178 ANATOMY FOR NUESES. [Chap. XV. 



ture leading from the mouth into the pharyjix or throat 

 cavity. 



The mucous membrane lining the mouth contains many 

 minute glands which pour their secretion upon its surface, 

 but the chief secretion of the mouth is supplied by the sali- 

 vary glands, which are three pairs of large compound saccular 

 glands 1 called the parotid, submaxillary, and sublingual, respec- 

 tively. Each parotid gland is placed just in front of the eai-, 

 and its duct passes forwards along the cheek, until it opens 

 into the interior of the mouth opposite the second upper molar. 

 The submaxillary and sublingual glands are situated below 

 the jaw and under the tongue, the submaxillary being placed 

 further back than the sublingual. Their ducts open in the 

 floor of the mouth beneath the tongue. The secretion of these 

 salivary glands, mixed with that of the small glands of the 

 mouth, is called saliva. 



The tongue. — The tongue is a freely movable muscular organ 

 attached by its base to the hyoid bone. Besides being the 

 special seat of the sense of taste, it is a useful aid in mastication 

 and deglutition.2 



The teeth. — The semicircular borders of the upper and lower 

 jaw-bones (the alveolar processes) contain thirty-two sockets for 

 the reception of the teeth ; extending over the bones and a little 

 way into each socket is a dense insensitive fibrous tissue covered 

 by smooth mucous membrane, the gums. 



There are two sets of teeth developed during life : the first 

 or milk teeth, and the second or permanent teeth. The cutting 

 of the milk teeth begins usually at six months and ends with 

 the second year ; there are only twenty of these teeth, and they 

 are replaced during childhood by the permanent teeth .^ 



Each tooth consists of two portions, the crown and the fang : 

 the crown projects into the cavity of the mouth, the fang is 

 embedded in the socket. According to their shape and use the 

 teeth are divided into incisors, canines, bicuspids, and molars. 



1 For description of compound glands see Section I. Chapter XIV. 



2 A detailed description of the tongue will be found in the chapter on the 

 organs of special sense. 



8 The milk teeth are usually cut in the following order, the teeth appearing 

 first in the lower jaw: central incisors, 7th month ; lateral incisors, 7th to 10th 

 month ; front molars, 12th to 14th month ; canine, 14th to 20th month ; back 

 molars, 18th to 36th month. ' 



