of

A'—

Fig. 64. — Mu>;cul;ir Fibre,
stained with hitmatoxy-
lin, of Staphylinuscaesa-
reus. {liollett.)

I, Interniefliate disc (Krause's
membrane or Dobie's
layer); L, secondarj' disc
(placed witliiii tlie lateral
disc ur Floi-'el's layer) ;
T, tranverss disc (sarcoiis
eleiiieats); x, nucleus of
muscle corpuscle.

Q4 Elements of Histology.

distribution ; in the muscular libres of many insects
it generally forms a cylindrical accumulation in the
centre of the muscular fibres, containing spherical
nuclei ; from it thinner septa pass between the groups
of muscular columns. In vertebrate muscular fibres
the sarcoplasm forms small plate-like or angular col-
lections on the surface of the muscular contents — i.e.
immediately under the sarcolemma. These collections
include spherical, or more generally oval, nuclei, and
are called the muscle corpuscles. The whole sarco-
plasm must be considered as a sort of protoplasmic
basis, and the muscle corpuscles as the nucleated accu-
mulations of it.

86. Each hbrilla shows along the whole length of
the muscular fibre regular alterations, as regards both
aspect and thickness of its sul)stance, and accordingly
can be considered as consisting of different portions
following each other endwise, and repeating them-
selves uniformly and in regular manner throughout
the whole length and thickness of the muscular fibre.
These portions are the sarcous elements of Bowman,
dim, homogeneous rods or prisms forming the chief
parts ; between each tw^o successive sarcous elements
of the saQie fibrilla, at equal distance, is a dark granule,
sometimes double, to whicli the end of each sarcous
element is joined by a thin bridge. In the fresh state
the sarcous elements are prisms, and those of con-
tiguous fibrilla?, almost touch each other at their sides,
so that little or no sarcoplasm intervenes between
them here ; but when the sarcous elements shrink
— e.g. after death or after hardening reagents, or
sometimes even duriiig life and during contraction —
they are more or less hourglass-shaped, and are
separated by thin layers of sarcophism from those
of contiguous fibrillse. The bridge by which each end
of a sarcous element is joined to the granule being
much thinner than the latter, there is more sarco-

Sir IP /CD Muscular Tissue.

granules of the

plasm present in the layer containing the bridge;
and since the sarcoplasm is more transparent than
either the sarcous elements or the
fibrilla^ the
nmscnlar libre
as a whole
shows a con-
s p i c u o u s
transparent
layer or disc
between each
layer of the
dark granules
and each layer
of the sarcous
elements. This
causes the
transverse
striation. The
layer of the
dark granules
corresponds to
tlie line of
Dohie, or the
line of Amici,
or the inter-
mediate disc of

Engelmann, or the yneinhrane of Krause. The
layer or disc of sarcoplasm in which the bridges
are placed, which join the sarcous elements to
the granules of the intermediate disc, is the lateral
disc. The layer or disc of sarcous elements corre-
sponds to the transverse disc. In many muscular
fibres of insects, notably in those of the crab (Ruther-
ford), there occurs in each fibrilla witliin the lateral
disc a short rod-like thickening midway between the
sarcous element and the dark granule ; the layer or

Fis.

05.— Striped Muscular Fibres of the Water
Beetle (Hydropliilns). {Atlas.)

Sarcoleiuraa; b, Krause's menibrane. The sarcous
eliiiient^; are well seen. In a the oblong nuclei of
tlie muscle corpuscles nre shown. In b the sarco-
lennua has become unnaturally raised from the mus-
cular contents. The contractile discs are M^ell
shown : so also are the sarcons elements.

Elements of Histology.

y^-\

disc of these rods or grannies forms
the secondary disc, or the Layer of
Flcigel.

cS7. A typical niuscnlar fibre shows
then, owing to the differentiation of
each fibrilla into the above portions,
the following layers in regular
alternation throughout the thickness
of the fibre : (1) 27ie dark inter-
mediate disc, Dobies line, or Kraiise's
membrane ; (2) the transparent
lateral disc ; (3) the dim transverse
disc of sarcous elements. Then fol-
lows another transparent lateral disc,
and then again the intermediate
disc.

As stated above, in some fibres
the line of Dobie is a double row
of granules, and the transparent
lateral disc contains a line of granules,
Flugel's layer.

The intermediate disc appears to
be intimately connected with the
sarcolemma ; hence Krause gave it
the name of a membrane. When a
muscular fibre contracts during life,
or when it shrinks after death, the
sarcolemma shows regular bulgings
between each two Krause's mem-
branes ; at these latter the sarco-

Fig. 66. — Three Fibrilke of Crab's Muscle, showing
the successive stages from complete relaxation
(?•) to complete contraction (t). (From Rtither-
foi'd's " .'itructui-e and Contraction of Striped
Muscular Fibre.")

b — 610, The various appearances of the sarcous ele-
ments; d—(l9, the appearances of Dol>ie's granules ;
/, Flogel's granules ; c, clear layer (lateral disc)
between Flogel's granules and end of sarcous
elements.

STK/r/lD Ml'SCULAR TiSSi'E.

lemma is drawn in. The part of a muscular fihn;
between two neighbouring Krause's membranes and
the corresponding portion of the sarcolemma is

Fij;-. t)7. — Semi-schematic representation of portions of Fibrils of Crab's
Muscle, showing the appearances of the fibrillar segments in the
several stages from complete relaxation at a to complete contraction
at F. (After Eutherjord.)

A.— &, Bowman's sarcous elements ; i, intermediate discs, comprising d, granules
of Dobie ; /, granules of Fli5?el ; c, clear layer between it and end of sarcous
element (lateral disc), b, I''frst stai,'e of contraction ; the clear layer be-
tween Dobie's granules and Fliiiirers' granules on the one side, and Fliigel's
granules and the end of the sarcous elements has disappeared. F, complete
contraction, showing sarcous elements comjiletely shortened : accumulation
of chromatic sulistauce at the ends, leaving the intervening shaft clear—
Hansen's median disc.

yS Elements of Histology.

spoken of as a muscular conipaitment of Krause
{See Fig. 65, a).

The lateral disc contains in some muscular fibres
{see above) a layer of granules or rods, the secondary-
disc, or Flogels layer ; but each of these granules or
rods is ioined to a granule of the
. 51 i intermediate disc, or Dobie's

^^^ |! I layer, on the one hand, and to

1 1 \ the end of a sarcous element on

,- »* \ the other ; so that in reality it is

vL 11 I a thickening of the bridges con-

V^ "-^ I necting the ends of a sarcous
Vl \\ I element to the granule of the
V 11 I intermediate disc.
^\\ • The transverse disc, or the

- '* \ laver of sarcous elements, shows

VV^ \ hardening, or after treatment
^\\ \ "^^'i^^ reagents, a median trans-
w\ 5 verse transparency, due to the

in muscular fibres during con-
traction (.y^e below) or after

1.1

\\\\8 substance of the sarcous ele-
"Wfi ments being here thinner, as
IllW i^'-Pi^tioned above. This corre-
Fig. GS.-Primitive Mus- ^ponds to the median disc of
euiar Fibriiia; from the Hensen. Eutlierford, however,
Si'-^^S'f- ^''■^'"' pointed out that this appear-
ance is due to the stainable or
chromatic substance of each sarcous element accumu-
lating at the ends (Figs. 66 and 67).

In muscular fibres treated with alcohol, the con-
nection between the sarcous elements and the rest of
the fibrillse is not recognisable ; hence the muscular
fibre seems split up into discs, apparently not con-
nected with one another {see Fig. 60).

The reticulation described by ^Nlelland, ^Marshall,
and others is due to coagulation of the sarcoplasma

Striped Muscular Tissue.

brought about by certain hardening reagents ; the
sarcoplasma between the granules of the layer of
Dobie or Krause would thus form a reticulated disc
extendinoj transversely across the muscular fibre, and
to it are joined lines of coagulated sarcoplasma ex-
tending longitudinally between the sarcous elements
of the tibrill^ (Fig. 69).

8''^. During contraction the transverse striation of
the tibre becomes much narrower, the different discs
becoming thinner in the
long, broader in the trans-
verse direction of the fibre.
In the naturally contracted
portion of a muscular fibre
— i.e. at the point of the
passage of the contraction
wave — the stripes alter their
character, inasmuch as at
the end of the transverse
and lateral discs the fibres
become darker, while the
middle of the discs of sarcous
elements becomes lighter.
Whether the former change
— i.e. of the lateral discs —
is due to compression, while

the latter — i.e. of the sarcous elements —is due to an
imbibition with water squeezed out of the sarcoplasma
in the lateral discs, as is maintained by Engelmann,
has not been fully established. Rutherford, on the
other hand, points out, what appeal^ a good explana
tion of this phenomenon — ^-iz. of the so-called re-
versal of the stripes during contraction — that during
contraction the chromatic substance of the sarcous
elements, together with Flogel"s granules and Dobie's
granules, forms one shortened mass ; hence the darkness
of these portions in each fibrilla. We reproduce

Fig. 69.— striped Muscular Fibres
in Cross-section. {Altos.)

Each fibre is limited by the sarco-
lemiiia ; the luuscular substance
is differentiated into Cohnheim's
areas.

loo Elemexts of Histology.

here from Rutherford drawinus illustrating these
points (Figs. 66 and 67).

Rollett considers, with Briicke, Kolliker, Engel-
mann, and many others, that the fibrillar are the
contractile parts : while Klihne, Ramon y Cajal, and
others, are inclined to think that the sarcoplasma —
which Kiihne calls sarcoglia— is the contractile part,
while the fibrillse — i.e. the rhabdia of Kiihne — or
rather the sarcous elements, are elastic elements.

The differentiation into intermediate, lateral, and
transverse discs, possessing the above-named different
structure and optical properties, produces the trans-
verse striation of the muscular fibres ; but it must
be also added that a fibre, though homogeneous but
moniliform (by shrinking or naturally so), would
show a transverse striation (Haycraft).

89. In the embryo the muscular tibres are
developed from spindle-shaped nucleated cells (Remak,
Weissmann. Kulliker). One spindle-shaped cell with

"^--^.s^*

Fig 70. — Striped Muscular Fibre of the Diaphragm of a
Guinea-pig. {Atlas.)

The muscle corpuscles are much increased iu size aud numbers ; tbey are
probably used here for the new formation of muscular substance.

an oval nucleus grows rapidly in length and thickness,
its nucleus divides repeatedly, and the offspring
become shifted from one another as the cell continues
to grow in lengtli. Tlius a ]<»ng spindle-shaped mass
of sarcoplasma, with iiunierous nuclei, is the result.

Striped Muscular Tissue. ioi

Tliis sarcoplasiiia in the middle of the cell becomes
converted into fibrilhe, and this formation continues,
while the sarcoplasma as a whole increases. The
muscle corpuscles of the adult fibres are remains of
this sarcoplasma (Fig. 70).

At all times in adult life, when muscular fibres
increase in thickness, as, for instance, when muscle
is kept at constant work, this increase is due to
increase of sarco})lasma, and joart-conversion of this
into fibrillin.

Paneth described in fishes, amphibia, birds, and
mammals a mode of new formation of muscular
fibres which supplements the one above described.
While in the embryo the first muscular fibres develop
from spindle-shaped cells in the manner stated above,
muscular fil^res are also newly formed from spherical
or oval cells — sarcoplasts ; in the interior of these
cells, the protoplasm is converted into contractile
substance, which is capable of enlarging and elon-
gating, and becoming converted into striped muscular
fil)res. According to Kdlliker and Weissmann,
muscle fibres divide longitudinally also, so that one
fibre is capable of giving origin to a bundle of thin
fibres each of which continues to increase in thickness
[see muscle spindles below).

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 exceptional cases — e.g. in the tongue ; here the
extremities of the muscular fibres, passing into the
mucous membrane, become richly branched previous
to their terndnation amongst the connective-tissue
fibres of the mucosa.

91. Muscular fibres terminate in tendons, either
by the whole fibre passing into a bundle of connective-
tissue fibrils (Fig. 71), or by the fibre ending abruptly
with a Ijlunt, conical end, and becoming here fixed to

102

Elements of Histology.

from one

end

a bundle of cuunective-tissue tibrils. TJie individual
fibres have only, as has been mentioned above, a
limited lensth : so that, following an anatomical bundle
to the other, we tind at many points
along the fasciculus some muscle fibres
terminating, others originating. This
takes place in the following way : the
contents of a fibre suddenly terniinate,
while the sarcolemma, as a fine thread,
becomes interwoven with the fine con-
necti\'e tissue between the muscular
fibres. Manv muscles contain peculiar
spindle-shaped enlargements ; these are
the muscle buds of Kolliker or the
inascle spindles of Kiihne ; each spindle
is a bundle of fine striped muscular
til ires formed bv lencjth division of a
mother fibre, and enclosed within a
thickened connective - tissue sheath,
which sheath is continuous with the
laminated connective - tissue sheath
(Henle's sheath) of nerve fibres — ^in
fact, the sjfiiidles occur at the entrance
of certain nerves into the muscle bundle
[see nerve endings).

92. Tlie striped muscular fibres of
the heart (auricles and ventricles) and
of the cardiac ends of the large veins
(the pulmonary veins included) differ
from other striped muscular fil)res 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
oft" all along its course short branches, or continually
dividinir into smaller fibres and forming a close

Fig. 71. — Two
Striped Mus-
cular Fibres
passing into
Bundles of Fi-
brous Tissue.
(Handbook.)

(Termination in
Tendon.)

Striped Muscular Tissue.

ro3

network (l^'ig. 72). A transverse section tlirough a
bundle of such fil)res shows, therefore, their cross-
sections irregular in shape and size. (4) Each nucleus
of a muscle corpuscle occupies the centre of one
lU'isuiatic portion ; each fibre and its branches thus
appear composed 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 trans-
parent substance.

93. Some mus-
cular fibres are
either markedly
pale or markedly
red (Ranvier) ; in
the former {(ijj.
quadratus lumbo-
rum, or adductor
magnus femoris of
rabbit) the trans-
verse stria t ion is
more distinct, and
the muscular cor-
puscles less nume-
rous, than in the ^ '
latter (ejj. semi-
tendinosus of rabbit,
diaphragm). Here
the longitudinal
striation appears very distinct, but these differences
are not constant in the same fibres of other animals
or of man (E. jMeyer).

94. Briicke has shown that striped muscular
fibres are doubly refractive, or anisotropous, like
uniaxial positive crystals (rock crystal), the optical
axis coincidini; with the lonsc axis of the fibres. The

Z.— striped Muscular Fibres of the
Heart.

A, Showinfe' tlie liniuching of the fll)res and their
anastomosis in networks; b, part of a thin
filire, highly mairnifled, showing the raouili-
forni primitive flbrillae; c, one inimitive
tibrilla more highly magnified.

I04 Elements of Histology.

sarcoplasiiia is isotropous, tlie tibrilhr alone being
anisotropoiis ; of these the sarcous elements were the
first recognised by Briicke to be doubly refractive.
They are, however, not the ultimate optical elements,
but must be considered as composed of disdiaclasts,
the real doubly refractive elements (Briicke).

lo;

CFI AFTER X.

THE HEART AXD BLOOD-VESSELS.

95. (a) The heart consists of an outer serous
covering, tJie visceral pericardium or exocard, an
inner lining, the endocardium, and Ijetween the two
the muscular suh-
stance (Fig- 73).
Underneath the
pericardium is a
thin layer of con-
nective tissue called
the subpericardial
tissue.

The free surface
of both the peri-
cardium and endo-
cardium has an en-
dothelial covering,
like other serous
membranes — i.e. a
single layer of trans-
parent nucleated cell
plates of a more or
less polygonal or
irregular shape. The
groundwork of these
two membranes is
tibrous connective
tissue, forming a

dense texture, and in addition there are many elastic
fibres arranged as networks. Capillary blood-vessels,

Fit

73. — Transverse Section through
Auricle of the Heart of a Child.

the

a, Endotbelium lining the endocardium; h, en-
docardium; c, muscular bundles cut trans-
versely ; d, muscular bundles cut longitudi-
nally ; e, pericardial covering ;/,endotlieliuui.

io6 Elements of Histology.

lymphatic vessels and small Ijranclies of nerve li))res
are met with in the pericardial layer. The sub-
pericardial tissue consists of trcibecula^ of tibrous
connective tissue, which are continuous with the
intermuscular connective tissue of the muscular wall
of the heart. The former contains in many places
groups of fat cells.

96. On the free surface of the papillary muscles,
in some parts of the surface of the trabeculse carnese,
and at the insertion of the valves, the endocardium is
thickened by tendinous connective tissue. Each valve
is covered with a prolongation of the endocard, but
the main body of the valve is dense tibrous connective
tissue ; on the surface of this connective-tissue matrix
is a somewhat looser connective tissue, containing
also a few elastic fibres.

All the corda3 tendineie and the \alves are of course
co\ ered on their free surfaces with endothelium.

Special tracts of uiuscle fibies occur in the sub-
endocardial tissue.

The fibres of Furkinje are peculiar beaded fibres
occurrinor in the subendocardial tissue in some mam-
mals — e.g. the sheep and the horse — and birds (not in
man). They are thin, transversely striped, muscular
fil^res possessed of local thickenings ; the central part
of each thickening is a continuous mass of protoplasm,
with nuclei at regular intervals, as is the case with
some skeletal muscular fibres of insects. These
beaded fibres of Purkinje must not be confused with
the inuscle spindles of Kiihne.

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 lamella?.

Like other striped muscular fi'hres, those of the

Heart and Blood-vessef.s. 107

wall of the iieart are richly supplied with blood-vessels
and lymphatics. The endocardium and valves have
no blood-vessels of their own, but the pericardium
possesses its own
system of Idood- , '•.-^n C"^ '~^\ "^^v - — ~ /'^^ --^

tics form a peri- Wi ;j_j^' -.==^^=.^^i^

cardial and an ^^^^ _j;_^ _ ^.^^s^ """^^^^^^'^^

endocardial net- ^^^ fe— .^^ .=^^=s. "^^

work connected g ^--^ss - _ ^^

with the lym-
phatics of the
muscular tissue
of the heart ; here
there are lym-
phatic clefts be-
tween the mus-
cular bundles,
and also net-
works of tubular

1 1 X- fig. 74.— i^roin a xransverse eectiou tiii<

i_) inpuaiicb. ^jjg Inferior Mesenteric Artery of the Pig.

Jg, inenerve <>, Endothelial lining; ?, elastic intinia; m, muscular
l>.^Ti-./-l-.«c. ,^^ ■*-!.« media; a, adventitia with numerous elastic

Dianciies Oi ine Ulinls, cut in transverse section. (Af/a.s.)

l^lexus cardiacus

torm 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
(Ludwig, Bidder), and in tiie auriculo-ventricular
septum of the frog (Dogiel). In man and mammals
numerous ganglia are found on the auricular nerve
branches, chiefly at the point of junction of the large
veins with the heart, Remak's ganglia, and at the
boundary between the auricles and the ventricles,
Bidder's ganglia.

91). (b) The artoi-ieN (Fig. 74) consist of : («) an

Fig. 74. — From a Transverse Section thiuugh

[o8

Elemexts of Histology.

endotheliaJ laijer 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

connective tissue, with
an admixture of net-
works of elastic fibres.

(«) The endothelium
is a continuous single
layer of flattened elon-
gated cell plates.

(6) The intima in
the aorta and larcje
arteries is a very com-
plex structure, consist-
ing of an innermost
layer of fibrous connec-
tive tissue, which is the
" inner longitudinal
fibrous layer " of Re-
mak, outside of which
^^^ is a more or less longi-

\^\ *~^^^^^^" tudinally arranged elas-

tic membrane. This is
laminated, and com-
posed of fenestrated
elastic meinhranes of
Henle. {See page 61.)
The larger the arte^^y
the thicker the intima.
In microscopic arteries
the intima is a thin
fenestrated membrane, the fibres having distinctly a
longitudinal arranfjement.

"^>*isa^>

Fis.

-Transverse Section through
a Microscopic Artery and Vein m
the Epiglottis of a Child. {Atlas. )

A, The artery, showing the nucleated en-
dothelium, the circular muscular
media, aud at a the fibrous-tissue ad-
ventitia: V, the vein, showing the
same layers ; the media is very Inuch
thinner than in the arterv.

Heart and Blood-vessels. 109

clastic laniellse (fenestrated membranes and networks
of elastic tibres), and between thern^ smaller or larger
Ijundles of circularly arranged muscular cells. The
larger the artery the more elastic tissue is there
present in the media, the smaller the artery the more
muscular tissue. In microscopic branches of arteries
the media consists almost entirely of circular non-
striped muscle cells with only few elastic fibres,

100. In the last branches of the microscopic
arteries the muscular media becomes discontinuous,
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 alternate
fashion.

When the media contracts, the intima is thrown
into longitudinal folds.

The aorta has, in the innermost and in the outer-
most parts of the media, numbers of longitudinal
and oblique muscle cells. According to Bardeleben,
all large and middle-sized arteries have an inner
longitudinal muscular coat.

101. Between the media and the next outer la3'er
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,
especially in the part next to the media ; they
form networks, and have chiefly a longitudinal
direction.

The larger the artery the more insignificant is
the adventitia as compared ^^•ith the thickness of
the media.

In microscopic arteries (Fig. 76) the adventitia
is represented by thin l)undles of fibrous connective
tissue and branched connective-tissue cells.

Large and middle-sized arteries possess their own

I lO

Elements of Histology.

system of blood-vessels (vasa
chiefly iu the adventitia and
vessels and lymphatic clefts are
these coats,
102. (c)

vasorum), situated

media: lymphatic

also present in

771 i.e

fli

^1 m

The veiiisi differ from the arteries in
the greater thinness of their wall. The
intima and media are similar to those
of arteries, only thinner, both abso-
lutely and relatively. The media con-
tains in most A^eins circularly arranged
muscular fibres ; they form a continu-
ous layer, as in the arteries, and there
is between them generally more fibrous
connective tissue than elastic. The
adventitia is usually the thickest coat,
and it consists chiefly of fibrous con-
nective tissue (Fig. 75). The smallest
veins — i.e. before passing into the
capillaries — are composed of a lining
endothelium, and outside this are de-
licate 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 j^art of the mus-
cular media.

103. There are many veins that
have no muscular fibres at all — e.g.
vena jugularis (interna and externa),
the vena -ubclavia, the veins of the bones and 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

n I fl J<te' i

Fig. 76.— ilinnte
Slicroscopic Ar-
tery. {Atlas.)

e, Endotheliaru ; i.
intima; m, mus-
cular media.com-
posed of a siDgk-
layer of circu-
larly - arranged
non-striped nius-
cular cells; a, ad-
ventitia.

Heart axd Blood-vessels. iir

muscular coat. Tlie intiina of the vena? pulmonales
in man is connective tissue containing circular bundles
of non-striped muscular cells (Stieda).

104. The trunk of the venie pulmonales and
ven?e cavre possesses striped muscular fibres, these
being continuations of the muscular tissue of the
auricles.

105. Hoyer showed that a direct communication
exists between arteries and veins witliout 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 form large irregular sinuses, the wall of
which is formed by fibrous and non-striped muscular
tissue.

lOG. (d) The capillary blood-vessels are
minute tubes of about a^oVo ^^ Wiro *^^ ^'^ inch in
diameter. Their wall is a single layer of transparent
elongated endothelial plates, united by thin lines of
cement sidistance (Fig. 77). Each cell has an oval
nucleus ; in fact, the wall of the capillaries is merely
a continuation of the endothelial membrane linins:
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
nervous system, the largest in the marrow of bone.
The capillaries form networks, the richness and
arrangement of which vary in the different organs,
according to the nature and arrangement of the
elements of the tissue (Fig. 78).

1 12

Elements of Histology

107. If capillaries are abnormally distended, as
ill inflammation, or otherwise injured, the cement

fc^'<-r

Fig. 77.- From a Preparation of the Peritoneum, stained ^vitli
Nitrate of Silver. (Handbook.)

a, Entlotlieliuin on the free surface of the membrane ; h, capillary blood sessels
in the membrane ; their wall is a layer of eQclotbelium.

Fig. 78.— Young Fat Tissue of the Omentum, its Blood-vessels injected.
n. Artery ; b, vein ; r, network of capillariei?. {Handbook.)

substance between the endothelial plates is liable to
o-ive way in tlie shape of minute holes, or stigmata,

Heart and Blood-vessels.

i»3

\\ liicli in;iyl>econie lur^er holes, or *•^(J'/y<^(^^ Tlie passage
of red bloofl cori)uscles (diapedesis) and the migration
of wJiite corpuscdes in inflammation through the un-
broken capillaries and small veins occur through
these stigmata and stomata.

108. Yoiiii^: and g^row iiig^ capillaries, Ijoth
of normal and pathological tissues, possess solid thread-
like shorter or longer nucleated protoplasmic processes
(Fig. 79), into which the canal of the capillary is

Fig. 70. —From a Pi-eparation of Omentum of Rabbit, after staining with
Xitrate of Silver. {Atkis.)

V, Minute vein ; a, solid protoplasmic prolongations of the wall of a capillary,
connected with connective-tissue corpuscles ; c, solid young bud.

gradually prolonged, so that the thread becomes con-
verted into a new capillary branch. Such growinor
capillaries are capable of contraction (Strieker).
All blood-vessels, arteries, veins, and capillaries.

114

Elements of Histology

d fibrous connective-tissue

both in the embryo and

ill their early .stages, both ill 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 material for the development of
the elastic, muscular, and
elements of the wall.

109. In the first ;•
in the adult, the vessel is re^jresented by solid nucle-
ated protoplasmic cells, spherical, elongated, spindle-
shaped, or bran-
ched — vasofor-
iiiative cells.
Such cells may
be isolated and
indej)endent of
any pre-existing
vessel, or they
ma}^ be solid
prot opl as mic
outgrowths of
the endothelial
wall of existing
capillarv vessels
(Fig. 80). In
both cases they
become hollowed
out by a process
of vacuolation ;
isolated vacuoles
appear at first,
but tliev oradu-
ally become Oion-
iiuent, and thus a young vessel is formed, at first
very irregular in outline, but gradually acquiring
more and more of a tulnilar form. In the case of

so. — Developing Capillary Blood-vessels from
the Tail of Tadpole. {Atlas.)

V, Capillary vein with clumps of pigiueat in the
■wait :«, nucleated protoplasmic sprouc ; /.solid
anastomosis between two neighbouring capil-
laries.

Heart and Blood-vessels.

11^

ail isolated cell, its protoplasmic processes grow l)y
degrees to th(! 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 islets or cysts of blood that appear early in the
area vasculosa of the embryo are due to vacuolation of

Fig. SI.— Cells from inesoblast of chick's blastoderm undergoing develop-
ment into blood-vessels in the area vasculosa. (Handbook.)

", Cavitj- of cell; b, cell wall ; /, cells not yet hollowed out ; d, hlood corpuscles.

spherical or elongated vasoformative cells of the meso-
blast, the islets or cysts being composed of a central
portion which are blood corpuscles, at first white, then
red, and a joeripheral protoplasmic nucleated envelope,
the future vascular wall. The central nucleated blood
cells develop by a process of endogenous division from
the original cell protoplasm. The blood cysts, at first
isolated, afterwards become connected by protoplasmic
processes with other cysts or other vasoformative cells,
ultimately forming a network of vessels (Fig. 81).

The. wall of young capillaries is granular-looking
})rotoplasm (the original cell substance), and in it

ii6 Elements of Histology.

are disposed, in uiore or less regular fashion, oblong
nuclei, derived Ijv multiplication from the nucleus of
the orkdnal cell. In a later stai:e. 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 linal 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 growtli give
origin to a whole set of new capilkries (Strieker,
Aftanasieff". Arnrild. Klein, Balfour, Ranvier, Leboucq).

I T

CHAPTER XI.

THE LYMPHATIC VESSELS.

110. The larg^e lymphatic trunks, such as the
thoracic duct, and the lymphatic vessels passing to and
from the lymphatic glands, are thin-walled vessels,

Fig. 82. — Lymphatic Vessels of the Diaphragm of the Dog, stained with
Nitrate of Silver. (Atlofi.)

The eadothelium foniiin',' tlie wall of tlie lymphatics is well shown ;
V, valves.

siaiilar in structure to arteries. Their lining endo-
thelium is of the same character as that of an artery,
and so are the elastic intima and the media with its
circular muscular tissue ; but these latter are very
much thinner than in an artery of the same calibre.

ii8

Elements of Histology

Tlie ach entitia is an exceedingly thin connective-
tissue membrane with a few elastic fibres. Tiie
valves are semi-lunar folds of the endothelium and
intima,

111. The lyiiipliatics 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. 82). The lym-
phatic is often many times
wider than a blood capillary.
Tlje endothelial plates are elon-
gated, but not so long as in a
Ijlood capillary, with more or
less sinuous outlines : but this
depends on the amount of
shrinking of the tissue in which
tlie vessel is embedded : when
there is no shrinking in the
tissue or in the vessel, the out-
lines of the cells are more or
less straight.

The lymphatics are sup-
ported by the tibrous connective
tissue of the surrounding tissue,
which does not, however, form
part of their wall

112. The outline of the

vessel is not straight, but more

or less moniliform, owing to

Fig. 83. -From silver-stained tlie slight dilatations present

specimen of the mesentery l^elow and at the senii-lnnar

of tne fro*"

o. Artery; %. perivascular VfdceS: thcSC are folds of the

iffendoibHiar'vaa "'"'''^ endothelial wall, and they are

met with in great numbers.

The vessel apjiears slightly dilated innnediately be-

vond the valve — that is, on the side farthest from

LvMPffAT/c Vessels. 119

the peripliery, or rootlet, whence the current of
lymph starts.

il3. Tracing the lymphatic vessels in the tissues
and organs towards their rootlets, we come to more or
less irregularly-shaped vessels, the wall of which also
consists of a single layer of polygonal endothelial
])lates; the outlines are very sinuous. These are the
IjimpJtatic capUJaries ; 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 valve.s.

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-
l»hatic capillary ; these are the perivascular hjm-
pliatics of His, Strieker, and others (Fig. 83).

114. The rootlets of the lyiiiphatic!^ are situ-
ated in the connective tissue of the different origans
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 ;
N\here these are branched cells anastomosing by their
processes into a network — such as the cornea, or
serous membranes — we tind that the rootlets of the
lymphatics are the lacunse and canaliculi of these cells
— the typical lymph- canalicular system of von
Recklinghausen (Fig. 84). The endothelial cells
forming the wall of the lymphatic caj^illaries are
directly continuous with the connective cells situated
in the rootlets. In tendons and fascife the minute
lymphatics lie between the bundles, and have the
shape of continuous long clefts or channels ; in
striped muscular tissue they have the same character,
being situated l^etween the muscular fibres.

I 20

Elements of HjsroLOGV.

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

Fig. S4- From silver-stained preparation of the Central Tendon of the
Rabbit's Diaphragm, showing the direct connection of the Lyniph-
canalicular System of the Tissue with the Lymphatic Capillaries.

a. LympUatlc vessel; h, lymphatic capillary lined wich "sinuous' endotheliom.

(Handbook.)

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

115. Lymph cavities. — In some cases 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

Lymphatic Vessels.

I 2 I

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, etc. 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 peritoneal cavities. In batrachian animals — e.g.
frogs — the skin all over the trunk and extremities is
separated from the subjacent fascipe and muscles by
large bags or sinuses — the subcutaneous lynipJi sacs.
These sinuses are shut
off from one another
by septa. Between the
trunk and the extremi-
ties, and on the latter,
the septa generally
occur in the region of
the joints. In female
froiifs in the mesoo-as-
trium smaller or larger
cysts lined with cili-
ated endothelium are
sometimes found. Be-
hind the peritoneal
cavitv of the fros:, on
each side of the ver-
tebral column, exists a
similar large lymph si-
nus, called the cisterna
lyniphatica magna.

116. The lymph cavities are in all instances in direct
communication with the lymphatics of the surround-
ing parts by holes or open mouths (stomata), often

Fi;

. 8.J. — Stuinata, lined witli Gennina-
ting Endothelial Cells, as seen froni
the Cisternal Surface of the Septuni
Cisternal I.yniphatici« Magnai of the
Frog. (Hundboolc.)

122

Elements of Histology.

surrounded by a special layer of polyLedral endothe-
lial cells — germinating cells (Figs. 85, %^). Such
stomata are numerous on the peritoneal surface
of the central tendon of the diaphragm, in which
are found straight lyn)ph channels between the tendon
bundles, and these channels communicate by nu-
merous stomata with
the free surface. A
similar arrangement
exists on the costal
pleura, the omentum,
and the cisterna Ivm-
phatica magna of the
frog. {See Chapter
IV.)

117. The serous
uieiiibraiies con-
sist of endothelium
upon a layer of
fibrous tissue with
networks of line
elastic fibres : they
contain networks of
])lood capillaries and numerous lymphatic vessels
arranged in (superficial and deep) plexuses. Plexuses
of lymphatics are very numerous in the pleura costalis
— or rather, intercostalis — in the diaphragm and pleura
pulmonalis. They are important in the process of
absorption from the pleural and peritoneal cavity
respectivelv. Lymph and lymph corpuscles, and other
solid particles, are readily taken uj:) by the stomata
{see Fig. 31) and brought into the lymphatics. Here
the respiratory movements of the intercostal muscles,
of the diaphragm, and of the lungs respectively, pro-
duce the result of the action of a pump.

118. There exists a definite relation between the
lymphatics on the one hand and the epithelium on the

Fig. 86. — Endotheliuia ami Stomata of tlie
Peritoneal Surface of the Septum Cis-
ternse Lj-mpbaticte Magnge of the Frog.
{Hawlhook.)

Lymphatic Vessels. 123

other, wliieli covers the mucous membranes and lines
the various glands, and also between the endothelium
covering serous membranes and that lining their vessels
and lymph cavities — namely this: the albuminous semi-
fluid cement substance {see former chapters) between
the epithelial or endothelial cells is tlie path by which
fluid and formed matter passes between the surfaces
and the lymph-canalicular system — i.e. the rootlets of
the lymi)liatics.

119. L.yiiii>li taken from the lymphatics of difl^er-
ent regions differs in composition and structure. That
from the thoracic duct contains a large number of
colourless or white corpuscles (lymph corpuscles), each
of which is a protoplasmic nucleated cell similar in
structure to a white blood corpuscle. They are of
various sizes, according to the stage of ripeness. The
smaller lymphocytes contain one, some of the larger con-
tain two and three nuclei corresjDonding to the typical
leucocytes. The latter show more pronounced amoeboid
movement than the former. Also "granular " oxyphile,
basophile, and amphophile cells are met with amongst
the leucocytes. A few red corpuscles are also met
with. Granular and fatty matter is present in large
(|uantities during and immediately 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 lym^^li
hearts. On each side of the os coccygis and under-
neath the skin is a pulsating posterior lymph heart.
The anterior lymph heart is oval, and is situated on
each side of the processus transversus of the third and
fourth vertebrae ; it is rather smaller than the posterior
one. Each lymph heart has afferent lymphatics, by
which it is in open communication with the lymph-
atics of the periphery, and from it passes out an efferent
vessel which opens into a large vein (a l)ranch of the

124

Elements of Histology.

sciatic and jugular veins resiDeetively). A valve
allows Ivmpli to flow out of the lymph heart into
the vein, but pre\'ents regurgitation of blood from

Fig. 87. — Developing Lyinph-capillaries in the Tail of Tadpole. {Atlas.)
a, Solid nucleated protoplas iiic branches not yet hollowed out.

the vein. The i?iternal surface of the lymph hearts
is 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.)

L YMPHA TIC Vessel s. 125

12U. Lvm})liatic vessels are developed and newly
formed under normal and pathological conditions in
precisely the same way as blood-vessels. The accom-
panying woodcut (Fig. 87) shows this very well. AVe
have also here to do with the hollowing out of (con-
nective tissue) cells and their processes previously
solid and protoplasmic.

126

CHAPTER XII.

FOLLICLES OR SIMPLE LYMPH fiLAXDS.

121. Under this name ^ve include the blood glands,
or the conglobate gland substance of Hewson, His,
and Henle. or the lymph follicles (Kolliker, Huxley,
Liischka). The ground sul)staneeof all lymph glands,
simple as well as compound (see below), is the lymph-
atic or o.denoid tissue, or leucocvtocrenous tissue.
Like all other gland tissue, it is supplied with a rich
network of capillaries derived from an afferent
artery, and leading into ett'erent veins.

122. The elements constituting this tissue are : —
(«) The adenoid reticnlura (Fig. 88), a network

of tine homogeneous fibrils, with numerous plate-like
enlargements.

(b) SiiiaU, transparent, fljif, endotlteloid cell phites,
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 ap[)ears
to belong to a nodal ])oint — i.e. to one of the
enlargements of the reticuluni : l>ut bv continued
shaking of a section of any lymphatic tissue, the oval
nuclei and their cell plates can be got rid of, so that
onlv the n^riculum is left, without any trace of a
nucleus.

(c) Lymph rorpiLScles completely fill the meshes of
the adenoid reticulimi. These can, however, be easily
shaken out. They are of different sizes ; some^the
young ones — are small cells, with a comparatively
large nucleus ; others — the ripe ones — are larger,
have a distinct protoplasmic cell body, with one or

S/MFLK Lymphatic Glands.

127

two nuclei. Ill all lyini)hatic tissues, be they part <jt"
a simple or ot" a compound lymph glantl, certain parts
are ot" greater transparency than others, due to the
lymph cells

being larger .. .. 1. '^\ J

and in a state
of division, as
indicated by
the various
phasesofmito-
tic division of
their nucleus
( F 1 e ni m i n g,
Heilbrunn).
These parts
form, there-
fore, centres
of germina-
tion, and con-
stitute what
are spoken
of as yenn
c e litres, or

germ nodules (Flemming). The germ centres are
not permanent structures.

123. The adenoid tissue occurs as :

(1) Diffuse adenoid tissue, without any detinite
arrangement. This occurs in the subepithelial layer
of the mucous membrane of the nasal fossae and
trachea, in the mucous membrane of the false vocal
cords and the ventricle of the larynx, in the posterior
})art of the epiglottis, in the soft palate and tonsils,
at the root of the tongue, in the pharynx, in the
mucosa of the small and large intestine, including the
villi of the former ; and in the mucous membrane of
the nasal cavity and vagina.

{'!) Cords, cijUnders, ov [xitclf-^ of adenoid tissue;

Fig. SS. — Adenoid Reticulum shaken out ; most of
the Lymph corpuscles are removed. From a Lym-
phatic Gland. {Atlo^.)

a, Reticulum ; c, capillary blood-vessel.

128

Elements of Histology

ill the omentum and pleura, and in the spleen
(^[alpigliian corpuscles).

(3) Lymph follicles, i.e. oval or spherical masses
more or less well detined ; in the tonsils, at the root
of the tongue, in the u[)per part of the pharynx
(phar3'nx tonsil), in the stomach, small and large

Fig. 89. — Lyinphangial Nodules, in the Omentum of a Guinea-pig, developini:
in connection with lymph vessels. {Klein's " Lymphatic Sydevi.")

A, Perilymphangial nodule: a. lymph vessel; b, lymphoid tissue: c, its enclo-
thelial wall; t', Tilood capillaries: b: endolyraphanarial structure: a, vein ;
b, artery; c, capillaries ; d, perivascular lymph vessel ; e, lymphatic tissue;
/, endothelial wall of the lymph vessel.

intestine ; in the nasal mucous membrane, in the
large and small bronchi ; and in the spleen (Mal-
pighian corpuscles).

Most of these masses of adenoid tissue mentioned
hitherto are developed in the wall or even in the
cavity of a lymph vessel or lymph sinus as pei'i- and
endo-lymphanr/ial nodules ; in the former case the
lymph tissue remains surrounded for a smaller or

Simple Lymphatic Glands.

129

l;ir<,^u' part of its periphery by a lymph siuus formini^
l)art of a network of lyin[>li tubes (Fig. 89, a and b).
124. The tonsils (Fig. 90) are masses of lymph
follicles anil diflfase adenoid tissue covered with a thin
mucous membrane, which penetrates in the shape of

• ■•'.**,■•'.'.

;'-'^i',\

/■' -^ ■^'^^^: --' III

Fig. 90.— Vertical Sectiun through part of the Tuiisil of Dog. {AUo.s.)

e. Stratified pavement epitbelluni covering tbe free surface of the raucous
membrane. The tissue of the mucous membrane is infiltrated wiih adenoid
tissue. /, lymph follicles ; m, raucous gland of tbe submucous tissue.

longer or shorter folds into the substance within.
Numbers of mucus-secreting cjlands 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 with similar stratified epithelium to that which
lines the oral cavity. Xumbers of lymph corpuscles

130 Elements of Histology.

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 cor-
puscles of the saliva, taken from the oral cavity, are
such discharged lymph corpuscles (Stohr). 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 pJuirynx tonsil of Luschka, occurring in the
upper part of the pharynx, is in all essential respects
similar to the palatine tonsil. Owing to large parts
of the mucous membrane of the upper portion of the
pharynx being covered with ciliated columnar epi-
thelium, some of the cryptr: in the pharynx tonsil are
also lined w4th it.

125. The lenticular g-laiitl*^ of the stomach are
single lymph follicles.

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

The agniinated g-lands of the ileum are groups
of lymph follicles. The mucous membrane containing
them is much thickened by their presence. These
groups of follicles are called a Peyer^s ixitcli or a
Peyers gland (see Intestine).

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
circumference of the follicles of the tonsils, pharynx,
intestine, bronchi, etc., is surrounded by a lymph
sinus leading into a lymj)hatic vessel. (See above.)
The lymphatic vessels and lymph sinuses in the
neighbourhood of lymphatic follicles or of diffuse
adenoid tissue are almost always found to contain

Simple Lymphatic Glands. 131

numerous lymph corpuscles, thus indicating that
these are produced by the adenoid tissue and absorbed
by the lymphatics.

r27. The tliyiiiiiH ^laiid consists of a frame-

'* ■" =« to '^ "

Fig. 91.— Section through the Thymus Gland of a Fcetus.

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

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. 91). The follicles are very irregular
in shape, most of them being oblong or cylindrical
streaks of adenoid tissue. Near the capsule they are
well defined from one another, and present a polygonal
outline ; farther inwards they are riiore or less fused.
Each shows a central transparent medulla (germ centre)
and a peripheral less transparent cortex (Watney).

132

Elements of Histology.

At tlie 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 liner and longer. The meshes of the
adenoid reticulum in the cortical part of the follicles
are filled with lymph corpuscles like those occurring in
the adenoid tissue of otlier organs, but in the medul-
lary part they are fewer, and the meshes are more or
less completely occupied by the enlarged but more
transparent cells : in many of these mitotic division of
the nucleus occurs. These conditions cause the neater
transparency of the medulla and represent the germ
centres above mentioned. Amongst the laro-e cells of

the medullary portion,
some are coarsely granu-
lar and include more
than one nucleus ; some
are even multinucleated
giant cells.

128. Amongst the cells
of the medulla occur also
larger or smaller, more
or less concerTErically arranged nucleated protoplasmic
ijiasses. which are the concentric bodies of Hassall
(Fig. 92). They are met with even in the early
stages of the life of the thymus, and cannot there-
fore be connected with the involution of the gland,
as maintained by Afanassief, according to whom
the concentric corpuscles are formed in blood-vessels
which thereby become obliterated. According to
Watney they are concerned in the formation of blood-
vessels and connective tissue.

The lymphatics of the interfollicular septa and
trabecular always contain numbers of lymph corpuscles.
The blood capillaries of the follicles are more richly
distributed in the cortex than in the medulla, and

Fig. 92. — Two Concentric or Hassall's
Corpuscles of the Thymus. Foetal
Gland.

S/MPf-F. LvMriiAric Glands. 133

they radiate from the periphery towards the central
parts.

129. After birth the thymus begins to undergo
involution, leading to the gradual disappearance of
the greater portion of the gland, its place l)eing taken
by connective tissue and fat. But the time when
the involution is completed varies within very wide
limits.

It is not unusual to find in persons of tifteen to
twenty years of age an appreciable amount of thymus
tissue. According to Waldeyer, about 60 per cent, of
adults examined had still a portion of thymus gland
left. In some animals— e.^. guinea-i)ig — the involu-
tion 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.

134

CHAPTER XTII.

COMPOUND LYMPHATIC GLAXDS.

130. The compound or true lymphatic glands are
nodules, generally of an oblong shape, directly inter-
]>olated in the course of lymphatic vessels. Such are
the mesenteric, portal, bronchial, splenic, sternal,
cervical, culntal, popliteal, inguinal, lumbar 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 traheculcn and septa of connective
tissue. The trabeculse havincj advanced a certain
distance, about one-third or one-fourth, towards the
centre, branch into minor trabecular, which in the
gland anastomose with one another so as to form a
plexus with small meshes. Thus the peripheral third
or fourth of the gland is subdivided by the septa and
trabeculte into relatively large spherical or oblong
compartments, while the middle portion is made up of
relatively small cylindrical or irregularly-shaped com-
partments (Fig. 93). The former region is the cortex^
the latter the meduUa of the gland. The compart-
ments 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 trabecuhe are
tlie carriers of the vascular trunks ; the trabeculse
consist of fibrous connective tissue and of a certain

Compound Lymphatic Glands.

135

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

Sometimes coarsely granular connective-tissue cells
(plasma cells) are present in considerable numl^ers in
the trabecuhe.

132. The com})artments contain masses of adenoid

Fig. 03.— From a Vertical Section through a Lj-mphatie Gland, the
Lymphatics of which had been injected. {Atlas.)

c, Outer capsule, with lymphatic vessels in section; «, corticallymph follicles;
around them are the cortical lymph sinuses; b, medulla; injected lymph
sinuses between the masses of adenoid tissue.

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

136

Elements of Histology.

and medullary cylinders consist of adenoid tissue with
germ centres of exactl}^ similar character to that
described in the previous chapter. And this tissue
also contains the last ramifications of the blood-
vessels— i.e. the last branches of the arteries, a rich
netwoik of capillary blood-vessels, and the first or
smaller branches of the veins. The capillaries and
other vessels receive also here an adventitious envelope
fiom the adenoid reticulum.

133. The cortical follicles and the medullaiy

cylinders do not
completely fill out
the compartments
made for them by
the capsule and
trabecular respec-
tively, but a nar-
row peripheral
zone in each com-
jmrtment is left
free; these are the
lymphatic sinuses.
In the cortex they
are spoken of as
the cortical (Fig.
94), in the medulla
as the medullary J
lyinj)h sinuses

(Fig. 95). The
former is a space
between the outer
surface of the cor-
tical lymph follicle
and the corre-
sponding part of the capsule or cortical septum, the
latter between the surface of a medullary cylinder
and the trabecuhe. From what lias been said of the

eT?:^'^^

04.— Fnnii a Section tlninigli a Lyiiiiiliatic
Gland. (Atlas.)

Outer caisiile; s, cortical lyiiii>li sinus; a,
adenoid tissue of cortical follicle. Numerous
nuclei, indicating lynijiL corpuscles.

Com POUND Lymphatic Glands.

137

relation of the compartments, it follows that the
cortical and medullary lymph sinuses form one inter-
communicating system. These are not empty free
spaces, but are filled with a coarse reticulum of fibres,
much coarser than the adenoid reticulum ] to it are
attached large transparent cell plates — endotheloid

Fig. 95. — From a Section Uirough the Medulla of a Lymphatic Gland.

a, Transition of the medullary cylinders of adenoid tissue into the cortical
follicles; 6, lymph sinuses occupied by a reticulum; c, fllirous tissue trabe-
culae ; d, medullary cylinders.

plates. In some instances (as in the calf) these cell
f)lates 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 cor-
puscles, the majority of which consist of a compara-
tively large protoplasmic body and one or two nuclei ;

138 Elements of Histology.

they show lively amoeboid movement ; a few small
lymphocytes are also amongst them.

The surface of the trabeculse 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, applied to the
reticulum of the sinuses, are stretched out, as it
were, between the endothelial membrane covering
the surface of the trabecular on the one hand and
that covering the surface of the follicles and cylinders
on the other.

In the mesenteric glands of the pig the distribu-
tion of cortical follicles and medullary cylinders is
almost the i-everse from that of other glands and in
other animals : the cortical part having the arrange-
ment of cylinders of adenoid tissue and trabeculai,
while the medulla shows lymph follicles and longer
septa between them.

134. The afferent lymphatic vessels having entered
the outer capsule of the gland, and having formed
within the capsule a dense plexus, open directly into
the cortical lymph sinuses. The medullary lymph
sinuses, on the other hand, lead into lymphatic vessels,
which leave the gland at the 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 this : From the afferent vessels, situated in
the capsule, the lymph flows 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 lymph sinuses the
current of the lymph will flow very slowly and with
difficulty, as if through a spongy Alter. Hence a

Compound Lympi/atic Glands. 139

large number of formed corpuscles, pigment, inflam-
matory or other elements, passing into the gland from
the afferent vessels are easily arrested and deposited
in the sinuses, and are there readily swallowed by the
amre'boid corpuscles lying in the meshes of, or de-
posited on the reticulum.

Passing a stream of water by way of the afferent
lymph vessels 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. Probably
also by the normal lymph-stream passing from the
minute arteries and capillary blood-vessels of the
adenoid tissue (follicles and medullary lymph
cylinders) into the lymph sinuses, lymph cells are
drained, as it were, from the follicles and cylinders
into the sinuses. The amoeboid movement of these
cells will greatly assist their passage into the sinuses.
From here the cells are carried away by the lymph
current into the efferent lymph vessels, and are ulti-
mately carried into the big lymph-trunks discharging
into the big veins — i.e. into the circulating blood — as
white blood corpuscles.

I40

CHAPTER XIY.

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 consider in each nerve fibre the peripheral and

Fig. 9(3.— From a Transverse Section tlirough the Sciatic Nerve of Dog.

ep, Epineurium ; }). periueuriuni ; n, nerve filires coustituting a nerve bundle in
cross-section ; /, fat tissue surroundiug the nerve. {Athig.)

central termination and the conducting part. The
latter, i.e. the nerve fibres proper, in the cerebro-
spinal nerves are grouped into bundles, and these
afifain into anatomical nerve branches and nerve
Each anatomical cerebro-spinal nerve con-

trunks

Nerve Fibres. 141

sists, therefore, of bundles of nerve fibres (Fig. 96).
The general stroma b}^ which these bundles are held
together is fibrous connective tissue called the epi-
neurium (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 or faiiiculi (Fig. 97) vary
in size according to the number and size of the nerve
fibres they contain. They are well defined by a
sheath of their own, called perineurium (Key and
Retzius). This perineurium consists of bundles of
fibrous connective tissue arranged in lamella?, every
two lamella? being separated from one another by
smaller or larger Ijmiph spaces, which form an inter-
communicating system, and anastomose with the
lymphatics of the epineurium wdience they can be
injected. Between the lamella, and in the spaces,
are situated flattened endotheloid connective-tissue
corpuscles.

The nerve bundles are either simple or compound.
In the former the nerve fibres are not subdivided
into groups within the bundle, in the latter the
bundles are subdivided 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
peripheral distribution — each branch of the bundle
receives a continuation of the lamellar perineurium.
The more branches the perineurium has to supply,
the more reduced 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 info single nerve
fibres, or into small groups of them, each of these has
also a continuation of the fibrous tissue of the

142

Elemexts of Histology.

perineurium. In some places this perineural con-
tinuation is only a very delicate endothelial membrane
as just mentioned, in others it is of considerable
thickness, and still shows its lamellated nature. Such

Fig. 07.— Transverse Section through a Xerve Bundle in
the Tail of Mouse. i^AtUs.)

p. Perineurium ; c, endoneurium separating the medullated nerve fibres
seen in cross-section ; i, lymph spaces in the perineurium; i, lymph spaces
in the endoneurium.

a lamellated sheath of single nerve fibres, or o a
small group of them, represents what is called a
He /lie's sheath.

