Sheep and goats agree together and differ from oxen in being usually of smaller size; the tail is shorter, the horns of females are much smaller than those of males, they lack the accessory column on the inner side of the upper molars, and the cannon bone is longer and more slender; but when it comes to a comparison of the one with the other, it is by no means always easy to tell the difference. It is true that the early Greeks seem to have had a rough and ready rule under which mistakes were not easy, for Aristotle tells us "Alcmaeon is mistaken when he says that goats breathe through their ears," but the severely practical methods of our own day leave us little but some very minute points of difference. One of the best of these lies in the shape of the basi-occipital bone, but naturally this can be observed only in the prepared skull. The terms often employed to denote difference in the horns can have only a general application, for they break down in certain species in which the two groups approach each other. The following table expresses some fairly definite points of separation: SHEEP (_Ovis_). GOAT (_Capra_). 1. Muzzle hairy except between 1. Muzzle entirely hairy. and just above the nostrils. 2. Interdigital glands on all 2. Interdigital glands, when the feet. present, only on fore feet. 3. Suborbital gland and pit 3. Suborbital gland and pit usually present. never present. 4. No beard nor caprine 4. Male with a beard and smell in male. caprine smell. 5. Horns with coarse transverse 5. Horns with fine transverse wrinkles; yellowish striations, or bold knobs or brown; sub-triangular in front; blackish; in male in male, spreading outward more compressed or angular, and forward with a sweeping backward circular sweep, points with a scythe-like curve or turned outward and forward spirally, points turned upward and backward. These features are distinctive as between most sheep and most goats, but the Barbary wild sheep (_Ovis tragelaphus_) has no suborbital gland or pit, a goat-like peculiarity which it shares with the Himalayan bharal (_Ovis nahura_), in which the horns resemble closely those of a goat from the eastern Caucasus called tur (_Capra cylindricornis_), which for its part has the horns somewhat sheep-like and a very small beard. This same bharal has the goat-like habit of raising itself upon its hind legs before butting. Both groups are a comparatively late development of the bovine stock, as they do not certainly appear before the upper Pliocene of Europe and Asia, and even at a later date their remains are not plentiful. Goats appear to have been rather the earlier, but are entirely absent from America.