Harris Hawthorne Wilder 453 



the finger patterns of twinned fingers in those cases of hyperdactylism in 

 which it is probable that the extra digit may be referred to a doubling 

 of one of the normal ones, as in a double thuml). I have received prints 

 of two individuals exhibiting this phenomenon, in both cases on the 

 right hand alone, and have special thumb prints of one of these. I had 

 naturally expected, a priori, that the patterns of the two right thumbs 

 would prove to be duplicates of one another, but such is by no means 

 the case. In this individual the "outer" (external or radial) thumb 

 shows a typical radial loop, a rare pattern for a thumb, while the " inner " 

 (internal) thumb is marked by a simple arch. The left thumb pre- 

 sents an ulnar loop. That the supernumerary digit is rightly classed 

 as a thumb is shown by its origin, evidently from a common 1st meta- 

 carpal, and the two thumbs are united as far as the middle of the 

 proximal phalangeal joint, and lie so near one another that the rolled 

 prints were taken with considerable difficulty. The pattern of the 

 right index finger adjacent to the inner thumb is an ulnar loop. Of the 

 other individual with double thumbs I possess only the general print of 

 the volar surface of the hand, but in this the inner thumb is turned in 

 such a way as to suggest that its pattern, as in the other case, is a simple 

 arch. This conclusion is not absolutely reliable on account of the incom- 

 pleteness of the print. In addition to the above, five cases of hyper- 

 dactylism in which the supernumerary digit is a post-minimus, have 

 come under my observation, but as in all of these the extra finger had 

 been removed the data obtained were those of the palm alone. 



It would be premature to offer any conclusion based upon a single 

 observation, but it may be allowable to point out that the occurrence of 

 patterns of distinct types upon the two terminal phalanges of a " double- 

 thumb " contrary to all expectation, is naturally in opposition to all 

 theories that suggest a splitting of the anlage, a double set of determi- 

 nants or any cause involving a duplication of parts, as an explanation 

 of such a phenomenon. If, with Zander, we believe that an originally 

 single anlage is split by the tension of amniotic threads, or if, with 

 Tornier, we consider one of the thumbs the result of super-regeneration 

 from the other, or " Stamm-individuum," we must in some way account 

 for the total lack of resemblance between the two resulting parts. This 

 would seem a fruitful field for investigation, and the comparison of the 

 finger patterns of supernumerary digits may lead to interesting results. 



Summing up the results obtained from a comparison of the finger- 

 patterns of the two types of twins, they corroborate in general the .con- 

 clusions reached from a similar comparison of the palms, although it 

 seems as though the correspondences are not of as exact a nature as is 



