AXIAL SKELETON OF THE PELECANID^. 349 



processes. The centrum is more laterally compressed than in Sula ; and there is a ridge 

 running antero-posteriorly on each side of the origin of the hypapophysis. 



The TWENTIETH VERTEBRA is like the nineteenth of Sula, except that it has become 

 distinctly opisthocoelous (fig. 36), and that there is a long hypapophysis, that it is 

 still more compressed laterally, and has no marked antero-posterior ridge on each 

 side of it. 



The Dorsal Vertebra. 



These are much more compressed laterally than in Sulci or Pelecanus. 



The TWENTT-FiRST VERTEBRA (Plate LVII. figs. 37-39) has on its preaxial articular 

 surface a median tract (of about one third of its total width) convex in both directions, 

 and external to this, on each side, a tract which is concave from within outwards. Its 

 postaxial articular surface is more simply and entirely concave than is that of the 

 twentieth vertebra. There is a long hypapophysis, a little antero-posteriorly expanded 

 at its distal end. This and the succeeding dorsal vertebrae have styliform ossifications 

 of tendon attached to the dorsum of the distal part of their transverse processes ; and 

 the neural spines are, to a less extent, similarly affected. 



The TWENTY-SECOND and twenty-third vertebr.<e (Plate LVII. figs. 40-45) are simply 

 convex in front, centrally, and concave behind, each surface being much more dorso- 

 ventrally than transversely extended. The hypapophyses are nearly as in the twenty- 

 first vertebra. 



The TWENTY-FOURTH VERTEBRA is the first to form part of the ankylosed pelvic mass ; 

 its preaxial surface is like that of its serial predecessor, except that it is somewhat 

 broader. The hypapophysis is slightly smaller (Plate LX. fig. 6, xxrv). 



The TWENTY-FIFTH VERTEBRA is like its predecessor, but is smaller, more compressed, 

 and with a smaller hypapophysis. Generally the hypapophysis of this vertebra is (like 

 its three serial predecessors) distinctly flattened ventrally ; but it may not be so, and 

 may be quite rudimentary, as in the smaller skeletons in the British Museum, 68. 8, 

 16. 3. 56. 11. 14. 17 and 66. 3. 28. 17. 



The Lumbar Vertebra, 

 the twenty-sixth, twenty-seventh, twenty-eighth, twenty-ninth, and thirtieth 

 VERTEBRiE resemble the lumbar vertebrae of Sula, save in their greater number, the 

 presence of distinct hypapophyses to the first two, and the presence, generally, of three 

 presacral foramina on each side, produced by the distal junction of the parapophyses of 

 the four most postaxial lumbar vertebrae ; there may, however, be as many as four 

 presacral foramina. 



The Lumbo-sacral Vertebile. 



From the intervertebral foramina there appear generally to be two lumbo-sacral 



3b2 



