258 THE VERTEBRATE SKELETON. 



externally, the transpalatine and pterygoid behind, and the 

 palatine on the inner side (fig. 43, A, 7). 



9. The Anterior palatine vacuity. This is unpaired 

 and is bounded by the premaxillae (fig. 43, A, 8). 



(b) THE LOWER JAW OR MANDIBLE. 



The mandible is a strong compact bony structure formed 

 of two halves or rami, which are suturally united at the 

 symphysis in the middle line in front. Each rainus is formed 

 of six separate bones. 



The most anterior and largest of these is the dentary (figs. 

 44, 20, and 45, 18), which forms the symphysis, and greater part 

 of the anterior half of the jaw, and bears along the outer part 

 of its dorsal border a number of sockets or alveoli in which 

 the teeth are placed. Lying along the inner side of the dentary 

 is a large splint-like bone, the splenial (fig. 45, 19), which does 

 not extend so far forwards as the symphysis, and is separated 

 from the dentary posteriorly by a large cavity. Forming the 

 lower part of all the posterior half of the jaw is the large 

 angular (figs. 44, 22, and 45, 20), which underlies the posterior 

 part of the dentary in front and sends a long process below that 

 bone to the splenial. On the inner side of the jaw there is an 

 oval vacuity, the internal mandibular foramen (fig. 45, 28), 

 between the angular and the splenial ; through this pass blood- 

 vessels and branches of the inferior dental nerve. Lying 

 dorsal to the angular is another large bone, the supra-angular 

 (figs. 44, 18, and 45, 21). It extends back as far as the pos- 

 terior end of the jaw and forwards for some distance dorsal 

 to the dentary and splenial. It forms part of the posterior 

 margin of a large vacuity, the external mandibular foramen, 

 which is bordered above and in front by the dentary and below 

 by the angular ; it gives passage to the cutaneous branch of 

 the inferior dental nerve. The concave surface for articulation 

 with the mandible and much of the posterior end of the jaw is 

 formed by a short but solid bone, the articular (fig. 45, 22), 



