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 the 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 border 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 thirds of the mandible. It forms the posteriorly 
directed angular process, and a small part of the bone appears in this region upon the 
outer surface. The spleniale is very much reduced in Necturus and is in the form of a 
little 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 the upper jaw. ‘The details of the above osseous elements follow. 
1. pentTaLe. 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 thin and its upper and lower 
edges are curved inwards, making its outer surface somewhat convex and the inner con- 
INWER ASPECT 
Fig. 19. 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 
vartilage 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 
