STEUCTUKE OF THE HORSE. HI 



THE DIGESTIVE SYSTEM. 



The digestive organs comprise the alimentary canal and its 

 accessories, extending from the lips to the anus. Its walls are 

 composed of muscular tissue, and lined throughout by mucous 

 membrane. It consists of a continuous series of tubes, each of 

 which will be considered in natural order. The food is pre- 

 pared in the mouth, where it is crushed between the teeth and 

 rolled about by the tongue, to mix it thoroughly with the saliva. 

 The mouth is lined by a mucous membrane, consisting of a 

 stratified epithelium, the superficial cells being flat and horny. 

 The tongue is a muscular organ, which plays an important part 

 in articulation, mastication, and as the organ of taste. The lips 

 of the horse are the organs of prehension, taking up the food. 

 They consist of skin, mucous membrane, muscles, vessels, 

 nerves, areolar tissue, and fat. The cheeks are continuous with 

 the lips, and close the mouth laterally; they consist of an exter- 

 nal cuticular, a central muscular, and an internal mucous. The 

 hard plate forms the roof of the mouth, and serves the purpose 

 of assisting the tongue to manipulate the food. The soft palate, 

 or velum pendulum palati, is the valvular curtain suspended 

 between the mouth and pharynx, and consists of a double fold of 

 mucous membrane, enclosing muscles, glands, and nerves. 



The salivary glands are accessories of the mouth. They 

 secrete the saliva, which is discharged into the mouth, and satu- 

 rates the food during mastication. There are three pairs — ^viz., 

 parotid, submaxillary, and the sublingual. The parotid, the 

 largest of the three, is situated in the space bounded by the pos- 

 terior border of the inferior maxilla and at the anterior border 

 of the wing of the atlas; it lies immediately below and partly 

 surrounds the ear. The glands form a duct, known by anato- 

 mists as Steno's duct. It enters the mouth at about the level of 

 the third upper molar. The submaxillary gland lies in the 

 maxillary space, below and behind the parotid, and terminates 

 in what is known as Wharton^ s duct. It opens into the mouth 



