PHYLOGENY OF THE PAL^EOGNATILE AND NEOGNATHJE- 229 



closely resembles, at this stage, the permament condition which this bone obtains 

 in Struthio. 



The extreme antero-ventral angle of the pre-ilium is sharply defined and produced 

 outwards, overlapping the penultimate thoracic rib, with which it ultimately becomes 

 completely fused. The innominates meet in the middle line above the synsacrum, 

 cephalad and caudad, but leave the neural spines of the synsacrum exposed at the 

 bottom of a groove over the sacral region. 



The ischia, which, it will be remembered, in Casuarius approached one another in 

 the mid-ventral line, in Rhea actually meet at a point corresponding with a line passing 

 downwards from behind the anti-trochanter. From this point backwards they remain 

 in close juxtaposition, later in life more or less completely fusing. These approximated 

 ischia form a lcng backwardly projecting median bar, produced caudad far beyond the 

 level of the post-acetabular ilium. Thus a kind of false roof is formed to the abdominal 

 cavity and a floor to the renal fossa. 



The pubes, as in Dromceus and to a lesser extent in Casuarius, are bowed outwardly 

 and terminate freely near the end of the ischia. 



The pectineal process is formed in part by the descending acetabular process of the 

 ilium and partly by the pubis. 



The adult pelvis differs in many respects from that of the nestling, carrying the points 

 wherein it is peculiar a stage further in development. 



The supra-trochanteric process now forms a large overhanging ledge, directly above 

 the acetabulum. The innominate bones now meet in the mid-dorsal line throughout 

 the whole of their length. The post-acetabular ilium fuses on either side by a broad 

 expanded foot with the ischia, and beyond this fusion — a point of contact only in the 

 nestling — is continued backwards a long pointed process. The pubes, turning suddenly 

 caudad and mesiad, fuse eventually with the ischia. 



The sacral vertebra? in Casuarius lay level with the ventral border of the innominate, 

 and extended outwards to articulate with the vertical acetabular process of the ischium. 

 In Shea these vertebrae are raised up so as to lie above the level of the acetabulum. 



The post-acetabular ilium, in the nestling Grebe, is subequal in length with the pre- 

 acetabula, in the adult it is longer than this. 



In Struthio the pelvis presents one or two points wherein it differs markedly from 

 that of the other Palceognathoe . 



Like Dromceus, the post-acetabular is longer than the pre-acetabular ilium, only the 

 difference is much greater in Struthio. The post-acetabular region remains permanently 

 and widely separate from the ischium, and is so narrow in proportion to its length as 

 to be almost rod-shaped. The pre-acetabular ilium is relatively as long as in Dromceus. 

 The fovea iliaca anterior is rather convex than concave. In this particular Struthio is 

 peculiar : since the pre-acetabular ilium instead of being concave externally, so as to,, 

 on this account, more or less completely embrace the neural spines of the synsacrum, 



vol. xv. — part v. No. 16. — December, 1900. 2 k 



