230 



THE ANATOMY OF THE HORSE. 



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 inwards. 



The Arttbnoideus Muscle (Fig. 28). 

 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 pos- 

 terior 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 cartilages, and thus narrow 

 the glottis. 



NERVES OF THE LARYNX. 



Two nerves are distributed to the 

 larynx — the superior and inferior laryn- 

 geal nerves. The latter is also known 

 as the recurrent nerve, and both are 

 branches of the vagus, or 10th cranial 

 nerve. 



The Superior Laryngeal Nerve has its 

 origin described at page 194. It gives 

 motor filaments to the crico-thyroid and 

 crico-pharyngeus muscles ; and then pe.ne- 

 trating the thyroid wing by the foramen 

 near its supero-posterior angle, the nerve 

 splits into sensory branches distributed to the mucous membrane of the 

 larynx, giving also twigs to the lining of the pharynx and oesophagus. 



The Inferior Laryngeal (Eecurrent) Nerve has its origin and 

 course described at page 149. It is the motor nerve to all the intrinsic 

 muscles except the crico-thyroid, and it also gives some sensory twigs to 

 the laryngeal mucous membrane. ^ 



Fig. 28. 

 Larynx, Back View. 

 I. Epiglottis ; 2. Arytenoid Carti- 

 lage ; 3. Thyroid Cartilage ; 4. Ary- 

 tenoideus ; 5. Crico-Arytenoideus Pos- 

 ticus ; 6. Cricoid Cartilage ; 7. 1st 

 Ring of Trachea ; 8. Thyroid Body. 



INTERIOR OF THE LARYNX. 



Directions.- — A vertical incision should be made along the middle line 

 of the larynx behind, severing the arytenoideus muscle and the bezel of 

 the cricoid cartilage. By separating the lips of this incision, a view of 

 the interior of the larynx from behind will be obtained, and this is to 

 be supplemented by looking into the tube from its upper and lower 

 apertures. 



The Superior Aperture of the larynx is a large orifice placed at the 

 floor of the pharynx. It is bounded in front by the epiglottis, behind 



