NORMAL ANATOMY OF THE LARYNX. 



107 



Fig. 27. 



Fig. 28. 



A side view of the larynx, the left wing of the thyroid 

 and the mucous membrane removed, and the fibres of 

 the arytenoid muscle depressed to expose the liga- 

 ments and chink of the glottis. 



a, the internal surface of the right wing of the 

 thyroid ; b b, the arytenoid cartilages ; c, the thyro- 

 arytenoid ligament ; d, the thyro-arytenoideus 

 muscle ; d', the thyro-arytenoideus superior vel 

 minor; e e, the crico-arytenoidei postici ; f, the 

 crico-arytenoideus lateralis ; n, the cricoid carti- 

 lage ; h, the trachea ; I, the external prominence 

 of the arytenoid cartilage. 



attachment or muscles appropriated to fix it as 

 a fulcrum for motions in an opposite sense. 



The crico-arytenoideus lateralis is an irregu- 

 lar quadrilateral muscle, arising from the supe- 

 rior margin of the cricoid, from thence passing 

 upwards and backwards, (f,fg. 28). It is in- 

 serted into the posterior surface of the external 

 prominence of the arytenoid cartilage by a tendon 

 common to it and the thyro-ary tenoid muscle. It 

 is deeply seated under cover of the thyroid car- 

 tilage and crico-thyroid muscle. The action of 

 this muscle has caused much diversity of opi- 

 nion. Cowper, Ilaller, Magendie, and others 

 consider that it opens the glottis ; but Bichat 

 and Soemmering that it closes it. Its action 

 has, however, been mechanically solved in the 

 following manner by Willis. The arytenoid 

 cartilage is loosely fixed to the cricoid by liga- 

 ments already described at B (Jigs. 28 and 29). 

 The direction of the force of this muscle is 

 represented by the line N X (Jig. 30), having 

 its point of insertion into the cricoid about X. 

 The fibres in passing thence to the arytenoid 

 (f, .fig. 28) lie nearly parallel to the projection 

 of the axis of motion, G C ; the tension of this 

 muscle in the direction N X (Jigs. 29 and 30) 



A section of the larynx similar to that of fig. 27, with 

 the thyro-arytenoideus muscle removed to give a full 

 view of the thyro-ary tenoid ligaments, and the rima 

 glottidis lying in the direction of A and B. 



The line G C is the vertical projection of the crico- 

 arytenoid articulating axis ; cc,f, g,h, represent 

 the same parts as injig. 27. 



tends to bring N X B into the same straight 

 line and approximate the point V to the mesial 

 plane; and as N is above the line joining B X, 

 it will depress N and still more V, because the 

 cartilage turns on the articulating surface be- 

 neath Q. The action, therefore, of this muscle 

 is to approximate the anterior arytenoid promi- 

 nences and depress them. 



The arytenoideus (obliquus and transversus). 

 Modern anatomists consider this as one 

 muscle, but owing to the obliquity of the fibres 

 of one of its fasciculi with respect to the other, 

 some have made a division of it into arytenoideus 

 obliquus and a transversus. It is a very short 

 thick muscle, occupying the concavities on the 

 posterior surface of the arytenoid cartilages and 

 the interval between them. It consists of two 

 layers; the superficial layer, which is composed 

 of the oblique fibres, which arise from the base 

 of the right arytenoid, and crossing the fibres 

 of the deep-seated layer, are inserted into the 

 summit of the left arytenoid cartilage : this is 

 the arytenoideus obliquus of Albinus. The 

 deep-seated layer is thicker and stronger than 

 the superficial ; its fibres, which are directed 

 transversely from one arytenoid to the other, 

 constitute the arytenoideus transversus of Albi- 

 nus. The arytenoid muscle is covered pos- 

 teriorly with mucous membrane, which is con- 

 nected to it by loose cellular substance, in which 

 some mucous follicles are found; anteriorly it 



