In a previous communication on a study of 6 cases of triphalangeal thumb, we1 postulated that triphalangism of the thumb should be regarded as incomplete development of one of the phalanges of the bifid thumb. According to this theory, "the additional phalanx of the triphalangeal thumb is not a true middle phalanx similar to that of the lesser fingers, but a remnant of the base of one of the phalanges of a bifid thumb." Six cases of triphalangeal thumb associated with bifid thumb in the same person were observed subsequent to our first communication1 and furnish supporting evidence for this theory. Six additional cases, found in the course of examination of draftees at the New York Recruiting and Induction Station, are presented here. REPORT OF CASES Case 1. —A Negro truckman, aged 27 years and a native of Georgia, was a well built, normal person except for his