THE LIPS, CHEEKS, AND VESTIBULE. 



1541 



Fig. 



I2Q5. 



with the free red surface. In the lower Hp the quadratus (depressor labii inferioris) 

 runs upward under the skin to break up into fibres ending in the lips. The tri- 



ang7ilaris (depressor anguli oris) passes 

 at the angle of the mouth into the upper 

 lip and ends as a series of separate fibres 

 inserted into the mucous membrane, many 

 of them crossing the middle line. This 

 muscle, before it breaks up, is in the same 

 plane as the buccinator, but farther from 

 the edge of the lips. Some German au- 

 thors, by grouping together the various 

 muscles of the upper lip, have made a 

 superior quadraHis and triangularis 

 which are disposed in a similar manner 

 to the lower ones. Besides these there 

 are two muscles, the zygomaticus, de- 

 scending, and the risorius, ascending, 

 which meet at the oral angles and end 

 there in the skin or mucous membrane, 

 or in both. There are also numerous 

 fibres, seen only with the microscope in 

 sagittal sections, passing from the skin 

 to the mucous membrane ; these consti- 

 tute the rectus} 



Philtrum - 



Tubercle - 



Labial region, from life, reduced one-fifth. 



Fig. 1296. 



^K^.^^ 



Labial glands. 



Fibres of orbicularis 

 oris 



Transition into true, 

 mucous membrane 



Modified mucous membrane 



Integument 



Sebaceous gland 



Transition into 

 modified skin 



Sagittal section of lip of young child. X 20. 



The mucous membrane, which is smooth, is so closely attached to the 

 muscles that it follows the movements of the latter. Mucous glands are lodged in its 



1 Aeby : Archiv f. mikro. Anat., Bd. xvi., 1879. 



