LABYRINTHODONTS. 211 



each outer margin of the long and narrow vomer ; the extinct Laby- 

 rintliodon combines both these dispositions of the vomerine teeth. 



The next fossil which I proceed to describe, and which, like the 

 preceding one, is from the sandstone in the neighbourhood of 

 Warwick, also throws much light upon the dental system and 

 affinities of the present singular genus of extinct reptiles. It is the 

 anterior dentigerous part of the ramus of the lower jaw, a portion 

 of which is figured at PI. 63 a, fig. 2. This ramus is slender, 

 straight, and with its symphysial extremity abruptly bent inwards, 

 the inner line of the symphysis here forming a regular and deep 

 curve. The breadth of the bone at the posterior fractured part 

 is ten lines ; at the anterior part, behind the inflected symphysis, 

 seven lines ; the breadth of the anterior fractured portion is one 

 inch. The structure of this long and straight ramus of the jaw 

 presents almost as striking a batrachian character as any of those 

 derived from the foregoing fossil ; that is to say, the angular piece 

 is of great breadth, and is continued forwards to near the sym- 

 physis, forming the whole of the inferior part of the ramus of the 

 jaw extending upon the inner as far as upon the outer side of the 

 ramus ; the inner plate performing the function of the detached 

 " OS operculare " in the lower jaw of the Saurians. The dentary 

 piece is supported upon a deep and wide groove, extending along the 

 upper surface of the angular piece and looking obliquely outwards. 

 The angular piece projects beyond the outer edge of the groove, 

 so as to form a strong convex ridge on the external side of the jaw 

 below the dentary piece ; this character, which in the large bull-frog 

 {Rana pipiens) is confined to the posterior part of the maxillary 

 ramus is here continued to near the anterior extremity, and forms a 

 conspicuous character of the jaw of the Labyrinthodon. The teeth 

 in the present ramus are long and slender, and so closely correspond 

 in size and shape with those in the upper jaw, just described, that 

 they must be regarded as belonging to the same species. (1) There are 

 not less than fifty sockets in a single linear series, and at the anterior 

 inflected part of the jaw there is the base of the socket of a large 

 tooth, six Knes in diameter : the serial teeth gradually diminish in 



(I) The specific name, leptognatlms, relates to the elenderness of this long lower jaw. 



p 2 



