548 PALMIPEDES. 



that that bone is the ulna, is nearly the same as in the 

 skeleton of the Albatross. 



On comparing the fossil with the lower end of the tibia 

 of a large Eagle, we perceive in this bird a prominence 

 on each side of the condyle, which does not exist in the 

 fossil. In the tibia of the Adjutant Crane, which is 

 more nearly of the size of the fossil, and resembles it 

 more in the sharper margins of the posterior half of the troch- 

 lear boundaries, there is a ridge on each lateral surface. 

 In the Albatross there is neither a prominent ridge nor 

 process : the sides of the condyle, especially the outer 

 one, are as even as in the fossil ; but the anterior margins 

 of the trochlea are more prominent and thicker in the 

 Albatross. 



The only other bone in a bird's skeleton which has a 

 similar trochlear extremity is the metacarpal of the wing, 

 the proximal end of which is formed by the confluent os 

 magnum. In the degree of obliquity, and the extent of 

 the sharp borders of this trochlea, some resemblance to 

 the fossil may be traced; but the fossil, in the greater 

 autero-posterior extent of the articular surface, with which 

 the median groove of the pulley is co-extensive, differs 

 much from the metacarpal joint, and agrees with the 

 tibial trochlea. Moreover, there is no trace of the process 

 which stands out from the radial end of the trochlea in 

 the metacarpus, nor of the smaller process for the attach- 

 ment of the ligament from its palmar side. 



I am at present unacquainted with any bone of the 

 Pterodactyle which presents a deep trochlea, describing 

 three-fourths of a circle, as in the fossil ; and I therefore 

 still regard my original view of the nature of these in- 

 teresting fossils, as the most consonant with known ana- 

 logies of structure. 



