PRENTISS : POLYDACTYLISM IN MAN AND DOMESTIC ANIMALS. 255 



digits. Digits v" and v* show ossification centres of only one phalanx, 

 while in ii, iii, and iv, two or three may be seen. This may indicate 

 that the development of digits v" and v* had been retarded, v* is slightly 

 smaller than v", but otherwise their skeletal structure is identical. 



Figures 1 and 2 (Plate 1) show a pair of feet from a fourth foetus 

 (number 6730), in both of which six distinct digits are present. The 

 right pes (Fig. 1) is noteworthy because of the condition of metatarsals 

 v" and V* ; these are nearly connected at their proximal ends, which 

 project further proximad than any of the other metatarsals. This is 

 another ground for assuming that v* and v* originated from the same 

 fundament. In the left foot (Fig. 2) these digits are considerably 

 smaller than the others and the proximal ends of their metatarsals also 

 project further proximad, i. e., toward the tarsus ; in both appendages 

 the first phalanx of digits v" and v* is the only one showing a centre of 

 ossification. 



To sura up our observations on these twelve cases of polydactylism, 

 we find : (1) the abnormalities in every instance affect the ulnar (fibular) 

 side of the extremity and probably only the fifth digit ; (2) in five cases 

 metacarpal (metatai'sal) v bears two digits ; these may be equally well 

 developed, or the one on the ulnar side may be more or less rudimentary ; 

 (3) in seven cases v" and v** are distinct from each other, although 

 showing evidence of a common origin; either one of these'digits may be 

 completely formed, or rudimentary, and it cannot be said that one of 

 them is the normal, and the other the abnormal, digit. 



There i^ no evidence of reversive modifications in the polydactyle ex- 

 tremities an account of which has been given here. Even if we admit 

 that the primitive ancestor of the mammalia was hexadactyle, there are 

 stili obstacles in the way of accounting for these abnormalities by rever- 

 sion. A discussion of these points- will be taken up in the theoretical 

 portion of this paper. 



III. Polydactylism in Carnivora. 



A. Literature. 



Hereditary digital variations in the extremities of the cat were ob- 

 served by Poulton ('83, '86); the anatomy of the skeletal parts has been 

 studied by Bateson ('94); and Howe (:02) has given a detailed account 

 of the general anatomy of a single case. Such abnormalities are com- 

 paratively rare in the dog, and of the few cases which have been 

 observed I know of none which have been carefully described. Blanc 



