254 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
conditions found in the hands and the right foot, it seems reasonable to 
assume that the fifth digit has been duplicated. 
These four cases of polydactylism are probably all abnormalities pro- 
duced by the splitting of the fundament of the fifth digit ; each instance 
differs slightly from the others, but the manus and pes of the right side 
are of somewhat similar skeletal structure, and the same is true of the 
left appendages. In the appendages of the right side the fifth digit is 
incompletely duplicated. In those of the left side the division is com- 
plete; in the manus the metacarpus of the more internal of the two 
digits (v*) is amorphous, while in the pes digits v* and v® are both 
distinct and perfectly developed. 
We are not warranted in assuming that either v¢ or v® is the extra digit. 
In the right hand v* is better developed, in the left hand v?’, while in 
the feet it is difficult to distinguish any difference between the two. 
Number 5809 is a foetus which, like 912, exhibits a hexadactyle con- 
dition in all four appendages. Both feet are identical in skeletal struc- 
ture with the pes shown in Figure 6 (Plate 1); the fifth metatarsal is a 
massive bone, as broad as long, and with it articulate two digits of nearly 
equal size, each consisting of two phalanges. 
The right manus (Plate 2, Fig. 8) resembles the left manus of number 
912 (Plate 1, Fig. 3); the digits v¢ and v® are distinct, but the meta- 
carpal of v* is amorphous. The left manus (ig. 7) exhibits a peculiar 
condition. Metacarpal v is abnormally large, especially at its distal 
end; with it articulate the two digits v* and v’.  v*% is apparently 
normal in form, size, and the number of its phalanges. v®, however, is 
small, and directed proximad. Its three phalanges are small and the 
distal one is double. 
There are, thus, three instances in which digit v is incompletely 
duplicated, and a single case in which there is complete splitting of this 
digit. Here, too, we are unable to say with certainty that either v* or 
v’ is the extra digit. 
In a third foetus, number 913 of the Warren Museum, only the 
left manus and right pes were preserved. The manus (Plate 2, Fig. 9) 
has a small supernumerary digit (v’) on the ulnar side of meta- 
carpal v, but net articulating with it. This digit is composed of three 
skeletal elements, of which the two distal from their form may be inter- 
preted as representing the first and third phalanges. The proximal 
element is a small nodule of bone, and may be the rudiment of a 
metacarpal. Metacarpal v is apparently normal, as is the digit v*% 
The right pes of the same foetus (Plate 2, Fig. 10) has six distinct 
