740 ANATOMY OF VERTEBRATES. 



The varieties of placental structures and modifications in the 

 Ungulate group are not yet exhausted. The chorion of the 

 Elephant, fig. 577, a, a' ', d, at about the middle of the period of 

 gestation, forms a transversely oblong sac, 2 feet 6 inches in long 

 diameter, and 1 foot 4 inches in short diameter, encompassed at 

 its middle part by an annular placenta, ib. b, b, 2 feet 6 inches 

 in circumference, varying from 3 to 5 inches in breadth, and from 

 1 to 2 inches in thickness : it is partially divided by opposite 



577 



•72 



F<Btal membranes and placenta, Repliant) 



constrictions into two moieties ; it presents the same spongy tex- 

 ture as does the annular placenta of the Carnivora; but the 

 laminate villosities enclosing the foetal filaments enter into its 

 formation in a larger proportion, and are of a relatively coarser 

 character. The greater part of the outer convex surface of the 

 placenta is smooth ; the rough part separated from the serotine 

 portion occupied a narrow tract, c, c. A thin brown deciduous 

 layer is continued from the borders of the placenta, for a distance 

 varying from 1 to 3 inches, upon the outer surface of the chorion. 

 Flattened folds of a similar substance could be raised from some 

 parts of the surface of the placenta; at other parts the substance 

 formed irregular fibrous bands, the fibres extending in the direction 

 of the circumference of the placental ring. The outer surface of 

 the chorion is for the most part smooth ; but at each of the obtuse 

 extremities of the sac there was a villous and vascular subcircular 

 patch, d, d, the villi being short and graniform, \t\\ of a line in 

 diameter, or less. Thus the chief points of attachment of the 

 chorion to the uterus are, at the equator, by the annular placenta. 



