DINOSAURIA 261 



wholly forms the marginal serrations. The base of the tooth 

 is coated with a smooth, lighter-coloured cement, forming a 

 thin layer, and becoming a little thicker towards the implanted 

 end of the tooth. The remains of the pulp are converted into 

 osteo-dentine in the basal part of the completely formed 

 tooth. Moderately magnified, the surface of the enamel pre- 

 sents a finely wrinkled appearance. The marginal serrations 

 show, under a somewhat higher power, that the points are 

 directed towards the apex of the tooth — a structure well adapted 

 for dividing the tough tissues of the saurian integument. 



The main body of the tooth consists of dentine, of that 

 hard unvascular kind of which the same part of the teeth ol 

 existing crocodiles and most mammals is composed. No part 

 of the dentine is pervaded by medullary canals, as in the 

 Iguanodon. 



A series of teeth from individual Megalosaurs, of different 

 ages, are preserved in the British Museum and in the geological 

 museum at Oxford ; although differing in size, they preserve 

 the characteristic form above described. In one specimen the 

 point of the crown and the trenchant margins have been rubbed 

 down to a smooth obtuse surface ; it seems to have come from 

 the hinder part of the dental series, where the teeth may have 

 been smaller and less sharp, or more liable to be blunted by a 

 greater share in the imperfect act of mastication, than the 

 teeth in advance. 



Successional teeth in different stages of growth are shown 

 in the original portion of jaw of the Megalosaur in the Oxford 

 museum. Some, more advanced, show their crowns projecting 

 from alveoli already formed by the plates extending across 

 from the triangular processes before described : vacant sockets, 

 from which fully formed teeth have escaped, occur, generally 

 in the intervals between these more advanced teeth. The 

 summits of less developed teeth are seen protruding at the 

 inner side of the basal interspaces of the triangular plate, 



