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Henry Gray (1825–1861).  Anatomy of the Human Body.  1918.
 
exists behind the sternum and rib cartilages, where the anterior thin margin of the lung falls short of the line of pleural reflection, and where the slit-like cavity between the two layers of pleura forms what is called the costomediastinal sinus.
  The line along which the right pleura is reflected from the chest-wall to the diaphragm starts in front, immediately below the seventh sternocostal joint, and runs downward and backward behind the seventh costal cartilage so as to cross the tenth rib in the mid-axillary line, from which it is prolonged to the spinous process of the twelfth thoracic vertebra. The reflection of the left pleura follows at first the ascending part of the sixth costal cartilage, and in the rest of its course is slightly lower than that of the right side.
  The free surface of the pleura is smooth, polished, and moistened by a serous fluid; its attached surface is intimately adherent to the lung, and to the pulmonary vessels as they emerge from the pericardium; it is also adherent to the upper surface of the diaphragm: throughout the rest of its extent it is easily separable from the adjacent parts.
  The right pleural sac is shorter, wider, and reaches higher in the neck than the left.

Pulmonary Ligament (ligamentum pulmonale; ligamentum latum pulmonis).—From the above description it will be seen that the root of the lung is covered in front, above, and behind by pleura, and that at its lower border the investing layers come into contact. Here they form a sort of mesenteric fold, the pulmonary ligament, which extends between the lower part of the mediastinal surface of the lung and the pericardium. Just above the diaphragm the ligament ends in a free falciform border. It serves to retain the lower part of the lung in position.

Structure of Pleura.—Like other serous membranes, the pleura is covered by a single layer of flattened, nucleated cells, united at their edges by cement substance. These cells are modified connective-tissue corpuscles, and rest on a basement membrane. Beneath the basement membrane there are net-works of yellow elastic and white fibers, imbedded in ground substance which also contains connective-tissue cells. Bloodvessels, lymphatics, and nerves are distributed in the substance of the pleura.

Vessels and Nerves.—The arteries of the pleura are derived from the intercostal, internal mammary, musculophrenic, thymic, pericardiac, and bronchial vessels. The veins correspond to the arteries. The lymphatics are described on page 719. The nerves are derived from the phrenic and sympathetic (Luschka). Kölliker states that nerves accompany the ramifications of the bronchial arteries in the pulmonary pleura.
 
1d. The Mediastinum
 
  
(Interpleural Space)


The mediastinum lies between the right and left pleuræ in and near the median sagittal plane of the chest. It extends from the sternum in front to the vertebral column behind, and contains all the thoracic viscera excepting the lungs. It may be divided for purposes of description into two parts: an upper portion, above the upper level of the pericardium, which is named the superior mediastinum; and a lower portion, below the upper level of the pericardium. This lower portion is again subdivided into three parts, viz., that in front of the pericardium, the anterior mediastinum; that containing the pericardium and its contents, the middle mediastinum; and that behind the pericardium, the posterior mediastinum.
  The Superior Mediastinum (Fig. 967) is that portion of the interpleural space which lies between the manubrium sterni in front, and the upper thoracic vertebræ behind. It is bounded below by a slightly oblique plane passing backward from the junction of the manubrium and body of the sternum to the lower part of the body of the fourth thoracic vertebra, and laterally by the pleuræ. It contains the origins of the Sternohyoidei and Sternothyreoidei and the lower ends of the Longi colli; the aortic arch; the innominate artery and the thoracic portions of the left common carotid and the left subclavian arteries; the innominate veins

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