THE LUNGS. 171 



Laterally, with the 



Common Carotid Arteries. Recurrent Laryngeal Nerves. 



Thyroid Gland. Pleurae. 



Inferior Thyroid Arteries. Pneumogastric Nerves. 



Describe the Bronchi. They are two tubes similar in formation to the 

 trachea, extending from its bifurcation into the lungs, where they divide and sub- 

 divide into bronchial tubes, losing their rings at the 2d or 3d subdivision, whence 

 plates of cartilage extend in their walls to their minuter ramifications. The 

 Right Bronchus, is the widest, and the most horizontal, about I inch long, 

 has 6 to 8 rings, and divides into 2 main divisions (though its lung has 

 3 lobes). 



Left Bronchus, -is the narrowest and most oblique, nearly 2 inches long, 

 has 9 to 12 rings, and divides into 3 main divisions (though its lung has 

 2 lobes). 



What are the Relations of the Bronchi ? Beginning opposite the 3d 

 dorsal vertebra, the right bronchus enters the lung opposite the 4th dorsal 

 vertebra, the left bronchus opposite the 5th. The Right Bronchus lies behind 

 the vena cava superior and the right auricle of the heart, having the right pul- 

 monary artery at first below, then anterior to it, and the vena azygos major 

 arching over it from behind forwards. The Left Bronchus passes beneath the 

 arch of the aorta and in front of its descending portion, also in front of the 

 oesophagus and the thoracic duct, having the left pulmonary artery above and 

 in front of it. 



Name the Vessels and Nerves of the Trachea and Bronchi. 

 Arteries, Tracheal Branches of the inferior thyroid (br. of thyroid axis), and 



the Bronchial (brs. of thoracic aorta). 



Veins, open into the thyroid plexus and the bronchial veins. 

 Lymphatics, terminate in the mediastinal glands. 



Nerves, are derived from the pneumogastric and its recurrent laryngeal 

 branch, also from the sympathetic. 



THE LUNGS. 



Describe the Lungs. The lungs are the two essential organs of respiration, 

 contained in the cavity of the thorax, covered by the pleurae, and characterized 

 by lightness (sp. gr. 0.345 to 0.746), sponginess, elasticity, and crepitation when 

 pressed. They weigh together about 42 ounces, the right lung being the heaviest 

 by about 2 ounces. At birth their color is a pinkish-white, mottled as age ad- 

 vances by slate colored patches, from the deposit of carbonaceous granules in 

 the areolar tissue of the organ. The Right Lung is the largest and has 3 lobes; 

 the Left Lung has 2 lobes. Each lung presents for examination an 



