PRENTISS: POLYDACTYLISM IN MAN AND DOMESTIC ANIMALS. 
The nerves of this manus also show important modifications. 
295 
The 
normal manus, like that of swine, is innervated by four branches of the 
median nerve ; the most radial and most ulnar branches (compare Fig. 
X, 2, 5) give off small twigs to the rudiments of digits m and v. 
Branch 5 is joined by the ulnar nerve im- 
mediately before it divides to form 5 a and 
5 &. In the polydactyle manus (Fig. X, 2, 
5) the modification is in connection with 
the small fasciculus (2°), which normally 
innervates the radial accessory hoof (rudi- 
ment of digit 1). This is no longer a 
mere filament ending at the distal end of 
the metacarpus, but a moderate-sized 
branch, which continues to the hoof and 
ungual phalanx of the supernumerary 
digit. The condition of this nerve branch, 
together with the fact that the accessory 
hoof of this side is absent, affords most con- 
vincing proof that this abnormality is not 
a monstrosity, or a duplication of digit 111, 
but is due to the development of digit mu. 
The second case, a right manus, con- 
firms by its structure the conclusion which 
we have drawn from the first. 
The line of demarkation between the 
second and third metacarpals is even more 
distinct (Plate 22, Vig. 30); the first 
and second phalanges of digit 11 are fused 
together and are abnormally short. 
Rosenberg (’73) states that metacarpals 
1 and v are present in the embryo of 
the sheep and ox, but later partially de- 
generate and fuse to the cannon bone, a 
small portion of v remaining distinct in 
the ox. In the Cervidae the distal ends 
of the metacarpals persist in the adult. 
It is not surprising therefore that we find 
JOVscoe LN Tele 
Fic. X. — Posterior view of 
left polydactyle manus of the calf, 
showing innervation. I, extra 
digit; v, metacarpal of fifth digit; 
m.m., median nerve; n. u., ulnar 
nerve; 2-5, four branches of me- 
dian nerve; 2¢, division of second 
branch which supplies the extra 
digit (11); 54, division of fifth 
branch which innervates the ac- 
cessory hoof (digit v). 4 natural 
size. 
these digital rudiments occasionally developed in the adult ruminant. 
Polydactylism in ruminants is thus of two types: (1) vestigial, due 
to the development of either digit 1 or v (or both); (2) teratological, 
produced by the duplication of one of the functional digits (1m or Iv). 
