ON BRITISH FOSSIL MAMMALIA. 67 



in the remaining bones of the extremities of the Ursus spelams, but the co- 

 incidence of such appreciable modifications in the femur, ulna, humerus, 

 with those in the form and proportions of the head, and in the form and the 

 relative size of certain teeth, seem to offer as good grounds for the specific 

 distinction of the Ursus spclceus as for that of the Ursus maritimus, or any 

 other existing species proposed by Pallas and Cuvier, and admitted by the 

 best modern zoologists. 



The question which the Palaeontologist ought to propose to himself in his 

 first survey of the fossils of any particular district, is the value of the distinc- 

 tive characters which such remains may present, as compared with those 

 which distinguish species, according to the zoological systems and principles 

 of the time being. For if he disregard or suppress such differential cha- 

 racters in the fossils, because the limits of variation by the influence of time 

 and surrounding circumstances may not be determined, he rejects one of the 

 valuable means whereby the ultimate resolution of such higher and more 

 general questions in zoology may be effected. 



To refuse to recognise such differences as have been .pointed out in the 

 skeleton of the great Cave Bear, because they may be possibly or hypothe- 

 tically accounted for by degeneration of the specific type, and thereupon to 

 record the fossil species as the primaeval Ursus arctos, seems a voluntary- 

 abandonment of the most valuable instrument in all ulterior inquiries. 



Observation has well determined the extent of modification 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 zygomatic arches 

 and the proportions of the canines to the other teeth are well known to vary 

 within certain limits. 



But in the Ursus speleeus 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 zygomata, with longer and higher 

 parietal crests ; for large frontal sinuses impressing a striking and readily 

 recognisable feature upon the skull. 



It has been endeavoured to explain the last-cited modification, by assert- 

 ing that the primasval Bears had their frontal sinuses more developed in 

 virtue of their respiring a fresher, drier, and more invigorating atmosphere 

 than their less fortunate and degenerated descendants*. 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 of North 

 America, than did the old Cave Bears of the German and British forests ; 

 and we may more than doubt that the cold and bracing sea-breezes inhaled 

 by the still flatter-headed Polar Bear, should be less efficient in expanding 

 the sinuses along the respiratory tract, than the musty air of the sepulchral 

 retreats in which the Cave Bears slept. 



Existing species of Bears, reckoned distinct by modern zoologists, do in 

 fact differ in the relative convexity of their forehead, and the flat-headed 

 species, as the Polar and American Bears, are unquestionably not those which 

 habitually respire the least pure and invigorating air. Instead of speculating 



* "L'intensitememe de l'acte respiratoire dans les lieux plus decouverts, ou l'air est plus vif, 

 plus sec, plus frais, developpe tous les sinus qui se trouventsur le tiajet 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 I'ecarteroent des deux lames de l'os, le gonflement des fosses frontales, independantes 

 et separees par un sillon." — De Blainville, Osleogr., p. 36. 



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