115

93

is nearly straight. In the Ostrich this part is concave, and a well-developed process
extends down, but does not join the pubis at the back part of the obturator notch.
The Apteryx resembles the great Dinornis in this part of the pelvis. The ischium be-
comes compressed and gradually expands vertically as it extends backwards, its lower
margin forming almost a straight line. In the Ostrich the ischium maintains its trie-
dral form for a much longer extent and suddenly expands, the lower margin curving
down to join the pubis (XIX. fig. 4 e) : there is no indication of such a junction in
the present specimen, nor does the superincumbent ilium curve down, as in the Bus-
tard, to join the ischium : both the ischiadic and the obturator notches seem to have
been unclosed by bone in the Dinornis as in the Apteryx.

The third specimen of the pelvis of a Dinornis, p 4 (Pl. XIX. fig 2. & Pl. XX. figs. 2
& 3.), is more entire, but much smaller than the foregoing. It seems to include all the
sacral vertebrae, which are eighteen in number : seven anterior ones with the lower trans-
verse processes, four without those processes, and seven in which they reappear, ex-
tending obliquely outwards and backwards to the line of junction of the ilia with the
broad posterior part of the sacrum. The most important feature in the present pelvis
is the demonstration of what was obscurely indicated in the foregoing specimen, viz.
that the ilia do not, as in existing Struthious birds, including the Apteryx, approximate
one another along the whole length of the sharp and narrow ridge formed by the spines
of the sacrum, but that they diverge above the acetabula, to give place to a broad hori-
zontal expanse of bone developed from the posterior sacral spines (Pl. XX. fig.3.b), as
in the Bustard and most other birds. This surface forms a smooth shallow concavity,
perforated as usual by two lateral series of small foramina. From the pelvis of the
Bustard that of the Dinornis differes in the greater relative depth and verticality of the
anterior plates of the ilia, which meet above to form a ridge, as in the existing Struthio-
nidae : the posterior expanded part of the pelvis is relatively shorter than in the Bustard,
and the difference is extreme which this part of the pelvis of the Dinornis presents, as
compared with that of the Apteryx 1, the Ostrich, the Emeu, and a fortiori the Rhea, in
which the ischiadic bones meet, and are united for a considerable extent below the
posterior part of the sacrum, which there becomes almost obliterated.

The acetabula are relatively nearer to each other than in the Bustard, but farther
apart than in the Ostrich, Emeu, and relatively than in the Apteryx. There is likewise
another difference in the relative position of the acetabula as compared with the Ostrich :
in this bird those cavities are so situated that their posterior wide orifice exposes to view
the neural arches and spinous processes of the intervening sacral vertebrae. In the
Dinornis only the lower part of the bodies of the corresponding vertebrae are seen by
looking directly into the acetabulum (Pl. XX. fig.2.f), and below these we have the
open cavity of the pelvis : the Apteryx and Emeu resemble the Dinornis in this respect :
nothing but the cavity of the pelvis is seen on looking directly through the acetabula

1 See Zool. Trans. vol. ii. p. 291.