104 



Cerebrum. 



444. Horizontal Section of the Cerebrum, 



the Left Lateral Ventricle being completely opened. 2 / 3 natural size. 



The Corpus callosum and Fornix tricuspidalis, which lies below it, form 

 the roof of the t h i r d v e n t r i c 1 e. Upon lifting up of the Corpus callosum, 

 the triangular Septum lucidum is found between its anterior half and the fornix 5 

 it is a thin, semi-transparent septum, placed between the anterior 

 cornua of the two lateral ventricles ; it is composed of two lamina having an 

 interval between them, the fifth ventricle or Ventriculus septi pettucidi. The 

 posterior half of the Corpus callosum is in immediate contact with the fornix. 



The Fornix is an arched longitudinal white commissure lying between 

 the two optic thalami ; it consists of two lateral halves, which are separated 

 from each other in front and behind, forming the anterior and posterior 

 pillars or c r u r a. The anterior pillars, Crura anteriora (Columiiae)fornicis } 

 cylindrical in form, can be traced downwards in front of the optic thalami, 

 curve backwards to the Corpora albicantia s. Corpora manimillaria, and from 

 there they can be traced upwards again into the substance of the optic tha- 

 lami. The interval between the anterior pillar of the fornix and the anterior 

 part of the optic thalamus on each side, is called the Foramen Monroi. 



