CIRCULATION IN ITS NERVINE BEARINGS 93 



lemmae. In other words, that the meningeal coverings of 

 the various nerves are not reflected back into the cerebro- 

 spinal cavity, but that they continue or progress with their 

 dividing interspaces to the ultimate extremities of each 

 terminal fibre, both sensory, motor, and sympathetic 



FIG. 24. SECTION THROUGH THE PLACE OF EXIT OF A SPINAL NERVE- 

 ROOT THROUGH THE DURA MATER. (Key and Retzius.) 



a, bundles of the nerve-root becoming collected into a single bundle as they emerge ; 

 b, dura mater ; c, arachnoid ; d, a reticular lamella of the arachnoid reflected 

 along the nerve-root ; s, subdural space ; s', s', subarachnoid space. 



" nerui communicantes" and that they end with the nerve 

 endings. Thus we find, as we strongly suspected we would, 

 that a great series of excretory tubes with safety-valve 

 outlets have been introduced into the mechanism of this 

 cerebro-spinal " shut sac," subserving, no doubt, impor- 

 tant, yea, absolutely essential functions, in the regulation of 

 intra-cranial and intra-spinal pressure and the provision of 

 excretory facilities. 



