NERVOUS CONSTITUENTS OF THE RETINA. 243 



Thus it appears that the'cone fibres are not, properly speaking, 

 interrupted by the cone granule, but originate in it ; for in most 

 instances the cone itself is attached to the outer surface of the 

 cone granule, whilst in the case of the rod granules, in conse- 

 quence of their not lying immediately beneath the limitans 

 externa, the connection of the rods is effected by a portion of 

 the rod fibre, of similar nature, only somewhat thicker than 

 the portion which extends to the external granulated layer. 

 This last-named internal division of the rod fibre must ob- 

 viously become shortened to a minimum, whilst the outer 

 division must be proportionately elongated in those rod granules 

 which are closely applied to the external granulated layer. 



The rod and cone granules are perfectly transparent during 

 life, the difference in the refractive power for light of the cell 

 substance, nucleus, and nucleolus being scarcely perceptible ; 

 granular cloudiness becomes apparent in them after death, 

 either in consequence of spontaneous coagulation, or owing to 

 the action of reagents. In like manner it appears that the 

 occurrence of transverse striae or bands in the rod granules, 

 described by Henle,* which can be observed sooner or later 

 after death in Man and Mammals, and which may be rendered 

 very distinct by the action of dilute acids,t is a post-mortem 

 appearance depending on a partition of the nucleus or of the 

 contents of the nucleus.^ 



If the external granules represent a peculiar form of nerve 

 cell introduced in the course of the nervous rod and cone fibres, 

 the rods and cones themselves must constitute the nervous 



between the cone and the cone granule is also increased. The peripheric 

 part of the cone fibre is then always thicker than the central part, extend- 

 ing from the granule to the granulated layer. (See below, fig. 355.) 



* Gottinger Nachrichten, May and November, 1864, No. 7. 



t Max Schultze, Archiv fur Mikroskop. Anatomic, Band ii., p. 219. 

 According to W. Krause (Membrana fenestrata, p. 32), they may also be 

 observed in the cone granules. 



W. Krause, Anatomie d. Kaninchens, p. 129. See also, in regard to 

 the still unexplained appearance of transverse striae, Hitter in Grafe's 

 Archiv, Band xi., Abtheil i., p. 89. G. Wagener (Sitzungsberichtc der J\V 

 turwissenschaft. Gesellschaft zu Marburg, 1868, No. 5) remarks in regard to 

 the transverse striation, that in fresh preparations it is more distinctly 

 visible with low, than with high powers. 



R 2 



