422 ELEMENTARY PHYSIOLOGY 



methods of staining many details have recently been 

 made out which seem to justify the construction of the 

 following diagrammatic figure (Fig. 137) in illustration of 

 the structure of the retina and of the relationships of its 

 several layers. In this figure the facts of chief and 

 immediate interest are those which refer to the mode of 

 connection between a rod on the one hand and a cone on 

 the other with the fibre of the optic nerve. 



In the case of a rod the rod-fibre (r./.) is seen to end 

 in the outer molecular layer ( V) as an extremely minute 

 knob. This knob is surrounded by processes from the 

 outer end of a rod bipolar cell (r.b.p.) whose body lies in 

 the inner nuclear layer (/T-^. 



The inner end of this cell ends in branching processes 

 which surrovnd the body of one of the cells in the 

 ganglionic-cell layer (JJ). which is itself in direct continuity 

 with a fibre of the optic nerve {op.f.). 



In the case of a cone the cone-fibre {cf.) ends as a 

 flattened expansion, fi-oni which fine processes extend, in 

 the outer molecular layer ( V). Immediately below these 

 processes of the base of a cone-fibre, but not actually 

 continuous with them, lie the processes from the outer 

 end of a cone bipolar cell (c.b.p.) whose body is again 

 situated in the inner nuclear layer (TV). The inner end 

 of this cell terminates in expanded branches in the 

 inner molecular layer (///). Facing these, but not in 

 actual continuity with them, lie the processes from the 

 outer end of one of the cells in the ganglionic-cell layer 

 (II) which, as before, is itself directly connected with a 

 fibre of the optic nerve. 



In this way each rod and cone is brought into relation- 

 ship with a fibre of the optic nerve ; but the path of 

 connection in each case shows tivo breaks in its structured 

 continuity. In the case of a rod these breaks lie in the 

 outer molecular layer (F) and ganglionic layer (11) ; in the 

 caoe of a cone they lie in the outer and inner molecular 

 layers respectively {V and ///). 



