402 THE MUSCLES AND FASCIJB. 



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 septum 

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

 orbicularis superioris) 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 (philtrum) seen on 

 the surface of the skin beneath the septum of the nose. The additional fibres for 

 the lower segment (Accessorii orbicularis inferioris) 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. 



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 Bucciiiator (Fig. 282) 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 Mne of the lower jaw. Its inner surface 

 corresponds 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 (see Fig. 282). 



The Risorius (Santorini) (Fig, 269) consists of a narrow bundle of fibres which 

 arises in the fascia over the Masseter muscle, and, passing horizontally forward, 

 is inserted into the skin at the angle of the mouth. It is placed superficial to the 

 Platysma, and is broadest at its posterior extremity. This muscle varies nmchin 

 its size and form. 



Nerves. The Orbicularis oris and the Risorius are supplied by the facial, the 

 Buccinator by the facial and by the buccal branch of the inferior maxillary nerve ; 

 which latter, however, is by many anatomists regarded as a sensory nerve only. 



Actions. The Orbicularis oris in its ordinary action produces the direct closure 

 of the lips ; by its deep fibres, assisted by the oblique ones, it closely applies the 

 lips to the alveolar arch. The superficial part, consisting principally of the 

 decussating fibres, brings the lips together and also protrudes them forward. 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. When 



