VI.J 



THE OPTIC VESICLE. 

 Fig. 51. 



143 



Section of the Eyu or Chick at the Foubth Day. 



ep. superficial epiblast of the side of the head. 



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

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

 b is placed at the extreme Up of the optic cup at what will 

 become the margin of the iris. 



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

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

 the front wall 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 epiblaat. 



