270 



THE ESSENTIALS OF HISTOLOGY. 



The outer nuclear layer and the layer of rods and cones are composed of 

 elements which are continuous through the two layers, and they should 

 properly, therefore, be described as one. It may be termed the sensory 

 or nerve-epithelium of the retina (fig. 302, 6 and 7). The elements of 

 which this nerve-epithelium consists are elongated, nucleated cells of 

 two kinds. The most numerous, which we may term the rod-elements, 

 consist of peculiar rod-like structures (rods proper) set closely side by 

 side, and each of which is prolonged internally into a fine varicose fibre 

 (rod-fibre] which swells out at one part of its course into a nucleated 

 enlargement, and ultimately ends in an arborisation within the outer 



FIG. 302. DIAGRAMMATIC REPRESENTATION OF SOME OF THE NERVOUS AND 



EPITHELIAL ELEMENTS OF THE RETINA. (After Schwalbe.) 

 The designation of the numbers is the same as in fig. 297. 



molecular layer. The rod proper consists of two segments, an outer 

 cylindrical and transversely striated segment, which during life has a 

 purplish-red colour, and an inner slightly bulged segment, which in 

 part of its length is longitudinally striated. The nucleus of the rod- 

 element often has, in the fresh condition, a transversely shaded aspect 

 {fig. 302). The cone-elements are formed of a conical tapering external 



