WEALDEN FORMATIONS. 21 



are completely exposed, when the gum has been removed. In the Megalosaur the 

 greater relative development of the inner alveolar wall narrows the groove, and covers 

 a greater proportion of the bases of the teeth, besides concealing more or less 

 completely the germs of their successors. Moreover, instead of the mere shallow 

 impressions upon the inner side of the outer alveolar plate, to which the teeth are 

 attached in modern Lizards, there are distinct sockets formed by bony partitions con- 

 necting the outer with the inner alveolar walls in the jaw of the Megalosaurus. 



These partitions rise from the outer side of the inner alveolar wall in the form of 

 triangular vertical plates of bone, having their plane parallel with that of the inner 

 wall ; and from the middle of the outer side of each plate a bony partition crosses to 

 the outer parapet, completing the alveoli of the fully-formed or more advanced teeth, 

 the series of triangular plates, t, t, fig. 1 , forming a kind of zigzag buttress along the 

 inner side of those alveoli. The outer parapet rises an inch higher than the inner one. 

 Of the fully-developed teeth only one had been preserved in situ, in the specimen 

 under description ; the others appear rather to have slipped out, than to have been 

 broken off, the anchylosis of the basal capsule of the tooth to the alveolar periosteum 

 being but slight, and apparently taking place tardily in the Megalosaurus. 



This tooth, T. XI, fig. 1, a, exhibits the average size of the fully developed teeth 

 of the Megalosaurus that have yet been discovered. The shape of the crown is 

 well exemplified in this figure, and in figs. 2, 4, and 5 of T. XII. It is sub-com- 

 pressed, slightly recurved, sharp-edged and sharp-pointed ; the edges being minutely 

 serrated : the edge upon the convex or front border becomes blunted as it descends 

 about two thirds of the way towards the base of the tooth ; that upon the concave 

 hinder border it is continued to the base. The lower half of the crown is thicker 

 towards the fore- margin than towards the hind one, so that a transverse section gives 

 a narrow oval form pointed behind, as in the lower section of fig. 5, T. XII : at the 

 upper half of the crown the sides slope more equably from the middle thickest part to 

 both margins, and the section is a narrow pointed ellipse, as in the upper section of 

 the same figure. The crown is covered by a smooth and polished enamel which 

 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- 

 dentin e in the basal part of the completely formed tooth. Moderately magnified, the 

 surface of the enamel presents a finely wrinkled appearance. The marginal serrations 

 present, under a somewhat higher power, the form shown in fig. 12, T. XI; their 

 points being 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 

 of existing Crocodiles and most mammals is composed. The dentinal tubules, in the 

 Megalosaurus, are extremely fine and close-set, presenting a diameter of 53,555th of an 



