470 PKACTICAL DIRECTIONS. [APR 



D. Separate the membranes from one another with- 

 out tearing them, 



and notice : 



1. The embryo surrounded by the amnion. 



2. The allantois; its position dorsal to the embryo; its 

 attachment to the chorion ; its circulation. 



3. The flattened yolk sac, ventral to the embryo ; its 

 long stalk; its circulation. 



4. The heart. 



E. The embryo in surface view. 

 The points to be observed are 



1. The cranial and body flexure, the spiral curvature 

 of the hinder portion of the body. 



2. The vesicles of the brain : cerebral hemispheres, 

 fore-brain, mid-brain and hind-brain. 



3. The eye, and the ear. 



4. The heart. 



5. The visceral arches and clefts. 



6. The fore and hind limbs, and the tail. 



