THE TEMPOROMANDIBVLAR REGION 377 



the internal oblique line of the mandible. Its deep surface corresponds to the 

 cavity of the mouth, and is lined with mucous membrane. Its superficial surface 

 is separated from the ramus of the mandible 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. 



The buccopharyngeal fascia (fascia buccopharyngea) is a thin fascia covering 

 the superficial surface of the Buccinator muscle. It is gradually lost in front of 

 the angle of the mouth. Posteriorly, it is continued over the superficial surface 

 of the Constrictor muscles. Its thickened cord-like portion is the stylomandibular 

 ligament. 



The RisorillS (m. risorius) (Fig. 289) consists of a narrow bundle of fibres 

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

 forward, is inserted with the Depressor anguli oris into the subcutaneous and 

 muscular tissue at the angle of the mouth. 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 muscles in this group are all supplied by the facial nerve. 



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 the cheeks have been previously distended with air, the Buccinator muscles expel 

 it from between the lips, as in blowing a trumpet. Hence the name (buccina, a trumpet). The 

 Risorius retracts the angles of the mouth, and produces the unpleasant expression which is 

 sometimes seen in tetanus, and is known as risus sardonicus, the sardonic laugh. 



9. The Temporomandibular Region. 



Masseter. Temporal. 



The masseteric fascia (fascia parotideomasseterica) covers the Masseter muscle. 

 It is firmly connected with this muscle and is derived from the deep cervical 

 fascia. Above, this fascia is attached to the lower border of the zygoma, and 

 behind, it invests the parotid gland, constituting the parotid fascia. 



The Masseter muscle (m. masseter) (Fig. 289) is a short, thick muscle, 

 somewhat quadrilateral in form, consisting of two portions, the superficial and 

 the deep. The superficial portion, the larger, arises by a thick, tendinous aponeu- 

 rosis from the malar process of the maxilla, and from the anterior two-thirds of 

 the lower border of the zygomatic arch; its fibres pass downward and backward, 

 to be inserted into the angle and lower half of the outer surface of the ramus of 

 the mandible. 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 deep 

 surface of the zygomatic arch; its fibres pass downward and forward, to be inserted 

 into the upper half of the ramus and outer surface of the coronoid process of the 

 mandible. The deep portion of the muscle is partly concealed, in front by the 

 superficial portion; behind, it is covered by the parotid gland. The fibres of the 

 two portions are continuous at their insertion. 



Relations. By its superficial surface, with the Zygomatici, the parotid gland, the socia paro- 

 tidis, the parotid duct, the branches of the facial nerve and the transverse facial vessels, which 

 cross it; the masseteric fascia; the Risorius, Platysma, and the integument. By its deep surface 

 it is in relation with the Temporal muscle at its insertion, the ramus of the mandible, the Buc- 

 cinator and the long buccal nerve, from which it is separated by a mass of fat (sucking pad). 

 The masseteric nerve and artery enter in on its deep surface. Its posterior margin is overlapped 

 by the parotid gland. Its anterior margin, which projects over the Buccinator muscle, is crossed 

 below bv the facial vein. 



