I824 HUMAN ANATOMY. 



-face of the epiglottis and the side and back walls erf * e j^ h^^T-m Ihoid 



uon ., - *. . 



lissnc is so constant and plentiful that laryngeal tonsil has been suggested 

 as an appropriate name for these collections. 



THE MUSCLES OF THE LARYNX. 



The extrinsic muscles of the larynx should include those going to the hyoid bone, 

 which is physiolog,, -ally a part of this apparatus. These have been described in the 



lirVntlOia. ami UlC urvunviu. i " . . i 



physiological stand-point these muscles may be divided into three groups : the con- 

 ttridors including both the adductors of the cords and those which draw together the 

 BUpragiottic portion of the larynx ; the dilators, which abduct the cords ; and those 

 which modify the tension of the cords without necessarily approximating or separating 

 them The constrictors are the lateral crico-arytenoids, the thyro-arytenoids and 

 the arytenoid. The dilators are the posterior crico-arytenoids. 1 hose modifying 

 the tension of the cords are the crico-thyroids, which stretch them, and a part of 



the thyro-arytenoids, which relax 



FIG. 1553. them. Moreover, many of these 



muscles, even antagonistic ones, 

 when acting together may be con- 

 sidered as parts of a sphincter. 

 The laryngeal muscles are ex- 

 tremely variable, especially the 

 thyro-arytenoid, detached fibres 

 of which have been described as 

 the thyro-epiglottideus. 



The crico-thyroid muscle 

 (Fig. 1510) is well defined, pass- 

 ing upward and outward from the 

 anterior ring of the cricoid to 

 the under border and the inferior 

 horns of the thyroid. The origin 

 is from the whole of the anterior 

 surface of the arch, except for a 

 slight interval between the mus- 

 cles. The internal fibres are nearly 

 vertical and the lateral ones nearly 

 horizontal. The insertion is into 

 the lower border of the thyroid 

 cartilage from a point a few milli- 

 metre- in front of the inferior tubercle to all the rest of the lower border and the front 

 lit the inferior horn. It often extends a little onto the posterior surface of the ala. 

 The muscle i> frequently divided into a superficial and a deep part. The distinction 

 in. iv \<<- \<iv striking, or may lie wanting. The superficial is the more internal 

 vertical part, which < -onceals a little of the origin of the deeper. The crico-thyroid 

 m.iv t>e continuous l>y some fibres with the inferior constrictor of the pharynx. It 

 in. iv descend to the first ring of the trachea, and it may give, oil fibres to the capsule 

 of the thvroid lx.(l\ . ( >. ,-a-ionallv the muscles of the two sides are connected at the 

 i I .on l.-r of the cricoid. In extreme rases each may cross the median line. 



This miiM-le U a tensor of the vocal cords by separating their points 

 of .it;. i, hinent on the thyn.id cartilage from those on the arytenoids. Although the 

 conventional name- of origin and insertion have been used, the more movable of the 

 two cartilages is tin- cricoid. an ,| the action of the muscles is to raise its anterior arch, 

 therel.v tipping the posterior plate with the arytenoids backward, and so stretching 

 the coid-. While the thvroid can he held fixed by many muscles, the only extrinsic 

 one attached to the cricoid i- a part of the inferior constrictor of the pharynx, so that 



Cartilage triticea 



Thyro-hyiiid 

 membrane 



Aryt-piglotticus 



Aryteiioi'li-us, 

 oblique portion 



Aryteiiiii'U-us, 



tru nren per- 



lion 



arytenoideus 

 posticus 



Epiglottis, dorsal surface 



Superior comu 

 of hyoid bone 



Superior thyroid 

 cornu 



Posterior margin 

 of thyroid car- 

 tilage 



Inferior thyroid 

 cornu 



ricoid cartilage 



Trachea 



MII-.I Ics of larynx from behind. 



