thoracomelus

Unequal conjoined twins in which the parasite, often only a single arm or leg, is attached to the thorax of the autosite. See conjoined twins, under twin. [thoraco- + G. melos, limb]

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tho·ra·com·e·lus (thor″ə-komґə-ləs) [thoraco- + Gr. melos limb] a fetus with a supernumerary limb attached to the thorax.