508 Mr. Owen on the Labyrinthodons 



of a series of vertical folds of the external substance, so extensive and so compli- 

 cated as they actually are. 



Accordingly, Professor Jaeger has described the tooth of his Mastodonsaurus 

 as being simply longitudinally striated on the superficies, noting where the striae 

 terminate, their relative distances, and where they are most marked : the texture of 

 the tooth where it was exposed by fracture, he states, as indeed it appears to the 

 naked eye, to be an uniform or homogeneous compact mass (gleichformig derbe 

 masse), and he concludes his description by stating that the tooth resembles most 

 closely that of the Lacerta Nilotica and of some species oi Monitor*. 



I may observe, however, that the teeth of those species of Lacerta, Monitor, and 

 other Lacertian genera which I have submitted to microscopic investigation, have 

 all presented the general structure of simple saurian teeth ; and that, since ascer- 

 taining the structure of the Lahyrinthodon's tooth, I have minutely inspected the 

 outer surface of the teeth of numerous species of Saurians, but have not detected 

 striae penetrating the substance of the tooth, like those which indicate the compli- 

 cated structure of the tooth of the Keuper Batrachian. 



The portion of the tusk of the Labyrinthodon Jcegeri, from which the microscopic 

 sections now described were prepared, included about the middle third part of a 

 tooth, nearly as large as the one figured by Professor Jaegerf . That tooth is three 

 and a half inches in length, one and a half inch in breadth at the basis, whence 

 it gradually converges with a sHght bend towards the apex, which is obtuse, with 

 a slightly depressed summit three lines in diameter, and having a small rising in 

 the centre of the terminal depression. 



The external longitudinal strise are regularly arranged, with intervals of about 

 one line at the base of the tooth, and they maintain nearly the same position 

 throughout the lower three-fourths of the tooth, by decreasing in number as the 

 tooth diminishes in thickness ; they finally altogether disappear about half an inch 

 from the summit of the tooth. Here therefore, I presume, the structure of the 

 tooth may be more simple ; but whether there be any inflected folds, or to what 

 extent they are continued into the summit of the tooth ; and whether, beside a 

 layer of cement, the tooth be at this part invested likewise by a coating of enamel, 

 can only be determined by the examination of sections similar to those which I have 

 had prepared from the middle part of the crown in the tooth of the Labyrinthodon 

 Jcegeri. 



At this part the dentine or body of the tooth is invested by only a very thin 

 sheath of cement, and it is a vertical fold or duplicature of this cement which 

 penetrates into the substance of the tooth at each of the strise, which, as before 



loc. cit. p. 36. f loc. cit. tab. 4, fig. 4. 



