Ruminantia (Lat. ruminare, to chew the cud), a group of ungulate even-toed mammals, characterized by the absence of incisors in the upper jaw in almost all cases, their place being supplied by a callous pad; six lower incisors; canines inconstant; molars usually six on each side in each jaw, with flattened crowns and irregularly crescentic folds of enamel; stomach compound, with three or four cavities, in connection with the act of rumination; caecum large; placenta generally cotyledonous; and feet ungulate and bisulcate. This group is equivalent to the pecora of Linnaeus, and includes such animals as the camel, deer, giraffe, antelope, gnu, goat, sheep, and ox. Almost all the genera are provided with horns, solid and deciduous as in the deer, or hollow and permanent as in the ox and sheep. They are large or moderate in size, and generally rapid runners; they feed in herds, headed by an old male, and are exclusively herbivorous; the shape in most is light and elegant, and the limbs long and slender; the skin is covered with hair or wool; the eyes are large, full, and often very beautiful; the ears long, erect, very movable, and more or less pointed; the tail varies much in length and covering.

They inhabit vast plains, the forests of the north, and the dry deserts of the tropics, their speed taking them in a few hours from an exhausted to a rich feeding ground, and from a sandy waste to a well watered region. They wage no war on each other or on other animals, except during the pairing season; taking to flight at slight causes of alarm, when brought to bay they fight boldly with their horns and antlers, and strike powerful blows with their sharp front hoofs. - The deciduous horns of the ruminants may be rounded as in the stag, roebuck, and Virginia deer, or palmated as in the moose, reindeer, and fallow deer; they are usually symmetrical as to position and size, but not as to arrangement of the divisions; there is an intimate connection between the horns and the generative system, as their development may be arrested and their periodical shedding prevented by castration. There are seldom more than two; but in the fossil sivatherium of the tertiary of the Sivalik hills there are four, also in the four-horned sheep, goats, and antelopes; sometimes there are even five in the domesticated sheep.

The solid horns have been described under Buck, and Deer; these antlers fall by a process having a close resemblance to that by which in necrosis the dead is separated from the living bone; after the pairing season has passed the circulation stops in the horns, and they become dry and dead, and separate from the frontal bone by absorption carried on by the Haversian canals; these, acting on one plane through the whole thickness of the bone just below the burr, remove the solid materials around them, so that each canal finally unites its cavity with that of an adjoining one; when this has extended entirely across the base the antler falls. Prof. J. Wyman (" Proceedings of the Boston Society of Natural History," vol. vii., p. 168, 1859) regards the antlers as dermal bones rather than parts of the internal skeleton, because they are developed in the integuments by a special centre of ossification, and become attached to the frontal only after ossification has somewhat advanced. In the hollow horns of the ox, sheep, and antelopes, the frontal bony cores are cylindrical shafts, more or less solid, protected by periosteum and an extension of the true skin, of which the epidermic portion is developed into a dense horny sheath; in most the frontal sinuses extend into the cores. - The tongue generally performs the office of prehension as well as deglutition; the anterior part collects and judges by the touch of the nature of the food, the next portion prepares the morsel and thrusts it backward toward the oesophagus, and the basal part regulates the movements of the whole organ from its insertion in the hyoid bone; the papillae, fungiform and filiform in front, conical and circumvallate behind, are largely developed.

The salivary glands are large, with long ducts; tonsils bulky, and oesophagus thick and muscular. The stomach is fourfold, the first three cavities (paunch or rumen, honeycomb bag or reticulum, and manyplies or psalterium) being essentially dilatations of the oesophagus for the purpose of rumination, and leading to the fourth or true digestive cavity; in the fourth or abo-masum, the only one developed in the newly born animal, there is in the calf an organic acid secreted, possessing the power of converting the albumen of milk into curd or whey, in the prepared condition called rennet. Concretions of balls of hair, the result of hairs swallowed when licking their own or others' hides, felted together by the movements of the stomach, and incrusted with a polished earthy deposit of great hardness, are often found in the stomachs of ruminants, especially of the cow.

Stomach of a Sheep.

Stomach of a Sheep. a. Oesophagus or gullet. 5. Rumen, paunch, or first stomach, c. Reticulum, honeycomb, or second stomach, d. Psalterium or manyplies. e. Abo-masum, fourth or true stomach.

