370 



SPECIAL HISTOLOGY. 



Fig. 303. 



elongated corpuscles, in which a larger external end, the proper 

 rod, is to be distinguished from a more slender internal portion, 



the prolongation or fila- 

 ment. The former por- 

 tion of the rods, which 

 alone almost has hitherto 

 been known to anato- 

 mists,is a cylinder, 0*0075 

 —0-012— 001 5'" long, 

 0*0008 /,/ broad, and trun- 

 cated at the outer end, 

 whilst the inner is pro- 

 duced into a short point, 

 0-002— 0-003"' in length, 

 which is often separated 

 from the rest of the "rod" 

 by a faint transverse line, 

 and might even perhaps 

 be assigned to the " fila- 

 ~. ment." The latter is an 



extremely delicate process, not more than 0*0002 — 0-0003'" in 

 thickness, of uniform width throughout, prolonged immediately 

 from the point of the u rod," and, extending through the 

 inner half of the bacillar layer ; it is connected with the other 

 elements of the retina in a manner to be afterwards described. 

 This filament is so delicate that it is usually torn off near its 

 origin on the slightest mechanical impression affecting the 

 bacillar layer; on which account also it has happened that 

 observers hitherto have been acquainted only with the " proper 



Fig. 303. Retinal elements of Man, x 350 diam. 1, "rods" and radiating fibres : 

 k, proper "rod;" r, prolongation of its pointed inner extremity; h, "granule" (cell) 

 of the outer granular layer ; /, enlarged extremity of the radiating fibres proceeding 

 from them to the surface of the optic layer; k', "rod" seated on a "cone," i; 

 r', fibre proceeding from the latter, connected with the "granule,"/, of the inner 

 granular layer, and the terminal enlargement, /, on the inner surface of the retina; 

 n, one of the fibrous bundles in which the radiating fibres frequently terminate at 

 their innermost extremity. 2, "rods" torn off from their fibres, in various states of 

 curvature, &c. 3, fibres of the optic nerve : a, b, straight, coarser and finer fibres, 

 with varicosities ; c, without varicosities. 4, two "cones," b, torn off from their 

 processes, d 1 with somewhat altered "rods," a, at their outer ends ; c, nucleus of the 

 "cones." 



