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axial skeleton[′ak·sē·əl ′skel·i·tən]
the section of the skeleton in chordates and man that is located along the longitudinal axis of the body. The axial skeleton provides the principal support for the body and protects the central nervous system.
In acraniates, the axial skeleton is represented by the notochord, whose supportive function is conditioned by the elasticity and the toughness of the outer membranes. In certain craniate vertebrates, the vertebral elements develop from the skeletogenic tissue that surrounds the notochord and the neural tube, with the notochord persisting throughout the organism’s life. The analogous skeletogenic tissue in cyclostomes gives rise to the neural arches of the vertebrae. In certain fishes—holocephalids, Acipenseridae, and dipnoans—the skelatogenic tissue develops into the vertebral centra, as well as into the neural arches.
In most vertebrates and in man, the axial skeleton takes the form of a notochord only in the early stages of embryonic development; the notochord is later supplanted by the developing bodies of the vertebrae. The prolongation of the trunk’s axial skeleton is called the axial cranium, or the neurocranium, or the cerebrocranium, and protects the brain and the organs of olfaction, sight, and hearing.