A longitudinal groove in the neural tube wall that divides the neural tube into dorsal (alar) and ventral (basal) halves (dorsal receives input from sensory neurons, ventral effects motor functions); stretches from the mesencephalon caudad[TMD]. [ http://www.ncbi.nlm.nih.gov/books/NBK10047 http://medical-dictionary.thefreedictionary.com/Sulcus+limitans ]