THE RETINA. 269 



be denominated the Miillerian filaments to the limitary 

 membrane ; the various bodies which constitute the white 

 cellular layer being connected with these filaments in the 

 manner already described. The branch which proceeds from 

 each of the Miillerian filaments in its course through the 

 inner stratum of the white cellular layer becomes continuous 

 with one of the radiations of one of the nucleated cells of the 

 grey cellular layer ; all the cells of this layer therefore being 

 connected with all the rods and cones of the retina. The 

 remaining radiations of the cellules of the grey layer, passing 

 inwards, form the commencements of the ultimate filaments 

 of the optic nerve in the filamentary layer of the retina. 



In reference to those parts in the structure of the retina 

 upon which that impression is made, which, when conveyed 

 to the sensorium, terminates in the perception of light, it may 

 be stated, that the non-sensibility of the retina at the entrance 

 of the optic nerve, and its perfect sensibility at the macula 

 lutea, as well as other considerations, prove that this function 

 is not performed by the filaments of the nerve. 



Kolliker concludes, by exclusion of the other elements, 

 that the rods and cones, with the Miillerian filaments, are the 

 structures on which objective light first impresses itself. He 

 believes the seat of this impression to be in the rods and cones, 

 and also probably in the inner ends of the Miillerian filaments. 

 He has examined with great care the chemical and structural 

 characters of these bodies, and has satisfied himself that they 

 are nervous structures. 



Briicke and Hannover conceive the rods and cones of the 

 bacillary layer to be structures which reflect the light back 

 again from the outer surface of the retina against the filament- 

 ary layer, on which it is thus impressed. Helmholtz, again, 

 who does not admit the sensibility to light of this layer, 

 believes the reflected light to act upon the grey cellular 

 layer. 



