324 PROF. 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 hemal 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 hemal arch and its ventral grooves are wider; and the arch itself does not 
extend preaxiad beyond the preaxial end of the centrum. Both the pre-and post- 
zygapophysial surfaces are somewhat broader. The former look more dorsad, and the 
Jatter 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 Struthio). The fossa 
behind the prezygapophysis (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 appear 
behind its postaxial end; and the hyperapophyses are merely slightly marked ridges 
diverging from the postaxial end of the neural spine. The hemal arch broadens, and 
its ventral grooves widen (Plate LY. figs. 22-24). 
The prezygapophyses 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 pre- 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 hemal 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 
