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 l^ody, 

 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 

 hps 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 oesophagus; (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 ahmentary 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 (\'estibulum 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 raolar 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 



f.ng of the pharynx. During life it is chiefly of a pink color, but may be more 

 less pigmented. 

 ,■ The lips (Labia oris) are two musculo-membranous folds which surround the 

 "onfice of the mouth. Their angles of union (Anguli oris s. commissurte 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 



'The term "mouth" is commonly used to signify either the cavity (Cavum oris) or the 

 entrance to it (Rima oris). 



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