THE EYE AS AN OPTICAL INSTRUMENT 



253 



The rods and cones appear to constitute the peripheral or 

 dendritic portions of bipolar sensory neurons. They communi- 

 cate with cell-bodies from which in turn pass typical, though 

 very short, axons. The third retinal layer is composed of these 

 cell-bodies with their axons. The axons of the rod and cone 

 neurons come into synaptic connection with dendrites of a second 



FIG. 83. Diagram of the structure of the human retina (Greeff) : /, pigment 

 layer;//, rod and cone layer; \R. rods;C, cones ;III-IX. intraretinal nerve-elements; 

 X, axons which pass to optic nerve. 



set of retinal neurons, the synapses making up the fourth retinal 

 layer. The fifth, sixth, and seventh retinal layers contain the 

 cell-bodies and short axons of these second retinal neurons; in 

 the eighth layer these come into synaptic connection with the 

 dendrites of the third set of retinal neurons. The large cell- 

 bodies of these neurons make up the ninth retinal layer, and 

 their axons, converging from all parts of the retina upon the optic 