138. The nerve fibresarehekl together or separated
respectively within the bundle by connective tissue,
called the endoneurium (Fig. 97 j. This is a homo-
geneous crround substance in which are embedded
tine bundles of fibrous connective tissue, and con-
nective-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. The endoneural
lymph spaces communicate with those of the peri-
neural sheath.

A^ER VE Fibres . 143

When nerve trunks anastomose so as to form a
plexus — e.g. in the brachial or sacral plexus — there
occurs a division, an exchange and re-arrangement
of nerve bundles in the branches. A similar con-
dition obtains in the ganglia of the cerebro- spinal
nerves. Nerve trunks and nerve branches passing
through a lymph cavity, such as the subdural spaces,
or the subcutaneous lymph sacs, or the cisterna lym-
phatica magna in the frog, receive from the serous
membrane an outer endothelial covering.

139. Most of the nerve fibres in the bundles of
the cerebro-spinal nerves, with the exception of the
olfactory nerve, are meduUatecl nerve fibres. These
are doubly - contoured smooth cylindrical fibres,
varying in diameter between ttoVo ^^ more and
iToooo ^^ ^^^ inch. Within the same nerve, and
even wdthin the same nerve bundle, there occur
fibres which are several times thicker than others,
and it is probable that they are derived from different
sources ; this, for instance, is very conspicuous in the
vagus nerve (Gaskell, Fig. 98). Schwalbe has shown
that the thickness of the nerve fibre stands in a
certain relation to the distance of its perijihery from
the nerve centre and to its 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
reagents — 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 called myeline droplets^ and are derived
from the fatty substance or myelin constituting the
medullary sheath or white substance of Schwann (see
below). When a nerve fibre within the bundle under-
goes degeneration during life, either after section of

144

Elemexts of Histology.

the ner\'e or after other pathological changes, or in
the natural course of its existence (S. Maver), the
medullarv sheath is the first to undergo cliange ; it
breaks uj) into similar smaller or larger globules or

Fig. 98. — From a Transverse Section through the Vagus Xerve, showing in
the nerve bundles nerve fibres (in cross-section) which differ markedly
in size, some being much larger than others. (Photo., highly imignified.)

particle-, whicli gradually l)ec'ome granular and
absorbed. Later also the axis cylinder dwindles
away, and only the neurilemma with the nucleated
corpuscles persist.

140. Each medullated nerve fibre (Figs. 99, 101)
consists of tlie following parts : {a) the central axis
cylinder, axon or neuraD:on. This is the essential
part of the fibre, and is a cylindrical or band-like.

Nerve Fibres. 145

pale, trans|>ureiit structure, which in certain locali-
ties (near the terminal distribiiiion, in tlie olfactory
nerves, in the centj'al nervous system), and especially
after certain reagents, shows itself composed of very
fine homogeneous or more or less beaded tibrilhe — the
elementary or jjriniitive Jibrillfe (Max Schultze) — held
together by a small amount of a faintly gianular in-
terstitial substance The longitudinal striation of
the axis cylinder is due to its being composed of
primitive librillcV. The thickness of the axis C3dinder
is in direct proportion to the thickness of the whole
nerve tibre. The axis cylinder itself is enveloped in
its own hyaline more or less elastic sheath — the axi-
lemma (Kiihne), composed of neurokeratin.

1-1:1. (b) The medidlarij sheath, or myeline sheath,
or white substance of Schwann, is also called the
medulla of the nerve fibre. This is a olisteninff
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 shrinking, stands farther
apart from the latter.

142. (c) The sheath of Scliicann, or the neurileinma,
closely surrounds the medullary sheath, and forms the
outer boundary of the nerve fibre. It is a delicate
structureless membiane. Here and there between
the neurilemma and the medullary sheath, and
situated in a depression of the latter, is an oblong-
nucleus, surrounded by a thin zone of protoplasm.
These nucleated corpuscles are the nerve corpuscles
(Fig. 99), and are analogous to the muscle corpuscles,
situated between the sarcolemma and the striated
muscular substance. They are not nearly so numerous
as the muscle corpuscles.
K

146

Eleisients of Histology

143. The neurilemma presents at certain definite
intervals annular constrictions — the nodes or constric-
tions of Rani-ier (Figs 99, 100, 101) — and at these

nodes of Ranvier the medullary
sheath, but not the axis cylinder and
its special sheath, is suddenly inter-
rupted, and sharply terminates at
the constriction. The neurilemma
is at the same time thickened by
annular permanent, folds (see b in
Fig. 101). The portion of the nerve
fibre situated between two nodes is
the internodal segment. Each in-
ternodal seojment has orenerallv one,
occasionally more than one, nerve
corpuscle. The medullary cylinder
of each internodal segment is made
up of a number of conical sections
(Fio-. 101, A) imbricated at their ends

¥W 99. -Two Nerve - ^ .

Fibre's, showing the (Schmidt, Lantermann ; and each

such section is again made uj) of a

large number of rod-like structures

(Fig. 102) placed vertically on the

been dissolved axis cvlinder (MacCarthy).
away. The deeply- „ - , ^ 1

ihese rods are, however, con-
nected into a network. The net-
work itself is verv likelv the neuro-
keratin of Ewald and Kiihne, where-
as the interstitial substance of the network is
probably the fatty substance leaving the nerve
fibre in the shape of myeline droplets, when pres-
sure 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
medullary sheath, form the entire white substance of

nodes or constric
tions of Ranvier
and the axis cy-
linder. The me-
dullary sheath has

stained oblong
nuclei indicate the
ner\'e corpuscles
within the neuri-
lemma. (Atlas.)

Ner I'E Fibres.

147

the brain and spinal cord. In these organs, in the
hardened and fresh state, numerous nerve fibres may
be noticed, whicli show

more or less regular f(iil//'i///(' l|-i N^I/f^PI

varicosities, owing to ((allllamlmru il/^^ h

local accumulations of /: M lUlnf/rnwi !Wm%

fluid between the axis /J l////tl W^lJ ///j > ^^^^

cylinder and medullary jl B ni f'lJ'/^^iJf'liHwV^

sheath. These are
called varicose nerve

B \\\l^

Fig. 101.— Medullated Xerve
Fibres.

A, Medullated nerve fibre, show-
ing the subdivision of tlie
medullary sheath into cylin-
drical sections imbricated with
their ends ; a nerve corpuscle
with an oval nucleus is seen
between tlie neurilemma and
the medullary sheath, b, me-
dullated nerve fibre at a node
or constriction of Kanvier ; the
axis cylinder passes uninter-
ruptedly from one se.L'inent
into the other, but the medull-
ary s sheath is interrupted.
(Key. and Retzius.)

Fig. 100.— Medullated Xerve Fibies, after
staining with nitrate of silver. {Key
and Retzius.)

rt. Axis cylinder; h, Ranvier's constriction.

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
neurilemma ; they are there-
fore without any nodes of
Ranvier. Varicose fibres are
common in them.

145. Medullated nerve
fibres occasionally in their
course divide into two me-
dullated fibres. Such divi-
sion is very common in

148

Elements of Histology.

medullated nerve libres supplying striped muscular
tissue, especially at or near the point of entrance
into the muscular fibres. (See below.) But also
in other localities division of nerve fibres may be
met witli. Tlie electric nerve of the electric fishes

— e.g. malapterurus, gym-
notus, silurus — shows such
divisions to an extraor-
dinary degree, one huge
nerve fibre dividinc; at
once into a bundle of
minute fibres. Division
of a medullated fibre
takes place generally at
a node of Ranvier. The
branches taken together
are generally thicker than
the undivided part of the
fibre, but in structure
they are identical with
the latter.

146. When medul-
lated nerve fibres ap-
proach their peripheral
Medullated xen-e Fibres, termination, they change

A, B. Showinc on a surface view the i x • 1

reticulated nature of the medullary SOOner Or later, inasmUCh
sheath; c, two nerve fibres showintr ±a • in 1 ji

the axis cylinder, the medullary aS their meOUJlary Slieath
sheath with their vertically-arranged i i i i

minute rods, and the delicate neuri- SUCluenlV CeaSCS ; and UOW
lemma or outer hyaline sheath. i ' 77

{.Atlas.) Ave have a non-meam-

lated or grey (trans-
parent) nerve fibre of Remak. Each of these consists
of an axis cylinder, a neurilemma, and between the
two a nucleated nerve corpuscle from place to place.
Xon-medullated nerve fibres alwavs show the fibrillar
nature of their axis cylinder. The olfactory nerve
branches are entirely made up of non-meduUated
nerve fibres. In the branches of the sympathetic

A^ER I 'E Fibres.

149

most tilnes arc iiou-medullated. Non-medullated
til)res do not show Raiivier's constrictions. Bundles of
non-medullated fibres are grey, bundles of medullated
Hbres are white, when viewed in reflected light ; the
former being without medullary sheath allo'.v light to

Fig. 103. — View of the anterior surface of Gold-stained Cornea of Guinea-
pig, showing the rich distribution of the terminal nerve tibrilhe and
their ramifications in the anterior epithelium of the cornea. {Photo.,
highly magnified.)

pass through them, while the latter owing to their
medullary (fatt}') sheath reflect light strongly.

In the extra-vertebral course of many branches
of the cerebro-spinal nerves — e.g. those supplying the
limbs, the wall of the chest and abdomen — there occur
non-medullated fibres generally in small groups ;

ISO

Elements of Histology.

these fibres are considered to be derived from the
sympathetic system, haviiii;' joined the cerebro spinal
nerves by the grey portions of the rami communi-
cantes (Gaskell). Tiie non medullated fibres near their
terminal distribution always undergo repeated divi-
sions. They form plexuses, large fibres branching
into smaller ones, and these again joining. Gener-

Fig. 104. — Dendritic terminations— Demlrons of Xerve Fibres. Transverse
section of the optic lobe of a binl prepared by Golgi's method. (R. y
Cajal. from Quain.)

a, Optic fibres; ft, c, rf, e, dendrons of same in the diifereiit layers of the optic
lobe ; 6 and 7 are the sixth and .seventh layers respectively of the organ.

ally at the nodal points of these plexuses there are
triangular nuclei, indicating the corpuscles of the
neurilemma.

147. Finally the non-medullated nerve fibres leav-
ing tlie plexuses ultimately lose their neurilemma and
l)reak up into tlieir constituent small bundles and
even single primitive nerve fihrillce, which occasion-
ally show regular varicosities (Fig. 105). Of course,
of a neurilemma or the nuclei of the nerve corpuscles
there is nothing left. The bundles of primitive fibrils

Nerve Fibres.

T51

and also single fibrils branch and interlace, whereby a
more or less dense dendritic ramification — avhoriHa-
tion or (/c?irfywi— is produced (Fig. 104). The indivi-

Fig. 105. — Nerve Fibres of tlie Cornea.

a, Axis cylinder near the anterior epithelium of the cornea splitting up into
its constituent primitive flbrillaj ; &, primitive flbrillae.

dual fibrils of the dendron are straight or twisted, and
often provided with smaller or larger terminal knobs.
In some localities — e.g. in the grey matter of the
central nervous system — the number of fibrils con-

152

Elements of Histology.

stituting a dendron is large, and hence the dendron
is conspicuous, in other localities the number of tibrils
is relatively scanty — e.g. in the anterior epithelium
of the cornea — and hence the arborising character
of the dendron is not very conspicuous (Fig. 103).

Fig. 106. — Intra-epitlielialXerve-teriniuation in the Anterior Epithelium of
the Cornea, as seen in an oblique section. (Handbook.)

a. Axis cylindei' ; b, sub-epithelial nerve flbrillie ; c, iutra-epithelial i-amiflcatiou ;
d, epithelial cells.

Pronounced dendrons are found in the nerve termin-
ation in muscle and tendon (the endplates) in the
branched processes (dendrites) of the ganglion cells
in the central nervous system, as will be described
and illustrated later.

In the skin, cornea and mucous membranes,
the peripheral termination — ■ i.e. the primitive
fibrils and their ramitications. are intra-epithelial
(Fig. lOG), i.e. they are situated in the stratum
Malpighii of the epidermis, in the epithelial parts of

NeR VE FlBR ES.

153

the hair follicle, in the anterior epithelium of the
cornea, or in the epithelium of the mucous mem-
branes. The primitive nerve fibrils lie in the inter-
stitial substance between the epithelial cells, and some
of them have been observed to end with minute

Fig. 107. — From gold-stained cornea of frog, showing the numerous beaded
line nerve fibrils and the branched corneal corpuscles. [Photo., highly
magnified.)

knobs in the cell substance itself close to the
nucleus (Pfitzner, Macallum).

148. Tracing then a nerve fibre, say one of com-
mon sensation, from the periphery towards the centre,
we have isolated primitive fibrils or their ramifications ;
they form by aggregation simple axis cylinders, which
vary in thickness according to the number of their

154 Elemexts of Histology.

constituent primitive til)rils. These axis cylinders
then become invested bv neurilemma and nuclei, and
form plexuses. By association they form larger axis
cylinders, and these form typical non-medullated nerve
fibres with neurilemma, and with the nuclei of nerve
corpuscles (Fig. 106). Lastly, if a medullary sheath
makes its appearance between the neurilemma and
the axis cylinder of each fibre we get a rneduUated
nerve fibre.

155

CHAPTER XV.

PERIPHERAL NERVE-ENDINGS.

149. In the preceding chapter we referred to the
termination of the nerves of common sensation, .as iso-
lated primitive fibrillre, and as ramifications and den-
drons of these in the epitlielium of the skin and mucous
membranes, in the anterior epithelium of the cornea,
and in the grey matter of the central nervous system.
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. These are all connected with a meduUated
nerve fibre, and are situated not in the epithelium
of the surface but in the tissue, at greater or lesser
depth. Such are the corpuscles of Pacini and Herbst,
the end-bulbs of Krause in the tongue and con-
junctiva, the genital end-corpuscles or end-bulbs in
the external genital organs, the corpuscles of Meiss-
ner or tactile corpuscles, in the papillae of the skin
of the volar side of the fingers, the touch-cells of
Merkel, the end-corpuscles of Grandry, in the beak
and tongue of the duck.

150. The Paciiiisiii corpuscles. — These are
also called Yater's corpuscles. They occur in large
numbers on the subcutaneous nerve fibres of the jDalm
of the hand and foot of man, in the mesentery of the
cat, along the tibia of the rabbit, in the genital organs
of man (corpora cavernosa, prostate). Each corpuscle
is oval, more or less pointed, and in some places
(palm of the human hand, meseutery of the cat)
easily percej)tible to the unaided eye, the largest

'56

Elemexts of Histology.

beino; about T.^rrtli of an incli Ioiijt; and ^th of an
inch broad ; in other places they are of microscopic
size. Each possesses a stalk, to which it is attached,
and which consists of a single medullated nerve fibre
(Fig. 108), differing froin an ordinary medullated

nerve fibre merely in the
fact that outside its neuri-
lemma there is present a
thick laminated connec-
tive-tissue sheath. This
is the sheath of Henle
— continuous with the
perineural sheath of the
nerve branch with which
the nerve fibre is in con-
nection. This medullated
nerve tibre within its
sheath possesses generally
a very wavy outline. The
corpuscle itself is com-
posed of a large number
of lamella, or capsules,
more or less concentric-
ally arranged around a
central elongated or cylin-
drical 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 tibre in the
shape of a simple axis cylinder. But this axis cylinder
does not fill out the central space, since there is
all round it a 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 tico or

Fig. lOS. — Pacinian Corpuscle, from
the Mesentery of Cat.

a, Medullated nerve fibre : b. concen-
tric capsules.

Per ipher a l Ner ve-endings.

^57

more branches, and these terminate in pear-shaped,
oblong, spherical, or irregularly-shaped granular-
looking enlargenients.

151. The concentric cajjsules forming the corpuscle
itself are disposed in a different manner at the peri-
phery and near the central space

from that in which they are dis-
posed in the middle parts, in the
former localities being much closer
together and thinner than in the
latter. On looking, therefoi-e, at
a Pacinian corpuscle in its longi-
tudinal axis, or in cross-section,
we alwaj^s notice the striation
(indicating the capsules) to be
closer in the former than in the
latter places. Each capsule con-
sists of — (rt) a hyaline, probably
elastic, ground substance, in which
are embedded here and there (b)
fine bundles of connective- tissiie
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 endotJielifd plates.
The oblong nuclei A'isible on the
capsules at ordinary inspection are "• ^'"^''" u\;^a\vay.'''^ ^''''^
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 capsules at one pole ; thus a canal is formed
in which is situated the medullated nervQ fibre, and

Fig. 109.— Herbst's Cor-
puscle, from the
Tongue of Duck.

1:^8

Elements of Histology.

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 intermediate 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 pirts 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 nerve fibre ; it penetrates the
peripheral capsules, and supplies them with a few
capillary vessels.

loo!^ The corpuscles of Horbst 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
tliat the capsules are thinner and
more closely placed (Fig. 109).
This applies especially to those near
the central space, and here between
these central capsules we miss the
nuclei indicatinii the endothelial
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 tliose of the rabbit, and in ten-
dons.

154. The tactile corpuscles,
or corpuscles of ^leissuer, oc-
cur in the }>apilhe of the corium of
the volar side of the fingers and toes
apes ; they are oblong, straight, or
In man they are about —t, to

Fig. IIO'.— Tactile Cor-
puscle of Meiss-
ner from the Skin
of the Human
Hand. (£. FiscUr
awl W. Flemming.)

Showing the convolu-
tions of the nerve
fibre.

in man and in
slightly folded.

3 0 0

pf an inch long, and

5 00

-i- of

2 0 0 ^^

an inch broad.

Per ip/fER A L Ner ve-endings.

159

They are connected with a medullated nerve fibre —
generally one, occasionally, V)ut rarely, two — with a
sheath of Henle, The nerve fibre enters the corpuscle,
but usually before doing so it winds lound the cor-
puscle 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 pene-
trates into the interior of the corpuscle, where the axis
cylinder branches ;
its branches retain
a coiled course all
along the tactile cor-
puscle (Fig. 110),
anastomose with one
another, and ter-
minate in slight en-
largements, pear-
shaped or cylindrical.
These enlargements,
according to ]Merkel,
are touch-cells. The
matrix, or main part
of the tactile cor-
puscle consists, be-
sides the fibrous
sheath with nuclei
and numerous elastic

fibres, of fine bundles of connective tissue, and
number of nucleated small cf-lls.

155. The end-bulbs of Krauze. — These occur
in the conjunctiva of the calf and of man, and are
oblong or cylindrical minute corpuscles situated in
the deeper layers of the conjunctiva, near the corneal
margin. A medullated nerve fibre, with Henle's
sheath, enters the corpuscle (Fig. 111). This possesses
a nucleated capsule, and is a more or less laminated

Fig. 111. — End-bulljof Kraii.sc.

Medullated nerve fibre : b, caiisule
corpuscle.

)f the

of a

i6o

Elemexts of Histology.

(in man more granuLir-looking) structure, numerous
nuclei being scattered between the lamina?. Of the
nerve fibre, as a rule, only the axis cylinder is pro-
longed into the interior of the corpuscle. Occasion-
ally 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 ex-
tremity, it l)ranches, and terminates with small
enlargements (Krause, Longworth, Merkel, Key and
Retzius).

The end-hidbs 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 €ori>ii«irIe«» of Graiidry, or tou.ch
corpuscles of Merkel, in the tissue of the papill?e in
the beak and tongue of birds, are oval or spherical
corpuscles of minute size, possessed of a very delicate
nucleated membrane as a capstile. aud 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

71 A B -^ C

Fig. 112. — Corpuscles of Grandry in the Tongue of Duck, {Iz2uierdo.)

A, Composed of three cells : b. composed of two cells ; c, showing- the develop-
ment of a Grandry's corpuscle from.tlie epithelium covering the papilla, p;
e, epithelinra ; 'i, nerve fibre.

row (Fig. 112). A medullated nerve fibre enters the
corpuscle from one side, and losing its medullary

Per ipheral Ner ve-endings.

i6[

sheatl), the axis cylinder brandies, and its branchlets
terminate, according to some (Merkel, Henle), in the
cells of the corpuscle (touch cells of Merkel) ; accord-
ing to others (Key and Retzius, Ranvier, Hesse,
Izquierdo), in the transparent substance between the
touch cells, thus forming the '• disc tactil " of Ranvier
or the " Tastplatte " of Hesse. Neither theory seems
to us to answer to the facts of the case, since we find

Fig. 113.— Bundles of Non-striped Musenlar Tissue surrounded by
Plexuses of Fine Xerve Fibres. (Hamlbook.)

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 conjunctival end-bulbs. According to
IMerkel, single or small groups of touch cells occur in
the tissue of the papilhe, and also in the epithelium,
in the skin of man and mammals.

157. In Jirtieiilatioiis — e rj. the knee-joint of
the rabbit — Xicoladoni 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 cor-
puscles. Krause described in the synovial membranes

l62

Elements of Histology

of the joints of the human fingers medullated nerve
fibres whicli end in peculiar tactile corpuscles, called
by him '^ articular nerve corjiuscles.'"

158. The nerve branches snpplyiiig^ non-
striped ninsenlar tissue are derived from the
sympathetic system. They are composed of non-
medullated fibres, and the branches are invested

in an endothelial

c 5 sheath (perineu-

^\"^ \ \\ \ » rium). The

branches divide
into single or
small groups of
axis cylinders,
which reunite
into a plexus —
the ground
plexus of Ar-
nold. Small
fibres coming oflf
from the plexus
supply the in-
dividual bundles
of non - striped
muscle cells, and
they form a
plexus called
the intermediary
lilexus (Fig.
113). The fibres
joining this plexus are smaller or larger bundles
of primitive filu'illa? ; in the nodes or the points
of meeting of these fibres are found angular nuclei.
From the intermediate plexus pass oft' isolated or
small groups of primitive fibrillar, which pursue
their course in the interstitial substance between
the muscle cells; these are the intermuscular

Fig. 114. — Termination of Nerves in Xon-striped
Muscular Tissue. {Atlas.)

a, 3Cou-inPduUated flltre of the iutermediary plexus;
b, fine intermuscular flbrils ; c, nuclei" of mus-
cul;ir cells.

Peri p HER a l Ner i 'e-end/xgs.

163

According to Frankenliaiiser

and
the
the
the

fibrils (Fig. lU)

Arnold, tlicy give oti' tiner tihrils, ending in
nucleus (or nucleolus). According to Elischer,
primitive fibrils terminate on the surface of
nucleus with a minute swellinij.

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

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

Fig. 115. — Plexus of Fine Xon-iiiedullated Xerve Fibres .surrounding
Capillary Arteries in the Tongue of Frog, after staining Avith chloride
of gold. (Handbook.)

a, Blood-Tessel ; 6, connective tissue corpuscles ; c, thick non-medullated fibres
rf, plexus of fine nerve fibres.

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 form a plexus
around the vessel (Fig. llo). In some localities the

1 64

Elements of Histology.

vascular nerve brandies are provided witli small
groups of ganglion cells.

160, In striped muscle of man and mammals,
reptiles and insects, the termination of nerve fibres

•^^^mfi'ID^-i^i-'K

•^•^>^'

Fig. 116. — Nerve-endings in Striped Muscular Fibres. (Kindly lint by
Professor Kiiline.)
A, In fresh muscular fibre of Lacerta, x ^^ ; b, in gold-stained muscular fibre
of lacerta, X ^^•, c, in gold-stained muscular fibre of flog, x ^-Y- !
m, medullated nerve fibre ; t, termination of axis cylinder underneath the
sarcolemma of the muscular flv>re.

takes place, according to the commonly accepted view
of Iviihne, in the following manner (Fig. 116) : — A
medullated nerve fibre, enclosed within a lamellated
sheath (Henle's sheath) divides at a node of Ranvier,
each branch — a medullated nerve fibre — enters under a
variable angle a striped muscular fibre, the neurilemma

Periphera l Ner ve-endings.

becoming fused with the
sarcolemuia, and the nerve
fibre, either at tlie point
of entrance or immediately
afterwards, loses its medul-
lary sheath, so that only the
axis cylinder, with its axi-
lemma, })asses on, and then
forms on the sui'face of the
muscular substance a ter-
minal arborisation or den-
dron, which is called the
nerve endpJate. Each axon,
on entering, gives off by
division several branches
like antlers : in amphibia
these branches are rodlike,
long, and of the form of
baj^onets ; in mammals they
are crooked, hook-like. In
all instances, however, the
divisions are unsymmetri-
cal. In many cases the
arborisation of the endplate
is embedded in a granular
mass of protoplasm con-
taining oblong nuclei. This
nucleated protoplasm is
identical with the substance
of the sarcoglia, or the
sarcoplasm mentioned on a
former page. When the
muscular fibre contracts,
this endplate naturally as- Fig. 117.— Muscle Spindle of the
sumes the shape of a pro- ^'^l^^it treated with gold chio-

t J i iide. (Kolliker, II.)

mmence — Boyere s nerve „^ ^^^^,.^ q^,,,^ terminating' iu the

Oiinoi'^if ^^'npl^ mnQpnlnr middle p;iit of the spiiidlt- us a

lUOUlil. JLaCil mUbCUiai spiral endiDg of fine Hbrils.

i66

Elements of Histology.

libre has at least one nerve endplate, but occa-
sionally has several in near pioximity. Each end-
plate is generally supplied by one nerve fibre, some-
times, however, by two. The contraction wave
generally starts from the endplate. The muscle

Fiy;. lis. — Termiuation of ilediillated Nerve Fibres in Tendon, near the
Insertion of the Striped Muscular Fibres. (Golgi.)

The nerve fibres terminate in peculiar arborising eudplates of primitive
fibrillae

huds of KoUiker or muscle spindles of Kiihne
(mentioned on a former page) contain numerous
medullated nerve fibres with lamellated Henle's
sheath, and these nerve fibres terminate in the
same manner, namely, by means of nerve endplates
(Fig. 117). In these endplates the fine nerve fibres
have a sj^iral arrangement (Ruffini). These are con-
sidered to be sensorv end-organs. According to Kol-
liker, from the primary nerve ending of the mother
fibre — i.e. of the undiWded portion of the spindle —
grow out the ner\e endings for the thin daughter
fibres.

PeRIPHERA L NeR I 'E- EN DINGS.

167

.-a

Besides this iutra-musciilar termination, tliere
is a plexus of tine nev\e fibres, many of them
said to terminate with free ends, situated outside
the sarcolemma — i.e. intermnscuh\r ; such free ends
are described by Beale, Kolliker, Krause, and
others. Kolliker and Arndt consider these intermus-
cular fibres

as sensory ,.:^:v -- :^

nerves,

161. Ten-
dons are sup-
plied w i t h
special nerve
endings,
studied by
Sachs, Rol-
lett, Gempt,
Rauber, and
particularly
G olgi, whose
work on this
subject is ex-
tensive. These terminations are most numerous near
the muscular insertion. They are of the follow-
ing kinds : — («) A medullated nerve fibre branches
repeatedly, and the axis cylinder, after having lost
the medullary sheath, breaks up into a small plate
composed of a dendritic ramification of fine primi-
tive nerve fibrils (Fig. 118). Owing to the number of
the fibrilla3 and their repeated crossing, it is difiicult to
say whether the appearances as shown in Fig. 119 cor-
respond to a real network or to a dendron. This end-
plate is occasionally embedded in a granular-looking
material, and thereby a similar organ as the nerve end-
plate in muscular fibres is produced (Fig. 119). (6) In
the tendons of man and many mammals Golgi has shown
that nerve fibres terminate in peculiar spindle-shaped

Fig. 119. — One of the Teriniual Ramitk-atioiis of the
previous figure, more highly magnified.

rt, Medullated nerve fibre ; ft, apiiareutly reticulated
endplate. {Golgi.)

i68

Vj^I

Fig. 120. — Two Tendon Spindles of Golgi in tlie rabliit, sliowing the distri-
bution and spiral terniination ol' the nerve fibres ou the spindles. {After
K oil Her.)

Per I pn ERA l Ner ve-en dings.

169

enlargements of tendon Ijundles (Fig, 120). These
tendon spindles of Golgi consist each of two, three, or
more tendon bundk's within a common sheath ; a
bundle of fine medullated nerve fibres enters the

Fig. 121.— Termination of Metlnllated Nerve Fibres in Tendon. {Golgi.)

a, End-lnilbs with couvoliited lueclullatecl nerve fibre ; b, end-bulb similar to a
Herlist's corpuscle.

spindle, their axis cylinders break up into primitive
fibril he, which are arranged as a network and as
spiral fibrillar. (c) A medullated nerve fibre ter-
minates in an end-lmlb (Fig. 121), similar to those of
the conjunctiva, or of a Herbst's corpuscle.

170

CHAPTER XVI.

THE SPINAL CORD.

1 G2. The spinal cord is enveloped in three distinct
membranes. Tiie outermost one is the dura mater.
This is composed of more or less distinct lamellag 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 extremely
delicate 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
subdural lyniph 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 lympli
space — with an endothelium.

164. The innermost memVjrane is the pia mater.
Its matrix is fibrous connective tissue, and it is lined
on its outer surface with an endothelial membrane.
Also the inner surface facing the cord j)roper has an
endothelial lining, but this is not as complete and
continuous as that of its outer surface. Between
the arachnoid and pia mater extends, from the fenes-
trated portion of the former, a spongy f)lexus of
trabeculse of fibrous tissue, the surfaces of the
trabeculse being covered Avith endothelium. By this

Sr/NA L Cord.

lyr

spongy tissue — tho snh-araclinoidal tissue (Key and
Ketzius) — the subarachnoidal space is subdivided into
a labyrinth of areohe. On each side of the cord,
between the anterior and posterior nerve roots,

-•_» j^f J

" -^■'^v*!

Fig. 12-2.— Transverse section tlirougli the Cervical Cord of aeliild, 2 years
old, sliowing well the anterior wliite commissure and the numerous
nieduUated fibres passing horizontally through the grey matter (col-
laterals) from and to the white columns. {Weigcrt.)

z, Tract of Goll ; B, tract of Burdach ; l, tract of Lissauer.

extends a spongy fibrous tissue, called ligamentuni
denticidatiiin, between the arachnoidea and pia. By
it the sub-arachnoid al space is subdivided into an
anterior and posterior division.

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

Elements of Histology.

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

li.C,

Fig. 123a. — Transverse section of the Spinal Cord in tlie Cervical region-
{M icrophotog raph of Weigcrt-Pal specimen.)

p. E. c, Postero-extenial column ;C.g., postero-niedian column or colmnu of
GoU ; p. u., the issuing posterior root ; L. c. lateral column : a. f., anterior or
ventral Assure. The white matter is more deeply stained than the more
central grey.

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

166. The cord itself (Fig. 122) consists of an outer
or cortical part composed of medullated nerve fibres :
the ichite matter, and an inner core of grey matter.
On a transverse section through the cord the

Spinal Cord.

17.3

contrast of colour between the white mantle and the
grey core is very conspicuous. The relation between
the white and grey matter differs in different parts ;
it gradually increases in favour of the former as we

P.E.C.

L.H.

L.C

A.F.

Fig. 123b. — Section of the Spinal Cord in the Dorsal region.
{Micropliotograph of a IVeigert-Pal specimen.)

Note the small aiii<iunt nf grey matter wbich project? iHterally at level L. h. to
fonu a lateral liorn. Xote, too. at tbe same level on the median side of tbe
posterior born a deflnite mass, forming Clarke's columns. The lettering is
as in the section through cervical region.

ascend from the lumbar to the upper cervical portion
(Figs. 123a, 123b, 123c). 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 cross-stroke being the grey commissure.

174 Elements of Histology.

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 commis-
sure in front of this canal is the anterior, the rest the
posterior, grey commissure. The shape of the whole
figure of the grey matter differs in the different
regions, and this difference is brought about by the
breadth and thickness of the grey commissure as also
of the grey horns themselves. In a section through
the cervical region the grey commissure is long and
thin ; in the dorsal region it becomes shorter and
thicker ; and in the lumbar region it is comparatively
very short and thick. 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 cervical and lumbar regions where the nerves of
the brachial and sacral plexus leave or join the cord
respectively, this latter possesses a swelling, and the
gre}^ matter is there increased in amount, the swelling
being in fact due to an accumulation of grey matter,
with which additional numbers of nerve fibres become
connected ; but the general shape of the grey matter
is retained.

167. The cornua of the grey matter are generally
thickest in the line of 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 jDostero-lateral fissures.
The anterior horns are in all parts thicker and project
less than the posterior, and therefore the latter reach
nearer to the surface, becoming attenuated and passing
into the posterior nerve roots.

There is generally a third projection of grey
matter — the lateral horn (see Fig. 123 b). This is,
however, conspicuous only in the upper two- thirds
of the thoracic cord.

Spinal Cord.

175

1G8. The white matter is composed chiefly of
medulhited nerve fibres riuiiiin<,^ a lon.<;itudinal course,
and therefore, in a transverse section through the
cord, appear in cross-section. They are arranged into

Fij

123c.— Section through the Spinal Cord in the Sacral region.
(Microphotogr((2^h of a Weigert-Pal speciinen.)

Tlie lighter stained trrey matter is larpe in amount compared with the darker
white matter. The tips of tlie posterior horns and around the central canal
are very lightly stained owing to the presence of much substantia tjclatinosa.
Many niedullated fibres are seen traversing the anterior horns.

cokimns, one anterior, one lateral, and one posterior
column for each lateral half of the cord, the two
halves being separated by the anterior and posterior
median longitudinal fissure. The anterior median
fissure is a real fissure extending in a horizontal

176 Elements of Histology.

direction from the surface of the cord to iiPAir 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 tilled
up by neuroglia. It extends as a continuous mass of
neuroglia in a horizontal 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,
beinof in reality filled up with neuroglia tissue, into
which extends a continuation from the pia mater
with laro-e vascular trunks. The white matter
between the anterior median and anterior 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 j^osterior
column.

169. Besides the septa situated in the two lateral
fissures respectively, there are other smaller septa,
neui^oglia and prolongations of the pia mater, which
pass in a horizontal and radiating direction into the
white matter of the columns, and these are thus sub-
divided into a number of smaller portions ; one such
big septum is sometimes found corresponding to the
middle of the circumference of ont; 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
(Figs. 123 a and 125).

170. Some of these various subdivisions bear

Spinal Cord.

177

definite names (Tiirk, Charcot, Goll, Flechsig,
Gowers) : —

{ct) The median division of the anterior column is
called the direct or uncrossed pyramidal tract, being

Fig. 124.

-Scheme of the subdivision of the White Cohimns.
Fleschsig and Kahler, from KolUker, II.)

{After

P V, Direct pyramidal tract of anterior white column ; v g, ventral ground tract
of anterior white column ; a L,antero-lateral tract of lateral column. Gowers's
tract; s r, remainder of antero-lateral part of lateral column; k s, direct
cerebellar tract of lateral column ; p s, crossed pyramidal tract of lateral
column.; H a, tract of Burdach of posterior white column ; G, tract of Goll in
posterior column. Grey matter, grey commissure around central canal,
anterior and posterior roots left unshaded.

a continuation of that part of the anterior pyramidal
tract of the medulla oblongata [see below) that does
not decussate in the medulla.

(h) The lateral division of the anterior column is
the ventral or anterior ground tract.

lyS Elements of Histology.

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 crossed

Fig. 125 — Section of Spinal Cord, one half of wliicli (left) shows the tracts
of the white matter ; and the other half (right) shows the grouping of
the ganglion cells in the grey matter (semidiagrammatic) . {After
Sherrington, from Kirke's " Physiology.")

7, 10, 9, and 3 are tracts of descending deseneration ; 1,4, 6, and 8 of ascending
degeneration ; 1. tract of CtoH; 2, tract of Burdach; 3, comma tract; 4, tract
of Lissauer ; all these belong to the posterior white column ; 6, direct cere-
bellar tract ; 7, crossed pyramidal tract ; 8, tract of Gowers ; 9, descending
antero-lateral trace ; 10, direct pyramidal tract.

pyramidal fasciculus or tract, 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 Jasciculus, or the tract of
Burdach,

Spinal Cord.

179

This part is connected directly witli the median
bundle of the posterior nerve roots, or rather by the
numerous collaterals passing off from the posterior
root fibres.

(y') Tiie median division of the posterior column
is called the J'ascicidus or tract of G oil.

(g) The tract or fasciculus of Lissauer (Fig. 125)
is a small mass of
white fibres situated
between the outer su-
perficial portion of the
tract of Burdach and
of the direct cerebellar
tract, and close to the
posterior lateral fis-
sure.

In addition to
these, a narrow mass
of fibres in the depth
of the tract of Bur-
dach, near the grey
commissure, represents
a separate group, called

the comma-shaped tract : and the superficial mass of
white matter in the anterior half of the lateral column,
which is called the anterolateral ascending tract of
Gotcers {see Fig. 124).

These various divisions can be traced from the
meduUata oblongata into the cervical, and more or less
into the dorsal part of the cord ; but farther down
many of them, like the direct cerebellar tract and the
tract of Goll, are lost as separate tracts, except the
crossed pyramidal fasciculus.

Experiments have been made which demonstrate
that these different tracts are physiologically of very
different character. According to a well-established
law — the AVallerian law — each nerve fibre has its

Fig. 12(3. — From a transverse section

"through a most peripheral part of

the White Matter of the Cord. {Atla^.)

c. Special peripheral collection of neu-
roglia ; w, white matter with the medul-
lated nerve fibres shown in cross section,
and nenroglia between them.

Elements of Histology.

nutritive centre in the ganglion cell with which it is
connected, and if a nerve fibre is cut, that part which
remains connected with the nutritive centre does not
degenerate, while that part severed from the centre
degenerates. Consequently, if by cutting the cord at

Fig. 127. — Stellate Neuroglia Cells of Golgi, with nimieroxis ramifying pro-
cesses ; from the cord of ox. {EdlliJcer, II.)

a particular level some fibres i-emain intact above the
section but degenerate below, they show descending
degeneration ; they have their nutritive centre above
the section and are jDrobably eflferent fibres. On the
other hand, those fibres w^hich degenerate above, but
remain intact below the section, show ascending
degeneration ; they have their nutritive centre below
the section and are probably aflerent fibres.

By means of Weigert's method it has been

Spinal Cord. i8r

possible to show (Weigert) not only that the nerve
fibres constituting tlie white cohimns are grouped iu
different tracts but that in the embryo they obtain
their medullary sheath at different but definite periods.

. /

Fig. 12S. — Longitudinal section through the Lateral White Column of the
Cord of the Ox, showing the axis cylinders of the meduUated nerve
fibres, numerous fine longitudinal and transverse fibrils of the neu-
roglia, and tlie stellate neuroglia cells of Golgi. {After Kolliker, II.
Highly magnified.)

Now in this way it has been made probable that
the tracts marked in the figures in the above-named
divisions of the anterior and lateral columns contain
partly efferent, partly afferent fibres, while almost
the whole of the fibres of the posterior columns are
afferent ; see exolanation of figures,

1 82 Elements of Histology.

171. Structure of the cord. — The most im-
portant and fundamental facts which have been
brought to light within recent 3"ears concerning the
intimate structure of the white and grey matter and
of the mutual relations of the different parts and the
different elements of the cord, the brain, the medulla,
and the symj^athetic system, are due to various new
methods of histological examination, as also to the
experimental methods of section of the cord and nerve
roots in the living, and observing the after-effects as
exhibited by degeneration of nerve tracts. As regards
the histological methods, Weigert and Pal's method of
staining medullated nerve fibres of the cord, INIarchi's
method of distinguishing between degenerated and
healthy medullated fibres, and, above all, Golgi's
silver method, by which nerve fibres and ganglion
cells can be easily traced in their finest ramifications,
have been the means of o^Dening uji an almost new
field of accurate inquiry concerning all parts of the
central nervous system as well as of the special senses.
Golgi's silver method has enabled himself, and, to a
very conspicuous degree, Ramon y Cajal and Kolliker,
to bring to light facts concerning the intimate struc-
ture of the central nervous system, the ganglia, and
the sense organs, which stand out in respect of
clearness and trustworthiness. Other histologists,
Lenhossek, Eetzius, and others, have by this method
also been enabled to contribute important facts.

172. The ^-oiiiid substance (Fig. 126) of both
the white and grey matter — i.e. the stroma in
which nerve fibres, nerve cells, and blood-vessels are
embedded — is a peculiar kind of connective tissue,
which is called by Yirchow neuroglia and by
Kolliker supporting tissue. It consists of three
diffeient kinds of elements : [a) a homogeneous trans-
parent semi-fluid iiwtrio:, which in hardened sections
appears more or less granular ; {}>) a network of very

Spinal Cord.

183

delicate fibrils — npurotjlia fibrils — which are similar
in some respects, but not quite identical with elastic
fibres. In the columns of the wliite matter the

p.m.

Cty.o.

a.c.

Fig. 129.— Cross-section of the central part of the Spinal Cord from tlie
Lumbar region of an Adult, showing the central canal, its lining epithe-
lium surrounded by neuroglia, forming the central grey nucleus,
(After Schdfer.)

/.a., Anterior median fissure; p.m.c, posterior white column ; ff.c, anterior
white comniissure.

fibrils extend chiefly in a longitudinal direction, in
the gi'ey matter they extend uniformly in all
directions, and in the septa between the columns

184

Elements of Histology.

they extend for the most part radially, (c) Richly
branched nucleated cells intimately woven into the
network of neuroglia fibrils. These cells are the
neuroglia cells or glia cells. Golgi was the first to
show that though richly branched they do not anasto-
mose with one another. The sweater the amount of

^^%f|^NiS»/

Fig. 1:30a.— Cross-section tlii-ongh
central canal of tlie cord,
sbowiug the lining epithe-
lium, from a child of sis.
(After Schdfer.)

Fig. 130b.— CUiated Epithe-
lium lining the central
canal of the cord in a
child of six, more highly
magnified than in Fig.
130a. {After Scha/er.)

neuroglia in a particular part of the white or grey
matter, the more numerous are these three elements
(Figs. 127 and 128).

In both the white and grey matter the neuroglia
has a very unequal distribution ; but there are certain
definite places in which there is always a considerable
amount — a collection, as it were, of neuroglia tissue.
These places are : («) underneath the pia mater —
i.e. on the outer surface of the white matter : here
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

Spinal Cord.

18:

divisions of columns of white matter ; at the exit of
the anterior and the entrance of the posterior nerve
roots.

(6) A considerable accumulation of neuroglia is
present immediately around the epithelium lining the

Fig. 131.— Central C'aual of the Cord of a Child, 1^ year old ; the cells of
ependyina are well shown, with their long filamentous processes.
{Kdlliker, II.)

central canal ; this mass is cylindrical, and is called
the central grey nucleus of KoUiker (Fig. 129). 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 inter-
woven with the network of neuroglia fibrils. In the
embryo and young state (Figs. 130a and 130b), the
free base of the epithelial cells has a bundle of cilia, but
in the adult they are lost amongst the epithelial cells

1 86

Elements of Histology

lining the central canal : some show in i:)reparations
stained after Golgis method processes of extreme
length (Fig. 131).

(<?) Another considerable accumulation of neuroglia
exists near the dorsal end of the posterior grey horns,
as the suh-^tnntia gdotinos<i of Rolando.

173. The white uiatter (Fig. 132) is composed,
besides neuroglia, of medullated nerve fibres varving
veiy much in diameter, and forming the essential and

chief part of it. They

possess an axis cy-
linder and a thick
medullary sheath
more or less lamin-
ated, but are devoid
of a neurilemma and
its corpuscles. Of
course, no nodes of
Ranvier are observ-
able. In specimens
of white matter of
the posterior co-
lumns, Avhere the
nerve fibres have
. been isolated by teas-
ing after hardening, many fine' medullated libres are
met with which show the varicose appearance mentioned
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-tissue septa with vessels, by which
the nerve fibres are grouped more or less distinctly
in divisions.

174. Although most of tiie nerve libres con-

Fig. 132. — From a transverse section
through the White Matter of the CorcL

Showing thetransversely-cat medullated nerve
fibres, the neuroglia between them with
two branched neuroglia cells. (Atlas.)

S/'/NAL Cord. 187

stituting the columns of white matter are of a
longitudinal direction — i.e. passing upwards or down-
wards 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 medul-
lated nerve fibres and groups of nerve fibres which
have an oblique or even horizontal course.

Thus : (1) The anterior median fissure does not reach
the anterior grey commissure, for between its bottom
and the latter there is the lohite commissure {see Fig.
129). This consists of bundles of medullated nerve-
fibres passing in a horizontal or slightly oblique
manner chiefly between the grey matter of the anterior
horn of one side and the anterior white column, in-
cluding the direct pyramidal tract, of the opposite side.
This anterior white commissure is in respect of
position a continuation of the decussation of the
pyramidal tract in the lower part of the medulla
oblongata. As mentioned above, this latter passes
down the cord as the crossed pyramidal tract in the
inner part of the postero-lateral column. From this
it follows that the fibres of the pyramidal tract of the
medulla ultimately all cross over to the opposite side
of the cord. The majority do this in the pyramidal
decussation of the medulla, the minority descend in
the cord as the direct pyramidal tract, but its fibres
gradually along the cord cross over by the anterior
white commissure.

(2) The medullated nerve fibres constituting the
anterior roots of the spinal nerves leave the cord at
and about the antero-lateral fissure; the fibres pass
mostly in a somewhat oblique, some also in a hori-
zontal direction through the white matter of the cord,
and each of them originates, some sooner, some later,
as the axon or axis cylinder process of a ganglion
cell of the anterior grey horn. This is the fate of
most of the anterior root fibres — that is to say, they are

1 88 Elements of Histology.

primarily tlie axons of ganglion cells of the anterior
grey horn of the same side ; this axon becomes
invested with a medullary sheath, and as an efferent
meduUated nerve fibre passes out through the anterior
nerve roots. It is, however, probable that some of
these fibres are axis-cylinder processes or ax^ns of
ganglion cells of the anterior horn of the opposite
side, and as such pass through the anterior commis-
sure, while a small number of anterior root fibres can
be traced into the posterior grey horn, where they are
evolved as the axis cvlinder or axon of a sfanglion
cell of this part of the grey matter.

As will be mentioned presently, the grey matter
of the cord contains, in the dorsal or thoracic portion
(between the seventh cervical and second or third
lumbar nerve), a special column of ganglion cells —
Clarke's column ; the axon of some of these cells
appears to pass through the anterior grey horn to
join the anterior root fibres.

But according to Fleclisig, with whom Kolliker
agrees, the axons of most of the ganglion cells of
Clarke's column pass in a horizontal direction from
the grey matter into the lateral white column, where
they pursue their course as longitudinal fibres towards
the cerebellum, thus forming the fibres of the direct
cerebellar tract.

(3) The posterior roots. The medullated nerve
fibres constituting the posterior roots are branches of
the axis-cylinder process of the ganglionic cells of the
spinal ganglion ; they enter the cord as small bundles
by the postero-lateral fissure, betw^een the lateral and
posterior columns of white matter, in a slightly
slanting direction, and at the same time turned more
towards the posterior column of white matter. Now
the fibres of the posterior roots may be roughly
grouped into a lateral and mediau bunale, the former
containing predominantly fine medullated fibres, the

Spinal Cord. 189

latter predominantly larger niedullated fibres ; the
former as well as th(^ latter, after their entry into the
cord, sooner or later divide, each into an ascendiny
and a descending medullated fibre. The ascending
and descending fibres resulting from the division of
the fibres of. the Literal bundle form part of and
pursue their longitudinal course in that portion of the
posterior white column which lies next to the posterior
grey horn and the lateral white column, and which
is known as Lissauer's tract or Lissauer's bundle {see
Fig. 122). The ascending and descending medullated
fibres resulting from the division of the fibres of the
median bundle also following a longitudinal course
are distributed principally over, and form part of, the
white matter of the posterior columns (Burdach's and
GoU's tract). Some of these fibres are said, however,
to enter directly into the grey matter of the posterior
horn and to terminate there.

(4) All medullated fibres constituting the dififerent
columns of white matter and descendinof or ascending
respectively in the cord send out at numerous levels
horizontal fibres which enter or pass out from the
grey matter. The discovery of these fibres by Golgi
and II anion y Cajal by means of the silver method
constitutes a fundamental advance in our knowledoe
of the minute anatomy and physiology of the cord.
These horizontal fibres which branch ofi' from, or join
respectively, the fibres constituting the different tracts
of the white matter are called collaterals {see Figs.
122 and 123 c). The collaterals give off branches
themselves. By means of the collaterals and their
branches numerous connections are formed between
the longitudinal fibres of the white columns on the
one hand and the grey matter on the other. The
collaterals terminate, or originate respectively, near
and around nerve cells in all jjarts of the grey matter
hy means of arborisations or dendrons (Fig. 133).

igo

Elements of Histology.

175. As mentioned just now, collaterals are not
limited to any one tract of the white columns, and are
not limited to any particular level, but are given off

or pass into re-
spectively the
longitudinal fibres
constituting the
white columns in
general and at
level
which
of the
made.

e ^' e r y

through

sections

cord are

Figs. 122 and 123c

give a

good
presentation
these facts.

re-

F o 1 lowi ng,
then, the longi-
tudinal medul-
lated fibres con-
stituting those
tracts of white
matter, which

were described
above as descend-
ing fibres (show-
ing descending de-
generation) — e.g.
the direct pyra-
midal tract, the
crossed pyramidal
tract, the inner
portion of the an-
terior part of the lateral column — -it is seen that
at many points each sends out horizontal colla-
terals which enter the grey matter and terminate

Fig. 133. — Collaterals passing from fibres of
posterior column into the grey matter, and
teiTuinatiug at « by dendrons. From the cord
of a newlj'-born child. {After Kolliker, II.)

Spina l Cor d. 191

there as arborisations or dendrons close to, or around,
ganglion cells ; and similarly the longitudinal medul-
la ted fibres constituting those tracts of white matter
spoken of above as ascending tracts — e.g. the tract of
Goll, of Burdach, of Lissauer, the dii-ect cerebellar
tract and the superficial parts of the anterior portion
of the lateral column (Gowers's tract) — are connected,
brought into relation, by means of collaterals and
their dendrons, with the grey matter and with the
ganglion cells situated in the latter. The bundles of
fine nerve fibres, so conspicuous in every horizontal
section, passing in a horizontal manner from the
posterior columns through and around the suhstantia
gelatinosa of Rolando of the posterior grey horn, are
bundles of collaterals given off by the longitudinal
fibres of the posterior columns.

176. The grey matter of the cord contains the
same kind of neuroglia as the white matter — viz. neu-
roglia fibres and neuroglia cells ; the fibres do not,
however, form longitudinal networks as in the white
matter — due to the peculiar (longitudinal) arrange-
ment of the nerve fibres — but are distributed more or
less as a uniform network ; every section, therefore,
be it longitudinal or transverse, shows the glia fibrils
cut transversely, obliquely and longitudinally. The
glia cells are the same in size and in their numerous
branched processes as in the white matter.

In this matrix of neuroglia are embedded nerve
cells or o-anolion cells and nerve fibres and their
ramifications. The ganglion cells are all possessed of
several processes, and are therefore multipolar ; they
differ in respect (ci) of position, {b) of size, (c) of
the structure, distribution and connections of their
processes.

