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LECTURES

ON THE

COMPARATIVE ANATOMY

OF THE

PLACENTA.

FIRST SERIES. fZ^ y ^.

DELIVERED BEFORE THE ROYAL COLLEGE OF SURGEONS
OF ENGLAND, JUNE, 1875.

BY

WM. TURNER, M.B. (Lond.)

PKOFESSOE OP ANATOMY, UNIVERSITY OF EDINBUEGn ; LECTUEEE ON ANATOMY

AND PHYSIOLOGY, EOYAL COLLEGE OF SUEGEONS, ENGLAND ;

MEMBEE OF THE GENEEAL MEDICAL COUNCIL.

EDINBURGH: A^

ADAM AND CHARLES BLACK. ^

1876.

{All Bights reserved. 1

©amtirtlrgj :

PRINTED BY C. J. CLAY, M.A.
AT THE UNIVERSITY PRESS.

PREFACE.

These Lectures on the Comparative Anatomy of the Placenta
were delivered in the Theatre of the Royal College of
Surgeons of England^ on the 14th, 15th and 16th June,
1875. They were illustrated by numerous preparations both
macroscopic and microscopic, and by many enlarged coloured
diagrams. The diagrams were enlarged from the preparations
by my assistant Mr A. H. Young. The figures from the
microscopic preparations, which are here reproduced on wood,
are from drav/ings kindly made by that gentleman ; whilst
the figures in the lithographic plates are, with two exceptions,
from drawings executed by my former assistant Mr J. C.
Ewart, M.B., to illustrate my Memoir on the Placentation of
the Seals in the Transactions of the Royal Society of Edinburgh.

The observations on the Placentae of the Narwhal, the
Lemurs, the Hyrax, and the Elephant, on the chorion of the
Giraffe, and on the post partuni condition of the mucous mem-
brane of the Cat's uterus, have been made since the Lectures
were delivered.

In a second series of Lectures to be given in the summer
of 1876, it is intended to describe the Anatomy of this Organ
in the other orders of Mammals.

December, 1875.

CONTENTS.

PAGE

Introductory Remarks , 7

Development of the Foetal Meiubranes 9

Form and Structure of the Chorion . 18

Structure of the unimpregnated Uterine Mucous Membrane . . 28

Structure of the Diffused Placenta ....... 33

Structure of the Polycotyledonary Placenta 59

Structure of the Zonary Placenta 70

General Morphology of the Diffused, the Polycotyledonary, and the

Zonary Placenta 102

Physiological Remarks . 114

Explanation of the Plates 123

THE COMPARATIVE ANATOMY

OF

THE PLACENTA,

Mr Peesident, Fellows of the College and Gentlemen.

When the Council of the College elected me to fill
the office of Lecturer on Anatomy and Physiology, I thought
that the best mode in which I could show my sense of the
honour conferred upon me was to select for consideration and
discussion in the Lectures, a department of Anatomy which
I had myself investigated. As the Anatomy of the Placenta
in the several orders of placental mammals has engaged my
attention for some years, and as during that period I have had
the good fortune to acquire the gravid uteri of several rare
mammals, the placentation of which had been little studied^
I have chosen as the subject of my Lectures the Comparative
Anatomy of the Placenta ; an organ, which, from its import-
ance as the medium of connection between mother and foetus
during intra-uterine life, is worthy of careful study by the
Anatomist and Physiologist. In the course of my remarks
I hope to submit to your notice several new facts and rela-
tions of structure, and to throw some additional light upon
previously recorded observations.

8 INTRODUCTORY REMARKS,

It was my original intention to have passed under review
during the present course the several modifications in the form
and structure of the placenta exhibited by the various orders
of placental mammals, and to have concluded with a descrip-
tion of the human placenta, but I found, when I began to
arrange the material I had gathered together, that it would
have been impossible to compress so extensive a subject into
three Lectures, without omitting much that I deemed it ina-
portant to communicate, both as regards facts in detail and
the principles to be deduced from them. I have therefore
limited myself on this occasion to an enquiry into the de-
velopment, form, and structure of the foetal membranes, the
structure of the unimpregnated uterine raucous membrane, and
the changes taking place, on the one hand in the chorion,
on the other hand in the uterine mucosa, which lead to the
formation of the diffused, the polycotyledonary and the zonary
forms of placenta. In the course of my description I do not
intend to enter at any length into the consideration of the
shape and more obvious arrangements of the placenta and
membranes, as these have already been fully described by
many able anatomists ; but to speak more especially of the
minute or microscopic structure of the organ, a branch of
enquiry of equal, if not of greater importance, than the deter-
mination of the macroscopic characters, for only after it has
been determined in the several orders of mammals can a
correct conception of the general morphology and physiology
of the organ be obtained.

In all inquiries into the anatomy of the Placenta, two series
of structures have to be investigated, the one belonging to the
,foetus, the Foetal Placenta ; the other to the mother, the Maternal
Placenta. The placenta is therefore a compound organ, and the
complexity of its structure in any given mammal is propor-
tional to the degree in which, in the course of its development
and growth, the originally separable foetal and maternal por-
tions have become interlaced with each other.

Development of the Fcetal Membkanes.

The observations on the structure and development of the
ovary, which have been made during the last few years, more
especially by Professors Pfliiger^ and Waldeyer^ and by Dr Foulis',
have satisfactorily demonstrated that the ova are derived from
the corpuscles of the epithelial layer which invests the surface of
the ovary. By a process of involution accompanied by a great
growth of the ovarian stroma, many of these corpuscles become
imbedded in the substance of the ovary. The nucleus of a
corpuscle swells out into a spherical germinal vesicle, and con-
tains in its interior a nucleolus, or germinal spot. Around the
nucleus the protoplasm of the cell-substance increases greatly
in amount to form the yelk. The peripheral portion of this
yelk-protoplasm then differentiates into a cell-wall — the zona
pellucida, or vitelline membrane — which completes the develop-
ment of the ovarian ovum. The vascular connective-tissue
stroma of the ovary forms a capsule aronnd each ovum, which
constitutes the vascular capsule of the Graafian follicle. This
capsule is lined at first by a single, but afterwards by more than
one layer of cells, which form the cells of the membrana granu-
losa, or so-called epithelium of the Graafian follicle. These cells
were believed by Waldeyer to be derived from certain of the
epithelial cells investing the ovary, which had been included in
the ovarian substance along with those which developed into
ova. But Br Foulis has pointed out that they are descended
from the connective-tissue corpuscles of the vascular stroma.
The Graafian follicle enlarges by the multiplication of the cells
of the membrana granulosa, and by the secretion of follicular
fluid. In the course of time it bursts, and the ovum is extruded.
Being received by the Eallopian tube it is conveyed into the
cavity of the uterus.

Should the ovum become fertilized by the penetration of
spermatozoa through the zona pellucida, a remarkable series of

^ Die EierstocTce der Sciugethiere und des Menschen. Leipzig, 1863.
^ Eierstock und Ei. Leipzig, 1870.

* Abstract in Proc. Roy. Soc. Edinburgh, 1874 — 75, and in extenso in
Transactions of the same Society, 1875.

10 DEVELOPMENT OF THE

developmental changes takes place in it, which leads to the pro-
duction not only of the embryo, but of the foetal membranes.
The germinal vesicle disappears, the yelk undergoes cleavage,
and in course of time becomes subdivided into multitudes of
minute cells, each consisting of a nucleated clump of protoplasm.
These cells are arranged immediately within the zona pellucida
to form a cellular membrane, the blastoderm, which in course of
time surrounds the undifferentiated central part of the yelk,
assumes a vesicular form, and is known to embryologists as the
blastodermic vesicle. At one part of the blastoderm a roundish
white spot then appears and forms the area germinitiva, or area
of formation of the future embryo. Commencing at the area
germinitiva the blastoderm splits into two layers, an outer,
epiderm or epiblast, and an inner, hypoderm or hypoblast.
Subsequently a third or intermediate layer is formed, the
mesoderm or mesoblast. By most embryologists the mesoblast
is regarded as derived from the hypoblast, but Kolliker, in a
recent memoir^ considers that it has no genetic relation with
the hypoblast, but arises from the epiblast by an increase of the
cells of the same.

Whilst these changes are taking place in the cells derived
from the differentiation of the yelk,, the zona pellucida assumes
a different appearance. At first it is quite smooth, but soon, at
least in the dog and rabbit, numerous short, very fine, simple
villi project from its outer surface, and form the villi of the
primitive chorion. Whether or not similar villous outgrowths
project from the zona pellucida of the human ovum has not yet
been determined. The villi are, like the zona itself, perfectly
structureless, and their apparent object is to attach the ovum in
the early stage of gestation to the surface of the uterine mucous
membrane. In a short time the primitive chorion disappears,
and is replaced by the secondary or permanent chorion, which
forms the outer envelope of the embryo, and is the proper
medium of attachment to the wall of the uterus.

The mode of origin of the secondary or persistent chorion
has now to be considered. To form a definite conception of its
production it will be necessary to glance briefly at the changes i

^ Verh. der PJiys. Med. GeseUscJiaft, Wiirzhurg. January, 1875.

FCETAL MEMBRANES. 11

which take place in the area germinitiva. From the three
layers of cells, into which the blastoderm divides in this area,
the several tissues and organs of the embryo arise, by a process
of multiplication and histological differentiation. Speaking
generally, one may say that the epiblast cells give origin to the
cuticle and its appendages and to the central organs of the
cerebro- spinal nervous system ; the mesoblast cells to the con-
nective, muscular, osseous and vascular systems, and to the
distributory part of the nervous system ; whilst from the hypo-
blast cells the epithelial lining of the alimentary canal and of the
various glands which open into it arises. The rapid multiplica-
tion of these cells in the area germinitiva leads to the production
of the body of the embryo. In the course of time a longitudinal
axial depression appears in the epiblast, which marks the posi-
tion of the brain and spinal cord, and below this groove an axial
cord, the chorda dorsalis, arises in the mesoblast, which indicates
the position of the future spinal column. On each side of the
chorda the mesoblast splits into two layers, which become
separated from each other by a space, the future pleuro-
peritoneal cavity. The outer layer of the mesoblast, or somato-
pleure, is intimately associated with the epiblast, and forms
with it the walls of the body of the embryo ; whilst the inner
layer of the mesoblast, or splanchno-pleure, is intimately as-
sociated with the hypoblast, and forms with it the walls of the
alimentary canal and its appendages.

From the margin of the area germinitiva a delicate fold
arises, which, by becoming more and more elevated, gradually
extends itself above the back of the young embryo, until at last
the folds from opposite sides meet in the middle line, become
continuous with each other, and form the membrane of the
amnion. Between the amnion and the back of the embryo
is a space, the cavity of the amnion, which increases in size
by, the secretion of the liquor amnii into it. The amnion
consists of two layers, an outer and an inner, and as it is
derived from the area germinitiva it is necessarily continuous
with the blastoderm. The inner layer of the amnion, which
lies next the amniotic cavity, consists of tessellated epithelial
cells, is derived from the epiblast, and is continuous with the
cuticular layer of the embryo. The outer layer of the amnion

9 9

12 DEVELOPMENT OF THE

is a thin stratum, continuous with the somato-pleure layer of
the mesoblast, and formed of stellate and spindle-shaped cells,
like the corpuscles of embryonic connective tissue\ The
amnion is the most internal of the foetal membranes, and forms
an ovoid bag in which the foetus and liquor amnii are contained,
- But before the amniotic folds meet to become continuous
with each other, the free edge of each fold is bent outwards,
and, by a continuous process of growth, gradually spreads around
the ovum immediately within the zona pellucida so as to form
a layer, which was named by von Baer^ the serous envelope
of the ovum, but which may more appropriately, from its posi-
tion within the zona, be named the sub-zonal membrane.
"When the union of the amniotic folds has taken place the sub-
zonal membrane becomes completely severed from the proper
amnion, and constitutes one of the layers of the secondary or
persistent chorion. The sub-zonal membrane consists essentially
of a layer of cells, which was originally continuous with the
cellular layer lining the inner surface of the proper amnion,
and through it with the epiblast cells forming the cuticular
covering of the embryo. But it is not unlikely that along with
this cell-layer a thin prolongation of the layer of stellate con-
nective-tissue corpuscles of the somato-pleure layer of the meso-
blast is present. Between the sub-zonal membrane and the
proper amnion a space exists, continuous with the general
pleuro-peritoneal cavity of the embryo, which is of interest in
connection with the formation of the permanent chorion, as the
space into which the allantois grows and expands.

Whilst the changes in the epiblast and somato-pleure,
which lead to the formation of the amnion and sub-zonal outer
layer of the persistent chorion are taking place, the hypoblast
and splanchno-pleure undergo important modifications. They
gradually extend over the undifferentiated part of the yelk,
which they enclose in a sac, the yelk-sac, or umbilical vesicle,
and at the same time they form along the ventral surface of the
embryo an elongated tube, the alimentary canal. This canal
at first freely communicates with the yelk-sac, but as the walls
of the alimentary canal thicken and become more closed in,

^ Schenk, Lehrbuch der vergleichenden Emhryologie. Wien, 1874.
2 Ueber EntioicMungsgescMchte der Thiere. 1828, p. 79.

FCETAL MEMBRANES. 13

the communication narrows, until at length nothing is left but
a slender duct, the omphalo- mesenteric duct, as the channel of
communication between the umbilical vesicle and the intestinal
part of the alimentary tube. In the course of time this duct
shrivels up and disappears.

In the splauchno-pleure forming the wall of the umbilical
vesicle and in the corresponding wall of the alimentary tube
blood-vessels are developed. As that pole of the umbilical
vesicle, which lies opposite the omphalo-mesenteric duct reaches,
and is, at an early period of its development, in contact with
a limited area of the sub-zonal membrane, the blood-vessels in
the wall of the vesicle may be, and in some mammals are,
conveyed by it up to the sub-zonal membrane.

But an important change also takes place at the pelvic end
of the alimentary tube. A small vesicular outgrowth appears,
which communicates with the intestine and forms the allantois.
The allantois rapidly increases in size, grows into the space
between the umbilical vesicle, amnion and sub-zonal membrane,
becomes more or less intimately united with these structures,
but more especially with the sub-zonal membrane. As the walls
of the pleuro-peritoneal cavity grow and close in towards the
ventral mesial line a part of the allantois becomes enclosed
within the abdominal chamber and forms the urinary bladder,
whilst a part remains outside this cavity and forms a dilated
bag, the sac of the allantois, which contains the allantoic fluid.
This sac keeps up its continuity with the urinary bladder by a
slender tubular stalk, the urachus, which passes through the
abdominal wall at th-e umbilicus. The wall of the sac of the
allantois, having reached the inner surface of the sub-zonal
membrane, spreads itself over the whole, or a great part of that
surface, and forms the inner layer of the permanent chorion.
As the allantois is a vesicular outgrowth from the alimentary
tube, its walls are necessarily derived from the same laj'^ers of
the blastoderm. It is lined by an epithelium continuous with
the epithelial lining of the intestine, which is derived from the
hypoblast, whilst external to the epithelium is a layer of con-
nective tissue continuous with and derived from the splanchno-
pleure layer of the mesoblast. In this outer connective-tissue
layer blood-vessels are developed, which are continuous with

u

DEVELOPMENT OF THE

the abdominal vessels of the embryo. When the sac of the
allantois reaches the sub-zonal, or external, layer of the perma-
nent chorion, the blood-vessels are necessarily brought there at
the same time, and as the allantois grows to form the inner
layer of the chorion its blood-vessels become the vessels of the
permanent chorion, or the vessels of the foetal placenta. These
vessels increase in size and numbers with the growth of the
chorion, their trunks become the umbilical arteries and vein,
they enter into the formation of the umbilical cord and pass
into the abdominal cavity at the umbilicus to join the aorta
and post caval vein.

There are thus four structures, of which one is developed
at the periphery of the ovum, whilst the remaining three

Fig. 1.

Diagram of the foetal membranes. Sti-uctures which either are, or have been
at an earlier period of development, continuous with each other are represented
by the same character of shading. pc, primitive chorion with its villi.
sz, sub-zonal membrane. JE, epiblast or cuticular covering of embryo continuous
with am, the amnion. M, mesoblast forming the bulk of the body of the
embryo, and prolonged into the wall of the sac of the Allantois al, and into the
wall of the Umbilical Vesicle, UV. H, hypoblast forming the epithelial lining
of the intestinal tube and prolonged into the wall of the sac of the Allantois and
of the Umbilical Vesicle. AG, cavity of Amnion. ALC, cavity of Allantois.

FCETAL MEMBRANES. 15

ultimately reach the periphery, which from their position may
enter into the formation of the persistent chorion, or outer
envelope of the foetus : viz. the zona pellucida, the sub-zonal
membrane, the allantois, and the umbilical vesicle. The
structureless zona, with its simple structureless villi, which
together form the primitive chorion, very early disappears,
either by becoming incorporated with the sub-zonal membrane,
so as no longer to be recognised as an independent membrane,
or by becoming absorbed. The sub-zonal membrane, or serous
envelope of the ovum of Von Baer, originally continuous with
the amniotic folds, and through them with the epiblast layer
of the blastoderm, persists, and forms the external or epi-
thelial non-vascular layer of the persistent chorion, and of
the villi which grow from it. The allantois forms the inner
or vascular layer of the persistent chorion, and the vascular
matrix of the villi ; but in some of the Rodentia the umbilical
vesicle reaches and remains in contact with a limited portion
of the sub-zonal membrane, to which it conveys connective
tissue and blood-vessels. The persistent chorion, therefore, is a
compound membrane, produced secondarily during the process
of development by the union of the sub-zonal membrane, from
which its epithelial layer is derived, with .the allantois from
which it derives its blood-vessels and connective tissue ; and
like the embryo itself it arises from the layers of the blastoderm.
The allantois undergoes considerable modifications in both
size and general disposition in the different orders of mammals.
In many mammals, as the Pachydermata, Ruminantia, Cetacea,
Carnivora, Pinnepedia, the Lemurs and the Scaly Anteaters
(Manis), the sac of the allantois persists as a distinct chamber,
and contains a considerable quantity of allantoic fluid. Of the
opposite walls of the sac, the one lines, to a greater or less
extent, the inner surface of the permanent chorion, which is
coated therefore by the epithelial lining of the allantois ; the
other invests, to a greater or less extent, the outer surface of the
amnion, which is covered therefore, in whole or in part, by the
wall of the sac of the allantois. As a consequence of this
arrangement the bag of the amnion in these mammals is alto-
gether or in great part separated from the inner surface of the
permanent chorion. * .;

IG

DEVELOPMENT OF THE

In Orca gladiator, when the allantois reached the chorion,
it became prolonged both to the right and left in the form of a
comparatively wide, almost cylindrical, sac-like horn. The left
horn-like prolongation extended to seven inches from the end
of the left horn of the chorion, where it formed a cul-de-sac.
The right horn-like prolongation entered the right cornu, but
did not reach to within twenty-one inches of the tip of the right
horn of the chorion. A large part of the wall of the allantois
was in apposition with the amnion, but, opposite the abdominal
aspect of the embryo, the wall of the allantois was united with
the inner surface of the permanent chorion by gelatinous- con-
nective tissue.

Fig. 2;

Outline diagram of the arrangement of the foetal membranes in Orca gladia-
tor.- E, the embryo, eh, the permanent chorion with its villi. The dotted line
am represents the amnion., al, the wall of the allantois.

So large and persistent is the sac of the allantois in the
ordinary Ruminantia, in the Camelidce, TraguUdce, Solipeda, and
cloven-hoofed Pacliydermata, that M. H. Milne Edwards has
grouped them together as Megallantoids : whilst he has placed the
Carnivora and Pinnepedia, from the smaller size of the sac of the
allantois, in a Mesallantoid legion of mammals. The Rodentia,
Insectivora, Cheiroptera, Quadrumana, and Man are charac-
terized by the small size of the sac of the allantois, or even by
its complete disappearance as an independent chamber: hence
Milne Edwards has grouped them together in a Micrallantoid
legion'. The disappearance of the allantois as a distinct sac is
correlated with the great expansion of the amnion, and increase
in the amount of amniotic fluid. As the bag of the amnion
expands it grows outwards towards the chorion, and in the

1 Considerations sur les affinites naturelles et la classification methodique des
Mammiferes. Paris, 1868.

FCETAL MEMBRANES. 17

Sloths, the Apes, and the Human Female, reaches, and adheres,
through the intermediation of a gelatinous connective tissue, to
the inner surface of that membrane, so that when the chorion is
cut through, the amnion is at once exposed.

The umbilical vesicle forms a sac situated in relation with
the abdominal aspect of the embryo, and continuous with that
part of the intestine which subsequently forms the ileum, by a
hollow stalk or pedicle,, the omphalo-mesenteric duct. In some
mammals,, as in the Pig, Mare, Cetacea and Ruminantia, it dis-
appears as development advances, so that no trace of it can be
seen in the membranes of an advanced embryo^. In others, as
the Human Subject, it persists, according to Schultze\ even up
to the end of intra-uterine life, as a minute vesicle at the pla-
cental end of the umbilical cord. In the Carnivava and Pin-
nepedia again it forms a well-defined sac, in relation to the
abdominal aspect of the fcetus, situated between the allantois
and amnion, and prolonged laterally into two horns. In the
Bitch I have seen its vessels persistent, and forming a well-
defined, plexus in its wall, though they did not reach the chorion.
In the frugivorous Bat {Pteropus medius) it is persistent. In
the Mole and Shrew it is large, and is described by Prof. Owen^
as supplying the outer envelope of the ovum with vessels. In.
the Rabbit, and probably also in other Rodentia, the umbilical
vesicle reaches the chorion, and forms a large sac in contact
with a considerable portion of that membrane, to which it
conveys blood-vessels; but the discoid placenta of the Rabbit
apparently derives- its foetal vessels only from that part of the
chorion which receives its vascular supply from the allantois.

1 Das Nalelbldschen ein constantes Gebilde in der Nachgehurt des ausgetra-
genen Kindes. Leipzig, 1861.

2 Comparative Anatomy of Vertebrates, Vol. in. p. 729^

18 FORM AND STRUCTURE

Form and Structure of the Chorion.

The chorion is the most external of the fetal membranes.
When first formed, it is globular or ovoid in shape. In uni-
parous mammals, as the Sloths, the Apes, and the Human
Female, where the uterus is single, it preserves, with but little
alteration, this form throughout intra-uterine life. In uniparous
mammals, as the Mare, the Ruminantia, the Cetacea, and the
Hare, where the uterus possesses two horns, the chorion be-
comes greatly elongated, and extends as far as the ends of both
horns. In the Seals, on the other hand, as was pointed out
by Barkow in Fhoca vitulina^, and as I have seen in Halichcerus
gryphus, where the uterus is also two-horned, the chorion of
the single foetus is limited to that horn in which the foetus is
situated, and the non-gravid horn, though slightly increased in
size, contains only a little mucus. In multiparous mammals,
again, as the Pig, the Rabbit, Guinea-pig, and the true Car-
nivora, where the uterus is two-horned, and each horn contains
one or more foetuses, the chorion is elongated, and the ends are
rounded, so that it becomes, as is so well seen in the Car-
nivora, lemon or citron shaped : but in the Pig a distinct pouch-
like sac of the allantois projects through and beyond each pole
of the chorion, and forms the diverticulum allantoidis described
by von Baer, The chorion, belonging to each embryo, is con-
fined to that horn in which the embryo is situated, though I
have seen in the pig's uterus, the chorion surrounding the foetus
situated lowest down in the left horn, passing across the corpus
uteri into the opposite cornu.

In its early stage of formation, the permanent chorion is
uniformly covered with delicate, slender villi, so that it possesses
a soft velvety appearance. In some animals, as the Mare, the
Cetacea, and Manis, even though the chorion increases during
gestation enormously in size, the villi continue to cover almost
the whole of its outer surface, though here and there a tendency
is exhibited for the villi to disappear and to leave a patch of

^ Zootomische Bemerkungen, Breslau, 1851.

OF THE CHORION. 19

bare non-villous chorion. In these and the other mammals in
which the villi are diffused over the greater part of the chorion,
the chorion is a chorion frondosum, and the placenta is termed
a Diffused Placenta.

But in the majority of mammals a much greater extent of
disappearance of the villi from the surface of the chorion takes
place as development advances. The villi become aggregated
into definite and limited areas, surrounded by smooth portions
of chorion, and with this limitation of area the individual villi
assume a more complex form. In many orders of mammals
the areas in which the villi are collected are so precise as to be
almost characteristic. In the ordinary Ruminants, for example,
the villi are collected into large tufts, called foetal cotyledons,
which cotyledons are scattered in considerable numbers over
the surface of the chorion, and the form of placenta produced
by this arrangement is called a Polycotyledonary Placenta.

In some other mammals the villi are collected together in a
zone-like or annular band, surrounding the equator of the
chorion, which, vdth a similar shaped band in the uterine
mucosa, forms a Zonary Placenta. The chorion is quite smooth
at and for a considerable distance away from the poles. This
mode of arrangement of the villi is best seen in the Carnivora.
The breadth of this zone, in proportion to the length of the
chorion, is much greater in the early than in the later stage of
gestation, so that if this membrane be examined, say in the cat,
when the ovum is only eight-tenths inch long, an area not more
than one-tenth inch long at each pole is free from villi, whilst
at the end of gestation, with a chorion seven inches in length,
the villous equatorial zone is only 1| inch in its transverse
diameter.

In some mammals the villi persist at one pole of the chorion,
and are distributed for some distance over its surface ; but the
opposite pole, i. e. the one next the os- uteri, is smooth and free
from villi. This arrangement leads to the formation of what
has been named a Dome-like, or Bell-shaped Placenta. In
Tamandua tetradactyla the villi, as M. A. Milne Edwards has
described ', occupy the larger part of the surface of the chorion,

^ Annates des Sciences Naturelles, xv. 1872.

20 FORM AND STKUCTURE

but the pole next the os uteri is smooth. They are not simple
in form, but consist of vascular, very compact vegetations. In
the Lemurs also the same anatomist has described a bell-shaped
placenta\ The anterior and middle parts of the chorion, he
says, are almost entirely covered by dense compact villi, con-
stituting a sort of vascular cushion, the result of the confluence
of a number of irregular cotyledons, whilst the villi have almost
entirely disappeared from the opposite pole of the chorion. In
the Sloths, as I have pointed out^ the villi are aggregated
together in disc-shaped lobes, Avhich are arranged on the an-
terior and middle portions of the chorion, but leave the pole
next the os uteri smooth, though vestiges of atrophied villi may
be seen on this smooth surface.

In the Bodentia, Insectivora, Cheiroptera, Apes, and Human
Female, the villi are collected into a comparatively circumscribed
area, which is not unfrequently circular or sub-circular in out-
line, and forms wi'h the corresponding surface of the uterus a
mass know as a Discoid Placenta.

When the villi first grow out from the chorion they are
short, simple, unbranched processes. In the Pig they preserve,
as a rule, their simple form, but in most mammals they increase
in length and breadth, and branch in a more or less complicated
manner, so as to present many modifications in shape in differ-
ent genera, which modifications will be desmbed in the course
of these Lectures,

In my description of the development of the permanent
chorion, I stated that this membrane is compound in structure,
and consists of an outer epithelial layer and an inner vascular
connective-tissue layer. The villi being outgrowths of the chorion,
are therefore composed of the same structural elements. When
the villi first appear on the permanent chorion they seem to con-
sist solely of cells, and are probably bud-like outgrowths of the
epithelial layer. Reitz^ considers that at their first appearance
they consist merely of protoplasm, in which nuclei are imbedded,
the differentiation into definite epithelial cells not taking place
until a later period. There is some difi'erence of opinion, whe-

^ Annales des Sciences Naturelles, xv. 1872.

" Trans. Roy. Soc. Edinburgh, 1873.

' Strieker's Handbuch der Gewebelehre. Article Placenta.

