THE LIPS AND CHEEKS 



1103 



continuous with the cheeks [buccae], which form the lateral walls of the mouth 

 cavity. 



In structure, the lips (fig. 849) consist essentially in a middle layer of cross-striated muscle 

 (orbicularis oris) covered externally by skin which is continuous through the rima oris with the 

 mucosa forming the inner layer of the lips. The mucosa lines the vestibulum oris and is reflected 

 upon the gums above and below. In the median line above and below, there extends from the 

 lip to the gum a small fold of the mucosa [frenulum labii superioris vel inferioris]. The structure 

 of the cheeks (figs. 847, 864) is similar to that of the lips but somewhat more complicated. 



Fig. 850. — ^Labial and Buccal Glands Exposed by Dissection of the Skin from in Front. 



(From Toldt's Atlas.) 



Labial glands ^VPet lip 

 Tunica mucosa oris (tela submucosa) 



Buccal glands 



Labial glands 



Parotid duct 



Lower lip 



Buccinator 



The muscular basis of the cheek is the buccinator muscle. External to this is a thick layer 

 of fat [corpus adiposum buccse] covered partly by the dermal muscles (platysma, zygomaticus, 

 etc.) and lastly the skin. Internally the cheek is lined by the mucosa, continuous with that 

 of the cheeks. The parotid duct opens into the vestibule opposite the second upper molar 

 tooth. 



Glands. — The skin of the lips and cheeks is well supplied with the usual sudoriparous and 

 sebaceous glands. The mucosa likewise presents two kinds of glands, the sebaceous and the 

 mucous glands. The sebaceous glands are relatively few in number and variable, being present 

 in about 30 per cent, of cases in the adult (Stieda). They are similar in structure to those of 



Fig. 851. — Section of Labial Mucosa, SHO-mxG Glands. X 16. (From Toldt's Atlas.) 

 Epithelium — j^^^^^^^^^B^g^^^^gTH I^TS^S^ ®^kMl^ •- Epithelium 



•••Duct 

 '-.Accessory gland 



Lamina propria 



Tela submucosa _; 



M. orbicularis oris 



"^ Mucous gland 



the skin (though not associated with hair follicles), and when present are visible as small yellow- 

 ish bodies in the mucosa. They occur chiefly near the free margins of the lips and along the 

 cheek opposite the teeth. 



The mucous glands are much more numerous and constantly present (figs. 850, 851). They 

 are aU of the racemose type. They are variable but small in size, and closely packed together 

 in the submucosa of the lips [glandulse labiales], where they may easily be felt. Those of the 

 cheeks [gl. buccales] are less numerous. A few of them especially in the region of the molar 



