GENERAL PHYSIOLOGY OF THE CEREBRUM. 



187 



paralysis, although in the animal last named there is at first a more 

 or less marked loss of voluntary control. But in man and the higher 

 types of the monkey the pyramidal system is more completely 

 developed, and corresponding with this fact it is found that the 

 paralysis from lesion of the motor cortex is more permanent. In 

 fact, observations upon men in whom 

 it has been necessary to remove 

 parts of the motor area by surgical 

 operation indicate that the voluntary /'/ 

 control of the muscles is lost or im- j'?^ 

 paired permanently. It would seem, 1% - J 

 therefore, that in an animal as high 

 in the scale as the dog voluntary 

 control of the muscles can be main- 

 tained through tracts other than the 

 pyramidal system, tracts, perhaps, 

 such as Monakow's bundle (rubro- 

 spinal tract) , arising in the midbrain 

 (see p. 171). In man, however, 

 along with the more complete de- 

 velopment of the pyramidal system, 

 the efficacy of the phylogenetically 

 older motor systems is correspond- 

 ingly reduced. 



The Crossed Control of the 

 Muscles and Bilateral Represen- 

 tation in the Cortex. It has been 

 known from very ancient times that 

 an injury to the brain on one side 

 is accompanied by a paralysis of 

 voluntary movement on the other 

 side of the body, a condition known 

 as hemiplegia. The facts given 

 above regarding the origin and course 



Fig. 83. 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- 

 Of the DVramidal fibers explain the bers to the anterior pyramidal tract 

 "J 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. 



crossed character of the paralysis 

 quite satisfactorily. The schema 

 thus presented to us is, however, 



not entirely without exception. In cases of hemiplegia in which 

 the whole motor area of one side is included it is known that the 

 paralysis on the other side does not involve all the muscles, and, 

 in the second place, it is said that there is some muscular weakness 

 on the same side. The paralysis in hemiplegia affects but little, 

 if at all, those muscles of the trunk which are accustomed to act 

 in unison, the muscles of inspiration, for instance, the diaphragm, 



