156 THE RESPIRATORY SYSTEM 



unite to form small veins of the pulmonary venous system. In a 

 section of a lung, the branches of the pulmonary vein are somewhat 

 distant from a bronchiole. The pulmonary venous system carries 

 to the left auricle blood partially depleted of carbon dioxide and 

 enriched with oxygen to be distributed to all organs and tissues. 



The lungs are innervated by branches of the sympathetic and 

 vagus (tenth cranial) nerve. The abundant supply of smooth 

 muscle and elastic tissue present play an important part in the 

 recurring movements of inspiration and expiration. In addition 

 to these are the muscular diaphragm and the intercostal muscles 

 which play a role in these movements. 



Before birth the lung resembles a compound tubulo-alveolar gland, 

 the terminal pieces being lined with cuboidal epithelium. At birth, 

 the contact of the air with the body usually- acts as a stimulus to 

 start up the series of inspirations and expirations that continue 

 until death. With the first few inspirations, the inspired air fills 

 and expands the lungs and the cuboidal cells of the terminal pieces 



are flattened. 



REFERENCES. 



Bremer, J. L. 1932. Accessory bronchi in embryos; their occurrence and 



probable fate, Anat. Rec, 54, 361. 

 JossELYN, L. E. 1935. The nature of the pulmonary alveolar lining, Anat. 



Rec.,' 62, 147. 

 Macklin, C. C. 1929. The musculature of the bronchi and lungs, Physiol. 



Rec.,' 9, 1. 

 Olkon, D. M., and Joannides, M. 1930. Capillaroscopic appearance of the 



pulmonary alveoli in the hving dog, Anat. Rec, 45, 121. 

 RoTHLEY, H. 1930. Ueber den feineren Bau der Luftrohre und der Lunge 



der Reptilien, Ztschr. f. wissensch. Biol., 20, 1. 

 Stewart, F. W. 1923. An histogenic study of the respiratory epithelium, 



Anat. Rec, 25, 181. 

 WiSLOCKi, G. B. 1935. The lungs of the Manatee (Trichechus latu-ostris) 



compared with those of other aciuatic mammals, Biol. Bull., 68, 385. 



See Appendix for general text references. 



