9C The Development of the Lungs 
from the first to last possess marked lumina. From the root of the lung, 
the lymphatics have now grown some distance into its substance. They 
have thin walls composed of young fibrils lined by endothelium with 
occasional valves. They are confined, however, to the immediate neigh- 
borhood of the main bronchi and their chief subdivisions. 
Text Fig. 24. 
Text Fig. 24. Section of the lung of an embryo pig 7 cm. long. Same 
preparations as used with the tissue shown in Fig. 21. X70. p=pleura. Db 
=pbronchus. a—connective tissue. /—lymphatics. This stage shows the 
beginning of the lobulation. 
Pig 7 em. long (Fig. 24). A number of interesting changes have 
taken place in the evolution of the lungs since the last stage other than 
in a further differentiation of the framework, which at this time is con- 
