260 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
found in the pes of the dog and cat. The skeletal parts of the poly- 
dactyle pes have been described by Cowper (’89), Howes (’92), 
Bateson (94), and Anthony (99). The last-named writer also ex- 
amined the pedal musculature of the Dorking. 
Polydactylism, generally rare in birds, is quite common among the 
Gallinaceae, especially the domestic fowl. It has become a fixed 
characteristic of the Dorking breed, and also occurs quite constantly 
in the Houdan variety. In the normal fowl, as is well known, the hallux, 
or first digit, is articulated at the side of the tarso-metatarsal, by a dis- 
tinct rudimentary metatarsal element. Digits 11—-1v have their meta- 
tarsals fused together ; vV is entirely wanting. In nearly all cases of 
polydactylism in the fowl a supernumerary digit (sometimes two) 
occurs on the tibial side of the hallux. The abnormalities may be 
grouped into three classes: 
(1) Pes of five digits, metatarsal 1 bearing a normal hallux, and 
tibial to this a digit of three phalanges (Cowper, ’89, p. 249). This 
is the most common condition. 
(2) Pes of five digits ; the supernumerary digit is borne upon the 
proximal phalanx of the hallux instead of articulating with its meta- 
carpal. This condition is quite frequent. 
(3) Pes of five digits; the hallux being completely divided into 
two digits of two or three phalanges each (Howes, ’92, Fig. 5). 
Single cases have been described in which two extra digits occur. 
Of these, one possesses three phalanges, is placed at the tibial side of 
the: hallux, and has an independent articulation with the tarso-meta- 
tarsus ; the other exhibits only two phalanges and is formed by the 
more or less complete duplication of the hallux. 
Bateson and Saunders (:02) by crossing the polydactylous Dorking 
fowl with white and brown Leghorn varieties, found that in the resulting 
offspring the polydactylous character is dominant, though not completely 
so, over the normal pes of the Leghorn. In addition, the supernumerary 
digits of the crossbreds varied greatly from their structure in the normal 
Dorking. They are described as follows (p. 97): 
‘When present the two hind toes may consist, as in the normal Dorking, of 
a short toe, like the hallux of a 4-toed bird, with a long many-jointed digit 
proximal to it pointing upwards. The two, however, may often be both short, 
pointing downwards, never both long. This condition ranges through many 
stages of bigemination down to mere bifidity of the nail. A form very rarely 
seen is an elongation of the hallux without any extra toe being present. 
1 “fA chick has lately occurred with a ‘long’ hallux bigeminus of this sort — 
probably a hitherto unrecorded form.] March, 1902.” 
