244 PETRIFACTIONS AND THEIR TEACHINGS. CHAP III. 



Inches. 



Greatest thickness at the posterior part 2| 



Length of the alveolar parapet for twenty teeth ... 15 

 Breadth from the anterior termination of the alveolar 



space across to the inner margin 4 



Height of the alveolar parapet at the posterior part. . 2 



Width of the alveolar space at the posterior part ... 1 



Width of the alveolar space at the anterior part ... f 

 Length from the first anterior tooth to the symphysial 



extremity 5 



Height of the successional tooth (a, Lign. 53) 1^ inch; 



greatest width |. 



The mesial or inner aspect of the fossil (Lign. 54) is flat 

 and smooth ; it shows the crown of a large successional tooth, 

 (a,) and the small germs of two other teeth, in their original 

 situations, and the sockets for nineteen or twenty teeth ; 

 the inner alveolar plate having been destroyed, and the 

 mature molars dislodged, before the bone was imbedded in 

 the rock. The deep conical groove or furrow, so constantly 

 present on the inner side of the dentary bone in reptiles 

 (and which, from its being covered by the splenial or 

 opercular piece, it may be convenient to designate the oper- 

 cular furrow), is here entirely exposed (6), in consequence 

 of the removal and destruction of that maxillary element. 

 It is very large, and prolonged anteriorly to within six inches 

 of the symphysis ; the opercular piece, in its elongated 

 form, must, therefore, have more nearly corresponded with 

 that of the Varariians or Monitors than with the Iguanas, in 

 which it is of a rhomboidal figure, and relatively of limited 

 extent. The lower margin of the jaw is thick and convex at 

 the posterior part, and gradually becomes thinner towards the 

 front, where it expands horizontally into a broad scoop-like 

 process, which is terminated anteriorly by an obtuse projection 

 or tubercle (Lign. 54, 55, c) - } it thins out mesially to form the 

 symphysial suture that connects it with the opposite ramus. 



The upper margin is formed by the alveolar process, which 

 has a thick external parapet, deeply furrowed on the inner 

 side by the sockets for the mature teeth ; strongly-defined 

 ridges occupy the interspaces, and rising above the sockets, 

 produce a sharp crenated upper border on the alveolar ridge. 

 The alveolar space is protected on the inner side by a mode- 

 rately, strong plate or wall, which must originally have almost 

 equalled the outer parapet in height, but is now in a great 



