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 obliquus, 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 (Hig. J, flz. perf.) ; this is composed of two 
cut. mt carp. ob. 
ext. mt’carp. mag.----\> 
---€xt. PVD. 
CU I ieee ae faa aa | A ext. com. dq. t. 
III. IV. 
Fic. H. — Left normal manus of pig, showing extensor muscles. eat. com. dg. i., ex- 
tensor communis digitorum internus; ext. mt’?carp. mag., extensor metacarpi magnus; ezt. 
mt’ carp. ob., extensor metacarpi obliquus; ext. prp., extensor proprius pollicis et indicis; 
ext. prp. t., extensor proprius internus, 3 natural size. 
distinct parts, the tendons of which are inserted into the second phalanges 
of digits 11 and Iv. These tendons form two sheaths for the large ten- 
dons of the flexor perforans muscle (flx. perf.!), the deep flexor of the 
