'Chap. -2 2.] 'The Lungs. 235 



the thorax being thus feparated, one may be wounded, 

 without impeding the functions of the other. 



The lungs fill the two faoks of the pleura, one of 

 which is placed on each fide of the mediaftimim. With 

 refpect to the form of the lungs, their bafes are broad, 

 and their fummits form an obtufe cone. Their ante- 

 rior furfaces, and thofe applied to the mediaftmum, are 

 flat, that next the ribs is fomewhat convex, and that 

 behind round. The lower part of the left lung is 

 excavated to make room for the heart. The colour 

 of the lungs is in infants reddifh, in adults greyifh, and 

 in old age they verge towards dark blue or black ; their 

 furface is ufually mottled. 



The lungs are connected above to the neck by 

 means of the windpipe, and below by blood- veflels to 

 the .heart. They have no other covering but the 

 pleura, connected to them by the intervention of thin 

 cellular fubftance, which in this part is always free 

 from fat. 



With refpect to the ftructure of the lungs, the right, 

 which is larger, confifts of three lobes, the left only 

 of two ; all of thefe are fubdivided into a number of 

 fmaller lobes called lobules. Thefe divifions are con- 

 nected to each other by the intervention of cellular 

 fubftance. The fubftance of the lungs is ultimately 

 made up of minute veficles, called the air-vefTels of 

 the lungs, which are the terminal: ions of the wind- 

 pipe. 



Thefe veficles have extremely thin coats, and on 

 thefe coats are diftributed the minute ramifications of 

 the blood-vefiels which go to the lungs. It has been 

 computed, from the extreme minutenefs of the air- 

 veffelsj that the internal furface of the lungs is not left 

 extenlive than the floor of a moderate fized fitting 

 room, Thefe air- veffels communicate with each other 



through 



