. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. PRENTISS: POLYDACTYLISM IN MAN AND DOMESTIC ANIMALS. 295 n. VI.' n. u. - 4 — 5?) J The nerves of this maniis also show important modifications. The normal manus, like that of swine, is innervated by four branches of the median nerve; tlie most radial and most ulnar branches (compare Fig. X, 2, 5) give off small twigs to the rudiments of digits ii and v. Branch 5 is joined by the ulnar nerve im- mediately before it divides to form 5 a and 5 b. In the polydactyle manus (Fig. X, 2, 5) the modification is in conn
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. PRENTISS: POLYDACTYLISM IN MAN AND DOMESTIC ANIMALS. 295 n. VI.' n. u. - 4 — 5?) J The nerves of this maniis also show important modifications. The normal manus, like that of swine, is innervated by four branches of the median nerve; tlie most radial and most ulnar branches (compare Fig. X, 2, 5) give off small twigs to the rudiments of digits ii and v. Branch 5 is joined by the ulnar nerve im- mediately before it divides to form 5 a and 5 b. 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 ii). 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 brand), together w^ith 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 in, but is due to the development of digit ii. 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, Fig. 30); the first and second phalanges of digit ii are fused together and are abnormally short. Rosenberg ('73) states that metacarpals II and v are present in tlie 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 these digital rudiments occasionally developed in the adult ruminant. Polydactylism in ruminants is thus of two types: (1) vestigial, duo to the development of either digit ii or v (or both) ; (2) terato
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