254 BULLETIN : MUSEUM OF COMPAKATIVE 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 pulydactylisui are probably all abnormalities pro- 

 duced by the splitting of tlie 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 witli it articulate two digits of nearly 

 equal size, each consisting of two plialanges. 



Tlie 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 (Fig. 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 tlie 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 tlicre is complete splitting of this 

 digit. Here, too, we are unable to say with certainty that cither 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 not articulating with it. Tliis digit is composed of three 

 skeletal elements, of which tlie two distal from their form may be inter- 

 preted as representing the first and third phalanges. Tlie proximal 

 element is a small nodule of bone, and may be the rudiment of a 

 metacarpal. IMetacarpal v is apparently normal, as is the digit v". 



The right pes of the same foetus (Plate 2, Fig. 10) has six distinct 



