350 BRITISH FOSSIL REPTILES. 



inch, with interspaces varying between two and three times that diameter. They 

 radiate from the pulp-cavity at right angles with the external surface of the tooth. 

 The primary curvatures correspond with those of the dentinal tubules in the Varanus, 

 figured in my •'Odontography,' pi. 67, fig. 2; but they are less marked, so that the 

 tubules appear straightcr in the Megalosaurus. After their origin they dichotomize 

 sparingly, but the number of minute secondary branches sent off into the intermediate 

 substance is very great. These secondary branches proceed at acute angles from the 

 primary tubules ; the divisions of the latter become very frequent near the periphery 

 of the dentine, and the terminal branches dilate into, or inosculate with, a stratum 

 of minute calcigerous cells, which separates the dentine from the enamel.* No part 

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



A series of teeth from individual Megalosauri of different ages has been selected 

 from specimens in the British Museum, and in the Geological Museum at Oxford, 

 progressively diminishing in size, but preserving the same characteristic form, from 

 fig. 4 to fig. 9, inclusive, PI. 33. Fig. 3 shows a specimen, imbedded in Stonesfield 

 slate, which shows a somewhat more slender termination than usual. Fig. 11 is a 

 much-worn and shed tooth, apparently of a small-sized Megalosaurus, in which both 

 the point and the trenchant margins had been rubbed down to a smooth obtuse surface : 

 it may 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 Megalosaurus in the Oxford Museum. Some more advanced, as at b, 

 fig. 1, PI. 33, show their crowns projecting from alveoli already formed by the plate 

 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, 

 as at c, c, at the inner side of the basal interspaces of the triangular plate, between 

 them and the true internal alveolar parapet. There can be no doubt that, in the 

 course of the development of these teeth, corresponding changes take place in the jaw 

 itself, by which new triangular plates and alveolor partitions are formed, as the old 

 ones become absorbed, analogous to these concomitant changes in the growth and 

 form of the teeth, alveoli, and jaws, which take place in so striking a degree in the 

 Elephant.f 



The peculiarity of the Megalosaurus, as compared with the Crocodiles and Lizards 



* The microscopic characters of the tooth of the Megalosaurus are represented in my ' Odontography,' 

 pi. 70 A, in part of a transverse section of the middle of the crown, including the pulp-cavity and its osteo- 

 dentine. 



f See ' Odontography,' p. 625. 



