DIGESTION IN THE MOUTH. 289 



and a special reservoir, or salivary bladder, exists beneath the mouth. In 

 these animals also the saliva, through its viscidity, assists in the prehen- 

 sion of food. In the carnivora mastication is incomplete ; since the food 

 of carnivorous animals contains a large quantity of water, the salivary 

 glands of these animals are therefore relatively small, and their function 

 is confined to the production of a secretion which may act simply as a 

 lubricant and assist in deglutition. In the herbivora, on the other hand, 

 from the necessity for perfect subdivision required by their food, they 

 are relatively very large. The salivary glands thus reach their highest 

 development in the rodents, the pachyderms, solipedes, and ruminants. 



Colin has divided the salivary glands into two different types. The 

 anterior system, or the mucous type, which empty their secretions into 

 the mouth in the neighborhood of the incisor teeth, comprise the 

 submaxillary and sublingual glands ; these glands are most developed 

 in carnivora and in aquatic animals, whose food must be lubricated for 

 deglutition, but not masticated. The posterior system, or serous type, 

 which empty their secretions into the mouth near the molar teeth, are 

 most developed in animals whose food requires thorough mastication, as 

 in the herbivora, and especially in non-ruminants. The parotid is the 

 type of this system. The glands which form these two systems are not 

 all developed in the same proportion. Thus, in the anterior system, 

 composed of the submaxillary, sublingual, and the gland of Nuck, the sub- 

 lingual maybe very small and the submaxillary very large, the former 

 being rudimentary in the dog. Again, they are rudimentary in the 

 dromedary, and are extremely highly developed in the ox. Again, as 

 regards the posterior system, in the horse the parotids are enormous, 

 while the submaxillary glands are rudimentary. In the ox the reverse is 

 the case. In herbivorous animals these glands have their largest volume, 

 but there is no relative proportion between the volume of the glands and 

 the volume of the secretion which the} r produce. Thus, in the ox the 

 weight of the salivary glands will amount on an average to six hundred 

 and twenty-four grammes ; the horse to five hundred and nine grammes ; 

 the pig, three hundred and five ; sheep, eighty-three; dog, twenty -five; 

 and the cat, ten. The parotid is the largest salivary gland in all animals 

 with the exception of the dog, and here the submaxillary gland is the 

 largest. In the pig, ox, and sheep the sublingual glands are sometimes 

 double, the one part emptying its secretion by a long duct opening at 

 the papilla at the side of the fraenum of the tongue, the other by a num- 

 ber of coiled ducts at the side of the floor of the mouth. 



In addition to these large salivary glands the fluid in the mouth is 

 also poured out by glands located in its mucous membrane, forming 

 the so-called buccal, lingual, palatine, and pharyngeal glands. The 

 secretion formed by all these glands combined is termed mixed saliva. 



