CEREBRAL VENTRICLES. 



165 



its interior, a great part of its surface is also covered with, 

 it. By the external convolutions of the cerebellum and 

 the cerebral hemispheres the surface over which this gray 

 substance is spread is very much increased (see Fig. 68). 



The Ventricles of the Brain. The minute central 

 canal of the spinal cord is continued into the brain and 

 expands there at several points into chambers known as the 

 ventricles. Entering the medulla oblongata it approaches 

 its upper surface and dilates into the fourth ventricle, 

 which has a very thin roof, lapped over by the cerebellum. 

 From the front of the fourth ventricle runs a narrow pas- 



VI 



FIG. 68. A vertical section across the cerebral hemisph,eres. Ccl*. the corpus 

 callosurn : VI, the anterior end of the right lateral ventricle: the gray mass on 

 its exterior is the corpus striatum. On the left side the superficial gray matter 

 covering the convolutions is shaded. 



sage (Her a tertio ad quartum ventriculum) which enters 

 another dilatation lying in the middle : Kne near the under 

 side of the fore-brain (just above the two small rounded 

 masses seen between the nerves // and /// in Fig. 70) and 

 known as the third ventricle. From the third ventricle 

 two apertures (the foramens of Monro) lead into the first 

 and second, or lateral ventricles, one of which lies in each 



