238 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



in the pig, and often has been noticed in the horse, there is considerable 

 reason for doubting that this is ever a normal method for the prehension 

 of liquids. 



d. Lapping. — This method of the prehension of liquids is seen in 

 the carnivora, as in the dog and cat ; since their mouths are relatively 

 much larger than the herbivora, they cannot be immersed in water up to 

 the commissure of the lips without also immersing the nose. Such ani- 

 mals, therefore, spoon up water with the tongue, like taking water to the 

 mouth with the hand. The tongue is protruded, its tip rendered cup- 

 shaped by the action of its intrinsic muscles, and a small amount of 

 water lifted up and carried by the repeated protrusion and retraction of 

 the tongue to the mouth. The process is a very slow one, and is seen 

 only in carnivora. 



Various other animals have different modes for the prehension 

 of liquids. Thus, in the elephant the trunk is a combined force-pump 

 and suction-pump. The trunk being immersed in water, \>y inspiratory 

 efforts it is filled with fluid; the tip is then directed toward the mouth 

 and the water is forced through it into the mouth. Birds drink by 

 filling their lower beak with water, elevating their heads and allowing the 

 water to flow back into their pharynx without the production of any 

 motion of deglutition. The single exception to this manner of drinking 

 seen in the birds is in the case of doves and pigeons. 



III. MASTICATION. 



The term mastication is given to the purely mechanical operations by 

 which the alimentary matters, through the action of jaws furnished with 

 teeth, are comminuted in the mouth, and is, in most animals, a necessary 

 preparation for the submission of food to the action of the gastric juice. 

 Its importance and completeness differ in different animals, depending 

 upon the nature of their food. Animals, such as the carnivora, which 

 feed on readily digestible matters, do not need this preliminary prepara- 

 tion, and as a consequence the food of carnivora is swallowed in bulk 

 without having been subjected to any, or, at best, to but slight division 

 in the mouth. This applies also to all animals which feed on liquid or 

 soft foods, where a masticatory apparatus is not needed. All animals 

 which feed on grain and other vegetable matters require the process of 

 mastication to render the food susceptible to the action of the digestive 

 juices ; for, as we have found in these animals, the food-constituents are 

 inclosed in unyielding envelopes which resist the action of the digestive 

 juices. To enable the nutritive matter to be released from these sub- 

 stances, such foods require mechanical subdivision before they can prove 

 of nutritive value. 



