THE NEUROM OSCULAR MECHANISM 99 



pen probably remains essentially a cerebral act, though 

 one may trace a copy with a minimum of conscious 

 attention. Disease of the cerebellum interferes chiefly 

 with movements which call for the poising and timely 

 control of the main mass of the body rather than with 

 skill of hand. 



Students are slow to realize the vast importance of 

 afferent impulses in the execution of coordinated move- 

 ments. When one sees a victim of spinal disease whose 

 disorderly and badly regulated motions make him a 

 painful spectacle, it is natural to infer that there is inabil- 

 ity to command the muscles. Yet if it is a case of typic 

 locomotor ataxia the chief trouble is with the ascending 

 paths. The afflicted man suffers from the want of a guid- 

 ing sense. He cannot readily perceive the extent of the 

 movements which he is executing, nor the resistances 

 encountered. He is likely to do much better when he 

 has the use of his eyes than he can in the dark. All people 

 are assisted by the eyes in the maintenance of equilib- 

 rium, but these receptors become still more important 

 when there is a failure of the impulses from the motor 

 apparatus itself. 



Breathing. An important subdivision of the general 

 neuromuscular system is that which stands in control of 

 breathing. The muscles used are such as we can employ 

 singly or in groups for various purposes. We can also 

 modify our breathing if we choose, but only within limits. 

 It is supposed to be impossible to commit suicide by 

 holding the breath. It is increasingly difficult to continue 

 forcing the breathing beyond one's inclination. Since 

 we cannot long underbreathe, nor yet overbreathe, it is 

 natural to assume that there is some positively acting, 

 involuntary mechanism normally dictating the rate and 

 depth of the breathing movements. We have evidence 

 of very long standing that this mechanism indeed exists 

 and that its chief center is in the medulla. 



Breathing is not dependent upon the cerebral cortex. 

 Complete division of the nervous axis at the level of the 



