MUSCLES OF THE LARYNX 



445 



The crico-tracheal membrane (Ligamentum crico-tracheale) connects the 

 cricoid cartihige with the first ring of the trachea. 



Muscles of the Larynx 

 A. Extrinsic Muscles 



The stemo-thyro-hyoideus is described on p. 226. 



The thyro-hyoideus (M. hyo-thyreoideus) is a flat, quadrilateral muscle, which 

 lies on the outer surface of the th3Toid lamina and the lateral part of the thyro- 

 hyoid membrane. It arises from the thyroid cornu of the hyoid bone, and ends on 

 the oblique line on the lamina of the thyroid cartilage. Its action is to draw the 

 larynx toward the root of the tongue. 



The hyo-epiglotticus (M. hyo-epiglotticus) is a feeble muscle which occupies a 

 median position above the central part of the thyro-hyoid membrane, inclosed by 

 an elastic sheath, the hyo-epiglottic ligament. It arises from the body of the hyoid 



Fig. 354. — L.^rynge.^l Muscles of Horse, Seen prom Left Side After Remov.^l of M.\jor P.\rt of L.\mina 



OP Thyroid C.\rtil.\ge. 

 a, Keiato-hyoideus; b, thyro-hyoideus; c, crico-thyroideus; d, sterno-thyroideu.s; e, ventricularis; /, 

 vocaUs; g, crieo-.arytenoideu.s lateraU.s; A, crico-arytenoideus post. s. dorsaUs; i, arytenoideus transversus; /, 

 lingual process; 2, small cornu; S. thyroid cornu, of hyoid bone; 4, thyroid cartilage; 5, cricoid cartilage; 6, epi- 

 glottis; 7, apex of arytenoid cartilage; S, trachea; 9, muscular process of arytenoid; 10, lateral lobe of thyroid 

 gland; 10', isthmus of thyroid gland; i^, laryngeal saccule. (Ellenberger-Baum, Anat. d. Haustiere.) 



bone by two branches which unite and are inserted into the front of the base of 

 the epiglottis. Its action is to draw the epiglottis toward the root of the tongue. 



B. Intrinsic Muscles 



The crico-thyroideus (M. crico-thjTeoideus) is a short muscle which fills the 

 groove on the lateral surface of the cricoid cartilage; its fibers are directed clorsally 

 and somewhat forward. It arises on the lower half of the lateral surface and 

 posterior edge of the cricoid cartilage, and is inserted into the posterior border and 

 adjacent part of the surfaces of the lamina of the thyroid cartilage. Its action is 

 to draw the thyroid cartilage and the ventral part of the cricoid cartilage together. 

 In this action the cricoid cartilage is probably rotated, carrying the liases of the 

 arytenoid cartilages with it and thus tensing the vocal cords. 



The crico-arytenoideus dorsalis s. posterior (M. crico-arytsenoideus dorsalis) 

 is a strong, somewhat fan-shaped muscle, which, with its fellow, covers the dorsal 

 surface of the lamina of the cricoid cartilage. It is partially divisible into two layers. 

 It has a l)road origin on half of the lamina of the cricoid cartilage, and its fibers 

 converge to be inserted into the processus muscularis of the arytenoid cartilage. 



