100 



FOSSIL MAMMALIA OF THE 



Fig. 19. 



Moschus, we should be justified, if we knew that animal solely by its petrified jaws and 

 dentition, in concluding that its canines, notwithstanding their formidable development 

 and their position as " held well apart," with " the points of penetration doubled, the 

 dilacerating and killing powers multiplied," ^ were, nevertheless, not used for predaceous 

 ends, but merely as weapons of sexual combat and defence. Similarly, a reference to the 

 molars of Plagiaulax and Thylacoleo teaches that the approximate laniaries, " placed colla- 

 terally in the axis of the jaws, one on each side, above and below,"^ were related to 

 carnivorous habits. 



As beautiful as they are true are the laws of correlation rightly discerned. With the 

 carnivorous type of dentition of I^lagimdax are associated the characters of the carnivorous 

 type of mandible (fig. 12). With the herbivorous teeth of Hypsiprymnus go the high-placed 

 condyle, the small sloping coronoid, and the extension of jaw below the condyle for adequate 

 implantation of the pterygoid muscles chiefly concerned in the working of molars framed 

 for grinding vegetable substances (figs. 13 and 14). 



In my memoir on the Aye-aye 1 had to note that the mandibular condyle was " sessile, 



narrow, rather long, convex both across and 

 lengthwise, and placed on the level of the 

 grinding teeth," and I remarked that " the 

 sessile condyle contrasts strongly with the 

 pedunculate one, especially in the small ex- 

 tinct ferines {Plagiaulax and Triconodon) of 

 the Purbeck beds, a concomitant difiference 

 being shown in the dentition ; trenchant 

 teeth, grooved as in the lower carnassials of 

 Thylacoleo, take the place of the flat-crowned 

 molars of Cheiromys."^ 

 Prior to this discovery no such low position of the mandibular condyle was known, "hi 

 any herbivorous or mixed-feeding Mammal," supposing the Aye-aye to be such. 



De Plain ville had stated that the condyle was " nearly at the posterior extremity of the 

 entire jaw,"* and he might have affirmed it to be quite there ; but of its relative position to 

 the alveolar series neither the text gave information, nor did the figure of the skull with the 

 co-articulated mandible permit of a certain conclusion on that point. Dr. Falconer 

 reproducing the same view of the detached mandibular ramus of Cheiromys which I 

 had given in pi. 20, figs. 7, 8, of my memoir (see fig. 19), omits any notice of that 

 figure. He cites only the work which I published the year before I received the unique 



' Falconer, ' Quarterly Journal,' &c., p. 352, ' Palaeontological Memoirs,' p. 435. 



2 lb., ib., p. 352; ib., p. 435. 



' 'Transactions of the Zoological Society of London,' vol. v, pt. 2, 4to, 1863 (read January 14 and 

 28, 1862), pp. 50, 81. 



* "Presque a I'extremite posterieure de toute la machoire," ' Osteographie, Memoire sur I'Aye-aye,' 

 p. 19. 



Cheiromys: mandible and teeth, the incisor exposed: nat. 

 size. 



