﻿432 
  EEPORT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  [6] 
  

  

  Getacea, 
  the 
  transverse 
  and 
  vertical 
  processes 
  (neural 
  and 
  hsemal 
  arches) 
  

   reach 
  a 
  more 
  nearly 
  equal 
  development 
  respectively, 
  bat 
  they 
  are 
  well 
  

   marked 
  to 
  nearer 
  the 
  end 
  of 
  the 
  caudal 
  series 
  of 
  segments 
  than 
  in 
  other 
  

   mammals, 
  obviously 
  in 
  correlation 
  with 
  the 
  subdivided 
  tendons 
  and 
  

   penniform 
  muscular 
  slips 
  into 
  which 
  the 
  vast 
  caudal 
  musculature 
  is 
  

   broken 
  up 
  in 
  these 
  animals. 
  

  

  (3) 
  Translocation 
  and 
  inclusion 
  of 
  the 
  hind 
  limbs, 
  and 
  their 
  degeneracy. 
  — 
  

   Upon 
  comparing 
  the 
  relation 
  of 
  the 
  hind 
  limbs 
  to 
  the 
  tail 
  in 
  Fissipedia, 
  

   Pinnipedia, 
  and 
  Cetacea, 
  certain 
  very 
  striking 
  facts 
  are 
  brought 
  to 
  

   light, 
  the 
  most 
  important 
  being 
  that 
  the 
  limbs 
  grow 
  out 
  and 
  are 
  pro- 
  

   gressively 
  pushed 
  backwards 
  distally, 
  in 
  the 
  series 
  included 
  by 
  two 
  of 
  

   the 
  above-mentioned 
  groups, 
  so 
  that 
  while 
  the 
  proximal 
  parts, 
  such 
  as 
  

   the 
  pelvis 
  and 
  femur, 
  retain 
  their 
  normal 
  position 
  in 
  relation 
  to 
  the 
  

   sacral 
  region 
  of 
  the 
  spinal 
  column, 
  the 
  bones 
  of 
  the 
  crus 
  and 
  foot 
  are 
  

   carried 
  backwards, 
  the 
  proximal 
  parts 
  being 
  involved 
  by 
  the 
  contiguous 
  

   soft 
  parts 
  and 
  lost 
  to 
  sight 
  externally. 
  

  

  This 
  view 
  it 
  will 
  be 
  seen 
  receives 
  support 
  upon 
  comparing 
  the 
  posi- 
  

   tion 
  of 
  the 
  hind 
  limbs 
  of 
  an 
  embryo 
  cat 
  (fig. 
  14, 
  pi. 
  I) 
  with 
  that 
  of 
  the 
  

   walrus 
  (Fig. 
  III). 
  While 
  it 
  must 
  be 
  borne 
  in 
  mind 
  that 
  the 
  tail 
  of 
  the 
  

   walrus 
  has 
  undergone 
  considerable 
  degeneration, 
  the 
  cat 
  has 
  retained 
  

   the 
  primordial 
  extension 
  of 
  the 
  caudal 
  appendage, 
  but 
  the 
  tail 
  even 
  in 
  

   this 
  last 
  instance 
  has 
  suffered 
  degeneracy 
  in 
  volume 
  or 
  rather 
  in 
  diam- 
  

   eter, 
  and 
  represents 
  a 
  condition 
  which 
  is 
  far 
  more 
  rudimentary 
  than 
  

   even 
  in 
  the 
  Reptilia, 
  caudal 
  degeneracy 
  having 
  apparently 
  begun 
  in 
  the 
  

   latter 
  and 
  Amphibia, 
  unless 
  we 
  except 
  the 
  extremely 
  specialized 
  gephy- 
  

   rocercal 
  fishes, 
  such 
  as 
  Mola. 
  The 
  tail 
  of 
  vertebrates 
  in 
  reality 
  rep- 
  

   resents 
  a 
  part 
  of 
  the 
  body 
  from 
  which 
  the 
  body 
  cavity 
  and 
  digestive 
  

   canal 
  has 
  retreated 
  forwards, 
  for 
  in 
  all 
  forms, 
  the 
  chorda, 
  medulla 
  spi- 
  

   nalis, 
  and 
  mesenteron 
  are 
  at 
  some 
  stage 
  practically 
  conterminous 
  pos- 
  

   teriorly. 
  

  

  Bat 
  even 
  when 
  we 
  leave 
  out 
  of 
  consideration 
  the 
  fact 
  of 
  caudal 
  de- 
  

   generacy, 
  there 
  is 
  a 
  residuum 
  of 
  other 
  facts 
  indicating 
  that 
  the 
  limbs 
  

   of 
  pinnipeds 
  have 
  had 
  their 
  proximal 
  parts 
  included 
  and 
  that 
  even 
  in 
  

   the 
  embryo 
  there 
  is 
  no 
  joint 
  of 
  the 
  leg 
  visible 
  outwardly 
  except 
  the 
  

   ankle. 
  This 
  has 
  carried 
  the 
  point 
  where 
  the 
  embryonic 
  hinder 
  limb- 
  

   fold 
  first 
  appears, 
  farther 
  back 
  in 
  relation 
  to 
  the 
  pectoral 
  limb 
  than 
  in 
  

   the 
  embryos 
  of 
  normally-developing 
  Carnivora, 
  of 
  which 
  the 
  cat 
  is 
  the 
  

   type. 
  While 
  the 
  femur 
  is 
  directed 
  forwards 
  in 
  the 
  Pinnipeds, 
  the 
  crus 
  

   and 
  the 
  foot 
  are 
  extended 
  backwards, 
  so 
  that 
  the 
  legs 
  become 
  tied 
  back- 
  

   wards, 
  so 
  to 
  speak, 
  by 
  the 
  integument 
  and 
  flesh 
  in 
  front 
  of 
  them. 
  In 
  

   the 
  cat's 
  embryo 
  the 
  joints 
  of 
  the 
  limbs 
  externally 
  apparent, 
  in 
  an 
  even 
  

   less 
  advanced 
  one 
  than 
  that 
  of 
  the 
  walrus 
  here 
  figured, 
  are 
  the 
  ankle 
  

   and 
  knee 
  joints 
  of 
  the 
  hind 
  limb, 
  and 
  there 
  is 
  nothing 
  of 
  that 
  backward 
  

   inclination 
  of 
  the 
  proximal 
  part 
  of 
  the 
  limb 
  as 
  in 
  the 
  walrus 
  and 
  other 
  

   Pinnipeds. 
  

  

  It 
  is 
  this 
  backward 
  inclination 
  and 
  inclusion 
  of 
  the 
  proximal 
  parts 
  of 
  

  

  