Ventral surface of the brainstem and cerebellum. The inferior and superior pontine sulci divide the brainstem into midbrain, pons, and medulla oblongata. Cranially, the brainstem is continuous with the diencephalon. Diencephalic structures seen here include the tuber cinereum (and pituitary stalk or infundibulum), and mammillary bodies of the hypothalamus. On the ventral surface of the hypothalalamus is the optic chiasm and the optic tracts (going to the lateral geniculate bodies).  The pathway of the corticospinal (pyramidal) tract may be seen as the fibers descend sequentially through the cerebral peduncle in the midbrain, the basis pons, and finally the pyramid in the medulla oblongata. The oculomotor nerve exits the ventral midbrain at the superior pontine sulcus or pontomesencephalic sulcus, medial to the cerebral peduncles.  The trigeminal nerve enters the mid-pons through the middle cerebellar peduncle. The middle cerebellar peducle is an important cerebellar afferent fiber system that contains transverse pontine (pontocerebellar) fibers that originate from the contralateral deep pontine nuclei.  They form part of the cortico-ponto-cerebellar pathway that connects the contralateral cerebral cortex to the cerebellum. The inferior cerebellar peduncle (restiform body) is an important cerebellar afferent fiber system that interconnects the medulla oblongata and spinal cord with the cerebellum. The fourth ventricle opens into the cerebellopontine angle through the foramina of Luschka (lateral apertures) which are located caudal to the middle/inferior cerebellar peduncles and medial to the flocculi. The olives or olivary bodies are located lateral to the pyramids and contain the inferior olivary nucleus. (Image courtesy of AL Rhoton, Jr.)