﻿472 
  REPORT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  [4GJ 
  

  

  tiation 
  of 
  the 
  lateral 
  musculature, 
  accouipauied 
  with 
  extensive 
  abortion 
  

   of 
  the 
  myotomes, 
  illustrates 
  this 
  principle. 
  In 
  this 
  case, 
  the 
  tail 
  being- 
  

   aborted 
  for 
  the 
  most 
  part, 
  the 
  muscles 
  of 
  the 
  sides 
  of 
  the 
  thorax, 
  

   which 
  is 
  much 
  elevated, 
  are 
  prolonged 
  backwards 
  and 
  end 
  in 
  tendinous 
  

   cords 
  which 
  actuate 
  the 
  rudder 
  like 
  caudal 
  as 
  well 
  as 
  the 
  dorsal 
  and 
  

   anal 
  fins. 
  Tbe 
  consequent 
  advance 
  of 
  the 
  origins 
  of 
  these 
  muscles 
  for- 
  

   ward 
  admits 
  of 
  their 
  nerve 
  supply 
  being 
  sent 
  to 
  them 
  farther 
  forward. 
  

   We 
  have 
  apparently, 
  as 
  a 
  consequence 
  of 
  this 
  advance 
  forward, 
  the 
  

   restriction 
  backward 
  of 
  the 
  medulla 
  spinalis. 
  

  

  The 
  inconsiderable 
  development 
  of 
  the 
  musculature 
  of 
  the 
  paired 
  

   fins 
  of 
  most 
  fishes, 
  and 
  the 
  segmental 
  arrangement 
  of 
  that 
  of 
  the 
  ver- 
  

   tical 
  fins, 
  would 
  obviously 
  tend 
  to 
  maintain 
  the 
  uniform 
  backwardly 
  

   tapering 
  form 
  of 
  tbe 
  medulla 
  spinalis, 
  as 
  seen 
  in 
  its 
  simplest 
  form 
  in 
  

   Branchiostoma, 
  in 
  which 
  we 
  also 
  behold 
  the 
  most 
  unmodified 
  and 
  

   archaic 
  type 
  of 
  the 
  myotome 
  or 
  muscular 
  segment. 
  

  

  A 
  consideration 
  of 
  these 
  facts 
  therefore 
  leads 
  me 
  to 
  state 
  the 
  follow- 
  

   ing 
  as 
  a 
  general 
  principle, 
  viz, 
  that 
  pari 
  passu 
  with 
  the 
  gradual 
  sup- 
  

   pression 
  of 
  myotomes 
  in 
  the 
  course 
  of 
  the 
  progressive 
  evolution 
  of 
  

   forms 
  and 
  the 
  differentiation 
  of 
  the 
  musculature 
  of 
  the 
  appendicular 
  

   skeleton 
  was 
  the 
  medulla 
  spinalis 
  differentiated 
  into 
  regions 
  and 
  its 
  rear- 
  

   ward 
  extension 
  curtailed 
  in 
  consequence 
  of 
  tbe 
  degeneration 
  into 
  ten- 
  

   don 
  of 
  the 
  musculature 
  of 
  the 
  urosome. 
  

  

  While 
  the 
  muscles 
  of 
  the 
  base 
  of 
  the 
  tail 
  of 
  cetaceans 
  are 
  pro- 
  

   digiously 
  developed 
  as 
  rearward 
  extensions 
  dorsally 
  of 
  the 
  erectores 
  

   and 
  multijidus 
  spinaj 
  and 
  ventrally 
  as 
  extensions 
  of 
  the 
  system 
  repre- 
  

   sented 
  by 
  the 
  psoas 
  of 
  terrestrial 
  types, 
  they 
  nevertheless, 
  in 
  the 
  region 
  

   of 
  the 
  caudal 
  peduncle 
  end 
  as 
  tendons, 
  these 
  animals 
  therefore 
  so 
  far 
  

   resembling 
  other 
  land 
  forms 
  with 
  degenerate 
  tails, 
  so 
  that 
  it 
  is 
  al- 
  

   together 
  doubtful 
  if 
  motor 
  nerve 
  fibers 
  enter 
  into 
  this 
  portion 
  at 
  all, 
  

   the 
  presence 
  of 
  sensory 
  and 
  vaso-motor 
  fibers 
  alone 
  being 
  indicated. 
  

  

  The 
  Cetacea, 
  according 
  to 
  Cunningham, 
  have 
  the 
  medulla 
  spinalis 
  

   swollen 
  in 
  the 
  same 
  way 
  as 
  other 
  mammal 
  in 
  the 
  cervical 
  and 
  lumbar 
  

   regions, 
  whence 
  the 
  limb 
  plexuses 
  originate. 
  A 
  similar 
  differentiation 
  

   is 
  foreshadowed 
  in 
  the 
  anterior 
  part 
  of 
  the 
  medulla 
  spinalis 
  of 
  the 
  

   skate, 
  Baia 
  batis, 
  according 
  to 
  Owen, 
  in 
  which 
  there 
  is 
  " 
  a 
  slight 
  (bra- 
  

   chial 
  or 
  pectoral) 
  enlargement 
  of 
  the 
  myelon, 
  where 
  the 
  numerous 
  

   large 
  nerves 
  are 
  sent 
  off 
  to 
  the 
  great 
  pectoral 
  fins; 
  a 
  feebler 
  brachial 
  

   enlargement 
  may 
  be 
  noticed 
  in 
  the 
  sharks. 
  I 
  have 
  not 
  recognized 
  it 
  

   in 
  osseous 
  fishes, 
  not 
  even 
  in 
  tbose 
  with 
  enormous 
  pectorals 
  adapted 
  

   for 
  flight, 
  e. 
  g. 
  } 
  Bxoccetus 
  and 
  Dactyloptenis 
  ; 
  in 
  tbe 
  latter 
  the 
  smaller 
  

   ganglionic 
  risings 
  upon 
  the 
  dorsal 
  columns 
  of 
  the 
  cervical 
  region 
  of 
  

   the 
  myelon 
  receive 
  nerves 
  of 
  sensation 
  from 
  the 
  free 
  soft 
  rays 
  of 
  the 
  

   pectorals 
  and 
  the 
  homologous 
  ganglions 
  are 
  more 
  marked 
  in 
  other 
  gur 
  

   nards 
  {Triglce), 
  which 
  have 
  from 
  three 
  to 
  five, 
  and 
  sometimes 
  six, 
  pairs, 
  

   e. 
  g. 
  in 
  Trigla 
  Adriatica. 
  Similar 
  myelonal 
  cervical 
  ganglions 
  are 
  pres- 
  

   ent, 
  also, 
  in 
  Bolynemus. 
  In 
  the 
  heterocercal 
  sturgeon 
  there 
  is 
  a 
  feeble 
  

  

  