130 INTRODUCTION. 



In Man, therefore, the tongue is not only subservient to his animal neces- 

 sities it is not only an agent in the acquisition of a knowledge of certain 

 of the properties of bodies, by means of the sense of taste, but it is a most 

 important organ for the communication of our thoughts, wills, and feelings, 

 by the moulding of sounds into words, eTrea Trrepoevra, symbols to our ears, 

 and, once uttered, never to be recalled. 



In many animals the cavity of the mouth is furnished with sacculi, 

 or sac-like appendages, commonly termed cheek -pouches, which open 

 into it, and serve as receptacles for food, which is carried in them, from 

 the spot where it is collected, to the retreats, or abodes, of the animals, 

 there either to be eaten immediately, or hoarded up for future use. 

 These cheek-pouches, in those of the Simiae which possess them, also 

 in the Hamster, the Arctomys, the Ornithorhynchus, &c., are formed 

 in the sides of the cheeks, exterior to the molar teeth, and run back 

 (lined with the membrane, which covers the cavity of the mouth), some- 

 times, to a great distance beyond the angle of the lower jaw, so as 

 to encroach upon the sides of the neck, as is seen especially in the 

 Hamster, the cheek-pouches of which, distended, are represented by the 

 following figure (131): the external skin, with the fur, is removed, so 

 as to exhibit their true form and extent. When filled with grain, they 

 are unloaded by the action of the muscles of the cheeks, and, among them, 



by the greatly-developed buccinator. 



In the Pacas (Ccelogenus), a group 

 of rodents, a fissure in the skin of the 

 cheeks, on each side, leads upward to 

 a cavity beneath the expanded zygoma : 

 but this cavity cannot be regarded as 

 a cheek-pouch ; it has no communica- 

 tion with the mouth, nor does it serve 

 as a receptacle for food: its use, in- 



The Cheek-pouches of the Hamster. deed, is not Understood. 



The lips having been mentioned, some notice may, in this place, be 

 taken of them ; and the rather, as, in several Mammalia, they are of 

 essential service, in the act of procuring food, or of transferring it to the 

 mouth. 



All Mammalia have an upper and under lip, though, in many, the 

 under lip is slightly developed : they may be described as flexible mus- 

 cular curtains, covering the teeth, and forming, between them, the oral 

 orifice. Of their form, in the human species, little need be said : their 

 use, in the act of drinking, and the manner in which we close them during 

 the mastication of food, are well known ; but, besides their utility in 

 the reception of food, they are powerful in the silent expression of the 

 passions : by their varied movements, they denote mirth, or pleasure ; 



