18/8.] THE PLACENTA OF HYOMOSCHUS AQUATICUS. 685 



the chorion corresponding to the more convex part of the gravid 

 uterine cornu was thinly covered with villi, and, indeed, in one or two 

 very limited areas was non-villous— these hare or thinly covered 

 patches being in contact with those portions of the uterine mucosa 

 (already described) where the crypts are either shallow or absent. 

 In all other localities the free surface of the chorion was as thickly 

 studded with villi as the uterine mucosa was with crypts ; so that it 

 furnished an excellent and characteristic example of a diffused pla- 

 centa. In the absence of villi from those parts of the chorion which 

 were situated in relation to the three uterine orifices, f. e the os uteri 

 and the two Fallopian tubes, the chorion of Hj/omoschus corresponded 

 with what one of us has elsewhere described in Orca, the Narwhal 

 and the Mare. ' 



The villi were arranged in small tufts, separated from each other 

 by very narrow intervals. The tufts varied in size; and the villi of 

 which they were composed were short and branched, usually in the 

 torm of filamentous processes. The basal substance of each villus and 

 of the chorion itself consisted of a delicate corpusculated connective 

 tissue. I he epithelium on the free surface of the chorion was partly 

 shed; but considerable patches of it were seen in many localities. 



1 he amnion formed a capacious bug, which extended to within half 

 an inch of the tip of the left horn of the chorion. It occupied the 

 rest of this horn and the part of the chorion situated in the corpus 

 uteri but did not extend into the right horn of the chorion. 



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. 

 1 he sac ot 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 foetus. 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 ammon was also prolonged over the tubular pro- 

 longation of the allantois which extended into this horn The 

 amnion enveloped the umbilical cord up to the abdominal wall of the 

 ioetus. Ihe amniotic investment of the cord was studded with 

 numbers ot small stunted whitish sessile corpuscles, which did not 

 however, project from the free surface of the amnion, where it was 

 in contact with the chorion and allantois. These bodies resembled 

 in torm and size the bodies projecting from the umbilical cord in the 

 Letacea. 1 hey 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 



