SHEEP. The animals commonly designated by this name constitute the genus Ovis of zoologists, a group belonging to the Artiodactyle or paired-toed section of the Ungulata or hoofed mammals (see MAMMALIA, vol. xv. p. 432). They are ruminants, and belong to the hollow-horned section, i.e., those having persistent horns composed of conical epidermic sheaths, encasing and supported by processes of the frontal bone. This section includes the various species of Oxen, Goats, and Antelopes, as well as the Sheep, animals all so closely related structurally that it is by no means easy to define the differences between them.
In nearly all wild sheep the horns are present in both sexes, though smaller in the female. They are trigonal in section, having always three more or less distinctly marked surfaces, divided by edges running longitudinally to the axis of the horn, sometimes sharply prominent and some-times rounded off. They are also marked by numerous transverse ridges and constrictions, and present a strong more or less spiral curve, which varies in direction in different species. The teeth resemble generally those of the other Bovidse. The upper incisors and canines are entirely wanting, their place being taken by a callous pad against which the lower front teeth bite. These are eight in number, all much alike and in close contact; the outer pair represent the canines, the rest the incisors. - On each side of the mouth above and below are six teeth close together, three of which are premolars (replacing milk teeth) and three true molars, all markedly selenodont (the grinding surfaces presenting crescent-like patterns) and hypsodont, or with long crowns and small roots. The dental formula is thusincisors ^, canines premolars f-, molars §, = j-^; total of both sides 32. The vertebral formula iscervical 7, dorsal 13, lumbar 6 or 7, sacral 4, caudal variable. In the feet the hoofs of the two middle toes (third and fourth) only reach the ground, and are equally developed. The outer toes (second and fifth) are very rudimentary, represented only by small hoofs, without bony phalanges, and by the proximal or upper ends of the slender splint-like metacarpal or metatarsal bones. Between the two middle toes, in most species, is lodged a deep sac, having the form of a retort and with a small external orifice, which secretes an unctuous and odorous substance. This, tainting the herbage or stones over which the animal walks, affords the means by which, through the powerfully developed sense of smell, the neighbourhood of other individuals of the species is recog-nized. The crumen or suborbital gland, which is so largely developed and probably performs the same office in some antelopes and deer, is present, but in a comparatively rudimentary form, though varying in different species. The tail, though long in many varieties of domestic sheep, is short in all the wild species, in which also the external covering of the body is in the main hairy,the fine fleecy coats of wool, or hair so modified as to have the property of "felting" or adhering together under pressure, which give such value to many breeds, having been especially cultivated by selective breeding.
The sheep was a domestic animal in Asia and Europe before the dawn of history, though quite unknown as such in the New World until after the Spanish conquest. It has now been introduced by man into almost all parts of the world where settled agricultural operations are carried on, but flourishes especially in the temperate regions of both hemispheres. Whether our well-known and useful animal is derived from any one of the existing wild species, or from the crossing of several, or from some now extinct species, is quite a matter of conjecture. The variations of external characters seen in the different domestic breeds
[IMAGE] Moufflon (Ovis musimon). From a living animal in the London Zoological Gardens.
are very great. They are chiefly manifested in the form and number of the horns, which may be increased from the normal two to four or even eight, or may be altogether absent in the female alone or in both sexes; in the form and length of the ears, which often hang pendent by the side of the head; in the peculiar elevation or arching of the nasal bones in some Eastern races; in the length of the tail, and the development of great masses of fat at each side of its root or in the tail itself; and in the colour and quality of the fleece. See AGRICULTURE.
The distinction of the various permanent modifications under which wild sheep occur is a matter of considerable difficulty. Trivial characters, such as size, slight variations in colour, and especially the form and curvature of the horns, are relied upon by different zoologists who have given attention to the subject in the discrimination of species, but no complete accord has yet been established. The most generally recognized forms are enumerated below.
The geographical distribution of wild sheep is interesting. The immense mountain ranges of Central Asia, the Pamir and Thian Shan of Turkestan, may be looked upon as the centre of their habitat. Here, at an elevation of 16,000 feet above the sea-level, is the home of the magnificent Ovispoli, named after the celebrated Venetian traveller Marco Polo, who met with it in his adventurous travels through this region in the 13th century. It is remark-able for the great size of the horns of the old rams and the wide open sweep of their curve, so that the points stand boldly out on each side, far away from the animal's head, instead of curl-ing round nearly in the same plane, as in most of the allied species. A very similar if not identical species from the same origin, in which the horns retain their more normal development, has received the name of 0. karclini. Eastward and northward is found the argali (0. ammtm), with a wide and not very well determined range. Still further north, in the Stanovoi Mountains and Kamchatka, is 0. nivicola, and away on the other side of Behring's Strait, in the Rocky Mountains and adjacent high lands of western North America, is the "bighorn" or mountain sheep (0. montana), the only one of the genus found in that continent and indeedexcept the bison,the musk-ox (Oviios), mountain goat (Aploceras), and the prongbuck (Antilocapra)the only hollow-horned ruminant, being like the rest obviously a straggler from the cradle of its race. Turning southward from the point from which we started, and still a little to the east, in Nepal and Little Tibet, is 0. hodgsoni, a species with large and strongly curved horns, and another with smaller and more spreading horns, the burrhel, 0. nahoor. Passing in a south-westerly direction we find a series of smaller forms, 0. vignei of Ladak, 0. cycloceros of northern India, Persia, and Baluchistan, 0. gmelini of Asia Minor, 0. ophion, confined to the elevated pine-clad Troodos Mountains of the island of Cyprus, and said at the time of the British occupation in 1878 to have been reduced to a flock of about twenty-five individuals, and 0. musimon, the moufflon of Corsica and Sardinia (see figure), believed to have been formerly also a native of Spain. Lastly, we have the somewhat aberrant, goat-like aoudad, 0. tragelaphus, of the great mountain ranges of North Africa.
We thus find that sheep are essentially inhabitants of high mountainous parts of the world, for dwelling among which their wonderful powers of climbing and leaping give them special advantages. No species frequent by choice either level deserts, open plains, dense forests, or swamps. By far the greater number of species are inhabitants of the continent of Asia, one or perhaps two extending into North America, one into Southern Europe, and one into North Africa. No wild sheep occurs in any other part of the world, unless the so called musk-ox (Oviios moschatus) of the Arctic regions, the nearest existing ally to the true sheep, may be considered as one. Geologically speaking, sheep appear to be very modern animals, or perhaps it would be safer to say that no remains that can be with certainty referred to the genus have been met with in the hitherto explored true Tertiary beds, which have yielded such abundant modifications of antelopes and deer. They are apparently not indigenous in the British Isles, but were probably introduced by man from the East in prehistoric times. (W. H. F.)
The above article was written by: W. H. Flower, LLD.