409 
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 hzmapophysis 
is ossified and synoyially articulated with the pleurapophysis above and with the hemal 
spine (‘sternum’) below. Towards its hamal end it expands and develops a tubercle. 
The size of the dorsals in D, mawimus 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 of the hemal surface of the 
centrum than in the third dorsal of S¢ruthio. 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 hayé 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 hamapophysis (‘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. 415), has the centrum less cuneiform in transverse 
section, the sides converging, with a certain convexity, hamad 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 heemal arch, I prefer to retain the character of a free 
plenrapophysis 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 hamapophysis 
(sternal vib). The hemapophysis 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 plenrapophysis. 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 1s so 
much like the twentieth that little need be said in its description” (p. 413). My 
ficure 28 may therefore be contrasted with figure 46 in Mivart's monograph (p, 411, 
loc. cit.) for Alustrations of the differential characters in question, : 
38 
