698 



THE NERVOUS SYSTEM 



covers the choroid plexus. When this epitheHum is torn through and the choroid 

 plexus pushed forwards, the fascia dentata is exposed; the latter structure is placed 

 above the dentate fissure, between the fiml)ria and the uncinate gyrus. 



The choroid plexuses are vascular fringes formed i)y an infolding of the pia 

 mater in the region of the so-called great transverse fissure. They extend from 

 the termination of the descending cornua to the foramina of Monro, through which 

 they disappear. The epithelial lining of the ventricle passes from the thin (appar- 

 ently free) edge of the fimbria over the choroid plexus to the taenia semicircularis. 

 This epithelium, which is the morphological wall of the cornu, excludes the choroid 

 plexus (strictly speaking) from the ventricular cavity. 



Tlie foramina of Monro are the apertures through Avhich the lateral ventricles 

 communicate with the third ventricle, forming at their communication a Y-shaped 

 passage, the foramen commune anterius, by means of which the lateral ventricles 



Fig. 418. — A Dissection showixg the Free or Intraventricular Portion of the Cau- 

 date Nucleus. The Mesial and Tentorial Surfaces of the Hemisphere are 

 also shown. 



(From a mounted specimen iu the Anatomical Department of Trinity College, Dublin.) 



EXTRAVENTRICULAR PART 

 OF OPTIC THALAMUS 



SULCUS 

 CHOROIDEUS 



CALLOSO-MARGISA I, 

 FISSURE 



CORPl'S CALLOSVM 



INTFR \ 4 /■ 



PAH It TO 



OCCII IT\r 



FIS:i L KL 



~ COMMISSrRE 

 BVSDLE OF 

 r/ry DAy.YR 



DENTA TE 



FLSSURE 



CORPUS GENICULA TUM 

 INTERXUM 



UNCUS 



of opposite sides communicate with one another. The clioroid plexuses of the 

 lateral ventricles are continuous with one another through this passage. Each 

 foramen of ]\Ionro is crescentic in outline, and is bounded in front and above by 

 the anterior pillars of the fornix; below and behind by the anterior extremity of 

 the optic thalamus; and l)ohin(l V)y the reflexions of ei)itlielium from the fornix and 

 optic thalamus on to tlic clioroid plexus. 



The fascia dentata, or dentate convolution, is the free edge of the grey 

 matter of the hemisphere, and derives its name from its characteristically notched 

 or indented appearance. It is placed above the dentate fissure, and follows this 

 fissure upwards towards the splenium of the corpus callosum, where it becomes 

 continuous with the fasciola cinerea. The fasciola cinerea is a grey lamina 

 resembling the fascia dentata but with a smooth margin. It ends just above the 

 splenium of the corpus callosum. 



