Scapula
Flat bone, part of the appendicular skeleton
Also known as: Shoulder Blade
Classification
Flat bone, part of the appendicular skeleton
Dimensions
Varies widely by animal size, generally forming a flat, triangular or fan-shaped plate with a prominent ridge running across the outer surface.
Key Features
Recognizable by its broad, flat, fan-like body, a distinct ridge dividing the outer face into two main hollows, and a narrowed neck leading to a smooth socket area where the upper arm connects.
Similar Bones
Can sometimes be confused with the pelvis due to its broad, flat shape and curved edges. However, the shoulder blade lacks the closed ring structure of the hip bones and features a much thinner, blade-like body with a distinctive surface ridge.
Across Species
In running mammals like horses and deer, the shoulder blade is elongated to help lengthen the stride. In digging animals like moles, it is short, robust, and heavily built to anchor powerful muscle digging machinery. Birds have a saber-shaped shoulder blade that fuses with other elements to brace the wing against powerful flight stresses.
Evolutionary History
The shoulder blade evolved from the pectoral girdle of early fish ancestors, transitioning from a cluster of inner skeletal pieces in water-dwellers to a sturdy flat brace anchoring front limbs as vertebrates conquered the land.
Photography Tips
Place the bone flat against a neutral background with strong, angled side-lighting to highlight the surface ridge and depressions. Take one photo showing the flat outer face and another showing the inner cupped side.