ischiomelus

Unequal conjoined twins in which the parasite, often only an arm or a leg, arises from the pelvic region of the autosite. See conjoined twins, under twin. [ischio- + G. melos, limb]

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is·chi·om·e·lus (is″ke-omґə-ləs) [ischio- + Gr. melos limb] a fetus with an extra limb attached at the base of the vertebral column.