420 



HARRIS HAWTHORNE WILDER ON 



these latter bones develop, they expand somewhat at their meeting with one another and 

 form a strong bony symphysis, suppressing the median ends of the cartilage. The dentale 

 is the largest of tlie dermal bones and covers the entire outer side of the mandible from 

 symphysis to posterior angle. It forms nearly the anterior third of the inner surface, and 

 two thirds of the lower edge, forming, with the lower Ijorder of the angulare, the fora- 

 men mandibulare. The angulare is next in size and is the main bone of the inner sur- 

 face, extending along the posterior two third.s of the mandible. It forms the posteriorly 

 directed angular process, and a small part of tlie bone ai)pears in this region upon the 

 outer surface. The spleniale is very much reduced in Necturus and is in the form of a 

 Uttle oval scale, set somewhat on the inner side, filling an interval between the angulare 

 and the dentale. It is dentigerous and bears a few (5 to 7) teeth, which form a row not 

 exactly continuous with that of the dentale, and opposed to that of the palato-pterygoid 

 in tlie upper jaw. The details of the above osseous elements follow. 



1. DENTALE. This bone gives the contour to the jaw and follows quite closely the 

 general outlines of the head, and thus the posterior part is nearly straight while the ante- 

 rior third curves somewhat abruptly inwards. It is quite tiiin and its upper and lower 

 edges are curved inwards, making its outer surface somewhat convex and the inner cou- 



X SPL 



( OPf j 



Inncr aspect 



X AfJC 

 Fig. 1!». Internal view of right dentale. X 3. Contact surfaces with other bones are designated by an x. 



cave. At the anterior third so much of the lower edge curves in that it forms a fairly 

 broad and flat submental surface involving about half of the total width. The dentale 

 bears a row of teeth which occupy nearly the anterior half. They are inserted along the 

 inner aspect, about half their length appearing above the upper edge of the bone. Just 

 posterior to this row of teeth the upper margin rises a little to form a very rudimentary 

 ramus which receives the insertion of the very stout tendon of the masseter muscle. 

 Internally, the dentale is chiefly characterized by its concavity, which lodges Meckel's 

 cartilage and forms a deep and narrow groove anteriorly which broadens out posteriorly 

 to the full width of the bone. 



The two dentalia form a strong symphysial articulation with one another at their 



