THE SENSES. 



589 



which interlace, and some of which are continuous with processes of 

 large nerve-cells forming the next layer. 



3. Layer of ganglionic corpuscles, consisting of large multipolar 

 nerve-cells, sometimes forming a single layer. In some parts of the 

 retina, especially near the macula lutea, this layer is very thick, consist- 

 ing of several distinct strata of nerve-cells. These cells lie in the spaces 

 of a connective-tissue framework. 



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

 It consists of a punctiform connective 



tissue traversed by numberless very fine 

 fibrillar processes of the nerve-cells. 



5. Internal granular layer. This con- 

 sists 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 

 outwards and another inwards. They 

 greatly resemble the ganglionic corpuscles 

 of the cerebellum. Besides these there 

 are large oval nuclei (e' } Fig. 396 A) be- 

 longing 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 con- 

 nective tissue with nerve fibrils. 



7. External granular layer; which con- 

 sists of several strata of small cells re- 

 sembling those of the internal granular 

 layer; they have been classed as rod and 

 cone granules, according as they are con- 

 nected 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 ex- 

 ternal granular layer stain very rapidly and 

 deeply with haematoxylin, while the rod 

 and cone layer remains quite unstained. 



8. Membrana limitans extern a; a deli- 

 cate, 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, consist- 

 ing of two kinds of elements: the " rods/' which are cylindrical and of 

 uniform diameter throughout, and the " cones/' whose internal portion 



FIG. 396. Diagram of the retina. 

 A, connective tissue portion; B, ner- 

 vous portion Cthe two must be com- 

 bined to form the complete retina) ; a 

 a, membrana limitans externa; 6, 

 rods; c, cones; &', rod-granuale ; c', 

 cone-granule; both belonging to the 

 external granule layer; e, Muller's 

 sustentacular fibres, with their nu- 

 clei e'; d, intergranular layer; /, in- 

 ternal granule layer; gr, molecular 

 layer, connective-tissue portion: g', 

 molecular layer, nerve-fibril portion; 

 h, ganglion cells; h'. their axis-cylin- 

 der process; i y nerve-fibre layer. (Max 

 SchultzeO 



