536 CHORD AT A, 



renders the animal quite unfit for terrestrial locomotion 

 {cf, bat and whale), the horse being equally unfitted for 

 climbing or burrowing. 



The pelvis is much smaller than in the terrestrial types, 

 the comparison in this respect with its near ally, the ground 

 sloth (Megatherium)^ being very striking. The hind-limb is 

 similar in general characters to the fore-limb. The femur 

 is long and slender ; the tibia and fibula are of about equal 

 size and allow the foot to face inwards. The foot, like the 

 hand, is elongated and has the same condition of the digits, 

 the second, third and fourth alone remaining. The tarsus 

 shows the same fusion and reduction of elements as the 

 carpus, all the bones but the astragalus becoming fused 



Fig. 370.— Stomach of Sloth. 



Note the complex folds and the two-chambered condition. 



together in many individuals. As in the case of the meta- 

 carpals, so here the three metatarsals are fused together into 

 one bone. The fibula has lost its connection with the 

 calcaneum, but articulates with the astragalus. 



At the base of the limbs the brachial arteries break up 

 into networks of vessels, known as retia mirabilia^ an adap- 

 tation apparently serving to overcome the effects of gravity 

 upon the circulation of the limbs (see page 464). The. 

 mammae are pectoral, a position common amongst arboreal 

 and aerial types. 



The stomach of the sloth, as in most herbivorous 

 animalS; is complex, consisting of at least two chambers, 

 each of which has an appendix or caecum. 



