AXIAL SKELETON OF THE PELECANID^. 323 



This vertebra unites with the seventh at a marked angle, but one which opens the 

 reverse way from that in which the angle formed by the seventh with the sixth ver- 

 tebra opens. The mode of flexion here initiated is repeated in the next articulation ; 

 so that the eighth vertebra has both its adjacent vertebrae bent up dorsad from it, 

 whereas the third, fourth, fifth, and sixth vertebrae have each their two adjacent 

 vertebrae bent down ventrad, while the seventh vertebra has its next preaxial vertebra 

 bent down ventrad from it, and its next postaxial vertebra bent up dorsad from it. 



The NINTH VERTEBRA (Plate LV. figs. 18-21) is very like the eighth, but slightly longer. 

 The preaxial articular surface of the centrum is directed somewhat more dorsad and less 

 preaxiad, and is a little more transversely extended. The preaxial openings of the canals 

 for the vertebral artery are even more plainly visible when the vertebra is viewed dorsally 

 (fig. 19). The articular surfaces of the praezygapophyses are directed more mediad ; and 

 the processes supporting these surfaces are seen to extend postaxiad as well as dorsad 

 when the vertebra is viewed laterally. The constriction (laterally) of the neural arch by 

 the fossae just postaxiad of the prsezygapophyses is more marked. The hyperapophyses 

 are similarly but more developed. The preaxial margin of the haemal (catapophysial) 

 arch extends as much preaxiad as does any part of the centrum. 



The plates bounding laterally the median subcentral groove do not end in such 

 distinct processes, the ventral margin postaxiad of each such process sloping more 

 obliquely to reach the postaxial end of the centrum. 



The TENTH VERTEBRA is like the ninth, but slightly longer. The hyperapophyses are 

 less marked, except at their postaxial ends. The neural spine stops short of the post- 

 axial end of the neural arch. The postzygapophyses look more externad. The haemal 

 arch is more antero-posteriorly extended, and the grooves on its ventral surface are 

 wider and deeper. The margins of the subcentral median channel subside gradually 

 postaxiad without there being any longer a noticeable process. 



The ELEVENTH VERTEBRA, compared with the same vertebra in Struthio and Dromceus, 

 presents striking differences. Thus the preaxial surface of the centrum looks dorsad 

 instead of ventrad, and its postaxial surface looks postaxiad instead of partly dorsad. 

 The praezygapophysial surfaces are differently directed, and are less long, relatively, than 

 in Struthio ; though not than in Dromceus. There are no styliform rib processes ; but 

 there is a haemal arch and subcentral channel. 



The whole vertebra is not so long a bone, in proportion to its other dimensions, as 

 in Struthio ; but it is longer relatively than in Dromceus. 



This vertebra is like the tenth of Pelecanus, save that it is stouter, though not 

 longer. Its postaxial articular surface expands less ventrad. Its praezygapophysial 

 surfaces lie more open, i. e. look rather more dorsad. The hyperapophyses are less 

 strongly marked ; and the neural arch is more flattened dorsally. The plates bounding 

 the subcentral channel laterally, subside still more postaxially. The praezygapophyses 

 (i. e. the processes supporting the articular surfaces) extend more dorsad and less post- 



VOL. x. PART vii. No. 2. August 1st, 1878. 2 y 



