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TEXT-BOOK OF PHYSIOLOGY. 



of origin and insertion: viz., two posterior crico-arytenoids, two lateral crico- 

 arytenoids, two thyro-arytenoids, one arytenoid, and two crico-thyroids 

 (Figs. 288 and 289). 



The posterior crico-arytenoid muscle lies on the posterior surface of the 

 quadrate plate of the cricoid cartilage, on either side of the median line, 

 from which it takes its origin. The fibers of the muscle pass upward and 

 outward and in their course converge to be inserted into the external angle of 

 the arytenoid cartilage. The superior and more horizontally directed fibers 

 rotate the arytenoid around its vertical axis; the inferior and obliquely 



FIG. 288. FIG. 289. 



FIG. 288. POSTERIOR VIEW OF THE MUSCLES OF THE LARYNX, i. Posterior crico-arytenoid 

 muscle. 2, 3, 4. Different fasciculi of the arytenoid muscle. 5. Aryteno-epiglottidean muscle. 

 (Sappey.) 



FIG. 289. LATERAL VIEW OF THE MUSCLES OF THE LARYNX, i. Body of the hyoid bone. 

 2. Vertical section of the thyroid cartilage. 3. Horizontal section of the thyroid cartilage 

 turned downward to show the deep attachment of the crico-thyroid muscle. 4. Facet of articula- 

 tion of the small cornu of the thyroid cartilage with the cricoid cartilage. 5. Facet on the cricoid 

 cartilage. 6. Superior attachment of the crico-thyroid muscle. 7. Posterior crico-arytenoid 

 muscle. 8, 10. Arytenoid muscle. 9. Thyro-arytenoid muscle, n. Aryteno-epiglottidean 

 muscle. 12. Middle thyro-hyoid ligament. 13. Lateral thyro-hyoid ligament. (Sappey.) 



directed fibers draw the cartilage downward and inward. As a result of the 

 action of the muscle in its entirety, the vocal process is turned upward and 

 outward, and as the vocal band is carried with it the glottis is widened, 

 a condition necessary to the free entrance of air into the lungs (Fig. 290). 

 Since the contraction of the crico-arytenoid has this result, it is generally 

 spoken of as the abductor or respiratory muscle. 



The lateral crico-arytenoid muscle arises from the side of the cricoid 

 cartilage. From this point its fibers are directed upward and backward 

 to be inserted into the external process of the arytenoid. Its action is to 

 draw the arytenoid cartilage forward and inward, thus approximating 

 and relaxing the vocal band. 



