The three fingers are, moreover, strengthened for their peculiar uses, the first two joints being united, and the tip or last joint being very long, and supporting the claw. Moreover, as the long claws are constantly half closed in the hand, and they are never required to be widely open, the tip of the finger is so made that flexion is possible, but not unclasping widely. The skin comes up to the base of the claws, and encloses the fingers, and the base of each claw is protected by a bony sheath. They form capital hooks; they grasp, and although there is no opposable thumb, they hold the food; and a tame Sloth may be seen holding a carrot very firmly between them and the wrist. In the case of the Unau Sloth, the outer claw is the longer. [Illustration: BONES OF HAND OF THREE-TOED SLOTH.] The Sloths walk on the outside of the extremities of the fore and hind limbs, and their claws are always curved in, and, as it were, retracted. Consequently, the animal cannot place the soles flat on the ground, and it cannot open its foot-claws to a great extent. This fixing of the claws assists in the clasping and hanging, which are the usual and commonest attitudes. The claws surpass the foot in length, and are so sharp and crooked that they readily seize upon the smallest inequalities in the bark of the trees and branches upon which the animals habitually reside. They and those of the fore limb are no mean weapons of offence and defence, for, situated at the end of long and muscular arms, they can drag, cling, and hold with great tenacity. The thigh bone (femur) of the Sloth is straight, and is thicker and shorter than the arm bone (humerus); it has no ligament to unite it to the joint (no ligamentum teres). On examining the lower bones of the leg (the tibia and fibula), they will be found to be bent, so as to leave a space between them, and they are shorter than the bones of the fore arm. The bones of the ankle joint, are united together immovably--that is to say, the usual bones seen in other Mammalia are there, but are united by bone. Moreover, this union includes the complete and ill-developed feet bones (metatarsals), and the first bones of the second, third, and fourth fingers. One bone is not included in this strange union. It is the astragalus, or the bone immediately jointed with the ends of the bones of the legs. The outer or small bone of the leg (fibula) fits into a pit in the outer part of the upper surface of this bone, and thus prevents any movement of the foot like a twisting outwards, and favours, but does not produce, the usual position of twisting inwards. Moreover, there are two powerful muscles in the front of the leg which are not opposed by others as strong, and they, by their contraction, keep the foot twisted inwards, as in club-foot (the anterior tibial and the long extensor of the great toe).