PACHYDER'MATA (Gr. thick•skins), in the system of Cuvier, an order of mammalia, including part of the britta (rhinoceros, elephant), and all the bellum (horse, hippopotamus, tapir, hog, etc.) of Lintimus. besides one genus (hyrax or (Inman) of the Limey:in (pr.'s, It has been often described as less natural than any other of Cuvier's mammalian orders, as it consists of animals among which there are wide diversities, and the associating characters are rather negative than positive; but it is now universally received by naturalists as indicating a real, though not a close affinity; and when we extend our view from existing to fossil species, numerous connecting links present themselves. As 'defined by Olivier, the order consists of those hoofed marnmalia (ungulate!) whirl] are not ruminants; all of which possess, as a more positive character, a remarkable thickness of skin. This order he divides into three sections: (1) Proboseidea, having :1 prolonged or proboscis, through which the nostrils pass as elongated tubes, a powerful organ of prehension, and a delicate organ of touch, and having also live toes on each foot, inclosed in a very firm horny skin; (2) ordinaria, destitute of proboscis, although in some (tapirs) there is such an elongation of the upper lip and nostrils as approximates to it; and the nose is employed by hogs, etc., in seeking their food, not only as an organ of smell, but as an instrument for turning up the ground, and as an organ of touch; the number of toes varies, four, three, or two on each foot; those with an even number of toes having in the cleft foot a resemblance to the ruminantia; and (3) so/id/moil/a, in which the foot has but one apparent toe, inclosed in a hoof. Some naturalists have thought it better to separate the solidangula or equithe (q.v.) from the pachydermata, as a distinct order; whilst others have enlarged instead of restricting the limits of the order, by adding, as a fourth section, the herbiroroas eciacea.
Those pachydermata which haven number of toes differ completely from the mam• malia having claws (ungaieulata)in their inability to bend their toes in order to seize any object. Some of the edentata have very large hoof-like claws, but this difference still subsists. Tate fore-limbs of the pachydermata are also incapable of any rotatory motion, Serving for support and locomotion only, not at all for prehension; the metatarsal and metacarpal bones being consolidated as in the raminantia, and they have no clavicles.
The largest terrestrial main malia belong to this order. Most of the pachydermata are of large size, although the damans ate a remarkable exception, and some of the hog family are also comparatively small. Most of them have a clumsy form, with a slow and awkward gait; but they are capable of activity beyond what might be supposed, and sometimes move at a pretty rapid pace. Gracefulness and fleetness are characteris tics of the otherwise exceptional solidunotla. The P. ordinaria have generally great strength, and the larger ones push their way through the entangled thickets of tropical forests, bending or breaking the lianas, small trees, and branches, which oppose their progress, their thick hides resisting the spines and broken branches by which the skins of other animals would be pierced. The horse and other solidangnla are not inhabitants of forests and jungles, but generally of grassy plains, and theirlddes are much less thick and hard than those of most of the paehydermata.
The pilysiognomy of the pachydermata in general is rather dull and unexpressive, the eyes being small, and having that character of which a familiar example is found in the common hog. When enraged, however, they manifest their fierceness in their eyes; and although, in general, mild and gentle. they are capable of being. aroused to great fury.
The skeleton of the 1'. °Miliaria and proboscides is strong and massive; the neck short, the processes of its vertebrae strongly developed; the skull affording a large sur face for the muscles which support and move it.
The pachydermata generally feed on vegetable substances. Some are omnivorous. The digestive organs are more simple than in the runtinantia, but exhibit considerable diversity. The stomach is simple to some, and in others is more or less completely divided into sacks, approaching to one of the most remarkable characters of the ruini vantia. The intestines are generally longer than in the ruminantia. The dentition exhibits considerable diversity; the adaptation to vegetable food being the most preva lent character. The most important peculiarities of the dentition and digestive organs are noticed in the articles on particular families and genera.