REGULATINa  THE  CONTEACTIONS  OF  THE  AETEEIES. 
625 
centre.  The  exsanguine  condition  of  the  web  in  the  former  case,  and  the  turgid  state 
of  the  vessels  in  the  latter,  were  simply  the  effects  of  the  variations  of  calibre  in  the 
arteries,  the  blood  flowing  more  freely  in  proportion  to  their  width  *. 
To  sum  up  the  principal  results  of  this  inquiry,  it  appears — 
1st.  That,  of  the  nervous  centres  usually  recognised,  the  cerebro-spinal  axis  is  the  only 
part  which  regulates  the  contractions  of  the  arteries  of  the  webs ; this  function  being 
apparently  exercised  by  the  whole  length  of  the  cord  and  the  posterior  part  of  the  brain, 
operating  through  fibres  which  arise  from  the  same  region  of  the  cord  as  do  those 
through  which  sensation  and  motion  are  effected  in  the  hind  legs. 
2nd.  That  there  exists  within  the  limb  some  means,  probably  ganglionic,  by  virtue  of 
which  the  fibre-cells  of  the  circular  coat  of  the  arteries  may  contract  in  concert  with 
each  other,  independently  of  any  ganglia  contained  in  the  trunk. 
And  3rd,  that  the  local  coordinating  apparatus,  though  capable  of  independent  action 
in  special  conditions  of  direct  irritation,  is,  under  ordinary  circumstances,  in  strict  subor- 
dination to  the  spinal  system ; while  a remarkable  provision  exists  for  the  maintenance  of 
this  control,  notwithstanding  almost  complete  severance  of  nervous  connexion  between 
the  cord  and  the  limb. 
* The  subject  of  the  effect  of  variations  in  the  calibre  of  the  arteries  upon  the  flow  through  the  capillaries, 
will  be  found  fully  discussed  in  the  paper  “ On  the  Early  Stages  of  Inflammation,”  published  in  this  volume. 
4 N 2 