OF THE CHORION. 21

ther these outgrowths are at first solid or hollow. "Whichever be
the case, there can be no doubt that the vascular delicate con-
nective tissue of the inner layer of the permanent chorion is
prolonged into the axis of each villus, so that they ultimately
possess a vascular core, with a cellular epithelial investment. It
is in the young chorion that the epithelium is most satisfactorily
seen. I have examined it both in the Pig and Cat, in both of
which it consists of a tessellated layer of squamous epithelial
cells, the nuclei in which are distinct. As the animal ap-
proaches the full period of gestation, the demonstration of an
epithelial layer on the surface of the villi becomes more diffi-
cult, and in the chorion at the time of birth it is often impos-
sible to distinguish any tissue in the villus, other than the
vascular connective tissue, in which many fusiform or stellate
corpuscles are imbedded.

The villi soon begin to assume a more complex form by put-
ting out buds both from their sides and free ends, and if this
process is frequently repeated they not only increase in size but
become arborescent. The part which first appeared becomes the
stem, whilst the primary and secondary buds form the branches
with their terminal off-shoots.

Each villus has, as a rule, at least one artery and one vein
extending along its axis, which are connected together by a
capillary plexus, that is distributed near the periphery of the
stem and branches and within the villous buds. In most
mammals the buds are large and allow room for many capillaries
within them ; but the filiform villi of the Mare and Cow are so
slender that a single, or at the most a double capillary loop,
alone is present, and a similarly simple arrangement exists in
the Human villi. The vessels of the villi are branches of the
umbilical artery and vein, which form the vascular trunks of
the umbilical cord. In the Garnivora and Pinnepedia the
umbilical vessels are not limited in their distribution to the
zonary placenta., but slender branches extend as far as the poles
of the chorion. In Cholopus Hoffmanni the non-placental pole
of the chorion contains slender ramifications of the umbilical
vessels.

The umbilical cord is the bond of union between the foetus
and the chorion. Its length varies much in different mammals.

22 FORM AND STRUCTURE

It is apparently the longest in the Human subject, where it
has an average length of about two feet, and is also of con-
siderable length in the Apes, the Sloths, in Orycteropus, and in
the Cetacea, whilst in the Carnivora and Pinnepedia it is
remarkably short.

The umbilical cord contains two umbilical arteries. Usually
only a single umbilical vein is present, but sometimes, as in
the Cetacea, Riiminantia, and the Pig, two veins occur; and the
arteries wind in a spiral manner around the vein or veins. In
all mammals in the earlier periods of intra-uterine life the
urachus, which connects the extra-abdominal part of the allantois
with the intra-abdominal part, or urinary bladder, forms an
important constituent of the cord. In those mammals in which
the extra-abdominal part of the allantois persists as a capacious
sac, the urachus remains pervious in the cord, sometimes, as
in the Cetacea, being funnel-shaped; at others, as in the
Pinnepedia, forming a very fine tube. Where the allantois
however disappears as a distinct sac, as in the Human subject,
then the urachus lying in the cord atrophies, and cannot be
recognised in the later stages of gestation. The umbilical
vesicle is also a constituent of the cord in the early stages of
formation of the membranes, but all trace of it disappears from
the cord as development advances, except in such mammals
as the Rodentia, in which the vesicle persists as a well-defined
sac. The vessels of the cord, the urachus and umbilical vesicle
when present in the cord, are surrounded by a mucous or
gelatinous connective tissue, well known as the gelatine of
Wharton. Virchow and others have described a net-work of
anastomosing, stellate connective-tissue corpuscles in this
gelatinous tissue. Dr Koester, who has carefully examined
its structure ^ states that it consists of a mucous basis sub-
stance in which fibrillar threads are interwoven and connected
together. The appearance of an anastomosing network with
thickened nodes is due to a canalicular system in which cells
rich in protoplasm are situated, so that the cord is permeated
by an anastomosing system of juice-canals capable of being
injected, which are identical with the connective-tissue cor-

^ Ueber die feinere Strnctur der menschUchen Nabelschnur. Inaugural Dis-
sertation. Wiirzburg, 1868.

OF THE CHORIOiSr. 23

puscles of Virchow. Virchow has also pointed oiit^ that
blood-capillaries, connected with the vessels of the abdominal
wall, extend for from 4 to 5 lines into the abdominal end of
the cord, but no further, Mr Lawson Tait describes in the
Human cord^ a saccular blood-vascular sinus situated at the
omphalic ring, which extends for about 45 millimeters into the
true substance of the cord and gives off, at short intervals,
trunks, which rapidly break up into capillaries, that enter
directly into the canalicular tissue. The cord does not appear
to have nerve-fibres passing into it. The several tissues of the
cord are invested by the amnion, which forms a sheath around
it, and is continuous at the abdominal end with the cuticular
covering of the embryo. In the Mare and some other mammals,
where the sac of the allantois is persistent, only the abdominal
or inner end of the cord is invested by the amnion, the outer
or placental end being in relation to the allantois. In the
Grey Seal [Halichoerus gryphus) I observed that the umbilical
vessels in the short cord began to branch two inches from the
abdomen, and that in the course of these branches to the
placenta they passed between the allantois and the umbilical
vesicle, and that some even were suspended in the cavity of
the vesicle.

In some mammals the amnion investing the umbilical
cord has small bodies connected with it, which project towards
the amniotic cavity. In the Cetacea they have been noticed
by Professors Owen, Rolleston, and other observers. I have
especially studied their arrangement and structure in Orca
gladiator, in which cetacean I found not only the amnion
covering the cord abundantly studded with yellowish-brown or
olive-tinted corpuscles smaller even than mustard-seeds, but
similar bodies were thickly congregated on the amnion, where
it covered the funnel-shaped sac and horns of the allantois;
whilst on that part of the amnion which was in contact with
the chorion, they were much more sparingly distributed. Some
of these corpuscles were pedunculated, others were sessile. They
had obviously been developed in relation to the attached, and
not to the free surface of the amnion, for each was invested by a

1 Cellular-Pathologie, 1858, p. 87.

* Proc. Royal Soc. London, June 17, 1875.

24 FORM AND STRUCTURE

prolongation of that membrane, and, where the corpuscles were
pedunculated, the pedicle, which was sometimes one-eighth of an
inch long, was formed by a slender filamentous process of the
amnion. When sections through these corpuscles were examined
with a magnifying power of 480 diameters they were seen to
consist of cells, closely packed together: some of the cells were
oval, others elongated, others samewhat polygonal in shape.
I also found between the amnion and allantois, close to the
trunks of the umbilical vessels passing to the left horn of the
chorion, three peculiar-looking bodies. The largest, tri-radiate
in form, was three-quarters of an inch long by half an inch in its
greatest breadth ; the others were much smaller, and ovoid in
shape. They were in linear series, the largest and highest was
one inch and a quarter from the second, and that again half an
inch from the third. When the allantois and amnion were
separated trom each other, they remained attached to the
amnion. Each body was invested by a fibrous capsule, and
contained a brown pultaceous mass, which when examined
microscopically was seen to consist of cells, the great majority
of which were circular in form, and had a yellowish colour.
The smallest of these cells were of the size of lymph-corpuscles,
but as a rule they were twice as large. Most of the cells con-
tained a single nucleus, but some had two or even more, and in
a few instances large brood-cells were seen packed with nuclei
or young cells. Patches of hexagonal cells were also occasionally
seen. These bodies, like the amniotic -corpuscles, already
described, were developed in relation to -the attached surface of
the amnion.

In the Ruminantia the inner surface of the amnion, more
especially where it invests the umbilical cord, is studded with
white, or yellowish white, bodies. As seen in the Cow they
are sometimes elongated in the form of papillae, at other times
in flattened patches slightly raised above the plane of the
amnion. Their longest diameter may reach a quarter of an
inch, but usually they are of smaller size. Sometimes a patch
or papilla lies singly, but more commonly they are collected
into large clusters. They could be readily peeled off the inner
surface of the amnion, and in injected specimens^ a net- work
of fine vessels could be seen ramifying in relation to the deep

OF THE CHORION. 25

surface of the membrane, but not entering the papilla? or
patches. Hence it seems that these bodies are formed on the
free surface of the membrane and are epithelial in position.
This view of their nature is borne out on microscopic examina-
tion, for they consist of large, flat, nucleated cells, not unlike
a squamous epithelium. Many of the cells contained minute
spherical strongly refracting particles, about half the size of the
nucleus, with well-defined outlines, which formed a prominent
appearance in the preparations when many cells were looked
at together.

Prof. Claude Bernard has carefully examined not only the
arrangement and structure, but the chemical -composition of
these bodies in the Ruminantia\ and has come to the con-
clusion that they are the seats of formation of a glycogenic
material. He states that they increase an size up to a certain
period of intra-uterine life and then degenerate; their organiza-
tion and development being in inverse relation to the develop-
ment of the liver; the place of which, as regards its glycogenic
function, they seem to supply during the earlier peried of intra-
uterine life.

In the Elephant Prof. Owen has shewn^ that<the inner surface
of the amnion is roughened by brownish hemispherical granules,
from 1 line to Y^^^th of a line, commonly about half a line, in
diameter, but nothing is said of their microscopic structure.
Prof. Rolleston described in the Tenrec {Centetes ecaudatus)
numerous corpuscles studding the inner surface of the amnion^.
In form, general arrangement, and microscopic structure, they
resembled, he says, les plaques de I'amnios ch&z les Ruminants
as described by Prof. Claude Bernard.

It is well known that in the Mare olive-green or brownish
bodies, varying in size from a pea to a walnut, or even larger,
and called by the veterinaman, " hippomanes", are found lying
free in the fluid filling the sac of -the allantois. Similar bodies
are sometimes seen attached by slender threads to the inner
surface of the sac. In a specimen which I examined I
found three of these bodies moored to the inner wall of the

^ Brown-Seqiiard's Journal de la Physiologie, Vol. ii. p. 31, 1859.
^ Philosophical Transactions, 1857.
^ Trans. Zoological Soc. Vol. v.

T. 3

26 FORM AND STRUCTURE

sac by several very slender threads, the longest of which
was four inches, but no thread was more than about half as
thick as the chordae tendinese in the human heart. These
threads were continuous with the lining membrane of the
sac, but the nature of their attachment to the body itself
could not accurately be ascertained, owing to the tangled
knot which they formed where they joined it. In another
specimen I found several brownish bodies, about the size of
kidney-beans, situated in the gelatinous tissue which connects
the chorion to the wall of the sac of the allantois. Both the
chorion and allantois were slightly elevated over them, and one
had projected so much towards the sac of the allantois, as to
have caused a thinning and absorption of that membrane; so
much so indeed that a portion of the brownish body was pro-
jecting into the sac of the allantois. I then removed the
chorion from the outer surface of this body, which was invested by
a fibrous capsule and contained a light brown pultaceous sub-
stance. Examined microscopically this substance was seen to
consist of multitudes of free granules and of cells. The cells
varied in form and size: some were circular and about the
size of lymph-corpuscles, others were two or three times
larger and polygonal. In many of these cells the nucleus was
distinct, but in others no nucleus could be seen. I regard
these bodies as the early stage of formation of the '"hippo-
manes". Arising originally between the chorion and allantois,
as they increase in size they grow towards the latter, cause
absorption of the membrane, and project into the cavity; for a
time they remain attached to the wall of the sac, but the
pedicles of attachment become so attenuated that they at last
give away and the " hippomanes " then lie free in the allantoic
fluid.

In the Pig numerous white spherical bodies of the size
of very small shot are situated in the gelatinous tissue which
connects the chorion to the wall of the sac of the allantois.
They are not to be confounded, as has apparently been done
by some writers, with the w^hite circular spots on the chorion
itself, to be subsequently described. Each spherical body
possessed a distinct capsule, which when squeezed gave way
and allowed a drop of fluid to escape. When examined micro-

OF THE CHORION. 27

scopically, multitudes of circular cells, about the size of lymph-
corpuscles, and quantities of granular particles, were seen in
this fluid. I agree with Prof Rolleston in regarding them as
in all probability homologous with the hippomanes in the
membranes of the Soliped.

In the Elephant also, as Prof. Owen has described, numbers
of flattened, oval or subcircular bodies, varying in diameter
from an inch or more to half a line, are situated between the
chorion and adherent part of the allantois, and project inwards
towards the allantoic cavity. Through the courtesy of Prof.
Flower I have been permitted to take for microscopic examina-
tion a portion of the allantois of this specimen, which, with the
other membranes, has been preserved in spirit for many years
in the Museum of the College. I found the bodies described
by Prof. Owen somewhat shrivelled by the prolonged action of
the spirit. They were tough and condensed, and difficult to
dishevel with the dissecting needles. Under the microscope
they were seen to be composed for the most part of fine fibres,
having the asjoect of white fibrous tissue, the fibres being
cemented together by a homogeneous inter-fibrous material, in
which nuclear-looking particles were imbedded, but I did not
see the abundant cell-forms and granular matter, such as I have
described in the bodies occupying a similar position in the pig
and mare.

3—2

28 STRUCTURE OF THE UNIMPREGNATED

Structure of the Mucous Membrane of the

UNIMPREGNATED UtERUS,

It will now be necessary to examine the structure of the
non-gravid uterine mucosa^ so that we may see what the tissues
are in which the changes occur which lead to the production
of the maternal part of the placenta.

In the Human uterus, and in that of some other mammals,
the mucous membrane is smooth : but in many mammals it is
elevated into folds. In the Pig these folds are transverse, but
usually they are arranged longitudinally, i.e. parallel to the
long axis of the body of the uterus, or of the uterine comu. In
the Mare, most Ruminants, the Seals, the Rabbit and the
Nycticehus tardigradus, the longitudinal folds are strongly
marked. In the Chimpanzee the folds are more feeble, and
separated by shallow intermediate fissures. The thickness of
the mucous coat, both absolutely and relatively to the thickness
of the muscular coat, varies considerably in different mammals.
In the Human uterus, as is well known, the mucosa is relatively
very thin, but in Tragulus javanicus it is equal in thickness to
the muscular coat. In the Pig, Mare, various Ruminants, in
Dasypus kappleri, and indeed in all mammals where the mucosa
is folded, it forms a well-defined layer.

The mucosa is covered on its free surface by an epithelium,
which rests on a delicate sub-epithelial connective tissue, in
which the utricular glands, the blood-vessels, lymph-vessels and
nerves of the mucous membrane are situated. In all placental
mammals, so far as yet examined, the cells of the epithelium
covering the mucosa lining the cavity of the body of the uterus
are columnar in shape, and the free ends of these cells give
origin to vibratile cilia which jDroject into the uterine cavity.
In the Human subject, and probably in other mammals which
possess a cervix uteri, the cells covering the part of the mucosa
nearest the body are ciliated and columnar, whilst those which
lie nearer the os uteri are, like the epithelium of the vagina,
squamous and stratified.

UTERINE MUCOUS MEMBRANE. 29

\

To Malpighi is ascribed the merit of having first recognised
the orifices of glands on the surface of the uterine mucosa. He
saw them in the cow and sheep, and since his time they have
been investigated by several anatomists, amongst whom I may
more especially refer to Weber, Eschricht, Sharpey, Bischoff,
Leydig, Ercolani and Lott, not only in these but in several
other mammals. I have myself examined the utricular glands
in the following placental mammals ; the Pig, Mare, Orca
gladiator, Sheep, Cow, Lama paca, Tragulus javanicus^, Cat,
Bitch, Fox, Badger, Paradoxurus pallasii, Halichoerus gryphus,
Gystophora cristata, Manis, Dasypus kappleri, Cholopus Hoff-
manni, Hedgehog, Nycticebus tar^digradus, Macacus rufescens,
Semnopithecus entellus, Ateles gricescens, Hylohates agilis, Tro-
glodytes niger and the Human Female.

I shall not in this section enter into a detailed description
of the stnicture and arrangement of the glands in these
mammals, but shall limit myself to a statement of a few
general observations, as in the course of the Lectures, when the
structure of the different forms of placentae is described, it will
be more convenient to speak of them in detail.

The utricular glands are branching tubes, which vary in
their length, direction, the amount of branches, and in their re-
lative numbers in different mammals. In many mammals they
extend perpendicularly to the plane of the surface for some
depth, and then incline with more or less obliquity, or possess
a tortuous course. Vertical sections through the mucosa, as in
Dasypus, Semnopithecus, the Sheep, Alpaca, Cat, Badger,
Bitch, Hedgehog, Mare, &c. give most satisfactory views of
the opening of these glands on the surface, whilst in the
deeper layer of the mucosa the glands are repeatedly cut
across obliquely or transversely. In Tragulus, Cholopus, Nyc-
ticebus, Macacus, Hylohates, the Chimpanzee and the Human
Female, the glands throughout their entire length have a more
oblique course, so that it is more difficult to see in vertical
sections their communication with the surface. Sometimes,

1 I am indebted to A. H. Garrod, Esq., Prosector to the Zoological Society,
for the titenis o^ this and of most of the rarer mammals named in this list. Thr
uteri were kindly placed by him in spirit of wine immediately after remova.
from the body, so that sections of the mucosa could be readily made and sub-
mitted to microscopic examination.

30 STRUCTURE OF THE UNIMPREGNATED

as in the Hedgehog and Dasypus, the glands divide into two
branches near the surface, and then give off no more branches,
but in other mammals, as the Pig, Mare, and Orci, the glands
divide repeatedly in the deeper part of the mucosa, so that
numerous branching tubes are connected with a single stem
or gland-duct. In the Cat, Bitch, Badger, Seal, Hedgehog,
Semnopithecus, the glands are so numerous and closely packed
together, that the amount of interglandular connective tissue
between any two adjacent glands is about equal to the trans-
verse diameter of a gland. In Cholopus, Macacus, Hylobates,
Chimpanzee, the glands are more sparingly distributed, so that
considerably wider intervals exist between them. The glan-
dular epithelium consists of columnar cells, which project verti-
cally into the gland-tube, but leave a central lumen. In 1852
Nylander and Leydig observed^ that the free ends of the
columnar cells lining the utricular glands in the Pig were
ciliated, and in 1870 Lett published a memoir in which he
stated that he had observed ciliary movement in the epithelium
of the uterine glands of the Pig, Cow, Sheep, Rabbit, Mouse
and Bat^ Further, he believed it to be probable, from the
agreement in characters of the epithelial cells of the Cat, Bitch,
Guinea-pig, Mare and Human Female with those of the mam-
mals in which ciliary movements were actually seen, that the
cells also in them were ciliated.

The utricular glands are not formed during intra-uterine
life, and it is probable that they are not fully developed until
the uterus reaches the stage of sexual maturity. I examined
the uterus of a foetal calf, six inches long, and though I found
its inner surface thrown into longitudinal folds which were in
many places still further subdivided by fissures, and covered by
a well-marked layer of columnar epithelium, no trace of utricu-
lar glands was to be seen. Again, I examined the uterus of a
new-born lamb without finding any glands, though the folds of
the mucous surface possessed a definite, columnar epithelial
investment. Both in the calf and lamb the su.b-epithelial con-
nective tissue was crowded with corpuscles, many of which had
the fusiform shape of the corpuscles of connective tissue, whilst

1 MuUer's Archiv, 1852.

" Strieker's J/andftMc/j der Gewehelehre; Article Uterus.

UTERINE MUCOUS MEMBR^VNE. 31

others were spherical in form, and resembled the white cor-
puscles of the blood, \^

From the observations of Dr G. J. Engelmann^, it is clear
that in the human uterus also no glands exist at the time of
birth. In the third or fourth year the mucosa, which had
previously been thin, increases in thickness, and small fossae
lined by an epithelium appear in it, which are apparently the
rudimentary glands. After the tenth year the glands assume
a tubular form, are more numerous, and extend through the
thickness of the mucosa into the muscular coat. In girls of
twelve or thirteen well-defined glands are present.

The blood-vessels of the uterine mucous membrane are con-
tinuous with those of the muscular coat. In those uteri in
which a definite sub-mucous coat exists the vessels ramify in it
before entering the mucous membrane. When in the mucosa
the larger vessels run almost vertically towards the surface and
form a capillary plexus, which invests the utricular glands, and
near the surface of the mucosa forms a ring around the mouth
of each gland.

The lymph-vessels of the unimpregnated mucosa have
recently been investigated by Dr Leopold ^ He considers that
lymph-spaces exist between the bundles of connective tissue,
the walls of which are formed by the endothelial cells investing
those bundles, and that similar endothelial sheaths invest the
glands and blood-vessels. He is of opinion that the glands and
blood-vessels may be regarded as traversing the lymph-spaces,
and separated only from their cavities by their sheaths invested
by the endothelial cells.

Nothing definite is known of the mode of arrangement and
termination of the nerves of the uterine mucosa. In the
mucous membrane of the placental area of the gravid Grey
Seal {Halichcerus gryphus), I have seen slender nerve-trunks
giving off fine branches, which ramified in the connective tissue,
until the finest branches consisted of but one or two fibres.

When the fertilized ovum is received into the cavity of the
uterus the mucosa undergoes important changes. It swells up,

^ American Journal of Obstetrics, May, 1875, p. 32.

2 Archiv filr Gyncekoloyie, vi. Abstract in Journal of Anatomy and Physiology,
VIII. p. 391.

32 IMPREGNATED UTERINE MUCOSA.

becomes thicker, softer, and more vascular. Its epithelial
covering usually, though not always, loses its columnar form ;
its glands enlarge throughout their entire length : the inter-
glandular tissue increases largely and- rapidly in quantity, by a
multiplication not only of the cells of the surface-epithelium,
but by a proliferation of the corpuscles of the sub-epithelial
connective tissue, so that the glands are separated from each
other by a much greater amount- of interglandular tissue than
in the non-gravid state ; the blood-vessels not only increase in
numbers but in size. At the same time the free surface of the
mucosa is perforated by multitudes of small openings, easily to
be seen, with a- pooket-lens. Those openings lead- into depres-
sions in the swollen mucous membrane, which are usually
regarded* as the dilated mouths of the tubular glands, but
which, as I shall show in the course, of these lectures, are the
mouths of crypt-like depressions in the interglandular part of
the mucous membrane. These crypts are for the lodgement
of the villi, which projeet from- the outer surface of the persis-
tent chorion. As the area of distribution of the villi on the
chorion varies very considerably in extent in the different forms
of placenta, the distribution of these crypts in the uterine
mucosa necessarily also varies ; for the crypts and the villi are
correlated with each other.

The structure of the placenta in those animals in which it
is said to be diffused will first engage our attention.

DIFFUSED PLACENTA. 33

Structure of the Diffused Placenta.

• In the diffused placenta the villi are distributed over almost
the entire outer surface of the chorion, and the uterine crypts
exist in a corresponding area of the mucous membrane. This
form of placenta is found in the Pigs, the Solipeda, the Cetacea,
in Manis, the CamelidcE, the Tragulidce, the Tapir, the Hippo-
potamus, the Lemurida, and probably the Khinoceros.

Pig. — I shall commence by describing the structure of the
placenta as I have^ myself observed it in the common Pig, and
shall in the first place speak of the foetal placenta. The surface
of the chorion of a pig, where the embryo- was 1"3 inch long,
was traversed by multitudes of feeble ridges, visible under low
powers of the- microscope, but no true villi could be seen. A
distinct and compact capillary plexus was present both in the
ridges and intermediate parts of the chorion. In the ridges
the plexus was elongated, but it formed a polygonal network in
the- intermediate ar.eas-. The polar ends of the chorion were
smooth and free from ridges for about three inches from each
pole. A uniform layer of squamous epithelial cells, the nuclei in
which were distinct, covered the face of the chorion.

In an older specimen, where the foetus was six inches long,
the chorion was thrown, into well-marked transverse folds in
conformity with the foldings of the uterine mucosa, and was
traversed by feeble ridges which were more elevated than in
the younger specimen, but still requiring a microscope for their
examination. The summit of each ridge was broken up into
numerous short, simple villi, just as a mountain-ridge may
be broken up into short peaks and summits. In injected pre-
parations these ridges and villi were seen to be very vascular \
Scattered irregularly over the surface of the chorion were quan-
tities of circular, or almost circular, slightly elevated spots,
which varied in number in a given area. Sometimes as many
as 30 were seen in a square inch, in other places not more than

■■• For valuable aid in injecting this and the other injected placentte described
in these Lectm-es, I have to express my thanks to my Museimi Assistant
Mr A. B. Stirling.

34 DIFFUSED PLACENTA.

20. The spots varied in diameter from gV^h to j^gtli inch, occa-
sionally one ith inch in diameter was seen. In most of the
red injected specimens these spots were white and free from
colour, as if non- vascular, but when the injection was pushed
further they became red also, though not so completely as the
rest of the chorion. Examined microscopically each spot was
observed to have a minute central depression surrounded by
villi, which were the terminal villi of a group of ridges, and it
was now seen that the villous ridges were arranged on the
chorion with especial reference to these spots ; for each spot was
a centre from which the ridges radiated outwards as the spokes
do from the centre of a wheel, so that it had a star-like
arrangement. After proceeding some distance the ridges not
unfrequently branched, and adjacent branches joined together
to form a network. Hence the villous surface of the chorion
may be regarded as mapped out into a number of areas, the
centre of each area being a circular spot, from which the villous
ridges radiate.

In the more fully injected parts of the chorion a vascular
ring was seen to surround each star-like spot. This ring con-
Fig. 3.

Portion of injected Chorion of Pig, as seen under a low magnifying power,
to show the minute star-hke spot b, enclosed by a vascular ring, from which
villous ridges, r, ?•, ?•, radiate. Magnified about 20 diameters.

PIG. 85

sisted of a double row of capillaries, which passed from the
capillaries of one villous ridge to those in the next adjacent
ridges, so that, the vessels in the whole series of ridges radiating
from any given spot being connected together, a vascular ring-
was formed. But it was particularly observed that this ring
was not formed of vessels passing between the central ends of
the ridges, but a little to their outer side, so that the ends were
enclosed by the vascular ring.

The existence of small circular spots whiter than the sur-
rounding parts of the chorion was recognised so far back as
1781 by John Hunter\ Von Baer gave a careful description^
of their star-like arrangement, and described and figured their
vascularity ; more particularly did he describe the relations of
their capillaries to the branches of the umbilical vein, so that
if a blue injection be introduced into the umbilical vein, and a
red into the artery, these spots would appear as blue stars on a
red ground. Eschricht also examined these spots ^ and arrived
at a similar conclusion as to their relation to the umbilical vein.
M. Flourens described* these spots as small discs, which are, he
states, a variety of the multiple form of placenta. He would
obviously associate them therefore with the foetal cotyledons of
a ruminant. But this mode of regarding them is quite erro-
neous, for the centre of each spot is non-villous, and when
the chorion is in situ, as I shall immediately point out, is in
contact with a feebly vascular part of the uterine mucosa and
not with the highly vascular crypts.

Each end of the chorion, for nearly three inches from the
pole, had a smooth non-villous surface, and though possessing
considerable vascularity was not so vascular as the villous part
of the chorion. Hence the chorion of the pig is not uniformly
villous, but the villi, as was indeed known to von Baer, are
distributed over the central and not the polar regions of the

1 Essays and Observatiom, edited by Prof. Owen, Vol. i. p. 198. London,
1861.

2 Viitersuchungen iiber die Gefdssverbindung zwischen Mutter und Frucht,
p. 9, Fig. 1, 2. Leipzig, 1828.

■* De organis qiice respirationi et nutritioni fcetus mammalium inserviunt,
p. 36. Hafnics, 1837.

* Cours sur la Generation, recueilli et public par M. Deschamps, p. 147.
Paris, 183G.

36 DIFFUSED PLACENTA.

chorion \ Though the structure of the placenta in the pig is
simple, like that of the mare and other animals with a diffused
placenta, yet, as regards the distribution of the villi, they are
arranged in a well advanced ovum as a very broad zonular
band which does not reach to within several inches from the
poles of the chorion.

On examining the maternal placenta in the gravid uterus of
& pig, where the foetus weighed only 12 grains, the free surface
of the mucosa was seen to present an undulating appearance,
owing to numerous shallow furrows and fossae separated by
intervening ridgelets. Opening on the surface of the mucosa,
the openings being marked by shallow depressions distinct
from the furrows above referred to, were the mouths of the
utricular glands, and not unfrequently a plug of epithelium
projected through the orifice. Each gland-orifice was sur-
rounded by a smooth portion of the mucosa.

