THE FCETAL MEMBRANES OP MAMMALS. 



231 



which was cut open in the process of preparation. The allantois {al) 

 is attached to the very end of the intestinal canal by means of the 

 attenuated stalk-like urachus. 



Up to this stage the correspondence in the development of the embry- 

 onic membranes in Mammals, Birds, and Eeptiles is clear. But frbm 

 now on the course of development in the Mammalia becomes more 

 and more divergent, since one portion of the embryonic membranes 



Tig. 134.— Itebiyo Dog of 25 days, extended and seen from in front, magnified 29 diameters. 



After BisoHOFF. 

 ■d, Intestine ; ds, yolk-sa« ; al, allantois, urinary sac ; un, primitive kidney ; I, the two lobes of 

 the liver, with the lumen of the omphalomesenteric vein between them ; ve, he, anterior and 

 posterior appendages ; h, heart ; m,, mouth ; au, eye ; g, olfactory pit. 



■enters into closer relations with the mucous membrane of the uterus, 

 wnd, is thus con/verted into pm organ of nutrition for the embryo. In 

 this manner a compensation is provided for the loss of the, yolk. 



The interesting adaptations for intra-uterine nutrition — they have 

 been studied especially by the English anatomist Tcrnee in a 

 series of profound comparative-embryological works — pre,sent very 

 great differences in the separate orders of Mammalia : sometimes 

 they are of a simple kind, at other times they are more com- 



