PREHENSION OF FOOD. 237 



the contraction of the genio-hyoid muscle, the root of the tongue being, 

 therefore, likewise depressed and drawn forward. At the same time 

 the genio-glossi muscles, contracting with their antagonists, the hyo- 

 glossi, have the effect of drawing the body of the tongue directly back- 

 ward, while the organ itself becomes flattened. The cheek-muscles are 

 entirely inactive in the act of suckling. 



b. Pumping. — The process of drinking by means of pumping with 

 the tongue is employed by the horse and ruminants and most herbivora. 

 The lips are immersed below the surface of the water, which seldom or 

 never rises above the level of the nose ; a small space is opened between 

 the lips, and the tongue is withdrawn in the mouth by a mechanism 

 similar to that employed in suckling ; the tongue thus acting as a piston, 

 the pressure of the atmosphere on the water without serves to force it 

 into the mouth, and it is then carried by a motion of deglutition to the 

 pharynx and gullet. 



That drinking in the horse is not due to the production of a vacuum 

 in the mouth by inspiration has been proved by performing tracheotomy 

 on a horse, when, of course, the production of a vacuum by inspiration 

 would be impossible, and yet it was found that this operation did not in- 

 terfere with suction and drinking. So also a case has been reported of a 

 horse who was unable to drink, in whom, on examination, it was found 

 that a second molar tooth of the upper jaw had been lost, and a fistulous 

 tract led through to the nasal cavity. The tongue, therefore, was unable 

 to produce a vacuum, even when the nose was immersed below the surface 

 of the water, from the large nasal chambers and pharynx being in direct 

 communication through the fistula with the fore part of the mouth. Here 

 evidently was sufficient proof of the fact that drinking in these animals 

 was not due to any inspiratory effort. In the case reported, plugging the 

 fistula served to restore the power of drinking. Even without this proof, 

 however, the anatomical relation between the mouth and pharynx in the 

 horse is sufficient to show that in these animals breathing cannot occur 

 through the mouth in drinking, or in any other natural action of the or- 

 gans situated in the oral chamber ; for the soft palate forms a complete 

 partition between the mouth and the throat, and can only be elevated to 

 allow the passage of fluid or solids backward by compression, such as 

 that which occurs in swallowing. 



c. Aspiration. — In this method of drinking the vacuum is produced 

 by the respiratory apparatus ; the mouth, then, is not entirely closed, and 

 air is also drawn in, the water and air together causing a rushing sound, 

 the palate is raised, and both the air and water enter the pharynx, 

 the water being swallowed with a part of the air. This method of 

 drinking is jerky, since it must be interrupted for respiration, as the 

 nose may be immersed in water ; and although it has been said to occur 



