THE RESPIRATORY SYSTEM 



315 



where carbon deposits in the interlobular connective tissue assist in 

 outlining the lobules. Thebase of the peripheral lobule is four- to eight- 

 sided and from i to 1.5 cm. in diameter. It is pyramidal in shape, 

 narrowing to an apex about i to 1.5 cm. from the base. In the inte- 

 rior of the lung the lobules are not pyramidal but irregularly poly- 

 hedral, the apex being, however, distinguishable by the entrance of 

 the lobular bronchus. 



The apex of each lobule is the point of entrance of the lobular 

 bronchus (branch of inter- or sublobular) (Figs. 212, 213 and 215, bl) 

 which is about 0.5 nini. in diameter, and of the lobular branch of the 



Bronchial artery 



Pulmonary vein — 



A^ 



Pulmonary artery 



Terminal bronchus 



Alveolar passage 



Pleural capillaries 



Fig. 213. — Scheme of a Pulmonary Lobule and its Blood Supply. (Stohr.) The 

 two main branches of the pulmonary vein are seen lying in the interlobular^connective 

 tissue. 



pulmonary artery. Accompanied by the artery (Fig. 213) the bron- 

 chus passes through the central axis of the lobule, giving off collateral 

 branches (Fig. 212, a, b), to about the middle of the lobule, where it 

 divides into two branches (Fig. 213). These branches and also the 

 collaterals branch dichotomously giving rise to from 50 to 100 ter- 

 minal or alveolar bronchi ("terminal", as being the last subdivision 

 of the bronchial tree which preserves its identity as a bronchus; 

 "alveolar", as it gives off, especially toward its distal end, some 

 alveoK) . From each terminal bronchus (Fig. 215. ba) open from three 



