PLATE 4 



EXPLANATION OF FIGUKES 



8 Wax reconstruction of epithelial tube and related developing skeletal 

 structures in the region of the tracheal bifurcation. Ventral aspect, X 50. 226 

 iiour chick embryo. 



:9 Same as 8. Dorsal aspect, X 50. 



10 Wax reconstruction of epithelial tube and related skeletal elements. 

 Yentral aspect, X 50. 284 hour chick embryo. 



11 Same as 10. Dorsal aspect, X 50. 



208 



