VIII. It might have been expected that the head would have escaped modifications, on account of the importance of the organs which belong to it. But such is not the case, and here again the modifications are much greater in animals than in man. Blumenbach remarked long ago that there was more difference between the head of a domestic pig and the wild boar than between that of the White and the Negro. There are no domestic species to which the same remark cannot be applied. But I shall only remind the reader of the heads of the bull-dog, greyhound and spaniel. The extent to which the modifications of the head can be carried is nowhere more plainly shown than in the _niata_ cattle of Buenos Ayres and La Plata. This ox exhibits the modifications of the specific characters similar to those which the bull-dog presents among dogs. All the forms are shortened and thickened, the head in particular seeming to have experienced a general movement of concentration. The inferior maxillary bone, although itself shortened, so far exceeds the superior in length that the animal is unable to browse the trees. The cranium is as much deformed as the face; not only are the forms of the bones modified, but also their relations, not one of which, according to Professor Owen, has been strictly preserved. This race, though perfectly established, is not therefore necessarily of less recent origin; for, as I remarked above, all the American oxen are descended from European stocks. It is already represented in the New World by two sub-races, one of which, that of Buenos Ayres, has preserved the horns, while that of Mexico has lost them. It is scarcely necessary to remark that no human group presents anything at all analogous to this. IX. The several facts which I have here enumerated seem to me sufficient to justify the proposition which I asserted at the commencement of the chapter, namely:—that the limits of variation are almost always more extensive between certain races of animals than between the most distant human groups. Consequently, however great the differences existing between these human groups may be, or may appear to be, to consider them as _specific characters_ is a perfectly arbitrary estimation of their value. It is, to say the least, quite as rational, quite as scientific, to consider these differences only as _characters of race_, and even on that account to refer all the human groups to a single species.