AXIAL SKELETON OF THE PELECANIDA. 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 /ast, or sixth, vertebral rib has its tuberculum very small indeed, so that the 
proximal end of this rib is characteristically small. There is no unciform process; and 
the bone is flattened and very little curved. 
The whole series of true ribs have at first (7. 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. 
Tue Sternau Rips. 
These are five in number, and rapidly increase in length as we proceed postaxiad 
(Plate LIX. fig. 4). 
The jirst (attached to the first true rib and eighteenth vertebra) has two miuute 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 yentrad. 
THE STERNUM. 
The sternum differs, of course, from that of the Struthionide 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 (¢) 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 
