FACE. 





maxillary bone, on the mucous membrane of 

 the mouth, and on the buccinator. Its action 

 is to raise the commissure of the lips, and 

 draw it a little inwards. Its action ^vhen as- 

 sociated with that of the zygomatics has been 

 already explained. 



Depressor anguli oris (triangularis orls) (t y 

 Jig. 134) is a thin, triangular, subcutaneous 

 muscle, situated at the lower part of the face. 

 It arises by a broad base from the lower border 

 of the inferior maxilla, and from the surface of 

 the bone between this border and the external 

 oblique line, extending from the chin to within 

 half an inch of the masseter. The fibres con- 

 verge and ascend towards the commissure of 

 the lips, the posterior fibres taking a direction 

 upwards and forwards, the middle nearly ver- 

 tical, and the anterior describing a curve up- 

 wards and backwards: they all terminate at the 

 commissure of the lips, where they become 

 united with those of the orbicubris and of the 

 buccinator, and more superficially with the 

 great zygomatic and levator anguli oris. 



Relations. Its superficial surface is covered 

 by the skin and by the fibres of the platysma, 

 with which it is mingled. Its deep surface 

 rests upon part of the depressor labii inferioris 

 and buccinator : above it is connected with all 

 the muscles of the commissure and with the 

 skin. 



Action. This muscle draws down the angle 

 of the mouth, and in this respect is the anta- 

 gonist of the great zygomatic and levator an- 

 guli oris. 



Depressor labii inferioris (quadratus menti), 

 (d, Jig. 136, 137) flat and of a square form, is 

 placed internal to the preceding, which partly 

 conceals it. It arises from the inner half of 

 the external oblique line of the lower jaw, and 

 also from the platysma, with whose fibres it is 

 continuous. Its fibres, which are parallel, pro- 

 ceed upwards and inwards to be attached to 

 the lip ; the deep fibres mingle with those of 

 the orbicularis; the superficial pass in front of 

 that muscle, and are fixed in the skin of the 

 lip. The inner fibres decussate above with 

 those of the muscle on the opposite side; 

 below, with those of the levator menti. 



Fig. 136. 



Relations. At its origin this muscle is co- 

 vered by the triangularis, and elsewhere by the 

 skin, to which it adheres intimately above. Its 

 deep surface covers part of the lower jaw, the 

 mental vessels and nerves, part of the orbicu- 

 laris oris and levator menti. Through the an- 

 gular interval between the two depressors of 

 the lower lip, the levatores menti pass to their 

 insertion. 



Its action is to draw downwards and out- 

 wards one side of the lower lip; if the muscles 

 on both sides act, the lip is drawn downwards 

 and extended transversely. The stronger ac- 

 tions of this muscle are usually accompanied 

 by those of the platysma, with whose fibres, 

 as we have seen, it is continuous. 



Levator menti (houppe du menton) (e, fig. 

 136,137) may be exposed by everting the lip and 

 dividing the mucous membrane : it is a small 

 round muscle, situated at the lower part of the 

 face, and forming on each side a great part of 

 the prominence of the chin. It arises in the 

 incisive fossa below the incisor teeth of the 

 lower jaw, external to the symphysis, and pro- 

 ceeds downwards and forwards : it passes under 

 the lower border of the orbicularis oris, and 

 emerging between the depressor labii inferioris, 

 expands a little to be inserted into the skin of 

 the chin. Its fibres below are mingled with 

 fat ; internally they are confounded with those 

 of the fellow muscle, and externally with the 

 fibres of the quadratus menti. 



In its action this muscle raises and corru- 

 gates the chin, and by so doing raises also the 

 lower lip and throws it forward. 



Fig. 137. 



VOL. II, 



Buccinator (b,fg. 136, 137). This muscle 

 is situated on the side of the cheek, and to ex- 

 pose it completely it is necessary to divide the 

 muscles attached to the angle of the mouth, 

 and to remove the ramus of the jaw and the 

 muscle attached to it. The buccinator is a 

 broad flat muscle, and arises, 1. behind and 

 in the middle from an aponeurotic line, the 

 pterygo-maxillary ligament or inter-maxillary 

 ligament, which is common to it aad the su- 

 perior constrictor of the pharynx, and which is 



Q 



