PROFESSOR OWEN ON THE GENUS DINORNIS. 165 
The centrum and neural arch show no notable differences from those of the sixteenth 
vertebra. The pleurapophysis, with a similar double articulation, has increased in size 
and conspicuously in length ; it also supports an ‘ epipleural appendage,’ which is broad 
and slightly curved upward, where it overlaps the succeeding rib. ‘The hemapophysis 
is ossified and synovially articulated with the pleurapophysis above and with the hzmal 
spine (‘sternum’) below. Towards its hemal end it expands and develops a tubercle. 
The size of the dorsals in ). maximus increases slightly as they recede, and chiefly 
in breadth, by the outgrowth of the diapophyses, accompanied by a greater size of 
the rib and greater length and divergence of its capitular and tubercular processes. 
In the present vertebra (third dorsal) the base of the hypapophysis, though shorter 
than in the second dorsal, occupies a greater extent ot the hemal surface of tlie 
centrum than in the third dorsal of Struthio. Not more of the fore part of the neural 
surface of the centrum is exposed than in the antecedent dorsals and terminal cervical 
vertebra. The postaxial surface continues to be narrow in proportion to its height ; 
but its transverse convexity increases, and is relatively greater than in Struthio. The 
transverse concavity of the preaxial surface has also increased; it is still convex ver- 
tically along its middle third. In a homologous vertebra of the present species of 
Dinornis I have noted a variety in the hypapophysis in the interruption of its basal 
extent producing a small guasi second hypapophysis near the postaxial surface. 
The pleurapophysis, with a slight increase of length, and of that of its appendage, is 
as in the second dorsal. The hemapophysis (‘sternal rib’) articulates by a trans- 
versely extended bitubercular end with the sternum. 
The nineteenth vertebra (fourth dorsal, figs. 27-29), corresponding with the first of 
those having their pleurapophyses free and articulating with their hemapophyses in 
Struthio (figures 47, 48, ‘ Mivart,’ p. 413), has the centrum less cuneiform in transverse 
section, the sides converging, with a certain convexity, hemad to a low and short ridge or 
keel, produced and thickened anteriorly, near the preaxial surface (fig. 27, hy). 
Prof. Mivart reckons the dorsal series as commencing with the vertebra thus typi- 
cally complete in regard to its hemal arch. I prefer to retain the character of a free 
pleurapophysis as denoting the present class of axial segments. 
Thus the nineteenth vertebra in Dinornis, or fourth of the dorsal series, answers to 
the twenty-first in Struthio, which is the fourth supporting a free pleurapophysis 
(vertebral rib), and the first in which this element articulates with its hemapophysis 
(sternal rib). The hxemapophysis of the twentieth vertebra in Struthio is developed, 
but is articulated only with its spine (sternum) and does not join by its opposite end 
the pleurapophysis. Such condition I have not yet seen in any species of Dinornis. 
With respect to the twenty-first vertebra in Struthio, Mivart remarks, that “it is so 
much like the twentieth that little need be said in its description” (p. 413). My 
figure 28 may therefore be contrasted with figure 46 in Mivart’s monograph (p. 411, 
loc. cit.) for illustrations of the differential characters in question. 
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