328 



MANUAL OF PHYSIOLOGY. 



windpipe by approximating the extremities of the C-shaped 

 springs that normally preserve its patency. 



In the bronchial tubes a large quantity of smooth muscle cells 



FIG. 147. 



deb 



Transverse section of part of the wall of a medium-sized bronchial tube, x 30. (F. 

 E. Schultze.) a. Fibrous layer containing plates of cartilage, glands, etc. 6. Coat com- 

 posed of unstriated muscle, c. Elastic sub-epithelium layer, d. Columnar ciliated 

 epithelium. 



FIG. 148. 



Section of a portion of Lung Tissue, showing part of a very small bronchus cut across. 

 (F. E. Schultze.) a. Fibrous layer containing blood vessels, b. Layer of unstriated 

 muscle, c. Layer of elastic fibres, d. Ciliated epithelium. 



