104 ME, H. Qt. SEELET ON THE 



manner of the Apteryoc, the two bones are usually united by 

 suture throughout their length, so as to leave a small obturator 

 foramen near to the acetabular border. If this foramen were larger, 

 the bones which enclose it would bear a close resemblance to those 

 of the Echidna, which is the more interesting since, ia common 

 with the lower mammals, the Ornithosaurs also possess prepubic 

 or marsupial bones. These bones are of different forms in the 

 several groups of Ornithosau ris, being triangular in DimorpJiodon, 

 T-shaped in some genera from the Lithographic slate, and pro- 

 bably forming by union with each other a bow-shaped arch in 

 another genus from Solenhofen. 



The exact position of the prepubic bone on the anterior margin 

 of the pubis is not quite certain, though probably placed in the 

 middle of the margin ; and there may be some doubt whether it 

 is truly homologous with the marsupial bone. In Chelonians 

 and Lacertilians a prepubic process is developed, often of large 

 size, and the ornithosaurian bone may be likened to what such a 

 process might become if converted into a distinct osseous ele- 

 ment. A smaller but similar process is also to be seen on the 

 pubic bone in some birds, such as the Apteryx, and in many 

 mammals. In Iguanodon the process is enormous. The pelvis 

 might perhaps as easily be regarded as of a modified mammalian 

 type as avian; but it does not closely resemble either, and is 

 somewhat intermediate between them. In this light it may serve 

 to point a caution by showing that monotreme characters in the 

 pelvis may coexist with lacertian characters in the articulations of 

 the vertebrse. The pelvic bones met in the median line of the 

 body, as in mammals and reptiles, and were not divided from each 

 other, as is usual among birds. 



The femur is in no respect a reptilian bone, unless it be in 

 sometimes having the articular head directed a little forward. 

 But in most English specimens there is a distinct articular head 

 separated from the shaft of the bone by a considerable neck, which 

 is directed upward as in carnivorous mammals ; though in the 

 genera from the lithographic slate the proximal end of the bone 

 is more like the same part in birds. The distal end is rarely so 

 deeply grooved in front as in the bird's femur, though, it corre- 

 sponds in thickness and form and does not approximate towards 

 mammals. 



The tibia and fibula are altogether avian, so much so that in 

 many genera no anatomist could distinguish them from the same 



