MR. W. K. PARKER ON THE OSTEOLOGY OF BAL.ENICEPS REX. 325 



Axis. (Pl.LXVI. fig. laa;.) 



The ' axis ' of BalcRniceps is a short, high, swollen bone, — the low neural spine, the 

 small hypapophysis, and the large post-zygapophyses being very cellular. The short 

 odontoid process is flat above and convex below, having at each side near the tip an 

 inferior facet to articulate with the atlas behind the rim of the cup. There is a distinct 

 neck to this process, which is very cellular, as is also the front of the centrum between 

 the branches of the U-shaped articular surface, corresponding with the posterior aspect 

 of the atlas. The pre-zygapophyses are small, and lie on the margin of the neurapo- 

 physis ; the post-zygapophyses are subtriangular, large, and concave. The posterior 

 articular facet of the centrum is perfectly ornithic, being convex from side to side, and 

 concave vertically. There is a rough oval facet in front, and another behind the low 

 spine for the elastic ligament. The upper and lower transverse processes together 

 form a vertical mass of thickened bone, perforated behind for air, but having extremely 

 small openings in front for the vertebral arteries. This is similar to what occurs in its 

 nearest congeners, Cancroma and Ardea, whilst the Storks, e.g. Ciconia argala and 

 alba, have these vessels bridged over by a well-defined convex arch of bone Grus 

 americana possesses not only this bridge, but also a small ' rib,' which does not appear 

 ever to have existed in the Stork and Heron groups, nor does it exist in the young 

 Emeu. In the Common Fowl there is a pair of lateral bridges on the atlas, but none on 

 the axis. 



In the immature skeleton of the Emeu the anterior end of the centrum of the axis, 

 including the odontoid process, all belongs to the atlas, and is quite distinct from the 

 axis for the first few months ; so that, if the atlas had all its rights, it would be much 

 nearer in size to the axis. In the Goose one-third of the centrum of the axis belongs 

 to the atlas, and the former bone has in this bird a small ' rib.' The neural canal of 

 the axis of Balseniceps is narrower than that of the atlas ; in the latter it is one-third of 

 an inch wide, in the former one-quarter of an inch in front, but full one-third behind, 

 the bone being bevelled away here between the post-zygapophyses. In the axis, and 

 the two next vertebrae in this bird, the posterior tubercle for the elastic ligament lies 

 in a recess formed by the projection backwards of the upper part of the bone. The 

 margin of this projecting portion is rounded and smooth, and forms a very elegant arch 

 over the inter-spinous tubercle, the piers of which arch lose themselves behind the 

 thick tubercular mass of bone which forms the upper part of the post-zygapophyses. 

 The articular facets of these latter processes lie directly under these tubercular masses. 



Cervical Vertehra. (PI. LXVI. fig. 1 cv, and figs. 5 & 6.) 



The facets of the post-zygapophyses of all the remaining cervical vertebrae are less 



concave and look a little more outwards (as well as downwards) than those of the axis ; 



they are sub-oval, and, measured in the antero-posterior direction, are more than a 



quarter of an inch long in the upper part of the neck, and nearly half in the lower, 



VOL, IV. — PART VII. 2 z 



