PRENTISS: POLYDACTYLISM IN MAN AND DOMESTIC ANIMALS. 273 



The innervation of the extra digit is also noteworthy. The median 

 nerve (Fig. L, n.in.) gives off on the radial side of its normal divisions 

 a small additional branch (1). This divides like the other branches, 

 sending one division to digit ii and the other to the pollex. 



Closely resembling the cases just described, are two instances of poly- 

 dactylism in which the trapezium is fused to the supernumerary meta- 

 carpal. The extra digit is very small, and the metacarpal articulates 

 well up on the radial side of the trapezoid. This condition favors the 



lun. 



cun. 



OS mag. 



trzd 

 trz. 



Fig. M. — Anterior view of left polydact3-le maiiits of the pic;, showing carpals and 

 metacarpals, i-v, first to fifth metacarpals; cun., cuneiform; lun., lunar; os ma;/., os 

 ma{j;num; pis., pisiform; sc/>/t., scaphoid; frz., trapezium ; iracZ., trapezoid; un., unciform. 

 I natural size. 



theory that the trapezium of the manus of the pig may represent the 

 carpal element plus the rudiment of digit i. 



Taking now a step further in our series, we come to a condition 

 in which the extra digit is still larger and consists of three phalanges 

 (Plate 6, Fig. 14). The four cases of this type studied showed practi- 

 cally the same anatomical conditions. Digit ii is relatively larger. 

 Digit I articulates with the trapezium, which is large and has facets for 

 the trapezoid, scaphoid, and metacarpal i (Fig. i/, trz.). The trapezoid 



