90 Mr. Owen on the Glyptodon clavipes. 



Megatherium. The long and compressed claw-bone of this gigantic Edental, with its 

 basis encompassed by a bony unguial sheath, bespeaks the fore-foot to have been 

 an instrument, the use of which, in scratching and digging, and perhaps occasion- 

 ally defending its possessor, were of more consequence in the living economy of 

 the individual, than mere subserviency to support and progression. The peculiarly 

 compact and robust structure of the foot of the Glyptodon, on the other hand, is 

 eminently suggestive of such a subserviency, and more especially as the base of a 

 column of support ; but as this fore-foot was associated with a rotatory condition 

 of the radius, it is probable that the Glyptodon had the power of applying its ante- 

 rior extremities to all the purposes to which the Armadillos, its nearest congeners, 

 apply theirs. 



Of the posterior extremities, Sir Woodbine Parish's collection of the bones of the 

 Glyptodon include the anchylosed distal extremities of the tibia and fibula ; an 

 astragalus, calcaneum, scaphoides, cuboides, external cuneiform bone, the three 

 phalanges of the second toe and the middle and distal phalanges of the third and 

 fourth toes, with a few sesamoid bones ; all belonging to the left side*', 



Sellow's collection also included most of these bones, but in a less perfect con- 

 dition than the present. Both collections, while they establish the identity of the 

 species possessing the ponderous bony covering, at the same time prove the close 

 correspondence which subsists between the fore- and hind-feet of the Glyptodon in 

 general form and structure. 



Tibia. — Sufficient of the tibia remains to show that it had the compressed form 

 and excavated inner surface characteristic of that of the Armadillos ; that a similar 

 wide space separated it from the fibula, with which it is also anchylosed ; and that 

 the anterior margin of the bone was continued obliquely as a strong ridge to the 

 inner angle of the distal surface. The distal articular surface presents two conca- 

 vities separated by a convexity, the outer hollow being the largest and deepest ; the 

 external malleolus forms a well-marked process, as in the Armadillos ; at the back 

 part of the tibia we find also two well-marked tendinous grooves separated by a 

 projecting ridge. The corresponding part of the skeleton of the Megatherium devi- 

 ates widely in the proportions of the tibia and fibula, and in the conformation of 

 the distal articular surface from that of the Glyptodon. 



Astragalus. — The upper surface of this bone (PI. XL fig. 3) describes a regular 

 convex curve in the antero-posterior direction ; transversely it forms, as in the 

 Armadillo, two marginal convex trochlese, separated by an intermediate wide con- 

 cavity : the internal or tibial trochlea is somewhat lower and broader than in 

 Dasypus, in which respects Glyptodon manifests an approximation to Scelidothe- 

 rium-f, which, in the structure of its astragalus, presents an intermediate step in 



» PI. X. fig. 3. t Fossil Mammalia of the Voyage of the Beagle, 4to, PI. XXVI. figs. 2, 4 and 6. 



