76 



to find that the Sloths alone amongst the existing Beuta show a suppression of certain 

 toes: in all the other existing genera of the order the hind foot retains the typical 

 number of digits. 



The Armadillos, including the Chlamyphorus, resemble the Megatherium in the ter- 

 minal confluence of the tibia and fibula ; but these bones articulate in the Dasypodidce 

 in the normal way with the astragalus, and the foot is planted firmly on the ground by 

 its flat surface. The hallux is not only present in the Chlamyphorus, but is longer than 

 the fifth toe. All the five toes are armed with claws ; and anomalous as the three-toed 

 hind feet of the Sloths may appear, they have more real resemblance with the feet of 

 the Megatherioids than have those of any of the Armadillo family. The great extinct 

 Glyptodm agrees with the Chlamyphvrus in the pentadactyle condition of the hind foot, 

 the OS naviculare having three facets for as many cuneiform bones, the innermost of 

 which supports a well-developed hallux. This toe is abortive in existing Sloths : it is 

 represented, in the Ai, by a small compressed bone, consisting apparently of the connate 

 en to-cuneiform and metatarsal : it retains its distinctness in the Unau (Plate, Bradypus 

 didactylus, i), as the similar representative of the second toe does in the Megatherium ; 

 and the meso- and ecto-cuneiform bones are also distinct ; but in the Ai each cuneiform 

 bone is confluent with its metatarsal, with each other, with the naviculare, and with the 

 cuboides. 



In the Megatherium, the mutilation of the foot has commenced on its outer side by 

 the removal of the ungual phalanx from the fifth and fourth toes ; in the Sloths the 

 mutilation is restricted to the fifth toe, but is carried further, viz. to the removal of all 

 the phalanges and the reduction of size of the metatarsal (Plate, Bradypus didactylus, v) : 

 nevertheless, the Sloths alone, amongst existing Bruta, manifest in any degree the cha- 

 racteristic megatherioid condition of the marginal toes, first and fifth, of the penta- 

 dactyle series : and the minor modifications of this character, differentiating the existing 

 from the extinct phyllophagous Bruta, are such as intelligibly relate to the different 

 powers and habits of creatures so different in size and mode of progression. 



The mutilation of the two outer toes in the Megatherium is accompanied by modifi- 

 cations which adapt them to the important office of the support and progression of the 

 body on level ground: in the scansorial Sloths, the three middle digits being equally 

 developed for prehensile purposes, and none being needed for walking, one toe on the 

 outer and one on the inner side of the foot is reduced to the metatarsal basis, and is 

 concealed beneath the skin. In the Megatherium the hallux and its cuneiform bone 

 are wanting : the second toe is represented by its cuneiform bone, with, perhaps, a con- 

 nate rudiment of a metatarsal : only the third toe can be compared, by its size and the 

 claw it supports, with the condition of the three unguiculate toes in the Sloths ; and, 

 like those of the Ai, it has but two moveable phalanges. The reduction of the claws 

 to one in the hind foot of the Megatherium, its enormous size and strength, its secure 

 attachment to the phalanx, and the solidity of the articulations of the constituent bones 

 of the whole toe, relate to the contrasted mode of obtaining the leafy food in the 



