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carpal directly opposes the drawing forward of the outer end of the base, and, 

 being itself similarly overlapped by the fifth metacarpal, both these bones must 

 give way before the middle metacarpal, which bears the chief strain in the 

 attempt to tear off a bough or to prostrate the tree, could be displaced. On 

 the radial side we see the base of the middle metacarpal extended into a pro- 

 minent tuberosity, which is locked into a cavity in the side of the second meta- 

 carpal ; this bone being itself strengthened by the abutment of the first meta- 

 carpal against the opposite side of its base. Thus, before the middle metacarpal 

 could be wrenched out, all the rest of the metacarpal series must give way ; in 

 other words, the bones of that series are so arranged as to combine in strength- 

 ening and wedging down the middle metacarpal. This strong organic masonry 

 equally characterizes the hand of the Megatherium, and cannot be contemplated 

 without the conviction that it has been designed for actions of the fore-hmb, 

 in which very unusual resistance had to be overcome ; a resistance surpassing in 

 degree any that the fingers of the Mole have to contend against in their sub- 

 terraneous excavations, and of a different kind from that which would be expe- 

 rienced in merely scratching up the soil. In fossorial actions the fingers must 

 overcome the tendency to backward inflection as well as direct extension, and 

 the joints of the great middle finger of the Dasypus gigas give it due strength in 

 both directions ; but the metacarpal of this finger might be dislocated forwards 

 without involving the displacement of the fourth or fifth metacarpals. The 

 whole of the interlocked metacarpal arch in the Megatherian quadrupeds opposes 

 the drawing out of the key-stone to which the digit supporting the great pre- 

 hensile claw is articulated. 



The obstacles to dislocation afforded by this mechanical arrangement of the 

 bones must have derived a great accession of force by the stout flexor and ex- 

 tensor tendons, inserted into or bound down upon the fore and back part of the 

 short, thick and strongly jointed phalanges, which, with their built-in meta- 

 carpal, formed the principal centre upon which the muscular forces converged. 

 The carpus would obtain its requisite stability by the mode in which the three 

 bones of the second row are interlocked together, and inclosed by the proximal 

 carpal bones and the metacarpals, and by the tendons passing over it ; of the 

 strength of which tendons, and of their muscles, ample evidence exists in the 

 deep grooves and sharp ridges of the bones of the fore-arm. 



