THE BACK. 25 



which would be between the eleventh and twelfth ribs. The 

 ball might be extracted here. The chest might also be 

 tapped here, but not with a trochar, since a trochar would 

 penetrate both layers of pleura, and go through the diaphragm 

 into the abdomen. 



The operation should be done cautiously, by an incision 

 beginning about two inches from the spine, on the outer 

 border of the ' erector spinae,' on a level between the spines 

 of the eleventh and twelfth dorsal vertebrae. The intercostal 

 artery will not be injured if the opening be made below the 

 middle of the space, which is very wide. 3 



THE BACK. 



48. Median furrow. In a muscular man, a furrow, 

 caused by the prominence of the erector spinae on each side, 

 runs down the middle of the back. The lower end of the 

 furrow corresponds with the interval between the spine of the 

 last lumbar and that of the first sacral vertebra. 



49. Spines of vertebrae. A little friction with the fin- 

 gers down the backbone will cause the spines of the vertebrae 

 to be tipped with red, so that they can be easily counted, 

 and any deviation from the straight line detected. Still it is 

 worth remembering that the spine of the third dorsal is on a 

 level with the commencement of the spine of the scapula 

 that the spine of the seventh dorsal is on a level with the 

 inferior angle of the scapula that the spine of the last dorsal 

 is on a level with the head of the last rib. 



Division of the trachea. The division of the trachea 

 is opposite the spine of the third, in some cases the fourth, 

 dorsal vertebra. In front this division is on the level of the 

 junction of the first with the second bone of the sternum. 



The root of the spine of the scapula is marked by a slight 

 dimple in the skin. This is on a level with the third inter- 

 costal space. A stethoscope placed on the inner side of this 

 dimple would cover the bronchus, more especially the right, 

 since it is nearer to the chest wall. 



