AXIAL SKELETO^^ OF THE PELECAJNTID^. 319 



No process extends postaxially from the postaxial margin of the pleurapophysial 

 lamella. 



The FIFTH VERTEBRA differs as much from the fourth as the corresponding one of 

 Struthio differs from its serial predecessor, except that the preaxial margin of the neural 

 arch is not more concave, and that there is no noteworthy difference as to the develop- 

 ment of the metapophyses. 



In addition to these points, in which it differs like the fifth of Struthio from its pre- 

 decessor, it also differs from the fourth vertebra in that the whole ventral surface of 

 the centrum is deeply channelled medianly and antero-posteriorly, two parallel ridges 

 running postaxially from the two catapophyses (Plate LV. fig. 5). 



The lateral vertebral canal is of about the same length as in the 'fourth vertebra ; and 

 therefore the part of the vertebra postaxial to it is slightly longer. The hyperapophyses 

 are developed to about the same degree as in the fourth vertebra ; and the styliform 

 rib is not longer. Both this vertebra and the first differ from the corresponding 

 vertebrae of Struthio and Bromceus in that the postaxial margin of tlie neural arch is 

 not nearly so concave, and that the neural spine is not excavated either pre- or post- 

 axially. The increase in length of this vertebra over the fourth is less than in Struthio ; 

 it unites with its serial predecessor at a veiy obtuse angle. 



A conspicuous foramen opens on each side of the ventral surface of the centrum, just 

 behind the catapophysis ; it leads into the lateral vertebral canal. 



When the vertebra is viewed ventrally a wide shallow median groove is seen, bordered 

 on each side by a continuous catapophysial ridge. Outside the anterior third of each 

 catapophysial ridge is an antero-posterior (fig. 5, ff) groove separating this ridge from 

 the postaxially extending parapophysial rib-like process. 



The SIXTH VERTEBRA (Plate LV. figs. 6, 7, 8) closely resembles the fifth, and is of 

 nearly the same size. It differs from the fifth as does that of Struthio from its pre- 

 decessor, except that, when viewed dorsally, the neural surface of the centrum is not 

 more exposed at the preaxial end of the vertebra, and that catapophyses do not here 

 begin, but only increase a little in size. The subcentral antero-posterior groove is deeper 

 and more strongly bordered. At its preaxial end the catapophysial antero-posterior ridges 

 project mesiad (fig. 8, c) , and draw inward (as it were) somewhat the parapophysial styloid 

 processes, which are here less developed than in the fifth vertebra, and are separated 

 from the catapophyses by a shorter, though still very conspicuous, antero-posterior 

 groove (fig. 8, g). The hyperapophyses are hardly smaller. 



The prsezygapophyses project preaxiad of the centrum to a greater rather than a less 

 degree than in the fifth vertebra ; and the pre- and postaxial margins of the neural arch 

 are not more concave. 



This vertebra differs from the fifth in the still greater production ventrad of the 

 lateral margins of the subcentral antero-posterior groove, and in the somewhat mofe 



