MOSASAURUS. 259 



ticus. They are arranged in a pretty close and regular series. There 

 appear to have been eight teeth on each pterygoid bone. 



In the mode and place of development of the successional teeth, 

 the Mosasaurus resembles the Iguanee and most other Lacertians. 

 In the great cranium above mentioned germs of new teeth in various 

 stages of growth are lodged in hollows of corresponding degrees of 

 depth on the inner side of the bases of the adherent teeth, and have 

 evidently owed the commencement of their formation to the mucous 

 membrane which originally covered those supporting cones of the 

 teeth in place. The attention of Camper was particularly arrested by 

 the observation of this fact, which appeared the more singular to him 

 as this mode of dental succession, which is common in reptiles and 

 osseous fishes, was not then known. 



" The dentition is so singular," he says, " in these fossil jaws 

 that it deserves a particular description. A small secondary tooth is 

 formed complete with its enamel and solid root in the osseous sub- 

 stance of the temporary tooth : in the progress of its growth it seems 

 gradually to form a cavity of corresponding size in the osseous root 

 of the primitive tooth ; but it is impossible for me to decide what next 

 befalls it, or in what manner it is shed." 



The crown of the tooth consists of a body of simple and firm 

 dentine, invested with a moderately thick coat of enamel ; the ex- 

 panded base is composed of a more irregular mass of dentine which, 

 by its progressive subdivision into vertical columnar processes, 

 assumes a structure resembling that of true bone : this part is covered 

 with a layer of cement, which is continued as an extremely thin coat 

 upon the enamel. 



The pulp-cavity generally remains open at the middle of the 

 base of the crown of the tooth ; irregular processes of the cavity 

 extend, as medullary canals into the conical base of the tooth ; but no 

 processes of the pulp-cavity are continued, as in the Iguanodon, into 

 the substance of the coronal dentine. This substance consists, as in the 

 Crocodile, of fine and close set calcigerous tubes, arranged according 

 to the usual law ; and much resembling that of the tooth of the vara- 

 nian Monitor figured in PI. 67 : the calcigerous tubes have a diameter 

 of 16 Jooth of an inch : with interspaces equaUing about four of these dia- 



s 2 