In a more advanced specimen, where the foetus was 6 inches
long, the mucosa was thrown into transverse folds. When ex-
amined with a pocket-lens fine ridges and furrows were seen,
which were adapted to furrows and ridges on the surface of the
chorion. When more highly magnified the furrows were seen
to be subdivided into shallow crypts into which the villi of the
chorion fitted. Scattered over the surface of the mucosa were
numerous smooth almost circular depressed spots, free from
ridges and crypts, corresponding in size and numbers to the
circular star-like spots on the surface of the chorion ; and, as
von Baer^ and Eschricht^ have already described, the star-like
elevations of the chorion are adapted to these smooth spots on
the mucosa when the two surfaces are in contact. These
smooth depressed spots were very definitely circumscribed by
the crypts which immediately surround them. In the minutely-
injected uterus the ridges and the walls of the crypts were
seen to contain a compact capillary plexus, whilst the smooth
spots possessed a feeble vascularity, so that they appeared as
distinct white spots, surrounded by highly vascular ridges, on

1 TJntersuchungen (op. cit.), p. 7, Plate, Fig. 1.

2 TJntersuchungen (op. cit.), p. 12, and Ueher Entioichelungsgeschichte der
Thiere, Zweiter Theil, p. 250, 1837.

3 De organis, &c. {op. cit.). HafniiE, 1837.

PIG. ^ 3?

the injected mucous surface. Beneath the superficial crypt-
layer of the mucous membrane was a well-defined glandular
layer, the glands in which were tubular and branched repeatedly,
so that each gland-stem or duct had connected with it numerous

Fig. 4.

Surface-view of a portion of the injected Uterine Mucosa of a Pig to show a
depressed circular spot in which the mouth of a gland g, opens. This spot
is sui'rounded by numerous vascular crypts cr, cr. The branching glands of
the glandular layer and the larger vessels lie deeper than the crypts.
Magnified same scale as Fig. 3.

branching tubes. The depressed circular spots had a special
relation to the ducts of these glands, for opening either in the
centre of each spot, or near its border, by an obliquely-directed
orifice, was a gland-stem, which could be seen running, some-
what tortuously, from the deeper" glandular layer of the mucosa
to the spot.

Eschricht had in 1837 described the mouths of the utri-
cular glands in the pig as situated in small circular spots
{areolce), distinct from the surrounding crypts (cellulce), which
circular spots in injected specimens, owing to their feeble vas-
cularity, appeared white, when compared with the highly
vascular crypts \ These observations by Eschricht seem to have

1 It should be said that von Baer {UntersiicJmngen, p. 12) in his description
of the depressed spots on the uterine mucosa of the gravid pig, stated that in
the middle of each spot a fine vessel arose by an open mouth, which was never
injected when the blood-vessels were filled. The true nature of this "vessel"
was not however at that time understood by von Baer, for he believed it to be a
lymphatic. Subsequently (EntwichelungsgescMchte, Zweiter Theil, p. 250), and
after the publication of Weber's researches on the glands of the uterus, he
recognised that this so-called vessel was an utricular gland.

38 DIFFUSED PLACENTA.

been overlooked by most subsequent anatomists. In 1871^ I
described a similar arrangement in the uterus of a pig which I
examined. In 1873 a description with a characteristic figure of
a spot in an uninjected specimen was given by Ercolani^ It
is clear therefore that in the pig the glands do not open into
the crypts of the gravid mucosa, but into special depressions on
the mucous membrane distinguished by a difference in form
and in the degree of vascularity from the surrounding crypt-
like surface. The crypts therefore are interglandular in posi-
tion, and are produced by modifications in the interglandular
part of the mucous membrane, and not by a dilatation of the
gland-orifices themselves. The free surface of the mucosa was
covered by an epithelium which also lined the crypts. The
epithelial cells were columnar in form, finely attenuated at
their deeper end ; and not unfrequently I saw an appearance as
if cilia projected from the broad end of the cell; but the animal
had been too long dead to enable me to determine their presence
by vibratile movements. Owing to the shallowness of the crypts
and the very short villi of the chorion in the pig the uterine
and chorionic surfaces separated from each other with great
readiness. As the tubular glands did not open into the crypts
their secretion did not come into immediate contact with the
general villous, surface of the chorion, but with the star-like
spots, enclosed by the vascular rings, from which the villous
ridges radiated. The mucous membrane of the gravid uterus
of the pig differs from that of the non-gravid animal in the
following characters : in the presence of a layer of crypts, in the
increased size and greater obliquity of the glands, and in the
much greater vascularity of the membrane generally.

Mare. — I have not had the opportunity of examining the
foetal placenta of the Mare in the early period of gestation, but
two specimens in advanced stages have come under my observa-
tion. In both, the surface of the chorion presented a soft, velvety,
vascular appearance, due to its being almost uniformly covered
with vascular villi, even up to the poles. But at each pole,
where the chorion was in relation to the orifice of the Fallopian
tube, a spot, a fraction of an inch in diameter, smooth and bare

1 Trans. Roy. Soc. Edinh. Vol. xxvi. p. 490.

2 Mem. deir Accad. delle Scienze di Bologna. Plate 2, Fig. 1.

MARE. 39

of villi, was present. Opposite the os uteri internum a well-
defined bare patch, which in one specimen was about an inch
in diameter, having in its centre a faint papillary elevation, was
present. Radiating outwards from this patch were five long
branching arms, also free from villi, and immediately beyond
these some irregularly-shaped bare patches were seen. The
surface of the uterine mucosa was also very vascular, except
opposite these bare patches on the chorion, and the folds and
depressions radiating from the os uteri corresponding to the
radiated patch on the chorion had a comparatively slight vascu-
larity. In the chorion from another mare the bare spot oppo-
site the OS uteri measured 2| inches long by from -^ to f inch
broad, and had distinct bare radii passing off from it. In each
specimen an irregular-shaped non-villous patch, about an inch
long, was found on a portion of the chorion not in relation to a
uterine orifice. Though in the mare the villi seem to the naked
eye to be closely set over the surface of the chorion, yet when
examined with low powers of the microscope they are seen to
be arranged in brush-like clusters or tufts, separated by narrow
non-villous intervals, an arrangement the importance of which
will appear when the corresponding surface of the mucosa is
described. The tufts are like minute foetal cotyledons, and the
villi in each tuft are filamentous in shape and contain a loop of
capillary blood-vessels. That part of the chorion which occu-
pied the corpus uteri was thrown into occasional longitudinal
folds, but at the horns, more especially near the free ends, the
longitudinal folds were numerous and closely adapted to similar
folds of the mucous membrane.

I have not yet been able to procure the uterus of the
mare in an early period of gestation. But on inspecting with
a simple lens the surface of the uterine mucosa of a mare
which had reached an advanced stage of pregnancy \ I found
it subdivided into multitudes of irregular polygonal areas, vary-
ing in diameter from jV^^ *^ 2V ^^ inch, by slender ridges,
which anastomosed with each other so as to have a reticu-
lated appearance. In injected preparations the ridges were
seen to be less vascular than the areas which they enclosed,

^ I am indebted to J. R. W. Dewar, Esq., V. S. of Midnaar, Aberdeen, for
this specimen.

40

DIFFUSED PLACENTA.

and consequently they were more readily recognised in injected
than in non-injected portions of the mucosa. But in addition
the ridges were smooth on the surface, whilst the enclosed
areas possessed a delicate punctated appearance. When more
highly magnified each area was seen to be subdivided into
multitudes of crypts, which passed more deeply into the mucosa
than in the pig. The arteries and veins of the mucosa occupied
the ridges, and broke up into small branches which ended in a

Surface view of the injected uterine mucosa of a, gravid Mare, to show the polj'-
gonal crypt-areas cr cr, with the anastomosing capillary network surround-
ing the orifices of the crypts, g, g, g, mouths of three utricular glands
opening on the surface of the ridges ?;, r, r, which separate adjacent crypt-
areas from each other. Magnified about 20 diameters.

compact capillary plexus situated in the walls of the crypts,
the artery in each ridge giving off branches to the crypt-areas
between which that ridge was situated. The capillaries also
surrounded the orifices of the numerous crypts opening on the
surface of each area, and formed an anastomosing network, the
meshes of which were not circular, but rather polygonal in
form.

The glandular layer of the mucosa contained numerous
branched tubular glands. Each gland possessed a stem or
duct which ascended almost vertically between the crypt-

MARE.

41

areas, and opened on the summit of a ridge by a circular or
oval aperture, which was usually situated at a spot where
convergent ridges became continuous with each other. In
the mare, therefore, as in the pig, the utricular glands do

Fia. 6.

Vertical section through the injected placenta of the Mare. Ch. the chorion
■with its villi, partly mi situ, and partly drawn out of the crypts, cr. E,
loose epithelial cells which formed the lining cells of a crypt, g, g, the
utricular glands. F, V, the blood-vessels of the mucosa imbedded in the
connective tissue.

not open into the crypts ; but on definite surfaces of mucous
membrane between the crypts, so that the crypts are inter-
glandular in position, and produced by changes in the inter-
giandular part of the mucosa. The demonstration of the want
of any communication between the utricular glands and the
crypts in the mucosa of the gravid mare, and the consequent
interglandular position of the crypts, was made a few years
ago by Prof. Ercolani^ of Bologna.

The surface of the mucosa and of the wall of the crypts was
covered by an epithelium, which when examined in situ showed

1 See his Memoire sur les Glandes UtricuJaires de V Uterus.
lation. Algiers, 1869, and the figures in Plates 3 and 5.

T.

French trans-

42 DIFFUSED PLACENTA.

a polygonal pattern, like the broad free ends of columnar epi-
thelium-cells. When the cells were teased asunder, some were
seen to have the elongated form of ordinary columnar epithe-
lium; others were so swollen out that their length but little
exceeded their breadth ; whilst others were irregular in shape.
The protoplasm was distinctly granular, more especially in the
irregularly-shaped cells, Avhich resembled in appearance the
large granulated cells of the serotina as seen in the higher
mammals. Numerous cells exhibiting forms transitional be-
tween ordinary columnar epithelium and serotina-cells were
seen, so that the large granulated cells of the serotina are to
be regarded as a modified epithelium.

The filiform villi of the tufts of the chorion occupied the
crypts in the mucosa, which represented therefore the maternal
cotyledons of a ruminant animal, and the size of the crypt-areas
corresponded to the size of the tufts. The ridges between the
areas filled up the intervals between the tufts. The secretion
of the uterine glands was not poured into the crypts, so as to
come into immediate relation with the villi, but opposite the
inter-villous surface of the chorion. The villi of the chorion
were so closely fitted into the uterine crypts, that, in the speci-
men of the gravid uterus near the full time, it required a
little force to draw the villi out of the crypts. As in the pig,
the gravid mucous membrane differed from the non-gravid in
the presence of a layer of crypts, in the increased size and
greater obliquity of the glands, and in the greater vascularity
of the membrane generally.

Cetacea. — The diffused distribution of the villi over the
surface of the chorion in the Cetacea, and the velvety appear-
ance due to this arrangement, have been recognised by several
anatomists, from observations made more especially on the
common porpoise. In 1869 I examined several square feet of
the chorion of Balcenoptera Sihhaldii^, and showed that the
whalebone whales agreed with the toothed whales in the dif-
fused distribution of the villi. But in the Cetacea, as in the
pig and mare, patches of chorion bare of villi are also present.
Some years ago Prof RoUeston pointed out^ that in a specimen

1 Trans. Boy. Soc. Edinburgh, 1870.
'■' Trans. Zool. Soc. p. 307, 1866.

CETACEA.

43

(species unknown), which he examined, a bare spot was situated
at each pole. In a gravid Orxa gladiator, which I examined
in 1871 \ I found not only the polar bald spots, about the size
of kidney-beans, but a stellate non-villous surface, nearly the
size of a crown piece, and with several bare lines radiating from
it opposite the os uteri; the arrangement corresponding very

Fi-. 7.

■4*

Stellate non-villous portion of the Chorion of Orca surrounded by vascular
villi, opposite the os uteri. About half the size of nature.

closely with that just described in the chorion of the mare in
the same locality. These large radiating bare spots in the
mare and cetacean are exaggerated representations of the
small radiating spots, so abundantly distributed over the cho-
rion of the pig.

The chorion of Orca was thrown into longitudinal folds,
more especially near the poles. The villi with which it was
covered were seen when examined microscopically to vary in
number and in arrangement in different parts. Sometimes
they were set in rows and formed parallel ridges : at others

1 Trans. Boy. Soc. Edmh. 1871.

4—2

44 DIFFUSED PLACENTA,

they were collected into tufts, irregular in form and size, which
sometimes consisted of two, three or four villi, but frequently
of a larger number. Solitary villi were also met with in the
irregular intervals between the tufts and ridges ; and it was
not uncommon, as Eschricht had observed in Phoccena^, to see
short stunted simple villi projecting from the general plane of
the chorion. The tufts not unfrequently swelled out into a
branching crown, which, to adopt Eschricht' s description of
the shape of the villi in Phocwna, formed a miniature repre-
sentation of the head of a cauliflower. The secondary villi of
a tuft, as well as the simple villi, were clab-shaped.

The basis substance of each villus consisted of a delicate
connective tissue, in which numerous spheroidal and fusiform
nucleated corpuscles were imbedded ; some of these corpuscles
were in the walls of the finer blood-vessels, but others were
proper to the tissue itself. A layer of spherical or ovoid cor-
puscles was situated immediately within the free surface of
each villus, and not unfrequently the periphery of the villus
was slightly elevated immediately above the individual cor-
puscles, so that the outline of the villus had a gently undulating
appearance. These corpuscles I have named from their posi-
tion the sub-epithelial corpuscles of the villus. In their form
and appearance they were not unlike the white corpuscles of
the blood, and it is possible that they might have migrated out
of the blood-vessels into the connective tissue of the villus.
The villi contained a distinct capillary network. Not only in
the Oi^ca, but in the pig and mare, the capillaries of the
chorion were not limited to the villi, but an extra-villous capil-
lary network, which freely anastomosed with the intra-villous
capillaries, was situated beneath the general plane of the cho-
rion. The blood in its passage from the terminal twigs of the
umbilical artery to the umbilical vein had to flow not only
through the capillaries within the villi, but through the extra-
villous network, from which the rootlets of the vein arose.

Eschricht in 1837^ and Stannius in 1848^ described the
presence of numerous little recesses on the free surface of the
uterine mucosa of the gravid porpoise, in which the villi of the

^ De Organis, &o., p. 6. 2 x)e Organis, &c.

3 MuUer's ArcMv, p. 402, 1848.

CETACEA, 45

chorion were lodged. In 1871^ I had the opportunity of dis-
secting the gravid uterus of Orca gladiator, and of determining
much more minutely than had previously been done, the
structure of the gravid uterine mucosa in this order of mam-
mals. The free surface of the mucosa had a delicate reticu-
lated appearance, due to an anastomosing arrangement of
slender bands of the membrane. Sometimes a division of
the surface into irregular polygonal areas was seen, at others
its surface was traversed by an elongated ridge and furrow

Fig. 8.

\b-<v. ^^ Z*"^

-^L^ * ^"^

* ^ t

Surface-view, under a low power of the microscope, of a portion of the
uninjected uterine mucous membrane of Orca gladiator.

arrangement. The polygonal areas and the furrows were sub-
divided by more delicate bands into small crypt-like compart-
ments, and the intermediate ridges and bands of the mucous
membrane were not unfrequently covered by similar crypts. In
some places the crypt-like recesses were so closely crowded
together that the surface of the mucosa had a honey-comb

^ Trans. Roy. Soc. Edinburgh, p. 167, 1871.

46 DIFFUSED PLACENTA.

appearance. As a rule the fundus of eacli crypt was more
dilated than its mouth, so as to adapt it to the form of the
club-shaped villi.

Beneath the crypt-layer was the glandular layer of the
mucous membrane. The glands, as in the pig and mare, were
tortuous tubes and branched repeatedly. Sometimes they
bifurcated, at others three branches arose close together, which
in some instances possessed considerable length, but in others
formed short diverticula. Each branch possessed an almost
uniform diameter, but the stem of the gland-tube Vv^as wider
than its various branches. In vertical sections through the
membrane only short lengths of any given gland could be
traced, for it was frequently divided, sometimes longitudinally,
at others, obliquely or transversely.

The mode of termination of the glands on the surface of
the mucosa was much more difficult to determine than in the
pig and mare, but after repeated examinations, both of vertical
sections through the membrane, as well as of surface-views, I
came to the conclusion that the tubular glands opened into the
bottom of some of the crypts \ In many of the vertical sections
undoubtedly no gland could be tra,ced into a crypt, a circum-
stance not to be wondered at when the oblique direction of the
stem of the gland-tube is considered ; but occasionally a gland-
stem could be traced to the bottom of one of the more deeply
situated crypts in the mucosa. More satisfactory evidence of
the opening of glands into certain of the crypts was obtained
by the examination of the free surface of the mucosa. In look-
ing into the crypts through a binocular microscope, I occa-
sionally saw an opening at the bottom of a crypt ; the direction
of this opening was usually oblique, corresponding indeed with
the obliquity of tlie gland-stem as it reached the surface, and
through this opening a little plug, apparently formed either
of epithelial cells, or of the coagulated secretion of the
gland, was sometimes seen to project into the crypt. Owing
to the complexity of the free surface of the mucosa, from

^ I am not prepared to say that on a surface so extensive as tlie mucous
membrane of the gravid uterus in Orca there may not be here and there
a spot free from crypts at which a tubular gland may open, but I did not
succeed in finding one.

CETACEA.

47

the multitude of crypts, it was not possible to say how many
gland-tubes opened in a given area. It was evident however
that numerous crypts, which did not have glands communicating
with them, lay around those crypts into which the glands
opened. It was also clear that the number of gland-stems
was very much smaller than that of the tubes in the deeper
portion of the gland-layer, so that the number of branches con-
nected with each stem was considerable.

As the crypts were obviously very much more numerous
than the ducts of the glands, and as those crypts into which

Diagrammatic section tlirougli the placenta of Orca gladiator, a. cup-shaped
crypt, b. funnel-shaped crypt, c. tubular gland-stem with its epithelial
lining, d. fusiform and e. spheroidal sub-epithelial connective-tissue
corpuscles. /. /. epithelial lining of crypts, g. g. maternal capillaries in
the walls of the crypts, h. h. chorionic villi occupying the crypts.
i. i. epithelial covering of the villi, k. spheroidal and I. fusiform cor-
puscles of the villi, m. m. intra-villous foetal capillaries continuous with
?i. n. extra-villous capillaries. The space represented between the foetal
epithelium i. i. and the maternal epithelium /. /. is to give distinctness
to the diagram, for in the placenta itself the two epithelial surfaces are
in close apposition.

tubular glands opened were deeper and more funnel-shaped
than those into which glands did not open, I was led to divide
the crypts into two groups, non-glandular cup-shaped crypts,
and glandular funnel-shaped crypts. The relation of the glands
to the funnel-shaped crypts seemed to justify the inference that
these pouch-like depressions in the mucosa were (as was stated,

48 . DIFFUSED PLACENTA.

by Dr Sharpey, to be the case In the pits or "cells" on the sur-
face of the uterine mucosa in the gravid bitch) the mouths of
the glands somewhat enlarged and widened. But however this
might be the case with the funnel-shaped crypts it obviously
could not be so with the cup-shaped crypts, which were inter-
glandular in position, and, as in the pig and mare, could only
have been produced by changes in the interglandular part of
the mucous membrane. I guarded myself however against
too absolute an acceptance of the view that the funnel-shaped
crypts were merely the widened mouths of the glands by stating
{op. cit. p. 501) that they, like the cup-shaped crypts, may be
formed by a folding of the greatly hypertrophied mucous mem-
brane : only in the one case the hypertrophy and folding take
place between the glands, in the other at the mouth of the
gland itself. The difference between the mode of opening of the
glaiads in Orca on the one hand, and in the pig and mare on
the other, seemed to be this : that in Orca the free surface of the
mucosa was much more uniformly crypt-like than in the pig and
mare, so that there were no intermediate surfaces destitute of
crypts on which the glands could open, whilst in the pig and
mare the crypts were collected into definite areas, with distinct
smooth surfaces intermediate to them. This more compact
arrangement of the crypts in Orca corresponds with the more
crowded condition of the villi on the surface of the chorion.
That the whole series of crypts however in the cetacean uterus,
as in the pig and mare, are- to- be regarded as interglandular
formations, is supported by the observations of Eschricht on the
mucosa of the gravid porpoise. For he states (p. 35) that in
this animal the glands open on the sur&ce of the mucous mem-
brane, not into the "cells" in which the villi are lodged, but into
separate shallow areolse ; that in the porpoise, as in the pig,
these areolae are much less vascular than the surrounding
crypts ; and that for so great a multitude of gland-ramifications
there are not more openings on the surface of the mucous coat
than in the pig.

The walls of the crypts and the interglandular connective
tissue in 07xa contained numerous nucleated corpuscles. In
the interglandular tissue they were mostly fusiform, but in
the walls of the crypts a distinct layer of globular lymphoid-

CETACEA. 49

looking corpuscles was seen close to the free surface, wliich
was not unfrequently elevated, in a sinuous outline, immediately
superficial to these corpuscles, which may, from their position,
be called the sub-epithelial corpuscles of the crypts. It is not
improbable that these corpuscles may have migrated through
the walls of the adjacent capillaries. The walls of the crypts
were very vascular and contained a compact capillary network.
Owing to the closer arrangement of the crypts, the surface of
the mucosa generally presented a more uniform vascularity
than in either the pig or mare. In all these animals in-
deed the great vascularity of the crypts was one of the most
striking features in the structure. The capillaries in the walls
of all the crypts belonging to the same group formed a con-
tinuous network, and in the Orca, owing to the more uniform
crypt-formation, the capillaries of one group freely anastomosed.
with those of adjacent groups. The capillaries in the crypt-
walls in each animal formed a series of anastomosing festoons,
and usually a, distinct capillary ring surrounded the mouth of
each crypt. Moreover there was a great difference between
the vascularity of the crypts and that of the deep layer of the
mucosa in which the glands were situated, for the vascularity
of the latter was not more than may be seen in connection with
the tubular glands of the intestine. The crypts in Orca were
lined by a well-defined layer of epithelium-cells, which closely
followed the various irregularities of the mucous surface. The
free ends of the cells were polygonal, often hexagons, or penta-
gons, though sometimes elongated into a pyriform shape. In
my original memoir on the placentation of Orca, I stated that
they had the appearance of a pavement- epithelium, though
they were not larger than the broad free ends of the cylindrical
epithelium lining the glands. I have since re-examined this
layer of cells, and have now come to the conclusion that they
cannot be associated with either the pavement-epithelium
(i.e. if we employ the term as equivalent to squamous), or with
the cylindrical epithelium. The cells are neither sufficiently
elongated for the one, nor flattened for the other, but have
an intermediate or transitional form.

The villi of the chorion fitted into the crypts, but were
easily extracted from them. Only those villi which occupied

50 DIFFUSED PLACENTA,

the funnel-shaped crypts were brought into immediate contact
witli the secretion of the tubular glands, but in all the crypts
the villi were in contact with the epithelial lining.

I have also been so fortunate as to acquire the gravid uterus
of a Narwhal {Jlonodon monoceros), the foetus in which was
5 ft. 5 in. long\ The uterus, as in Orca, consisted of two horns
united together in the corpus uteri, and the foetus lay in the
left horn. The chorion extended from the tip of the left to
that of the right horn, as in the Orca and the Mare. The
chorion immediately enveloping the foetus was not folded :
but in the whole length of the right, and at the free end of
the left horn it was raised into strong longitudinal folds, which
corresponded in reverse order with a similar series of folds of
the uterine mucosa radiating from the orifices of the Fallopian
tubes. At the os uteri the mucosa was also thrown into strong
folds which radiated for some distance into the gravid cornu,
and in some parts of their length projected as much as three
inches from the general plane of the mucosa, though at the
OS they had not more than one-half that projection : the chorion
in apposition with this part of the mucosa was also folded.

Except in the localities to be immediately specified the
whole of the extensive surface of the chorion was so covered
with vascular villi that, by the naked eye, at least, no non-
villous intervals were recognised. The chorion was so adherent
to the uterine mucosa that gentle traction was needed to draw
them asunder, and, as the one was peeled off the other, the
villi were seen to be drawn out of multitudes of crypts opening
on the free surface of the mucosa.

The chorion, in apposition with the os uteri and sur-
rounding folds of mucous membrane, was for the most part
non-villous, and presented a smooth, feebly vascular appearance,
which contra,sted strongly with the adjacent villous vascular
chorion. This smooth spot was irregular in form, measured
six inches by four, and from it narrow bands of smooth chorion
radiated outwards from two to three inches between the villous-

'^ I am indebted for this valuable specimen, tbrougb the kindness of my
friend Mr C. W. Peach, to Mr John Maclauchlan, Chief Librarian and Cm'ator
to the Free Library, Dundee. For additional details as to the position of the
foetus, &c., I may refer to Proceedings Royal Society, Edinburgh, Feb. 7th, 1876.

CETACEA. 51

covered folds : it was similar to but much larger than the
corresponding spot in the Mare, and in Orca. Small isolated
patches of villi were scattered irregularly over the surface of
this smooth spot, A smaller non-villous spot If in. by f in.
was situated three inches from this large bare surface. The
uterine mucosa opposite these smooth portions of the chorion,
though folded, was smooth and free from crypts, except where
the isolated patches of villi were in apposition with it. Radi-
ating for about one inch from the pole of the chorion in the
gravid horn were narrow non-villous bands separated by inter-
mediate villous surfaces. The bands were in apposition with
the folds of the mucosa free from crypts, which radiated from
the orifice of the Fallopian tube. In the non-gravid horn the
chorion was feebly vascular, and devoid of villi, for about five
inches from its pole ; and even for a greater distance the villi
were irregularly scattered, so that well-defined smooth spots
could be traced as far as ten or twelve inches from the
pole.

When examined microscopically the villi were seen to be
arranged in tufts, which varied in size and in the number of
villi. Some tufts had not more than two or three villi, but
more usually numbers were collected together; though not
unfrequently short single villi arose from the chorion in the
intervals between the tufts. They had, as a rule, the same
shape as those in Orca, but some were seen to divide into
filiform branches. They contained a capillary network, and a
layer of extra-villous capillaries ramified beneath the inter-
villous surface of the chorion.

The free surface of the uterine mucosa was, as in Orca,
pitted with multitudes of recesses and furrows, which again
were subdivided into innumerable crypts. In the polar regions
of the cornua and in the corpus uteri the mucosa was more
spongy and succulent than in the greatly distended part of
the gTavid cornu, in which the mucosa was obviously more
stretched, so that the pits and furrows were almost obliterated,
and the crypts opened on the general plane of the mucosa.
In their general arrangement and in the vascularity of their
walls the crypts in the Narwhal so closely resembled the crypts
in Orca that no special description is required. But the layer

52 DIFFUSED PLACENTA.

of cells lining the crypts was a well defined cylindrical epitlie-
linm, many of the cells of which were howe\^er so swollen that
the breadth almost equalled the length.

Scattered over the surface of the mucosa in the more dis-
tended part of the cornu were numerous smooth, depressed, ovoid
or circular spots, the largest of which was not more than y^o ths
inch in diameter, though as a rule they were less than j'^th
inch, so as almost to escape observation with the naked eye. 25
or 30 of these spots were on an average in each square inch ; and
each was surrounded by a minute fold of the mucosa subdivided
into crypts. The corresponding surface of the chorion possessed
occasional smooth spots from j^th to j^ths inch in diameter,
surrounded by villous tufts, which were in apposition with the
depressed spots on tlie mucosa, but tbey had not the definite
stellate form which one sees in the corresponding spots on the
chorion of the pig. The extra-villous layer of capillaries rami-
fied beneath these non-villous spots of the chorion. In the
succulent parts of the mucosa the depressed spots could not be
seen with the naked eye, and were found only after a careful
search with a pocket-lens at the bottom of some of the pits or
trenches in the membrane.

