VOCAL AND RESPIRATORY APPARATUS. 255 



thelium, and surrounded by a minute capillary net-work of 

 blood-vessels, which intervene between the terminal branches of 

 the pulmonary artery and the commencement of the pulmonary 

 veins. Between the cells the capillary net-work forms a single 

 layer. 



The pulmonary artery conveys the venous blood to the lungs 

 and terminates in the capillary net-work about the air-cells, from 

 which proceeds the pulmonary vein, which proceeds along the 

 bronchial tubes to the left auricle of the heart. The bronchial 

 arteries supply the structure of the lungs. They are derived 

 from the aorta, and follow the course of the bronchial tubes, 

 the bronchial veins returning the blood to terminate in the hemi- 

 azygos or superior intercostal vein on the left. 



The lymphatics are numerous and consist of a superficial 

 set converging to the root and a deep set along the course of 

 the tubes, and both enter the bronchial glands. 



The nerves are derived from the anterior and posterior pul- 

 monary plexuses of the pneumogastric and sympathetic, the lat- 

 ter the larger. Ganglia are found upon these nerves. 



THE PLEURA. 



Each lung is invested by a delicate serous membrane, the 

 pleura, which lines the internal wall of the thorax and is reflected 

 at the root of the lung over that organ. It consists essentially 

 of two layers, a parietal, or pleura costalis, and visceral, or pleura 

 pulmonalis. It adheres accurately to the subjacent structures, 

 and is called, from its position, costal, diaphramatic, mediastinal, 

 and pulmonary. The space between the two layers of each 

 pleura, known as the cavity of the pleura, contains a thin, serous 

 secretion. 



A fold extending downward from the root of the lung to 

 the diaphragm forms the so-called pulmonary ligament, or liga- 

 mentum latum pulmonis. 



Kach pleura is a closed sac; the right is wider, shorter, and 

 extends higher in the neck than the left. They do not meet in 

 the median line, except opposite the upper part of the gladiolus, 

 but have a space between them known as the mediastinum. 



The arteries are from the intercostal, bronchial, pericardiac, 

 internal mammary, musculo-phrenic, and thymic. 



The veins accompany the arteries. 



The lymphatics are numerous, and empty into the intercostal 

 and posterior mediastinal glands. 



The nerves are from the phrenic and sympathetic. 



