72 



PSYCHOBIOLOGY 



medial and peripheral zones of the retina) the rods are relatively more 

 numerous, adjacent cones being separated by 2, 3, 4 or more rods. 



The rod and cone may be considered as special forms of dendrites. 

 The rod is connected with the cell body by a slender fiber, whereas the 

 inner segment of the cone is practically a continuation of the cell body. 



From the inner side of the cell body a short axon proceeds, which, 

 in the case of the cone cell, has branches in contact with the dendrites of 

 the bipolar cells in the ' inner nuclear layer ' of 'the retina. The rod 

 cell axons end in a single knob, in contact with the dendritic branches 

 of the bipolar cells. Each cone cell axon has synaptic connection with 



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Fig. 6o. Schematic representation of some of the principal neurons of the olfac- 

 tory conduction paths. (Barker, Nervous System.) 



one cone-bipolar cell. The axons of several rod cells may arborize with 

 the dendrites of a single rod-bipolar. In this layer there are also hori- 

 zontal cells whose axon and dendrite branches are in contact with the 

 terminations of the rod and cone cell dendrites. These horizontal cells 

 are therefore interconnecting cells (so-called association cells). 



The bipolar cells send axons inward to varying distances, which 

 touch the dendritic terminations of the ganglion cells in the next to the 

 innermost layer of the retina, or possibly in some cases touch the 

 ganglion cell bodies. The axons of these ganglion cells run to the 

 blind spot or disc of the eye, and from thence in the optic nerve, to the 



