AXIAL SKELETON OF THE PELECANID^. 325 



vertebra. On the postero-outer ventral margin of the pleuropophysial lamella is a 

 small concave fossa. This is bounded in front by a minute tubercle, which is the 

 reappearance of a parapophysial process, while mediad of and behind the concave 

 surface is a slight ridge, which is the serial homologue of the catapophysial ridge of 

 more preaxial vertebrae (Plate LV. figs. 25-29). 



From the diapophysial process a ridge runs preaxiad along the dorsum of the pleur- 

 apophysial lamella, and slightly mesiad, ending preaxially in a marked antero-posterior 

 metapophysial ridge, separated from the adjacent margin of the prsezygapophysial 

 surface by an antero-posterior shallow groove. 



The hsemal arch has disappeared altogether, and in its place is a median hypapo- 

 physis, which bends strongly preaxiad beneath the preaxial end of the centrum. On 

 each side of this is a wide groove, bounded externally by the parapophysial tubercle, 

 fossa, and ridge above noticed. 



The neural arch is not cut away obliquely ; for its preaxial margin projects almost 

 as much preaxiad as does the centrum. 



The neural spine is higher than in the fourteenth vertebra ; and the concave surface 

 postaxiad of it is much reduced in extent. 



Not only do the praezygapophyses again extend preaxiad (though only slightly so) of 

 the centrum, but the postzygapophyses (for the first time since the tenth vertebra) 

 extend considerably postaxiad of the postaxial end of the centrum. 



The canal for the vertebral artery is still more capacious. 



The preaxial articular surface of the centrum looks mainly ventrad (which it has not 

 done since the seventh vertebra) instead of preaxiad ; and the postaxial articular surface 

 looks dorsad instead of postaxiad, in this respect returning to the condition of the tenth 

 vertebra. Moreover this surface is less convex transversely than in the preceding 

 vertebra, and its ventral margin is less concave. 



The SIXTEENTH VERTEBRA exaggerates the characters already given of the fifteenth. 

 The preaxial surface of the centrum is somewhat flattened out, less concave trans- 

 versely. The ventral margin of the postaxial articular surface of the centrum is either 

 very slightly concave or even slightly convex. All the zygapophysial surfaces are 

 smaller. The praezygapophyses scarcely extend preaxiad of the centrum. The neural 

 spine is higher, and is inclined over preaxially at the summit of its preaxial end. Its 

 postaxial fossa is still more reduced. The dorsum of the transverse process is more 

 extensive, and it extends outwards further beyond the ridge, extending preaxiad and 

 mesiad from the end of the diapophysial process to the metapophysis, which latter is 

 more widely separated from the praezygapophysis. 



The ventral enclosure of the lateral vertebral canal (i. e. the pleurapophysial lamella) 

 is reduced to a delicate bridge of bone, very narrow antero-posteriorly. At the dorsal 

 end of this bridge is a slightly marked and convex (articular ]) surface. 



2 Y 2 



