Mr. Owen on the Glyptodon clavipes. 101 



origin is extended directly over the posterior oblique processes of the adjoining 

 vertebra. 



Now if we find so peculiar, so complicated, and so perfect a mechanical modi- 

 fication of the vertebral column of the Armadillo, relating immediately to the 

 peculiar weight it is required to bear, we are surely justified in expecting a cor- 

 responding modification in the same part of the skeleton of the Megatherium, on 

 the hypothesis that it had also to sustain armour corresponding with its enormous 

 bulk. We look in vain, however, for these long oblique columnar apophyses in 

 the vertebral column of the extinct giant ; their analogues here maintain the ordi- 

 nary condition of short transverse processes* directed outwards at right angles 

 with the spinous process f ; and the Megatherium in this respect corresponds with 

 the hair-clad Sloths and Anteaters. 



With respect to the ribs, I may observe that the armour of the Armadillo does 

 not immediately rest on any part of these bones as it does on the vertebrse above- 

 mentioned : a stratum of muscular substance intervenes between the armour and 

 ribs, and the latter are left free, and necessarily so, for the movements of respira- 

 tion. The Sloths and Anteaters have broader and stronger ribs than the Arma- 

 dillos ; nay, they have relatively broader and stronger ribs than the Megatherium 

 itself, and the angles of the ribs show the rough impressions of the insertions of 

 the levatores costarum in the same relative degree as do the angles of the ribs of 

 the Megathere, on which M, de Blainville supposes the carapace to have directly 

 rested. 



With respect to the relation of the bones of the extremities to a dermal armour, 

 the difference of structure observable between the Megatherium on the one hand 

 and the Glyptodon and Dasypi on the other, has already been pointed out. The 

 columns supporting the trunk of the Megatherium are unquestionably of colossal 

 proportions, but I conceive that the prodigious strength of the bones of the legs 

 of the Megatherium was called for by the weight of the enormous superincumbent 

 pelvis, which exceeds in the thickness and expanse of its several bones, relatively 

 as well as absolutely, that of any other animal. And when to the weight of this 

 ponderous cincture of bone, is added the mass of soft parts which must have en- 

 compassed and been lodged within it, I feel disposed to protest strongly against 

 laying an additional load even upon the stalwart legs of the Megatherium. 



But if the burthen of a bony coat of mail must needs be placed upon his heavy 

 haunches, let us endeavour to form a true conception of its expanse. If we com- 

 pare the average dimensions of the component tesserse of the armour of existing 

 Armadillos with their skeletons, we shall find that there is the same correspondence 

 between the internal and external bones of these small cuirassiers, as between the 

 endo- and the exo-skeleton of the Glyptodon. 



* PI. XIII. fig. 3, b, b. t Ibid, a. 



