Early head development.
A. During Stage 8-9 (5 somite chick stage), neural crest (pre-migratory along the developing neural tube) and the unsegmented head (cranial) paraxial mesoderm, will contribute to the head mesenchyme which populate the developing branchial arches (BAs). Distinct paraxial mesoderm populations are annotated for their actual contribution to head skeletal muscles (blue colored circles).
B. Two days later in development (35 somites), cranial neural crest cells migrated from the neural tube to the periphery, along the rostro-caudal axis, and populated the pre-chordal mesenchyme and the forming BAs (BA1-4).
C. In parallel, head mesoderm move along the same routes and form the corresponding head skeletal muscles.
Abbreviations: FB, Forebrain; MB, Midbrain; r1-7, Rhombomeres 1-7; Branchial Arches 1-4 BA (1-4); NCCs, Neural Crest Cells; OV, Otic Vesicle.