﻿Almost 
  as 
  soon 
  as 
  they 
  unite 
  they 
  again 
  divide, 
  a 
  branch 
  pass- 
  

   ing 
  to 
  each 
  side 
  through 
  the 
  brain 
  tissue, 
  and 
  at 
  a 
  point 
  

   somewhat 
  posterior 
  to 
  their 
  division, 
  they 
  unite 
  with 
  the 
  two 
  

   returning 
  branches 
  alread}' 
  mentioned, 
  to 
  form 
  lateral 
  ves- 
  

   sels, 
  one 
  on 
  each 
  side 
  of 
  and 
  just 
  along 
  the 
  base 
  of 
  the 
  brain, 
  

   which 
  pass 
  into 
  the 
  auricle, 
  and 
  so 
  form 
  a 
  complete 
  circuit 
  

   of 
  vessels 
  for 
  blood 
  transmission 
  ; 
  for 
  by 
  this 
  time 
  a 
  passage 
  

   has 
  been 
  made 
  from 
  the 
  ventricle 
  along 
  the 
  floor 
  of 
  the 
  head, 
  

   and 
  just 
  beneath 
  the 
  oesophagus, 
  to 
  the 
  already 
  mentioned 
  

   branchial 
  vessels. 
  

  

  Through 
  the 
  passage-way 
  thus 
  formed, 
  a 
  flow 
  of 
  blood, 
  or 
  

   same 
  kind 
  of 
  fluid 
  containing 
  roundish 
  or 
  irregular 
  bits 
  of 
  

   tissue 
  material, 
  takes 
  place. 
  This 
  flow 
  of 
  blood 
  serum, 
  with 
  

   its 
  white 
  or 
  transparent 
  corpuscles, 
  through 
  the 
  2d 
  branchial 
  

   vessels, 
  forms, 
  in 
  the 
  young 
  Smelt, 
  the 
  first 
  blood-system, 
  

   which 
  is 
  entirely 
  a 
  head 
  circulation. 
  Fig. 
  3, 
  PI. 
  V. 
  The 
  

   same 
  thing 
  takes 
  place 
  in 
  the 
  Shad. 
  Up 
  to 
  this 
  time 
  no 
  con- 
  

   nection 
  exists 
  between 
  the 
  rest 
  of 
  the 
  branchial 
  vessels 
  and 
  

   the 
  2d 
  vessel, 
  or 
  between 
  each 
  other. 
  But 
  soon 
  the 
  3d, 
  4th 
  

   and 
  5th 
  vessels 
  turn 
  forward 
  and 
  unite 
  into 
  a 
  common 
  vessel, 
  

   which 
  passes 
  forward 
  to 
  supply 
  the 
  head 
  and 
  brain 
  with 
  

   blood, 
  and 
  which, 
  sooner 
  or 
  later, 
  unites 
  with 
  the 
  dorsal 
  

   branch 
  from 
  the 
  2d 
  branchial 
  vessel, 
  since 
  all 
  the 
  branches 
  

   eventually 
  unite 
  into 
  the 
  vessels 
  (jugular 
  veins), 
  which 
  run 
  

   along 
  the 
  basal 
  side 
  of 
  the 
  brain 
  to 
  return 
  the 
  blood 
  to 
  the 
  

   heart. 
  The 
  sixth 
  branchial 
  aorta, 
  which 
  originates 
  from 
  

   the 
  fifth, 
  passes 
  directly 
  upward, 
  inward 
  and 
  backward, 
  

   until, 
  upon 
  the 
  median 
  line, 
  it 
  unites 
  with 
  its 
  fellow 
  branch 
  

   of 
  the 
  opposite 
  side 
  to 
  form 
  an 
  open, 
  isolated 
  tube 
  around 
  

   the 
  head, 
  which 
  has 
  connection 
  only 
  with 
  the 
  ventral 
  aorta 
  

   through 
  the 
  fifth 
  vessel, 
  just 
  anterior 
  to 
  the 
  bulbus 
  arterio- 
  

   sus, 
  which, 
  by 
  this 
  time, 
  has 
  formed 
  in 
  front 
  of 
  the 
  ventricle 
  

   of 
  the 
  heart, 
  and 
  connected 
  with 
  it. 
  During 
  the 
  time 
  the 
  

   first 
  circulation 
  is 
  in 
  progress, 
  corpuscles 
  can 
  be 
  followed 
  

   from 
  the 
  heart 
  into 
  these 
  posterior 
  four 
  pairs 
  of 
  partially 
  

   excavated 
  vessels, 
  where 
  they 
  are 
  stopped 
  in 
  their 
  onward 
  

  

  