VI FORM AND FUNCTION III 
greater girth of the hollow bones in proportion to their 
length is at once obvious. But to bring this out still 
more clearly, I have taken the wing bones of the Skua 
Fic. 28. 
a 6 ¢ 
Humerus of Pomatorhine Skua (a); Rhinoceros Hornbill (6); and Vociferous Sea 
Eagle (c). Drawn to scale. 
as the standard, and calculated what would have been 
the length of the same bones and of the whole wing in 
the Sea Eagle and the Hornbill, if they had been built 
upon the same lines : 