The glandular layer of the mucosa corresponded so closely
in the direction and mode of branching of the tubular glands
with the corresponding layer in Orca, that I need not give a
special description. The glands were subjacent not only to the
crypts, but to the smooth depressed spots, and as these spots
bore so close a resemblance to the smooth spots on the mucosa
of the pig, I was naturally led to examine if the mouths of the
utricular glands opened there. In one instance I saw a tube
lined by epithelium lying obliquely beneath the membrane of
a spot, and opening near the middle by a distinct orifice
bounded by a crescentic fold of the membrane. In a second
instance the end of a gland appeared from under cover of the
surrounding crypts, and then seemed to open by an obliquely
directed mouth near the edge of the spot. But upwards of
80 other spots examined with equal care gave no evidence of
gland-mouths opening on them. Hence it would appear that
these smooth surfaces on the mucosa are by no means neces-
sarily associated with the mouths of the utricular glands, and

CETACEA. 53

one is disposed to conclude that the gland-orifices are usually
concealed amongst the crypt-like foldings of the mucosa. The
very much greater number of the crypts, than of the gland-
stems, negatives the idea of the crypts being merely dilatations
of the mouths of the glands, so that in the Narwhal, as in the
Pig, Mare and Orca, the crypts are to be regarded as inter-
glandular in position.

Through the kindness of Dr Allen Thomson I have had the
opportunity of examining a portion of the uterus of a Narwhal, in
his possession, at a much earlier stage of gestation, the foetus
in which was only 3^ inches long. The free surface of the
mucosa was gently undulating and traversed by shallow fur-
rows, but no definite crypts could be seen. The gland-tubes
were remarkably numerous, tortuous and branching. I made a
comparative measurement of their size, with that of the glands
in my much more developed specimen, and found them to have
only one-half the transverse diameter. The gland-stems in-
clined obliquely to the plane surface of the mucosa, on which
their orifices could occasionally be seen. The free surface of
the chorion was not villous, but traversed by faint ridges, which
without doubt fitted into the shallow furrows of the mucosa.
Patches of epithelium-cells could be seen covering the surface
of the chorion.

It is clear, therefore, that in the Narwhal, as I have pre-
viously described in the pig, the villi do not form on the
surface of the chorion, nor the crypts on the surface of the
mucosa, until the embryo has reached a stage of development
in which its body, though small, has assumed a form which
enables its ordinal characters to be recognised.

The amnion in my specimen formed an immense bag, which
reached to 5 inches from the free end of the left horn of the
chorion, but did not pass into the chorion occupying the right
uterine cornu. It was so closely adherent to the inner surface
of the chorion, that when that membrane was divided the sac
of the amnion was opened into. Opposite the abdominal
aspect of the foetus the wall of the allantoic sac was in contact
with the chorion, and the amnion was reflected over its surface.
The allantois formed a large funnel-shaped sac at the bifur-
cation of the funis, and was prolonged along the adjacent

54 DIFFUSED PLACENTA.

surface of the chorion to within two inches of its free end in the
left cornu, and nine inches of its free end in the right cornu.

Fig. 10.

Diagrammatic transverse section through the foetus and membranes to show
the relations of the aUantois to the abdominal aspect of the foetus, and the
relations of the amnion to the chorion. E. embryo, ch. the villous
chorion, al. the aUantois, the letters are in the sac. The dotted line
am. am. represents the amnion, the letters are in the sac.

The amnion investing the cord was studded with yellowish-
brown corpuscles, similar to those that I have described in
Orca gladiator (p. 23) ; similar corpuscles were scattered in
considerable numbers over the amnion covering the aUantois,
and a few were seen on the amniotic lining of the chorion.
But in addition, numerous dull white corpuscles were found,
some of which were slender rods, from jV^h to j%th inch long,
and arranged end to end like the links of a chain; whilst others
were globular, like small shot. The rods were most numerous
on the abdominal half of the cord, the globules at and near its
bifurcation. These corpuscles were, like those of a yellowish-
brown colour, covered by the amnion. When examined micro-
scopically they were found to be composed of crowds of squa-
mous epithelial cells, so that they resembled in structure the
yellowish- white bodies developed in connection with the amnion
of the Cow (p. 25).

Manis. — In Manis, as was pointed out by Dr Sharpey\
the chorion was covered with fine reticulating villous ridges,
interrupted here and there by round bald spots, giving it an

1 Quoted in Huxley's S^emente of Comparative Anatomy, 'p. 112, 1864; and
■with additional details in my Memoir on the Placentation of the Sloths in
Trans. Roy. Soc. Edinh. 18713.

CAMELS. 55

alveolar aspect, something like the inside of the human gall-
bladder, but finer. A bare band free from villi ran longitudi-
nally along the concavity of the chorion, and there was a cor-
responding bald space on the surface of the uterine mucous
membrane. The ridges of the chorion started from the margins
of the bald stripe and ran round the ovum. The mucous
membrane of the uterus possessed a finely corrugated appear-
ance on the surface, in correspondence with the ridges on the
chorion, and was punctated with the orifices of numerous
shallow crypts in which the villi had been lodged. Branched
cylindriform glands were very abundant in the deeper layer of
the mucosa, but their mode of opening on the surface could
not be satisfactorily ascertained, owing to the condition of the
specimen.

Camels. — The Camelidce, unlike the ordinary Ruminant
mammals, possess, as has for many years been recognised, a
diffused placenta. I have recently, through the courtesy of
Professor Flower, had the opportunity of examining a con-
siderable part of the chorion of a Dromedary, preserved in the
Museum of your College. The free surface of the chorion was
thickly studded with short villi, but at one spot a bare patch
about 1|- inch long was seen ; the relation of which to the wall
of the uterus, owing to the absence of that organ, could not be
ascertained. The villi were not arranged in tufts but arose
singly from the chorion, having a somewhat constricted base,
and expanding at the free end in a club-shaped manner. The
villi varied in length from about the 2V th to -^ th inch. The
larger proportion were unbranched, but some of the longer villi
were divided into two or three short offshoots at the free end.
The vessels of the chorion had been injected with size and ver-
milion, and a beautiful intra-villous network of capillaries was
displayed. An extra-villous plexus of capillaries, not unlike
that which I have described in the Mare, in Orca and in the
Narwhal, was also seen. Although the gravid uterus itself was
not in the museum for examination, yet there can be no doubt
that its free surface must have been thickly studded with
crypts for the reception of the villi.

I have examined the non-gravid uterus of the Alpaca (Lama
paca) Avith reference to the arrangement of the utricular glands.

56 DIFFUSED PLACENTA.

The mucous membrane was thicker than the muscular coat.
The glands were numerous; the deeper ends were very tortuous
and branched repeatedly, so that in vertical sections througb
the membrane they were many times divided. As they as-
cended to open by distinct mouths on the free surface they
became much more straight, so that long portions of the tubes
could be seen. The intervals between the glands occupied by
the connective tissue was about equal to the transverse diameter
of the glands. A columnar epithelium lined the glands and
covered the free surface of the mucosa.

In the Ti^agulidcB also, as has been described and figured by
M. A. Milne-Edwards in Ti-agulus Stanleyanus^, the villi are
not collected into cotyledons, but are uniformly diffused over
the surface of the chorion.

In the non-gravid uterus of a Tragulus javanicus, which I
examined, the glands were tortuous and branched in the
deeper j)art of the mucosa, so that they were repeatedly divided
in vertical sections through the mucous membrane. As they
approached the free surface they became much straighter, so
that long portions of gland-tubes could be seen passing to
open on the surface. The glands were so close together that
the interglandular tissue between any two glands was about
as broad as the transverse diameter of the gland-tube. The
epithelium in the glands and on the free surface of the mem-
brane was columnar.

In the Tapir, as was shown by Sir Everard Home^ the
chorion is villous as in the mare. In Tapirus Malayanus,
I am told by my friend Dr John Anderson, there is "a long
bare area as in Manis, Flatanista and Orcella, but propor-
tionally of much greater size. The uterus also has the general
characters of that organ in the gravid Flatanista^." In the
Hippopotamus M. H. Milne-Edwards has described* large villi
disseminated over the whole surface of the chorion, except at
the poles, where the membrane is smooth. Mr A. H. Garrod

1 Ann. des Sciences Naturelles, p. 101, Vol. ii. 1864.

2 Lectures on Comp. Anatomij, v. p. 328, and Plate 27.

3 The characters of the gravid uterus in the rare Cetacean genera, Flatanista
and Orcella, have been specially studied by Dr Anderson, and will be described
by him in a memoir to be shortly published.

■* Legons sur la Physiologic, ix. p. 562, 1870.

LEMURS. 57

has also seen'^ the uniformly villous covering of the chorion in
the placenta of this animal.

Lemurs. — I have already stated (p. 20) that M. Alphonse
Milne-Edwards has described the Lemurs as possessing a bell-
shaped placenta. Since that was written I have had the oppor-
tunity of examining specimens of gravid uteri in a well-advanced
state of development in Propithecus diadema and Lemur rufipes^.
In all these specimens the mucous membrane in the anterior
and middle thirds of the uterus was thrown into numerous
shallow convoluted folds separated by intermediate sulci,
constituting " une multitude d'anfractuosit^s irregulieres " as
described by M. Milne-Edwards. Multitudes of crypts were
situated on the summits and sides of the folds, as well as at the
bottom of the intermediate sulci. The crypts in their general
form and arrangement closely corresponded to the uterine
crypts in Orca and in the Narwhal, though no glands were
seen to open into them. They were lined by a columnar
epithelium, beneath which was a very compact capillary plexus,
similar in arrangement to that seen in Orca and in the Nar-
whal. Scattered amidst the crypt-covered folds were irregularly
elongated smooth depressed areas, the largest of which did not
exceed half an inch in their long diameter.

Utricular glands, somewhat tortuous in their course and
occasionally branching, were seen in the deeper layer of the
mucosa. They converged to the smooth areas just described, ran
for a little distance beneath the membrane, and then opened,
usually by an obliquely directed mouth, on the surface of
the smooth area ; as many as ten, twenty, or even a greater
number of gland orifices, being found in a single area. These
areas corresponded therefore to the smooth depressed spots on
the surface of the gravid mucosa of the pig, but in the Lemurs
each area had a much larger number of glands opening in it.
It is clear therefore that in the Lemurs, as in the pig, the
crypts are to be regarded as situated in the interglandular part
of the surface of the mucous membrane.

1 Proc. Zool. Soc. Nov. 19, 1872.

2 I am indebted for these sjiecimens to the kindness of Dr Andrew Davidson,
of Antananarivo, Madagascar, and have communicated to the Eoyal Society of
London a detailed description of their characters.

T. 5

58 DIFFUSED PLACENTA.

The chorion was elongated in form, but gave off from the
depending part, lying near the os uteri, a short diverticulum,
which passed into the cavity of the uterine cornu in which the
foetus was not situated ; so that the chorion occupied not only
the body, but both horns of the uterus. A large part of the
surface of the chorion, more especially its anterior and middle
thirds, was traversed by ridges from which numerous villi pro-
jected. The ridges fitted into the sulci between the folds of
the mucosa, and the villi occupied the crypts. By gentle traction
the chorion could be raised from the mucosa and the villi drawn
out of the crypts, as in the Mare, Narv/hal, or other animals
with a diffused placenta. The posterior third of the chorion
was smooth and without villi, and the corresponding area of
the mucosa, surrounding the os uteri, was also smooth and
without crypts. Smooth patches on the chorion also corresponded
to the irregularly elongated, depressed, smooth areas on the sur-
face of the mucosa. In Lemur rufipes a smooth surface was
seen on the mucosa extending from the orifice of the Fallopian
tube into the fundus of the horn in which the foetus was lodged,
and a smooth patch was situated on the pole of the chorion
which corresponded to that surface ; but in the Propithecus
these surfaces were on the one hand covered with villi, on the
other with crypts. In Lemur rufipes the chorion prolonged into
the non-gravid horn was mostly non-villous, and the mucous
lining was almost free from crypts.

The arrangement and structure of both chorion and uterine
mucosa in the Lemurida prove these animals to possess a diffused
placenta, and as, not only the surface of the chorion near the os
uteri, but both its poles may be devoid of villi, the comparison
which M. A. Milne-Edwards has made between its form and
that of a bell is not generally apphcable. The statement, which
has frequently been made, that the Lemurs have a disc-shaped
placenta, is therefore, quite without foundation.

POLYCOTYLEDON^ARY PLACENTA. 59

Structure of the Polycotyledonary Placenta.

Since the time of Fabricius, who figured and described
two and a half centuries ago the gravid uterus of the Sheep,
the Polycotyledonary Placenta has been known to be the form
of placenta in animals belonging to the order Ruminantia. It
consists of a number of thick tuft-like masses of villi — the
foetal caruncles or cotyledons, which are lodged in crypts
situated in an equal number of thick, spongy elevations of
the uterine mucous membrane — the maternal cotyledons. The
foetal cotyledons are separated from each other by considerable
areas of smooth chorion, and the maternal cotyledons have
equally large areas of smooth mucous membrane between them.
Each cotyledon is complete when the foetal are lodged within
the maternal cotyledons, and each when complete forms a
miniature placenta.

The first indication of the formation of a maternal cotyledon,
as has been pointed out by Ercolani\ is an elevation of the
uterine mucosa, so as to present an irregular undulating surface.
As the development proceeds this irregularity increases, until
well-defined depressions or crypts are formed. The walls of
the crypts continue to grow in length, and the crypts are not
only deepened, but smaller compartments branch off from them.
In the course of time they assume the appearance of deep pits,
subdivided into numerous crypt-like compartments, into which
the villi of the chorion closely fit.

The shape of the fully-formed cotyledons and the disposi-
tion of the pits vary in different Ruminants. I shall describe
in detail what I have seen in the well-advanced gravid uteri
of both the Sheep and Cow.

Sheep. — In the Sheep the maternal cotyledons, as has fre-
quently been pointed out by other observers, projected as cup-
shaped mounds from the uterine wall. They were covered on
the outer convex surface by the iiterine mucosa, which was

1 Mem. delV Accad. delle Scienze di Bologna, 1870, Plate L and 1873,
Plate II.

60

POLYCOTYLEDONARY PLACENTA.

smooth on its free surface, and was prolonged as far as the free
inverted edge of the cup. The inner substance of the cotyle-
don was composed of a soft, spongy material, containing nume-
rous pits, which extended almost vertically, and divided as they
passed deeper into its substance into smaller crypt-like com-
partments, which radiated towards the outer wall of the cotyle-
don, without diverging much from each other. The pits were
lined by well-marked cells, most of which were irregular in

Fig. 11.

Semi-diagrammatic vertical section through a portion of a maternal cotyledon
of a Sheep, cr. cr. pit-like crypts, with e. e. the epithelial lining, v. v.
the veins, and c. c. the curling arteries of the sub-epithelial connective tissue.

shape, polygonal, ovoid, or even somewhat caudate, and of con-
siderable size, though some appeared like modified columnar
cells. They consisted of granulated protoplasm, in which one,
two, or sometimes three, well-defined ovoid or elliptical nuclei
were imbedded, but without a cell-wall. Not unfrequently the
outline of the individual cells was very indistinct, and they
seemed as if arranged as a layer of protoplasm studded with
nuclei.

The cells rested on a highly vascular sub-epithelial con-
nective tissue, which formed the proper wall of the pits. The
mucous membrane investing the cotyledon was continuous at

SHEEP. 61

the mouth of the cup with the walls of the pits in the spongy
tissue, so that the cells lining the pits were in the same mor-
phological plane as the epithelium covering the mucosa. The
cotyledons were highly vascular. Some of the arteries in the
sub-cotyledonary connective tissue were corkscrew-like; and in
the deeper part of the cotyledon itself I have seen tortuous
vessels. The greater number of the vessels within the cotyledon
passed, however, vertically towards the surface, lying in the
connective-tissue walls of the pits ; and branching repeatedly,
as a rule, in a dichotomous manner, prior to forming a compact
maternal capillary plexus, but not dilating into maternal blood-
sinuses.

The mucous membrane of the uterus between the cotyle-
dons was smooth on its free surface, and contained numerous
tortuous, branched, tubular glands. Some of these extended
almost vertically to the surface, and could be seen in almost
their entire length in vertical sections — others ran more
obliquely, and, owing to their tortuosity, were repeatedly
divided in vertical sections. The mouths of the glands could
readily be seen with a pocket-lens opening on the surface,
the orifice being partially surrounded by a minute elevation of
the mucosa. In the mucosa around the base of the cotyledons
a ring-like series of gland-openings was seen. In the mucosa
covering the cotyledons, glands were also present, but their
orifices were much stretched, as if by the pressure due to the
great growth of the subjacent spongy tissue of the cotyledon.
The sub-epithelial connective tissue, in which the glands lay,
was not by any means so vascular as that which formed the
walls of the pits within the cotyledons. In some sections
through the cotyledons and adjacent mucosa no glands were to
be seen in the connective tissue intervening between the coty-
ledon and muscular wall, but they were collected in considerable
- numbers around the cotyledon, as if pushed outwards by its
rapid growth. In other sections, however, tubular glands were
seen in the sub-cotyledonary connective tissue; but they seemed
to be the deep ends of branching glands, the stems of which
had inclined obliquely, so as to open on the surface of the
mucous membrane covering the cotyledon. None of these
subjacent glands, or those situated on the surface of the coty-

62 POLYCOTYLEDONAHY PLACENTA.

ledon, were seen to open into, or in any way to communicate
with, the pits within the cotyledon itself.

The foetal cotyledons consisted of numerous villi, which
collectively formed a ball-like mass, called caruncle by the
veterinary anatomist, and occupying the concavity of the
maternal cotyledon. Each villus consisted of a main stem,
which gave off a tuft or cluster of spatulate branches. The villi
entered the maternal pits and branched along with them, so
that every comjpartment was occupied by a brarich of the villus;
but there was necessarily no great divergence of these branches
from the main stem. At their deeper end these spatulate
branches gave off slender terminal offshoots. The villi were
formed of gelatinous connective tissue, in which very distinct
fusiform and stellate corpuscles were arranged in an anasto-
mosing network. At the periphery of the villus was a layer of
flattened cells, with small but distinct nuclei arranged so as to
form an epithelial-like investment. The umbilical vessels rami-
fied within the villi and formed networks of capillaries. The
villi were in close contact with the epithelial cells lining the
maternal pits. Owing to the inversion of the free edge of the
maternal cotyledon and the radiated arrangement of the pits,
with their contained villi, it was impossible to disengage the
maternal and foetal cotyledons from each other without drawing
away with the foetal villi portions of the maternal cotyledon. I
invariably found that, in drawing the foetal villi out of their
compartments, flakes of epithelial cells accompanied them, which
showed how readilj'- this element of the maternal issue is shed.
During parturition, however, when the parts are relaxed, the
disengagement of the two structures can necessarily be more
easily accomplished.

Coiu. — In the Cow the maternal cotyledons, as is well
known, differed in form from those in the sheep. They were
fungiform or umbrella-shaped, and were connected to the
uterine wall by a broad peduncle, around which the uterine
mucosa was prolonged as far as the border of the umbrella.
The whole convex surface of the cotyledon was riddled with
pits, which passed vertically into its spongy substance, and
divided into smaller compartments in the deeper part of
the cotyledon. Projecting from the wall of each pit were

cow. 63

delicate bands, visible to the naked eye, arranged as a rule
in a vertical direction, and in the intervals between these
bands the wall was perforated by numerous orifices, easily seen
with a pocket-lens, which were the mouths of depressions or
crypts in the wall of the pit, some lying almost at right angles,
others obliquely to the wall of the pit itself. The pits, with
their numerous crypts, were lined by cells, similar in character
to those of the sheep. But I should state that a larger pro-
portion of these cells ha,d preserved the columnar form of the
epithelium of the non-gravid uterine mucosa. They rested on
a highly vascular connective tissue, in which the maternal
capillaries formed a compact network.

The surface of the uterine mucosa between the cotyledons
was perforated with the mouths of the tubular, branched, utri-
cular glands. Each gland as a rule opened alone, but occa-
sionally two lay together, a narrow band of mucosa intervening.
Sometimes the mouth was a distinct funnel leading vertically
into the gland-stem, but more usually the gland-stem was
directed obliquely to the surface, so that in vertical sections
through the membrane the glands were frequently cut through
and divided. Glands were also present in the mucous mem-
brane covering the peduncle of the cotyledon, but instead of
communicating with the pits they opened on the free surface of
the mucosa.

The foetal cotyledons were concave and adapted to the fungi-
form maternal cotyledons, the pits of which were occupied by
their villi. The stems of the villi v/ere comparatively large, and
studded with multitudes of minute tufts, which, arising obliquely
or almost at right angles to the main stem, entered and occupied
the crypts. The minute villi forming these tufts were so slender
and filiform that each terminal offshoot contained only a single
capillary loop. The villi were in contact with the epithelium-
cells, and in drawing them out of the pits, more especially in
drawing the tufts out of the crypts, multitudes of cells of the
lining epithelium came away with them. From the differences
in shape of the maternal cotyledon in the Cow and in the Sheep,
there is not the same difficulty in unlocking the foetal from the
maternal placenta in the former animal as in the latter.

In both the Cow and Sheep the branches of the umbilical

64 POLYCOTYLEDONARY PLACENTA.

artery aud vein, which passed to and from the cotyledons, rami-
fied in the smooth inter-cotyledonary part of the chorion.
Numerous small branches arose from them, which did not
enter the cotyledons, but dividing in an arborescent manner
ended in a compact capillary plexus which formed a layer
immediately beneath the smooth epitheliahcovered surface of
the chorion. This plexus was nearer the surface than the
arteries and veins with which it was continuous. Slight varia-
tions in the closeness of the network were seen ; in many places
the capillaries were as small and the mesh-work as fine as in the
walls of the pulmonary air-sacs, though elsewhere they were a
little larger and the mesh-work more open. The plexus ob-
viously represented on a large scale the extra-villous plexus
already described in the diffused form of placenta. In both
animals the highly vascular surface of the chorion presented a
striking contrast to the non-vascular yellow-coloured diverticula
allantoidis which projected through and beyond the poles.

Von Baer has described in his U liters uchimg en (p. 18) the
highly vascular character of the inter-cotyledonary part of the
chorion in the Cow and Sheep, and states that a successful
injection in the sheep forms one of the most beautiful ana-
tomical objects with which he is acquainted. He further
points out that these Ruminants possess in the later period of
pregnancy a very large number of smaller "cotyledons" of a
peculiar kind. In the Sheep they are so small and transparent
as to be recognised with difficulty, though when injected they
are more distinct. In the Cow they are about a line in
diameter, and more easily recognised. They consist, he says,
of collections of folds of the chorion, which are more vascular
than the surrounding surface. E. H. Weber has also seen
these structures, and speaks' of them as consisting of "cells"
separated from each other by partitions, and having branches
of the umbilical vessels distributed to them. He regards them
as receptacles for the secretion of the utricular glands^. But

' Hildebrandt's Anatomic, iv. 506, 1832.

^ Von Baer, who, as has ah'eady been stated (note, p. 37), at one time
regarded the structures, now known to be the utricular glands, as lymjohatic
vessels, believed the collections of folds to be about as numerous as the termi-
nations of the so-called "lymphatics" on the surface of the iiterine miicous
membrane, and that these folds corresponded with the star-like spots on the
surface of the chorion of the pig.

cow, 65

little attention seems to have been paid by subsequent writers
to these observations of von Baer and Weber, though Franck
in his recently published treatise on Veterinary Anatomy^ pro-
bably refers to the same structures when he says :

"Besides the proper cotyledons, numbers of small villi of 1mm.
in diameter, covered by epithelium, are found on the outer surface
of the chorion in the first half of pregnancy. They do not com-
pletely disappear, and in the last third of pregnancy one finds in
addition to the proper foetal villi numbers of small rounded groups
of similar papillae, which lie loosely in apposition with the uterine
mucosa, and in some measure represent a second series of small
foetal villi. At times some are more developed and become con-
nected with the mucosa in places where no cotyledonary villi are
formed."

I have examined the chorion of a cow, the foetus in which
measured 10 inches from the nose to the root of the tail, with
the especial object of determining the nature of these struc-
tures. The free surface of the inter-cotyledonary part of the
chorion was mottled with faint yellow spots, the largest of
which were about 1 line in diameter, and between 25 and 30
spots were on an average in each square inch. The chorion
at each spot was slightly thicker and more opaque than in the
surrounding surface. In non-injected specimens their structure
was not very distinct, but where the inter-cotyledonary capil-
laries had been injected their characters could without difficulty
be ascertained. The simplest form was a shallow pouch, or
pocket-like depression, opening on the outer surface of the
chorion. Sometimes a pocket lay singly, but more usually two,
three, or more, were closely grouped together, and in one case
I saw as many as twelve placed side by side. Not unfrequently
a pocket had a circular outline, but it was often elongated, and
occasionally had a horse-shoe form. The walls of the pockets
were formed of the chorion, and a compact capillary plexus was
distributed in them, and frequently had a whorl-like arrange-
ment around the open mouth of the pocket. The pockets were
lined by an epithelium continuous with the squamous epithelium
covering the plane surface of the chorion, and their epithelial
lining was not so easily washed off as that on the plane surface.

^ Handhuch dcr Anatovde der IlamtUicre, p. 1017. Stuttgart, 1871.

66 POLYCOTYLEDONARY PLACENTA.

Under a magnifying power of 320 diameters numerous yellow
granules were seen in the epithelial lining, which seemed
occasioned by a fatty degeneration of the nuclei of many of
the cells. From this description it is clear that these spots
cannot be regarded either as cotyledons, or as villi, in the strict
sense in which these terms are now employed by anatomists.
It was not possible to say precisely what part of the uterine
mucosa they were in direct apposition with ; but from the
general correspondence in numbers between the spots and the
mouths of the utricular glands it is most probable that they
were opposite the gland orifices. Hence I agree with Weber
in regarding them as receptacles for the secretion of these
glands.

JDeer. — In the Red-deer the cotyledons do not exceed twelve
in number, and vary in diameter from 5 to 1 inch. They are
not scattered generally over the surface of the uterus and
chorion, but are arranged in linear series along the lesser cur-
vature of each cornu. The uterine cotyledons are not peduncu-
lated as in the Cow, though their free surface is convex. The
villi of the chorion formed tufts, the branches of which resem-
bled in shape those of the Sheep, though somewhat longer than
in that animal.

The form and to some extent the structure of the cotyle-
dons in the Roe-deer have been described by E. H. Weber^ and
Bischoff^. The number of cotyledons, which in the Cow and Sheep
amounts to from 60 to 100, does not in the Roe-deer exceed
5 or 6. The long vascular villi of the foetal cotyledons fit into
the tubular depressions in the maternal cotyledons, in the walls
of which a capillary plexus is distributed. Bischoff has satis-
fied himself that no utricular glands exist in the maternal
cotyledons. He figures numerous ramifications of the um-
bilical vessels in the inter-cotyledonary part of the chorion.

Giraffe. — Prof. Ov/en has given a description with some
beautiful figures of the chorion of a Giraffe^ shed during partu-
rition; and has pointed out that numerous cotyledons, some of
which were 4 inches in diameter, and of an oval or reniform

1 Hildehrandt's Anatomie, iv. 506, 1832.

^ Entivickhmgsgeschichte des Rehes, Giessen, 1854.

3 Trans. Zool. Soc. Vol. iii.

GIRAFFE. 67

shape, were arranged in longitudinal rows. I have examined
microscopically the villi from the larger cotyledons of this speci-
men as preserved in your Museum, and have found them to
possess some variations in form. Some were filiform and almost
cylindrical, others broader and more flattened. Some were un-
branched except at the free end, where they gave origin to two
or three short bud-like offshoots : others were much more
deeply cleft, but none could be said to have an arborescent
form. The cotyledons were very vascular, and each villus con-
tained a compact capillary network.

But, further, Owen has described {Op. cit.) numerous smaller
cotyledons

"of irregular form and unequal dimensions, developed from the
external surface of the chorion in the interspace of the normal
cotyledons : these smaller ones varied in diameter from two inches
to two lines : their component villi were proportionately short, and
in the smallest ones simple and unbranched j so that the parts of the
chorion where these were thickly scattered, presented a structure
approachmg to that of the non-placentiferous chorion of the Camel
and certain Pachyderms."

In addition to the smaller cotyledons described by Owen,
I have seen, under a magnifying power of 40 diameters, short
club-shaped villi springing from the plane surface of the
chorion, either singly, or in clusters of 2, 3 to 6 villi, or in
linear rows, containing as many as 20 short, simple, clavate
villi closely resembling in form the villi of the Camel, so that
the Giraffe in this particular approximates more to the diffused
placenta than do the Cow, Sheep and Deer.

