

90 ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 



* 



sorial quadrupeds are destitute of even the smallest rudiment of a clavicle, as I 

 have ascertained by repeated careful dissection. 



Since, therefore, a clavicle in any degree of development is not essential to a 

 climbing quadruped, we must seek for some other relation and use of that remark- 

 ably strong, and perfect bone, as it exists in the Megathere, Megalonyx, and 

 Scelidothere. The absence of ' dentes primores ' or of anterior or incisive teeth in 

 these quadrupeds at once sets aside any idea of its connection with an action of 

 the fore extremities, very common in the mammals which possess clavicles, 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, although our surprise would hardly 

 be less at seeing a beast as bulky as an elephant climbing a tree, than it would 

 be to witness it moving through the air. If now we restrict our comparison to the 

 relations of the clavicle in that order of Mammalia to which the extinct species in 

 question belonged, we shall see that it is most constant, strongest, and most com- 

 plete in those species which make most use of their strong and long claws in dis- 

 placing the earth, as the Armadilloes and Orycteropus : and, as the clavicle is 

 incomplete in one climbing Edental, we are naturally led to conclude that its 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. Buck- 

 land* that the Megatherium — and with it the Megalonyx and Scelidotherium 

 had 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 unin- 

 telligible 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 move- 



- 



ments of the shoulder-joint, as in the Horse and Ruminants, but exhibit a struc- 

 ture and disposition conformable to those which characterize the proximal extre- 

 mity 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 



* Bridge water Treatise, p. 152. 



