334 PEOF. ST. GEORGE MIVAET 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. 



The Ischium. 



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 (?'. e. mesiad) by a rounded antero-poste- 

 riorly directed prominence, which runs on preaxially to the junction of the ischium 

 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 Struthionidae. 



The ischium extends about as postaxiad as does the ilium, but much less so than 

 does the pubis. 



The Ribs. 

 There are eleven ribs on each side in all^namely, six vertebral ribs, and five sternal 

 ones. 



The Vertebeal Ribs. 



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 (/. 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 



