On the Tarsus and Carpus of Birds. 153 



Asrassiz a lono- time ao-o, as Avell as the fact that in the 

 embryo robin, the toes are webbed. In the early embryo 

 the toes are always webbed, and for a long- time in the 

 embryo all the toes point forward ; these are two characters 

 highly characteristic of lower groups of birds. The turning 

 back of the first toe is a subsequent modification. 



The first metatarsal appears last in development. The 

 phalanges of the third and fourth toes appear first, and the 

 others in regular succession. The phalanges of the foot 

 appear before those of the hand. 



The metacarpals and phalanges are widely separated in 

 the early embryo, and were it possible for the wing at this 

 stage to make a track in the mud, the impression would be 

 like that made by a tridactyle foot. In fact it is a tridactyle 

 foot at this stage. The metatarsals are also separated at the 

 same stage, but not so widely as the metacarpals. 



There is a difi:erence of opinion among anatomists in their 

 interpretation of the fingers of the wing. Gegenbaur, 

 Huxley, Rolleston and others, regard the marginal finger 

 on the radial side as representing the first finger, or pollex, 

 while Wyman, Owen and Coues, believe this digit to repre- 

 sent the index, or second finger. It seems more reasonable 

 to believe that this latter interpretation is right ; for when 

 the number of fingers or toes is reduced in Mammalia and 

 Reptilia, they are always taken away from the sides of the 

 member, the thumb first disappearing and then the little 

 finger. 



If we compare the leg and wing of Sjnzella (figs. 1 and 

 32, pi. IV and v) we shall see that in this early stage there 

 are but three metatarsals and three metacarpals, and it seems 

 reasonable to compare them together. 



As the first toe appears much later and is reduced to two 

 phalanges, and has its metatarsal also greatly reduced, and 

 as at the stage just cited the first toe is represented only by 

 a few granules, it seems natural to infer that in the wing, the 

 first finger never makes its appearance. 



