Scapula (fragment)
Flat bone, appendicular skeleton
Also known as: Shoulder blade, wing-bone
Classification
Flat bone, appendicular skeleton
Dimensions
Typically thin and plate-like, often wider at the top and narrow at the bottom where it meets the shoulder joint. These bones vary greatly in thickness depending on the animal's size.
Key Features
The most distinctive feature is a raised ridge called the spine that runs across the flat surface. This ridge acts like a structural beam for muscle attachment. The bone is generally triangular or fan-shaped, with one corner ending in a cup-shaped socket for the upper arm bone.
Similar Bones
Large fragments may be confused with the flat bones of the skull or the pelvis. However, the shoulder blade usually has a much smoother, flatter surface on one side and a very prominent, singular raised ridge on the other, unlike the curved bowls of the pelvis.
Across Species
The shoulder blade is a masterpiece of adaptation. In running animals like deer or horses, it is long and narrow, positioned on the side of the ribcage to allow for a huge range of front-to-back motion. In humans and apes, it is broad and flat, sitting on the back to allow for reaching out to the sides and overhead. Birds have a very narrow, blade-like version called the scapula that works with the wishbone to support flight muscles.
Evolutionary History
Originally part of a complex of several bones in early fish and tetrapods, the shoulder blade simplified over millions of years. As land animals moved their limbs from a sprawling position (like a lizard) to an upright position tucked under the body (like a dog or cat), the shoulder blade migrated to provide a stable platform for powerful leg muscles while disconnected from the spine to absorb the shock of movement.
Photography Tips
Place the bone on a neutral background with a common object like a coin or ruler for size reference. Take a top-down photo to show the overall outline and a side-view photo to capture the height of the central ridge.