482 NEUROLOGY. 



occupies the anterior region of the floor of the lateral ventricle. 

 Its broad anterior extremity stretches into the anterior cornn, 

 while its narrow posterior extremity passes into the descending 

 cornu, and is embedded in the substance of the hemisphere. The 

 furrow along its oblique inner side, which separates it from the 

 hippocampus and the optic thalamus, contains the choroid plexus 

 and the taenia semicircularis. The corpora striata are grey 

 externally, and are composed of grey matter, with numerous 

 white fibres traversing it, which give it a striated appearance 

 when cut across. They are the anterior ganglia of the cerebrum. 



The tcenia seif)iicircularis is a narrow, white, semi-transparent 

 band, which separates the corpus striatum from the optic 

 thalamus. In front it is continuous with the fornix, becoming 

 lost near the foramen of Monro ; and posteriorly it disappears in 

 the descending cornu. A vein beneath this band {vena corporis 

 striati) receives the blood from the corpus striatum, and empties 

 itself into the vena Galeni. 



The velum interpositum is a double fold of pia mater, which 

 passes into the anterior of the brain by the transverse fissure, 

 passing between the corpora quadrigemina and the posterior part 

 of the corpus callosum ; it supports the fornix, being interposed 

 between that body and the third ventricle. It is triangular in 

 shape, its apex corresponding to the anterior common opening ; 

 it consists of a layer derived from the posterior surface of the 

 cerebrum, and another from the anterior surface of the cere- 

 bellum. A process from it embraces the pineal gland ; and its 

 sides, projecting into the lateral ventricles, form the free borders 

 of the choroid plexuses. 



The choroid plexus is the vascular fringe in the lateral 

 ventricle, which stretches from the foramen of Monro to the 

 descending cornu, in the furrow between the hippocampus and the 

 corpus striatum. It is a highly vascular membrane, containing 

 looped plexuses of blood-vessels, and often calcareous matter. 

 The two plexuses are united by a cord which passes through the 

 foramen of Monro. 



The optic thalami (beds of the optic nerves) are the two large 

 oval bodies, seen when the fornix and hippocampi are removed, 

 embracing the anterior portion of the crura cerebri, and placed 

 in front of the corpora quadrigemina. They form the inferior 

 ganglia of the brain, and, like the corpora striata, consist of grey 

 matter, with intersecting white fibres, derived from the crura 



