THORACIC WALL 5 



inner surface of the lower rib, close to the upper margin. 

 The internal intercostal muscles are prolonged anteriorly 

 to the sternum. Posteriorly they extend to the angles 

 of the ribs. The posterior intercostal membranes extend from 

 the spine to posterior borders of the internal intercostals 

 where they become continuous with the fascial layer between 

 the external and internal intercostal muscles. They will 

 be seen when the thorax is opened. 



If the internal oblique muscle of the abdomen has not been removed, 

 the dissector should note that the anterior fibres of the lowest two internal 

 intercostal muscles become continuous with the fibres of that muscle. 



Sternum 



M. transversus thoracis /' 

 Internal mammary artery ' / 

 Anterior intercostal membrane / 

 Anterior cutaneous nerve 



Pleura/ 

 Lateral cutaneous nerve 



Anterior root 

 Posterior root 



Trunk of thoracic nerve -'H / X ^^^HlIlBS^^ Anterior branch of thoracic 

 Posterior branch I)/ /> I nerve (intercostal) 



- / External intercostal muscle 



Anterior costo-transverse ligament ' 



Posterior intercostal membrane 



FIG. 2. Diagram of one of the Upper Intercostal Nerves. 



Intercostal Nerves. The intercostal nerves are altogether 

 out of sight in the present stage of the dissection. They are 

 hidden by the lower borders of the ribs which bound the 

 intercostal spaces superiorly. By gently pulling upon their 

 lateral cutaneous branches they can be drawn downwards, 

 and they are then seen to lie between the two muscular strata as 

 far anteriorly as a point midway between the vertebral column 

 and sternum. There they sink into the substance of the in- 

 ternal intercostal muscles, amidst the fibres of which they may 

 be traced to the anterior extremities of the bony parts 

 of the ribs, where they reach the deep surface of internal 



