As the embryo develops, mesodermal cells leave the primitive streak, migrating laterally and anteriorly to occupy lateral and dorsal positions along the anteroposterior axis. They subsequently form axial and paraxial mesoderm structures. The presomitic paraxial mesoderm is located adjacent to the notochord and neural tube and constitutes a longitudinal column of cells on either side of the notochord.
During the third week of human embryonic development, the paraxial mesoderm forms paired "balls" of mesoderm on either side of the neural groove. Segmentation of the paraxial mesoderm into somites occurs along the dorsal–ventral axis and in a rostral-to-caudal direction. In response to signals from the notochord, neural tube and surface ectoderm, the somites subdivide and differentiate to give rise to the embryonic structures of the dermomyotome, myotome and sclerotome. The paraxial mesoderm contributes extensively to many adult tissues, including most of the axial skeleton, the muscles of the trunk, and the dermis of the skin. In the head region, the unsegmented cranial paraxial mesoderm contributes to the developing heart, specific skull bones and skeletal muscles of the head and neck regions.