DRAINAGE AREAS OF THE SKULL 147 



into the great inter-meningeal cavities, or channels, sur- 

 rounding the spinal cord (Figs. 59, 60), as well as of 

 what escapes from the fourth ventricle by way of the 

 central canal, a truly considerable, or even large, quantity, 

 but ideally adapted, through inter-meningeal distribution 

 and attachments, to provide a fluid encasement and 

 yielding surrounding medium, in which the spinal cord is 

 floated without the possibility of contact with its skeletal 

 framework the ligamentum dentatum acting as a dual 

 valve against sudden, or large, lateral displacement, while 

 maintaining free longitudinal movement or circulation. 



Under these circumstances over-pressure is relieved, 

 when necessary, both in brain and cord, through the 

 cephalic and spinal nerve continuations of the sub- 

 arachnoid and sub-dural spaces, by calls being made on 

 both the afferent and efferent systemic nervatures, 

 whereby the skin and muscles are made to provide the 

 required outlet facilities, or excretory agencies. 



