I 



PLATE 9 



EXPLANATION OF FIGURES 



33 Vanellus custatus. One-third of incubation period. Lower view. Note 

 slight attachment of ribs, but only sutural separation of sternum and coracoid. 

 After Parker. 



34 Echnidna histrix. Upper view of adult specimen. Drawn from a speci- 

 men in Washington University, Department of Zoology, and in part after Parker. 



35 Shoulder-girdle of a marsupial embryo, Trichosurus. Scapulae, cora- 

 coids, and sternum are continuous parts as in the shark embryo. After Broom. 



36 Anterior view of girdle in an 8.5-mm. Trichosurus embryo. Dotted 

 portions are mesenchymatous. After Broom. 



Ac, acromian Pro, pre-omosternum 



CI, clavicle R 1 , first rib 



Cr, coracoid R 2 , second rib 



ECr, epicoracoid Sc, scapula 



Gl, glenoid Sp, spine 



ICl, interclavicle SSc, suprascapula 



OSt, omosternum St, sternum 



PCr, precoracoid XSt, xiphisternum 



108 



