The least technical, and for the present purpose the most useful of the characters distinguishing existing deer from all of the bovine stock, lies in the antlers, which are solid, of bony substance, and are annually shed. They are present in the males of all species except the Chinese water deer, and the very divergent musk-deer, which probably should not be regarded as a deer at all. They are normally absent from all females except those of the genus Rangifer. Most deer have canine teeth in the upper jaw, though they are absent in the moose, in the distinctively American type and a few others. The cleaned skull always shows a large vacuity in the outer wall in front of the orbit, which prevents the lachrymal bone from reaching the nasals. No deer has a gall bladder. There are many other distinctions, but as all have exceptions they are of value only in combinations.
The earliest known deer, belonging to the genus Dremotherium, or Amphitragulus, from the middle Tertiary of France, were of small size and had four toes, canine teeth and no antlers. Their successors seem to have borne simple forked antlers or horns, probably covered with hair, and permanently fixed on the skull. Very similar animals existed in contemporaneous and later deposits in North America. From this point the course of progress is tolerably clear as to deer in general, although we are not sure of all the intermediate details—for it must not be forgotten that a series of types exhibiting progressive modifications in each succeeding geological period is quite as conclusive in pointing out the genealogy of an existing group as if we knew each individual term in the ancestral series of each of its members. Thus we do not yet know whether the peculiar antler of the distinctively American deer, of the genus Mazama, is derived from an American source or took its origin in the old world, for the fossil antlers known as Anoglochis, from the Pliocene of Europe, are quite suggestive of the Mazama style, but as nothing is known of the other skeletal details of Anoglochis, any such connection must at present be purely speculative, but the element of doubt in this special case in no way disturbs the certainty of the general conclusion that all our present Cérvidae have come through distinct stages in the successive periods, from the simple types of the middle Tertiary.
The family is undoubtedly of old world origin, and for the most part belongs to the northern hemisphere, South America being the only continental area in which they are found south of the equator.
The analytical habit of mind which finds vent in the subdivision of species, is also exhibited in a tendency to break up large genera into a number of small ones, but in the present group this practice has the disadvantage of obscuring a broad distinction between the dominant types inhabiting respectively the old world and the new. The former, represented by the genus Cervus, has a brow-tine to the antlers; has the posterior portion of the nasal chamber undivided by the vertical plate of the vomer; and the upper ends only of the lateral metacarpals remain, whereas in all these particulars the typical American deer are exactly opposite. As there are objections to considering these characters as of family value, arising from the intermediate position of the circumpolar genera Alces and Rangifer, as well as the water deer and the roe, a broader meaning is given to classification by retaining the comprehensive genera Cervus and Mazama, and recognizing the subordinate divisions only as sub-genera.
The one representative of Cervus inhabiting America is the wapiti, or "elk" (C. canadensis), which is without doubt an immigrant from Asia by way of Alaska, and it may be of interest to state the grounds upon which this conclusion rests, as they afford an excellent example of the way in which such results are reached. It is an accepted truth in geographical distribution, that the portion of the earth in which the greatest number of forms differentiated from one type are to be found, is almost always the region in which that type had its origin. Now, out of about a dozen species and sub-species of wapiti and red deer to which names have been given, not less than eight are Asiatic, so that Asia, and probably its central portion, is indicated as the region in which the elaphine deer arose; in confirmation of which is the further fact that the antler characteristic of these deer seems to have originated from the same ancestral form as that which produced the sikine and rusine types, which are also Asiatic. From this centre the elaphines spread westward and eastward, resulting in Europe in the red deer, which penetrated southward into north Africa at a time when there was a land connection across the Mediterranean. In the opposite direction, the nearer we get to Bering's Straits the closer is the resemblance to the American wapiti, until the splendid species from the Altai Mountains (C. canadensis asiaticus), and Luehdorf's deer (C. c. luehdorfi) from Manchuria, are regarded only as sub-species of the eastern American form, which they approach through C. c. occidentalis of Oregon and the northwestern Pacific Coast.
This evidence is conclusive in itself, and is further confirmed by the geological record, from which we know that the land connection between Alaska and Kamtschatka was of Pliocene age, while we have no knowledge of the wapiti in America until the succeeding period.
While there is not the least doubt that the smaller American deer had an origin identical with those of the old world, the exact point of their separation is not so clear. Two possibilities are open to choice: Mazama may be supposed to have descended from the group to which Blastomeryx belonged, this being a late Miocene genus from Nebraska, with cervine molars, but otherwise much like Cosoryx, which we have seen to be a possible ancestor of the prong-horn; or we may prefer to believe that the differentiation took place earlier in Europe or Asia, from ancestors common to both. But there is a serious dilemma. If we choose the former view, we must conclude that the deciduous antler was independently developed in each of the two continents, and while it is quite probable that approximately similar structures have at times arisen independently, it is not easy to believe that an arrangement so minutely identical in form and function can have been twice evolved. On the second supposition, we have to face the fact that there is very little evidence from palaeontology of the former presence of the American type in Eurasia. But, on the whole, the latter hypothesis presents fewer difficulties and is probably the correct one; in which case two migrations must have taken place, an earlier one of the generalized type to which Blastomeryx and Cosoryx belonged, and a later one of the direct ancestor of Mazama. There is little difficulty in the assumption of these repeated migrations, for evidence exists that during a great part of the last half of the Tertiary this continent was connected by land to the northwest with Asia, and to the northeast, through Greenland and Iceland, with western Europe.
The distinction between the two groups is well marked. All the Mazama type are without a true brow-tine to the antlers; the lower ends of the lateral metacarpals only remain; the vertical plate of the vomer extends downward and completely separates the hind part of the nasal chamber into two compartments; and with hardly an exception they have a large gland on the inside of the tarsus, or heel. The complete development of these characters is exhibited in northern species, and it has been beautifully shown that as we go southward there is a strong tendency to diminished size; toward smaller antlers and reduction in the number of tines; to smaller size, and finally complete loss of the metatarsal gland on the outside of the hind leg; and to the assumption of a uniform color throughout the year, instead of a seasonal change.
The two styles of antler which we recognize in the North American deer are too well known to require description. That characterizing the mule deer (Mazama hemionus) and the Columbia black-tailed deer (M. columbiana), seems never to have occurred in the east, nor south much beyond