102 



any approximative degree of completeness ; these are the Megatherium and 

 the Megalonyx. The collection of bones of the Megatherium, presented to the 

 Royal College of Surgeons by Sir Woodbine Parish, fortunately includes the 

 entire carpus, and the first, third and fourth metacarpal bones of the left fore- 

 foot, with probably some of the terminal phalanges of the same foot. 



The carpus consists of seven bones, three in each row, and the seventh 

 common to both. This bone consists, as in the Sloths and Mylodon, of the con- 

 joined scaphoid and trapezium*. It has the same tendency to the unciform 

 figure, being bent towards the palmar aspect of the wrist. The radial articulation 

 is convex, obUque, with the part corresponding with the anterior angle of the 

 scapho-lunar in the Mylodon truncated, and the articular surface continued at 

 right angles upon the dorsal surface of the bone, for the overlapping ridge of the 

 radius. The facet by which it joins the lunare, and the concave palmar surface 

 much resemble those in the Mylodon ; thetrapezial portion is relatively smaller ; 

 and the surface for the metacarpal of the thumb is still more so, being absolutely 

 less than in the Mylodon ; it does not extend to the extremity of the process, 

 but is confined to the dorsal or outer side. The whole dorsal surface of the 

 scaphoid is narrower in the axis of the hand than in the Mylodon, and is ex- 

 cavated for the reception of the trapezoides by an angular notch. The process 

 for the articulation with the os magnum separates the trapezoides from the 

 lunare, and much resembles that in the Mylodon, save that the articular surface 

 for the OS magnum is convex instead of concave ; but the most essential differ- 

 ence between the scapho-trapezium of the Megatherium and that of the 

 Mylodon, is the presence in the former, on its concave or distal surface, of a 

 second detached articular surface for the os magnum, which surface is oval, flat, 

 and close to the palmar margin. 



The OS lunare of the Megatherium bears a general resemblance to that of the 

 M3dodon, but it preserves a more equal thickness as it arches from the fore to 

 the back part of the carpus ; its radial surface is more convex transversely, but 

 is separated by a similar rough tract from the concavity which receives the 

 cuneiform bone. The cuneiforme is proportionally smaller in the Megatherium 

 than in the Mylodon. The articular surface for the ulna is absolutely smaller, 



* It is the bone called ' cuneiforme ' by Cuvier, and marked r in the copy of Pander's figure intro- 

 duced into pi. 217, fig. 13, of the Ossemens Fossiles, ed. 1836. 



