PRENTISS: POLYDACTYLISM IN MAN AND DOMESTIC ANIMALS. 253 
skiagraphs of the more important abnormalities. In every case ex- 
amined the extra digit appeared on the ulnar side of the manus 
or pes. 
The polydactyle extremities were from late foetal stages ; the carpals and 
tarsals, therefore, show little or no calcification, and only the diaphyses 
of the digital elements are ossified. The specimens were on exhibition 
in the cases of the museum, and so could not be dissected. 
Number 912 (Plate 1, Figs. 3-6) is an interesting case. This foetus 
shows an extra digit on each hand and foot. In the right manus (Fig. 
4) there are only five metacarpals, but the fifth shows evidence of dupli- 
cation. It is abnormally large at its distal extremity, and from the ulnar 
side of this end projects a bony process. This process is directed some- 
what proximad, and with it articulates the supernumerary digit (v°), 
which is little more than half the length of v*, and consists of but two 
phalanges. ‘The other digits of this manus are apparently normal in all 
respects. 
The structural conditions of the right foot (Fig. 6) are very similar 
to those of the right manus. The fifth metatarsal is short, and nearly 
as broad as long; a small protuberance on its ulnar side marks the 
point of articulation for the extra digit. The supernumerary digit 
shows only two ossification centres, but the incompletely calcified 
condition exhibited by the normal digits leads one to suppose that three 
phalanges might have been developed eventually. The supernumerary 
digit (v’) is somewhat smaller than v*, which may be interpreted as 
the normal fifth digit. 
The left manus (Fig. 3) presents a different skeletal structure. The 
first four digits are normal as before, but the supernumerary one (v*) is 
apparently located on the radial side of the normal fifth digit (v°). 
The two are entirely independent of each other, and are of nearly the 
same size. From the appearance of the phalanges it is difficult to say 
which is the normal digit ; however, the metacarpal of V® is ossified at 
its distal end only, thus indicating that it is the interpolated digit. 
The digits of the left pes (Fig. 5) resemble in their structure those of 
the corresponding manus. There are six distinct digits, and all of the 
metatarsal bones are well developed. The four external (ulnar) digits 
are similar in structure, each being composed of a metatarsal and two 
phalanges ; the ossification centre of the middle phalanx has not yet ap- 
peared. The phalanges of digit v’ are smaller, and its metatarsal 
bone is shorter than the corresponding skeletal elements of the other 
digits. We may therefore consider it as the extra digit, and from the 
