Tibia
Long Bone; part of the limb (appendicular) skeleton.
Also known as: Shinbone, Drumstick (in poultry), Shank bone
Classification
Long Bone; part of the limb (appendicular) skeleton.
Dimensions
Generally the second largest bone in the body, it is characterized by a long, straight shaft with a wide, flared top and a slightly smaller flared bottom.
Key Features
Look for a triangular cross-section in the middle of the shaft. The top is very broad with two flat surfaces for the upper leg bone to rest upon. A prominent, roughened ridge—the 'shin'—runs down the front of the bone. The bottom end usually has a distinct downward-pointing projection on the inner side that forms the inner ankle bump.
Similar Bones
The femur (thigh bone) is often confused with it, but the femur has a distinct round ball on a 'neck' at the top, whereas the shinbone has a flat, flared top. The humerus (upper arm bone) is also similar but has a more rounded top and a very different pulley-shaped bottom for the elbow junction.
Across Species
In nature, the shinbone is a master of weight-bearing. In horses and deer, it is exceptionally long to provide leverage for running. In birds, it merges with some ankle bones to form a single 'tibiotarsus,' which is the long part of a chicken leg. In contrast, swimming mammals like seals have very short, thick shinbones that serve as powerful anchors for flippers.
Evolutionary History
The shinbone can be traced back to the first lobe-finned fish that began to haul themselves onto land. Over millions of years, as land animals became heavier and more active, this bone grew sturdier and more vertical to support the body against gravity, eventually becoming the primary weight-bearing column of the lower leg.
Photography Tips
Lay the bone flat on a neutral background like soil or wood. Take one photo from directly above to show the full length, and another looking straight down at the wide top surface. Including a common object like a coin or a ruler helps show the size of the animal it came from.