Which of the following is NOT a component of the ventricular system?

Which of the following is NOT a component of the ventricular system?

• A. Lateral ventricles
• B. Third ventricle
• C. Fourth ventricle
• D. Arachnoid villi

Answer: (D)

The main idea is to recognize what structures actually form the brain’s ventricular system. The ventricles are four CSF-filled cavities: two lateral ventricles, then the third ventricle, and the fourth ventricle. Arachnoid villi are not part of this system; they are small projections of the arachnoid mater that protrude into the dural venous sinuses and function to reabsorb CSF from the subarachnoid space into the bloodstream. So, while CSF flows through and around the ventricles, its absorption happens at the arachnoid villi, not inside the ventricular cavities.

The main idea is to recognize what structures actually form the brain’s ventricular system. The ventricles are four CSF-filled cavities: two lateral ventricles, then the third ventricle, and the fourth ventricle. Arachnoid villi are not part of this system; they are small projections of the arachnoid mater that protrude into the dural venous sinuses and function to reabsorb CSF from the subarachnoid space into the bloodstream. So, while CSF flows through and around the ventricles, its absorption happens at the arachnoid villi, not inside the ventricular cavities.