178 THE HUMAN BODY 



It appears that most of the fibers of the direct pyramidal tracts 

 cross the mid-line in the spinal cord before reaching their termi- 

 nations; so that the pyramidal tracts are finally crossed tracts. 

 All the pyramidal axons have synaptic connection with the cells 

 of motor neurons in the ventral horns of gray matter of the cord. 



The pyramidal axons are branched at their tips, so that each 

 communicates with several motor neurons. On page 136 we saw 

 that each motor neuron connects with a number of muscle-fibers. 

 It follows that a considerable group of muscle-fibers is under the 

 control of each pyramidal axon. When we recall the large numbers 

 of fibers which go to make up even our smallest muscles, we see 

 that this arrangement, which cuts down the number of nervous 

 elements required to operate the muscular system, does not at all 

 impair the delicacy and efficiency of our muscular movements. 



Since the pyramidal axons arise from cell-bodies within the 

 cortex it is evident that the pyramidal tracts must be efferent 

 paths. The intimate way in which the pyramidal fibers connect 

 with the cell-bodies of motor neurons indicates that they form 

 the paths by which the cerebrum exercises control over bodily 

 movements. The anatomical evidence for that view has been 

 corroborated and strengthened by physiological evidence. The 

 German physiologists, Fritsch and Hitzig, showed that in dogs 

 electrical excitation of those areas of the brain from which spring 

 the pyramidal tracts is followed by movements of the muscles of 

 the Body. They showed also that these are the only areas from 

 which such movements can be elicited. 



Upon the basis of all this evidence we are justified in looking 

 upon the regions immediately in front of the Rolandic fissures 

 as motor areas. These areas have been much studied physiologi- 

 cally in recent years. The brains of the higher apes have been 

 preferred in these studies to those of lower animals because of 

 their greater similarity to the human brain. 



There have been a few observations upon the brains of human 

 beings in cases where the surgical treatment of certain diseases 

 has involved removal of portions of the skull overlying the Ro- 

 landic areas. 



These recent studies have shown that there is a considerable 

 localization within the motor areas themselves; stimulation of one 

 point causes movements of the hand, of another the foot, of still 



