PRENTISS: POLYDACTYLISM IN MAN AND DOMESTIC ANIMALS. 297 
b. Four metacarpals; digit 1 is represented by a splint radial to 
digit u, which is fully developed and composed of three phalanges 
(Fig. Y). 
In these cases there are four large bones present 
in the distal row of carpals. Digit 1 is large, and 
its metacarpal is fused throughout most of its length 
to that of digit mr. Four cases are cited by Marsh 
(’92), and one is carefully described by Bateson (94). 
A different interpretation from that here as- 
sumed may be brought forward in explanation of 
these cases. The digit designated as 1 in Figure 
Y may be regarded as a duplication of digit 111, and 
the so-called trapezoid of the carpus may represent 
a duplication of the os magnum. Then the bone 
designated as trapezium must be the true trapezoid, 
and its splint bone the second, not the first, meta- 
carpal. Only by a careful examination of the 
skeletal, muscular, and nervous structures can we 
determine which interpretation is correct ; whether 
eee a oe a: 7 
digit 1 is of vestigial origin, oF due to a duplication ee 
of digit 11. The fact that in phylogeny the pollex — yiew of left polydac- 
disappeared long before the fifth digit is a strong tyle manus of horse. 
. : . I, metacarpal of first 
argument against the former interpretation. For cw Manni 
: 5 supernumerary digi 
by that interpretation we should here have the pol- (pollex); su, second 
lex reappearing, and the second digit almost as large | supetnumerary digit; 
1 hed b Mawlanteelitdaee 4 eed iI, functional digit; 
as the third, while the fourth digit is unmodified  \y’ jetacarpal (splint) 
and the fifth is entirely absent. of fourth digit; 7, 
radius; trz., trape- 
é : zium; wn., unciform. 
borne on metacarpal 11. One case is described by (After Marsh.) 
Piitz (89) in which the trapezoid bears digit 11; 
this consists of a well-developed metacarpal bone and three phalanges. 
Radial to this is a large trapezium, articulating with the scaphoid and 
trapezoid and bearing a splint six cm. long; metacarpal Iv is normal, 
and on its ulnar side is another metacarpal element supposed to rep- 
resent digit v. The supernumerary elements in this case can only be 
c. Five metacarpals ; one supernumerary digit, 
explained as of vestigial origin. 
(2) Two digits borne on metacarpal 111. 
These are clear cases of duplication, and have been described in the 
manus only. The doubling may extend to the metacarpal bone, but is 
