The thigh bone, which is the longest and strongest bone in the body. As the upper end is set at an angle of about 120 degrees to the rest of the bone, and the weight of the body is entirely borne by the two femora, fracture of one of these bones close to its upper end is a common accident in old people, whose bones are often weakened by OSTEOPOROSIS. The femur fits, at its upper end, into the acetabulum of the pelvis, forming the hip-joint, and, at its lower end, meets the tibia and patella in the knee-joint.