But the chorion of the Giraffe presents other peculiarities.
The free surface of the inter-cotyledonary chorion was mottled
with irregularly-shaped spots, varying in diameter from half
an inch to one line ; so numerous indeed were they, in the
portion of chorion I had for examination, that they occupied
the larger proportion of the surface, and left only very narrow
lanes of unspotted chorion between. The membrane was
slightly thickened at each spot, but was not elevated as with
the smaller cotyledons of Owen. Under a simple lens the free
surface of each spot was minutely pitted, and when magnified
40 diameters the pits were seen to be pocket-like depressions
similar in form, arrangement and structure to those that I have

G8 POLYCOTYLEDONARY PLACENTA.

described in the corresponding part of the chorion of the Cow.
Owing to the spots being so much bigger than in the Cow, the
number of pockets in a spot was much greater, 100 and up-
wards being not unfrequently grouped together. The pockets
were in some places separated from each other by well-defined
septa just as in the Cow-, but in other members of the group
the septa were split up into villous processes, and adjacent
pockets communicated with each other. The short villi which
sprang from the plane surface of the chorion were usually
found in close proximity to a group of pockets. The chorion
had been minutely injected with size and vermilion, and a
compact plexus of capillaries was seen immediately beneath its
free surface, as in the Sheep and Cow ; they were also distri-
buted in the walls of the pockets, in the villous subdivisions of
the septa and in the scattered, villi. Fragments of the epi-
thelial lining could be seen in some of the pockets, though for
the most part it had been removed. There can, I think, be no
question that the pockets in the Giraffe fulfil the same office
as the corresponding structures in the Cow.

Although the uterine mucosa of the gravid Giraffe has not
apparently been examined, there can be no doubt that maternal
cotyledons containing pits for the reception of the foetal villi
must exist, and Owen has shown that, even in the non-gravid
state, elevations are to be seen in the uterine wall, which cor-
respond in position to the future cotyledons. Utricular glands
also without doubt exist, and it is probable from the number of
spots coniposed of pockets in the chorion that they occur in
large numbers.

It is necessary that we should now consider whether the
pits and crypts in the maternal cotyledons of the ruminant
placenta, in which the villi of the chorion are lodged, are merely
the greatly-enlarged mouths of the utricular glands of the
mucosa, or are structures specially formed during pregnancy,
by great hypertrophy and folding of the inter-glandular part
of the mucous membrane, as in the diffused form of placenta.
Prof. Spiegelberg^ was of opinion, from some observations which

1 Henle and Pfeuffer's Zeitschrift, xxi. , quoted by Ercolani, p. 17 of the
French translation of his Memoir.

POLYCOTYLEDONARY PLACENTA. G9

he had made,, that they were only remarkable dilatations of the
utricular glands, and BischofF was at one time disposed to regard
them as the largely-developed glands of the uterus. Subse-
quently however BischofF figured, in the uterus of the Roe-
deer\ the utricular glands ascending to open on the surface of
the uterus, not in the cotyledons, but around its circumference.
Eschricht however had previously stated that in the Cow the
glands open, not into the cotyledons, but on the intermediate
surface of the uterus. Ercolani also has figured and described^
both in the Sheep and Cow the glands as situated around the
cotyledons, and not communicating with the cavities within
them. In the description which I have given of the cotyledons
in the Sheep and Cow, I have stated that I was unable to detect
any communications between the glands and crypts : the glands
indeed appeared as if they had been pressed to the periphery of
the cotyledons by the great development of its spongy sub-
stance. Hence it would appear that in the polycotyledonary,
as in the diffused placenta, the crypts in which the foetal villi
are lodged are not produced by an enlargement and dilatation
of the tubular glands of the mucosa; but are new structures
formed, during pregnancy, by a great hjrpertrophy and folding
of the inter-glandular part of the mucous membrane.

1 EntwichlungsgescMchte des Eehes, Plate VIII. 1854.

2 Memoir of 1873, Plate 2.

70 ZONARY PLACENTA.

Structure of the Zonary Placent\.

The Zonary or Annular placenta forms a belt surrounding
the equatorial part of the chorion and contiguous portion of the
uteriiie mucous membrane. It is found in its best-known
form in the Carnivora and Pinnepedia, though it occurs also in
Hyrax and in the Elephant.

But in some of the Carnivora modifications in the form of
the zone are met with. Thus Daubenton pointed out^ that in
the Ferret {Mustela fmv) the zonary arrangement is so far
modified that two portions of the zone are thicker than the rest,
so as to look like two lobes, but an intermediate thinner tract
unites these lobes together. Bischoff has described in the Stone-
marten {Mustela foina), and Pine-marten {Mustela martesY, on
the side corresponding to the free border of the uterus, a gap in
the continuity of the ring-like band of the zonary placenta, in
which gap the chorion formed a pouch. The villi bounding
this gap were strongly developed, and like the outer surface of
the pouch itself possessed an epithelium, coloured of a rich
reddish yellow, in which the pigment was partly in the form of
granules, partly of rhombohedral crystals. The pouch con-
tained effused blood, the liquid part of which was intensely
coloured and contained hsematoidin granules and crystals. In
the Otter (Lutra vulgaris) a similar pouch has been described^
by Bischoff, but larger and containing more free blood. The
same anatomist has also pointed out* that in the Weasel {Mustela
vulgaris) the placenta does not form a complete zone, but is
divided into two lateral halves by two gaps, the one opposite
the free border of the uterus, the other opposite its mesenterial
attachment. The chorion at the space opposite the free border
was not quite smooth, but possessed some tolerably long villi,
and had a reddish-yellow colour on the surface. Between this
part of the ovum and the uterus some extravasated blood was
also found.

^ Buffon's Histoire Nahirelle, vii. PI. 27.

2 Sitzbericht. Akacl. Wissensch. Muvchen, 13 May, 1865, p. 339.

3 Idem, p. 213, 1865.
* Idem, p. 3-13, 1865.

CARNIVORA. 71

It has long been known that the free borders of the pla-
centa in the Bitch and Cat are coloured of a deep green,
not unlike the colour of bile, and a beautiful drawing of this
appearance in the Bitch has been published by von Baer in his
tfntersuchungen. Bischoff, who examined the coloured border
microscopically, found ^ it to contain long pointed crystals, soluble
in water ; a beautiful green pigment in irregular granules ; a
quantity of small rounded globules, also soluble in water; larger
feebly-granulated cells, with a round or somewhat elongated
nucleus; a brown mass and a few large fat-cells. BarrueP had
previously regarded the green colouring material as like that of
the bile, and H. Meckel in a more recent paper had applied to
it the name of haemato-chlorine*. I have seen the placenta of
the Fox with a similar green coloration at the borders of the
zoue.

The gravid uterus of the Dog, Cat, and other pluriparous
Carnivora possesses a moniliform appearance. Each dilatation
is a compartment of the uterus containing an embryo, with its
membranes, and between adjacent compartments the uterine
cavity forms a narrow tube. If one of these compartments be
opened, in a well-advanced stage of development of the embryo,
the chorion will be seen to be smooth and bare of villi, except
in about its middle third, where the villi are arranged as a
zonular band around the transverse circumference of the ovum.
The uterine mucosa possesses a similar zone closely blended
with the zonular band of the chorion. The mucous membrane
on each side of the zone is smooth and vascular : it lies in ap-
position with the smooth pa,rt of the chorion, but has no attach-
ment to it. Where the zonary and smooth parts of the mucosa
are continuous with each other a narrow strip of mucous mem-
brane is reflected on the margin of the zonular band of the
chorion, and forms a rudimentary decidua reflexa. In the true
Carnivora the decidua reflexa is so very narrow that it has often
been overlooked ; but in the Grey Seal, where the placenta is
large, the reflexa is from f to 1^ inch broad. As the zonary
placenta is much more complex in structure than either the

1 Entwicklungsgeschichte des Hunde-Eies, p. 106.
^ Ann. des Sciences Nat. xix. 1830.
' Deutsche KUnik, 1852, p. 4GG.

72 ZONARY PLACENTA.

diffused or polycotyledonary forms, it is necessary, to understand
the relations of its constituent parts, that it should be examined
in different stages of development. I shall describe what I have
seen in the domestic Cat. (PI. I. II., figs. 1, 2, 3, 9, 10.)

Cat. — In the earliest impregnated Cat's uterus, which I have
examined, the compartments were ovoid, and the long diameter
of each, measured along the arc, did not exceed ^th inch.
When a compartment was opened the chorion readily separated
from the mucous lining. At each pole of the compartment an
area of mucosa yV^^ I'ixch in its long diameter was smooth ; but
the rest of the membrane was hypertrophied, spongy, swollen,
and elevated above the smooth polar portions, and formed the
placental area. The placental area was marked on its surface by
an extreniely delicate reticulation, many of the strands of which
had a sinuous direction. It was thickly studded with minute
orifices barely visible to the naked eye, but easily seen with a
pocket-lens. These orifices were the mouths of the pits or
crypts in which the villi of the chorion had been lodged. A few
of these openings were two or three times larger than the rest.
The appearance which I saw in the Cat is evidently similar to
the "cells" figured by Dr Sharpey in the Bitch (Fig. 211)\ and
by Bischoff in the same animal (Fig. 48, A)^, though, as will be
seen further on, I interpret its mode of production in a different
manner from those anatomists. The crypts passed vertically into
the spongy substance, and when vertical sections were made
through it, they were seen to be separated from each other by
trabeculse ; the chief beams of which lay vertically, and when
they reached the free surface formed the strands of the reticulum
already described. The vertical trabeculae were connected to-
gether by others directed obliquely or in a sinuous manner, and
these lateral connections were especially seen about midway in
their length. Hence not only on the surface, but when hori-
zontal sections were made through the placental area, a reticu-
lated arrangement was seen, and the crypts constituted the
interstices of the reticulum. As these trabeculse were formed
of the thickened mucous membrane of the placental area, they

^ Baly's Translation of Muller's Physiology, note p. 1576.
2 EnUnckluvgsgeschichte des Hitnde-Eies, 1845.

CAT, 73

were necessarily composed of the somewhat modified tissues
of that membrane. On the surface was a definite layer of epi-
thelium, the cells of which were short columns, with distinct,
circular or ovoid, brightly-refracting nuclei. These cells rested
on a delicate sub-epithelial connective tissue in which the
maternal capillaries ramified.

The trabeculse and the sub-mucous connective tissue were
carefully examined with the object of ascertaining their relations
to the tubular glands. In vertical sections the glands were dis-
tinctly seen, transversely or obliquely divided, lying in a definite
layer of connective tissue situated deeper than the crypts.
Sometimes the divided glands were separated, by comparatively
broad bands of connective tissue, from the crypts and trabecular
structure, but in other places they were immediately subjacent.
They were lined by a well-defined columnar epithelial layer. I
examined many sections with the object of ascertaining if the
stems of the glands opened into the crypts or passed along the
trabeculse to open on the free surface of the mucosa, but owing
to the complexity of the arrangement due to the formation of
the numerous crypts which I have described, I did not succeed
in tracing them to their orifices.

As it was important however to ascertain if the crypts
equalled in number in a given area the glands of the mucosa
in the same area, or if the crypts much exceeded in number
the glands, I submitted different parts of the mucosa of the
gravid uterus of this cat to microscopic examination, and com-
pared the appearances seen with those presented by the mucosa
of the non-impregnated uterus. In the non-gravid cat the
stems of the glands were almost perpendicular to the free sur-
face of the mucosa. They were so tortuous at their deeper
ends as to be repeatedly cut across in a vertical section through
the membrane. The interglandular connective tissue, contain-
ing numerous corpuscles, formed well-marked septa between
the glands. Vertical sections made through the mucosa lining
the constrictions between the compartments of the uterus of
this gravid cat showed the tubular glands to be on the average
^-th wider than in the non-gravid condition, the interglandular
connective tissue was much smaller in quantity, so that the
glands were more closely crowded together; but in the placental
T. 6

74 ZONARY PLACENTA.

area of the mucosa of the same cat the interglandular tissue
was greatly increased in quantity, so that the glands were
much further apart. The glands themselves were, as in the
non-placental area, dilated, but the number of glands seen in
the sections did not nearly equal the number of crypts.

In a cat's ovum, which had reached a somewhat more
advanced stage of development, where the long diameter of
the uterine compartment, measured along the arc, was 1| inch,
I found that the villi of the chorion readily disengaged from
the uterine crypts. By far the larger part of the chorion was
still villous, not more than -^ ths inch at each pole being
smooth. The line of demarcation between the placental and
non-placental polar areas of the mucosa was very distinct. The
placental area, or the hypertrophied and spongy mucosa, pos-
sessed a reticulated appearance, the principal strands of which
were sinuous, and gave off numerous collateral branching off-
shoots, which joined adjacent branches to form the walls of the
numerous pits or crypts which opened on the surface. The
strands and branches were larger and the pits, and crypts were
more dilated than in the younger ovum already described, and
on looking down the larger pits, their subdivision into smaller
crypts could be seen. The crypts were lined by an epithelium,
numbers of the cells of which possessed a columnar form,
though others were swollen and otherwise altered in shape,
so as to be irregularly polygonal. The cell-protoplasm v>?as
granulated and the nucleus was distinct. The sub- epithelial
connective tissue was vascular. When vertical sections were
made through the placental area the more dilated size of the
crypts and pits than in the younger specimen was distinctly
recognised, being thus in conformity with the larger size of the
chorionic villi. Between the deeper closed end of the crypts
and the muscular coat was a definite layer in which portions of
gland-tubes, lined by an epithelium, some of which were trans-
versely, others obliquely divided, could be seen. The glands
were dilated as in the younger specimen, and not so numerous
as the crypts, neither could I obtain satisfactory evidence of the
communication of the mouths of the glands with the crypts.

I am led therefore to the conclusion that the crypts formed
in the early period of gestation in the placental area of the Cat

CAT. 7o

are not due to a mere widening of tlie mouths of the tubular
glands ; but are produced, as in the pig and mare, by a great
increase in the amount of the interglandular part of the
mucosa, which becomes folded so as to form the crypt-like
arrangement which I have just described. In this respect,
therefore, my observations agree with those of Ercolani on
the same animal^ The interpretation, therefore, which Erco-
lani and I have put on the appearances seen in the placental
area of the cat in the early stage of gestation, differs from that
given by Dr Sharpey on the appearance seen in the uterine
mucosa of the bitch at a similar stage. As is so well known,
Dr Sharpey held that the pits and "cells" (crypts) seen on the
inner surface of the uterus, which receive the villi of the
chorion, are the mouths of the utricular glands enlarged and
widened. It is possible that in the cat, as in the Orca, the
utricular glands may open into some of the crypts, so as to
seem to justify the inference that they were formed by a
widening of the mouths of the pre-existing glands. But this
interpretation obviously cannot be given of the formation of
those crypts which are interglandular in position. Hence it
seems to be more in conformity with the structural arrange-
ments of the organ to conclude, that the crypts which arise
in the uterine mucosa during pregnancy are new formations,
produced by a great hypertrophy and folding of the surface
of the mucous membrane.

When the ovum of a cat, which had completed about one-
half the period of gestation, was examined, a most important
advance in placental formation was observed. The zonary villous
band on the chorion was restricted to its middle third, and an
equally large smooth surface was found at each pole. The zone
on the chorion was now so completely interlocked with the cor-
responding zone in the uterine mucosa, that the two surfaces
could not be disengaged from each other. The placenta could
only be separated from the uterus by rupturing the slender
marginal band of decidua reflexa, and tearing through, or
altogether pulling off, the placental area of the mucosa, which
formed a well-defined decidua serotina.

1 Mem. deW Accad. dellc Scienze di Bologna, 1870, Plates 2, 3, 4.

6—2

76 ZONARY PLACENTA.

The villi of the chorion had the form of broad sinuous leaf-
lets, which became attenuated at their uterine ends and gave
off bud-like offsets from the free border. When vertical sec-
tions were made through the placenta the villi were seen to
pass vertically through the organ up to its uterine aspect.
The trabeculse of maternal tissue, which formed the walls of
the pits or crypts in which the villi were lodged, passed between
the villi up to the chorion, and closely followed the sinuosities
of the villi, so as to form an intimate investment for them, and
in horizontal sections through the oi'gan they were seen to be
arranged as a series of laminse, winding in a sinuous manner
between the leaf-like villi. Between the placenta proper and
the muscular coat was a well-defined layer of serotina, equal
in thickness to the muscular coat itself. It was traversed by
the numerous blood-vessels which passed into and out of the
placenta, and which formed not unfrequent anastomoses with
each other. The decidua serotina consisted not only of the
vascular connective tissue, but of the epithelial cells of this
part of the mucosa, which were similar in character to those
described in the preceding stage of development. In thin
sections, tubes were seen cut transversely or obliquely, and lined
by an epithelium; they were about equal in diameter to the
gland- tubes seen in the serotina in a less advanced stage of
gestation, and were without doubt the dilated glands of this
portion of the mucosa. It may here be stated, that in the
non-placental area of the same uterus the tubular glands were
distinctly seen separated from each other by comparatively
wide intervals of interglandular tissue.

The trabeculse and laminse of maternal tissue, which were
prolonged into the substance of the placenta between the villi,
were continuous with the serotina and were invested by an
epithelial layer, the cells of which were modified columns, like
the cells of the decidua serotina. The blood-vessels of the sero-
tina entered the laminee and trabeculse and ramified in them
throughout the maternal part of the placenta. In the placenta
of one of the embryos, where the maternal vessels were injected,
they formed a network of capillaries of ordinary magnitude. In
the other placentae from the same uterus the maternal capillaries
when injected with red gelatine were dilated to two or three

CAT. 77

times the size of the capillaries in the foetal villi, and ascended
almost vertically in the trabeculae. Not unfrequently near the
chorionic surface they dilated into sinus-like enlargements,
which were crowded with blood-corpuscles. It is possible that
these dilatations may, to some extent, have been due to the
force employed in filling the maternal vessels with injection,
but this will not, I think, account for the whole extent of the
dilatation \ The vessels of the capillary network of the foetal
villi were injected with a blue colour and showed no dilata-
tions ; and the contrast between the two systems of vessels
within the organ was well seen both in horizontal and vertical
sections.

The placenta of a cat, shed in the ordinary course of partu-
rition, was covered on its uterine surface by a layer of soft
yellowish-white tissue, which was smooth and uniform in
charactei', and was without any flocculent, ragged processes pro-
jecting from it. This layer consisted of that part of the sero-
tina which remained attached to the placenta, came away with
it at the time of birth, and was therefore deciduous. From
it laminae and trabeculse passed into the substance of the pla-
centa, which had a similar sinuous arrangement and relation
to the foetal villi as has just been described in the placenta at
half time. Examined microscopically, the vascular connective
tissue of the intra-placental prolongations of the serotina with
their epithelial investment was recognised, but as it was not
possible in a detached placenta to inject the maternal blood-
vessels their disposition could not be made out. I examined
thin sections through the deciduous or placental layer of the
serotina for the presence of utricular glands. I saw indistinct
appearances of tubes transversely or obliquely divided, which
mio-ht be interpreted as tubular glands, but the aggregation of
cells within and around them was so great that it was difficult
to speak positively on this point. The chorionic system of
foetal blood-vessels was injected, and the leaf- like villi, with
their remarkable compact capillary plexus, were readily seen.
On examining with a pocket-lens the uterine surface of the
deciduous layer of the serotina, many minute, rounded, scat-

1 The dilatation of the maternal vessels in the feline placenta has also been
referred to by Eschricht and other observers.

78 ZONARY PLACENTA.

tered holes were seen in it, through each of which a ter-
minal bud of a leaf-like villus projected so as to reach the
uterine surface of the placenta. These buds were often clavate
in form, and contained a capillary plexus, continuous with that
of the body of the villus. It is clear, therefore, that when the
placenta of the ca,t is shed at the time of parturition, a con-
tinuous layer of serotina, interrupted only by these minute
orifices, is shed along with it.

The presence of a layer investing the uterine surface of the
cat's placenta, analogous to the caducous layer of the human
placenta, was distinctly recognised by Eschricht ; who also de-
scribed the thin, perpendicular, fiexuose laminae of maternal
structure passing through the entire thickness of the organ and
investing the foetal villi as if with sheaths^. Though Eschricht
was at first inclined to the view that the layer investing the
uterine surface of the placenta was nothing else than the
mucous tissue of the uterus, further consideration led him to
state that it altogether differed from that tunic. But he also
came to the conclusion that the mucous tunic was left entire on
the placental zone, exhibiting only torn and broken-off vessels..

There can be no doubt, from both its position and structure,
that this layer belongs to the mucosa of that part of the uterus
which corresponds to the placental zone, for it and the intra-
placental laminae and trabeculoe are merely a more advanced
condition of the crypt-like modification of the mucosa, which I
have described in the earlier stages of placental formation in
this animal. Does this layer however represent the whole
thickness of the mucosa belonging to the placental zone ? or is
it merel}'- the superficial part of the mucous membrane ? are
questions v>diich may now be asked. In the uterus of the cat
killed in the mid period of gestation, I found, on peeling off
the placenta, that the serotina did not split into two layers,
the one a deciduous serotina attached to the placenta, the
other a non-deciduous serotina remaining connected to the
uterine wall, but that the whole thickness of the mucosa came
away with the placenta, leaving the muscular coat exposed ;
moreover, the uterine face of the placenta presented a smooth

^ Be Organis, &c., pp. 14, 18.

CAT. 79

surface similar in appearance to tliat exhibited by the organ
when shed at the full tiiiie ; and a similar separation also took
place in the process of injecting the vessels of the gravid
uterus.

From these specimens I was at one time inclined to think
that the entire thickness of the mucosa in the placental area of
the cat was shed along with the placenta duriug parturition.
As I knev/ however that this important point could only be
satisfactorily decided by an examination of a uterus imme-
diately pJter the birth of the placentee, I procured, through the
kindness of my friend Dr Foulis, the uterus of a cat which had
been killed five hours after having given birth to four kittens.
The uterus was contracted, and the mucous lining was elevated
into rugse. Each placentad area was a narrow zonular trench
bounded at each margin of the zone b}^ a fold of the mucosa.
The surface of the non-placental part of the mucosa was un-
broken and covered by epithelium. The surface of the pla-
cental zone v/as blood-stained, and with a number of shreds of
membrane hanging from it, so that it had a torn and flocculent
appearance. When thin flakes were removed from the surface
of the placental zone, and examined microscopically, they were
seen to consist of multitudes of free red blood-corpuscles, of
very delicate fibres of connective tissue, intermingled with
which were fusiform and lymph-like corpuscles, and here and
there a patch of cells, evidently epithelium. A series of vertical
sections was then made through the placental area and adja-
cent non-placental part of the mucosa, and examined with both
low and high ma.gnifying objectives. The free edge of the
section in the non-placental area was covered by a well defined
layer of columnar epithelium, deeper than which was a thick
layer of sub-epithelial connective tissue, intervening between
the epithelium and the muscular coat. Lying vertically in
this connective tissue were numerous utricular glands, which
opened on the free surface of the mucosa, and were lined by
columnar epithelium. In the placental area itself the surface
epithelium was absent, and the free edge of the section had not
a smooth outline, but was irregular and with slender filaments
of connective tissue projecting from it. The thickness of the
connective-tissue layer on the surface of the muscular coat was

80 ZONARY PLACENTA.

appreciably less (on the average about one-third) than in the
non-placental area. In this connective tissue sections through
utricular glands were seen. Some of these sections were trans-
verse to the tube of the gland, others oblique, others almost
longitudinal. The epithelial lining of the glands was present,
and it is not unlikely that the occasional patch of cells found on
the surface of the placental area may have belonged to the
glands and not to the surface epithelium. In more than one of
the sections I saw in the placental area gland-structures, which
had not the form of cylindrical tubes, but were somewhat
irregularly dilated. Numerous blood-vessels which were the
vascular trunks going to the placenta were also seen plugged
with collections of blood-corpuscles.

From this description it will be seen that in the normal
separation of the placenta at the time of parturition, so com-
plete a shedding of the mucosa in the placental zone did not
take place as was effected by artificially tearing off the placenta
in an earlier period of gestation. But from a comparison of the
placental and non-placental areas in this uterus, it is clear that
during parturition not only is the epithelium, but a portion of
the layer of sub-epithelial connective tissue, shed along with
the placenta as a deciduous serotina; whilst the deeper part of
the connective tissue, with tlie remains of the blood-vessels and
glands, persists as a covering for the muscular coat, and forms a
D on-deciduous serotina.

A few words may now be said on the non-placental part of
the chorion in the Cat. Many anatomists have pointed out
that in the Carnivora slender branches of the umbilical vessels
pass as far as the poles of the chorion ; but it has not suffi-
ciently been recognised that they form immediately beneath
its free surface a compact capillary plexus, which, though
not quite so close perhaps as in the smooth parts of the
chorion of the Cow and Sheep, is yet so abundantly pro-
vided with capillaries as to give to this part of the chorion,
when the vessels are injected, a distinct colour. This well-
marked vascularity of the smooth chorion is seen not only in
the membrane about the mid-period of gestation, but in speci-
mens shed at the normal period of parturition.

The outer surface of the smooth chorion of the cat pos-

BITCH. 81

sesses also another character worthy of notice. In specimens
about the mid-period of gestation, the membrane was mottled
with faint yellowish spots and lines, so as not to be perfectly
translucent. When examined with a pocket lens the outer
surface had a faintly corrugated appearance, as if slightly
roughened with some extraneous material, which could easily
be scraped off with a knife. When examined microscopically,
this substance was seen to consist of cells which varied con-
siderably in form. Some were flattened scales, others were
more elongated, or even columnar, others again w^ere rounded ;
and, in nearly ail, the nucleus was relatively large and very
distinct. The cells were probably produced by a proliferation
of the epithelial cells normally coating the free surface of the
chorion. The corresponding surface in the shed placenta of
the cat was free from corrugations, but had a clouded mottled
appearance, so as not to be uniformly translucent. Where the
faint opacities were present large collections of very fine
granules were visible, amidst which the outlines of nuclei and
cells could be indistinctly seen, so that the opacity seemed due
to collections of epithelial cells undergoing a minute granular
(fatty) degeneration.
B Bitch. — Though the placenta in the Bitch, as in the Cat,
possesses the zonary form, yet its minute structure in these two
animals presents sufficient differences to enable the anatomist
readily to distinguish the one from the other. If the description
and figures by Sharpey and Bischoff of the early stages of for-
mation in the Bitch be compared with the corresponding stages
in the Cat, a close resemblance is seen ; but in the more ad-
vanced stages characteristic differences can be recognised.

In the Bitch, both at half and full time, when the placenta
was stripped off the uterine zone, a distinct mucous membrane
was left on the uterus, which was continuous at the margins of
the zone with the narrow band of decidua refiexa and through it,
with the mucosa covering the non-placental area. This zonary
mucous membrane was subdivided into numerous irregular
polygonal pits or trenches, bounded by folds of the mucous
membrane. These folds had a ragged, flocculent appearance.
The membrane was very vascular, and at the ragged edges of
the fold numerous torn blood-vessels were seen. When ex-

82 ZONARY PLACENTA.

aminecl microscopically "the free surface not only of the pits and
trenches, but of the folds, Vvas seen to be covered by a layer of
cells^the epithelium of the mucous membrane — which rested
on the vascular sab-epithelial connective tissue. When this
epithelium was looked at from the surface, a pattern of poly-
gonal cells was seen like the free ends of columnar epithelium;
but the cells were bigger than one usually finds this form of
epithelium to be, and had, more especially in the uterus at full
time, a distinct yellow colour, as if the cells were undergoing
fatty degeneration. When the cells were scraped off, so as to
be seen in profile, their cokunnar form was easily recognised.
As this mucous membrane was not detached from the uterus
along vfith the placenta, it is to be regarded as a non-deciduous
serotina.

