develops from P4l fiber tract founder cluster P5l fiber tract founder cluster P5m fiber tract founder cluster protocerebral embryonic fiber tract lateral protocerebral tract fly_anatomy.ontology Tract of the embryonic protocerebrum. One of the two axon fascicles that pioneers the protocerebral connective. It is composed of axons of the P5l and P4l clusters that converge and extend anteriorly. At a later stage, axons of the P5m cluster join this tract. FBbt:00001629 VFB:FBbt_00001629