The intestinal canal is very long and simple; compared with the length of the body it is, according to Meckel, as 12 to 1 in the camel and deer, 22 to 1 in the ox, and 28 to 1 in the sheep; the large intestine is often scarcely wider than the small; the caecum is always large, smooth, and without lateral bulgings. The eyes are wide apart, and so prominent that the range of vision is very extensive; the opening of the pupil is transverse, and the tapetum is exceedingly brilliant. The senses of hearing and smell are highly developed, and the cranial sinuses are extensive. The mammae are inguinal, and the teats four, except in sheep and goats, which have only two. The panniculus carno-sus muscle is remarkably developed, serving as a means of defence by shaking off flies and other stinging insects from the skin. In the camel there is a hump on the back, consisting principally of adipose matter developed in the subcutaneous areolar tissue, probably serving as a storehouse of nutriment to the animal during its long fasts in the desert. The hair is generally coarse, and never what would be called fur; it varies from the harsh and shaggy coat of the camel and the somewhat softer one of the llama to the fine wool of the sheep.

Rumination is rendered necessary by the bulky character of the food as compared with its nutrient qualities; the timid animals of this order are naturally forced to take in a large amount of food in a short time, and then to flee from the carnivorous beasts always lying in wait for them to some retired place where they can remasticate it quietly. In camels the bolus is triturated alternately from side to side; in horned ruminants and in the giraffe it is always in one direction, either from right to left or from left to right. - Ruminants embrace the animals most useful to man and the most easily domesticated; whole races of men count their wealth by the numbers they possess of them, whether camels, llamas, goats, sheep, reindeer, or cattle. They are distributed all Over the world except in Australia; the reindeer and musk ox are found in the polar regions of both hemispheres, the llamas and alpacas in South America, the camels in Asia and Africa, the giraffe and most antelopes in Africa, and the deer everywhere in suitable feeding places; in North America there are only two antelopes, only one of the sheep family, and two of the ox family; there are no hollow-horned ruminants in South America as original species, though there are vast herds of wild cattle of foreign introduction.

The distribution of fossil ruminants was in some respects different from that of the living species; for instance, the giraffe has been found fossil in France and the Sivalik hills, showing a warmer climate than now prevails in those regions; on the contrary, the reindeer has been found in S. Europe, indicating also a temporary diminution of heat, probably from the extension southward of the ice during the glacial period. There are many interesting coincidences of geographical distribution in geological and the "present times, bearing on the point of the origin of existing mammals, and in favor of the theory of such origin from the development of previously existing types, rather than from a distinct creative act after the entire destruction of the preceding fauna. Camels are found fossil in the Sivalik hills of India, llamas in the caverns of Brazil, musk deer in Asia and Africa, etc.; deer (cervidoe) are numerous in the diluvial formations of Europe, greatly resembling the present species, and, according to Pictet, some may be considered as the stock from which have been derived the present stag, reindeer, fallow deer, and roebuck, these, with also the goat and sheep, having survived the catastrophes of this disturbed period, and preceded the appearance of man in Europe. The fossil deer of Asia and America also very much resemble the existing species of these continents.

The urus described by Julius Caesar (De Bello Gallico, vi. 28) among the animals of Germany, and the aurochs even now living in the forests of Lithuania, are interesting in connection with the origin of domestic cattle; these were probably indigenous, as a fossil urus and aurochs have been found in the diluvium of Europe. The fossil musk ox (ovibos) has been found in Siberia and North America, like the one now living in the polar regions. The ruminants show more transitions to other orders than would be supposed from the study of their living species, especially in the direction of the odd-toed ungulates; they appeared after the latter, and under forms very nearly resembling existing species; there were none in the eocene tertiary, when almost all herbivorous mammals were of the latter, but appeared first in the miocene, and then became so numerous that in the subsequent epoch (pliocene) and during the diluvium they had entirely displaced the latter, at least in Europe. The sivatherium of the Sivalik hills resembled proboscidians in its heavy form, short neck, and probable trunk (as indicated by the nasal bones). Among the gigantic animals of this order may be mentioned the great Irish elk, with enormous horns, found in the diluvium of Europe. The genus macrauchenia, as large as a rhinoceros, is peculiar to the southern regions of South America, and forms another remarkable transition form between ruminants and proboscidians. (See Macrauchenia).