260 bulletin: museum of comparative zoology. 



fouud in the pes of the dog and cat. The skeletal parts of the poly- 

 dactyle pes have been described l)y Cowpcr ('89), Howes ('92), 

 Bateson ('94), and Anthony (99). Tlie last-named writer also ex- 

 amined the pedal musculature of the Dorking. 



Polydactylism, generally rare in birds, is quite common among the 

 Gallinaceae, especially tlie domestic fowl. It has become a fixed 

 chai'acteristic 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 ii-iv have their meta- 

 tarsals fused together ; v 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 bo 

 grouped into three classes : 



(1) Pes of five digits, metatarsal i 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 polydactyloua Dorking 

 fowl with white and brown Leghorn varieties, found tliat in the resulting 

 offspring the polydactylous character is dominant, though not completely 

 so, over the normal pes of the Leghorn. In addition, the superjiumerary 

 digits of the crosshreds varied greatly from their structure iti 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-toe(l bird, with a long niany-joiiited digit 

 proximal to it pointing upwards. Tlie two, however, may often be both short, 

 pointing downwards, never both long. This condition ranges through many 

 stages of bigeniination 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 "[A chick lias lately occurrefl with n 'lonq' hallux bigeminus of tin's sort — 

 probably a hitherto unrecorded form.] March, 1902." 



