CH. LV.] 



THE RETINA. 



751 



inwards (fig. 570). The large oval nuclei (fig. 5 70) belonging to 

 the Mullerian fibres occur in this layer. 



6. Outer molecular layer. This layer closely resembles the 

 inner molecular layer, but 



is much thinner. It con- 

 tains the branchings of the 

 rod and cone fibres on the 

 one hand and of the 

 bipolar cells on the other. 



7. External nuclear layer. 

 This layer consists of 

 small cells resembling at 

 first sight those of the in- 

 ternal nuclear layer ; they 

 are classed as rod and cone 

 granules, according as they 

 are connected with the 

 rods and cones respectively, 

 and will be described with 

 them. They are lodged in 



the meshes of a frame- 

 work, which is formed by 

 the breaking up of the 

 Mullerian fibres. 



8. Membrana limitans 

 externa. A delicate well- 



Fig. 572. The posterior half of the retina of the 

 left eye, viewed from before ; *, the cut edge 

 of the sclerotic coat ; ch, the choroid ; r, the 

 retina ; in the interior at the middle the 

 macula lutea with the depression of the fovea 

 centralis is represented by a slight oval shade ; 

 towards the left side the light spot indicates 

 the colliculus or eminence at the entrance of 

 the optic nerve, from the centre of which the 

 artena centralis is seen spreading its branches 

 into the retina, leaving the part occupied by 

 the macula comparatively free. 



(After Henle.) 



defined membrane, clearly 



marking the internal limit of the rod and cone layer, and made up 



of the junction of the bases of the susteutacular fibres externally. 



m.l.c 



tn.l.i. 



Fig. 573. Diagram of a section through half the fovea oentralis. 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 intern*. Kchafer and Oolding Bird.) 



Small hairlike processes project outwards between the rods and 

 cones to support them. 



