200 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



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, 

 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 may 

 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 fasciculus in the cord on both sides, show- 

 ing 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 

 pyramidal cells that give origin to the fibers of the pyramidal 

 system makes it possible histologically that other functions may 

 be mediated in the same region. Tnis 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, that is, in 

 muscular and cutaneous sensibility, but especially the former. 

 It was suggested, therefore, at one time that one and the same 

 spot in the cortex might serve as the origin of the motor impulses 

 to a given muscle and as the cortical termination of the sensory 

 impulses coming from the same muscle, the reaction in con- 

 sciousness, the muscular sensations, being mediated perhaps 

 through cells other than those giving rise to the pyramidal fibers. 

 Recent physiological and clinical work has, however, not tended 

 to support this view. The motor areas appear to be confined 

 to the region in front of the central sulcus of Rolando, while the 

 cortical area, in which the afferent fibers mediating body sensibility 

 (muscular-cutaneous) make their final termination extends back of 

 this sulcus in the posterior central convolution. Whether, 

 on the other hand, the sense areas for the body (cutaneous and 



