This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anatomy
Floor of 4th ventricle is not formed by ? 
Select and explain. 
A. Sulcus limitans, B. Anterior medullary velum, C. Posterior surface of pons, D. Posterior surface of medulla
C: Posterior surface of pons
Answer: C: Posterior surface of pons 
Explanation: Floor of the fouh ventricle is not formed by Anterior medullary velum.Anterior medullary velum forms the roof.All the other options are associated with the floor of the ventricle. Fouh ventricle: It is a tent like structure, it is situated in front of the cerebellum and behind the pons and upper half of the medulla oblongata. It is lined by ciliated epithelium. Communications: 1. Cerebral aqueduct (of Sylvius): in the superior median plane (superior angle), it communicates with third ventricle. 2. Central spinal canal: in the inferior median plane (inferior angle). Boundries: 1. Roof consists of Upper poion of roof: The superior peduncle and the anterior medullary velum; Lower poion of roof: The posterior medullary velum, the epithelial lining of the ventricle covered by the tela chorioidea inferior and the taeniae of the fouh ventricle. 2. Floor: Upper pa :Fascial colliculus on the dorsal surface of pons. Intermediate pa:Vestibular nuclei medulllary striae. Lower pa:Upper pa of medulla oblongata containing hypoglossal and vagal triangles. 3. Laterally: bounded by superior and inferior cerebellar peduncles,gracile tubercle and cuneate tubercle. Apeures: Through these, the CSF leaves the fouh ventricle to the subarachnoid space One median foramen (foramen of Magendie): in the lower pa of the inferior medullary velum. Two lateral foramens (foramens of Lushka): one in each lateral recess. Ref: 1. Color atlas of neuroscience: neuroanatomy and neurophysiology, By Ben Greenstein, Adam. Greenstein, Page 16 2. BD Chaurasia's Human Anatomy,Volu III, 4Th edition, Page 397