196 PHYSIOLOGY AT THE FAEM. 



tween the inferior incisor teeth and the fibre-mucous rim of 

 the upper jaw. 



The pig, as before stated (p. 161), makes much use of his snout 

 when his food has to be dug from the ground ; when he eats 

 from a trough he thrusts his snout to the bottom to seize 

 what lies there. His lower lip is short and pointed, and this 

 he may be seen to use when he gathers grain from the ground 

 his teeth in this case afford no aid. 



The dog in the prehension of his food brings his teeth and 

 jaws into action. He fixes the bone which he gnaws to the 

 ground by means of his fore paws, and uses the incisor teeth 

 of both jaws, like cutting -pliers, while his long and curved 

 canines tear the prey. 



The prehension of liquids in these animals takes place in 

 several different ways. 



The suction by which the young of mammals obtain their 

 first food is a very peculiar process. It is sometimes ascribed 

 to the suction or enlargement of the chest, but this is an 

 error. It is performed by the suction of the mouth, which 

 is found to be much more powerful than the suction of the 

 chest. An animal which drinks by suction can still drink freely 

 after the windpipe has been opened, and even after the nostrils 

 and the windpipe have been effectually stopped up. In suction 

 the lips and tongue are principally concerned the lips form a 

 tube which is filled up by the tongue ; if, then, a tube, communi- 

 cating with fluid subject to the pressure of the atmosphere, is in- 

 troduced into the mouth, like the nipple in sucking, the tongue 

 being drawn backwards, a vacuum is created which is imme- 

 diately filled by the rush of the fluid through the tube into 

 the mouth. There is no other difference between this suction 

 and the mode of drinking in the horse, the ox, and the sheep, 

 than that, the extremity of the head being plunged into the 

 water, the water rises a little way into the tube formed by the 



