and of a Bird from the London Clay, 207 



which propel the bird of flight through the air, possess a long sternum with a well- 

 developed keel. 



The coracoid bones or posterior clavicles are even less available in this question, 

 as they relate much more closely to the respiratory actions than to the movements 

 of the wings, and accordingly are always present and strongly developed, even in 

 such birds as the Apteryx, in which the wings are reduced to their feeblest rudi- 

 ments. 



In the present fossil, however, the lateral extent and convexity of the sternal 

 plate, the presence and course of the secondary intermuscular ridges, the com- 

 mencement of the keel a little way behind the anterior margin of the sternum, all 

 prove the fossil to have no affinity with the Brachypterous family. 



There then remain for comparison the ordinary birds of flight, and of these our 

 native species, which resemble the fossil in size, are the first to claim attention. 

 It would have been by no means difficult to have assigned its natural family to the 

 Eocene Bird, if we had possessed the sternum entire or with its characteristic 

 posterior margin, but this part is unfortunately wanting in the fossil. Sufficient, 

 however, of the bone remains to enable us to set aside the Gallinaceous and those 

 Grallatorial and Passerine birds which have deeply incised sternums ; and the field 

 of comparison is thus restricted to such species as have the sternum either entire 

 or with shallow posterior emarginations. Between the fossil and the corresponding 

 part of the skeleton of such birds it became requisite to institute a close compa- 

 rison in regard to many minor details and modifications, as, for example, the se- 

 condary muscular impressions and ridges on the flat surface of the sternum ; its 

 costal margin and anterior angle ; the form and extent of the coracoid groove ; the 

 conformation of the sternal end of the coracoid bone, combined with the form and 

 relative size of the preserved articular extremities of the femur and tibia. 



It is unnecessary, however, to recount all the details of these comparisons : 

 suffice it to say, that after pursuing them from the Sea-gull and other aquatic species 

 upwards through the Grallatorial and Passerine orders, omitting few of the species 

 and none of the genera of these orders to which belong British birds approaching 

 or resembling the fossil in size, the greatest number of correspondences with the 

 fossil were at length detected in the skeletons of the Accipitrine species. 



The resemblance was not, however, sufficiently close to admit of the fossil being 

 referred to any of the existing native genera of Raptorial birds. The breadth of 

 the proximal end of the coracoid removed the fossil from the Owls (^Strigidce) , and 

 the shaft of the same bone was too slender for the Falconida ; the femur and tibia 

 were likewise relatively weaker than in most of our Hawks or Buzzards. It is with 

 the skeletons of the Vultures that the fossil presents the closest agreement. In the 



