Metacarpal and Phalanx Bones
Long Bones; Appendicular Skeleton
Also known as: Hand Bones (Palm and Finger Bones)
Classification
Long Bones; Appendicular Skeleton
Dimensions
These consist of five elongated bones making up the palm, followed by smaller, segmented bones that form the fingers. They generally range from a few inches down to less than an inch in length.
Key Features
The palm bones appear as straight shafts with rounded, knob-like ends. The finger bones are shorter and more cylindrical, narrowing slightly in the middle with flat or cupped joints at the ends for hinge-like movement.
Similar Bones
These can be confused with the metatarsals and phalanges of the foot. Hand bones are typically more slender and have a greater range of motion at the base compared to the more squared and robust bones of the foot.
Across Species
In many mammals, these bones are adapted for specialized movement. In horses, the middle metacarpal has evolved into a singular, stout cannon bone to support high-speed running, while in bats, these bones are extremely thin and elongated to support the flight membrane of the wing.
Evolutionary History
These structures evolved from the lobe-finned fish's pectoral fins. Over millions of years, the transition from water to land saw these elements differentiate into the 'pentadactyl' (five-fingered) limb pattern common to most modern land vertebrates.
Photography Tips
To identify these from a specimen, photograph from the top (back of the hand) and from the side. Using a neutral background and a ruler for scale helps distinguish between species of varying sizes.