﻿[17] 
  DEVELOPMENT 
  OF 
  THE 
  CETACEA. 
  443 
  

  

  there 
  is, 
  however, 
  no 
  connection 
  or 
  close 
  relation 
  with 
  the 
  tendinous 
  in- 
  

   sertions 
  of 
  any 
  muscles 
  whatsoever, 
  such 
  as 
  is 
  the 
  case 
  in 
  the 
  flukes. 
  

   The 
  muscular 
  connection 
  of 
  the 
  flukes 
  is 
  indirect 
  ; 
  that 
  is 
  to 
  say, 
  the 
  

   tendons 
  of 
  the 
  supra- 
  and 
  infra-caudal 
  muscles 
  send 
  only 
  a 
  small 
  portion 
  

   of 
  their 
  fibers 
  into 
  the 
  flukes, 
  yet 
  even 
  this 
  is 
  a 
  condition 
  which 
  con- 
  

   trasts 
  very 
  sharply 
  with 
  the 
  relations 
  of 
  the 
  superficial 
  tendinous 
  fibers 
  

   of 
  the 
  dorsal 
  fin, 
  which 
  have 
  absolutely 
  no 
  connection 
  with 
  any 
  mus- 
  

   cles 
  either 
  directly 
  or 
  indirectly. 
  

  

  (10) 
  The 
  nervous 
  supply 
  of 
  the 
  flukes 
  of 
  Cetaceans. 
  — 
  The 
  sensory 
  nerv- 
  

   ous 
  supply 
  of 
  the 
  flukes 
  has 
  a 
  distribution 
  slightly 
  deeper 
  but 
  similar 
  

   to 
  the 
  vessels, 
  and 
  is 
  derived 
  from 
  the 
  four 
  great 
  lumbo-caudal 
  cords,* 
  

   which 
  represent 
  the 
  lumbar 
  plexus 
  of 
  normal 
  Mammalia 
  extended 
  

   backwards 
  into 
  the 
  tail. 
  In 
  my 
  own 
  dissections 
  I 
  have 
  found 
  it 
  diffi- 
  

   cult 
  to 
  make 
  out 
  more 
  than 
  two 
  or 
  three 
  pairs 
  entering 
  the 
  anterior 
  

   basal 
  part 
  of 
  the 
  flukes, 
  and 
  these 
  arise 
  from 
  the 
  dorsal 
  pair 
  of 
  cords 
  

   dorsally, 
  and 
  from 
  the 
  ventral 
  pair 
  ventrally. 
  There 
  are, 
  doubtless, 
  

   other 
  smaller 
  pairs 
  behind 
  those 
  found 
  by 
  me, 
  but 
  the 
  excessive 
  tough- 
  

   ness 
  of 
  the 
  fibrous 
  tissues 
  in 
  their 
  vicinity 
  has 
  rendered 
  the 
  determi- 
  

   nation 
  of 
  their 
  number 
  a 
  difficult 
  undertaking. 
  The 
  nervous 
  supply 
  is 
  

   obviously 
  not 
  derived 
  from 
  the 
  continuation 
  of 
  a 
  homologue 
  of 
  the 
  

   great 
  sciatic 
  as 
  in 
  normal 
  Mammalia, 
  unless, 
  as 
  seems 
  probable, 
  it 
  would 
  

   be 
  possible 
  to 
  trace 
  the 
  terminal 
  fibers 
  of 
  the 
  great 
  caudal 
  plexus 
  as 
  

   the 
  homologue 
  of 
  those 
  of 
  the 
  terminal 
  part 
  of 
  the 
  great 
  sciatic 
  trunk 
  

   of 
  normal 
  forms. 
  This 
  aspect 
  of 
  the 
  question 
  under 
  consideration 
  must, 
  

   however, 
  be 
  viewed 
  in 
  another 
  connection, 
  but 
  it 
  may 
  not 
  be 
  amiss 
  to 
  

   now 
  point 
  out 
  the 
  fact 
  that 
  the 
  four 
  cords 
  found 
  to 
  enter 
  into 
  the 
  lumbo- 
  

   caudal 
  plexus 
  of 
  Cetaceans 
  are 
  represented 
  by 
  structures 
  which, 
  even 
  

   in 
  so 
  highly 
  a 
  differentiated 
  organism 
  as 
  man, 
  may 
  be 
  homologized 
  with 
  

   what 
  is 
  found 
  in 
  the 
  Cetacea. 
  The 
  dorsal 
  cord 
  in 
  the 
  latter 
  is 
  repre- 
  

   sented 
  in 
  man 
  by 
  the 
  posterior 
  branches 
  of 
  the 
  lumbar 
  and 
  sacral 
  

   nerves, 
  the 
  ventral 
  cord 
  by 
  the 
  anterior 
  lumbar 
  and 
  sacral. 
  While 
  the 
  

   ventral 
  system 
  is 
  mainly 
  developed 
  in 
  man 
  in 
  correspondence 
  with 
  the 
  

   massive 
  and 
  essentially 
  ventral 
  musculature 
  of 
  the 
  pelvic 
  limbs, 
  on 
  the 
  

   contrary, 
  the 
  dorsal 
  and 
  ventral 
  systems 
  are 
  about 
  equally 
  developed 
  

   in 
  the 
  cetaceans, 
  in 
  consequence 
  of 
  the 
  fact 
  that 
  functional 
  hind 
  limbs 
  

   have 
  been 
  aborted 
  in 
  the 
  latter, 
  while 
  the 
  dorsal 
  aud 
  ventral 
  caudal 
  

   muscles 
  have 
  been 
  more 
  posteriorly 
  developed, 
  and 
  have 
  acquired 
  about 
  

   equal 
  volumes, 
  a 
  condition 
  which 
  has 
  called 
  for 
  an 
  equally-developed 
  

   nerve 
  supply 
  for 
  both 
  the 
  upper 
  and 
  lower 
  set 
  of 
  hypertrophied 
  caudal 
  

   muscles. 
  

  

  (11) 
  Translocation 
  of 
  muscular 
  insertions 
  in 
  hind 
  limbs. 
  — 
  The 
  manner 
  

   in 
  which 
  the 
  limbs 
  of 
  pinnipeds 
  have 
  been 
  bent 
  backwards 
  has 
  already 
  

  

  been 
  considered, 
  but 
  the 
  remarkable 
  shiftiug 
  backwards 
  of 
  the 
  muscu- 
  

  

  — 
  , 
  — 
  ■ 
  

  

  * 
  These, 
  were 
  first 
  described 
  by 
  D. 
  J. 
  Cunniughani, 
  Journ. 
  Anat. 
  and 
  Physiol., 
  XI, 
  

   pp. 
  209 
  to 
  228, 
  Plate 
  VII, 
  the 
  title 
  of 
  his 
  paper 
  on 
  the 
  subject 
  being 
  "The 
  spinal 
  

   nervons 
  system 
  of 
  the 
  porpoise 
  and 
  dolphin." 
  

  

  