86 The Bird 



mankind and most birds, have less varied movements of 

 the fore Hmbs, the clavicles have fallen into disuse, as 

 in the lion and the horse. But in climbing, burrowing, 

 and flying animals, such as the squirrel, mole, and bat, 

 these bones have been of active use and are well devel- 

 oped. But to keep its wish-bone a bird must contirme 

 to fly: for Nature is opposed to useless parts. So, in 

 the flightless cassowary and ostrich, the wish-bone is 

 very small or altogether absent. Parrots are almost 

 alone in appearing to suffer no inconvenience in flight 

 by the lack of clavicles, — these being greatly reduced in 

 some species. 



In that anomalous bird the Hoatzin, the clavicles 

 are fused not only at their base, but the tips are ossified 

 firmly to a projecting spine of bone from the upper part 

 of the breast-bone. 



In glancing back over the lower back-boned animals 

 Ave realize that a shoidder-girdle of bones is of no use 

 without a limb. Therefore we find the first hint of the 

 shoulder-girdle in sharks, in w^hich we also find the first 

 limbs, or fins. In these fishes it is nothing but a single 

 bar of soft cartilage. In the girdle supporting the pec- 

 toral fin of such a fish as the trout or other bony fish, 

 we find the adumbration of some of our bird's bones. 

 When we remember how^ very wing-like is the movement 

 of a fin in the water, we will not be surprised to learn 

 that the girdle is almost all epiclavicle; these bones 

 being the forerunners of clavicles, and giving place, in 

 the higher forms, to the real wish-bones which steadily 

 increase in size and importance. We would hardly 



