352 DISSECTION OF THE RABBIT 



a. The anterior commissure is a small band of 

 transverse nerve-fibres, in the substance of 

 the anterior wall of the ventricle, and 

 immediately in front of the fornix. 

 /?. The middle commissure is a very large band 

 of fibres, connecting the two optic thalami 

 across the ventricle. It is nearly circular 

 in outline, and is placed about the middle 

 of the ventricle, a great part of which it fills 

 up. 



y. The posterior commissure is a small band of 



transverse fibres in the roof of the hinder 



end of the ventricle, just in front of the 



optic lobes. 



iii. The velum interpositum is the thin membrane 



which forms the roof of the ventricle. 

 iv. The stalk of the pineal 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 chiasma is 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 1 anterior pillar of the fornix is a slender 

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



