THE CEREBRUM 431 



part is the portion of the ventricle which extends from the 

 interventricular foramen to the splenium of the corpus cal- 

 losum. At the level of the splenium the posterior and 

 inferior horns diverge from the posterior end of the central 

 part. The posterior horn curves backwards and medially 

 into the occipital lobe. It is very variable in its length and 

 capacity. The inferior horn passes, with a bold sweep, round 

 the posterior end of the thalamus, and then tunnels, down- 

 wards and forwards, through the temporal lobe, towards 

 the temporal pole (Fig. 166). 



Behind the anterior horn the floor of the central part of 

 the ventricle is fully exposed and the following parts should 

 be distinguished, (i) Extending backwards and laterally 

 from the interventricular foramen is the vascular fringe called 

 the chorioid plexus of the lateral ventricle. Posteriorly it 

 descends into the inferior horn. (2) Medial to the chorioid 

 plexus is the upper surface of the body of the fornix. Its 

 posterior extremity, on each side, becomes a crus of the fornix, 

 which accompanies the chorioid plexus into the inferior horn, 

 where it terminates in the fimbria of the hippocampus. (3) 

 Lateral to the chorioid plexus is a part of the upper surface 

 of the thalamus. (4) Running along the lateral margin of the 

 thalamus, in a shallow sulcus, is a white strand called the stria 

 terminalis. It descends posteriorly into the roof of the 

 inferior horn. (5) Lateral to the stria terminalis lies the 

 convex upper surface of the body of the caudate nucleus. 



Dissection. When the parts mentioned have been identified, 

 the central part of the corpus callosum, which is still in position, 

 should be carefully raised to display the septum pellucidum, which 

 descends from the lower surface of the corpus callosum to the 

 upper aspect of the fornix, and so intervenes between the lateral 

 ventricles of the opposite sides, forming the medial wall of the 

 central part and the anterior cornu of each ventricle. Whilst 

 the central part of the corpus callosum is still elevated the fornix 

 should be followed forwards. It will be found to divide into two 

 rounded bundles, called the columns of the fornix, which descend, 

 one on each side, in front of the corresponding interventricular 

 foramen (Fig. 160). 



Plexus Chorioideus Ventriculi Lateralis. The chorioid 

 plexus of each lateral ventricle is a plexus of blood vessels 

 enclosed in the lateral margin of a triangular fold of pia 

 mater called the tela chorioidea of the third "ventricle. The 

 body of the fold is concealed at present. It will be displayed 

 at a later stage of the dissection (Fig. 174). 



