PREHENSION OF LIQUID FOOD. 105 



folded into a tubular shape for that purpose. But 

 suction among the mammalia is generally per- 

 formed by the muscles of the lips and cheeks, 

 aided by the movements of the tongue, which, when 

 withdrawn to the back of the cavity, acts like the 

 piston of a pump. In the Lamprey, this hydraulic 

 action of the tongue is particularly remarkable. 

 Many quadrupeds, however, drink by repeatedly 

 dipping their tongue into the fluid, and quickly 

 drawing it into the mouth. 



§ 2. Prehension of Solid Food. 



When the food consists of solid substances, organs 

 must be provided ; first, for their prehension and 

 introduction into the mouth ; secondly, for their 

 detention when so introduced ; and thirdly, for their 

 mechanical division into smaller fragments. 



Of those instruments of prehension which are 

 not portions of the mouth itself, and which form a 

 series of variously constructed organs, extending 

 from the ten taenia of the polypus to the proboscis 

 of the elephant, and to the human arm and hand, 

 some account has already been given in the history 

 of the mechanical functions; but, in a great num- 

 ber of instances, prehension is performed by tlie 

 mouth, or the parts which are extended from it, 

 and may be considered as its appendices. The 

 prehensile power of the mouth is derived princi- 

 pally from the mechanical form and action of the 

 jaws, which open to receive, and close to detain the 

 bodies intended as food ; and to this latter purpose, 

 the teeth, when the mouth is furnished with them, 



