“The thoracic nerves (T1–T12) maintain a segmental organization, each dividing into a posterior ramus for the back and an intercostal/subcostal anterior ramus for the chest and abdomen. Their predictable dermatomes (e.g., T4 nipple, T10 umbilicus) and motor supply make them clinically useful for localizing spinal cord or peripheral nerve lesions, assessing sympathetic function, and planning surgical incisions.”