6 MR. ST. GEORGE MIVART ON THE 
The thirteenth vertebra may be compared with the fifteenth of Struthio. The most 
noticeable differences are the still rudimentary condition of the styloid rib, the forked 
central postaxial surface, and the decided extension of the pleurapophysis preaxiad of 
the prezygapophysis. This vertebra is hardly less extended pre- and postaxially than is 
the twelfth vertebra; and its proportions are more slender than in Struthio. 
The fourteenth vertebra, if compared with the sixteenth of Struthio, differs in that 
the ventral surface of the centrum is not of increased*width, and that the styliform rib 
(though still very small) is rather more instead of less developed than is its preaxial 
predecessor. There is no trace of a hypapophysial ridge. The pleurapophysis still 
extends preaxially beyond the prezygapophysis. 
THE CERVICO-DORSAL VERTEBR. 
The fifteenth vertebra agrees with the eighteenth of Struthio, except that its preaxial 
central articular surface is almost divided into two lateral surfaces. The postaxial 
central surface widely diverges ventrally, and (as in the fourteenth vertebra) exhibits 
half its extent when the vertebra is laterally viewed. There is a hypapophysis, which 
springs from a single root, but tends to bifurcate laterally. The ribs are more developed 
than in any of the cervical vertebre ; they still extend preaxiad of the preezygapophyses. 
There is no true neural spine, the neural laminz being medianly grooved pre- and post- 
axially. 
The siateenth vertebra, which may be taken as equivalent to the nineteenth of 
Struthio, is but very slightly larger than the fifteenth. The postaxial articular surface 
of the centrum differs greatly from that of its predecessor, there being no diverging 
ventral extensions, and its ventral margin being almost convex. The hypapophysis is 
relatively larger than in Struthio, extending the whole length of the ventral surface. 
It is much more inclined preaxiad, and both relatively and absolutely more extended 
ventrad. The neural spine may be said to bifurcate laterally, there being a deep median 
pre- and postaxial groove, thus differing greatly from the same part in Struthio. 
The seventeenth vertebra has a hypapophysis somewhat larger relatively than the 
hypapophysis of the twentieth vertebra of Struthio. There is a stumpy neural spine, 
the preaxial surface of which is nearly vertical. The postzygapophyses are not entirely 
postaxial to the centrum. The prezygapophyses are hardly less extended laterally than 
in the sixteenth vertebra. 
THE DORSAL VERTEBRZ. 
The eighteenth vertebra differs from its predecessor much as the twenty-first of 
Struthio differs from its two predecessors. The neural spine is at once higher and 
