THE LATERAL VENTRICLES 327 



The anterior cornu projects into the anterior lobe and runs 

 outward around the nucleus caudatus. Above and in front of 

 it is the corpus callosum. 



The posterior cornu, or digital cavity, runs back into the 

 posterior lobe, its direction being backward, outward, and 

 lastly inward. Its floor presents the eminence of the hippo- 

 campus minor, or calcar avis. At the junction of the posterior 

 and middle cornua is the eminentia collateralis, or pes accessorius. 



The middle or descending cornua curves around the back of 

 the optic thalamus, descending at first backward and out- 

 ward. It then runs downward, forward, and lastly inward. 

 In its floor are the hippocampus major and pes hippocampi, 

 corpus fimbriatum, and choroid plexus; the fascia dentata 

 lies within the hippocampal or dentate fissure, and the trans- 

 ver^e fissure runs along the inner side of the cornu. 



The fornix is an arched longitudinal commissure of white 

 matter below the corpus callosum, its lateral margins forming 

 part of the floor of the body of the lateral ventricles. In front 

 its two lateral halves are divergent, and form the anterior 

 pillars; behind they diverge into the two posterior pillars; 

 the central part is the body. The body is triangular, attached 

 above to the corpus callosum and septum lucidum; below 

 the velum interpositum separates it from the third ventricle 

 and optic thalami. From under each side project the choroid 

 plexuses. 



The anterior pillars descend through the gray matter on the 

 sides of the third ventricle and form the anterior boundaries 

 of the foramen of Monro. Then they emerge at the base of 

 the brain to form the corpora albicantia, from which each 

 pillar turns upward and ends in the corresponding optic thala- 

 mus. In their course each communicates with the peduncle 

 of the pineal gland and the tsenia semicircularis. 



The posterior pillars are connected with the corpus callosum, 

 then enter the dscending cornua, and are partly prolonged 

 into the upper surface of the hippocampus major and partly 

 into the corpus fimbriatum. 



The foramen of Monro is a foramen connecting each lateral 

 ventricle with the anterior part of the third. In front it is 

 bounded by the anterior pillar of the fornix; behind, by the 

 anterior part of the optic thalamus; above, by the anterior 

 extremity of the body of the fornix. 



