310 THE MUSCLES AND FASCIA. 



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. 208). 



The Risorius (Santorini) (Fig. 195) 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 outer extremity. This muscle varies much 

 in its size and form. 



Nerves. The muscles in this group are all supplied by the facial nerve. The 

 buccal branch of the inferior maxillary nerve pierces the Buccinator muscle, and 

 by some anatomists is regarded as partly supplying this muscle. Probably it 

 merely pierces it on its way to the mucous membrane of the cheek. 



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 for- 

 ward. 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 pro- 

 duces the unpleasant expression which is sometimes seen in tetanus, and is known 

 as "risus sardonicus." 



9. Temporo-mandibular Region. 



Masseter. Temporal. 



Masseteric Fascia. Covering the Masseter muscle, and firmly connected with 

 it, is a strong layer of fascia derived from the deep cervical fascia. Above, this 

 fascia is attached to the lower border of the zygoma, and, behind, it covers the 

 parotid gland, constituting the parotid fascia. 



The Masseter is exposed by the removal of this fascia (Fig. 195) ; it is a short, 

 thick muscle, somewhat quadrilateral in form, consisting of two portions, super- 

 ficial and deep. The superficial portion, the larger, arises by a thick," tendinous 

 aponeurosis from the malar process of the superior 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 jaw. 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 inner 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 jaw. 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 united at their insertion. 



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

 and Socia parotidis, and Stenson's duct; the branches of the facial nerve and the 

 transverse facial vessels, which cross it ; the masseteric fascia ; the Risorius, 

 Santorini, Platysma myoides, and the integument ; by its deep surface, with the 

 Temporal muscle at its insertion, the ramus of the jaw, the Buccinator arid the 

 long buccal nerve, from which it is separated by a mass of fat. The masseteric 

 nerve and artery enter in on its under surface. Its posterior margin is over- 

 lapped by the parotid gland. Its anterior margin projects over the Buccinator 

 muscle, and the facial vein lies on it below. 



The temporal fascia is seen, at this stage of the dissection, covering in the 

 Temporal muscle. It is a strong, fibrous investment, covered, on its outer surface, 

 by the Attrahens and Attollens auriculam muscles, the aponeurosis of the Occipito- 



