GENERAL USES OF THE CEREBRUM 585 



paralysis of the opposite leg ; 5, brachio-facial monoplegia, or paralysis 

 of the arm and face. 



In addition to the motor areas just described, there probably is a 

 group of sensory areas on the mesial surface of the brain that has been 

 called the tactile centre. This is in the gyrus fornicatus, just above the 

 corpus callosum. The centres for the special senses, which will be 

 more fully considered, however, farther on, are the following % olfactory 

 centre and taste centre, at the anterior extremity of the temporal lobe ; 

 the simple visual centre, on the mesial surface of the cerebrum above 

 and below the calcarine fissure ; the psychical visual centre, on the con- 

 vex surface of the occipital lobe, behind the auditory centre and on 

 the left side only ; the simple auditory centre, in the superior and mid- 

 dle temporal convolutions ; the psychical auditory centre, in the superior 

 temporal convolution, on the left side only. 



One of the most important of the cerebral centres is the centre for 

 speech, which will be described after the consideration of the general 

 uses of the cerebral hemispheres. 



GENERAL USES OF THE CEREBRUM 



The cortical substance of the cerebral hemispheres not only is capa- 

 ble of generating motor impulses of the kind known as voluntary and of 

 receiving sensory impressions, including those connected with the special 

 senses, but its anatomical and physiological integrity, and its connec- 

 tions, especially with sensory conductors, are essential to what are 

 known as mental operations. The existence of the mind and the possi- 

 bility of normal operations of the intelligence depend on the existence 

 of the gray matter of the cerebral cortex and its normal physiological 

 condition and relations. Mental operations involve a slight elevation of 

 temperature and slightly increase some of the excretions. It is prob- 

 able, therefore, that they involve changes of matter ; and these changes, 

 if they occur, can be effected only by the cells of the brain. Without 

 defining or analyzing the intellectual faculties or attempting to locate 

 different faculties in special parts, it is sufficient to state that certain of 

 them reside probably in that portion of the brain which is anterior to 

 the motor-cortical zone ; that is, in the frontal lobes. These lobes, so 

 far as is known, do not present motor or sensory areas ; and recent 

 observations have shown that lesions of the frontal lobes especially are 

 attended with marked impairment of the intellectual faculties and little 

 or no motor disturbance. 



The brain and the intellectual power of man are so far superior in 

 their development to this organ and its properties in the lower animals, 



