MUSCLES OF THE LARYNX 519 



of the thyroid cartilage. Its action is to draw the larynx toward the root of the 

 tongue. It is related laterally to the external maxillary vein and the anterior part 

 of the mandibular gland. 



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

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

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

 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-thyreoideus) is a short muscle which fills the 



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



and somewhat forward. It arises from the ventral part of the lateral surface and 



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



Fig. 462. — Laryngeal Muscles. of Horse, Seen from Left Side After Removal of Major Part of Lamina op 



Thyroid Cartilage. 

 a, Kerato-hy oideus ; b, thyro-hyoideus ; c, crico-thyroideus; d, sterno-thyroideus; e, ventricularis ; /, vocalis; g, 

 crico-arytenoideus lateralis; A, crico-arytenoideus dorsalis; i, arytenoideus transversus; 1, lingual process; 2, small 

 cornu, 3, thyroid cornu, of hyoid bone; 4> thyroid cartilage; 5, cricoid cartilage; 6, epiglottis; 7, apex of arj'tenoid 

 cartilage; 5, trachea; 5, muscular process of arytenoid; iO, lateral lobe of thyroid gland; 70', isthmus of thjToid gland; 

 11, laryngeal saccule. The saccule is larger than it ia represented in this figure, and extends almost to the vocal 

 process. (Ellenberger-Baum, Anat. d. Haustiere.) 



adjacent part of the lateral surface 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 about a trans- 

 verse axis through the crico-thyroid joints, carrying the bases of the arytenoid 

 cartilages with it and thus tensingthe vocal cords. 



The crico-ar3rtenoideus dorsalis (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 broad origin on half of the lamina of the cricoid cartilage, including the me- 

 dian ridge, and its fibers converge to be inserted into the processus muscularis of 

 the arytenoid cartilage. Its action is to dilate the rimaglottidis by rotating the 

 arytenoid cartilage so as to carry the vocal process and cord outward (abduction). 



The crico-arytenoideus lateralis (M. crico-arytsenoideus lateralis) lies on the 

 medial face of the thyroid lamina. It arises from the anterior border of the lateral 

 part of the arch of the cricoid cartilage. The fibers pass in a dorsal direction and 

 converge on the processus muscularis of the arytenoid cartilage. It closes the 

 rima glottidis by rotating the arytenoid cartilage inward (adduction). 

 '■ Also known as the crico-arytenoideus posterior s. posticus. 



