TEMPORO-MAXILLARY REGION. 327 



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 the mucous membrane. 



The Buccinator is a broad, thin muscle, quadrilateral in form, which occupies 

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

 maxillary ligament. The fibres converge towards the angle of the mouth, 

 where the central fibres intersect each other, those from below being continuous 

 with the upper segment of the Orbicularis Oris ; and those from above with the 

 inferior segment ; 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 rarnus of the lower jaw, the Masseter, and a small portion 

 of the Temporal muscle; anteriorly, with the Zygomatici, Eisorius, Levator 

 Anguli Oris, Depressor Anguli Oris, and Steno's duct, which pierces it opposite 

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

 from below upwards ; it is also crossed by the branches of the facial and buccal 

 nerve. 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 Su- 

 perior 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 corresponds to the cavity of the mouth, and is lined by mucous mem- 

 brane. 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 Con- 

 strictor of the pharynx : its anterior border, to the fibres of the Buccinator. 



The Risorius (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 mouth, 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 by the buccal branch of the inferior maxillary nerve. 



Actions. Tue Orbicularis Oris is the direct antagonist of all those muscles 

 which converge to the lips from the various parts of the face, its ordinary 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 tee.th. 



9. TEMPORO-MAXILLARY EEGION. 

 Masseter. Temporal. 



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

 from the side of the face (Fig. 215) ; it is a short thick muscle, somewhat quad- 

 rilateral in form, consisting of two portions, superficial and deep. The superficial 

 portion, the larger, arises by a thick tendinous aponeurosis from the malar pro- 

 cess of the superior maxilla, and from the anterior two-thirds of the lower 

 border of the zygomatic arch : its fibres pass downwards and backwards, to be 

 inserted into the angle and lower half of the ramus of the jaw. The deep portion 

 is much smaller, and more muscular in texture ; it arises from the posterior 

 third of the lower border and the whole of the inner surface of the zygomatic 