177. (a) ill respect of position, the nerve cells
form groups and aggregations which, in the longitu-
dinal axis of the grey matter^ are more or less

192 Elements of Histology.

discontinuous, so tliat to each particular spinal nerve
or segment corresponds a more or less separate mass.
The following groups can be distinguished on each
side (Fig. 125) : —

(1) The centro-lateral group, situated in that part
of the anterior cornu which is in contact with the
ventral portion of the lateral column ;

(2) The dorso-Jateral grotip, also situated laterally
in the anterior cornu immediately behind or dorsal ly
to the tirst-named group ;

(3) The ventro-median group, situated in the
foremost portion of the anterior cornu where this is
in contact with the anterior column ;

(4) The dorso-Tiiedian group, immediately behind
the former — i.e. next the anterior white commissure.

(5) As mentioned above, that portion of the grey
matter which projects laterally between the anterior
and posterior cornu of each side and about midway
(Figs. 122 and 125) — i.e. the lateral cornu — -contains
in the upper two-thirds of the thoracic cord groups of
ganglion cells which represent the cells of the lateral
horn, but they are present only as scattered ganglion
cells in the corresponding portion of the grey matter
above and below the proper lateral horn (Waldeyer).

(6) Throughout the thoracic cord there is present
a conspicuous group of ganglion cells, which groujD is
in cross-section of a rounded or oval shape ; this is the
2)osterior vesicular column of Clarke or Stilling's group^
and is situated at about the same level as the group
of cells in the lateral horn ; but while this latter is
lateral, the column of Clarke is situated medially,
and it has to be added that it really belongs more
to the base of the posterior cornu. These two groups
5 and 6 belong therefore to the middle region of the
grey matter.

(7) The posterior cornu contains in all parts
only scattered cells not definitely grouped. Like those

Spinal Cord. 193

mentioned in the anterior cornu and the middle
region of the grey matter. Also in the substantia
gelatinosa of Rolando occur solitary ganglion cells.
Amongst the cells of the posterior cornu the so-
called marginal cells of Waldeyer and Lissauer
deserve special mention ; they are situated at the
margin of the posterior horn, or rather of the sub-
stantia gelatinosa, where this is in contact with the
dorsal and lateral columns of white matter. The
marginal cells are long and spindle-shaped and
different from most other cells of the posterior cornu
in their being possessed of a distinct axon or axis-
cylinder process.

178. {h) In respect of size the ganglion cells
show considerable differences ; the biggest cells are
those of the anterior cornu mentioned as groups 1,
2, and 3 ; the cells of these groups measure about
70 — 130yu in diameter ; while those of group 4, dorso-
median group of the anterior horn, are considerably
smaller, 30 — 80 ^ ; between these two sizes are the
cells of the lateral horn and of Clarke's column,
while those of the posterior cornu, with few
exceptions, are comparatively small cells.

179. (c) 111 respect of structHre each gan-
glion cell possesses a vesicular nucleus with a promi-
nent nucleolus, and the substance of the cell is in all
cases, when examined in the fresh state or in suitably
prepared specimens, of the nature of a more or less
fibrillated substance, between which a finely granular
matrix can be recognised (M. Schultze). The fibrillse
are grouped in bundles, and appear continuous and
radiating from around the nucleus towards and into
the fibrillated processes ; around the nucleus the
fibrillEB appear more or less concentrically arranged.
In the anterior cornu the ganglion cells contain
normally pigment granules grouped near and around
the nucleus (Klonne and Midler) {see Fig. 134).

194

Elements of Histology.

Between the fibrill?e constituting the substance
of the ganghon cells are found masses of granules
(distinct from the just-mentioned pigment) which
take the stains well : these are the chromatic granules
of Nissl. In some ganglion cells they are distinct

Fig 134. — Section tlirougli the Lower Lumbar Cord of Man. After a pre-
paration of Klonne and Mailer in Berlin. {Kdlliker, 11.)

^y, White lateral column in cross-section ; g, grey matter of anterior liorn,
showing ganglion cells with pigment granules, and many meduUated nerve
fibres.

and conspicuous, in others less so. The presence of
these chromatic granules indicates, it is suggested, a
phase or phases of normal activity of the ganglion
cells, whereas their disappearance and absence cor-
responds to a pathological state of diminished or
abnormal function.

180. The most important differences,^ however.

Spinal Cord.

195

are noticed on the ganglion cells with regard to the
nature and coniKM^tioniS of their processes.

As mentioned on a previous page, all ganglion
cells of the cord are multipolar ; amongst the processes

Fig. 133. — Isolated Ganglion Cell of the Anterior Horn of the Human
Cord. (Gerlach, in Strieker's " Manual of Histology.")

o, Axis cylinder process; 6, pitrinenr.. The braucUed dendrites of the ganalion
cell break up into the fine arborisation shown in the upper part of the
figure.

into which the substance of the cells is continued
there is one, occasionally two, which become sooner
or later the axis cylinder of a medullated nerve
fibre ; this is the axon or neuraxon of the ganglion

196

Elements of Histology.

cell (Fig. 135). Such an axon is seen to come otf
from each of the ganglion cells of the anterior cornu

Fig. 136. —Isolated Multipolar Gauglioii Cell ;of the Grey Matter of
the Cord. {Gerlacli, in Strieker's Manual.)

The dendritically-branclied processes (dendrites) break up into the flue
arborisation into which is seen to pass a fine nerve fibre and its ramiflca-
tion derived from a posterior nerve rf)Ot fliire.

and of Clarke's column, and of some cells in the
posterior cornu. The axon of most of the anterior

Spina l Cord. 1 9 7

cells is continued as the axis-cylinder process of a
medullated nerve fibre passing out as an anterior
root fibre. The axon of other cells in the anterior
cornu, as also to a lesser extent of the posterior
cornu (including those of the substantia gelatinosa),
does not, however, pass into anterior root fibres, but
becomes the axon of longitudinal medullated nerve
fibres forming part of the lateral, and to a lesser
extent the anterior, columns of white matter.

These important facts were discovered by Golgi
and Ramon y Cajal, and were confirmed by KoUiker.
According to Golgi and Ramon y Cajal, axis-cylinder
processes or axons of ganglion cells from all parts of
the grey matter may pass into the anterior commissure.

Cells of this character — i.e. possessing axons
which pass as longitudinal medullated fibres into the
white columns — are Kolliker's " Tract cellsJ^

181. Another very striking fact discovered by Golgi
and by Ramon y Cajal is this : that the axon of the
ganglion cells ramifies. In some, like those cells of
the anterior cornu, whose axon passes into an anterior
root fibre, the axon for some distance gives off few
or no branches (Golgi's group A). In other cells, like
those of the posterior cornu, the axon is much
branched and its fibres are lost in the grey matter
(Group b). The former are considered by Golgi as
motor, the latter as sensory cells.

Besides the axon, all ganglion cells in all parts of
the grey matter possess more or less numerous pro-
cesses which, owing to their rich and dendritic
branching and their distinctly fibrillated nature, are
the protoplasmic or branched processes, or the den-
drites (Fig. 136). In the cells of the anterior cornu, in
those of Clarke's column and of the lateral horn, the
dendrites are numerous and distinctly arborescent ;
they are less numerous in the cells of the posterior cornu ;
thicker branches give off laterally smaller branches,

198

Elements of Histology

which by euntinut'il raniiticatioii become greatly attenu-
ated and ultimately resolve themselves into arbores-
cent terminations or dendrons (Fig. 136).

While the dendrites and their terminal dendrons
of most of the ganglion cells are distributed in the
grey matter, Golgi has proved that of some cells
some of the dendrites pass into and are distributed
amongst the nerve fibres of the white columns, a

Fig. 137. — From the Lateral Horn of the Cervie<il CoM of the Ox. Highly
magnified. (KoUiker, II.)

s, Lateral colanin of white matter in cross-section ; F, fine dendrites of the
ganglion cells penetrating into the white cc^ituran.

fact wliieh Kolliker has emphasised, and whicli par-
ticularly holds good for the cells of the lateral horn
in the cervical cord of the ox. (Fig. 137.)

182. Besides the ganglion cells, their axons, den-
drites and dendrons, the grey matter contains nerve
fibres of a ditierent origin and connection. As
mentioned on a former page collaterals of longitu-
dinal fibres of all white tracts enter, or pass out
respectively from the grey matter : here they ramify
and terminate 1)V arborisations or dendrons, wliicli

Spinal Cord.

199

are either interiningliiig with, or surrounding the
arl>orising dendrons of the dendrites of ganglion cells
or surround the hody of the ganglion cells. Owing to
the great number of such collaterals, as mentioned
on a former page,
their arborisations
or dendrons form a
considerable por-
tion of the grey
matter.

Sherrington sug-

gests

W.W

the term of
synapsis {avv and
(tTr-w) as indicating
the contiguous but
not continuous re-
lation of the arbo-
rising terminations
of axons surround-
ing the arborising
dendrites or the
body of a ganglion ■m\^
cell. Such synapsis
would then occur
everywhere in the
central nervous sys-
tem (cord, brain,

medulla, Sympa- t^ig- 137A.-Scheme of the Elements of the Conl

, . ' T concerned in Reflex Actions. Longitudinal

thetlC ganglia, re- view. (Kdlliker,II.)

where .s- rj, Ganglion cell of a spinal ganglion ; s, sen-
sory flhre coming from the periphery; sth,
division of a posterior root fibre into sa, an
ascending and descending fibre; sc, collaterals
of same passing to motor ganglion cells, m ;
m ('•, motor (anterior) root fibres being axons of
anterior nerve cells.

tina, etc. )
neuraxons and their
collaterals of a near
or distant ganglion

cell arborise ( ter-

minate) around dendrites or the cell body of a

ganglion cell.

A second, also considerable, portion of the grey

200

Elements of Histology.

— L/i<?

matter is made up of dendrons, the developing fibres
of which are not collaterals but are direct con-
tinuations of longitudinal fibres of the white columns;
thus the descending branches of posterior root fibres
terminate in this way in the grey matter, many of

the main fibres of the
anterior and particularly
the lateral columns pass
into or pass from the grey
matter, and after a shorter
or longer course, either on
the same side or after
crossing through the an-
terior or posterior com-
missure terminate as den-
drons around ganglion
cells or intermingle with
the arborisations of den-
m IV drites of ganglion cells.
The manner of the most
probable connections and
actions of the grey matter
of the cord are illus-
trated by the accom-
panying diagrams (Figs.
137a and 137b), copied
from Kolliker.

Before the introduc-
tion of the method of
Weigert, and its modifi-
cation by Pal (by which
the medullary sheath of
nerve fibres is stained),
it was unknown that the o'rev matter of the cord
contains medullated nerve fibres to any large extent.
By the above methods, if successfully applied to the
examination of suitablv stained sections of the cord.

miv

Fig. 137e.— Scheme of the Con-
duction of Inipiilses in Volun-
tary Movement. (Kolliker, II.)

2>s, Fibres of the crossed pyramidal
tract in the cord ; these fibres had
crossed (pyramidal crossing) m
the medulla ; collaterals of these
fibres pass into and terminate
in the grey matter of the cord :
p o, fibres of the direct pyramidal
tract in the cord, collaterals cross
in the cord ; m, nerve cells in the
anterior grey horns; 7?i. if, axons
of same forming the fibres of the
motor (anterior) roots.

Spinal Cord. 201

it is shown that tlie grey matter contains a really
astonishing number of medullated nerve fibres, run-
ning singly or in small bundles, horizontally and
obliquely. All the above collaterals, as also the
continuations of the fibres passing from the white
columns into the grey matter, or vice versd, are
medullated fibres {see Figs. 122 and 123a).

183. The large vascular branches enter the white
matter of the cord from, or pass out by way of the pia
mater, being invested in neuroglia continuous with
the tissue of the pia mater. By continued division
they resolve themselves into fine branches, which pass
into, or pass from, the network of capillaries.

The capillaries are more abundant and form a
more uniform network in the grey than in the
white matter. In the latter most of them have a
course parallel to the nerve fibres, i.e. longitudinally.
The blood-vessels and the orano^lion cells are ensheathed
in lymph spaces (perivascular and pericellular spaces).

202

CHAPTER XVII.

THE MEDULLA OBLONGATA OR SPIXAL BULB.

184. As the cervical portion of the spinal cord
passes into the medulla oblongata its parts alter in
position and relation. It is possible, to a large
extent, to recognise in the bulb, regions which
correspond to different areas of the cord. Many of
the cord areas are, however, lost in the bulb, and on
the other hand, many new areas appear.

185. The anterior or ventral fissure is continued
as far as the bulb extends. The posterior or dorsal
fissure of the cord is also continued for a certain
distance along the medulla, but this widens out in the
upper part of the bulb into the lower end of i\\e foui^th
ventricle. The line of origin of the anterior roots of
the spinal cord is continued into the medulla, being
marked out by the exit of the roots of the hypoglossal
nerve. In the upper portion of the medulla this line
of origin develops into a marked fissure. The shallow
groove existing dorsally between the postero-median
and postero-external columns of the cord is even better
marked in the bulb, and divides the funiculus gracilis
(median) from the funiculus cuneatus (external).
The postero-lateral groove into wliicli the posterior
roots pass to the cord is continued up as the external
boundary of the funiculus cuneatu.s and the internal
boundary of yet another longitudinal projection,
leading u]3 to a prominence, the tubercle of Rolando.
In the upper portion of the cervical cord there project
from the lateral columns the roots of the spinal

Med ul la Oblo nga ta .

203

accessory nerve. The line of origin of these roots is
continued up along the lateral surface of the bulb and
there arise successively along this line the roots of

Fig. 138.— Section through the Lower Eud of the Pyramidal Decussation.
The section is slightly distorted. {Microphotograph of section stained
with aniline Nue-blacl-.)

A. F., Anterior or ventral Assure lying obliquely on accountiof fibres passing from
crossed pyramidal tract on left side to anterior column on risht ; p. k., pos-
terior Assure ; i. f., corresponds to septum l)etweenGoirs columnand postero-
external column : p. li., posterior root of first cervical nerve ; on the left side
at level a. h. the anterior horn is separated from rest of grey matter. The
substantia gelatinosa at tip of posterior horn is increased, and the angle
between the posterior horns is greater than below.

the spinal accessory, the vagus, and the glosso-
jyharyngpxd. At the junction of the bulb with the
pons the seventh nerve passes out in the same line, and
passing through the substances of the pons \\\q fifth
nerve possesses a corresponding origin.

204

Elements of Histology.

186. It will be found most convenient in order
to determine the relation of the different regions in
the bulb with those of the cord, to examine the
appearances presented by successive sections of the

Fig. 139.— Section thi'ougli the Upper Part of the Pyramidal Decussation
in the Medulla Oblongata. {Microphotograph of a Weigert-Pal specimen.)

A.F., Remains of anterior Assure; the dark mass immediately above consists
of the decussating pyramidal fibres ; at the level A. H. is a light mass on
either side represeatinff the remains of anterior liorn; at tue level c. c. in
the middle line is the grey matter round the central canal ; the posterior
nuclei are not clearly distinguishable.

bulb, cut in a dorso-ventral direction, and com-
mencing at a level immediately above the cervical
spinal cord.

187. The region of the pyraiiiiclal decus-
sation (Figs. 138 and 139). — In this region the fibres

Mrd ul l a Ob long a ta .

205

of the crossed pyramidal tract, lying in the dorsolateral
portion of the cord, take on an oblique course and,
passing across the middle line, again resume their direct
course in what would correspond in the cord to the

P.F.

•c.c

S D.

A.F.

Fig. 140.— Section through the Medulla Oblongata at the level of the
Sensory Decussation. {Photograph of a Weigert-Pal specimen.)

The section has not involved the olives ; the pyramids are completely formed
and project at p, and extend inwards as far as the level sr, meeting in the
middle line. At level of c.c. on middle line is the central canal, and at a
short distance from this are seen numerous fibres arching round and decus-
sating on middle line at level s.u. ; k, lies between funiculi gracilis and
cuneatus.

anterior or ventral column. In their passage across to
the other side of the medulla these fibres separate oft'
the head of the anterior horn so that the grey matter
of the cajnit lies in the anterior area disconnected
from the main mass of the grey matter. The angle
formed by the median boundaries of the two posterioi^

2o6 Elements of Histology.

horns increases very considerably, so that these horns
come to lie more transversely across each half of the
medulla than was the case in the cord. There
develop also from this inner margin of the posterior
horns, in the iij)per part of the pyramidal decussation,
certain protuberances of grey matter ; a median mass
projecting into the funiculus gracilis and known as the
mideus of the funiculus gracilis Rud a more externally
situated mass, projecting into the funiculus cuneatus,
and known as the nucleus of the funiculus cuneatus.
The substantia gelatinosa at the tip of the posterior
horn also becomes more conspicuous and causes the
medulla to project in this region, forming the funiculus
uf Rolando. Higher up this projection becomes even
more conspicuous and is known as the tubercle of
Rolando. In the region of the pyramidal decussation
the substantia gelatinosa of Rolando is separated from
the surface by a longitudinal mass of medullated fibres
which pass to the origin of the fifth nerve. This mass
of fibres is spoken of as the ascending root of the
fifth nerve.

188. The region between the npper end
of the pyramidal cleenssation and the
eouiniencenient of the olives (Fisf. 140). — In
this region the central canal is seen to lie more
posteriorly corresponding to its gradual approach
towards the posterior surface. The p3Tamids oc-
cupy well defined positions on the ventral side
of the bulb immediately abutting on the anterior
fissure and bounded laterally by the fibres of the
hypoglossal nerve coursing from the nucleus of the
twelfth, across the medulla. There is to be seen lying
in the lateral region between the substantia o^latinosa
of Rolando and the fibres of the twelfth, a mass of
cells, which correspond to some extent to the more
dorsal portion of the separated anterior horn, but
which in part is to be regarded as a new formation.

Medulla Oblongata. 207

This mass of cells is spoken of as the lateral
HKc/f'us. It is to be noticed tliat the ])Osterior white
matter is gradually undergoing absorption, being
invaded by the grey matter of the corresponding
nuclei. The grey matter of these nuclei gradually
becomes more marked, the nucleus of the funiculus
gracilis early absorbing the white matter of the
column and lying quite close to the surface. The
nucleus of the funiculus cuneatus lies rather more
deeply, but is gradually invading the white substance.
The central portion of the medidla becomes broken
up, and fibres are seen passing in an arched manner
from the nucleus gracilis mainly, and, to some extent,
from the nucleus cuneatus towards the middle line.
These arched fibres on reaching the middle line,
for the most part bend longitudinally, and thus form
a mass of fibres lying dorsal to the pyramids, and
spoken of, higher up, as the inter-olivary layer. This
decussation of fibres passing from the gracile and
cuneate nuclei is sometimes referred to as the supei'ior
or sensory decussatior.

189. The region of the lower portion ol
the olives (Fig. 141). — A few millimetres higher up
than the last section the olives are seen to be distinctly
formed, though they have not reached their greatest size
and though the central canal is still closed. The central
canal has at this level approached yet more closely to
the posterior suiface. Each lateral half of the bulb
may be more or less distinctly marked off into three
areas : a median area lying between the middle line
and the roots of the twelfth nerve as they coui^e across
the bulb from the hypoglossal nucleus : a lateral area,
lying between the roots of the twelfth and those of the
eleventh, which issue more laterally ; and an area,
posterior to the eleventh roots, which may be called
the posterior area. The lateral nucleus lies in the
dorsal portion of the lateral area. The main

2o8

Elements of Histology.

mass of tlie olive lies
of the lateral area. Imt

in the ventral portion

two additional masses,

S.G.

XI.

N 3. A.

M.H.

Fig. 1-tl. — Section through the Medulla Oblongata at level of commence-
ment of Olives. {Microphotograph of a specimen stained with aniline
hlue-hlack.)

The central canal is not yet opened out, and is at level of x.s. a. : the posterior
grey matter is arranged iu three masses, >'. g., nucleus gracilis, x.c, nucleus
ciineatus, and s. g.. the substantia gelatinosa of Rolando: with respect to
grey matter round central canal, that at level x. s. a, has cells forming
nuclei of the xi, that at level x. h. forming nuclei of xii ; xi is placed
against the line of issue of the spinal accessory, xii against hyi>oglossal ;
the grey matter lying slightly beneath surface at level l.x. is the lateral
nucleus; o, is at level of the twisted dark 1>and, the olive; the large light
areas at level of p are the pyramids : the area more dorsal at level R. f. is the
reticular formation, in the middle line of which is the raphe (.above a. f. i.

similar in structure to the olive, may also be
seen, one lying in the lateral area, dorsal to the
main olive, kno^vn as the dorsal accessory olives
and the other lying in the median area, separated

Medulla Oblongata. 209

from the iimin olive by the roots of the liypoglossal
nerve and known as the menial accessory olive. The
more central ]»ortion of the section is seen to be
broken np by til)res passing horizontally, separating
others which are proceeding longitudinally; and yet
other strands are to be noticed intersecting both of
these. Nerve cells are scattered through this area,
and more conspicuously in its lateral portions, and
these nerve cells with attendant neuroglia may be
regarded as representing the much ditiiised grey
matter of the ventral horn which was separated by
the decussation of the pyramidal fibres. This broken
tissue is spoken of as the reticular formation, the more
lateral portion, which appears darker on account of the
nerve cells being more numerous, being referred to as
the grey reticular formation, and the central j^art as the
■?r/n"<e reticular formation. In the middle line, wdi ere
the reticular formations of either side are continuous,
the decussation of the fibres coursing transversely, and
the presence of many fibres running in a dorso- ventral
direction, give a somewhat peculiar appearance to
the reticular region. The narrow^ intermediate band
is called the raphe, and it contains a larger proportion
of nerve cells than the remainder of the median
reticular formation. The lateral nucleus is still
prominent at this level, the substantia gelatinosa
of Rolando and the ascending root of the fifth are
also seen. This latter is gradually becoming separated
from the surface by a band of fibres running longi-
tudinally but somewhat obliquely wdiicli represents
the commencement of the resti/orm body or inferior
peduncle of the cerehelhua. The longitudinal fibres
lying outside the lateral nucleus represent the upward
continuation of the direct cerebellar tract and these
fibres gradually pass into the restiform body. Fibres
are seen proceeding in a ventral direction from
the raphe, originating in part from cells of the raphe
0

2IO Elemests of Histology.

but having some connection proljably with the nuclei
gracilis and cuneatus, and these fibres passing from
the anterior fissure encircle the pyramids and olives
and pass towards the commencing restiform bodies.
These fibres are spoken of as external arcuate fibres.
There is to be seen at about this level for the first
time a somewhat compact bundle of longitudinal fibres
lying between the central canal and the substantia
jjelatinosa, though consideraljlv nearer the former.
This bundle is surrounded by grey matter, with
the cells of which the fibres are connected. The
fibres of the bundle mainly pas^s out with the roots
of the glossopharyngeal nerve and it therefore has been
called the ascending root of the glossopharyngeal :
the names /'rtSC2C?//?/6' solitarius and respiratory bundle
are sometimes applied to the same tract. In addition
to the nerve cells already referred to other important
masses of cells are now to be seen distinctly. («) llie
nucleus of the tvnelfth nerve. This consists of a group
of nerve cells representing, probably, the most dorsal
portion of the separated anterior horn, lying slightly
ventral to the central canal. The cells are multipolar
and vary in size from 40-70 yu, and the neuraxons of
these cells, after a somewhat irregular course, become
the fibres of the hypoglossal nerve. The fibres on each
side pass in a ventro-lateral direction across each half
of the medulla and issue i'rom the groove lying
immediately lateral to the pyramids. (6) The nucleus
of the eleventh nerve. It must be noted that the
eleventh, tenth, and ninth nerves pass off' at different
levels from a group of cells longitudinally continuous.
This group of cells can be spoken of as the combined
nucleus of the spinal accessory (more correctly the
bulbar accessory), the vagus and tlie glossopharyngeal.
It is not possible to define precisely the divisions
of the nucleus corresponding to each nerve. In
the region of the medulla we are now describing,

Medulla Oblongata. 211

liowever, the roots belong to the spinal accessory nerve.
Here the nucleus, consisting of a mass of somewhat
spindle-shaped cells, oO-l:0/.i long and 12-20/li wide,
occupies a position dorsal to the twelfth nucleus and
adjacent to the central canal. From this nucleus
tiljres may be traced passing laterally across each half
of the medulla, and emerging from the l)ulb between
the restiform body and the olive, ic) The nucleus of
the funiculus gracilis, {d) TJie nucleus of the funiculus
cuneatus. There may be seen external to this nucleus
an isolated mass of cells, this is to be regarded as
an accessory cuneate nucleus. (e) The lateral
nucleus.

190. The region of the iiiiddle of the loAver
half of the fourth ventricle (Fig. 142). — At this
level the central canal has opened out into the fourth
ventricle. This fourth ventricle is furnished with a
lining membrane, consisting of columnar cells (which
may be ciliated), resting upon neuroglia. This lining
membrane is spoken of as the ependyma. With the
opening out of the central canal the gracile and cuneate
nuclei have retreated from their median position and
come to lie in the dorso-lateral region. The two gracile
nuclei therefore are separated from one another by the
width of the fourth ventricle. The nucleus of the
twelfth nerve lies now in the median position at the
dorsal surface, and in this locality a slight bulging
into the ventricle exists which corresponds to the
funiculus teres. Lateral to the nucleus of the twelfth
lies the combined nucleus of the eleventh, tenth and
ninth, here corresponding to the vagus nerve. The
restiform Vjody has increased in size and has now
largely absorlied the direct cerebellar tract. The
olives are also much more prominent, and have
here reached their full development. These bodies
each consist of a lamina of grey matter folded back
upon itself, enclosing a space filled with white

212

Elements of Histology.

matter. The convex portion of the fold corresponds to
the external protuberance. This lamina has, in addition
to the main fold, numerous secondary longitudinal

N V.

N H
R.

A.V.

"\ X.

■(,?

'V-^--^'

Xli

Fig. 142. — Section throufrli the Medulla Oblongata at level of middle of
Olives. {Microphotograph of a specirueii stained rvith aniline llue-black.)

B lies over the raphe ; a mass of grey matter just beneath x. h. is nucleus of the
xiith, beneath y. v. is nucleus of the xth : beneath x. g. and y. c. are the
nuclei of the fasciculi gracilis and cuneatus ; c. k. lies atrainst the light
mass of the restiform body, slightly deeper at level a. v, is the ascending vth ;
X is placed against the issuing x., and running down towards xii, from
nucleus of the xiith are the fibres of the xiith : y. a. is against grey matter
forming the nuclei of the external areiform fibres : the olive is seen lateral
to the roots of xiith as a deeply stained undulating band ; a part is separated
on the dorsal side (the dorsal olive) and a small part lies on median side of
roots of xiith (the median accessory olive i ; at level of c. R.and immediately
beneath f.s. is a light circular area, the fasciculus solitarius; the grey
matter lying at level of x and a little below the surface is the lateral nucleus.

folds, so that in transverse section it presents the
appearance of a Avavy Ijand of grey matter passing
from the formatio reticularis towards the surface,

Med ulla Oblonga ta. 213

and then arching back it continues its wavy course
towards the region from which it started. Inter-
nally there pass into the interior of the olive tracts
of white fibres which radiate outwards towards the
concave surface of the lamina. The lamina itself is
composed largely of neuroglia, broken by nerve fibres
passing across, there are also present many multi-
polar nerve cells. These cells possess axis-cylinder
processes which possibly pass down into lateral
columns of the cord and become connected with
motor cells in the grey matter. They are themselves
connected with nerve fibres which, springing originally
from the cells of Purkinje in the cerebellum, course
through the restiform body and, becoming cerebello-
olivary fibres in the medulla, pass across the opposite
olive. It may also be that the olives are connected
by longitudinal fibres with the cerebral hemispheres.

It is possible to classify to some extent the
numerous fibres passing transversely across the
medulla in this region.

Somewhat lower than the transverse section
we are at present considering were decussating
fibres from the gracile and cuneate nuclei, called
internal arcuate fibres, forming the inter-olivary layer.
With the development of the restiform body and the
olives, other fibres proceeding transversely become
prominent. The external arcuate fibres may be
held to comprise three minor groups. («) Those
passing from the raphe and encircling the pyra-
mids and olives. Amongst these fibres in the
upper part of the bulb are a mass of nerve cells
known as the nucleus arciformis. (6) Fibres passing
from the lateral tract into the restiform body. These
are largely the more superficial of the fibres of the
direct cerebellar tract. (c) Fibres passing dorsally
from the gracile and cuneate nuclei to the restiform
body of the same side. These fibres are also spoken

2 14 Elements of Histology.

of as superficial dorsal arcuate fibres. In adrlition
to the so-called arcuate fibres there are other fibres
which have a somewhat arched course, but which are
best separated into a distinct class, and spoken of as
cerehello- olivary fibres. These include a majority of
the fibres forming the restiform body. They pass
from the restiform body either laterally to the ascend-
ing root of the fifth, or to some extent intersecting it,
and proceed towards the dorsal lamina of the olive.
Most of the fibres then penetrate the grey matter
(a few perhaps becoming lost therein), and passing
into the white core of the olive emerge at the olivary
peduncle and proceed to the raphe. The more
dorsal of these fibres passing from the restiform body
do not intersect the olive ; the more ventral pass
round the olive (and are hence regarded by some as
external arcuate fibres), and entering between the
olive and pyramid pass to the raphe. Having
crossed the raphe these fibres either bend longitudi-
nally or pass to the olivary grey matter. The
longitudinal fibres Ivino^ between the olives in the
ventral portion of the formatio reticularis are known
as the inter-olivary layer. This diffuse column of
fibres becomes more distinct higher up, and is then
known as the fillet or lemniscus. In the posterior
part of the formatio reticularis near the raphe, a
fasciculus of longitudinal fibres is gradually becoming
more distinct. This is known as the posterior longi-
tudinal bundle, and is to be regarded as representing
a part of the anterior or ventral column of the cord.
The hypoglossal nucleus lies now on the floor of
the ventricle, and external to it lies the nucleus oj
the vagus. The cells forming this nucleus may be
divided into two groups, a more median and a more
lateral. The median group consists of the larger cells.
In addition to this superficial nucleus there lies in
the formatio reticularis, midway between the fibres

Med ulla Obl onga ta. 215

of the twelfth aiul clcveiitli nerves, a second nucleus
known as the nucleus amhijaus or motor nucleus oj
the tentli. Fibres from this nucleus pass dorsally to-
wards the main vagus nucleus, and issue with the
vagus roots. Fibres from the fasciculus solitarius
also pass out with the vagus. The vagus fibres thus
have three centres of origin.

A section taken somewhav higher than that just
considered would show the issue of the glosso-
pharyngeal nerve. A majority of the fibres of
the fasciculus solitarius pass out with the glosso-
pharyngeal, running first towards the main nucleus,
and then turning back and coursing with the fibres
of the ninth nerve. There are also to be seen at
this level, rather more distinctly than in the lower
section, lying somewhat external to the fasciculus
solitarius, and near to the grey matter corresponding
to the nucleus gracilis, some scattered longitudinal
bundles of fibres, which are connected with the
auditory nerve, and are known as the asceruJimj root
of the eighth.

2l6

CHAPTER XVIII.

CONTINUATION OF THE MEDULLA OBLONGATA
THROUGH THE PONS VAROLII AND THE REGION OF

THE CRURA.

191. Tliereg:ioii of the iiii<l<1loof the fourth
veiitriele (Fig.14.3). — Adorso-ventral section passing
through that part of the fourth ventricle across which
the striae acusticse course would be somewhat below
the precise middle of the ventricle, but may be con-
veniently considered first. Such a section would not
involve the pons varolii and would probably just
miss the exit of the sixth nerve. In such a section
the upper part of the diminishing olive would be
seen still. The formatio reticularis occupies the
median portion of each half, and, laterally, the resti-
form body is here at its maximal size. Coursing
ventro-laterally with respect to the restiform body
are seen the higher roots of the ninth nerve ; on the
median side of this there appears the ascending root
of the fifth. On the median side of the dorsal portion
of the restiform body are seen longitudinal fibres
belonging to the ascending root of the eighth nerve,
and lying somewhat dorsal to this are nerve cells
belonging to the same nerve. The dorsal edge of
the section appears to be composed of transverse
dbres coursing from the raphe round the restiform
body and directed towards the exit of the eighth
nerve. These are the stance aciisticd'.

Lying on the ventrolateral side of the restiform

Medulla Oblongata.

2 I 7

body is a mass of nerve cells connected with the
fibres of the acoustic nerve and called the ventral
ganglion of the eighth. A section taken slightly
higher would involve the pons and show some slight

Fig. 143.— Part of a transverse section of the Medulla Oblongata through
the exit of the Auditory Nerve. (Micropliotograph of a IVeigert-Fal
specimen.)

The section is slightly obliiiiie, ;uid lience at the level d the cochlear nerve
(N. c.) is seen dividing into ascending (the more median) and descending (the
more lateral) divisions. The half-moon-shaped mass, dark in C(dour at level
C. E., is the restiform body. The dark mass lying in centre of the photograph
at level of v is the ascending root of the fifth nerve. The lighter substance
at level of D lying mainly on inner side of the cochlear nerve is the ventral
ganglion, the cells of the tulierculum acusticum are in the lighter substance,
rather above the level of D, and lateral to the cochlear nerve. s.R;, lateral
portion of stri® acusticae.

changes when compared with the section just described.
The most conspicuous difference in the higher section
consists in the presence of a prominent mass of
transverse fibres passing across on the ventral aspect

2iS ELEME^rs OF Histology.

and breaking up the pyramids into smaller bundles.
The auditory nerve is to be seen issuing as before, and
on the median side of tlie eighth a second nerve, the
seventh, passes out. It must be remembered that
neither the sixth nor the seventh nerves pass by direct
dorso-ventral courses outwards. The seventh nerve
originates from a nucleus lying in the formatio
reticularis midway between the ventral acoustic
nucleus and the raphe, and at about the same level
as the nucleus. The libres from the facial nucleus at
first pass dorsally and then turn longitudinally and
pass for a short distance upwards, becoming involved
in the nucleus of the sixth. After a short upward
course they turn back again towards the lower region
of the bulb, and, takimj o^raduallv a more ventral
direction, finallv emerije near the exit of the eio'hth
nerve. There also pass out with the facial nerve
fibres derived from the hinder portion of the nucleus
of the third nerve. These fibres sujDply the orbicu-
laris palpebrarum and frontalis muscles. The nerxe
cells composing the nucleus of the seventh are about
40-60/i in size, their neuraxons are directed dorsally
to form the nerve fibres of the facial nerve.

A mass of grey matter is also seen lying slightly
median, and ^■entral to the seventh nucleus. This
mass of grey matter contains nerve cells, and is known
as the superior or little olive. This, in adults, is about
4-5 mm. in lengtli, but is better developed in lower
animals. The cells are similar to those of the olive,
about 30— tO/z in diameter, with neuraxons and much-
branching dendrites. Another mass of cells is to
be made out on the ventro-median aspect of the
superior olive. This is known as the trapezoid
nucleus. Fibres may be seen proceeding from the
ventral nucleus of the eighth, and passing on the
ventral side of the superior olive and the trapezoid
nucleus. These fibres constitute the trapezium.,

Med ulla Obl onga ta. 219

and form the most tlorsal portion of the transverse
fibres of the pons.

The connection of tlie auditory nerve with its
different origins is now to be described. There are
three main nuclei from which origin takes place : —
(a) the ventral or accessory nucleus lying near the
place of exit of the nerve, and, from its resemblance
to a spinal ganglion^ sometimes called the acoustic
ganylion ; (b) a mass of cells lying on the floor of the
fourth ventricle, midway between the restiform body
and the median furrow, called the dorsal median
nucleus ; and (c) a mass of cells lying near the
ascending root of the eighth, between the median
nucleus and the restiform body, but somewhat deeper
than' the former, called the dorso-lateral nucleus or
nucleus of Deiters. The ventral nucleus is really
divisible into two ; a more lateral portion and the
main ventral nucleus. The lateral portion forms the
tuherculum acusticum. The eighth nerve can be
seen to consist of two parts, one part passes to the
median side of the restiform body, the other to the
lateral aspect. The former is called the vestihidar
nerve, and the latter the cochlear nerve, corresponding
to the destination of these two divisions. The
cochlear nerve has finer fibres than the vestibular,
the fibres of the former being 1-2*5^, those of the
latter 2-4^, The fibres of both nerves divide, like
a spinal posterior root fibre, into an ascending and
descending branch after enterins; the medulla. The
ascending branches of the cochlear nerve pass to
the ventral nucleus, the descending branches to both
the tuberculum acusticum and the ventral nucleus.
From the ventral nucleus fibres pass as already
stated into the trapezium and become connected in
part with the cells of the superior olive and the
nucleus trapezoides. The cells of the tuberculum
acusticum, and partly also those of the ventral nucleus,

220

Elements of Histology.

originate the fibres composing the strua acusticce.
(Fig. 152.) The fibres, therefore, coursing round the

'^m

FiK. 144.

-.•Section through the .Sixth Nucleus aud Genu of Seventh.
(Pliotograph of a Weigert-Pal preparation.)

The lower half constitutes the hulk of the pons proper, with laterally the middle
peduncles; the two syuiinetriCHl dark masses at level F are the longitudinal
fibres of tbe fillet ; on the left side and lateral to the fillet is seen a darkish
mass with a lighter centre, the .-uperior olive. The floor of the fourth ven-
tricle forms tbe median part of the upper edge, two symmetrical light masses
beneath vi are the vith nuclei. Fibres from the inner side are seen passing
downwards near the middle line, these are the fibres of the vith. The
fibres of the viith are seen passing apparently from the outer side of the
vith nucleus on the left side. The nucleus of the viith lies on dorsal side of
the olive. The darkest tissue Ijing beneath v and at level a constitutes the
somewhat scattered fibres of the ascending root of vich. The genu of the
viith is between the nucleus of vith and the median sulcus and Is better
seen in the enlargement of this region. (Pig. 145).

restiform body, though apparently the continuation of
the cochlear nerve, are really the neuraxons of cells of

Med ul la Obl onga ta .

221

the tuberculuni acusticum and ventral nucleus, wliich
are connected with the terminal arborescences of
fibres composing the cochlear nerve. The vestibular

N.A. G.F.

F.N. i

A N

Fig. 145.— Section througli the Nucleus of the Sixth, being a part more
highly magnified of Fig. 144. {Microphotograph of a Weigert-Pal
specimen.)

The letters x.a., g. f.. aud r. lie over the cavity of the fourth ventricle, r lies
ahove the raphe. A dark circular patch a little below g. f. corresponds to
the genu of tlie viith nerve, x. a. lies above a circular light area wlaich is
the nucleus of tlie vith. F. N. lies against the lower end of a darkly stained
mass of fibres which can he dimly traced round the nucleus of the vith
towards the outer side of the genu of vii. This corresponds to the facial
nerve just before it issues from the medulla. Fibres are seen passing from
inner side of vith nucleus towards a. n., the fibres of the vith nerve.

nerve fibres also divide,

ascending and descending
branches become

on entering the bulb, into

branches. These different

connected with the cells of the

2 22 ElEMF.XTS of HlSTOLOGV.

clorso-inedian nucleus, Deiters's nucleus, and the
cells around the ascending root of the eighth. As
regards the further course of the stria? acusticse, these
bundles show many fibres passing vertically into
the central mass of the bulb or the tegmentum^
as it is termed ; other fibres of the striES acusticse
decussate at the raphe, some pass thence towards
the superior olive and turn longitudinally, others
pass towards the restiform body.

192. Region of iiiicleiis of seveiitli nerve.
The nucleus of the seventh extends towards the mid-
brain, almost to the upper limit of the nucleus of the
sixth. A section taken through the junction of the
upper and middle thirds of the fourth ventricle would
pass through Vjoth these nuclei, showing the appearance
seen in Fig. 14 4-. The fibres here are seen passing
from the nucleus of the seventh towards that of
the sixth, which is seen on the floor of the fourth
v^entricle. Towards the inner side of this a more or
less prominent mass of fibres of the seventh turn
longitudinally, forming the genu of the seventh
(Fig. 145), and there are seen laterally fibres about
to pass out of the bulb, belonging to this same nerve.
The nucleus of the sixth or abducens nerve consists
of multipolar cells, about 40-50 fx in diameter. The
neuraxons of these cells pass from the median side
ventrally towards the pons and run through this
Avitli an oblique backward course so as to issue at
the lower edge of the pons in line with the roots
of the twelfth. The nucleus is connected with the
superior olive by a bundle of fibres, which is called
the pedicle of the superior olive. Other connections
exist with the pyramidal bundles and the posterior
longitudinal bundle.

193. The region of the upper end of the
fourth ventricle. (Fig. 146.) — A section through
the nuclei of the fifth nerve would show the

Med ul la Ob long a ta .

characters uf a transverse section in this region. The
origins of the fifth seen in this section consist of
two more or less distinct masses of cells, the outer
being described as the sensory nucleus, the inner

Fit

140. — SectioL chrough the Nucleus of the Fifth Nerve.
graph of a Weigert-Fal preparation.)

{Microphofo-

Below is seen a small part of the pons proper, and at p are fibres passing circuni-
ferentially towards tbe pons. At level F is a dark mass on left side of
middle line of section, the fillet (above this and near the centre of the micro-
pbotoeraph) at level s. o. is tbe superior olive. At level x. and beneath vm.
and vs. are tbe two nuclei of the vth ; from these and between these, at level
T, are seen fibres passing downwards towards the pons fibres— these form the
vth nerve.

as the motor nucleus. From these masses of cells
nerve fibres are seen to pass in a ventro-lateral
direction to the fifth nerve. The more exact origin
of this nerve may be now referred to. In the first

2 24 Elements of Histology,

place the nerve consists of two parts, the motor and
the sensory divisions. Tlie sensory divisioit proceeds
from the Gasserian ganglion, and, on reaching the
deeper layers of the pons, the different fibres divide into
ascending and descending portions, like an ordinary
sensory nerve. The descending portions form a
bundle of fibres, the so-called ascending root of the
fifth, which has been referred to in most of the regions
already described. This can be traced down distinctly
as far as the pyramidal decussation. The bundle
diminishes in amount on tracing it downwards,
and is always associated with a mass of grey matter
lying on the median side, the substantia gelatinosa.
In this substantia gelatinosa are cells round which
the fibres of the '' ascending " root form arborescences.
At the level of the exit of the fifth these cells of
the substantia gelatinosa are more evident, and are
referred to as the chief sensory nucleus. The
ascending branches of the bifurcating sensory root
])ecome connected with the cells of the chief nucleus.
From the cells lying in the substantia gelatinosa
against the " ascending " fifth along its whole length
there pass, towards the middle line, arched fibres,
which cross the raphe, then become longitudinal
in their course and enter the fillet. On their
way towards the upper part of the brain these fillet
fibres of the fifth give off numerous collaterals which
are connected with cells in the reticular formation.
The motor root sjDrings from the motor nucleus. This
occupies the position somewhat of an upward con-
tinuation of the seventh nucleus. It consists of large
multipolar cells (50-70/.f) having, however, blunt,
unbranched processes. The fibres forming the motor
root are partially decussated, so that the root on one
side is composed of fibres derived from the motor
nuclei of both sides. There are connections between
the motor and sensory nuclei which may furnish the

Med ul l a Ob long a ta. 225

path for reriex masticatory action. There must
also exist connections with fibres of the pyramidal
system. Passing dorsally between the two nuclei
are seen fibres which turn longitudinally and form
a small tract traceable, upwards, about as far as the
anterior corpora quadiigemina. This is known as the
" descending " or cerebral root of the fifth. It will
perhaps be well to describe its course here. In
the region of the posterior corpora quadrigemina it
lies near the dorsal angle of the superior cerebellar
peduncle and dorso lateral to the outer angle of the
posterior longitudinal bundle. It is separated from
this bundle by a mass of pigmented cells, known
as the substantia fer rug inea (Fig. 147). The "des-
cending " root can be traced upwards as a bundle
of large fibres aoainst which lies scattered round or
spindle-shaped nerve cells, less deeply pigmented than
those of the substantia ferruginea. Passing to the
level of the anterior corpora quadrigemina, the root
can be seen for some distance, lying at the edge of
the grey matter surrounding the Sylvian aqueduct
and near the upper end of the anterior corpora
quadrigemina it becomes lost. Returning to other
structures seen at the level of the exit of the fifth
nerve, it will be well to refer to the appearance
now presented by the fillet.

In the middle of the fourth ventricle the fillet
consists of a mass of longitudinal fibres lying on either
side near the middle line and separating the formatio
reticularis from the transverse fibres of the pons.
In the sub-pontine region the fillet fibres lie between
the olives, forming the inter olivary layer. In the
upper portion of the fourth ventricle the fillet on
either side divides into two masses, one part lying
between the superior olive and the middle line,
forming the median fillet, the other lying dorsal to
the superior olive and known as the lateral fillet.
p

2 26 Elements of Histology.

The fibres of the median fillet are derived originally
from the nuclei of the funiculi gracilis and cuneatus
as well as from the nuclei of the vagus, glasso-
pharviigeal. ami ^■r^tilal^;^l■ nerve. The lateral fillet
probably originates (Ij from fibres of the trapezium,
passing from the ventral acoustic ganglion of the
ojiposite side and, therefore, connected with the
cochlear root of the eighth; (2) from the superior
olives on both sides and, higher ui>, from a collection of
cells in the course of the lateral fillet, known as the
nucleus qftJie lateral jillet j (3) from longitudinal fibres
lying against the superior olive, which increase in
ntmiber on proceeding upwards; (4) possibly, from
fibres derived from the striae acusticae, which have
passed ventrally into the tegmentum and turned into
the tract of the"^ fillet.

The ^jo/is proper is made up of numbers of
transverse fibres passing laterally from the middle
peduncles of the cerebellum on one side to that
on the other. In crossing ventrally upon what is the
continuation of the substance of the bulb these fibres
divide the pyramids into groups of longitudinal fibres.
The more dorsal of these transverse fibres (those
lying immediately adjacent to the upward con-
tinuation of the formatio reticularis) are known
by the special name of the trapezium. Amongst the
transverse fibres of the pons are numerous scattered
masses of grev matter with which manv of the
loncjitudinal fibres become connected.

194. The reg^ioii of tlie posterior coi*pora
qiiadri^eiiiina and upper part of tlie poii^>.
— The first section taken is immediately below (distal)
the posterior corpora quadrigemina. The fourth
ventricle has here narrowed to form the commence-
ment of the aqueduct of Sylvius. Surrounding the
channel is the ependyma enveloped on all sides by
a considerable thickness of ^rex matter. In that

Med ulla Obl onga ta .

227

portion lying on the ventral side maybe seen masses
of cells foi-mini: the commencement of the nuclei of

S.C.P IV. I. IV. V. S.C.P.

P.L.B

L.F

M.F

Fig. 147. — Section throu<:li the Pons Varolii immediately below the
Posterior Corpora Quadrigemina. {Fhotograph of a U'eigert-Pal
specimen.)

The main mass of the section forms the fibre? of the pons (P). The two large
dark masses in the upiier part (under >s. c. p. », the lower ends meeting in
middle line, are the superior cerebellar peduncles or lirachia conjunctiva.
The area included between their lower halves forms tbe teirmentum. Tbe
iiuadrangular space lielow i is the Sylvian aiiueduct. Decussating in the
valve of Vieussens above are seen fibres of the ivth nerve, the two small dark
masses below iv being the main trunks lying obli.iuely. Lying a short
distance below the aqueduct at p. l. b. are two dark comma-shaped masses,
the posterior longitudinal bundles. The twu elongated dark masses one
lying against l. f.. the ntlier passing l)etween the pons fibres and the superior
cerebellar peduncles opposite M. f. are the lateral and median fillets. The
darkish mass lying below v, just on the median side of the upper part of
the peduncle is the descending root df vth.

the fourth nerve. Lying again ventral to thi.s grey
matter are two prominent longitudinal bundles on

2 28 Elements of Histology.

either side of the middle Une, tapering towards the
lateral region. These are the posterior longitudinal
bundles. Near the lateral tapering end of these
bundles may be seen the desceitdiag root of the fifth
nerve, separated by a mass of cells forming the
substantia femiginea or locus cceruleus. Lying to
the median side of the root of the fifth may be
seen bundles of white fibres pa^^sing into the superior
nieduUary velum or valve of Vieussens, decussating
here (Fig. 1J:7) and issuing literally as the fourth
nerve. Lying again ventrally and laterally to the
posterior longitudinal bundles, and separated from
them by what is an upward continuation of the
reticular formation, are the upward prolongations
of the superior cerebellar peduncles or brachia
conjunctiva. There at the level of the nuclei of
the fifth nerve, in section, two semicircular masses
lie immediately lateral to the side of the fourth
ventricle. Passing upwards, they gradually take
a more venti-al position till, as in the present
section, they commence to fuse in the middle line.
At a short distance externally and ventrally to the
superior cerebellar peduncle is seen another band
of longitudinal fibres. This band is of considerable
thickness between the peduncle and the lateral surface,
then passing ventrally it narrows somewhat^ and
widens again to a fairly broad band lying on the dorsal
side of the pons proper. This is the fillet or lem-
niscus, the lateral portion witli nerve cells forming
its nucleus being the lateral fillet, that portion lying
adjacent to the pons being the median fillet. Ventrally
to this again is the substance of the pons proper,
having the characters described in ^ 193.

A section slightly higher would pass through the
posterior corpora quadrigemina. Here, there would
appear two protuberances, dorso - laterally to the
aqueduct. The lateral fillet forms connections with

Medulla Oblongata. 229

these bodies. Tlie pons pioper is here soinewliat
smaller, the up])er limit being appruuched. The two
superior cerebellar peduncles gradually lessen in width,
their lateral extensions disappearing by degrees. The
nucleus of the fourth nerve consists of a mass of large
multipolar cells lying in the grey matter on the
ventral side of the aqueduct and near the middle line,
and reaching from the upper to almost the lower
extremity of the posterior corpora quadrigemina.
The fibres from these cells take a somewhat oblique
backward course to the lower limit of the posterior
corpora quadrigemina where they decussate, as already
described. In the region of the posterior cor[)ora
quadrigemina the posterior longitudinal bundle is
very prominent. The basal ends of the ependyma
lining the aqueduct are frequently continued into a
set of fine fibres which pass through the grey matter
(and even beyond) and give a radially striated
appearance to the region adjacent to the aqueduct.

195. The region ot llie anterior eorpora
quadrigemina and the cinra eei ebri. —
At this level (Fig. 148) the pons has disappeared,
and its position is occupied by two well-marked
protuberances on the ventral side, spoken of as
the crura cerebri. Lying dorsally to the crus on
each side is a broad band of black pigmented
cells, forming the substantia nigra. The grey
matter around the aqueduct is considerable, the
posterior longitudinal bundle is somewhat less con-
spicuous than below and forms a narrow band
lying at the ventral edge of the central grey matter.
Large nerve cells lie in the ventral portion of this
grey matter, forming the nuclei of the third nerve, the
fibres of which can be seen passing ventrally in many
bundles. In the middle line between these roots
a well-marked raphe is visible. Lying midway
between the central grey matter and the substantia

230

Elements of Histology

nigi'a is a large mass of cells, known as the red
nucleus. In man this nucleus consists of cells vary-
ing in size from 20-7 5yu. These nuclei have some

R.N

Fi<

14S.— Section through the Anterioi- Corpora Quadrlgemina.
graj^li of a Weigert-Pal preparation.)

