The upper limbs develop mostly during the first eight weeks of gestation, arising from the limb buds, which are mesodermal outgrowths into the overlying ectoderm. Two types of mesodermal cells migrate into the limb buds: the somatic and lateral plate mesoderm. The vascular structures of the upper extremity originate from the somatic mesoderm, along with the neural and muscular structures. The lateral plate mesoderm gives rise to the bony, cartilaginous, and tendinous structures.