324 PEOF. ST. GEORGE MIVART ON THE 



axiad. The postzygapophyses scarcely extend postaxiad to the postaxial end of the 

 centrum ; and their articular surfaces look more externad than in the tenth vertebra. 

 The preaxial margin of the haemal arch may extend a little preaxiad of the preaxial 

 end of centrum. 



The TWELFTH VERTEBRA is a little shorter and stouter than the eleventh. The 

 flattened neural arch is seen to expand more postaxiad when viewed dorsally ; but its 

 postaxial margin is somewhat less concave. 



The haemal arch and its ventral grooves are wider ; and the arch itself does not 

 extend preaxiad beyond the preaxial end of the centrum. Both the prse- and post- 

 zygapophysial surfaces are somewhat broader. The former look more dorsad, and the 

 latter slightly more externad. 



For the first time in the whole vertebral column yet examined, the postzygapophyses 

 fail to extend postaxiad as far as the postaxial end of the centrum. 



The THIRTEENTH VERTEBRA is shorter and more massive, proportionally, than its pre- 

 decessor, and wider transversely (like the sixteenth vertebra of Struihio). The fossa 

 behind the prsezygapophysis (which has been getting less marked since the ninth 

 vertebra) has almost disappeared. Seen dorsally the vertebra appears more hourglass- 

 shaped; the neural spine begins to rise again; and a concavity begins to appeal- 

 behind its postaxial end; and the hyperapophyses are merely slightly marked ridges 

 diverging from the postaxial end of the neural spine. The haemal arch broadens, and 

 its ventral grooves widen (Plate LV. figs. 22-24). 



The prsezygapophyses incline again slightly preaxiad and extend preaxially as far as 

 the centrum and even a little further. 



The FOURTEENTH VERTEBRA repeats and carries further the characteristics of the pre- 

 ceding vertebra. 



Especially marked is the lateral expansion of both pra?- and postzygapophyses ; and 

 now the transverse extent of the vertebra in the situation of the former begins greatly 

 to exceed its transverse extent as measured across the postzygapophyses. The neural 

 spine is more elevated. From the dorsal end of the postaxial margin of the pleurapo- 

 physial lamella a small inconspicuous process projects postaxiad. This is the repre- 

 sentative of the diapophysis. 



Sometimes the haemal arch is medianly cleft, so that there seem to be two, lamellar, 

 closely approximating catapophyses. The canal for the vertebral artery is greatly 

 enlarged. 



The FIFTEENTH VERTEBRA exhibits very marked changes when compared with the 

 fourteenth (it thus .corresponding with the eighteenth vertebra of Struthio). It is 

 rather shorter antero-posteriorly, rather wider transversely, with the width of its pre- 

 axial part greatly predominant. The pleurapophysial lamella sends back postaxiad a 

 marked diapophysial process (d) from the postero-outer dorsal margin of the enormously 

 expanded lateral vertebral canal, which has been gradually widening since the sixth 



