190 BRITISH FOSSIL REPTILES. 



exoccipitals. The rough sutural surfaces for the articulation of these elements 

 were divided by a deep and narrow channel, which gradually expanded towards 

 the condyle. The anterior flat vertical articular surface of the basioccipital was 

 smooth, indicative of a persistent harmonia between it and the basisphenoid, 

 analogous to that which exists between the centrum of the axis and the odontoid 

 process. Two very thick and short exogenous processes (hypapophyses) diverge from 

 the under part of the anterior half of the basioccipital, and terminate in oblique and 

 slightly convex surfaces, irregularly pitted ; they resemble the hypapophyses sent off 

 from the basisphenoid in the great Monitor (Varanus), against which the pterygoids 

 abut. This form and structure of the basioccipital of the Mosasaurus harmonizes 

 with the other indications of its Lacertian affinities. The basi-occipital in the 

 Crocodilia sends down a single hypapophysis. 



No part of the organisation of the Mosasaurus is so little known as that of the 

 locomotive extremities. Cuvier gives copies of drawings which had been transmitted 

 to him of a portion of the scapula,* clavicle,! and coracoid,;}; of a portion of a long 

 bone, which he likens to the cubitus of a Monitor,'^ and of an os pubis, || all of which 

 he believes to have belonged to the Mosasaurus. 



The portion of the ulna would indicate, Cuvier remarks, that the Mosasamiis had 

 moderately elevated extremities ;^[ but he adds that " the bones of the fore and hind 

 feet, so far as they are known, would seem, on the contrary, to have belonged to a kind 

 of contracted fin, like that in the dolphin or Plesiosaur.^* He, however, figures two 

 bones comparable with the two principal bones of the carpus of the Crocodile,tt and 

 which one would scarcely expect to be associated with metacarpals and phalanges like 

 those of the Enaliosaurs. And if the ungual phalanx, figured in pi. xx, fig. 21, of 

 the * Ossemen's Fossiles,' be rightly attributed to the Mosasaurw-:, it determines the 

 question in the negative, as to whether that Lacertian reptile had plesiosaurian 

 paddles ; the phalanx in question much resembles that in the British Museum (No. 384, 

 Mantellian Catalogue), which has been described as "The Horn oi the Iffuanodon." The 

 phalanx represented in PL xx, fig. 5, of the same work, with almost flat articular 

 ends, must have belonged to a natatory form of foot ; but as large Chelonians were 

 associated with the Mosasaurus in the Maestricht beds, it would be rash to conclude 

 that this phalanx absolutely belonged to the Mosasaurus. Cuvier, in fact, sums up 

 by admitting the hesitation which he feels in offering his conjectures as to the nature 

 of the extremities of the Mosasaurus, which were founded on the inspection of drawings 



* Ossemen's Fossiles, torn, v, jot. 2, 4to, pi. xLx, fig. 9. t lb., fig. 14. 



X lb., fig. 15. § lb., pi. XX, fig. 24. II lb., pi. xLx, fig. 10. 



^ "11 annoncerait que ses extremites etaient assez 61evees." (lb., p. 336.) 



** "Les OS des mains et des pieds, autant qu'ou les coniiait, semblernieut au coutraire avoir appartenu 

 k des espfeces de nageoires assez coiitractees, et plus ou moius seuiblables a celles des dauphins ou des 

 plesiosaurus." (lb. p. 386.) -j-j- lb., pi. xx, figs. 4 and 5. 



