NERVOUS SYSTEM 63 



two diverging bands of fibres {the posterior pil- 

 lars of the fornix), which pass out along the floor 

 of the lateral ventricles between the corpus stri- 

 atum and the hippocampus major, (Plate VII., 

 B and c.) 



Cut across the posterior pillars of the fornix and 

 hippocampus major, and reflect them. 



8. The Optic Thalamus is the rounded prominence 

 immediately below the hippocampus major and 

 the posterior pillars of the fornix. It lies just an- 

 terior to the corpora quadrigemina. The optic 

 tracts pass over its lateral surface. 



9. The Corpus Geniculatum is a small, prominent 

 elevation, just posterior to the optic tract and be- 

 tween it and the corpora quadrigemina. 



10. The Foramen of Monro is a narrow, slit-like 

 opening, lying between the descending pillars of 

 the fornix and the optic thalamus. This passage, 

 together with its fellow of the opposite side, forms 

 a Y-shaped canal, connecting the two lateral ven- 

 tricles with a median cavity, already mentioned, 

 the third ventricle. 



Remove the portion of the corpus callosum remain- 

 ing between the posterior pillars of the fornix, 

 being careful not to injure the delicate mem- 

 brane immediately below. 



1 1. The Velum Interpositum is the thin membrane 

 forming the roof of the cavity (third ventricle) 



