Identify and clean the deep structures of the posterior triangle of the neck.

1. (ON BOTH SIDES) Blunt dissect the clavicle free of all surrounding structures. Saw both clavicles near the coracoid process of the scapula   and the sternoclavicular joints   (or disarticulate the sternoclavicular joints.   Remove the clavicles. Saw the 1st and 2nd ribs (both sides) just anterior (medial) to the attachment of the scalene muscles.   Saw the sternum at the sternal angle. Remove the manubrium and medial aspect of the 1st and 2nd ribs. On both sides, blunt dissect the internal jugular vein from the common carotid artery and vagus nerve. Cut the internal jugular vein approximately 5 cm superior to the level of the jugular notch (sternum). On the right side you may cut the vein at the level of the embalming suture. Reflect (but do not remove) the internal jugular vein in both the superior and inferior directions. There are many nerves and vessels coursing from medial to lateral or superior-medial to inferior-lateral through the posterior triangle. You need to clean structures along this axis (similar to cleaning the axilla).
2. (ON BOTH SIDES) Identify and clean the inferior belly of the omohyoid muscle. (G 8.10;N 28;Gl 39.31)
3. (ON BOTH SIDES) Return to the axillary artery (upper extremity dissection). Trace (clean) this artery in the proximal direction until it passes posterior to the anterior scalene muscle. (G 8.5F;N 29 and 417;Gl 39.31) At this point the vessel is the subclavian artery. Clean the anterior scalene muscle and identify the phrenic nerve and transverse cervical and suprascapular arteries. You may clarify this dissection field by removing any veins except the internal jugular and subclavian veins.
Important Relationships
• The subclavian artery passes directly posterior to the anterior scalene muscle.
• The phrenic nerve and subclavian vein pass directly anterior to the anterior scalene muscle.
• The suprascapular and transverse cervical arteries typically pass directly anterior to the anterior scalene muscle.
4. (ON BOTH SIDES) Identify and clean the trunks of the brachial plexus where they emerge posterior to the anterior scalene muscle. Identify the suprascapular nerve arising from the upper trunk. Trace the suprascapular nerve and artery to the superior transverse scapular ligament (Shoulder and Posterior Arm dissection).
   Important Relationships

   • The brachial plexus (roots) are positioned directly anterior to the middle scalene and directly posterior to the anterior scalene muscles.