236 



THE ANATOMY OF THE HORSE. 



The Posterior Crico-abytenoid Muscle (Figs. 30 and 32). This is 

 the most powerful of the intrinsic muscles. Its muscular tissue is dark 



red, and mixed with tendinous 

 tissue. Its fibres take origin 

 from the outer surface of the 

 cricoid bezel, and are inserted 

 into the prominent tubercle 

 on the external angle of the 

 arytenoid cartilage. 



Action — To swing out- 

 wards the arytenoid carti- 

 lage, and thus to separate the 

 vocal cords and dilate the 

 glottis. 



The Lateral Cbico-aey- 

 TENOiD Muscle (Fig. 31). 

 This muscle is placed below 

 the thyro-arytenoid, under 

 concealment of the thyroid 

 wing. Its fibres arise from 

 the upper border of the side 

 of the cricoid cartilage ; and, 

 passing backwards and up- 

 wards, they become inserted 

 into the same tubercle on the base of the arytenoid as the posterior 

 muscle, and into the outer surface of the arytenoid in front of that 

 tubercle. 



Action. — The muscle acts on the crico-arytenoid joint in a manner 

 antagonistic to the preceding muscle, approximating the vocal cords 

 and narrowing the glottis by swinging the arytenoid cartilage in- 

 wards. 



The Arytbnoidbus Muscle (Fig. 32). This may be regarded either 

 as a single muscle, or as a double muscle whose right and left fibres 

 meet at a median raphe. Its fibres are inserted on each side into 

 the posterior surface of the arytenoid cartilage, and superiorly 

 it is joined by the higher fibres of the thyro-arytenoid muscle. 



Action. — To approximate the right and left arytenoid cartilage, and 

 thus narrow the glottis. 



Fig. 31. 



Larynx, Side View (thyroid ala removed). 



1. Glossal Process of Hyoid ; 2. Cut Base of Thyroid 

 Cormi ; 3. Small Cornu ; 4. Great Cormi ; 5. Epiglottis ; 

 6. Arytenoid Cartilage ; 7. Cut Wing of Thyroid Carti- 

 lage ; 8. Facet on Cricoid for Articulation with Thyroid 

 Cartilage ; 9. Pouch of iVIucous Membrane from Ven- 

 tricle of Larynx ; 10. and 11. Upper and Lower Bundles 

 of Thyro-Arytenoideus ; 12. Crico-Arytenoideus Later- 

 alis ; 13. Crico-Arytenoideus Posticus ; 14. Thyro- 

 Hyoideus ; 15. Hyo-Epiglottideus ; 16. Thyroid Body ; 

 17. 1st Ring of Trachea. 



NERVES OF THE LARYNX. 



Two nerves are distributed to the larynx — the superior and inferior 

 laryngeal nerves. The latter is also known as the recurrent nerve, and 

 both are branches of the vagus, or 10th cranial nerve. 



