THE INTERMAXILLARY REGION. ,'509 



palpebrarum, but consists of numerous strata of muscular fibres, having different 

 directions, which surround the orifice of the mouth. These fibres are partially 

 derived from the other facial muscles which are inserted into the lips, and are 

 partly fibres proper to the lips themselves. Of the former, a considerable number 

 are derived from the Buccinator and form the deeper stratum of the Orbicularis. 

 Some of them namely, those near the middle of the muscle decussate at the angle 

 of the mouth, those arising from the upper jaw passing to the lower lip, and those 

 from the lower jaw to the upper lip. Other fibres of the muscle, situated at its 

 upper and lower part, pass across the lips from side to side without decussation. 

 Superficial to this stratum is a second, formed by the Levator and Depressor 

 anguli oris, which cross each other at the angle of the mouth, those from the 

 Depressor passing to the upper lip, and those from the Levator to the lower lip, 

 along which they run to be inserted into the skin near the median line. In 

 addition to these there are fibres from the other muscles inserted into the lips the 

 Levator labii superioris, the Levator labii superioris alaeque nasi, the Zygomatici, 

 and the Depressor labii inferioris ; these intermingle with the transverse fibres 

 above described, and have principally an oblique direction. The proper fibres of 

 the lips are oblique, and pass from the under surface of the skin to the mucous 

 membrane through the thickness of the lip. And in addition to these are fibres 

 by which the muscle is connected directly with the maxillary bones and the sep- 

 tum of the nose. These consist, in the upper lip, of four bands, two of which 

 (Musculus incisivus superior) arise from the alveolar border of the superior 

 maxilla, opposite the lateral incisor tooth, and, arching outward on each side, 

 are continuous at the angles of the mouth with the other muscles inserted into 

 this part. The two remaining muscular slips, called the Naso-labialis, connect 

 the upper lip to the back of the septum of the nose : as they descend from the 

 septum an interval is left between them. It is this interval which forms the 

 depression seen on the surface of the skin beneath the septum of the nose. The 

 additional fibres for the lower segment (Musculus incisivus inferior} arise from 

 the inferior maxilla, externally to the Levator labii inferioris, and arch outward 

 to the angles of the mouth, to join the Buccinator and the other muscles attached 

 to this part. 



Eelations.- 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 (Fig. 208) 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 toward 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 uninter- 

 ruptedly 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 Stenson's duct, which pierces it opposite the 

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

 upward ; 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 pterygo-maxillary ligament separates the Buccinator muscle from the 

 Superior 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 



