290 PALEONTOLOGY. 



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 shewn 

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

 museum. Some, more advanced, shew 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, 

 between them and the true internal alveolar parapet. In 

 the course of the development of these teeth, corresponding 

 changes take place in the jaw itself, by which new triangular 

 plates and alveolar partitions are formed, as the old ones 

 become absorbed ; analogous to those concomitant changes 

 in the growth and form of the teeth, alveoli, and jaws, 

 which take place in so striking a degree in the elephant. 

 The peculiarity of the Megalosaur, as compared with the 

 crocodiles and lizards, which have a like endless succession of 

 teeth, is the deeper position of the successional tooth (fig. 98, 

 c), in relation to the one (ti) it is destined to replace, and the 

 great proportion of the tooth which is formed before it is pro- 

 truded. The anterior tooth a in this specimen shews at the 

 inner side of its base the commencing absorption stimulated 

 by the encroaching capsule of the successional tooth c below, 

 the crown of which is completed externally, though not con- 

 solidated. On one of the fractured margins of this piece of jaw, 

 a part of the basal shell of an absorbed and shed tooth remains, 

 with part of the root of the successional tooth, which has risen 

 into place, but which shews its base full of matrix, the pulp 

 not having been calcined at that period of the tooth's growth. 



