58 THE LUNGS, BY FRANZ EILHARD SCHULZE. 



and in the longitudinal folds that are here present. The 

 internal epithelial investment at first consists of ciliated epi- 

 thelial cells with interspersed cup cells, similar to those with 

 which we are already familiar in the larger bronchia. But 

 as the termination of the smallest bronchia is approximated, 

 the epithelial cells gradually become lower, so that after a 

 little while their height does not materially exceed their 

 breadth, and they may even ultimately assume a flattened form. 

 Near the point of transition of the bronchia into the alveolar 

 passages the cells lose their cilia, and the cup cells cease to 

 appear. 



The nutrition of the bronchia is effected by means of capil- 

 lary plexuses, the meshes of which are irregularly arranged in 

 the outer fibrous layer, circularly in the muscular, and longi- 

 tudinally in the internal fibrous layer. The supply of blood 

 is chiefly derived from the branches of the bronchial artery 

 distributed in the adventitia and external fibrous layer ; the 

 ultimate bronchia only receiving here and there branches 

 from the pulmonary artery, the capillaries of which anastomose 

 with those of the bronchial arteries. The blood that has 

 become venous in the capillary plexuses on the walls of the 

 larger bronchia, alone enters the corresponding bronchial vein 

 running towards the root of the lung ; that of the smaller 

 bronchia flows directly into the pulmonary veins. 



Lymphatic vessels are abundant, especially upon the inter- 

 nal layer of the bronchia, the internal fibrous investment of 

 which they traverse to pass towards the roots of the lung, 

 where they enter the lymphatic glands that are there 

 situated. 



Small scattered ganglia that were first discovered by Eemak, 

 are found in the course of the nerves proceeding from the 

 plexus pulmonalis, which ramify upon the bronchia, and are 

 in great measure destined for the supply of the smooth 

 muscular tissue that is here so abundantly present. 



The structural characters of the alveolar tissue of the 

 lungs of all Mammals are, like their bronchia, essentially 

 similar. 



The lateral walls of the contiguous alveoli of one and the same 

 infundibulum or alveolar passage, uniformly coalesce to form thin 



