The skull is large and massive. Its large and heavy character is, as has been stated in the definition of the sub-order, due to the immense development of air cavities in the diploe; the diameter of the wall of the skull is actually greater than that of the cranial cavity. These cavities are not obvious in the young animal. They are most conspicuous in the roofing bones of the skull, but are seen elsewhere, and thicken the basis cranii, {219} the maxillae, and so forth. This state of affairs, together with the presence of the huge tusks, has, as it were, pushed back the nasal orifices to near the top of the skull in a very Whale-like fashion. As in the Cetacea, the nasal bones are limited in size, and the premaxillae send up processes to join the frontals and the nasals. There is a straight and somewhat slender zygomatic arch, but the orbit is not separated from the temporal fossa. The malar bone is small, and, as in Rodents, forms the middle part of the zygoma. This is not the case with most Ungulata. The symphysis of the mandibles forms a spout-like rim. The scapula has a narrow prescapular, but a very wide postscapular region. The spine has a strong process projecting backwards from near its middle; this is a point of likeness to certain Rodents. No Elephant has a clavicle. The most remarkable feature about the fore-limb is the separation and crossing of the radius and ulna. The arms of these animals are permanently fixed in the position of pronation. The foot is short, and the bones of the carpus are serially arranged. There are, however, traces of a commencing interlocking of these bones in many forms. The hind-feet are somewhat smaller than the fore-feet, and the tibia and fibula are both developed.