Femur.

The femur is the large upper leg bone that extends from the hip to the knee. It is the largest bone in the human body. Because of its significant size and strength, the femur plays a crucial anatomical role as a base for soft tissue attachment and weight bearing. The femur is one of the body's long bones, which means that it is longer than it is wide. Being a long bone also means that the femur is composed of a hard outer surface called compact bone and a criss-crossed strutted interior referred to as cancellous bone. Each end of the femur connects with a major joint. The proximal end of the femur, or the end that is closer to the center of the body, connects with the pelvis at the acetabulum to form the hip. The distal end of the femur, or the end farthest from the center of the body, forms the knee joint with the tibia and patella.