{Photo-

The section is somewhat oblique, lieing slightly higher on the right side than
the left. The symmetrical projections above are the anterior corpora quadrl-
gemina. The openiii!.' between them is the Sylvian aqueduct. Tlie lighter
substance around this is the grey matter surrounding the iter. The darker
masses forming tlie lower Ijoundary of this L'rey matter arranged in discrete
areas on right side are the posterior longitudinal bundles, lyins in which are
cells forming the nucleus of the third nt- rve. The bundles of fibres passing
in an arched manner downwards from the third nucleus are the fibres of the
third nerve. At level r. x. on right side is a large dark mass lyin.L' in a still
darker patch, having the tibres of the third passing throusrh its median
region. This is the commencement of the red nucleus, which is not yet
evident on the left side, where a corresponding dark mass consists of the
decussated fibres of the suiierior cerebellar peduncle. On the left side lying
below and laterally to this mass and light in shade is the substantia nigra,
this forms the base of a projection (the cms cerebrii, in which the fibres of
• thepyramids and other fibres pass longitudinally. The dark band somewhat
arched passing upwards to the anterior corpus quadrigeminum from the dark
mass of the superior cerebellar peduncle is the fillet.

Medulla Oblongata. 231

connection with the superior cerebellar peduncles,
which terminate liere in their uj)\vard course.
Laterally, the tillet is seen passing dorsally towards
the prominent <niferior corpus quadrigeminum. A
small portion of the brachiuiii of the latter may also
be seen. The ujjward continuation of the reticular
formation corresponds to the mass between the ventral
aspect of the central grey matter and the substantia
nigra, and is called the tegmeiituni. The locus
coeruleus is no longer seen, but the descending fifth
is still apparent.

Structure of the anterior corpus quadrigeiidnurn.
Externally there is a thin layer of white matter about
30-40)1/ in thickness. This is known as (a) the
stratum zonale. The white fibres in this layer pass
through the superior brachium from the optic tracts.
From the layer many fibres enter the inner layers,
and in them form dendritic ramifications, {h) The
stratum cinereum. In this layer are numerous cells,
whose neuraxons pass inwards, (c) The stratum alho-
cinereum. externum. This layer contains numerous
small and large cells and nerve fibres. The nerve
fibres enter the layer largely from the optic tract by
the superior brachium. A considerable amount of de-
cussation of these fibres occurs on the median side with
those of the opposite corpus quadrigeminum anterius.
(d) The stratum cdbo-<-inereuin internum. (Stratum
lemnisci.) This layer is subdivided into three minor
layers : (a) the fillet layer, formed from a continua-
tion of the dorsal part of the median fillet and from the
lateral fillet ; (/3) a layer of grey matter ; (y) a layer
of arched filjres bordering the central grey matter
and decussating in the middle line. All these layers
are pervaded by radial fibres passing from the central
grey matter.

The optic lobes of birds have been more fully
examined as regards the various layers and their

232 Elements of Histology.

connections. Dilierent authors divide these structures
in various different layers. Adopting Kulliker's
description, a vertical section may be regarded as
showing^(l) a superficial layer of fibres from the optic
tract ; (2) and (3) layers of grey matter or molecu-
lar layers : in (2) the optic nerve fibres form their
dendritic ramifications ; (4) a layer of white fibres
arranged in a kind of lattice work ; (5) an inner layer
of white fibres in which course the cerebral visual
fibres ; (6) a layer of grey matter lying against the
ependyma of the ventricle of the optic lobes. The
connections of the cells and fibres of this layer have
been established by Golgi's method by Ramon y Cajal
and V. Gehuchten.

In the corjDora quadrigemina important con-
nections are made by the fillet fibres. Some of these
connections have already been referred to (s$193). Tlie
fillet fibres in their upward course give ofl' collaterals
which ramify or actually terminate themselves in the
cells of the nucleus of the lateral fillet. Many of the
fillet fibres terminate in dendritic ramifications in
the cells of the posterior corpora quadrigemina, many
others pass into the anterior. The cells of the lateral
nucleus originate fibres which pass possibly towards the
cerebrum; some, however, descend towards the superior
olive. Some of the fibres entering both corpora
quadrigemina decussate dorsally and pass to the
opposite corpora. There may also be some connection
amongst the fillet fibres with those of the superior
cerebellar peduncle.

The nucleus of the third nerve has been described
as consisting of many various groups of cells. It is to
be regarded as mainly one nucleus, extending through
the whole length of the anterior corpus quadri-
geminum and somewhat above it. It consists of a
main mass with two less distinct masses : a dorso-
lateral with larsre cells, and a dorso-median with

Med ul l a Ob l onga ta. 233

smaller cells. At 3ts cerebral end there is a central
mass having large cells. It has been suggested that
the dorso-niedian group of small cells supplies the
internal muscles of the eye (sphincter, ciliary). The
nucleus is presumably connected with the pyramidal
tracts. Arborescences around cells of the third
nucleus are to be seen in new-born animals, and the
fibres forming them may be followed to the raphe,
crossing here and coursing ventrally. Connections
also exist with the posterior longitudinal bundle.
This bundle is to be regarded as the upward
continuation of part of the anterior column of the
cord, forming short longitudinal commissures It is
associated with the hypoglossal nucleus, tho>e of the
vago-accessory, the fifth and the acoustic (vestibular
branch). Connections also exist with the sixth,
fourth, and third nuclei. The posterior longitudind
bundle furnishes, therefore, commissural connections
between the different eye muscles. Connections
of the third nucleus also exist with the optic
nerves.

The hracJiia passing to the corpora quadrigemina
are spoken of as the superior or anterior and the
inferior or posterior. The fibres of the superior pass
to the lateral corpus geniculatum and to the
occipital tract. The fibres of the inferior brachium
are connected with the median corpus geniculatum
and possibly may pass through the tegmentum by
the internal capsule to the temporal region.

That portion of a transverse section through the
region of the corpora quidrigemina which projects
ventrally into the two crura is sometimes S[)oken
of as the crusta, being separated from the remainder
(tegmentum) of the region ventral to the aqueduct by
the substantia nigra. The crusta contains, in addition
to the fil)res derived from the pyramids which occupy
a central portion in each crus, other fibres derived

23 4 Elemexts of Histology.

from the pons. Those on the median side pass to
the frontal region, those on the lateral portion
to the temporal and occipital regions. Some fibres
on the median side are derived from the median
fillet.

235

CHAPTER XIX.

THE CEREBRUM AND CEREBELLUM.

196. The structure of the dura mater, araclinoidea,
and pia mater of the brain is simihir to that of the
same membranes of the cord.

As has been shown by Boehm, Key and lletzius,
and others, the deeper part of the dura contains
peculiar ampullated dilatations connected with the
capillary l)lood- vessels, and forming in fact the roots
of the veins.

The glanduhe Pacchioni^ or arachnoidal villi of
Lnschka, 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-shajDed, 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. Injected material
passes from the sub-arachnoidal sjiaces through these
stalks into the villi. Tlie spaces of their spongy
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
in the young subject.

197. As was mentioned of the cord, so also in the

236 Elements of Histology.

brain the subdural lymph space does not commu-
nicate with the sub-arachnoidal spaces or with the
ventricles (Luschka, Key and Retzius). Nor does
there exist a communication between the sub-
arachnoidal space and a space described by His to
exist between pia mater and brain surface, but
doubted by others. The relations between the cere-
bral nerves and the membranes of the brain and
the lymph spaces of both, are the same as those
previously described in the case of the cord and
the spinal nerves.

The pia mater ])asses 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. In tlie brain also it is
composed of a homogeneous matrix, of a network of
neuroglia fibrils, and of branched, flattened neuroglia
cells, called Deit^rss cells.

In the white matter of the brain the neuroglia
contains between the bundles of the nerve fibres
rows of small nucleated cells ; tliese form s})ecial
accumulations 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 witli a layer of neuroglia, being a direct
continuation of that lining the fourth ventiicle,
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.

The blood-vessels form a denser capillary net-
work in the grey than in the white matter ; in the

Cerebrum and Cerebellum. 237

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-A'essels have an arrange-
ment 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 separate lymphatic vessels in the grey
or white substance.

198. The white iiiaftei* 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 the fibres show the
varicosities mentioned in the cord.

The grey iiiattei* consists, like that of the cord
and medulla, of a basis of neuroglia in which are
embedded nerve cells. The dendritic ramifications
from the nerve cells, with medullated and non-
medullated nerve fibres, form a large proportion also
of the grey matter.

With regard to the structure of the ganglion cells
of the brain and medulla, what has been mentioned
of the ganijlion cells of the cord holds good as to
them. Like the former, those of the medulla and
brain are situated in pericellular lymph spaces
(Obersteiner).

199. We now proceed to consider in detail the
structure of the different parts of the cerebellum and
cerebrum.

The cerebelliiiii is composed of laminated folds,
or convolutions, and these again are composed of

238

Elements of Histology

secondary folds, each of which consists of a central
tract of white matter covered with grey matter. The
tracts of white matter of neisfhhourinfr convolutions of
one lobe or division join, and thus form the principal
tracts of wdiite matter.

The white matter of the cerebellar hemisphere is

Fig. 149. — Photograiu through the grey matter of the cereliellmn of tlie
dog, showing the hiyer of Purkinje's ganglion cells with their dendrites
ramifying in the grey cortex. {Lov magnification.)

connected (a) with the medulla oblongata by the
corpus restiforme, this forming the inferior peduncle
of the cerebellum ; (6) with the cerebrum by the
processus cerebelli ad cerebrum, this forming the
superior peduncle ; and (r) with the other cerebellar
hemisphere by the tracts connecting with the pons

Cerebrum and Cerebellum. 239

varolii ; these are the pedunculi cerebelli ad pontem,
or the middle peduncles.

200. On a vertical section through a lamina of the
cerebellum (Fig. 149), the following layers are seen: {a)
the pia mater covering the general surface, and pene-
trating with the larger blood-vessels into the superficial
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
long-branched and pursuing a vertical course towards
the surface ; sooner or later they all break up into
the fine nervous network of the grey cortex. The
longest processes reach near to the surface. The
layer (6) 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. San key maintained, before the adoption of
more modern methods of research, that in the human
cerebellum there are also small multipolar ganglion
cells connected with the processes of Purkinje's cells.

202. The connections and distributions of the
different cells of the cerebellum have been exhibited
to a considerable extent by the labours of observers
who have followed the methods of Golgi. A
scheme of the main points on these results is
shown in Figs. 150 and 151. Fig. 150 indicates
the appearance represented in a section across a
lamina. Fig. 151 corresponds to a section taken in

240

Elements of Histology.

the direction of a lamina.
Purkinje first, they are
extensive dendritic ramification, viewed transversely,

Considering the cells of
seen to possess a very

'\^jn\

i~Ta

■ml

Fig. 150.— Scheme of the Connectiou of the Cells in the Superficial Grey
Substance of the Cerebellum. (After KoUiker.)

p, Xeuraxons of Purkinje's cells with collaterals : k, tendril-like fibres with k^
their terminations; gU glia cells; /, nio^s fibres; m, small cells of the
molecular layer; vi^, larare cells of the same layer (basket cells) forming
synapses round Purkinje's cells, 3A-; gr, cells of the nuclear layer witli
neuraxons passing into molecular layers, here turning horizontally and
giving a punctated appearance in cross-section ; n, the luxuriant branching
of a Gblgi's cell of the second type.

passing through the whole thickness of the molecular
layer, as the cortical grey matter is sometimes called.
This ramification is less extensive viewed in the longi-
tudinal section of a lamina (Fig. 150). The neuraxon

Cerebrum and Cerebellum.

241

passes throu,<;li the uucle;ir layer oblkjuely, giving off
collaterals which to some extent re-enter the molec-
ular layer, then the axon passing fiom the nuclear
layer enters the central white matter. There are also
seen in the molecular layer other fairly conspicuous

Fig. 151.— Longitudinal Section of the Grey Substance of the Ceiebelliun.
{After Kolliker.)

The restricted branching of the cells of Purkinje (v) is seen. Tbe nuclear
cells below are seen sending axons upwards inio the luoleciilar layer which
divide dichotomously, and run longitudinally.

cells (m'), which are termed backet cells. These cells
have dendrites Avhich ramify amongst those of the
Purkinje's cells, and a neuraxon which gives off
collaterals, and these again form arborescences around
the Purkinje cells. Other smaller cells [in) have
])rocesses all of which i-amify in the neighbourhood of
the cell. On the border line between the nuclear and
molecular layers may be seen large multipolar cells

242

Elements of Histology

(sometimes spoken cf as Goh/i's* cells), which exhibit
a dendritic ramification in the nuclear laj^er, and in
which the neuraxon, on entering the molecular layer,

Ne -

Fig. 152.— From a Transverse Section through the Edge of the Restiform
Body, PC, and the Tuberculuia Acustieum of the new-born Cat.
{Gofgi. Kolliker, II.)

Xe, Xerve fibres of the coclilear nerve : Ne', the same fibres passing round the
peduncle ; c, collaterals : T, large ganglion cells of the tuberculinu ; n, their
axons becoming fibres of the stria? acustica'.

divides up not far from the main cell. In the nuclear
layer are numerous small cells (fjr), the dendrites
dividing verv near to the cells, the neuraxons.

* Though referred to frequently as ^^ cells of Golgi,'''' these
are more correctly described as "alls of the, second tt/pe of Golgi.'"
Some authors use the term "cells of Golgi" to refer to neu-
roglia cells.

Cerebrum and Cerebellum. 243

however, pass into the iiiolecuhir hiyer and bifurcate
longitudinally (Fig. 150) at various levels. The so-
called "molecular" condition of the cortical grey matter
is largely due to the appearance of these fibres being
cut across as well as to the sections of the processes
of the cells of Purkinje. The central white matter
shows other fibres than those representing the
neuraxons of the Purkinje cells (Fig. 151). One set
of these terminate in arborescent tufts in the nuclear
layer, and are referred to as moss fibres {/). Another
set pass into the molecular layer and break up on
connection with the dendrons of the cells of Purkinje.
These are spoken of as tendril fibres. These two
sets of fibres are to be regarded as conducting to the
grey matter of the cerebellum. In addition to the
proper nerve cells already described, may be seen
neuroglia cells (gl). These are also present in the
central white matter (Fig. 152).

20.3. The structure of the cerebral con-
volutions in g-eneral. — In a vertical section
through a cerebral convolution one is able to see with
the naked eye a central core of white matter sur-
rounded by a cap of grey or reddish-grey matter,
which again, on careful observation, can be seen to
consist of several alternate strata of lighter or
darker substance. The exact appearance of these dif-
ferent layers varies in different parts of the cerebral
hemispheres.

In general, a vertical section of a convolution
shows three main layers : (1) a superficial molecular
layer, (2) a layer of pyramidal cells, (3) a layer of
poly mor pilous cells. These layers are subdivisible into
several others in different parts of the hemispheres
(Fig. 153).

204. Structure of the cerebral convolu-
tions in the reg^ion of the Rolandic fissure. —
In this region one can distinguish six layers, showing

Fig. 153.— Vertical Section through tlie Grey Cerebral Cortex in the
Parietal Region. (KoUikcr, II.)

a, .Superficial white layers : 6, onter layer of small pyramidal cells: c, outer
laver of large pyramidal cells; d, inner layer of small pyramidal cells ; e,
inner layer of large pyramidal cells ; /, polymorphous cells.

Sir. zon.

c.s.c.

R.F.
Fig. 154. — For description see next page.

246 Elements of Histology.

different characters. Superficially is the stratum
zonale or moJecidar layer (a), then the outer layer of
small 2^y'i'<^'i>^^d^^ cells {b), then (c) the outer layer of
large pyramidal cells, followed by (cZ) the inner layer
of small iiyramidal cells, then (e) the inner layer of
large lyyramklal cells, and, adjacent to the white
matter (/"), the layer of polymorphous cells. These
cells are, to some extent, separated into vertical
columns by intercolumnar bundles of nerve fibres.
There are also, running horizontally, following the
contour of the gyrus, other more or less defined
bundles of fibres. Some of these run in the super
ficial molecular layer ; two other bands are disposed
tan^fentially, in the pyramidal cell layer, the more
superficial being the band of Vicq d'Azyr or Geunari,
the deeper that of Baillarger. In general, the
neuraxons of the cells descend towards, and finally,
pass into the white matter (Fig. ISt). There are
some cells in the cortex which do not conform to
this rule. Amongst the pyramidal cells may be
found cells known as Martinotti's cells, from which
the neuraxons ascend towards the superficial molec-
ular layer. Cells known as Golgi's cells are also
to be found, with neuraxons passing towards
the surface and dividing up not far from the
cell. The general relation of the different cells and
fibres is sliown in the accompanying scheme (Fig. 15-i)

Description o/Fig. 154 [-f- --15).

Fie. 154.— Scheme of the Connection of the Cells of the Cerebral Cortex.
{After KoUiker.)

Pj, Pi, Smaller aud larger pyramidal cells, the neuraxons passing downwards
on their way to the inner capsule ; P3, pyramidal cells forming a termination
in tlie corpus striatum ; at level M a cell of Martinotti with neuraxon passing
upwards and terminating in stratum zonale ; at level G a Golgi cell (2nd order)
with much-branched neuraxon immediately aliove it ; Ac, association
cell, on inner side of G is a cell (Cc) with neuraxon passing into corpus
c-allosum : C.S.C., a cell of corpus striatum with neuraxon passing into cortex ;
R.F.. a fibre from the fillet passing up into the cortex, one of Ramon y
Cajal's fibres ; Str. zon., stratum zonale, or superficial white layer.

Fig. 155. — Pyramidal Cell of the Cortex of the Brain, its axon giving off
unmerous collaterals. {Kollilcr, II,)

Fig. 156. -Fascia Dentata and adjoining part of C-nim Amnionis of Human
Embryo. (Aft'^r KoUiker.)

^^■'.^'ifL^^iK^^S'^^^^^ bundle, an accessory bundle pasMnsr out to the rights •
^^f. ■. ""i-'? ''■*^"'" radwtuni of fascia dentata: «. cell with ascendiiis axon
(cell of Martinott.) : Pi/r.. pyramidal cells; F, flml.ria: K. nuclear laNer

Cerebrum and Cerebellum. 249

from Kolliker. The pyramidal cells have a conspicuous
apical process, which passes vertically, giving off
lateral processes, and forms a system of dendrites in
the superficial molecular layer. Other dendritic
ramifications occur closer to the cell and the neuraxon
passes towards the white matter, giving off collaterals
as it traverses the grey substance (Fig. 155). Some of
the pyramidal cells (Cc) have neuraxons which pass to
the opposite hemisphere in the corpus callosum, and
not towards the inner capsule, through which a large
number of the neuraxons course. Some pyramidal
cells again probably have their neuraxons ter-
minating in connection with cells of the corpus
striatum (P'*). The connections of a cell of Marti-
notti are seen (M), and those of a Golgi cell (G).
Fibres conducting towards the cortex are repre-
sented by (1) Ramon y Cajal's fibi-es (R.F.), passing
from the fillet and subdividing in the cortex ;
(2) fibres from cells of the corpus striatum (C.S.C.)
passing up into the grey matter of the cortex in a
similar manner.

205. Structiii-e of the liippocaiiipus major
and the fascia deiitata (Fig. 156).

The hippocampus as it projects into the ventricle
is invested beneath the ependyma with a layer of
wdiite fibres called the alveus. Lying against the
alveus are pyramidal cells, the neuraxons of which
pass into it ; the conspicuous apical process passes
through a large ):»ortion of the thickness of the hippo-
campus, giving it a radiate appearance (the stratum
radiatum), and forming a dendritic ramification above
this in the stratum lacunosum. Tracing the sub-
stance of the hippocampus towards the fascia dentata,
these pyramidal cells become less conspicuous and are
not to be regarded as forming any definite layer in
this region. The fascia dentata has externally a
superficial layer or stratum zonale into which pass the

250

Elements of' Histology.

dendritic ramifications of a layer of small cells, the
stratum (jranuJosum. From these small cells
neuraxons pass to the central substance of the fascia

olfc.

Fig. 157. — Diagram of the Probable Connections of Cells and Fibres in the
Olfactory Bulb. {After Schafer.)

olf.c, Sensory cells of tlie olfactor.v epithelium ; olf.n., deepest layer of the liulb
composed of the olfactory nerve fibres which are prolonsed from the olfac-
tory cells ; f//., olfactory shjiueruli, containing dendrons of hoth the olfactory
nerve fibres and the mitral cells; mc, mitral cells; tx. their axons ; J4.fr.,
nerve fibres of tlie bulb becoming continuous with the olfactory tract.

dentata, and from this also many so called "moss
fibres " issue, passing to the granular layer [Mf
and 31/").

206. Structure of tlie oHaetory bulb (Figs.
157 and 158). — A vertical section through the olfac-
tory bulb indicates considerably more development
on the side lying against the cribriform plate than

Cerebrum and Cerebellum.

251

on the dorsal side. Passing from the surface lying
on the ethmoid bone, one can make out the following
la3^ers : (1) Bundles of olfactory nerve fibres; (2) the
zone of olfactory glomeruli ; (3) a layer pervaded

Fig. 158.— From the Olfactory Bulb of a Mouse 24 days old. {Highly
magnified. Golgi. KoUiker, II.)

C, Collaterals ; C;^ glomeruli ; M, mitral cells; J/', large brush cell ; .172, small
ditto ; n, neuraxon.

by many irregular fibres, giving it the character of
a molecular layer, and containing the so-called ^nitral
nerve cells ; (4) a nuclear layer composed of small
cells ; (5) a layer of longitudinal nerve fibres ; (6)
the neuroglia forming the central substance. The

252 Elements of Histology.

connection of these mitral cells is indicated in Figs. 157
and 158. One or two processes pass horizontally and
an axis-cylinder process passes through the nuclear
layer towards the layer of longitudinal nerve fibres.
One conspicuous process passes towards the glomeruli
and, entering one of the masses, forms a dendritic
clump. Similarly axons from the olfactory cells in the
nose pass to these glomeruli and form dendritic clumps.
These glomeruli are definite localities where connec-
tions are established between cells of the olfactory
bulb and the olfactory mucous membrane.

25.

CHAPTER XX.

THE CEREBRO SPINAL GANGLIA.

207. The ganglia connected with the posterior
roots of the spinal nerves, and with some of the
roots of the cere-
bral nerves — Gas-
serian, otic, genic-
n 1 a t e, ciliary,
Meckel's ganglion,
the ganglia of the
branches of the
acoustic nerve, the
submaxillary gan-
glion, etc. — possess
a capsule of fibrous
connective tissue
continuous with the
epineurium of the
afferent and efferent
nerve trunks (Fig.
159). The interior
of the ganglion is
subdivided into

smaller or larger
divisions, contain-
ing nerve bundles
with their perineu-
rium, or larger and
smaller groups of

c'an.a'lion cells In Fig- 1j9— Spinal Ganglion of the Lumbar

^, ° . , '■ ,. Region of a Puppy. {KoUiler, II.)

the spinal ganglia c, Ganglion with its cells and their axons; Bp,
fVlpop latter ^''^^ posterior; Ita, anterior branch ; M, motor ; S,

are

sensory root.

254

Elements of Histology.

generally disposed about the cortical part, whereas
the centre of the ganglia is chiefly occupied by
bundles of nerve fibres.

208. The ganglion cells differ very greatly in size —

YVj.. Ii30.— Transverse Section of the Spinal Cord of a Chick of the 9th day
of incubation. {Afttr Ramon y Cajal, from Quain's " Aimtomy.")

A, Axons— anterior root fibres— issuing from large ganglion cells of anterior
horn. C : B, posterior root fibres passing from the bipolar ganglion cells (/), O
of the spinal arangliou into the posterior white column Z>. where they bifur-
cate to become longitudinal ; e,f,g, collaterals from these fibres : b, fibres of
anterior white column in cross-section.

some being as big, and bigger, than a large multipolar
ganglion cell of the anterior horn of the cord, others much
smaller (Fig. 162). Each cell has a large oval nucleus,
including a network with one or two large nucleoli.

Cerebrospinal Ganglia.

255

Its substance shows a distinct fibrillation. Each cell
of the spinal ganglia in man and mammals is }inipolar
(Fig. 1G2), tiask- or pear-shaped, and invested in a
hyaline cajisule, lined with a more or less continuous

Fig. 161. — From a Longitudinal Section tlirougli the Gasseiian Ganglion of
the Calf. {Koinier, //.)

layer of nucleated endothelial cell plates. The single
process of the ganglion cell is finely and longitudi-
nally striated, and is an axis-cylinder process. Im-
mediately after leaving the cell body it is much
convoluted (Retzius) ; it is then covered with a
medullary sheath, and so becomes a medullated nerve
fibre. The capsule of the ganglion cell is continued
on the axis cylinder process, and, farther on, on the

256

Elements of Histology.

meclullated ner\'e fibre, as the neurilemma ; the

endothelial plates of the capsule pass into the nerve

Fig. 1(32. — Large and Small
Ganglion Cell of the Ganglion
Gasseri of RabVdt. (A'ei/ and
Retzhts.)

The axis cylinder, after leaving the
cell, becomes convoluted and
transformed into a medullated
nerve filire. which divides into
two medulLited fibres.

Fig. 163.— Lsolated Ganglion Cell
of Spinal Ganglion of Toad.
{Key and Retzius.)

The axis cylinder process becomes
transformed into a medullated
nerve fibre. The capsule of the
cell IS prolonged as the neu-
rilemma of the nerve fibre.

corpuscles linin^ the neurilemma, their number greatly
diminishing (Fig. 162).

209. In the rabbit this medullated nerve fibre at
its first node of Ranvier, which is not at a great dis-
tance from the ganglion cell, divides into two medul-
lated nerve fibres in the shape of T ; one branch

Cer ebr 0-spina l Ga ngl I a. 257

passes to the cord as a posterior root fibre, the other
to the peripher}^ (^ig- 1(^3). In man, this T-shaped
division has also been observed by Retzius, but,
though liighly proljable, it cannot be said to have
been actually pro\ed that in rabbit or man every
axis-cylinder process shows this T-shaped division.
Retzius obser\'ed this T-shaped division also in the
Gasserian, geniculate, and ^■agus ganglia in man.

The ganglion cells are not unipolar in all cerebral
ganglia ; in the ciliary and optic ganglia there are
ganglion cells which are multipolar.

210. Numerous ganglia of microscopic size are to
be found in the submaxillary (salivary) gland : they
are of ditferent sizes, and are in reality ganglionic
enlargements of larger or smaller nerve bundles.
Each ganglion is invested in connective tissue con-
tinuous with the perineurium, and the ganglion cells
are unipolar, and of the same nature as those described
above, each cell being possessed of an axis-cylinder
process, which becomes soon a nerve fibre. At the
back of the tongue there are similar small micro-
scopic ganglia.

258

CHAPTER XXI.

THE SYMPATHETIC SYSTEM.

211. The sympathetic nerve branches exactly re-
semble the cerebro-spinal nerves in their connective-
tissue investments (epi-, ])eri-, and endoneurium)^ and

Fig. 164.— Sympathetic Nerves. (Atlas.)

A, Small Imndle invested in an endothelial sheatli, iierineurium ; b, one
raediillated and three non-medullated nerve flbres of various sizes; the
largest shows division ; c, two varicose nerve flbres.

in the arrangement of the fibres in bundles (Fig. 164, a).
Most of the nerve fibres in the bundles are non-
medullated or Remak's fibres (Fig. 164a), each being
an axis cylinder invested in a neurilemma, with

5 J -MP A TH E TIC SyS TEM.

259

oblong nuclei indicative of nerve corpuscles (Fig.
1G4, b). But there are some meJullated nerve fibres
to be met with in each bundle, at least, of the
hirger nei"ve trunks. These in some cases show
the medullary sheath more or less discontinuous,
and "with a vari-

cose outline (Fig.
lG-1, c), owing to
a uniform local
accumulation of
fluid between it
and the axis cyl-
inder. The small
or microscopic
bundles of nerve
fibres possess an
endothelial (peri-
neural) sheath.
The small and
large branches
always form
plexuses.

212. The gan-
glia of the sym-
pathetic chain
(Fig. 16 5)— lateral
gancjlia, as also
the further sym-
pathetic ganglia
— the collateral
ganglia like the

' - t-'^^ ;^;"' ^^;> /r.% ■

Fig. 164a.— Cross-Section through part of Branch
of the Splenic Nerse of the Ox, showing
bundles of non-medullated or Remak's fibres
in cross-section ; the nerve fibres being com-
posed of fibrillK appear granular in cross-
section ; the nuclei here shown belong to the
neurilemma of the fibres. {Kolliker, II.)

semilunar and the

cardiac ganglia, and the peripheral ganglia, like those
on and in the abdominal viscera, are microscopic
in size, but possess in a general way the same structure
as the cerebro-spinal ganglia. The ganglion cells are
bipolar, or more commonly multipolar. Such are the

26o

Elements of flisroLOGV.

microscopic ganglionic enlargements on many of the
sympathetic nerve l)ranclies in the thoracic and
abdominal organs.

Thev occur in some organs very numerously — e.g.
,■7,,^,,^ alimentary canal,

urinary bladder (Fig.
166 and Fig. 167),
respiratory organs,
salivary glands — and
are of all sizes, from
a few ganglion cells
placed between, or
laterally to, the nerve
tibres of a small bundle,
to oval, spherical, or
irregularly - shayyed
masses of ganglion
cells placed in the
course of a large nerve
bundle, or situated at
the point of anasto-
mosis of two or more
nerve branches ( Fig.
167).

213. The fjanglia
in connection with the
plexuses of nerve
branches of the heart,
the cjanwlia in the
plexus of non-medul-
lated nerve tibres ex-
isting between the
longitudinal and cir-
cular coat of the exter-
nal muscular coat in
the aliuientary canal, known as the plexus myen-
tericus of Auerbach, the ganglia in the plexus of

fig. 165.— Sixth Ganglion Thoracicuni of
the Left Sympathetic of the Rabbit.
(KoUiker, //.)

Re, Rami communicantes ; S, lirauch of
sranslion containing two coarser and
several finer fibres: Spl, srlanchnicus ;
T, sympathetic trunk; 3, ganglion cells.

Si -MPA THE TIC SVS TEM.

26t

nerve Blanches of tlie submucous tissue in the
aliiuent;iry canal, known as Meissner's plexus (Fig.
172), the ganglia in the nervous plexuses in the

Fig. 166.— Group of Ganglion Cells interposed in a Bundle of Sympa-
thetic Xerve Fibres ; from the Bladder of Rabbit. (Handbook.)

outer wall of the Vjladcler, in the bronchial wall, and
in the trachea, and lastly the ganglia in connection

Fig. 1G7. — Small Collection of Ganglion Cells along a small Bundle of
Sympathetic Nerve Fibres in the Bladder of Rabbit. {Atlas.)

Each gangliou cell possesses a capsule. Tlie substance of the ganglion cell is
prolonged as the axis cylinder of a nerve flljre.

with the nerves supplying the ciliary muscle of the
eye, all belong to the sympathetic .system.

262

Elements of Histology

The ganglion cells (Fig. 170) are of very different
sizes, each possessing a large oval or spherical nucleus
with one or two nucleoli. Their sliape is spherical or
ova], flask -shaped, club-shaped, or pear-shaped ; they

Fig. 168.— Microscopic Ganglion in the Submaxillary GlaudofDog. i^AtUs.')

c. Connective tissue surrounding tlie ganglion : g, tlie ganglion cells with their
capsule ; n, nerve fibres.

possess either one, two, or more processes, being uni-,
bi-, or multipolar. The cell is invested in a capsule
lined with nucleated cells, both being continued on
the processes as neurilemma and nerve corpuscles
respectively.

214. By the aid of Golgi"s method it has been
definitely established (Golgi, Ramon y Cajal, Retzius)

Sympathetic System. 263

that, like the ganglion cells in the cord, the cells in
the ganglia of the sympathetic system possess one
axis - cylinder process, axon or nenraxon, which
remains unramified (R^Diun y Cajal, Van Gehuchten,

Fig. 100.— Plexus of Auerbacli iu Rectum of Toad. {Atlas.)
n. Xerve branches ; g, ganglion cell.

L. Sala. Von Lenhossek, Kolliker), though sometimes
it is possessed of nodose swellings (Fig. 171). It
passes into the periphery as a non-medullated
fibre (as, for instance, the non-medullated fibres
passing from the lateral ganglia of the sym-
pathetic back to the spinal nerves as the grey
ramus communicans) ; or as a medullated fibre
(as for instance, the medullated fibres passing from
the ciliary ganglion into the ciliary nerves). The

264

Elements of Histology.

2)ost-ganglionic fibres of Langley are fibres which
originate as the neuraxon of a sympathetic gan-
glion cell (in the lateral, collateral or peripheral
ganglia, as the case may be), and hence pass into

muscle (wall of
intestine, blood-
vessels, the viscera).
The ganglion cells
in the microscopic
peripheral ganglia
are also multipolar,
although there oc-
cur amongst them
bi- and unipolar
cells (Ramon y
Cajal, Dogiel, Kol-
liker).

Besides the
neuraxou or axon
the sympathetic
ganglion cells pos-
sess ramifying pro-
cesses - — dendrites,
which resolve them-
selves like those of
the cells of the grey
matter of the cen-
tral nervous system
into fine fibres,
some of them form-
ing more or less
distinct arborisa-
tions or dendrons
(Fig. 171). An
interesting relation exists between the medullated
nerve fibres which pass into a sympathetic gan-
glion from a spinal nerve [motor fibres passing from

Fig. 170.— Synipatlietic Gauglion Cell of Man.
(Key and Itetzius.)

The arnnarlion cell ii^ iiniltiiiolar : each proce.-s re-
ceiving a iieiirileiunia from the eapsiile of the
cell beeouies a iion-inediiUated aerve fibre.

Sv^'ifPA THE TIC SyS TEM.

265

anterior roots, as also sensory fibres from the j)osterior
roots and spinal ganglia], as, for instance, those
passing from the motor roots by the white rami com-
miinicantes into the
lateral and farther
into the collateral
ganglia, i.e. the
free - i/anc/ lionic
fibres of Langley ;
these fibres ter-
m i n a t e (Van
Gehuchten, L,

Sal a, Dogiel, Von
Lenhossek) as fine
ramifications be-
tween and around
the ganglion cells, or
they form curious,
more or less dense,
convolutions and
plexus surrounding
the body of the
ganglion cell —
circ II m c ellul a r
plexus^ as is shown
in Fig. 173 (Kol-
liker).

215. By the
observations of
Beale, Arnold, Axel,
Key and Retzius, it
was known that in

the ganglion cells of the sympathetic nerves of the
frog, the ganglion cell substance passes on as a straight
neuraxon wdiich continues its course peripherally as a
non-medullated nerve fibre surrounded by a nucleated
sheath or neurilemma — continued from the capsule of

Fig. 171. — Three Multipolar Ganglion Cells
with their Axon, n. From the Ganglion
Semilunare of Dog one day old. {Kolliker,
II.)

266

Elements of Histology.

the ganglion cell. This straight process is entwined by
a thin spiral fibre which, farther away from the body of
the irancvlion cell, is a medullated fibre ; it ramifies
on the substance of the ganglion cell (Fig. 174).

Fig. 172. — Group of Ganglion Cells from the Plexus of Meissner of a Puppy ;
amongst them a Multipolar and several Unipolar Cells. (Kolliker, II.)

Arnold, then Ehrlich and further Retzius (the last
two by ibjection of methylene blue into the blood-
vessels of the living frog) have shown this spiral fibre
(stained blue) to terminate on and around the sub-
stance of the ganglion cell as an arborisation ; a
condition which occurs in many parts of the central
nervous system (anterior grey cornu, cerebellum,
sympathetic ganglion cells, previously mentioned,

SVMPATHETIC SvSTEM.

267

etc.), that is to say, the l)odj of a ganglion cell
becomes surrounded and ensheathed as it were by a
dendron of an afferent nerve fibre, the dillerence being

Fig. 173.— Circunicellular Plexus
from tlie Gauglioii Cervieale
Supremuin of Calf. (KoUiker,
II.)

Fig. 174. — Sympathetic Ganglion
Cell of Frog, showing the
straight process and the spiral
fibre ; the latter becomes a
metlullated fibre, {Key and
Eetzius.)

tliat in the sympathetic cells of the frog this afferent
(inedullated) fibre entwines as the spiral fibre the
efterent axon (non-mednllated) of the ganglion cell.

26S

CHAPTER XXri.

GEXERAL COXSIDERATIOXS AS TO THE ANATOMICAL
COXSTITUTIOX AND NATURE OF THE NERVOUS
SYSTEM.

216. We are now in a position to summarise the
general structure and relation of the constituent
parts of the nervous system.

The nervous system consists of nerve cells or
ganglion cells and of nerve fibres — the cells forming
the centres, the fibres the conducting paths. The
ganglion cells form an integral part of the central
nervous system — brain, medulla, and cord — as also of
the ganglia of the sympathetic and of the peripheral
collections and special nerve end-corpuscles in the
various viscera and in the sense organs. The ner%e
fibres, on the other hand, are all, as far as at present
known, axons or neuraxons — that is to say, pro-
longations of the substance of the ganglion cells : by
these axons near and distant centres, or ganglion
cells, are brought in relation to one another, as also
by the peripheral terminations of the axons with
muscles, skin, mucous membranes, glands, etc. The
whole nervous svstem mav be considered as consistincr
of a collection of units (Ramun y Cajal), each such unit
being called a neuron (Waldeyer). A neuron, then,
is a ganglion cell with all its processes, axon or axons,
and dendrites — be they short or long — as well as all
the ramifications and terminations of such axons and
dendrites. While of many parts of the nervous

SPINAL OAN&LION CELL

MUITI POLAR CELL
OF ANT. HORN

1 SMN

Fie. 175.— Sr-heme of Relationship of Cells and Fibres of Brain and Cord,
° prepared by Halliburton and Mott. (From Kirke's " Physiology.")

AB, Middle line tlirough brain medulla and cord; pyr. ijyraniidal ganglion cell
of the cerebral cortex in the Uolandic area ; ax, axon of this same gangl on
cell, a collateral of this axon passes in the cr)rpus callosum (c. call.) to
terminate in the cortex of the other cerebral hemisphere ; c.stk., is the corpus
striatum : K.a.c, s-'anulion cell in the cerebral cortex (nerve unit of associa-
tion of Cajali, around which arborises an axon coming from a ganglion cell
of the optic thalamus ; o.th., thalamus opticus ; f, mesial hllet ; s.g., nucleus
gracilis of the meduUa ; i. a., axon ..f a ganglion cell in the nucleus f-'rac Us.
passing to the other side as an internal arcuate hbre; v, ganglion cell ot
Purkinje in the corte.x of cerebellum ; p.ax., its axon ; g.m., succession ot
cell stations (units) in the erey matter of the cord to the optic thalanu.

qc.fi,lc. Leu.

clcuo ocuIoTaoLorU'.S

1 T Cbrtci CCrcV:

Ficr 176.— Diagram of the probable Connections and Relations of the Optic
Xerve Fibres between the Ganglion Cells of the Retina and the Cortex
Cerebri. {After Schdfcr.)

Between the ganffliou cells of the retina and the lateral corpus geniculatum
or anterior corpus quadrit:eminura respectively is the rirst neuron ; between
the corpus nuadritrennnum anterius and the nucleus oculomotorms is a
second neuron, so also between the lateral corpus ireniculatum and the cortex
cerebri ; between the nucleus oculomotorius and the cortex cerebri on the
one hand and the axons of the tranarlion cells of the nucleus oculomotorms
by the nerve tibres constituting the ocuhiraotor nerve terminating in the
muscles supplied by this on the other hand is a third neuron.

Of the Nervous System. 271

system the constituent units or neuronic are under-
stood and traced out, tliere are other parts in which
the constituent neurons have not been as yet fully
worked out. Of the former it has been established
by the new methods that the older theory as to
anatomical continuity between different parts of the
nervous system — i.e. the units or neurons — is not
correct ; but, on the contrary, that the processes
(axons as well as dendrites) of one ganglion cell form
only contact with those of others, as also with peri-
pheral organs, ivifhout direct contimdty (Fig. 175).
Thus, for instance, it has been shown that there
exists no direct or uninterrupted continuity between
a motor (pyramidal) ganglion cell, say of the limb
centres in the grey cortex of the brain, and the nerve
fibres which terminate as motor end-plates or
dendrons in the muscles of the limbs, but that the
whole of this path is made up of a succession or chain
of neurons or units ; and similarly beginning with a
dendritic nerve termination in the epithelium of the
skin of the limbs up to the arborising termination of
nerve fibres in the sensory centres of the grey cortex
of the brain, we have no anatomical continuity, but a
succession or chain of units or neurons.

In each case, a ganglion cell with its axon, in-
clusive of its collaterals, and its dendrites, is possessed
of arborisations or dendrons which do not form con-
tinuity with, but are only in close contiguity to, the
arborising axons, or dendrites respectively* of another
unit or neuron (synapsis). A further point that
has been established is this, namely, all nerve fibres,
be they medullated or non-medullated, afferent or
efferent fibres, be they of a relatively short course
— e.g. those beginning and ending within the central
nervous system — or do they extend over long dis-
tances like those passing out from, or passing into,
the cord, medulla, and brain as spinal and crainial

272 Elements of Histology.

nerves respectively, are, in reality, axons or direct
prolongations of the substance of ganglion cells,
which, after a longer or shorter course, terminate
as arl>orisations or dendrons in the periphery or in
the central nervous system, as the case may be.

217. We will illustrate, by selecting a few from
the many known examj)les, the nature and extent
of such neurons : —

(1) A motor neuron of the grey cortex cerebri con-
sists of the following parts (Fig. 175) : («) the cell body
of a pyramidal ganglion cell ; (6) its dendrites, with
their arborisations in the grey cortex ; {c) the axon
given off as the median basilar process and its col-
laterals becoming medullated nerve fibres of the white
substance of the cortex, passing further through the
internal capsule, the pons, the anterior pyramidal
tract of the medulhi, the direct or crossed pyramidal
tract of the cord, and forming the tinal arborisations
or dendrons of them and their collaterals in the
anterior cornu around the body and dendrites of the
ganglion cells in the grey matter of the cord.

(2) A motor neuron of the grey anterior cornu
of the cord consists of : («) a ganglion cell in the
anterior grey cornu of the cord ; (6) its dendrites
terminatinix in f^itu as arborisations or dendrons;
(«:) the axon passing out as a medullated nerve fibre
through the anterior root, and further through a
spinal nerve, and terminating finally in the periphery
in a striped muscle fibre as a dendron — i.e. the nerve
end-plate.

(3) A sensory neuron : (a) a ganglion cell of the
spinal ganglia ; {h) the afferent nerve fibre — i.e. the
distal portion of the T-shaped division of the axon,
coming from the periphery — e.g. the skin — by way of
a medullated nerve fibre of a spinal nerve ; in the skin
it terminates or originates either in or around special
nerve end-corpuscles or as ramifying fibrillae in the

Of the A^F.Ri'ous System.

273

epithelium of tlie smface ; (c) the efferent fibre —
i.e. the proximal branch of the axon of the spinal

•/•if"'^^^Nkf^)i /V---"-'

Fig. 177.— Diagrniu showing the Mode of Termination of Sensory Nerve
Fibres in 1, the auditory, 2, the gustatory, and 3, the tactile sense
organs of vertebrata. Each of these represents one sensory neuron.
(After Retzius,frorii Qnuin.)

ganglion cell passes into the cord as a medullatecl
fibre by way of a posterior root and farther into the

274

Elemexts of Histology

posterior white colunni ; it or its collaterals finally
enter into the grey matter of the cord or pass on into

the nucleus gracilis of the
bulb, terminating as dendrons
around or close to a ganglion
cell (body or dendrites) in
such grey matter (Fig. 175).

(4) A neuron of a special
sense (Figs. 177, 178): (a)
the fjcinolion cell in the san-
glion cell laj^er of the retina ;
(J)) its dendrites terminating
as arborisations or dendrons
in the inner molecular layer ;
(c) the axon passing out in
the opposite direction and
forming a fibre of the nerve
fibre layer and further pass-
ing into the optic disc and
optic nerve as a niedullated
fibre, pursuing its course as
such through the chiasma and
optic tract, and terminating,
finally, in an arborisation
around cells in the corpus
geniculatum or the anterior
corpus quadrigeminum (Fig.
176).

Fig. ITS. — Diagram of the Ar-
rangement of the Sensory
Xerve Fibres in the Olfactory
Organ and Bixlb. {After
Eetzius, from Quain.)

n, Neuraxon : (il. glomerulus in
the olfactory bulb. This repie-
seuts two consecutive neurous.

275

CHAPTER XXIII.

THE TEETH.

218. A HUMAN tootll,

sists (Fig. 17!)) of (a) the

(b) the denfine forming
tiie bulk of the whole
tooth, and surrounding
the pulp cavity both of
the crown and fangs,

(c) the pulp cavity, and
{d) the ceinent, or crusta
petrosa. The cement
covers the outside of the
dentine of the fang or
fangs, the enamel covers
the dentine of the crown.
The cement is covered
on its outside by dense
fibrous tissue acting as
a 27eriosteuni to it, and
is fixed by it to the
inner surface of the
bone forming the wall
of the alveolar cavity.

219. The enamel
(Fig. 180) consists of
thin microscopic pris-
matic elements, the
enamel prisms placed
closely, and extending
in a vertical direction

adult and milk-tooth, con-
enamel covering the crown,

Fiji 17*> — Loii„Mtu(linal Section
till oUj^h the Piceniolai Tooth of Cat.
{Waldeyer, in Strieker's Manual.)

a, Enamel ; 6, dentine ; c, crusta petrosa;
c/ande, periosteum ;/, bone of alveolus.

276

Elements of Histology.

from the surface to the dentine. When view^ed in
transverse section, the enamel prisms appear of a
hexagonal outline, and are 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

Fig. ISO.— Enamel Prisms. (Kdllikc,:)
A, In longitiuliual view ; B.in eross-section.

into bundles, which are not quite parallel, but more
or Jess slightly overlap one another. On a longitudinal
section through a tooth, the appearance of alternate
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
of lime salts — phosphate, carbonate, and fluoride of
calcium — with corresponding magnesium salts.

In young teeth the free surface of the enamel
is covered with a delicate cuticle (the cuticle of
Nasmyth), a single layer of non-nucleated scales.
In adult teeth this cuticle is wanting, having been
rubbed off.

Teeth.

^11

220. The €l«'iitiii«» is tlic principal part of the hard
substances of the tooth, it forms a coniph^te invest-
ment of tlie pnl[) cavity
of the crown and fang,
being sUghtly thicker in
the former than in the
latter region. The den-
tine is composed of (Fig.
181): (l)a homogeneous
matrix ; this is a re-
ticular tissue of fine
tibrils impregnated with
lime salts, and thus re-
sembling the matrix of
bone ; (2) long fine
canals, the dentinal
canals or tithes, passing
in a more or less spiral
manner, and vertically
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 smaller as
they approach the outer
surface of the dentine.
Each canal is lined with

a delicate sheath — the Fig. ISl.— From a Section through a
7 ,• 7 7 ,7 T •! Canine Tooth of Man. (Waldeyer, in

dentinal, sheath. ^ Inside Strieker's Mamud.)

the tube is a fibre, the ((.Crustapetrosa, with large bone corpus-
7 ,• 7 /•/ T 1 ties; b, interglobular substance: c,

dentinal JlOre, a solid dentinal tubules.

elastic fibre originatinsf

with its thickest part at the pulp side of the dentine
from cells lining the outer surface of the pulp, and
called odontoblasts.

278

Elements of Histology.

On the outer surface of tlie dentine, both in the
region of the enamel and crusta petrosa, the dentinal
tubes pass into a layer of intercommunicating irregular
branched spaces, tlie interglohular spaces of Czermak,

Fi"^. 18'2.— From Section through the Pulp and Dentine of Tooth of Guinea-
pig. {Photograph, highly magnified.)

Pulp tissue with vessels in cross-section; o, odontoblasts; d, dentine acci-
' dentally detached from odontoblasts.

or the granular layer of Purkinje. These communi-
cate with spaces existing between the bundles of
enamel prisms of the crown, as well as with the bone
lamina of the crusta petrosa of the fang. The inter-
o-lobular s})aces contain each a branched nucleated cell.
The dentinal fibres anastomose with the processes of
these cells. The inrrempntal lines of Salter are lines
more or less parallel to the surface, and are due to

Teeth.

279

imperfectly calcilied dentine— the inter (jlohuhir anb-
stance of Czerniak. The lines of Schreger are curved
lines parallel to the surface, and are due to the optical
eflect of simultaneous curvatures of dentinal fibres.

Fig. 183.— Early Development of Tooth. (Photograph Inj ^[,•. A. Pringle.)

l.Tonfrue in cross-section ; 2, bone of jaws; 3, rudiment of enamel organ and
tooth papilla, the former still connected with the surface epithelium.

221. The eeiiieiit is osseous substance, being
lamellated bone matrix with bone corpuscles. There
are no Haversian canals.

222. The pulp is richly supplied with blood-
vessels, forming networks, and extending chiefly in
a direction parallel to the long axis of the tooth.
Xumerous medullated nerve fibres forming plexuses
are met with in the pulp tissue ; on the outer surface

2 So Elements of Histology.

of the pulp they become non-mediillated 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.

223. On the outer surface of the pulp — i.e. the
one in contact ^vith the inner surface of the dentine —
is a layer of nucleated cells, which are elongated, more
or less columnar. These are the odontoblasts proper
(Fig. 182). 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 a
petrification of this increment, according to others
by a secretion by the cell of the dentinal matrix.
Waldeyer, Tomes, and others consider the odonto-
blasts proper concerned in the production both of the
dentinal matrix and dentinal iibres. The odontol)lasts
proper and the spindle-shaped cells are continuous
with the branched cells of the pulp matrix.

224. Devolopiiieiit of teetli. — The first rudi-
ment of a tooth in the embryo appears as early as the
second month. It is a solicl cylindrical prolongation
of the stratified epithelium of tlie surface into the
depth of the embryonic mucous membrane. Along the
border of the jaws the epithelium appears thickened,
and the sul>jacent 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 is the
Y\\([\mQ\\t oi the enamel organ. While continuing to
grow- towards 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

Teeth.

28r

of the enamel organ continues to grow towards the
depth, it grtidually embraces the tooth ])apilla in the
shape of a cap — the enamel caj) (Fig 183). During
this time the connection between the surface epithe-

184. — From a Section tlirough the Tooth and Lower Jaw of Fatal
Kitten.

a, Epithelium uf the free surface of the gum {b, the raucous membrane of same;
c, spongy bone of jaw: rf, papilla of tooth; e, odontoblasts:/, dentine; </,
enamel ; h, membrane of Nasmy th ; /, enamel cells ; j, middle layer of enamel
organ; A, outer layer of enamel organ.

Hum and the enamel cap becomes greatly thinned out
and pushed on one side, owing to the growth of the
enamel cap and papilla taking place chiefly to one side
of the original dental groove.

225. The enamel cap (Fig. 184) is composed of
three strata — an inner, middle, and outer stratum.
The inner stratum is a layer of beautiful columnar
epithelial cells — the enamel cells; they were originally

2«2

Elements of Histology

continuous with tlie deep layer or the columnar cells
of the surface e[jithelium. The middle stratum is the
thickest, and is of great transparency, owing to a

\\ '■

Fig. 185.— From a Vertical Section through Foetal Tooth of Dog. (^Atlos.")

a. Spindle-shaped cells of tbe tooth pulp; b, the layer of O(lontol)lasts : c, the
ludst recently formed layer of dentine; cl, older dentine; d, the layer of
enamel cells; C'J, the enamel ; e, outer cells of enamel organ ; /, tissue of the
tooth sac.

transformation of the middle layer of the epithelial
cells into a spongy gelatinous tissue, due to accumu-
lation of fluid between the epithelial cells of this

Teeth. 283

layer, and to a reduction of their substance to thin
nucleated plates, apparently branched. The outer
stratum consists of one or more layers of polyhedral
cells, continuous on tlie one hand with the surface
epithelium by the bridge of tlie rudiment of the
enamel organ, and on the other Nvitli the enamel cells.

