THE INTEENAL COAT THE NEEVOUS TUNIC 



657 



most part,, disposed in horizontal planes, though a few spread throughout 

 the entire thickness of the reticular layer. 



9. The ganglion cell layer (ganglion nervi optici, inner ganglionic 

 layer, layer of large nerve cells') is of variable thickness. Its greatest 

 depth is in the region of the macula lutea, where it consists of five or 

 six superposed ganglion cells. Toward 



the equator of the eye it becomes progres- 

 sively thinner, until near the ora serrata 

 its single layer of cells only forms an in- 

 complete stratum. 



The cells comprising this layer are 

 mostly large, stellate, pyriform, or sphe- 

 roidal nerve cells, from whose peripheral 

 border dendrons pass to the inner reticu- 

 lar layer, and from whose central border 

 an axon passes to the nerve fiber layer to 

 eventually become the axis cylinder of a 

 fiber of the optic nerve. 



These cells, though varying much in 

 size and shape, possess a body of the usual 

 structure with neurofibrils and chromo- 

 philic granules, and a pale vesicular nu- 

 cleus with a distinct chromatic nucleolus. 

 Intermingled with the nerve cells are 

 many fine branches of the sustentacular 

 cells which here form an open-meshed 

 network within whose spaces the nerve 

 cells are inclosed. 



10. The nerve fiber layer, in inti- 

 mate relation with the preceding, forms 

 the innermost of the retinal zones. It 

 consists of naked axis-cylinders passing 

 from their origin in the ganglionic layers 



to their immediate destination, the optic nerve. They are, therefore, 

 mostly if not wholly centripetal fibers. A few centrifugal fibers have been 

 demonstrated in this layer, but they would appear to be probably vaso- 

 motor in function, a few possibly ending in relation to the amacrine cells. 

 The nerve fibers of this layer converge from all portions of the retina, 

 follow a meridional course through the open meshes of the network of 

 branching sustentacular cells, and converge toward the optic papilla, the. 



FIG. 557. A NERVE CELL OF 

 THE LARGE GANGLION CELL 

 LAYER; FROM THE RETINA OF 

 A CAT. 



n, n, axon; c, c, collaterals. 

 X 325. (After 



