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Show 90 ZOOJ.,OGY OF TilE VOYAGE OF THE llEAGI,E. sorial quadrupeds are destitute of eve~ the .smallest rudiment of a clavicle, as I have ascertained by repeated careful dtssectwn. . . l Since, therefore, a clavicle in any degree of devel~pment IS not essen~ta t~ a climbing quadruped, we must seek for some other relatwn and use of that 1emark~ abl stron , and perfect bone, as it exists in the Megat~ere, ~e~a~onyx, a~ S yl'd 1 g Th bsence of 'dentes primores ' or of an tenor or mctsive teeth m ce 1 ot 1ere. e a . · h t' f' h d d t Once sets aside any idea of its connectiOn w1t an ac wn o t ese qua rupe s a . 1 · 1 · t h e 1i' 0re ex t rem1' t'1 es, ver· y common in the mammals whtch possess c av1C es, viz., that of carrying the food to the mouth, and holding it there to be. gnawed by the teeth. Flying is of course out of the question, althou~h o~r surpnse woul~ haruly be less at seeing a beast as bulky as an elephant chm~wg a tree, th~n 1t would be to witness it moving through the air. If now we restnct our co~panson ~o t~e relations of the clavicle in that order of Mammalia to which the extmct species m question belonged, we shall see that it is most con~tant, strongest, and mos~ co~nplete in those species which make most use of theu strong and long claws I.n di~placing the earth, as the Armadilloes and Orycteropus : and, as the ~laviCle IS incomplete in one climbing Edental, we are naturally led to co?clude t~at 1ts perfect development in an extinct species must have been associated with uses and relations analogous to those with which it coexists in other genera of the same order. Thus it will be seen, that, in rejecting the conclusion drawn by M. Lund from the presence of a clavicle, I concur in the opinion expressed by Dr. Buckland"" that the 1\fegatherium-and with it the Megalonyx and Scclidotheriumhad the shoulder-joint strengthened by the clavicle, in reference to the office of the fore-arm, as an instrument to be employed in digging roots out of the ground. Not, however, that these gigantic quadrupeds fed on roots, but rather, as the structure of the teeth would show, on the foliage of the trees uprooted by the agency of this powerful mechanism of the fore-legs, and of the otherwise unintelligible colossal strength of the haunches, hind-legs, and tail. The humerus presents a large convex oval head, on each side of which is a tuberosity for the implantation of the supra- and sub-scapular muscles: these tuberosities do not rise above the articular convexity, so as to restrict the movements of the shoulder-joint, as in the Horse and Ruminants, but exhibit a structure and disposition conformable to those which characterize the proximal extremity of the humerus in other mammalia which enjoy rotatory movements of the upper or fore-limb. The tuberosities are, however, relatively more developed, and give greater breadth to the proximal end of the humerus in the Scelidothere than in the Megathere. The distal end of the humerus, although mutilated, clearly indicates that it had the same characteristic breadth of the external and internal • llridgewater Treatise, p. I 52. FOSSIL MAMMALIA. 91 condyles, as in the Megatherium · In fig . 1 . PI . XXV . w h'I c 11 gi·v es a f ront vt·e w of the le~t h.umerus, the broad internal condyle, with its extremity broken off, is ~een pt'OJ~ctmg to the left hand; both in this figure and in fig. 2. in which the ~nternal s1de of the humerus is turned towards the observer, the wide groove, with Its two osseous boundar~es, is shewn, which plainly indicates that the Jeft condyle was perforated for the duect passage of the artery or median nerve, or of both, to the fore-a~·m. The groove for the musculo-spiral nerve on the outer side of the humerus .Is over-arched at its upper part by a strong obtuse process; which is compamtlvely less developed in the Megatherium. The trochlear or inferior articular s~1~face ?f the humerus presents, as in the Megatherium, two well-marked convexities, With an intervening concavity: this indication of the rotatory powe of the fore-leg is confirmed by the form of the head of the radius. r In Pl. XX:V. fig. 4. a view is given of this articular surface: it presents the form of a.subcu:cular gentle co~cavit~, which plays upon the outer convexity of the hume1al artJCular surface: Immed1ately below the upper concavity the radius presents a lateral smooth convex surface, which rotates upon a small concavity on the ulna.' analogous t.o the 'lesser semilunar,' in human anatomy, in which ~he mechamsm for rotatwn, so far as the upper joint of the radius is concerned, IS not more elaborately wrought out than in the present extinct edentate quadruped. Tl~e ~·adi.us expands as it proceeds to the elbow-joint, where it attains a ?readth mdwattve of the great power and size of the unguiculate paw, of which It may be called the stem, and. to t~e movem~nts of which it served as the pivot. Al~ the ~on~s of the fore-ltmb JUSt descnbed-the scapula, the humerus, and the radm~,-mdwate b~ t~e bold featu~es and projections of the muscular ridges and tubercles the prodigiOus force wluch was concentrated upon the actions of ~he .fore?aw, and the ulna, in its broad and high olecranon (of which a side-view IS gtve~ m .:fig. 2. Pl. XXV.) gives cotTesponding evidence. The great semilunar concavity IS traversed by a sub-median smooth ridge, which plays upon the inters~ ace of the.t~o .hume~·al c.onvexi~ies. The body of the bone is subcompressed, str~Ight, .and dummshes m size as It approaches the carpal joint: the immediate a~tteulatmg ~~rfaces .are wanting in both the radius and ulna, the epiphysial tltstal extremities. havmg become detached from their respective diaphyses. Of the termmal segment of the locomotive extremities, the only evidence among the remains of the skeleton of the Scelidothere is the ungueal phalanx :fig·ured at P~. XXVII. 3, 4, and 5; but as it is uncertain whether it belong to the fore or hmd-foot, it will be described after the other bones of the extremities have been noticed. Of these bo11es tl1 e f·i e mur J·S tl1 e mos t remar k a bl e b ot1 1 1i'0 r its great proportional size, and its extreme breadth, ns compared with its length or thickN 2 |