1176 THE ORGANS OF VOICE AND RESPIRATION 



Actions. In considering the action of the muscles of the larynx, they may he conveniently 

 divided into two groups viz.: (1) Those which open and close the glottis. (2) Those which 

 regulate the degree of tension of the vocal cords. 



1. The muscles which open the glottis are the two Posterior cricoarvtenoids ; and those 

 which close it are the Arytenoid'eus and the two Lateral cricoarytenoids. 



2. The muscles which regulate the tension of the vocal cords are the two Cricothvroids, which 

 render tense and elongate them, and the two Thvroarytenoids. which relax and shorten them. 



The Posterior cricoaruten-oids separate the chordae vocales. and consequently open the glottis, 

 by rotating the arvtenoid cartilages outward around a vertical axis passing through the crico- 

 arytenoid joints, so that their vocal processes and the vocal cords attached to them become widely 

 separated. 



The Lateral cricoanitenoids close the glottis by rotating the arvtenoid cartilages inward so 

 as to approximate their vocal processes. 



The ArutrnoidcitJi mu~le approximates the arytenoid cartilages, and thus closes the opening 

 of the glottis, especially at its back part. 



The Cricothyroid muscles produce tension and elongation of the vocal cords. This is effected 

 as follows: the thyroid cartilage is fixed by its Extrinsic muscles; then the Cricothyroid muscles, 

 when they act, draw upward the front of the cricoid cartilage, and so depress the posterior por- 

 tion, which carries with it the arytenoid cartilages, and thus elongate the vocal cords. 



The Thy roar ytenmd muscles, consisting of two parts having different attachments and dif- 

 ferent directions, are rather complicated as regards their action. Their main use is to draw 

 the arytenoid cartilages forward toward the thyroid, and thus shorten and relax the vocal cords. 

 But, owing to the connection of the inner portion with the vocal cord, this part, if acting sepa- 

 rately, is supposed to modify its elasticity and tension, and the outer portion, being inserted 

 into the outer part of the anterior surface of the arytenoid cartilage, may rotate it inward, and 

 thus narrow the rima glottidis by bringing the two cords together. 



The manner in which the superior aperture of the larynx is closed during deglutition is referred 

 to on page 400. 



The mucous membrane of the larynx is continuous above with that lining the mouth and 

 pharynx, and it is prolonged through the trachea and bronchi into the lungs. It lines the pos- 

 terior surface and the anterior part of the upper surface of the epiglottis, to which it is closely 

 adherent. In the rest of the larynx, above the true vocal cords, it is lax and rests upon a con- 

 siderable submucous layer. The mucous membrane, with the submucous coat, ligamentous 

 and muscular fibres, forms the arytenoepiglottic folds, which folds are the lateral boundaries 

 of the superior aperture of the larynx. It lines the whole of the cavity of the larynx, forms 

 by its reduplication the chief part of the superior or false vocal cord, and, from the ventricle, 

 is continued into the laryngeal saccule. It is then reflected over the true vocal cords, where it 

 is thin and very intimately adherent; covers the inner surface of the ericothyroid membrane 

 and cricoid cartilage; and is ultimately continuous with the lining membrane of the trachea. 

 The fore part of the anterior surface and the upper half of the posterior surface of the epiglottis, 

 the upper part of the arytenoepiglottic folds, and the true vocal cords are covered by stratified 

 squamous epithelium; the rest of the laryngeal mucous membrane is covered by stratified ciliated 

 cells. 



The mucous membrane above the rima glottidis is extremely sensitive, and during life the 

 lightest touch of a foreign body produces cough. 



Glands. The mucous membrane of the larynx is furnished with numerous muciparous 

 glands, the orifices of which are found in nearly every part; they are very numerous upon the 

 epiglottis, being lodged in little pits in its substance; they are also found in large numbers along 

 the posterior margin of the arytenoepiglottic fold, in front of the arytenoid cartilages, where 

 they are termed the arytenoid glands. They exist also in large numbers upon the inner surface 

 of the laryngeal saccule. None are found on the surface of the true vocal cords. 



Vessels and Nerves. The arteries of the larynx (Fig. 890) are the laryngeal branches 

 derived from the superior and inferior thyroid. The superior laryngeal artery from the 

 superior thyroid accompanies the internal branch of the superior laryngeal nerve; the inferior 

 laryngeal artery from the inferior thyroid courses along with the recurrent laryngeal nerve. 

 The veins accompany the arteries; those accompanying the superior laryngeal artery join the 

 superior thyroid vein, which opens into the internal jugular vein; while those accompanying 

 the inferior laryngeal artery join the inferior thyroid vein, which opens into the innominate 

 vein. The lymphatics consist of two sets, superior and inferior. The superior accompany the 

 superior laryngeal artery, pierce the thyrohyoid membrane, and terminate in the nodes situated 

 at the bifurcation of the carotid artery. Of the inferior lymphatics, some pass through the 

 cricothyroid membrane to terminate in a node lying in front of that membrane or in front of 

 the upper part of the trachea, while others pass to the deep cervical nodes and to the nodes 

 along the inferior thyroid artery. 



The nerves are derived from the internal and external laryngeal branches of the superior 

 laryngeal nerve, from the inferior or recurrent laryngeal, and from the sympathetic. The 



