URSUS SPEL^EUS. 99 



instrument in ulterior endeavours to solve the higher and 

 more general problems in zoology. 



Observation has well determined the extent of modifica- 

 tion which the skull of a carnivorous species may undergo 

 according to age, to sex, to the free or the constrained 

 exercise of its destructive weapons ; and the relative size of 

 the intermuscular crests, the relative strength of the zygo- 

 matic arches, and the proportions of the canines to the other 

 teeth are well known to vary within certain limits. 



But in the Ursus spelaus we have to account for the 

 greater relative size and complexity of certain molar teeth ; 

 for the more extended diastemata, accompanying more 

 lengthened jaws ; for a premature loss of certain teeth and 

 their sockets, without any predominating development of 

 neighbouring canines to account for it ; for narrower zygo- 

 mata, with longer and higher parietal crests ; for large 

 frontal sinuses impressing a striking and readily recognis- 

 able feature upon the skull. 



M. de Blainville has endeavoured to explain the last- 

 cited modification, on the supposition that the primaeval 

 Bears had their frontal sinuses more developed in virtue of 

 their respiring a fresher, drier, and more invigorating atmos- 

 phere than their less fortunate and degenerated descend- 

 ants.* But we may question whether the flat-headed 

 Ursus ferox has a less exposed locality or breathes a more 

 humid and impure atmosphere on the rocky mountains in 

 the far west of North America, than did the Cave Bears 

 of the ancient German and British forests ; and we may 



* " L'intensite meme de Tacte respiratoire dans les lieux plus decouverts, ou 

 fair est plus vif, plus sec, plus frais, developpe tous les sinus que se trouvent sur 

 le trajet de Pair, et, des-lors, les frontaux sent dans ce cas aussi bien que tous 

 ceux qui entourent les fosses nasales ; des-lors aussi, par 1'ecartement des deux 

 lames de 1'os, le gonflement des fosses frontales, independantes et separees par un 

 sillon." De Blainville, Osteoffr., des Ours, p. 36. 



H 2 



