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.
The number of distinct species of sheep in our fauna is a matter of too much uncertainty to be treated with any sort of authority at this time. Most of us grew up in the belief that there was but one, the well-known mountain sheep (Ovis canadensis), but seven new species and sub-species have been produced from the systematic mill within recent years, six of them since 1897. It is no part of the purpose of the present paper to dwell upon much vexed questions of specific distinctness, and it will only be pointed out here that the ultimate validity of most of these supposed forms will depend chiefly upon the exactness of the conception of species which will replace among zoologists the vague ideas of the present time. Whatever the conclusion may be, it seems probable that some degree of distinction will be accorded to, at least, one or two Alaskan forms.
As sheep probably came into America from Asia during the Pleistocene, at a time when Bering's Strait was closed by land, it might be expected that those now found here would show relationship to the Kamtschatkan species (Ovis nivicola); and such is indeed the case, while furthermore, in the small size of the suborbital gland and pit, and in comparative smoothness of the horns, both species approach the bharal of Thibet and India, which in these respects is goat-like.
When one considers the poverty of the new world in bovine ruminants, it seems strange that three such anomalous forms should have fallen to its share as the prong-horn, the white goat and the musk-ox, of none of which have we the complete history; two of the number being entirely isolated species, sometimes regarded as the types of separate families.
The prong-horn is a curious compound. It resembles sheep in the minute structure of its hair, in its hairy muzzle, and in having interdigital glands on all its feet. Like goats, it has no sub-orbital gland nor distinct pit. Like the chamois, it has a gland below and behind the ear, the secretion of which has a caprine odor. It has also glands on the rump. It is like the giraffe in total absence of the accessory hoofs, even to the metapodials which support them. It differs from all hollow horned ungulates in having deciduous horns with a fork or anterior branch. There is not the least similarity, however, between these horns and the bony deciduous antlers of deer, for, like those of all bovines, they are composed of agglutinated hairs, set on a bony core projecting from the frontal region of the skull.
It is well known that these horn sheaths are at times shed and reproduced, but the exact regularity with which the process takes place is by no means certain, although such direct evidence as there is goes to prove that it occurs annually in the autumn. Prong-bucks have shed on eight occasions in the Zoological Gardens at Philadelphia, five times by the same animal, which reached the gardens in October, 1899, and has shed each year early in November, the last time on October 22, 1903,[1] and the writer has seen one fine head killed about November 5 in a wild state, on which the horn-sheaths were loose and ready to drop off.
[Footnote 1: It is interesting to note that the first pair shed measured 7–¼ inches, on the anterior curve; the second pair 9–½, and the last three 11 inches each. The largest horns ever measured by the writer were those of a buck killed late in November, 1892, near Marathon, Texas, and were 15–¾ inches in vertical height and 21 along the curve.]
But few of these delicate animals have lived long enough in captivity to permit study of the same individual through a course of years, and the scarcity of observations made upon them in a wild state is remarkable. That irregularity in the process would not be without analogy, is shown by the case of the Indian sambur deer, of which there is evidence from such authority as that king of sportsmen, Sir Samuel Baker, and others, that the shedding does not always occur at the same season, nor is it always annual in the same buck; and by Pore David's deer, which has been known to shed twice in one year.
When resemblances such as those of the prong-horn are so promiscuously distributed, the task of fixing their values in estimating affinities is not a light one, and in fact the most rational conclusion which we may draw from them is that they point back to a distant and generalized ancestor, who possessed them all, but that in the distribution of his physical estate, so to speak, these heirlooms have not come down alike to all descendants. There is again a complicating possibility that some may be no more than adaptive or analogous characters, similarly produced under like conditions of life, but quite independent of a common origin, and it is seldom that we know enough of the history of development of any species to conclude with certainty whether or not this has been the case. At all events, the prong-buck is quite alone in the world at present, and we know no fossils which unmistakably point to it, although it has been supposed that some of the later Miocene species of Cosoryx—small deer-like animals with non-deciduous horns, probably covered with hair, and molars of somewhat bovine type—may have been ancestral to it, but this is little more than a speculation. What is certain is that Antilocapra is now a completely isolated form, fully entitled to rank as a family all by itself.
In the musk-ox (Ovibos moschatus), or "sheep-ox," as the generic name given by Blainville has it, we meet with another strange and lonely form which has contributed its full share to the problems of systematic zoology. Its remote and inaccessible range has greatly retarded knowledge of its structure, and it is only within the last three years that acquaintance has been made with its soft anatomy, and at the same time with a maze of resemblances and differences toward other ruminants, that perhaps more than equals the irregularities of the prong-buck. But unlike that species, there is in the musk-ox no extreme modification, such as a deciduous horn, to separate it distinctly from the rest of the family. A recapitulation of these differences would be too minutely technical for
