abnormal floor plate morphology small floor plate MP:0000927 MPheno.ontology decreased floor plate size reduced floor plate size reduced size of the specialized glial structure (non-neuronal cells) situated at the ventral midline of the embryonic neural tube; this structure spans the anteroposterior axis from the midbrain to the tail regions, separating the left and right basal plates of the developing neural tube, and serves as an organizer to ventralize tissues in the embryo as well as to guide neuronal positioning and differentiation along the dorsoventral axis of the neural tube small floorplate