196 PETRIFACTIONS AND THEIR TEACHINGS. CHAP III. 



of the original, and was presented to me by Baron Cuvier in 

 1825. It is four and a half feet in length, and two and 

 a half in width. It consists of both jaws, with numerous 

 teeth, (the pterygoids bearing teeth as in the Iguanas,) and the 

 os quadratum; and there are likewise fragments of costal 

 processes, and one of the metatarsal or metacarpal bones : 

 two of the large echinoderms that abound in the Maestricht 

 deposits are imbedded in the block. The parts preserved in 

 this celebrated specimen are the following : 



The superior maxillary, or jaw-bone, of the right side, with eleven 

 teeth ; seen on its inner aspect. 



The anterior part of the upper maxillary bone of the left side, which 

 is displaced, and lies across the posterior part of the left ramus of the 

 lower jaw. 



The right pterygoid, with eight teeth. 



The left pterygoid ; all the teeth are wanting. 



The premandibular part of the left ramus of the lower jaw, with 

 fourteen teeth, seen on its outer aspect : a row of ten or twelve vascular 

 foramina runs parallel with the alveolar ridge. 



The right ramus of the lower jaw, with the teeth, seen on the inner 

 aspect ; the posterior part is somewhat concealed by the palatine bones. 



The left os quadratum, or tympanic bone, lying above the concave 

 articular facet of the lower jaw. 1 



The crown of the tooth of the Mosasaurus is of a pyra- 

 midal form, slightly recurved backwards, with a smooth coat 

 of enamel ; the largest is from 2| to 3 inches in length. 

 The tooth expands at the base into a large conical mound or 

 root (If inch in diameter), which is anchylosed to the 

 summit of the alveolar ridge ; a mode of implantation that 

 is termed acrodont. The outer face of the crown is very 

 slightly convex, and separated by two sharp crests from the 

 inner, which is semi-conical. The pulp cavity is generally 

 found open in the centre of the base of the crown j and 

 the germ of the successional tooth appears on the inner 

 side of the expanded base. The teeth of the pterygoid bones 

 are symmetrical, their transverse section being elliptical. 



Part of a lower Jaw of Mosasaurus. On the ledge over 

 the specimen above described is placed a very fine example 



1 For details, consult " Ossemens Fossiles" tome v. p. 319. I cannot 

 explain why the tympanic bone, which is so striking an object in the 

 model, is omitted in the figures of Faujas St. Fond, Cuvier, &c. and in 

 the hundred engravings of this fossil that have since appeared. 



