VI.] 



THE OPTIC VESICLE. 



Fig. 51. 



143 



pCh 



Section op the Eye of Chick at the Fourth Day. 



ep. superficial epiblast of the side of the head. 



R. true retina : anterior wall of the optic cup. p. Ch. pigmeut- 



epitheUum of the choroid : posterior wall of the optic cup. 



h is placed at the extreme lip of the optic cup at what will 



become the margin of the iris. 



I. the lens. The hind waU, the nuclei of whose elongated cells 

 are shewn at nl, now forms nearly the whole mass of the lens, 

 the front waU being reduced to a layer of flattened cells el. 



m. the mesoblast surrounding the optic cup and about to form 

 the choroid and sclerotic. It is seen to pass forward between 

 the lip of the optic cup and the superficial epiblast. 



