PRENTISS: POLYDACTYLISM IN MAN AND DOMESTIC ANIMALS. 277 
A still greater development of digit I was exhibited in two of the 
cases studied. Such a manus is shown in Figure 17 (Plate 9). The three 
phalanges and metacarpal of digit 1 are larger than those of digit 1; 
the digit is borne on the trapezium, which is also large and articulates 
with the scaphoid and trapezoid. The other Skeletal elements of the 
manus are normal in structure. The musculature and innervation 
of these two cases were identical with those Shown in F igures OQ, Yi 
and Z, 
The cases thus far described possess but one extra digit. Continuing 
the examination of the polydactyle Series, it is found that this digit may 
be partially or completely doubled. 
b. Two SUPERNUMERARY Diairts, 
Ten cases were Studied. From the intermediate conditions found, it 
tions of those instances which have but a single extra digit. Figure 18 
(Plate 10) shows the skeletal structure of one of the simplest of these 
conditions. The anatomy of the manus resembles in general that seen in 
Figure 17 (Plate 9). Metacarpal 1 ig large and articulates with the tra- 
pezium, but instead of & single set of phalanges two series of bones are 
Present. One of these series (Plate 11, F ig. 19, 1°) may be small, pollex- 
like and composed of two phalanges, or both sets may be of nearly equal 
size and each consist of three elements (Plate 10, Fig. 18, 17, en OF 
four cages examined, three showed the latter condition, The trapezium 
and scaphoid are abnormally large in all cases, The musculature ig like 
that of the pentadactyle manus (Figs. O, P), but the tendons which there 
Supply the Single extra digit may here bifurcate, and be inserted into the 
two digits. The nerve branch which Supplies the first digit in Figure Z 
also divides (Fig. Q), so that in these cases there is undoubtedly a dupli- 
cation of digit 1, Eliminating this digit, the rest of the manus, save for 
the large size of the trapezium, would be entirely normal. 
We now pass to a polydactyle condition in which digit 1 is completely 
divided. The manus Shown in Figure 20 (Plate 12) ig interesting ag 
hexadactyle condition, and as additional evidence that the two extra 
digits are produced by the duplication ORAigib: TH - Hor in this case, al- 
though each is composed of a metacarpal and three phalanges, 1% and 
I” are alike in size and form ; still more noteworthy is the fact that the 
two ungual Phalanges are enveloped in a single hoof, and that the two 
metacarpals articulate with the Single trapezium, This carpal is large ; 
