In the Artiodactyla are included the following living groups:-- _a._ Suina. Pigs and Hippopotami. _b._ Tylopoda. Camels and Llamas. _c._ Tragulina. Chevrotains. _d._ Ruminantia or Pecora. Deer, giraffes, oxen, sheep and antelopes. _Suborder_ (2). PERISSODACTYLA[127]. In this group there are never any bony outgrowths from the frontals. The grinding teeth form a continuous series, the posterior premolars resembling the molars in complexity, and the last lower molar generally has no third lobe. The cervical vertebrae with the exception of the atlas almost always have markedly opisthocoelous centra, but in _Macrauchenia_ they are flat. The nasals are expanded posteriorly, and an alisphenoid canal is present. The thoraco-lumbar vertebrae are never less than twenty-two in number and are usually twenty-three. The femur has a third trochanter (except in _Chalicotherium_). The third digit of the manus and pes is symmetrical in itself, and larger than the others, and in some cases the other digits are quite vestigial. The number of the digits of the pes is always odd. The astragalus is abruptly truncated distally, and the facet by which it articulates with the cuboid, is much smaller than that by which it articulates with the navicular. The calcaneum does not articulate with the fibula, except in _Macrauchenia_. The group includes many extinct forms, and the living families of the Tapirs, Horses and Asses, and Rhinoceroses. _Section II._ SUBUNGULATA. In this group is placed a heterogeneous collection of animals, the great majority of which are extinct. There is really no characteristic which is common to them all, and which serves to distinguish them as a group from the Ungulata vera. But the most distinctive character common to the greatest number of them is to be found in the carpus, whose bones in most cases retain their primitive relation to one another, the os magnum articulating with the lunar and sometimes just meeting the cuneiform, but in living forms at any rate not articulating with the scaphoid. The feet frequently have five functional digits, and may be plantigrade. The proximal surface of the astragalus is generally flattened instead of being pulley-like as in Ungulata vera. _Suborder_ (1). TOXODONTIA.