AFFERENT, OR SENSORY PATHS. 385 



of the optic tracts. From the right halves of both retinas and 

 from the left halves of both, impulses run through the correspond- 

 ing tract to the lateral geniculate body and the pulvinar of the 

 thalamus; also to the superior quadrigeminal colliculus. The 

 latter produces ocular and pupillary reflexes. From the lateral 

 geniculate body and pulvinar the occipito-thalamic radiation 

 carries the impulses through the pars occipitalis of the internal 

 capsule to the half-visual center in the cuneus, gyrus lingualis 

 and the pole of the occipital lobe. Impulses from the nasal halves 

 of the retinas decussate in the optic commissure; those from the 



Fig. no. The chief retinal elements. (After Brubaker.) 



Cells, s' 2'. Visual cells with their peripheral terminations, s. Rods. z. Cones, b. Bipolar 

 cells, g. Ganglion cells from which arise the axones of the optic nerve. 



temporal halves, for the most part at least, remain on the same 

 side, but a few may cross through the quadrigeminal colliculi 

 and brachia superiora. Impulses from the nasal half and from 

 the temporal half of the macula lutea are conducted equally by 

 both optic tracts. Hence destruction of one tract causes hem- 

 ianopsia, preserving the vision in the corresponding half of each 

 visual field, and also diminishes the acuteness of macular vision 

 in both eyes. 



Auditory Paths. There are two auditory paths, cochlear 

 and the vestibular. The former is concerned with hearing and 

 the latter with equilibrium. 

 25 



