642 THE SENSE OF SIGHT. 



The structures of which the granular layer is composed 

 are indicated in the figure! 



The nervous layer is composed of nerve-corpuscles and 

 nerve-fibres. The nerve- corpuscles are the outermost, and 

 are most numerous over the yellow spot, and absent alto- 

 gether from the point of entrance of the optic nerve. 

 They are imbedded in fine molecular matter, which also 

 forms a layer outside them. The nerve-fibres radiate as a 

 fine membranous network from the point of entrance of 

 the optic nerve, of whose fibres they are the continuation. 

 They end probably in the nerve-corpuscles. The fibres are 

 absent from the yellow spot. 



Two of the fibres of Muller, about the connections of 

 which there is still considerable uncertainty, are, for the 

 sake of illustration, arranged in the figure separately on 

 each side of the layer which they perforate. They are 

 supposed to be connected by their outer ends with the rods 

 and cones ; and by their inner , which are thought to be 

 modifications of connective tissue, they rest on the mem- 

 Irana limitans. Between these points they are supposed 

 to have connections also with some of the other structures 

 through which they pass, especially with the inner layer of 

 nuclei. 



The retinal blood-vessels ramify chiefly in the nervous 

 layer. 



The structures which have been just described are modi- 

 fied in their distribution over the yellow spot in the follow- 

 ing manner : Of the columnar layer, or membrana Jacobi, 

 the cones greatly predominate ; of the nervous layers the 

 cells are numerous, while the nerve -fibres are absent, 

 There are capillaries here, but none of the larger branches 

 of the retinal arteries. Opposite the fovea centralis, there 

 are, moreover, neither the granular, nor the fine molecular 

 layer, nor the fibres of Muller. 



By means of the retina and the other parts just described, 

 a provision is afforded for enabling the terminal fibres of 



