PEDIGREES— THE FOUNDERS OF THE HOUSE. 229 



bands, to the region where the scapula and 

 coracoid join one another. The fixed ends of 

 this merry-thought, the apex of the "horse-shoe " 

 which the two fixed bones form, is joined by 

 ligament to the deep keel of the breast-bone. 

 (In flightless birds there is often no keel and 

 no merry-thought, but this does not affect the 

 question.) 



These bones, then, the scapula, coracoid and 

 furcula, make up the shoulder-girdle. 



Now, here follows a point to be borne in mind 

 for future guidance. In young birds all these 

 bones are represented first in what is called 

 cartilage. Later this is replaced by bone. Ex- 

 actly how this is done does not concern us here. 

 This transformation from cartilage to bone is 

 not effected all at once. In the penguin, for 

 instance, the shoulder-girdle becomes bony, or 

 ossifies, long before the breast-bone or sternum. 

 Now, if one of these birds died during this stage 

 of its growth and became fossilised, we should 

 have no record of the sternum left. It would 

 decay with the fleshy parts, and only the 

 shoulder-girdle bones would be left. 



In the ancient dinosaur, we get a shoulder- 

 girdle bearing many strong resemblances to that 

 of the bird. As the dinosaur is not a flyiog 

 reptile, we cannot expect it to do more than 

 roughhj resemble the birds. The dinosaur then 

 has modified the original shoulder-girdle in one 

 direction to suit its requirements, and so has 

 changed its original form, just as the bird has 

 changed its shoulder-girdle to suit yet other re- 

 quirements. Neither then represents the original 



