Syrin.r of Fuid. 305 



Fig. \'l. — liitL'ilnonihial, veiitro-laturiil, iind dorso-lateral sacs 

 shown. 



Fig. 13. — Interbronchial and lateral sacs shown in relation to the 

 membranae internae and externae. 



Fig. 14. — Dorso-lateral sac, in relation to the membrana externa. 



Fig. 15. — Main recurrent interclavicular branch shown, together 

 with the interbronchial and dorso-lateral sacs. 



Fig. IG. — Showing how the dorso-lateral sac passes up from the in- 

 terbronchial region, dorsal to the bronchus, and at its caudal 

 end. 



Figs. 17-24. — Transverse sections through the bronchi and meso- 

 bronchi of the lung, showing the origin of the interclavicular 

 and anterior thoracic air sacs from the thii-d entobronchus of 

 the lung-. 



Figs. 17, 18. — Stage of 10 days' incubation, showing the third 

 entobronchus, the anterior thoracic air sac. and the inter- 

 clavicular sac, with its recurrent branch. 



Figs. 19-24. — Stage of 13-14 days' incubation, slicnving the third 

 entobronchus, and the origin of the common stem of the inter- 

 clavicular and anterior thoracic sacs. Recurrent inter- 

 clavicular liranch, shown in Figs. 20, 21, 22; interbronchial 

 sacs shown in Fij;. 19. 



Reference Letters. 



ao Dorsal aorta. 



bl-])3 Bronchial cartilaginous semi-rings. 



Bm Mesobronchus of the lung. 



Br Bronchus. 



bv Lar!.re blood vessels of the heart. 



d Dorsal triangular plate. 



En Entobronchus of the lung. 



En^ Third entobronchus of the lung. 



Lg Lung tissue. 



Lv Liver tissue, 



mb Membrana bronchi desnius. 



mc Tracheo-clavicular muscle, 



me Membrana externa, 



mi ]\Iembrana interna. 



ml Membrana semilunaris. 



mt Membrana trachea. 



ms Syrinereal muscles. 



16 



