212 MR. W. P. PYCRAFT ON THE MORPHOLOGY AND 
Seen dorsally in the half or even three-quarter grown birds the neural spines from 
above the acetabulum backwards for some considerable distance are found to take 
the form of vertical transverse plates, forming a series of loculi between the post-ilia. 
‘Though further back in the series the transverse plates become columnar, the loculi 
remain. In the adult these loculi are completely covered in by a thin sheet of bone, 
formed by the fusion of a series of thin plates capping the neural spines. 
In the embryo Dromeus (Pl. XLIV. fig. 6) it is worth noting that the lofty 
transversely expanded neural spines of the sacral and anterior post-sacral vertebra of 
the adult are represented only by low cartilaginous ridges, and bounded on either side 
by the free edge of the dorsal border of the ilium. In the dried skeleton the carti- 
laginous portion shrinks up, revealing (1) a pair of ossified neuroids, which fail to 
meet one another in the middle line, and (2) a low osseous ridge marking the 
foundation of the similar cartilaginous ridges already described. The increase in 
height of the neural spines is followed by a corresponding increase in depth of the 
ilium (p. 227). 
The centra of these synsacral vertebre in this early stage are, in the dried skeleton, 
represented only by a flat bony plate, so that a single vertebra, with its neural arches, 
is stirrup-shaped. ‘The thinness of the centrum makes the neural space of a relatively 
much greater size than in the adult. ‘The nerve-apertures are single and not paired 
as in the adult. This 1s well shown in Pl. XLIV. tigs. 5-6. 
In Struthio there are ten pre-sacral and eight post-sacral vertebre. 
The series commences with the last two thoracic vertebra. Then follow seven 
lumbar vertebre. The parapophysial elements of these are all short and thick. 
The diapophyses of the lumbar vertebre from the 4th backwards extend upwards 
on to the inner side of the ilium as forwardly directed spikes. Short and triangular 
on the 4th, they gradually increase in length up to the 8th, where they form long 
rod-shaped bars of bone. On the 10th, this process is short and rod-shaped. 
The lumbo-sacral vertebra are possibly represented by a single vertebra which bears 
vestigial parapophyses. In one skeleton in the Museum collection the lumbo-sacrals 
were certainly unrepresented. The last lumbar bore distinct parapophysial elements, 
which on the left side extended backwards to join the first sacral rib. 
The sacral vertebree are two in number and have large diapophyses. They lie more 
caudad than those of Casuwarius, resting against the hinder border of the downward 
ischiadic or post-acetabular process of the ilium, and therefore conspicuously caudad 
of the acetabulum. In Casuarius the sacral ribs lie immediately behind the 
acetabulum. ‘The outer free ends of the sacral ribs give rise to a large swollen process 
from the dorsal surface, which extends upwards and backwards to reach the diapophysis 
of the 2nd sacral, sometimes extending forward to that of the Ist. In one specimen 
in the Museum collection the lumbo-sacral has developed a parapophysial process on 
the left side. 
