Scapula
Flat bone, part of the limb skeleton
Also known as: Shoulder Blade
Classification
Flat bone, part of the limb skeleton
Dimensions
Varies widely from a few inches in small mammals to over a foot in large ungulates like deer and cattle, generally forming a broad, triangular, flattened plate with a prominent ridge across the outer face.
Key Features
Look for a broad, flat, triangular body paired with a distinct raised ridge that runs down the outer surface, ending in a projecting tip near the socket area. The edges are often thin and slightly curved, while one corner features a smooth, cup-like depression where the upper arm bone connects.
Similar Bones
Pelvic bones share a somewhat flat, broad, and triangular shape with ridges, but pelvic bones usually form a complete ring or heavy basin structure with a deeper socket and thicker struts. Ribs are long and curved rather than flat and triangular.
Across Species
In mammals, the shoulder blade rests against the ribcage to anchor the front limb. In running animals like horses and dogs, the collarbone is often absent or reduced, leaving the shoulder blade as the primary suspension system supported entirely by powerful muscles and soft tissues. In swimming marine mammals, the bone changes proportions to adapt to powerful flippers, while in fossorial digging animals, it becomes robust and stout to handle heavy soil resistance.
Evolutionary History
Tracing back to early tetrapods, the shoulder girdle underwent significant remodeling. As ancestors moved from crawling sprawling movements to upright limb carriage beneath the body, the internal elements shifted orientation. The broad blade evolved to provide extensive surface area for increasingly complex shoulder and arm musculature.
Photography Tips
Place the bone on a solid, neutral-colored background like a plain paper towel or dark mat. Take a top-down photo showing the flat face and the raised ridge clearly. Include a small ruler or coin for scale, and use bright, indirect natural light from the side to cast gentle shadows that highlight the ridges and contours.