BACK AND POSTERIOR CERVICAL REGION. 125 



of the heart making the concavity of the left lung the 

 greatest. The anterior border is sharp, and the posterior 

 rounded. Each lung is divided into an upper and lower 

 lobe by a deep fissure, the upper lobe of the right side 

 being subdivided by a more shallow fissure, thus making 

 a third, or middle lobe. The lobes are sometimes multi- 

 plied, and offer great variety in shape. The lungs vary in 

 color, according to age, or their more or less healthy state ; 

 usually, they are of a grayish tint, mottled with blackish 

 spots. The sitrface is figured with irregular polygonal 

 outlines, indicating the lobules of which they are made 

 up, and these lobules are subdivided by still smaller lines 

 which are the walls of the cells that compose them ; the 

 lobules are best seen in infant's lungs, or in those of very 

 young persons. When cut into, the lungs are found to be 

 of a spongy texture, and if in a natural state, upon pres- 

 sure, the air may be felt escaping in fine bubbles from the 

 air-cells, giving the sensation called crepitation. 



The lung is made up of the various structures which enter 

 it at its root. The bronchi may be traced by a director and 

 scissors, dividing into principal trunks for each lobe, and 

 then subdividing, until lost by their extreme tenuity ; the 

 cartilaginous rings which were found at their commence- 

 ment, becoming less and less apparent. 



At the divided root of the lungs, the bronchus is poste- 

 rior, and the pulmonary veins anterior, the pulmonary 

 artery being between the two. In the direction from above 

 downward, the position on the right side is bronchus, pul- 

 monary artery, and pulmonary veins ; but, on the left side, 

 it is changed to the order artery, bronchus, and veins. 



DISSECTION V. 



THE BACK AND POSTERIOR CERVICAL REGION. 



The dissection of the back comes next in order, but if the other 

 members of the class are not ready to turn the subject over, the dis- 

 section of the arm may be resumed, the description of which will be 

 found in Dissection VII. 



The subject must be turned upon its face, and rest upon blocks as 

 before ; the head should hang over the end of the table, and the arms 

 over its sides ; by so doing, the muscles will be put upon the stretch. 

 A longitudinal incision is to be made along the median line, from the 



11* 



