By the fourth week of development, the embryo has upper limb outpouchings, which later develop into limb buds. By the eighth week, it has visible limbs with fingers and toes (Sadler 2019). Both lateral plate and somite-derived mesoderm, or myotome, migrate to the upper limb buds to form the vasculature and musculature of the upper limb, respectively (Dudek 2014). As the limb buds elongate, the lateral plate mesoderm tissue develops into veins that elongate with them. Initially, the limb buds are drained by the preaxial and postaxial marginal veins (Cotter et al. 2014). Eventually, the preaxial vein becomes the cephalic vein and the postaxial vein the basilic vein (Cotter et al. 2014).