APP.] FCEl-AL MEMBRANES. 469 



4. The two lateral tubes of the heart, and the com- 

 mencement of the two vitelline veins. 



5. The rudinient of the primitive streak. 



6. The commencing head and tail folds. 



7. The commencing folds of the amnion. 

 Compare Fig. 106. 



XYII. Examination of the foetal membranes of an embryo 

 of 14 days. 



A. To obtain tite embryo, with its membranes. 



Manipulate as in XV. A, only dissect under salt 

 solution instead of picric acid. 



B. Observe before removing the em,bryo from the 



titerns ; 



1. The attachment of the vesicle to the mesometric 

 side of the uterus over a discoidal area, the 

 placental area. 



2. The position and form of the placenta. 



C. Remove the embryo with its membranes intact, 

 and observe : 



1. the vascular yolk sac, extending completely round 

 the chorion with the exception of a com]>aratively 

 small area where 



2. the allantois is situated. The vascularity of the 

 allantois. The foetal villi projecting into the 

 maternal placental tissue. 



