PRENTISS : POLYDACTYLISM IN MAN AND DOMESTIC ANIMALS. 259 
vestigial digit). Whether this underlying cause is reversion, will be 
discussed later. 
CS]. me ewocioe woe 
Fia. D. — Left pes of dog, showing hallux 
fully developed. 1, hallux; asg., astragalus; cac., 
calcaneum; cub., cuboid; ec’cun., ecto-cuneiform ; 
en’cun., ento-cuneiform; ms’cun., meso-cunei- 
form; nav., navicular. 
Fic. E.— Left pes of dog, showing 
duplicated hallux. 1, rudimentary meta- 
tarsal of hallux;,1%, 1°, accessory digits ; 
asg., astragalus; cac., calcaneum; cwb., 
cuboid; ec’cun., ecto-cuneiform; en’cun., 
ento-cuneiform; ms’cun., meso-cunei- 
form; nav., navicular. 
IV. Polydactylism in the Fowl. 
Although the domestic hen is tetradactyle, the fifth digit was lost so 
early in phylogeny that it never appears in polydactyle abnormalities. 
As the hallux of the pes is reduced, however, polydactylism is entirely 
limited to this digit ; the condition is'thus directly comparable to that 
VOL. XL. — NO. 6 2 
