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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.