LUNGS. 



LtTNOa 



*.. 



r | ( ipinal column ; 2, rib ; 3, cartilages of ribs ; 4, sternum. 



by the diaphragm, a large muscle represented in /</. 3 whom form mny 

 be roughly compared to that of the expanded part of an umbrella 



UM thorax ; 2, portion of catUjr of the abdomen ; 3, lateral or 

 portion* of the diaphragm ; 4, central or tcmlinoui portion of the 



iU concavity downward*. The diaphragm forma a moveable 

 the. cavity of the chart and that of the abdomen, 

 permitting only the panage of certain TMM!*, Ac., from the one to 

 m other. By it* alternate contraction* and relaxation* it increases 

 awl diminubei the capacity of the chad 



The ipaoe* between the Mveral ribs are filled by the intercostal 

 mtucUc, of which two are nrpraented in fg. 4. Between each 

 two rib* there are two layer" of mtucle, the fibres of each of which 

 croat thoM of the other. The fibre* of the outer layer, which 

 are raunnuUJ between the two upper rib* in the annexed figure, 

 paw obliquely from above downward*, and from behind forward*; 

 thoee of the Inner layer, here drawn between the two lower rib*, paat 

 with a similar obliquity from before backward*. 



The upper aperture of the chest between the pine, firrt rib*, and 

 Hernum (*y. 2) in that at which the trachea paaee* into the chert to 

 the lung*, and at which the great artcrien of the head, neck, and arm* 

 paw out of the chert from the aorta. The space* left between them 

 and the bone* are occupied by the ouophagna, by certain muwle* and 

 by the great rein* of the upper part of the body, and by 

 . 



The whole chert thn* form* a cavity cloeed on all tidea, but per- 

 itting the pwMg) of certain tube* (the trachr*, conophagn*, Wood- 



mitting 



Tonnoln, 4c.) through iU walla. Thin cavity contains within it three 

 subordinate cavities ; the middle one contains the heart in the peri- 

 cardium, and each of the two at the aide* contains one of the lung* 

 These are called the pleura! cavities. 



Flf. 4. 



Each lung is as it were hung into the cavity appropriated to it by 

 its bronchus and by the trunks of its pulmonary artery and veins, 

 which, inclosed together by cellular tissue, form what is called the 

 root of the lung. The lung exactly fills the cavity in which it is 

 placed, BO that their surfaces are everywhere in contact, or separated 

 only by the very small quantity of fluid necessary to keep them suf- 

 ficiently slippery to move upon each other without difficulty. For 

 the sake of more easy motion, the wall of the cavity is lined and the 

 surface of the lung is covered by a fine smooth membrane, the pleura, 

 which is arranged like other serous membranes [MEMBRANES], that 

 is, having lined the cavity, it is reflected upon the root of the lung, 

 and then passes over its surface and those of its great divisions 

 or lobes. 



Fisr. 5. 



l.traolica; J, right lung ; 3, left lung; 4, fluurc* dividing each lung into 

 large portion* (5) In med lube* ; 8, mailer dlriiloni termed lobule* ; 7, ] ii. 

 cardium; 8, heart ; 9, aorta; 1 0, diaphragm ntparating tlic cavity of the thorax 

 from that of the abdomen. 



The plcural cavities are completely closed on all side*, so that no 

 air can enter them, but the lung in each communicates with tin- 

 external air by its bronchus, which lead* to the trachea anil larynx ; 

 and hence, when the chest is enlarged by the contraction of the 

 diaphragm, the elevation of the ribs, &<., the air passes not into the 

 cavity of the chest, but through the windpipe into the interior of the 

 lung. It in as if one had a pair of bellow* with the valve closed, and 

 the tube of the n-i/.zlr opening, not as it usually docs, into all the 



