GENERAL PHYSIOLOGY OF THE CEREBRUM. 



199 



must be applied with caution to the conditions in man. As 

 we have seen, the entire cerebral cortex may be removed from 

 the frog, the pigeon, and the dog without causing permanent 

 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 devel- l 

 oped, and corresponding with this 

 fact it is found that the paralysis 

 from lesion of the motor cortex is 

 more permanent. In fact, observa- 

 tions upon men in whom it has 

 been necessary to remove parts of 

 the motor area by surgical opera- 

 tion indicate that the voluntary 

 control of the muscle is lost or im- 

 paired permanently. It would seem, 

 therefore, that even in an animal as 

 high in the scale as the dog volun- 

 tary control of the muscles can be 

 maintained through fibers other 

 than those belonging to the pyra- 

 midal system. A system such as 

 that found in the rubrospinal tract 

 (p. 180) may be considered as ade- 

 quate to fulfil such a function. In 

 man, however, along with the more 

 complete development of the pyr- 

 amidal system, the efficacy of the 

 phylogenetically older motor sys- 

 tems is correspondingly 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 of the 

 pyramidal system of fibers explain the crossed character of 

 of the paralysis quite satisfactorily. The schema thus pre- 

 sented 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. 



Fig. 89. Schema representing 

 the course of the fibers of the pyra- 

 midal system: 1, Fibers to the nuclei of 

 the cranial nerve ; 2, uncrossed fibers 

 to the lateral pyramidal fasciculus : 

 3, fibers to the anterior pyramidal 

 fasciculus crossing in the cord ; 4 and 

 5, fibers that cross in the pyramidal 

 decussation to make the lateral 

 pyramidal tract of the opposite side. 



