60 



SPECIAL SENSES. 



FIG. 4. 



readily understood if we accept the following explanation : 

 The filaments from the bases of the rods and cones pass in- 

 ward, presenting, in their course, the corpuscles which we 

 have described in the granule-layers, and finally become, as is 

 thought, directly continuous with the poles of the ganglion- 

 cells. The cells, in their turn, 

 each send one filament to 

 the layer formed by the ex- 

 pansion of the optic nerve, 

 which is continuous with a 

 nerve -fibre. This arrange- 

 ment is shown in Fig. 4. 



The arteries of the retina 

 branch from the arteria cen- 

 tralis, presenting a beauti- 

 fully arborescent appearance 

 when viewed with the oph- 

 thalmoscope. They pass into 

 the layer of gray nervous mat- 

 ter and send their branches 

 to the periphery, where they 

 supply a wide plexus of very 

 small capillaries in the ora ser- 

 rata. The capillaries empty 

 into an incomplete venous 

 circle, branches from which 

 pass back by the sides of the 

 arteries to the vena centra- 

 lis. The macula lutea is pro- 

 vided with a rich plexus of 

 minute capillaries. 



Scheme of the connection of the rods and cones 

 with the true nervous elements of the reti- 

 na. (KoLLiKEK, Handbuch der Gewebe- 

 Wvre, Leipzig, 1867, S. 684.) 



Crystalline Lens. The anatomy of the crystalline lens, 

 as far as it bears upon the physiology of vision, is very sim- 

 ple. It is a double-convex lens, transparent, and exceedingly 

 elastic. It has a function in the refraction of the rays of 



