PRENTISS: POLYDACTYLISM IN MAN AND DOMESTIC ANIMALS. 291 
cular attachments and the innervation of the extra digit are entirely 
distinct from those supplying and innervating digit 11. We can only 
conclude, therefore, that in these cases the supernumerary digit is not a 
duplication of digit 1. If it were such a duplication, why should not 
the fifth digit be affected as often as the second? On the contrary, a 
every polydactyle manus so far observed the supernumerary digit is found 
on the radial side of digit u. 
There is no doubt that abnormalities due to the duplication of a func- 
tional digit may occur in the manus of the pig as in other mammals; 
but in the majority of cases the origin of the extra digit must be vestigial. 
By variation and duplication of this vestige in its development, two or 
more supernumerary digits may be formed. Whether or not the develop- 
ment of this digital vestige is due to reversion, we will discuss in the 
theoretical portion of this paper. 
Summing up the facts obtained as to polydactylism in the pig, it is 
found that — 
1. Polydactylism is confined almost entirely tothe manus. (This fact 
is interesting, as the condition restores that found in fossil swine. In the 
pes of Ancodus the hallux is entirely gone, although in the manus the 
pollex is well developed. If we regard the extra digit as due to duplica- 
tion of digit 11 we should expect this duplication to occur as often in 
the pes as in the manus; but if the extra digit is vestigial in its origin, 
the early and complete reduction of the hallux in fossil swine is good 
reason for its never being developed in the pig of the present day.) 
2. The supernumerary digits in every case occur on the radial side 
of the second normal digit. 
3. In nineteen of the thirty-six cases examined, a single super- 
numerary digit is present ; in five instances this digit is composed of two 
phalanges ; in nine cases, of three ; and in five instances its metacarpal 
is fused to that of digit 11. 
4. In the remaining seventeen specimens thirteen are hexadactyle, 
although in three cases the metacarpal of one supernumerary digit (1°) 
is fused to that of digit 11; in three instances two supernumerary digits 
are present, but digit 1 is entirely wanting ; and in one specimen there 
are evidences of three extra digits. . 
5. In more than a third of the cases examined, the skeletal, muscular, 
and nervous organs of the manus give some evidence that the extra 
digit is vestigial. 
6. The trapezium (so-called) may represent this carpal element plus 
the rudiment of digit 1, 
VOL. XL. — NO. 6 4 
