The brain-stem is rostral continuation of the spinal cord, which has three parts: medulla oblongata, pons and midbrain. It lies upon the basal portion of the occipital bone and part of the sphenoid bone body (clivus). Majority of dorsal surphace of the brain-stem is covered by cerebellum, which is connected with particular parts of the brain-stem by pedunculi cerebellares.The brain-stem contains ascending and descending tracts, cranial nerve nuclei, reticular formation and peculiar nuclei. Cerebellum growth during evolution evoked opening of the neural tube within pons and rostral part of the oblongata. Central canal is there spread to the third ventricle and four parts of neural tube are side by side.