PRENTISS: POLYDACTYLISM IN MAN AND DOMESTIC ANIMALS. 255 
digits. Digits v* and v’ show ossification centres of only one phalanx, 
while in 1, 111, 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 sum 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 (metatarsal) 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 is 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 
stil: 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. Blane 
