has part has part characteristic of inheres in has modifier Partial absence of thumb Aplasia/Hypoplasia of the 1st metacarpal Aplasia of the 1st metacarpal 2009-05-27T04:25:14Z In contrast to the proximal phalanges of the digits 2-5, the proximal phalanx of the thumb is embryologically equivalent to the middle phalanges of the other digits, whereas the first metacarpal is embryologically of phalangeal origin and as such equivalent to the proximal phalanges of the other digits. HP:0010035 Absent first metacarpal Absent first metacarpal (long bone) of the hand. UMLS:C1838610 HP:0006027 Absent 1st long bone of hand Aplasia of metacarpal bones Aplasia of the proximal phalanges of the hand abnormal aplastic metacarpal bone of digit 1