399 Dr. Knox on the Structure of 
The anatomy and natural history of any species of animal, fully 
observed and clearly understood, may enable us to decide on the 
anatomy and natural history of an animal unknown to us, pro- 
vided they accord entirely or nearly so: and more especially in 
some natural families, such as the strictly carnivorous tribes, a tooth, 
a fragment of bone, or other remains of structure, may enable us to 
conjecture, with some show of probability, that the animal, whether 
fossil or otherwise, may have belonged to a species or genus allied 
in a certain degree to those with which we are already acquainted ; 
and we may even admit-as certain, that a hoof such as that-of the 
horse and ox, never yet were combined with other structures im- 
plying carnivorous habits. Neither will it require any great stretch 
of the imagination to believe, that animals having the bulk of the 
mammoth, could not possibly subsist amidst the frozen regions of 
Siberia ; nor plants having a seeming resemblance to our present 
intertropical vegetable kingdom, could possibly grow and flourish 
in regions deomed to a comparative absolute sterility, and to a 
dwarfish stunted vegetable growth. To theories of this kind we 
may fairly object that heat is essential to life ; and to theorists of 
another kind, who venture to declare a priori, and without having 
any knowledge of the animal previously, its anatomy and its natu- 
ral history,—from the observance of a portion or a fragment of the 
bones of the foot, a portion of the skull or a tooth,—that they can- 
not preduce a single instance of their having ever done so, as not 
to admit of refutation, or at least of doubt. The claws and nail- 
bones of the sloth, indicate nothing of its peaceful and frugiverous 
habits ; and to assimilate its habits and anatomical structure with 
certain gigantic fossil remains, is it, not to use a harsher style of 
criticism, eminently imaginative and fantastic? The molar teeth 
of bears are not carnivorous molar teeth ; and it is only by the ob- 
servation of the living species, that we have become aware of the 
frugivorous habits of some of the strictly carnivorous polar species. 
To speculate from such facts as these on the anatomy and natu- 
ral history of the extinct Ursus speleus, must to every reflecting 
mind appear exceedingly ridiculous. The strength of the zygoma- 
tic arch of the dugong exceeds that of the lion, and yet how op- 
posed these animals are to each other in their habits and general 
economy. The habits even of genera closely resembling each other, 
occasionally do net accord. Antelopes live in pairs, in small fami- 
lies, er congregated in thousands: the zebra is seen in groupes only 
of two or three ; whilst the quagga, resembling it so as to be often 
confounded with it, feeds in flocks on the wide-extended plains of 
Africa. Lastly, by what fact in the internal or external structure 
of the hippopotamus, could the anatomist have decided, a priort, 
that the animal was aquatic? | 
Nor can we decide on the relation of different organs or struc- 
tures to each other. We cannot predict, for example, that an ani- 
mal will necessarily ruminate, because we find its upper jaw un- 
provided with incisive teeth, nor that there is any constant relation 
