340 PHYSIOLOGY. 



white. Its epithelium is of the ciliated columnar form. The vibra- 

 tory movement of the cilia being directed upward removes dust 

 from the lungs. Minute glands of the racemose variety, which open 

 upon the surface, are found in the trachea and bronchi. The nerves 

 supplying the trachea and lungs are the pneumogastric and the 

 sympathetic. 



The Lungs are in the thorax, one on each side, separated by the 

 heart and the large blood-vessels. In the constantly changing 

 diameters of the chest they accurately fill the chest which contains 

 them. They are free, and attached only by their roots. They are 

 closely invested with a serous membrane, the pleura. The root of 

 the lung is placed near its middle internally, and consists of the 

 bronchus, the pulmonary arteries and the veins, the blood-vessels of 

 the bronchia, nerves, and lymphatics, all invested with a reflection 

 of pleura. The right lung has its root behind the superior vena 

 cava. The root of the left lung lies partly beneath the arch of and 

 partly in front of the descending portion of the aorta. In the root 

 of the right lung the bronchus is the highest; in the root of the 

 left lung the pulmonary artery is the highest. The bronchi, before 

 entering a depression at the root of the lungs, the hilus, subdivide, 

 the right into three branches, the left into two, corresponding to the 

 number of lobes in each lung. Each lung is conical, with a broad, 

 concave crest resting on the diaphragm and a rounded apex standing 

 above the level of the first rib into the neck. Its outer surface is 

 convex and its inner surface is concave and faces the heart. 



The weight and the capacity of the lungs vary according to 

 many conditions. Their average weight is about two and one-half 

 pounds and their total capacity three hundred cubic inches. Their 

 long diameter is the greatest and deepest on the posterior surface. 

 The right lung is shorter than the left, but wider and of somewhat 

 greater bulk. The right lung has three lobes, of which the middle 

 one is the smallest and the lowest one the largest. The left lung 

 has two lobes, of which the lower is the larger. Between the lobes 

 of the left lung in front there exists a large angular notch, corres- 

 ponding with the position at which the impulse of the heart is felt 

 against the walls of the chest. 



Normal lung-tissue always shows a specific gravity less than that 

 of water; consequently it will float when thrown into water. No 

 other tissue does this. However, should lung-tissue in which con- 

 solidation has resulted from some disease or the lung-tissue from a 

 child that has never breathed be thus tried, it will sink like other 



