GENERAL PHYSIOLOGY OF THE CEREBRUM. 



185 



use of electrical stimulation, unipolar method, have explored care- 

 fully the motor areas in the monkey. They state that these areas do 

 not extend back of the Rolandic fissure, but lie chiefly along the 

 anterior central convolution, as represented in Figs. 81 and 82, 

 extending 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 shown that lesions in this part of the 

 cortex are accompanied by % paralysis of the muscles on the other 



Sulc. Central. Anu3 Vagina, 

 Sutecottoso \ ' SuUi.frecentr.marg. 



Sulc.cdicj,rin 



C.S.8. del. 



Fig. 82. To show extension of motor areas on to the mesial surface, brain of chim- 

 panzee. (Sherrington and Ureenbaum). 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. 



side, particularly in the limbs. Pathological or experimental 

 lesions here, moreover, are followed by a degeneration of the 

 pyramidal neurons, a degeneration which extends to the ter- 

 mination of the neurons in the cord. With these data we can con- 

 struct a fairly complete account of the mechanism of voluntary 

 movements. The initial 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. 83. Arising in the cortex, they take the following route 

 (see also Fig. 76, B): 



