This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Thalamus, Hypothalamus and Basal Ganglia, Subject name: Physiology
Not a part of basal ganglia is? 
Select and explain. 
A. Caudate nucleus, B. Corpus striatum, C. Lenticular nucleus, D. Sub-Fornical organ
D: Sub-Fornical organ
Answer: D: Sub-Fornical organ 
Explanation: Ans. (d) Sub-fornical Organ* The subfornical organ (SFO), situated on the ventral surface of the fornix (the reasoning behind the organs name), at the interventricular foramina (foramina of Monroe), is one of the circumventricular organs of the brain, meaning that it is highly vascularized and does not have a blood-brain barrier, unlike the vast majority of regions in the brain.* The SFO is a sensory circumventricular organ responsive to a wide variety of hormones and neurotransmitters, as opposed to a secretory circumventricular organ.