348 DIGESTIVE SYSTEM OF THE HORSE 



The submaxillary duct (Ductus submaxillaris Whartoni) is formed by the union 

 of small radicles which emerge along the concave edge. It runs forward along this 

 border, and, after leaving the anterior extremity, crosses the intermediate tendon 

 of the digastricus, passes between the hyo-glossus and mylo-hyoideus, and 

 gains the inner surface of the sublingual gland. Its terminal part lies on 

 the body of the mandible, under the mucous membrane, which it pierces 

 opposite the canine tooth. The orifice is at the end of a flattened papilla 

 (Caruncula sublingualis). 



Blood-supply. — Occipital, external carotid, and external maxillary arteries. 



Nerve-supply. — Chorda tympani and sympathetic nerves. 



The sublingual gland (Glandula sublingualis) is situated beneath the mucous 

 membrane of the mouth, between the body of the tongue and the ramus of the 

 mandible. It extends from the symphysis to the third or fourth lower cheek tooth. 

 Its length is about five or six inches (ca. 12 to 15 cm.) and its weight about half an 

 ounce (ca. 15 to 16 g.). 



It is flattened laterally, and has a thin upper border which causes an elevation 

 of the mucous membrane of the floor of the mouth, termed the sublingual crest 

 (Plica sublingualis). The external surface is related to the mylo-hyoideus muscle, 

 and the internal surface to the genio-glossus and stylo-glossus, the submaxillary 

 duct, and branches of the lingual nerve. The inferior border is related to the genio- 

 hyoid muscle. 



The sublingual ducts (Ductus sublinguales minores), about thirty in number, 

 are small, short, and twisted; they open on small papillae on the sublingual crest. 



Blood-supply. — Sul)lingual artery. 



Nerve-supply. — Trigeminal and sympathetic nerves. 



THE PHARYNX 



The pharynx is a musculo-membranous sac which belongs to the digestive and 

 respiratory tracts in common. It is funnel-shaped, the base joining the mouth 

 and nasal cavity, while the apex is continued by the oesophagus. Its long axis 

 is directed obliquely downward and backward, and has a length of about six inches 

 (ca. 15 cm.). 



The pharynx is attached by its muscles to the palate, pterygoid, and hyoid 

 bones, and to the cricoid and thyroid cartilages of the larynx. 



Its principal relations are : dorsally, the base of the cranium and the guttural 

 pouches; ventrally, the larynx; laterally, the internal pterygoid muscle, the great 

 cornu of the hyoid bone, the internal and external maxillary arteries, the glosso- 

 pharyngeal, superior laryngeal, and hypoglossal nerves, the sul)maxillary salivary 

 gland, and the pharyngeal l^^mph glands. 



It presents seven openings. The posterior nares (Choanae) communicate 

 dorsally with the nasal chambers. The pharyngeal orifices (Ostia pharyngea) of 

 the two Eustachian tubes are situatcMl on the lateral wall behind th(Miares and a little 

 below the level of the inferior nasal meatus. They are slit-like openings, slightly 

 oblique downward and backward, and are a little more than an inch (ca. 3 cm.) in 

 length. They are bounded internally by a valvular flap formed by the expanded 

 extremity of the cartilaginous Eustachian tube. The isthmus faucium is situated 

 below and in front. It is closed l)y the soft palate except during swallowing. The 

 laryngeal orifice (Aditus laryngis) occupies the greater part of the ventral wall or 

 floor of the j)harynx. Behind this is the oesophageal opening. 



The wall of the pharynx comprises from without inward: the muscles, the 

 pharyngeal ai)oneurosis, ant! the mucous membrane. 



The muscles (Figs. 243, 244) are covered by the pharyngeal fascia, which is. 



