628 



The shoulder girdle in the Therapsida and in Mammals. 



Fig. 1. Shoulder girdle of Galeops whaitsi, Broom, a Dromasaurian. 



Fig. 2. Shoulder girdle of Ictidosuchus primaevus, Broom, a Therocephalian. 



Fig. 3. Shoulder girdle of Dicynodon sp., an Anomodont. 



Fig. 4. Shoulder girdle of Cynognathus crateronotus Seeley, a Cynodont. 



Fig. 5. Shoulder girdle of Ornithoi'hynchus anatinus Shaw, a Monotreme. 



Fig. 6. Shoulder girdle of early foetus of Trichosurus vulpecula, Kerr, a I)i- 

 protodont Marsupial. 



Fig. 7. Shoulder girdle of later foetus of Trichosurus vulpecula, Kerr, a Di- 

 protodont Marsupial. 



Fig. 8. Shoulder girdle of mammary foetus of Dasyurus viverrinus, Shaw, 

 a Polyprotodont Marsupial. 



Fig. 9. Shoulder girdle of mammary foetus of Perameles obesula Shaw, a Poly- 

 protodont marsupial. 



In the Monotreme (fig. 5) for the first time the precoracoid loses attachment 

 to the scapula. In the early foetal Marsupial (fig. 6) the precoracoid can be detected 

 as a thin layer of imperfectly differentiated cells. In the later stage of development 

 (fig. 7) the precoracoid becomes lost. The coracoid is here a large development 

 which articulates with the sternum. In the Polyprotodont foetus (fig. 8) the coracoid 

 is smaller but still attached to the sternum. In the later mammary foetus of Pera- 

 meles the coracoid no longer meets the sternum and has become much reduced in 

 size. The shoulder girdle is somewhat rotated so that the coracoid which originally 

 is directed inwards and backwards is now directed mainly forwards. 



