PHYLOGENY OF THE PAL^OGNATH^E AND NEOGNATHLE. 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 18th backwards this gradually 

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

 neural spines of the thoracic vertebrae. 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 vertebra? from the middle of the neck backwards have these fossa? of 

 very considerable size. They lodge a ligament. 



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

 bone to the hyperapophysis. 



The vertebra? 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 postzygapophysis, and one dorsad, lying between the anterior zygapophysis 

 and the base of the neural spine. This last is represented by a deep fossa in Dromceus. 

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

 Dromceus. 



The cervical ribs (pleurosteites) and hypapophyses resemble those of Dromceus. 



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

 transversely expanded neural spines are wanting, though the ligamental neural fossa?, 

 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 spine. The sides of the fossa?, moreover, are smooth, not obscured 

 by cancellated tissue as in Casuarius. 



In Struthio the centra of the vertebra? are relatively much longer than in Dromceus or 

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

 a sharp median ridge. The ligamental fossa? are narrow grooves channelled out of 

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

 posteriorly, and they are deeply hollowed for the ligament. 



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

 these. As in Dromceus they 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 this region of the vertebra and 

 that in Dromceus and Casuarius lies in the fact that in Struthio 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 1 

 for the artery. 



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

 aperture in the interzygapophysial ridge of the anterior cervicals as in Dromceus. In, 



