Scapula
Flat bone, part of the appendicular skeleton
Also known as: Shoulder Blade
Classification
Flat bone, part of the appendicular skeleton
Dimensions
Varies immensely by species, ranging from a few centimeters in small rodents to over half a meter in large mammals like elephants and cetaceans. It is generally a flattened, triangular plate.
Key Features
Look for a broad, flat, triangular body with a prominent ridge (the spine) running across the outer surface, ending in a distinct hook-like or shelf-like projection near the socket area.
Similar Bones
Pelvic bones (hip bones) are often confused with shoulder blades because both are large, flat, and feature a socket or deep depression. However, hip bones typically have a more complex, loop-like ring shape and multiple fused sections, whereas shoulder blades feature a simpler triangular plate with a single prominent surface ridge.
Across Species
In running mammals like horses and deer, the shoulder blade is elongated and lacks a collarbone, helping to lengthen the stride. In burrowing animals like moles, it is extremely short, stout, and heavily modified to provide enormous leverage for digging. In birds, it is fused with other shoulder bones to form a rigid brace that withstands the tremendous forces of flight.
Evolutionary History
The shoulder blade evolved from the pectoral girdle of early fish ancestors, transitioning from an internal support structure for fins into a versatile anchor for forelimb muscles as vertebrates moved onto land.
Photography Tips
Place the bone flat on a neutral background with a clear ruler or scale reference alongside it. Take one photo capturing the broad flat side showing the prominent surface ridge, and a second photo showing the profile to highlight the socket and edges. Use soft, angled lighting to make the surface ridges and contours stand out.