1916] HoUiger: Anatomical Adaptations in the Pocket Gopher 461 



the base of metacarpal 2, and the latter with the remainder of the 

 base of this metacarpal, with the base of metacarpal 1, and prox- 

 imally with the falciform bone. The falciform is a long, curved 

 bone, its base tightly wedged in on the radial side of the carpus, and 

 its body curving around until it meets the pisiform, to which it is 

 bound by ligaments. There is thus formed on the palmar side of 

 the carpus a strong, bony arch composed of the falciform and pisi- 

 form bones. Under this arch pass the tendons of the flexor muscles 

 of the hand, and on it is inserted the flexor carpi ulnaris, the 

 strongest muscle of the forearm (see p. 479). 



In the carpus of the rabbits the falciform bone is absent, but 

 the pisiform is very long and heavy. In the chickaree the arrange- 

 ment is similar to that in the gopher, except that the falciform bone 

 is small or absent. Hoffmann and Weyenbergh (1870, p. 27) in their 

 description of the carpus of Sciums vulgaris fail to mention the 

 falciform bone ; it is undoubtedly present, however, in Sciurus d. 

 alholimbaius. In the ground squirrel the falciform is almost as 

 well developed as in the gopher. The rat also possesses a long falci- 

 form bone. 



Metacarpals (figs. K, L). The first metacarpal in the gopher 

 is a short, triangular bone ; the fifth metacarpal is also short and 

 irregular. The smallness of these two bones has much to do with 

 the shortness of digits 1 and 5. The three middle metacarpals are 

 long and heavy, especially the third, which is the longest and 

 stoutest. The bases of the metacarpals are irregular, and tightly 

 wedged in among the carpal bones. Sesamoid bones occupy the 

 palmar sides of the metacarpo-phalangeal articulations. 



In the rabbits the four lateral metacarpals are long, rounded, 

 rod-like bones, while the first is small and triangular. The lateral 

 four metacarpals in the squirrels are also fairly even in length, 

 while the first is extremely small. In the rat the metacarpals are 

 considerably like those in the gopher, but are more slender. 



Phalanges {ph., figs. K, L). The five digits in the gopher vary 

 somewhat regularly in length from the long middle one to the 

 short first and fifth. This variation is due partly to the meta- 

 carpals, as described above, and partly to the phalanges. The 

 latter are longest and strongest in the middle digit and shortest in 

 the outside fingers. Since the first digit, or thumb, has only two 

 phalanges, it is about a third shorter than digit 5. The bones of 

 the terminal phalanges or claws of the gopher are long and curved ; 



