200 LABYRINTHODONTS. 



from the prevalence of this structure in the simple conical teeth of rep- 

 tiles, I did not build any very strong hopes of detecting such modifica- 

 tions of dental structure in the similarly simple teeth of the so 

 called Mastodonsaurus and of the tooth from the Warwick sandstone, 

 as would be sufficiently marked and obvious to carry conviction of 

 their generic, much less specifi.c identity. But in this I was agreeably 

 and unexpectedly deceived. 



When I refer to figure 1 in plate 64 a, and state that the first 

 transparent transverse section of the tooth of the Labyrinthodon (Masto- 

 donsaurus) Jaegeri that was placed under the microscope and viewed by 

 transmitted light, with a low magnifying power, presented the singu- 

 larly complicated structure there exhibited, the anatomist, conversant 

 with the known modifications of dental structure in the animal king- 

 dom, may well conceive my surprize. It was not, indeed, until I 

 had had sections made in various directions, from the portions of the 

 tooth of the Lah : Jaegeri transmitted to me, and had studied them 

 intently at several successive examinations, comparing the appear- 

 ances they presented with those of numerous examples of the teeth of 

 Saurians, Batrachians and other animals, that I at length compre- 

 hended the nature and principle of the singular cerebriform convolu- 

 tions or sinuosities which pervaded every portion of the tooth of this 

 most remarkable reptile of the Keuper sandstone. 



A transverse section from the base of the tooth of the Ichthy- 

 osaurus gave the first clue to the structure of that of the Labyrintho- 

 don. Before investigating the latter I had been accustomed to regard 

 the tooth of the Ichthysaurus as presenting, at its base, the most 

 complicated condition of dental structure in the class of reptiles ; 

 but it is simple as compared with the structure which pervades almost 

 the entire tooth of the Labyrinthodon Jaegeri. 



To render intelligible the plan of this structure, I may first refer 

 to that of the base of the tooth of the Ichthyosaurus communis (PL 64 b, 

 fig. 3). Teeth in general, as has been shown, vary in structure ac- 

 cording to the number of substances which enter into their composition, 

 and according to the disposition of those substances. In the ungulate 

 mammalia, as the elephant, rhinoceros, horse, etc., in which the 

 crown of the tooth consists of dentine, enamel and cement, vertical 

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



