The brain (supraoesophageal ganglion) is the most complex of the segme
ntal ganglia composing the nerve cord of the locusts Schistocerca greg
aria and Locusta migratoria. In this paper, we describe the ground pla
n of the commissures crossing the midline of the brain and propose a n
omenclature with the aim of making a complex neuropil more understanda
ble at the level of individual neurons. For developmental and comparat
ive reasons the neuroarchitecture of the brain is related to the neura
l axis, not to the body axis. We have identified 73 commissural fiber
bundles belonging to the adult brain, and these are named according to
their location (ventral, dorsal, anterior, posterior, medial) with re
spect to the central complex as reference point. Reconstructions of id
entified neurons from intracellular stainings, cobalt backfills, or im
munohistochemical studies demonstrate the various configurations in wh
ich fibers cross the brain.