AXIAL SKELETON OF THE OSTRICH. 399 
The length of the free part of this process is less than half the antero-posterior 
extent of the centrum, though its extremity may project beyond the antero-posterior 
median point of the centrum. 
The postaxial margin of the pleurapophysial band is irregular, often more or less 
slightly concave, and proceeds obliquely dorsad and postaxiad. 
At the anterior part of this band a slight metapophysial prominence may appear 
between the preaxial end of the parapophysis and the prezygapophysis. 
The zygapophyses closely resemble those of the third vertebra. 
The hyperapophyses on the postzygapophyses are absolutely, and still more relatively, 
smaller than in the third vertebra, though they are still noticeable prominences (figs. 20, 
& 23, hp). 
The neural spine and the neural arch generally agree with those of the third 
vertebra, except that the latter is less quadrate when viewed from above. ‘This is 
owing to the transverse diameter of the preaxial part of the vertebra (measured across 
the prezygapophyses) considerably exceeding that of its postaxial part (measured across 
the postzygapophyses), instead of these two dimensions being equal as in the third 
vertebra. The postaxial margin of the neural arch is also always decidedly concave 
(fig. 23), instead of being nearly straight as sometimes is the case in the third vertebra. 
Tue Firra VERTEBRA. 
The fifth vertebra, though again a large bone antero-posteriorly, more closely 
resembles in shape the fourth vertebra than does the fourth the third (fig. 1, C, v). 
The preaxial surface of its centrum quite agrees with that of the fourth vertebra, 
while its postaxial surface differs only in having its articular surface relatively broader 
and narrower dorso-ventrally in its middle (the two sides of the hour-glass coming 
there nearer together), and in having the ventral margin of that surface very consider- 
ably more extended than its dorsal margin, and, concomitantly, its lateral margins 
rather more concave. 
The neural surface is similar to that of the centrum of the fourth vertebra, except 
that it is perhaps rather more exposed at its preaxial end, through the slightly greater 
cutting away, as it were, of the more preaxial part of the neural arch. 
The ventral surface of the centrum agrees with that of the fourth vertebra, except 
that its postaxial part is more decidedly and extensively concave transversely, and that 
the median hypapophysial ridge is still less developed. 
The neural arch is, of course, longer than that of the fourth vertebra, but is other- 
wise very like it. The pleurapophysial band more decidedly fails to attain the post- 
zygapophysis; while at the dorsal end of its slightly concave, oblique, postaxial margin 
a slight pointed process projects postaxiad, which process is the homotype of the slight 
projection noticed as extending from the postaxial margin of the band in the axis 
