258 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



Digital variations arc extromely rare in the manus of the dog. Tho 

 pes, however, is quite often affected, and in the larger breeds (St. Bernard, 

 mastiff, and collie) the hallux is frequently present. All of the digital 

 variations which have come under ray observation were of the pes. As 

 we have seen, this consists of four digits, the hallux being normally 

 represented by only the proximal end of its metatarsal bone. The four 

 functional digits remain unmodified in all cases of polydactylism, and 

 the supernumerary digits occur on the radial side of digit ii, as varia- 

 tions of the hallux. We may distinguish three classes of these ab- 

 normalities : (1) Hallux, or "dew-claw," j)resent and formed of two 

 ])halanges articulating with the distal end of a rudimentary metatarsal. 

 This digit does not articulate with the proximal rudiment of meta- 

 tarsal I, but is merely held in place by the skin. Six cases were 

 observed in the shepherd dog, and five cases in the St. Bernard. 



(2) Hallux (Fig. D) presenting two well developed phalanges, of 

 which the proximal articulates with the rudimentary metatarsal bone; 

 this element is much longer than the normal phalanx. Three cases were 

 observed in the mastiff, and one case in the Scotch collie. 



(3) Hallux present as in (1), and more or less completely duplicated, ex- 

 hibiting two phalanges and the distal rudiment of a metatarsal. This is 

 the common condition in the pes of the St. Bernard dog. The duplica- 

 tion of the hallux may give rise to the rudiment of only a single ungual 

 phalanx, or there may be complete duplication, with the formation of 

 two similar digits (Fig. E. i", i''). In some cases tlio two ungual pha- 

 langes of i" and 1^ bear but a single large claw, which, however, usually 

 shows evidence of duplication. 



The cases of polydactylism which we have observed in Carnivora may 

 all be accounted for as modifications of the pollex and hallux. Except 

 for the change in symmetry of the phalanges of the extremities of the 

 cat, the rest of the manus or pes is unmodified. The conditions fuund 

 in the vianus of Carnivora are thus similar to the digital variations 

 whicli occur in the hand of man. In each case a functional, but reduced, 

 digit is affected. In man, however, it is the miniiuus which is normally 

 reduced, whereas in Carnivora it is the pollex. 



In the pes of Carnivora the conditions are spmewhat different. Only 

 a vestige of the hallux is normally present ; in cases of polydactylism, 

 this is developed and duplicated to a greater or less degree. It would 

 seem, however, that the same underlying cause which produces poly- 

 dactylism iu the manus (variation of a reduced but functional digit), 

 brings about also the digital abnormalities in tlie pes (variation of a 



