120 PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



layer — i. e., of the optic nerve — turn back through the 

 granular and nuclear layer and terminate in the rods 



and cones (see Fig. 

 83). These, there- 

 fore, must be re- 

 garded as fiber ter- 

 minals of the optic 

 nerve. It is proba- 

 ble that the connec- 

 tion between the 

 nuclear cells and the 

 rods and cones is by 

 means of dendrites; 

 and, furthermore, 

 that the dendrites of 

 a nuclear cell touch 

 those of severalrods, 

 while the cells cor- 

 responding to the 

 cones, especially 

 those of the fovea, 

 communicate with 

 much fewer, per- 

 haps with only one 

 cone, as seen in the 

 The importance of this 



Fig. 85. — Diagram showing the mode of con- 

 nection between nucleated cells and the rods 

 and cones: 1, fibrous layer; 2, ganglionic 

 layer ; 3, first granular layer ; 4, first nuclear 

 layer ; 5, second granular layer ; 6, second 

 nuclear layer ; 7, bacillary layer. 



accompanying figure (Fig. 85). 

 will be seen hereafter (page 131). 



The Distinctive Function of the Layers. — The 



function of the fibrous layer is wholly transmissive. It 

 is made up of sensory fibers, which transmit impressions 

 on the retina to the brain. The function of the middle 

 layer is doubtless intermediary between the elements of 

 the bacillary layer and the fibers of the optic nerve. The 

 true receptive layer is the bacillary. This is proved (1) 

 by the fact that there is only one spot where this layer is 



