PEOFESSOR OWEN ON THE REXTJS DIXOKNIS. 



153 



surface. Hence, in a direct front view (fig. 9), little more than the concave fore border 

 of the preaxial surface (ac) is seen : while the whole surface is fully in view in the 

 under view of the vertebra (fig. 10, ac). It looks almost wholly downward (hsemad) in 

 Binornis, not obliquely downward and forward (hsemo-preaxiad) as in Struthio '. 

 The postaxial surface (fig. 8, pc) much resembles that of the axis vertebra : its trans- 

 verse contour is sinuous, a medial convexity dividing two concavities ; the aspect is 

 more upward than backward; the vertical exceeds the transverse diameter, but in a 

 minor degree than do the reverse proportions of the preaxial surface. 



The pleurapophysis (fig. 8, pi) is more prominently marked than in Struthio ; a low 

 tuberosity represents the diapophysis (fig. 10, d) ; the interzygapophysial bar (fig. 11, r) 

 has gained breadth ; the interzygapophysial foramen (fig. 11, .s) is well defined. 



On the under part of the centrum (fig. 10) the transverse preaxial articular concave 

 tract is followed by a broad depression beyond. From this begins the medial ridge, which 

 expands into the tuberous hypapophysis (hy). This is less produced than in the axis. 



The chief differences from the Ostrich, besides the shorter or broader and deeper 

 proportions of the entire vertebra, are seen in the more distinct hypapophysis, the better- 

 developed hyperapophyses (fig. 8, hp), and the more distinctly bifid character of the 

 neural spine (figs. 9 & 11, ns). 



This spine rises a short way before it divides ; a ridge extends from the fore and hind 

 margins of each division, and defines the depression (for the insertion of elastic li.<ja- 

 ments) in front and behind the undivided base : this, at its summit, is not more than 



POURTH VERTEBRA (| natural size). 

 Fig. 12. Fig. 13. 



Aspects. 

 Fig. 12, lateral ; 13, haemal. 



one fifth of the antero-posterior extent of the neural platform. (The specimen figured 

 is from a higher and larger individual than the articulated skeleton.) 



' ilivart, loc. cit. p. 394. 



