506 Mr. Owen on the Labyrinthodons 



species of Mastodonsaurus or Lahyrinthodon to be made in various directions, and 

 had studied them intently at several successive examinations, — comparing the ap- 

 pearances they presented with those of numerous examples of the teeth of true 

 Saurians, Batrachians, and other animals,— that I at length comprehended the 

 nature and principle of the singular cerebriform convolutions or labyrinthic gyra- 

 tions which pervade every portion of the tooth of this most remarkable reptile of 

 the Keuper formation. 



Fig. 1. 



Part of a transverse slice of the tooth oi Lahyrinthodon Jcegeri, as seen by transmitted light ; magnified 10 diameters. 



A transverse section from the base of the tooth of the Ichthyosaurus gave the 

 first clue to the structure of that of the Ldbyrinthodon. Before investigating the 

 latter, I had been accustomed to regard the tooth of the Ichthyosaurus as presenting 

 at its base the most complicated condition of dental structure in the class of Rep- 

 tiles ; but it is simple as compared with the structure which pervades nearly the 

 entire tooth of the Lahyrinthodon. 



It is scarcely necessary to observe, that teeth vary in structure according to the 

 number and disposition of the substances which enter into their composition. 



In the herbivorous Mammalia, as the elephant, rhinoceros, horse, &c., where the 

 crown of the tooth consists of dentine or tooth-bone, enamel, and cement, vertical 

 folds of the enamel and cement penetrate the body of the tooth, and receive in 

 their interspaces corresponding vertical processes of the dentine : the consequence 

 of this disposition in maintaining a grinding surface of the tooth, by the unequal 

 attrition of the edges of the interblended laminae of the three different substances, 

 is well known. 



The pattern, however, in which the folds of enamel and cement are arranged in 

 the substance of the tooth in these and other herbivorous Mammalia, although 



