Digestion. 101 



.diameter ; the food can therefore be swallowed not only 

 with rapidity but with ease, which the physiological condition 

 of the stomachs of these animals requires. Reversed muscular 

 action of the oesophagus assists the process of rumination. 



The Saliva. 



During the process of mastication the food becomes mixed 

 in the mouth with a fluid known as the saliva ; the secretion 

 of which occurs in three distinct pairs of glands. The 

 method by which it is formed is important for us to under- 

 stand, as much the same process occurs in other secretory 

 glands which we have not the same opportunity of watch- 

 ing during activity. 



The three glands which secrete saliva are the parotid, 

 submaxillary, and sublingual; and these are divided into 

 two systems, anterior and posterior. The former comprises 

 the submaxillary and sublingual ; the latter the parotid. 

 The two systems are further divided into mucous and 

 serous (or albuminous), the submaxillary and sublingual 

 being types of the first, the parotid the type of the last. 



The salivary glands in the herbivora are of considerable 

 size, the anterior system in the ox being well developed, 

 whilst in the horse it is rudimentary. According to Colin, 

 there is no connection between the weight of the glands 

 and the amount of fluid they secrete. The parotid in all 

 cases secretes more than the others ; in the horse it is four 

 times heavier than the submaxillary, but it secretes 

 twenty-four times as much saliva. In the ox the parotid 

 is not so large as the submaxillary, but it secretes four or 

 five times as much saliva. The same observer places the 

 daily secretion of saliva in the horse at 84 lbs., and in the 

 ox at 11*2 lbs., though the amount will vary depending on the 

 nature of the food consumed ; thus, hay absorbs more than 

 four times its weight of saliva, oats rather more than its own 

 weight, green fodder half its own weight. The amount of 

 saliva secreted, therefore, depends on the dryness of the food. 



Mixed saliva is an opalescent or slightly - turbid fluid 

 which readily froths. On standing it throws down a 



