Ansa cervicalis

The ansa cervicalis (or ansa hypoglossi in older literature) is a loop formed by muscular branches of the cervical plexus formed by branches of cervical spinal nerves C1-C3. The ansa cervicalis has two roots - a superior root (formed by branch of C1) and an inferior root (formed by union of branches of C2 and C3) - that unite distally, forming a loop. It is situated anterior to the carotid sheath.

Branches of the ansa cervicalis innervate three of the four infrahyoid muscles: the sternothyroid, sternohyoid, and omohyoid muscles (note that the thyrohyoid muscle is the one infrahyoid muscle not innervated by the ansa cervicalis - it is instead innervated by cervical spinal nerve 1 via a separate thyrohyoid branch).

Its name means "handle of the neck" in Latin.

Anatomy

The ansa cervicalis is typically embedded within the anterior wall of the carotid sheath anterior to the internal jugular vein.

Superior root

The superior root of the ansa cervicalis (formerly known as descendens hypoglossi) is by fibres of the cervical spinal nerve 1 (and, according to some sources, of cervical spinal nerve 2 as well) that have joined and run with the hypoglossal nerve (CN XII) for some distance before progressively branching off the CN XII in the carotid triangle to form the superior root.

The superior root is situated within the carotid triangle. It passes anterior-ward between the internal carotid artery and the common carotid artery. It curves around the occipital artery before descending upon the anterior aspect of the internal carotid artery and the common carotid artery.