Ch. XXIL] fossil kemalns of labyeinthodon. 



339 



438) of part of one is given from his "Odontography," plate 64, A. 

 The entire length of this tooth is supposed to have been about three 

 inches and a half, and the breadth at the base one inch and a half. 



Tig. 438. 



Transverse section of tooth of LabyrintTiodon Jaegeri, Owen (Masiodonsaurus Jaegeri, 

 Meyer) ; nat. size, and a segment magnified. 



a. Pulp cavity, from which the processes of pulp and dentine radiate. 



"When Prof. Owen had satisfied himself, from an inspection of the cra- 

 nium, jaws, and teeth, that a gigantic Batrachian had existed at the 

 period of the Trias or Upper New Red Sandstone, he soon found, from 

 the examination of various bones derived from the same formation, that 

 he could define three species of Labyrinthodon, and that in this genus 

 the hind extremities were much larger than the anterior ones. This 

 circumstance, coupled with the fact of the Labyrinthodon having existed 

 at the period when the Cheirotherium footsteps were made, was the first 

 step towards the. identification of those tracks with the newly-discovered 

 Batrachian. It was at the same time observed that the footmarks of 

 Cheirotherium were more like those of toads than of any other living ani- 

 mal ; and, lastly, that the size of the three species of Labyrinthodon 

 corresponded with the size of three different kinds of footprints which 

 had already been supposed to belong to three distinct Cheirotheria. It 

 was moreover inferred, with confidence, that the Labyrinthodon was an 

 air-breathing reptile from the structure of the nasal cavity, in which the 

 posterior outlets were at the back part of the mouth, instead of being 

 directly under the anterior or external nostrils. It must have respired air 

 after the manner of saurians, and may therefore have imprinted on- the 

 shore those footsteps, which, as we have seen, could not have originated 

 from an animal walking under water. 



It is true that the structure of the foot is still wanting, and that a more 

 connected and complete skeleton is required for demonstration ; but the 

 circumstantial evidence above stated is strong enough to produce the 



