The longitudinal organization of the neuraltube (A1) can still be recognized in the brainstem. However, it is modified through the widening of the central canal into the fourth ventricle (A2, A3).
The dorsoventral arrangement of motor basal plate (A4), visceromotor (A5) andviscerosensory (A6) regions, and sensory alar plate (A7) changes to a mediolateral ar-rangement on the floor of the rhomboid fossa when the neural tube unfolds (A2). The somatomotor zone lies medially, next comes the visceromotor zone; the viscerosensory and somatosensory zones aretransposed laterally. The cranial nerve nu-clei in the medulla oblongata are arranged according to this blueprint (A3).