334 PROF. ST. GEORGE MIVART ON THE 
In shape it remarkably resembles the most posterior ribs; so that, were we guided by 
its appearance in this animal alone, the pubis would certainly be reckoned as a 
pleuropophysis. 
Tue Iscurum. 
This is the shortest of the three bones forming each os innominatum. 
It expands preaxially to form part of the acetabulum, then remains narrow to its 
antero-posterior middle, and then expands dorso-ventrally to join the ilium. It does 
not ankylose with the pubis postaxially, unless perhaps it may do so in aged individuals. 
Its outer surface postaxiad of the ventral part of the acetabulum presents a smooth 
groove, bounded ventrally at its preaxial end by a slight process (figs. 2 & 3, ps) pro- 
jecting preaxiad and somewhat ventrad. This process is really the preaxial end of the 
ventral margin of the ischium; and mesiad of the margin is a long antero-posteriorly 
directed groove (fig. 3, g), bounded internally (7. e. mesiad) by a rounded antero-poste- 
riorly directed prominence, which runs on preaxially to the junction of the ischitum 
with the pubis beneath the antero-posterior middle of the acetabulum. Postaxially 
this ridge runs on to the postaxial extremity of the bone. Such a groove exists in 
Casuarius alone amongst the Struthionide. 
The ischium extends about as postaxiad as does the ilium, but much less so than 
does the pubis. 
Tue Riss. 
There are eleven ribs on each side in all—namely, six vertebral ribs, and five sternal 
ones. 
THe VERTEBRAL Riss. 
The first vertebral rib, that of the cervico-dorsal vertebra, or seventeenth vertebra, 
ends freely distad, but proximally it is provided with a distinct tuberculum and capi- 
tulum. Compared with the apparently corresponding rib of Struthio, the capitulum is 
much longer and the tuberculum is much shorter. The pneumatic foramen (which is 
double) is situated more ventrad. There is a large unciform process, which is longer 
than the length of the rib distal to it. 
The second vertebral rib, or the first true rib (i.e. the first which is connected by a 
sternal rib with the sternum), has again a much shorter tuberculum than in Struthio. 
The unciform process is a little more dorsad in position, so that the part of the rib 
ventral to it is larger than it. The rib is rather more flattened than is its serial pre- 
decessor, and more bent convex preaxiad ; and its dorsal end is wider. It is a more 
slender bone, relatively as well as absolutely, than in Struthio. 
The third vertebral rib has again a very short tuberculum. The unciform process is 
more dorsad than in the first true rib. The tuberculum and capitulum are wider apart, 
and the whole bone is antero-posteriorly wider, than is the case in the second rib. 
In the fourth vertebral rib the tuberculum and capitulum are not so wide apart as 
