Royal Society. 245 



for its size or the expansion of the iliac bones. But in the Mega- 

 therium the extraordinary size and massive proportions of the pelvis 

 and hind limbs arrest the attention of the least curious beholder, and 

 become eminently suggestive to the physiologist of the peculiar 

 powers and actions of the animal. The enormous pelvis was the 

 centre whence muscular masses of unwonted force diverged to act 

 upon the trunk, the tail, and the hind legs, and also by the ' latis- 

 simus dorsi ' on the fore-limbs. The fore-foot being adapted for 

 scratching as well as for grasping, may have been employed in 

 removing the earth from the roots of the tree and detaching them 

 from the soil. The fore-limbs being well adapted for grasping the 

 trunk of a tree, the forces concentrated upon them from the broad 

 posterior basis of the body may have co-operated with them in the 

 labour, to which they are so amply adapted, of uprooting and pro- 

 strating the tree. To give due resistance and stability to the pelvis, 

 the bones of the hind-legs are as extraordinarily developed, and the 

 strong and powerful tail must have concurred with the two hind-legs 

 in forming a tripod as a firm foundation for the massive pelvis, and 

 affording adequate resistance to the forces acting from and upon 

 that great osseous centre. The large processes and capacious spinal 

 canal indicate the strength of the muscles which surroundedthetail, 

 and the vast mass of nervous fibre from which those muscles derived 

 their energy. The natural co-adaptation of the articular surfaces 

 shows that the ordinary inflection of the end of the tail was back- 

 wards as in a cauda fulciens^ not forwards as in a cauda prehensilis. 

 Dr. Lund's hypothesis, therefore, that the Megatherium was a 

 climber and had a prehensile tail, is destroyed by the now known 

 structure of that part. 



But viewing, as the author conceives, the pelvis of the Mega- 

 therium as being the fixed centre towards which the fore-legs and 

 fore-part of the body were drawn in the gigantic leaf-eater's efforts 

 to uprend the tree that bore its sustenance, the colossal proportions of 

 its hind extremities and tail lose all their anomaly, and appear in 

 just harmony with the robust claviculate and unguiculate fore-limbs 

 with which they combined their forces in the Herculean labour. 



The author then referred to the Mylodo7i robustus, a smaller ex- 

 tinct species of the same natural family of phyllophagous Bruta, and 

 to the additional arguments derivable from the skeleton of that 

 animal in favour of the essential affinity of the Megatherium to the 

 Sloths ; and the light which the remarkable healed fractures of the 

 skull of a specimen in the Museum of the College of Surgeons 

 threw upon the habits and mode of life of the species. 



Fmally, with reference to the hypothesis of the German authors 

 and artists of the degeneration of the ancient Megatherioids of South 

 America into the modern Sloths, the author remarked that the 

 general results of the labours of the anatomist in the restoration of 

 extinct species, viewed in relation to their existing representatives 

 of the different continents and islands, commonly suggested the idea 

 that the races of animals had deteriorated in point of size. Thus 

 the palmated Megaceros is contrasted with the Fallow-deer, and the 

 great Cave-bear with the actual Brown Bear of Europe. The huge 



Phil. Mag. S. 4. Vol. 2. No. 10. Sept. 1851. S 



