648 



RESPIRATORY AND BUOYANCY SYSTEMS 



■ PMARVNGEAL 



LOWER LOBE 



Fig. 309. Lung development in the mammal. (A-F modified from Flint, '06; G modi- 

 fied from Maximow and Bloom, '42, A Textbook of Histology, Philadelphia, Saunders.) 

 (A-F) Development of the bronchial tree in the pig. (G) Terminal respiratory relation- 

 ships in the human lung. Respiratory bronchioles arise from terminal divisions of the 

 terminal bronchiole; from the respiratory bronchiole arise the alveolar ducts which may 

 terminate in spaces, the atria; from the atrium the alveolar sacs arise; and the side walls 

 of each alveolar sac contain the terminal air sacs or alveoli. 



provide buoyancy but effect a more thorough utilization of the available air 

 by the respiratory areas of the lungs. That is, all the air passing through the 

 respiratory parts of the lung is active, moving air. (See Locy and Larsell, 16b, 

 pp. 42-43; Goodrich, '30, pp. 600-607.) 



4) Trachea, Voice Box, and Ultimate Position of the Bird's Lung in the 

 Body. The trachea of the bird's lung is an elongated structure, reinforced by 

 cartilage rings or plates in the tracheal wall. The voice box of the bird is de- 

 veloped at the base of the trachea in the area of the tracheal division into the 



