ORDINARY PACITYDERMATA, which are unpro vided with a proboscis, and characterized by possessing four, three, or two large digits on their feet, which are cased in homy hoofs--the last group being distinguishable from the Itumi nantia by the simple construction of their stomachs, although closely approaching them in many points of their economy. The above division, however useful to the zoologist, is nevertheless by no means based on nature, the proboscis of the Elephant being only a maximum degree of developement of the snout of the Pig and the semi-proboscidean nose of the Tapir.
The following genera of Pachydermatous Quadrupeds have been distinguished by natu ralists, many of which are still in existence, but the majority are met with only in a fossil state, the names of the latter being printed in italics.
Elephas, (fig. 464.) Hippopotamus Mastodon Toxodon Dinotherium Coryphodon Tapirus - Acerotherium Palteotherium Elasmotherium lophiodon Macrauchenia Hyrax flexaprotodon Rhinoceros Anthracotherium Anoplotherium Chreropotamus Dicotyles Hyracotherium Phacochmrus Dichobune.
Sus Osseous system.—The skeleton of the Pachy dermata is generally remarkable for the massive character which is conspicuous in every region, indicative, at a glance, of the ponderous strength and generally inactive habits of the animals belonging to this order ; but inasmuch as they are destined to obtain their food under very various circumstances, which demand a cor responding diversity of structure in different parts of their bony framework, some detail will be necessary in adverting to this part of their economy.
Cranium.—The cranium of the Elephant, the only living genus of Proboscidian Pachyderms, is quite' unique in its external configuration, and from its vertical elevation confers a re markable aspect of sagacity to the animal ; its intelligence, however, although really surpri sing when contrasted with the stupidity of other genera belonging to this class of quadru peds, has doubtless been rnuch exaggerated in consequence of its imposing appearance. This peculiar contour of the skull depends upon several circurnstances having nothing whatever to do with cerebral developement, but being entirely dependent upon mechanical arrange ments required to support the enormous tusks that project from the upper jaw, and to give origin to the muscles of the proboscis, a nasal apparatus here only met with in a state of complete developement. The extreme short
ness of the bones of the nose, the nearly vertical position of the upper maxilla and ossa incisive, and the swollen vault of the forehead produced by an excessive enlargement of the frontal sinuses, (fig. 466,) which gives extent of sur face to the exterior of the skull, all concur to inask the real condition of the cranial cavity, which, as is easily seen in the next figure, (fig. 465,) occupies but a very small portion of the posterior and central portion of this gigantic cranium.
The general character of the individual bones of the cranium and their modifications in the principal Pachydermatous races will be under stood from the appended figures better than from any lengthened description.
The occipital bone is very extensive, forming by itself the entire posterior wall of the cranial cavity, and even in the Elephant advancing considerably uponits upper surface, where at an early period it becomes so firmly consolidated with the parietals, and these again with the fron tals and temporals, that the whole roof of the skull appears to be formed of one bone. In the hog tribe, the Hippopotamus and the Tapir, it termi nates superiorly in an abrupt and broadly ex panded crest, into which the muscles of the neck are inserted; and not unfrequently the deep fossw and prominent ridges visible upon its posterior aspect testify to the massive strength required in this part of the muscular system, either to support the unwieldy head or to tear up the ground in search of food, as the hog tribe do with their powerful snouts. In the young animal this bone always consists of four sepa rate pieces—a basal, two lateral, and a superior occipital (fig.471, c 1, c 2, c 3 :) but these soon become inseparably united into one mass.