658 



THE EYE 



entrance, or rather the point of exit, of the optic nerve. Hence the 

 nerve fiber layer, being augmented by the constant acquisition of new 



axons from the ganglion cells, becomes pro- 

 gressively thicker toward the posterior pole 

 of the eye, and is thickest at the margin of 

 the optic papilla, where it is so highly de- 

 veloped as to almost exclude the other 

 retinal layers. 



The course of these non-medullated 

 nerve fibers is not straight; on the contrary, 

 they interlace to form a delicate fibrillar 

 network. At the margin of the papilla op- 

 tica the nerve fibers bend outward with a 

 sharp curve almost at right angles to their 

 former course. At this point also they grad- 

 ually acquire a medullary sheath and, unit- 

 ing into many bundles, penetrate the nu- 

 merous openings of the lamina cribrosa of 

 the sclerotic and choroid coats to form the 

 optic nerve. 



THE SUPPORTING TISSUES OF THE RETINA 



FIG. 558. A FIBER CELL OF 

 MULLER, OR SUSTENTACU- 

 LAR CELL, FROM THE DOG'S 

 RETINA. 



1, nerve fiber layer; 2, gan- 

 glion cell layer; 3, inner retic- 

 ular layer; 4, inner nuclear 

 layer; 5, outer reticular layer; 

 6, outer nuclear layer; a, a 

 process extending into the 

 inner reticular layer; 6, nu- 

 cleus of the cell; m.l.e., exter- 

 nal limiting membrane; m.l.i., 

 internal limiting membrane. 

 Golgi's stain. Highly mag- 

 nified. (After Cajal.) 



The nucleus of the fiber 

 layer. 



These consist of a gliaform reticulum 

 distributed throughout the cerebral portion 

 of the retina., and of a special supporting 

 tissue, Miiller's fibers, which may also be re- 

 garded as glia tissue, though they are com- 

 mon to both the neural and epithelial por- 

 tions. 



The fibers of Miiller (radial fibers; 

 sustentacular cells') comprise numerous large 

 glia cells whose processes begin with an ex- 

 panded base at the inner surface of the 

 nerve fiber layer, and can be traced all the 

 way through the retina to the membrana 

 limitans externa, which is likewise formed 

 by the terminal expansions of these cells, 

 cell lies in the mid-region of the inner nuclear 



