Chap, xxxix.] THE RETINA. 313 



of the rod- or cone-fibre, to become connected with a 

 rod or cone respectively, while inwards it passes into 

 a longer, more conspicuous fibre, the inner part of the 

 rod- or cone-fibre. This branches, and penetrating 

 into the outer molecular layer, is lost with its 

 branchlets among the fibrils of this layer. 



443. (9) The rods and cones. Each rod is 

 of cylindrical shape, with rounded or conical outer 

 extremity ; it consists of an outer and inner member, 

 joined by linear cement. Its substance is bright and 

 glistening, and that of the outer member is composed 

 of the neurokeratin of Kiilme and Ewald. In 

 the fresh state the outer member shows a more or 

 less fine and longitudinal striation, due to longitudinal 

 fine ridges and furrows (Hensen, Max Schultze). 

 After certain reagents, such as serum, liquor potassae, 

 the outer rod-member disintegrates into numerous 

 transverse, thin, homogeneous-looking discs (Hannover). 

 The inner member in the human rods is slightly 

 broader than the outer ; it is pale or finely and longi- 

 tudinally striated, and contains in many instances a 

 peculiar lenticular structure ; in the human and 

 mammalian retina this is absent, but in its stead is a 

 mass of longitudinal fibrils (Max Schultze). The 

 inner member passes through a hole in the limitans 

 externa, and becoming thinner, represents the outer 

 part of the rod-fibre. 



444. Each cone is composed of an outer, short, 

 pointed, conical member, and an inner larger member 

 with convex surface: this is the body of the cone. 

 The outer member of the cone separates under certain 

 conditions also into thin transverse discs. The body 

 of the cone is longitudinally and finely striated. 

 The outer extremity of the body of the cones in 

 many birds, reptiles, and amphibia contains a spheri- 

 cal corpuscle of red, orange, yellow, green, or even 

 blue colouration. 



