720 



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 urachus expands into a small 

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



569 



Uterine foetus, membranes and appendages, l^faa't.pus major. (The fcetusis magnified twice the 



natural size.) 



wrinkled external surface. This ban insinuates itself between 

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

 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 





