A, The suboccipital surface is located below and between the sigmoid and lateral sinuses and is the surface that is exposed in a wide suboccipital craniectomy. The vermis sits in a depression, the posterior cerebellar incisura, between the hemi-spheres. The cerebellomedullary fissure extends superiorly between the cerebellum and medulla along the inferior half of the ventricular roof. The vallecula extends upward between the tonsils and communicates through the foramen of Magendie with the fourth ventricle. The PICA supplies the suboccipital surface. B, Enlarged view. The lower parts of the vermis behind the ventricle are the pyramid and uvula. C, The right tonsil has been removed to expose the lower part of the roof formed by the inferior medullary velum and tela choroidea. The nodule on which the velum arises is hidden in front of the uvula. The uvula hangs downward between the tonsils, thus mimicking the situation in the oropharynx. The choroid plexus arises on the inner surface of the tela and extends through the foramen of Luschka behind the glossopharyngeal and vagus nerve. The inferior medullary velum arises on the sur-face of the nodule, drapes across the superior pole of the tonsil, and blends into the flocculus laterally. D, Both tonsils have been removed to expose the inferior medullary velum and tela choroidea bilaterally. The telovelar junction is the junction between the velum and tela. The cerebellomedullary fissure extends upward between the rostral pole of the tonsil on one side and the tela choroidea and inferior medullary velum on the opposite side. The segment of the PICA passing through this cleft is called the telovelotonsillar segment. The rhomboid lip is a sheet-like layer of neural tissue attached to the lateral margin of the ventricular floor, which extends posterior to the glossopharyngeal and vagus nerves and joins the tela choroidea to form a pouch at the outer extremity of the lateral recess. E, The right half of the tela has been removed to expose the ventricle and the lateral recess. The inferior medullary velum extends laterally to form a peduncle, the peduncle of the flocculus, which blends into the flocculus at the outer margin of the lateral recess. F, The tela has been removed on both sides. The lateral wall of the upper half of the ventricle is formed by the superior cerebellar peduncles. The inferior cerebellar peduncles ascend along the dorsolateral medulla and form the anterior and rostral margins of the lateral recess. (Images courtesy of AL Rhoton, Jr.)