Thoracic Vertebra
Irregular bone, part of the axial (core) skeleton.
Also known as: Backbone segment, spinal bone, or chine bone.
Classification
Irregular bone, part of the axial (core) skeleton.
Dimensions
These bones are generally small to medium-sized, characterized by a rounded central block and a very long, sloping 'fin' or spike that stands up from the top.
Key Features
The most obvious sign is the tall, narrow blade (spine) pointing away from the main block. Look for the small, flat circular spots on the sides where ribs used to tuck in, and the hollow tunnel in the middle where the spinal cord once rested.
Similar Bones
Neck bones (cervical) usually have holes on the sides for blood vessels and lack the long top spike. Lower back bones (lumbar) have wider, flaring 'wings' on the sides rather than the tall vertical spike seen here.
Across Species
In long-necked animals like giraffes, these segments are elongated, whereas in heavy grazers like bison or horses, the spikes on top are incredibly tall to provide anchor points for massive neck ligaments. Whales have flattened versions to help with streamlining in the water.
Evolutionary History
These segments evolved from simple protective arches in early fish to complex interlocking structures in land animals. The tall spikes developed as land-dwellers needed to hold their heavy heads up against the pull of gravity, serving as a biological crane system.
Photography Tips
Place the bone on a plain surface and take one photo looking straight through the central tunnel. Take a second 'profile' shot from the side to show the full height and angle of the tall upper spike.