98 Mr. Owen on the Glyptodon clavipes. 



similar to that we find on the analogous parts of the skeleton of the Armadillo : " 

 he has likewise adduced the massive proportions of the hind-legs and tail, as con- 

 ditions consistent with the necessity for carrying so ponderous a cuirass as that 

 which he supposes to have covered the body of the Megatherium. 



But the above-cited modifications of the vertebrae, pelvis and ribs are more 

 strongly marked in the skeleton of the Anteater and Sloth than in that of the 

 Armadillo ; and if the skeleton of this mailed Edental be studied in reference to its 

 subserviency to the support of the dermal armour, the modifications for this end 

 will be found to be widely different from, and more striking than, any which have 

 been pointed out in the remains of the Megatherium. 



The modifications of this nature which we observe in the pelvis of the Armadillo, 

 are the following : — 



1st. The anchylosis of a great number of vertebrae, so as to form a very long 

 sacrum, which, in the Dasypus tricinctus, for example, includes twelve vertebrse*. 

 2ndly. The great antero-posterior development of the spines of these vertebrse, 

 which thus form a continuous vertical ridge of bone, bearing immediately the super- 

 incumbent weight, and, in some species, as in the Dasypus tricinctus, by the corre- 

 sponding development of a ridge from the median line of the under surface of the 

 armour. 3rdly. This weight is transmitted from the sacrum to the thigh-bones 

 by two converging bony columns on each side : one of these is formed by the 

 ischium, which is anchylosed to the posterior part of the sacrum ; the second 

 and more characteristic mode of transferring the weight of the armour from the 

 sacrum to the femur, is by the conversion of the iliac bone into a stout three-sided 

 beam, passing straight from the thigh-joint to abut against the anterior part of 

 the sacrum, where the weight of the shell is greatest. In no species of Armadillo 

 is the ilium expanded ; in some species a small angular process projects outwards 

 from the sacral, or upper extremity of that columnar bone ; in others, as the 

 D. tricinctus, there is not even this feeble representative of the expanded ilia of the 

 Megatherium. The Megatherium, in fact, resembles the Elephant in the size, form 

 and position of its iliac bones, as well as in their expanded and flattened labrura, more 

 nearly than it does any other existing quadruped. The Edentata which make the 

 nearest approach to this characteristic structure of the Megathere are the Sloths, 

 and next to them the great hairy Anteater {Myrmecophaga juhata) . To argue that 

 the broad and flattened ilia of the Megatherium are conditions of those bones by 

 which they are adapted to sustain a heavy coat of bony armour, seems to imply 

 that a continuous transverse wall would be a better support to a solid and un- 

 yielding roof than the judicious disposition of a less amount of material in the 



* PI. XIII. fig. l.c,c. 



