AXLAL SKELETON OF THE OSTRICH. 393 



ment to a ligament going ventrad to the pit on the middle of the dorsal surface of the 

 quasi-centrum of the atlas. 



The most preaxial of the three surfaces is smooth and articular, and in part joins with 

 the preaxial articular facets of the dorsal surface of the quasi-centrum of the atlas ; 

 in part it joins the occipital condyle (fig. 9, o). It completes, as it were, the cup 

 mainly formed by the preaxial concavity of that quasi-centrum, the dorsal excavation of 

 which it fills up, occupying as it does the space between the horns of the preaxial arti- 

 cular surface of the atlas. 



The neural arch is very much more extended antero-posteriorly, more solid, and fur- 

 nished with more annexed processes than is the neui'al arch of the axis. 



The pedicle, or part ventral to the zygapoyhyses, is so little extended dorsally as to be 

 insignificant. The postaxial margin of the pedicle is very concave (fig. 8). 



A flat band of bone ascends obliquely on each side (figs. 8, 9, ^j ^ ) from the antero-lateral 

 side of the centrum (where the transverse oblique ridge runs into the parapophysis) to 

 between the prezygapophysis and the postzygapophysis, the band expanding dorsally 

 and forming a sort of antero-posterior ridge or plate, connecting these zygapophyses. 



This band shelters beneath it the vertebral artery. 



On the side of the centrum and neural arch, within the band, are irregular foramina 

 leading into the substance of the vertebra. 



The oblique band of bone is essentially the neck of a rib, and corresponds with the 

 spiculum before noticed as sometimes existing beside the atlas. 



The dorsal expansion of the band is the diapophysis ; its inferior origin is the para- 

 pophysis. 



The preaxial margin of the oblique band of bone is more or less concave. A slight 

 angular process projects postaxially from its postaxial margin (fig. ^, pi). 



Each prezygapophysis is small and rounded, looks outwards and slightly dorsad, is a 

 little convex dorso-ventrally, and nearly straight antero-posteriorly (figs. 8, 9 & 11, az). 



The postzygapophysis is between two and four times the size of the prezygapophysis ; 

 its antero-posterior decidedly exceeds its transverse diameter. It looks mainly ventrad, 

 but slightly postaxiad also (figs. 10 & 12,^2;). 



On its dorsal surface each postzygapophysis bears a very prominent and conspicuous 

 hyperapophysis (figs. 8, 10, & 12, hp). 



The neural laminae at their point of union dorsally, develop a low but strong and 

 stout neural spine or, rather, ridge (figs. 8, 9, 10, & 11, ns). 



This neural spine gradually rises as we proceed from the preaxial margin of the 

 neural arch postaxially. It attains its greatest elevation at the postaxial end of the 

 middle third of the neural arch. From that point it descends rather sharply to the 

 postaxial border of the neural arch, presenting a margin which is slightly concave 

 postaxially. 



VOL. VIII. — PART Yii. March, 1874. 3 k 



