Page 686. 
458 ON THE PLACENTA OF HYOMOSCHUS AQUATICUS. 
The sac of the allantois occupied the whole of the right horn of 
the chorion, extending as far as its tip; and its wall was in close ap- 
position by its attached surface with the deep surface of the chorion. 
The sac of the allantois was also prolonged into the left horn of the 
chorion to within half an inch of its tip: but in other respects its 
distribution in this horn was limited; for instead of being in contact 
with the whole extent of the deep surface of the chorion, it formed 
only a circumscribed tubular prolongation attached to that part of 
the chorion which was opposite the belly of the footus. The remain- 
ing part of the deep surface of the chorion in this horn was in con- 
tact with the attached surface of the amnion, which membrane ex- 
tended as far as the edge of the non-villous circular spot opposite the 
os uteri. The amnion was also prolonged over the tubular prolonga- 
tion of the allantois which extended into this horn. The amnion en- 
veloped the umbilical cord up to the abdominal wall of the foetus. 
The amniotic investment of the cord was studded with numbers of 
small stunted whitish sessile corpuscles, which did not, however, pro- 
ject from the free surface of the amnion, where it was in contact with 
the chorion and allantois. These bodies resembled in form and size 
the bodies projecting from the umbilical cord in the Cetacea. They 
had not, however, the yellowish-brown colour of the corresponding 
corpuscles in Orca and the Narwhal, but like them they were developed 
in relation to the deep surface of the amnion and caused an elevation 
of that membrane by their growth. 
The umbilical cord was 3} inches long. It contained two arteries 
and two veins; and a slender tubular prolongation of the sac of the 
allantois could just be traced into the chorionic end of the cord. 
Some injection was passed into the vessels of the cord, which filled 
the principal vessels of the chorion; but as the specimen had been 
for some time in spirit before the injection was made, it did not 
enter the vessels of the villi. Slender vessels, however, traversed 
the non-villous spot opposite the os uteri, and some also were seen 
subjacent to the amnion where it was in contact with the wall of the 
tubular prolongation of the allantois situated in the left horn of the 
chorion. 
EXPLANATION OF PLATE 29. (XLIV.) 
Fig. 1. Fota membranes of Hyomoschus aquaticus, opened into and foetus removed ; 
reduced from natural size. Ch. Villous chorion of the fetal horn. Ch’, 
Villous chorion of the opposite horn. A/. Sac of allantois in the non- 
fecundated cornu, the communication of which with the tubular prolonga- 
tion in the fcetal horn is seen to the right of the letters. Am. Sac of the 
amnion; the letters are placed on the amnion where it is in contact with 
the chorion. w. The umbilical cord; the letter is placed on the amnion 