226. The foetal tooth papilla is a vascular em-
bryonic or gelatinous tissue ; on its outer surface a
condensation of its cells is soon noticeable into a more
or less continuous stratum of elongated or columnar
cells, the odontoblasts.

227. Both the dentine and enamel are developed
in connectiou with the odontoblasts and the enamel
cells (Fig. 185) ; the former produce the dentine
on their outer surface, while the latter, i.e. the
enamel cells, deposit the enamel on their inner
surface ; thus it happens that the enamel is in
close contact with, and on the outside of, the
dentine. The dentine and enamel are de]josited
gradually and in layers. At first they are soft
tissues, showino- a vertical differentiation corre-
sponding to the individual cells of the enamel cells
and odontoblasts respectively. Soon lime salts are
deposited in them, at first imperfectly, but afterwards
a perfect petrification 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 enauiel being
situated next to the enamel cells, that of the dentine
next to the odontoblasts (Fig. 186). The amount
of enamel and dentine formed is always greatest
in the upper part, i.e. that corresponding to the
future crown. The milk teeth, while continuing
to grow, remain buried in the mucous membrane
of the gum, till after hirth their proper time
arrives, when by active growth and enlai'gement
they break through the gum. During this process

:84

Elements of Histology.

the enamel of the crown remains co\'ered, i.p. carries
with it the inner stratum of the enamel organ only,
i.e. the enamel cells (Fig. 186, ec) ; these, at the
same time as the surface of the enamel increases.

Fig. 18(3.— From a Section through the developing Tooth of Kitten.
(Photograph, higTibj magnified.)

p, Pulp of the tooth papilla; o, layer of odontoblasts ; d, dentine ; e, enamel ; ec,
enamel cells; w, middle layer of enamel organ; oit, outer layer of enamel
organ.

become much flattened, and, finally losing their nuclei,
are converted into a layer of transparent scales, the
membrane or cuticle of Ncismyth (Fig. 18-4, It).

228. Long before the milk tooth breaks through
the gum, there appears a solid cylindrical mass of
epithelial cells extending into the depth from the
orifdnal connection between the enamel organ and the

Teeth. 285

epitlielium of tlie surface of the gum mentioned above.
This new epitheh'al 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
same changes of growth as the enamel organ of the
milk tooth did in the first j^eriod 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.

Mummery has shown that the dentine contains
petrified fibres and traljecuhe, which are direct con-
tinuations of the pulp tissue, and are comparable to
the fibres of Sharpey in bone,

286

CHAPTER XXIV.

THE SALIVARY GLANDS.

229. The salivary glands, according to tlieir

structure and secretion, are of the following kinds : —

(1) True salivnrif (Fig. 187), s^?'o?<5, or albuminous

^v~^^^/i'!u

Fig. 187. — From a Section througli a Serous or True Salivary Gland ; part
of the Human Submaxillary. {Atlas.)

a. The gland alveoli, lined with the alhuniinous " salivary cells " ; b, intralobular
duct cut transversely.

glands, such as the parotid of man and mammals,
the submaxillary and orbital of the rabbit, the sub-
maxillary of the guinea-pig. They secrete true, thin,
watery saliva.

Salivary Glands,

287

230. (2) Jfncons (/lands. Of these there are several
varieties. In the first phxce, there is the picre mucous
gland (Fig. 188), represented by the subUiigual gland
of tlie guinea-pig and many of the simple buccal glands
of the mouth. In the next place^ the secreting

Fig. 188.— From a Section through the Orhital (mucous) Gland of Dog.
Quiescent State. (Heidenkain.)

The alveoli are lined witli trans^iiarent " mucous cells," and outside these are the
demilunes of Heidenhain.

alveolus may contain other cells than true mucous
cells (mucous (/lands ivith deniilunes). There may be
comparatively few of this second variety of cell in the
alveolus, and such cells may have an entirely peripheral
position in the alveolus, and, being thus adapted in shape
to the globular character of the alveolus, may become
flattened between the basement membrane and more
centrally disposed mucous cells, so that in section they
have the appearance of half-moon-sha])ed masses,
and are hence called dem.ilutie cells. The alveolus
may contain few of these demilune cells, as in the
orbital or submaxillary gland of the dog (Fig. 188), or

288

Elements uf Histology

a more or less complete ring of such cells may exist,
as in the submaxillary gland of the cat (Fig. 190).
Finally, this second variety of cell may be so largely

Fig. 1S9.— Section tliruugli a Pure Mucous Gland in the Resting State. The
nuclei are seen flattened at the iieripliei-y of the alveoli. The cells are
not deeply stained. There are no demilune cells. (Microphotograph.)

represented as to cause the gland to be described as
belonging to a separate variety — mixed glands.

231. (3) Mixed salivary, muco-salivary, or sero-
mucoiis glands. Here some alveoli may be entirely
serous, some may belong to one of the varieties of
so-called mucous glands. Sometimes the alveoli may
contain both serous and mucous cells similarly
situated around the lumen, so that we may have
actually a mixed salivary alveolus (Fig. 191). It
is justitiable to assume that demilune cells really

Salivary Glands.

289

represent occasional serous cells present in a mucous

alveolus, and these cells occupy a peripheral position.

In addition to the three salivary glands— parotid,

submaxillary, and sublingual — there are in some

Fig. 190.— Section througli the Submaxillary Gland of Cat. The alveoli are
in nearly all cases surrounded by a dark rim, composed of demilune
cells. More deeply-stained masses consisting of ducts are also seen.
{Microphotograph. )

cases, as in the rabbit and the guinea-pig, two minute
additional glands, one intimately joined to the parotid
and the other to the submaxillary, and both of the
nature of a mucous gland. These are the superior and
inferior admaxiUary glands.

232. The framework. — Each salivary gland
is enveloped in a fibrous connective-tissue capsule,
in connection with which are fibrous trabeculse and

290

Elements of Histology

septa in the interior of tJie gland, h\ 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

Fig. 191.— Section tlirougb a Human Submaxillary Gland. Nearly all the
alveoli consist of albuminous cells. There is also to be seen a fairly
large number of somewhat larger and less deeply-stained alveoli which
consist largely of mucous cells. (Microphotograph.)

to and from the gland by the hilum. The connective
tissue is of loose texture, contains elastic filjres, and, in
some instances more, in others less, numerous lymphoid
cells. In the sublingual gland they are so numerous
that they form continuous rows between the alveoli.
The connective-tissue matrix between the alveoli is
cliieHy rejDresented by fine bundles of fibrous tissue
and branched connective-tissue corpuscles.

Sal/vanv Glands. 291

•1X\. Tlio 4lii<'l*!i. — Following the chief duct of

tlio ij;l;in(l thi'oiii;h tho liilum into tlio interior, we s(;e
that it divides into several larne branches, according
to the number of lobes ; each of these takes up several
branches, one for each lobule. Following it into the
lobule, the branch is very minute, and is seen to take
up several more minute tubes ; all these tubes within
the lobule are the intrnlohidar chiefs or the salivari/
tubes of Pliiiger ; the bigger ducts being the inter-
lohu^ar, and, further, the interlobar ducts. Each of
the latter consists of a limiting membrana propi-ia,
strengthened, according to the size of the duct, by
thicker or thinner trabecuhe of connective tissue. In
the chief branches there is present in addition non-
striped muscular tissue. The interior of the duct is
a cavity lined with a layer of colunmar epithelial cells.
In the largest branches there is, outside this layer and
inside the membrana propria, a layer of small poly-
hedral cells.

234. The intralobular cliicts, or the salivary
tubes of Pliiiger, have each a distinct lumen or cavity,
which is lined with a single layer of columnar epithe-
lium, and outside this is a limiting mend)rana propria.
Each of the lining epithelial cells has a s})herical
nucleus in about the middle ; the outer half of the
cell substance shows very marked longitudinal stria-
tion, due to more or less coarse tibrilljc (see Fig. 187).
The inner half — i.e. the one bordering the lumen — is
granular, or oidy very faintly striated. The outline
of these salivary tubes is never smooth, but irregular —
i.e. the diameter of the tube varies from place to ])lace.

Not in all salivary glands do the epithelial cells
of the intralobular ducts show this coarse Hbrillation
in the outer part of their substance — e.g. it is
not })resent in the sublingual gland of the dog or
the guinea-pig.

235. The ends of the branches of the salivary

292 Elements of Histology.

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.

The last part of the duct which is in immediate
connection with the alveoli is the intermediate pcwt,
this being interposed, as it were, between the alveoli
and the salivary tube with librillated epithelium. The
intermediate part is much narrower than the salivary
tube, and is lined with a single layer of very flattened
epithelial cells, each ^vith a single oval nucleus ; the
boundary is formed by the membrana propria, con-
tinued from the salivary tube. The lumen of the
intermediate 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 intermediate 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 intermediate part , In
some salivary glands, especially in the mucous, this
neck is the only portion of the intermediate part
present — e.g. in the submaxillary and orbital glands
of the dog and cat, and in the sublingual of the
rabbit. In others, especially in the serous salivary
glands, as the parotid of man and mammals, the sub-
maxillary of the rabbit and guinea-pig, and in the
mixed salivary — as the submaxillary and sublingual
of man — there exists after the neck a long inter-
mediate part, which gives off several shorter or longer
branches of the same kind, all ending in alveoli.

236. The alveoli or aeiiii are the essential or
secreting portion 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

Salivary Glaxds. 293

of them are branclied. Generally several open into
the same intermediate part of a salivary tube. The
acini are much lari^er in diameter than the inter-
mediate ])art. and slightly larger, or about as large as
the intralobular ducts. But there is a difference in
this respect between the acini of a serous and of
a mucous salivary gland ; in the former the acini
are smaller than in the latter.

The membrana propria of the intermediate duct
is continuous with the membrana propria of the
acini. This is a reticulated structure, being in reality a
basket-shai)ed network of hyaline branched nucleated
cells (Boll). The lumen of the acini is minute in the
serous, but is larger in the mucous glands ; it is in
both glands smaller during secretion than during rest.

237. The epithelial cells lining the acini are called
the saUi-ary 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,
(i.) In the serous or true salivary glands, as parotid of
man and mammals, submaxillary of rabbit and guinea-
pig, the salivary cells form a single hiyer of shorter or
longer columnar or pyramidal albuminous cells, com-
posed of a reticulated protoplasm, and containing a
spherical nucleus in the outer part of the cell, (ii.)
In the mucous glands, such as the sublingual of the
guinea-pig, or the admaxillary of the same animal, the
cells lining the acini form a single layer of goblet-
shaped mucous cells, such as have been described
above. Each cell consists of an inner principal part,
composed of a transparent mucoid substance (contained
in a wide-meshed reticulum of the protoplasm), and of
an outer small, more opaque part, containing a com-
pressed and flattened nucleus. This part is drawn
out in a fine extremity, which, being curved in a
direction parallel to the surface of the acinus, is

294 Elements of Histology.

imbricated on its neighbours. In the case of tlie sub-
maxillary and orljital glands of the dog and the sub-
lingual of the rabbit, there exist, in addition to and
outside of the mucous cells lining the acini, but within

the membrana
propria, from
place to place
crescentic
1 > -r^ masses, being
the demilunes of
-. /: ^l) ': Q, Ileidenhain, or

; \; . ' Tl ■' ^^ the crescents of

■ • .' ^' , '7 . ^^- • ^ J ji>:; Gianuzzi (see
'i-^i-J- 'l-:'^ ' -^ -f Fig. 188). Each
0 ^ ^^ "^ V, _ '^ is composed of

>' '- A il-' -■;^^^ :: ^"1 several polyhe-
dral granular-

r--'(vi

\VT

^ - . -> ^ , •„^.-v lookmor cells,

\^>§^' ^ -^-r- ■ O ^^- each with a

Fig. 192.— From a Section through the Orbital spherical IIU-

Gland of Dog, after prolonged electrical Stimu- „i„„„ . j.i,p ppil^
lation. The acini are lined with small granular ^it;u^5 , tiic ccjio

cells. (Lavdovsid.) " at the margin

of the crescent
are, of course, thinner than those forming the middle.
Heidenhain and his pupils, Lavdovski and others,
have shown that, during prolonged exhausting
stimulation of the submaxillary and orbital of the
dog, all the lining cylindrical mucous cells become
ref)laced by small polyhedral cells, similar to those con-
stituting the crescents, while at the same time the acini
become smaller (Fig. 192). These observers 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 from the crescent cells. This
is improbable, since during ordinary conditions of secre-
tions there is no disappearance of the mucous cells as
such ; they change in size, becoming larger during

Salifakv Glands. 295

secretion, and tboir contonts are converted into perfect
mucus. It is prol)able that, on prolonged exhaustive
stimulation, the mucous cells collapse into the small
cells, seen by Heidenliain and his pupils.

238. (iii.) The acini of the sublingual of the dog
are again different in structure both from those of the
submaxillary of the dog and of the sublingual of the
guinea-pig, for the acini are there lined either with
mucous cells or with columnar albuminous cells, or
the two kinds of cells follow one another in the same
alceolus.

This gland is a sort of intermediate form between
the sul)lingual of man and the submaxillary of man
and ape (Fig. 191). These are the mixed or muco-
salivary glands. In these the great number of acini
are serous— ■i.e. small — with small lumen, and lined
with albuminous cells, whereas there are always present
a few acini exactly like those of a mucous gland. The
two kinds of acini are in direct continuity with one
another. In some conditions there are only very few
mucous acini 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 they form only a fraction of
the number of the serous acini. In the sublingual 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 acini
of the human gland are an oblique view of albuminous
cells lininof the acini at the transition between the
mucous and serous part of the same gland-tube.

239. The columnar salivary cells lining the acini
of the submaxillary of the guinea-pig in some condi-
tions show two distinct jjortioiis : an outer homogeneous
or slightly and longitudinally striated substance, and
an inner, more transparent, granular-looking part, and

296

Elements of Histology.

in this respect the cells resemble those of the pancreas.
{See pp. 330-2.)

240. Langley has shown (Fig. 193) that during
the period preparatory to secretion the cells lining
the acini of the serous salivary glands become en-
larged and tilled with coarse granules : during
secretion these granules become used up, so that the

Fig. 193. — Acini of Serous Gland. (Langley.)
A, At rest ; B, first stage of secretion ; c, prolonged secretion.

cell-substance grows more transparent, beginning from
the outer part of the cell and gradually advancing
towards the lumen of the acini. These granules may
be seen in the fresh gland, but reagents very rapidly
destroy them. Salivary glands hardened by the
usual reagents, though not themselves showing the
granules, may, however, present appearances corre-
sponding to the removal of the granules from the
outer zone of the alveolus. It is found that in
such cases the outer zone stains more deeply
(Fig. 102), an appearance frequently met with in the
pancreas.

AYhen the outer part of the alveolus is devoid
of granules, the alveolus is said to be active or
partially exhausted; when the granules reach practi-
cally to the outermost part of the cells, the alve-
olus is said to be resting. Under normal conditions

Salivary Glands. 297

secretion in the salivary glands never approaches ex-
haustion, though in the pancreas it is not uncommonly
the case.

241. Blood-vossels and lyiiiplialics.— The

lobules are richly supplied with blood-vessels. The
arteries break up into numerous capillaries, which
with their dense networks surround and entwine the
acini. Between the interalveolar connective tissue
carrying the capillary blood-vessels and the membrana
ju'opria of the acini exist lymi^h spaces surrounding
the greater part of the circumference of the acini
and forming an intercommunicating system of spaces.
They open into lymi-iliatic vessels accomjoanying tlie
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.

242. The iierve-braiiclies form plexuses in the
interlobular tissue. In connection with them are
larger or smaller ganglia (Fig. 168). They are very
numerously met with in the submaxillary, but are
absent in the parotid. Some ganglia are present in
connection with the nerve-branches surrounding the
chief duct of the suljlingual gland.

Pfliiger maintains that the ultimate nerve fibres
are connected with the salivary cells of the acini in
man and mammals, but this remains to be proved.

298

CHAPTER XXV.

THE MOUTH, PHARYNX AND TONGUE.

2-43. The jflaiids.— 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
U[)S, in the ]:)uccal 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 Ijack of the tongue, and in the
raucous membrane of the pharynx. The serous
glands are found in the back of the tongue, in close
])roximity to the parts containing the special organs
for the perception of taste — the taste goblets or buds
(see below). All the glands are very small, but
when isolated the}^ 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.

244. 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.

Mouth, Pharyxx and Tongue.

299

In man, all ducts are lined with a single layer of
columnar epitliclial cells, longer in the larger than
in the smaller ducts ; in mammals the epithelium
is a single layer
of polyhedral cells.
No fibril lation is
noticeable in the
epithelial cells. At
the transition of the
terminal ducts into
the acini there is
occasionally a slight
enlargement, called
the infundibuhtm ;
here the granular-
looking epithelial
cells of the duct
change into the co-
lumnar transparent
mucous cells lining
the acini.

245. The acini
of these glands are
identical with those
of the mucous glands
described above (Fig.
194) — e.g. the sub-
lingual gland as regards size, tubular branched nature,
the lining epithelium, and lumen.

In some instances (as in the soft palate and
tongue) the duct neir the opening is lined with
ciliated columnar epithelium. The stratified epithelium
of the surface is generally continued a short distance
into the mouth of the duct.

246. The serous glands at the root of tlie
tongue (von Ebner) differ from the mucous chiefly
in the epithelium, size, and lumen of the acini. These

Fig. 194. — Part of a Lobule of a Mucous
Gland iu the Tongue of Dog. {Atlas.)

«, Gland tubes (alveolii viewed in various
directions : they are lined with transparent
■'mucous ceils" ; d, duct lined with small
polyhedral cells.

300 Elements of Histology.

are of exactly the same nature and structure as those
of the serous or true salivary glands.

247. Saliva obtained from the mouth contains
numbers 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.

248. The mucous nionibrane lining the cavity
of the mouth consists of a thin membrane covered
on its free surface with a thick stratified pavement
epithelium, the most superficial cells being scales,
more or less changed into horn.

Underneath the epithelium is a somewhat dense
feltwork of fibrous connective tissue, with numerous
elavstic fibrils in networks. This part is the corium or
mucosa, and it projects into the epithelium in the
shape of cylindrical or conical papilla.

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 vivula.

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 suhmucosa. It is looser
in its texture, but it also is composed of fibrous con-
nective tissue with elastic fibrils. The glands are
here embedded ; adipose tissue in the shape of groups
of fat cells or continuous lobules of fat cells are here
to be met with. The large vascular and nervous
trunks pass to and from the sub mucosa.

249. Striped uiiiscular tissue is found in
the submucosa. In the lips, soft palate, uvula, and
palatine arches it forms a very conspicuous portion :

Mouth ^ Pharynx and Tongue.

301

namely, the sphincter orbicularis, with its outrunners
into the mucous membrane of the lips, the muscles of
the })alate, uvula (levator and tensor palati), and the
arcus palato-pharyngeus and palato-glossus.

250. The last branches of the arteries break up in

Fig. 195.— Section through the Tongue of Cat ; the Blood-vessels injected.
The lower part of the figure shows the injected muscular tissue, in the
middle part the mucous membrane with large vessels ; the ui)per part
shows the papillae filiformes, with their capillary blood-vessels.
(Photograph by Mr. A. Priiuilc.)

a dense capiUary net 1 cork on the surface of the mucosa,
and from it loops ascend into the papillae. Of course,
fat tissue glands and muscular tissue receive their
own supply. There is a very rich i^lexus of veins in
the superficial part of the mucosa. They are con-
spicuous by their size and the thinness of their wall.

302 Elements of Histology.

Tlie lymjohatics form networks in all layers of the
mucosa, including the papilla^. The large efferent
trunks are situated in the submucosa. The last out-
runners of the nerve-hranches form a j^^^^ris of notv-
meduUated fibres in the superficial layer of the mucosa,
whence numerous primitive fihrilUe. 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.

251. In the pharynx the relations remain the
same, except in the upper or nasal part, where we
find many places covered with columnar ciliated
epithelium. As in the palatine tonsils, so also here,
the mucosa is infiltrated with difiiise adenoid tissue,
and with lymph follicles in great numbers. This forms
the pJuiryngeal tonsil of Luschka.

In the palatine tonsil and in the pharyngeal tonsil
there are numerous crypts leading from the surface
into the depth. This is due to the folding of the in-
filtrated mucosa. Such crypts are, in the pharynx,
sometimes lined all through with ciliated epithelium,
although the parts of the free surface around them
are covered with stratified pavement epithelium.

252. The tongue is a fold of the mucous mem-
brane. Its bulk is made up of striped muscular tissue
(genio-, hyo-, and stylo-glossus ; according to direction:
longitudinalis superior and inferior, and transversus
lingupe). The lower surface is covered with a delicate
mucous membrane, identical in structure with that
lining the rest of the oral cavity, whereas the upper
part is covered with a membrane, of which the mucosa
projects over the free surface as exceedingly numerous
fine and short hairdike processes, the papiUct jilijormes,
or as less numerous, isolated, somewhat longer and
broader mushroom-shaped papiUce fungiformes. The
papilla?, as well as the pits between them, are covered
with stratified pavement epithelium. Each has numbers

MOUTH^ F/fARVNX AND ToNCUE.

;o3

of minute secondary papillne. Their substance, like
the mucous membrane of the tongue, is made up of
fibrous connective tissue. Tlie mucous membrane is on
the whole thin, and is firmly and intimately connected

/*»»!».

Fig. 196. — Section through the Papilla Foliata of Rabbit, showiug the Taste
Buds amongst the Epithelium. In the depth are Imndles of muscular
libres and glands. Magnifying power, 40. {Photograph by Mr. A
Pringlc.)

with the fil3rous tissue forming the septa between the
muscular bundles of the deeper tissue. It contains
large vascular trunks, amongst which the plexus of
veins is very consj^icuous (Fig. 195). On the surface of
the mucosa is a rich network of capillary blood-vessels,
extending as complex loops into the papillse. Lym-
phatics form rich plexuses in the mucosa and in the
deep muscular tissue. Adipose tissue is common

104

Elements of Histology.

between the muscular bundles, especially at the back
of the toncfue.

253. 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

Fig. 197.— Section through Taste Organ (Papilla Foliata.) From same
preparation as Fig. 196, more magnitied, to show the taste buds.
{Photogrcq^h by Mr. A. Pringle.)

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 Xuhn) at the tip.
All the glands at the back are embedded between the
bundles of striped muscular tissue, and thus the move-
ments of the tongue have the effect of squeezing out
the secretion of the glands. About the

glands

Mouth, Pharynx and Tongue. 305

numerous nerve bundles are found connected with
minute ganglia.

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
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.

254. The psipilltii! circiiiiivallatae are large
papill?e fungiformes, each surrounded by a fold of the
mucosa. They contain taste goblets or buds — i.e. the
terminal taste organs. At the margin of the tongue,
in the region of the circumvallate papillae, there are
always a few permanent 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, jiainlla foliata (Fig. 196).

255. 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 papilla? circum-
vallatae and foliatse. 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 papilla foliata
the pits are represented by grooves separating the
individual folds from one another.

256. The taste jfoblets or taste buds are
barrel- or llask-shaped structures (Fig. 197) extending
in a vertical direction through the epithelium, from the
free surface to the mucosa. Each is covered with flat-
tened, elongated epithelial cells, forming its periphery ;
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 extremity.

;o6

Elements of Histology.

The former extends to the free surface, projecting just
through the mouth of the goblet, and resembles a tine
hair ; the latter is generally y)ranched, and passes
towards the mucosa, where it probably becomes
connected with a nerve fibre. The mucosa of these
parts contains rich plexuses of nerve fibres.

Accordmtr to Eetzius the meduUated nerve fibres

Pig. 198.— Ending of Nerve Fibres in and around Taste Buds of Rabbit. {G.

SetziiiSffrom Quain.)
n, Xerve fibres; 5. taste bud ; i, iutrabulbar ramification of nerve fibrils; p,

peribulbar ramification of nerve fibrils ; s, sulcus between two adjacent folds

of the papilla f oliata.

entering from the mucosa lose their medullary
sheath and continue their course, either as peribulbar
ramifications between the tegmental cells, or as iutra-
bulbar fibres between and amongst the taste cells.
Both sets of fibres terminate with free knoblike
endings (Fig. 198).

Into the pits surrounded by taste goblets open the
ducts of the serous glands only (von Ebner).

3° 7

CHAPTER XXVI.

THE (ESOPHAGUS AND STOMACH.

257. I. Tlic €BSO|>liag^ii§. — Beginning with the
cesophagiis, 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
muscular 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 suh mucosa ; in it lie small mucous glands, the
ducts of which pass in a vertical or oblique direction
through the mucosa, in order to open on the free
surface. In man these glands are comparatively
scarce ; in carnivorous animals (dog, cat) they form
an almost continuous layer (Fig. 199).

258. Between the mucosa and submucosa are
longitudinal bundles of non-striped muscular tissue.
At the beginning of the oesophagus they are absent,
but soon make their appearance — at first as small

3o8

Elements of Histology.

bundles sejDarated from one another by masses of con-
nective tissue ; but lower down, about the middle,
thej form a continuous stratum of longitudinal
bundles. This is the miiscularis mucosce (Fig. 200).

re-^^*^

—^^n

Fig. 199.— From a Longitudinal Section througli the Mucous Membrane of
the ffidopliagus of Dog. {Atlo.s.')

c, Stratified pavement epithelium of the surface; m, muscularis mucosa;
between the two is the mucosa ; g, mucous irlands ; d, ducts of same.

Outside the submucosa is the muscularis externa.
This consists of an inner thicker circular and an outer
thinner loncjitudinal coat. And outside this is the
outer, or limiting, fibrous coat of the oesophagus. In
man the outer muscular coat consists of non-striped
muscular tissue, except at the beginning (about the
upper third, or less) of the oesophagus, which is
composed of the striped variety ; but in many

(Esophagus.

309

mammals almost the whole of the external muscular
coat, except the part nearest the cardia, is made up of
stripe* I tihres.

259. The large vessels pass into the submucosa,

Fig. 200. — Ti'ansverse Section through the (Esophagus of a Newly-born
Child. {Photograph. Lovj magnification.)

1, Stratified epillieliura of the inner surface; 2, mucosa containing cross-cut
hundles of non-striped muscle, muscularis raucoss ; 3, outer muscular coat.

whence their liner 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 mucosae 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
submucosa ^Teichmann). The nerves form rich

3IO Elements of Histology.

plexuses in the outer fibrous coat ; these plexuses
include numerous ganglia. A second plexus of non-
medullatecl fibres lies between the longitudinal and
circular muscular 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.

260. II. The istoniacli. — 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 i^yloric
glands : in the rest of the stomach, the mucous
membrane presents a reddish or red-brown appearance,
and here the glands have a different character. This
second variety of gland is typical of the cardiac end
of the stomach as distinct from the pyloric, and hence
is described as the cardiac gland.

261. The part of the mucous membrane containing
the glands is the mucosa ; outside this is a loose
connective 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
contains the gland tubes, arranged more or less in
small groups. Between them is a delicate connective
tissue, in which the minute capillary blood-vessels
pass in a direction vertical to the surface. Numerous
small l)undles of non-striped muscular fibres pass from
the muscularis mucosae towards the surface — up

Stomach.

;ii

to near the epitheliuin of the surface — forming
longitudinal muscular sheaths, as it were, around
the gland tubes.

The plicce villos?e of the suj)erficial part of the

Fig. 201.— Cardiac Glands.

A, Under a low power ; d, duct ; n^ neck, b, part of the fundus of a gland tube
under a high power ; Pi parietal cells ; c, chief cells.

mucosa contain fibrous connective tissue and numerous
lymphoid cells.

312 Elements of Histology.

262. The car<liac g'laiicls (Fig. 201) are more
or less wavy tubes, extending down to the mnscularis
mucosae. The dee}) 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 may join and open
into a short cylindrical duct. The duct is lined with
a layer of columnar ej)ithelial cells, continuous and
identical wdth that covering the free surface between
contiguous glands. The duct may be really represented
by a shallow depression from the surface ; it is then
more usual to speak of the mouth of the gland.

263. The epithelium covering the surface consists
of mucous cells. The outer two-thirds stain very
slightly as a rule, the nucleus is oval and situated in the
inner third of the cell, where the cell substance stains
more deeply. At the base of these cells more deeply
staining rejjlacement cells may be seen. The neck
and fundus of the cardiac gland is made up of two
kinds of cells. The first variety occupies in general a
more central position around the lumen, the cells are
as a rule very indistinct in their outlines, the nucleus
is in the outer half of the cell and usually somewhat
shrunken. These cells are usually spoken of as the
central, i-)ei')tic, or c/n'e/ cells. The shape of these cells
is cubical or short columnar. The other variety of
cell is characterised by a more peripheral position — at
any rate, in the fundus of the gland, their outlines are
much more distinct ; the nucleus is oval and situated
in the centre of the cell. These cells may impinge on
the lumen at the neck of the gland, where they are
most numerous ; in the fundus they are scattered and
placed between the investing membrane and the
central cells. These cells are spoken of as jjarietcd,
oxijntic, or ovoid cells. The cardiac glands may
present appearances showing the secretion in the

Stomach.

condition of granules in the cells. Granules are
observable ])oth in the parietal and central cells ;
they are more conspicuous and more easily j^reserved
in the latter.

264. The pyloric g^laiids (Fig. 202).— Thec^t^c^

Fig. 202.— Vertical Section through the Pyloric Region of the Gastric
Mucous Membrane. (Microphotogrcq^h.)

The wide funnel-shaped mouths are seen at the level M, the twisted ends cut
across in various planes at level f; the darkish band at level m.m. is the
niuscularis mucosse ; s.m., submucous layer.

of each pyloric gland is several times longer than that of
the cardiac. 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.

314 Elements of Histology.

The epithelium lining the duct of the pyloric
glands is similar to that of the free surface. Several
tubes open into one duct by a short neck. The
fundus or tube is much convoluted and generally
branched. It is lined by only one variety of cell,

Fig. 203. — From a Section throngli the Transition of the Pj'lorus into the
Duodenum. (Micwphotograjyh. Lov: poicer.)

a. Duodenal mucous membrane with villi ; ft, pyloric mucosa with lymph
follicles ; c, Brunner's glauds directly continuous with the pyloric glands.

which bears some resemblance to the central cell of
the cardiac glands. It is difficult to make out any
appearance of granules either in the fresh or hardened
condition.

265. Between the mucous membrane with cardiac
glands and the pyloric end of the stomach with pyloric

Stomach. 315

glands there is a narrow intermediate zone, in which
the cardiac ghxnds appear ])y degrees to merge into
the pyloric glands. That is to say, the short duct of
the former gradually eloDgates, the gland tubes get
shorter in proportion and convoluted, their lumen
gradually enlarges, and the parietal cells become fewer
and ultimately disappear.

266. The mucosa contains isolated lymph follicles,
the so-called glandular lenticulares (Fig. 203).

The spaces between the glands themselves and
between the glands and the muscularis mucosfe are
filled up by a delicate connective tissue somewhat
condensed immediately around the tubes. Leucocytes
are plentiful in the meshes of this network. One
particular variety of leucocyte, the so-called basophile
cell, may under certain conditions be very conspicuous.

267. The submucosa is of very loose texture, and
enables the mucosa to become easily folded in all
directions.

268. 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.

Tiie gland tubes are ensheathed in a network of
cajnllary blood-vessels derived from the 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 mucosae possess their own vascular
supply.

269. The lymphatics form a network in the
mucosa near the fundus of the glands. Into this
plexus lead lympathics wdiich run longitudinally
between the glands ; they anastomose with one
another freely, and extend to near the inner surface
(Loven). Another plexus is found in the submucosa.

3i6 Elements of Histology.

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 flexus of Auerhach 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
corresponds to the p/e^^s of Meiasner of the intestine,
and is destined for the muscularis mucosae and the
mucosa.

According to Ralje, the gastric gland tubes in the
horse are surrounded by a rich plexus of nerve fibres,
terminating in peculiar spindle-shaped cells.

CHAPTER XXVII.

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

Fig. 204. — Epithelium covering the Surface of a Villus of Small Intestine.

(Atlas.)
a. Striated free border ; b, goblet cell.

fibrillated ; their free surface appears covered with
a vertically and finely striated free border (Fig. 204).
Many cells are goblet cells. Underneath the epithe-
lium is a basement membrane, the sub-epithelial
endothelium of Debove.

As in the stomach, so also in the small and large
intestine, the mucosa is connected with the outer
muscular coat by a loose-textured fibrous subrnucosa,
in which lie the large vascular trunks, and in many
places larger or smaller groups of fat cells and lymph
corpuscles. Between the mucosa and subrnucosa, but

3i8 Elements of Histology.

belonging to the former, is a layer of non-striped
muscular tissue, the muscularls inucosce. This is in
many places composed of inner circular and outer
longitudinal bundles, but there are a good many
places, especially in the small intestine, where only a
layer of longitudinal bundles can be made out.

The tissue of the mucosa is similar in structure
to adenoid tissue (Fig. 205), consisting of a reticular

Fig. 205. — From a Longitudinal Section through a Villus of the Small

Intestine.

«, Epithelium of the surface; ft, 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
lymph corpuscles.

matrix with flattened large nucleated endotheloid
cells and numerous lymph corpuscles. These are
either small lymph corpuscles like leucocytes, or they
are somewhat larger and filled with coarse granules
— plasma cells. The mucosa of the small and large
intestine contains simple gland tubes, the cryiJts or
follicles of Lieberkilhn (Fig. 206) ; they are placed
vertically and closely side by side, extending from the
free surface, where they open, to the muscularis
mucosae. 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 intestme the mucosa projects
beyond the surface as numerous longer or shorter,
cylindrical, conical, or leaf-shaped villi (Fig. 206).
These are, of course, covered with the columnar

Small and Large Intestine.

319

epithelium of the general surface, and their tissue is the
same as that of the mucosa — i.e. adenoid tissue (Fig.
207) — with the addition of: {a) One or two central wide
chyle (lymph) vessels (Fig. 209), their wall being a
single layer of endothelial plates. {b) Along these

'V mM'^

Fig. 206.— From a Vertical Section tlirougli a Fold of the Mucous Mem-
brane of the Jejunum of Dog. (Atlas.)

c, Mucosa, coutaining the crypts of Lieberkilbn, and projecting as the villi;
in, muscularis mucosae ; s, submucosa.

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 basement membrane — i.e. the sub-epithelial endo-
thelium, (c) A network of capillary blood-vessels ex-
tending over the whole of the villus close to the
epithelium of the surface (Fig. 208). This capillary
network derives its blood from an artery in about the
middle or upper part of the villus. Two venous
vessels carry away the blood from the villus.

320

Elements of Histology.

The Lieberkiihn's crypts open between the bases
of the villi.

About the base of the villi of the small intestine,

Fig. 207. — Transverse Section through Villus of Small Intestine of Dog.
(B.e.idzn'ho.in.)

Showing the columnar epithelium lining the free surface, the adenoid tissue
forniini-' the groundwork ; amongst the lymph cells of this adenoid tissue
there are numerous large cells filled with fat-droplets ; the central lacteal as
also the capillary blood-vessels are shown cut across.

and about the base of the plicae villosas of the stomach
(p. 311), there exist amongst the epithelium of the
surface peculiar goblet-shaped groups of epithelial
cells, which, as AYatney has shown, are due to local
multiplication of the epithelial cells.

272. Lymph follicles occur singly in the submucosa,

Small and Large Intestine.

321

and extend witli their inner part or summit through
the muscularis mucosie into the mucosa to near the
internal free surface of the hitter (Fig. 209). These
are the solitary lymph foUicIes of the small and large
intestine ; in the latter they are larger than in the
former.

Agminated glands, or Peyers ylands, are larger or
smaller groups of lymph follicles, more or less fused
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
(Fig. 210). In the
lower part of the
ileum these
Peyer's glands are
very numerous.
The epithelium
covering the sum-
mits of these

lymph follicles is invaded by, and more or less
replaced by, the lymph corpuscles of the adenoid
tissue of the follicles (Watney), similar to what
is the case in the tonsils [see par. 124). Isolated
]vmph corpuscles are met witli amongst the epithelium
also of other parts of the intestine — e.g. the epithelium
covering the villi (Fig. 204).

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.

Fig. 20s.— From a Vertical Section through the
Siual] Intestine of Mouse ; the blood-vessels
are injected. (Atlas.)

The networks of the capillaries of the villi are well
shown.

;22

Elements of Histology.

273. The blood-vessels form sepaiate systems of
capillaries for the serous covering, for the outer mus-
cular coat, for the muscularis mucosa?, 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 mucosae (Fig. 208).

Fig. 209.— From a Section through a part of a Human Peyers Patch,
showing the distribution of tlie lynijihatic vessels in the mucosa and
submucosa. (Frey.)

a. Villi, with central chyle vessel ; b, Lieberkiihn's crypts: c, region of muscu-
laris mucosEB : /, lymph follicle ; g, network of lymphatics around the lymph
follicle; I, lymphatic network of submucosa: k, efferent lymphatic" trunk.

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 j^lexus of lymphatic vessels and
sinuses belon^inor to the mucosa, and situated be-
tween the crypts of Lieberkiihn (Fig. 209). This

Small and Large Intestink.

323

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

Fig. 210. — Cross section tlinnmh tiie C;t'cuiu of Rabbit, sliowiiig a Fever's

ratch. ' ■

(!, >[iicous membrane; b. summits of the lymph follicles reaching the free
surface; c, body of the lymph folliclfs iu the submucous tissue: d, outer
muscular coat. {PItoto. Loic Maynijication.)

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.

324 Elements of Histology.

L'74. The cliyle, composed of granules and fat
globules of different but minute sizes, passes from the
inner free surface of the mucous membrane of the
small intestine through the epithelium into the spaces

Fig. 211.— Vertical Section through the Mucous Membrane of the large
Intestine. {Micropliotograph.)

Some six elands are shown occupying almost the full height of the photograph.
Ihe luiuen of the ^land is large, the glands being hardened in the distended
condition. The epii helium lining is seen to include a very large number of
roundish, clear, and but slightly staining cells, these being goblet cells.
The nucleated cells of the sub-epithelial reticular tissue are seen between the
glands.

of the reticulum of the villi, and from here into
the central chyle vessels. The plasma-corpuscles
in the reticulum of the matrix may, and sometimes
do, take up chyle globules : but it is a mistake to
ascribe to these lymph cells an important role in

Small and Large Intestixe.

3^5

passing chyle gloljules from the epitheliuin into the
central chyle vessel (Fig. 214).

Owing to the peripheral disposition of the
capillaries in the villi, and owing to the greater
tilling with blood of the capillaries during digestion,

.p ^^

■.ch

i.i

r-/..''/t?'*»

N '^.

#M^

r****

Fig. 212. — From a Horizontal Section through the Mucous Membrane of
Large Intestine of Pig, showing the gland tubes of Lieberkiihn in
cross-section, their lining columnar epitlielium with numerous goblet
cells amongst them. Between the gland is the tissue of the mucosa.
(Photo. Moderately magnified.)

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-
testine greatly facilitates the absorption and discharge
of the chyle.

326 Elemenis of Histology.

275. The non-medullated nerves form a rich
plexus, called the i^lexus myentericus of Auerhach
(Fig. 215), with groups of ganglion cells in the
nodes ; this plexus lies between the longitudinal and
circular muscular coat. Another plexus connected

Fig. 213. — Transverse Section through the Human A]ipendix Verniiforiuis ;
showing the mucous membrane with the densely arranged glands of
I.ieberkiilin, the subuiucous layer with the cross-cut large vessels, and
the outer muscular coat covered by the peritoneal layer. {Photo.
Low poicer.)

with the former lies in the submucous tissue ; this
is the plexus of Meissner, with ganglia. (Fig. 172.)
In both plexnses the branches are of a very variable
thickness ; they are groups of simple axis cylinders,
held together by a delicate endothelial sheath.

Small and Large Intestine.

3^7

Fig. 214.— Part of a Villus filled with Chyle, from the intestine of a puppy-
four days old. (ReidenJui.in.)

rt, Epithelium of surface of villus; b, tissue filled with chyle globules.

rMmmM^

^...

Fig, 215. — Plexus Myentericus of Auerbaeh of the small intestine of a
newly-born child. (Atlas.)

The minute circles and ovals indicate sranglion cells.

.28

CHAPTER XXVITI.

THE GLANDS OF BRUNNER AND THE PANCREAS.

276. At the passage of the pyloric end of the
stomach into the diiodeniini (Figs. 'JOS, 216), and in the

P.G.

<^- ;;-sO^U^T,f^

MM.

M.C.

Fig. 216.— Section througli the Gastro-duodeiialJunction. (Microphotograph.)

A bandisseen runninf,' across from m.m. to m.m., the muscularis mucosa?. In
tlie suljimicoiis coat beneath on the right side are seenBrunuers glands,
B.G. In the mucous coat pyloric ghands are seen on left side, p.g. ; villi, v.,
and crypts of Lieberkuhn, c.l., on right side. A small piece of muscular coat
is seen at Ji.c.

Glands of Brunwkk.

329

first part of tlie 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.

^»

fti»^

Fig. 217. — Section tlirougli Pancreas of Cat. {Micropliotogrwph.)

Three lobules are cut across. In the middle of the small lobule on the right a
lighter patch is seen; this is an interlobular clump. Similar clumps are
seen on the other lobules.

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 with the crypts of Lieberkiihn
between the bases of the villi. The gland tubes of
Brunner's glands are identical in structure tvith the
pyloric glands, with ichich they form a direct ana-
tomical continuity.

35^

Elements of Histology.

111. The pancreas (Fig. 217) is in most respects
identical in structure with a serous or true salivary
gland. The distribution of the blood-vessels and
lymphatics, and the arrangement of the connective
tissue, so as to separate the ghmd tissue in lobes and
lobules, with the corresponding inter- and intra-lobular

Fig. 218. — From a Section through Pancreas of Dog. {Atlas.')

a. Alveoli (tuhes) of the gland; the liuin? cells show an outer homogeneous
and an inner granular-looking portion ; d, minute duct.

ducts, are simihxr in both cases. The epithelium lining
the latter ducts is only faintly striated, not by any
means so distinctly as in the salivary tubes. The
alveoli or acini are much more elongated than is the
case in the serous salivary glands, and in section the
tubular character of the alveoli is marked (Fig. 218).
The intermediate part of the duct leading to the
alveolus resembles the ductule of the salivary gland.
The cells of the alveolus are somewhat pyramidal, and
show in specimens hardened by ordinar}^ reagents an
outer more deeply staining zone varying in width.

Pancreas.

331

and an inner less deeply staining area (Fig. 218).
Tiiis lighter zone represents the part of the cell in
which tlie secretory grannies are collected (Fig.
219). The outer more deeply staining zone may

Fig. 219.— Section througli Pancreas. { Micro-photograph of specimen
hardened in osrnic acid.)

Several alveoli are seen, the darker masses in the centre of each being accumu-
lations of secretory granules.

sometimes show a radial striation. In some animals
the cells lining the ductule appear to be continued as
an internal lining into the alveolus. These constitute
the so-called centro-acinous cells of Lancjerhans.
There are also to be seen in the pancreas of most
animals masses of cells possessing no alveolar arrange-
ment, staining less deepl}"", but having large oval

2>2>^

Elements of Histology.

nuclei, which masses lie here and there between
the alveoli. These groups of cells are very well

":^.. '^L.- ^

Fig. 220. — Seetior. through the Pancreas of Cat. (Micropliotograph.)

In the central lobule is seen a large, slightly-stained mass, which is an inter-

tiihiilar clump.

supplied witli blood-vessels, and are spoken of as
intertiihii.lar chimjj.'i, or iiiteralveolar cell islets (see
Fig. 220).

333

CHAPTER XXIX.

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 liilum
or porta hepatis
this connective
tissue is continued
into the interior,
where it joins the
connective tissue
of the GJisson's
ccqysuh, or the in-
terlobular connec-
tive tissue (con-
nective tissue of
the portal canals).
This tissue is
fibrous, and more
or less lamellated ;
by it the substance

of the liver is subdivided into numerous, more or less
polyhedral, solid lobules or acini (Fig. 221), each
about 2V of than inch in diameter. According to

-A

Fig. 221.— From a Section through the Liver of
Pig. Five lobules are shown. " They are well
separated from one another by the inter-
lobular tissue. {Atlas.)

.*, Interlobular connective tissue, containing the
interlobular blood-vessels, i.e., the branches of
the hepatic artery and portal vein. and the inter-
lobular bile ducts ; i, intralobular or central
vein.

334

Elements of Histology

whether the interloltular tissue forms complete
boundaries or not, the acini appear well defined from
one another (pig, ice-bear), or more or less fused (man
and carnivorous animals and rodents).

AVithin each acinus there is only very scanty
connective tissue, in the shape of extremely delicate

Fig. 222.— From a Vertical Section through the Liver of Rabbit ; the blood-
vessels and bile-vessels injected. i^Atlo.s.)

a. Interlobular veins sun-ounded by interlobular bile ducts ; these latter take
up the network of fine intralobular bile capillaries ; the mesbes of this net-
work correspond to the liver cells ; h, Intraloliular or central vein.

bundles and flattened connective-tissue cells. Occa-
sionally, esjDecially in the young li\'er, lymph cells are
to be met with in the acini and in the tissue between
them.

279. The vena portie having entered the hilum
gives off' rapidly numerous branches, which follow the
interlobular tissue in which they are situated, and
they form rich flexuses around each ac.invs : these
are the interlohdar veins (Fig. 222). Xumerous

LlVEK.

335

large

capillary blood-vessels are derived from these veins.
These capillaries pass in a radiating direction to the
centre of tlie acinus, at the same time anastomosing
with one another by numerous transverse branches.
In the centre of the acinus the capillaries become
confluent into one

vein, the cen-
tral or intralohular
vein. The intralo-
bular veins of se-
veral neighbouring
acini join so as to
form t\iQ sublohular
veins, andthe-e lead
into the efterent
veins of the liver,
or the hepatic veins,
which finally pass
into the vena cava
inferior.

280. The sub-
stance of each acinus
— i.e. the tissue

Fig. 223. — From a Lobule of the Liver of
Rabbit, in Avhicli blood- and bile-vessels had
been injected, more highlv magnified than
in Fig. 222. (Atlas.)

b, Bile capillaries between the liver cells, which
are well shown as nucleated polj'gonal cells,
each with a distinct reticulum ; c, capillary
blood-vessels.

between the capillary blood-vessels — is composed of
uniform polygonal protoplasmic epithelial cells, of
about jQ^j-yth 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 centre
of the acinus. The cells contain particles of glycogen
in various amounts. According to Brunton and
Delepine, the amount gradually increases in the
rabbit's liver after a meal, and reaches its maximum
between the third and eighth hour. They also contain
pigment granules, which, being derived from the
disintegration of haemoglobin in the spleen, include

336 Elements of Histology.

iron. Each liver cell shows a more or less fibrillateJ
protoplasm (Kupfer), and in the centre a spherical
nucleus with one or more nucleoli.

The liver cells are joined by an albuminous cement
substance, in which are left fine channels ; these are the
hile capillaries (Figs. 223 and 2'2-i). In a successfully
injected preparation the liver cells appear separated
everywhere from one another by a bile capillary, and
these form for lite ivhole acinus a continuous inter-
cominunicating network of minute channels. Where
the liver cells are in contact with a capillary blood-
vessel, there are no bile capillaries.

281. At the margin of the acinus the bile capil-
laries are connected with the lumen of minute tubes ;
these jDOssess a membrana propria and a lumen lined
with a single layer of transparent polyhedral epithelial
cells. These are the small interlobular hile ducts
(Fig. 222). Their epithelial cells are in reality
continuous with the liver cells. These ducts join
and form larger interlobular hile ducts, lined with
more or less columnar epithelium. The first part of
the bile duct lined with polyhedral cells corresponds
to the intermediary part of the ducts of the salivary
glands. The interlobular bile ducts form networks
in the interlobular tissue. Towards the hilum they
become of great diameter, and their wall is made up
of fibrous tissue, and in it are bundles of non-striped
muscular cells. 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 a large bile duct.

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 connective
tissue, and especially of the bile ducts. The capillary
blood-vessels of the bile ducts join so as to form

Liver.

337

small veins, wliicli finally empty themselves into
the hepatic veins. The anastomoses between the
capillary blood - vessels, derived from the arterial
branches, and the capillary blood-vessels of the acini,

Fig. 224.— From a Section tlirougli the Liver of Rabbit, of which the bile
ducts had been injected ; showing the distribution of the bile capillaries
and their branchlets between the liver cells. (Fhotograpli. Moderately
magnified.)

are insignificant (Cohnheim and Litten). The serous
covering of the liver contains special arterial branches
— rami capsulares. Networks of lymphatics — deep
lymphatics — are present in the interlobular 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 repre-
w

^T,S Elements of Histology.

sented only by spaces and clefts existing between the
liver cells and capillary blood-vessels ; these are the
intralohidar lymphatics (Macgillivray, 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
of lymphatics called the superficial lyinphatics.
Numerous branches pass between this network and
the interlobular lymphatics.

539

CHAPTER XXX.

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-
epiglottic fold, are also elastic. The thyroid, cricoid,
and arytenoid cartilages are hyaline. All these are
covered with the usual perichondrium.

A small no lule of elastic cartilage is enclosed in
the front part of the true vocal cord. This is the
cartilao^e of Luschka.

The mucous membrane lining the cavity of the
larynx (Fig. 225) has the following structure : —

The internal or free surface is covered with
ciliated stratified columnar epithelium : the most
superficial cells are conical cells with cilia on their
free 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 cords are covered
with stratified pavement epilheli^im.

Underneath the epithelium is a basement mem-
brane separating the former from the mucous mem-
brane proper.

284. Themucojs membrane is delicate connective

;4C

Elements of Histology.

tissue with numerous lymph corpuscles. In the pos-
terior surface of the epiglottis, in the false vocal cords,
and especially in the ventricle of the larynx, this

7n —

\ ^^^ >- ^ ^

In ^-S2> ^^*'.\

„H(^

Fig. 225.— From a Longitudinal Section through the Ventricle of the Larvnx
of a Child. (Atlas.)

a, True vocal cord ; b, false vocal cord ; c. nodule of elastic cartilage (cartilage
of Luschka): d, ventricle; I, lymphatic tissue ; m, bundles of the thyro-
arytenoid muscle in transverse section.

infiltration amounts to diffuse adenoid tissue, and
even to the localisation of this as lymph follicles.
In both surfaces of the ej^iglottis, and in the true
vocal cords, the mucosa extends into the stratified
pavement epithelium in the shape of minute papillae.

In the lower part of the larynx the mucous mem-
brane contains bundles of elastic fibres connected into

Larvnx.\

341

networks, antl running in a longitudinal direction.
Those elastic fibres are found chieHy in the superficial
parts of the mucous membrane. Tn the true vocal

X 40. {Photograph by Mr

Fig. 226. — Section through Trachea of Foitus.

A. Pringle.)

1, Ciliated columnar epithelium of internal surface; 2, mucous membrane with
its glands ; ?,, cartilage ; 4, outside this the thyroid gland.

cords the mucosa is entirely made up of elastic fibres
extending in the direction of the vocal cords.

