EDENTATA. 



small, triangular and slightly concave; but the 

 most extraordinary articulation is that of the 

 jibula with the astragalus; its inferior extremity 

 terminates in a conical point, which enters and 

 plays in a corresponding cavity in the latter 

 bone. This peculiarity of the articulation of 

 the ankle, which was considered by Cuvier as 

 only additional evidence of the imperfection 

 of the animal's structure, is no less admirably 

 adapted to its habits than those points which 

 have been previously noticed. The feet, it is 

 true, are turned inwards, and there is no pos- 

 sibility of placing the sole on the ground ; but 

 it is the better adapted for clasping boughs, 

 and the freedom of rotation which is provided 

 by this curious joint allows of every kind of 

 motion required in such circumstances. The 

 tarsus consists of the astragalus and os calcis, 

 which are separate, and of the usual anterior 

 series of bones, which in the aged individuals 

 are anchylosed together as well as to the meta- 

 tarsal bones, which are themselves united as 

 in the carpus. The tubercle of the os calcis is 

 very long, and so situated as to afford a sort of 

 opposing thumb to the flexed phalanges. The 

 latter bones very nearly resemble those of the 

 anterior extremity. 



It is impossible not to be struck, even on a 

 superficial view of the extraordinary structure of 

 the anterior and posterior extremities of the Sloth, 

 with the complete adaptation of this deviation 

 from the normal form to its peculiar mode of 

 life. Grasping the boughs of trees on which it 

 both feeds and reposes, crawling along with 

 the back downwards and the belly pressed 

 against the tree, and culling, with the long 

 arms, the leaves at the inaccessible extre- 

 mities of the branches, the usual construction 

 of the members would be absolutely useless, 

 and an incumbrance instead of an assistance. 

 But by the great breadth of the pelvis, the di- 

 rection of the femora, the long and curved claws, 

 the consolidation of the tarsus, and the curious 

 structure of the articulation of the fibula with 

 the astragalus, every requirement of security 

 and progression is obtained ; whilst in the an- 

 terior extremity the extensive motion of the 

 shoulder-joint, the great length of the arms, the 

 complete flexion of the fingers, and other peculia- 

 rities, combine, with that security and facility of 

 progression, the most effective means of ob- 

 taining the animal's peculiar food. 



Of the Edentata proper. The extremities 

 in animals of this class are, as may be con- 

 cluded from their habits, very 

 differently constituted from those 

 which have just been described. 

 In all of them the object to be 

 obtained is facility in digging 

 the ground, or scratching up 

 immense nests, in search of 

 the insects which constitute 

 the principal food of most of 

 these animals. The gigantic 

 Megatherium, however, appears 

 to have combined the phytopha- 

 gous character of the Sloth with 

 the fossorial habits of the Dasy- 

 pus, and is supposed to have 

 lived upon roots, which it 



snatched or dug up with its enormous claws. 

 The scapula of the^Ant-eaters and Armadillos is 

 found nearly like that of the Sloth ; in the 

 Myrmecophagajubuta a process of bone extends 

 from the coracoid process to the anterior margin, 

 rendering that which is a notch in other species 

 a complete foramen. A second spine inferior 

 to the true one is also observed in that species, 

 in which respect it resembles the Unau or 

 two-toed Sloth. The scapula of the Armadillos 

 is very high and narrow. In that of the Mega- 

 therium there exists a large process of bone ex- 

 tending from the coracoid process to the acro- 

 mion,andthus completely uniting these processes. 

 The clavicle exists in many of the Edentata, as 

 the Armadillos and Ant-eaters, but is wanting 

 in the Manis or Pangolin. That of the Megathe- 

 rium offers a remarkable peculiarity. It extends 

 from the acromion, not to the sternum as in all 

 other cases, but to the first rib. The humerus is 

 in most of the order very short and robust, and 

 its elevations strongly marked. In the Ant-eaters 

 the part above the inner condyle is extremely 

 developed, to give attachment to the powerful 

 flexors of the claws ; and the crests for the in- 

 sertion of the deltoid and great pectoral muscles 

 are very prominent and angular, a structure 

 which is also conspicuous in the Armadillos and 

 Manis. The humerus of the Megatherium has 

 a similar general form; it is rude, short, and 

 excessively strong, with abrupt and large ele- 

 vations for the different muscular attachments ; 

 the inferior part especially becomes suddenly 

 larger, from the existence of a strong and ele- 

 vated external crest. 



The habits of the Edentata proper demand 

 a very different construction of the fore-arm 

 from that of the Sloth. Requiring immense 

 strength in digging the ground, the short ole- 

 cranon which exists in the Sloth would be 

 wholly inefficient. A long lever is necessary, 

 and hence we find that in the whole of these 

 the olecranon is of an extraordinary length, and 

 that in the Megatherium its more moderate 

 length is compensated for by its immense 

 strength. In the five-toed Armadillo this pro- 

 cess is so extensive as to render the ulna no 

 less than twice the length of the radius, and 

 in the other species of the same genus it is 

 not much less. The radius is broad, robust, 

 and strongly marked, particularly towards the 

 carpal extremity. The hand in the Myrmeco- 

 phaga (jig 36) and its kindred genus Manis 



Fig. 36. 



Hand of the Ant-eater. 



E 2 



