92 The Development of the Lungs 
the same time, there are more connective-tissue cells. Under the pleura 
(Fig. 25 p) and in the interlobular spaces, the fibrils are gathered into 
slight trabecule, which limit small spaces in the connective-tissue net- 
work. 
The larger bronchi show an increase in the characteristics indicated in 
the last stage. The epithelium is thrown out into longitudinal folds, 
Texr Wig. 25. 
Text Fic. 25. Section of the lobule of the lung of a pig 13 cm. long 
Same preparation as used with the tissue shown in Fig. 21. <X 70. p—=pleura. 
a@—=connective tissue. b—=bronchus. c—end bud. /=lymphatics. 
which are accompanied by folds of the basement membrane and sub- 
mucosa. This is composed of trabeculae formed from the young con- 
nective-tissue fibrils. In the young submucosa, the simple muscle bundles 
lie, and still external to the muscularis the cartilagenous rings are in 
process of formation. Proceeding peripherally, the bronchi grow essen- 
tially younger and the epithelium is first reduced to a single columnar 
