LABYRINTHODONTS. 21o 



other processes, at first simple like the preceding, begin to pene- 

 trate the dentine at the interspaces of the primary folds ; these 

 likewise take on a sinuous course a little nearer the base of the 

 tooth ; the diverging plates of dentine send off lateral lobes or pro- 

 cesses corresponding with these sinuosities, and a transverse section 

 at this part of the tooth exhibits the modification of the labyrin- 

 thic structure exhibited in PI. 63 b, fig 2. 



The anchylosis of the base of the teeth to distinct and shallow 

 sockets is a structure in which the Labyrinthodon resembles certain- 

 fishes, as the Sphyrena ; I am disposed also to believe, from the 

 absence of any excavation in the base of the fixed teeth, or of any 

 trace of alveoli of reserve for the successional teeth, that these were; 

 developed, as in many fishes, in the soft mucous membrane or gun) 

 which covered the alveolar margin, and that they subsequently became 

 fixed to the bone by anchylosis. Thus, notwithstanding the close 

 resemblance to the Crocodilian type which the Labyrinthodon pre- 

 sents in the form and superficial sculpturing of the skull, it deviates 

 widely in the mode of fixation and reproduction of the teeth. 

 Nor is it extraordinary that the present extinct Batrachian genus 

 should have its relations of affinity thus radiating in different direc- 

 tions, since we find in the extinct reptilian forms of a later epoch 

 the combination of Saurian characters with Ichthyic vertebrae and 

 extremities. 



89. Labyrinthodon pachygnathus. — A second and larger species of 

 Labyrinthodon is established upon certain fossils from the lower sand- 

 stones of Warwick, of which I shall here describe those that appertani 

 to the dental system. The most instructive specimen is a well pre- 

 served and considerable proportion of the right ramus of the lower 

 jaw, measuring nine inches and a half in length ; the anterior extre- 

 mity of this specimen is represented of the natural size at Plate 63 a , 

 fig. 4 and 5. The bone is thick and rounded, one inch and a hall 

 deep, and one inch broad at the posterior fractured part, thirteer 

 lines broad and eight lines deep at the anterior expanded and sub 

 depressed end, which is curved inwards towards the symphysis of tht 

 jaw, and which supports two of the great cuspidate or laniary 

 teeth, and the socket of a third. The structure of this lower jaw. 



