The Hyracoidea and family Hyracidoe com prise only a few species of small rodent-like animals of the genera Hyrax or Procavia and Dendrohyrax, inhabiting Africa, Syria and Arabia. They present certain resemblances to the elephants on the one hand, and to the rhinoceroses on the other, but in most respects are quite isolated. The Hyrax syriacus is be lieved to be the °coney° of Scripture. The front feet have four and the hind feet three toes, enclosed in hoof-like nails. No clavicles exist. The nose and ears are short, and the tail is rudimentary. No canine teeth exist, and the incisor teeth grow from permanent pulps like those of rodents. The placenta is zonary and deciduate, and there are six teats. The intestine is remarkable in having a large sac ciliated and a pair of small conical caeca. These animals live in burrows in rocky moun tainous districts, and are known as "rock rabbits" or “dassies,'> while the species of Dendrohyrax are arboreal and live in hollows of trees.
The elephants (q.v.), although usually placed in a distinct order of mammals — Proboscidea, are related to the other ungulates through the Hyracoidea and Amblypoda. Each foot pos sesses five toes. There are no clavicles. The nose is prolonged to form a flexible proboscis, at the extremity at which the nostrils open. The testes are abdominal throughout life. The breasts are pectoral in position, and the placenta is non-deciduate and zonary. The canine teeth are wholly wanting, and the molars are few in number and are ridged or tuberculate on their crowns, very high and complex in structure in the specialized forms and appear in the jaws from behind, one at a time. The upper incisors grow from persistent pulps and form tusks. No lower incisors are developed in the elephants but existed in Dinotherium and some species of Mastodon. The extinct Proboscidea are of exceptional interest. The various species of mammoth, mastodon, etc., which belong to the family Elephantichr, possessed enormous tusks curved nearly into a circle in the former, straight in the latter, and their remains are associated with those of early man. The Dinotheriider, remains of which are found in the Pliocene formation, possessed simple tuber culate molars and the lower incisors were greatly enlarged to form downwardly-turned tusks, on which account these animals were formerly associated with the walruses.
The Ungulata Vera (or piplarehra of Cope) include the great majority of living ungulates, most of which are highly specialized in respect to foot and tooth structure. They never have more than four fully-developed toes on each foot; these toes being provided with hoofs, and are never plantigrade. No clavicles or collar bones are developed, though transitory ones sometimes occur during foetal life. The placenta, Which is either diffuse or cotyledonary, is of the non-deciduate type. The molar teeth have broad crowns and vary in the different families. The mamma or milk-glands of the female are usually few in number and placed in the groin; or more numerous and abdominal. The intes
tine is very usually provided with a large rtecum; and the stomach may be complex. Re garding the classification, a primary character is found in the number of the toes, with which many other characters are correlated.
The section Perissodactyla includes those forms in which the toes are usually present in an odd number (solid-hoofed). The third or middle toe tends to predominate, while in the Artiodactyla the number is even and the second and third predominate (split-hoofed). The dorso-lumbar vertebra (that is, the vertebra of the back and loins collectively) do not num ber less than 22. The dentition varies, but the premolars and molars are always similarly formed. The third digit or toe of each foot is symmetrical by itself, that is, does not form a pair with its neighboring digit. The thigh or femur bears a third trochanter. The stomach is of simple character, and the cacum of very large size. The teats are inguinal in position and the placenta is diffuse. If horns are developed they belong merely to the epidermis, are not sup ported by a bony core, and are never paired in living forms. Where two horns exist (as in some rhinoceroses) the second is situated be hind the first. Belonging to the perissodactylate Ungulata, besides many extinct Teritary fam ilies, are three living ones typified by the tapirs, rhinoceroses and horses (qq.v.). The group is declining.
The Artiodactyla, or "even-toedp ungulates, are distinguished by the presence of either two or four toes, the third toe of each foot forming a symmetrical pair with the fourth. The premolar teeth, whatever their character, are always simpler than the molars. When horns are developed they nearly always exist in pairs, and are supported on bony "cores." The stomach is very complex in the ruminating forms, and the cacum is small. The dorso lumbar vertebrae number 19, and the femur wants a third trochanter. Unlike the Perisso dactyla the Artiodactyla are a dominant group and, while in the early Tertiary times they were surpassed by the former in number and variety, they have steadily progressed as the latter have declined, and to-day are represented by about one-third of the known families, very numerous genera and species and often vast numbers of individuals. The living families are arranged under the sections Suina, or pig like Artiodactyla, Tylopoda, or camel-like Artiodactyla, Tragulina, the chevrotains, and Pecora or ruminants.
Consult Flower and Lydekker, 'Mammals' (London 1891); Lydekker, 'Wild Oxen, Sheep and Goats' (London 1898); 'Deer of All Lands' (London 1898); 'Great and Small Game of Europe, Asia and Africa' (Lon don 1901) ; Bryden, 'Great and Small Game of Africa' (London 1899) ; Sclater and Thomas, 'Book of Antelopes' (London 1894-1900); Caton, 'Antelope and Deer of America' (Boston 1881) ; Marsh, 'Dinocerata' (Wash ington 1884) ; Cope, 'Organic Evolution' (Chicago (1896) ; Osborn, 'Age of Mammals' (New York 1910).