AXIAL SKELETON OF THE OSTRICH. 405 
of the ventral surface of the centrum has notably increased in width. ‘The styliform 
ribs are no longer styliform, but stout obtusely pointed processes, projecting, however, 
postaxiad and slightly ventrad as usual (fig. 54, ps). 
The catapophyses (figs. 33 & 34, ¢) are very largely developed, projecting not only 
ventrad but somewhat proximad also; they are so extended inwards that the interval 
between their ventral ends is decidedly less than the breadth of the middle of the 
ventral surface of the centrum behind them, a condition which we have not yet met 
with. The middle of the ventral surface of the centrum may still show a trace of 
the antero-posteriorly extended hypapophysial ridge (fig. 34, hy). 
SIXTEENTH VERTEBRA (2 natural size). 
Fig. 33. Fig. 34. 
Aspects. 
Fig. 33, lateral; 34, ventral. Letters as before. 
The pleurapophysial lamella is beginning decidedly to diminish in antero-posterior 
extent; but the metapophysis is largely prominent beneath a prezygapophysis, which 
may project very considerably preaxiad beyond the parapophysis (figs. 33 & 34, m). 
The low neural spine is as thick as in the fifteenth vertebra and also shorter antero- 
posteriorly ; its posterior excavation is enlarged into a deep conical fossa, the dorso- 
lateral margins of which diverge to the postzygapophyses—without, however, sheltering 
it or covering it in, except to a minute extent on each side. 
The articular surfaces of the postzygapophyses are nearly as wide transversely as 
long pre- and postaxially. 
THE SEVENTEENTH VERTEBRA. 
The seventeenth vertebra differs very considerably from the sixteenth, and more than 
the latter differs from the fifteenth. It is shorter and at the same time broader, while 
the breadth of its preaxial part is still more in excess of that of its postaxial part (fig. 38) 
than was the case in the sixteenth vertebra. Thus we have a return to a predominance 
which existed in more preaxially situated cervical vertebre (fig. 25). 
