The ventral nerve cord (VNC) makes up a part of the central nervous system of some phyla of the bilaterians, particularly within the nematodes, annelids and the arthropods. It usually consists of cerebral ganglia anteriorly with the nerve cords running down the ventral ("belly", as opposed to back) plane of the organism.
Ventral nerve cords from anterior to posterior (the thoracic and abdominal tagma in the arthropods) are made up of segmented ganglia that are connected by a tract of nerve fibers passing from one side to the other of the nerve cord called commissures [1]. The complete system bears some likeness to a rope ladder. In some animals the bilateral ganglia are fused into a single large ganglion per segment.
Developmental
Engrailed is a transcription factor that helps regulate the gene frazzled in order to separate neuroblast during embryonic development. The segregation of neuroblast is essential for the formation and development of the ventral nerve cord.