458 



MUSCULAR MOTION. 



198. 



ligaments tense. 2dly. Thecrico-arytenoideipostici, and crico-arytenoidei 

 later ales; the former of which pass from the posterior surface of the cri- 

 coid to the outer angle of the base of the arytenoid; and the latter from 

 the upper border of the side of the cricoid to the outer angle of the base of 



the arytenoid. The use of the crico-arytenoidei 

 postici is to carry the arytenoid cartilages 

 backwards, separating them at the same time 

 from each other, and thus opening the glottis; 

 the action of the crico-arytenoidei laterales is 

 like that of the arytenoidei to bring together 

 the inner edges of the arytenoid cartilages, and 

 close the glottis. 3dly. The arytenoid muscle 

 of which there is only one. It extends across 

 from one arytenoid cartilage to the other; and, 

 by its contraction, brings them towards each 

 other. 4thly. The thy ro- arytenoid muscle, 

 which, according to M. Magendie, 1 is the most 

 important to be known of all the muscles of 

 the larynx, as its vibrations produce the vocal 

 sound. It forms the lips of the glottis, and 

 Magendie describes it as constituting, also, 

 "the inferior, superior, and lateral parietes of 

 the ventricles of the larynx." Generally, it 

 is considered to arise from the posterior surface 

 of the thyroid cartilage, and the ligament 

 connecting itwith the cricoid, and to beinserted 

 into the anterior edge of the base of the ary- 

 tenoid. By drawing the point of the thyroid 

 back, it must relax the vocal ligaments. 

 Lastly. The muscles of the epiglottis the 

 thyro-epiglottideus, aryteno-epiglottideus supe- 

 rior, aryteno-epiglottideus inferior (Hilton's 

 muscle), 2 and some fibres that may be looked 

 upon as vestiges of the glotto-epiglotticus, 

 which exists in many animals. These mus- 

 cles, the position of which is indicated by 

 the name, modify by their contraction, the 

 situation of the epiglottis. 



The principal governors of the pitch of the 

 voice, which is almost wholly regulated by 



Origin and Distribution of the the de g ree f tensi n f the VOCal ligaments, 



Eighth Pair of Nerves. are the crico-thyroid and thyro-arytenoid. 



1, 3, 4. Medulla oblongata. 1. Corpus pyramidale of one side. 3. Corpus olivare. 4. Corpus resti- 

 forme. 2. Pons Varolii. 5. Facial nerve. 6. Origin of glosso-pharyngeal nerve. 7. Ganglion of 

 Andersch. 8. Trunk of the nerve. 9. Spinal accessory nerve. 10. Ganglion of pneumogastric nerve. 

 11. Its plexiform ganglion. 12. Its trunk. 13. Its pharyngeal branch forming the pharyngeal plexus 

 (14), assisted by a branch from theglosso-pharyngeal (8), and one from the superior laryngeal nerve (15) . 

 16. Cardiac branches. 17. Recurrent laryngeal branch. 18. Anterior pulmonary branches. 19. Pos- 

 terior pulmonary branches. 20. CEsophageal plexus. 21. Gastric branches. 22. Origin of spinal 

 accessory nerve. 23. Its branches distributed to sterno-mastoid muscle. 24. Its branches to the 

 trapezius muscle. 



1 Precis, &c., 236, and his Memoire sur 1'Epiglotte. 



3 Wilson's Anatomist's Vade Mecum, Amer. edit., p. 483, Philad., 1843. 



