522 COLOR OF THE LUNGS. 



artery are rather above and before, and the veins below and 

 before them. 



Each of these vessels ramifies before it enters into the 

 substance of the lungs : the bronchia and the branches of the 

 pulmonary artery send each a large branch downwards to the 

 inferior part of the lungs, from which the lower pulmonary 

 veins pass in a direction nearly horizontal. In general, each 

 of the smaller ramifications of the bronchia in the lungs is 

 attended by an artery and a vein. 



Each lung is divided, by very deep fissures, into portions 

 which are called Lobes. The right lung is -composed of three 

 of these lobes, and the left lung of two. (See fig. 128, page 

 515.) 



Each of these lobes are subdivided into many smaller parts 

 called lobules, which are marked out on the surface of the lungs, 

 by various angular lines. The left bronchium divides into two 

 principal branches for the lobes of the left lung, and the right 

 into three for the lung of that side ; after which, a still further 

 subdivision takes place, so that a terminal bronchial branch is 

 sent to each lobule. 



The lungs are covered, as has been already stated, with the 

 reflected portion of the pleura continued from the mediastinum, 

 which is very delicate and almost transparent. They have, 

 therefore, a very smooth surface, which is kept moist by exuda- 

 tion from the arteries of the membrane. 



a* The Color of the Lungs is different in different subjects. 

 In children they are of a light red color ; in adults they are 

 often of a light gray, owing to the deposition of a black pig- 

 ment in the substance immediately under the membranes 

 which form their external surface. Their color is often 

 formed by a mixture of red and black. In this case they are 

 more loaded with blood, and the vessels of the internal mem- 

 branes being distended with it, the red color is derived from 

 them. 



The black pigment sometimes appears in round spots of three 

 or four lines in diameter : under the external membrane it is 

 often in much smaller portions, and sometimes is arranged in 



