152 SURGICAL APPLIED ANATOMY. [Chap. x. 



space be selected there is great danger of wounding 

 the diaphragm, especially upon the right side. The 

 trochar should be entered during inspiration, the space 

 being widened thereby, and should be kept as near as 

 possible to the lower border of the space, so as to 

 avoid the intercostal vessels. Tapping of the chest 

 through any space posterior to the angles of the ribs 

 is not practicable, owing to the thick covering of 

 muscles upon the thoracic wall in this place, and the 

 fact that the intercostal artery, having a more 

 horizontal course than the corresponding ribs, crosses 

 the middle of this part of the space obliquely. Beyond 

 the angle the intercostal vessels lie in a groove on the 

 inferior border of the rib forming the upper boundary 

 of the space. The vein lies immediately above the 

 artery, and the nerve immediately below it. In the 

 upper four or five spaces, however, the nerve is at 

 first higher than the artery. 



Owing to the protection it derives from the ribs 

 and the intercostal muscles, it happens that the inter- 

 costal artery is seldom wounded, and when wounded 

 it will be understood that considerable difficulty is 

 experienced in securing the vessel without doing 

 damage to the pleura and adjacent parts. 



Pus may readily be conducted along the loose 

 tissue between the two layers of intercostal muscles. 

 Thus, in suppuration following upon disease of the 

 transverse processes or bodies of the vertebrae, or of the 

 posterior parts of the ribs, the pus may be conducted 

 along the intercostal spaces to the sternum, and may 

 thus present at a considerable distance from the real 

 seat of the disease. 



The internal mammary artery runs parallel 

 to the border of the sternum, and about half an inch 

 from it. It may give rise to rapidly fatal haemorrhage 

 if wounded. The vessel may readily be secured in the 

 first three intercostal spaces, and with some difficulty 



