Mechanism of the Larynx. 345 



These ventricles ajjpear to have no use considered as cavities, but to 

 arise merely from the form of the lining of the Larynx, which, after se- 

 parating above the glottis to isolate the vocal ligaments, and leave them 

 free for vibration, again returns to form the pair of folds which constitute 

 the pseudo-glottis, and serve to protect the glottis from the accidental 

 intrusion of foreign bodies. 



The most ordinary appellation of the vocal ligaments is vocal chords, 

 but this term, which implies an isolated vibrating ligament, ought certainly 

 to be abandoned as conveying a most erroneous notion of the structure of 

 the parts in question. They have also been termed the lips of the glottis. 



Note B.—Page 328. 



Let CD, AB, Fig. 22, be the longitudinal section of a tube, the trans- 

 verse section of which is a parallelogram, whose longest side is considerably 

 greater than its shortest, which is equal to AC. 



Let this tube be terminated on its upper side by an elastic membrane 

 DE, attached on three sides to the tube, but having a free edge opposite B, 

 (similar to the membrane in Fig. 9). 



Suppose the extreme position of this membrane in performing vibrations 

 to be DF and DG, and let a current of air be passing along the tube 

 in the direction of the arrow. Now when a membrane vibrates under these 

 circumstances its motion will be influenced by two causes. 



First, — It is well known that when a current of air passes through a 

 diverging tube, such as ACDGB, that, by what is called the lateral com- 

 munication of motion, it gradually communicates its onward motion to the 

 particles of air which were at rest in EDG, and carries them away with it 

 creating a rarefaction in EDG, which occasions a superabundant pressure on 

 the outer surface of DG, by which it will be urged towards DE. This there- 

 fore acts as a retarding force when the membrane is passing in the direction 

 EG, and as an accelerating force when it is moving in the opposite direction. 



