i8o 



PHYSIOLOGY FOR BEGINNERS 



CHAP. 



nerve fibres, and nerve cells ; and of these elements the brain 

 and spinal cord are made up. 



The Membranes of the Brain and Spinal Cord. The 

 brain is protected by the bones which form the walls of the 



FIG. 82. Transverse section of one half of the spinal cord in the lumbar region, 

 t, Anterior fissure ; 2, posterior fissure ; 3, central canal ; 4, 5, bridges connecting the 



grey matter in the two halves of the cord ; 6, posterior column of white matter ; 



7, lateral column ; 8, anterior column ; 9, posterior root ; 10, anterior root. 

 a, Posterior horn of grey matter ; e, anterior horn ; blood-vessels are represented 



passing in from the pia mater covering the cord. 



cavity of the cranium, and the spinal cord is protected by the 

 vertebrae which form the walls of the vertebral canal in which 

 the spinal cord lies. The bony walls of these cavities are 

 lined by a tough fibrous membrane, which serves as the inside 



