64 THE SURGICAL ANATOMY OF THE HORSE 



to its extremities the lateral plates or wings are attached by their 

 antero-superior angles. 



Each wing possesses two surfaces, four edges, and four angles. The 

 inner surface is concave, and bounds the interior of the laryngeal tube, 

 whilst the outer surface is slightly convex. The supero-posterior angle 

 presents an upwardly projecting process called the superior cornu, near 

 the root of which the wing is pierced by a foramen, through which the 

 superior laryngeal branch of the pneumogastric nerve enters the larynx. 



The postero-inferior angle is also drawn out into a process which 

 terminates in an acute angle, where it is articulated to the cricoid cartilage. 



The thyro-hyoid membrane connects the superior edge with the 

 styloid cornu of the hyoid bone, and to the inferior edge the crico- 

 thyroid muscle is attached. 



The Epiglottis. — The epiglottis is soft and flexible, and overhangs 

 the opening into the larynx, which it closes by being bent over it 

 during the passage of the bolus of food backwards from the isthmus of 

 the fauces to the entrance to the oesophagus. In outline it resembles 

 an ovate leaf, and excepting during deglutition its apex is directed 

 forwards. In the horse a small muscle is attached to its anterior surface 

 near the base. This is the hyo-epiglottideus muscle, which arises from 

 the superior face of the body of the hyoid bone, and which assists the 

 cartilage to resume its " respiratory " position after the voluntary act 

 of deglutition has been accomplished. 



The borders of the cartilage are curved, and slightly serrated, antl 

 to them are attached inferiorly folds of mucous membrane, which run 

 horizontally backwards to the arytenoid cartilages. 



The Cricoid. — The cricoid cartilage is in the form of a ring, which 

 has a greater depth posteriorly than in front, and which is attached to 

 the superior extremity of the trachea. 



The Arytenoid Cartilages. — The arytenoid cartilages in shape are not 

 unlike three-sided pyramids. The inner surface is directed towards the 

 interior of the larynx, the posterior surface gives attachment to the 



