34° 



I'OrULAR SCIENCE MONTHLY 



dog. Normally the hallux, or great toe, is represented only by the 

 proximal end of the metatarsal bone ( Fig. 2, A ) . Not infrequently, a 

 claw and one or two phalangeal bones may appear at the point where 

 the hallux should be; occasionally the distal end of the metatarsal bone 

 is also represented, and sometimes a complete digit with all the bones 

 and articulations of a functional hallux may be developed. Such cases, 

 which may be regarded with certainty as reversions to the five-toed type 

 of foot, occur not rarely on the pes of the Scotch collie, St. Bernard 

 and Newfoundland (Fig. 2, B, C). 



In the foot of the pig the hallux is gone and the pollex is normally 

 represented by a small carpal rudiment (Fig. 3, C). A small pollex 

 was, however, present in the manus of Ancodus, one of the fossil swine 



Fig. 4. X-ray photographs of the pig's manus showing normal structure and reversionary 

 pol>dactylism. A, bonesof normal manus; B, manus in which the pollex is represented by 

 two phalanges and the distal end of the metacarpal bone (I.); C, manus with pollex completely 

 developed; irz., trapezium. 



(Fig. 3, A). It is, therefore, an interesting fact that in the polydactyl 

 swine observed by the writer the extra digits were in every case located 

 upon the manus, and in most instances were undoubtedly developed 

 from the rudiment of the pollex ; for the extra digit was attached to the 

 carpal bone as a normal pollex would be, and careful dissections of 

 muscles and nerves gave no evidence of duplications. This does not 

 support Gegenbaur's assertion that the extra digits of swine were devel- 

 oped by the splitting of the second toe. His conclusion was based on 

 the dissection of two ' pig's knuckles ' cut off below the carpus. Conse- 

 quently he could not tell how the extra digit was attached. In any case 

 this was scanty evidence on which to base a general conclusion. The 

 writer was fortunate enough to obtain for study thirty-six perfect speci- 

 mens. In one type observed, a small hoof, two phalanges and the 



