318 PEOF. ST. GEOEGE MIVAET ON THE 



marginal ridges, and sometimes also a median one in addition. The preaxial articular 

 surface of centrum is plainly visible, while immediately postaxial to it is a fossa deeper, 

 relatively, than in Struthio. Catapophyses begin to appear ; but conspicuous on each 

 side is the postaxially projecting short parapophysial styloid rib-like process. 



Seen laterally, the bony lamella enclosing the lateral vertebral canal extends through 

 the preaxial half of vertebra, while, as before said, a rudimentary styliform parapophysial 

 process projects postaxiad from the ventral end of its postaxial margin. This pleur- 

 apophysial lamella is not continued back to reach the postzygapophysis, though a 

 faintly marked ridge extends so far. 



The neural arch does not extend postaxiad beyond the centrum nearly so much as in 

 the axis, but more than in the third vertebra of Struthio or Dromceus. 



Hyperapophyses plainly exist ; and metapophyses may be distinguished. The neural 

 spine is much less developed than in the axis. 



Viewed dorsally, the lateral margins of the vertebras are more concave than in 

 Struthio. The preezygapophyses are convex and very elongated, and look preaxiad, 

 mesiad, and dorsad. 



The postzygapophyses oval, look externad and ventrad, are concave transversely, and 

 slightly convex antero-posteriorly. 



The third vertebra unites with the axis at a sharp angle, and one which opens in an 

 opposite direction to the angle formed by the junction of the axis with the atlas. 



The preaxial end of the canal for the vertebral artery opens beside the preaxial 

 articular surface of centrum and beneath the prazygapophysis. 



The FOURTH VERTEBRA is a little larger in most dimensions than the third. It differs 

 from the latter much as that of Struthio differs from its third ; but the hypapophysis has 

 more completely disappeared, and the neural arch more nearly approaches the preaxial 

 end of the centrum. The free portion of the styliform parapophysial rib is not longer 

 than is that of the third vertebra. There is not so much difference as to the squareness 

 of outline of the bone when viewed dorsally (and compared with the third vertebra) as 

 in Struthio, the fourth vertebra being, indeed, more antero-posteriorly elongated than 

 the third, but not being relatively so much more elongated in proportion to its trans- 

 verse breadth. 



The lateral vertebral canal is much less spacious, relatively, than in Struthio or 

 Dromceus; and the styliform rib is much less, relatively, extended. The postaxial 

 margin of the neural arch is also less concave. 



The preaxial articular surface of the centrum occupies less of the ventral surface of 

 the bone ; the catapophyses are rather more marked, and the hyperapophyses are rather 

 less marked than in the third vertebra. 



The neural spine is longer and lower ; and, instead of any hypapophysis, the ventral 

 surface of the centrum is very slightly grooved medianly throughout. 



