ORGANS OF THE BODY. 



639 



cone granule 



r 



C 



The fibres which descend perpendicularly from 

 through the external granu- 

 lar layer (tig. 589), differ 

 from the rod fibrillee in their 

 greater thickness (reaching 

 0-0029 ram.) though still of 

 great delicacy. They tra- 

 verse the layer just men- A 

 tioned in a straight course, 

 coming likewise to an end 

 at the outer surface of the 

 stratum intergranulosum in 

 a conical swelling. In this 

 course they present consider- 

 able resemblance to axis 

 cylinders, and give indica- 

 tions of being made up of 

 the most delicate axis-cylin- 

 der fibrillae (comp. 176). 

 Schnltze states (the expan- 

 sion on the fibres having 

 been recognised, however, 

 before by Muller and Henle) 

 that in the stratum inter- 

 granulosum he has distinctly 

 seen a splitting up of those 

 cone fibres into extremely 

 delicate fibrillae, whose 

 course from that on is hori- 

 zontal (fig. 595, B, d). 

 Hasse, on the other hand, 

 never observed more than 

 three of these processes, one 

 single in the middle, and 

 one at either side. He re- 

 girds this expansion as tri- 

 angular and smooth. The 

 central process, he believes, 

 moreover, he has followed 

 up in a perpendicular course 

 into the inter-granular layer. 



It seems almost super- 

 fluous to remark that the external granular layer is only composed of rod 

 corpuscles when the retina is destitute of cones. 



Finally, this layer appears to possess no connective-tissue cells. 



317. 



Passing on now to the consideration of the remaining layers of the 

 retina, we take the next in succession. 



(4.) The stratum intergranulosum or intergranular layer (fig. 595, A, 

 By d, d) which is about O'OIO mm. thick, is crossed, as we know already, 

 by the radial fibres of Muller. The finely dotted substance of the 

 intergranular layer, which presents the appearance of being streaked 



Fig. 595. Diagram of the retina, after Schttltze. B, neural 

 constituents; 6, rods with external and internal members; 

 c, cones with style and body ; 6 / , rod-granule, and c / , cone 

 granule; d, expansion of the cone fibre forming very 

 delicate fibrillae in the intergranular layer ; /, granules of 

 the internal granular layer; g, maze of very delicate fila- 

 ments in the molecular stratum; h, ganglion cells; A', 

 their axis-cylinder process ; t, nerve-fibre layer. 



