LABYRINTHODONTS. 209 



of the large anterior fang of the maxillary series, and situated 

 internal to the anterior small serial teeth. The crocodilian affinities 

 of the Labyrinthodon we have just seen to have been manifested in 

 the character of the bones forming the upper surface of the maxillary 

 part of the cranium, and by the interception of a wide and shallow 

 nasal cavity between two horizontal plates of bone. The main test 

 of the value of this manifestation would be the actual condition of the 

 bony palate, first in regard to the bones composing it, and secondly 

 in relation to the dental system. In Crocodiles the floor of the nasal 

 cavity is chiefly formed by the maxillary bones, in Batrachians by 

 the divided and expanded vomer ; in all Crocodiles the bones of the 

 palate are edentulous, in most Batrachians they support teeth. There 

 was evidence in the fossil in question of a large laniary tooth project- 

 ing from the palatal surface of the mouth, internal to the series of max- 

 illary teeth ; it remained to be determined whether this was supported 

 upon the same bone which supported the serial teeth, viz. the superior 

 maxillary, or whether it was a true palatal or vomerine tooth. A 

 careful removal of the adherent matrix brought to light this very 

 instructive part of the cranial anatomy of the Labyrinthodon, (PI. 

 63 A, fig. 3). The palatal processes of the maxillary bones instead 

 of extending to the middle line, as in the Crocodiles, are very 

 narrow, as in the Batrachians. The osseous roof of the mouth is 

 principally constituted by a pair of broad and flat bones analogous 

 to those which Cuvier describes as a divided vomer in the Batra- 

 chians. These bones are, however, of greater relative extent than 

 in any existing Batrachians ; they defend the mouth with a more 

 complete bony roof than is present in most Lacertian reptiles. 

 Physiologically the Labyrinthodon in this part of its structure 

 comes nearest to the crocodile, but the structure itself, morphologi- 

 cally, is essentially Batrachian ; that is to say, the bony palate is 

 formed by largely developed vomerine bones, situated, as in the 

 Batrachians, at a part of the skull which is occupied solely by the 

 maxillary bones in the crocodiles. 



The divided vomer varies much in form in the Batrachians ; that 

 of the Menopome most resembles the vomer of the Labyrinthodon 

 in its broad anterior extremity, and the large tooth (fig. 3, c) is 



p 



