50 PHYSIOLOGY. 



brane inclosing muscular fasciculi and diverging from the base of the 

 uvula, on each side of the palate outward and downward, one to the 

 side of the tongue, the other to the side of the pharynx. These folds 

 are known as the half-arches of the palate. The one in front is known 

 as the anterior palatine arch, the one posterior as the posterior pala- 

 tine arch. 



The Fauces. The fauces is the strait, or passage, leading from 

 the mouth to the pharynx, and corresponds with the space included 

 between the half-arches of the palate. 



The Tongue. The tongue is composed of muscle and is covered 

 with a mucous membrane. It is composed of two symmetrical halves 

 joined in the middle line. By the freedom of its movements it aids 

 in mastication and deglutition; it is also a great help in articulation, 

 and by the papilla? on its surface forms an organ of taste. The 

 root, or base, is the posterior part, where it is attached to the hyoid 

 bone and inferior maxilla. The body is the great bulk of the organ. 

 Its tip is the anterior free extremity. On the anterior two-thirds of 

 the upper surface of the tongue, we find a mucous membrane, which 

 adheres most intimately to the muscles beneath. Its surface is rough- 

 ened by the presence of a number of little papillae. On the surface 

 of the tongue there are many mucous glands. 



Papillae. The papillae are the fungiform, filiform, and circum- 

 vallate. These are more minutely described in the section on the 

 sense of taste. 



Nerves. The nerves of the tongue are the lingual of the fifth 

 pair, the glosso-pharyngeal, and the hypoglossal. 



THE TEETH. 



In form, structure, and number, the teeth vary very considerably 

 in different animals; this is markedly shown in the classes, car- 

 nivora and herbivora. In most animals the teeth are worn down 

 by use and eventually decay. The exception is found in that class 

 of animals that constantly nibble; their incisors are peculiar in that 

 there are deposits of fresh dentine within and upon the pulp and 

 of enamel upon the anterior surface, thus giving a continuous growth. 

 They are the rodentia. 



Among mammalia, and particularly in man, the teeth are devel- 

 oped in two sets: (1) the first, less numerous and smaller set, called 

 the temporary, or milk, teeth:, (2) the second set, larger and more 

 numerous, called the permanent teeth. 



The temporary, or milk, teeth are usually 20 in number, 10 in 



