with abundant air cavities in the roofing and other bones. The incisors are developed into long tusks, which exist in the upper jaw alone, in the lower jaw alone, or in both jaws. There are no canines. The molars are lophodont. The clavicle is absent. The femur has no third trochanter. The bones of the carpus are serially arranged and do not interlock. The stomach is simple. The brain has much convoluted cerebral hemispheres, but the cerebellum is completely uncovered by them. The intestine is provided with a wide caecum. The testes are abdominal. The teats are pectoral in position. The placenta is non-deciduate and zonary. There are two venae cavae superiores.
The position of the limbs in the Elephant tribe is unique among living animals: their straightness that is to say, and the absence or very slight development of angulation at the joints of the limb bones. This same feature has been observed in the extinct Dinocerata and in the Titanotheria. It must not, however, be assumed from the resemblance to these ancient forms that there is much affinity between them and the Proboscidea, or that the latter have retained an ancient feature of organisation. The oldest Ungulates for the most part, and the Creodonts to which they are undoubtedly related, have much bent limbs. It must be considered, therefore, that the arrangement obtaining in the Elephants is purely secondary. Professor Osborn has put forward the reasonable view[1] that the vertical limbs of all these colossal creatures are due to "an adaptation designed to transmit the increasing weight" of these animals. The huge bulk of the body is better borne by vertical pillars than by an angulated limb. Other points, however, such as the exposure of the cerebellum, the two venae cavae, the five digits, and the absence of a third trochanter, argue a low position for the Proboscidea in the Eutherian group.
The group can be readily divided into two families, the Elephantidae and the Dinotheriidae. We will commence with the former.
The Elephants proper, Elephantidae, differ from the Dinotheriidae in, and are characterised by, a number of anatomical features. They possess long tusks (incisors) either in both jaws, or, if only in one jaw, in the upper. The molar teeth are very large—so large that only a few of them are simultaneously in use. There are but three definable genera of Elephantidae, of which
- ↑ American Nat. February 1900, p. 89.
