:540 



HUMAN ANATOMY. 



border and about twice as far from it in the upper. In both jaws, but especially in 

 the lower, the line approaches the teeth as it passes backward. There is a distinct 

 fold or frenuni of mucous membrane passing from the anterior nasal spine to the 

 middle of the upper lip. The free edge is often irregular, and may' have a nodular 

 enlargement. A much smaller fold is often found on each side in the region of 

 the bicuspids. A median fold to the lower lip is small and inconstant. Externally 

 the lips present a red region of modified mucous membrane, intermediate between 

 the skin of the face and the mucous membrane of the mouth. A sagittal section 

 through either lip shows these three parts. In the new-born the intermediate ^ part 

 is subdivided into two, of which the inner — rather the broader — more closely resem- 

 bles true mucous membrane than the latter. After death in the young child it 

 assumes a brownish color, which has been mistaken for the effect of acid. In the 

 adult these two subdivisions lose their distinctness. The lower lip is the larger and 



Temporal — j f , ^ 



muscle I r/'/i 



Zygoma 



W" 17/ t j—>*'asal septum 



/ jr / ) i i L_Maxi!lary 



Middle 

 turbinate 

 Zygoma 



! sint 



Inferior 

 turbinate 



Mucous mem- 

 j brane coveF- 

 iiig palate 



Vestibule 



Facial artery _i A_ — L^ 



Mandible 



Mylohyoid 

 Platysma 



Anterior belly of digastric 



-i — Tongue 



-P — -j- — Submaxillary duel 

  Lingual nerve 



Sublingual gland 

 Submental artery 



Genio-hyoid 



Genio-arlossus 



Frontal section, showing oral cavity and lower part of nasal fossae ; plane of section passes through anterior end of 



zygoma. Three-fourths natural size. 



fuller, showing more red except towards the angles of the mouth, where it disap- 

 pears. Its lower border is slightly indented in the middle. The upper lip shows a 

 more marked indentation below a little gutter, t\\& philtrum, running down from the 

 nasal septum. A slight median prominence of the lower edge of the upper lip is the 

 tubercle, which interrupts the straightness of the cleft when the lips are closed, making 

 the line resemble a Cupid's bow. 



The muscles of the lips are a complicated interlacement from many sources. 

 The orbicularis oris, formerly supposed to form a sphincter, has no separate exist- 

 ence. The general plan is as follows. The upper fibres of the buccinator enter the 

 lower lip and pass out at the opposite angle to ascend into the upper part of the other 

 buccinator. Those of the lower part traverse the upper lip in a similar manner. 

 The layer formed by the buccinator lies under the mucous membrane nea| the border 

 of the lips, and bends forward so that its edge is nearest the skin at about its junction 



* Otto Neustatter : Ueber den Lippensaum, etc., Inaug. Dissert., Munich, 1894. 



