AXIAL SKELETON OF THE OSTRICH. 389 



Its pre- and postaxial margins would be nearly parallel, but that the latter is en- 

 croached on by the lateral extensions preaxiad of the postaxial articular surface, as 

 before mentioned. 



Its preaxial margin is similarly, though to a less extent, encroached on, on each side, 

 by the postaxiad lateral extensions of the preaxial articular surface. The little lateral 

 facets thus formed on each side of each end of the dorsal (or nem-al) sui^face articulate 

 with the sides of the odontoid process of the axis (fig. 5, p d). 



The ventral surface of the quasi-body is gently convex from side to side, and slightly 

 concave antero-posteriorly in its middle. 



Its preaxial margin is generally slightly concave, though it may be (as in specimen 

 1362 b) slightly convex; its postaxial margin is nearly straight, except for the sudden 

 production postaxiad of the median hypapophysial process before referred to (fig. 6, hy). 



This process has a width equal to about a third of that of the postaxial surface of the 

 quasi-centrum ; and the length of its free projection may nearly equal or may slightly 

 exceed its breadth. 



A small rounded tubercle or lateral hypapophysial process (figs. 4, 6, x) may be 

 developed on each side of the root of the median hypapophysial process, close to the 

 postaxial margin of the ventral surface of the quasi-body ; and a slight ridge may run 

 obliquely outwards and preaxiaUy from each of these tubercles nearly to the preaxial 

 margin of such ventral surface. 



The hypapophysial process is directed postaxiad, and but slightly ventrad ; indeed its 

 free extremity (as in specimen 1362 b) may have a slightly dorsal curvature. 



The dorsal surface of this process articulates with the middle of the front part of the 

 ventral surface of the centrum of the axis vertebra. 



The neural arch may be considered as consisting of two lateral halves dorsally united 

 in the middle line. 



Each lateral half springs from the side of the quasi-centrum by a narrow portion or 

 pedicle, expanding dorsally into a neural lamina. 



A narrow band or a mere spiculum of bone (figs. 2 & 3) may spring from the more 

 postaxial part of the side of the quasi-centrum, and may fuse above with the posterior 

 part of the pedicle, forming a foramen or short bony canal for the vertebral artery. The 

 preaxial margin of the pedicle is strongly concave, but develops no process of any kind. 



Its postaxial margin is also strongly concave, and ends above in a decided postzyga- 

 pophysis ; but before reaching that postzygapophysis it develops a more or less marked 

 rounded prominence, which is a rudimentary tubercular process or diapophysis^ (figs- 2, 

 3, & 5, d). 



The little band or spiculum of bone before noticed, wherever it is developed, fuses 



' I use the word diapophysis to denote all parts which are homotypes of the process articulating with the 

 tubercle of the rib when this exists. Similarly I employ the term parapophysis to denote the part with which 

 the head of the rib articulates. 



