262 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
cases. Of these, there was only one instance where the supernumerary 
digits occurred on the posterior extremity. In four cases the abnor- 
mality was found on both fore feet ; and in all the specimens which he 
himself examined, or which were described by other observers, the extra 
digits occurred on the radial, or thumb, side of the manus. The ab- 
normalities as figured by Ercolani (Tav. 1, Fig. 1-6) consist in the 
presence of from one to three supernumerary digits. He found also 
that the trapezium of the carpus was well developed in most cases, and 
occasionally duplicated. In two cases, however, it was entirely absent, 
and Ercolani therefore concludes that its presence in connection with 
the supernumerary digits is no proof that polydactylism is atavistic ; 
for the trapezium is present also in most normal swine. Its absence is 
a deformity by defect and may occur in the normal manus. 
Blanc (93) considers most of the cases of polydactylism in swine as 
due to reversion. He figures four types: (1) Manus with an extra digit 
of two phalanges, representing the developed pollex (Fig. 7, p. 70). 
(2) An extra digit of three phalanges, which he regards as the pollex 
strongly developed; digit m is also abnormally large (Fig. 8). (8) 
Manus resembling (2), but with a small digit of two phalanges and a 
rudimentary metacarpal occurring on the radial side of digit 1 (Fig. 9). 
(4) Manus of six completely formed digits, the two supernumerary 
being large and of nearly equal size (Fig. 10). Blane considers types 
(3) and (4) as reversions to the hexadactyle ancestor of mammals. 
Two other cases are figured to illustrate the duplication of digits 
1 and IL. 
Gegenbaur (’80) examined two cases of polydactylism in the manus 
of the pig. In one specimen the carpals had been entirely removed, in 
the other they were partly cut away. From this fragmentary material 
he draws his conclusion, — that all cases of polydactylism in swine are 
monstrosities and not due to atavism. ‘The conclusions of Blanc and 
Gegenbaur are thus completely contradictory. 
If we reject the prae-pollex theory as untenable, the hexadactyle cases 
regarded by Blanc as reversions must be accounted for in some other 
way. On the other hand, Gegenbaur bases his arguments on the slender 
evidence of two mutilated specimens; there is need therefore of further 
investigation into the structural conditions peculiar to polydactyle swine, 
before his refutation of reversion can be accepted. In proceeding with 
our description of digital abnormalities in the pig we shall keep especially 
in mind their bearing on this question. 
