226 



FACE. 



extended between the lower extremity of the 

 internal pterygoid plate of the sphenoid bone 

 and the posterior extremity of the internal ob- 

 lique line of the lower. Above, the buccinator 

 arises, 2. from the outer surface of the upper 

 alveolar process, between the first malar tooth 

 and the tuberosity; 3. below from the outer 

 side of the alveolar border opposite the three 

 last malar teeth. From these three origins the 

 fibres proceed forwards, the superior curving a 

 little downwards, the inferior upwards, and 

 the middle passing horizontally towards the 

 angle of the mouth, where they mingle with 

 the fibres of the orbicularis and the elevators 

 and depressors of the commissure. The infe- 

 rior and superior fibres become shorter as we 

 trace them forwards, and some of them decus- 

 sate at the angle of the mouth to unite with 

 the opposite labial half of the orbicularis. 



The fibres of the buccinator are wavy, over- 

 lapping each other, so that they admit of great 

 distention, which is, however, limited by a 

 buccal fascia, which is given off from the 

 pterygo-maxillary ligament. 



Relations. The buccinator is deeply situated 

 behind, where it is covered by the ramus of 

 the jaw and the edge of the masseter, from 

 which it is separated by a quantity of fat, 

 which projects beyond the mass, fills up the 

 hollow in front of the masseter, and is always 

 found even in thin subjects. In the middle 

 it corresponds to the buccal vessels and nerves 

 and to the transverse facial artery, which runs 

 nearly parallel to its fibres, and to the duct 

 of the parotid gland, which, resting at first 

 upon its fibres, pierces them opposite the 

 second molar tooth of the upper jaw, and 

 opens obliquely into the mouth. A buccal 

 fascia covers the posterior half of the muscle. 

 At the commissure the buccinator is covered 

 by the muscles which are attached to the angle 

 of the mouth, and is crossed at right angles 

 by the external maxillary artery and vein. By 

 its internal surface this muscle covers the 

 mucous membrane of the mouth, from which 

 it is only separated by a layer of buccal 

 glands. 



Action. This muscle, being fixed behind, 

 above, and below, acts principally in front on 

 the commissure of the lips, which it draws 

 horizontally backwards, elongating the aperture 

 of the mouth transversely, and throwing the 

 cheek into the vertical folds which are so re- 

 markable in old age. In this respect it is 

 the direct antagonist of the orbicularis oris : 

 if both these muscles act together, the lips are 

 extended and pressed against the teeth. When 

 the cavity of the mouth is distended" with air 

 or liquids, this muscle is protruded at the 

 cheeks, and its fibres become separated and 

 curved. If now the muscle acts, the fibres 

 become straightened, and the fluid is expelled 

 from the mouth either abruptly or gradually 

 according to the resistance of the orbicularis. 

 This action of the orbicularis is exemplified 

 either in spirting fluids from the mouth, or 

 in playing on wind instruments. In mastica- 

 tion the buccinator presses the food from 

 between the cheek and gums into the cavity 



of the mouth. It assists also in deglutition 

 when the mouth is closed, by pressing the 

 food backwards towards the pharynx. 



Among the muscles of the face, it is ne- 

 cessary to allude to some parts of the platysma, 

 which are not only seen in this region, but 

 which contribute materially to the motion and 

 expression of the face. The platysma (p,p,p, 

 fig. 138) is a large, broad, membranous layer of 

 fibres, which extend from the upper and an- 

 terior part of the chest, where they commence 

 in the subcutaneous tissue, upwards over the 

 anterior and lateral part of the neck, to the 

 jaw and lower part of the face, where they 

 are inserted above. The whole superficial 

 surface of the muscle is subcutaneous, but 

 less firmly attached to the integument just 

 under the jaw than elsewhere. The under 

 surface of its cervical portion is in relation 

 with numerous important parts on the faces 

 it covers from before backwards the lower 

 part of the chin, the quadratus menti, the 

 triangularis oris, the base of the lower jaw, 

 the facial vessels, and part of the masseter. 

 The arrangement of its facial portion is all 

 that need be described here. 



Fig. 138. 



As the fibres of the muscle incline upwards 

 towards the median line, they meet below the 

 symphysis of the chin, and some ascend as 

 high as the levator rnenti. Externally the 

 fibres seem to split to enclose the depressor 

 anguli oris, and to proceed upwards and for- 

 wards with that muscle and the quadratus 

 menti to the lower lip and its angle. The 

 middle fibres are attached to the base of the 

 jaw, and posteriorly they mount over the 



