292 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
7. The extra digits articulate with the trapezium in nearly every case ; 
they therefore represent the development of a vestigial pollex, but may 
vary extremely from the normal pollex structure. 
8. There may be cases where the extra digit is formed by the dupli- 
cation of digit 1, but there is strong evidence against this being the 
general rule. 
9. Two supernumerary digits may be formed by the duplication of 
the vestigial pollex ; there are no grounds for considering one of them a 
“ prae-pollex.”’ 
VI. Polydactylism in Ruminants. 
A. LITERATURE. 
Observations have been made on polydactylism in ruminants and 
descriptions given by Geoffroy St. Hilaire (32-37), Goodman (’68), 
Chauveau et Arloing (79), Boas (90), Baumiiller (92), Blanc (93), 
and Bateson (94). In the normal manus of ruminants, 111 and Iv are 
the functional digits, and in all forms save the water chevrotain their 
metacarpals are fused to form a single “cannon bone.” The pollex is 
always wanting; digits m and v are reduced in varying degrees in the 
different groups of ruminants. In the came] they are wanting; in the 
ox metacarpal Vv remains as a proximal rudiment; the phalanges are 
completely gone, but a “dew-claw” represents each hoof. The sheep 
has the two distal phalanges and hoofs of m and v persistent, while in 
the Cervidae these digits are represented by three well-developed pha- 
langes and the distal ends of the metacarpal bones; the hoofs of digits 
1 and v are functional when the deer is running or travelling over soft 
ground. Inthe water chevrotain there are four complete digits, each 
formed of a distinct metacarpal and three phalanges. 
I know of no instance of polydactylism in the camel, and there are 
few descriptions of such abnormalities in sheep. Geoffroy St. Hilaire 
(32-37) describes the manus of a lamb in which digits 1, 11, and v were 
developed ; digits 1 and 1 were borne on the same metacarpal and 
probably represent a duplicated condition of digit mu. The best de- 
scription of polydactylism in the sheep is that of Chauveau et Arloing 
(79). The manus of a lamb is figured, in which both the second and 
fifth digits are developed, each being composed of a distinct metacarpal 
element and three phalanges nearly as large as those of the functional 
digits. This condition is certainly due to the development of vestiges, 
and has been attributed to reversion. 
