THE PULMONARY BLOOD-VESSELS. 99 



4. The external layer, (a) Its extent. (It includes the remain- 

 der of the section.) (b) Large cartilage plates, C, stained blue. 



(c) Cartilage cells. (Note their differing forms and disposition in 

 rows next the surfaces of the plates. ) (d) Periosteum, stained pink. 

 (e) Mucous gland coils. (They are usually between the cartilage 

 and the muscular coat, (f) Section of bronchial arteries and 

 veins, (g) Collections of adipose tissue on the outer surface, (h) 

 Portion or whole of pulmonary artery and medullated nerve 

 trunks outside of and accompanying the bronchus. (They do not 

 appear in the illustration.) 



(H.) 



5. Epithelial lining, (a) Cilia of columnar cells, (b) The 

 ovoid cells between the tapering columnar cells, (c) The round 

 cells, "basement membrane," upon which the columnar cells rest. 



(d) The goblet or Weaker cells. 



6. The mucosa. (a) The reticulum of the adenoid tissue. 

 (Will appear only where the lymph corpuscles have been accidentally 

 brushed out.) (b) The transversely divided ends of the elastic 

 fibres. (They appear as a pink mosaic.) (c) Capillaries. (They 

 may frequently be traced for a considerable distance in their tortuous 

 course.) 



7. The cartilage plates, (a) Several cells in a single cavity. 

 (b) The intracellular network. 



8. The mucous glands, (a) That some of the cells are stained 

 precisely like the (other) mucous cells, the beakers, (b) If possible, 

 a gland tube leading up to the lumen of the bronchus. (An am- 

 pulliform dilatation is shown in the upper part of the drawing.) 



THE PULMONAEY BLOOD-VESSELS. 



The prominent accompaniments of the bronchus, at the root of 

 the lung, are the pulmonary artery (carrying venous blood) and the 

 pulmonary veins. 



The pulmonary artery enters the lung with the bronchus, following 

 in its ramifications, to end in capillary plexuses in the wall of the sac- 

 like dilatations, which are in connection with the ultimate bronchi. 

 The blood is then collected in venules, which unite to form the pul- 

 monary veins. The latter pursue an independent course in their exit, 

 not accompanying the bronchi until the root of the lung (nearly) has 

 been reached. 



The bronchial artery (nutrient) enters with the bronchus, supplying 

 its walls and the connective-tissue framework of the lung. 



