470 ORGANS OF DIGESTION. 



finer; is furnished every where with an epidermis; is very vas- 

 cular, and has beneath it a great number of muciparous glands. 

 Its texture undergoes some changes, according to its position, 

 upon the lips and cheeks, upon the gums and palate, and upon 

 the tongue ; all of which will be explained in due season. 



This lining membrane of the mouth, for the most part thin 

 and very flexible, forms, at several points, folds or duplicatures. 

 Four of them are situated on the middle line of the body, and 

 are called frenula: one goes from the posterior face of the upper 

 lip to the middle palate suture in front of the central alveolar 

 processes of the upper jaw ; a second goes from the posterior 

 face of the lower lip to the front of the symphysis of the lower 

 jaw; a third goes from the under part of the tongue to the pos- 

 terior face of the symphysis of the lower jaw, (frcenulum lin~ 

 guce ;) and the fourth goes from the front of the epiglottis carti- 

 lage to the middle of the root of the tongue. Besides these, 

 there are some other duplications, which wilt be mentioned in 

 their proper order. 



The lips (Labia) are always somewhat thicker at their loose 

 margins than elsewhere; the skin which covers them there, is 

 remarkable for its vascularity, and changes its texture insensi- 

 bly, as it is continued from the face to the lining membrane of 

 the mouth. 



The upper lip is longer and thicker than the lower, is some- 

 what pointed in the centre, and has on its front surface a ver- 

 tical depression, (philtrum,) beginning at the septum of the nose 

 and going downwards to the centre of the lip. This depression 

 is the remains of a fissure which always exists between the two 

 halves of the lip, in the early foetal or forming stage. The 

 junction of the extremities of the lips constitutes the corners of 

 the mouth (anguli oris.) 



The lips are composed of muscular fibres, much blended with 

 adipose matter. The muscles which concur to form them are 

 the orbicularis oris and the buccinators ; besides which, the up- 

 per lip is furnished on each side with the two levators, with the 

 depressor, and the zygomatici ; while the lower lip has its two 

 depressors and a Jevator. See muscles of the face. 



