629 



10 



13 



14 



15 



The shoulder girdle in Primitive Reptiles. 



Fig. 10. Shoulder girdle of Procolophou trigoniceps Owen, a highly evolved 

 Cotylosaur probably nearly related to the ancestor of the typical reptiles. 



Fig. 11. Shoulder girdle of Ophiacodon mirus Marsh (after Williston). Ophia- 

 codon, though not for removed from the ancestral Pelycosaurs, is probably as nearly 

 related to the ancestral Diaptosaurians. 



Fig. 12. Shoulder girdle of Varanosaurus brevirostris, Williston. Varanosaurus 

 though resembling Ophiacodon and the Pelycosaurs in a number of characters seems 

 very clearly specialised along the Diaptosaurian line. There is no trace of un ossified 

 coracoid though possibly a small cartilaginous one way have been present as indicated. 



Fig. 13. Shoulder girdle of Heleosaurus scholtzi, Broom. In the shoulder 

 girdle there are no trace of sutures but the ventral portion is probably all precoracoid. 

 Heleosaurus is a primitive Diaptosaurian. 



Fig. 14. Shoulder girdle of Mesosaurus brasiliensis McGregor (after McGregor). 

 In Mesosaurus there is pretty certainly only a small ventral element. 



Fig. 15. Shoulder girdle of Palaeohatteria longicaudata, Credner. Eistored. 



Fig. 16. Shoulder girdle of Sphenodon punctatus Gray (Young embryo) after 

 Howes and Swinnerton. 



the mammal-like groups — the Pelycosaurs, the Dromasaurs, the Dino- 

 cephalians, tho Therocephalians, the Anomodonts and the Cynodonts, 

 and ending in the Monotremes. In these latter the precoracoid is 

 feeble and no longer articulates with the scapula. The marsupial 



