436 THE MUSCLES 



Upon the deep surface lies the mucous membrane of the mouth, separated from 

 the muscular fil)res by the mucous and small salivary glands, together -with the 

 superior and inferior coronary arteries. 



Transverse ^Muscles of the Mouth 

 This group comprises only the buccinator, 



BUCCINATOR 



The buccinator — named from its action, as it is the muscle used by the 

 trumpeter' {buccinator) — is a somewhat oval sheet of muscular fibre, distinct in its 

 origin, but blending in front with the orbicularis oris. It forms a part of the third 

 stratum of the facial muscles. 



Origin. — (1) The outer surface of the alveolar process of the maxilla above 

 the molar teeth; (2) the anterior border of the pterygo-maxillary ligament, a 

 fil:)rous band or raphe extending from the hamular process of the internal pterygoid 

 plate of the sphenoid bone to the back of the mylo-hyoid ridge of the mandil)le; 

 (3) the outer surface of the alveolar process of the mandible below the molar 

 teeth. 



Insertion. — The outer part of the orbicularis oris. 



Structure. — It rises by fleshy fibres which run forwards in four sets. The 

 upper set pass directly into the facial portion of the orbicularis oris which belongs 

 to the upper lip; the next pass downwards and forwards to that which belongs to 

 the lower lip; the third upwards and forwards, decussating with the second set to 

 join the lower part of the orl)icularis in the up])er lip. Finally, a fourth set which 

 pass from the mandil^le to the lower part of the facial portion of the orl)icularis 

 oris belonging to the lower Hp. 



Nerve-supply. — The buccal branch of the lower division of the facial, which 

 sends filaments into the back part of its outer surface; it is also pierced by the 

 buccal branch of the inferior maxillary division of the fifth nerve on its way to 

 supply the mucous membrane lining the cheek. 



Action. — (1) To draw outwards the corner of the mouth, widening it and 

 pressing the lips against the teeth; (2) to diminish the concavity of the cheek, 

 compressing the air contained in it, as in using the blowpipe or playing the 

 cornet; or forcing inwards the food when, in mastication, any portion of it 

 has escaped into that part of the mouth which is external to the bicuspids and 

 molar teeth. 



Relations. — Superficially, the skin, suljcutaneous fat, Stenson's duct, the zygo- 

 maticus major, risorius, a large mass of fat (the buccal fat-pad) Avhich separates 

 the buccinator from the masseter, and a layer of deejj fascia continuous with that 

 which covers the upper part of the pharynx; deeply, the mucous membrane of the 

 mouth. The upper part of the muscle is perforated by Stenson's duct. The 

 buccinator is almost continuous behind with the superior constrictor, from which 

 it is only separated by the tendinous intersection of the pterygo-maxillary ligament. 



Angular Muscles of the ISIouth 



The angular series are four in numl)er: viz. the zygomaticus major, levator 

 anguli oris, risorius, and depressor anguli oris. Two descend to the corner of the 

 mouth obli(]uely from al)ove, one runs almost horizontally forwards, and one 

 ascends from below. They })lend at the corner of tlie mouth, and form there a 

 thick muscular mass, l)ehind which is a depression filled up witli tlie fat covering 

 the buccinator. In a lean face tins depression is often very conspicuous, and in 

 some faces its position is indicated by a dimple when the zygomaticus major 

 contracts. 



