THE THORACIC WALL. g - 



intercostal arteries without concomitant injuries of the ribs are rare. (2) In resection of a por- 

 tion of a rib, the arteries should be carefully avoided by shelling out the bone from the perios- 

 teum (subperiosteal resection) and exercising great care at the lower costal margin. (3) In 

 opening the pleural cavity the instrument should be introduced in the middle of the intercostal 

 space, avoiding the margin of the rib. (4) In fractures of the rib the artery may occasionally 

 be lacerated; in rare cases the internal intercostal muscles and the pleura may also be torn and 

 a fatal effusion of blood take place into the pleural cavity (hemothorax). (5) It is usually 

 necessary to resect a portion of a rib in order to expose the intercostal artery from without. 



On account of the free anastomosis of the anterior and posterior intercostal arteries, it is 

 possible in compression or stenosis of the thoracic aorta (by tumors, for example) for the blood 

 from the inner surface of the thoracic wall to gain access to the aorta below the site of the com- 

 pression through the dilated internal mammary artery and the anastomoses between the ribs. 



The veins of the thoracic wall consist of those which accompany the arteries and are called 

 by the same names (intercostal veins, Fig. 43) and of the cutaneous veins. The costo-axillary 

 veins are situated over the upper intercostal spaces and allow the blood from the intercostal 

 veins to pass into the axillary vein. The thoraco-epigastric veins are also of importance; one of 

 these, the vena thoraco-epigastrica tegumentosa longa (Braune), runs in the anterior axillary 

 line and forms a subcutaneous connection between the femoral and axillary veins. 



The sensory nerves of the thoracic wall are furnished from several sources. The region 

 near the posterior median furrow is supplied by the posterior branches of the dorsal nerves, 

 the skin of the infraclavicular region obtains its nerve-supply from the supraclavicular branches 

 of the cervical plexus, and the remainder of the thoracic wall is provided with sensation by the 

 intercostal nerves. The intercostal nerves (Fig. 43) are the anterior divisions of the dorsal spinal 

 nerves. Alongside of the vertebral column they run upon the inner surface of the external in- 

 tercostal muscles immediately beneath the pleura and are consequently exposed to irritation 

 in inflammation of this membrane. At the angle of the rib, where the free border of the internal 

 intercostal muscle commences, they pass between and supply the two intercostal muscles, and 

 follow the lower margin of the rib, being situated below the intercostal artery. Their proximity 

 to the ribs explains the occasional occurrence of neuralgic pains in costal fractures. In the lat- 

 eral region of the thorax they give off the lateral cutaneous nerves which subdivide into an 

 anterior and a posterior branch (read the description of the nerves of the mammary gland). 

 Anteriorly, beside the sternum, their terminal branches pass between the costal cartilages to the 

 skin of the sternum region as the anterior cutaneous nerves. 



The motor nerves of the thoracic wall, with the exception of the intercostal nerves supply- 

 ing the intercostal muscles and the branches to the long muscles of the back, are branches of the 

 brachial plexus. This plexus receives almost the entire anterior division of the first dorsal 

 nerve. This nerve is situated in the thorax at the point where it passes over the neck of the first 

 rib, and is occasionally compressed by tumors (aortic aneurysm) and gives rise to violent pains 

 in the arm. The long thoracic nerve, which is given off from the brachial plexus and runs upon 

 the serratus magnus muscle, and the long subscapular nerve (for the latissimus dorsi muscle), 

 which accompanies the subscapular artery, have been previously described (see pages 75 and 

 76). The branches for the pectoralis major and minor and for the subclavius muscles are 



