554 
MR. BISHOP ON THE PHYSIOLOGY 
of the glottis, then takes place, which being communicated to the contiguous air, the 
sounds of the voice are produced. 
The relative length of the vibrating edge of the glottis is regulated by the pressure 
of the column of air in the trachea, and the resistance of the vocal ligaments. The 
intensity of the voice in the same medium, and under similar collateral circum- 
stances, depends on the pressure of the column of air in the trachea, and the range 
of motion performed by the vibrating edges of the glottis. The vocal ligaments do not 
vary the pitch of the voice by their tension alone, but by their variations in length and 
tension conjointly. The author has learnt this from his own experiments on the vocal 
functions of the larynx, which have been confirmed both by Majendie and Mayo ; 
the former having observed in the larynx of a dog that a longer portion of the liga- 
ments of the glottis vibrated during the utterance of grave tones, and that the length 
was diminished as the tones became acute. The latter had an opportunity of inspect- 
ing the movements of the glottis in a man who had made an attempt to destroy him- 
self by cutting his throat. In this case the larynx was divided immediately above 
the vocal cords, and in consequence of the oblique direction of the wound, the aryte- 
noid cartilage and the vocal cord on one side were injured. During respiration the 
glottis was observed to assume a triangular form, but when a sound was uttered, the 
chordae vocales became nearly parallel, and the rima glottidis of a linear form. The 
posterior part of the aperture did not appear to be closed. In a second case of this 
kind, he observed that the arytenoid cartilages, as long as the vocalization of the 
breath continued, maintained the position which they had assumed when the glottis 
was closed entirely*. The vibrations of the thyro-arytenoid ligaments are considered 
by Ferrien'|~ to be analogous to those of strings ; hence he denominated these liga- 
ments (though improperly) chordae vocales. He imagined that the longitudinal 
tension of these cords alone governed the pitch of the voice. Mr. Willis^; has 
embraced the hypothesis of Ferrien ; he observes, that to obtain the various notes 
of the glottis, it is only necessary to vary its longitudinal tension after the ligaments 
have been placed in the proper position; but M. Biot§ remarks, “ Qu’y a-t-il en 
effet dans la glotte qui ressemble a une corde vibrante ? Comment pourroit-on en 
tirer jamais des sons d’un volume comparable a ceux que l’homme produit ? Les 
plus simples notions d’acoustiques suffisent pour faire rejeter cette etrange opinion.” 
On inspecting the larynx from above, we see two very nearly rectangular-shaped 
laminas, one on each side the chink of the glottis, but nothing resembling an isolated 
cord. The mucous membrane which lines the thyro-arytenoid ligaments (to which 
it closely adheres), as well as the rest of the vocal tube, must be considered as form- 
ing a part of the weight of the vibrating surface upon which the air acts ; the thyro- 
arytenoid ligaments confer on this membrane the requisite tension and resistance 
during vocalization, and it is this membrane which gives the sides of the glottis their 
* Mayo, Outlines of Physiology, p. 991. + Memoires de l’Academie. 
J Cambridge Philosophical Transactions, vol. iv. § Precis, Elem. de Phys. tom. i. 398. 
