Scapula
Flat bone, part of the appendicular skeleton
Also known as: Shoulder Blade
Classification
Flat bone, part of the appendicular skeleton
Dimensions
Varies widely from a few inches in small mammals to over a foot in large ungulates. It is typically a broad, flat, triangular or fan-shaped plate with a raised ridge running across one surface.
Key Features
Look for a flat, thin, fan-shaped plate marked by a prominent ridge of bone (the spine) stretching diagonally across the outer surface, ending in a distinct corner hook or socket area where the upper arm bone connects.
Similar Bones
Can sometimes be mistaken for large pelvic bones due to their flat, blade-like shape. However, shoulder blades feature a prominent spine running down the center of the flat surface, whereas hip bones have a thicker, rounded rim and a deep socket for the leg.
Across Species
In running mammals like horses and deer, the shoulder blade is elongated and narrow to maximize the stride length of the front leg. In burrowing animals like moles, it becomes exceptionally broad and sturdy to anchor powerful digging muscles. In birds, it fuses with other elements to form a sturdy brace for flight wings.
Evolutionary History
The shoulder blade traces its deep evolutionary roots back to the earliest land-dwelling backboned animals, evolving from ancient shoulder girdle elements found in primitive fish to help connect the front limbs to the main body frame.
Photography Tips
Place the bone flat against a neutral, high-contrast background. Take one photo of the side with the raised ridge facing up, and flip it over to capture the smooth, slightly scooped inner surface. Include a small coin or ruler next to the bone for scale.