100 Mr. Owen on the Glyptodon clavipes. 



tainly covered with an osteodermal carapace, by the disposition of the spinous pro- 

 cesses of the vertebrae, by the angles of the ribs, by tlie articulation of the pelvis 

 with the vertebral column, etc.*. 



Now pending the appearance of the description of the pieces of the carapace of 

 the Megatherium, of which the discovery is announced by M. de Blainville, and 

 the nature of which armour is as yet unknown to science, I may be permitted 

 to offer a few observations, tending to show that the possession of such a carapace 

 cannot be deduced by a priori reasoning, founded on the parts of the skeleton of 

 the Megatherium cited by M. de Blainville. And in the first place I would observe, 

 that in reasoning from the analogy of the Armadillos, — the only quadrupeds which 

 possess a bony carapace, — we have the advantage of having presented to our ob- 

 servation a skeleton which presents throughout that family a constant and un- 

 varying series of well-marked modifications in direct relation to such a carapace 

 as the Megatherium is stated by M. de Blainville to possess. 



Although I have cited the enormous sacrum, with its consolidated spines, and the 

 buttress-like disposition of the strong columnar ilia, as among the modifications of 

 the skeleton of the Armadillos which bear a physiological relation to their peculiar 

 armour, these are by no means the most striking evidences of this relationship. 

 What first catches the eye of the anatomist, in quest of these indications in the 

 skeleton of the Armadillo, is the remarkable production of a process f of the ver- 

 tebrae extending from above the anterior articular process on each side in an 

 oblique direction upwards, outwards, and forwards to nearly the level of the 

 extremity of the true spinous process J : now these oblique processes, which are 

 thus developed in no other quadrupeds, save the loricated Edentata, precisely and 

 beautifully correspond in form and use with the tie-bearers in the architecture of a 

 roof ; but if we look deeper into the nature of the sustaining mechanism of the 

 roof-hke armour of the Armadillo, we shall find another purpose obtained by 

 these processes, besides the ofiice of the tie-bearer : the ordinary spinous process 

 transmits the superincumbent weight simply to the vertebra from which it springs ; 

 the oblique processes transmit the weight partly to the vertebra to which they 

 belong and partly to the vertebra next in front, because one half of their base or 



* " Par Fensemble de I'organization, comme par sa forme et par la carapace osteo-dermique dont il 

 etait certainement couvert, comme on peut aussi bien le prouver a priori qu a. posteriori, c'est a dire, par 

 la disposition des apophyses epineuses des vertebres, de Tangle des cotes, de T articulation de la ceinture 

 osseuse posterieure avec la colonne vertebrale, etc.; aussi bien que par le fait, c' etait une espece gigan- 

 tesque de Tatou, plus voisin du Tatou chlamyphore que de tout autre, quoique celui-ci soit le plus petit 

 du genre." — Comptes Rendus, 21re Janv. 1839, p. 68. 



t PI. XIII. figs. 1 and 2, b, b. 



J Ibid, a, a. 



