THE SENSES. 201 



4. Molecular layer. This presents a finely granulated appearance. It 

 consists of a punetiform connective-tissue traversed by numberless very 

 fine fibrillar processes of the nerve-cells. 



5. Internal granular layer. This consists chiefly of numerous small 

 round cells with a very small quantity of protoplasm surrounding a large 

 nucleus; they are generally bipolar, giving off one process outward and 

 another inward. They greatly resemble the ganglionic corpuscles of the 

 cerebellum (Fig. 330). Besides these there are large oval nuclei (e, Fig. 

 370, A) belonging to the sustentacular connective-tissue fibres. 



6. Inter granular layer; which closely resembles the molecular layer, 

 but is much thinner. It consists of finely-dotted connective tissue with 

 nerve fibrils. 



7. External granular layer; which consists of several strata of small 

 cells resembling those of the internal granular layer; they have been 



FIG. 371. FIG. 372. 



FIG. 371. Ciliary processes, as seen from behind. 1, posterior surface of the iris, with the 

 sphincter muscle of the pupil; 2, anterior part of the choroid coat; 3, one of the ciliary processes, of 

 which about seventy are represented. ^. 



FIG. 372. The posterior half of the retina of the left eye, viewed from before; s, the cut edge of 

 the sclerotic coat; c/j, the choroid: ?, 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; toward the left side the 

 light spot indicates the colliculus or eminence at the entrance of the optic nerve, from the centre of 

 which the arteria centralis is seen spreading its branches into the retina, leaving the part occupied by 

 the macula comparatively free. (After Henle.) 



classed as rod and cone granules, according as they are connected by very 

 delicate fibrils with the rods and cones respectively. They are lodged 

 in the meshes of a connective-tissue framework. Both the internal and 

 external granular layer stain very rapidly and deeply with haematoxylin, 

 while the rod and cone layer remains quite unstained. 



8. Membrana limitans externa; a deMcate, well-defined membrane, 

 clearly marking the internal limit of the rod and cone layer 



9. Rod and cone layer, bacillar layer, or membrane of Jacob, consisting 

 of two kinds of elements: the "rods," which are cylindrical and of uni- 

 form diameter throughout, and the "cones," whose internal portion is 



