1 68 HEAD AND NECK 



is attached to the upper temporal line on the lateral aspect 

 of the parietal bone, and anteriorly to the temporal line of the 

 frontal bone. As it approaches the zygomatic arch, it splits into 

 two laminae, which are separated from each other by a narrow 

 interval filled with fat. The two laminae are attached one to 

 the upper border of the zygomatic arch and the posterior 

 border of the zygomatic bone, and the other to the medial 

 surfaces of those two portions of bone. They can readily 

 be demonstrated by dividing the superficial layer close to its 

 attachment, and throwing it upwards ; by the handle of the 

 knife the attachment of the deep layer can then be made out. 

 In the upper part of its extent, the temporal fascia is com- 

 paratively thin and the fibres of the subjacent muscle may 

 be seen shining through it ; below, it is thicker, and owing 

 to the fat which is interposed between its laminae, it is 

 perfectly opaque. It is pierced immediately above the 

 posterior part of the zygomatic arch by the middle temporal 

 branch of the superficial temporal artery and by the middle 

 temporal vein (p. 48). 



Musculus Masseter. The masseter is a thick quadrate 

 muscle which covers the ramus of the mandible. Its 

 fibres are arranged in two sets a superficial and a deep. 

 The superficial part of the muscle arises from the anterior two- 

 thirds of the lower border of the zygomatic arch, and its 

 fasciculi are directed downwards and backwards. The deep 

 part springs from the whole length of the medial aspect of the 

 zygomatic arch, and also from the posterior third of its lower 

 border. Its fibres proceed downwards. Only a small piece 

 of the upper and posterior part of the latter portion appears 

 on the surface. The masseter is inserted into the lateral 

 surface of the ramus of the mandible, over an area which 

 extends downwards to the angle, and upwards so as to include 

 the lateral aspect of the coronoid process. The masseter 

 raises the mandible and helps to protract it. The deeper 

 fibres which run downwards and forwards when the mandible 

 is protracted help to retract the protracted bone. The nerve 

 of supply is derived from the mandibular division of the 

 trigeminal nerve. 



Dissection. Turn the upper part of the posterior margin of 

 the masseter forwards and secure its nerve and artery of supply 

 which pass to it through the incisura mandibularis, behind the 

 tendon of the temporal muscle. To display the temporal muscle, 



