The cutaneous vascular anatomy of the proximal one-half of the dorsum (the thoracic region) and its role in flap design was studied in the rat. The investigation included anatomical dissection, ink injection into the axial artery, and flap harvesting in live animals. Anatomical dissection and india ink injection of the thoracic region revealed that the skin derives its principal blood supply from the lateral thoracic artery. The cutaneous vascular territory of the lateral thoracic artery was defined as follows: the medial border, along the midline of the back from the level of the inferior angle of the scapula to the lower border of the last rib; the lateral border, anterior axillary line corresponding with the length of the medial border; the cephalic border, a line joining the medial and lateral border at the level of the inferior angle of the scapula; and the caudal border, a line corresponding to the lower border of the last rib. Bilateral vascular pedicle island cutaneous flaps were harvested in living rats based on the vascular territory demarcated by India ink injection. All flaps survived; hence, this flap is reliable, with consistent vascularity, and is easy to harvest, and therefore, can be used as a vascular pedicle experimental model to study flap hemodynamics.