120 ON THE TRAIL OF AN EXTINCT BIRD, 



The fossil ulna which has led to these measurements is in its 

 greatest diameter 47*5 mm.; in its smallest, 3'5mm.; it has con- 

 sequently an index of 7*38. 



Proceeding to compare it with those of recent birds, we may at 

 once exclude from further consideration those which have a 

 greatest index below 7*38, or a smallest index above it. Nine 

 families will then remain, the Paradiseidce, Oriolidce, Gampo- 

 pliagidce, Cucididce, Psittaci, Columbce, Megap>odidaz, and Anatidce. 



Form of Shaft: The ulnar shaft in birds assumes towards its 

 distal end four modifications of form, which may be distinguished 

 as cylindrical, subcylindrical, compressed, and trihedral. It is 

 compressed in the Paradiseidce and Cuculidce ; subtrihedral in the 

 Megapodidce ; cylindrical in the Psittaci. In the remaining five 

 families, and in the fossil, it is subcylindrical, the cylinder being 

 flattened on the dorsal surface. 



Curvature of Shaft : To afford space for the interosseous bodies 

 and tendons of the long flexors and extensors the avine ulnar 

 curves outwards, the curvature varying considerably in degree 

 and location. In the majority of birds the curvature is almost 

 confined to the proximal half or third of the shaft, which becomes 

 straight, or nearly so, for the rest of its length ; in others the 

 shaft is curved throughout, its contour forming a continuous and 

 almost symmetrical arch. The Gampophagidce, Oriolidce, Paradi- 

 seidce, Rallidce, and the larger Anatidce conform to the general rule. 

 The fossil ulna, on the other hand, is regularly arched, as it is in 

 the pigeons and ducks, and the bird represented by it probably 

 belonged to one or other of these last groups. 



Remigial processes ; Arranged in a single or double row along 

 the bone, but generally more or less indistinct at either end, these 

 outgrowths present themselves in much diversity of size and 

 number, the latter in correspondence with the length of the bone, 

 the former exhibiting no such correspondence, but being, on the 

 contrary, frequently greater, though not unfrequently nearly 

 obsolete, in the shorter winged birds. The contrast here 

 indicated is exemplified by the pigeons and ducks, and it enables 

 us to make a final selection in our determination of the fossil. 



