1054 DK. R. BROOM ON THE ORIGIN [DeC. 10, 



scapular border. In Pariotichus, according to Case, there is no 

 cleithrum, and in none of the members of the Diapsidan phylum 

 does the cleithrum ever reappear. The Pelycosaurs, Procolophon 

 and its allies and Mesosaurus, all retain the ossified precoracoid, 

 but soon this too becomes lost as a bone and is never again found 

 in any of the Diapsida, Anterior developments of the scapula 

 sometimes take the place of the lost precoracoid, as in the Ohelonia, 

 the Plesiosaurs, and in the Ostrich ; and the coracoid and scapula 

 occasionally have anterior developments which ai-e somewhat 



Text-%. 245. 



Shoulder-girdles of Mammal-like Reptiles and of Ornithorhynchus . 



A. Frocoloplion trigoniceps. 



B. Galecliirus sclioltzi. 



C. Ictidosiwlius jtrimavus. 



D. Oudenodon haini. 



E. Galesuchus hrowni. 



P. Ornitliorhynchus anatinus. 



Sc, scapula; Co., coracoid; P. Co., precoracoid. 



precoracoid-like as in the Lizards, but a distinct precoracoid 

 never appears Avhen once lost. In Procolophon the scapula is 

 short and broad, the precoracoid of large size with a round 

 foramen, and the coracoid also well developed. These three 

 elements are never anchylosed even in old specimens. The 



