AXIAL SKELETON OF THE STRUTHIONID. 19 
THE CERVICO-DORSAL VERTEBR2, 
The eighteenth vertebra is like the first cervico-dorsal (fifteenth) of Rhea, except that 
the preaxial central surface is not nearly divided medianly, and that the postaxial central 
surface does not diverge ventrad, the ventral margin being scarcely at all concave, though 
more in excess of the dorsal margin than in Struthio, while the degree to which it is 
visible in profile is also intermediate. The hypapophysis bifurcates distally, though 
having a single root. It does not extend so much ventrad, relatively, as in Rhea. The 
rib may be rather more or rather less developed than in the preceding vertebra. It 
may, in the adult condition (as e. g. in No. 1558), be unankylosed. The przygapo- 
physes exceed the preaxial extension of the parapophyses more than in Struthio, and 
much more than in Rhea. The neural spine is not dorsally grooved, but is excavated 
both pre- and postaxially. 
The nineteenth vertebra, compared with the sixteenth of Rhea, has the postaxial 
surface of its centrum less different from its predecessor ; yet its ventral does not so much 
exceed its dorsal margin. The hypapophysis is much more like that of Struthio than 
that of Rhea. The neural spine is not grooved dorsally. The diapophysis is more 
axially extended. The parapophysial articular surface is deeper and more dorso-ventrally 
extended; and that of the diapophysis is also rather more concave. 
The twentieth vertebra has its hypapophysis more like that of Struthio than that of 
Rhea, although, as in the last-mentioned genus, it extends much postaxiad. ‘The trans- 
verse processes are more axially extended, and the neural spine is smaller, than in 
Rhea’s seventeenth vertebra, which this one otherwise much resembles. 
The twenty-first vertebra has its hypapophysis as large as that of the twentieth ver- 
tebra, except when (as in No. 1558) an extra intercalated vertebra alters the relations. 
The transverse process is rather more, and the neural spine rather less extended axially. 
The postaxial excavation of the neural spine is less in defect of that of the preceding 
vertebra than in Rhea; otherwise the characters of this vertebra are much like those 
of the first dorsal vertebra in that genus. As in Struthio, there is a pit on each side 
of the preaxial surface of the neural spine. ‘This pit is serially homologous with the 
interzygapophysial canal. 
THE DORSAL VERTEBRZ. 
The twenty-second vertebra has a very small hypapophysis, though a larger one than 
in the other two genera. The diapophysial articular surface is preaxiad to the middle 
of the transverse process. The neural spine is not so axially extended as in the pre- 
ceding vertebra, but more dorsally. There is a deep fossa on each side of the preaxial 
surface of the neural spine. The postzygapophyses do not extend postaxiad of the 
centrum. 
The twenty-third vertebra has no hypapophysis at either end of its centrum. The 
D2 
