MUCOUS MEMBRAjSIE AND GLANDS OF THE LARYNX. 293 



With the aid of the laryngoscope it may be seen that in ordinary breathing the 

 rima glottidis is widely open (fig. 191, B. b'), and that in vocalisation the vocal 

 cords come closely together ; which is eilected prmcipally, no donljt, by the action 

 of the lateral crico -arytenoid muscles, assisted by the arj-tenoid aud perhaps by the 

 thyro-arj-tenoid, and accompanied with a varying amount of contraction of the 

 crico-thjToid muscles. The regulation of the tension of the vocal cords and of 

 the width of the aperture of the glottis, in the in'oduction of high and low 

 liitched notes, is probably accomplished by the crico-thj-roid and thjTO-arytenoid 

 muscles. The movement of the tlajToid on the cricoid cartilage, effected by 

 these muscles during the passage of the voice from one extreme of the scale to 

 the other, may be detected by placing the tip of a finger over the crico-thyroid 

 ligament. The ai-j'tenoid and arj'teno-epiglottidean muscles come into action 

 in spasmodic closure of the upper aperture of the larj-nx ; the complete descent 

 of the epiglottis, however, can only take place when the tongue is retracted 

 and the thyroid cartilage pushed against it, as in the act of swallowing. 



It is remarked by Henle that, with the exceirtion of the crico-thyroid and 

 posterior crico-arytenoid. the miiscles of the larynx, namely, those '• which lie in 

 the space enclosed by the laminse of the thjiroid cartilage, and ab>ove the cricoid, 

 the fibres of which are substantially horizontal, may be regarded in their totalitj' 

 as a kind of sphincter. Such a spliincter is found in its simple form embracing 

 the entrance of the larjTix in reiDtiles ; and the comiilication -which it attains in 

 the higher vertebrates arises, like the comj^lication of the muscles generally, from 

 the fibres finding various points of attachment in their coiu"se, by which means 

 they are broken up and divided."' 



THE MUCOUS MEMBRANE AND GLANDS OF THE LARYNX. 



The laryngeal mucous membrane is thin and of a pale colour. In 

 some situations it adheres intimately to the subjacent parts, especially 

 on the epiglottis, and still more in passing over the true vocal cords, on 

 which it is extremely thin and most closely adherent. About the 

 upper part of the larynx, above the glottis, it is extremely sensitive. 

 In or near the aryteno-epiglottidean folds it covers a quantity of loose 

 areolar tissua, which is liable in disease to infiltration, constituting 

 oedema of the glottis. Like the mucous membrane in the rest of the 

 air-passages, that of the larynx is covered in the greater part of its 

 extent with a columnar ciliated epithelium, by the vibratory action of 

 which the mucus is urged upwards. The cilia are found higher up in 

 front than on each side and behind, reaching in the former direction as 

 high as the widest portion of the epiglottis, and in the other directions 

 only to a line or two above the superior vocal cords : above these points 

 the epithelium loses its cilia, and gradually assumes a stratified 

 squamous form, like that of the pharynx and mouth. Upon the vocal 

 cords also the epithelium is squamous, although both above and below 

 them it is ciliated columnar. 



Glands. — The lining membrane of the larynx is provided with 

 numerous glands, which secrete an abundant mucus ; and the orifices 

 of which may be seen almost everywhere, excepting upon and near the 

 true vocal cords. They abound particularly upon tlie epiglottis, in the 

 substance of which are found upwards of fifty small comijound glands, 

 some of them perforating the cartilage. Between the anterior surface 

 of the epiglottis, the hyoid bone and the root of the tongue, is a mass 

 of yellowish fat, erroneously named the epiglottideau gland, in or upon 

 which some real glands may exist. Another collection of glands, 

 namely arytenoid, is placed within the fold of mucous membrane in 

 front of each arytenoid cartilage, from which a series may be traced for- 



