364 DISSECTION OF THE BABBIT 



the anterior wall of the ventricle, and 

 immediately in front of the fornix. 

 /3. The middle conunissure is a very large band 

 of fibres, connecting the two optic thalami 

 across the ventricle. It is nearly circular 

 in outline, and crosses the ventricle about 

 its middle, filling up the greater part 

 of it. 

 y. The posterior commissure is a small band of 

 transverse fibres in the roof of the hinder 

 end of the third ventricle, just in front of 

 the optic lobes, 

 iii. The velum interpositum is the thin membrane 



which forms the roof of the third ventricle, 

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

 longation, upwards and backwards, of the roof 

 of the ventricle, just in front of the posterior 

 commissure. 

 V. The lamina terminalis is the thin anterior wall 



of the ventricle, 

 vi. The optic ehiasma is a thickening in the floor 



of the anterior end of the ventricle, 

 vii. The infundibulum is a funnel-hke 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 swelhng 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 ven- 

 tricle, running backwards and downwards 

 from the body of the fornix, beneath the 



