8 Jeffries on the Fingers of Birds. 



gross examination by soaking in a solution of glycerine and 

 ammonia carmine. By this means I have obtained specimens 

 that have shown all the bones distinctly. 



With this knowledge of the carpus and the light thrown by 

 the new specimen of the Arclnvoptcryx it would seem possible 

 to decide the homologies of the fingers in the class of birds. The 

 questions to be solved are : ( I ) Are the fingers homologous 

 throughout the class? (2) Are they the I- IV or the II- V ? 



The only author known to me who considers that the fingers 

 among living birds are not homologous is Dr. Coues. This dis- 

 tinguished ornithologist says (Key, p. 30): "The forefinger 

 hand-bone sticks out a little from the side of the principal one. 

 and bears on its end one finger-bone (sometimes two), which is 

 commonly, but wrongly, called the bird's • thumb'. For although 

 on the extreme border of the hand, it is homological with 

 the forefinger; birds have no thumb (exc. Arc/nvoptcryx. 

 Strut Jiio. Rhea) ; and no little finger." The mistake concerning 

 the Arclnvoptcryx was natural and is merely taken from Owen's 

 memoir on the first fossil found. It has since, however, been 

 shown that it had only three fingers. But why the Ostrich and 

 Rhea should be included is hard to understand, since these have 

 hand bones like all flying birds.* 



Among the birds with undeveloped hands the "index" finger 

 is the most constant, those on either side aborting before this. 

 The genus Dronnviis is a good example of this. 



When the hand is developed it is of precisely the same form in 

 all birds,. 



On the second question, which is virtually whether the first 

 finger of birds is the first of the series or the second, much has 

 been written ; all, however, with the idea that two were lost. 



Owen, Coues, and Morse have at separate times held that birds 

 have no thumb, while Nitzsch, Meckel, Huxley, Gegenbaur and 

 Rosenberg claim that birds have a thumb. 



The arguments used against the existence of the thumb are as 

 follows: (1) The first fossil remains of Archcvopteryx longi- 

 cauda show the remains of a detached finger, which Owen sup- 

 posed to be a first digit placed on the radial side of the " thumb." 

 Of this, however, he expresses some doubt. f (2) In Todd's 



* See Selenka, Bronn's Thier-Reichs, Vogel, p. 75; D'Alton, Die Skelete d. Strauss- 

 artigen Vogel, p. 17; Owen, Anat. of the Vertebrates, Vol. II., p. 73. 

 f Owen, "On the Archceopteryx." Phil. Trans., 1864, Vol. CLIII. 



