222 



THE ESSENTIALS OF HISTOLOGY 



inner molecular layer, with the formation of which they are probably 

 connected. Others, which are larger and more rounded, are applied 

 to the outer molecular layer. The fibres of Miiller have nucleated 

 enlargements in the inner nuclear layer. 



The outer molecular layer is thin, and is composed of flattened and 

 branched cells, the ramified cell-processes being united into a close 

 network (fig. 258). 



FIG. 258. BRANCHED CELLS WITH THE UNITING FELTWORK OF FIBRES FROM THE 

 OUTER MOLECULAR LAYER OF THE HORSE'S RETINA. 



As far as the outer molecular layer the retina may be said to con- 

 sist of nervous elements, but beyond this layer it is formed of modified 

 epithelium - cells . 



The outer nuclear layer and the layer of rods and cones are com- 

 posed of elements which are continuous through the two layers, and 

 they should properly, therefore, be described as one. It maybe termed 

 the neural or sensory epithelium of the retina (fig. 260, 6 and 7). The 

 elements of which the neural epithelium consists are elongated, nucle- 

 ated 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. 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. 259). The cone-elements are formed of a conical taper- 

 ing external part, the cone proper, which is directly prolonged into 

 a nucleated enlargement, from the farther side of which the cone- 

 fibre, considerably thicker than the rod-fibres, passes inwards, to ter- 

 minate by an expanded base at the outer molecular layer. The cone 

 proper, like the rod, is formed of two segments, the outer of which, 

 much the smaller, is transversely striated, the inner, bulged segment 



