CERTAIN SETS OF NERVES 87 



of the jaw must at the same time so act as to make use both of the mouth 

 and the teeth in the one proper manner. All of these parts meanwhile 

 are sending inward to the brain and spinal cord a continual stream of 

 afferent, sensory (kinesthetic) impulses by which alone the centers can 

 guide the muscles to contract to the requisite extent. The mental aspects 

 of speech (the one human function) require a multitude of other impulses 

 of which we know essentially nothing. Thus complicated is the func- 

 tion of nervous coordination going on continually all over the body 

 for hundreds of complex acts. The details of the nervous currents 

 cannot be made out in any case, but the principle is now sufficiently 

 clear. 



In the illustration just given there is one dominant center, that of 

 speech, but it exerts control over a number of coordinating centers cor- 

 responding to the organs employed in the act. Besides the respiratory 

 center, that of the tongue is regulated and that portion of the nervous 

 system directing mastication, in itself a complicated act. In the process 

 of swallowing nearly the same organs (save in part for the larynx) are 

 involved. The movements of each are then different, however, and the 

 center of deglutition is the dominant center while that of speech is 

 affected in part only as subsidiary. 



Thus continually all through the body a vast but exactly ordered mul- 

 titude of impulses is passing to and fro between all the parts. The com- 

 plexity of these groups of influences along nerves cannot be even imagined 

 unless one impresses on his mind the number and the variety of interests 

 and of purposes of the body's sense-organs and of its muscular and gland- 

 ular and metabolic units. Uncoordinated these would make a chaos, 

 but coordinated by the nervous system they are the essential part of a 

 living animal body. 



CERTAIN SETS OF NERVES. 



Forty-three pairs of nerves connect the body-tissues of man with his 

 central nervous system, one of each pair going outward on each side. 

 Twelve of these pairs arise from the base of the brain and the medulla 

 oblongata; these are called, therefore, cranial nerves. The other thirty- 

 one pairs arise from the various segments of the cord ; these are hence 

 known as spinal nerves. Besides these, numerous sets of ganglia and 

 nerves exist in the body and perform various vegetative functions; these 

 ganglia and nerves are (but none too well) termed the sympathetic 

 "system" as if they in some way were distinct from the rest of the 

 nervous system. This, of course, they are not, but rather an important 

 portion of the common neural fabric and very intimately related to all 

 its parts in many ways. If we speak of these three "sets" of nerves 

 as separate, it is only for convenience and because they have been thus 

 unduly and arbitrarily separated in anatomical treatises for many years 

 and have so in a sense really become to the science sets of nerves. 

 Functionally, however, it must be continually remembered they are only 



