URSUS SPELAMUS. 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 speleus 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 primeeval 
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 
* “T,intensité méme de I’acte respiratoire dans les lieux plus découverts, ou 
Yair est plus vif, plus sec, plus frais, développe tous les sinus que se trouvent sur 
le trajét de l’air, et, des-lors, les frontaux sont dans ce cas aussi bien que tous 
ceux qui entourent les fosses nasales ; des-lors aussi, par l’écartement des deux 
lames de l’os, le gonflement des fosses frontales, indépendantes et separées par un 
sillon.”—De Blainyille, Ostéogr., des Ours, p. 36. 
H 2 