The uterine surface of the placenta also had a ragged ap-
pearance, for the numerous folds of the mucous membrane had
entered the placenta, and, when it was stripped off, their torn
ends were seen on its outer surface, but the flocculent appearance
was still further increased by the free ends of the chorionic
villi, which reached the surface. The prolongations of the
mucous folds entered the placenta at a multitude of points in
the interspaces between the villi, and as they ascended to the
chorion they branched repeatedly, so as to give investments to
the brandies of the villi of the chorion. These intra-placental
prolongations of the mucosa consisted of sub-epithelial con-
nective tissue, in which the maternal vessels ramified, and of an
epithelium composed partly of columnar cells, and partly of
cells the regular columnar form of which had been modified
into irregula,r polygons. These cells were larger and more dis-
tinct than the cells on the corresponding structures in the cat,
and their protoplasm was so very granular as in many cases to
obscure the nucleus. These prolongations of maternal tissue
constituted a deciduous serotina. The shed placenta of the
Bitch, whilst possessing in its substance numerous prolongations
of maternal tissue not unlike those previously described in the
Cat, yet differs from the latter animal, as has also been pointed
out by Prof. Rolleston^, in the absence of a continuous layer of
deciduous serotina on its uterine aspect.
- ^ Trans. Zool Soc. y. 18QB.

BITCH. 83

The chorionic villi in the bitch were not so sinuous and
leaf-like as in the cat. They were more subdivided, and
branched, so as to terminate in short villous tufts. Branches
of the umbilical arteries ended within the villi in a compact
capillary plexus. The villi were in close contact with the epi-
thelial cells investing the intra-placental prolongations of the
mucous membrane.

The non-placental areas of the chorion, as in the cat, con-
tained ramifications of the umbilical vessels ending in a capil-
lary plexus. The membrane was however uniformly trans-
lucent, and in none of my specimens did I see collections of
epithelial cells such as I have described in the cat.

I may now relate some observations which I have made on
the glands in the non-gravid uterine mucous membrane of the
Bitch. It is well known that two kinds of glands were described
by Dr SharpeyMn the uterine mucous membrane of this animal,
viz. short, simple, unbranched tubes, and compound tubes having
a long duct dividing into convoluted branches, both kinds open-
ing close together on the surface of the mucosa. These obser-
vations were supported by Weber and Bischoff, and generally
accepted by anatomists and physiologists ; but Prof. Ercolani
of Bologna, in his first memoir on the Structure of the Placenta^,
stated his inability to distinguish more than one kind of gland,
and concluded that only the long tubular glands were present.
I have felt it necessary therefore ca,refully to examine the
uterine mucous membrane of the unimpregnated bitch with
reference to this question. On a surface view the mouths of
the glands could be distinctly seen closely crowded together, as
is so well represented in Dr Sharpey's figure (fig. 209), and
in Bischoff's memoir (Entwicklimgsgeschichte cles Hunde-Eies,
Plate XIV. Fig. 47). When horizontal sections were made through
the membrane near its surface the glands were seen to be trans-
versely divided, and so closely set together that the interval
between any two adjacent glands was in some cases not equal
to, in other cases about equal to, the transverse diameter of a
gland-tube ; further, all the gland-tubes in any given transverse

1 Baly's Translation of MiUUr's Physiolorjy, Note, p. 1576.

2 Memoire sur Us Glandes Utriculaires de V Uterus, p. 22, French Transla-
tion, Algiers, 1869.

84 ZONARY PLACENTA.

section exhibited the same structural characters. The inter-
glandular connective tissue contained not only the usual fusi-
form corpuscles, but round cells like those of lymph or the
white blood-corpuscles. When vertical sections through the
membrane were examined, long compound tubular glands were
readily seen passing into the deeper part of the mucosa, and
between these, short and simple tubes were also recognised,
so that, under low magnifying powers, at first sight these
sections seemed to confirm the observations of Sharpey,
Bischoff and Weber, which were made under magnifying
powers of 10 and 12 diameters. When magnified more highly
these apparently short simple glands were seen to vary consider-
ably in length, some dipping for only a short distance from the
surface of the mucosa, others for a greater distance, and exhibit-
ing indeed every gradation in length up to the branched tubular
glands themselves. But in the connective tissue, immediately
deeper than the short glands, portions of tubes were seen
extending in line with the short tubes though apparently not
continuous with them, but often with careful focussing a con-
tinuity could be traced, though obscured by overlying connective
tissue. I am therefore of opinion that the utricular glands in
the bitch, as in so many other mammals, lie in the mucosa,
some almost vertically, others in various degrees of obliquity, so
that, when vertical sections are made, some are cut short across,
others longer, whilst others again may be seen in almost their
entire length. I conclude that all the glands belong to the
type of compound tubular glands, that the apparent differ-
ences in length are simply due to the mode in which the glands
are cut across in making the section, and that the physio-
logical division proposed by Bischoff into simple mucous crypts
and proper tubular glands cannot be supported. (PI. 1, fig. 6, 7.)
I have also examined the non-gravid uteri of the Badger
{Meles taxus) and Paradoxurus pallasii with the object of
seeing whether they did or did not correspond with the bitch in
the arrangement of the utricular glands. In the badger, when
vertical sections were made through the mucosa, an appearance
of short simple tubes and of long compound tubes was recog-
nised without difficulty, but on closer examination it was seen
that between the shortest and longest tubes every gradation of

FOX. 85

lensftli existed, so that I came to the same conclusion, as with
the bitch, that the short tubes were merely utricular glands cut
across in making the section. In Paradoxurus the glands had
a similar arrangement.

Focc. — From a dissection which I have made of the gravid
uterus of a Fox at about the mid-period of gestation, I have satis-
fied myself that it corresponds in many respects with the bitch,
though with specific differences. A layer of mucosa remained
on the uterus when the placenta was stripped off, and possessed
pits or trenches with intermediate ragged folds. The uterine
face of the placenta was flocculent, owing to the prolongations of
these folds into the substance of the placenta being torn across
in the process of separation. These prolongations entered the
placenta at a number of points, and passed with a sinuous
course up to the chorion, dividing in their course into numbers
of trabeculse, which formed a meshwork, in the meshes of
which the lateral offshoots of the villi were lodged. The
intra-placental laminae and trabecules were very vascular, and
their vessels, which were larger than ordinary capillaries, formed
an anastomosing network. Compared with the capillaries of
the foetal villi they were from twice to four times as big, so
that they may be spoken of as colossal capillaries, and undoubt-
edly represent the early stage of a dilatation into maternal
blood-sinuses, such as is still more clearly seen in the sloth,
and reaches its maximum development in the human placenta.
Owing to the subdivision of the maternal laminae, the tra-
beculse usually contained only a single colossal capillary; and as
many of these vessels ran vertically through the placenta, when
horizontal sections were made through the organ they were
seen in transverse section. In many cases these transversely
divided vessels were surrounded by little more than a ring
of cells — the epithelial investment of the trabecula of maternal
tissue in which the vessel lay — the sub-epithelial connective
tissue of the trabecula being so attenuated as to be scarcely
perceptible, and at times even not visible, so that the epithelial
cells rested upon a very delicate adventitia enveloping the wall
of the colossal capillary. The epithelial cells investing the
intra-placental laminae and trabeculse were remarkably large
and distinct, and on the average about |th or even |rd as large

86 ZONARY PLACENTxi.

as the corresponding cells in the bitch. The fox therefore, like
the bitch, has no continuous layer of modified mucosa, such as
is seen in the cat, on the uterine face of the separated placenta.

The villi of the chorion were broad laminse, deeply cleft,
so as to assume an arborescent arrangement, and gave off
both lateral and terminal offshoots in which a compact net-
work of capillaries ramified. (PL I. Figs. 4, 5.)

Seal. — I have studied the structure of the zonary placenta
of the Pinrtepedia in the Grey Seal, Haliclicerus giyphns, a
specimen of which, in the sixth month of gestation, 1 examined
in 1872\ (PL II. III. Figs. 11—16.)

In this animal the inner or foetal face of the placenta pos-
sessed a convoluted appearance, with intermediate depressions
or sulci, and the convolutions ran parallel to each other. When
a vertical section was made through the placenta and adjacent
part of the uterine wall, and the placenta gently drawn away
from the uterus, its uterine face was also seen to be convoluted,
with the convolutions and sulci in reverse order to those seen
on its chorionic aspect. A well-defined layer of mucous mem-
brane, which, from its position, represented the serotina, inter-
vened between the muscular coat of the uterus and the pla-
centa, and followed closely the windings of the convolutions,
dipping down into the primary fissures between the convolu-
tions in the form of broad laminee, just as the pia mater dips
between the convolutions of the cerebrum. Each convolution
was split up into elongated plates by secondary fissures, into
which processes of the mucosa, derived not only from the broad
laminse just referred to, but from that in contact with the
uterine face of the convolutions, penetrated. Each plate was
again subdivided by tertiary fissures into small pol3^gonal
lobules, into which more delicate processes of the mucosa
entered, and these could be traced through the thickness of
the placenta up to the chorion.

The mucosa could readily be peeled off the uterine face of
the placenta, as in the Dog and Fox, and when this was done the
laminae were dravN^n out of the primar}'- fissures, just as one can
draw the pia mater out of the cerebral sulci when the grey matter

1 Trans. Roy. Soc. Edinburgh, 1875.

SEAL. 87

on the surface of the cerebrum is exposed. The more delicate
processes, however, Avhich entered the secondary and tertiary
fissures were torn through in the act of peeling, and remained
in the substance of the placenta entangled between the foetal
villi. When these processes were seized with a pair of fine
forceps, and gentle traction employed, they could be withdrawn
without much difficulty from the substance of the placenta.
From the ease with which the processes lying in the secondary
and tertiary fissures tore across in the act of peeling off the
placenta, there could be little doubt that a simila,r disruption
occurs in the separation of the placenta during normal partu-
rition. This opinion was confirmed by an examination of the
placenta of a Phoca vitulina, shed at the full time, which is in
the Museum of the College. The part of the mucosa, there-
fore, which is shed along with the placenta^ consists of the
delicate easily torn processes which dip into the secondary and
tertiary fissures, and are entangled between the placental
lobules and amidst the foetal villi. The uterine face of the
separated placenta is not covered by a continuous layer of
decidua, for the greater part of the mucosa is not shed when
the placenta is expelled, but remains as a layer of membrane of
considerable thickness on the inner surface of the muscular
coat, and presents on its placental aspect numerous irregular
pits or trenches into which the convolutions of the placenta
are received when the organ is in situ.

Before describing the minute structure of the serotina,
I shall relate some observations on the structure of the mucosa
in the non-gravid uteri of some sea,ls, which I have had the
opportunity of examining, and also the structure of the uterine
mucosa in the gravid uterus of H. gryphus, both in the non-
gravid horn and in the non-placental area of the gravid horn.

In the non-impregnated uterus of a young seal (species
unknov^'n) elongated, tubular, utricular glands were very nu-
merous, and closely packed together in the mucosa. The
glands lay perpendicular to the plane of the surface, were
tortuous, and apparently branched at their deeper ends ; by
their opposite extremities they opened by funnel-shaped
mouths on the free surface of the mucosa. They were lined
by a columnar epithelium, and possessed a central lumen. The

58 ZONARY PLACENTA.

interglandular connective tissue contained multitudes of cor-
puscles.

In the uterus of an adult non-gravid Grey Seal the mucous
membrane formed strong folds extending in the longitudinal
direction. By its deep surface this membrane was connected
to the muscular coat by a lax connective tissue. Vertical sec-
tions through the mucosa, examined microscopically, displayed
numerous tubular glands, which opened freely on the surface.
Their main stems lay almost perpendicular to the plane of the
surface, but as the glands were somewhat tortuous, and gave
off lateral offshoots, they were not unfrequently transversely
or obliquely divided. The epithelium did not fill up the gland-
tubes, but left a central lumen. The exact form of the epithe-
lium cells could not definitely be made out, but the end which
lay next the lumen was rounded, or somewhat polygonal, like
the broad free end of a columnar epithelium cell. The inter-
glandular connective tissue was vascular, and a well-marked
capillary plexus ramified immediately beneath the surface of
the mucosa around the mouths of the glands.

In the uterus of a Cy.stophora cristata, which died about
three and a half months after the birth of a cub, I was able to
confirm the observations previously made on the uterus of
H. gryphus. On the free surface of the mucosa was a layer of
columnar epithelium, the cells of which were large and well-
formed. The mouths of the utricular glands were seen without
difficulty opening on the summits and sides of the longitudinal
folds of the mucous membrane ; their orifices were circular,
closely set together, and each Avas surrounded by a capillary
vascular ring. The free surface of the mucosa was thus studded
with multitudes of minute orifices — the mouths of the glands.
The glands were comparatively short both in H. gryphus and
G. cristata, and the capillaries of the mucosa formed a closely-
set network around them.

The free surface of the non-gravid horn of the pregnant
uterus of H. gryphus possessed no longitudinal folds of its
mucous membrane such as were observed in the non-gravid
uteri of H. gryphus and C. cristata. The surface of its mucosa
was to the naked eye almost perfectly smooth, but when
examined with a simple lens, slight irregularities were seen,

SEAL. 89

partly due to the presence of minute ridges with intervening
depressions, and partly owing to a granulated condition of the
membrane. When examined with higher powers of the micro-
scope the tubular utricular glands were readily seen. They
were more elongated, and less tortuous than in the unimpreg-
nated uterus ; the branches at their deeper ends were much more
distinctly seen, and they were much less closely crow^ded toge-
ther, owing to the increase in the amount of the interglandular
connective tissue. The glandular epithelium was abundant,
the cells being elongated, though I could not satisfactorily
determine that they possessed a precise columnar form. The
granulated appearance of the mucosa seemed to some extent
due to the presence of these glands in the membrane.

The free surface of the mucous membrane of the non-
placeutal area of the gravid horn of the same uterus was
smooth in appearance, both to the naked eye and under a
simple lens. With higher powers the tubular utricidar glands
were also seen wdthout difficulty, but they were more elongated,
so slightly tortuous as in many instances to be almost straight,
and separated by greater intervals, occupied by the interglan-
dular connective tissue, than in the non-gravid horn. In some
of the glands the columnar form of the cells was distinctly
recognised, and the almost circular form of the gland-orifice on
the free surface of the mucosa was in many preparations readily
seen. The mucous membrane of the septum between the two
horns was smooth on the aspect directed both to the gravid
and non-gravid horn. The appearance and form of the glands,
and the proportion of interglandular connective tissue, was
almost alike on both aspects.

From a comparison of the mucosa of the gravid with the
non-gravid horn of the pregnant uterus, and of these with the
unimpregnated uteri in these seals, it is evident that the
changes which take place in the mucous membrane, in connec-
tion with the great distension of the uterus during pregnancy,
consist in an obliteration of the strong longitudinal folds of the
mucosa ; in a large increase in the absolute and relative amount
of the interglandular part of the mucous membrane ; in an
elongation of the tubular glands, which elongation is in great
part due to an untwisting of the gland^s, so that they become
T. 7

90 ZONARY PLACENTA.

much less tortuous, though from the very considerable length
which some of these glands possessed, it is possible that they
and their branches may have actually grown in length. The
similarity in the appearance of the septal mucous membrane on
its two aspects was evidently due to the growth of this parti-
tion being equal for the non-gravid as for the gravid horn.

A broad band of mucous membrane reflected on to the
border of the placenta (decidiia reflexa) was smooth on its free
surface, like the adjacent part of the uterine mucosa with which
it was continuous. When peeled off the placenta, and placed
under the microscope, utricular glands were seen in it, which
in form and relative numbers closely corresponded with the
arrangement just described in the mucosa of the non-placental
area of the gravid horn. Many of the glands, however, dis-
played an appearance such as I had not previously observed ;
for their lumen, instead of being empty, was occupied by a
bright yellow material, which probably was the secretion con-
fined within the lumen through some obstruction near the
mouth of the gland preventing its excretion.

I then proceeded to examine the structure of the mucosa in
the placental area. In the non-deciduous serotina, i.e. in the
layer of mucous membrane left on the wall of the uterus after
the placenta was peeled off, utricular glands were seen, but
they were much more sparingly distributed even than in the
mucosa of the non-placental area of the gravid horn. In
various of these glands an appearance was observed, indica-
tions of which had also been seen in some of the glands both
in the mucosa of the non-placental area and in the reflexa, of
a breaking up within the gland-tubes of the epithelium into
scattered masses, separated by intermediate irregular in-
tervals.

On that surface of the non-deciduous mucosa, which was
exposed by peeling off the placenta, irregular scattered patches
of cells were seen when examined with a magnifying power of
300 diameters, which were obviously portions of the originally
continuous epithelial layer of the mucosa, that had become
broken up into patches by the removal of some of the cells in
the act of peeling off the placenta. It was observed that the
cells remained in position on those parts of the mucosa im-

SFAL. iU

mediately superficial to its larger blood-vessels, whilst tliey
were frequently absent from the surface of the membrane
situated between these vascular trunks. The cells in a patch
were in close contact with each other. They were short
columnar cells ; their free ends being either circular, or ovoid.,
or polygonal, and in many cases having the diameter of a
white blood-corpuscle, though others were somewhat larger.

Both the non-deciduous serotina and the decidua reflexa
were much more vascular than the mucosa of the non-placental
area of the uterus. The increased vascularity was due to the
blood-vessels being larger, and apparently more numerous in a
given area. In all these localities vessels of capillary size were
present, but the veins and arteries of the serotina and reflexa
w^ere considerably larger than those of the non-placental mucosa.
This increase in size was not due to the formation of varicosi-
ties on limited portions of their walls, but to a general expan-
sion of the vascular tube. No curling or cork-screw-like arteries
were seen, and the veins presented no unusual tortuosity. The
sub-epithelial connective tissue contained multitudes of well-
marked connective-tissue corpuscles.

The broad laminae of mucosa which dipped into the primar}^
fissures betw^een the convolutions of the placenta had an inter-
rupted layer of epithelial cells on their free surface, similar in
shape but somewdiat bigger than those of the non-deciduous
mucosa just described. The arrangement and relative size of
the blood-vessels were also the same, and utricular glands were
present, though sparingly distributed in the sub- epithelial con-
nective tissue.

The structure of the delicate bands of deciduous mucosa
which passed into the secondary and tertiary fissures in the
substance of the convolutions was then examined. The free
surface of these bands was covered by an epithelial layer, the
cells of which were columnar like those of the non-deciduous
mucosa ; but their contents were more opaque and yellow,
as if in process of fatty degeneration. Flake-like layers of
cells were not unfrequently seen lying loose in the fluid in
which these specimens were examined, as if they had become
detached from the free surface of the decidua. In one or two
instances rows of cells, as if the cellular contents of utricular

7—2

92 ZONARY PLACENTA.

glands, were observed, but no glands were seen in these deli-
cate processes. The bands of decidua, lying in the secondary
and tertiary fissures, consisted of a delicate membranous con-
nective tissue, into which the blood-vessels of the non-deciduous
mucosa were prolonged. These decidual bands dipped between
the lobules of the placenta, almost up to the chorion, and the
maternal vessels branched and formed in them a capillary net-
work. From these bands slender processes passed into the
interior of the placental lobules, where they formed a lattice-
like arrangement of very slender trabeculae, winding in a sinuous
manner through the lobule. These trabecles could be pulled
out of a lobule with a pair of fine forceps, and in many speci-
mens the bud-like processes of the chorionic villi, lodged in the
interstices between the trabecles, were drawn out along with
them. Each trabecle was formed of a capillary blood-vessel,
surrounded by a thin layer of connective tissue, which again
was invested by a layer of columnar epithelial cells similar to
those already described on the free surface of the bands of deci-
dua. These cells were very easily detached from the surface
of the trabecular, and quantities of loose cells floated about the
fluid in which the specimens were examined. The deep at-
tached end of a cell was often attenuated into a fine process.
The trabecles were, therefore, delicate bands of the uterine
mucosa., and were composed of its several constituents minus
the utricular glands.

When the uterine face of the placenta, from which the non-
deciduous mucosa had been peeled off, was examined, a greyish
membrane was seen, which lay in contact with the uterine face
of the placental lobules. It was not, however, prolonged from
the uterine surface of one lobule to the corresponding surface
of the adjacent lobules, so as to form a continuous layer over
the whole uterine surface of the placenta, but was continued
for some distance down the side of each lobule into the sub-
stance of the placenta, so as to form an investment for the
individual lobules. Hence the uterine face of the placenta was
broken up into polygonal areas, each of which corresponded to
a placental lobule, and the areas were separated from each
other by bands of the uterine mucosa, which dipped into the
secondary and tertiary fissures of the placenta. The greyish

SEAL. 93

membrane belonged to the foetal and not to the maternal part
of the placenta ; for whilst the mucosa readily peeled off from
the one surface of the grey membrane, the other surface was
continuous with the tissue of the villi, and could not be sepa-
rated without tearing through small blood-vessels and con-
nective tissue which passed from the villi into it.

The greyish membrane was composed of connective tissue,
the corpuscles of which were ovoid and fusiform, relatively
large in size and granular. Eamifying in the membrane were
small blood-vessels continuous with those of the chorionic villi,
which had been torn through when the grey membrane was
stripped off. On that surface of the greyish membrane which
lay next the non-deciduous mucosa, patches of epithelial cells
similar to those previously described on the free surface of the
mucosa were seen. I believe that these cells, though adhering
to the membrane, did not properly belong to it, but to the
mucosa, from which they had separated in peeling off the pla-
centa ; and in this manner one may explain why the epithelial
covering of the mucosa seemed to form an interrupted and not
a continuous layer.

Numerous vertical sections were now made through the
entire thickness of the placental lobes, and examined with the
view of determining the arrangement and structure of the villi
of the chorion, their more exact connection with the greyish
membrane, and their relations to the intra-lobular parts of the
mucosa. The stems of numerous large villi arose at frequent
intervals from the placental surface of the chorion, and passed
through the placental lobules almost perpendicular to the plane
of the chorion, and branched in a highly arborescent manner.
From the sides of the stems of the villi, from the sides of their
branches, and from the extremities of the greater number of
these branches, much smaller branched villous processes arose
which gave origin to multitudes of villous tufts. Some of the
larger branches from the parent stem had, however, a different
mode of termination : they reached the periphery of the lobule
and blended with the greyish membrane, which was obviously
formed by the junction with each other of the ends of those
branches of the villi which reached the periphery of the lobule ;
and by their union a continuous layer of foetal tissue was

5)4 Z(3NA11Y PLACENTA.

fonned, not only on tlie uterine siuface of each lobule, but
reaching for some distance down its sides. From the placental
surface of the chorion, in the intervals between the origins of
the stems of the large arborescent villi, numbers of short
branching villi arose, which soon subdivided into terminal
branching tufts. The terminal branching tufts were, as a rule,
slender elongated structures, but some were shorter and more
club-shaped.

The matrix substance of the villi consisted of a delicate
connective tissue containing multitudes of distinct corpuscles.
Where this tissue formed the terminal tufts the corpuscles
were very numerous, and appeared in some cases not only
imbedded in the substance of the tuft, but as if arranged, after
the manner of an epithelium, on the free surface. In some of
my prejDarations the more superficial cells were detached, and
were seen to have the form of delicate scales of nucleated pro-
toplasm. The larger blood-vessels lay in the stems of the villi
and branched in an arborescent manner, ending in a capillary
plexus in the terminal villous tufts. In some of the larger
branches of the villi, a vessel ran parallel and close to the
surface of the villus, which communicated with the capillaries
of the tufts arising directly from the sides of the branches.

The intra-lobular prolongations of the maternal mucosa did
not pass uninterruptedly into the lobules, for the greyish mem-
brane situated on their uterine surface, and on the adjacent
part of the sides of the lobule, prevented a direct entrance.
The intra-lobular decidua was, therefore, derived from those
processes of the mucosa which dipped into the secondary and
tertiary fissures. These processes, in the form of slender bands
and laminae, penetrated up to the chorion, and then branched
off laterally into the lobules, when they at once broke up into
the reticulated lattice-like arrangement of sinuous trabecule
already described. In sections made through the lobules,
where no displacement of the relative position of the foetal
and maternal structures had taken place, the meshes of the
reticulum were seen to be occupied by the villous tufts, and
not unfrequently the tufts were surrounded by a ring-like
arrangement of trabecles. In this manner, throughout the
entire lobule, the maternal and fo2tal parts of the jolaccnta

HYRAX. 95

were . so closely intertwined that the two systems of blood-
vessels were brought into close juxtaposition with each other :
the structures which intervened being, on the maternal side,
the epithelial investment of the trabeculse, and on the foetal,
the flattened scale-like superficial cells of the villi.

From the mode in which the placental lobules were walled
in on the uterine aspect by the greyish membrane of foetal
tissue, from the processes of decidua having to penetrate up to
the chorion before their capillaries entered the lobules, and
from the recurrent course which so large a proportion of the
intra-lobular trabeculse had to take in order to reach the villi
situated nearest to the greyish membrane ; the maternal blood-
vascular system penetrated throughout the entire lobule, and
was brought into relation with the numerous offshoots of the
villi. In the separation of the placenta during parturition
a quantity of maternal vascular tissue comes away therefore
with the placenta.

The seal, in the reticulated arrangement of those portions
of its mucosa which are in direct contact with the terminal
villi, presents a general correspondence with the fox, but the
subdivision of the mucosa is more complete, and the cells of
the epithelial investment are not so big as in the fox.

Hyrax. — The zonary form of the placenta in Hyrax capen-
sis was pointed out many years ago by Sir Everard Home ^ and
the presence of the sac of the allantois equal in length to the
chorion was figured though not described by him. Although
the structure of its placenta has since been examined by several
anatomists, there is by no means an agreement on the exact
relations of its foetal and maternal portions. Prof. Owen refers,
in his description of the placenta of the Elephant, to the pla-
centa of Hyrax as similar in spongy texture and vascularity to
the annular placenta of the Carnivora, and subsequently states^
that the villi are imbedded in a decidual substance, and the
surface of attachment to the uterus is less limited than in the
Elephant. Prof Huxley is convinced from his investigations^

^ Lectures on Comparative Anatomrj, v. 325, and vi. PI. 61, 62. 1828.
^ Comparative Anatomy of Vertebrates, iii. 742.

^ Elements of Comparative Anatomy, 1864, p. 111. Manual of the Anatomy
of Vertehrated Animals, 1871, p. 434.

96 ZONARY PLACENTA.

that the placenta in Hyrax has such an interblending of the
foetal and maternal portions that it is as truly deciduate as that
of a Rodent. The maternal vessels, he says, pass straight
through the thickness of the placenta towards its foetal surface,
on which they anastomose, forming meshes, through which the
vessels of the foetus pass towards the uterine surface of the
mother. The allantois spreads over the interior of the chorion
and gives rise to the broad zone-like placenta. The amnion is
not vascular. In the foetus the yelk-sac and the vitello-intes-
tinal duct early disappear. On the other hand, M. H. Milne-
Edwards describes^ the placenta as only adhering very feebly
to the walls of the uterus. Its villi, he says, are mostly simple,
very analogous to those of an ordinary pachyderm. In the
midst of the zone there are vascular vegetations engaged in cor-
responding uterine cavities, but they adhere no more, than do
the analogous prolongations in the Ruminant, to the crypts in
which they are included : they can be detached with the same
facility without tearing through anything and without carrying
away any portion of uterine tissue. There is nothing, he con-
cludes, to indicate the presence of a caduca, and the allantois
does not overstep the limits of the placental zone. In an
elaborate monograph on the genus Hyrax published a few
months ago ^ M. George figures not only the placenta but the
gravid uterus of this animal. He says nothing however of the
structure, which he was apparently precluded from examining,
but adopts the view of M. Milne-Edwards that it was non-
deciduate.

Owing to the great discrepancy, not only as regards the
structural details, but the conclusions as to the nature of the
placentation, it was obviously advisable that the placenta of
the animal should be re-examined, and with great liberality Prof.
Huxley has placed at my disposal his specimen, which had
been preserved in spirit. I shall now describe what I have
seen^

The uterus was two-horned. In one cornu were two well-
developed ova, each about 3^ inches long. One ovum had

^ Considerations sur la Classification des Mammiferes, Paris, 1868.

' Annates des Sciences Naturelles, June, 1875.

^ See also Proc. Roy. Soc. London, Dec. 16th, 1875.

