THE SENSE ORGANS 



587 



branches of the central retinal and of the anterior and posterior ciliary 



arteries, and veins. The retina, however, is supplied by its central 



PALLIUM 



rECTUM OPTICUM 



'CEREBELLUM 



MAMMAL 



Fig. 484. — A diagram illustrating the course of optic nerve fibers in A, a fish, B, a 

 reptile, and C, a mammal. The definitive centers of vision lie in the occipital lobes 

 of the cerebral hemispheres. The primitive centers in the optic lobes persist in mam- 

 mals as reflex centers located in the superior colliculi. (Redrawn after Monakow.) 



vessels. Most of the blood leaves the eye ball by way of four to six 

 vorticose veins. 



The ganglion cells of the retina give off neurites which converge towards 

 the "blind spot," where the optic nerve fibers leave the retina, and rods 

 and cones are absent. Of the fibers of the optic nerve, half pass to the 



