910 THE OSTEOLOGY AND MYOLOGY OF THE DEATH ADDER, 



The articular surface bears a resemblance to the greater sigmoid 

 cavity of the ulna. Its axis slopes from above downwards and 

 inwards. A median ridge running back from a small "coronoid "- 

 like process in front divides the cavity into two portions, each of 

 which is concave from before back. The external portion is the 

 smaller though deeper of the two, and serves to prevent the too 

 ready dislocation of the jaw. The internal is large and shallow, 

 and owing to the obliquity of the axis its excavated surface 

 approaches much nearer the inferior edge than does the surface 

 on the external side. The trochlear surface of the quadrate meets 

 this sigmoid surface at an acute angle, and so, when the mandible 

 is depressed, rotation takes place in such a way that the anterior 

 portion of the mandible moves downwards, backwards, and out- 

 wards, thus allowing the gape to be opened to its fullest extent 

 without dislocation of the bones. 



The dentary presents an external and internal surface, a 

 superior and an inferior edge. The bone is bent into two curves ; 

 the first portion is at right angles to the long axis of the head, 

 the second is parallel to the long axis, at the same time having a 

 small curve inwards so as to make the external surface concave. 



The external surface runs backwards and bifurcates, enclosing 

 the anterior extremity of the splenial. The greater portion of 

 this surface is covered by the gland. A large mental foramen is 

 placed close to the bifurcation. 



From the inferior portion of the anterior third of the interior 

 surface, there arises, in a well marked excavated surface, the 

 genio-glossus muscle, and above this the genio-trachealis. Below 

 the genio-glossus, and running along the inferior border, the inter- 

 mandibular muscle arises. 



The anterior extremity gives attachment to the intermandibular 

 ligament. 



The superior border contains about a dozen teeth. The inferior 

 border gives attachment to the muscles as stated above. 



