ORAL MUSCLES 



333 



the mouth, where it becomes attached to the skin and sends some fasciculi into the orbicularis of 

 the lower Up. Between the caninus and the quadratus labii superioris there is a certain amount 

 of fatty areolar tissue through which the infraorbital vessels and nerves run. Its deep surface 

 extends over the canine fossa, the buccinator muscle, and the mucosa of the Up. The external 

 maxillary (facial) artery passes over its inferior extremity. 



The zygomaticus (z. major) is a long, ribbon-shaped muscle which arises by short tendinous 

 processes from the zygomatic bone near the temporal suture under cover of the orbicularis ocuU. 

 It passes obliquely to the corner of the mouth, where it is attached to the skin and mucosa. 

 The body of the muscle is subcutaneous and is usually surrounded by fat. It crosses the 

 masseter and buccinator muscles and the anterior facial vein. 



The risorius is a thin, triangular, subcutaneous muscle which extends across the middle of 

 the cheek and lies in a more superficial plane than the platj^sma, with which it is often fused. It 

 arises from the tela subcutanea above the parotid fascia. Its fibres converge across the masseter 

 muscle toward the angle of the mouth and are attached to the skin and mucosa in this vicinity. 

 It Ues above the anterior facial vein and external maxillary artery. 



The platysma has been described above. 



The triangularis (depressor anguli oris) is a broad, flat, well-developed, subcutaneous muscle 

 which arises from the base and external surface of the body of the mandible below the canine, 

 bicuspid, and first molar teeth. From here its fibres converge toward the corner of the mouth, 

 where they are in part inserted into the skin and in part are continued into the orbicularis oris 

 of the upper lip. It overhes the buccinator and the quadratus (depressor) labii inferioris 

 muscles. Not infrequently (58 out of 92 bodies— LeDouble) some fascicuU are continued into 



Fig. 343. (After Eisler.) Buccinator Muscle and Pterygomandibular Raphe, 



AS SEEN FROM THE BuCCAL SiDE. 



The alveolar processes of both jaws have been removed in the region of the molar teeth. 

 The soft palate and its muscles have been removed. 



Nasalis 



Orbicu- / 



laris oris 



Levator veli 

 palatini 



Mentalis 



Constrictor 

 pharyngis 

 superior 



Mylo-hyoid 



Buccinator 



Internal pterygoid 



the neck as the transversus menti, a fibro-muscular band formed by the interdigitation of the 

 sUps prolonged from each side below the chin and superficial to the platysma. Santorini 

 described the transversus menti as an independent though inconstant muscle. According to 

 Eisler the true transversus menti muscle is to be distinguished from aberrent slips of the tri- 

 angularis or of the platysma in this region. In one instance Eisler found a slender nerve 

 emerging through the platysma and passing to this muscle. 



Nerve-supply. — The zygomatic branch of the seventh nerve supplies the canine (levator 

 anguli oris) and zygomatic (major) muscles. Branches enter the middle of the deep surface of 

 the latter muscle and the superficial surface of the former near its lateral border. The risorius 

 is supplied by branches from the buccal rami of the seventh nerve, which enter its deep sur- 

 face. The triangularis (depressor anguli oris) is supplied by the buccal branch through branches 

 which enter its deep surface near the posterior margin. 



Action. — The caninus (levator anguli oris) and zygomatic (z. major) muscles raise the corner 

 of the mouth, the former at the same time drawing it medially, the latter, laterally. The 

 caninus gives rise to expression of bitterness or menace. The zygomaticus is active in smiling or 

 laughing. When contracted greatly it elevates the cheek and the lower eyelid and produces 

 crow's-foot wTinkles at the corner of the eye. The risorius draws the angle of the mouth later- 

 ally. In spite of its name it is not used to express pleasure, but instead gives rise to an e.xpression 

 of pain. The triangularis (depressor anguli oris) depresses the corner of the mouth and draws 

 it laterally, giving rise to the expression of grief. 



