LAKYNGEAL MUSCLES. 1077 



lateral crico-arytaenoid muscles act in exactly the opposite manner. By drawing the 

 muscular processes of the arytsenoid cartilages ventrally and medially, they approximate 

 the vocal processes and close the rima glottidis. The actions of the other muscles 

 have been sufficiently described already. 



Closure of the Larynx during Deglutition. The muscles of the larynx have, 

 however, another function to perform besides vocalisation and regulating the amount of 

 air passing to and fro through the glottis. During deglutition it is requisite that the 

 communication between the pharynx and larynx should be closed, to prevent the fluid 

 or solid parts of the food entering the respiratory passages. In the process of closing 

 the laryngeal entrance the epiglottis stands erect, whilst the dorsal wall formed by the 

 arytsenoids is carried ventrally, the arytsenoid cartilages are closely approximated, glide 

 ventrally, and are then inclined towards the epiglottis. The result of this is that the 

 laryngeal opening is converted into a T-shaped fissure. The median limb of the T is formed 

 by the interval between the closely applied arytsenoid cartilages, whilst the cross limb, 

 which lies ventrally, is bounded ventrally (anteriorly) by the epiglottis and dorsally by the 

 aryepiglottic folds. The apices of the arytsenoid cartilages, with the corniculate cartilages 

 (Santorini), are pressed against the tubercle of the epiglottis, whilst the lateral margins 

 of the epiglottis are pulled dorsally so as to make the transverse limb of the fissure 

 distinctly concave in a dorsal direction. The muscles chiefly concerned in producing 

 these movements are the thyreo-arytsenoid and the transverse arytsenoid muscles. These 

 form a true sphincter vestibuli. The thyreo-epiglottic and aryepiglottic muscles also 

 come into play. They pull upon the epiglottis so as to produce tight application of 

 its tubercle to the arytenoid cartilages and the corniculate cartilages (Santorini), and 

 they also curve its margins dorsally so as to increase its dorsal concavity. 



Vessels and Nerves of the Larynx. Two branches of the vagus nerve, viz., the" superior 

 laryngeal and the recurrent (laryngeal) nerves, supply the larynx. The superior laryngeal 

 divides into the internal and external laryngeal branches. The external laryngeal nerve 

 supplies the crico-thyreoid muscle ; whilst the internal laryngeal nerve enters the larynx, by 

 piercing the lateral part of the hyothyreoid membrane, to supply the laryngeal mucous mem- 

 brane. The recurrent nerve reaches the larynx from the thoracic direction, and, by its terminal 

 inferior laryngeal branch, supplies all the intrinsic laryngeal muscles, with the exception of 

 the crico-thyreoid. 



The superior laryngeal artery, a branch of the superior thyreoid, accompanies the internal 

 laryngeal nerve ; whilst the inferior laryngeal artery, which springs from the inferior thyreoid, 

 accompanies the inferior laryngeal nerve. These two vessels ramify in the laryngeal wall and 

 supply the mucous membrane, the glands, and muscles. 



Growth-Alteration and Sexual Differences in the Larynx. A considerable 

 amount of variation may be noticed in the size of the larynx in different individuals. 

 This is quite independent of stature, and explains to a great extent the difference in the 

 pitch of the voice in different persons. But quite apart from these individual variations, 

 there is a marked sexual difference in the size of the larynx. The male larynx is not 

 only absolutely, but also relatively, larger than the female larynx in all its diameters, but 

 more particularly in the ventro-dorsal diameter ; and to a large extent the increase in that 

 direction is produced by the strong development of the prominentia laryngea in the male. 

 The greater ventro-dorsal diameter of the male larynx necessarily implies a greater length 

 of the vocal folds and a lower or deeper tone of the voice in the male than in the female. 



In a newly born child the larynx, in comparison with the rest of the body, is 

 somewhat large (C. L. Merker), and it continues to grow slowly and uniformly up 

 to the sixth year of childhood. At that period there is a cessation of growth until 

 puberty is reached, and then a stage of active growth supervenes. Up to that time the 

 larynx in both sexes is similar in its dimensions, and although the growth which now 

 occurs affects both the male and the female larynx, it is much more rapid and much more 

 accentuated in the male than in the female. As a result the voice of the male " breaks " 

 and assumes its deep tone. 



It is interesting to note that the growth activity of the larynx, at puberty, is intimately 

 connected with the development of the sexual organs. In a male subject who has been 

 castrated, when young, the larynx attains a size which exceeds that of the female only to 

 a small degree, and the high pitch of the voice is retained. 



Appearance of the Interior of the Larynx when examined by the Laryngoscope. 



When the cavity of the larynx is illuminated and examined by laryngoscopic mirrors, the 

 parts which surround the superior aperture of the larynx, as well as the interior of the organ, 

 come into view. Not only this, but when the vocal folds are widely separated it is possible 

 to inspect the interior of the trachea as far as its bifurcation. 



69 a 



