Femur
Long bone of the appendicular skeleton
Also known as: Thigh bone
Classification
Long bone of the appendicular skeleton
Dimensions
The longest and strongest bone in the human body, typically making up about one-quarter of a person's overall height, featuring a long straight central shaft and rounded ends.
Key Features
Recognizable by its ball-shaped top end designed to fit into the hip socket, a long sturdy middle shaft, and two prominent knobby bumps at the bottom end that help form the knee joint.
Similar Bones
Can sometimes be confused with the humerus of the arm, but the femur is distinguished by its larger overall size, more robust shaft, and the distinct spherical ball at the upper end set at a sharp angle.
Across Species
In birds, the femur is held nearly horizontally and remains largely hidden within the body feathers, while the visible leg segment is actually the lower leg. In whales and dolphins, the femur is reduced to a tiny, floating vestigial remnant hidden deep within the muscle, reflecting an evolutionary shift away from walking.
Evolutionary History
Originating from the robust limb bones of early tetrapods that first crawled onto land, the femur evolved over hundreds of millions of years to support upright posture, shifting from a sprawling side-to-side stance to a vertical, weight-bearing pillar beneath the body.
Photography Tips
Place the bone on a neutral, solid-colored background with a coin or ruler placed alongside it to show scale. Take multiple photos from the top, bottom, and side profiles using soft, natural lighting to highlight the curved ends and surface contours.