THE LUNG 



315 



diameter of their bronchus. Throughout their course the branches of 

 the pulmonary arteries lie on the wall of the bronchi, viz., in the outer 

 fibrous coat or attached thereto by a broad band of fibrous tissue. More- 



FIG. 298. FROM THE LUNG op A CHILD. 



At a, the origin of a pulmonary venule in the wall of a lobule is shown; at 6, the 

 pulmonary venule is just coming into relation with the bronchiole. Hematein, 

 Weigert's elastic stain, and picrofuchsin. Photo. X 105. 



over each bronchus is accompanied by only one branch of the pulmonary 

 artery and receives no capillaries from it. 



At the apex of the secondary pulmonary lobule the pulmonary artery 

 enters with the bronchiole ; it resolves into smaller arterioles correspond- 

 ing in number approximately to the number of respiratory bronchioles, 

 each of which again breaks into several small twigs one for each atrium, 

 according to Miller which supply the capillary networks in the walls of 

 the alveolar ducts and alveoli. The pulmonary capillaries form an ex- 



