Ansa cervicalis

The ansa cervicalis (or ansa hypoglossi, an archaic synonym) is a component of the cervical plexus which gives muscular branches to the geniohyoid muscle of the suprahyoid group and most of the infrahyoid (strap) muscles (excluding the thyrohyoid muscle).

It lies within the carotid triangle, superficial to the carotid sheath.

Gross anatomy

Roots

• superior root: derived from the anterior primary rami of C1
• inferior root: derived from the anterior primary rami of C2 and C3

Course

• superior root
  • passes with the hypoglossal nerve between rectus capitis anterior and rectus capitis lateralis muscles
  • leaves the hypoglossal nerve lateral to the occipital artery
  • runs with the common carotid artery to join the inferior root
• inferior root
  • pierces the prevertebral fascia at the level of C2/3
  • passes around the internal jugular vein
  • runs anteriorly to meet with the superior root anterior to the common carotid artery

Branches

• branch to geniohyoid
• branches to infrahyoid (strap) muscles
  • branch to omohyoid
  • branch to sternohyoid
  • branch to sternothyroid

Note: the thyrohyoid muscle is innervated by the ventral ramus of C1 via the hypoglossal nerve rather than via the ansa cervicalis.

Variants

• accessory phrenic nerve

History and etymology

Ansa cervicalis is Latin for handle of the neck. It comes from the loop shape of the structure, which resembles a handle.