135 
of Edinburgh, Session 1872 - 73 . 
arteries, utero-placental veins, and a very remarkable system of 
intra-placental maternal sinuses, continuous with the uterine 
vessels, freely anastomosing with each other within the substance 
of the lobes, and lying between and in contact with the foetal villi. 
Definite walls, distinct from the walls of the foetal villi, could be 
traced around the sinuses. Crowds of red blood corpuscles were 
situated within the sinuses, and it was observed that many of 
these seemed to be nucleated, an appearance which had been 
recognised a few years ago by Kuhne, Eolleston, and Moseley, in 
the blood corpuscles of the Tardigrada. This sinus system pos- 
sessed a special interest, because it presented a gradation between 
the capillary net-work of the uterine mucous membrane, occurring 
in the diffused placenta of the mare or the cetacean, and the freely 
anastomosing cavernous maternal blood spaces seen in the highly 
concentrated human placenta. The amnion lay in close contact 
with the inner surface of the chorion, as in the human foetal mem- 
branes. The foetus possessed a special envelope, like that figured 
and described by Welcker, as investing the foetus of B. tridactylus , 
and named by him an Epitricliium. Numerous additional details 
respecting the structure of the placenta and membranes are con- 
tained in the memoir. 
The conclusions drawn from the examination of this placenta 
were, that in the sloths the placenta is not cotyledonary and 
non-deciduate as in the Ruminants, but in the fullest sense of the 
word deciduate. If the inference drawn by Huxley from Sharpey’s 
observations on the structure of the placenta of Manis be correct, 
then, if the placental system of classification is to be of any value, 
the non-deciduate scaly ant-eaters can no longer be grouped along 
with the deciduate sloths in the order Edentata, which order will 
have therefore to be subdivided. The author then compared the 
placentation of the sloth with that of the other deciduate mam- 
mals, and pointed out a series of very interesting affinities between 
its placenta and that in the Primates. 
VOL. VIII. 
