LOCALISATION OF FUNCTION. 



269 



than in any other animal, when we measure them by 

 means of the area which they occupy in cross-sections 

 of the bulb or cord, for since the fibres are in the 

 several cases approximately of the same diameter the 

 area of the bundle corresponds to the number of fibres 

 which it contains. The relations are shown in the 

 accompanying figure. 



These anatomical relations are inadequate to fully 

 measure the physiological differences, for man surpasses 

 the dog in the adjustment of his limbs to a greater 

 degree than is here indicated, because the total 



MONKEY 



DOG 



FIG. 59. Schemas of a cross-section of the spinal cord in the 

 dorsal region in three mammals, the sections being all 

 enlarged to the size of that representing man, which has been 

 magnified 4 diameters. The cross-lined portions indicate 

 the area of the pyramidal tracts. (Sherrington, in Foster's 

 Physiology.} 



complexity of the reactions must be expressed by the 

 increased complexity of all the structural elements in- 

 volved in producing it, and not that of any one alone. 



Since the fibres of the pyramidal tract take origin in 

 the efferent elements of the cortex, the greater the 

 extent of the area the more abundant should be the 

 fibres coming from it. Thus it is evident that the 

 bundle of fibres coming from the large cortical area for 

 the arm should have a greater cross-section than that 



