398 THE VERTEBRATE SKELETON. 



the alveolar border, and along it are attached the canine, 

 premolar, and molar teeth. 



The anterior part of the upper jaw on each side is formed 

 by a small bone, the premaxilla, which bears the incisor teeth. 

 It, like the maxilla, has a palatal portion (fig. 75, 20), which 

 meets its fellow in the middle line, and an ascending portion, 

 which passes backwards as the nasal process, 'tapering regu- 

 larly and lying between the nasal and the maxilla. The two 

 premaxillae form the outer and lower borders of the anterior 

 nares. The last bone to be mentioned in connection with the 

 upper jaw and face is the jugal or malar (figs. 73, 8, and 75, 14), 

 a strong bone which forms the anterior half of the zygomatic 

 arch. It is firmly united in front to the maxilla, and behind 

 meets the zygomatic process of the squamosal, being drawn 

 out dorsally into a short postorbital process at the point of 

 meeting. This process lies immediately below the postorbital 

 process of the frontal, and if the two met, as they do in some 

 mammals, they would partially shut off the orbit from a larger 

 posterior cavity, the temporal fossa. In the living animal a 

 ligament unites the two postorbital processes. 



(b) THE LOWER JAW OR MANDIBLE. 



This consists of two elongated symmetrical halves, the 

 rami, which are united to one another at the median 

 symphysis in front, while behind they diverge considerably, 

 and each articulates with the glenoid surface of the corre- 

 sponding squamosal. In young animals the rami are united at 

 the symphysis by fibrous tissue, but in old animals they some- 

 times become fused together. The upper or alveolar border- 

 bears the teeth, and behind them is drawn out into a high 

 laterally compressed coronoid process (fig. 72, 24), which is 

 hollowed on its outer surface. Immediately behind the coronoid 

 process is the transversely elongated condyle (fig. 72, 25), 

 which fits into the glenoid cavity in such a way as to allow 

 free up and down movement of the jaw, with but little rolling 

 motion. The posterior end of the jaw below the condyle forms 



