612 



THE EYE. 



Fig. 422. 



Fig. 422. — The Nervous and Epithelial 

 Elements op the Retina (Semidiagram- 

 MATic). After Schwalbo. 



The members are the same as in fig. 419. 

 The extent of the molecular layers is indicated 

 merely by lines of shading. 



directly connected, or there is at 

 most a short, comparatively thick 

 stalk uniting the two (see fig. 422). 

 At the macula lutea, however, 

 where only cone-granules are met 

 with, many of them are further 

 removed from the limiting mem- 

 brane, and the stalk is then longer 

 and more attenuated. Tlie nucleus 

 of each, whicli, as in the case of 

 the rod-granules, occupies almost 

 all the enlargement, contains a 

 distinct nucleolus. The cone-fibre 

 is very much thicker than the 

 rod-fibres above described. It 

 passes from the smaller end of the 

 pear-shaped enlargement straight 

 through the outer nuclear layer 

 to reach the outer molecular layer, 

 upon which it rests by a some- 

 what spread-out end. From the 

 edges of this, numerous exces- 

 sively-fine fibrils pass into the 

 substance of the molecular layer. 

 Moreover a delicate striation or 

 fibrillation has occasionally been 

 described in the cone-fibre itself. 



7. The layer of rods and 

 cones. — Bacillary layer (fig. 422, 

 7). The elements which compose 

 this layer are, as their name im- 

 plies, of two kinds, those of the 

 one kind — the rods — having an 

 elongated cylindrical form; the 

 cones on the other hand being 

 shorter, much thicker, bulged at 

 the inner end or base, and termi- 

 nated externally by a finer taper- 

 ing portion. Both rods and cones 

 are closely set in a pallisade-like 

 manner over the whole extent of 

 the retina between the raembrana 

 limitans externa and the pigmen- 

 tary layer (fig. 419, 7); except at 

 the macula lutea, where only cones 

 are met with, the rods far exceed 

 the cones in number. Their rela- 

 tive number and arrangement is 

 well exhibited when the layer is 

 viewed from the outer surface, as 

 in fig. 423, where a represents a 

 portion of the layer from the 

 macula lutea ; I>, from the im- 



