The eighth thoracic ventral rami pass into the intercostal space between the pleura and internal intercostal membrane (fascia).  They then pass below the intercostal vessels in the neurovascular plane between the eighth internal and innermost intercostal muscles below the intercostal vessels.  Before reaching the costal angle they give rise to lateral and collateral branches.

The eighth lateral cutaneous branch pierces the intercostal and abdominal muscles and superficial fascia obliquely, close to the midaxillary line before dividing into anterior and posterior branches.  The anterior branch runs forwards to terminate in the external oblique muscle and overlying skin, while the posterior branch passes back over latissimus dorsi to terminate in the overlying skin.

The eighth anterior cutaneous branch is the terminal part of the collateral nerve.  The collateral nerve follows the inferior border of its intercostal space to pierce the rectus abdominis muscle and the anterior layer of the rectus sheath, where it becomes the eighth anterior cutaneous branch of the thorax and terminates in the overlying skin.

Supply
The eighth lateral cutaneous branch supplies the muscular slips of the external oblique muscle, skin over the eighth intercostal space and adjacent parts of the seventh and ninth intercostal spaces, and skin of the upper abdomen antero-inferiorly as far as the linea semilunaris.  The anterior cutaneous branch supplies the rectus abdominis muscle and skin over the anterior thoracic wall of the eighth intercostal space and skin of the upper abdomen close to the midline.