396 MR. ST. GEORGE MIVART ON THE 
The ventral surface of the centrum is strongly concave from side to side at its most 
preaxial fourth ; and its preaxial margin is concave. A little preaxiad of the middle of 
the ventral surface a median hypapophysial process (figs. 16 & 19, hy) arises, which, for 
a little, gradually increases in depth postaxiad, and then proceeds directly postaxiad, 
coinciding with the ventral surface of the centrum—the postaxial part of the hypapo- 
physial process being flattened on its ventral surface, so that this may be said to have 
two lateral margins which diverge postaxially. The hinder margin of the hypapophysis 
is at the same time the hinder margin of the centrum and is strongly convex. 
The hypapophysis does not extend nearly so suddenly and prominently ventrad as 
does the hypapophysis of the axis. 
No oblique ridges diverge postaxially from near the preaxial margin of the third ver- 
tebra, as they do in that of the axis; but there is a great prominence on each side near 
the preaxial margin, and it is their projection ventrad which makes the preaxial part of 
the ventral surface concave. 
The neural arch is much like that of the axis, except that its prezygapophysial and 
pleurapophysial parts (fig. 19, az & pl) are much more developed, while its neural spine 
is less so. 
The pedicle is similarly low, with a concave postaxial margin. Its preaxial margin is 
more extended dorso-ventrally and more concave than is that of the pedicle of the axis 
vertebra. 
The flat pleurapophysial band of bone (for the vertebral artery) has greatly increased 
in antero-posterior extent, compared with that of the axis vertebra, being about equal to 
half the extent of the centrum in this dimension. It extends oblique dorsad from the 
parapophysis and expands till it merges into, or, rather, comes to constitute an interzyga- 
pophysial ridge, the anterior end of which may appear as a slight prominence (metapo- 
physial) outside and beneath the prezygapophysis (as in specimen 1362 B on the left side). 
The preaxial margin of the pleurapophysial lamella is concave. Its postaxial margin 
is irregular from defective ossification; but it may (as in 1362 A, right side) develop a 
slight median, postaxial, bluntly pointed prominence (fig. 19). 
At the middle of the side of the neural arch, near the dorsal postaxial end of the 
plurapophysial lamella, is a depression with irregular foramina, leading into the sub- 
stance of the bone. 
Each prezygapophysis presents an oblong articular surface, which looks preaxially and 
dorsally, and is nearly, if not quite, twice as long antero-posteriorly as it is broad. It is 
slightly convex in both directions, but more so antero-posteriorly (figs. 15, 17, & 19, az). 
Each postzygapophysis (figs. 16, 18, & 19, pz) is about the same size as the prezyga- 
pophysis, but is slightly less developed in the antero-posterior direction. Its antero- 
posterior diameter very much exceeds its transverse diameter, as much as, or more so, 
than in the axis vertebra. The articular surface is slightly concave transversely and 
nearly flat antero-posteriorly. 
