THE NERVOUS SYSTEM 



the adhesions would interfere with the movements of the 

 vertebra upon each other. The dura mater sends off 

 branches over each of the spinal nerves. The arachnoid 

 membrane is continuous with that of the brain. Its spaces 

 contain a watery fluid in which the cord may float. 



The pia mater immediately invests the cord, and 

 serves to support it; it plays a different role here, there- 

 fore, than it does in the brain. It is less vascular and 



I -p. 



FlG. no. Spinal cord, cervical region (diagrammatic), showing secondary 

 tracts of white matter, the dark area representing descending fibers, dotted 

 area ascending fibers, cross-lined area mixed fibers, and clear area gray mat- 

 ter : /./., Direct pyramidal tract ; a.g.b., anterior ground-bundle ; d.c. t direct 

 cerebellar tract ; a.a.l., ascending anterolateral or Gowers' tract ; c.p., crossed 

 pyramidal tract; d.a.l., descending anterolateral tract; m./., mixed lateral 

 tract; g, column of Goll; b, column of Burdach (Leroy). 



more fibrous in structure than the pia mater of the brain. 

 It is closely adherent to the cord, forming what is called 

 the neurilemma. The pia mater sends off ligaments from 

 each side to steady the spinal cord; these are called the 

 ligamenta dentata; they are eighteen to twenty in number 

 on each side, and lie between the anterior and posterior 

 roots of the spinal nerves. 



The Spinal cord is that part of the cerebrospinal axis 

 contained in the vertebral canal. It is a continuation of 



