354 



PULMONARY MUCOUS TISSUE. 



to pass through a larynx, in which he had represented the 

 contraction of the crico-thyroid muscles, by the traction of a 

 weight fastened in front of the thyroid cartilage ; he thus 

 obtained a sound by the vibration of the vocal cords, stretched 

 by the rocking movement of the thyroid cartilage. 



Nothing, however, proves that this is the case in phona- 

 tion : if the edges of the glottis were stretched in this man- 

 ner, the glottis would be necessarily elongated; close ex- 

 amination, however, shows that the glottis is elongated 

 scarcely at all during phonation, and since the tension by rock- 

 ing of the thyroid cartilage is produced by the crico-thyroid 

 muscle, the latter would then play the chief part in the 



process of phonation. If the 

 nerve leading to it (the exter- 

 nal branch of the upper laryn- 

 geal nerve) be cut, its paralysis 

 has hardly any effect on the 

 voice, while section of the in- 

 ferior laryngeal nerve produces 

 immediate loss of phonation, 

 although this nerve leads only 

 to the intrinsic muscles of the 

 larynx, and not to the crico- 

 thyroid. 



It is plain that the lips of 

 the glottis must be stretched, 

 in order to vibrate, but we 

 do not yet know which of the 

 tissues composing these lips 

 is susceptible of tension, nor 

 what it is which produces this 

 tension. 



If we review the three tissues 

 which compose the substance 

 of the lips of the glottis, from 

 the surface to the depth, that 

 is to say, the mucous, the elastic 

 ligament (vocal cord) and the muscle (Fig. 92), and seek 

 to discover which of these three constitutes the vibrating 



* This figure plainly shows that the edges of the glottis are essentially 

 formed of muscular tissue. 1, Thyroid cartilage. 2, Cricoid cartilage. 3, First 

 ring of the trachea. 4, Epiglottis. 5, Its median cushion. 6, Upper vocal 

 cords. 7, Lower vocal cords. 8, Morgagni's ventricles. 9, Thyro-arytenoid 

 muscle (the real vocal cord, in a physiological point of view). 10, 'Lateral crico- 

 arytenoid muscle. (Bcaunis and Bouchard, "Anatomic Descriptive.") 



Fig. 92. Vertical section of the 

 larynx.* 



