The middle cervical ganglion is the smallest of the cervical ganglia, and is occasionally absent or fused with the superior cervical ganglion.  It probably consists of the fused ganglia of C5 and C6.  It is usually situated at the level of the sixth cervical vertebra, in front of the inferior thyroid artery.  It is connected to the superior cervical ganglion superiorly and the cervicothoracic (stellate) ganglion inferiorly by the sympathetic trunk.  It gives rise to the ansa subclavia, thyroid and cardiac branches.  It also gives branches to the trachea and esophagus, and grey rami communicantes to the fifth and sixth cervical nerves.

The ansa subclavia is a loop of fibers, which originate from the anterior branch of the middle cervical ganglion.  The fibers pass anteriorly around the subclavian artery, which it sends fibers to, then posteriorly to the inferior or cervicothoracic (stellate) ganglion.  There may be more than one loop present; they lie adjacent to the cervical pleura and usually connect with the phrenic nerve.