Metatarsal or Metacarpal (Cannon Bone)
Long bone, part of the limb (appendicular) skeleton
Also known as: Cannon bone, hand bone, foot bone
Classification
Long bone, part of the limb (appendicular) skeleton
Dimensions
In medium-to-large hoofed mammals like deer or sheep, these main limb bones typically measure between 6 and 12 inches in length. They are characteristically long, straight, and slender with a distinctly flattened cross-section.
Key Features
Look for a long, straight shaft with a clear vertical groove running along the surface like a shallow trough. The lower end broadens out into rounded, spool-like joint surfaces separated by a distinct ridge, which helps lock the toe joints in place during rapid forward movement.
Similar Bones
Can be easily confused with the upper arm bone (humerus) or thigh bone (femur). However, cannon bones are much straighter, more uniform in width throughout the shaft, and lack the offset rounded head characteristic of a thigh bone or the twisted shape of an upper arm bone.
Across Species
In hoofed mammals like deer, cattle, and horses, the middle bones of the hand or foot have fused together over millions of years to form a single, exceptionally strong structural pillar known as the cannon bone. A deer's cannon bone has a prominent vertical channel running down its front surface, marking where two separate bones joined into one. In contrast, humans and bears retain five individual, separate palm and foot bones, allowing for flexible grasping rather than pure running speed.
Evolutionary History
As early mammal ancestors adapted to open grasslands and swift running, their foot structure underwent dramatic changes. To increase stride length and speed, early ungulates stood higher on their toes. Over deep evolutionary time, side toes were reduced or lost entirely, while the central hand and foot bones lengthened and fused together to act as a lightweight, shock-absorbing lever.
Photography Tips
Lay the bone flat on a plain background with a ruler or coin alongside for scale. Capture a straight-on photo of the full length to show the central groove, followed by clear, close-up shots of both ends to highlight the joint surfaces.