THE MUSCLES OF THE LIPS AND MOUTH. 287 



other, so that the muscle is narrowed and proportionally thickened near the angle of 

 the mouth, where it becomes incorporated with the orbicularis. The fibres near the 

 middle of the muscle cross each other, those from above passing into the lower lip, 

 and those from below into the upper one ; but the higher and lower fibres are 

 directed into the corresponding lip without decussation. 



Relations. The buccinator is covered and supported by a thin fascia, which is closely 

 adherent to the muscular fibres, and is overlapped by the depressor anguli oris, by the upper 

 fibres of the platysma myoides, and by the masseter and zygomaticus major, from which it is 

 separated by a quantity of fat (see p. 293). Embedded in the last are the facial vessels and the 

 buccal branches of the inferior maxillary and facial nerves. Opposite the second molar tooth 

 of the upper jaw, its fibres give passage to the duct of the parotid gland. 



The depressor anguli oris, or triangularis menti muscle, is broad at its 

 origin from the external oblique line of the lower jaw ; passing upwards it is 

 collected into a narrower bundle, which ends in a similar way to the levator anguli 

 oris, being partly inserted into the skin, and partly continued into the orbicularis in 

 the upper lip. 



Relations. This muscle is covered only by the skin and fat ; it conceals part of the 

 buccinator and of the depressor of the lower lip. 



Variety. The tranxrcrxus me nil is a small band of muscular fibres sometimes found 

 arising from the inner border of the depressor, and curving downwards and inwards below 

 the chin across the median line to the corresponding part of the opposite side. 



At the corner of the mouth the decussating fibres of the elevator and depressor muscles, as 

 well as of the buccinator, give rise to a dense mass of muscle which may be felt during life as 

 a hard knot between the skin and mucous membrane a little external to the commissure of 

 the lips. 



The depressor labii iuferioris, or quadratus menti muscle, arises from the 

 lower jaw by a line of attachment extending from near the symphysis to a little 

 beyond the mental foramen ; thence it ascends with an inward inclination, unites 

 with its fellow, and blending with the orbicularis oris is inserted into the lower lip. 

 Its fibres are intermixed with much adipose matter. 



The levator labii inferioris, or levator menti muscle, arises by a narrow 

 head from the incisor fossa of the lower jaw, and expands as it is directed down- 

 Fig. 2/0. SCHEME OP THE FOR- NASO-LABIALIS 



MATION OP THE ORBICULARIS . / INC1S sup i 



ORIS MUSCLE. (G. D. T.) / ^ I I 



\ ^^^=^ -^^^^ / . 



wards and slightly forwards, 

 between the depressors of 

 the lower lip, to be inserted 

 into the integument of the 



Chin. 



The orbicularis oris 



is an elliptical muscular 



sheet of considerable thickness, making the foundation of the lips, and composed 

 for the most part of fibres prolonged from the buccinator and elevator and 

 depressor muscles of the angle of the mouth. Its peripheral margin reaches 

 above to the base of the nose, and below to the groove which separates the lip 

 from the chin. The deeper fibres, together with a somewhat distinct marginal 

 fasciculus beneath the red border of the lip, are continued from the buccinator, 

 and cross from side to side without interruption. The fibres of the levator and 

 depressor anguli oris, which have crossed at the corner of the mouth, enter the 

 more superficial portion of the orbicularis, and are inserted into the skin of the 