285. The deeper part of the mucous membrane is
of loose texture, and corresponds to the submucosa ;
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,

342

Elements of Histologw

however, also alveoli lined with columnar albuminous
cells, and such as have Ijoth side by side, as is the case

i^t^-^'iVmrr/r-^i^'-r-i-'.

g»y'.;?j7-^[7f^|

•^

iV^

Fig. 227.— From a Longitudinal Section tlirougli the Trachea of a Child.

{Atlas.)

a. Stratified columnar ciliated epitheMum of the internal free surface: ft, base-
ment nienihrane ; c, mucosa ; d. networks of longitudinal elastic tihres ; the
oval nuclei bL-tween them indicate connective-tissue corpuscles; e, sub-
mucous tissue containing mucous glands; /, large blood-vessels; g, fat
cells ; h, hyaline cartilage of the tracheal rings.

in the sublingual dand of the dof?. The ciliated
epithelium of the surface in some places extends also
for a short distance into the ducts. The true vocal
cords have no mucous glands.

The Ijlood-vessels terminate with the capillary net-

Trachea. 343

work in the superficial — i.e. &u)>epithelial — layer of
the mucosa ; where tliersj are papilla; — i.e. in the
epiglottis and true vocal cords — these receive a loop
of capillary blood-vessels. The lymphatics form super-
ficial 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, some of which ter-
minate, according to Luschka and Boldyrew, as end
bulbs. Taste buds have been found in the epithelium
of the posterior surface of the epiglottis (V( rson,
Schofield, Davis), and also in that of 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
of hyaline cartilage, and in containing, in the posterior
or membranous portion, transverse bundles of non-
strijoed mnscrdar tissue, extending horizontally between
the ends of the rings. Its com])onent parts are (Figs.
226,227, 228):—

{a) a stratified columnar ciliated epithelium ;

{Jj) a basement membrane ;

{d) a layer of longitudinal elastic fibres connected
into networks ;

(e) a loosely textured submucous tissue, contain-
ing the large vessels and nerves and small mucous
glands. Occasionally the gland or its duct is em-
bedded in a lymph follicle.

287. III. The bronchi and the lung:

The bronchi ramify 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

344

Elements of Histology.

and smaller oblong or irregularly-sliaped 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

Fig. 228.— From a Section througli the Traclieal Mucous Membrane of a
Newly -born Child. {Photo. Highly magnified.)

e. Ciliated columnar epithelium ; amongst the ciliated cells are numerous
goblet cells ; m, mucosa ; </, acini of mucous glands.

basement membrane, the sub-epithelial mucosa, and
the layer of longitudinal elastic fibres, remain the
same as in the trachea. The submucous tissue con-
tains small mucous glands.

288. Between the sub-epithelial mucosa and the
submucosa is a continuous layer of circidar non-
striped muscular tissue. In the smaller microscopic

Bronchi and Lung. 345

bronchi this layer is one of the most conspicuous. By
the contraction of tlie circuhir muscular coat the
mucosa is placed in longitucliiuil folds.

The state of contraction and distension of the
small bronchi bears an important relation to the aspect
of the epitheliuui, wliich appears as a single layer of
columnar cells in the distended bronchus, and as
stratified when the bronchus 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.

The lymphatic networks of the bronchial mucous
membrane are very conspicuous. Those of the sub-
mucous tissue — i.e. the peribronchial lyniphatics —
anastomose 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 lymphatics.

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
infundibula ; 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 cdveoli — opening by a wide aperture
into the alveolar duct or infundibulum, but not com-
municating 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

346

Elements of Histology.

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 deli-
cate fibrous connective tissue : this forms a continuity

Fig. 229. — From a Section through the Lung of Cat, stained with nitrate of
silver. {Atlas.)

a, Infun(iil>ulum or alveolar duct in cross-section ; b. groups of polyhedral
cells lining one part of the infundibulum, the rest being lined with fliittened
transparent epithelial scales ; c, alveoli lined with flattened epithelial
scales ; here and there between them is seen a polyhedral trranular epithelial
cell.

with the coDiieetive tissue accompanying the bronchial
tubes and large vascular trunks, and with these is
traceable to the hilum. On the other hand, the inter-
lobular connective tissue of the superficial parts of the
lung is continuous with the fibrous tissue of the

Brlwchi axd Lung. 347

surface called the pleura pulmonalis. This membrane
contains numerous elastic libres, and on the free
surface is covered with a hiyer of endothelium.

In some instances (guinea-pig) the pleura pulmo-
nalis contains bundles of non-striped muscular tissue.

The lobes of the lung are separated from one
another by large septa of connective tissue— the liga-
menta pulmonis.

291. The teriiiiiial bronchi contain no cartilage
or mucous fflands in their wall. This is made up of
three coats : («) a delicate epithelium — a single layer
of small jxjhjhedral (jranular-Jooking cells ; (h) a
circular coat of non-striped muscular tissue ; and (c)
a tine ad\entitia 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. 229) we find the following changes : {«) the
polyhedral granular-looking epithelial cells forming
a continuous lining in the terminal bronchiole are
traceable into the infundibulum only as larger or
smaller groups : between these groups of small poly-
hedral granular-looking cells large, flat, transparent,
homogeneous, nucleated, epithelial scales make their
appearance. The farther away from the terminal
bronchiole, the fewer are the groups of polyhedral
granular-lookinf; cells. In all infundibula. however,
the transparent scales form the chief lining. This
becomes still rnoie marked in the air cells. There the
small polyhedral granular-looking cells are traceable
only singly, or in groups of two or three (Elens), the
rest of the cavity of the fir cells being lined with the
large transparent scales.

In the foetal state all cells lining the infundibula
and air cells are of the small polyhedral granular-
looking variety (Kuttner). With the expansion of
the lungs during the first inspiration many of these

348

Elements of Histology.

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 infundiljula, and
isolated or in twos or threes in the alveoli.

Fig. 230.— Network of Capillary Blood-vessels surrounding the Alveoli of
the Human Lung. (Photograph by Mr. A. Pringle.)

293. (b) The circular coat of non-striped muscular
tissue of the terminal bronchiole passes as a continuous
circular coat — but slightly thinner — on to the alveolar
ducts or infundibula, in their whole extent, but not
beyond them, i.e. not on to the air cells.

Bronchi and Lung. 349

it forms 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 connec-
tive-tissue cells, contained as usual in similarly-shaped
branched lacun?e, which are the radicles of the lym-
phatic vessels.

294. The blood-vessels and lyiiipliatics. —
The branches of the pulmonary artery and veins are
contained within the connective tissue separating the
lobes and lobules, whence they can be traced into
their finer ramifications towards the infundibula and
air cells. Each of these latter is surrounded by a sort
of basket-shaped dense network of capillary blood-
vessels (Figs. 230 and 231). The capillary networks
of adjacent alveoli are 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 bronchial walls,
which are supplied by them with capillary networks.

The lacunse 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 lympJtatics. They are
connected also with the networks of lymphatics sur-
rounding the bronchi, i.e. the peribronchial lymphatics.
The rootlets of the superficial air cells empty them-
selves into the siib-j)leural j^le.mis oflymj^hatics., 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. 229), leading from the cavity of the air cells into
the lymph lacunae of the alveolar wfiU. These stomata.

350

Elements of Histology.

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, greatly favours absorption. Through these
stomata, and also throuirh the interstitial cement

Fig. 231.— Injected Lung of Cat. (Photograph.)

substance of the lining epithelium, formed particles
— such as soot particles of a smoky atmosphere,
pigment artificially inhaled, cellular elements, such
as mucous or pus corpuscles, bacteria, etc. — find their
way into the radicles of the lymphatics, thence into
the perivascular and sub-pleural lymphatics, and finally
into the bronchial glands.

The cellular elements just mentioned, containing
particles of soot, are spoken of as " dust cells."

.53

CHAPTER XXXI.

THE SPLEEX.

296. The capsule enveloping the spleen is a
serous membrane — the peritoneum. It is a connec-

c i

0* '0 ,

Tig. 232.— From a Vertical Section through the Spleen of Ape. (Atlas.)

a. Capsule; b, rrabeculEe; c. Malpighian corpuscle: d, artery ensheathed in a

Malpit'hian corpuscle ; e, pulp tissue.

tive-tissue membrane with networks of elastic fibres,
and covered on its free surface with an endothelium.

v5D-

Elemexts of Histology.

The deep part of the capsule contains bundles of non-
striped miLscuIar tissue forming plexuses. In man
the bundles are relati\ely 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 (Fig. 232).

In connection with the capsule are the trahecuhe-
(Fig. 232). 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
trabeculye 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
trabecul^e in the human spleen consist chieflv of

fibrous tissue with an admixture of longitudinal

non-striped muscu-
lar tissue. This is
more pronounced in
the dog, horse, pig,
guinea-pig, in which
the trabeculae are
chiefly composed of
non-striped muscu-
lar tissue. Folio v\--
ingasmalltrabecula
after it is given off
from a larger one,
we tind it branch-
ing into still smaller
ones, winch ulti-
mately lose them-
selves amongst the
spleen tissue called

Fig. 233.— From a Section through the Pulip
of the Spleen of Pig. ( Atlas. )

a. Last outrunners of the muscular trabecule ;
b, flattened cells forming the honevcomhed
matrix of the pulp: in the meshes of this
matrix are contained lymphoid cells of various
sizes.

of the

elements of that part
spleen pulp (Fig. 233).

Tlie meshes of the network of the trabecular are
filled up with the parenchyma. This consists of two

Spleex. 353

kinds of tissues : {a) the Malpighian corpuscles ; and
(Jj) the pulp tissue.

297. The .llal|ii;:liiaii 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 trabeculfe towards the interior
of the spleen, they are seen to give off numerous
smaller l>ranches 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 b}^
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, es^^ecially
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 honeycomljed 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. 234), udiich are oblong spaces lined
with a layer of more or less polyhedral endothelial cells.
These sinuses form networks, and lead into the large

354

Elements of Histology.

venous branches passing in the big trabeculse to the
hihun. The venous sinuses in man and ape possess a
special adventitia formed of circular elastic fibrils.
Not all arterial branches are ensbeatlied in

-AL

Fig. 234. — From a Section through the Spleen of a Guinea-pig ; the blood-
vessels had been injected. {Atlas )

a, Artery 'of Malpighian corpuscle; h. pulp; hetween its cells are the minute
blood-ctiannels opening into c, the radicles of the veins.

Malpighian corpuscles; some few fine arterial branches
open directly into the veins of the pulp matrix, being
invested in a peculiar reticular or concentrically
arranged 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

Spleex. 355

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 pnlp 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
corpuscles 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 hjmphatics form plexuses in the capsule
(Tomsa, Kyber). These are continuous with the plexus
of lymphatics of the trabecul^e : and these again with
the plexus of lymphatics in the adventitia of the
arterial trunks.

Xon-meduUated nerve fibres have been traced along
the arterial branches.

356

CHAPTER XXXII.

THE KIDNEY, URETER AXD 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
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 submucosa 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
alands (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

Kidney, Ureter and Bladder. 357

there are gland-tubes similar in structure to sebaceous
follicles.

301. The large vascular trunks enter, or pass from
the tissues 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 a few longitudinal bundles of non-striped muscular
tissue, thereby separating the individual Malpighian
pyramids.

The parenchyma itself contains ver}^ scanty fibrous
connective tissue, chiefly around the Malpighian cor-
puscles and around the arterial vessels, especially in
the young kidney. In the jDapilhe there is relatively
a great amount of fil>rous tissue. On the surface of
the papillae (facing the calices) there is a continuous
layer of tibrous 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 pareiicliyma. — I. The urinary
tubules (Fig. 235). — In a transverse or longitudinal
section through the kidney we notice the cortex, the
houndary layer of Ludwig and the papillary j)ortions,
the last terminating in the conical ^;«^?j<7/rti 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,
constitutes a MalpiyJiian pyramid. The medulla of
the human kidney contains about a dozen of such
Malpighian pyramids.

303. The cortex contains vast numbers of

358

Elements of Histology.

Fig. 235. — Diagram showing the course of the Uriniferous Tubules in the

difterent parts of the cortex and medulla. {Atla&,)

(For description of this Fig. see foot of next page.)

Kidney, Uri:ti:r and Bladder. 359

convoluted tubules with their c.ecal origin in the
Malpighian corpuscles ; this is the lahnrinth separated
into numerous divisions of ecjual breadth by regulai-ly-
disposed straight stria? originating a sliort distance
from the outer capsule, and ratliating towards the
boundary layer through which they pass. Each of
these stria3 is a bundle of straight tubules, and
represents a mednUary ray. The boundary layer
shows a uniform vertical striation, in which opa(pie
and transparent strife alternate with one another. The
opacpie stria^ are continuations of the medullar}^ I'ays,
the transparent striae are bundles of blood-vessels.

The papillary portion is uniformly and vertically
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
Cfecal 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.

Ai Cortex limited on it* free surface hy the capsule; a, subcapsular layer not
containing Malpitfliian corpuscles ; a' inner stratum of cortex without
Malpighian corpuscles ; b, lioundary 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 9, the ascending linil) of Henle's loop-tube ; 10, the
irreu'ular tubule ; 11, the distal convoluted tul)ule ; 12, the first part "f the
collecting tube; 13 and U, larger collecting tube; in the papilla itself, not
represented here, the collecting tube joins others, and forms the duct.

360

Elements of Histology

From \X> >tart to it^ end there is a continuous
fine memhrana propria forming the boundary wall
of the urinary tubule, and this memhrana propria is
lined with a single layer of ejnthelial cells differing in

Fig. 236. — From a Section through the Cortical Substance of the Kidney
of a human Foetus, showing a 3Ialpighian corpuscle. (HandbooJ:.)

a.Glomemlu* ; 6. tissue of the glomerulus : c. epithelium covering the glomer-
ulus ; d, flattened epithelium lining Bowmans capsule ; e, the capsule itself ;
/, uriniferous tubules in cross section.

size, shape, and structure from place to place : in
the centre of the tubule is a lunifn, differing in size
according to the size of the tubule.

305, (1) Each Mcdpigldan corpuscle (Fig. 236)
is composed of the capsule — the <-apsv.le of Bou-man —
and the glomerulus, or Malpighian tuft of capillary
blood-vessels.

The capsule of Bowman is a hyaline membrana
propria, supported, as mentioned aljove, by a small
amount of connective tissue. On its inner surface

Kidney, Ureter and Bladder. 361

there is a continuous layer of nucleated epithelial
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
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 of the t^vo.

Between Bowman's capsule and the glomerulus
there is a space, the size of which difiers 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 -^^-^
of an inch.

306. (2) 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 proj^ria and

36;

Elements of Histology

lining epithelium of the tubule respectively, an<l
the space between the ca[)sule of Bowman and

"@t,;;,;^. :.:;:^V ,Cr^^^^

Fig. 237. — From a Vertical Section througli tlie Kidney of Dog, showing
jiart of the labyrintli ami the adjoining medullary ray. {Atlas.)

a. Capsule of Bowman ; tlie capillaries of the glomerulus are arranged in
lobules; n, neck of capsule; b, irregular tubule; c, proximal convoluted
tubules ; d, collecting tube ; e, part of the spiral tubule : /, portion of the
- ascending limb of Henle's loop-tube ; d, e,f, form the meduliarj- ray.

the glomerulus becomes the cavity or lumen of the
urinary tubule.

307. (3) After it has passed the neck, the urinary
tubule becomes convoluted ; this is the joroximal con-

K/DXKV, Ureter axd Bladder. 363

vohded tubule (Fig. 237). It is of considerable length
and is situated in tlie labyrinth. It has a distinct
lumen, and its epithelium is a single layer of polyhedral
or short, columnar, angular, or club-shaped cells, each
with a spherical nucleus. These cells commence gene-
rally at the neck, but in some animals — e.g. in the
mouse — they already have begun in the ]N[alpighian
corpuscle. The outer part of the cell protoplasm — i.e.
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 matgin — appears granular. Epithelial cells the
protoplasm of which possesses the above rod-shaped
tibrils will in the following paragraphs be spoken of
as fibrillated cells.

The proximal convoluted tuVje 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
connected with the state of secretion.

308. (4) The convoluted tube passes into the
spiral tuhule (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 tilirillation.

309. (5) Precisely at the line where the cortex
joins the boundaiy 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 llattened nucleus.
This altered tubule is the descending loop-tube of

364 Elements of Histology.

Henle, and it pursues its course in the boundary
layer as a straight tuljule, in the continuation of the
medullary ray.

In aspect and size this part of the urinary
tul)ule resembles a capillary blood-vessel, but differs
from it inasmuch as, in addition to the lining laver
of flattened epithelial cells, it possesses a membrana
propria.

31u. (6) The so-constituted 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 looi) 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. (7 and 8) Having entered the boundary layer
it pursues its course in this latter to the cortex in a
more or less straiglit direction within the medullary
ray as the ascending loop-tube. Besides being bigger
than the descending limb and the loop, its lumen is
comparativelv smaller, and its lining epithelium is a
layer of polyhedral, distinctly librillated epithelial
cells. The tube is not quite of the same thickness all
along the boundarv 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.

(9) 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 straiiiht or wavv. Its lumen is verv
minute, its lining cells are flat polyhedral witli a
small flattened nucleus, and there is an indication of
librillation (Fig. 237).

(10) Sooner or later on its way in the cortex in

Kidney^ Ureter and Bladder. 365

a medullary ray it leaves this latter to enter the
labyrinth, where it Avinds between the convoluted
tubes as an angular irregular tubule (Fig. 237). 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
— according to the thickness of the tube ; each cell
possesses a flattened oval nucleus next to the lumen,
and a very coarsely and conspicuously tibrillated
protoplasm.

312. (11) 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.

(12) 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
labyrinth.

(13) 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.

(14) It then passes unaltered as a straight collect-
ing tube through the boundary layer into the papillary
portion.

313. 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 — namely,

;66

Elements of Histology.

i.^j-'-r-.-^-^^^^a^

Fig. 23S. — Diagram of the Vessels
of the Kidney. {Ludicig, in
Strieker's Manual.)

whether more or less co-
lumnar— are in direct re-
lation to the size of the
coUectinQ' tube. The sub-
stance of the epithelial
cells is a transparent pro-
toplasm, and the nucleus is
more or less oval.

314. In many places
nucleated cells, spindle-
shaped or branched, can be
traced from the membrana
propria of the tubule be-
tween the lining epithe-
lium ; and, in some cases,
even a delicate nucleated
membrane can be seen
lininor the surface of the
epithelium next the lumen.
In the frog, the epithelium
lining, the Malpighian cor-
puscles, and the exceed-
ingly long neck of the
urinary tubule, are pos-
sessed of lonij hlamentous
ciHa, 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.

«/, Interlobular artery ; vi, interlobular
vein : g. glomerulus of Malpighian
corpuscle; vs. vena stellata; ar,
arteriiB rectas : rr, vena; rects ; ob,
Imndle of arteria; rectae: rb. bundle
of venffi rectse ; rp, network of vessels
around the nioutti of the ducts
at the apex of the papillK.

K/DN/:v, Ureter and B [.adder.

367

Heideiihaiii lias sliown tliat indigo-sulphate of
sodium, injected into the circulating blood of the dog
and rabbit, is excreted through certain parts of tlie
urinary tubules only — viz. those which are lined with

r V: '-'v yf.

"-^^k:-^ ■-'V.v. ■■^•■-^■^ "^ -'"-S:'

.■>»•/ -J . .,- '/• -. . ^.

* •.■■•• '■% .. ■ . . (. , « ,,

/ * .1 •' 1'

Fig. 239. — Vertical Section through the entire Kidney (injected) of a Rat.
{Photo. Low Power.)

(I, Cortex ; b, papilla ; c, boundary layer.

"fibrillated^' epithelium. He maintains that this
excretion is effected through the cell substance ; 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 substance between
the epithelial cells.

315. 11. The blood-vessels. (Figs. 238 and 239).

568 Elements of Histology.

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 tlie cortex
and medulla.

(1) In the cortex the arterial trunks give off to
the cortex small branches, which singly enter the
lahijrinth in a direction vertical to the surface of the
kidney. These are the interlohidar 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
one entering a Malpighian corpuscle and breaking up
into the capillaries of the glomerulus.

On their way towards the external capsule, the
arteries become greatly reduced in size, and finally
enter the capillary network of the most peripheral
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 surround in all direc-
tions the urinary tubules of the labyrinth. This
network is continuous with that of the capillaries of
the medullar}^ I'ays, the meshes being here elongated,
and the capillary blood-vessels, for obvious reasons,
more of a straight 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

Kidney, Urkter and Bladder. 369

radicles connected with the capillaries of the most
peripheral ^Axt of tlie cortex. These are the venoi
steUata; ; they pass into the labyrinth of the cortex,
where they follow a vertical course in company with
the interlobular arteries. On tliis passage the}?" com-
municate with the capillaries of the labyrinth, and
ultimately open into the large venous branches
situated between cortex and boundary layer.

317. (2) In the medulla. From the large arterial
trunks short branches come off, w^hich 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 arterim recUt
(Fig. 238). 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 netw^ork 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 rectca — and ultimately enter
the venous trunks situated between the boundary
Jayer and cortex.

The bundles of the arterise rectae and venae rectse
form severally, in the boundary layer, the 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.

J) /

Elements of Histology.

318. The outer capsule of the ki(hiey contains a
network of capillary blood-vessels ; the arterial
branches leading into them are derived from two
sources : («) from the outrunners of the interlobular

Fig. 240.— From Transverse Section through Urinary Bladder of Dog.
{Photo. Low Pov:er.)

a, Inner surface of folded mucous membrane, covered with stratified transitional
epithelium ; b, raucous membrane : c, outer coat of non-striped muscle.

arteries of the cortex, and (b) from extra-renal arteries.
The veins lead [a) into the vena? stellatie, and (b) into
extra-renal veins.

The li/mpJtatic 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 lym-
phatics, which take up lymph spaces between the

KlDNKV, UrKTER and B LADDER. 37 1

urinary tubules, both in the cortex and the boundary
layer.

oil*. The ureter is lined with stratified transi-
tional e]>itlieliam. 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 tibrous coat or adventitia.
In this last have been observed minute cjanfjlia 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, can be distinguished an inner circular,
a middle oblique, and an outer longitudinal stratum.
The last is best developed in the fundus (Fig. 2-10).

Xumerous sympathetic ganglia, of various sizes,
are found in connection with the nerve-branches
underneath 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 bladiler.

172

CHAPTER XXXIII.

THE xMALE 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. Inside the
tunica adnata, and firmly attached to it, is the
tunica cdbnginea, a fibrous connective-tissue mem-
brane of lamellar structure. Towards the posterior
maro-in of the human testis its thickness increases,
and forms there (Fig. 241) 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
other leads into the efferent vessels that accompany
the vas deferens.

The testis of the dog, cat, bull, pig, rabbit, etc.,
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

Male Genital Organs.

373

septa of connective tissue, which, passing in a radiat-
ing direction towards the alhuginea, with which tliey
form a continuity, sul)divide the testis into a large

Fig. 241.— Passage of Convoluted Seminiferous Tubules into Straight
Tubules and into the Rete Testis. {Mihalkovics, Quain's " Anatomy.") ^
a, Seminiferous tubules ; b, fibrous tissue : c, rete testis.

number of more or less conical compartments, or
lobules, the basis of which is situated at the tunica
albuginea, the apex at the corpus Highmori. Kolliker

374 Elements of Histology.

mentions that non-striped muscular tissue occurs in
these se[)ta.

From these septa thin connective-tissue lamellte
pass into the compartments, and they form the
supporting tissue for the blood-vessels, and also
represent the interstitial connective tissue between
the seminal tubules.

This intertubular or interstitial tissue is distinctly
iamellated, the lamella? being of different thicknesses,
and consisting of thin bundles of fibrous connective
tissue — arranged more or less as fenestrated mem-
branes— and endotheloid connectixe plates on their
surface. Between the lamella? are left spaces, and
these form, through the fenestra? or holes of the
lamellae, an intercommunicating system of lymph
spaces — being, in fact, the rootlets of the lymphatics
(Ludwig and Tomsa).

AVithin 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,
dog, cat, sheep, especially in the boar, these cells form
large, continuous groups — plates and cylinders — and
the cells are polyhedral, and exactly similar to epithe-
lial cells. They are separated from one another within
the grouj:) 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 fcetus.

323. The seminal tiibiile!^ (Fig. 242). —
Within each compartment, above mentioned, lie
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
uncommon.

Male Genital Organs.

375

Each seminal tubule consists of a membrana
propria, a lining epith(4iuin, and a lumen. The
membrana propria is a hyaline membrane, with oval
nuclei at regular intervals. In man it is thick and
lamellated, several such nucleated membranes being

Fig. 242.— Section of parts of three Seiniuiferous Tubules of Rat.
(£. A. ScMfer.)

a, "With the spermatozoa least advanced in development; &, more, and c, most
advanced. Between the tubules are strands of interstitial cells.

superimposed 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 ditferent 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

376

Elements of Histology.

nucleus. After puberty, however, the following
different t3qies 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 menibrana propria. These
are considered as («) the outer and ih) the inner
seminal cells. The former are next to the membrana

'243

-From a Section through the Testis of Dog, showing portions of
three seminal tubules. {Atlas.)

j», Seminal epithelial cells and mimerous small cellt- loosely arranged ; B, small
cells or sperniatohlasts becoming converted into spermatozoa; c, groups of
these in a further stage of development.

propria ; they are ])olyhedral in shape, transparent,
and the nucleus of many of them is in the process
of karyomitosis or indirect division (see par. 8) ;
in some the nucleus is oval transparent, but containing
a distinct network. The inner seminal cells generally
form two or three layers, and are more loosely con-
nected with one another than the outer seminal cells,
and therefore possess a more rounded appearance.

Male Genital Oh cans. 377

Between these a nucleated reticuluiii of fine fibres
is sometimes noticed, the i^erm reticulum of von
Ebner. But this is merely a supporting tissue, and has
nothing to do with the germination of the cells or the
spermatozoa (Merkel). The inner seminal cells show
very abundantly the process of indirect division of the
nucleus, almost all being seen in one or another phase
of it.

325. The division of the inner seminal cells yields
numerous small spherical cells ; these lie nearest the
lumen, and are very loosely connected vi^ith one
another. It is these which are transformed into
spermatozoa, and hence are appropriately called
spermatoblasts (-t'ig. 242).

Amongst the seminal cells, especially of cat and
dog, are found occasionally, but not very commonly,
large multinuclear cells, the nuclei of which are also
in one or other stage of karyomitosis.

(b) The innermost cells — i.e. the spermatoblasts — -
become pear-shaped, the nucleus being situated at the
thinner extremity, becoming at the same time flattened
and homogeneous (Fig. 24.')). The elongation of the
spermatoblasts gradually proceeds, and in consequence
of this we find numerous elongated, club-shaped
spermatoblasts, 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
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.

378 Elements of Histology.

326. The original cell-body of the spermatoblasts
goes on elongating until its protoplasm is almost, but
not quite, used to form a 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 present, even for some time
afterwards, a last remnant of the granular cell-body of
the original spermatoblast. Some of the inner seminal
cells not used for the formation of spermatozoa dis-
integrate and yield the granular substance between
the spermatozoa of the groups, and also between these
latter.

When the granular interstitial substance holding
together the spermatozoa of a group has become dis-
integrated, the spermatozoa are isolated. \\'hile this
development of the spermatozoa goes on, the inner
seminal cells continue to produce spermatoblasts, some
of which are converted into spermatozoa.

327. Spermatozoa (Fig. 24-4). — Fully formed
spermatozoa of man and mammals consist of a homo-
geneous flattened and slightly con\-ex-concave head
(the nucleus of the original spermatoblast), a rod-
shaped middle 2nece (derived directly from the cell-
body of the spermatoblast), and a long hair-like tail.
While living, the spermatozoa show very rapid oscilla-
tory and propelling movement, the tail acting as a
Hagellum or cilium ; its movements are sj^iral.

In the newt there is a tine 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 tail. Also in the mam-
malian and human spermatozoa, a similar spiral thread,
closely attached to the middle piece, and terminating
as the tail, has been observed (H. Gibbes).

328. The seminal tubules of each lobule pass into
a short straight tubuU-. the vas rectum. This is

Male Genital Organs.

379

narrower than tlie 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 irregu-
lar in diameter, being at one place narrow clefts, at

Fig. 244. — Various Kinds of Spermatozoa.

A, Spennatr)zoon 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,
spermatozoon of h(jrse ; d, spermatozoon of newt.

another wide tuljes, but never so wide as the seminal
tubules ; this network of channels is the rete testis.

329. (2) The epidid.vnii«». — From the rete testis
we pass into the rasa eferentia, each being a tube
wider than those of the rete testis, and each leading
into a conical network of coiled tubes. These are the
coiii vascalosi. The smn total of all the coni vasculosi
forms the globus major or head of the epididymis.

330. The vasa efferentia and the tubes of the coni

•So

Elements of Histology.

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.
245). Outside these is generally a layer, more or
less continuous, of small polyhedral cells. The sub-
stance of the columnar cells
is distinctly longitudinally
tibrillated. The membrtaia
propria is thickened by the
presence of a circular layer
of non - striped muscular
fibres. The rest — i.e. the
globus minor, or tail of the
epididymis — is made up of
a continuation of the tubes
of the globus major, the
tubes diminishing gradually
in number by fusion, and
thereby at the same time
becoming larger. The

columnar epithelial cells,
facing the lumen of the
minor, are possessed of cilia

Fig. 245.— Tubule of the Epi-
didymis in cross-section.

The wall of the tubule is made up of
a thick layer of roncentrically ar-
ranged n(tn-:<triped muscular tissue,
a layer of columnar epithelial cells
witii extraoi'diuarily lonsr cilia pro-
jecting into the lumen of the tube.

tubes of the globus
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 pedun-
culated hydatid of Morgagni attached to the globus
major,

331. The seminal tubules and the tubes of the
epididymis are surrounded 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

Male Genital Organs. 381

into the superficial networks of lymphatics — i.e.
those of the albuginea ; the arrangement of these
networks is somewhat (liferent in the testis and
epididymis.

332. (3) Vas ^leferciis and vesiciila? seiiii-
iiales. — 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
submucous tissue is the muscular coat, which consists
of non-striped muscular tissue, arranged as an inner
circular and an outer longitudinal stratum. At the
coQimencement 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 (Henle). 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 semiiiales 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-
sists of an inner and outer longitudinal and a middle
circular stratum. The orano-lia in connection with the
nerve trunks of the adventitia are very numerous.

334. In the ductus ejacidatorii we find a lining of

382 Elements oe Histology.

columnar epithelial cells ; outside of this is a delicate
mucosa 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 rejDlaced by stratified
pavement epithelium.

335. (4) The prostate inland. — 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
adndxture of fibrous connective tissue. The latter
is chietlv limited to the outer capsule and the thin septa
passing inwards, whereas the non-striped muscular tis-
sue surrounds and separates the individual gland alveoli.

336. The pareiicliyiiia consists of the chief
ducts, which open at the base of and near the colli-
culus seminalis, and of the secondary ducts, minor
brandies of the former, which ultimately lead into the
alveoli. These are longer or shorter, wavy or con-
voluted 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 longitudinally 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
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.

Male Genital Organs. 383

In the pei-iplieral portion of the gland numerous
ganglia are inter[)Osed in the rich plexus of nerves.
Also Pacinian corpuscles are to be met with.

337. (T)) TIk' iii-<'tlirsi. — The mucous membrane
of the male uiethra 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 longi-
tudinal 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 membrane, where they follow a longitudinal
course between large veins arranged in a longitudinal
plexus. These veins empty themselves into small
etTerent veins. 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 lacunas 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 ^landfi» of Cowper. — Each gland
of Cowpei" 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
cells, the outer portion of the cell being distinctly
striated (Langerhans). In the cell the reticulum is

384 Elements of Histology.

also distinct. In this respect the alveoli completely
resemble those of the submaxillary of the dog, but
there are no real crescents in the alveoli of Cowper's
gland.

339. (7) Tlie corpus «ipoiig'io«^iiiii. — 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 laro^e veins are
bundles of non-striped muscular tissue. The capillary
blood-vessels of the raucous membrane of the urethra
open into the veins of the plexus. The outer portion
of the corpus spongiosum, including the bulbus
urethn^, shows, however, numerous venous sinuses,
real caverna?, into which open capillary blood-
vessels.

340. The glaiis penis is of exactly the same
structure as the corpus spongiosum. The outer
surface is covered with a delicate fibrous tissue
membrane, ^^•hich on its free surface bears minute
papillae, extending into the stratified pavement epi-
thelium. At the corona glandis exist small sebaceous
follicles, the glands of T3^son ; they are continued
from the inner lamella of the prepuce, where they
abound. The papilla? 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) Tlie corpora cavernosa penis. —
Each corpus cavernosum is enveloped in a fibrous
capsule, the albuginea, made up of lamellae of fibrous
connective tissue. Numerous Pacinian corpuscles
are met with around it. The matrix of the corpus

Male CiEnital Okgans. 385

cavernosiun consists of trabecular of fibrous tissue,
between wliicli pass bundles of non-striped muscular
tissue, all in different directions. Innumerable
cavernie or sinuses, intercommunicating with one
anotlier, are present in this matrix, capaljle of such
considerable repletion that in the maximum degree
of this state the sinuses are almost in contact, and
the trabeculaj 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 capillary
blood-vessels. These are derived from the arterial
branches which take their course in the above tra-
beculae 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 caver-
nosum, the muscular trabecular forming part of the
matrix are contracted, and the minute arterial
branches embedded in them are therefore much
coiled up ; these are the arterise helicina3.

;S6

CHAPTER XXXIY.

THE FEMALE (GENITAL ORGANS.

343. (1) The ovary (Fig. 24G). — In tlie ovary,
as in other glands, the framework is to be dis-
tinguished from
the parenchyma.
In the part of
the ovary next
to the hilum there
are numerous
blood-vessels, in
a loose fibrous
connective tissue,
with numerous
longitudinal bun-
dles of non-striped
muscular tissue
directly contin-
uous with the
same tissues of
the lioamentum
latum. This por-
tion of the ovary
is the zona vas-
culosa (Wal-
deyer). All parts
of the zona vas-
culosa — i.e. the
bundles of tibrous
connective tissue,
the blood-vessels, and the bundles of non-striped
muscular tissue— are traceable into"; the parenchyma.

Fig.: 246.— Vertical Section through Ovary of

half -grown Cat. {Atlas. )
fi, Albuginea; the geminal epitlieliuia i3 not
distinguishable owing to the low power under
which the section is supposed to be viewed; 0,
layer of smallest Graaflan follicles and ova; c,
medium-sized follicles ; d, layer of large follicles ;
e, zona vasculosa

Female Gexital Organs. ^87

The stroma of this latter, however, is made up
of bundles of shorter 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 distribution the Graafian
follicles. Around the lai-ger examples of the latter
the spindle shaped cells form more or less con-
centric layers. In the human ovary bundles of
librous 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 fcetal 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, in-
timately interwoven. In man, an outer and inner
longitudinal, and a middle circular, layer can be made
out (Henle). In some mammals an otiter longi-
tudinal, an inner circidar, or slightly oblique layer
can be distinguished in the albu2:inea.

The free surface of the albuginea is covered with
a single layer of polyhedral, or short columnar
granular-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. [h) TJie cortical layer (Schron). — This is a

;88

Elements of Histology

mBmmm

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
stroma. These follicles are spherical or slightly oval,
of about Y-u\,o inch in diameter, and each of them is
limited by a delicate raemhrana propria. Inside of
this is a layer of flattened, trans-
parent, epithelial cells, each with an
oval, flattened nucleus ; this is the
membrana 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 pro-
toplasm, 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
karyomitosis, thus indicating division
of the ovum.

346. (c) From this cortical layer to

the zona vasculosa we find embedded

the stroma isolated Graafian follicles of various

increasino- from the former to the latter.

Fig. 247.— A small
Graafian Follicle,
from the Ovary of
Cat. {Atlas.)

The follicle is lined
with a layer of
colunmar epithe-
lial cells — the
lueinbrana granu-
losa. The ovum
fills out the cavity
of the follicle; it
is surrounded by
a thin zona pellu-
cida, and it in-
cludes a germinal
vesicle or nucleus
with the intra-
nuclear reticulum.

sizes

The

2 0

biggest follicles measure in diameter about
Those of the middle laj^ers are of me-

inch

In them we find inside
the membrana granulosa,
layer of transparent, co-
The ovum, larger than in
the small cortical follicles, fills out the cavity of the
follicle, and is limited by a thin hyaline cuticle — the
zona peUncida. This appears as an excretion of the
cells of the membrana granulosa. The protoplasm of

dium size (Fig. 247).
the membrana propria
made up of a single
lumnar, epithelial cells.

Female GEyiTAL Organs.

3S9

tlie OMiiii is tibrillateil. The part siuTOunding the
germinal vesicle is more ti-auspaient, and stains
ditlerently in osniic acid than the peripheral part.
The big nucleus, or germinal vesicle, is limited by a
distinct membrane, and inside this meml^rane is a
reticulum ^vith
generally one
big nucleolus
or germinal

0J)Ot.

Between
these medium-
sized follicles
and the small
follicles of the
cortical layer
we lind all in-
termediate de-
grees as regards
size of the fol-
licle and the
ovum, and es-
pecially as re-
gards the shape
of the cells of
the merabrana
granulosa, the
intermediate sizes of follicles being lined by a granu-
losa made up of a layer of polyhedi-al epithelial
cells.

347. The deeper Graafian follicles — i.e. those
that are to be regarded as big follicles — contain an
o\um, occasionally two or even three ova, which is
similar to that of the previous follicles, except that it
is larger, and its zona pellucida thicker. The ovum
does not fill out the whole ca^-ity of the follicle, since
at one side, between it and the membrana granulosa,

Fii:. 248.— Large Graafian Follicle of the Ovan" ot
Cat.

The follicle is limited by a capsule. the thecafolliculi ;
tlie lueiubraDa granulosa is composed of several
layers of epithtlial cells. The ovum with its distinct
1) valine zona pellucida is emliedded in the epithelial
cells of the discus proligerus. The cavity of the
follicle is filled with fluid, the liciuor foUiculi.

390 Elements of Histology.

there is an albuminous riuid, tljc ludiment of the
liquor folliciili,

348. The largest 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. 248).
In fact, the ovum occupies only a small part of the
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
strenothened bv concentric lavers of the stroma
cells, and this represents the tunica fibrosa (Henle)
or outer coat of the follicle — theca folliculi externa.
Xumerous 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-
oTowths of the membrana o'ranulosa 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 alto-
gether. In the first case, we have one large follicle
w^itli two or three ova, according as a parent follicle
Itg-s given origin to one or two new outgrowths.

Female Genital Organs. 391

Amongst the epithelial cells constituting the
stratified niembrana 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
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
hyperh?emic. 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 l)lood, 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
multiplication of the cells of the granulosa. New
capillaries 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,^tlie blood pigment being the remains of the
original blood eflused into the follicle. But, ulti-
mately, all the pigment disappears, and a sort of
gelatinous tissue occupies the centre, while the peri-
phery— i.e. the greater part of the follicle — is made
up of the hypertrophied granulosa, with young capil-
lary 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

392 Elements of Histology.

luteum is complete, and has reached the height of its
progressive growth. The tissue is then gradually
al)Sorbed, and cicatricial 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 follicles, of
which the ovum has been impregnated, grows to a
much larger size than under other conditions, the
granulosa becoming by overgrowtli much folded.

351. Development of tlie ovary and Oraa-
Han follicles.— The germinal epithelium of the sur-
face 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 — namely, the
epithelial or glandular part sutlers 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 diflferentiated ofi' from the superficial epi-
thelium. These nests are largest in the depth and
smallest near the surface. They remain in connec-
tion 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.
249). These correspond to the ovarial tubes (Pfiiiger).
While in the rabbit these nests are solid collections,
in the dog they soon assume the character of tubular
structures (Pfiiiger, Schafer). The cells constituting
the nests undergo multi})lication (by karyomitosis),
in consequence of which the nests increase in size,
and even new nests may be constricted off from old
ones {see also above).

Female Genital Organs.

193

3.")2, At the earliest stages we notice in the
germinal epithelium some of the cells becoming en-
larged in their cell body, and especially their nucleus :
these represent the primitive ova. AVhen the ger-
minal epithelium undergoes the thickening above men-
tioned, and when this thickened epithelium separates

Fig. 240. — From a Vertical Section tlirough Ovary of a Xewly-borji Child.
{Wo.ldeyer, in Strieker's Manual.)

a, Germinal epithelium ; 6, ovarian tube ; c. primitive ova ; d, longer tubes be-
coming consiricted off into several Graafian follicles; e, large nests; /,
iso'ated finished Graafian follicles ; ^, blood-vessels.

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 nucleus
by which they are converted into primitive ova.
Like the other epithelial cells, tlie primitive ova
of the nests and ovarial tubes undergo division into
two or even more primitive ova after the mode

394 Elements of Histology.

of karyomitosis (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 the
number of ova in a nest or in an ovarial tube, a sub-
division 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 Graafian
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
})ropria, theca externa, stroma, and vessels — are de-
rived from the foetal stroma.

There is a ofood deal of evidence to show that ova
and Graafian follicles are, as a rule, reproduced after
birth (Pfliiger, Kolliker), although other observers
(Bischofi", Waldeyer) hold the opposite Adew.

3.54. (2) Till' oviduct. — The o\nduct 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

Female Gexital Orgaxs. 395

oblique aiul longitudinal bundles. The serous cover-
ing contains numerous elastic tii)ril~^ in a connective-
tissue matrix.

355. (3) The uterus. — The epithelium lining
the cavity of the uterus is a single la^'er of columnar
cells, each with a l)undle of cilia on their free sur-
face. These are very easily detached, and therefore
difficult to tind in a hardened and preserved specimen.
But in the fresh and well-preserved human uterus
(Friedlander), as well as in that of mammals, the
cells are distinctly ciliated. The whole canal of the
cervix is in the adult lined with ciliated epithelium,
but in children, according to Lott, only in tlie upper
half. The surface of the portio vaginalis uteri is,
like that of the vagina, covered with stratitied pave-
ment epithelium.

356. The mucous membrane of the cervix is
diflerent from that of the fundus. In the former
it is a fibrous tissue possessed of permanent folds —
the palma? plicatoe. Few thin bundles of non-striped
muscular tissue penetrate into these from the outer
muscular coat. Between the palma? plicata? are the
openings of minute gland-tubes, more or less cylin-
drical in shape. They possess a membrana propria
and a distinct lumen lined with a single layer of
columnar epithelial cells, which, according to some
observers, are ciliated in the newly-born child, but,
according to Friedlander, are alwavs non-ciliated.
Goblet cells are met with amongst the lining e^rti-
thelium. Several observers (Kolliker, Hennig, Tyler
Smith, and others) maintain the existence of minute,
thin, and long vascular papilhe projecting above the
general surface of the mucous membrane in the lower
})art of the cervix ; these apparent papilla? are, how-
ever, only due to sections through the folds of the
mucous membrane. The mucous membrane of the
fundus is a spongy plexus of tine bundles of fibrous

396 Elements of Histology.

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 — glaiKliilii' iitei'iiiSB — are
short tubular glands lodged in the mucous mem-
brane and opening into the uterine cavity. During
puberty their number and their size increase con-
siderably, 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 Tliomson,
Nylander, Friedliinder, and others).

358. Durino- 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 linally altogether
detached. Afterwards its restitution takes place from
the remnant in the depth of the glands. But accord-
ing to J. Williams and also Wyder, the greater part
of the mucous membrane, in addition to the epithe-
lium, 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

FiiMAr.E Gkxital Okgaxs. 397

layer of ciivular 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
capillaries are distinguislied by the great thickness of
their wall. The mucous membrane contains the
capillari/ netioorks. These discharge their blood into
veins situated in the muscular coat. Here the veins
are very numerous and arranged in dense j^lexuses,
those of the outer and inner stratum beinof smaller
than those of the middle stratum, where thev corre-
spond 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 lympliaties are very numerous ; in
the connective tissue of the muscular coat are lymph
sinuses and lymph clefts forming an intercommuni-
cating system ; they take up the lymph sinuses of the
mucous membrane above mentioned, and on the other
hand lead into a plexus of efferent lymphatic vessels
with valves, situated in the subserous connective tissue.

The nerves entering the mucous membrane are
connected with ganglia. According to Lindgren,
there is in the mucous membrane a plexus of non-
medullated nerve fibres which, near the epithelium,
break up into their constituent primitive fibrill^.

361. (4) Tlie vag-iiia — 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, simple or compound papillae, each with a single
or complex loop of capillary blood-vessels. The
mucosa with the covering epithelium projects above

398 Elements of Histology.

the general surface in the shape of longer or shorter,
conical or irregular, pointed or blunt, permanent
folds — the rugse. These contain a plexus of large
veins, between which are bundles of non-striped
muscular tissue ; hence they resemble a sort of
cavernous tissue.

Outside of the mucosa is the loose submucosa,
containing a second venous plexus ; its meshes are
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 l^e 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
Wndles 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. Yon Preuschen and also Hennig described
tubular glands in the upper part of the fornix and in
the introitus vagina?.

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.

'J'here are in the mucous membrane solitary lymph
follicles and difi'use 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 XV.

Female Genital Organs. 399

362. (5) TIk' iirrllira. -^The structure of the
female urethra is siinihir to that of the male, except
that the lining epithelium is a sort of stratified
transitional 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 ]3avenient epithelium.

The muscular coat is composed of an inner longi-
tudinal, and an outer circular, layer of non-striped
muscular tissue.

363. (6) Tlie iiyiiiplise, clitorif^, aii<l vcsti-
biiliiiii. — These are lined with thick stratified epi-
thelium ; underneath is a fibrous connective-tissue
mucous membrane, extending into the epithelium in
the shape of C3^1indrical pajjill^e with capillary loops
and nerve endings (end bulbs). The nympha^ contain
large sebaceous follicles, but no hairs.

The nymphse contain a plexus of large veins with
bundles of non-striped muscular tissue ; hence it
resembles a cavernous tissue (Gussenbaur). The
corpora cavernosa of the clitoris, the glans clitoridis,
and the bulbi vestibuli, corresjjond to the analogous
parts in the penis of the male. The glands of
Bartholin correspond in structure to the glands of
(Jowper in the male.

400

CHAPTER XXXV.

THE MAM M A R Y r; L A X D .

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 tine bundles of fibrous
tissue with branched connective-tissue corpuscles pass
between the alveoli of the gland substance. The
amount of this interalveolar tissue varies in difterent
places, l3ut in the active gland is always relatively
scanty.

Migratory or lymph 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 o'land alveoli. Granular large vellow
(pigmented) nucleated cells occur in the connect! v%
tissue, and also in the alveoli of the resting'
o^land, and Creio:hton 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

jlfA MM.l K ) ' GlANP.

401

derived from tlie bundles of non-striped muscular
tissue present in the skin of the nipple of the ])re;ist.

The small ducts in the lolniles 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

Fig. 2oO.— From a Section through the JIamniary Gland of Cat in a late
stage of pregnancy. {Atlas.)

a. Epithelial cells lining tlie gland-alvedli, seen iu profile; b, the same, seen
from the surface. Many epithelial cells coutiiiu an oil globule. In the cavity
of some of the alveoli are milk globules and granular matter.

before these latter pass into the alveoli — are lined ^vith
a single layer of flattened pavement epithelium cells ;
they are analogous to the intermediate portion of the
ducts of the salivary glands [see Chap. XXIII.).

365. Each of these terminal branches divides and

takes up several alveoli (Fig. 250). These are wavy

tubes, saccular or flask-shaped. The alveoli are

larger in diameter than the intralobular ducts. Each

A A

40 2 Elements of Histology.

alveolus in tlie 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
membrana propria, like that of the salivar}^, lachrymal
and other glands, is a basket-work of branched cells.

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 linally pass out from the cell
protoplasm into the lumen of the alveolus, and
represent 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
aerain forming: oil orlobules in the above manner
without being themselves destroyed (Langer). The
milk globules, when in the lumen of the alveoli, are
enveloped in a delicate cuticle — the albumin mem-
brane of Ascherson, which 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-preg-
nant or non-suckling individual — contains, compara-

Ma.umakv Gland. 403

tivfly sj»eal<iii,i,% few alveuli, but a great <leal of tilnous
connective tissue ; the alveoli are all solid cylinders,
containing within the limiting nieinbrana propria
masses of polyliedral granular looking epithelial cells.
During pregnancy these solid cylinders undergo mul-
tiplication, elongation, and thickening, owing to the
rapid division of the constituent 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. The central cells are the
cohstrum corpj'.sries, and consequently they are found
in the milk of the first few days only.

3G7. Ordinary milk contains no colostrum corpus-
cles, ])ut 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
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,

3G8. Each gland alveolus is surrounded V^y a dense
network of' capWarij Wood-vessels. The alveoli are
surrounded by hjmpJi spaces like those in the salivary
glands (Covne), and these spaces lead into aetiKorks of
hjiiii)lifdic vessels of the interlobular connective tissue.

404

CHAPTER XXXVI.

THK SKIN.

369. The skin consists of the following layers
(Fig. 252) : — (1) The epidermis; (2) the corium, or
cutis vera, with the papilla? : (3) the subcutaneous
tissue, with the adipose layer or the adipose tissue,

370. (1) The epidermis (Fig. 25), 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
tlie stratum corneum. This is of great thickness in
the palm of the hand and the sole of the foot. The
stratum Malpigliii fits into the depressions between
the papilla? of the corium as the interpapillary pro-
cesses. The i^resence of prickle cells, of pigment
granules, and of branched interstitial nucleated cells,
etc., has been mentioned in Chapter III.

There occur in the stratum ]Malj)ighii migrator}-
cells of granular aspect ; they appear to migrate from
the papillary layer of the corium into the stratum
IMalpighii (Biesiadecki).

In the coloured skin — p.g. of the negro — pigment
granules are abundant in the cell substance of the
stratum Malpigliii, especially in the deeper layers ;
but there is present an almost continuous layer of
pigment in the superficial layers of the stratum
corneum (Fig. 251).

371. (2) The coriiiiii is a dense feltwork of
bundles of fibrous connective tissue, w^ith a large
admixture of networks of elastic fibres. From the

Sa'/iv.

405

surface of the coriuui project small conical or cylin-
drical papilla'.. These are best developed in those
parts where the skin is thick — e.g. volar side of
hand and foot, scalp, lips of mouthy etc. Between

Fig, 261. — From Vertical Section througli Epidermis of Skin of Finger of
Negro. (Photo. Moderate magnification.)

a, Surface of stratum corneura, much pijjiuented; ft, stratum corneum ; e,
stratum Maliiighii, containing pigment ni its cells; (?, corinm with papilhe
extending into the stratum Malpigliii.

the surface of the coriuni and the epidermis there
is a basement membrane. Migratory cells, with and
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.

4o6

Elements of Histology.

372. (3) The supei^cial part of the subcuta-
iieoii«» tissue insensibly merges into the deep part of
the corium ; it cjiisistsof bundles of fibrous connective
tissue aggi-egated into trabeculse crossing one another
and interlacing in a complex manner. Numerous

Fig. 252. — ^Vertical Section through the Skin of Human Finger.

fl. Stratum comeuin : h, stratum lucidtim ; c. stratum Malpighii ; d, Meissner's,
or tactile corpuscle ; e, blood-vessels cut across ; /, sudoriferous canal or
duct.

