2 5 8 



Anatomy of Skeleton 



riddle 



A-T 



Nerve 



long IHK. 



/V. 



External Pterygoid, and passes immediately behind the Temporal tendon : its course 



below the outer Pterygoid is thus different from that of the masseteric nerve, which is 



above the muscle, between it and the base of the skull (see Fig. 182), and is therefore 



not a relation of the mandible. 



The Temporal insertion is on the edge of the coronoid process, from the bottom 



of the notch almost to the alveolus ; 

 it only extends slightly on to the 

 surfaces of the process, usually 

 more so on the inner than on the 

 outer side. 



The roughness of the masse- 

 teric area indicates that it also has 

 tendinous fibres at its insertion. 

 Observe that the area of insertion 

 extends very high ; this is for the 

 attachment of the more vertical 

 posterior fibres, which have little 

 play in the normal opening of the 

 mouth and can therefore be fastened 

 nearer their origin. The fibres that 

 have most movement and more 

 powerful action arise from the malar 

 further forward and are directed 

 downwards and backwards to the 

 lower part of the ramus. 



The upper part of the posterior 

 margin of the ramus slopes back 



into the neck. Thus a triangular area of bone is exposed behind the level of the margin 



of the Masseter, and the parotid gland comes into relation with the bone here, being 



otherwise separated from its outer surface by the muscle. The gland also lies in contact 



with the border of the ramus, turning round it deeply to come into relation with the 



inner aspect and with the Internal Pterygoid, and the lower and deep part of its capsule 



is thickened to form the " stylo-mandibular ligament " which is attached to the lower 



part of the posterior margin. 



The temporo-mandibular joint is a complex one, 



divided by an interarticular fibro-cartilage into two 



distinct cavities. The outer edge of the neck of the 



bone presents a ridge for the attachment of the 



external lateral ligament, the fibres of which are 



directed downwards and backwards from the emin- 



entia articularis (Fig. 204) . On the inner side another 



ridge marks the short internal ligament ; both these 



are thickened parts of the capsule. The capsule is 



very thin behind, but thicker in front where it 



receives some fibres of the External Pterygoid : it is 



attached all round the periphery of the fibro-cartilage, so that the menisco-mandibular 



and menisco-squamous cavities are quite distinct. 



The fibro-cartilage fits on the articular eminence and in the articular cavity so 



that its upper surface is concavo-convex, while its lower surface is deeply concave to 



rest on the condyle of the mandible. The head of the mandible can plainly only 



FIG. 207. To show the structures lying in relation with the 

 lower jaw above the level of the inferior dental foramen. 

 For comparison with Figs. 204 and 206. 



FIG. 208. To illustrate the different 

 curves of the dental arcades in 

 upper and lower jaws ; lower 

 arcade is shaded. 



