What is the alar plate?
As the neural tube is formed, a longitudinal groove appears on each side and divides the neural tube into a dorsal half, or alar plate, and a ventral half, or basal plate.
The alar plate gives rise to the prosencephalon; the sensory and coordinating nuclei of the thalamus; the sensory neurons of the cranial nerves; the coordinating nuclei including cerebellum, inferior olives, red nucleus, and quadrigeminal plate; and the posterior horn area (sensory) of the spinal cord.
The alar plate of the midbrain is strongly developed and it consists of a pair of bilateral hemispherical lobes that enclose the midbrain ventricle which is largely reduced in batoids.
It is named optic tectum because it is the main center of termination for retinofugal fibers and the primary center for the perception of vision, but it also receives fibers from centers in the telencephalon (dorsal pallium), diencephalon (pretectum, thalamus, and prethalamus), hindbrain (octavolateral and vestibular areas), and spinal cord.