This study describes the mesodermal pattern adjacent to the region of migration of prosencephalic neural crest cells. The paraxial mesoderm is organized into somitomeres, which are composed of extended, radially oriented mesenchyme cells. The mesodermal pattern is mimicked by the cranial neural crest cells as they migrate inthe extracellular space between mesoderm and surface ectoderm. The prosencephalic crest spreads over the dorsal surface of the second somitomere and assumes a swirled configuration. Extending cranially, prosencephalic crest follows the contours of the posterior portion of the first somitomere and also spreads over the posterior and rostral surface of the optic vesicle. It is suggested that the somitomeric (segmental) partitioning of the mesoderm, as well as the surface contours of the somitomeres themselves, may provide topographic information that influences cranial crest migration.