32 



VERTEBRATE PHOTORECEPTORS 



mop bipolars (d) and some of the brush and flat bipolars 

 (e, f), and probably all varieties of ganglion cells (m, n, o, 

 p, r, s). The rods are thus related to the ganglion cells by 

 diffuse bipolars only. This system does not involve the 

 midget bipolars (h) or association cells (c) or the amacrine 



4WWW^w 



Ql./.i^ A/ 



Fig. 26. Scheme of the primate retina, showing types of neurones and their 

 synaptic relations as shown by Polyak, 1941, Chicago University Press. 



cells (i, k, 1). The rod system is thus thought of as made up 

 of physiological units, each composed of a group of rods, of a 

 fascicle of diffuse bipolars, and a group of ganglion cells. 

 These units are not completely separated, but overlap and 

 merge throughout the retina. 



In the cone system (Figure 27, D), the cones may synapse 

 with all varieties of centripetal bipolars (d, e, f, h), which in 



