Development of the Central Nervous System
The central nervous system (CNS) and spine develop between the 14th and 28th day after conception. The CNS and skin develop from the same tissue layer (neuro-ectoderm). As development occurs the nervous system and skin split and migrate away from each other. If the “splitting” is incomplete then the skin can drag the nerves with it and thus they end up on the “outside”. This ongoing connection also stops the normal spine closing around the nervous tissue. This is the derivation of the term spina bifda (bifid spine). If the connection persists in the head the lesion formed is an encephalocele, if it persists in the spine it is a spina bifida.