472 



length, before the division of the vascular trunks, and about 3 inches 

 in circumference. The inner surface of the amnios is roughened by 

 brownish hemispherical granules, from 1 line to T ^th of a line in 

 size commonly about a line ; the outer surface is finely wrinkled, 

 but smooth ; the amnios is continued from the base of the umbilical 

 cord upon the allantois, which is of considerable size, and is so in- 

 terposed between the chorion and amnios as to prevent any part of 

 the amnios attaining the inner surface of the placenta. The amnios 

 consists of two layers : one is the granular layer, continued upon 

 the inner or foetal surface of the allantois, and thence upon the 

 umbilical cord ; the other is the smooth outer layer, continued upon 

 the outer or chorional surface of the allantois, and thence upon the 

 inner surface of the chorion. The allantois divides where the am- 

 nios begins to be reflected upon it into three sacculi ; the disposition 

 of these sacculi is described in detail. The chief peculiarity was the 

 presence, upon the inner layer of the allantois, and chiefly upon the 

 endochorionic vessels, of numerous flattened oval or subcircular 

 bodies, varying in diameter from an inch to half a line : their tissue 

 was compact, structureless, and of a grey colour. On dissecting some 

 of the vessels over which these bodies were placed, the vessel was 

 found to pass on the chorionic side of the body without undergoing 

 any apparent change, the body being developed from the allantois, 

 and from that part which forms the allantoic side of the sheath of 

 the vessel. These bodies were most numerous near the placenta : 

 their free surface was smooth, not villous like the cotyledons of the 

 Ruminantia, from which they likewise differed in projecting inwards 

 towards the cavity of the allantois. The most important modifica- 

 tion of the vascular structures connecting the chorion with the 

 uterus, in the Elephant, is their combination of two forms of the 

 placenta, viz. the ' annular' and the ' diffused,' which have hitherto 

 been supposed to characterize respectively distinct groups of the 

 class Mammalia. 



The author concludes by a comparison of the different known 

 forms of the placenta, including those of the Pteropus or large fru- 

 givorous Bat, and of the Chimpanzee ; and fTy remarks on the value 

 of placentary characters in the classification of the Mammalia. 



