272 THAUMATOSAURUS. 



tion of the middle of the crown, including the pulp-cavity and its 

 ossified contents ; the natural size of the section is given at fig. 1 ; 

 a reduced figure of the same, magnified sixty diameters, at fig. 2, 

 and a more highly magnified view of the terminations of the calcige- 

 rous tubes, at fig. 3, a ; the marginal cells being shown at &, and the 

 enamel with its thin coat of cement at c. 



The highly organized nature of a tooth is well illustrated in this 

 example of one of the simplest of Saurian teeth ; in which, in addi- 

 tion to the tubular and cellular modifications of the dentine, there is 

 also enamel, cement, and an internal coarse kind of bone. 



The dentition of the Megalosaurus, besides exemplifying, on a 

 large scale, the mechanical advantages of the varanian form of tooth, 

 exhibits an interesting transitional character betw^een the squamate 

 and loricate types of Saurians, the distinct sockets making the ap- 

 proach to the crocodiles, while the raised external alveolar wall shows 

 the retention of the lacertine structure. 



THAUMATOSAURUS. 



1 16. In a great extinct species of Saurian, whose remains have been 

 discovered in the oolitic formation at NeufFen, in Wurtemberg, and 

 which has received the name of Thaumatosaurus oolithicus from 

 M. Hermann von Meyer, the teeth were conical, slightly curved, 

 straighter on the inner side of the crown ; implanted by a long and 

 strong root rather obliquely in a deep socket. The base and basal 

 portion of the crown presents a nearly circular transverse section ; 

 the wide pulp-cavity in this part of the tooth presented an elliptical 

 transverse contour ; the tooth becomes slightly compressed towards 

 the apex. 



The broadest part of the tooth is its implanted base ; the breadth 

 of the crown is to its height as one to three ; the crown is invested 

 with a thin layer of enamel, the basal half of which is marked by 

 longitudinal strise ; these striae seem to consist of folds of the enamel, 

 which do not extend into the dentine. 



The successional teeth penetrate into the interior of the fixed 

 teeth in the progress of their development. 



