I cannot accept the theory that _os centrale carpi_ is merely a detached portion of the scaphoid bone. In a very young chimpanzee this bone is undoubtedly superficially indented with two transverse furrows, but the three segments display only one uniform development of bone. The distinct formation of _os centrale_, and its occasional appearance in man, testify that it has an independent existence. Rosenberg holds that this bone is not merely the _os centrale_ of mammals, but that it is homologous with the two _ossa centralia_ of the fossil _Enaliosauria_. It has become abortive in proportion to the reduction in size which has taken place.[52] There would be no great difficulty in tracing back this bone to remote types of vertebrate animals, even as far as the _Urodela_ (Wiedersheim) of Eastern Asia.[53] The persistence of this bone in man must be regarded as a reversion, not as an arrest, of development. [Illustration: Fig. 42.--Skeleton of human hand, back view. _a_, Scaphoid bone. _b_, Semi-lunar bone. _c_, Cuneiform bone. _d_, Pisiform bone. _e_, Trapezium. _f_, Trapezoid bone. _g_, Os magnum. _h_, Unciform bone. _l-l′_, Metacarpal bones. _m-m′_ and _nn_, Phalanges. ] On the femur of several mammals, especially in the horse, ass, rhinoceros, and tapir, and more slightly indicated in the carnivora and other families, there is, in addition to the two great and small trochanters, a third, termed by Waldeyer _trochanter tertius_.[54] Such a formation, low, blunt, and generally placed at the top of the outer ridge of the superior bifurcation of the _linea aspera_, may be observed in human skeletons of all races, but is either absent in anthropoids or only faintly indicated. Virchow justly regards its presence as theromorphic, but not as a characteristic of savage or lower races.[55] The human tibia displays in some instances a compression or lateral flattening of its shaft or centre-piece, so that its transverse diameter is quite out of proportion to its depth. Such a tibia is termed sword-bladed, or platycnemic. Bones of this form have been chiefly discovered in ancient deposits, as, for instance, at Gibraltar, at Perthi-Chwareu, in Wiltshire, in Lozère, at Clichy, at Saint-Suzanne (Sarthe), and especially at Cro-Magnon (Fig. 43), Janischwek, etc.