Chap, vir.] SPECIAL MUSCULAE MECHANISMS. 1085 



the laryngeal respiratory movements, as indeed of the respiratory 

 movements as a whole ; though the respiratory laryngeal move- 

 ments are in the main worked by a bulbar mechanism, they can 

 be influenced by cortical changes. 



As in the case of the other cortical motor areas, the path 

 from the cortical area for phonation to the muscles whose ac- 

 tions it governs runs in the pyramidal tract through the in- 

 ternal capsule. Moreover in the bulb there appears to be a 

 subordinate nervous mechanism, with which the impulses or 

 influences descending the pyramidal tract make connection be- 

 fore they issue as coordinate motor impulses along the laryngeal 

 nerves ; and indeed by local electrical stimulation of the bulb, 

 in the floor of the fourth ventricle, adduction or abduction of 

 the cords may be brought about. The bulbar mechanism for 

 abduction is placed higher up than that for adduction, and 

 stimulation of either side produces in both cases bilateral move- 

 ments. 



§ 674. So far we have mainly spoken of the voice as the 

 result of two gross acts, the narrowing of the glottis and the 

 tightening of the cords. We must now say a few words on 

 some other changes in the larynx, especially in reference to the 

 various qualities and kinds of voice. Many of the features of 

 the voice are conferred upon it by means of the parts of the 

 respiratory passage above or below the vocal cords, by what we 

 have spoken of as the resonance chamber or tube ; these we 

 shall deal with in treating of 'speech,' and may here confine 

 ourselves, in the main, to changes in the larynx itself. It 

 should be noted however that whenever voice is uttered the 

 larynx is more or less firmly fixed by the extrinsic laryngeal 

 muscles, such as the thyro-hyoid, sterno-thyroid, pharyngeal 

 muscles and others. The exact position in which it is fixed 

 will depend on the pitch of the notes which are uttered; it is 

 raised for high notes and lowered for low ones, and may be fixed 

 either above or below or at the natural position of rest. 



We are accustomed to classify voices according to the range 

 of pitch within which the voice can sing truly and with ease, 

 and we thus distinguish, in ascending scale, such voices as bass, 

 barytone and tenor in the male, alto, mezzo-soprano and soprano 

 in the female. Could we consider the vocal cord as a membra- 

 nous edge, possessing a form and nature which was constant or 

 varied only with age, so that the rapidity of its vibrations, and 

 hence the pitch of the voice, depended solely upon its length, 

 fixed by the growth of the individual, and upon its varying ten- 

 sion, determined by muscular contraction, the result being 

 influenced by the varying width of the glottis, the structural 

 basis of the distinction between the several kinds of voice would 

 be simple enough ; the bass and the contralto voices would have 

 long vocal cords, and the other voices in each sex would be 



