MUSCLES OF MASTICATION. 



455 



External ptei-y- 

 goid (insertion) 



M. triangularis 

 (origin) 

 M. quadratus 

 labii inferioris 

 (origin) 

 M. mentalis 

 (origin) 



Platysma 

 (insertion) 



FIG. 403. MUSCLE- ATTACHMENTS TO THE LATERAL ASPECT OF THE MANDIBLE. 



directed downwards and backwards towards the angle of the mandible ; the deeper 



fibres are directed vertically downwards. 



The muscle is inserted- by fleshy and tendinous fibres into the lateral surface 



of the ramus and angle of the mandible and the coronoid process (Fig. 403). 



The deepest fibres 



blend with the 



fibres of the sub- 

 jacent temporal 



muscle. 



The muscle is 



partially concealed 



on the face by the 



parotid gland, ac- 

 cessory parotid 



gland, and parotid 



duct; by the ex- 

 ternal maxillary 



artery; the branches 



of the facial nerve ; 



and by the- zygo- 



matic and platysma 



muscles. It conceals 



the ramus of the 



mandible, and, at its 



anterior border, is 



separated from the buccinator muscle by the corpus adiposum luccce. 



M. Temporalis. The temporal muscle is a fan-shaped muscle arising from 



the whole area of the temporal fossa, as well as from the temporal fascia which 



covers it. Its converging fibres pass medial to the zygomatic arch. 



The muscle is in- 

 serted into the deep 

 surface and apex of the 

 coronoid process, and 

 into the anterior border 

 of the ramus of the 

 mandible (Figs. 403 

 and 404). 



The origin of the 

 muscle is concealed by 

 the temporal fascia. 

 As it passes to its in- 

 sertion the muscle is 

 concealed by the zygo- 

 matic arch, the masseter 

 muscle, and the coronoid 

 process of the mandible. 

 It is separated from the 

 external pterygoid in a 

 majority of cases by the 

 internal maxillary 

 artery. The masseteric 



nerve and vessels appear at its posterior border ; the buccinator nerve and vessels 



at its anterior border. 



M. Pterygoideus Externus. The external pterygoid muscle is deeply placed 



under cover of the temporal muscle, in the infra-temporal fossa. It arises by two 



heads, superior and inferior. The superior head is attached to the infra-temporal 



surface of the great wing of the sphenoid ; the inferior head takes origin from the 



lateral surface of the lateral pterygoid lamina of the pterygoid process. 



The muscle is directed laterally and backwards, to be inserted into (1) the 



30 c 



External ptery- 

 goid (insertion) 



Genio- 



glossus 

 (origin) 



Genio-liyoid 

 (origin) 



FIG. 404. MUSCLE-ATTACHMENTS ON THE MEDIAL SIDE OF THE 

 MANDIBLE. 



