1186 



THE ORGANS OF VOICE AND RESPIRATION 



TOPHRENIC 

 NUS 



border of the transverse process of the seventh cervical vertebra. This is covered 

 and strengthened by a few spreading muscular fibres derived from the Scaleni. 



In the front of the thorax, where the parietal layer of the pleura is reflected 

 backward to the pericardium, the two pleura! sacs are in contact for a short dis- 

 tance (Fig. 909). At the upper part of the thorax, behind the manubrium, they 

 are not in contact, the point of reflection being represented by a line drawn from the 

 sternoclavicular articulation to the midpoint of the junction of the manubrium 

 with the body of the sternum. From this point the two pleurae descend in close 

 contact to the level of the fourth costal cartilages, and the line of reflection on 

 the right side is continued downward in nearly a straight line to the lower end of 

 the gladiolus, and then turns outward, while on the left side the line of reflection 

 diverges outward and is continued downward, close to the left border of the sternum 

 as far as the sixth costal cartilage. The inferior limit of the pleura is on a con- 

 siderably lower level than the corresponding 

 limit of the lung, but does not extend to the 

 attachment of the Diaphragm, so that below 

 the line of reflection of the pleura from the 

 thoracic wall on to the Diaphragm the latter 

 is in direct contact with the rib cartilages and 

 the Internal intercostal muscles. In ordinary 

 inspiration the thin margin of the base of the 

 lung does not extend as low as the line of 

 pleural reflection, with the result that the costal 

 and diaphragmatic pleura are here in contact, 

 the narrow slit between the two being termed 

 the costophrenic sinus (sinus phrenicocostalis) 

 (Fig. 900). A similar condition 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 sometimes called the costome- 

 diastinal sinus (sinus costomediastinalis^). 



The line along which the right pleura is re- 

 flected from the thoracic wall to the Diaphragm 

 starts in front, immediately below the seventh 

 costosternal joint, and runs downward and 

 backward behind the seventh costal cartilage 

 FIG. goo. Section of the wall of the so as to cross the tenth rib in the mid-axillary 



thorax, showing the phrenicocostal sinus. . ... , . * 



(Poirier and charpy.) line, from which it is prolonged to the spine 



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 higher 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 surface of 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 some- 

 what thicker, and may be separated from the adjacent parts with extreme facility. 



The right pleural sac is shorter, wider, and reaches higher in the neck than 

 the left. 



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 the pleura, and that 

 at its lower border the investing layers come into contact. Here they form a sort of 

 mesenteric fold, the ligamentum latum pulmonis (licj. pulmonale), which extends 



