'20 



ANATOMY OF VERTEBRATES. 



At a later period of uterine development, when the foetus, 

 measured in a straight line from the mouth to the root of the 

 tail, is ten lines in length, the uraehus expands into a small 

 allantois, iig. 569, d, of a flattened pyriform figure, and finely 



569 





Tterinc foetus, mcml>r;uies and appendages, M<icr<.]ii<i* major. (.The fretus is magnified twice the 



natural size.) 



wrinkled external surface. This ba" insinuates itself between 



o 



the amnios and chorion, carrying alono- with it two small hypo- 



*/ O O 



gastric arteries and a vein, but not establishing by their means an 

 organised and vascular surface of the chorion by which a placental 

 attachment is formed between the ovum and the womb. The 



