by which Crabs throw off their Claws. 3 



the shell ; and these motions are produced by two long muscles 

 occupying the second phalanx. The motion of this phalanx upon 

 the third, is lateral in two directions, and tolerably extensive ; 

 but less so than any of the direct motions. It is performed by a 

 pair of muscles of considerable power which lie in the third phalanx. 

 The motion of this on the fourth, is a motion of extension and 

 flexion, like that of the first ; the latter being, in the same manner, 

 considerable, while the former is limited ; and the muscles that 

 produce them are of considerable power, as occupying the great 

 length of the fourth phalanx. 



The fifth phalanx is very short, and is articulated to the fourth 

 in an oblique manner, by a very narrow ligament ; while the" 

 lower shell surmounts the upper one in such a manner as to limit 

 the motion of the latter on the former to a very minute space 

 laterally, which is also somewhat more considerable in one 

 direction than another, but which varies, in this respect, in dif- 

 ferent species of crabs. These lateral motions are produced by 

 two broad, but very short, muscles ; as it will be shortly seen that 

 but a small part of this fifth phalanx can be allowed for them, a 

 great part of it being allotted to the arrangement provided for 

 detaching the limb. 



The sixth, or last, phalanx, is extremely short, and is articulated 

 by a somewhat lax ligament to the preceding, which admits also 

 of a direct motion like those of the first and third ; but which is, 

 on the contrary, much more free and extensive backwards than 

 forwards. This phalanx is also connected with the former, by 

 short and feeble muscles ; but the principal motions in this fifth 

 phalanx, which are amongst the most powerful in the limb, are 

 produced by two long muscles, a flexor and an extensor, which 

 pass quite through the sixth phalanx, and are inserted within the 

 body of the animal. The fifth phalanx therefore moves imme- 

 diately on the body, independently of the sixth, or is, at least, 

 capable' of so doing. 



The last, or sixth phalanx, is connected with the body by a very 

 wide ligament, admitting of a very considerable lateral motion, 

 but more extensive inwards than outwards, and allowing the limbs 



B2 



