CH. LVI.] 



THE FOVEA CENTRALIS 



775 



with the uvea, where, however, the cells become rounded, and 

 arranged two or three deep. 



Differences in Structure of different parts. Towards the centre 

 of the macula lutea all the layers of the retina become greatly 

 thinned out and almost disappear, except the rod and cone layer, 

 and at the fovea centralis the rods disappear, and the cones are long 

 and narrow. At the margin of the fovea the layers increase in 

 thickness, and in the rest of the macula lutea are thicker than else- 

 where. The ganglionic layer is especially thickened, the cells being 

 six to eight deep (2, fig. 576). The bipolar inner granules (cone 



in.l.c. 



in. 1. 1. 



FIG. 576. Diagram of a section through half the fovea centralis. 2, Ganglionic layer ; 4, inner nuclear; 

 6, outer nuclear layer, the cone fibres forming the so-called external fibrous layer ; 7, cones ; m.l.e., 

 membrana limitans externa ; m.l.i., membrana limitans interna. (Schafer and Golding Bird.) 



nuclei) are obliquely disposed (figs. 576 and 577) on the course of 

 the cone fibres, and are situated at some distance from the membrana 



FIG. 577. Scheme of the retinal elements. A, Cones of the fovea centralis ; B, granules (nuc'ei) of 

 these cones ; C, synapse between the cones and bipolar cells in external molecular layer ; D, syi apse 

 between the bipolar and ganglion cells in the internal molecular layer ; a and b, rods and cones in 

 other regions of the retina ; c, bipolar cell destined for the cones ; d, bipolar cell destined for the 

 rods ; E, e, ganglion cells ; /, spongioblast ; g, efferent fibre (? trophic), originating from the cell m, 

 in geniculate body; h, optic nerve; i, terminal arborisations of optic nerve-fibres in geniculate 

 body ; j, fibres from the cells of geniculate body on the way to cerebral cortex. (R. y Cajal.) 



limitans externa, which is cupped towards the fovea (fig. 576). The 

 yellow tint of the macula is due to a diffuse colouring matter in the 

 interstices of the four or five inner layers ; it is absent at the centre 

 of the fovea. 



