GENERAL PHYSIOLOGY OF THE CEREBRUM. 



197 



use of electrical stimulation, unipolar method, have explored 

 carefully the motor areas in the monkey. They state that 

 these areas do not extend back of the central sulcus, but lie 

 chiefly along the anterior central convolution, as represented 

 in Figs. 87 and 88, and extend for only a small distance on to 

 the mesial surface of the cerebrum. The area thus delimited 

 by physiological experiments is the region from which arises 

 the pyramidal system of fibers, and clinical experience has 



Sulc.catloso 

 marg." 



SuZc.parieto 

 'oceif. 



Sulc.calca,rin. 



C.S.S. dd. 



Fig. 88. To show extension of motor areas on to the mesial surface, brain of chim- 

 panzee. (Sherrington and Greenbaum). Mesial surface of left hemisphere: Stippled region 

 marked LEG gives the motor area for lower limb; /, s, and h indicate regions from which 

 movements were obtained occasionally with strong stimuli; /, foot and leg; s, shoulder and 

 chest; h, thumb and fingers. The shaded area marked EYES indicates a region stimulation 

 of which gives conjugate movements of the eyes. 



shown that lesions in this part of the cortex are accompanied 

 by a paralysis of the muscles on the other side, particularly 

 in the limbs. Pathological or experimental lesions here, more- 

 over, are followed by a degeneration of the pyramidal neurons, 

 a degeneration which extends to the termination of the neurons 

 in the cord. With these data we can construct a fairly complete 

 account of the mechanism of voluntary movements. The ini- 

 tial outgoing or efferent impulses arise in the large pyramidal cells 

 of the motor areas, and proceed along the axons of their neurons 

 to the motor nuclei of the cranial or spinal nerves. The neurons 

 of the pyramidal tract constitute the motor tract for voluntary 

 movements; a lesion anywhere along this tract causes paralysis, 

 more or less complete, and on the other side of the body in general, 

 if the lesion is anterior to the decussation. The path of the 

 motor fibers is represented in the schema given in Fig. 89. Arising 

 in the cortex, they take the following route (see also Fig. 82, B): 



