434 



(Fig. 1 2) which is situated along the boundary line between the 

 fibrous and muscular layers. This second plexus gives origin to 

 venous radicles (Fig. 1 3) which, in the deeper part of the lung, form 

 one of the sources of origin of tlie pulmonary vein (broncho-pulmonary 

 veins of Le Fort). These radicles leave the smaller bronchi and 

 bronchioli at the place where they divide, but along the course of the 

 larger bronchi they may leave at other points. The venous radicles 

 which arise from the first two or three divisions of the bronchi do 

 not join the pulmonary vein but form true bronchial veins which 



Fig. 1. Reconstruction model of the bronchial blood vessels. For the s:ike of 

 clearness only two of the arterial radicles passing to the mucosa are shown. 1 Super- 

 ficial venous plexus situated in the mucosa. Only a small portion is represented. 

 2 Deeper venous plexus situated along the boundary between the fibrous and muscular 

 layers. S Venous radicle leaving the fibrous layer to become one of the radicles of 

 origin of a pulmonary vein. 4- One of the main bronchial arteries giving rise to 

 smaller branches which form a plexus in the fibrous layer. 5 Arterial radicles passing 

 to the mucosa. * One of the units of distribution. Only the Ijeginning of a few of 

 the capillaries is indicated. This unit is shown complete and more highly magnified 

 in Fig. 2. 



empty into the azygos, one of the intercostals, or into the superior 

 vena cava. 



The preceding description applies to the divisions of the bronchi 

 as far as the bronchiolus respiratorius. When this division of the 

 bronchial tree is reached we find the bronchial artery is reduced to a 

 single network of capillaries which can be traced as far as the distal 

 end of the ductulus alveolaris. The blood contained in this capillaiy 



