242 OUTLINES OF EVOLUTIONARY BIOLOGY 



consider the way in which this type has been adapted to form 

 organs of flight in different vertebrate groups. 



The wing of the extinct pterodactyls (Fig. 99) was formed 



by an expansion of the skin of the body stretched between the 

 fore and hind limbs, and the phalanges of the little finger were 

 enormously elongated so as to aid in the support of its anterior 



