The fourth thoracic ventral spinal rami exit the vertebral column through the intervertebral foramina between the pedicles of T4 and T5.  They emerge above the transverse processes of T5 and pass into the intercostal spaces between the pleura and internal intercostal membrane (fascia), where each ramus receives at least one grey (proximal) and white (distal) rami communicantes from adjacent sympathetic ganglia.

The rami then pass below the intercostal vessels in the neurovascular plane between the fourth internal and innermost intercostal muscles.  Before reaching the costal angle they give rise to collateral and lateral branches.  The collateral branches follow the inferior borders of the intercostal spaces and near the sternum they pass anterior to the internal thoracic vessels, pierce the internal intercostal muscles, external intercostal membrane and pectoralis major muscles, to terminate as the fourth anterior cutaneous nerves of the thorax.  The lateral cutaneous branches pierce the intercostal muscles obliquely and then divide into anterior and posterior branches, which pierce serratus anterior to supply the overlying skin

Supply
The fourth thoracic ventral rami supply the fourth intercostal muscles and adjacent skin over the front and sides of the chest.