FOSSIL MAMMALIA. oU 



present skeleton, which indicates the nonage of the individual in the unanchylosed 

 condition of most of the epiphyses. 



In regard to the presence of a clavicle in the Megalonyx M. Lund has 

 deduced certain conclusions, which, if well founded, would be equally applicable 

 to the present allied species, and to the great Megatherium. I am induced, 

 therefore, to offer a few physiological observations on that bone, which appear to 

 me to lead to a more correct interpretation of its uses and relations in the great 

 mammiferous animals now under consideration. 



When the anterior extremities in mammalia are used simply for the purpose 

 of progressive motion on dry land, as in the Pachyderms and Ruminants, or in 

 water, as in the Cetaceans, there is no clavicle ; this bone is introduced between 

 the sternum and acromion, in order to give firmness and fixity to the shoulder- 

 joint when the fore-leg is to discharge some other office than that of locomotion. 

 In these cases, however, the clavicle exists in various degrees of develop- 

 ment, and even its rudiment may be dispensed with in some of the actions which 

 require a considerable extent of lateral or outward motion, and of freedom of 

 rotation of the fore-limb. When, therefore, we find the clavicle fully developed 

 in the skeleton of an extinct mammiferous animal, and so placed as to give the 

 humeral articulation all the benefit of this additional mechanism, we may confi- 

 dently expect that it will afford an insight into the habits and mode of life of such 

 extinct species. M. Lund* has argued from the clavicle of the Megalonyx, that 

 it climbed like a Sloth. " Animals," says Sir C. Bell,| " which fly or dig, or 

 climb, as Bats, Moles, Porcupines, Squirrels, Ant-eaters, Armadilloes, and Sloths, 

 have this bone ; for in them, a lateral or outward motion is required." But in re- 

 gard to the present problem, we have to enquire whether the clavicle manifests any 

 modifications of form, of strength, or development in relation to the special dif- 

 ferences of these several actions, with which its presence is asserted to be associated? 



In mammals which fly, the clavicle is always complete : the rabbit, the 

 fox, and the badger are instances of burrowing animals in which the clavicle is 

 absent or rudimental. The presence of a perfect clavicle is not more constant in 

 climbing quadrupeds. The Ai, for example, has an incomplete clavicle, which is 

 attached to the acromion process, and terminates in a point about one-fourth of 

 the distance between the acromion and the top of the sternum, to which the 

 clavicular style is attached by a long slender ligament : the advantage, therefore, 

 which a perfect clavicle affords in the fixation of the shoulder-joint, is lost to this 

 climber par excellence. Again, the Bears, which are the bulkiest quadrupeds that 

 are gifted with the faculty of climbing, and this in so perfect a degree that the 

 Sun-bears of the Eastern Tropics may be termed arboreal animals,— these scan- 



* Loc. cit. f Bridgewater Treatise, p. 46. 



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