398 MR. ST. GEORGE MIVART ON THE 
The ventral surface of the centrum agrees with that of the third vertebra, except that 
the median hypapophysis is much less developed (fig. 20, hy), being only in the form 
of a slight ridge extending antero-posteriorly along the middle third of the centrum. 
FOURTH VERTEBRA (natural size). 
Aspects. 
Fig. 20, lateral; 21, preaxial; 22, postaxial; 23, dorsal; 24, ventral. 
Letters as before, except that p denotes parapophysis, and ps the rib-like, freely projecting, pleurapophysial 
process. 
It also differs from the third vertebra in that its most postaxial part is decidedly, 
though slightly, concave transversely, and in that the parapophyses, project a little 
more sharply and strongly ventrad. 
The neural arch is very like that of the third vertebra, except that its pleurapo- 
physial part is more developed, while its neurapophysis, being actually about the same 
size, is relatively less. 
The pleurapophysial band is rather more extended antero-posteriorly, though it does 
not quite attain the postzygapophysis as it does in the third vertebra; while from the 
ventral end of its postaxial margin (i. ¢. from the parapophysis) a long, tapering, 
styliform, rib-like process projects in nearly a straight line postaxially (fig. 20, ps). 
