268 THE RETINA. 



meuts of the filaments of the rods and cones, which terminate 

 ou its outer surface by expanding into conical brushes, or still 

 more minute threads, which would almost appear to constitute 

 the membrane itself. 



At the entrance of the optic nerve, the bacillary, white 

 cellular, and grey cellular layers, are necessarily absent ; the 

 limitary membrane alone covering the inner surface of the 

 mass of nervous filaments, which, with the arteries, spreads out 

 on all sides. 



Over the macula lutea the bacillary layer consists of cones 

 alone, the filaments of which do not reach the limitary layer, 

 at least at the fovea centralis, but terminate in the white cell- 

 ular layer. The latter exists, except at the fovea. The grey 

 cellular layer is distinct throughout ; but towards the centre, 

 and at the fovea, its granular stratum is deficient, the nu- 

 cleated cellules being crowded together under the limitary 

 layer. The filamentary layer is deficient as a lamina, over 

 the entire macula lutea ; but its constituent filaments may be 

 detected in the midst of the nucleated cellules of the spot. 

 The peculiar yellow pigment is diffused through all the 

 textures, with the exception of the bacillary layer. 



The structure of the retina is so delicate, and its investiga- 

 tion so difficult, that much remains still to be determined 

 regarding the precise connection of its different elements. 

 The structure of the bacillary layer having been more parti- 

 cularly examined by Gottsche and Hannover, and the white 

 cellular layer by Bowman, Pacini traced the filaments inwards 

 from the rods and cones into the white cellular layer. The 

 discovery of the filaments themselves, and their passage 

 inwards to the limitary layer, is due to Heinrich Miiller, by 

 whom, along with Kolliker, the general anatomical connec- 

 tions of the microscopic elements of the retina have been 

 more particularly traced. According to H. Miiller and 

 Kolliker, the rods and cones are connected by what may now 



