As Cuvier remarked, the length of the os femoris depends in general, in most classes of animals, upon the length of the metatarsus. In the horse it is much shorter than in the lion, where, instead of a long cannon bone, we find five distinct metatarsal bones, supporting as many digits. In man the smooth articulating surface for the patella is continuous with that for the tibia; but in many animals (solipeds and ruminants for example) it forms a distinct articulating surface, and is more symmetrical in its extent over the outer and inner condyle. In man there is no trace of that bony prominence which in the beaver is continued from the linea aspera, and is called the third trochanter.