396 MR. ST. GEOEGE MIVAET 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. IG & 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 8cj)l) 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- 

 phi/sial) 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 1862 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 u-regular 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-posterior] y as it is broad. It is 

 slightly convex in both directions, but more so antero-posteriorly (figs. 15, 17, & 19, az). 



'Ea.ch. postzygapophysis (figs. 16, 18, «& \%, 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. 



