THE MOUTH. 319 



hyoid muscles, forming the floor ; anteriorly by the lips ; 

 posteriorly by the soft palate, and laterally by the cheeks. 



Dissection. To expose the cavity of the mouth, make an 

 incision through its angles, carried laterally through the 

 cheeks, dividing the buccinator, masseter and insertion of 

 temporal muscles ; then, in sawing through the lower jaw 

 on one side, the cavity will be fully laid open for examin- 

 ation. 



The tongue, teeth, gums, velum, uvula, tonsils, and 

 sublingual glands, are some of the contents already de- 

 scribed of this cavity ; the whole of which, as well as the 

 cavity itself, has one common covering, i. e. the mucous 

 membrane of the mouth, which extends into the pharynx, 

 and is continuous with the great gastro-pulmonary mucous 

 membrane. 



The mucous membrane of the mouth and pharynx has 

 already been considered in a general way in the description 

 of this elementary tissue, under the head of alphabet of 

 anatomy. But there are some modifications in its course, 

 not there mentioned, which require notice. 



It will be recollected that mucous membrane is usually 

 soft, pulpy, easily torn, and when deprived of blood, of a 

 pale, grayish, or ashy hue. Now, in the mouth and on the 

 lips this membrane has considerable firmness, and pre- 

 sents a distinct epithelium, corresponding to the cuticle of 

 the skin. The nucleated cells of which this epithelium is 

 at first composed, as they advance to their full development 

 gradually lose their nuclei and present the form of scales, 

 so that the epithelium of the mouth is called squamous. 



As the mucous FIG. 94. 



membrane passes 

 from the posterior 

 surface of the lips to 

 the front portions of 

 the alveolar pro- 

 cesses of the upper and lower jaw, it is folded or duplicated, 



Fio. 94 represents a Tiew of the inner side of the Lips, a a Ducts of Steno 

 or parotid ducts. 6 6 Labial glands. 



