The ansa cervicalis (or ansa hypoglossi in older literature[citation needed]) is a loop formed by muscular branches of the cervical plexus formed by branches of cervical spinal nerves C1-C3.

[1]: 344 The superior root of the ansa cervicalis (formerly known as descendens hypoglossi[1]: 500 ) is by fibres of the cervical spinal nerve 1 [1]: 344 [3] (and, according to some sources, of cervical spinal nerve 2 as well[3]) that have joined and run with the hypoglossal nerve (CN XII) for some distance before[1]: 344  progressively[1]: 369  branching off the CN XII in the carotid triangle to form the superior root.

[citation needed] It issues a branch to the superior belly of the omohyoid muscle,[1]: 344  and the upper parts of the sternothyroid and sternohyoid muscles before uniting with the inferior root.

[citation needed] The inferior root of the ansa cervicalis (formerly known as descendens cervicalis[1]: 500 ) is formed by the union of fibers of the anterior rami spinal cervical nerves C2-C3 that unite as part of the cervical plexus.

[1]: 344 The inferior root curves posteroanteriorly around[1]: 344  the lateral side of the internal jugular vein[1]: 343  before descending to unite with the superior root upon the (inferior portion of) the internal jugular vein.