AXIAL SKELETON OF THE STKUTHIONID^. 13 



The second rib is much. as in Strut/do, but somewhat shorter relatively. There is no 

 noticeable convexity on its postaxial margin. 



The third rib has its capitulum rather larger, compared with that of the second rib, 

 than is the case in Strut/do. Its shaft is more vertical. The tubercular suirface is but 

 little larger than is that of the second rib. The postaxial margin is proximally concave, 

 then slightly convex. 



The fourth rib is remarkably diflferent in its curvature from that of Struthio ; and its 

 excess in length over the thu'd rib is less. Owing to this curvature, it seems to be 

 rather the tuberculum than the capitulum which carries on proximad the general curva- 

 ture of the rib. This curvature is slightly sigmoid, and there is no "angle," the pro- 

 minence being preaxiad and below the capitulum instead of, as in Struthio, postaxiad 

 and below the tuberculum. The vertebral margin is as sharply concave as in the third 

 rib. The articular surface of the tuberculum is not much larger than in the third rib. 

 The preaxial margin of the shaft is proximally convex, then more or less concave. The 

 postaxial margin is at first markedly concave, then (distad) slightly convex. Both mar- 

 gins are sharp, the lamella of bone (described in Struthio as being on the ventral pre- 

 axial side of a ridge running down from the capitulum) of the proximal part of the 

 shaft projecting strongly preaxiad and scarcely at all postaxiad, thus doing away with 

 an " angle " (such as exists in Struthio), and producing a curious preaxial convexity, 

 whence a ridge is continued on proximad, over the divergence of the tuberculum and 

 capitulum, right up to the vertebral margin and preaxial edge of the tuberculum, as is 

 the fifth rib of Struthio. There is an articulated uncinate process ; but its distal por- 

 tion is not bent dorsad, but continues on obliquely in one line with the proximal part, 

 the direction being mainly postaxiad, but slightly dorsad. 



The fifth rib has, again, a singularly difi'erent curvature from that of Struthio. The 

 capitulum and tuberculum diverge at a rather more acute angle than in the fourth rib ; 

 otherwise it generally agrees with the fifth rib of Struthio. 



The sixth rib has also a reversed curvature compared with that of Struthio. The 

 capitulum and tuberculum diverge much as in the fifth rib ; and the uncinate process is 

 as long as that of the rib last named. The proximal prominence is more marked, 

 causing the preaxial margin distad to it to be more concave than in the fifth rib. 



The seventh rib is free distally, and is much shorter than the sixth, and rather so -than 

 the fourth. Its shaft also is more curved. The capitulum and tuberculum also form a 

 wider angle than in the sixth rib, namely about 75°. The pneumatic foramen is of about 

 the same size as in the sixth rib ; but the articular surface for the diapophysis is not so 

 large. The preaxial prominence of the preaxial margin is slightly more marked still ; and 

 the concavity of the preaxial margin is more marked also. There is no uncinate process. 

 The eighth rib is again more curved than in Struthio. In length it is intermediate 

 between the second and third ribs. The capitulum is about as long compared with the 

 tuberculum as in the seventh rib. The preaxial frontal convexity is still very marked. 

 There is no trace of an uncinate process. 



