60 UNIVERSALITY OF DEGENERATIVE EVOLUTION 



more perfect, the modifications entailed are much 



greater and have been accompanied by further signs 

 of degeneration. In the fowl 

 (fig. 29) all the claws have 

 disappeared (degeneration No. 1) ; 

 the thumb (i.) and the index 

 finger (ii.) have each lost a 

 phalanx ; the middle finger (iii.) 

 has lost three (degeneration No. 

 2) ; finally, the metacarpals of 

 the index and middle fingers 

 have fused (a.) thus entailing 

 the degeneration of the muscles 

 between those parts (degeneration 

 No. 3). 



(&) The Pterosaurians. These 

 reptiles, which are now extinct, 

 were able to fly, like bats, by 

 means of a membrane. There 

 is no connection between them 



FIG. 29.-skeieton of wing and birds which fly in quite a 



i,Fir8tdigi f tor Wl thumb; ii, different way. 



The membrane of the Ptero- 

 !! saurians (fig. 30) was supported 



digit,. (After Huxley.) by ft framework of which the 



most important part was the fifth finger (v.), the 

 digit corresponding to our little finger, which was 

 greatly elongated. 



The patagium (the flight membrane) consisted of 

 two kinds of membrane, the antebrachial membrane 



