THE EYE 



limiting membrane than else- 

 where in the retina. 



The pigment of the epithe- 

 lial layer is much diminished 

 and may even be absent at the 

 fovea. Because of the diminu- 

 tion in the number of ganglion 

 cells in this area the nerve 

 fibre layer is greatly dimin- 

 ished in thickness on approach- 

 ing the margin of the fovea, 

 and toward its center entirely 

 disappears. 



THE OPTIC NERVE is a 

 large nerve trunk, composed, 

 like the white matter of the 

 brain of which it is an onto- 

 genetic portion, of medullated 

 nerve fibres without a neuri- 

 lemma. It receives an invest- 

 ing sheath from each of the 

 cerebral membranes. These 

 sheaths are continued as far 

 forward as the eyeball, at 

 which point they become con- 

 tinuous with the sclera. 



Lying in the axis of the 

 nerve, the arteria central is 

 retinae with its accompanying 

 vein enters the eye and ap- 

 pears on the inner surface of 

 the 'retina at the porus opticus 

 in the center of the optic 

 papilla. Here it divides, its 

 several branches at first pur- 

 suing a meridional course be- 

 tween the hyaline membrane 

 and the retinal surface; soon 

 they pierce the latter to sup- 

 ply the cerebral portion of the 

 retina. No vessels penetrate 



