318 "PROF. ST. GEORGE MIVART 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 Dromeus. 
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 vertebre are more concave than in 
Struthio. The prezygapophyses 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 prezygapophysis. 
The FOURTH VERTEBRA is a little larger in most dimensions than the third. It differs 
from the latter much as that of Struthio diflers 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 
Dromeus; 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. 
