84 



the outside serous ; middle muscnlav (longitudinal and circular) ; 

 the inside covered with epithelium and a mucous membrane, 

 and well studded throughout with various glands. 



223. Besides the above-named, which are found not only in the horse, 

 but also in the pig and dog, and in a general sense also in cattle and 

 sheep, there are also the accessory digestive organs, that perform 

 functions which assist digestion, that is to say, they convert the 

 food into such a state that it can be absorbed and taken into the 

 blood, and conveyed to the different parts of the system, to 

 be assimilated for nourishment. {See Eighth Lecture, Circulation — the 

 Lymphatic System.) Such accessory digestive organs are the Liver; 

 the Spleen ; the Pancreas, or sweetbread ; and the Portal Vein ; 

 all of which will be further noticed under the Digestive Organs, 

 Part II. 



224. The Processes of Digestion are as follows, and in the order 

 given : — 



ist, — The food is taken into the mouth ; in tlie horse, it is gathered 

 in by the mobility of the upper lip, called the prehensile 

 property, when it is siezed by the incisors or front teeth. 



2nd. — It is then pushed between the back (molars) teeth by the 

 tongue ; the cheeks assist the tongue in keeping it there, 

 while it is masticated, or chewed, by these teeth. 



3rd. — During this process of Mastication, the salivary glands pour 

 out saliva (an alkaline fluid, secreted from the blood). This 

 moistens the food, thus making it easier to swallow, and, also, 

 acts chemically on a small proportion of the starchy matter, 

 converting it into sugar, by the action of a special ferment 

 in the saliva. 



4th. — The food, having been well masticated, is formed by the tongue 

 and cheeks into a bolus, which is passed to the back of the 

 mouth, where it is seized by the action of the muscles of the 



