Identify and clean the external and internal intercostal muscles. (G 3.18;N 186;Gl 7.10)

1. Locate the 3rd intercostal space (the 2nd rib is at the level of the sternal angle). Identify the external intercostal muscle in this space. Note that the muscle does not extend to the sternum.
2. Expose the internal intercostal muscle by carefully removing the external intercostal muscle and its associated membrane from the 4th intercostal space. Blunt dissect between the external and internal intercostals and then use scissors to cut away the external intercostal muscle. Note the internal intercostal exending to the sternum. There may be an innermost intercostal muscle fused to the internal intercostal muscle.
3. Carefully remove the external intercostal membrane and the internal intercostal muscle from the 2nd intercostal space adjacent to the sternum. (G 3.21;N 186;Gl 7.17) Identify the internal thoracic artery and vein. Attempt to identify an anterior intercostal artery and vein branching from (or draining into) the internal thoracic artery and vein.
Important Relationship
1. The intercostal nerves, arteries and veins are positioned deep to the internal intercostal muscles.