10-* 



THE THIRD DAY. 



[CHAP. 



Fig. 31. 



c.t 



Section of the Eye of Chick at the Fourth Day. 



( . p. superficial epiblast of the side of the head. 



JR. true retina : anterior wall of the optic eup. p. Ch. pigment-epithelium of 



the choroid : posterior wall of the optic cup. b is placed at the extreme 



lip of the optic cup at what will become the margin of the pupil, 

 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. 

 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. 

 Filling up a large part of the hollow of the optic cup is seen a hyaline mass 

 vh, possibly the rudiment of the vitreous humour. It has fallen away from 

 the retina at x, and is also (apparently accidentally) wanting at y. In the 

 neighbourhood of the lens it seems to be continuous as at cl with the tissue a, 

 which in turn is continuous with the mesoblast m, and appears to be the 

 rudiment of the capsule of the lens and suspensory ligament. 



/. 



m. 



