AXIAL SKELETON OF THE PELECANID^E. 335 



in the second true rib. The unciform process is smaller and more dorsad. This bone 

 is very nearly of the same length as are the two ribs preaxial to it. 



The fifth vertebral rib has its tuberculum still shorter and its unciform process 

 smaller and more dorsad, if it is not entirely absent. This bone is not quite so curved 

 as is the one preceding. 



The last, or sixth, vertebral rib has its tuberculum very small indeed, so that the 

 proximal end of this rib is characteristically small. There is no ujiciform process ; and 

 the bone is flattened and very little curved. 



The whole series of true ribs have at first (i. e. towards the preaxial end of the series) 

 their main curvature situated more ventrally than at their more dorsal parts. Gradually 

 as we proceed postaxiad the curvature becomes more dorsad ; this is less marked in the 

 last but one ; and in the last there is one nearly equal curve throughout, 



The true vertebral ribs are all nearly of equal length, 



THE STERNAL RIBS, 



These are five in number, and rapidly increase in length as we proceed postaxiad 

 (Plate LIX. fig. 4). 



The first (attached to the first true rib and eighteenth vertebra) has two mitiute distal 

 articular surfaces. 



The second is almost twice the length of the first, and has a, postaxial pneumatic 

 foramen ; in shape it resembles its predecessor. 



The third is about twice the length of the first, 



The fourth is not quite twice the length of the second. It is much curved, and may 

 be considerably flattened and expanded dorsally. 



The fifth sternal rib is more than twice the length of the second, but is not quite 

 equal to the length of the second and third added together. It is more curved than its 

 predecessor, and is always singularly expanded proximally, with a postaxial process 

 simulating a blunt unciform process, which has, as it were, slipped down ventrad. 



THE STERNUM, 



The sternum differs, of course, from that of the Struthionida? in being keeled, The 

 keel is ankylosed to the clavicles, and extends much preaxiad of the preaxial end of the 

 sternum proper. The keel subsides postaxially a little behind the middle of the 

 sternum (Plate LIX. figs. 4 & 5). 



The general surface of the sternum is more convex ventrally, and more concave 

 dorsally, than in Struthio. It is proportionally narrower transversely, and antero- 

 posteriorly longer. 



The coracoid grooves (c) form together a right, if they do not even form a slightly 

 acute angle. They are medianly separated. Their ventral and dorsal margins extend pre- 

 axiad about equally; but the dorsal margin is expanded and rounded towards its inner end 



