350 DIGESTIVE SYSTEM OF THE HORSE 



preceding muscle — from which it is not distinctly separated — crosses the levator 

 palati, and is inserted into the median raphe. Its action is similar to the preceding. 



4. The hyo-pharyngeus may consist of two portions: 



(a) The kerato-pharyngeus is a small and inconstant muscle which arises 

 from the inner surface of the great cornu of the hyoid bone near its lower end. 

 It passes upward and backward, turns inward toward the raphe, and spreads out 

 under the next muscle. 



(6) The chondro-pharyngeus, broad and fleshy, arises from the thyroid cornu 

 of the hyoid ])one and by a thin fasciculus from the wing of the thyroid cartilage and 

 ends at the median raphe. 



5. The thyro-pharyngeus arises from the lateral surface of the wing of the 

 thyroid cartilage. Its fibers pass forward and inward to the median raphe. 



6. The crico-pharyngeus arises from the cricoid cartilage and ends at the 

 raphe. The fibers are directed upward, forward, and inward; they blend behind 

 with the longitudinal fibers of the oesophagus. 



The last three muscles are constrictors of the pharynx. 



The pharyngeal aponeurosis is attached to the base of the cranium. It is 

 well develoi)ed on the inner face of the palato-pharyngeus muscle and forms a 

 median raphe (Raphe pharyngis) dorsally, which is wide in its posterior part. 



The mucous membrane of the pharynx is continuous with that of the several 

 cavities which open into it. It is thin and closely adherent to the base of the skull 

 in the vicinity of the posterior nares, where the muscular wall is absent. Behind 

 the Eustachian openings is a median cul-de-sac, the pharyngeal recess. The recess 

 is somewhat variable, but is usually about an inch in depth and will admit the end 

 of the finger. In the ass and mule it is much deeper. Here also the muscular 

 wall is absent and the mucous membrane lies against the guttural pouches. From 

 the Eustachian opening a fold of the mucous membrane (Plica salpingo-pharyngea) 

 passes toward but does not reach the laryngeal opening. Below, a horizontal fold, 

 the posterior pillar of the soft palate (Arcus pharyngo-palatinus), passes along the 

 lateral wall and unites with its fellow over the entrance to the oesophagus. The 

 upper part of the cavity (the naso-pharynx) is lined with a ciliated epithelium, 

 while the lower part (oro-pharynx) has a stratified squamous epithelium. The 

 communication between the two is oval and is l)Ounded liy the free edge of the soft 

 palate and its posterior pillars; it is termed the pharyngeal isthmus. On either side 

 of the laryngeal opening is a narrow deep depression, the pyriform sinus (Recessus 

 piriformis) . 



The sul)mucous tissue contains numerous mucous glands (Glanduhp pharyn- 

 gese). In the young subject the lymph follicles are numerous and form a collection 

 dorsally and between the Eustachian openings, known as the pharyngeal tonsil. 



Blood-supply. — External carotid, external maxillary, and thyro-laryngeal 

 arteries. 



Nerve-supply. — Glosso-pharyngeal, vagus, and sympathetic nerves. 



THE (ESOPHAGUS 

 The oesophagus is a musculo-memliranous tube, a])Out 50 to 60 inches (ca. 

 125 to 150 cm.) in length, which extends from the pharynx to the stomach. It 

 begins in the median plane above the cricoid cartilage of the larynx. In its course 

 it shows several changes of direction. At the level of the fourth cervical vertebra 

 it inclines to the left side of the trachea, and continues this relation to the level of 

 the third thoracic vertebra. Here it again gains the dorsal surface of the trachea, 

 and passing backward, crosses the left bronchus, being here almost in the median 

 plane. It continues in the mediastinum between the lungs backward, upward, 

 and a little to the left, to reach the hiatus ocsophagcus of the diaphragm. Passing 



