appendicular skeleton The part of the vertebrate endoskeleton that is composed of paired fin or limb bones, and the pelvis. Fins of vertebrate fish have a basic morphology composed of three elements: a small number of fan-like basal elements support a greater number of cylindrical radials, which in turn support a large number of fin rays. These may be soft and flexible (soft rays) or hard and inflexible (fin spines), supporting the fin web. The limbs of tetrapods articulate with a pectoral (scapula) or pelvic (pelvis) girdle and consist of five segments: the propodium (humerus or femur); epipodium (ulna/radius or fibula/tibula); mesopodium (carpus or tarsus); metapodium (metacarpus or metatarsus); and phalanges. Although pectoral and pelvic fin and limb appendages have an apparently homologous structure, they are derived serially from different body segments. Compare AXIAL SKELETON. See also PENTADACTYL.

appendicular skeleton The components, collectively, of the vertebrate skeleton that are attached to the main supporting, or axial, skeleton. The appendicular skeleton is made up of paired appendages (e.g. legs, wings, arms) together with the pelvic girdle and pectoral girdle.