THE VOCAL APPARATUS 141 



No sharp line of separation can, however, be drawn. The 

 sounds of ordinary speech are due to regular vibrations, 

 and are hence musical. 



193. Pitch depends upon the rapidity of the vibrations, 

 and that varies with the length of the cords and with 

 their tension. In women the vocal cords are shorter than 

 in men, and the voice is an octave higher in pitch. Pitch 

 due to tension of the cords is a matter of voluntary con- 

 trol within the range of a voice. Loudness depends upon 

 the force of expiration. Stammering is due to lack of 

 coordination in the muscles of speech. 



194. Nervous Mechanism of the Larynx. A certain area 

 in the left hemisphere of the cerebrum is recognized as the 

 nervous center in which impulses resulting in speech origi- 

 nate. From the cells of this center nerve fibers run to 

 other cells in the wall of the fourth ventricle of the brain, 

 to the medulla oblongata, and on into the spinal cord. By 

 means of these communicating fibers the center for speech 

 is brought into connection with other groups of nerve 

 cells, from which arise the various nerves which are con- 

 cerned in vocalization. These are very numerous, for the 

 muscles of the face, the tongue, the thorax, and the abdo- 

 men, as well as those of the larynx, are called into action in 

 speaking, singing, etc. Those nerves distributed to the 

 muscles of the larynx are branches of the vagus, or pneu- 

 mogastric, which is the tenth cranial nerve and rises from 

 the medulla oblongata. 



Suppose there arises in a man's mind a thought which 

 he desires to express in audible speech. He remembers 

 the sounds of the words which will serve his purpose, and 

 impulses arise in that part of the speech center called the 

 auditory word center, from which they pass to the motor 

 center. Thence the nerves of the various parts of the 



