The second cell corresponded to which ventricle?

• A. Third ventricle
• B. First ventricle
• C. Second ventricle
• D. Fourth ventricle

Answer: (A)

Understand the layout of the ventricular system: two lateral ventricles sit in each hemisphere, then the midline third ventricle sits between the thalami, and below/back lies the fourth ventricle between the brainstem and cerebellum. In many diagrams, the lateral ventricles are shown first and second in sequence, and the next space in line is the third ventricle. So the second labeled cell in that figure corresponds to the third ventricle. The third ventricle is a narrow midline cavity in the diencephalon, bounded by the thalami and surrounding structures; cerebrospinal fluid flows from the lateral ventricles through the foramina of Monro into this space, then through the cerebral aqueduct into the fourth ventricle. The fourth ventricle is located lower and posteriorly, near the brainstem and cerebellum, so it wouldn’t be the second in a straightforward labeling of the cavities.