184 



PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



baum,* making 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 Rolandic 

 fissure, but lie chiefly along the anterior central convolution, 

 as represented in Fig. 83, 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 a paralysis of the 

 muscles on the other side, particu- 

 larly in the limbs. Pathological or 

 experimental lesions here, moreover, 

 are followed by a degeneration of the 

 pyramidal neurons, a degeneration 

 which extends to the termination of 

 the neuron in the cord. With these 

 data we can construct a fairly com- 

 plete account of the mechanism of 

 voluntary movements. The initial 

 impulse arises in the large pyramidal 

 cells of the motor areas and proceeds 

 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 move- 

 ments; a lesion anywhere along this 

 tract causes paralysis, more or less 

 complete and on the other side 

 of the body in general, if the le- 

 sion is anterior to the decussation. 

 The path of the motor fibers is 

 represented in the schema given in 

 Fig. 84. Arising in the cortex, they 

 take the following route (see also 

 Fig. 77, 5) : 



1. Corona radiata. 



2. Internal capsule. 



3. Crus cerebri (pes). 



4. Pons Varolii, in which they are broken into a number of 



smaller bundles by the fibers of the middle peduncle of the 



* "Reports of the Thompson- Yates and Johnston Laboratories," 4, 351, 

 1902; 5, 55, 1903. 



Fig. 84. Schema representing 

 the course of the fibers of the pyram- 

 idal tract: 1, Fibers to the nuclei of 

 the cranial nerve; 2, uncrossed fibers 

 to the lateral pyramidal tract; 3, fi- 

 bers to the anterior pyramidal tract 

 crossing in the cord; 4 and 5, fibers 

 that cross in the pyramidal decussa- 

 tion to make the lateral pyramidal 

 tract of the opposite side. 



