The ansa cervicalis (or ansa hypoglossi in older literature) is a loop of nerves that are part of the cervical plexus. It lies superficial to the internal jugular vein in the carotid sheath.
Branches from the ansa cervicalis innervate three of the four infrahyoid muscles: the sternohyoid muscle, the sternothyroid muscle, and the omohyoid muscle. It does not innervate the thyrohyoid muscle, which receives its innervation from the ventral root of C1.
Read more about Ansa Cervicalis: Roots