PRENTISS: POLYDACTYLISM IN MAN AND DOMESTIC ANIMALS. 279 



bears a large hoof, and the two hoofs are connected posteriorly by a cush- 

 ion of horny tissue, as are the functional digits. The trapezium, which 

 ai'ticulates with both extra digits, is very large, and shows evidence of 

 duplication ; the scaphoid also is abnormally large and broad. The 



ext. mt'carp. mag. 



ext. prp. i 



•'ext. mfcarp. oh, 

 •' ext. com. dg. i. 



Fig. R. — Anterior view of left polydact3'le manus of the pig, showing extensor 

 muscles, ext. com. dg. i., extensor communis digitorum internus; ext. mVcarp. mag., 

 extensor mctacarpi magnus; ext. mV carp, ob., eyAensor metacarpi obliquus; ext. prp. i., 

 extensor proprius internus; i", i*, supernumerarj' digits. 5 natural size. 



trapezoid is narrow, being flattened by the large trapezium ; the proxi- 

 mal end of metacarpal ii also suffers in this respect. 



When i" and i* are so large as to be functional, the muscles of the 

 manus show some important modifications. Extensor proprius internus 

 (Fig. B, ext. prp. i.) sends a tendon to i**; extensor metacarpi obliquus 



