The ansa cervicalis (or ansa hypoglossi in older literature) is a loop of nerves that are part of the first, second and third spinal nerve from the cervical plexus. It lies superficial to the internal jugular vein in the carotid triangle.
The superior root of the ansa cervicalis is formed from cervical spinal nerve 1 of the cervical plexus. These nerve fibers travel in the hypoglossal nerve before separating in the carotid triangle to form the superior root. The superior root goes around the occipital artery and then descends on the carotid sheath. It sends off branches to the superior belly of the omohyoid muscle, and the upper parts of the sternothyroid and sternohyoidmuscles and is then joined by the inferior root.
The inferior root of the ansa cervicalis, also known as descendens cervicalis, is formed by fibers from spinal nerves C2 and C3. The inferior root gives off branches to the inferior belly of the omohyoid muscle, and the lower parts of the sternothyroid and sternohyoid muscles.