152 ANATOMY OF THE WOOD RAT 



In most of the skeletons the fore foot was disarticulated, 

 and of those in which it could be measured, the digits were 

 flexed in varjdng degree so that the entire length of the hand 

 could be calculated only approximately. Tentatively, then, 

 the entire fore foot, including the digits and claws, is about 

 24 to 25 per cent of the arm length in Homodontomys; 26 to 

 28 in Neotoma; and 28 to 31 per cent in Teonoma. 



Carpus. The bones of the carpus number 9, as follows: 

 Beginning at the lateral side, the first bone is the triquetrum, 

 articulating with the ulna. Articulating with the trique- 

 trum upon its palmar face is the pisiform bone, of charac- 

 teristic shape, with a palmar, spherical process. Upon the 

 latter is inserted the flexor carpi ulnaris, and from it origi- 

 nates the abductor digiti quinti.^ To it is also attached, as an 

 anchor, the tough tissue about the extremity of the falciform. 

 Next mediad to the triquetrum is the larger scapholunar 

 bone, articulating with the radius. Next, upon the medial 

 border of the carpus may be the falciform, which is usually 

 lost during the cleaning of the bones, with attachment to the 

 scapholunar. From the vicinity of its base originates the 

 abductor pollicis brevis. In Homodontomys and Neotoma 

 it may be more proper to consider this as two bones — a 

 sesamoid articulating loosely with the scapholunar, with a 

 slender falciform bone extending over the palm, imbedded 

 in and lending substance to the cartilaginous tissue of the 

 palm and attached by the same to the pisiform. Beneath it 

 pass most of the tendons of the palm. In Teonoma the 

 falciform is absent. 



In the second series of carpal bones, from the lateral side, 

 are the hamatum, which is relatively large, and adjoins the 

 strongly triangular capitatum. The smaller centrale comes 

 next, followed respectively by the multangula minus and 

 ma jus, the latter lying laterad to metacarpus one. 



^ The attachments of the smaller muscles of the hand proper are not 

 shown in the osteological illustrations. 



