1911 Encyclopædia Britannica/Ungulata
UNGULATA, the name of an order of placental mammals in which the terminal joints of the toes are usually encased in solid hoofs or covered with broad hoof-like nails, while the molar (and not infrequently some or all of the premolar) teeth have broad tuberculated crowns adapted for crushing vegetable substances. The teeth (when all are present) are differentiated into the usual four series; and milk-teeth, not completely discarded till the full stature is attained, are invariably developed. All the existing members of the group are eminently adapted for a terrestrial life, and in the main for a vegetable diet. Though a few may in some circumstances kill living creatures smaller than themselves for food, none are habitually predaceous. In none of the existing, and in but few of the extinct types, are collar-bones, or clavicles, developed; and the scaphoid and lunar bones of the carpus are separate. The typical ungulates are the members of the suborders Artiodactyla and Perissodactyla (q.v.), in both of which the bones of the foot articulate with each other by means of groove-and-tongue joints, whence the name of Diplarthra (equivalent to Ungulata Vera), which has been proposed for these two groups collectively, as distinct from the other representatives of the order. The remaining and less typical sub ordinal groups—sometimes ranked as orders by themselves—include among living animals the Proboscidea, or elephants, and the Hyracoidea, or hyraxes, and among extinct groups the Amblypoda, Ancylopoda, Barypoda, Condylarthra, Litopterna and Toxodontia. The characteristics of these groups will be found under their respective headings, with the exception of the Barypoda and Condylarthra, for which see Arsinoitherium and Phenacodus.
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| Right Fore Foot of Indian Elephant. |
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U, ulna; R, radius; c, cuneiform; l, lunar; sc, scaphoid; u, unciform; m, magnum; td, trapezoid; tm, trapezium; I to V, first to fifth digit. |
In the great majority of the Subungulata the bones of the upper and lower rows of the wrist-joint, or carpus, retain the primitive or more typical relation to each other (see fig., and contrast with Perissodactyla, fig. 1); the os magnum of the second row articulating mainly with the lunar of the first, or with the cuneiform, but not with the scaphoid. On the other hand in the Diplarthra, the group to which the vast majority of modern Ungulates belong, the second or lower row has been shifted altogether towards the inner side of the limb, so that the magnum is brought considerably into relation with the scaphoid, and is entirely removed from the cuneiform, as in most existing mammals.
In the typical Ungulata or Diplarthra, the feet are never plantigrade, and the functional toes do not exceed four—the inner digit being suppressed, at all events in all forms which have existed since the Early Eocene period. The os magnum of the carpus articulates freely with the scaphoid. The allantois is largely developed, and the placenta, so far as known, is nondeciduate, the chorionic villi being either evenly diffused or collected in groups or cotyledons (in Pecora). The testes descend into a scrotum. There is never an os penis. The uterus is bicornuate. The teats are usually few, and inguinal, but may be numerous and abdominal (as in Suina), although they are never solely pectoral. The cerebral hemispheres in existing Ungulates are well convoluted. (R. L.*)