OSSEOUS SYSTEM OF MAMMALIA. 91 



that the quick ears of the timid prey may not catch the foot-fall of the 

 prowler ; and, secondly, that the concussion produced by the impetuosity 

 of the bound, and which, in spite of the angle made by the bones of the 

 limb, with respect to each other, would, to a certain extent, still be felt, 

 may be farther broken, so that neither the shoulder nor the spine may 

 receive a shock from the violence of the plunge an act, in which the 

 whole of the muscular energy is concentrated. These pads, moreover, give 

 a certain springiness and elasticity to the tread, facilitating the usual move- 

 ments of this and similar animals, which consist of a succession of easy 

 bounding steps, and, at the same time, so raising the tips of the toes, as 

 to throw the sheathed talons upward, and prevent their being worn, or 

 blunted, against the ground. This will be easily understood by consult- 

 ing the annexed sketches. We see, in the first (fig. 91), the talon re- 

 tracted into its sheath ; so that its point is barely visible amidst the fur ; 

 which, indeed, must be parted a little to discover it at all : while, in this 

 state, the pad effectually prevents its being brought into contact with 

 stones, or the inequalities of rugged and uneven ground. 

 91 92 



Figs. 91,92. A toe of the Lion's paw, with the claw sheathed and unsheathed. 



But this talon can be unsheathed and thrown forward in a moment, 

 as in the figure (92). This effort is voluntary ; not so the return of 

 the weapon to its scabbard. In the Sloth, as already noticed, the ten- 

 dency of its hooks, governed by an elastic ligament, is to press toward 

 the palm: but here, an elastic ligament so acts, that the talon rolls 

 back on its hinge, resuming its retracted condition, the counteracting 

 effort being suspended. The talon encases the last phalangal bone of 

 the toe : this bone is so articulated to the next, by a rolling, hinge-like 

 joint, on which it freely works, as to pass down by its outer side (which 

 is flattened off in order to remove every obstruction), and thus gain a 

 more ample sweep of retraction. This action is effected by a ligament 

 which passes from the upper arch of the last phalangal bone, obliquely 

 downward to a sesamoid bone, placed on the next bone near the joint, 

 to which it is firmly bound.* The action of this elastic spring is 



* Sesamoid bones are rather to be regarded as a deposition of bony matter, in parts disposed to its 

 reception, as ligament, cartilage, &c., than as intrinsic portions of the skeleton : they are larger and 

 more numerous in the hands and feet of such as take laborious exercise. 



