THE DIGESTIVE SYSTEM 
This apparatus (Apparatus digestorius) consists of the organs directly con- 
cerned in the reception and digestion of the food, its passage through the body, 
and the expulsion of the unabsorbed portion. These organs are conveniently 
grouped under two heads, viz.: (1) the alimentary canal; (2) the accessory organs. 
The alimentary canal (Tractus alimentarius) is a tube which extends from the 
lips to the anus. It has a complete lining of mucous membrane, external to which 
is an almost continuous muscular coat. The abdominal portion of the tube is 
largely covered with a serous membrane—the visceral peritoneum. The canal 
consists of the following consecutive segments: (1) The mouth; (2) the pharynx; 
(3) the cesophagus; (4) the stomach; (5) the small intestine; (6) the large intestine. 
The accessory organs are the teeth, tongue, salivary glands, liver, and pancreas. 
DIGESTIVE SYSTEM OF THE HORSE 
THE MOUTH 
The mouth! (Cavum oris) is the first part of the alimentary canal. It is 
bounded laterally by the cheeks; dorsally, by the palate; ventrally, by the body of 
the mandible and the mylo-hyoid muscles; behind, by the soft palate. In the 
horse it is a long, cylindrical cavity, and when closed, it is almost entirely filled up 
by the contained structures; a small space remains between the root of the tongue, 
the soft palate, and the epiglottis; this may be termed the glosso-epiglottic space. 
The entrance to the mouth (Rima oris) is closed by the lips. 
The cavity of the mouth is subdivided into two parts by the teeth and alveolar 
processes. The space external to these and inclosed by the lips and cheeks is 
termed the vestibule of the mouth (Vestibulum oris). In the resting state of the 
parts the walls of this cavity are in contact, and the space is practically obliterated. 
Its existence becomes very evident in facial paralysis, when the food tends to collect 
in it laterally, pouching out the cheeks. The space within the teeth and alveolar 
processes is termed the mouth cavity proper (Cavum oris proprium). When the 
teeth are in contact, it communicates with the vestibule only by the interdental 
spaces and the intervals behind the last molar teeth. Posteriorly it communicates 
with the pharynx through the isthmus faucium. 
The mucous membrane of the mouth (Tunica mucosa oris) is continuous at 
the margin of the lips with the common integument, and behind with the mucous 
lining of the pharynx. During life it is chiefly of a pink color, but may be more 
or less pigmented. 
The lips (Labia oris) are two musculo-membranous folds which surround the 
orifice of the mouth. Their angles of union (Anguli oris s. commissure labiorum) 
are situated near the first cheek tooth and are rounded. Each lip presents two 
surfaces and two borders. The external surface is covered by the skin, which pre- 
sents long tactile hairs in addition to the ordinary fine hair. The upper lip has 
a shallow median furrow (Philtrum), the lower a rounded prominence, the chin 
1The term “mouth” is commonly used to signify either the cavity (Cavum oris) or the 
entrance fo it (Rima oris). ae 
