390 DIGESTIVE SYSTEM OF THE HORSE 
of the petrous temporal bone and from the lateral lamina of the Eustachian tube, 
and passes at first forward, lateral to the latter; it then inclines ventrally across 
the deep face of the anterior pharyngeal muscles and turns mediaily into the soft 
palate, in which it spreads out above the glandular layer. It raises the soft palate, 
thus closing the posterior nares during deglutition. 
The tensor palati (M. tensor veli palatini) is larger than the levator, and is 
fusiform and flattened. It arises from the muscular process of the petrous tem- 
poral bone, the pterygoid bone, and the lateral lamina of the Eustachian tube, 
and passes forward, lateral to the levator, across the medial surface of the origin of 
the pterygoideus medialis. Its tendon is then reflected around the hamulus of the 
pterygoid bone, where it is held in position by a fibrous band and lubricated by a 
bursa, turns inward and expands in the aponeurosis of the soft palate. It tenses 
the soft palate. 
Vessels and Nerves.—The blood-supply of the soft palate is derived from the 
internal and external maxillary arteries and the blood is carried away by the corres- 
ponding veins. The lymph vessels go to the pharyngeal lymph glands. The nerves 
come from the trigeminus, vagus, and glosso-pharyngeal nerves. 
The floor of the mouth in its anterior part is free and is formed by the body of 
the mandible, covered by mucous membrane. The remainder is occupied by the 
attached portion of the tongue in the undisturbed state of the parts. The follow- 
ing features are exposed by raising the tongue and drawing it to one side. About 
opposite the canine tooth on each side is a papilla, the caruncula sublingualis, 
through which the duct of the mandibular gland opens. Just behind these papille 
is a median fold of mucous membrane which passes to the ventral surface of the 
tongue, constituting the frenum lingue. On either side is the sublingual fold 
(Plica sublingualis) which extends from the frenum to the level of the fourth cheek 
tooth. The fold indicates the position of the underlying sublingual gland, and 
presents numerous small papillee, through which the ducts open. Behind the last 
tooth a vertical fold of the mucous membrane passes from upper to lower jaw. This 
is termed the plica pterygomandibularis; it contains a ligament of like name. 
The isthmus faucium is the orifice of communication between the mouth and 
the pharynx. It is bounded above by the soft palate, below by the root of the 
tongue, and laterally by the anterior pillars of the soft palate. It is relatively 
small and not very dilatable in the horse, and is closed by the soft palate under 
normal conditions, except during deglutition. 
THE TONGUE 
The tongue (Lingua) is situated on the floor of the mouth, between the rami of 
the mandible, and is supported mainly in a sort of sling formed by the mylo-hyoid 
muscles. Its posterior part, the root (Radix lingue), is attached to the hyoid bone, 
soft palate, and pharynx. Only the upper surface of this part is free, and slopes 
downward and backward. The middle part, the body (Corpus linguze), has three 
free surfaces. The dorsal surface is slightly rounded. The lateral surfaces are 
nearly flat for the most part, but anteriorly become rounded and narrower. The 
ventral surface is attached to the mandible. The apex or tip (Apex linguz) is 
free, spatula-shaped, and presents upper and lower surfaces and a rounded border. 
The term dorsum lingua is applied to the dorsal surface; it is free throughout, 
and in the resting state of the parts is in contact with the palate except at the glosso- 
epiglottic space. 
Structure-—The tongue consists of: (1) The mucous membrane; (2) the 
glands; (3) the muscles; (4) vessels and nerves. 
The mucous membrane (Tunica mucosa linguee) adheres intimately to the 
subjacent tissue, except on the lower part of the lateral surfaces of the body and 
