394 MUSCULAR ACTION 



partly because the number of nervous and muscular movements is much 

 greater, the fatigue is much more than in this ratio. The cerebral center 

 may be the corpus striatum. 



Speech. The neuromuscular mechanism by which we use our voices 

 is one of the most complex in the body. While complicated in the large 

 number of nerves of muscles and muscle-bundles employed, it is doubt- 

 less vastly more so as respects its central neural apparatus. This has to 

 put it in intimate relation on the one 'hand with practically all aspects of 

 our intelligence, and on the other with the centers of many of the motor 

 functions. It is only artificially, then, that we can separate the phenom- 

 ena of speaking from the more mental principles of language; they are 

 aspects of one and the same broad function, the expression of intelligence. 

 Without this we would still be brutes. In writing, the same language- 

 phenomena are employed, but the voice-muscles, etc., partake in it only 

 reflexly and sympathetically. Here we are concerned, then, only with 

 voice-production and not at all with language itself or with the other 

 modes of its expression. The physiology of language, merging into the 

 formation of spoken and written words on one side and the abstruse 

 psychology of conception on the other, is outside our present range 

 (see page 417). 



The apparatus concerned in vocalization includes the muscles and 

 nerves of most of the external respiratory mechanism; the larynx; the 

 air-chambers connected with the nose; and the mouth-cavity, including 

 the tongue and lips. These all are active instruments of speech. For 

 the detailed anatomy of these parts the reader is earnestly referred to 

 anatomical text-books in order that he may clearly understand the rela- 

 tions of these organs to each other. The most complex part of this 

 mechanism, aside from the nerves connected with it, is the larynx; 

 its parts and their respective functions are even yet, after three centuries 

 of study, only partly determined. The thorax furnishes most of the 

 motive power of vocalization. The larynx contains the vibrating sound- 

 producers proper. The nasal air-chambers are the chief resonators of 

 this sound-producer. The mouth-cavity and the lips, tongue, and teeth 

 within it or part of its walls are largely the means by which the "sound" 

 sent into it from the larynx are differentiated into words and other 

 utterances with a myriad shades of tones and meaning. Controlling 

 all of these and coordinating them into one useful mechanism, the valued 

 servant of the individual, are the nerves and the nerve-centers connected 

 with them. 



THE KESPIRATORY BELLOWS is concerned with voice chiefly in the 

 expiratory phase of its movements. In very high-pitched singing or 

 speaking the current sent through the trachea is a powerful one, one 

 estimate making the tracheal air-pressure 70 mm. of mercury or more. 

 In ordinary tones it is probably not over one-sixth of this amount. It is 

 to furnish this draft of the tidal air that the thorax is used in speaking. 

 In this function of the bellows-mechanism of the trunk one sees how 

 perfectly under voluntary guidance the respiratory muscles are. With- 



