primitive streak morphology trait primitive node morphology trait Hensen's node morphology trait Trait.ontology VT:0004066 primitive knot morphology trait Any measurable or observable characteristic related to the shape, structure, color or pattern of the regional thickening of cells at the rostral tip of the vertebrate primitive streak through which gastrulating cells migrate anteriorally to form tissues in the future head and neck; this region organizes the formation of the three embryonic layers and establishes the longitudinal axis and the polarity of the embryo. embryonic node embryo node