116 SURGICAL ANATOMY OF 



A wound penetrating the sternum, on a line with the 

 nipple, and striking upon the vertebra at right angles 

 with the axis of the body, would traverse three cavities 

 of the heart, two ventricles, and the left auricle. 



If an instrument traversed the lower intercostal spaces 

 during inspiration, it would wound the base of the lung, 

 the diaphragm, and corresponding abdominal viscera, 

 but during expiration would avoid the lung. 



Spinal Region of Thorax. The posterior wall of the 

 thorax is formed by the dorsal spine and its coverings, 

 and is represented by a region bounded superiorly by 

 the first, and inferiorly by the last dorsal vertebra, and 

 laterally by the angles of the ribs. 



The integument is very thick and dense, and con- 

 tains a quantity of sebaceous follicles ; the subcutaneous 

 cellular tissue is intimately united to the spinous pro- 

 cesses of the dorsal vertebra (which can be plainly felt 

 throughout the region), thus preventing fluid infiltrat- 

 ing or pus appearing superficially, except along the 

 sides of these processes. The dorsal aponeurosis in- 

 vests the anterior and posterior surfaces of the trapezius 

 and latissimus dorsi, uniting superiorly with the cervi- 

 cal, and inferiorly with the lumbar aponeurosis, split- 

 ting to inclose the serrati postici ; it is attached to the 

 spinous processes of the dorsal vertebrae and tubercles 

 of the ribs, inclosing all the muscles of the back, and 

 separating the superficial from the deep layer. The 

 first layer of muscles consists of the lower part of the 

 trapezius and the latissimus dorsi, the former overlap- 

 ping the latter. Beneath these muscles lie the rhom- 

 boidei and serrati postici. The deep layer consists of 

 the sacro-lumbalis internally with its necessary muscles, 



