PRENTISS: POLYDACTYLISM IN MAN AND DOMESTIC ANIMALS. 267 



pollicis et indicis {ext.prp.) is a rudimentary muscle in the pig ; it arises 

 with the extensor metacarpi obhquus, and its threadlike tendon is lost in 

 that of the extensor communis digitorum internus. 



Of the posterior muscles we may mention (1) the flexor perforatus, or 

 superficial flexor of the digits (Fig. /, fix. perf.) ; this is composed of two 



ext. mt'carp. 



ext. prp 



Fig. n. — Left normal manus of pic^, showing extensor muscles, ext. com, dff. i., ex- 

 tensor communis digitorum internus; ext. mVcarp. mag., extensor metacarpi majiiuis; ext. 

 mt'carp. ob., extensor metacarpi obliquus; ext.prp., extensor proprius pollicis et indicis; 

 ext.prp. i., extensor proprius internus. 1 natural size. 



distinct parts, the tendons of which are inserted into the second phalanges 

 of digits III and iv. These tendons form two sheaths for the large ten- 

 dons of the flexor perforans muscle {flx-perf.'), the deep flexor of the 