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, foinning
the stratum adiposam. 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
(Fig. 41, and on pp. 55 and 56). The deep part of the
subcutaneous tissue is loose in texture, and contains
the large vascular trunks and big nerve branches.
373. The superficial part of the subcutaneous

tissue, or, as sonic liavc it, the deep part of the
coriiiin, contains the sudoriparous or stveat (jlaiuh.
Each gland is a single tube coiled up into a dens"^
mass 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-
pajjillary process of the stratum Malpighii and the
rest of the ej)idermis, 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
a continuation from the deep layers 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.

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 —

4o8

Elements of Histology.

of the coiled tube (Fig. 253) is of the same stnu-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 these
essential respects, that its epithelium is a single layer

Fig. 253. — From a Section tlirough Human Skin, showing the sweat gland
tubes cut in various directions. {Atlas.)

u, First part of the coiled tuljs seen in longitudinal section ; b, the same seen
in cross-section ; c, distal part seen in longitudinal section ; d, the same

seen in cross-section.

of transparent columnar cells, and that tliere is
between this and the limiting merabrana propria a
kfjjer 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, tlie nipple of the breast, the scalp, Init
especially in the axilla, this distal portion of the coiled
tube is of \evy 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

S/c/x. 409

chief cells of the gastric ghmds (Langley), inasmuch
as they produce in their interior hirger or siualler
granules which are used up during secretion, from the
periphery towards the lumen.

376. The ceriiiiiiiioiis g-laiids 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 w^ax of the ear.

Around the anus there is an elliptical zone, in the
skin of which are found large coiled gland tubes — the
circiim-anal glands of A. Gay — which are identical in
structure with the distal portion of the sweat gland-
tubes.

377. The sweat gland develops 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 liaii'-follicles (Fig. 254).— The skin
almost everywhere contains cylindrical yb/Zic^es, planted
more or less near to one another, and in groups. In
each of them is fixed the root of a hair ; that part of
the hair which i^rojects beyond the general surface of
the skin is the slia/t.

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.

Tn size, the hairs and hair-follicles differ in dif-
ferent parts. Those of the scalp, the cilia of the eye-
lids, the hairs of the axilla and pubic region, those of
the male whiskers and moustache, are coarse and

4TO

Elemexts of Histology.

thick, while the hairs of other places — e.fj. the outer
surface of the eyelids, the inside of the arm and fore-
ann, etc. — are very minute ; but as regards structure,
they are all very much alike.

379. A complete hair and hair-follicle — that is,

trO

Fig. 254.— Longitudinal Section through a Human Hair. (Atlas.)

1, Epidermis; 2, moutli of hair follicle: 3. sebaceous follicle; 4, musculus
arrector pili ; 5, papilla of hair ; 6, adipose tissue.

the papillary hair of Unna — shows the following
structure : —

The hair-foUide. Each hair-follicle commences on
the free surface of the skin with a funnel-shaped
opening or movJlt : it |;asses in an ohlique direction

throiiiili the corium into the subcutaneous tissue, in
whose middle strata — i.e. in the stratum adiposum —
it terminates with a sli^itly enlarged extremity, with
which it is invaginated over a relatively small fungus-
shaped papiUa. This latter is of tibrous tissue, con-
taining 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 wnerallv 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 "*
hail' — 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-foHicle is curved, sometimes
even slightly upwards.

380. The structure of a liair-folliele is as follows
(Fig. 255) : There is an outer coat composed of fibrous
tissue : this is the fibrous coat of the liair-sac. It is
merely a condensation of the surrounding 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 tibrous layer of the hair-
sac a single contintious layer of transversely or circu-
I a rhj-ar ranged spimUe-sliaped ceUs, each with an oval
flattened or staff"- shaped nucleus, completely resembling,
and generally considered to be, non-striped muscle-
cells. Inside of this layer of the hair-sac is a glassy-
looking, hyaline, basement membrane, which is not
very distinct in minute hairs, but is suthciently con-
spicuous in large adult hair-follicles. This glassy
membrane, as it is called, is a direct continuation of
the basement membrane of the surface of the corium,
and it can be traced as a delicate membrane also over
the surface of the hair-papilla.

412

Elements of Histology.

381. Next
rootsheath, the

to the glassy membrane is the outer
most conspicuous part of the hair-
follicle. It consists of a thick stratified epithelium of
exactly the same nature as the stratum Malpighii of

the epidermis,
I '. ,. — ^i^-,^ _ with which it

is directly con-
tinuous, and
from which it
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 Mal-
pighii ; then fol-
low inwards seve-
ral layers of poly-
hedral cells; and,
finally, flattened
nucleated scales form the innermost boundary of the
outer root -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, it is there continuous with the
cells constituting the hair-bulb.

382. The centre of the hair-follicle is occupied by
the root of the hair, which terminates with an enlarged
extremity — the Itair-hulb ; this grasps the whole
papilla. The hair-bulb is composed of polyhedral
ei)ithelial cells, separated from one another by cement
substance, and continuous with the cells of the ex-

Fig. 255. — Cross-section through a Hiunau Hair
and Hair- follicle.

«, ^farrow of liair; h. cortex of hair; c, cuticle of
hair ; d, Huxley's layer of inner root-sheath ; e,
Henle's layer of inner root-sheath ; /. outer root-
sheath ; g, glassy Jiienibrane; /(, fibrous coat of hair-
sac ; i, lymph spaces in the same.

Sa'/n. 4 1 3

tremity of tlie outer root-sheatli, from wliicli they
originate in the first instance ; just over the papilla
there is a special row of sJiort cohunnar cells, which
are in an active state of multiplication, in consequence
of which new cells are constantly being formed over
the papilla. As a result of this there is a gradual
pushing outwards, within the cavity of the hair-
follicle, of the cells previously formed ; these cells
form the hair itself. Nearest to the papilla all the
cells of the hair are polyhedral, farther outwards — i.e.
towards the surface of the skin — they become more
elongated and spindle-shaped, and constitute the cells
of the hair-substance ; except in the very centre of the
hair, where they remain polyhedral, so as to represent
the cells of the marrow of the hair, and in the peri-
phery of the hair, where they remain more or less
polyhedral, so as to form the inner root-sheath.

383. The root of the liair, 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 mentioned.
They can be isolated by strong acids and alkalies. In
pigmented hairs there occur numerous figment
(jranules between the hair-fibres, but also diffused
pigment in their substance. The same is noticed with
reference to the hair-bulb — namely, pigment granules
being present in the intercellular cement, and pig-
ment also in the cell substance. In the centre of
many hairs is a cylindrical marroiv, containing
generally one row of ])olyhedral cells, which are, to a
great extent, filled with air.

414

Elements of Histology.

a I

•384. On the surface of the haii--substance is a thin
cuticle, a single layer of horny non-nucleated hyaline
scales arranged more or less transversely ; they are
imljiicated, and, according to the degree of imbrica-
tion, the cuticle shows more or less marked projec-
tions, which give to the circumference
of the hair the appearance of minute
teeth, like those of a saw.

385. The inner root-sheath in
well-formed, thick hairs is very dis-
tinct, 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
remnant of a nucleus ; and, finally,
an outer, or HenleJs, layer — a single
layer of non-nucleated horny cubical
cells.

The shaft of the hair (Fig. 256),
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-
stance, cuticle, and inner root-sheath — and the con-
tinual new production of cells over the jmpilla causes a
gradual progression and conversion of the cells, and a
corresponding growth in length of the hair.

Pigmented hairs, as mentioned above, contain pig-
ment granules between — i.e. in the interstitial sub-
stance cementing together — the hair-fibres, and diffuse
pigment in their substance. According to the amount
of these pigments, but especially of the interstitial
pigment granules (Pincus), the colour of the hair is

Fig. -2.56. —Longitu-
dinal View of the
Shaft of a Pig-
mented Human
Hair.

ilarroAV of
b, fibres of
substance ;
cuticle.

hair ;

liaii-

Sa'/x.

415

of a greater or lesser dark
is oliieHy ditlVise pigment,
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
absence of pigment.

Sleek hairs are circular,
curly oval, in cross-section.
Sleek hairs are implanted
with their h a i r - b u 1 b
straight ; in curly hairs the
hair-bulb forms a more or
less pronounced hook. This
is the cause for the more
or less si)iral twisting of
the hair-shaft of curly hairs
during its growth outwards.

387. Xew formation
of liair (Fig. 257). —
Every hair, be it fine and
short or thick and long,
\mder normal conditions,
has only a limited exist-
ence, for its hair-follicle,
including the papilla, sooner
or later undergoes degener-
ation, 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, de-
generate and are gradu-
ally absoi'bed. Then there

tint, in red luiirs there
In white or albino hairs

fe''i'l't.:->.? -^

Fig. 257. — From a section through
Human Scalp, showing a degen-
erating hair. (Atlas.)

a. Epidermis ; b, hair ; c, outer root-
sheath of hair follicle ; d, sebace-
ous follicle; f, arrector pili ; /,
cyst grown out of the outer root-
sheath; g, hair-kuob ; h, new out-
growth of the outer root-sheath ;
/, new papilla.

4i6 Elements of Histology.

is left only the uj^per part uf the follicle, and in the
centre of this is the remainder — i.e. non-degenerated
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 repre-
sents the hair-knoh (Henle). Xow, from the outer
root-sheath a solid cylindiical outgrowtli of epithelial
cells into the depth takes place ; against the extremity
of this a new papilla is formed. In connection with
this new papilla, and in the centre of that cylindrical
outgrowth, a new hair-bulb and hair are formed, and
as the latter gradually mows outwards towards the
surface, it lifts, or rather pushes, 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 j^apillarv hairs side by side with
degeneratincT hairs or hair-knobs.

388. Developiiieiit of liair. — In the human
fcetus the liair-follicles make their first appearance
about the end of the third m.onth, as solid cylindrical
outgrowths from the stratum INIalpighii. This is the
rudiment of the outer root-sheath. After having pene-
trated a short distance into the corium, this latter
becomes condensed around it as the rudiment of the
hair-sac. and at the distal extremity forms the papilla
2:rowinc( against the outer root sheath and invajicin-
ating it. On the surface of the papilla a rapid mul-
tiplication 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
and the inner root-sheath are formed. As growth
and multij^lication proceed at the hair bulb, so the
new hair, with its pointed end, gradually reaches the
outer surface. It does not at once penetrate the
epidermis, but remains growing and burrowing its
wav for some time in the stratum corneum of the

Sa'/.v.

417

epidermis in a more or less horizontal direction, till it
finally lifts itself out of this beyond the free surface.

3iS9. In many mammals occur, amongst ordinary
hairs, special large hairs, with huge hair-follicles
planted deeply into the subcutaneous tissue ; such

Fig. 25S.— Section througli the «kiii nf tlie Lip of a Rabbits Mouth.
(Fhotorjraph. Loiv power.)

Small ordinary hair-follicles, one hirge tactile hair and hair-follicle. Tlie dark
thick hoiindarj- is the tissue of the hair-sac. the clear parts in.side are the
masses of blood spaces, the dark line next to the hair itself is the outer
root-sheath.

are the big hairs in the skin about the lips of the mouth
in the dog, cat, rabbit, guinea-pig, mouse and rat, etc.
These are the tactile hairs (Fig. 258). Their hair-follicle
possesses a thick hair-sac, in which are contained large
sinuses intercommunicating with one another and
with the blood system ; these sinuses are separated
B B

41 8 Elemexts of Histology.

\)\ trabecul?e of non-strined muscular tissue, and
represent, therefore, a cavernous tissue. The papilla
is large, 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-sneath (Arnstein).

390. With each hair- follicle are connected one or
tvro sehaceous foUirles. These consist of several fiask-
shaped or oblong alveoli, joined 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 cavity 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. Towards
the duct they become shrivelled \\\} into an 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 proprise
— the products of this multiplication are gradually
shifted forward towards the duct, and through this
into the neck and rnoutli of the hair-follicle, where
they constitute the elements oi sehuin.

There is a very characteristic misproportion be-
tween the size of the hair-follicle and that of the
sebaceous gland in the embryo and newly-ljorn, the
.sebaceous cjland Ijeing there so larije 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-

Sa'/jv.

419

daily where they are of good size — as in the scalp —
there is a bundle, or rather group of bundles, of non-
sti-iped muscular tissue ; this is tlie arrector pili. It is
inserted in the liaii--sac near the bulbous portion of the

Fig. 259. — Vertical Section through the Human Xail and Nail-bed.

a. Stratum Malpigbii of uail-bed; I), stratum .arrauulosuin of uail-bed • c Aeev
layers of nail sulistaucc ; d, superfieiallayers of same. ' '

hair- follicle, and passes in an oblique direction towards
the surface of the coriuni, grasping, as it were, on its
way the sebaceous follicle, and terminating near the
papillary layer of the surface of the corium. The
arrector pili forms with the hair-follicle an acute
angle — this latter being planted into the skin in an

42 o Elements of Histology.

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
muscular tissue (Kolliker), independent of the hairs ;
these run in an oblique and horizontal direction, and
form plexuses.

393. The nails (Fig. 259).— We distinguish the
hody of the nail from the free margin and from the
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 j)art of the nail-bed. The
nail is inserted, with the greater part of its lateral and
wdth its posterior margin, in the nail-groove, a fold
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 corium of the nail-bed is higlily vascular : it
is firmly fixed by stifi" bands of fibrous tissue on the
subjacent periosteum ; it is covered with a stratum
]\Ialpighii of the usual description, except that the
stratum irranulosum is absent in the nail-matrix, but
is present in a rudimentary state in the rest of the
nail-bed. The nail itself rej^resents 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 coriuni 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 fcetal nail is produced.
At this early stage the nail is covered by stratum
corneum. By the end of the fifth month the nail
marcrin breaks throuijh this stratum corneum. and bv
the seventh month the greater part of tlie nail has
become clear of it.

306. Till' bIood-ves«»eIs of the »kiii. — The
blood-vessels are arranged in diflerent system < for the
different parts of the skin (Tomsa) : —

{(() There is. fir^^t, the vascular sy.stem of the
adipose tissue, diflering in no way from the dis-
tribution of blood-vessels in fat tissue of other places.

(6) Then there is the vascular system of the hair-
follicle. The papilla has a capillary loop, or rather
a minute arteriole, a capillary loop, and a descending
vein, and the fibrous ti.ssue of the hair-sac possesses
capillaries arranged as a network with elongated
meshes, with its afferent arteriole and eflerent vein.

(c) The sebaceous follicle has its afferent arteriole
and eflerent 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 \\ ith elongated meshes.

(d) The sweat glands have an afferent arteriole,
from which proceeds a veiy rich network of capil-
laries, twining and twisting round the gland-tube.
The duct possesses its separate aff'erent arteriole and
capillaries, forming elongated meshes.

42 2 Elements of Histology.

(e) The last arterial branches are those that reach
the surface of the corium, and there break up into a
dense capillarv network with loops for the papillae.
In connection with these capillaries is a rich plexus of

veins in the superficial layer of the corium.

Fig. -260. —Skin of the Web of Frog of which the lymphatics had been in-
° jected, showing the dense plexus of lympliatic vessels. {Photograph.
Lov: poi'-er.)

(/) In the nail-bed are dense networks of capil-
laries, with loops for the above-named folds.

397, The lysiipliatics (Fig. 260). — There are net-
works of lymphatic vessels in all strata of the skin ;
they are, more or less, of horizontal expansion, with
oblique branches passing l^etween them. Their wall
is a sinfde laver of endothelial cells, and some of them
possess valves. Those of the surface of the corium

Sa'/x. 4-3

take up lyiuplKitics of the papilla?. 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 iierve^». — The nerve-branches break up
into a dense plexus of fine nerve fibres in the super-
ficial layer of the corium. This plexus extends hori-
zontally, and gives ofi" 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, Podkopaefi", Eberth,
Eimer, Ranvier, and others). According to some,
they teraiinate with a minute swelling ; according to
others, they form networks ; according to more
recent observations, some of the fibrils terminate
also in the substance of the deep epithelial cells {see
Chap. XIV.).

The subcutaneous nerve-branches of some places
— palm of hand and foot, and skin of penis — give
off' single niedullated nerve fibres, terminating in a
Pacinian corpuscle, mentioned in a former chapter.
In the volar side of the fingers and toes there occur
in some of the papillfe of the corium the tactile or
Meissner's corpuscles, each connected with one or two
meduUated 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 fibrillte (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.

424

CHAPTEE XXXVII.

THE CONJCXCTIVA AXD ITS GLANDS.

399. (1) The eyelids (Fig. 261).— The outer
layer of the eyelids is skin of ordinary description :
the inner is a delicate, highly vascular membrane —
the conjunctiva palpehrcn. This includes a firm plate
— the tarsal plate. — which is not cartila^re, 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 sidi-s sliort minute ducts, each of which becomes
enlarged into a spherical, saccular, or llask-shaped
alveolus. This is identical in structure and secretion
icith 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 nrbicidaris — 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 Riolani. This sends bundles
around the mouth of the ^Meibomian ducts.

401. At the anterior angle of the free margin of
the lid are the evelashes or cilia, remarkable for their

Conjunctiva and its Glands.

425

thickness and rapid reproduction. Xear the cilia, Viut
towards the ^leiboniian ducts, open the ducts of

\iT&,

- ^® "P^^-

*:■$•

Y-^

"=S^

Fig. -261.— Vertical Section through the Upper Eyelid. (Waldeger.)

1 CoDfunetiva • 2, skin ; 3. permanent folds of the conjunctiva ,- 4, bundles of

' the sphincter orbicularis; 5, eyelashes : 6. mouth of the gland of ilohl ; 7,

duct of the Meibomian gland : >, tarsal gland>.

peculiar large glands — the glands of Mold. Each of
these is a wavy or spiral tul>e, pa^^sing in a vertical

426 Elements of Histology.

direction from the margin of the lid towards its distal
part ; it comjdetely coincides in structure with the
large portion of a sweat gland — i.e. that part contain-
ing 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
mucous membrane extends in the shape of minute
papillae. In the conjunctiva palpebral the epithelium
is a thin stratified pavement epithelium ; there are
no papilhe, 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 palpebrse
— i.e. the fornix conjunctivae — -and, further, the con-
junctiva fixed to the sclerotic, and terminating at the
margin of the cornea — the conjunctiva l)ul])i. 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 (Stiedn, Waldeyer). Towards the cornea the
epithelium of the conjunctiva assumes the character
of stratified pavement epithelium, and minute papillae
extend into it fi-om the mucosa.

403. The mucous membrane is fibrous tissue, con-
taining 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
terminate as the capillary network of the su])erficial

Conjunctiva and its Glands. 427

layer of the mucosa, and as capillaiy networks for the
Meibomian glands, Krause's gland, etc. Around the
corneal margin the conjunctival vessels are particu-
larly dense, and loops of ca})illaries extend from it
into the very margin of the cornea.

405. The lyiii|>liafic«» form a superficial and
deep network. Both are connected by short branches.
The deep vessels are possessed of valves. The super-
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 conjunctiva.

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 conspicuous,
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
numbers in man and calf. They have been mentioned
in a former chapter.

407. (2) The lacliryiiial g-laiids 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 — especially of the
intralobular ducts— and alveoli, the distribution 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, transparent, and slightly

428 Elements of Histology.

granular during rest ; but during secretion they grow
smaller, more opaque and more granular, their outlines
are not well defined, and the nucleus becomes more
spherical and placed more centrally.

408. In most mammals there is in the inner angle
of the eye, and closely placed against the surface of
the eyeball, a gland called Harder's (jiand. Accord-
ing 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 Harders gland
exists also in the ape and man.

429

CHAPTER XXXVIII.

CORNEA, SCLEROTIC, LIGAMENTUM PECTINATUM AND
CILIARY MUSCLE.

400. T. The roriiea (Fig. 262) of man and many
mauiDials consists of the following layers, counting
from front to back : —

(1) The epithelium of the anterior surface [see
Fig. 26). 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
tlie 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 'ineinhrane, or elastica anterior. It
is best shown in the human eye, but is present, even
though only rudimentary, in the eye of mammals.

(3) Then follows the ground suhstaiice, or sub-
stantia propria, of the cornea. This is composed of
iamelhe of bundles of fibrous connective tissue.
Neiofhbourinor lamellse are connected with one another
by oblique bundles.

The fibre bundles within each lamella run parallel
to the surface 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 librse arcuatse.

43°

Elements of Histology.

The fibrils within the bundles, and the bundles,
and the lainelhv of bundles are held together by an

interstitial, albu-
;g7 niinous, semi-fluid ce-
ment sul)stance, which,
like other similar in-
tei'stitial substances,
belono's to the globu-
lins, and is soluble in
10 per cent, saline
solution (Schweigger
Seidel). A few elastic
tibrils are seen here
and thei'e. Between
the lamellae are left the
lacunas and canal iculi
for the branched, flat-
tened, nucleated, cor-
neal corpuscles^ de-
scribed in a previous
chapter (Figs. 37, 38).
They anastomose with
one another within the
same plane, and also,
to a limited degree,
with those of neigh-
bouring planes.

411. (4)Thenieni-
l>i'aiia Desceiiioti,
or elastica posterior,
is a resistant elastic
membrane, conspic-
uous by its thickness
in all corne?e,

(5) The posterior
surface of this mem-
l^rane is covered with

Fig. 2(32. — From a Vertieal Section
through the Membranes of the Eve of a
Child. {Atlas.)

a. Cornea; b, sclerotic : c. \v\> ; d, processus
ciliaris; e, ligameunnn pectinatiiui : /,
ciliary imisck", Its meridional bundles; n
choroid membrane; h. retina of the nra
serrata; i, sphincter piipilla^ in cross-
section.

Cornea. 431

a mosaic of ])eautit'vil pohjijomd endotlielidJ ceUs^
eacli with an oval nucleus — the endotheliuiii of
Descemet's membrane. Under stimulation 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 processes.

There are no blood-vessels in the normal cornea,
except in fretal life, when there is underneath the
anterior epithelium a plexus of capillaries.

The lymphatics are represented as the intercom-
municating lymjih-canalicular system — i.e. the lacun?e
and canaliculi of the corneal corpuscles ; and in con-
nection with these are lymph channels lined with a
continuous endothelium and containing; the nerve
bundles.

412. The nerves (Figs. 103, 105, 106) are distri-
buted as the nerves of the anterior layers, and as
those of the Descemet's membrane. The first form
rich plexuses of tibrillated 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 (Kfilliker) — and these imme-
diately underneath the epithelium break up into their
constituent primitive fibrils, the latter coming off
the former brush-like (Cohnheim). These primitive
fibrilhe ultimately ascend into the anterior epithelium
(Hoyer, Cohnheim, and others), where they branch,
and nearly reach the free surface. They always run
between the epithelial cells, and are connected into
anet\Aork. According to some observers, they ter-
minate w^ith free ends, pointed or knobbed : but
according to others these apparent free ends are
not in reality free endings (Figs. 107, 263 and
264).

43 2

Elemests of Histology

413. The nerves of Descemet's membrane form
also a j^lexus of non-medullated fibres in the posterior
lavers of the o-round substance : from them come
off vast numbers of primitive fibrilla?, running a more

Fi'^'. 263. — From a Horizontal .Section through the Gokl-stained Cornea of

" Rabbit ; the corneal (branched) cells are faintly indicated, but the

nerve tibrillse are well marked, also their lateral branchlet.s, terminating

apparently with a minute knob. {Photograph. Moderate magnification.)

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 wdth their protoplasm.

414. II. The sclerotic consists of lamella? of
tendinous tissue. The bundles of fibrous tissue are
opaque as compared with those of the cornea, although

SCLEKDl^IC.

433

they pabs insensibly into them. There are lymph
clelts bet^veen the lamella? and trabeculse, and in
them lie the flattened connective-tissue corpuscles,
which, in the dark eyes of some mammals only, contain

Fig. 264. — From the same preparation as in ijrecediiig tigiue, shuwing tlie
tine Nerve Fibrils jiassing along the processes and bodies of the
branched corneal corpuscles. (Pliotograph. Moderate magnification.)

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-
jjorting tissue for the blood-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
c c

43+ Elements of Histology.

i« then called lamina Jusca. The rest — i.e. next
to the choroid membrane — is the supra-choroidal
tissue.

416. There H re blood-vessels in the sclerotic, whicli
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 li»Jiiii«*iitiii" pec tiiiatuiii
iridic [see Fig. 262) is a conical mass of spongy tissue
joining hrndy 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, withtliat of the iris and ciliary pro-
cesses. This ligament is composed of trabeculse and
lamella? of stiff elastic fibre-, 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
trabecular anastomose, so as to form a honeycombed
plexus, and the spaces in this plexus are lined
with a layer of flattened endothelial cells, directly
continuous with the endothelium 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 band. In some mammals, the sjiaces
in the ligamentum pectinatum near the iris 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
neii^hbonrhood of the ligamentum pectinatum iridis,
is a circular canal — the canal of Sclilemni ; this is

Ciliary Muscle. 435

lined with (nidotheliuin, and is considered Ijy some
(Schwalbe) as a lymphatic canal ; Ijy others (Leljer)
as a venous vessel.

418. IV. The <'iliar.v muscle (Fig. 2G-J), or

tensor choroideie, is tixed to this ligamentum pecti-
natum ; it is composecl 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 ; {h) 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 pectinatuDi, sclerotic, ciliary processes, and
the adjoining portion of the choroid membrane.
The bundles of the muscle are arranged more
or less in lamellpe ; within each lamella they form
plexuses.

A rich plexus of non-medullated nerve fibres, with
groups of ganglion cells, belongs to the ciliary muscle.

436

CHAPTER XXXIX

IRIS, CILIARY PROCESSES AND CHOROID.

419. I. The ii'is 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 throucjh the trabecule of the lisramentum
pectinatum with the membrana Desceraeti of the
cornea.

(3) The substantia propria : this i-, 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 CDntain, in all but albino and blue
eyes, yellowish-brown pigment granules. The depth
of the colour 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 on the ])osterior 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,

JRIS.

437

where there are no pigment granules This enchj-
theliuiu is called the uvea, or iapetum nigrum. The
interstitial cement substiince
between the cells is not pig-
mented, but transparent.

The name "uvea" is some-
times applied to the whole of the
iris, ciliary processes, and choroid
membrane.

In blue eyes the posterior
epithelium is the only pigmented
part of the iris, and so it is
also in new-born children, whose
iris appears blue. In all cases
where the iris appears blue,
this is due to the dark back
— i.e. the pigmented epithelium
of the posterior surface — being
viewed throutjh a dull layer —
i.e. the substance of the iris.

421. Near the pupillary
border the posterior section of
the substantia propria contains
a broad layer of circular bundles
of non-striped muscular tissue :
this is the spliincter pupiUct.
In connection with this are
bundles of non-striped mus-
cular fibres, passing in a radi-
ating direction towards the
ciliary margin of the iris : these
are the bundles of the dila-
tator pupiUc(;, 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 (Ivanoff).

Fi-;

I - vessels

I injected) uf the Iris and
Choroid Membrane of the
Eye of a Child. {Kolliker,
after Arnold.)

a, Capillaries of the choroid ;
b, era serrata; c, iilood-
vessels connected with, d,
those of the ciliary pro-
cesses, and with e, those
of the iris; /, capillary
network of the pupillary
sphincter.

43^ Elements of Histology.

422. The blood-vessels (Fig. 265) of the iris
are very numerous. The arteries are derived from
the eirculus arteriosus iridis major, situated at the
ciliar}" margin of the iris, and from the arteries of
the ciliary processes. These arteries run in a radi-
ating direction towards the pupillary margin, where
they terminate in a dense network of capillaries for
the sphincter pupilla?. But there are also numerous
capillary blood-vessels of a more or less longitudinal
direction near the posterior surface of the iris. The
veins accompany the arteries, and both are situated
in the middle stratum of the substantia propria.

In the sheath of the Ijlood -vessels are lymplt clefts
and lympli 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
pupilla3 : (h) a network of fine non-medullated fibres
for the anterior surface ; and (c) a network of non-
medullated fibres for the sphincter pupilhe.

The capillary blood-vessels are also accompanied
by fine nerve fibres (A. Meyer), and, according to
Faber, there exist ganglion cells in these nerve net-
works.

424. TI. The miliary processes are similar in
structure to the iris, except, of course, that they do
not ])0ssess an anterior endothelium or an anterior
basement membrane. The suhstantia 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. Muller). The
inside of it is covered with a layer of pigmented poly-

Ciliary Processes.

439

licdral v\\\\\\v\\w\\\^W\(^ inpotu))i nigriDii : the cells are
polygonal when viewed from the surface. The in-
divkliial cells are separated by thin lines of a trans-
parent cement substance. This pigmented epithelium
is covered with a layer of transparent columnar

Y'v^. 2(i(l — Fi-()iii a Vertical Section thr()uc;li the Ciliary Processes of the
Ox's Eye. {Atlas.)

u. Fil)roiis tissue with iiigiiiented cells; 6, loose niirons tissue fciniiiiiLr the
proiier ineiiihi-ane of the ciliary process ; c. iiigiiieiited epithelium rovermg
the posterior sui-fac-e of the ciliaiy process; (/, epitheloid cells, lorniiug the
j>ars ciliaris rctiiuv covering the l)ai-l\ of the ciliary jirocesses; e, Zonula
Zinnii, with laindles of lilircs.

epitheloid cells, each w^ith an oval nucleus. These are
closely fixed on the tapetum nigrum, and are the
continuation of the retina over the ciliary processes :
this is thenars ciliaris retince (Fig. 266).

425. The arterial branches for the ciliary processes

440 Elements of Histology.

and muscle are cliieliy derived from the ciivulus
arteriosus iridis major, and fnrn a dense network of
capillaries for the former ; eacli ciliar}^ process pos-
sesses a conical group of capillaries (Fig, 'l^o).

426. III. The €lioi"oi<l membrane consists —
counting from outwards, i.e. from the sclerotic, in-
wards, i.e. towards
.,.'"%•.. ,,-. the retina — of the fol-

'^■^^!-0^'' ''^''^0^.. lowing layers :^

iiii^^^^'.'fi^^^ ^^^^"^^^h^: ( 1 ) The membrana

'^0''^''y.!f^^:-' ■:|M^-%... " supra- choroidea. This
vi^^^^^j.v^^'^^li^ ..•;jU5:^Sl?^ i'^ ^ Continuation of

■^i^-^i}lv^^0^ •••■^'^v;^^''" the sclerotic, with

which it is identical

Fjir -ly^-, — Pimneuted Connective-tissue . ^•,

"cells of the Choroid Coat. (Atlos.^ lU structure ; the spaCCS

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
and veins, and, in its outer portion, pigmented cells
(Fig. 267).

427. (3) Then follows the membrana chorio-capil-
laris, a dense network of capillary blood-vessels em-
bedded in a tissue containing numerous branched and
unbranched pigmented and unpigmented connective -
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 reofion of the ora serrata of the retina — i.e.
next to the ciliary processes — also this zone of the
choroidea is lined with a layer of transparent,
columnar, epitheloid cells, representing the jDars
ciliaris retinte.

428. The arteriae ciliares breves and recurrentes,
situated in the outer part of the choroidal tissue, form

Choroip. 441

iiltiniatcly tlx' tlciisc networks of capillaries fof the
cliorio-capillai-ies. The veins derived from this pass
into the outer part of the choroid, where they anasto-
mose so as to form the peculiar large veins, which are
called the vente vorticosse.

In the eyes of some animils (cat, dog, sheep, ox)
there exists a special layer of cells (cat, dog) or
fibres (herbivora), which, owing to its capability of
reflecting a great deal of light, is called the tapetum
hicidnm or me iibrana versicolor of Fielding. This
layer when present is situated between the stroma
of the choroid (laver 2) and the membrana chorio-
capillaris (layer 3).

442

CHAPTER XL.

THE LENS AND VITREOUS BODY.

429. (1) TIk* lens consists of a thick, firm, elastic
capsule and of the lens substance. The former shows
fine longitudinal strijB, 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 pol^^hedral,
granular-looking, epithelial cells, each with a spherical
or oval nucleus. This epithelium stops as such at the
margin of the lens, where its cells, gradualh'^ elongat-
ing, 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 neigh-
bouring 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
is 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. 268) are arranged in
concentric lamelLie, 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 extremities are in contact

ViTRF.ous Body.

443

with the ends of the fibres of the sjinie lamelhi in tlie
siUiires, or the rays of the so-called lens stars. In
the lens of the newly-born child, the stars of both
anterior and ])Osterior lamellae possess three such rays,
while in the adidt each of these rays has secondary
rays. Tn these rays there is a homogeneous thin layer
of an albuminous cement substance ; a similar sub-
stance in minute quantity is also present between the
lamellve, and in it occur smaller or larger clefts and
channels, which evidently carry the nutritious fluid for
the lens fibres.

431. (:2) The vitreous bo<ly is a fluid substance
enclosed in a delicate hyaline capsule — the memhrana
hyaloidea. This membrane, at

tlie margin of the fossa patel-
la ris of the vitreous body — i.e.
the fossa in wliich the lens is
lodged — and without covering
this fossa, passes as the zonula
ciliaris, or zonula Zinnii, or
suspensory ligament of the lens,
to tlie margin of the latter, to
whicli it is firmly adhering. So
it adheres also to the surface of
the ciliary processes. The zonula
Zinnii is hyaline and firm, and
is strentjthened bv numbers of
bundles of minute stifl' fibrils.

Between the suspensoi y liga-
ment of the lens, the margin of the lens and of the
fossa patellaiis is a circular lymph space, called the
canalis Petiti.

Beneath tlie membrana hyaloidea are found iso-
lated nucleated granular-looking cells (the sub-hyaloid
cells of Ciaccio), possessed of amoeboid movement
(Ivanofl).

432. The substance of the corpus vitreum appears

i ,:^'^>)^j ■^^)/ A jj^ - -

Fig. 2(iS. — From a Section
through the Lens of Dog.
(Atlus.)

Sliciwing four lamellse ; in
each the component lens
filires are cut across ; they
appear as flattened hexa"-
u'ons.

444 Elements of Histot.ogy

didereiitiuted by clefts, conct-ntric in the })Hripberal,
radiating in the central part (Briicke, Hannover,
Bowman, Ivanoff, Schwalbe). But these do not con-
tain an}' 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, possessed of amoeboid move-
ments, and some contain vacuoles, indicating com-
mencinjj desfeneration. Thev are all identical with
white blood-corpuscles (Lieberklihn, Schwalbe).

Fine V)undles of fibrils are occasionally seen in the
substance of the vitreous body.

445

CHAPTER XLT.

THE RETINA.

±iJj±ULH

SMAlAAl~---{

-A

434. The retina (Fig. 269) consists of the follow-
ing layers, counting from inwards towards the choroid
membrane : — (1)
The membrana li-
mit ans interna,
wliich is next to
the membrana hya-
loidea of the vi-
treous body ; (2)
the nerve fibre
layer ; (3) the layer
of c(anglion cells ;
(4) the inner gi-an-
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)
th e m em br ana
limitans externa ;
(9) the layer of
rods and cones ;
and (10) the pig-
mented epithelium of the retina, or the tapetum
nigrum mentioned above (p. 439), which forms, at the

^ ,- o .
; o 0 oo

o ^3 Oa
3 3 o a tt_

5-— 771

Fi<r. 269. — From a Transverse Section through
tlie Eye of Sheep ; peripheral portion of
retina. (Atlas.)

a. Inner parr of sclerotic ; b, supra-choroidal
Cpigmeiited) lamellse; c, d. layers of choroid
C'lat; e. pigmented epithelium of retina; /,
hiyer of rods ; jr, cones ; 7i, layer of outer nuclei ;
i," outer molecular layer; j, layer of inner
nuclei ; k. inner molecular layer ; I, layer of
Kanglion cells, •with the radial or Muller's
fibres between ; jh, layer of nerve fibres.

446

Elemexts of Histology.

same time, the inner lining epithelium of the choi-oid
membrane.

435. From this arranixement are excepted (n) the

mm.

\-J} f-fC-, ^r ^ ;

Fig. 270.— Diagram of the Ner- Fi^
voiis Elements of the Retina.

•271.— Diagram of the Connective-
Tissue Substance of the same.

« xro,.-<> fihrps ■ 1 •'in^'lion ceUs:4, inner molecular layer; 5. inner nuclear
- ';lver:^6.omermole6u^rl^y^ riourernuclearlaver ; 8. membranahmitans
externa ; 9, rods and cones. (Jfojc Schultze.)

papiUa nervi optici, (b) 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

Retina. 447

the retina, represents the entrance of tlie optic nerve
fibres into the retina; thence, as from a centie, they
spread out in a radiating direction into the sancer-
sliaped retina, of which they form the internal 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 circular 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 Miiller's
fibres, is continued over the ciliary processes in the
shape of columnar epitheloid nucleated cells men-
tioned above : this is the pars ciliaris retime.

436. Structure of the layers of the retina (Figs.
270, 271).

(1) The iiieiiibraiia liiiiitaii!^ iiiteriia is
composed of more or less }jolygonal areas, which are
the ends or bases of pyramidal, finely-striated fibres
— the radial fibres of JlilUer. Each radial fibre passes
from the limitans interna in a vertical direction
through all lavers 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 ol nerve fibres. — The
optic nerve fibres at their entrance into the eyeball

448

Elements of Histology.

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
libres retain their medullary sheath in the retina

jectiou of Retina of Dog. \\Aflei
" Anatomy.")

Cajal, from Quain's

u. Cone rtbre ; h, rod fibre aud nucleus ; c, d, bipolar cells ■with inner nuclei, with
vertical ramifications to receive the knobbed ends of the rod fibres, e,f, with
flattened ramifications for the arborising ends of the cone fibres ; g. gan-
glion cell sending an axon to the outer molecular layer; /), spongioblast ;
1, nerve fibres passing to the outer molecular layer ;], centrifugal nerve fibres
passing into, and terminating in, inner molecular layer : m, nerve fibres
passing toinner molecular layer ; n, ganglion cells ; a, outer molecular layer;
B, inner molecular layer; c, nerve fibre layer.

(Bowman). The nerve fibres remain grouped in
bundles in the retina, and even form plexuses. For
obvious reasons, the number of nerve libres in the
nerve fibre lay^n* diminishes towards the ora serrata.

438. (3) Tlie layer of g^sin^l ion cells. — There
is one stratum of these cells only, except in the
macula lutea, where they form several strata. Each

Retina.

449

cell is multipolar, and possessed of a lar^e nucleus.
One process is directed inwards and Ijeconies the
axon, being a fibie of the nerve fibre layer. Several
branched processes or dendrites pass from the opposite
side of the cell into the next outer layer — i.e. the
inner molecular layer.

From the researches of Eamon y Cajal, it is clear

Fig.273. — From the Retina of Dog. i^Afttr Ca}al,fTom Quaiiis ''Anatomy.

A, Small amacrine (spougiuhlast) of the inner molecular layer : c, large ganglion
cell ; /,g,h, i, small ganglion cells arborising in the inner molecular layer.

that the dendrites terminate by arborisations or den-
drons in the next or inner molecular layer (see Figs.
L'72, 27:3, and 274).

The ganglion ceils are separated from one another
by the radial fibres of Miiller.

439. (4) The inner nioleciilai' 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 ^luller. This layer is, on account of its thickness,
a conspicuous part of the retina. In lower vertebrates
it a])pears stratified.

As mentioned just now, it contains the terminal
arborisations of the dendrites of the ganglion cells.

440. (5) The inner nnrlear 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.

D D

45°

Elements of Histology

Js^ext to the molecular layer are small nuclei belonging
to flattened branched cells (Vintschgau). the spongio-
hh.sts of W. Miiller. These cells have been shown
by Golgi's method to be possessed of rich arborisations,
^vhich extend horizontallv into the outer and inner

Fig. 274— Section of Retina of Bird. {After Cajal,/rom (^uain's ^'Anatomy."\

A, B. Large sponsioljlasts of inner nuclear layer; c. small spongioblast; d.
bipolar cell of inner nuclear layer wirh a and b arborising in inner mole-
cular layer and also terminating at k at the limitans externa ; f, g, rod and
cone nuclei ; H, i, cells with arborisations in outer molecular layer ; j, radial
fibre of Muiler.

molecular layers (see Fig. 272). Ramon y Cajal
desicrnates them as amacrines. But the ofreat
majority of the nuclei of this layer are slightly 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

Retina. 451

ganglion cell (Max Scliultze), of which ono i)rocess (the
innei") ))asses as a fine varicose fibre into the inner
molecular layer, where it terminates as a delicate den-
dron, while the other or outer process passes into the
next outer layer of the retina — i.e. the outer molecu-
lar layer, to terminate here by a rich arborisation or
dendron (Fig. 272).

(6) Tlie outer iiiolenilai* layer is of the same
structure as the inner molecular layer- — i.e. a fine
reticulum of fibrils — but is considerably tliinner than
the latter. It also contains the dendrons of cells
inside and outside it (Fig. 272).

441. (7) The outer uuclear 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 trans^'ersely-ribbed differ-
entiation of their contents (Henle, Krause). The
honeycombed matrix of this layer is in connection
with lateral branchlets of the radial fibres of Miiller,
with which it forms a sort of limiting delicate mem-
brana propria at the outer surface of the layer;
this is

442. (8) The liuiltaus 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 throuorh
holes in the limitans externa. Each nucleus of
the outer nucleai- 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
of the rod- or cone-fibre, to become connected with a

452 Elements of Histology.

rod or cone respectively, while inwards it passes into
a longer, more conspicuous fibre, the inner part of the
rod- or cone-fibre (Fi,cj. 272). According to Ramon
y Cajal, the cone-fibre terminates as a flat dendron
in contact witli the tufty arborisation of the outer
process of the cells of the inner nuclear layer— f 6". in
the outer molecular layer : the rod-fibre on the other
hand terminates in the outer moleculai- layer as a
small knob (Fig. 272) in tlie outer dendron of the
same cells

443. (*.)) The rods and cones. — Each rod is
of cylindrical shape, Avith rounded or conical outer
extremity : it con.sists 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 Kiihne and E^vald. 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 8chultze). After
certain reagents, such as serum, liquor potass^e, the outer
rod-member disintegrates into numerous transverse,
thin, homogeneous-looking discs (Hannover). The
inner member in tlie human rods is slightly broader
than the outer : it is pale or tinely and longitudinally
striated, and contains in many instances a peculiar
lenticular structtire : in the human and mammalian
retina this is aljsent. but in its stead is a mass of
lono-ittidinal fibrils (^fax ►"^cliultze). The inner member
passes through a hole in the limitans externa, and
becoming thiniif-r. represents the outer part of the
rod -fibre.

4-4-1:. Each cone is composed of an outer, short,
pointed, conical member, and an inner larger member
with convex surface : this is the hody 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

Rktina.

453

outer extremity of tlic body
birds, reptiles, and amphibia
contains a spherical corpuscle
of red, orange, yellow, green,
or even Ijlue colouration.

The cones are shorter than
the rods, the pointed end of
the former not reaching much
farther than the junction be-
tween 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 decrease
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) show in
the fresh and living state a
peculiar ditiuse purplish colour
(Leydig, Boll, Kiihne) : this is
the visual purple or Rhodopsin
of Kiihne. When exposed to
sunlight it passes through
red, orange, and yellow, and
finally disappears altogether
— becomes bleached. There is

of the cones in many

Fig. 275. — Vertical Section
through Ketiiia of Frog.
(Atlas.)

a. Pigmented epitbeliiim of
retina or tapetum nigrum;
5, outer nieml>ers of rods,
those of cones l)etween them ;
c, inner mem tiers of rods and
cones; d, liniitaus externa;
e, outer nuclei ;/, outer mole-
cular layer ; </, inner nuclei ;
/(, inner molecular layer ; i,
nuclei of ganglion cells; j,
nerve fibres; the pyramidal
extremities of the radial
fibres arc well shown.

454 Elements of Histology.

no visual purple in tlie rods of Rhinolophus hipposi-
deros, fowl and pige )n : in those retinae in which the
cones contain coloured globides {ses above) the sur-
rounding 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, onlv within certain limits.

•446. (10) The pij?iiiL'iite<l epitlieliiiiii (Fig.
275), or tapetum nigrum, is composed of polygonal
protoplasmic 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. Eacli 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). Tliis part is prolonged into numerous
tine fibrils, each containing a row of the pig-
mented 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 protrusion 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. 276) of man and
ape contains a diffuse yellow pigment, between the
elements of the retina (M. Schultze). In man and
most mammals, as mentioned above, there are
hardly any rods here, but cones only ; these are

Retina.

455

longer than in other parts, and in the fovea centralis
tliey are longest, and, at the same time, very thin.
Since there are only cones here, the nuclei of the
outer nuclear laj^er are limited to a very few layers
(generally about two) next to the membrana limitans

Fig. 276. — From a Vertical Section through the Macula lutea and Fovea
centralis. (Diagram by Max Schultze.)

a. Nerve fibre* : b, ganarlion cells ; c. Inner molecular layer : d, inner nuclei ;
e, outer molecular layer ; /, coue-flbres with their outer nuclei ; g, cones.

externa. For this reason, the rest of the outer nuclear
layer is occupied by the cone-Hbres only, which in the
fovea centralis pass in a slanting, or almost horizontal,
direction sideways into the outer molecular layer. The
ganglion cells fi)rm several strata in the macula lutea.
In the fovea centralis are present the cones (very long
and thin), the limitans externa, the few nuclei repre-
senting the outer nuclear laj^er, a thin continuation of
the inner molecular layer, and the limitans interna.
448. In the embryo, the primary optic vesicle

456 Elements of Histology.

becomes invaginated so as to form the optic cup,
which consists of two layers — an outer, giving origin
to the pigmented epithehum : and an inner, the retina
proper. In this Jatter the rods and cones, with their
hbres and the nuclei of the outer nuclear layer, are
represented by columnar epithelial cells (the sensory
epitlieJium), while all the other layers — i.e. the outer
molecular, inner nuclear, inner molecular layer, gan-
glion cells, nerve fibres, and limitans interna — are re-
presented by a separate layer : Briickes 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 as far as
the outer molecular layer.

The lyiiipliatics of the retina exist as perivas-
cular lymphatics of the retinal veins and capillaries
(His). Lymph channels are present in the ner\e fibre
layer.

450. The lamina eribrosa is the part of the
sclerotic and choroid membrane through which the
optic nerve filires 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 sur-
rounded by perineurium {see Chapter XI Y.) ; these
groups are surrounded by septa of connective tissue,
^nd they pass through corresponding holes of the
sclerotic and choroid.

451. The optie nerve possesses three sheaths,
composed of fibrous connective tissue : an outer, or
dural : a middle, or arachnoidal ; and an inner, or
pial, sheath — all continuations of the membranes of
the brain. The pial sheath is the perineurium, the
optic nerve being comparable to a compound nerve-

Retina. 457

bundle {see Chapter XIY.). The dural slieath of
the optic nerve, at its entrance into the lamina
cribrosa, jiasses 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 space— the supravaginal sj>ace : and also
between these various sheaths are lymph spaces — the
subdural or sub vaginal space of Schwalbe, and the
subarachnoidal space. The supravaginal and suit-
vaginal spaces anastomose with one another (Michel).
452. Around the sclerotic is a lymph space limited
bv a tiVji'ous membrane — the Tenonian co.ps.ii.le : the
space is called tlie 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 snpra-
choroidal lymph spaces communicate also with the
subarachnoidal space of the optic nerve.

458

CHAPTER XLII.

THE OUTER AXD 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 in em bran a tyinpani sej^arating the
outer from the middle ear has for its matrix a firm
stratum of stiff trabecuhe 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
M'ith a continuation of the delicate mucous membrane
lining the cavum tympani. In the middle stratum of
the membrana tympani the trabecule^ radiate more or
less from the junction of the manubrium mallei with
the membrane ; but towards the periphery many are
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 memljrane is delicate connective tissue, covered
with a single layer of polyhedral epithelial cells.

The blood-vessels form capillary networks for all
three layers — i.e. 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

Outer and Mmni.E Ear. 459

this way. An intercommunicating system of lym-
phatic sinuses and ck^fts (Kessel) is left between tlie
trabeculiu. The non-medullated nerve fibres form
plexuses for the skin and mucous layer ; from these
pass ott' fine fibrils, which form a sub-epithelial net-
work, and from this the tilji'ils pass into the epithelium.

455. The tuba E:ii«itsicliii is lined with a
uuicous meml)rane, which is a continuation of that
lining the upper part of the phar^'nx, 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
approaches in structure the elastic cartilages of other
parts.

456. The caviiiii tympaiii, including the cellulte
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
cellulae mastoidea3 ; 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-
ments of the bones are, like other ligaments, made up
of straight and parallel bundles of tiV)rous 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.

460

CHAPTER XLTII.

THE INTERNAL E A K.

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 am^^ulla at one extremity. The
vestibule shows two divisions — the fovea hemispherica
next to the cochlea, and the fovea hemi-elliptica next
to the semicircular canals. The cochlea consists of
two and a 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 tlie cavity of each turn
into an upper passage, or scala vestibuli, and a lower,
or scala tympani. At the top of the cochlea the two
seal* 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 hemi-elliptica of the vestibule.

The fenestra ovalis leads from the cavum tympani
into the vestibule — its hemispheric division ; and this
fenestra ovalis is, in the fresh 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.

Internal Ear. 461

460. Tilt' osseous labyi-inth in all parts consists of
ordinary osseous suUstaiice, with the usual periosteum
lining its outer surface and its inner cavities. These
cavities contain the albuminous fluid called perilymph.
But they ;ire not tilled 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
hemi-elliptica is an ellij^tical sac, the lUi^icle ; in each of
the three semicircular canals is a membranous semi-
circular tube, which jiossesses 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 a 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 menil)ranous
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 endolymphaticus, situated in a cleft of
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 reuniens of Reichert. Thus the

462 Elements of Histology.

cavity of the whole membranous labyrinth is in
direct communication throiigliout 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 cavum
tympani, since the fenestra ovalis and fenestra rotunda
both separate the perilymphatic space, or the cavity
of the bony labyrinth, from the cavum tympani. The
vibrations of the membrana tynjpani, 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 tlie top of the cochlea, then by the heli-
cotrema into the scala t3^mpani, and find their conclu-
sion on the membrana secundaria closing the fenestra
rotunda. On their way they affect the membrane of
Reissner, which separates the scala media from the
scala vestibuli, and also the membrana basilaris separ-
ating the scala media from the scala tympani ; the
vibrations of these membranes affect the endolymph,
and therefore tlie nerve-endings {see below).

463. Sti'U€tiire of seiiiicirciilai* canals,
utricle and saccule. — The memhranous 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 regaid to the saccule
and utricle, which are fixed by the inner periosteum
to one side of the bony part.

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
oute7' coat ; inside this is a glassy-looking tunica

I.XTEKNAL Ear.

463

propria. At one side (the one away from the bone)
this tunica propria forms numerous papillary projec-
tions. The internal surface of the membrane is
covered with a single layer of polyhedral epithelial cells.

464. Each of the branches of the nervns vestibuli
— i.e. one for the sac-
cule, one for the utricle,
and three for the three
ampullae — possesses a
ganglionic swelling. The
nerve - branch, having
passed through the mem-
branous wall, enters
special thickenings of
the tunica propria, on
that part of the mem-
branous wall next to the
bone : in the saccule and
the utricle the thicken-
ing is called macula
acustica, in the ampullae
crista acustica ( Fig. - 7 7)
(M. 8chultze). This
thickenin*^ is a lar^je
villous or fold-like pro-
jection of the tunica
})ropria, into which pass
the nerve fibres of the
several branches. These
tibres are all meduUated nerve fibres, and, ascending
towards the internal or free surface of that pro-
jection, form a plexus. In this plexus are in-
terspersed numerous nuclei. From the medullated
fibres pass oS minute bundles or primitive fiVjrillse,
which enter the epithelium that covers the free
surface of the projection.

