The cerebellum is first noted at 5-6 weeks as the
rhombic lips of the
cranial edge of the thinned
roofof the
fourth ventricle of
the hindbrain. The lips develop from the dorsolateral portions of the alar
plates forming the cerebellar primordia. Growth causes the 2 rhombic lips to
fuse in the midline to form the
cerebellar plate
which covers the 4th ventricle caudal to the
mesencephalon.
