296 MR. W. p. P¥CRAFT ON THE [^P^- l^j 



normally related, yet the latter fails to reach the sternum. In 

 some cases the last pair of sternal ribs may be represented only 

 by vestiges fused with the last fractional pair. 



The uncinates vary considerably in their development. In the 

 Polyhorinoi and the Falcons the uncinates are long and slender ; 

 but 'in the remaining Accipitres the base of attachment to the rib 

 has increased enormously, extending often nearly as far down as 

 the articulation with the sternal segment. In the Cathartse, and 

 in some species of Aqicila, the inferior angle of this base is 

 produced into a short spine. Generally the uncinates do not 

 extend backwards beyond the level of the rib next behind. This 

 is exceeded in Ulanoides, and in Pandion (in P. carolinensis) they 

 extend each to the thii-d rib. In Serpentarius the uncinates are 

 very degenerate, losing themselves in the rib, forming thereon 

 nothing but a broad irregular plate. The uncinate of the first 

 thoracic rib, however, is less degenerate, projecting distinctly 

 backwards. 



The preacetabular ilium overlaps from two to three pairs of 

 ribs. 



v. The Sternum and Pectoral Girdle. 



Perhaps the most striking features of the sternum of Falconi- 

 formes are the great size of the corpus sterni and the relatively 

 slight development of the carina. Amongst the different 

 members of the group, however, much variation occurs, in the 

 relative proportions in the length and breadth of the sternal 

 plate, the development of the keel, the position of the coracoid 

 grooves and articular surfaces for the sternal ribs, and the de- 

 velopment of notches or fenestrse on the metasternum. 



In Serpentarius (text-fig. 33, p. 297) the sternum is distinctly 

 Oiconiine in character, not only on account of the great size and 

 shape of the carina, but also in the fact that the latter affords a 

 broad articular surface for the furcula. There is one peculiarity 

 about the keel of Serpentarms, however, and this lies in the fact 

 that the carina, swollen by pneumatic tissue, passes gradually into 

 the corpus sterni. This last, it should be mentioned, is pointed 

 posteriorly, instead of notched as in the Storks. 



The sternum of the Cathartse is pecviliar in that the greatest 

 curvature of the free margin of the carina is near its middle, and 

 in that the keel extends backwards to the extreme posterior end 

 of the sternal plate. The corpus sterni is notched posteriorly, 

 and in Cathartes the posterior lateral processes are fenestrated. 

 The coracoid grooves are shallow and broad, curving abruptly 

 upwards and inwards to the middle line, not overlapping. The 

 spina externa and interna are both wanting. The linea aspera 

 for the origin of the subclavius extends backwards to within a 

 short distance of the posterior end of the sternal plate : thus 

 extending further back than in any other Falconifoi-mes. 



In the Falcons only is there a distinct spina interna ; in Herpe- 

 totheres it is very broad and deeply hollowed ; the spina externa 



