PEENTISS: POLYDACTYLISM IN MAN AND DOMESTIC ANIMALS. 261 



" In such a hallux there is increase in the number of phalangeal joints. 

 This of course corresponds to the three-jointed pollex in man. ... In the 

 highest form of the reduplication the short toe is itself represented by two 

 digits, making six in all. Of this, also, there are many grades. 



" Lastly, any of these conditions may be seen on one foot only, while the 

 other foot shows one of the other states or is normally four-toed. Generally 

 speaking, however, there is a fairly close symmetrical agreement between the 

 two feet." 



Thus we see that a single cross between the Dorking and Leghorn 

 varieties produces all of the polydactylous abnormalities which investi- 

 gators have so far observed in the fowl. 



The conditions presented are interesting and noteworthy from their 

 structural similarity to the digital variations found in man and the 

 Carnivora. For here, too, we find that the abnormalities are mainly 

 confined to a reduced or modified digit, which becomes partially or 

 completely doubled. 



Howes ('92) and Anthony ('99) regard these abnormalities as due to 

 the splitting of the hallux, not as reversions to a five or six-toed ances- 

 tor. Bateson and Saunders (:02, p. 137) evidently agree with them, for 

 besides their allusions to " the reduplication " of the hallux, they class 

 the abnormalities as ''new characters " — "a palpable sport" (p. 137). 



The significance of their experiments and the bearing of " Mendel's 

 law " upon polydactylism will be discussed later with other theoretical 

 considerations. 



V. Polydactylism in Swine. 



A. Literature. 



Although polydactylism is quite common in the pig, and many cases 

 have been recorded, few careful descrii^tions have been given, and those 

 deal only with the skeletal parts. As a consequence, very conflicting 

 statements are made by different authors concerning the causes produc- 

 tive of the conditions, some maintaining that polydactylism in the pig is 

 atavistic, others that it is due to duplication of the whole foot, and still 

 others that it is to be accounted for only by haphazard variation. 

 Geoffrey St. Hilaire ('32-37), Gurlt ('77), Gegenbaur ('80), Bateson 

 ('94), and Werner ('97) have observed instances of digital variation in 

 swine. Otto ('41), Ercolani ('8l), and Blanc ('93) have given good 

 descriptions of the skeletal parts of a few cases. 



Ercolani obtained data as to the skeletal structure in twenty-five 



