DEVELOPMENT OF THE SENSE ORGANS 



377 



In an embryo of 10 mm. (Fig. 376) the essential plan of the eye is 

 foreshadowed. The lens vesicle has separated from the ectoderm, which 

 will form the epithelium of the cornea. The lens vesicle in earlier stages 



Anlage of lens 



Fore-brain 



Optic vesicle 



Optic vesicle 



Optic stalk Optic vesicle 



Retinal layer 



Lens vesicle 



FlG. 374. vStages in the early development of the human eye. A, B, 4 mm. (X 27); C, 5 mm. 

 (X 23); D, 6.25 mm. (X 18); (after Keibel and Elze). 



(Fig. 374 D) is closely applied to the inner wall of the optic cup, but now 

 it has separated from it, leaving a space in which the vitreous body de- 

 velops. The inner retinal layer of the optic cup has become very thick 



Diencephalon ; 



'rystalline lens 

 'Chorioid fissure 



Optic stalk 



FIG. 375. The optic stalk, cup and lens of a human embryo of 12.5 mm. Thechorioid fissure 

 has not yet extended along the optic stalk (from Fuchs, after Hochstetter). X 9- 



and is applied to the outer layer, so that the cavity of the primitive optic 

 vesicle is nearly obliterated (Fig. 376). Pigment granules have begun 

 to appear in the outer layer of cells to form the pigment layer of the retina. 



