390 ME. ST. GEOEGE MIVAET ON THE 



dorsally with this diapophysial tubercle. It is thus essentially the " neck" of an undeve- 

 loped rib ; and its ventral junction with the quasi-centrum is essentially a parapophysis 

 or capitular process. 



Sometimes the postaxial margin of this diapophysial tubercle is slightly produced 

 postaxially, thus affording a faint indication of a prominence much more developed in 

 succeeding vertebrae. 



The ^JOsfe?/^fflpoj;/(j/s?'s projects strongly postaxiad, and has on its inner side a small 

 rounded articular surface, which looks inwards and also slightly ventrad (figs. 3, 6, z). 

 This surface is slightly concave dorso-ventrally, and nearly straight antero-posteriorly. 



On its dorsal surface each postzygapophysis bears a more or less marked rounded 

 tubercle, which is a hyperapojihysis ' (figs. 3, 4, & 5, hp). 



From each postzygapophysis the neural lamina extends preaxially and somewhat 

 dorsad, meetuag its fellow of the opposite side without (as before said) developing any 

 neural spine. The conjoined neural laminae thus form a low flat arch of bone, the pre- 

 axial margin (fig. 5) of which is slightly convex, but the postaxial margin very strongly 

 concave, on account of the strong postaxiad projection of the two postzygapophyses 

 (fig. 3, 6, z). 



No foramina are developed, other than those for the vertebral arteries before described. 



The immature condition of the atlas vertebra (as seen in the specimen 1397 a of the 

 CoUege-of-Surgeons Museum) shows that the neural arches meet together dorsally, so 

 as to form a straight, though short, antero-posteriorly directed line of junction. , 



Similarly each pedicle joins the quasi-centrum by a line of junction which is nearly 

 straight or slightly concave dorsally. 



The ventral ends of the neural laminae furnish the dorsal ends of the crescentic arti- 

 cular surface for the occipital condyle, also the articular facets for the side of the 

 odontoid process and for the ventral surface of its root (fig. 7, ac'). 



The Axis. 



The axis of the Ostrich exceeds the atlas in size far more than is the case in the axial 

 skeleton of any mammal. It also differs from a mammalian axis in that it is, for all its 

 predommance over the atlas, insignificant in size when compared with the more pos- 

 terior cervical vertebrae. 



In the small size of the odontoid process when compared with the centrum, the 

 Ostrich's axis vertebra also differs from that of the highest vertebrate class. 



As compared with the atlas of the Ostrich, the axis differs most markedly in the 

 great excess of its antero-posterior development over that in other directions. 



The axis consists of a centrum, odontoid process, and neural arch, with z)rgapophyses 

 and other outgrowths or annexations. 



' This process is well seen in the cervical vertebrie of the Dingo, where it was first described. See Proc. 

 Zool Soc. 1865, pp. 574 & 579, figs. 5, 7, & 9, h. 



