PHYLOGENY OF THE PALJ<:OGNATH/E AND NEOGNATH^:. 209 



line to form two high curved ridges sloping downwards and backwards to terminate in 

 metapophyses. At about the 15th vertebra the two ridges again coalesce and form a 

 very high vertical transverse neural spine. From the ISth backwards this gradually 

 becomes more and more laterally compressed, so as to pass insensibly into the typical 

 neural spines of the thoracic vertebrse. Every neural spine, from that of the axis 

 backwards, bears a fossa at its base, both anteriorly and posteriorly. The latter is the 

 deeper. The vertebrae from the middle of the neck backwards have these fossae of 

 very considerable size. They lodge a ligament. 



From 6-10 in C. casuarius and C. c. ausfralis the diapophysis sends back a bar of 

 bone to the hyperapophysis. 



The vertebrae are all pneumatic. In the hinder cervicals there is a large pneumatic 

 aperture dorsad of the interzygapophysial ridge. In the thoracic there are several 

 very large ones — one below the transverse process, one between the transverse process 

 and the postzygapopliysis, and one dorsad, lying between the anterior zygapophysis 

 and the base of the neural spine. This hist is represented by a deep fossa in Lromceus. 

 The aperture ventrad of the anterior zygapophysis is feebly developed or wanting in 

 Lromceus. 



The cervical ribs (pleurosteites) and liypapophyses resemble those of DronueuH. 



In Lromceus the vertebrae are less specialized than in Casuarius. The high 

 transversely expanded neural spines are wanting, though tlie ligamental neural fossae, 

 especially that caudad of the neural spine, are very deep. The pneumatic fossa in, or 

 above, the interzygapophysial ridge is very deep, as also is that lying at the base and 

 in front of the neural s[)iue. The sides of the fossae, moreover, are smooth, not obscured 

 by cancellated tissue as in Casuarius. 



In Struthio the centra of the vertebrae are relatively much longer than in Lromceus or 

 Casnariits. The neural spines of the anterior cervicals are long, low, and rise to form 

 a sharp median ridge. The ligamental foss;e are narrow grooves channelled out of 

 this ridge. The posterior cervicals have the neural spines wider and shorter, autero- 

 posteriorly, and they are deeply hollowed for the ligament. 



The cervical ribs, as in Casuarius and Lromceus, are long, but more slender than in 

 these. As in Lromceus tliey fuse with a plate of bone depending from the diapophysis 

 and a lateral parapophysial outgrowth from the anterior end of the centrum below 

 the prezygapophysis. The presence of this rib serves to enclose a canal for the 

 vertebral artery. One great point of difference between tliis region of the vertebra and 

 that in Lromceus and Casuarius lies in the fact that in ISfruthio the lamella depending 

 from the diapophysis, and with which the rib articulates, is continued backwards along 

 the centrum for a considerable distance, forming an extensive and tunnel-like passage 

 for the artery. 



The pneumatic apertures are not so conspicuous as in Lromceus. There is no 

 aperture in the interzygapophysial ridge of the anterior cervicals as in Lromceus. In 