HYRAX. 97

been opened, the membranes and placenta examined and the
foetus removed. The other ovum was entire. The placenta
was zonary and varied in different parts of the zone from
between :J to | inch in breadth, whilst the average thickness
was jig- inch. The non-placental areas of the chorion were
smooth and translucent, and, as in the Carnivora, branches of
the umbilical vessels ramified in them. The zone on the
chorion was intimately united to a corresponding zone in the
uterine mucosa. When the placenta was stripped off the
uterus, not only was the mucosa in the placental zone removed
along with the chorion, but, for some distance on each side
of the zone, the mucosa tore away from the muscular coat
of the uterus.

The foetal surface of the placenta was smooth, and on it the
umbilical vessels ramified before entering the villi of the
chorion : some injection was passed into them, but it did not
flow into their intra- villous branches. The uterine surface
of the artificially separated placenta was flocculent, and the
flocculi were seen on microscopic examination to consist of
bundles of connective tissue intermingled with corpuscles —
obviously the sub-mucous connective tissue of the placental
zone.

A toughish membrane, continuous on each side with the
mucosa of the non-placental area of the uterus, could without
difficulty be peeled off the uterine surface of the placenta as a
well-defined layer. When examined microscopically, the sur-
face of this membrane which lay next the uterus was seen to
have the structure of the flocculi which projected from it ; whilst
the part next the placenta was much more abundantly cellular,
and stained readily with carmine. The surface which had been
in apposition with the placenta, was irregularly undulating, and
divided into numerous shallow crypt-like recesses, separated from
each other by raised folds of the membrane. These crypts were
lined by a layer of cells, the nuclei of which were very distinct.
I regard this membrane as the serotina, or modified uterine
mucosa in the placental zone, whilst the crypts with their
epithelial lining are the closed ends of the deep pits in which
the villi of the chorion are lodged.

The substance of the placenta was then examined with the

98 ZONARY PLACENTA.

object of determining not only the form of the foetal villi, but
if prolongations of the maternal mucosa passed into the pla-
centa between the villi. In vertical sections the villi appeared
as if simple filamentous structures, extending from the chorion
to the crypt-like recesses in the serotina. But when portions
of the placenta were teased out with needles, and the villi not
iijjured, although an occasional simple villus was seen, the
majority were broad, sinuous, leaf-like villi, with bud-like
offshoots at the free borders, such as I have described and
figured in the cat (PI. I. fig. 3). In horizontal sections
through the placenta, the sinuous outline of the villi had so
close a resemblance to the cat, that it was difficult in this par-
ticular to distinguish Hyrax from Felis. Under a magnifying
'power of 820 diameters, a layer of flattened cells, the nuclei in
which were almost circular and bright with transmitted light,
was seen at the surface of the villus. Intermingled with the
foetal villi were laminar prolongations of the maternal mucosa,
which invested and closely followed the sinuous outline of the
villi, similar to the arrangement described in the domestic cat
(p. 76 and fig. 2). This intra-placental maternal tissue was pre-
sent not only in those sections in which the serotina was in situ,
but in others from which this membrane had been peeled off.
The maternal laminae were covered by a layer of cells, obviously
continuous with the cellular lining of the crypt-like recesses on
the free surface of the serotina, and the laminae themselves
were prolongations into the placenta of the folds of the mucosa
which separated the crypts from each other.

As the placenta of Hyrax, in both the form of its villi and
the mode in which they are interlocked between the intra-
placental maternal laminae, so closely resembles the domestic
cat, and as these laminae remain in situ, after the membrane,
which I have named the serotina, is peeled off" the placenta,
there can be no doubt that they are shed at the time of sepa-
ration of the placenta. Hence Hyrax in its placentation is one
of the Deciduata. Whether the membrane just referred to is
also shed during parturition is more difficult to say. The fact
that it peels off' the uterus along with the placenta, when they
are artificially separated, is not of itself sufficient evidence, and
it may be that in Hyrax, as in the Cat, the superficial portion

HYRAX. 99

only of this membrane falls off with the placenta, whilst the
rest remains on the zone of the uterus. The question, how-
ever, can only be decided by the examination of a uterus
immediately after parturition.

The non-placental area of the mucosa contained tubular
glands, which relatively to the extent of the membrane, were
not nearly so numerous as in the gravid mucosa of animals
having a diffused or polj^cotyledonary placenta. The glands
were long, and the gland-stem was unbranched and almost
straight : the closed end was dilated, bent on itself, and seemed
to give off a short branch. The secreting epithelium did not
fill up the tube, but left a central lumen.

When the chorion was cut through on either side of the
placental zone, the sac of the allantois was opened into and
seen to extend up to the poles of the chorion. At and close
to the margin of the placenta the allantois was reflected on to
the outer surface of the amnion, to which it obviously gave a
complete investment, so that the bag of the amnion was sus-
pended in the sac of the allantois by the bands of the latter
membrane reflected on to its outer surface. The amnion was
large relatively to the sac of the allantois. The umbilical
cord was short and somewhat' flattened.

Numerous flattened plates, the largest of which were about
Y^fth inch in diameter, projected from the inner surface of the
amnion. They were situated, not only in the neighbourhood
of the umbilical cord, but scattered as far as the poles. Some
were sessile, others were slightly pedunculated, and as they
were all covered by the epithelial lining of the amnion, they
were apparently developed between it and the layer of allan-
tois which covered its outer surface. The plates were obviously
composed of cells, the nuclei of which were distinct, but the
toughness of the tissue, due probably to the prolonged action of
the spirit in Avhich the specimen had been preserved, rendered
it difficult to isolate them. In position and structure these
plates apparently corresponded to the amniotic corpuscles
which I have described (p. 23) in Orca gladiator.

The mucous membrane of the non-gravid uterine cornu
was greatly hypertrophied in sympathy with the changes in
the sjravid horn. There was no extension of the fcetal mem-

100 ZONAE Y PLACENTA.

branes into this cornii, and the cavity seemed as if ahuost
obliterated by the thickening of the raucous membrane. Hyrax
agrees, therefore, with Felis not only in the form and structure
of the placenta, but in the large size of the sac of the allantois;
it differs in the condition of the umbilical vesicle, which disap-
pears in Hyrax apparently at an early period, but remains in
Felis to the end of utero-gestation.

Elephant. — No observations have been recorded on the
structure of the uterine mucosa in the gravid Elephant, but
Prof Owen has described and figured^ the foetal membranes
at about the mid-period of utero-gestation. The chorion was
encompassed at its middle by an annular placenta, 2 ft. 6 in. in
circumference, varying from 3 to 5 in. in breadth, and from
1 to 2 in. in thickness :

" The placenta presents the same spongy texture and vascularity
as does the annular placenta of the Hyrax and of the Carmvora; but
the capillary filaments or villosities enclosing the foetal vessels enter
into its formation in a larger proportion, and are of a relatively
coarser character. The greater part of the outer convex surface of
the placenta is smooth : the rough surface, which had been torn from
the maternal or uterine placenta, exposed the foetal capillaries,
and occupied chiefly a narrow tract near the middle line of the
outer sui'face. A thin brown deciduous layer is continued from the
borders of the placenta, for a distance varying from one to three
inches, upon the outer surface of the chorion. In addition, at each
of the poles of the chorion was a villous and vascular subcircular
patch, between two and three inches in diameter, the villi being short,
■g^th of a line in diameter, or less.

" The bag formed by the mucous or unvascular layer of the allan-
tois is of considerable size, is continued from the base of the umbilical
cord, so expanding between the chorion and amnios as to prevent any
part of the amnios attaining the inner surface of the placenta. The
allantois divides, where the amnios begins to be reflected upon it, into
three sacculi ; one extends over the inner surface of the annular
jolacenta and a little way into one end of the choiion: a second
extends into the opposite end of the chorion, it thei'e bends round
toward the placenta, and its apex adheres at that part to the first
division of the allantois : the third prolongation subdivides into two
smaller cavities, each terminating in a cul-de-sac, encompassing, and
closely attached to the primary divisions of the umbilical vessels."

This specimen is preserved in the Museum of your College,
and through the courtesy of Professor Flower I have been

^ Phil. Trans. 1857, p. 347, and Com}). Anat. of Vert. in. 7-10.

ELEPHANT. 101

permitted to obtain a slice of the zone for microscopic exami-
nation. The size and thickness of the zone prove it to be the
functionally active part of the placenta, for the villous patcli at
each pole is so small as to be of little physiological importance.
Notwithstanding the number of years the placenta had been
in spirit, I succeeded in passing some injection into the
vessels of the chorion and the larger trunks in the stems of
the villi, so that I could follow the villi more precisely into
the substance of the placenta than I should otherwise have
been able to do. The placenta was very compact and was
clearly composed both of a foetal and a maternal portion closely
interlaced with each other. Many of the villi were of large
size and passed through the entire thickness of the organ,
branching repeatedly in an arborescent manner. Others again
were of smaller size, and did not pass more than one-third
through the organ, but, like the longer villi, branched repeat-
edly. The tissue of the villi was delicately fibrillated, and in it
ran the branches of the umbilical vessels.

Interlocked between the villi was a tissue, which contained
a very distinct network of minute tubes, obviously capillary
blood-vessels, and on the surface of this tissue a layer of cells
was seen with some difficulty. I succeeded more than once in
isolating a few of these cells, and found them to be rounded or
ovoid, with definite nuclei and with granulated protoplasm. I
believe these cells to be the epithelial covering of the laminae of
maternal mucosa, forming the walls of the highly-developed
crypts in which the villi were lodged, whilst the capillary net-
work subjacent to these cells belonged to the intra-placental
maternal vascular system. Several times I saw an appearance
as if the intra-placental mucosa was split up into a reticulated
arrangement of trabeculge, similar to what I have described in
the seal, but from the condition of the specimen it was difficult
to speak positively on this point. There could be no doubt
however that in this separated placenta of the elephant a large
amount of uterine mucosa was inextricably locked in between
the foetal villi.

102 GENERAL MORPHOLOGY

General Morphology of the Diffused, the Polycoty-
ledonary, and the zonary placenta.

I shall now proceed to make some general observations on
the Morphology of the Placenta. In the study of the mor-
phology of the placenta in any mammal the presence of two
parts, a foetal and a maternal, originally quite distinct and
separable from each other, must be clearly kept in view.

The morphology of the foetal part presents no difficulty. It
consists simply of a vascular villous membrane covered by an
epithelium. The sub-epithelial part of the membrane is com-
posed of a delicate connective tissue, containing numerous
corpuscles, in which the terminal branches of the umbilical
vessels, with their capillary network, are distributed. The
vascular villi may be either simple or branched, and in some of
the mammals, whose placentation has just been described, e.g.
the seal, the branching may assume a highly arborescent
arrangement.

The morphology of the maternal part of the placenta pre-
sents greater difficulty, not only because the uterine mucous
membrane, out of which it is produced, is more complex in
structure than the chorion, but because this membrane be-
comes greatly modified in the course of placental development,
and not unfrequently becomes so interlocked between the
foetal villi as to be separated from them with great difficulty.

In all the forms of placenta which have just been described,
alonsf with the OTOwth of the villi from the surface of the
chorion, depressions or Crypts arise in the uterine mucosa for
their reception, and the walls of these crypts are formed by
foldings of the hypertrophied mucosa.

In the Diffused placenta the changes in the uterine mucosa
are less complicated than in the other forms. The villi of the
chorion are short, and branch but slightly. The crypts in the
uterine mucosa are consequently shallow, so that the relations
of the foetal and maternal parts can be easily seen. Two free

OF THE PLACENTA. 103

surfaces are in close apposition, the villi of the chorion fit into'
the crypts of the mucosa, but they can be drawn asunder
without difficulty, as the hand is drawn out of a glove ; so that
the compound nature of the placenta can be at once demon-
strated.

In the Polycotyledonary placenta the villi are longer and
more branched. The pits or crypts for their reception are
consequently deeper and divided into smaller compartments,
and the maternal mucosa in the site of the cotyledons is more
hypertrophied, thicker, and more spongy. Two free surfaces are
here also in apposition ; but the length and branching of the
villi, and the depth and subdivision of the crypts, render it
somewhat more difficult to draw the two surfaces asunder than
in the diffused placenta.

In the Zonary placenta as seen in the Carnivora, Pinnepedia
and Eleplias, the villi are long and usually arborescent, though
in the Cat and Hyrax they are leaf-like and very sinuous. The
foldings of the uterine mucosa, which have led to the production
of the crypts, are more complicated, so much so indeed in the
Fox and Seal, as to give rise to a remarkable subdivision of the
membrane into a microscopic network. The two surfaces in
apposition have become so interlocked that it is almost im-
possible to disengage them from each other. Hence in the
process of parturition more or less of the uterine mucosa in
the placental area is separated and shed in the substance of the
placenta.

The morphological elements in the gravid mucosa of all
mammals, are, as in the non-gravid membrane, epithelium,
sub-epithelial connective tissue, blood- and Ijanph-vessels, glands
and nerves. Of the arrangement of the lymph-vessels and
nerves in the placenta we have no precise information. The
epithelium, the sub-epithelial connective tissue, and the blood-
vessels form the walls of the crypts in which the villi are lodged.
The glands have no necessary relation to the crypts. In the
Pig, as has been shown by Eschricht, myself, and Ercolani ; in
the Mare, as has been pointed out by Ercolani and myself ; in
the Porpoise, as has been described by Eschricht ; in the Nar-
whal, as I have occasionally seen ; in the Lemurs, as I have also
describeil, — the mouths of the glands can be distinctly seen

10 i GENERAL MORPHOLOGY

opening on tlie surface of the mucosa, in smooth areas sur-
rounded by and quite distinct from the crypts. In Orca
gladiator, though at first sight the funnel-shaped crypts seemed
to he the dila.ted mouths of glands, further consideration
has satisfied me that neither they nor the cup-shaped crj'pts
are derived from the glands. In the Euminantia, Eschricht,
Bischoff, Ercolani and I have been unable to see any com-
munication between the glands and the pit-like crypts of the
cotyledons. In the Carnivora, though, as was interpreted by
Sharpey, "Weber, and Bischofif, the crypts seen in the placental
area in the early stage of gestation may seem to be merely
the moutlis. of the glands enlarged and widened, yet a more
minute analysis of the structure shows that, though some of
the glands may, as in Orca, open into crypts, the crypts
are much more numerous than the glands, and are conse-
quently not derived from them. In the Pinnepedia, Hyrax
and the Elephant, there is also no reason to believe that
the crypts are formed by a widening of the glands. Hence
in all these, and I believe in other placental mammals, the
crypts are not modified glands, but are intei'-glandular in posi-
tion. The crypts do not exist in the non-gravid uterus, but,
as was first definitely shown by Prof. Ercolani, from the exami-
nation of the placenta, in several orders of mammals, are formed
during pregnancy by foldings of the mucous membrane.

The crypts are lined by an epithelium, which is derived
by descent from, and lies in the same morphological plane as,
the epithelial lining of the uterus : the increase in the number
of epithelial cells, required by the much greater magnitude of
the mucous surface, being effected by proliferation of the pre-
existing epithelial cells. In many mammals the cells lining
the crypts have the columnar form, like the epithelium of the
non-gravid mucosa, and in the pig the cells are apparently
ciliated : but in some mammals the columnar form is not pre-
served, and the cells are rounded, or polygonal, and with granu-
lated protoplasm. These cells form the cells of the decidua
serotina, and they are homologous with the rounded, or poly-
gonal, colossal, granulated cells of the decidua serotina in the
human placenta.

The connective tissue in the walls of the crypts is derived

OF THE PLACE.NTA. 10.)

from the sub-epithelial connective tissue of the non-gravid
mucosa, through a rapid increase in the number of its cor-
puscles, though it is possible that there may also be a migra-
tion of white blood-corjjuscles into it. The blood-vessels in the
walls are continuous with the vessels of the mucosa, and are
greatly increased in numbers. In the diffused and polycotyle-
donary forms of the placenta they are arranged as a capillary
network, but in the zonary placenta they exhibit a tendency
to dilate into colossal capillaries, which are the first indications
of a maternal intra-placental blood-vascular sinus system, such
as attains much greater development in the Sloth, and acquires
its maximum size in the Quadrumana, and the Human Female.
The vascular connective tissue forming the walls of the crypts
constitutes the vascular part of the Decidua Serotiua, by which
term is signified the maternal mucous membrane situated
between the foetal placenta and the muscular wall of the
uterus ; or, in other words, the maternal part of the placenta.
In the diffused form of placenta the Serotina consists of the
whole of the mucous surface in which the crypts are met with.
In the polycotyledonary it forms the maternal cotyledons. In
the zonary placenta it consists of the annular band of mucosa,
with the intra-placental laminse and trabeculas.

As is well kuowai, the form of the placenta, the arrangement
of the foetal membranes, and the behaviour of the uterine
mucosa at the time of parturition, have been taken by many
zoologists as affording a basis of Classification of the placental
mammals.

Fabricius was well aware* that the placenta varied much
in shape, size and position, in different mammals, and that a
particular form of placenta was also associated with certain
other anatomical characters. Thus, he says, the single pla-
centa, found in the human female, the mouse, rabbit, guinea
pig, dog and cat, is associated with the presence of incisor
teeth in both jaws and with distinct toes. In some of these
L mammals, as the human female, rabbit, hare, mole, mouse and
[guinea pig, the single placenta resembles a cake (whence indeed
its name placenta) ; in others, as the dog, cat and ferret, the

I De Fonnato Fcstit. Folio ed. 162-1. Part 1, Caput in. p. 4.
T. ' 8 '

106

GENERAL MORPHOLOGY

placenta is like a girdle or zone. When the placenta is multiple,
as in the sheep, cow, goat or deer, the incisors are present in
one jaw only, and the hoofs are cloven. These observations
by Fabricius are quoted, with approbation, by the illustrious
Harvey^, and they express very clearly the conjunction of
certain well-defined characters with a particular form of pla-
centa. In 1823 Sir Everard Home proposed^ an arrangement
of the Animal Kingdom founded on modifications of the egg,
and laid down certain characters of the mammalian orders
taken from the structure of the placenta. Although some,
Avhich he gives, are sufficiently precise, as for example tbe
belt-like form of the placenta in the Carnivora, and the coty-
ledonary form in the Ruminandd, yet in other respects the
characters he has laid down are too indefinite to be of much
value.

It was not until a few years later, when von Baer published
the first part of his most important treatise on the Develop-
ment of Animals, that a definite system of Classification based
on their development was propounded. In his Entwicklungs-
gesddchte^ he divides the placental mammals into groups,
according to the size of the umbilical vesicle and allantois, as
in the followins^ Table :

The Umbilical
Vesicle

very little, Rodentia.
persists.
The Allantois grows ■{ moderately. Insectlvora.

L strongly. Carnivora.

f grows little.
Funis very long. Ai^cs, Man.

grows little.
L The Allantois

1

r in isolated clumps, or
cotyledons. Ruminantia.

I persists. J
L Placenta | ^iffugg^_ Pachydermata,
i_ Cetacea.

In his Untersuchungen* published in the same year, 1828,
he added an important character to this classification, by

1 Works, translated by Dr Willis, p. 564.

^ Lectures on Comparative Anatomy, iii. pp. 470 and 501.

3 Ueber Entivickehingsgeschichte der Thiere, Erster Theil, p. 225, Konigsberg,
1828.

* Unterstickungen iieicr die Gefdssverhindung zwischen Mutter und Frucht,
p. 26. 1828.

OF THE PLACENTA. 107

pointing out that in the diffused and cotyledonary forms the
foetal placenta was merely applied to the maternal placenta,
whilst in the Carnivora, with their zonary placenta, and in
the Rodentla, Insectivora and Man, where the placenta is at
one end of the ovum, the foetal and maternal elements were
grown together. Von Baer had therefore, as Professor Huxley
has already stated, recognised not only important differences
in the form of the placenta in different mammals, but in the
degree in which the foetal and maternal parts of tlie organ
were incorporated with each other.

In 1835 Prof. Weber communicated to a meeting of German
Naturalists^ a classification of the placental mammals in two
groups based on the presence or absence of maternal parts in
the separated placenta : 1st, where the vascular folds or " cells"
of the uterus are so closely attached to the vascular folds or
villi of the chorion, that they are torn through at the time of
birth, so that the uterus is wounded ; and the organs which
serve to connect the mother and foetus fall away at the birth of
the placenta, and they are, as he says, "hiiifdlUg, organa caduca,"
e.g. in the bitch, cat, rabbit and man: 2nd, where the uterine
and foetal parts are so loosely attached that they separate at
birth, without the uterus being torn, just as a sword is drawn
from its sheath, there being no " zufdlUge organe" e. g. in the
cow, roe-deer, sheep, stag, mare and pig. Eschricht in his
essay published in 1HS7^ employs a similar classification, and
divides placental mammals into two families, in one of which
the uterine placenta is caducous, in the other non-caducous.
M. H. Milne-Edwards published in 1844" a system of classifica-
tion in which he attached great weight to the size and dis-
position of the allantois and the form of the placenta. In a
subsequent memoir published in 1868^ he lays stress upon the
presence of a caduca uterina in mammals with a zonary or
discoid placenta, and as these animals lose blood at the time
of birth he groups them together under the common term
Hematogemtes. In 1863 Prof. Huxley, in his Lectures on

1 Froriep's Notizen, Oct. 1835, p. 90.

- De Organis, p. 30.

' Ann. des Sciences Naturelles, 1844, p. 92.

* Considerations sur la Classification des Mamviiferes, Paris, 1868, p. 22.

8—2

108 GENERAL MORPHOLOGY

Classification \ delivered as Hunterian Professor, suggested
that the terms deciduate and non-deciduate were to be
preferred to caducous and non-caducous, and arranged the
placental mammals into the groups Deciduata and Non-de-
ciduata; an arrangement which has been adopted by several
subsequent writers. By the term Deciduata is meant those
mammals which shed, along with the foetal placenta, more or
less of the vascular constituents of the maternal mucosa in the
placental area, whilst the Non-deciduata do not part with any
of the mucosa in the act of partarition.

A sharp line of demarcation is therefore drawn by these
eminent anatomists between the mammals whose uterine
mucosa during parturition is caducous or deciduate, and those
in which it is non-caducous or non-deciduate. In employing
these terms it should be distinctly kept in mind that the
same anatomical elements exist in both types of placenta,
and that the shedding or non-shedding of maternal tissue is
determined by the degree of interlacement of the foetal and
maternal parts of the organ, and not from the presence in
the deciduata of structures which do not exist in the non-
deciduata.

I shall reserve until the concluding course of Lectures the
consideration of the question how far the modifications in the
form and structure of the placenta may be taken as affording
a reliable basis for the Classification of the placental mammals.
On this occasion I shall confine myself to making a few obser-
vations on the deciduate or non-deciduate character of the
placentae described in the present course.

All anatomists agree in regarding the Diffused Placenta as
non-deciduate, for the uterine crypts are so shallow that the
chorionic villi can be drawn out of them with great ease ; and
the foetal membranes are shed in the act of parturition, without
entangling and drawing away the maternal mucosa.

The Polycotyledonary Placenta is also regarded as non-
deciduate. But from observations made on the shed mem-
branes of the sheep and cow, I recently ascertained^ that inter-
mingled with the villi of the foetal cotyledons were quantities

1 Elements of Comparative Anatomy , London, 1864, p. 103.
^Proc. Boy. Soc. Edinburgh, May, 1875,

OF THE PLACENTA.

109

of cells, wblcli possessed the characters of the epithelial cells of
the pits and crypts of the maternal cotyledons.

For the purpose of studying the shed placenta of the Sheep,
T procured the after-birth from the ewe as soon as it was passed,
and immersed it in strong spirit. Some foetal tufts were then
examined without any other preparation; but others v;ere im-
mersed in glj^cerine jelly, so as to bind the several constituents
of the tuft together. Thin slices were then removed from the
hardened tufts, whilst from others small portions were taken
and teased out with needles. In the examination, a magnifying
power of 820 diameters was employed. Quantities of cells,
having the form and appearance of the epithelial cells lining
the pits in the cotyledons (p. 60), were seen to be intermingled
with the foetal villi. In some cases small patches of cells were
seen lying free in the spaces between the villi, but more fre-
quently the cells were isolated. In a few instances I saw
groups of such cells in immediate contact with the terminal
villi, as if they, in being drawn out of the pits in the maternal
cotyledon, had pulled an envelope of epithelial cells along with
them.

Fi-. 12.

Maternal epithelial cells found intermingled with the fcetal cotyledons in the
shed membranes of S the sheep, and C the cow. x 320.

When the cotyledons of the shed placenta of the Cow were
examined microscopically, quantities of granular debris were
to be seen floating in the fluid in which the specimens were
placed. Along with these granules were small flakes of proto-
plasm ; rounded or ovoid bodies, with distinct outlines looking
like free nuclei; and large cells composed of granular proto-
plasm, containing one, two, or three nuclei, having the anato-

110 GENERAL MORPHOLOGY

mical characters of the cells lining the pits in the cotyledons.
The amount of debris and of decidual cells varies considerably
in the different slides which I examined ; in some being so
abundant as to render the fluid in which the specimen was
examined quite turbid, whilst in others only slight traces were
to be recognised.

From these observations I am of opinion that, both in the
sheep and cow, the cotyledons of the foetal placenta carry away
with them, during the act of parturition, a portion of the
maternal structure, so that in these animals, and presumably
in other ruminants, the placenta is deciduate. So far as my
observations have gone, 1 have only detected the epithelial
element of the uterine mucosa intermingled with the foetal
villi ; but from the bloody state of the external parts of the
ewe for some hours after the bii'th of the lamb, I think it not
improbable that the disruption of some of the maternal coty-
ledons has been deeper than a mere epithelial shedding, — that
the maternal vessels have, in some places at least, been torn
lacross, so as to give rise to the haemorrhage.

There is no difference of opinion as to the deciduate nature
of the Zonary Placenta in the Carnivora, Pinnej)edia and
Elephant, and although doubts have been thrown by M. H.
Milne-Edwai'ds on the deciduate character of the placenta in
Hyrax, the observations which I have made satisfactorily
show that it is undoubtedly deciduate. But it has not been
sufficiently recognised that considerable variations occur in
the relative proportion of maternal tissue shed along with the
foetal placenta. In the seal, the dog and the fox, the decidua
serotina, or mucous membrane of the placental zone, does
not form a continuous layer on the uterine face of the sepa-
rated placenta. A definite layer is however left, when the
placenta is shed, on the uterine zone itself, which layer is
divided on its surface into pits or trenches by projecting
folds. When the organ is in situ these folds dip into the
■substance of the placenta, but are torn through in the pro-
cess of parturition, so that the only portions of maternal tissue
which are shed are the intra-placental prolongations. That
"the membrane left on the uterus in the placental zone is the
mucosa is proved by its vascularity, the layer of columnar

. OF THE PLACENTA. Ill

epithelium on its free surface, and the utricular glands ; which
structures, the glands excepted, are also in the intra-placental
prolongations. In the feline Carnivora, again, as illustrated by
the common cat, the mucosa not only sends prolongations into
the substance of the shed placenta, but forms a continuous
.layer on its uterine surface ; whilst the layer of tissue left on
the placental area of the uterus itself consists not of the entire
thickness of the mucosa, but only of the deeper part of the
sub-epithelial connective tissue with the remains of glands and
blood-vessels. Hence though all the Carnivora part with a
considerable portion of the maternal mucosa in the separa-
tion of the placenta, yet they exhibit differences as regards the
degree in which the shedding takes place. The Felidce have a
higher grade of deciduation than the Canidce, and with thp
Litter the Phocidce correspond. Hence the Dogs and Seals, in
their placental affinities, are less re.noved from the Cetacea, the
Suidoi and the Solipedia than are the Cats. The pits and
trenches of the mucosa, which one sees on the uterine zone,
after the separation of the placenta in a seal, a fox, or a dog,
are obviously similar in their morphological characters to the
crypts of the mucosa of a mare, a cetacean, or other animals
with a diffused placenta. In the seal the pits and trenches
possess a precision of form more than is seen in the dog and
fox, a circumstance which is undoubtedly due to the sub-
division of the placenta of the seal into definite minute lobules.
The higher grade of deciduation in a cat may perhaps be ac-
counted for by the broadly laminated villi, their very sinuous
form, and the depth in the mucosa to which their terminal
bud-like offshoots penetrate, giving to the foetal part of the
placenta such a "grip," if I may so term it, over the maternal
part, as to interlock the latter more firmly with the villi, and
thus to cause the mucosa to be to a greater extent shed in the
process of parturition.

