Cervical and Upper Thoracic Segments
The cervical ganglia are reduced to three; the uppermost, the superior cervical ganglion (D10), lies below the base of the skull near the nodose ganglion (inferior ganglion of the vagus nerve). It receives fibers from the upper thoracic segment via the intergan-glionic branches. Its postganglionic fibers form plexuses around the internal carotid artery and external carotid artery. Branches extend from the internal carotid plexus to the meninges, to the eyes, and to the glands of the head region. The superior tarsal muscle of the upper eyelid and the ophthal-mic muscles at the posterior wall of the orbit are innervated by sympathetic fibers. Injury to the superior cervical ganglion therefore leads to drooping of the upper eyelid (ptosis) and to a backward displace-ment of the eyeball (enophthalmos).
The middle cervical ganglion (D11) may be absent, and the inferior cervical ganglion has in most cases fused with the first thoracic ganglion to form the stellate ganglion (D12). Its postganglionic fibers form plexuses around the subclavian artery and around the vertebral artery. Fiber bundles connect-ing the stellate ganglion with the middle cervical ganglion extend across the sub-clavian artery and form the subclavian ansa (D13). Nerves from the cervical ganglia (D14) and nerves from the upper thoracic ganglia (D15) extend to the heart and to the hila of the lungs, where they participate to-gether with the parasympathetic fibers of the vagus nerve in the formation of the car-diac plexus (D16) and the pulmonary plexus(D17). The branches of the fifth to ninth sympathetic trunk ganglia join to form the greater splanchnic nerve (D18) which ex-tends to the celiac ganglia.