PKENTISS: POLYDACTYLISM IN MAN AND DOMESTIC ANIMALS. 253 



skiagraphs of the more important abnormalities. In every case ex- 

 amined the extra digit appeai'ed 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 



