Clavicle
Long bone, but shaped uniquely like a flattened strut; part of the appendicular skeleton.
Also known as: Collarbone
Classification
Long bone, but shaped uniquely like a flattened strut; part of the appendicular skeleton.
Dimensions
Typically ranges from 12 to 15 centimeters in length for an average adult. It is slender, elongated, and noticeably curved in a gentle S-shape.
Key Features
The most defining feature of this bone is its distinct, gentle S-curve when viewed from above or below. One end is broad and flattened like a tiny paddle, while the other end is thicker and more blocky or triangular. The shaft is relatively smooth and rounded on top but has small bumps and grooves underneath where supporting structures attach.
Similar Bones
Beginners might occasionally mistake a small rib for a clavicle, but ribs are uniformly curved in a C-shape and feature distinct grooves along their inner edge. A clavicle can be easily distinguished by its double-curved S-shape and its flattened, widened ends.
Across Species
The clavicle varies wildly across the animal kingdom depending on how an animal moves. In humans and climbing primates, it acts as a rigid strut to keep the shoulder joint out to the side, allowing a wide range of arm movement. Running mammals like horses and dogs have a greatly reduced clavicle or lack it entirely, which frees their front legs to swing forward and backward like a pendulum for maximum running speed. Conversely, burrowing animals like moles have exceptionally robust clavicles to anchor the powerful muscles needed for digging.
Evolutionary History
The clavicle is one of the oldest bones in the vertebrate skeleton, originating in early bony fish as part of the shoulder girdle. Over millions of years of evolution, as creatures transitioned from swimming to walking and climbing, the clavicle adapted from a simple bracing plate into a dynamic strut that links the upper limb to the central core of the body.
Photography Tips
To photograph this bone for identification, place it flat on a neutral, solid-colored background with a ruler or coin next to it for scale. Take one clear shot from directly above to capture the complete S-curve, and a second shot from the side profile to show the thickness and curves of the ends. Use soft, even lighting to highlight the surface texture without casting harsh shadows.