412 ME. ST. GEOEGE MIVAET ON THE 



The neural surface of the centrum is still more exposed than heretofore by the cutting 

 aM'ay, as it were, of the preaxial part of the neural arch, which has a more marked 

 median process. 



The ventral surface is nowhere concave transversely, though somewhat so antero- 

 posteriorly; not, however, to the same degree as in the nineteenth vertebra. The 

 preaxial margin is also somewhat less concave, and the postaxial margin less convex. 



There is a median hypapojihysis which may or may not be somewhat expanded laterally 

 towards its tip, and which may or may not project more strongly preaxiad than in the 

 nineteenth vertebra, and may have its dorsal surface concave transversely. The ventral 

 surface of its apex may be marked with a short, faint, antero-posterior groove, the last 

 trace of the bifurcation of the process in more preaxial vertebrse. 



The side of the centrum is continuous with that of the neural arch, exhibiting an 

 undulating expanse (concavo-convex dorso-ventrally), which is smooth, save that there 

 may be a scarcely perceptible indication of a ridge running obliquely ventrad from the 

 capitular process to the postaxial margin of the centrum. 



The parapojihysis extends less both preaxially and outwards than in the nineteenth 

 vertebra ; but the articular fossa for the head of the rib is larger, though nearly, if not 

 quite, as deep (fig. 45, ^). 



The diapophysis again projects more outwards, is more extended antero-posteriorly, 

 and more remote from the parapophysis than in the preceding vertebra. It bears on 

 its ventral side, more close to its external margin, a convex articular surface (fig. 45, d) 

 for the tubercle of the rib, which surface is rather moi'e elongated and less rounded 

 than it is in the nineteenth vertebra. It is placed about as near to the preaxial margin 

 of the diapophysis as to its postaxial margin, or rather nearer ; and therefore more 

 postaxially with relation to the whole, more extended, diapophysis than in the more 

 preaxial vertebra. 



Ventral and preaxial to this surface the preaxial aspect of the neural lamina (pedicle) 

 is deeply, widely, and irregularly excavated ; and another excavation is placed near the 

 postaxial margin of the pedicle, in the same position as in the nineteenth vertebra, but 

 larger in size. 



The neural spine is more extended both dorsally and antero-posteriorly, having a 

 straight dorsal margin, which about equals in length its preaxial margin and also the 

 transverse diameter of the postaxial articular surface of the centrum. 



The postaxial excavation of the spine extends less dorsally, the dorsal part of the 

 neural spine presenting postaxially a single margin, instead of aflat surface bounded by 

 two ridges as in the nineteenth vertebra. 



From the side of the neural spine two laminae of bone proceed postaxially to the 

 postzygapophyses, bounding externally that fossa behind the neural spine which repre- 

 sents the postaxial excavation of that spine, which we have seen to exist in vertebrae 

 nearer the skull. 



