Medical Definition of arch
1: an anatomical structure that resembles an arch in form or function: asa: either of two vaulted portions of the bony structure of the foot that impart elasticity to it: (1): a longitudinal arch supported posteriorly by the basal tuberosity of the calcaneus and anteriorly by the heads of the metatarsal bones (2): a transverse arch consisting of the metatarsals and first row of tarsals and resulting from elevation of the central anterior portion of the median longitudinal archb: arch of the aorta
2: a fingerprint in which all the ridges run from side to side and make no backward turn
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