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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 Bateson (’94), the 
observations of Morand (1773), Forster (61), Struthers (’63"), Ahlfeld 
(85-86), Fackenheim (’88), Windle (’91), Zander (’91), 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 the others. 
The most of the cases cbserved 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 (1°) 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 (6) incomplete, of two or three phalanges which articulate with the 
ulnar side or distal end of metacarpal 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, however, 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 
