PRENTISS: POLYDACTYLISM IN MAN AND DOMESTIC ANIMALS. 271 



On examining the other skeletal elements of the manus, in order to 

 determine whether they show reversive modifications, one is at once 

 struck by the form of the trapezoid (Fig. A", trzd.). Although of normal 

 size, there is a remarkable change at its distal end ; instead of projecting 

 as a wedge between metacarpals ii and in (see normal manus, Fig. F, 

 trzd.., p. 264), and presenting two distal facets nearly equal in size, 



cun. 



OS mag. .._ 



II. 



pis. 



Ull. 



III. 



IV. 



Fig. K. — Anterior view of left polydactyle manus of tlie pi,£^, showing carpals and 

 metacarpals, i-v, first to fifth metacarpals; cun., cuneifoiin; lun., lunar; os maf/., os 

 magnum; ^js., pisiform; scj)h., scaphoid; trz., trapezium; trzd., trapezoid; un., unciform. 

 3 natural size. 



there is only one articular surface, which is slightly convex and occu- 

 pied entirely by metacarpal ii. The trapezoid barely touches metacarpal 

 III ; its form and relations to the other skeletal parts thus approach those 

 of the trapezoid of fossil swine (Fig. G, p. 265). 



In correspondence with these carpal variations, the metacarpals show 

 some changes. The metacarpal of digit ii is slightly larger than nor- 



