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500 



MONOGRAPnS OF NORTH AMERICAN RODBNTIA. 



hand is rather thinly but uniformly clothed to the ends of the fingers with 

 i»hort adpressed hairs like those on the concavity of the ear. The palms and 

 under surfaces of the fingers are perfectly naked. The hand is large, measur- 

 ing in length from the wrist to end of the claws but little less than the dis- 

 tance from wrist to elbow. There are five perfect digits. Of these, the Ist, 

 or thumb, is very short, its tip falling far short of the base of the 2d digit ; 

 its axis is very oblique to the line of the other digits, from which it stands 

 apart quite as much as the human thumb does from the fingers ; nor can it 

 be readily pressed into line with the other digits, on account of its intimate 

 connection with the inner one of two great palmar tuberosities, to be 

 presently noticed. The thumb bears a small, stumpy, obtuse claw, com- 

 pressed nevertheless, and a true claw, not a flat nail, as is so frequently 

 witnessed in Rodents when the thumb is very short or rudimentary. The 

 thumb in this case, though relatively very short, is functionally developed 

 beyond doubt, and its curious opposition to the other digits almost indicates 

 true prehensile or grasping powers of the hand. The remaining digits are 

 long and well formed ; the 3d is longest ; the 4th and ■2d successively shorten 

 in nearly constant ratio ; the 5th is relatively shorter, the tip of its claw 

 falling but little in advance of the base of the 4th claw. The clav/s are all 

 nearly or quite as long as their respective digits, reaching about the develop- 

 ment witnessed in Geomyidce. They are little curved, and much compressed ; 

 for most of tiieir length underneath their sides come together in a single 

 ridge, leaving but a slight scooped-out portion toward the ends. The tuber- 

 culation of the naked palms is conspicuous. Near the wrist, opposite the 

 thumb, are two immense prominences, side by side (inner and outer) ; the 

 ulnar, or outer one, about in the site of the human pisiform bone, is smaller, 

 and more compressed than the radial tubercle, at the base of the thumb, 

 which attains the size of a pea, and is irregularly nodular, with a tendency 

 to lateral compression and the formation of a decided lengthwise keel. These 

 wrist-tubercles have almost the development seen in Geomys. At the bases 

 of the digits are three large, smooth, flattened tubercles, one common to the 

 3d and 4th digits, the others respectively proper to the 2d and 5th. The 

 ends of the digits are somewhat callous. For the rest, the palm is smooth, 

 with an irregular network of lines of impression, and the under surfaces of 

 tlic digits arc strongly annulate with similar transverse lines. 



The hind limbs correspond in length with the fore. The massive thigh 



BBI 



