THE RABBIT. 373 



500. The septum lucidum {sp.lu), a somewhat tri- 

 angular body, formed externally of grey matter, lying 

 beneath the anterior end of the corpus callosum and 

 immediately in front of the anterior end of the hippo- 

 campus : it forms the inner wall of the anterior cornu of 

 the lateral ventricle. 



501. The choroid plexus {ch.pl), an extremely vascular 

 membrane lying in a depression just in front of the hippo- 

 campus major, and passing beneath the corpus callosum 

 to join its fellow of the opposite side through a transverse 

 passage, which puts the third ventricle (§ 513) in com- 

 munication with the -lateral ventricles ; this passage is the 

 foramen of Monro. The connection of the two choroid 

 plexuses through the foramen of Monro is best seen by 

 exerting a slight traction on one of them. 



502. The corpus striatum {cp.s), an eminence of grey 

 matter forming the floor of the anterior cornu of the 

 lateral ventricle, and separated from the septum lucidum 

 and hippocampus major by the depression in which the 

 choroid plexus lies. 



LIX. Dissect the other hemisphere in the same way, 

 'observing the same points again, and noting further : 



503. The connection of the corpus callosum with the 

 underlying parts of the brain, namely with the lyra behind 

 and with the septum lucidum in front. 



504. By dividing the corpus callosum trarisversely, care- 

 fully separating its two ends from the underlying parts and 

 reflecting them, it is seen to bend slightly downwards at its 

 anterior end, forming the anterior genu, while at its 

 iposterior end it bends sharply downwards and then forwards, 

 forming the posterior genu. 



505. By the removal of the corpus callosum the septum 

 lucidum is found to consist of two layers, between which is 



