fourth ventricle morphology trait fourth ventricle size trait Any measurable or observable characteristic related to the physical magnitude of the irregularly shaped cavity in the rhombencephalon, between the medulla oblongata, the pons, and the isthmus in front, and the cerebellum behind; it is continuous with the central canal of the cord below and with the cerebral aqueduct above, and through its lateral and median apertures it communicates with the subarachnoid space. EFO:0010303 Trait.ontology VT:0000829 fourth ventricle volume ventricle of rhombencephalon size trait ventriculus quartus size trait