In the fox and seal the intra-placental prolongations of the
mucosa are subdivided into a reticulated arrangement of slender
trabeculse, each bar of which contains only a single dilated
capillary; but in the seal this subdivision is carried out to a
greater extent than in the fox. In the seal occurs that very
remarkable anastomosis of the distal ends of the primary branches

112 GENERAL MORPHOLOGY

of the chorionic villi, which gives to the placenta its precise
lobular subdivision, and walls in each lobule at its uterine
periphery Avith the greyish membrane. From a somewhat
cursory examination which I have made of the placenta of a
Phoca vituUna, in the Museum of your College, it appeared
to me that a similar membrane existed also in this animal;
so that I am disposed to consider the arrangement as one
which is of more than generic, indeed of ordinal value.

From the general correspondence in shape and structure
between the placenta of the Pinnepedia and that of the true
C'Cirnivora, there can be no doubt that, in both orders, the
early stage of formation is marked by the production of crypts
in the placental area of the uterine mucosa. In the grey seal
the villi of the chorion, which are lodged in these crypts, ac-
quire, not only a considerable length, but a highly arborescent
form, and give origin to multitudes of villous tufts. As the
branching and growth of the villi proceed in the course of
development, the crypts will necessarily become divided into
smaller compartments ; and as the villous tufts increase in
number and size, the walls of the crypts will become no doubt
thinned, until at length they will lose their uniformly con-
tinuous surface, and become subdivided into the reticulated
arrangement already described, in the meshes of the network
of which the villous tufts are lodged. That the increased area
of the uterine mucosa in the pregnaiit seal is due to a great
increase in the inter-glandular part of the membrane, is proved
by the much wider separation of the glands seen in both the
non-placental and placental areas of the gravid as compared
with the non-gravid uterus of H. GrypJms.

It has been customary to regard a placenta as deciduate
only when the vascular constituents of the uterine mucosa are
shed with the foetal membranes. This acceptation of the term
seems to me, however, to be too limited, and does not cover all
the cases in which maternal tissue is shed in the separated
placenta. I would suggest therefore that the definition should
be enlarged so as to embrace those cases in which epithelium
alone is parted with, as well as those in which both the epi-
thelium and the sub-epithelial vascular uterine tissue come
aAvay in the separated placenta. In studying the types of

OF THE PLACENTA. 113

placenta whicli have formed the subject of these Lectures we
have passed by successive gradations from the diffused pla-
centa, which is apparently non-deciduate, to the polycotyledo-
nary placenta, in which the epithelial layer of the mucosa only
has been found ; then to the zonary placenta of the Canidce and
JPhocidce, where the entire constituents of the intra-placental
prolongations of the mucosa are shed, but where a well-marked
layer of mucous membrane is left on the uterine zone ; and
lastly to the Felidce, where, together with the intra-placental
laminae, the superficial layer of the mucosa in the uterine zone
is shed as a part of the placenta. It follows, therefore, that
the line of demarcation between a diffused non-deciduate, and
a zonary deciduate placenta, is not so sharp as has usually
been supposed, but is graded over by the ruminant poly-
cotyledonary placenta, in which the epithelial layer is the
preponderating if not the only element of the mucosa which
deciduates during parturition. But to prevent misconception
it should be stated, as indeed has been already done by 0\ven\
Ercolani^, and myself, that if not during parturition, at least
afterwards, all placental mammals are deciduate, for in the pig,
mare, and cetacean, " during the period of involution which fol-
lows parturition, it is obvious that great changes, either from
actual shedding of portions of its substance, or from degene-
ration and interstitial absorption, must take place in the con-
stituents of the crypt-layer before it can be restored to its
proper non-gravid condition^," In the Ruminants also, the
thick, vascular, spongy tissue of the maternal cotyledons must
disappear before the uterus can assume its normal unimpreg-
nated aspect.

^ The Anatomy of Vertebrates, Vol. in. p. 727, 1868.

2 Sur les Glandes utriculaires de V Uterus, &c. Algiers, 1869.

3 Trans. Boy. Soc. Edinburgh, 1871) and Proceedings, May. 1875.

114) PHySIOLOGICAL REMARKS.

Physiological Remarks.

The foetal placenta possesses an absorbing surface; the
maternal placenta a secreting surface. The foetus is a para-
site, which is nourished by the juices of the mother.

The absorbing surface of the foetal placenta is the chorion,
the vessels it contains are the structures which transmit the
materials absorbed to the foetus, and the villi are the chief,
though not the exclusive, structures engaged in absorption.
In the Diffused Placenta not only the villi, but the smooth
inter- villous part of the chorion, are undoubtedly absorbing
surfaces, for in both a compact capillary network is diffused
beneath the free surface of the membrane. In the Polycotyle-
donary Placenta, both the foetal cotyledons and the smooth
inter-cotyledonary part of the chorion are absorbing surfaces, for
not only are the villi highly vascular, but, as I have described
in the sheep, cow, and giraffe, a remarkably compact capillary
plexus is diffused beneath the smooth part of the chorion between
the cotyledons. In the Zonary Placenta the vascularity of the
chorion is not conj&ned to the villi projecting from the annular
equatorial band, but, as I have seen in the cat, bitch, fox,
and grey s.eaP, the branches of the umbilical vessels, which are
distributed to the poles of the chorion, terminate in a compact
capillary plexus, and I have little doubt that if the umbilical
vessels in other animals with a zonary placenta were mini'itely
injected, a similar vascular plexus would be found in them.
Though the villi in the cotyledonary and the zonary placenta
are much fewer in relation to the extent of the chorion than in
the diffused placenta, they are longer, more branched, or more
sinuous, so that the surface for absorption provided by them is
probably as great.

The secreting surface of the placenta is the remarkably
modified mucous lining of the uterus. That the maternal
placenta is a secreting organ, the secretion of which is em-

1 I have omitted to state, in the description of the placenta of the Grey
Seal, that the umbilical vessels, distributed to the smooth polar areas of the
chorion, terminated in a capillary plexus, as well marked as that which I have
described in the Cat and Bitch.

PHYSIOLOGICAL EEMAEKS. 115

ployed in the nutrition of the fetus, has from time to time
been definitely stated by various physiologists. The immortal
Harvey distinctly recognised that the placenta prepared for
the foetus alimentary matters derived from the mother. In
the deer, he says, the maternal cotyledons are

" of a spongy character, and constituted, like a lioney-coinb, of
innumerable shallow pits filled with a mxico-albuminous fluid (a
circumstance already observed by Galen), and that from this source
the ramifications of the umbilical vessels absorbed the nutriment
and carried it to the fcetus; just as, in animals after their birth,
the extremities of the mesenteric vessels are spread over the coats
of the intestines, and thence take up chyle."

And again :

"In my opinion the placenta and carunculre liave an office analo-
gous to that of the liver and mamma. The liver elaboi'ates for the
nourishment of the body the chyle previously taken up from the
intestines : the placenta in like manner prepares for the foetus ali-
mentary matters which have come from the mother. The mammse
also, which are of a glandular structure, swell with milk, and although
in some animals they are not even visible at other times they become
full and tumid at the period of pregnancy ; so too, the placenta, a
loose and fungus-like body, abounds in an albuminous fluid, and is
only to be found at the period of jtregiiancy. The liver, I say then,
is the nutrient organ of the body in which it is found ; the mamma
is the same of the infant, and the placenta of the embryo'."

Needham also' wrote of the nutritious juice formed in the
cotyledons of the Ruminantia. Wharton and Haller applied''
to this fluid the name of milk or milky humor ; by several sub-
sequent writers it has been called uterine milk, and the cot}'-
ledons themselves have been regarded as uterine maramai.

By what structures in the maternal placenta can this fluid
be secreted, is a question which miist now be considered.
E. H. Weber pointed out* not only the formation of a chylou.s
fluid from the capillaries of the "cells" (crypts), within the
cotyledons of the cow and roe-deer ; but that the secreting
surface of the uterus was much increased through the presence
of the utricular glands, which opened on the free surface of the
mucous membrane between the cotyledons. The secretion of

1 The Works of Harvey, translated by Dr Willis, pp. 562, 563,

^ Disqidsitio Anatoniica, 1667, p. 25.

3 Elementa Physiologice, 1766, viii. p. 24o.

* Hildebrandfs Anatomie, iv. 505, 1832, and Froriep's Notizen, October,

116 PHYSIOLOGICAL REMARKS.

these glands in the cow he believed to be received into the
pocket-like depressions of the chorion to which I have previously
referred (p. 65), where it comes into relation with the capillary-
network of the chorion. Yon Baer coincided with Weber in
regarding the glands as secreting a material to be applied to the
nutrition of the ovum. Eschricht looked upon the utricular
glands as the sources of the secretion of this nutrient albuminous
fluid, whilst he apparently regarded the "cells" (crypts) as the
places of formation of ordinary mucus ; and this conclusion, at
least as regards the function of the glands, has been adopted by
various anatomists. Dr Sharpey, from his researches on the bitch,
thought it not improbable that in viviparous animals gener-
ally, a matter deposited from the maternal system by means of
a glandular apparatus may be absorbed into that of the foetus
and serve for its nutrition. Prof. Goodsir in his description of
the human placenta^ showed how the cells of the decidua were
prolonged into the interior of the placenta, so as to invest the
villi, and regarded them as secreting cells, the remains of the
secreting mucous membrane of the uterus ; corresponding,
therefore, with the cellular lining of the cotyledons of the
E-uminants. He considered these cells to perform during intra-
uterine life a function similar to that performed after birth,
by the gastro- intestinal mucous membrane.

Signer Ercolani, of Bologna, whose Memoirs on the Struc-
ture of the Placenta in various animals equal in importance
and interest the classical Essays of von Baer and Eschricht,
has given a more precise aspect to this question. He admits
the presence of utricular glands in the mucosa in most orders
of mammals, and their increase in size during pregnancy, but
conceives that their chief function is to furnish nutritive
materials during only the earliest stages of gestation, before
the crypts are formed. But further, he points out that in all
mammalia, during pregnancy, the surface of the uterine mucosa
becomes folded into multitudes of crypts (or follicles as he terms
them) in which the foetal villi are lodged. These follicles form
a new glandular organ which prepares a secretion that super-
sedes that of the utricular glands and is absorbed by the
foetal villi.

^ Anatomical and Pathological Ohservation^, pp. 63, 114. 1845. .

PHYSIULOGICAL KKJMARKS. 117

On this important subject a few words will now be said.
There can be no doubt that the Utricular Glands are secreting
structures, that they enlarge during pregnancy, and that their
secretion is poured out between the mucous membrane and the
chorion. In the Diffused form of placenta they have the ap-
pearance of being structurally perfect up to the completion of
gestation ; and their secretion is poured out so as to be brought
into direct relation with the inter-villous, and not with the
villous portion of the chorion. But as the whole free surface
of the chorion is provided with capillaries, the one is no doubt
as capable of absorj)tion as the other, and the glands are pre-
sumably active throughout intra-uterine life. In the pig,
mare, and Lemurs, well-defined areas of vascular chorion are
in apposition with the equally well-defined areas on the sur-
face of the mucosa in which the glands opened, and in the
Lemurs the mouths of the glands are concentrated in a very
remarkable manner in these areas, so that a considerable quan-
tity of secretion would be brought into contact with the ap-
posed non-villous, but vascular, areas of the chorion. In Orca,
and possibly also to some extent in the Narwhal, the secretion
of the glands being poured into some of the crypts is brought
into relation with the villi which occupy those crypts ; but in
other parts of the NarAvhal's placenta their secretion is poured
out opposite non-villous areas of the chorion. The observations
on the Narwhal not only show that the foetus may attain a
precise stage of development before any appearance of crypts
can be observed, but that after the crypts are fully developed
the utricular glands have a diameter much greater than before
the crypts had made their appearance. In the Polycotyledonary
placenta the utricular glands are not situated in the cotyledons,
so that the uterine milk cannot be formed by them. They exist
abundantly in the inter-cotyledonary parts of the mucosa, and
their secretion is brought in contact with the svirface of the cho-
rion in which the curious pockets described by von Baer, Weber,
and myself in the cow, and by me in the giraffe, are situated.
I agree with Weber in regarding these pockets as receptacles
for the secretion, and the vessels in their walls as engaged
in its absorption. I may mention that I have seen the
smooth surface of the chorion of the sheep smeared with a
white substance, apparently the secretion of the utricular glands.

118 PHYSIOLOGICAL REMARKS.

In the Zonaiy placenta tlie glands are altered, and degene-
rated in the placental zone. In the non-placental area of
the mucosa they also show an apparent want of structural
completeness, at least at the end of gestation. But in the
earlier period of intra-uteriue life the glands are undoubtedly
active, and as their secretion is poured out it is brought into
contact with the smooth but very vascular polar portions of the
chorion, by which it is in all probability absorbed. I am of
opinion therefore that the utricular glands in all these placenta?
have a more enduring function in foetal nutrition than is
admitted by Ercolani.

The Crypts, newly formed during pregnancy, possess the
structural characters of secreting organs. Each crypt is lined
by an epithelium, descended from the epithelial lining of the
uterine mucosa ; which from the size and appearance of the
cells is obviously endowed with great functional activity. This
epithelium rests upon a highly vascular, sub-epithelial tissue,
the vascularity of which is doubtless proportioned to the amount
of secretion formed by the epithelial cells. At one time I was
disposed to think that the epithelial lining of the crypts in
Orca had not a form which one usually associates with the
possession of the power of secretion, and that its placenta
offered a difficulty in the way of accepting the theory that the
crypts were secreting organs. A re-examination, however, of
the mucosa in that animal, together with the evidence afforded
by the form of the cells lining the crypts in the allied genus,
the Narwhal, has satisfied me that the Cetacea are no exception
to what is seen in other mammals, so that I have now no
hesitation in regarding the crypts as secreting organs. The
appearance of these crypts in the early stages of placental
formation, and their persistence throughout intra-uterine life,
though in the zonary form they may become somewhat difficult
to recognise, owing to complexities arising during growth, fur-
nish evidence of their importance. The intimate relation which
they bear to the villi, which, in the whole series of placentae
described in these Lectures, are lodged within the crypts, shows
that the secretion they form is in a position best fitted for
being absorbed by the villi.

In no form of placenta has the secretion of the utricular
glands been collected and analysed, and indeed the arrange-

PHYSIOLOGICAL REMARKS, 119:

ments of parts do not admit of a sufficient amount being
collected for that purpose. In the diffused and zonary forms
of placentae the arrangements are not such as to permit the;
secretion of the crypts to be collected and examined free from
mixture with the secretion of the utricular glands. In the
polycotyledonary placenta, where the spongy tissue of the ma-
ternal cotyledons consists exclusively of crypts, the secretion of
uterine milk can not only be shown to be derived from the
crypts, but can be obtained in sufficient quantity for analysis.
In the analyses published by Prof. Prevost^ the secretion was
stated to contain water, albumen, fibrin, casein, a gelatinous
substance, blood-colouring matter, osmazome, fat and salts.
Prof. Schlossberger afterwards gave an account^ of its com-
position, and stated that it contained water, fat, albumen, salts,
no sugar, and that its reaction was acid. More recently Dr
Arthur Gamgee has published an analysis^, in which the aque-
ous, fatty, albuminous and saline constituents were determined,
and the absence both of sugar and casein definitely stated : in
his specimens the reaction of the fluid was either alkaline or
neuter. From its composition the uterine milk is well suited
to act as a nutrient material.

As there are, therefore, two sets of secreting structures in
the gravid maternal mucosa, the Glands and the Crypts, each of
which has in relation to it a definite and usually distinct sur-
face of the chorion, it may be a matter for consideration how
far these secreting organs perform simil?vr or different functions
in foetal nutrition. No definite information can however as yet
be given on this matter, which is still open to physiological
enquiry. The fact however is not to be doubted that under
the stimulus imparted by the presence of the fertilized ovum
the uterus undergoes enormous development and growth. The
muscular coat increases so as to provide an apparatus capable
of expelling by its contraction the foetus, when its period of
intra-uterine development is completed. In the mucous coat
the pre-existing utricular glands are enlarged, and in addition,

1 Ann. des Sc. Nat., 1829, xti. p. 157, and in conjunction with M. Moriu
in Mem. de la Soc. de physique de Geneve, 1841, ix. p. 235.
^ Ann. der Chemic und Pharm., 1855.
3 Brit, and For. Medico-Chir. Review, 1864, xxxni. p. 180.

120 PHYSIOLOGICAL REMARKS.

multitudes of crypts are developed, in which secretions are pro-
duced capable of nourishing the foetus during its intra-uterine
life, so that the maternal placenta is a great secreting organ.

The presence of a ring of colouring matter at the margins of
the placenta in the Carnivora would seem to show that in the
performance of its secreting function certain pigmentary mate-
rials may be separated, which perhaps are to be regarded as
excretions, just as the bile is separated by the secreting cells of
the liver in the performance of its glycogenic function.

If this view of the function of the maternal placenta be
admitted, then the current doctrine that the nutrition of the
foetus is provided for by a simple percolation or diffusion of
materials through the walls of the vessels from the maternal
blood to the foetal blood can no longer be accepted. Even if
the secreting function of the layer of cells on the free surface of
the maternal mucosa be disputed by the advocates of the diffu-
sion theory, it would I think be conceded that the presence of
such a layer would offer some mechanical obstruction to the
direct passage of materials between the two systems of vessels ;
a difficulty which would be still further increased by the layer
of interposed fluid which undoubtedly exists in the cotyledonis
of the Ruminantia.

An important argument in favour of the diffusion theory
must not however be forgotten in the discussion of this ques-
tion. The interesting series of facts collected by Dr Alexander
Harvey^ rendered the conclusion extremely probable that a
portion of the blood of the foetus is constantly passing into the
body of the mother. This subject was experimentally investi-
gated by Mr W. S. Savory^, who found when strychnia was
injected into the body of the foetus, the umbilical cord being
intact, that some time afterwards the mother died from symp-
toms of strychnia poisoning. Now, as we know of no secreting
apparatus by which the constituents of the foetal blood may be
separated and transmitted to the mother, it is difficult to see
how the poison can have affected the mother except by diffu-

1 On the Foetus in Utero as inoculating the Maternal with the pecuharities
of the Paternal Organism. — Monthly Journal of Medical Science, Oct., 1849,
Sep., 1850.

^ An Experimental Inquiry into the effect upon the Mother of poisoning the
Foetus.

PHYSIOLOGICAL REMARKS. 121

sion from the fcetal into tlie maternal vessels. The passage
of the poison does not take place however with great rapidity,
as the first tetanic symptoms did not in any of the experi-
ments begin until nine minutes, and in one case even an
interval of half an hour elapsed, after the injection of strychnia
into the fcetus. But Mr Savory's experiments also show, when
into some only of the embryos the poison had been injected,
although the mother lived in one instance 19 minutes after she
began to be convulsed, the remaining embryos in her womb
that had not been injected showed no symptoms of strychnia
poisoning. The transmission therefore of the poison from her
to them had not occurred either by diffusion, or through the
intermediation of a secretion; so that whatever be the mode in
which the nutrition of the foetus be effected the passage of
materials from the mother to the fcetus takes place apparently
at only a slow rate. At the same time it should be remem-
bered that experiments have been made which prove the pas-
sage of materials from the maternal to the foetal vessels. Thus
early in the century A. C. Mayer ^ administered cyanide of
potassium to gravid animals and found the salt not only in
the umbilical vessels of the foetus, but in the fluids of the
amnion and allantois. M. Flourens also^ fed a gravid pig with
madder, and found not only its own bones, but those of the
foetuses within the womb, coloured. It does not however follow
that in these cases the transmission had been due to direct
diffusion from one set of vessels to the other, as the saline and
colouring substances might have been separated through the
action of the secreting cells in the maternal placenta.

But the placenta is also regarded by physiologists as an
organ, which not only provides nutriment for the foetus, but
serves as its respiratory apparatus, and it is believed that an
interchange of gases takes place between the foetal and ma-
ternal blood-vessels. Undoubtedly there are many facts on
record which seem to show that the foetus in utero needs to
respire, and that the placenta is the organ in which respiration
is conducted. But there is no evidence that the respiratory
changes during intra-uterine life are actively carried on. The

1 MecheVs Archiv., p. 503, 1817.

^ Ann, des Sciences Nat., 4th series, xii. p, 245.

122 PHYSIOLOGICAL REMARKS.

experiments of Buffon, Legallois and Wm. Edwards^ indeed
show that asphyxia can be resisted by new-born animals for
more than half an hour, and that for some days after birth the
need of respiration is not so great as at a later period. The
interposition of a layer of cells, possessing some thickness, on
the surface of the maternal placenta between the two systems
of vessels, whether these cells be regarded as secreting or not,
necessarily throws a mechanical difficulty in the way of the
ready passage of gases from the one set of vessels to the other,
and might be used as an argument against the theory of intra-
uterine respiration.

It seems to me therefore that, before the problems of nutri-
tion and respiration in the foetus can be regarded as satisfac-
torily solved, a further series of experiments, with the aid of
the additional light which has now been thrown on the struc-
ture of the placenta, will require to be made by the physiologist.

1 Quoted in M. H. Milne-Edwards's Legons sur la Physiologie, ii. p. 560.

EXPLANATION OP THE PLATES.

Figure 11 was drawn from nature under my superintendence by Mr
John R. Reid. Fig. 5 by Mr J. H. Scott, M.B. For the series of micro-
scopic drawings from which tlie remaining figures have been engraved,
I am indebted to my former assistant, Mr J. C. Ewart, M.B.

Plate I.

Fig. 1. Vertical section through the placenta, PI, of a Cat, about
half time (p. 76). Ch, the chorion, the vessels of which are coloured blue,
so that the blue network which passes through the thickness of the
placenta represents the vessels of the villi ; D, the decidua serotina ; the
red-coloured vessels are the vessels of the uterine mucosa, which ascend in
the walls of the crypts as far as the chorion, where they not unfrequently
show considerable dilatations, s ; h, bud-like terminal offshoot of a villus
penetrating into the serotina ; ms, the muscular coat, x Hartnack
3 obj. 3 Oc.

Fig. 2. Horizontal section through the placenta of the same Cat.
VV, transversely divided sinuous villi, the capillaries in which are coloured
blue ; /, I, laminae of uterine mucosa, forming the walls of the crypts. The
red colour represents maternal vessels, as in Fig. 1.

Fig. 3. Villi, V, with a portion of the chorion, ch, of the shed placenta
of a Cat at full time ; h, a terminal bud, such as in Fig. 1 h penetrates
deeply into the serotina. x 40.

Fig. 4. Horizontal section through the placenta of a Fox (p. So).
V, the blue-coloured vessels of the foetal villi ; m, the transversely divided
colossal maternal capillaries.

Fig. 5. Section through the placenta of a Fox magnified to show the
secreting epithelium, mm, the colossal maternal capillaries injected red.
e, e, the columnar epithelial cells which invest the maternal vessels, vc,
the vessels of the fcetal villi injected blue, x 160.

Fig. 6. Vertical section through the non-gravid uterine mucosa of a
Bitch (p. 84). e, ends of columnar epithelial cells covering free surface of
mucosa ; g, tubular gland shown in its entire length ; g', a tubular gland
cut short. At a the continuity of an apparently short gland, with the
deeper end of a tube, is shown, ct, interglandular connective tissue, with
its corpuscles ; h, arteries passing into the mucosa ; ms, muscular stra-
tum X 100.

Fig. 7. Horizontal section through the non-gravid uterine mucosa of a
Bitch, near the free surface. The close relation which the glands have to
each other is shown ; also the small proportion of interglandular tissue, in
which rounded cells, not unlike lymph or white blood-corpuscles, may be
seen, x 100.

Fig. 8. Surface view of the non-gravid uterine mucosa of the Crested
Seal {CystopJiora cristata). At e the columnar epithelium is i7i situ, else-
where it has been removed ; g, mouth of a tubular gland. The capillary
network of the mucosa is coloured red. x 100.

Plate IL

Fig. 9. Vertical section through the placental area of the mucosa of
the Cat, described on p. 72. cr, the layer of branching crypts ; the epi-
thelial lining of the crypts ep, ep, and their highly corpnsculated connective-
tissue walls ct, ct, are represented ; gl, the glandular layer ; the glands
are seen in section, much less numerous than the crypts, and surrounded
by connective tissue ; m,s, the muscular coat, x Hartnack 3 obj. 4 Oc. ;
tube out.

124 EXPLANATION OF PLATES.

Fig. 10. Horizontal section through the ci'ypt-layer of the same
uterus, cr, cr, cavities of the crypts with their epithelial lining. At e the
epithelium covering the free surface of the vpalls of the crypts is seen ; at
e the walls are in section, and the sub-epithelial connective tissue, with its
corpuscles, ct, is exposed, x Hartnack 7 obj. 3 Oc. ; tube out.

Fig. 11. Portion of placenta, PI, of the Grey Seal partially dissected
off the uterus, m^n, the uterine mucosa forming the non- deciduous part
of the serotina ; folds of this membrane may be seen entering the sulci or
primary fissures, ss, between the convolutions of the placenta. The broader
red lines on the exposed surface of the placenta are intended to represent
the secondary fissures of the placenta, and the finer lines the tertiary
fissures, by which it is subdivided into the ultimate lobules, I. np, np,
non-placental portions of the mucous membrane. Natural size.

Fig. 12. Surface view of the uterine mucosa of the same Seal forming
the non-deciduous serotina. At e, e the broad ends of the columnar epi-
thelium cells, still in situ, are represented. In the rest of the figure the
epithelium has been removed, tiv, larger trunks of the blood-vessels of
the mucosa ; c, capillary network ; ct, corpusculated sub-epithelial con-
nective tissue ; gl, portion of one of the utricular glands, x 250.

Plate III.

Fig. 13. Vertical section through one lobule and a portion of an
adjacent lobule of the jjlacenta of the Grey Seal. Ch, chorion ; VV, stems
of the large arborescent villi ; V, smaller villi arising directly from the
chorion, Tlie blue-coloured vessels in the chorion and villi are the rami-
fications of the umbilical vein, g.g., greyish membrane at the periphery of
the lobule in which the blue-coloured vessels of the villi ramify ; b.h, bud-
like offshoots of the finer branches of the villi ; imn, uterine mucosa forming
the non-deciduous serotina in relation with the placental lobule; gl,
utricular gland ; uv, uterine blood-vessels, coloured red, passing into f, a
tertiary fissure between the two lobules. At the upper end of this fissure
these vessels form a network continuous with the intra-lobular maternal
capillaries. At tr the intra- placental trabecular arrangement of the
mucosa is shown isolated and drawn away from the finer branches of the
villi. In the greater part of this figure the maternal trabeculse are shown
in situ intertwined amidst the fretal villi, x 40.

Fig. 14. Uterine surface of four of the lobules of the placenta, g.g.,
greyish membrane forming the periphery of the lobules ; at g' the mem-
brane has been dissected off; the blue-coloured vessels are branches of the
umbilical vein ; t, processes of the uterine mucosa, with the vessels coloured
red, dipping into the tertiary fissures between the lobules, x 4.

Fig. 15. Intra-placental maternal trabeculse, tr. At ep, ep the
columnar secreting epithelial covering is seen in situ; at ep', ep' partially
shed. Elsewhere the epithelium has been entirely removed, so as to show
the sub-epithelial tissue with its corpuscles, and the single capillary c, in
each trabecula. V, a single bud-like offshoot of a villus lying between the
trabeculse in contact with their epithelium, x 200.

Fig. 16. Branch of a villus, V, with its terminal bud-like offshoots.
The vascularity of the villus is shown in the upper part of the figure, whilst
at the lower end its cellular structure is represented, x 200.

CAMBRIDGE : PRINTED BY C. J. CLAY, M.A. AT THE UNIVERSITY PEEFS.

PIs!

fi^. I.

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Fuji. 6.

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ZONARY Placenta

M= Farlane * 'F.rskme Lift" Edin'

Plate II

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J C Ewart,M B del'

ZONARY PLACENTA

M< Kiirliir,! Ji V.vsl<ino, l.illi" K.1m'

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