TSE LABYNX. 453 



the superior is attached to the inferior border of the arytenoid cartilage, 

 towards the angle which separates this from the posterior border. The 

 articulation of sounds is principally due to the vibration of these cords. 



P. The epiglottis is fixed by amphiarthrosis to the body of the thyroid 

 cartilage, by means of elastic fasciculi mixed with fat, which pass from the 

 base of the first to the upper face of the second. It is not rare to find among 

 these fasciculi small synovial bursse. 



Gr. The epiglottis is united, laterally, to the inferior border of the 

 arytenoids, through the medium of the two mucous folds already noticed, in 

 the substance of which are the cartilaginous prolongations annexed to the 

 base of this fibro-cartilage. These prolongations circumscribe, anteriorly, 

 the ventricles of the larynx, and are sometimes designated the superior vocal 

 cords : a name we rarely give them, as they do not merit it. 



H. Finally, the first ring of the trachea is attached to the cricoid 

 cartilage by a circular elastic membrane. 



All of these articulations have neither the same importance nor mobility. 

 The kind of movements they permit is easily understood, and they are suf- 

 ficiently indicated in the description of the muscles which execute them. 



It is sufficient here to state, that these movements may either produce 

 the shortening or elongation of the larynx, its dilatation or contraction in a 

 transverse directioH, or the occlusion of its anterior opening. 



2. Muscles of the larynx. — The laryngeal apparatus is elevated or 

 depressed with the hyoid bone, which it follows in aU its movements. It 

 is also moved by proper muscles, which either produoeits total displacement, 

 or cause the several pieces of its cartilaginous framework to play upon each 

 other. Among these muscles there are three extrinsic : the sierno-thyroideus, 

 hyo-thyroideus, and the hyo-epiglottideus. The others are intrinsic, or 

 attached in their origin and termination to the different pieces of the larynx ; 

 they are : the crico-thyroid, posterior crico-arytenoid, lateral crico-arytenoid, 

 thyro-arytenoid, and the arytenoideus muscles. All are pairs, except the last 

 and the hyo-epiglottideus. 



Sterno-thteoideus. — (See page 198.) 



Hto-thyeoideus. — This is a wide, triangular muscle formed entirely of 

 muscular fasciculi, which originate from the whole extent of the hyoid 

 cornu, and terminate on the external face of the thyroid ala ; the most 

 inferior are longest. This muscle covers the thyroid cartilage and the 

 thyro-hyoid membrane. It is covered by the maxillary gland. 



In contracting, this muscle brings the thyroid cartilage within the branches 

 of the hyoid bone, and in this way carries the larynx forward and upward, 



Hto-epiglottideos. — ^By this name is designated a small cylindrical 

 fasciculus, whose fibres are buried in the middle of a mass of adipose tissue, 

 and which extend from the superior face of the body of the hyoid bone to the 

 antero-inferior face of the epiglottis. Partly covered by the mucous 

 membrane of the pharynx, this muscle concurs in restoring the epiglottis 

 to its normal position after the passage of the alimentary bolus. But it is 

 also necessary to state that the epiglottis is carried forward more particularly 

 bv its own proper elasticity, as well as that of the ligamentous fasciculi 

 which attach it to the thyroid cartilage. 



Ckico-thtkoideus (Fig. 229, 8). — This small muscle, applied to the 

 external side of the cricoid cartilage, is elongated from above to below, 

 and composed of strongly tendinous fibres Vv^hich cross, more or less, the 

 general direction of the muscle. They arise from the above-named cartilage, 

 and pass to the posterior border of the thyroid plate. 

 32 



