TEMPORO-MAXILLARY REGIO.N. 249 



The additional fibres for the lower segment, Accessorii orbicularis inferioris, 

 arise from the inferior maxilla, externally to the Levator labii inferioris ; arching 

 outwards to the angles of the mouth, they join the Buccinator and the other 

 muscles attached to this spot. 



Relations. By its superficial surface, with the integument to which it is closely 

 connected. By its deep surface, with the buccal mucous membrane, the labial 

 glands, and coronary vessels. By its outer circumference, it is blended with the 

 numerous muscles which converge to the mouth from various parts of the face. 

 Its inner circumference is free, and covered by mucous membrane. 



The Buccinator is a broad, thin muscle, quadrilateral in form, occupying the 

 interval between the jaws at the side of the face. It arises from the outer surface 

 of the alveolar processes of the upper and lower jaws, corresponding to the last 

 three molar teeth ; and, behind, from the anterior border of the pterygo-maxil- 

 lary ligament. The fibres converge towards the angle of the mouth, where the 

 central ones intersect each other, those from below being continuous with the 

 upper segment of the Orbicularis oris, and those from above, with the inferior 

 segment ; but the highest and lowest fibres continue forward uninterruptedly into 

 the corresponding segment of the lip, without decussation. 



Relations. By its superficial surface, behind, with a large mass of fat, which 

 separates it from the ramus of the lower jaw, the Masseter, and a small portion of 

 the Temporal muscle ; anteriorly, with the Zygomatici, Risorius, Levator anguli 

 oris, Depressor anguli oris, and Stenon's duct, which pierces it opposite the second 

 molar tooth of the upper jaw ; the facial artery and vein cross it from below 

 upwards, and it is also crossed by the branches of the facial and buccal nerves. By 

 its internal surface, with the buccal glands and mucous membrane of the mouth. 



The ptery go-maxillary ligament separates the Buccinator muscle from the Supe- 

 rior constrictor of the pharynx. It is a tendinous band, attached by one extremity 

 to the apex of the internal pterygoid plate, and by the other to the posterior 

 extremity of the internal oblique line of the lower jaw. Its inner surface corre- 

 sponds to the cavity of the mouth, and is lined by mucous membrane. Its outer 

 surface is separated from the ramus of the jaw by a quantity of adipose tissue. 

 Its posterior border gives attachment to the Superior constrictor of the pharynx ; 

 its anterior border, to the fibres of the Buccinator. 



The Risorius of Santorini consists of a narrow bundle of fibres, which arises in 

 the fascia over the Masseter muscle, and, passing horizontally forwards, is inserted 

 into the angle of the rnouth, joining with the fibres of the Depressor anguli oris. 

 It is placed superficial to the Platysma, and is broadest at its outer extremity. 

 This muscle varies much in its size and form. 



Nerves. The Orbicularis oris is supplied by the facial, the Buccinator by the 

 facial and buccal branch of the inferior maxillary nerve. 



Actions. The Orbicularis oris is the direct antagonist of all those muscles which 

 converge to the lips from the various parts of the face, its action producing the 

 direct closure of the lips ; and its forcible action throwing the integument into 

 wrinkles, on account of the firm connection between the latter and the surface of 

 the muscle. The Buccinators contract and compress the cheeks, so that, during 

 the process of mastication, the food is kept under the immediate pressure of the 

 teeth. 



9. TEMPORO-MAXILLARY REGION (fig. 151). 

 Masseter. Temporal. 



The Masseter has been already exposed by the removal of the integument from 

 the side of the face (fig. 148). 



The Masseter is a short thick muscle, somewhat quadrilateral in form, consisting 

 of two portions, superficial and deep. The superficial portion, the largest, arises 

 by a thick tendinous aponeurosis from the malar process of the superior maxilla, 

 9.nd from the anterior two-thirds of the lower border of the zygomatic arch : its 



