Clavicle
Long bone; part of the limb (appendicular) skeleton forming the shoulder girdle
Also known as: Collarbone
Classification
Long bone; part of the limb (appendicular) skeleton forming the shoulder girdle
Dimensions
A slender, double-curved bone roughly 5 to 6 inches long, resembling a gentle 'S' shape. It is typically horizontal and connects the breastbone to the shoulder blade.
Key Features
It has a distinct 'S' curve when viewed from above. The inner end near the breastbone is rounded and thick, while the outer end reaching toward the shoulder is flattened and broad. The top surface is relatively smooth, while the bottom surface often has small ridges where powerful muscles and ligaments attach.
Similar Bones
In isolation, it might be confused with a small rib. However, ribs have a much sharper, single curve and a distinct 'head' with flat facets for docking with the spine, whereas the clavicle has a more complex double curve and lacks those specific spinal joints.
Across Species
The clavicle varies significantly across the animal kingdom based on locomotion. In birds, the two clavicles are fused into a 'V' shape known as the furcula, or wishbone, which acts like a spring during flight. In mammals that use their front limbs for climbing or manipulation like primates and bats, it is well-developed. However, in many fast-running mammals like horses, deer, and dogs, it is either absent or tiny, allowing the shoulder blades to move more freely along the ribcage for a longer stride.
Evolutionary History
This bone is among the oldest in the vertebrate skeleton, originating from the dermal armor of ancient fish. Over millions of years, it transitioned from a protective outer plating to an internal structural support. In early land-dwelling tetrapods, it helped stabilize the chest while walking. In humans, its presence is a hallmark of our primate ancestry, providing the leverage needed for wide-ranging overhead arm movements.
Photography Tips
Lay the bone flat on a neutral background to capture its 'S' profile from above. Take a second shot from the side to show the difference between the thick rounded end and the thin flat end. Include a ruler to show the length and use soft, overhead lighting to highlight the gentle curves without creating harsh shadows.
Notes
What is the highlighted part?