188 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



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 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- 

 bility, 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 consciousness, the muscular sensa- 

 tions, being mediated perhaps through cells other than those 

 giving rise to the pyramidal fibers. Recent physiological and clin- 

 ical work has, however, not tended to support this view. The 

 motor areas appear to be confined to the region in front of the fis- 

 sure of Rolando, while the cortical area, which gives rise to that 

 kind of consciousness that we designate in general as body sensi- 

 bility, extends back of the Rolandic fissure in the posterior central 

 gyrus. Whether, on the other hand, the sense areas for the body 

 (cutaneous and muscular) extend forward into the cortex of 

 the frontal lobe is not clearly shown by experimental or clinical 

 evidence. Flechsig, from his studies upon the time of myelini- 

 zation of the afferent fibers in the embryo brain, concludes that 

 this is the case, and that therefore the motor and sensory areas 

 overlap for a part at least of their extent (see p. 212 and Fig. 92). 



