414 CORNUA OF THE LATERAL VENTRICLES. 



The choroid plexus presents upon the surface a number of minute 

 vascular processes, which are termed villi. They are invested by a 

 very delicate epithelium, surmounted by cilia, which have been seen 

 in active movement in the embryo. In their interior the plexuses 

 not unfrequently contain particles of calcareous matter, and they are 

 sometimes covered by small clusters of serous cysts. 



The Corpus fimbriatum is a narrow white band, which is situated 

 immediately behind the choroid plexus, and extends with it into the 

 descending cornu of the lateral ventricle. It is in fact the lateral thin 

 edge of the fornix, and being attached to the hippocampus major in 

 the descending horn of the lateral ventricle, is also termed, tenia 

 hippocampi. 



The Fornix is a white layer of medullary substance, of which a 

 portion only is seen in this view of the ventricle. 



The Anterior cornu is triangular in its form, sweeping outwards, 

 and terminating by a point in the anterior lobe of the brain, at a short 

 distance from its surface. 



The Posterior cornu or digital cavity curves inwards, as it extends 

 back into the posterior lobe of the brain, and likewise terminates near 

 the surface. An elevation corresponding with a deep sulcus between 

 two convolutions projects into the area of this cornu, and is called 

 the hippocampus minor. 



The Middle or descending cornu, in descending into the middle lobe 

 of the brain, forms a very considerable curve, and alters its direction 

 several times as it proceeds. Hence it is described as passing back- 

 wards and outwards and downwards, and then turning forwards and 

 inwards. This complex expression of a very simple curve has given 

 birth to a symbol formed by the primary letters of these various terms ; 

 and by means of this the student recollects with ease the course of the 

 cornu, BODPI. It is the largest of the three cornua, and terminates 

 close to the fissure of Sylvius, after having curved around the crus 

 cerebri. 



The middle cornu should now be laid open, by inserting the little 

 finger into its cavity, and making it serve as a director for the scalpel 

 in cutting away the side of the hemisphere, so as to expose it com- 

 pletely. 



The Superior boundary of the middle cornu is formed by the under 

 surface of the thalamus opticus, upon which are the two projections 

 called corpus geniculatum internum and externum ; and the inferior 

 wall by the various parts which are often spoken of as the contents 

 of the middle cornu : these are the 



Hippocampus major, 



Pes hippocampi, 



Pes accessorius, 



Corpus fimbriatum, 



Choroid plexus, 



Fascia dentata,* 



Transverse fissure. 



