342 



TEXT-BOOK OF PHYSIOLOGY. 



13 



from the bodies of theJJEsLjhlge or fouj^lumbar vertebrae and neigh- 

 boring fascia, from the border of the six lower ri^s^SSTPOnrthe 

 ensiform cartilagefrFTg. 165). From this extensive origin the muscle- 

 h tiers "pass centrally to be inserted into a common tendon. As the 

 direction of the fibers is from below upward and inward, the dia- 

 phragm is somewhat dome-shaped. Its inferior border is for a short 



distance in con- 

 tact with the 

 sides of the 

 thorax, y As a 

 result of the 

 complete closure 

 of both the su- 

 perior and infe- 

 rior openings of 

 the thorax, its 

 cavity is abso,-, 

 lutely air-tight.// 

 The pleurae. 

 Each lung is 

 surrounded by a 

 closed invagin- 



FIG. 165. DIAPHRAGM, INFERIOR ASPECT, i. Anterior and ated serous sac, 

 middle leaflet of central tendon. 2. Right leaflet. 3. 

 Left leaflet. 4. Right cms. 5. Left crus. 6, 6. In- 

 teryals for phrenic nerves. 7. Muscular fibers, from 

 which the ligamenta arcuata originate. 8. Muscular fi- 

 bers that arise from the inner surface of the six lower ribs, 

 p. Fibers that arise from ensiform cartilage. 10. Open- 

 ing for inferior vena cava. n. Opening for esophagus. 

 12. Aortic opening. 13, 13. Upper portion of trans- 

 versalis abdominis, turned upward and outward. 14. 

 Anterior leaflet of trans versalis aponeurosis. 15, 15. 

 Quadratus lumborum. 16, 16. Psoas magnus. 17. 

 Third lumbar vertebra. 



15 



the pleura, of 

 which the inner 

 portion is re- 

 flected over and 

 is closely adher- 

 ent to the sur- 

 face of the entire 

 lung as far as its 

 root; the outer 



portion is re- 

 flected over the inner wall of the thorax, the superior surface of the 

 diaphragm, and the viscera of the mediastinum. Under normal 

 conditions these two layers of the pleura, the visceral and parietal, 

 are in contact, or at most separated only by a thin capillary layer of 

 lymph. The presence of this fluid prevents friction as the two 

 surfaces play against each other in consequence of the movements 

 of the lungs. 



THE MECHANIC MOVEMENTS OF THE THORAX. 



The blood receives oxygen from, and yields carbon dioxid to, the 

 alveoh of the lungs, as it flows through the pulmonary capillaries. 



