THE BRAIN. 393 



end of the third ventricle, j ust in front of 

 the optic lobes. 



iii. The velum interpositum, which forms the roof 

 of the third ventricle, has already been seen 

 and removed. 



iv. The stalk of the pineal body is a tubular pro- 

 longation, upvyards and backwards, of the roof 

 of the ventricle, just in front of the posterior 

 commissure. 



V. The lamina terminalis is the thin anterior Avail 

 of the ventricle. 



vi. The optic chiasma appears in this section as a 

 thickening in the floor of the anterior end of 

 the ventricle. 



vii. The infundibulum is a funnel-like depression of 

 the floor of the ventricle, about the middle 

 of its length : to its apex the pituitary body is 

 attached. 



viii. The corpus albicans is a rounded swelling on 

 the ventral surface of the floor of the ventricle, 

 in the hinder wall of the infundibulum. 



ix. The foramen of Monro is a vertical slit-like 

 opening at the anterior end of the ventricle, 

 between and slightly above the anterior and 

 middle commissures. It leads from the third 

 to the lateral ventricle. 



X. The anterior pillar of the fornix is a slender 

 band of nerve-fibres in the side-wall of the 

 ventricle, running backwards and downwards 

 from the body of the fornix, beneath the 

 middle commissure, to the corpus albicans, in 

 which it ends. 

 The mid-brain, or mesencephalon, 

 i. The Sylvian aqueduct, or iter a tertio ad quar- 

 tum ventriculam, is the cavity or ventricle of 

 the mid-brain. 



