The femur (pl. femurs or femora), or thigh bone, is the most proximal (closest to the center of the body) bone of the leg in tetra-pod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in the rear legs. The femur is the largest bone in the human body. The head of the femur articulates with the acetabulum. By most measures the femur is one of the strongest bones in the body.