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Show BG ZOOLOGY OF THE VOYAGE OF TilE DEAGLE. . d Sl th "an animal, great part of whose life, With respect to the At, or three-~oe ~ ' t .., 11 easy attitude for repose . . · t m sleepmg on recs,-u. when not engaged m eatmg, lS spebnl · t e . an d accor d'm g1 Y we find • that the is most essential to its comforta e exls enc ' ,.b t to produce that flexibility of . . b th b c of the neck coutn u e auxll~ary vertc r::e at e as . 1 · 1' r 01.wards and rest upon . h h d f the annna to me me 1 this organ whiCh allows t e ea 0 . tl "Adar)tation of the Struc- . b " D · Buckland from whose Paper on 1e . . . 1ts osom. I. ' . f L'f "* the precedino- JUdiciOus ture of the Sloths to their peculiar Mode 0 1 e, 0 . . . k . t d adduces the authority of Mr. Burchell m proof Physwlogical remar 1s quo e • . · · · h d · . ·k ble manner and with great fac1hty tw1st Its ea that the Sloth can 111 a remai a · · 1 ·1 't d d look l·n tlle face of a I)erson standing directly behmd It, w u e q n• e rou n , an · 1 tl at the same time the body and limbs remain unmove~l. A smg1e g .ance at ~e length and slenderness of the cervical region of the spmc, and of t~e feeble condition of the transverse and spinous processes in the vertebr::e co~posmg that part of the skeleton of the Sloth, is enough to show its adaptation to mcrcase the rotatory motion and flexibility of the neck. . . . . .. In describing the skeleton of a species of Armad1llo (Dasypus fi-c~nc~~s, Lmn .) I 1 was led in like manner to point out the subserviency of the pecuhar.Ities of the cervical vertcbrre to the habits and mode of life of that animal; obser~mg that the "anchylosis of the cervical vertebr::e obtains in the Cetacea,. as wc~l as 111 th.e genus Dasypus, and that as in the aquatic order this firm connex10n of th~ cerviCal vertebr:: e assists materially in enabling the head to overcome the res1st~nce of ~he dense fi.uid through which they perpetually move, so in the Arma.dtllos. a hke advantage may be derived from this structure during the act of dtsplacmg the denser material in which they excavate theit· retreats."j: Having in view these well-marked examples of the subserviency of the structure of the bones of the neck to tho habits of existing species of the order B1·uta, I proceeded to investigate the structure of the corresponding part of the sk~leton in the Scelidotherittm, hoping thereby to gain a new and useful element m the determination of the problem at present under discussion, as to the affinities and habits of the extinct Megatherioid quadrupeds. The fossil, iu its original state, yielded a view of so much of tho anterior part of the bodies of the cervical vertebr::e as proved that they were neither so nume· rous as in the Sloth, nor anchylosed together as in the Armadillos: after a long and careful chiselling at the hard matrix in which they were imbedded, the trans- * Liuu. Trans. vol. xvii. (1833) p. 17. t Zoo!. Proceeding, 1832, p. 134. t The anterior prolongation of the sternum in front of the neck and the correspondiug anterior position of the clavicles and scapulre occasions a transference of such a proportion of tho moving powers of tho head from the cervical vcrtebrre to these bones in the mole, as renders any modifications of those vertcbrre, like those in tho Armadillo, uncalled for. FO SIL MAMMALIA. 87 verse and spinous processes were exposed to view, as they are represented in Plates XX. and XXIV. The description of these processes has already been given. . ?n comparing the cervical vertebrm of the Scelidotherium with those of the extstmg B1·uta, the closest resern blanco to them was found in the skeleton of the Orycterope. Now t?is quadruped, though not so rapid a burrower, 01• so strictly a subterranean spec1es as the Armadillos, participates, nevertheless to a certain ~xte.nt, in their fossorial habits, and is closely allied to them in gene:al structure: 1t differs from them, indeed, mainly in a modification of the dental system, in the absence of dermal armour, and of anchylosis of the cervical vertebrre. But the advantages which, as a burrower, it would have derived from the latter structure, are compensated ~or b.y the shortness of the cervical vertebrre, and by the great dev~Jopm~nt and ImbriCated 01· interlocking co-adaptation of the transverse and ~nteno1· spmous p•:ocesses o~ the cervical vertebr::e. The analogous quadrupe~ m the ~outh Amencan Contment-the great ant-eater (rn,yrmecopllagajttbata) whiCh uses 1ts powerful compressed fossorial claws for breaking throuO'h the hard walls of the habitations of its insect prey, but which does not excava~e a subterraneo~ s retreat for itself, presents the cervical vertebrre of a more elongated form, and Without that development of the spinous and transverse processes which tend to fix the neck and increase the size of the muscles which move the head: and, if :we could conceive that its fore-feet were employed to scratch up vegetable roots, mstead of disinterring termites, there would be no reason to expect any modification of the cervical vertebrm as a direct consequence of such a difference in the application of its fossorial extremities: when, therefore, we find that the cervical vertebrre do actually differ in two myrmecophagous species, to the extent observable in the Cape and South American ant-eaters, we arrive legitimately at the co~clusion. that such difference relates to fossorial habits of the one species, in wlnch habits the other does not participate. Now, therefore, if this conc1usion be just in regard to the Orycterope, it must bear with more force upon the question of the habits of the Scelidotherium ns the mechanism for strengthening the connection of cervical vertebrre, and for augmenting the surface of attachment of the muscles which worked the hea(l and neck, is more strongly wrought out in that extinct species. The great size and strength of the spinous process of the dentata, and the mode in which it is interlocked with the spinous and oblique processes of the third cervical, together with the imbricated disposition of the transverse processes of this and the succeeding vertebr::e, and the remarkable height of the 'dorsal spines, all combine to indicate in a very striking manner, if not to demonstrate, that the conical head of the present species, which is comparatively small and slender, and |
