PRENTISS: POLYDACTYLISM IN MAN AND DOMESTIC ANIMALS. 263 
B. OBSERVATIONS. 
The thirty-six specimens of polydactylism in the pig which are to be 
described were collected at The North Pork Packing establishment, 
Somerville, near Boston, Mass., by Mr. Charles Bullard. In certain 
cases the manus was severed from the arm at the inter-carpal joint, and 
consequently the upper row of carpals was lost. These bones, however, 
are fortunately not so important for study as those of the lower row, 
which were saved in all but one case. 
In preparing the specimens for study they were first dissected merely 
enough to allow a spreading of the digits, and were then skiagraphed. 
I am indebted to the Director of the Jefferson Physical Laboratory of 
Harvard University, and to Professor Sabine for kindly allowing me the © 
use of electrical apparatus for this purpose. After obtaining skiagraphs 
of the more important abnormal types, the muscles and nerves were 
dissected. Finally the bones of the carpus and metacarpus were studied 
and separately compared, first with the corresponding parts of the nor- 
mal manus, and next with those of the fossil swine figured by Kowa- 
levsky (73) and by Scott (95). By the latter means it was possible to 
ascertain whether or not the manus of the polydactyle pig reverts to 
that of more primitive fossil forms in characters other than the presence 
of extra digits. 
Before passing to a description of the various abnormal specimens 
which have been studied, it may be well to examine the normal manus 
of the pig, and compare its skeletal elements with those of its fossil 
ancestors. 
The pollex, or digit 1, is normally absent in all living artiodactyles, 
and the remaining digits are arranged in two pairs (Plate 3, Fig. 11). 
Of these, 1 and Iv are large, functional, and of equal length ; 1 and 
v are only two thirds as long, and do not ordinarily reach the ground, 
11 being usually the smaller. Each digit consists ofa metacarpal and three 
phalanges. The metacarpals of digits 11 and Iv are large and their 
proximal extremities interlocked ; rv articulates with the ulnar side of 
ui and is partially over-lapped proximally by the large process of the 
latter. In the same way a radial process from digit 11 overlaps meta- 
carpal 1, and, as we shall see, is a distinguishing mark in the manus of 
the modern pig. The phalangeal region of the manus is bilaterally sym- 
metrical, the ungual phalanx and hoof being concave on the side facing 
the median plane of the manus, and convex on the side turned away 
