356 



RESPIRATION. 



-11 



the Blower jaw, and is inserted into the hyoid bone ; and genio- 



hyoid, which arises from the inferior genial tubercle of the lower 



jaw, and is inserted into the hyoid bone. 



The action of this group of muscles is to ra*ise the hyoid bone 



and the larynx during deglutition ; or if the hyoid bone is de- 

 pressed and fixed, their contrac- 

 tion depresses the lower jaw. 



Intrinsic Muscles (Figs. 194, 

 195). These are eight in num- 

 ber : 



(1) Cricothyroid. This mus- 

 cle arises from the front and side 

 of the cricoid cartilage, and is 

 inserted into the lower border 

 of the thyroid and the anterior 

 border of the lower cornua. The 

 action of the two muscles is to 

 make tense and elongate the 

 vocal cords. Their action will 

 be better understood after a con- 

 sideration of the thyrohyoid mus- 

 cles. 



(2) Crico-arytenoideus Posti- 

 cus. It arises from the posterior 

 surface of the cricoid, and is in- 

 serted into the muscular process 

 of the base of the arytenoid. The 

 action of the two muscles is to ro- 

 tate outward the arytenoid carti- 

 lages, and thus separate and make 

 tense the vocal cords and open the 

 glottis. 



(3) Crico-arytenoideus Lat- 

 eralis. This muscle has its ori- 

 gin from the upper border of 

 the side of the cricoid cartilage, 

 and is inserted into the mus- 

 cular process of the arytenoid. 

 The action of the pair of mus- 

 cles is to rotate the arytenoid 



cartilages inward, approximating the vocal cords and closing the 

 glottis. 



(4) Arytenoideus. This is a single muscle and arises from the 

 posterior surface and outer border of one arytenoid cartilage, and 

 is inserted into the same parts of the other arytenoid. Its action 

 is to approximate the arytenoid cartilages and close the glottis, 

 especially at the posterior portion. 



17 



FIG. 195. Larynx and its lateral mus- 

 cles after removal of the left plate of the 

 thyroid cartilage: 1, thyroid cartilage; 

 2, thyro-epiglottic muscle ; 3, cartilage 

 of Wrisberg ; 4, ary-epiglottic muscle ; 

 5, cartilage of Santorini ; 6, oblique ary- 

 tenoid muscles ; 7, thyro-arytenoid mus- 

 cle ; 8, transverse arytenoid muscle; 9, 

 processus muscularis of arytenoid car- 

 tilage ; 10, lateral crico-arytenoid mus- 

 cle; 11, posterior crico-arytenoid mus- 

 cle ; 12, cricothyroid membrane ; 13, cri- 

 coid cartilage ; 14, attachment of crico- 

 thyroid muscle ; 15, articular surface for 

 the inferior cosnu of the thyroid car- 

 tilage ; 16, cricotracheal ligament ; 17, 

 cartilages of trachea ; 18, membranous 

 part of trachea (Stoerk). 



