PRENTISS: rOLYDACTYLISM IN MAN AND DOMESTIC ANIMALS. 263 



B. Observations. 



The thirty-six specimens of polydactylism in the pig which are to bo 

 described were collected at The Noi-th Pork Packing establishment, 

 Sonierville, near Boston, Mass., by Mr. Charles Ballard. In certain 

 cases the luanus was severed from the arm at the inter-carpal joint, and 

 conseqnently 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 w^as 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 poUex, or digit i, is normally absent in all living artiodactyles, 

 and the remaining digits are arranged in two pairs (Plate 3, Fig. 11). 

 Of these, iii and iv are large, functional, and of equal length ; ii and 

 v arc only two thirds as long, and do not ordinarily reach the ground, 



II being usually the smaller. Each digit consists of a metacarpal and three 

 phalanges. The metacarpals of digits in and iv are large and their 

 proximal extremities interlocked ; iv articulates with the ulnar side of 



III and is partially over-lapped proximally by the large process of the 

 latter. In the same way a radial process from digit iii overlaps meta- 

 carpal II, 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 



