supraesophageal embryonic fiber tract supraesophageal commissural pioneer tract Pioneer commissural tract of the embryonic supraesophageal ganglion. It is formed by the continuing axons of the medial cervical, lateral cervical and lateral protocerebral pioneer tracts that form three fascicles. First axons of the medial cervical tract (P2l and D/T clusters) grow medially towards the P2m cluster. Following the outline of this cluster, the axons reach the dorsal midline where they meet and fasciculate with their contralateral counterparts, and form the anterior ventral commissural tract (anterior VCT). A second commissural tract, the posterior VCT, is formed just posterior to the anterior VCT by collaterals of the lateral cervical tract. The third tract, the dorsal commissural tract, is formed by axons of the P4l and P3l clusters that grow anteriorly, make a sharp turn medially and form a commissural bundle dorsally to the anterior VCT. FBbt:00001632 fly_anatomy.ontology VFB:FBbt_00001632 commissure