The ansa cervicalis is a loop of fibers formed by the superior and inferior roots.  The superior root arises from the ventral ramus of C1 and the inferior root arises from the ventral rami of C2 and C3.  The C1 fibers run with the hypoglossal nerve (XII cranial nerve) before being given off as a specific branch.  The inferior root descends on the lateral side of the internal jugular vein, crossing it in the middle of the neck and continues forward to join the superior root, anterior to the common carotid artery.  

Supply
The ansa cervicalis supplies the sternothyroid, sternohyoid and omohyoid muscles.