THE LIPS THE CHEEKS. 77 



muscle, a layer of small salivary glands subjacent to it, and the 

 mucous membrane, complete these two movable, extensible, 

 and contractile veils. The lips are an organ of prehension 

 and suction; they prevent, especially the under lip, the 

 escape of saliva; they assist in the articulation of sounds 

 and in playing upon wind-instruments; and lastly, they take 

 an extensive part in the expression of the physiognomy. 

 Abundantly provided with nerves and vessels, the lips are 

 extremely sensitive, especially on their borders, where the 

 skin grows thin, takes a carnation tint, and is insensibly 

 transformed into mucous membrane. Although the orbicular 

 muscle limits them in a measure, and imposes upon them 

 certain functions and a distinct region, they are in reality 

 only the anterior portion of the cheeks, with which they are 

 in constant communication by movement and function. 



The cheeks form the sides of the face and the lateral walls 

 of the mouth. They embody in their substance the muscles 

 intrusted with the performance of the complex functions 

 of the mouth. One of these muscles, peculiar to that part 

 of the cheek which forms the buccal wall, brings the food 

 between the jaws and reacts against the distension of the 

 cheeks by the air. Its action in playing on wind-instru- 

 ments has given it the name of buccinator; it contributes 

 also to the expression by drawing the commissure of the lips 

 backward, while the great and small zygomatic muscles raise 

 it. The triangular muscle of the lips, on the contrary, lets 

 it fall ; and lastly, the masseter, a thick muscle of great power, 

 brings the lower jaw against the upper one, and with the 

 temporal muscle performs mastication. The internal face of 

 the cheeks is covered with mucous membrane, and its whole 

 surface is scattered over with little openings, which give pas- 

 sage to the saliva, which is secreted by a great number of 

 glandules analogous to those in the lips. Near the middle 

 is the opening of the canal of Stenon, through which the saliva 

 secreted by the parotid gland is poured into the mouth. This 

 gland is situated, as its name indicates, in front of the ear, 

 and is the most important of the salivary glands. 



The teeth are implanted in the alveolar border of the upper 

 and lower jaw, forming two symmetrical arcades, and when the 



