390 



MAMMALIAN ANATOMY 



At the anterior end of the surface is the roughened area for articu- 

 lation with the other half of the jaw. This area is pear-shaped, the 

 apex pointing downward and backward. Its anterior straight, slightly 

 serrated border is the anterior border of the bone. The upper half of 

 its posterior upper border is sharp and elevated, forming with the 

 border of the other half a prominent median ridge, below which are 

 attached the hyo-glossus and genio-hyo-glossus muscles. Between this 

 ridge and the superior border of the bone is a shallow, vertical groove. 



The superior border of the body of the mandible is known as the 

 alveolar border, because it contains the alveoli, or cavities for the roots 

 of the teeth. It consists of a long posterior portion for the molars and 

 premolars, and a short, elevated anterior portion for the canines and 



FIG. 312. 



Coronoid Process. 



Condyle. 



MAXILLO-AURICULAR. 



Second 

 Premolar. First 



Premolar. 



Symphysis. 



Angle. 



OENIO-HYO- GENIO-HYOID. 

 QLOSSUS. 



INTERNAL 



PTERYGOID. Foramen 



LOWER JAW, LEFT SIDE, INNER SURFACE. 



incisors. The two parts are separated by a transversely depressed 

 interval called the diastema. The posterior part is of moderate width ; 

 it is arcuate externally and faces outward as well as upward. It con- 

 tains six deep pits, or alveoli, arranged in three groups of two each, to 

 receive the roots of the three posterior lower teeth. Each group of 

 two alveoli is placed slightly obliquely to the axis of the bone, so that 

 the anterior alveolus is nearer to the median line of the skull than the 

 posterior. The alveoli increase in size from before backward, except 

 the last alveolus, which is as small as the first. The posterior roots of 

 the first two teeth therefore are stouter than the anterior roots, but the 

 anterior root of the last tooth is stouter than the posterior. The alveoli 

 are directed downward and inward, and the larger ones extend more 



