The parietal bones(figs.465,467,468,471,f) are rnoderately extensive, covering the superior and lateral portions of the skull. In the young animal they are always separated by a mesial suture, (fig.469,b,b,) but in the adult are united by the obliteration of this suture into one piece, so as to appear but a single bone ; a pro vision, no doubt, for admitting the enormous force of the temporal muscles to be exerted without danger of divaricating the two lateral halves, which might otherwise be tom asunder at the line of junction. In the Tapir there is a lofty interparietal crest, giving great additional surface for the origin of the temporal muse/es.
The frontal bones are of very great extent, and besides enclosing the anterior part of the cranial box, form a large proportion of the orbital cavity. In the young animal (fig. 469, a, a) they are invariably two in number, separated by a suture along the mesial line, and in the American Tapir this separation is permanent; but generally they become con solidated at an early age, leaving no trace of their original separation.
The cethmoid is, in the Pachyderrnata, of very considerable size, proportioned to the acuteness of the sense of smell with which these animals are gifted. The cribriform plate holds a posi tion exactly similar to that which it presents in the human subject, implanted between the frontal and sphenoid bones, and testifies, by its great extent of surface and the numerous foramina which pierce it, that the olfactory organs are highly developed. Towards the nasal surface, likewise, the cethmoidal cells and minores almost along their whole length and mask the pterygoid processes, so as to give a very peculiar appearance to the base of the cranium .
The bones of the face are remarkable for their massive developement, but as their posi tion is sufficiently indicated in the next wood cuts, it would be useless to particularize them further.
Ribs and sternum.— The thoracic cavity throughout all the Pachydermatous genera is enormous in proportion to the great bulk and excessive weight of the viscera. The ribs, in fact, are continued backwards almost to the pelvis, and from their extraordinary size and turbinated laminre are very large, so that the delicacy of the sense with which they are con nected is evidently only inferior to that of the carnivorous quadrupeds.
The sphenoid occupies the same position as in the skull of Man, and in the hog tribe is very similar in its shape and the general ar rangement of its processes to the human. In the Elephant the anterior and posterior clinoid processes are but slightly developed, so that the base of the cranium internally has a very flat appearance, whilst externally, such is the enor mous developement of the sphenoidal cells, that they stretch on each side beneath the alve breadth constitute a kind of osseous case, en closing a considerable portion of the abdominal cavity, and calculated to give origin to muscles of power proportioned to its ponderous con tents.
In the Hyrax, dissected by Pallas, there were twenty-two ribs on the left side and only twenty-one on the right : of these seven were true ribs, six false attached to the sternum by the intervention of costal cartilages, and the rest merely imbedded in the muscles of the flanks. The sternum consisted of six pieces, of which the last or ensiform was further pro longed by a spathulate cartilage.
In the Taper the ribs are twenty in number on each side, whilst there are but four lumbar vertebrze. The Elephant, likewise, has twenty pairs of ribs and only three lumbar vertebrm. The Rhinoceros has nineteen pairs of ribs, and the Hog only fourteen.
The sternum is of considerable length and compressed latemlly. In many genera, more over, it is prolonged in front to a considerable distance, in order to allow more ample space for the attachment of muscles.
Anterior extremities.— The limbs of the Pachydermata are necessarily constructed more with a view to ensure strength adequate to sus tain their ponderous bulk than to permit of agile and active movements. The smaller genera, indeed, such as the Suid, have their bones so arranged as to permit of considerable fleetness in running, but in the more colossal genera the condition of the extremities secures support at the expense of speed, and flexibility is sacrificed to solidity and firmness.
Scapula.—The shoulder-blade of the Ele phant, independently of its size, might be disting,uished from that of any other living animal by the following circumstances. When in situ, its posterior side, which is deeply con cave, is by far the shortest of the three, while the anterior and spinal costm are of nearly equal length. In consequence of the preceding circumstance this scapula is broader in propor tion to its length than that of any other large quadruped, and, moreover, the spine of this bone, besides its acromial process, has towards its middle a broad sickle-shaped pro jection, lookhag backwards and spreading over the infra-spinatus muscle. In all other Pachy dermata the shape of the scapula is that of an elongated triangle, with the angles of the base much rounded off and the spine very short in proportion to the extent of the dors= ; never theless, in the Rhinoceros there is a falciform process projecting from the spine something like that of the Elephant, and both in the Hippopotamus and the Tapir rudiments of a coracoul process. The scapula of the Tapir (fig. 475) is also remarkable for a deep and almost circular notch between the rudimentary acro mion and its anterior costa.