Final answer:
The slender canal that connects the third ventricle with the fourth ventricle is the aqueduct of Sylvius.
Step-by-step explanation:
The slender canal that connects the third ventricle with the fourth ventricle is the aqueduct of Sylvius. It is a narrow tube-like structure located in the midbrain. The aqueduct of Sylvius carries cerebrospinal fluid (CSF) from the third ventricle to the fourth ventricle, which is then distributed to the subarachnoid space surrounding the brain and spinal cord.
Learn more about Aqueduct of Sylvius