BY W. J. McKAY. 909 



baur, Owen, Parker, Wiedersheim ; Complenientare, Harting, 

 Hoffmann. 



The mandible is composed of two moities ; an anterior single 

 piece or dentary, and a posterior compound piece consisting of 

 splenial, coronoid, angular, surangular, and articular. The shaft of 

 the compound portion is bent so that the external side is convex. 

 It has two surfaces and two borders. 



The external surface runs from the dentary back to the extremity 

 of the articular. The anterior two-thirds of it is made up of 

 angular, and is convex ; the posterior third of articular, and presents 

 two concave surfaces and a ridge between them which runs from 

 behind downwards and forward. The masseter is attached to the 

 anterior two-fifths of the surface, the posterior temporal to the 

 anterior of the two concave surfaces ; between and above these 

 muscles we have the anterior temporal inserted. The lower head 

 of the internal pterygoid arises from the posterior of the two 

 concave surfaces ; while on the ridge between these surfaces the 

 mylohyoid is inserted. 



The internal surface is concave from before back. Anteriorly 

 the splint-like splenial may be seen running back from the dentary, 

 and expanding joins the coronoid ; this lies immediately below the 

 surangular no longer now to be made out as a separate element, 

 though well seen in Morelia. From the posterior third of the 

 surface the upper head of the internal pterygoid muscle arises. 

 The middle third is convex and smooth, and over this portion the 

 internal pterygoid glides. 



As the superior edge runs back from the alveolar border 

 of the dentary it bifurcates to enclose the large mandibular fossa 

 into which is inserted the external pterygoid muscle. Immediately 

 in front of the fossa the parieto-mandibularis is inserted ; imme- 

 diately behind is placed the sigmoid cavity of the articular, and 

 posterior to this the edge expands into a triangular surface whereon 

 the digastric is inserted, and over the external edge of which the 

 retractor oris glides. 



