vn.j 



THE TAIL FOLD, 

 Fig. 67. 



197 



Embryo at the End op the Fourth Day seen as 

 a transparent object. 



The amnion has been completely removed, the cut end of the 

 somatic stalk is shewn at S.S. with the allantois {Al.) protruding 

 from it. 



C.H. cerebral hemisphere. F.B. fore-brain or vesicle of the third 

 ventricle (thalamenoephalon) with the pineal gland (Pn.) 

 projecting from its summit, if. B. mid-brain. C6. cerebellum. 

 IV.V. fom-th ventricle. L. lens. ch.s. choroid slit. Owing to 

 the growth of the optic cup the two layers of which it is com- 

 posed cannot any longer be seen from the surface ; the pos- 

 terior surface of the choroid layer alone is visible. Cen. V. 

 auditory vesicle, s.m. superior maxillary process. IF, 2F, etc. 

 first, second, third and fourth visceral folds. V. fifth nerve 

 sending one branch to the eye, the ophthalmic branch, and 



