THE LUNGS. 143 



CHAPTER III. 



OF THE LUNGS. 



THE Lungs (Pulmones) are the essential seat of the process 

 of respiration, and occupy the greater part of the cavity of the 

 thorax, as formed by the ribs and the intercostal muscles on 

 the sides, by the sternum and its cartilages in front, by the dor- 

 sal vertebras behind, and by the diaphragm below. They are 

 two bodies, placed one on either side of the thorax, and separated 

 from each other by the heart and its great vessels. As the 

 heart is the only organ of much volume which is also included 

 in the cavity of the thorax, the size of the lungs is in a direct 

 relation with the capacity of the latter; and may, therefore, 

 be known by external indications in the living body. It is 

 probable that there is no void, or only a very small one, be- 

 tween the sides of the lungs and the sides of the thorax. 



Each lung forms an irregular cone, the apex of which is 

 above, and the base below ; the latter, from resting upon the 

 diaphragm, is, consequently, oblique from before backwards and 

 downwards, and is also concave, /fhe surface which reposes 

 against the periphery of the side of the thorax, is, uniformly, 

 rounded, but that which looks towards its fellow, is concave, 

 from being pressed in by the heart. The vertical diameter of 

 the lung behind, when it is fully distended, goes from the head 

 of the first to that of the last rib, and is, from the oblique di- 

 rection of the diaphragm, consequently, much more considera- 

 ble than the vertical diameter in front, which extends only from 

 the first rib to the inferior end of the second bone of the ster- 

 num, or, in other words, to a level with the tendinous centre of 

 the diaphragm. 



The lungs of the adult are of a light pink colour, with specks 

 or patches of black : in early life there is much less of the lat- 

 ter, and in advanced life it becomes more abundant. 



The left lung is divided into two lobes by a deep fissure, 

 which begins behind, on a level with the fourth dorsal verte- 

 bra, and runs obliquely downwards and forwards to the ante- 



