133 



NATURE STUDIES 



feature " of reptiles, of birds, and of the frog-class as 

 well, in the structure of the shoulder. In the shoulder 

 of an ordinary quadruped, and of a kangaroo and its 

 marsupial race as well, there are but two distinct 

 bones. One of these is the shoulder-blade, or scapula, 

 the other being the collar-bone, or clavicle. In the 

 shoulder of a bird (Fig. 8) there are three distinct 



B 



Fig. 8. Shoulder-bones of (A) an Eagle, and (B) an Ostrich. 



elements, the scapula (Fig. 8, d) clavicle (c), and the 

 coracoid bone (6, b). This last in quadrupeds, a mere 

 process of the shoulder-blade, forms, as shown in 

 Figure 8, the chief support of the wing in birds, and 

 arises directly from the breastbone (a). Now, it is a 

 remarkable fact that the Ornithorhynchus and Echidna, 

 alene of all quadrupeds, possess a distinct coracoid 

 bone, which, as in birds and reptiles, springs from the 



