PROFESSOR OWEN ON THE GENUS DINORNIS. 167 



I subjoin three views (figs. 27, 28, 29) of the nineteenth, or fourth dorsal, vertebra 

 of Dinornis maicimus, corresponding with those views of the twenty-first vertebra of 

 Struthio given by Mivart in figs. 47, 48 (loc. cit.). In this comparison, among the 

 distinguishing characteristics of the Dinomithic vertebra, are, first, the greater relative 

 height of the neural arch and spine, whereby the distance of the parapophysial, p, from 

 the prezygapophysial, z, surfaces is relatively greater. The diapophysis, d, is less ex- 

 tended lengthwise, but more produced transversely and vertically ; it also terminates with 

 a tuberosity which might be reckoned as a low metapophysis, fig. 28, m, overtopping 

 the small articulation, d, which now looks outwardly for the attachment of the rib's 

 tubercle. 



A reticulo-pneumatic fossa [rn, fig. 27) intervenes, as in Struthio, between the par- and 

 diapophysis. A larger pneumatic foramen (ib. pn) opens behind the diapophysis {d). 

 The neural spine {ns) retains its characteristically greater height and thickness, with 

 minor relative antero-posterior extent than in Struthio. Its fore and hind surfaces 

 are occupied by well-defined rough tracts for the elastic ligaments (fig. 28, /). 



The preaxial surface (ib. ac) less transversely and more vertically extended than in 

 the antecedent vertebra, retains something of its bilobed character by the emargination 

 of its upper and lower articular borders. The parapophysis (/;) projects with its rib- 

 surface distinct from the articular facet {ac) of the centrum. The postaxial surface 

 shows an unsymmetrical form in two examples of this vertebra, encroaching further 

 upon the left side of the centrum in one, and upon the right side in the other. Both 

 are individual varieties. 



The hypapophysis {hy, fig. 29), reduced vertically, is coextensive with the imder 

 surface of the centrum, and slightly produced and expanded at both ends (fig. 27, hy, hy'). 

 In the direct view from beneath (fig. 29) the more advanced position of the diapophyses 

 {m) and the less produced hind part of the neural platform and its postzygapophysial sur- 

 faces {pz) are well shown, in contrast with Mivart's figure 48, in Struthio {loc. cit. p. 413). 



The hsemapophysis of the fourth dorsal did not, in the specimen under description, 

 articulate directly with the costal border of the sternum, but through the medium of 

 the hsemapophysis of the third dorsal. 



In the fifth dorsal (twentieth) vertebra the fore and hind productions of the hsemal 

 keel of the centmm assume the character of distinct hypapophyses, of which the 

 anterior {hy) is unciform, being produced forward with the end upcurved, so as to 

 receive the tuberous hind part of the hypapophysial ridge of the fourth dorsal into its 

 concavity ; the posterior one {hy') is low and simple. Figure 30 is a side view of the 

 centrum of this vertebra, showing this singular and, as far as I have observed, unique 

 development of pre- and post-hypapophyses. 



The parapophysial rib-cup {p) is rather larger, and the neural spine has greater fore- 

 and-aft breadth than in the preceding (fourth dorsal) vertebra. This spine greatly 

 exceeds in both height and thickness that in Struthio. A pair of depressions, answering 



