460 University of California Piihlications in Zoology [Vol. 13 



pollicis lougus muscle which occupies this groove (see p. 478). 

 Contrary to what might be expected, the nearest approach to this 

 structure in any of the rodents examined is found in the jack rabbit, 

 the animal otherwise most widely different from the gopher. In 

 the jack rabbit, and to a lesser extent in the cottontail, -a strong 

 ligament connects the lateral condyle of the humerus with the 

 ventro-lateral border of the ulna. It does not, however, bridge 

 over any muscle, and its length is only about one-ninth that of the 

 ulna, while in the gopher it is nearly one-half as long as the ulna. 



A probable explanation of the existence of this ligament in the 

 gopher is the fact that the flexor muscles of the manus are much 

 stronger than the extensors. Being attached to the high mesial 

 condyle of the humerus, the flexors would tend to adduct the fore- 

 arm were this effect not counteracted by a very strong lateral 

 humero-ulnar ligament. 



The carpus (figs. K, L) in the gopher is composed of nine 

 bones. Three of these form the proximal row — the scapholunar, 

 cuneiform, and pisiform — and six the distal row — the falciform, 

 trapezium, trapezoid, centrale, magnum, and unciform. Of these 

 six the centrale and pisiform articulate only with other bones of the 

 carpus; all the other members are in relation either with the bones 

 of the forearm or with the metacarpals. The pisiform and falci- 

 form are generally considered to be developed as sesamoid bones. 

 The following brief descriptions should be supplemented by refer- 

 ence to the figures and it should be remembered that here, as in 

 most quadrupeds, the radius is the mesial and the ulna the lateral 

 bone in the distal part of the forearm. 



The scapholunar is the largest of the carpal bones, and articu- 

 lates proximally with the radius, distally with all the bones of the 

 second row, and on the lateral (ulnar) side with the cuneiform. 

 The cuneiform lies between the ulna and the unciform, and sup- 

 ports the pisiform on its palmar surface. The pisiform is very 

 large in the gopher {pis., fig. L) and projects out at right angles 

 to the surface of the carpus. The unciform is an irregular bone 

 supporting the bases of the fifth, fourth, and part of the base of the 

 third metacarpal. The magnum is small and articulates with parts 

 of the bases of the third and second metacarpals. The centrale is 

 a tiny wedge of bone seen only on the dorsal surface. The trap- 

 ezoid and trapezium are also small and do not appear on the 

 palmar view of the carpus ; the former articulates with a part of 



