HUMAN PHYSIOLOGY. 



Figure 31 will illustrate the conditions in the various forms of aphasia. 

 Impressions are constantly passing from eye and ear to the visual and audi- 

 tory centers and are there being registered. Commissural fibers connect 

 these centers with the arm and speech centers, which in turn are connected 

 by efferent fibers with the muscles of the hand and of the vocal apparatus. 



Muscular movements of the 

 eye, hand, and mouth are also 

 registered by means of the 

 efferent fibers, s, s', s". 



Sensor Centers. These are 

 the centers in which the affer- 

 ent impulses are translated 

 into conscious sensations. The 

 most important are: 



The visual center, located in 

 the occipital lobe and especially 

 in the cuneus. Unilateral de- 

 struction of this area results in 

 hemianopsia, or blindness of 

 the corresponding halves of the 

 two retinae. Destruction of 

 both occipital lobes in man 

 results in total blindness. 

 Stimulation or irritation of the 

 visual center causes photopsia, 

 or hallucinations of sight, in 

 corresponding halves of the 

 retinae. There have been in- 

 stances of injury of these parts 

 when sensations of color were 

 abolished with preservation of 

 those of space and light, thus 

 showing a special localization of the color center. Recent experiments 

 show that the centers of the two hemispheres are united, as ocular 

 fatigue of an unused eye was found to be proportional to the fatigue of the 

 exercised one. 



The auditory centers are located in the temporosphenoid lobes. Word- 

 deafness is associated with softening of these parts, and their complete 

 removal results in deafness. 



The gustatory and olfactory centers are located in the uncinate gyrus, on the 



FIG. 31. 



