832 



THE SENSE OF SIGHT 



The nerve fibers derived from the different regions of the hemispherically 

 expanded retina, leave at the optic pore where they pierce the other two coats of the 

 eyeball and are continued onward as the optic nerve. Inside this point they are 

 not in possession of a medullary sheath nor of a neurolemma. Most of these fibers 

 are formed by the axis cylinder processes of the cells of the second layer, but some 

 also originate in the inner molecular and inner granular layers. The ganglion cells 

 of the second layer differ greatly in their size and shape, their single unbranched 

 axones entering the fiber layer. They are especially numerousin the vicinity of the 

 yellow spot, where they are arranged in three consecutive rows. The inner 

 molecular layer is granular in its appearance and is made up of the arborescent 



Outer or cfiormdai surface. 



! i. 



ra.t.i 



Inner or vitreous surface. 

 FIG. 436. DIAGRAMMATIC SECTION OF THE HUMAN RETINA. (Schultze.) 



terminations of the processes of the cells constituting the two neighboring layers. 

 The inner nuclear contains two types of closely packed cells of which the bipolar 

 type is the most conspicuous. Their inner processes usually extend to the internal 

 molecular layer within which they terminate in the vicinity of its ganglion cells. 

 Their outer processes are usually thicker and pursue a more direct course to the 

 outer molecular layer, where they arborize together with the horizontal cells of the 

 inner nuclear layer. The outer molecular presents an appearance similar to that 

 of the inner molecular, but is not quite so thick. The outer nuclear layer consists 

 of nuclear corpuscles having an oval or elliptical shape. They are known respec- 

 tively as the rod-granules and cone-granules. The former are the more numerous 

 and appear as swellings upon the delicate fiber emitted by the rods of the outermost 



