AXTAL SKELETON OF THE STRUTHIONID2. Val 
compared with a bird’s skull, has the beak smaller and the cranium less dorsally convex, 
while the upper of the two anterior bars (7. e. the ischiwm) joins the beak by ossification 
of the ligament uniting it with the ilium. Moreover the pelvis differs from that of 
Struthio in that the two bars (ischium and pubis) extend postaxiad beyond the ilium to 
a greater degree, and do not curve ventrad distally. The supratrochanteric process is 
also decidedly preaxiad to the antitrochanteric process, instead of slightly postaxiad as 
in Struthio. ‘The ilio-pectineal process is much shorter; and the vertebral column is 
scarcely to be seen through the acetabulum; while the latter cavity is placed nearer the 
middle (pre- and postaxially) of the total length of the ilium. The os innominatum is 
much less deep dorso-ventrally in proportion to its pre- and postaxial extent. The pre- 
acetabular part of the ilium has its external surface more concave than in Struthio, as is 
also the preaxial margin of the ilium. 
Viewed dorsally, the pelvic ribs are relatively larger than in Struthio. The antitro- 
chanteric processes project at about the middle of the ilium’s length pre- and post- 
axially and behind the anterior third of the total length of the pelvis. Just in front of 
the processes the supraacetabular processes project strongly outwards, relatively as well 
as absolutely much more so than in Struthio. In Rhea only three processes are seen to 
extend postaxiad (instead of five as in Struthio), all joining together distally. The 
median process of these three (ilia and ischia in one) expands distally so that its lateral 
margins are concave. No vertebral spines are visible in the adult (as they are in 
Struthio), the two ilia ankylosing together dorsally in the adult, and even in the im- 
mature (e.g. in No. 1361 £) meeting together, though in the very young (e. g. in 
No. 1361 F) the lumbo-sacral and sacral spine-tips come to the surface between the ilia 
from a little preaxiad to a little postaxiad of the preacetabular process. The two 
lateral processes above spoken of are, of course, the two pubes, each pubis forming a 
gentle curve (not so bowed outwardly as in Struthio) with a convex external margin and 
a concave internal one. 
The transverse diameter of the pelvis is pretty uniform. It is greatest between the 
ends of the pelvic ribs, and next greatest across the pubes. The posterior ends of the 
ilia do not diverge as in Struthio. 
When viewed ventrally, the most striking differences between the pelvis of Rhea 
and that of Struthio are, the greater size of the pelvic ribs in the former, the fact that 
but three bony processes extend postaxiad, and the binding of the sacro-caudal vertebre 
and the postaxial parts of the ilia by the medianly united ischia. Also the iliopectineal 
eminences are smaller, and the centra postaxiad to the sacral vertebre are aborted. 
Although there are from three to five /wmbo-sacral vertebre (i. e. without parapo- 
physes and between the lumbar and sacral vertebrae), yet they are so closely approxi- 
mated antero-posteriorly as to leave but a very small fossa between them on each each 
side and the adjacent acetabulum. 
