624 PHYSIOLOGY 



inner molecular layer. Here the process of the rod bipolar forms an 

 arborisation around the body of a cell m the ganglion-cell layer, while 

 the processes of the cone bipolars end at various levels in the inner 

 molecular layer, forming synapses with the dendrites of the ganglion- 

 cells. 



(3) The ganglion- cells, which represent the third relay, receive the 

 impulses from the more peripheral parts of the retina and send them 

 towards the brain along the fibres of the optic nerve, each of which 

 is the axon of one of the ganglion-cells. These axons, which form 



FIG. 284. Schema of retina. (From BOHM and DAVIDOFF after CAJAL.) 

 1, nerve-fibre layer ; 2, ganglion-cell layer ; 3, inner molecular layer ; 



4, inner nuclear layer ; 5, outer molecular layer ; 6, outer nuclear layer ; 



c, cone ; r, rod ; &, bipolar cells ; S, spongioblast ; am, amacrine cell ; 



c.n, centrifugal nerve fibre ; M, fibre of Miiller ; n. M, nucleus of fibre of 



Muller ; n, neuroglia ; o, outer limiting membrane. 



the inner layer of the retina, the so-called ' nerve- fibre layer,' are 

 non-medullated as they pass over the surface of the retina, but acquire 

 a medullary sheath as they pass out of the eyeball through the 

 cribriform plate of the sclerotic and join to form the optic nerve. 



Most of the bipolar cells are connected with several rods or cones ; 

 only in the fovea centralis do we find a special bipolar cell provided 

 for every cone. Every ganglion-cell comes into connection with 

 and receives the impulses from a considerable number of bipolar cells, 

 so that the number of fibres in the optic nerve running centrally is not 

 so great as the number of sense elements in the rod and cone layer 

 of the retina. Besides these cells situated on the direct path of the 

 visual impulse, other cells of a nervous nature are found in the inner 

 nuclear layer (the outer and inner horizontal cells), and also in the 



