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THE NERVOUS SYSTEM 



connecting all regions of the brain with the neural 

 cavity of the spinal cord. In life this cavity (the ven- 

 tricles) is filled with a liquid known as the cerebrospinal 

 fluid and the entire cavity is lined with 

 a layer of ciliated epithelium. The 

 third, fourth, and lateral ventricles are 

 also supplied with blood from a net- 

 work of blood vessels called the choroid 

 plexus. Rupture and hemorrhage of the 

 blood vessels of the lateral ventricles pro- 

 duces pressure upon the inside of the 

 hemispheres and is one cause of apoplexy. 

 If we cut slices at right angles to the 

 longitudinal fissure in either hemisphere, 

 we find that, like the cerebellum, the 

 solid part of the cerebral hemispheres 

 is composed of two kinds of matter, 

 white and gray, surrounding a central 

 cavity (the lateral ventricle). The out- 

 side of the hemispheres and folds is 

 called the cortex and is composed of 

 gray matter: the white matter forming 

 the core of this part of the brain. 



The human spinal cord. — This cord, 

 which is an extension of the medulla, 

 extends from the foramen magnum 

 through the spinal cavities of the ver- 

 tebrae to the articulation of the first 

 and second lumbar vertebrae. From 

 here it narrows off into a slender filament which runs 

 back to the end of the neural canal behind the sacrum. 

 It is nearly cylindrical in form, being sUghtly flattened 



Fia. 186 — The human 

 spinal cord and its 

 branches. 



