theoddmentemporium:

Polydactyly is the anatomical abnormality of having more than the usual number of digits on the hands orfeet. It is a congenital abnormality, usually geneticallyinherited as an autosomal dominant trait. There are several varieties of polydactyly; this X-ray photographshows a left hand with middle ray duplication. In Western societies, the additional digits are usuallysurgically removed during early life.

Photo credit: Drgnu23 and Grendelkhan