26 THE ARTISTIC ANATOMY OF ANIMALS 



represented by a small osseous plate only (Fig. 17), 

 which is not connected with any of the neighbouring 

 bones. 



It is on the deep surface of a muscle which passes from 

 the head and neck to the humerus (mastoido-humeral, a 

 muscle common to the arm, neck, and head) in which this 

 rudimentary bone is found to be developed. 



The clavicle exists in perfect state in mammals which 

 use their limbs for digging, grasping, or flying ; the insecti- 

 vora (hedgehog, mole) and some rodents (squirrel, wood- 

 chuck) are provided with it. 



The cheiroptera (bats) possess an extremely well-developed 

 clavicle, on account of the varied movements which their 

 thoracic limbs execute. 



This formation of the shoulder which favours flight in 

 the bat is even more remarkable in birds. In these latter 



Fig. 16. — Left Clavicle of the Cat: Fig. 17. — Clavicle of tup, 

 Superior Surface (Natural Size). Dog (Natural Size). 



I, Internal extremity ; 2, external ex- 

 tremity. 



(Fig. 18) the clavicles, fused together by their lower extremi- 

 ties, form one bone, having the shape of the letter V or U, 

 which is known as the fourchettc ; this bone, acting as a 

 true spring, keeps the shoulders apart, and prevents their 

 approximation during the energetic movements which flight 

 necessitates. 



In birds whose power of flight is strong, the two limbs 

 of this bone are widely separated and thick, and the four- 

 chette is U-shaped. Those whose flight is awkward and 

 but slightly energetic have the limbs of the fourchette 

 slender ; they unite at a more acute angle, and the bone is 

 V shaped. 



Furthermore, a bone named the coracoid joins the scapula 

 to the sternum ; this bone, often fused with the scapula, 

 where it contributes to the formation of the glenoid cavity, 

 represents in birds the coracoid process of the human 



