develops from P4m fiber tract founder cluster protocerebral embryonic fiber tract medial protocerebral tract FBbt:00001628 Tract of the embryonic protocerebrum. One of the two axon fascicles that pioneers the protocerebral connective. It is formed by the anteriorly projecting axons of the neurons of the P4m cluster, which project toward the P3m cluster. VFB:FBbt_00001628 fly_anatomy.ontology