202 SPECIAL PHYSIOLOGY. 



55 ; this leads, anteriorly, into a pouch of the mucous membrane 

 called the laryngeal sac, the surface of which is scattered over with 

 sixty or seventy mucous glands, the secretion from which serves to 

 maintain the vocal cords, and surrounding parts, in a moist condition. 



Fig. 56. 



Fig. 56. Two bird's-eye TJews of the larynx, the back part of the organ being turned towards the top of 

 the page: the Irft-hand figure, A, has the mucous membrane partly left on; the right-hand and large fig- 

 ure. B, is dissected, to show the muscles and separated vocal cords. In the former figure the epiglottis is 

 marked 1, thyroid 2, 2, the right arytenoid *, and the vocal cords 7; between them is the glottis, or rima 

 glottidis or chink of the glottis; outside them are the ventricles of the larynx. In the left-hand figure, a 

 is the posterior crico arytenoid muscle; b, the arytenoid muscle passing across the middle line; c, the 

 lateral crico-arytenoid muscle; d, the thyro-arytenoid muscle; 7, the right vocal cord. 2, is the thyroid 

 cartilage ; 5, the cricoid ; *, the right arytenoid. 



Connected with the laryngeal cartilages, are several small muscles, 

 which, with one exception, exist in pairs. The crico-tliyroid muscle, 

 Fig. 55, a, 6, extends from the side of the thyroid cartilage to the 

 cricoid cartilage. Arising from the side of the cricoid, and passing 

 upwards and outwards to the lateral process of the base of the aryte- 

 noid cartilage, is the small posterior crico-arytenoid, Fig. 56, B, a. 

 The lateral crico-arytenoid, c, passes backwards and upwards, from 

 the cricoid to the lateral process of the arytenoid cartilage. On the 

 outer side of each vocal cord, and lying parallel with it, is the thyro- 

 arytenoid muscle, d, which extends from the recessed angle of the 

 thyroid cartilage, to the base of the corresponding arytenoid cartilage. 

 The arytenoid, b, is a single muscle connected with the posterior sur- 

 faces of the cartilages of that name. 



The tnucous membrane of the larynx is covered in the greater part 

 of its extent with a columnar, ciliated epithelium ; but the vocal cords, 

 and the mucous membrane above them, except for a short distance in 

 the middle line anteriorly, are covered with epithelium of the squa- 

 mous variety. It is continuous above, with the membrane lining the 

 mouth and pharynx, and below, with that of the trachea, and, with the 

 exception of the parts covering the vocal cords, is studded with mucous 

 glands, the secretion of which keeps the surface duly moistened ; on 

 the epiglottis these glands are very numerous. Its nerves are derived 

 from the superior and inferior laryngeal branches of the pneumogastric, 

 together with filaments from the sympathetic. The inferior laryngeal 

 nerve supplies all the muscles except the crico-thyroid ; the superior 

 laryngeal supplies that muscle and the mucous membrane. The ary- 

 tendld muscle is said to receive branches from both nerves. A portion 



