208 PRACTICAL ANATOMY. 



What is the relation of the visceral and parietal pleune at t/ie roof of tlic lung f 

 They are continuous, since the pleura is an invaginated sac. (Fig. 146.) 

 Name the three structures produced by a simple invagination of the pleura. 



1. The visceral layer, or the pars pleurae invaginata pleura pulmonis. 



2. The parietal layer, or the pars pleura costalis parietal pleura. 



3. The space between the two layers, the pleural cavity. 

 What are the grand divisions of the parietal pleura f 



The diaphragmatic, the mediastinal, the external or costal. The diaphrag- 

 matic rest on the diaphragm ; the costal on the ribs and internal intercostal mus- 

 cles ; the mediastinal is in relation with the contents of the mediastinum. 



Has the upper extremity of the pleura pulmonis any important relations / 



Yes ; it extends an inch above the first rib, and is in relation to the sub- 

 clavian vessels, which lie in front and internal to the apex of the pleura. 



Is there any special provision made for strengthening- or protecting that part of 

 the dome of the pleura that projects abm>e the first rib ? 



Yes ; there is a heavy layer of subpleural connective tissue, called Sibson's 

 fascia, that descends from the scaleni muscles to the first rib and gives strength 

 to the dome. 



HOIV is the root of each lung secured to tJie diaphragm f 



By a fold of pleura called the ligamentum latum pulmonis. 



Name the geometrical parts of the lung. 



The apex, base, outer surface, inner surface, posterior border, anterior border, 

 and pulmonary root. 



What is the inner surface of the lung ? 



That part in contact with the mediastinum and pericardium ; it is concave. 



Where is the base of the lung and what is its shape f 



It is in contact with the diaphragm ; it is concave. 



What can you say about the anterior border of the lung ? 



It is sharp and thin, and separates the external from the inner border. The 

 posterior border is thick and round, and occupies the deep groove on each side 

 of the vertebral column. 



Is there any provision made for possible physiological increase of breathing- 

 space in the pleural spaces ? 



Yes ; the same principle is here seen as is observed in the tortuous arteries of 

 some localities a condition apparently foreseen to meet an emergency. The 

 lung, under ordinary conditions of man, is less extensive than the pleural sacs. 

 The parietal pleura is really tortuous in the region of the anterior border of the 

 lung. The emergency that would take the kinks out of this pleura would be 

 physical training, where wind is the prime desideratum, as in pugilistic mills. 

 The same principle is seen in a pregnant uterus, reducing the tortuosity of uter- 

 ine arteries. 



THE MEDIASTINAL SPACES. 



1. Anterior Is the space between the heart and sternum. 



2. Middle Is the space occupied by the heart and its root structures. 



3. l\>stcrior Is the space behind the heart. 



The Contents of the Anterior Mediastinal Space : 



1. The remains of tlic thy inns gland a fu-tal structure. 



2. The left bracJno-ccplictlic or left innominate rein. 



3. The internal mammary artery and its companion veins. 



4. The nearly obsolete triangnlaris sterni muscle. 



5. The origin of the sterno-hyoid and sterno-tltyroid muscles. 



6. The large amount of connective /issue you noticed when you opened the 

 thorax. 



