In cross section, the cord consists of bilateral cell groupings within Alar and Basal Plates that are joined in the midline by Roof and Floor Plates. These four plates organize the neurotube into sensory (dorsal) and motor (ventral) regions.

• In cross section, the cord consists of bilateral cell groupings within Alar and Basal Plates that are joined in the midline by Roof and Floor Plates. These four plates organize the neurotube into sensory (dorsal) and motor (ventral) regions.

• An additional, demarcation in development is the sulcus limitans that separates sensory alar plate, dorsally, from the basal motor plate, ventrally and this depression remains a distinction into adulthood.

• The floor plate joins the paired basal plates and the roof plate joins the paired alar plates.

• Floor Plate (Ventral) is usually thin but thickens for pathway decussation. The roof plate is thin in the cord.
• The Basal Plate is thickened, massively, by motor-cell groups & pathways