465. This epithelium is composejcl of a laver of

Fig. 277.— From a Transverse Section
through the Macula acustica of the
Utricle of the Labyrinth of Guiuea-
pig. {Atlas.)

a, Medullated nerve fibres, forming plex-
uses ; b, nuclei of the membrane ; c,
sensory epithelium (diagrammatic); the
spindle-shaped sensory cells possess
long auditory hairs projecting between
the conical epithelial cells beyond the
free surface.

464

Elements of Histology.

columnar or conical cells, between which are wedged
in spindle-shaped cells ; V^oth 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 fibrillse coming from under-
neath : whereas, towards and beyond the free surface,

Fig. 278. — Xerve Terminations in the Epithelium of tlie Macula acustica.
The nerve fibres form denclrons in the epithelial layer. (After
Betzius, from Quain.)

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
fibrillse, and that each sendi^ <jut over the internal free

iNTKRXAr, Ear. 465

surface almiidle of iiiie 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 l)y holes which correspond
to the epithelial cells and the auditory hairs.

By Golgi's method Retzius has, however, obtained
evidence (Fig. 278) which shows that fine nerve
fibres terminate by arborisations or dendrons amongst
the epithelial cells (Fig 177).

On the internal surface of the macula and crista
acustica are found the oUAithx., rhombic crystals, and
amorphous masses, chiefly of carbonate of lime, em-
bedded in a gelatinous or granular-looking basis.

\^^>. The coc'lilca (Fig. 279), 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 for-mer. The difference between
the cochlea and the semicircular canals is this, that in
the cochlea there is a division of the perilymphatic
space by an osseous projection — the lamina spiralis
ossea — and bv the scala media into two scalse, viz. the
(upper) scala vestibuli and the (lower) scala tympani.

467. In the osseous modiolus are numerous
parallel 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 c^ansflion connected with the nerve.

Coo

The nerve bundles are situated in the canals of the
modiolus, and opposite 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 niedul-
lated) can be traced into the lamina spiralis ossea, in
which they form rich plexuses extending to its outer

E E

Fig. 279.— From a Vertical Section through the Cochlea of Ear of Guinea-
pig, seen in the long axis of the Modiolus. (Atlas.)

a, Scala vestibuli ; b, scala tympani ; c, srala media ; d, membrana tectoria ; e,
cells of Claudius ; /, upper outer angle of scala media ; g, region of outer
hair cells nn membrana basilaris : /*, membrane of Reissner; ?, epithelium
linintr «ulcus spiralis (internus) ; j, tunnel of Corti's arch ; k. stria vascularis ;
?, ligamentum ppirale : ?», crista spiralis; n, nerve Hbres in lamina spiralis
ossea • o gansliun spirale; p, nerve fibres in modit)lus ; q. channels in bone
containing blood-vessels ; r, masses of bone in modiolus ; s, outer bony
capsule.

Internal Ear. 467

margin — l.p. as far as the membrana basilaris of the
scala media {see below).

-4G(S. From the margin of the himina spiralis ossea
to the external bony shell extends the membrana basi-
laris (Fig. 279), 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 an^le from near the marcrin of the

O o

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 Avail is placed close against
the periosteum lining the internal surface of the bony
shell ; it consists of lamellar fibrous tissue, with
numerous stitf elastic bands, and is the vestibular
part of a peculiar ligament — the ligamentuTti spirale
(Kulliker) — semilunar in cross-section, and with its
middle angular })rojection tixed 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
an acute angle from the upper outer angle of the scala
media to the lamina spiralis ossea. But here it is not
tixed on the osseous substance, but on a peculiar pro-
jection on this latter — the crista spiraUs (Fig. 279, m)
— which is a sort of tissue intermediate between tibrous
and osseous tissue, and is added to the vestibular
surface of the lamina spiralis ossea. This crista spiralis
has on one surface — i.e. that directed towards the
scala media — a deep sulcus, called the sulcus spiralis,
or sulcus 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 s})iralis (Fig. 279).

471. (3) The lower wall of the scala media

468 Elemexts of Histology.

is the memhrana hasilaris, extending in a straight
line betAveen the labium tynipanicum of the crista
spiralis and the above-mentioned projection of the
ligamentum spirale. 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 vestibuli are likewise lined with a continuous
layer of flattened cells — an endothelium, which on
the lower or tympanic surface of the mernbrana
basilaris is somewhat modified, being composed of
cjranular-lookinof irre^cnlar cells.

472. As regards the scala media, the epithelium
lining its internal surface is of the following aspect :—
Starting with the lower outer angle — i.e. Avhere the
mernbrana basilaris is fixed to the ligamentum spirale
— we find a single layer of polyhedral or short
columnar transparent cells, lining this outer angle —
the cells of Claudius ; ascending on the ligamentum
spirale, the cells become shorter, more squamous ; as
such they are found over a slight projection on the
outer wall — i.e. the ligamentum spirale accessorium —
caused by a small blood-vessel, the vas prominens.

473. Then we come to the stria vascularis,
lining nearly the up[)er 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 liga-
mentum 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 Eeissner. This consists
of a homogeneous thin mernbrana propria, covered on
its outer vestibular surface with a layer of flattened
endothelium, and on its inner surface — i.e. that facing

Internal Ear. 469

the scala media — with a layer of less flattened, smaller,
poljdiedral epithelial cells.

475. We come next to the vestibular labium of
the crista spiralis, on which are found cylindrical
horizontal projections anastomosing with one another :
these are the auditor y teeth (Huschke). The epi-
thelium of Reissner's membrane is continued into the
grooves and pits between the auditory teeth as small
polyhedral cells, but over the teeth as large, flattened,
squamous cells, which, passing on, line the sulcus
spiralis and cover also the tympanic labium of the
crista spiralis. Xow we arrive at the membrana
basilaris, on which the epithelium l)ecomes modified
into the organ of Corti.

476. The me 111 bra 11 a basilaris consists of a
hyaline basement membrane, on which the organ of
Corti is fixed : underneath this is the 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
there is also a hyaline basement membrane. The
endothelial cells covering this on the tympanic surface
haA'e been mentioned above.

477. The org:aii of Corti (Fig. 280). — Passing
outwards from the epithelium lining the sulcus sjiiralis,
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 —
a columnar, or conical, epithelial cell, with a bundle
of stitf hairs, or rods, extending beyond the surface.
The inner hair-cells form a sina^le file alonsr the whole
extent of the two and a half turns of the scala media.

478. Xext to the inner hair-cell is the inner rod, or
inner pillar, of Corti, and next to this the outer rod,

470

Elements of Histology

or outer -pillar, of Corti. Each forms a single file for
the whole extent of the two and a half turns of the
scala media. The two rods are inclined towards one
another, and in contact with their upper extremity,

Fig. 2S0.— Organ of Corti of the Cochlea of Guinea-pig. (Atlas.)

a. Outer rod or pillar of Corti : b, inner rod or pillar of Corti ; c, tunnel of
arch of Corti ; d, oucer hair-cells ; e, inner hair-cell ; /, outer supporting cells
containing fat globules; g, inner supporting cells; /*, cells of Claudius;
i, epithelial cells lining the sulcus &i>iralis internus ; j. nerve fibres ; fc, part
of crista spiralis.

or head : whereas the opposite extremity, the foot,
rests under an acute angle on the membrana basilaris,
on which it is firuily fixed. The rest of the rod is a
slender, more or less cylindrical, piece — the body. The
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
possesses a concave surface grasping the convex
surface of tiie head of the outer rod. This latter

Internal Ear. 471

possesses a process directed outwards, which is tirnily
applied to the outer process of the head of the inner
rod, the two together forming part of the niein))rana
reticularis {see below).

The relation in size 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
mass of protoplasm, probably the remnant of the
epithelial cell from which the lower half of the rod is
derived ; the upper part sometimes has a similar
nucleated remnant, proving that this also has been
formed b}^ an ei3ithelial 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 seen in a section
belongs to a file of hair-cells, extending on the mem-
brana 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 stifl:
rods, or hairs, disposed in the shape of a horseshoe in
the outer jjarb of the free surface of the cell.

Four, and even five, rows or files 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 to-
gether 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 memhjrana
reticularis {see below).

482. Farther outwards from the last row of outer

472

Elemexts of Histology.

hair-cells are columnar epithelial cells, called the outer
supporting cells of Hensen : they form the transition

•s

5f •-

f^ Si

S 5

i i §t

^•3

^ CO ...

Internal Eak. 473

to the epitlu'lium lininij tlie outer angle of the scala
media — i.e. to the cells of Claudius.

In the guinea-pig, the outer suppDi-ting cells
include fat globules.

483. The iii€»<lullat<'d nerve fibres, which we
traced in a former page to the margin of the lamina
spiralis ossea, form rich plexuses in this, and pass
through 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
habenula perforata of Kolliker — a little to the inside
of the reofion 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 tibrillse
— the inner bundle of spiral nerve fibres — become
connected 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 rods of Corti, they reach the outer hair-cells,
with which they become connected (Gottstein, Wal-
deyer). (Fig. 281.)

484-. In connection wdth 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 of this membrane between
the heads of the rods of Corti and between the outer
hair-cells appear of the shape of narrow phalanges —
phalanges of Deiters. A cuticular membrane extends
from the head of the inner rods 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

474 Elements of Histology.

spiralis to the outer hair cells of the organ of Corti
extends a peculiar tibrillated membrane ^the tnem-
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
probable 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-per-
ceiving elements of the organ of Corti. Their connec-
tion with the terminal tilirilhv of the nerves points in
the same direction.

As indicated on p. 460, all structures of the scala
media, described in the foregoing pages, form an
uninterru[)ted succession through all the turns of
the cochlea.

475

CHAPTER XLIV.

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 mucus-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 lympli 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.

476

Elements of Histology.

489. In the upper or olfartory i'eg:ioii (Fig. 282)
of the nasal cavity the mucous membrane is of a
different tint, Ijeing more of a brownish colour; it

Fig. 2S-2.— From a Section throiigli the Ulfactorj- Region of Guinea-pig.

{Atlas.)

a. Thick olfactorv epithelium; b, thin olfactory epithelium; c, ciliated non-
olfactorv einthelium ; d. bone. The transverse sections of the olfactory
nerve bundles and the tubular glands of Bowman are well seen.

contains the ramifications of the olfactory nerve, and
is the seat of the organ of smell.

490. The free surface is covered with a columnar

Nasal Mucous Membrane

All

cpitlicliuin, composed of tlie followirg kinds of cells
(Fig. 283):—

(«) A superficial layer of long coluniiiar, or rather
conical, epithelial cells, each with an oval nucleus. In

iMjlJ j I IJ ill ,1/

!i|ipij|i]|i,!,i;jji|,|fir|!i!j||]pi^^^

Fig. 283.— From a Vertical Section tlirongh the Olfactory Mucous Mem-
brane of Guinea-pig. {Atlas.)

a, Epithelial cells; ?^, eensory or olfMctory cells; c, deep epithelial cells; d,
bundles of olfactory uerve fibres; e, the alveoli of serous (Bowniau's)
glands.

some places the free surface of these cells is covered
with a bundle of cilia, similar to the superficial cells
of the respiratory j^ai-t of the nasal cavity ; in most
places, however, the cilia are absent ; the former

Elements of Histology.

condition obtains in those places which are in close
proximity to the respiratory region.

[h) Between the epithelial cells extend spindle-
shaped cells, each with a spherical, or very slightly

Fig. 284.— From a Vertical Section through Olfactory Membrane of Guinea-
pig. {Photo. Moderate inagnijicat ion.)

a, Olfactorv epithelium ; b, mucous membrane with blood-vessel and glands ; c
oliactoiy nerve fibres cut longitudinally.

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 line
varicose filament passes from the cell body towards
the mucosa, and, as shown first by M. Schultze, be-
comes connected with a fibrilla of the plexus of the
olfactory nerve fibres.

Nasal Mucous Membrane.

A19

(c) In some places there i.s a deep layer of epithe-
Hal celh^ each "svitli a spliorical rjiicleus of an inverted
conical shape, their pointed extremity passing be-
tween the other cells just mentioned and their broad
basis resting on the basement membrane (Fig. 283),

. '.x^.

Fig. 285. — Transverse Section through the Lower Part of the Nasal Septum,
showing the (bilateral) Organ of Jacobson in cross section. {Photo.
Loic poicer.)

1, Cartilage extending above and iiartially around tlie organ ; -J. cavity of
the tuljular organ, showing on its nit-sial wall olfactory epithelium, on its
lateral wall cohnnnar eiutheliuni ; 3, cavernous tissue in the lateral wall.

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

4S0 Elements of Histology.

nerve fibres, extending chiefly in a direction parallel
to the surface (Fig. 284). Each nerve fibre is non-
meduUated — i.e. is an axis ( ylinder composed of minute
or primitive til)rilhe. and invested in a neurilemma with

Fig. 286.— Section tlirough the Front Part of Nasal Septum of Rabbit,
showing the bilateral organ of Jacobson in transverse section. The
tube of the organ of Jacobson is lined on its mesial wall with olfactory
epithelium. (Photo. Loiv pov:er.)

g. Glands extendiug from the upper part of the septum to the junction of the
mesial and lateral wall of the organ of Jacol'son ; c, rartilage extending as a
nearly complete capsule around each organ of Jacobson. The lateral wall of
the organ contains cavernous tissue.

the nuclei of the nerve corpuscles. Near the surface
tlie fibres of the plexus ai-e thin, and they split up
into the constituent fibrils which are directly con-
tinuous with the fine varicose processes of the sensory
cells above named (Fig. 178).

492. The blood-vessels supply with capillary net-

Nasal Mucous Mi'Imbrane.

481

works the superficial part of the mucous membrane
and the numerous glands. These are tlie (/lands of
llownKut, extending through the thickness of the
mucous membrane. They are tubes, slightly branched,

Fig. 287.— From the same yeetiou througli the Organ uf Jaeobsou as in the
preceding figure, more magnified. (Photo.)

c, (';irtila,i,'c of mesial wall ; cf., cavernous tissue of lateral wall. The mesial will
is lined with thick olfactory epithelium.

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
canal ; it is that part of the gland which is situated
in the epithelium of the free surface ; it passes ver-
tically through this, and consists of a fine limiting

F F

482 Elements of Histology.

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 l3undles of the olfactory nerve
fibres, 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
this is, the longer are the inlands of Bowman.

494. The org-aii of Jacobsoii (Figs, 'l^^'d.
286, 287) is a minute tubular organ present in
all mammals, and, as has been shown by Dursy
and Kolliker, 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 f)lough-
shaped capsule — the cartilage of Jacohsoa — and
opens in front directly into the nasal furrow (guinea-
pig, rabbit, rat, etc.); 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 bliud extremity.

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
identical with that of the olfactory region of the nasal
cavity. Branches of olfactory nerve fibres also pass
into the median wall, and behave in exactly the same
manner as in the olfactorv rejjfion. Numerous serous

Nasal Mucous Membrane. 483

glands — belonging ehietiy to the i^pper and hnver
wall — open into the cavity of the organ of Jacobson.

In the lateral wall there is in many instances a
plexus of veins, extending iii a longitudinal direction,
and between the vessels are Imndles of non-striped
muscular tissue, thus constituting a sort of cavernous
tissue.

4«4

CHAPTER XLV.

THE DUCTLESS G L A X D S.

496. I. The liypopliy«»i!^ cerebri. — The upper
or smaller lobe belongs to the cential nervous system.
The lower or larger lobe is surrounded by a librous
capsule, which sends numerous minute septa into the
interior. These split up into numerous trabeculfe of
librous tissue, which, by di^dding and reuniting, 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, j^yramidal, 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 S23indle-shaped cells, with a
small flattened imcleus. 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
o-lands.

497. II. The lliyroid gland (Fig. 288).— 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
trabecular forming the septa between the gland alveoli.
These are closed vesicles of a sjjherical or oval shape,
and of various sizes. Each vesicle is lined with a

Due TL ESS Gl a XDS.

4B:

^ 44^#i^^ .^

single layiM- of polylicdral ov c »luimi;ir <'[)itli('lial 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, albuminous fluid — the
so-called colloid. In this often occur degenerating
nucleated lymph corpuscles ^

and coloured Mood corpuscles
(Baher).

498. The vesicles are
surrounded by networks of
blood capillaries. In the
connective-tissue framework
lie networks of lymphatics ;
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

and

%..

// d

Fi.i,M'8.S. — Fi-Din a Section through
the Thyroid Gland of Dog.

((, Epitheliiam lining the vesicles;
h, coll{ lid contenr s of the vesicles;
c. lymphatic tilled with the same
material as the vesicles ; cl,
tlbrous tissue between the gland
vesicles.

the

discharged

carried away by

into the circu-

produced in the vesicles
lymphatics, to be finally
lating blood.

499. Its formation in the vesicles is probabh^ due
to an active secretion by the epithelial cells of the
vesicles, and to a mixture with it, or maceration by
it, of the effused blood mentioned above. In some
instances Bal)er found the amount of blood effused
into the cavity of the vesicles very considerable, and
hence it is justifiable to assume that the destruction of
red blood corpuscles forms one of the functions of the
thyroid gland.

" 500. III. The supra-venal bodies (Fig. 289).
— The supra-renal body is envelojDed in a fibrous cap-

486

Elements of Histology

sule ; in connection with this are septa and trabeculae

Y-)assing inwards,
and the}^ are ar-
ranged differently
the cortex and
the

@ a ., ^ t o O^^S) * • .'?o-fe- <^

...e

P'ig. 2S;\ — From a Vertical 8eetioii tlirougli
The Supra-renal Bod}' of JVIan. {Eberth, in
Stricl-er's Manual.)

1, Cortical sulistance : 2,mP(iullary part ; a, outer
capsule; />, zona glonierulosa ; r. zona fascicu-
lata; d, zona reticularis; e, medulla: /, large
vein.

m
in

of the
will be
sently.
The

medulla
gland, as
seen pre-

cortex of
the n;land consists
of an outer, middle,
and inner zone, ail
three being di-
rectly contin n o u s
with one anothei-.
The outer one is
the zona rjlomerv-
losa ; it contains
numerous sphe-
rical, or, more com-
monly, 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
t ran s verse man ner.
Occasionally a sort
of lumen can be

discerned in some of these cell masses.

Ductless Glands. 487

501. Next follows the middle zone, or zona
fascicvlata. Tliis 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 tine 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 zone, or zona reticu-
laris, composed of smaller or larger groups of poly-
hedral cells, with more or less romided 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 tliey 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 caj)illary blood-vessels ; their meshes are
polyhedral in the outer and inner zone, elongated in
the middle zone, or zona fasciculata. In the medulla
numerous plexuses of veins are met with. In the
centre of the supra-renal 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-

4SS Elemexts of Histology.

medullated fibres ; in the medulla they form rich
plexuses. In connection with these and with those of
the outer capsule are smill ganglia (Holm, El)9rth).

505. IV. The g^laiidiila coccygea and

iiiter-rarotic-a. — The lirst of these is a minute
corpuscle situated in front of the apex of the os
coccygis, and was discovered by Luschka. The
glandula carotica of Luschka (ganglion inter-caro-
ticum) 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 trabecular. The septa and trabeculae
contain in some placs-s 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 newly-born child they are ciliated. In the centre
of each of the cell masses lies a capillary blood-v^essel,
much convoluted and wavy.

Numerous non-medullated nerve fibres forming a
plexus are situated in the framework of the gland.

I X D E X

Alxlneens, 222
Absorption {see Lymphatics)
Accessory nucleus, 210
Achruiiiatin, 11
Acini of glands, 292

of liver, 333

of pancreas, 330

Acoustic ganglion, 219
Adenoid reticulum, 62, 126

tissue, 126

A' 1 maxillary glands, 289
Adveutitia of arteries, 108

of capillaries. 111

of veins, 110

lymphatic vessels, 118

Agminated glands, 130
Air cells, 345
Alje nasi, 63
Albuginea of ovary, 3S7

of testis, 372

Albumin membrane of Ascherson,

402
Albuminous cells, 293
Alloplasmatic organs, 6
Alveolar ca\'ity, 275

ducts, 345

Alveoli of glands, 292

of lung, 345

of pancreas, 330

Alveus, 249
Amacrines, 450
Amitotic division, 12
Amwboid corpuscles, 4

■ movement, 4, 5, 24, 58

Amphophile cells, 27

Ampulla, 460

Anterior column of cord, 17<'>

corpus quadrigeminura, 231

grey commissure. 174

horn of cord, 173

lateral tract, 179

nerve-roots from cord, 187

white commissure, 187

Aorta, 109
Aponeurosis, 47
*

of spinal

Aqueduct us Sylvii, 220

vestibuli, 461

Arachnoid membrane

cord, 170

of brain, 235

Arachnoidal villi, 235

Arborisation, 151

Arenate fibres of medulla, 213

Areolar tissue, 48

Arrector pili, 419

Arteriaj ciliares breves, 440

recurrentes, 440

helicinte, 385

rectse, 369

Arteries, 108
Arterioles, Afferent, 55

of uterus, 397

Articular cartilage, 63, 82

nerve-corpuscles, 161

Arjiienoid cartilage, 339
Ascending degeneration, 180

loop-tube, 364

root of glosso-pharyngeal nerve,

210

of the eighth nerve, 215

of the fifth nerve, 224

Aster stage in nucleus, 15
Attraction sphere, 9
Auditory hairs, 464

nen'e. Origin of, 217

, Division of, 219

teeth, 469

Auerbaoh's plexus, 326

Auricle of heart, 107

Aiiriculo-ventricular valves, 106

AxUemma, 145

Axis cylinder, 144

process of sympathetic

ganglion cell, 263
Axon, 144

Bartholin's glands, 399
Basement membranes of skin, 405

490

Elements of Histology.

Basilar membrane of cochlea, 46ft

Basket cells of cerebellum, 241

Basophile cells, 27

Bellini's ducts, 305

Bile-duets, 330

Bile capillaries, 336

Bilirubin, 23

Bioblasts, 9

Bladder, S7, 371

Blastoderm of chick, 2

Blood, 19

corpuscles, 19

, their origin, 2S

cysts, 115

islets, 115

glands of His, 126

platelets of Bizzozero, 27

-vessels, 105

Bone, 6S

cartilage, 6S

cells, 71

corpuscles, 71

, Development of, 74

trabecultf , 74

Bowman's capsule, 360

elastica anterior, 42!'

glands, 481

membrane, 429

sarcous elements, 94

Brachia, 233

Brain membranes, 235

structure, 243

Bronchi, 343

BrowTiian molecular movement.

300
Bruch, Glands of, 427
Briicke's elementary organisms, 5

oikoid and zooid, 22

tunica nervea, 456

Brunner's glands, 328
Buccal glands, 298
Bulbus olfactorius, 250
Biitsclili's nuclear spindle, 15

Calcification of bone, So

of cartilage, 65

• of dentine, 283

Calices of kidney, 356
Canal of Schlemm, 434

of Stenson, 482

of Stilling, 444

Canalis hyaloideus, 322, 444

Petiti, 443

reuniens, 461

Canaliculi in bone, 70

in cartilage, 65

Capillaries of marrow-bone, 111

Capillaries of nerve system, 111
Capillary bile-ducts, 336

blood-vessels. 111

• lymphatics, 119

network in mucosa, 801

sheaths, 354

Capsule of Bowman, 360

of ganglion cells, 255

of Glisson, 333

of kidney, 356

of the spleen, 351

Cartilage, 63

, Articular, 64

capsule, 64

cells, 63

, Elastic, 67

, Fibrous, 66

, Hyaline, 63

, Lacun*, 63

of Jacobson, 482

of Luschka, 339

Cavernous tissue in tactile liairs,
418

in organ of Jacobson. 483

tissues in genital oigans, 384

Cavities of tendon sheaths, 121
Cavum tympani, 459
Cell enclosures, 9

protoplasm, 7

Cells, 5

, Muscular, of blood-vessels, 88

, of intestine, 88

, of respiratory organs, 88

-, of stomach, 88

, of urinary organs, 88

in tadpole's tail, 50

of Claudius, 468

of Corti, 471

of Deiters, 236. 471

of Golgi, 242

of Martinotti, 246

of Purkinje, 239

Cellulai mastoide*, 4.59
Cellular tissue, 48
Cement of teeth, 279

substance, 30

of endothelium, 40

of epithelium, 30

of fibrous tissue, 47

Central canal, 185

grey nucleus, 185

Centroacinous cells, 331
Centrosome, 9
Cerebellum, 237
Cerebrum, 243
Ceruminous glands, 409
Cer\ix of uterus, 395
Chalice cells, 36
Chondrin, 46, 63

l.VDEX.

491

Chondroclasts, S:'>

Choroidal portion of ciliary muscle,

87
Choroid lueinbrane, 440
Chromatic granules in ganglion

cells, 1H4
Chromatin, 11
Chromosomes, 11
Chyle, S-M

vessels, 31i>

Ciliary muscle, 435

nerves, 43S

processes, 438

Cilia, 404
Ciliated eells, 3o
Circulus arteriosus in iris, 438
Circumanal glands, 409
Circumcellular plexus, 265
Cisterna lymphatica magna, 1-21
Clarke's columns, H»2
Cleavage of ovum, 2

of white blood corpuscles, 25

Clitoris, 309

Cochlea, 465

Cohnheim's areas, 93

Colloid, 4S5

Colostrum corpuscles, 403

Coloiu-ed blood corpuscles, 19

Colourless blood corpuscles, 23

Columnar epithelial cells, 30

Commatract, 179

Commissure, Grev, of spinal cord,

173

, Wliite, of spinal cord, 187

Compound lymphatic glands, 134
Concentric bodies of Hassall, 132

lamellie, 72

Cone fibre, 451
Cones of retina, 452
Coni vasculosi, 379
Conjunctiva, 424

blood-vessels, 426

bulbi, 426

lymphatics, 427

nerves, 427

palpebrse, 424

Connective tissue, 46
Contractility of corneal corpuscles,

of pigment cells, 54

Contraction of muscle, 99

wave, 99

Convolution of brain, 243

in nucleus, 13

Corda? tendinete, 106
Cords of adenoid tissue, 127
Coriuni, 404
Cornea, 50, 429
nerves in, 431

Corneal cells, 50

corpuscles, 50, 430

Cornuain cord, 173
Cornua uteri, 396
Corpora cavernosa, 384

geniculata, 270

quadrigemina, 226

striata, 249

Corpus callosum, 249

Highmori, 372

luteum, 391

restiforme, 209

spongiosum, 384

Corpuscles, Malpighian, 353, 359

of blood, 20, 23

of bone, 71

of connective tissue, 48

of Grandry, 160

of Herbst, 158

of lymph, 123

of Meissner, 158

of muscle, 94

of nerve, 145

■ of Pacini, 155, 423

of Vater, 155

, Tactile, 158, 423

Corti's arch, 470

cells, 471

ganglion, 465

organ, 469

rods, 469

Cortical layer of ovary, 387

lymph-sinus, 136

Costal cartilages, 63

pleui-a, 122

Cowper's glands, 383
Cremaster internus, 381
Crenate blood corpuscles, 21
Crescents of Gianuzzi, 294
Cricoid cartilage, 339
Crista acustica, 338

spiralis, 342, 347

Crus cerebri, 229

, Crusta of, 233

Crusta petrosa, 463
Crypts, 129

of Lieberklihn, 318

Cuticle of Xasmyth, 284
Cutis anserina, 420

■ vera, 404

Cystic duct, SS
Cytogenous tissue, 126
Cytoplasm, 7

Deiters' cells, 236, 471

phalanges, 473

Demilunes of Heideuhain,

294

492

Elements of Histology,

Dendrite, 197
Dendron, 151
Dentinal canals, 277

fibres, 277

sheaths, 277

tubes, 85

Dentine, So

Descemet's membrane, ijl, 430

Diapedesis. 113

Diaphragm, 44, 122

Diaster stage in nucleus, 16

Diffuse adenoid tissue, 127

Dilatator puiiiUte, 437

Direct division, 12

"Disetactil," 161

Discus p>roligerus, 390

Disdiaclasts, 104

Dispireme, IG

Distal convoluted tubes, 365

Division, Remak's mode of, 12

Doyere's nerve-mount, 165

Ductless glands, 484

Ducts of pancreatic gland, 330

of salivary gland, 291

Ductus ejaculatorii, 381
Dui-a mater, 170
Dural sheath, 457

Ear, External, 458

, Internal, 460

Ectoplasm, 8
Eosinophile cells, 27
Efferent lymphatics, 138

medullated nerve-fibres, ISS

veins, 56

Elastic fenestrated membrane of

Henle, 61
Elastin, 60
Electric nerve, 14S
Eleidin, 33
Elementary fibrill*, 145

fibrils, 47

organisms, 5

Enamel, 275

cap, 281

cells, 281

organ, 280

• prisms, 275

End-bulbs of Krause. 159

Endocardium, 105

Endochondral formatio of bone,

75
EndoljTQph, 461
Endolympliangial nodules, 128
Endomysium, 91
Endoneurium, 142
Endoplasm, 8

Endothelial cells, structure, 40

membrane, 40

Endothelium, 40

Endotheloid ceU-plates, 126

Energid, 6

Engelmann's intermediate disc,

95
Ependvma, 211
Epidermis, 33, 404
Epididvmis, 379
Epiglottis, 67, 339
Epineurium. i41
Epithelial cells, 30

, Division of, 38

, Regeneration of. 38

Epithelium, 30
Ergastic structures, 6
Erythi-oblasts, 28
Eustachian tube, 459
External arcuate fibres, 213
Eyeball, 426

lashes. 424

lids, 424

Fascise, 48, 49
Fascia dentata, 249
Fascicles, 91
Fasciculus cuneatus, 178

of Goll, 179

of Lissauer, 179

pjrramidal, 177

Fat cells, 55

and starvation, 58

Fenestra ovalis, 460

rotunda, 460

Fenestrated membrane, 45, 48

of Henle, 61

Fertilisation of ovum, 2

Fibrfe arcuat«, 213

Fibres. Connective tissue, 46

, Elastic tissue, 60

of muscle, 86, 91

of nerves, 140

of Puikinje, 106

Fibrillie of connective tissue, 47

of muscle, 92

of nerve, 145

Fibro-cartilage, Q()

Fibrous tissue development, 59

Fillet, 225

Fissura orbitalis, 88

Fissure of Rolando, 243

Fissures of spinal cord, 175

of medulla, 202

Foetal tooth papilla, 280
Follicles, Hair, 409
, Lieberklihn's, 318

Index.

493

Follicles, Lyinpb, 12ti

, 8ebac»'oiis, 418

, Thyiuus, 131

Fornix conjunctivae, 426

vatdna?, 3'.»S

Fossa glenoidalis, 66

navicularis, 383

IKJtcllari.s, 443

Fovea centralis, 455

hemielliptica, 460

hemispherica, 460

Fuhilus of peptic gland, 312
Funiculus cuneatus, 202
gracilis, 202

Gall-bladder, 336

Ganglia, Cerebro-spinal, 253

, Svmpathetic, 25tt

Ganglion ceUs, 191, 239, 243, 253
Gasserian ganglion, 253
Gelatinous tissue, 62
Geniculate ganglion, 270
Genital coq>uscles of Krause, 160

end-corpuscles, 1 55

organs (male), 372

(female), 386

Germ reticulum of von Ebner, 377
Germinating cells, 44

endothelial cells, 43

epithelium, 387

spots, 1, 388

vesicle, 1, 388

Giralde's organ, 380
Gland, Prostate, 382
Glunds. agminated, 130, 321

, Bartholini, 399

, Bionchial, 349

, Brunner, 328

, Buccal, 298

, Carotic, 488

, Ceruminous, 409

, Coccygeal, 4SS

, Harder, 428

, Krause, 426

, Laclirymal, 427

-. Lieberkiihn's, 318

. Littre's, 383

, Lymphatic, 126, 134

. Meibomian, 424

. Mohl, 425

, ilucous, 287, -298

. Peptic. 312

. Pever, 321

, Pyloric, 313

, Salivary, 286

, Sebaceous, 418

, Serous, 286, 299

Glands, Solitary, 130

, Submaxillary, 286

-: , Sweat, 407

, Thynuis, 131

, Thyroid, 484

Glandulie agminat^e, ISO

lenticulares, 315

Pacchioni, 235

uteri nte, 396

Glans clitoridis, 399

penis, 384

Glassy membrane, 411
Glissons capsule. .333
Globulin, 21
Globus major, 380
Glomeruli. 251, 360
Glycogen, 9, 23, 335
Goblet cells. 36
Golgi's eeUs, 242

method, 182

tendon spindles, 167

Goll's tract, 179
Graafian follicles, 388
Grandry's corpuscles, 160
Granular leucocytes, 26, 58
Granules in blood, 27
Granulosa, membrana, 388
Grey commissure, 174
Ground lamelhe, 73

plexus of Arnold, 162

substance, 46

Growing capillaries, 113

Habenula X'erforata, 473
Hajmatin, 23
Haematoidiu, 23
Hsematoplasts, 27
Hiemin crystals, 23
H*nioglobin, 22

cnstals, 23

Hah-, 414

bulb, 412

, Development of, 416

fibres, 413

foUicles, 409

knob, 416

, Marrow^ of, 413

, Xew formation of, 415

l>apilla. 411

, Root of. 413

sheath of, 412

sac. 411

, Shaft of, 414

Harder's gland, 428
Haversian canals, 72

lamellie, 72

spaces, 74

494

Elements of Histology.

Heart anrl blond-vessels, 105

Helicotrenia, 469

Henle. Fenestrated membranes of,

•51. lOS

, Fibres of, 62

, Sheath of, 142

. Stratum nervemii of, 456

, Tulies of, 364|

Hensen's cells, 472

median disc, 9S

Hepatic cells, 335

duct, 336

lobules, 333

veins, 335

Herbst, Corpuscles of, 158
Hilum of lymph glands, 134

of salivarj- glands, 291

of spleen, 352

Hippocampus, 249

Homogeneous elastic membranes,

61
Howship's lacunse, 85
Huxley's layer, 414
Hyaline cartilage, ii3

leucocyte, 26

Hyaloid membrane, 443
Hyaloplasm, 7
Hypophysis, 484

Ileum, 321

Incremental lines of Salter, 278

Incus, 459

Indirect division, 13

Infundibula, 88

of bronchiole, 345

of gland, 299

Inner molecular layer, 449

nuclear layer, 449

Interarticular cartilages, 66
Interfascicular spaces, 49
Interglobular spaces of Czermnk.

278
Interlobar ducts, 291
Interlobular bile-ducts, 336

connective tissue of liver, 333

ducts, 291

Intennediate cartilage, 66

disc, 96

plexus, 162

zone, 315

Intermembranous formation of

bone, S3
Intermuscular fibrils, 163
Internal arcuate fibres, 213

cajjsule of brain, 233

Intervertebral discs, 66
Intestine, Large, 317

Intestine, Small, 317
Iiitima of arteries, 108
Intralobular bile-capillaries, 336

veins, 335

Intranuclear network, 11
Iiis, 436

. Blood-vessels of, 438

; Lymph-clefts of, 438

, Lymph-sinuses of, 438

, Nerve-fibres of, 438

Jacobson's organ, 482

Karyokinesis, 13
Karyomitosis, 13
Karyoplasm, 11
Keratin, 33
Kidney, 356

, Afferent arterioles of, 368

blood-vessels, 367

glomerulus, 360

lymphatics, 370

parenchyma, 357

vessels, 367

Killliker's muscle buds, 102, 166

muscle spindle, 102

osteoclasts, 85

tract cells, 197

Kilhne's nerve-ending in muscle,
164

rhabdia, 92

rhodopsin, 453

sarcoglia, 100

Labia pudendi majora, 420
Labium tymjianicum, 467

vestibulare, 467

Labyrinth, Osseous, 460
Lachrj'mal glands, 427
Lacunfe Morgagni, 383

of bone, 70

of cartilage, 63

— — of lymphatics, 51
Lamellai of bone, 70

of cornea, 429

of lens, 442

Lamina cribrosa, 456

elastica of cornea, 429

fusca, 434

reticularis, 473

spiralis ossea, 460

vitrea, 438

Langerhans' gi'anular layer, 34

Index.

495

Larvnx, 330 r
Lateral fillet, 228

horn, 174

nucleus, 211

tract, 175

Lemniscus, 214
Lens. 442

tibres, 442

stars, 443

Lenticular plands, l.iO
Lencajmia, 20
Leucocyte, 23
Leucocj-tosis, 20
Leucopenia, 20
Ligamentuni denticulatum, 171

latum, 386

pectinatum, 434

pulmonis, 347

spirale, 4(57

suspensory of lens, 443

Liniitans, externa, 451

interna, 447

Lines of Salter, 278

of Schreger, 279

Liquor folliculi, 390

sanguinis, 19

Littre's glands, 388
Liver, 333

, Vessels of, 335

Lobes of pancreas, 330

of salivary gland, 200

of thymus gland, 131

of lung, 346

Lobules of liver, 333

of lung, 346

of salivary glands. 290

of thymus gland, 131

Locus ccenileus, 228
Lung, 346

blood-vessels, 349

Ivmphatics, 349

Lymph, 123

Lvmphatic capillaries. 119

^— clefts, 119

glands, 126, 134

rootlets, 119

sinuses, 120

tissue, 62, 126

vessels, 117

Lymphatics, 117

in mucosa, 302

Lymph-canal system in cornea, 51

-canalicular system, 119

cavities. 120

corpuscles, 123

follicles, 126

hearts, 123

Lymphocyte, 25, 58, 123
Lymiihoid cells, 25

Macula acustica, 463

lutea, 454

Malleus, 459

Malpighian corpuscles of kidney,
359

of spleen, 353

pyramids of kidney, 357

stratum of skin, 33

Mammary gland, 401
Manubrium mallei, 459
Marchi's method, 182
Marrow of bone, 68
Matrix of osseous substance, 70
^Meatus auditorius extemus, 458
Meckel's ganglion, 253
Media of arteries, 108
Median fillet, 228

lateral fissure, 176

^fediastinum testis, 372
Medulla oblongata, 202

of gland, 134

Medullary cylinders, 135

lymph-sinus, 136

ray, 359

sheath of nerve-fibres, 145

Medullated nerve-fibres, 143
Meibomian glands, 424
Meissner's corpuscles, 158, 423

plexus, 261, 266, 326

Membrana basilaris, 469

• chorio capillaris, 441

Descemeti, 430

granulosa, 388

hyaloidea, 443

reticularis, 473

secundaria, 460

supra-choroidea, 434

tectoria, 474

tympani, 458

Membrane of Krause, 96
Mesencephalon, 229
Mesentery, 122
Mesogastrium, 45
Metakinesis, 15
Microcytes, 20
Microsomes, 9
Migratory cells. 44
Milk, 403

• globules. 402

tooth, 283

Mitoina, 11
Mitral cells, 251
Modiolus, 465
Monaster, 15
Motor ganglion cells, 197
Moss fibres, 243
Movement of cilia, 35
Mucin, 37
Mucosa, 300

496

Elements of Histology.

Mucosa, Lymph follicles of, 128
Mucous cells, 2'.)3

glands, 2Sr, 298

membrane, 300

Miico-salivary glands, 288
Mucus, Formation of, 36
Miiller's fibres, 447

muscle, 435

Muscle bundles, 87, !)1
— — buds, 102

cells, 86

column, 92

corpuscles, 94

libres, 86, 90

librillEe, 92

sheath, 87

spindle, 102

tissue, Striped, 90

. Non-striped, 86

Muscular compartments, 98
Muscularis externa, 308

mucosEe, 308

Musculus ciliaris Riolani, 424
Myeloplax, 7, 85
Myeloplaxes of Robin, 85

Xail, 420

cells, 420

groove 420

substance, 420

Xasal mucous membrane, 475

sei)tum, 63

Nerve bundles, 141

corpuscles, 145

end plate, 16o

endings, 155

fibres, 140

plexus, 143, 150

unit, 268

Network of fibrill*, 153, 167
Neurilemma, 145
Neuroglia, 182

cells, 184

fibrils, 183

of Virchow, 182

• tissue, 62

Neuraxon, 144

Neuron, 268

Neurokeratin, 146

Neutropliile cells, 27

Nipple, 401

Non-medullated nerve-fibres, 148

Nuclear layer in bulbus olfae-

torius, 251
membrane, 11

substance, 11

zone, 442

Nucleoli, 11
Nucleoplasm, 11
Nucleus, .Structure of, H
Nucleus ambiguus, 215

arciformis, 213

cuneatus, 206

gracilis. 206

Nuclei, Inner, of retina, 449

, Outer, of retina, 451

Nymphae, 399

Odontoblasts, 277, 280
0']sophagus, 307
Olfactory bulb, 250

cells, 478

glomeruli, 251

nerves, 148, 480

Olivary bodies, 206, 207

nucleus, 207

Omentum of cat, 44

of frog, 122

of guinea-pig, 45

of rat, 45

, Structure of, 48

Optic chiasma, 270

lobes, 231

nerve, 456

nerve-fibres, 447

tract, 270

■ vesicle, 455

Ora serrata, 447
Organ of Corti, 469

of Giralde, 380

of Jacobson, 482

Ossein, 70

Osseous labyrinth of ear, 460

lamella;, 70

substance from osteoblasts, 85

Ossicula auditus, 459

Ossifying cartilage, 77
Osteoblasts forming bone, 84
Osteoclasts, 85
Osteogenetic layer, 68
Otoliths, 339
Oval nucleus, 41
Ovary, 386

, Development of, 392

, Lymphatics of, 282

, Nerves (jf, 282

Oviduct, 394
Ovum, 1, 388
Oxyntic cells, 312
Oxj-phile cells, 27

Pacinian corpuscles, 155
Palate, 298

Index.

497

Palmiii plicata\ 305
Pallicbni', 4-24
Pancreas, 330
Papilla oircimivallata, 305

liliJormis, 30-'

foliata, .•i05

fmi^iformis, 302

iiervi optiri, 44t)

Papillary hair ofUiiiia, 410

muscle, ItiC.

Paraglobiilin, 22
Paraiiuck'i, IS
Paraplasm, 51
Parenchyma of kidney, 357
Parenchymatous cartilage, 66
Parietal cells, 312

Pars ciliaris retiuic, 430

niembranacea, 3S3

prostatica, 383

Pedunculated hydatid of .Alor-

gagni, 380
Pedunculus cerebelli, 238
Penis, 384

corpora caveinosa, 3S4

nerve-endings, IGO

Peptic glands, 312
Peribronchial lymphatics, 340
Pericardial cavity, 121
Pericellular space, 201
Pcrichimdriuni, ti3
Perilymph, 401
Perilynjphangial nodules, 128
Perimysium, 01
Perineurium, 141
Periosteal bone, 75

f(jrmation, 84

j)tocesses of Virchow, 75

Periosteum, 68

Peripheral nerve-endings, 155
Peritoneal cavity, 121
Peritoneum, 41
Perivascular lymphatics, 110

lymph spaces, 201

Peyer's ulands, 321

- - pat'rh, 130
Phagocvtes, 25, 50
Pharynx, 208

tonsil, 302

Pia mater, 170, 235
Pial sheath, 456
Pigment cells, 52
Plasma, 10

cells, 50

Pleura pulmonalis, 347
Pleural cavities, 121
Plexus choroideus, 235

myentericus, 326

Meissner, 326

venosus vaginalis, 308

Plica} villosa?, 311
Polar bodies, 18
Pons Varolii, 226
Porta, hepatis, 333
Portio iMiilleri, 435

vaginalis uteri, 305

Posterior nerve roots from spinal

cord, 188
Postganglionic libres, 2r)4
Pricganglionic fibres, 265
Prickle cells, 37
Primitive dental groove, 280

tibrilhe, 15U

fibrils, 02

ova, 393

Prostate, 382
Protoblast, 6
Protoplasm, 1, 7

, ^5tructure of, 7

Protoplasmic memlirane, 55
Proximal convoluted tubule, 362
Pulp tissue, 270

Purkinje's ganglion cells, 239
Pyloric glands, 313
Pyramid of Ferrein, 350
Pyramidal decussation, 204

tracts, 177

Rami capsulares, 337

Ranii'm y Cajal's discoveries, 182,

180, 440, 450
Ranvier's constrictions, 146

nodes, 146

Raphe, 209

Red blood corpuscles, 20
Red nucleus, 230
Reissner's membrane, 46
Eemak's fibrous layer, 108

nerve-fibre, 148

Rete Malpighii, 33

mucosum, 33

testis, 370

Reticular cartilage, 67

formation, 200

Restiform body, 200
Retina, 445

, Blind spot of, 446

, Blood-vessels of, 456

, Ganglion cells of, 448

, Lymphatics of, 456

Rhabdia of Kiihne, 92

Rhodopsin of Kiihne, 453

Rods and cones, 452

Rollett's secondary substance,

03
Rosette stage in nucleus, 13
Rugse, 30S

49S

Elements of Histology.

Rutherford's scheme of ir.uscle
contr.iction, 99

Saccules, -k52

Saccus endolvmphaticus, 461

Saliva, 300

Salivary cells, 293

• glands, 2S6

. Blood-vessels of. 297

, Ducts of, 291

. Lobes of, 290

: Lobules of, 290

, Lnnphatics of. 297

, Xenes of. 297

Sarcode of Dujardin, .j
Sarcoglia, 100
Sareolemma, 91
Sarcoplasma, 92
Sarcoplasts, 101
Sarcous elements, 94
Scala tAiupaui, 465

vestibuli, 335, 465

Schultze's protoplasm, 5
Schwann's cells. 5
Sclerotic, 432
Scrotum, S7
Sebaceous follicles, 41S
Semicircular canals, 462
Seminal cells, 375

tubules, 374

Sensory decussation, 207

end-organs in muscle, 166

in tendon, 16S

ganglion cells, 197

Septum cistenise lymphatiese. 45
Serous glands, 2S6, 299

membranes, 122

Sesamoid cartilages, f>*^
Sharpevs perforating fibres, 74
Sheath" of Henle, 142

of Schwann, 145

Simple axis cylinders, 153

Ivmphatic glands, 126

Skin, 404

-, Blood-vessels of, 421

, Lymphatics of, 422

. Nerves of, 423

Solitarv glands. 130

lymph follicles, 321

Spaces of Foutana, 434
Spermatoblasts, 377
Spermatozoa, 37S
Sphincter pupillae, 437
Sphincters, SS
Spinal accessor^-, 203

conl, 170 !

grey matter, 191

.Spinal cord white matter, 186
Spiral fibre. 267

tubule, 363

Spireme, convolution, 13
Spleen, 3jl

, Capsule of, 351

, L^Tiiphatics of, 355

, Xerve-tibres of, 242, 355

. Parenchyma of, 352

, Pulp o.^'353

. Red blood corpiLScles of, 2S

, Trabecule of, 352

Spongioblast, 450

Spongioplasm, 7

Spong'y bone substance, 74

Squamous epithelial ceils, 32

Sternal cartilage, 63

Stigmata, 112

Stomach, 310

Stomata, 112, 121, 349

Stratified columnar epithelium, 35

pavement epithelium, 32

Stratum adiposmn. 406

cinereum, 231

comeum, 33

■ glomerulosum, 251

granulosum, 34, 250

lacunosum, 249

lemnisci, 231

liicidum, 33

Malpighii, 33

optieum, 232

radiatum, 249

zonale, 231

Strife acusticte 220

Stria vascularis, 468

Stroma, 22

Subarachnoidal spaces, 121, 170

tissue, 171

Subcutaneous lymphatics, 422

tissue, 406

Subdural spaces, 121, 170
Subendocardial tissue, 105
Subepithelial endothelium of De-

l)Ove, 51
Subhyaloid ceUs, 443
Submaxillary ganglion . 253
Submucosa, 300
Submucous lymphatics, 121
Subpericardial nerve branches, 107

ti.ssue, 106

Substantia ferruginea, 225

gelatinosa, iS6

nigra. 229

Subvaginal space, 457
Sudoriferous canal. 407
Sulcus hippocampi, 249
spiralis, 467

Superior pedunculus cerebelli, 22S

Index.

499

Suprachoroiilal tissue, 434
.Suprarenal bodies, 480
Supravaj^iiial space, 457
Suspt'usory ligament, 443
Sweat glan< Is, 407
Sympathetic system, "258
Synapsis, ]9f>
Synovial cavities, 121

Tactile eurpuscles, 1-38, 423

hairs, 417

Tapetuni nigrum, 43!>, 454
Tarsal plate, 424

Taste buds, 305

cells, 305

goblets, 305

Teeth, 275

cement, 279

develoimient, 280

pulp. 279

Tegmental cells, 305
Tegmentum, 231
Teichmann's crystals, 23
Tendon cells, 49

spindles, 167

Temlons, 49
Tendril fibres, 243
Tenoniau capsule, 457

space, 457

Tensor choroidete, 435
Ternainal bronchi, 347
Testis, 372
Thoracic duct, 117
Thymus fullicles, 131

■ gland, 131

Thyroid cartilage, 63

gland, 484

Tongue, 302

, Serous glands of, 304

Tonsils, 129

Touch-cells of Merkel, 161

corpuscles of Merkel, 169

Trabecule carne*, 106

of lymphatics, 134

of sjileen, 352

Trachea, 343

Tracts of white matter in cord, 17
Tract cells, 197
Transitional epithelium, 35
Transverse disc, 95
Trapezoid nucleus, 218
Trapezium, 218, 226
Tuba Eustachii, 459
Tubercle of Rolando, 202
Tnberculuni acusticum, 219
Tubes of epididymis, 379
Tunica adnata, 372

Tunica albuginea, 37

dartos, 88

fibrosa. .390

prnpriii, 4i>9

• vaginalis, 372

Tyson's glands, 384

Ureter, 371
Urethra, Female, 399

, Male, 383

Urinary tubules, 361
Uterus, 395
Utricle, 462
Uvea, 437

Vagina, 397

Varicose nerve-fibres, 147

Vas deferens, 381

rectum, 378

Vasa etferentia, 379
Vascularisation of cartilage, 75
Vater's corpu.scles, 155
Veins, 110

, Intima of, 110

, Media of, 110

of the bones, 110

Veins of the l)rain, cord, gravid
uterus, membranes, and retina,
110

, Valves of, 110

Vena axillaris, azygos, cava, cru-
ralis, hepatica, intima, iliaca,
mcsenterica, jtoplitea, I'enalis,
spermatica, and umViilicalis, 110

jugularis, and subclavia, 110

Venae rectie, 369

stellatfce, 370

vorticosse, 441

Venous radicles, 353

sinuses, 353

Ventricle, Fourth, 211
Ventricles, 106
Ve.sicula; seminales, 381
Vestibulum of labyrinth, 460
Virchow's crystals, 23
Visceial pericardium, 105

peritoneum, 333

Visual purple, 453
Vitreous body, 443

Wandering cells, 58
Weigert's method, 182
White blood corpuscles, 23

500

Elements of Histology.

White commissure, 187

fibrous tissue, 40

substance of brain, 237

of cord, ISiJ

of Sclnvann, 145

Wolffian body, 374, 3S7

Wreath arrangement of nucleus, 14

Yellow elastir cartilai

Yellow elastic tissue. 00

Zona fasciculata, 487

glomerulosa, 486

pel In ei da, 1, 388

reticularis, 487

vasculosa, 386

Zonula ciliaris, 443
Zinnii, 443

I'rintedbyC'AssKLL & Company. LnnTED. La Belle Sau\aye, Louilon, E.G.

K67*^
1698

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