﻿ON 
  THE 
  BHANOIIIAL 
  VESSEL^ 
  OF 
  STBUNASFIS. 
  5 
  

  

  to 
  the 
  braucliial 
  plate, 
  from 
  which 
  the 
  gills 
  arise; 
  and 
  the 
  

   second 
  region 
  is 
  the 
  intermediate 
  part, 
  generally 
  swollen, 
  and 
  

   differing 
  in 
  structure 
  from 
  the 
  other 
  two. 
  

  

  Taking 
  til 
  e 
  third 
  region 
  first 
  (figs. 
  1, 
  12, 
  13 
  and 
  14), 
  we 
  

   find 
  that 
  it 
  contains 
  a 
  slender 
  blood-vessel 
  with 
  thin 
  walls 
  (figs. 
  

   12, 
  13 
  and 
  14, 
  cr). 
  This 
  is 
  the 
  branchial 
  artery 
  of 
  Vejdovsky 
  

   and 
  Rietsch, 
  which 
  we 
  may 
  call 
  the 
  communicating 
  vessel, 
  

   for 
  reiisons 
  which 
  will 
  appear 
  later. 
  Its 
  walls 
  are 
  formed, 
  

   like 
  those 
  of 
  any 
  other 
  small 
  blood-vessel, 
  of 
  a 
  single 
  layer 
  of 
  

   granular 
  cells 
  with 
  ordinary 
  rounded 
  nuclei 
  irregularly 
  dis- 
  

   tributed. 
  The 
  communicating 
  vessel 
  is 
  capable 
  of 
  consider- 
  

   able 
  distension; 
  but 
  in 
  section 
  it 
  generally 
  appears 
  much 
  

   folded, 
  and 
  with 
  a 
  very 
  contracted 
  lumen 
  (fig. 
  5, 
  cv). 
  

  

  The 
  so-called 
  "axis," 
  along 
  one 
  side 
  of 
  which 
  this 
  

   vessel 
  is 
  closely 
  applied, 
  is 
  in 
  reality 
  a 
  second 
  blood- 
  

   vessel 
  with 
  specialised 
  contractile 
  walls. 
  It 
  is 
  in 
  

   fact 
  the 
  most 
  important 
  blood-vessel 
  in 
  the 
  whole 
  branchial 
  

   circulation. 
  This 
  highly 
  contractile 
  vessel, 
  which 
  may 
  be 
  

   called 
  the 
  dorsal 
  branchial 
  vessel, 
  has 
  its 
  walls 
  formed 
  

   of 
  a 
  regular 
  series 
  of 
  ring-shaped 
  cells, 
  with 
  their 
  large 
  oval 
  

   nuclei 
  situated 
  in 
  a 
  row 
  on 
  the 
  surface 
  opposite 
  to 
  that 
  to 
  

   which 
  the 
  connnunicating 
  vessel 
  is 
  attached 
  (figs. 
  5 
  and 
  lo,7i). 
  

   These 
  nuclei 
  have 
  been 
  well 
  figured 
  by 
  Vejdovsky 
  (6). 
  Inside 
  

   the 
  dorsal 
  branchial 
  vessel 
  runs 
  a 
  peculiar 
  rod 
  of 
  tissue, 
  to 
  

   which 
  alone 
  the 
  name 
  " 
  axis" 
  should 
  be 
  applied. 
  

  

  This 
  axial 
  rod 
  consists 
  not 
  of 
  longitudinal 
  fibres, 
  as 
  

   described 
  by 
  Rietsch, 
  but 
  rather 
  of 
  cartilage-like 
  cells, 
  as 
  

   mentioned 
  by 
  Vejdovsky 
  in 
  his 
  first 
  memoir 
  (5). 
  As 
  will 
  be 
  

   understood 
  on 
  comparing 
  figs. 
  12 
  and 
  13, 
  it 
  is 
  formed 
  of 
  a 
  

   slightly 
  irregular 
  row 
  of 
  cells, 
  with 
  a 
  thick 
  hyaline 
  common 
  

   wall 
  turned 
  towards 
  the 
  cavity 
  of 
  the 
  blood-vessel 
  (fig. 
  13, 
  oa). 
  

   The 
  cells 
  are 
  attached 
  to 
  the 
  wall 
  of 
  the 
  vessel, 
  on 
  the 
  same 
  

   side 
  as 
  the 
  communicating 
  vessel 
  lying 
  outside, 
  by 
  means 
  of 
  

   obliquely 
  placed 
  stalk-like 
  bases. 
  In 
  the 
  living 
  tissue 
  the 
  

   cells 
  of 
  the 
  axis 
  are 
  seen 
  to 
  present 
  a 
  peculiar 
  vacuolated 
  

   appearance, 
  with 
  a 
  few 
  highly 
  refractive 
  granules 
  (fig. 
  12). 
  

   Lying 
  on 
  the 
  surface 
  of 
  ihe 
  axis 
  are 
  occasionally 
  seen 
  small 
  

  

  