IO Jeffries on the Fingers of Birds. 



possible means of support down its long axis, i. e., a post. (2) 

 Ease of flexion combined with rigidity when extended. Tbis 

 problem has been successfully worked out by the horse and other 

 Ruminants. In the wing of a bird the object is very different ; 

 here no direct support is' required but the power to resist a force 

 applied along the whole of the haemal surface. With this is 

 combined the requisite that the wing should close in such a way 

 as to oppose little resistance to the air in the advance of a bird 

 through it. 



Again this law is an absolute failure when applied to the leg 

 of a bird, since the little toe is aborted but not the thumb. It 

 may not be out of place here to mention the greater tendency of 

 the radial side to produce digits, as shown by the extra toes in 

 dogs, cats and hens. On the other hand the anatomists who con- 

 sider the first digit of a bird to be the first of the series have not 

 brought forward any particular argument, but have taken it to be 

 a matter of course. Yet there are facts that seem to point this 

 way. (1) There are no signs of any metacarpals developed radiad 

 of the "thumb." This, of course, is of value only in so far as 

 it seems to imply that there never was any. (2) If we study 

 the myology of the hand we find several long muscles to the I 

 and II fingers. These are the extensor metacarpi radialis 

 longus, * and extensor carpi radialis to the first metacarpal, the 

 extensor pollicis longus and the extensor indicis proprius. The 

 last two muscles are so named from their similarity to these mus- 

 cles in man. At all events, long, separate muscles to the digits are 

 characteristic of the I, II, and V digits. Thus finding them in 

 birds seems to imply that the first and second fingers are the I, II 

 of the series. 



Very marked characteristics of a bird's arm are that the flexor 

 muscles are numerous, the pronators and supinators performing 

 this function, and that all the long finger muscles are brought up 

 to the radial sides of the fingers so as to act as adductors. This 

 means a strong application of force to the radial side of the wing, 

 hence correspondingly strong bones. Now, unless the thumb 

 was lost before the modifications for flight were brought about, 

 this application of force to the radial side points to the develop- 

 ment of the thumb and index. 



* Rodinger considers this to be a muscle of the thumb, not tha carpus. Nat. Ver- 

 hand. v. d. Hollandsche Maadschappy d.Wetenschappen te Haarlem. II. Verzame- 

 liog, 25 deel, 1868. 



