PRENTISS: POLYDACTYLISM IN MAN AND DOMESTIC ANIMALS. 251 



II. Polydactylism in Man. 



A. Literature. 



On account of its importance to the medical profession, polydactylism 

 has been more often observed in man than in other vertebrates, numerous 

 cases having been described. Unfortunately the majority of the descrip- 

 tions are confined to the external appearance of the abnormalities, and to 

 the structure of the skeletal parts ; the anatomy of the muscles, and 

 still more important, that of the nerves, has seldom been thoroughly 

 worked out. Besides the many instances cited by Batesou ('94), the 

 observations of Morand (1773), Forster ('6l), Struthers ('63*), Ahlfeld 

 ('85-86), Fackenheim ('88),WindIe ('9l), Zander ('9l), and Wilson ('96) 

 are of especial importance. From the descriptions of the above investi- 

 gators, it appears that the supernumerary digits are more frequently 

 found on the manus than on the pes, and on both the right and left 

 extremities than on one side only. But in those cases where the abnor- 

 malities are symmetrically placed, the structural conditions of each 

 extremity may be different from those of tiie others. 



The most of the cases observed fall readily into two classes : 



(1) A supernumerary digit occurs on the radial side of the extrem- 

 ity (Fig. A) ; this digit may be of two or three phalanges, and in 

 the latter case the pollex (i*) is often composed of three elements instead 

 of two. In most cases where an extra digit is present on the radial side 

 of the manus, the abnormality is evidently due to a duplication of the 

 pollex, and it is not possible to say that either of the digits is the normal 

 thumb. These conditions hold good for the foot as well as the hand. 



(2) A supernumerary digit occurs on the ulnar side of the extremity 

 (Plate 1, Fig. 3). This digit may be (a) complete, of three phalanges, 

 and having its metacarpal articulating with the unciform (in the manus), 

 or (b) incomplete, of two or three phalanges which articulate with the 

 idnar side or distal end of metacai'pal v (minimus) ; in some cases the 

 extra digit may be merely attached to the minimus loosely by a peduncle 

 of the skin. Here again the digital variation usually occurs simulta- 

 neously on both hands, or both feet, or even on hands and feet ; the 

 conditions on the right and left sides, howevei-, may be different. It is 

 often impossible to tell whether the fifth or sixth digit is the true mini- 

 mus. In the well known case originally described by Morand (1773) 

 the muscular attachments peculiar to the minimus were transferred to 



