248 PETRIFACTIONS AND THEIR TEACHINGS. CHAP. III. 



ridges. The whole surface is covered with minute punctua- 

 tions and striee. 



The numerous and large vascular foramina which aiforded 

 passage to the vessels and nerves from the dental canal to the 

 external integuments, form a striking character in this aspect : 

 they open obliquely forwards ; nine are distributed at regular 

 intervals in a line with the alveolar margin, from the posterior 

 end of the bone to nearly opposite the successional tooth in 

 place. A fracture in the middle of the outer surface, at the 

 distance of 4J inches from the posterior end, exposes the 

 dental canal filled with sandstone : its diameter is here two- 

 fifths of an inch. 



At the anterior termination of the alveolar space, a slight 

 protuberance marks the commencement of the upper margin 

 of the symphysial region, which is defined by a sharp smooth 

 ridge, that sweeps downwards and inwards to form the front 

 of the jaw. A deep groove, beset with foramina, constitutes 

 a strong line of demarcation between the inner and outer 

 boundary of this area ; the latter is thick and convex, and 

 terminates anteriorly, as already mentioned, in a mammillary 

 protuberance or tubercle. A series of foramina, eight in 

 number, extends along the outer and inferior surface of the 

 symphysis ; the terminal one, which is three-fourths of an 

 inch in its transverse diameter, is situated immediately under 

 the mental tubercle (c) above described. The mesial or inner 

 edge of the symphysis, which in connexion with the ramus of 

 the left side formed the median suture of the lower jaw, is thin 

 and expanded ; the articulating surfaces of the two dentary 

 bones appearing to have overlapped each other, but as the 

 edge of the bone is somewhat broken, the line of junction is 

 not quite determinable ; but the two rami do not seem to 

 have been united by anchylosis. On the under surface of the 

 symphysis there is a depressed oval area, bounded laterally 

 and posteriorly by a slightly elevated ridge, probably for the 

 insertion of the protractor muscles of the tongue. The coro- 

 noid bone (d), which is incomplete, is expanded more out- 

 wardly than in any recent saurian. 



With respect to the length of the jaw to which this speci- 

 men belonged, an approximative estimate only can be formed, 

 since we have no means at present of determining the relative 

 size of all the different pieces that entered into the construe- 



