10 



THORAX 



artery. Follow the nerve through the internal intercostal muscle. 

 It reaches the deep surface of the muscle at the junction of the 

 cartilage with the bone of the rib and then passes onwards either 

 between the internal intercostal and the pleura or between 

 the internal intercostal and the transversus thoracis muscle to the 

 internal mammary artery, which descends behind the costal car- 

 tilages about 13 mm. (half an inch) from the margin of the 

 sternum. Follow the nerve across the front of the internal 

 mammary artery and note that it terminates as an anterior 

 cutaneous nerve. As the intercostal nerve is cleaned small 

 branches will be found passing from it to supply the intercostal 



Sternum 



M. transversus thoracis 

 Internal mammary artery ' 

 Anterior intercostal membrane ,' 



Anterior cutaneous nerve 



Pleura/ 

 Lateral cutaneous nerve 



Internal inter- 

 costal muscle 



Anterior ramus of thoracic 

 I nerve (intercostal) 

 External intercostal muscle 



Trunk of thoracic nerve 

 Posterior ramus 



Anterior costo-transverse ligament '' 



Posterior intercostal membrane 



FIG. 3. Diagram of one of the Upper Intercostal Nerves. 



muscles. If one of the lower six intercostal nerves is followed it 

 will be found to pass out of the anterior part of the intercostal 

 space, into the abdominal wall, where it will be traced by the 

 dissector of the abdomen. 



Nervi Intercostales. The intercostal nerves are the 

 anterior rami of the upper eleven thoracic nerves on each 

 side. Each nerve gives a white branch to and receives a 

 grey branch from a ganglion of the sympathetic trunk, and 

 then enters the corresponding intercostal space. At the 

 angle of the ribs it passes into the interval between the 

 external and internal intercostal muscles and runs forwards, 

 between the muscles, to about the mid-axillary line. Then 

 it begins to pass obliquely through the internal intercostal 

 muscle, reaching the internal surface of the muscle at the 



