﻿4-12 
  Prof. 
  Vlntosh 
  on 
  the 
  

  

  to 
  the 
  arch 
  of 
  the 
  canal. 
  It 
  is 
  now 
  noticed 
  that 
  the 
  wall 
  of 
  

   the 
  pharynx 
  is 
  greatly 
  thickened 
  by 
  muscular 
  layers, 
  which 
  — 
  

   with 
  the 
  massive 
  retractors 
  — 
  fill 
  up 
  a 
  large 
  part 
  of 
  the 
  body- 
  

   cavity 
  superiorly. 
  The 
  insertions 
  of 
  the 
  great 
  retractors 
  in 
  

   the 
  lateral 
  regions 
  are 
  crossed 
  by 
  the 
  circular 
  fibres, 
  which 
  

   extend 
  from 
  the 
  superior 
  fohl 
  (beneath 
  the 
  arch) 
  of 
  one 
  side 
  

   to 
  that 
  of 
  the 
  opposite, 
  thus 
  forming 
  a 
  strong 
  constricting 
  

   layer, 
  very 
  well 
  marked 
  inferiorly. 
  External 
  to 
  the 
  latter 
  at 
  

   the 
  ventral 
  surface 
  is 
  a 
  complex 
  layer 
  consisting 
  of 
  longi- 
  

   tudinal 
  fibres 
  mixed 
  with 
  a 
  radiating 
  series 
  which 
  pass 
  from 
  

   the 
  inner 
  margin 
  through 
  the 
  circular 
  coat. 
  Behind 
  the 
  

   foregoing 
  the 
  attachment 
  of 
  the 
  retractors 
  to 
  the 
  superior 
  

   raphe 
  is 
  evident, 
  the 
  breadth 
  of 
  the 
  circular 
  layer 
  is 
  increased, 
  

   especially 
  inferiorly, 
  and 
  the 
  vertical 
  series, 
  which 
  radiate 
  

   downward 
  through 
  the 
  latter, 
  form 
  a 
  prominent 
  mass 
  — 
  ■ 
  

   striated 
  with 
  cross-fibres 
  — 
  inferiorly. 
  The 
  ventral 
  region 
  

   or 
  floor 
  of 
  the 
  pharynx 
  has 
  again 
  opened 
  out 
  into 
  a 
  less 
  

   compact 
  and 
  apparently 
  a 
  chitinous 
  tissue. 
  The 
  structure 
  

   remains 
  similar 
  in 
  the 
  next 
  section 
  superiorly, 
  but 
  inferiorly 
  

   the 
  mobile 
  glandular 
  region 
  of 
  the 
  pharynx 
  appears 
  in 
  the 
  

   middle 
  of 
  the 
  great 
  muscular 
  mass, 
  the 
  sides 
  and 
  ventral 
  

   region 
  being 
  formed 
  by 
  a 
  complex 
  meshwork 
  of 
  muscular 
  

   fibres 
  — 
  longitudinal, 
  oblique, 
  and 
  radiating 
  — 
  which 
  connect 
  

   the 
  inferior 
  to 
  the 
  superior 
  mass. 
  In 
  full 
  development 
  this 
  

   system 
  shows 
  a 
  great 
  central 
  region 
  of 
  folded 
  glandular 
  

   tissue, 
  surrounded 
  superiorly 
  by 
  the 
  circular 
  fibres 
  and 
  the 
  

   retractors, 
  laterally 
  and 
  inferiorly 
  by 
  the 
  densely 
  interlaced 
  

   muscular 
  fibres, 
  those 
  next 
  the 
  canal, 
  however, 
  being 
  chiefly 
  

   circular 
  in 
  direction. 
  The 
  muscular 
  envelope 
  next 
  diminishes 
  

   in 
  thickness, 
  and 
  is 
  confined 
  for 
  the 
  most 
  part 
  to 
  the 
  lower 
  

   half 
  of 
  the 
  canal. 
  Within 
  is 
  the 
  circular 
  coat, 
  which 
  pro- 
  

   ceeds 
  almost 
  to 
  the 
  superior 
  arch 
  (in 
  transverse 
  section) 
  ; 
  

   then 
  inferiorly 
  is 
  a 
  considerable 
  belt 
  of 
  longitudinal 
  fibres 
  

   with 
  interfascicular 
  substance. 
  This 
  coating 
  descends 
  lower 
  

   until 
  it 
  forms 
  — 
  for 
  the 
  somewhat 
  specialized 
  ventral 
  floor 
  

   of 
  the 
  region 
  — 
  an 
  inner 
  strong 
  circular 
  band, 
  and 
  a 
  radiated 
  

   mass 
  (with 
  longitudinal 
  fibres) 
  nearly 
  as 
  broad 
  beneath, 
  the 
  

   fibres 
  passing 
  vertically 
  through 
  the 
  former 
  to 
  the 
  glandular 
  

   border. 
  This 
  complex 
  arrangement 
  — 
  diminishing 
  to 
  a 
  mere 
  

   speck 
  — 
  finally 
  disappears, 
  and 
  leaves 
  the 
  chamber 
  surrounded 
  

   ouly 
  by 
  its 
  proper 
  walls, 
  which 
  at 
  the 
  termination 
  of 
  the 
  

   pharyngeal 
  poition 
  are 
  a 
  thick 
  basement-tissue 
  and 
  an 
  outer 
  

   layer 
  of 
  longitudinal 
  and 
  circular 
  fibres. 
  

  

  The 
  pharyngeal 
  region 
  is 
  interesting 
  as 
  containing 
  that 
  

   portion 
  of 
  the 
  canal 
  which, 
  to 
  a 
  greater 
  or 
  less 
  extent, 
  is 
  

   thrust 
  into 
  the 
  proboscis 
  in 
  extreme 
  extrusion, 
  and 
  the 
  

  

  