186 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



tracts other than the pyramidal system, tracts, perhaps, such as 

 Monakow's bundle (rubrospinal tract), arising in the midbrain. In 

 man, however, along with the more complete development of the 

 pyramidal system, the efficacy of the phylogenetically older motor 

 systems is correspondingly reduced. 



The Crossed Control of the Muscles and Bilateral Repre- 

 sentation 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 fibers explain the 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 is involved 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 mus- 

 cular weakness on the same side. The paralysis in hemiplegia 

 affects but little, if at all, those muscles of the trunk which are accus- 

 tomed to act in unison, the muscles of inspiration, for instance, 

 the diaphragm, abdominal and intercostal muscles, and the muscles 

 of the larynx. It would appear that these muscles are bilaterally 

 represented in the cortex; so that if one side of the brain is intact 

 the muscles of both sides are still under voluntary control. The 

 mechanism of this bilateral representation is not definitely known ; 

 one might conceive several possibilities. The motor area on 

 each side may send down a double set of pyramidal fibers, one 

 of which crosses and the other remains on the same side, or the 

 fibers may bifurcate. Or it is possible that the bilateral control is 

 due to commissural connections between the lower centers in the 

 cord. Some evidence in favor of the former view is found in the 

 undoubted histological fact brought out by Mellus and others, that 

 small unilateral lesions in the motor area the center of the great 

 toe in the monkey, for instance are followed by degeneration in 

 the lateral pyramidal tract in the cord on both sides, showing that 

 some portions of the motor area send fibers to both sides of the 

 body. In cases of hemiplegia it may be added that the muscles 

 of the limbs are not all equally affected. 



Are the Motor Areas Only Motor in Function? The great 

 number of nerve cells in the cortex in addition to the large pyram- 

 idal cells that give origin to the fibers of the pyramidal tract make 

 it possible histologically that other functions may be mediated 

 in the same region. This possibility has been kept in view since 

 the early experiments of Munk, in which he showed that lesions in 

 the Rolandic region are followed by disturbances in what are 

 designated as the body sensations, muscular and cutaneous sensi- 



