﻿BLOOMEE 
  : 
  ON 
  THE 
  ANATOMY 
  OF 
  PSA3IM0BIA. 
  233 
  

  

  longitudinal 
  in 
  direction, 
  beginning 
  from 
  the 
  outside. 
  The 
  outer 
  

   longitudinal 
  muscles 
  form 
  a 
  broad 
  band, 
  whilst 
  the 
  inner 
  longitudinal 
  

   ones 
  are 
  grouped 
  into 
  six 
  semicircular 
  masses 
  facing 
  inwards. 
  

   Kunning 
  from 
  the 
  outer 
  to 
  the 
  inner 
  annular 
  band 
  are 
  a 
  number 
  of 
  

   muscle-fibres 
  constituting 
  the 
  transverse 
  muscles 
  which 
  pass 
  between 
  

   the 
  longitudinal 
  muscles 
  and 
  through 
  the 
  middle 
  annular 
  band. 
  At 
  

   the 
  proximal 
  end 
  of 
  each 
  lateral 
  side 
  the 
  muscles 
  of 
  the 
  siphonal 
  tubes 
  

   are 
  drawn 
  together 
  into 
  a 
  short 
  rounded 
  muscle, 
  which 
  quickly 
  

   spreads 
  out 
  into 
  a 
  large 
  disc 
  and 
  forms 
  the 
  enlarged 
  portion 
  of 
  the 
  

   siphonal 
  retractor 
  muscle 
  that 
  is 
  inserted 
  into 
  the 
  shell. 
  As 
  

   before 
  mentioned, 
  the 
  siphonal 
  tubes 
  are 
  capable 
  of 
  not 
  only 
  great 
  

   elongation 
  but 
  also 
  of 
  great 
  contraction. 
  In 
  the 
  latter 
  case 
  the 
  

   contracted 
  tubes 
  often 
  widen 
  to 
  large 
  dimensions, 
  whilst 
  the 
  proximal 
  

   portions 
  are 
  partly 
  introverted 
  into 
  the 
  pedal 
  cavity. 
  

  

  The 
  anterior 
  adductor 
  muscle 
  (Fig. 
  2, 
  A. 
  A.) 
  is 
  wide, 
  convex 
  on 
  

   the 
  dorso-anterior 
  surface, 
  slightly 
  concave 
  on 
  the 
  veiitro-posterior 
  

   surface, 
  and 
  spreads 
  out 
  towards 
  the 
  ends, 
  which 
  conform 
  to 
  the 
  

   curvature 
  of 
  the 
  shell. 
  On 
  the 
  convex 
  surface 
  it 
  is 
  attached 
  to 
  the 
  

   pallium, 
  and 
  on 
  the 
  dorso-posterior 
  surface 
  to 
  the 
  anterior 
  retractor 
  

   and 
  anterior 
  protractor 
  muscles. 
  

  

  The 
  posterior 
  adductor 
  (Fig. 
  2, 
  P. 
  A.) 
  is 
  a 
  large 
  muscle 
  spreading 
  

   out 
  towards 
  the 
  ends, 
  and 
  likewise 
  conforming 
  to 
  the 
  convexity 
  of 
  the 
  

   shell. 
  It 
  is 
  attached 
  to 
  the 
  pallium, 
  except 
  at 
  the 
  antero-dorsal 
  

   surface, 
  where 
  the 
  bifurcations 
  of 
  the 
  retractor 
  pedis 
  posterior 
  muscle 
  

   rest 
  upon 
  it. 
  

  

  The 
  musculus 
  crucifurmis 
  (Fig. 
  2, 
  II.C.) 
  situated 
  at 
  the 
  postero- 
  

   ventral 
  edge 
  of 
  the 
  pallium, 
  and 
  ventrally 
  to 
  the 
  posterior 
  adductor 
  

   muscle, 
  is 
  divided 
  at 
  each 
  end 
  into 
  two 
  branches. 
  One 
  branch 
  proceeds 
  

   some 
  distance 
  anteriorly 
  and 
  buries 
  itself 
  in 
  the 
  mantle-lobe, 
  then, 
  

   emerging 
  on 
  the 
  outside, 
  is 
  inserted 
  into 
  the 
  shell. 
  The 
  other 
  

   branch 
  goes 
  some 
  distance 
  dorso-posteriorly, 
  and 
  in 
  a 
  like 
  manner 
  also 
  

   becomes 
  attached 
  to 
  the 
  shell. 
  

  

  Pedal 
  Muscles. 
  — 
  The 
  foot 
  (Fig. 
  2, 
  F.) 
  is 
  large, 
  very 
  muscular, 
  and 
  

   capable 
  of 
  great 
  expansion. 
  The 
  intrinsic 
  muscles 
  are 
  annular, 
  

   longitudinal, 
  and 
  transverse. 
  The 
  annular 
  muscles 
  constitute 
  the 
  

   pedal 
  integument, 
  and 
  near 
  its 
  lateral 
  inside 
  walls 
  run 
  the 
  powerful 
  

   longitudinal 
  muscles 
  which 
  traverse 
  nearly 
  the 
  whole 
  length 
  of 
  the 
  foot, 
  

   whilst 
  passing 
  from 
  side 
  to 
  side 
  are 
  transverse 
  muscle 
  bundles 
  ; 
  in 
  the 
  

   proximal 
  part 
  they 
  are 
  of 
  some 
  length 
  and 
  pass 
  through 
  the 
  viscera, 
  

   the 
  ends 
  spreading 
  out 
  and 
  going 
  between 
  the 
  longitudinal 
  muscles 
  

   to 
  tlie 
  integument; 
  in 
  the 
  middle 
  of 
  the 
  foot 
  they 
  also 
  occupy 
  the 
  

   central 
  area, 
  having 
  spaces 
  between 
  them 
  which 
  form 
  the 
  pedal 
  sinus, 
  

   but 
  towards 
  the 
  distal 
  end 
  they, 
  together 
  with 
  the 
  longitudinal 
  ones, 
  

   fray 
  out, 
  resulting 
  in 
  a 
  large 
  muscular 
  meshwork. 
  

  

  The 
  retractor 
  pedis 
  anterior 
  muscles 
  (Fig. 
  2, 
  P.P. 
  A.) 
  are 
  short 
  and 
  

   tliick, 
  but 
  not 
  bifurcated 
  ; 
  they 
  pass 
  dorsally 
  along 
  the 
  rear 
  side 
  of 
  

   the 
  anterior 
  adductor 
  muscle, 
  and 
  are 
  inserted 
  into 
  the 
  shell 
  close 
  to 
  the 
  

   latter, 
  and 
  the 
  fibres 
  of 
  their 
  proximal 
  part 
  pass 
  ventrally 
  through 
  the 
  

   foot, 
  spreading 
  out 
  fan-shaped. 
  

  

  The 
  protractor 
  pedis 
  anterior 
  muscles 
  are 
  large 
  but 
  short, 
  and 
  

  

  