77 



colossal extinct Sloth as compared with the diminutive climbing species which still 

 exist. 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 striking upon the root itself. 



§10. 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 f, the 

 Megatherium resembles the Anteaters (Myrmecophaga%); but it does not resemble the 

 Armadillos (Dasypm^) in having long metapophyses, the peculiar development of which 

 in those loricated Bruta has a direct relation to the support of their bony dermal armour. 

 In the mesozygapophyses of the middle dorsal vertebrae ||, the Megatherium appears to 

 be peculiar amongst Mammalia In the small extent of the produced and pointed 

 symphysis pubis it resembles the Sloths ; and in the junction of both ilium and ischium 

 with the sacrum, it manifests a character common to the Edentate order ; but in the 

 expanse and massiveness of the iliac bones, it can only be compared with other extinct 

 members of its own peculiar family of phyllophagous Bruta. The habits of the Mega- 

 therium necessitating a strong and powerful tail, we find this resembling in its bony 

 structure that of other Bruta with a similar appendage, especially in the independency 

 of the two haemapophyses of the first caudal, a character which obtains in the Ant- 

 eaters % and in some Armadillos; but this is no evidence of direct affinity to either of 

 those families : the habits of the small arboreal Sloths render their eminently prehensile 

 limbs sufficient for their required movements, and the tail is wanting. Had that 

 appendage been proportionally as large as in the Megatherium, we cannot suppose that 

 the caudal vertebrae would have materially differed from those of other Bruta. 



In the coalescence of the anterior vertebral ribs with the bony sternal ribs, the Mega- 

 therium resembles the Sloths. This essential affinity is still more marked in the pecu- 



* Plate I. and Bradypu* didactylus, C 1...7. t Plate III. figs. 4 & 5, a and^. 



% See Philosophical Transactions for 1851, Plate XLIX. fig. 20. § Ibid. Plate XLIX. figs. 18, 19. 

 || Plate III. mz. % Philosophical Transactions for 1851, Plate LIII. fig. 60. 



