THE SKULL. 419 



they articulate with the quadrates, and firmly 

 unite together in the median plane in front. 

 Like the upper jaw it bears no teeth, but is 

 covered by a horny epidermal sheath. 



Each ramus of the mandible . really con- 

 sists of five bones, one of which is developed 

 in the primary cartilaginous arch, while the 

 others are formed around it. 



a. The articular forms the expanded posterior 

 end of the ramus. On its dorsal surface 

 is the elongated and slightly concave arti- 

 cular surface for the quadrate : behind this 

 the bone is produced backwards and up- 

 wards into the curved posterior articular 

 process ; and on the inner side into a similar 

 but stouter internal articular process. 



The articular is continuous in front 

 with Meckel's cartilage, the cartilaginous 

 bar of the mandibular arch, which persists, 

 even in the adult, along the greater part of 

 the length of the mandible, ensheathed in 

 membrane-bones. 



/J. The angular is a splint-like bone which 

 underlies the articular, and extends for- 

 wards along the ventral edge and inner 

 surface of the proximal half of the lower 

 jaw. 



7. The supra-angular forms the dorsal part of 



the posterior third of the mandible, along 

 both outer and inner surfaces. Its dorsal 

 border is raised into a small coronoid pro- 

 cess, about the middle of its length. 



8. The dentary is the largest of the bones of 



the jaw, and forms the distal half of each 

 ramus : it is fused with its fellow in front 

 at the symphysis : and posteriorly it extends 



