THE DIGESTIVE ORGANS 131 



long, having a capacity of 4 gallons ; the colons, large 

 and floating, 20 feet long, with a capacity of 1 2 gallons ; 

 and the rectum, which is the termination of the intestinal 

 canal, 2 feet long, and with a capacity of 3 gallons. 

 The estimated average length of a horse's intestines 

 is 97 feet, and total capacity 30 gallons. Like the 

 stomach, the walls of the intestines have three coats : 

 the outside serous ; the middle muscular (longitudinal and 

 circular) ; and the inside, covered with epithelium and 

 a mucous membrane, and well studded throughout with 

 various glands. 



222. 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 Lecture VIII., ' 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. 



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

 order given : 



(1) The food is taken into the mouth; in the horse it is 



gathered in by the mobility of the upper lip, called 

 the prehensile property, when it is seized by the 

 incisors, or front teeth. 



(2) 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. 



(3) 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 



