THE MANDIBLE 



63 



the licnial tubercles there is a shallow smooth depression, the sublingual fossa ; 

 below this is the digastric fossa for the insertion of the anterior l)elly of the diiias- 

 tric muscle. Posterior to the genial tubercles, the internal oblique line (mylo- 

 hyoid ridge) commences and extends backwards, becoming more and more promi- 

 nent as it approaches the alveolar border. The mylo-hyoid muscle arises along the 

 whole length of this ridge. At the posterior part the mperior constrictor takes origin, 

 and the pterygo-maxillary ligament is attached to its posterior extremity. Below 

 the internal oblique line is the submaxillary fossa, which is in n'lation with the 

 su bm axilla ry gla n d . 



The inferior border of the body of the mandible is smooth and rounded; in the 

 anterior part of its extent it gives attachment to the platysma; near its junction with 

 the ramus there is a groove for the facial artery. The superior border is comjjosed 

 of spongy bone, and is named the alveolar process; it presents sockets or alveoli 

 for eight teeth. From the external surface of the alveolar process, as far forwards 

 as the first molar tooth, the buccinator muscle takes origin. 



Fig. 73.— The Mandible. (Outer view.) 



Temporal CORONOID PROCESS SIGMOID NOTCH External pterygoid 



CONDYLE 

 NECK 



Capsular 

 / ■/ and 



* ' External 

 ' lateral 



/ ligament 



THE CHIN OR 

 MENTAL PRO- 

 TUBERANCE 



Platysma 



Depressor anguli oris 



EXTERNAL OBLIQUE LINE 



GROOVE FOR FACIAL ARTERY 



The ramus is quadrilateral in shape. It has two surfaces, four l)orders, and 

 two processes. The external surface is for the insertion of the nin.^sseter muscle. 

 The internal surface presents near its middle the mandibular (inferior dental) 

 foramen which leads into the mandibular (inferior dental) canal which traverses 

 the body of the bone and emerges at the mental foramen. This canal ])resents a 

 series of fine apertures above, through which filaments of the mandibular nerve 

 and artery pass to the teeth. In its posterior two-thirds, the canal is nearer the 

 internal, in its anterior third, it is nearer the external surface of the mandil)le. The 

 posterior orifice of the canal is surmounted by the mandibular spine to which the 

 spheno-mandibular ligament is attached. Running ob]i(pioly downwards behind 

 this spine is the mylo-hyoid groove, which lodges the mylo-hyoid nerve and 

 artery. In the embryo, ^Sleckel's cartilage also occujjies the groove. The triangular 

 rough space behind this groove is for the insertion of the internal pterygoid muscle. 



The inferior border of the ramus is thick, rounded, and continuous with the 

 lower liorder of the body of the bone. The posterior l)order is roundi^l: to its 

 lower part the stylo-mandibular ligament is attached. This border is surmounted 



