THE CLAVICLE 31 



muscular ossification. Even the simple use of the fore- 

 limb as a paddle is carried out in the absence of any strut, 

 and the clavicle fails to be developed in aquatic paddlers. 

 It is the wider range of movements of the shoulder-joint, 

 such as culminates in the free action of circumduction, 

 that preserves in full functional development this primi- 

 tive vertebrate heritage in the mammalian shoulder 

 girdle. 



Within the groups Carnivora and Rodentia, it is easy 

 to see that freedom of fore-limb and clavicular develop- 

 ment go hand in hand. It is safe to assert that a Mammal 

 possessing a fore-limb which, from any cause whatever, 

 has become in an}^ considerable degree emancipated 

 from the function of mere quadrupedal progression will 

 also possess a clavicle of fairly complete development, 

 no matter what the systematic zoological position of the 

 Mammal may be. 



Emancipation of the fore-limb has preserved the 

 clavicle, inherited in the general vertebrate make-up of 

 the first mammalian type, and has insured its survival 

 in a simple yet very perfect form in Man. 



The arboreal habit, as the great factor in preserving 

 and increasing the original mobility of the fore-limb, 

 has also been the great factor in preserving in the human 

 shoulder girdle a well-developed collar-bone. 



