Clavicle
Long Bone; part of the appendicular (limb) skeleton connecting the arm to the trunk.
Also known as: Collarbone, Beauty Bone
Classification
Long Bone; part of the appendicular (limb) skeleton connecting the arm to the trunk.
Dimensions
This is a slender, horizontal bone typically measuring between 5 to 7 inches in length. It is characterized by its thin, elongated body and distinct double curve.
Key Features
The most defining feature is the 'S' shape when viewed from above. One end is rounded and chunky (where it meets the breastbone), while the other end is flattened and broad (where it meets the shoulder blade). The shaft is smooth on the top surface and rougher on the bottom surface where muscles and cords attach.
Similar Bones
It is often confused with a rib or a small arm bone. However, ribs have a single, uniform curve and a deep groove along one edge, whereas the clavicle has a signature 'S' curve. Unlike the straight shafts of finger or toe bones, the clavicle's twist and specialized flat-and-round ends are unique.
Across Species
The clavicle varies wildly across nature. In birds, the two collarbones fuse together to form the furcula, or 'wishbone,' which acts as a spring for flight. In many fast-running mammals like horses and dogs, the clavicle is completely lost or reduced to a tiny remnant to allow the shoulder blades to slide freely for a longer stride. In primates and digging animals, it remains robust to provide a sturdy brace for complex arm movements.
Evolutionary History
One of the oldest parts of the shoulder gear, the clavicle first appeared in ancient bony fish as part of the armor-like plating behind the gills. As vertebrates moved onto land, this bone transitioned from being part of the skull's edge to a structural bridge that supports the forelimbs, allowing land-dwellers to lift their bodies off the ground.
Photography Tips
To capture the distinctive 'S' shape, photograph the bone lying flat from directly above. Take a second shot from the side to show the transition from the thick rounded end to the thin flat end. Including a ruler, as seen here, is excellent for showing scale.