THE LARYNX. • 455 



function is particularly marked in phonation, when it modifies the length, 

 separation, and tension of the vocal cords. 



Aextenoideus.— Situated beneath the pharyngeal mucous membrane, 

 above the arytenoid cartilages, this, the smallest of the laryngeal muscles, is 

 composed of two lateral portions whose fibres arise from a median raph^ 

 and, diverging, pass to the superior part of the external face of the before- 

 mentioned cartilages, where they terminate by becoming inserted into the 

 "^^^mT 'V™^ ^^^^ ^^'^'^' ^^"^ uniting with the thyro-arytenoid muscle. 



The French works on Veterinary Anatomy cite this muscle— we do not 

 know why— as a dilator of the larynx. Its position in front of the crico- 

 arytenoid cartilages sufBciently indicates that it cannot act otherwise than 

 m bringing the two arytenoid cartilages together. And the continuity of 

 a large number of its fibres with those of the thyro-arytenoideug, does not 

 allow it to have any other action than that of this muscle. 



Z. Mucous membrane of the laryme.— This membrane is only a con- 

 tinuation of the pharyngeal mucous membrane, which, after covering the 

 prominence formed by the opening of the larynx, is folded over the cir- 

 cumference of that opening, to be spread on the posterior face of the epi- 

 glottis and the internal face of the arytenoid cartilages, to dip into the 

 ventricles, pass above the vocal cords, line the inner face of the cricoid 

 cartilage, and, finally, to be prolonged into the tracheal tube. Its deep face 

 adheres closely to the parts it covers, except in the lateral ventricles. The 

 free face is perfectly tense, and is covered with stratified tesselated epi- 

 thelium at the epiglottis and vocal cords, but only with ciliated epithelium 

 elsewhere. 



The glandules of the larynx are racemose, and are numerous on the 

 posterior face of the epiglottis, where they are lodged in the minute depres- 

 sions of the cartilage ; they are also found on the arytenoid cartilages and 

 the aryteno-epiglottidean folds. The mucous membrane of the larynx 

 possesses an exquisite sensibility, owing to which admission to the air- 

 passage is denied to the solid or liquid alimentary particles, which, during 

 deglutition, might deviate from their normal course and pass into this 

 opening. The slightest touch brings into play this sensibility, and deter- 

 mines an energetic reflex excitation of the constrictor muscles of the larynx 

 and chest ; from this results the almost complete occlusion of the laryngeal 

 tube, and a violent cough which expels the substances whose contact has 

 occasioned the irritation of the membrane. Everyone has experienced the 

 efiects of this reflex action, and knows by experience the great sensibility of 

 the larynx. 



4. Vessels and nerves. — Blood is carried to the larynx by the laryngeal 

 arteries, which pass between the cricoid and the posterior border of the 

 thyroid cartilages. Their branches spread over the ventrical of the glottis 

 and the thyro-arytenoid muscle, to be expended in the substance of the 

 muscles and mucous membrane. The terminal ramifications form red 

 plexuses on certain parts of the larynx. The veins are satellites of the 

 arteries. The lymphatics form a superficial and a submucous network. 



The pneumogastric furnishes the larynx with its principal nerves — the 

 superior and inferior lanjngeal. The first is distributed to the upper part 

 of the organ and to the entrance to the glottis, endowing the mucous 

 membrane with that high degree of sensibility that distinguishes it. The 

 second is more especially a motor nerve, and supplies all the muscles, 

 except the crico-thyroid muscle. A filament of the recurrent nerve is 

 distributed in the mucous membrane of the subglottal portion, and to the 



