THE EYE. 369 



abruptly. Notwithstanding this various thickness, the follow- 

 ing layers from without to within may be evidently distin- 

 guished in all parts of it : 1. the layer of rods and cones 

 [bacillar layer]; 2. the granular layer; 3. the layer of grey 

 nerve-substance; 4. the expan- 

 sion of the optic nerve; and 5. Fi 8- 302 - 

 the limitary membrane. These 

 layers, with the exception of 

 the innermost, which is of uni- 

 form thickness throughout, in 

 general become thinner towards 

 the front, in correspondence 

 with the diminished thickness 

 of the whole retina. 



1 . The bacillar layer, stratum 

 bacillorum s. memb. Jacobi (fig. 



302 i, k), presents a very remarkable structure, being com- 

 posed of innumerable rod-like and conical corpuscles, dis- 

 posed with the utmost regularity and reflecting the light 

 very strongly. With the exception of H. Miiller (vid. infra), 

 this structure, in animals, has been understood quite erro- 

 neously; and even in Man it has been but very super- 

 ficially known. It consists of two elements — the rods, 

 bacilli (k), and the cones, coni (i), which together constitute 

 a single layer, 0*036'" thick at the bottom of the eye, 

 more anteriorly 0-024 7 ", and quite in front not more* than 

 0*0 15"' in thickness. In general these bodies are so arranged 

 that the more numerous rods have their largest end directed 

 outwards, whilst the cones are disposed in the reverse direc- 

 tion, whence the latter, when imperfectly examined, appear to 

 constitute an inner, distinct, thinner layer, lying between the 

 inner extremities of the " rods." 



In Man, the rods (fig. 303, 1, k, 2) are cylindrical, slender, 



Fig. 302. Vertical transverse section of the retina of Man, from the posterior 

 portion of the memhrane, x 250 diam.: a, hyaloid membrane with decumbent 

 nuclei ; b, membrana limitans ; c, clear globules (epithelium ?) ; d, expansion of the 

 optic nerve ; e, layer of grey nerve-substance ; /, internal granular layer ; g, fine- 

 granular layer, in which the radiating fibres are more distinct than elsewhere ; h, 

 external granular layer ; i, internal division of the bacillar layer, with the " cones ;" 

 Xt, external division, with the prolongations of the " cones" and the true " rods." 



ii. 24 



