Structure of the Fossil Sauria?is. 347 



3. Mosasai/rus Conybeare. 

 The remains of this colossal animal, which was long known 

 by the name of the Crocodile of Maestricht, have employed 

 several of the most distinguished anatomists in various ways. 

 The teeth of this animal are hollow only during their period 

 of growth: they fill out at a later period, and become quite 

 solid. The crowns of the teeth are pyramidal, and somewhat 

 bent; their outer side is even, and possesses two sharp edges, 

 by which it is distinguished from the inner side, which is 

 round, or, at least, semiconical. The crowns of the teeth are 

 placed on a basis of a peculiar substance, with which they are 

 intimately connected ; and with these bones the teeth are 

 placed in actual alveoli. The replacing tooth arises in a pe- 

 culiar alveolus, and presses, now aside, now across, through the 

 bony substance which bears the tooth. The existing tooth 

 thus became loosened, and fell out by a kind of necrosis. 

 The structure of the teeth is therefore similar to that of the 

 osseous Fishes, Monitors, other Saurians, and Ophidians : that 

 of the Crocodiles and Cetacea, is different. In the lower jaw 

 are 14 teeth, and the creature may have had as many in the 

 upper. In the arrangement of the lower jaw it closely re- 

 sembles the Monitor; from which, however, it is distinguished 

 by other peculiarities. The palate bone has, it appears, borne 

 8 teeth. By means of this provision, the animal approaches 

 the actual Lizards or Iguanas. These teeth are formed like 

 those of the jaw, but are smaller. As regards the resemblance 

 of the head, the animal is placed between the Monitor and 

 Iguana. As respects the vertebra?, the posterior surface is 

 evidently convex, and the anterior only concave * ; in which 

 particular it resembles those of the Crocodile. But the other 

 arrangements of the vertebrae differ considerably from those 

 which have been discovered in the Saurians hitherto known. 

 Five different kinds of vertebrae, characterised by their pro- 

 cesses, are distinguished in the spinal column. The last caudal 

 vertebra? have no processes, and their length is one half less 

 than their height. The animal must have possessed a very 

 broad vertical tail, which it could only move sidewise right 



* In his Discours stir les Revolutions, &c, as well as in the previous 

 4to edition of his Osscmens Fossiles (p. 152.), as also in the 8vo editions, 

 and even in the last, the 6th, 1830 (p. 320.J, Cuvier says that the verte- 

 bra? of this animal are anteriorly convex and posteriorly concave ; which 

 directly contradicts what he states in describing the single parts of the 

 animal (Oss. Foss., torn. ii. p. 326.), where he expressly remarks, "All 

 the vertebra?, like those of the living Crocodiles, Monitors, and most of 

 the Saurians and Ophidians, are anteriorly concave, and posteriorly con- 

 vex." As yet, the former statements have passed into the translations. 



