A cone-shaped appearance of the epiphysis of the proximal phalanx of the thumb of the hand, producing a 'ball-in-a-socket' appearance. This epiphysis is located at the proximal end of the phalanx and is normally nearly flat. The related entity 'angel-shaped' epiphysis refers to a pronounced cone-shaped epiphysis in combination with a pseudoepiphysis at the distal end of the phalanx. 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. [from HPO]