OCR Text |
Show 1878.] 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 bare 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 placenta. In the absence of villi from those parts of the chorion which were situated in relation to the three uterine orifices, i. e. the os uteri and the two Fallopian tubes, the chorion oi Hyomoschus 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 form of filamentous processes. The basal substance of each villus and of the chorion itself consisted of a delicate corpusculated connective tissue. The epithelium on the free surface of the chorion was partly shed; but considerable patches of it were seen in many localities. The amnion formed a capacious bag, which extended to within half an inch of the tip of the left horn of the chorion. It occupied the rest oi 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 tbe allantois occupied the whole of the right horn of the chorion, extending as far as its tip ; and its wall was in close apposition 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 foetus. The remaining part of the deep surface of the chorion in this horn was in contact with the attached surface of the amnion, which membrane extended as far as the edge of the non-villous circular spot opposite the os uteri. The amnion was also prolonged over the tubular prolongation of the allantois which extended into this horn. The amnion enveloped 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, project 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 3j inches long. It contained two arteries and two veins; and a slender tubular prolongation of the sac of the |