212 ME. W. P. PTCEAFT ON THE MOEPHOLOGY 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 Dromceus (PI. 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 (]) 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 vertebra? 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 is well shown in PL XLIV. figs. 5-6. 



In Strutldo there are ten pre-sacral and eight post-sacral vertebras. 

 The series commences with the last two thoracic vertebras. Then follow seven 

 lumbar vertebrae. The parapophysial elements of these are all short and thick. 

 The diapophyses of the lumbar vertebras 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 vertebrae 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 vertebras are two in number and have large diapophyses. They lie more 

 caudad than those of Casuarius, 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 1st. In one specimen 

 in the Museum collection the lumbo-sacral has developed a parapophysial process on 

 the left side. 



