212 CENTRAL NERVOUS SYSTEM 



destroyed. When starved he would show signs of hunger, and 

 learned to feed himself when his nose was placed in contact 

 with the food. He would reject food of disagreeable taste. 

 When sleeping 'he gave no signs of dreaming. 



The loss of the cerebral hemispheres would, no doubt, to 

 a monkey be a heavier and more irremediable blow than to a 

 dog. No one has succeeded in keeping a monkey alive after 

 complete removal of even one hemisphere. In man, the gradual 

 destruction of considerable masses of brain substance is not 

 necessarily fatal. The result depends largely upon the situa- 

 tion of the lesion, for the cerebral cortex is not homogeneous in 

 function. This is expressed by the term localization of function. 



The Motor Area. Definite experimental proof of cerebral 

 localization was furnished by Pritsch and Hitzig in 1870, who 

 showed that stimulation of the cortex in dogs in the region of 

 the crucial sulcus gave definite movements. An enormous 

 amount 'of experimentation has made it probable that the motor 

 area in man lies along the anterior central convolution, and 

 extends for only a small distance on to the mesial surface of the 

 cerebrum (Fig. 13). It dips down to the bottom of the cen- 

 tral sulcus, but does not extend behind it. Anteriorly it shades 

 off gradually into inexcitable cortex. Within this area are 

 localized movements of the head, face, mouth, tongue, ear, 

 nostril, and vocal cords; movements of the neck, chest, abdomen, 

 arm, and leg. Within each area smaller centres may be located 

 by careful stimulation; thus, the arm and hand area may be 

 subdivided into regions for the wrist, fingers, and thumb. 

 The distribution of the areas follows in a general way the order 

 of the cranial and spinal nerves. 



The motor area, thus outlined physiologically, is the region 

 from which the pyramidal system of fibers arises, and lesions 

 in this part of the cortex are accompanied by paralysis of the 

 muscles of the other side of the body, particularly of the limbs. 

 The path taken by motor impulses is through the following 

 structures: Corona radiata, internal capsule, cerebral peduncle, 

 pons, anterior pyramids, pyramidal decussation, direct and 

 crossed pyramidal tracts of the cord. In the pons some of the 

 fibers cross the midline to end in the motor nuclei of the third, 

 fourth, fifth, sixth, and seventh cranial nerves. Clinically, it 

 is important to recognize the difference between the effects of 



