Chap. xxviii.] ORGANS OF RESPIRATION. 



22$ 



alveolar ducts or infundibula, in their whole extent, 

 but not beyond them, i.e., not on the air-cells. 



(c) The adventitia of elastic networks is con- 

 tinued on the infundibula, and thence on the air- 

 cells, where they form an essential part of the wall 

 of the alveoli, being its framework. 



Amongst the network of elastic fibres forming 

 the wall of the alveoli is a network of branched con- 

 nective tissue cells, contained as usual in similarly 

 shaped branched lacunae, which are the radicles of 

 the lymphatic vessels. 



294. The blood-vessels and lymphatics. 

 The branches of the pulmonary artery and veins 

 are contained within the connective tissue separat- 

 ing the lobes and lobules, whence they can be 

 traced into 

 their finer 

 ramifications 

 towards the in- 

 fundibula and 

 air-cells. Each 

 of these latter 

 is surrounded 

 by a sort of 

 basket - shaped 

 dense network 

 of capillary 

 blood - vessels 

 (Fig. 129). The 

 capillary net- 

 works of adja- 

 cent alveoli are 

 continuous 

 with one another, and stand in communication on the 

 one hand with a branch of the pulmonary artery, and 

 on the other with branches of the pulmonary vein. 

 The branches of the bronchial artery belong to the 



Fig. 129. Networks of Capillary Blood-vessels 

 surrounding the Alveoli of the Human Lung. 

 (Kolliker.) 



