Costal rib
Flat bone, part of the core axial skeleton
Also known as: Rib bone, ribcage bone
Classification
Flat bone, part of the core axial skeleton
Dimensions
Curved, elongated, and flattened in cross-section, varying significantly in length depending on its specific position along the chest wall.
Key Features
Distinguished by a pronounced sweeping curve, a flattened ribbon-like shaft, and a smooth outer surface paired with a grooved inner bottom edge.
Similar Bones
Can sometimes be confused with small curved fragments of limb bones or jawbones, but lacks the dense central cavity or tooth sockets typical of jaws.
Across Species
Ribs are found across almost all vertebrates with a backbone, though their number and shape vary wildly. Birds have specialized ribs with tiny backward-pointing overlapping tabs to stiffen the flight cage, snakes possess an extensive series of ribs attached to nearly every backbone segment for locomotion, and marine mammals have flexible ribs that can bend as water pressure changes during deep dives.
Evolutionary History
Ribs first evolved from ancient protective bony dermal elements and skeletal supports associated with the backbone in early fish ancestors, eventually shifting to form a protective basket around the heart and lungs in land-dwelling vertebrates.
Photography Tips
Place the bone flat against a neutral background next to a clear ruler for scale, and use overhead, diffused lighting to highlight the gentle curves and groove details.