PHYLOGENY OF THE PAL^EOGNATPLE AND NEOGNATHvE. 213 



Tlie 1st caudal bears both para- and diapophyses. Sometimes the former fuse with 

 those of the sacral. Behind this lie seven caudals without parapophyses, before the first 

 free caudal is encountered. The neural spines of these are not transversely expanded 

 as in Casuarius. 



In JRhea there are ten pre- and five post-sacral vertebrae. 



The pre-sacral comprise two thoracic, four lumbar, and four lumbo-sacral ; the last 

 of these may develop parapophysial processes. 



The sacral ribs fuse with the ilium more dorsad than in Struthio, Casuarius, or 

 Dromceus. In the last three they abut more or less extensively against the post-acetabular 

 ascending process of the ischium. In Rhea they rise dorsad, so as to reach the level 

 of the centre of the acetabular arc. 



The 1st sacral is intermediate in position, with regard to the acetabulum, between 

 Casuarius and Struthio. In the latter, it will be remembered, it lies considerably behind 

 the acetabulum, in Casuarius level with its hinder border. 



The sacral ribs are very short and almost indistinguishably fused with their 

 diapophyses. In the possession of diapophyses these vertebrae differ from those of 

 Casuarius and Dromceus, and resemble Struthio, in which, however, they are much 

 more extensively developed. 



The first post-sacral, or 1st caudal, bears both para- and diapophysial processes, 

 but they are almost indistinguishably fused. The 2nd caudal bears diapophyses only. 

 The 3rd to 5th caudals are somewhat remarkable in that they are represented only by 

 atrophied vertebra?. The centra of these are reduced to thin delicate rods, supporting 

 slender diapophyses and feeble neural spines. The 6th vertebra resembles the 5th, 

 but has a stronger neural spine. It is the first vertebra to escape from the clasp of 

 the post-acetabular ilium. The 7th has a much stronger neural spine and slightly 

 thicker centrum, but like the 6th has lost its diapophyses. The 8th and 9th have 

 inflated cancellous centra and short neural spines ; they fuse by their ventral aspects 

 with the ischia. The 10th is the first free caudal, of which there are eight in all : 

 these have short thick centra and short neural spines. 



In Apteryx there are nine pre- and five or six post-sacral s, with the true sacrals 

 sixteen in all. 



The pre-sacrals represent two thoracic, four lumbar, and three lumbo-sacral. The 

 first post-sacral (1st caudal) bears short para- and diapophysial processes. The post-sacral 

 are chiefly remarkable for the great lateral compression which they have undergone. 



The synsacrum of the Dinomithidce differs in many respects from that of all the 

 other Palceognathce. It resembles in many ways that of Dromceus and Casuarius 

 on the one hand, and that of Struthio on the other. The pre-sacrals are apparently 

 eleven in number, viz., two thoracic, six lumbar, and three lumbo-sacral. There is an 

 indication of a fourth lumbo-sacral bearing parapophysial processes, which have almost 

 completely fused with those of the 1st sacral. There are five post-sacrals. 

 vol. xv. — part v. No. 14. — December, 1900. 2 h 



