4. Identify the triangles of the neck and clean the strap muscles and reflect them to expose the ansa cervicalis and the thyroid gland.
Begin to clean and expose the sternocleidomastoid muscle at its medial border. With the muscle exposed, notice its two heads: first its sternal head, followed by its clavicular head. Reflecting the muscle superiorly will expose some of its vasculature: superiorly, a cervical branch providing sensory fibers. Next, note the sternohyoid and omohyoid muscles. Begin blunt dissection of these strap muscles. Work in a medial to lateral direction to preserve the underlying nerves that enter the strap muscles at their lateral border. With the superficial strap muscles exposed, you can see the sternohyoid muscle. Its nerves enter it laterally. Here is the omohyoid muscle. Grasping its intermediate tendon, note the superior belly and the nerves entering the lateral border of the muscle. Trace these nerves to the ansa cervicalis. Here is the ansa cervicalis with many of its muscular branches. Next, reflect the sternohyoid muscle superiorly. It will be necessary to sever some of its nerves on the lateral border to completely reflect the muscle. Next, reflect the omohyoid muscle laterally, by severing its attachment to the hyoid bone. Next, begin to uncover the sternothyroid muscle, beginning at its medial border. With the sternothyroid muscle completely exposed, reflect it superiorly to reveal the thyroid gland. Next, expose the thyrohyoid muscle beginning at its medial border. When cleaning the thyrohoid muscle, locate the nerve to thyrohoid and trace it back to the hypoglossal nerve. Recall that the nerve to thyrohoid comes from C1 to C2 and is not a branch of ansa cervicalis.