DEVELOPMENT OF THE SENSE ORGANS 



375 



that the cavity of the primitive optic vesicle is nearly obliterated. Pigment 

 granules have begun to appear in the outer cells which form the pigment layer 

 of the retina. Mesenchymal 

 tissue surrounds the optic cup 

 and is beginning to make its 

 way between the lens vesicle 

 and the ectoderm. Here is later 

 developed the anterior chamber 



(ft 



Diencepha/on 



Crystalline lens 



of the eye as a cleft in the meso- 

 derm. The distal mesenchy- 

 mal tissue (next the ectoderm) 

 forms the substantia propria of 

 the cornea and its posterior 

 epithelium, while the proximal 

 mesenchyma (next the lens) 



differentiates into the vascular capsule of the lens. The mesenchyme surround- 

 ing the optic cup is continuous with that which forms the cornea and later 



Lens I vesicle ,1/iTreous body I Optic stalk 



.. i I I I Opticrecess 



Iviesenchyma. / / / / 'of brain 



Choriod fissure 



Opfic\stalK 



FIG. 356. The optic stalk, cup and lens of an embryo 

 of twenty-seven days. On the ventral surface of the optic 

 cup is seen the chorioid fissure of the primitive eye (from 

 Fuchs, after Hochstetter in Kollmann's Handatlas). 



Epithelium 

 of Cornea. 



^Pigment layer 

 of retina 



Nervous layer 

 of retina 



FIG. 357. A transverse section through the optic cup, stalk and lens of a 10 mm. human embryo. X 100. 



gives rise to the sclerotic layer, to the chorioid layer and to the anterior layers 

 of the ciliary body and iris. 



