DIET ADAPTATIONS IN VARANUS NILOTICUS. 69 



grams. The difference in favour of the latter is thus 98 grams 

 and 2 decigrams. The skull of V. niloticus is consequently 

 not far from three times as heavy as that of the other one. 

 Several of the large teeth of the former are missing, had 

 they been present the weight had been increased with three 

 or four grams as each of the large molars weigh from three 

 to four decigrams or more. 



The stoutness that has been requisite for the skull of 

 Varanus niloticus to enable it to crush with its jaws as härd 

 objeets as Achatina-shells has influenced the development of 

 almost every part of it, but of course in the highest degree 

 the jaw-bones and adjoining parts of the skull. The diffe- 

 rence in this respect between the skulls of V. niloticus and 

 V. salvator may, to a great extent, be conspicuous on the 

 accompanying figures, but some measurements make this still 

 more plain. The greatest thickness of the lower jaw of V. 

 salvator in the posterior part of the dental region is 5 mm. 

 but in V. niloticus more than twice that, or 11 mm. The 

 greatest transverse thickness of articular e -ang ulare midway 

 between the coronoid and the articular surface is, in the former, 

 8 mm. in the latter 15 mm. The greatest thickness just in 

 front of the articular surface is in the former about 12 V 2 

 mm., in the latter I6V2 mm. The greatest transversal thickness 

 of articulare posteriorly is, in V. salvator 8 V 2 mm. and its 

 vertical thickness 5 mm., in V. niloticus resp. 17 and 10 mm. 

 The thickness of processus coronoideus anteriorly is in the 

 former about 4 V 2 mm. in the latter 7 V 2 mm., and so on. 

 In other words the lower jaw of V. salvator is a rather 

 slender bone and concave on the median side; in V. niloticus , 

 on the other hand, it is very heavy and not concave on the 

 inside. In a similar way the upper jaw is also much stouter 

 in V. niloticus than in V. salvator. The anterior expanded 

 part of the premaxillary has quite a difFerent shape in the 

 two species as it, in the former, is quadrangular (or some- 

 what pentagonal), in the latter it is semilunar. This differ- 

 ence in shape is due to the position of the suture between 

 the maxillary and the premaxillary,* which in V. niloticus 

 is longitudinal, in V. salvator transversal. I presume 

 that this also is an adaptation in V. niloticus standing 



The direction of the sutures may to same extent be seen on fig. 1 and 2. 



