HISTORY. 



" We gaze around ; 



We read their movements ; we sigh; and w] ile 

 We sigh, we sink, and are what we deplored." Youo. 



of the lungs. The blood is 

 raised into the kings by 

 one set of tubes or vessels 

 termed arteries, and passes 

 back by another set of vessels 

 termed veins. When the ribs 

 are raised and the floor of 

 the chest drawn down by the 

 muscles of inspiration, the walls of the chest fall in, or when they 

 are brought nearer together by the muscles of expiration, the due 

 proportion of air and blood is, by gentle pressure, sent out from 

 the interior of the lungs. A firm and elastic membrane lines ths 

 inside of the chest, and the same membrane passing back, covers 

 in the lungs, forming their outer coat. By this doubling of the 

 membrane, the lungs without being attached except at their roots, 

 where the lobes enter, are held by their own elastic action in clou* 

 contiguity to tfee chest, and thus they move freely with itn 

 movements. 



83. The right lung is divided into three parts or lobes; the left lung is divide*. 



into two lobes, between which is a 

 space where the point of the heart 

 lies. Each lung is contained in & 

 email membranous bag called the 

 pleura, and the air-vessels whiA 

 are connected with the windpipe, 

 through which we breatiie, run. 

 along between the blood-vessels in 

 the lungs, and so give to them 

 that quantity of air which is re- 

 quired to change the colour of the 

 blood and to render it fit for ir- 

 eulatiou. The accompanying en- 

 graving will serve to illustrate 

 the structure and position oft-h 

 lungs ; in the centre is a membrane 

 which divides the chest. The ribs 

 are cut ofl, so as to show the in- 

 Bide of the chest. The diaphragm 

 which divides the chest from the 

 has been removed. Th* 



