Thoracic Vertebra
Irregular Bone; part of the axial (core) skeleton
Also known as: Backbone segment, Spine bone, Mid-back vertebrae
Classification
Irregular Bone; part of the axial (core) skeleton
Dimensions
In medium-sized mammals like deer, these bones are generally 2 to 4 inches tall, characterized by a long upright spike and a chunky, drum-shaped base.
Key Features
Look for a tall, blade-like fin on the top side and a solid, rounded cylinder on the bottom. To the sides, you will find smaller wing-like knobs and smooth, flat circular areas where the ribs once tucked into the bone.
Similar Bones
Can be confused with Neck (Cervical) Vertebrae, which usually have larger openings for nerves and shorter spikes, or Lower Back (Lumbar) Vertebrae, which have wider horizontal 'wings' and lack the smooth indented areas for rib attachment.
Across Species
Across the animal kingdom, these bones adapt to unique lifestyles. In bison and rhinos, the upright spikes are incredibly long to provide anchor points for massive neck muscles. In birds, many of these bones are fused together to provide a rigid platform for flight, while in snakes, they are simplified and numerous to allow for extreme slinking flexibility.
Evolutionary History
These structures evolved from simple protective arches over the nerve cord in early fish-like ancestors. As animals moved onto land, these bones became sturdier and more interlocking to support the body's weight against gravity, eventually developing the specialized mid-back forms that serve as the main stabilizers for the rib cage in modern mammals.
Photography Tips
Place the bone on a flat surface and take one photo looking straight down at the top 'spike.' Take a second photo from the side to show the profile of the drum-shaped base, and include a common object like a coin or a ruler for size reference.