1292 A MANUAL OF ANATOMY 



inwards, the result of which is to swing the vocal processes outwards. 

 The actions of the intrinsic muscles may be tabulated thus : 



Tension. Relaxation. 



Crico-thyroids. Thyro-arytenoids. 



Posterior crico-arytenoids. Lateral crico-arytenoids. 



Parallelism and Closure. Divergence and Opening. 



Lateral crico-ar5rtenoids. Posterior crico-arytenoids. 



Arytenoid. 



Function of the Epiglottis. — Two views are held as regards the 

 function of the epiglottis, (i) According to one view it is folded 

 down, like a Ud, over the superior aperture of the larynx. This Ud-like 

 action is brought about by (a) the pressure exerted by the base of 

 the tongue, {b) the action of the aryteno-epiglottidei muscles, and 

 (c) the action of the thyro-hyoid muscles, which elevate the thyroid 

 cartilage. (2) According to Anderson Stuart, the epiglottis is never 

 folded down like a lid. The superior aperture of the larynx is, accord- 

 ing to this author, closed during deglutition by the action of (i) the 

 transverse arytenoid muscle, and (2) the external portions of the 

 thyro-arytenoid muscles. The transverse ar5^enoid muscle approxi- 

 mates the arytenoid cartilages, and the external portions of the thyro- 

 ar5rtenoid muscles draw the arytenoid cartilages forwards, until their 

 apical parts come into contact with the cushion of the epiglottis. 



The sphincter-like action of the aryteno-epiglottidei muscles 

 upon the superior aperture of the larynx must, however, be taken 

 into account. 



Prima facie the lid-like action appears to be the most natural one. 

 The results, however, of ulceration of the epiglottis, and consequent 

 loss of function, would tend to support Anderson Stuart's view. 



Nerves. — The nerves of the larynx are the superior and inferior, or 

 recurrent, laryngeal, both of which are branches of the pneimio-gastric. 



The superior laryngeal nerve divides into two branches, external 

 and internal. The external branch (external laryngeal nerve), which 

 is comparatively small, supplies the crico-thyroid muscle, and also 

 furnishes twigs to the inferior constrictor muscle of the pharynx. 

 The internal branch (internal laryngeal nerve), which is sensory, 

 passes beneath the posterior border of the thyro-hyoid muscle, and 

 enters the larynx by piercing the th5n:o-hyoid membrane, in com- 

 pany with the superior laryngeal artery, above which it lies. In 

 the interior of the larynx it breaks up into branches, some of 

 which ascend to the aryteno-epiglottidean fold and posterior surface 

 of the epiglottis, a few of them passing through the latter to reach 

 its anterior surface. The other branches descend to supply the 

 laryngeal mucous membrane, and one of them joins a twig from 

 the inferior or recurrent laryngeal nerve. 



The inferior or recurrent laryngeal nerve is the principal motor 

 nerve of the larynx. On the rig/it side it arises from the vagus at 

 the root of the neck, and hooks round the first part of the right sub- 

 clavian artery. On the left side it arises from the vagus in the upper 

 part of the thorax, and hooks round the arch of the aorta. 



