PEOEESSOE OWEN ON THE MEGATHEEIUM. 
823 
amongst existing Bruta, manifest in any degree the characteristic megatherioid condition 
of the extreme toes of the pentadactyle series : and the minor modifications of this cha- 
racter, difierentiating the existing from the extinct phyllophagous Bruta, are such as 
inteUigibly relate to the difierent 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 
colossal extinct Sloth as compared with the diminutive climbing species which still 
exists. If the hind foot were put by the Megatherium to the preliminary work of 
exposing and loosening the roots of the tree about to be prostrated, its efficiency for 
that purpose would be greater by having but one claw, than if it had two or three : for 
the single claw, like a pickaxe, would clear away the soil from the interstices of the 
root-ramifications, the more easily by not being associated with a second contiguous 
claw, impeding such operation by stri kin g upon the root itself. 
Physiological Summary. 
To sum up the results of the foregoing descriptions of the known fossilized parts of the 
extinct giant of the order Bruta, as indicative of its habits and affinities. The teeth 
agree in number, kind, mode of implantation, and growth, with those of the Sloth 
[Bradypus), and their structure is a modification of that peculiar to the same genus. 
All the modifications of the skull relating to the act of mastication, especially the large 
and complex malar bones, repeat the peculiarities presented by the existing Sloths. 
There are the same hemispheric depressions for the hyoid bone in the Megatherium as 
in the Sloth. In the number of cervical vertebrae, the Megatherium, like the Two-toed 
Sloth, agrees with the Mammalia generally *. In the accessory articular surfaces afforded 
by the anapophyses and parapophyses of the hinder dorsal and lumbar vertebrae the 
Megatherium resembles the Anteaters {Myrmeco^haga'!^)', but it does not resemble the 
Armadillos {Dasypus §) in having long metapophyses, the peculiar development of which 
* Philosophical Transactions, 1855, Plate XVII. O. f Ibid. Plate XXVI. a and^. 
t Ibid. 1851, Plate XLIX. fig. 20. § ibid. Plate XLIX. figs. 18, 19. 
