. The principles and practice of dental surgery. nferioredge of the malar bone and the zygomatic arch as far back asthe glenoid cavity ; and is inserted, tendinous and fleshy, intothe external side of the ramus of the jaw and its angle as far upas the coronoid process. The use of this muscle, when both portions act together, is toclose the jaws; if the anterior acts alone, the jaw is broughtforward, if the posterior, it is drawn backward. Pterygoideus Externus (a and b Fig. 33) arises from theouter surface of the external plate of the pterygoid process ofthe sphenoid bone, from the tuberosity
. The principles and practice of dental surgery. nferioredge of the malar bone and the zygomatic arch as far back asthe glenoid cavity ; and is inserted, tendinous and fleshy, intothe external side of the ramus of the jaw and its angle as far upas the coronoid process. The use of this muscle, when both portions act together, is toclose the jaws; if the anterior acts alone, the jaw is broughtforward, if the posterior, it is drawn backward. Pterygoideus Externus (a and b Fig. 33) arises from theouter surface of the external plate of the pterygoid process ofthe sphenoid bone, from the tuberosity of the superior maxilla,and from the ridge on the sphenoid bone separating the zygo-matic from the pterygoid fossa; and is inserted into the innerside of the neck of the lower jaw, and capsular ligament of thearticulation. 66 ORGANS OF MASTICATION. Pterygoideus Internus arises, tendinous and fleshy, from theinner surface of the pterygoid plate, fills up the greater part ofthe pterygoid fossa, and is inserted, tendinous and fleshy, into Fig. Fig. 33. a and b Superior and inferior portions of the pterygoideus externus; c Pterygoideusinternus : d Root of zygomatic process; e Condyle. The ramus is cut away to show the internal pterygoid muscle. the inner face of the angle of the inferior maxilla and the rourhsurface above the angle. These tAVO muscles are the great agents in producing thegrinding motion of the jaws, and this they do by acting alter-nately. The external one is triangular, having its base at the ptery-goid process aud running outwards and backwards to the neckof the condyle. When the pair act together, the lower jaw isthrown The internal is strong and thick, placed onthe inside of the ramus of the jaw, and running downwards and4>ackwards to the angle. When the pair act together, the jawis drawn forward and closed. CHAPTER OF INSALIVATION. The Organs of InsaJivation are the salivary glands, six innumber, three on each side of the face,
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