71 



The above-described composition of the tarsus of the Megatherium has been deduced 

 from the study of three entire specimens of the bones of the hind foot. The distal 

 articular surfaces demonstrate that the digits of that foot were but three in number, 

 and that they answered to the 'third,' 'fourth,' and 'fifth' of the pentadactyle type. 

 Not a rudiment of the ' second ' exists independently, and every vestige of the first, 

 together with the cuneiform bone supporting it, is absent. There are no little bones 

 missing on the inner side of the ' mesocuneiforme,' as Dr. Pander conjectured might be 

 the case in the Madrid skeleton ; and there is no ' os cuneiforme ' for the hallux (' grand 

 doit du pied '), as Cuvier supposed. 



Metatarsus.— The metatarsal of the 'third' toe (Plates XXV. & XXVI. fig. 1, m 3 ) 

 resembles rather an ' os cuneiforme,' by reason of its extreme shortness, or fore-and-aft 

 compression. Its upper non-articular surface is the broadest, and is rough and convex, 

 like that of the ectocuneiforme. The proximal or posterior surface for that cuneiform 

 bone is triangular and slightly concave (Plate XXVI. fig. 3, ci) ; the bone is prolonged 

 into a tuberous process beneath it, forming a lever of advantage for the insertion of a 

 flexor tendon. On the inner side of the bone, at its upper part, is the small flat surface 

 (cm) adapted to that on the mesocuneiforme ; on the outer side of the bone is a larger 

 surface, partly convex, partly concave, for articulating with the side of the base of the 

 fourth metacarpal (Plate XXVI. fig. 1, m <) ; the rest of the outer surface is very irre- 

 gular, as if honeycombed. The distal or anterior articular surface presents a vertical 

 median prominence, passing into a partly flat surface internally, and into a vertically 

 concave surface externally. The lower part of the vertical prominence is most produced 

 (ib. fig. 2, p). 



The fourth metatarsal (Plate XXVI. fig. 1, m *) has its base compressed laterally, and 

 expanded vertically ; but the distal end is still more produced in that direction, so as 

 to be almost hammer-shaped. The vertically extended articular surface at the base of 

 this metatarsal is narrow, convex transversely, and adapted to the channel in the 

 cuboides (Plate XXV. fig. 2, p iv). On the inner or tibial side of the base is the articular 

 surface, concave posteriorly, less convex anteriorly, for the interlocking joint with the 

 ' third ' metatarsal. In front and below this articular surface is a very rough honey- 

 combed tract of bone for firm syndesmotic junction with the similarly modified surface 

 of the third metatarsal. 



On the outer or fibular side of the base are two articular surfaces for the fifth meta- 

 tarsal : the hinder and smaller one is flat, and is continued, at right angles, with the 

 basal surface ; the larger surface is subcircular and rather undulating : in front and 

 below these surfaces is a narrow rugged tract for ligamentous junction with the fifth 

 metatarsal. The part of the shaft of the fourth metatarsal which stands out free is 

 smooth upon its inner and upper sides, is traversed by a wide oblique tendinal groove 

 below, and is rather rough and irregular externally. 



The vertically produced distal surface presents a large rough protuberance at its upper 

 part (Plate XXV. fig. 1, iv), and three protuberances at its under part, of which the 



