area (PL XXXV, fig. 6) corresponding to the similar bare area in the chorion of
Orcella, &c. There may, or may not, be a corresponding bald area on the uterus,
but if present it is very feebly developed. The villi of the chorion are much larger
,and more crowded together on* the right than on the left horn, which is the exant
opposite of what has been described by Turner in the chorion of the Narwhal.
They are most numerous and attain their greatest size on its posterior or umbilical
area, and are least developed on its anterior aspect. The whole surf ace is studded
over with them with the exception of certain bare patches, and they have a distinct
tendency to arrange themselves in wavy ridges on the more rugose portions and in
rounded clusters on the areas where they are less developed.
Plate XXXVII, figures 12 and 13, respectively show a vertical section through
the chorion at a bare spot (b) with the partially injected villi on each side, and a
surface view of the chorion also partially injected, the tufted villi in this case
surrounding the middle bare spot.
Smooth spots of Chorion (PI. XXXV, figs. 7 and 8).—The whole surface of the
chorion is covered with small circular smooth spots (PI. XXXV, fig. 7) and with
others bearing very fine rugosities or folds, such patches being devoid of villi and
varying in size, but corresponding to the smooth spots of the uterine mucous membrane
(fig. 9) to which they would appear to be opposed. They are best seen on
the anterior, ventral and dorsal walls of the left horn, i.e., where the villi are sparse.
They vary in size from 006 to 0*25 inch in diameter, and are irregular in form. In a
square inch of some regions, as many as eighteen to twenty such spots may be counted.
A bare patch of a special character occurs on the left pole of the left horn of the
chorion. I t forms a crescentic linear bare area at the pole, the horns of the crescent
having an interval of an inch between them, and from the concavity of the crescent
a very narrow linear area extends towards the pole. This smooth area corresponds
to the mouth of the Eallopian tube (PL XXXI, fig. 3). There is no other bare area
on the pole of the right horn, its apex being covered with villi. But it must be
borne in mind that this portion of the chorion (figs. 2 and 3) being neither distended
with amnionic nor allantoic fluid lies comparatively loose in the Eallopian end of the
right horn. The extremity, however, of the short uterine pouch (Pl. XXXIV, fig. 2
sp. and fig. 3) is perfectly devoid of villi as in Orca,1 for about an inch in extent, and
this bare area corresponds to the os uteri internum (Pl. XXXI, fig. 2).
The most characteristic bare surface of this chorion (Pl. XXXV, fig. 1),
however, is a long narrow linear area on that side of the funis which lies towards
the dorsum of the mother. I t stretches from within 5 inches of the left to
within 17 inches of the right pole of the chorion, having thus an extension
of 19‘50 inches in a straight line and a serpentine course of 25-75 inches. Opposite
the umbilical attachment it attains a breadth of about 0*50 inch, rapidly diminishing
in diameter on either side of this to 0’06 inch. Erom the left it passes on to the
right horn, running for some way along the dorsal wall of the latter and following
the course of the larger vessels.
In the umbilical expansion of this bare tract, there is a small cul de sac with
a crescentic orifice (fig. 1, c). Moreover, near its termination on the right horn, a
small pedunculated corpuscle (fig. 1, p.) of the same character as the amnionic
corpuscles of the cord and allantois occurs, with a small pear-shaped tubercle at its
base. Eacing towards the pole, and from the base of the peduncle of the corpuscle,
there is a raised, somewhat moniliform and tubular-looking fold which can be traced
along the middle of the bare tract to near its left termination.
As I did not succeed in injecting the villi of the chorion (Pl. XXXVTI, fig. 12),
I cannot give any idea of their true form when charged with blood, and I can say
nothing regarding the arrangement of the blood vessels in them.
Membrana intermedia.—Even when the membranes are comparatively dry, a
thin delicate membrane can be demonstrated to exist between the chorion and
amnion, between the amnion and allantois, and between the allantois and chorion.
But when they have been placed in water for about an hour, this structure in the
right horn of the chorion swells up into a gelatinous mass, and it also assumes the same
character, but in a more limited degree, between the chorion and amnion in the left
horn. When the amnion is stripped off the chorion in the last mentioned locality,
it has a gelatinous feeling on its outside, which is due to the presence of this membrane,
which is also apt in every part of its extent to drag the vessels of the chorion
along with it. Between the amnion and allantois the membrane does not tend to
swell up on soaking, but preserves an extremely fine character.
Ammon.—This is entirely confined to the left horn of the chorion and can be
.easily separated from off the allantois over which it has only a limited distribution. I t
does not follow the allantois into the right horn of the chorion, nor does it invest the
portion of the chorion depending into the cavity of the body of the uterus. I t is
elosely related to the membrana intermedia. Towards the left pole its surface which
covers the allantois is studded over with small corpuscles and evidently identical with
the corpuscles of the amnion of Orca described by Turner1 and having the same
relation to the amnion. Towards the left of the funis the same surface of this
membrane has a broad transverse area devoid of these corpuscles, but further to the
right and towards the middle of the allantoic surface these corpuscles are again
numerous. Some of them are extremely minute and scarcely visible to the naked
eye, and they are confined to the allantoic surface of the amnion. These corpuscu-
lated surfaces of the amnion are also studded over, in certain parts in great profusion,
with minute sessile grey papilla-like structures, which give a rough feeling to the
membrane. Corpuscle-like bodies, stalked and sessile, also occur on the amnion as
it sheathes the cord (Pl. XXXI, fig. 1, c).
The first mentioned bodies of the amnion, which vary, in size from 0'04 inch
to 0’70 inch, are nearly all pedunculated, and appear to be structurally identical
with the long pedunculated and sessile bodies which stud the amnionic covering of
the cord. The microscopic structure of these bodies I have not been able to satisfactorily
determine, as all those which I have examined had been long preserved in
1 Turner: Lectures on Placent., p. 23.