﻿[33] 
  DEVELOPMENT 
  OF 
  THE 
  CETACEA. 
  459 
  

  

  transfer 
  of 
  function 
  is 
  contemplated 
  or 
  even 
  necessary. 
  In 
  fact, 
  the 
  ex- 
  

   change 
  in 
  all 
  probability 
  occurred 
  in 
  the 
  water, 
  in 
  which 
  medium 
  it 
  

   would 
  be 
  alone 
  possible 
  to 
  develop 
  a 
  tail 
  like 
  that 
  found 
  in 
  cetaceans, 
  

   in 
  which 
  it 
  indeed 
  attains 
  the 
  maximum 
  of 
  importance 
  as 
  an 
  organ 
  of 
  

   locomotion. 
  While 
  an 
  old 
  organ 
  was 
  vanishing 
  and 
  itself 
  no 
  longer 
  

   capable 
  of 
  dissipating 
  vital 
  energy 
  in 
  the 
  execution 
  of 
  its 
  office 
  as 
  a 
  part 
  

   subservient 
  to 
  locomotion, 
  a 
  part 
  of 
  this 
  old 
  organ 
  combined 
  with 
  an- 
  

   other 
  coexisting 
  degenerate 
  organ, 
  the 
  tail 
  was 
  hypertrophied 
  and 
  as- 
  

   sumed 
  the 
  office 
  of 
  the 
  posterior 
  pair 
  of 
  limbs. 
  

  

  IV. 
  — 
  Degeneracy 
  of 
  the 
  pelvic 
  girdle 
  and 
  hind 
  limbs 
  in 
  

  

  CETACEA. 
  

  

  One 
  of 
  the 
  most 
  striking 
  features 
  in 
  the 
  structure 
  of 
  the 
  pelvis 
  of 
  

   Pinnipcdia 
  and 
  Cetacea 
  is 
  the 
  absence 
  of 
  a 
  well-defined 
  symphysis 
  pubis, 
  

   the 
  pubes 
  forming 
  no 
  extensive 
  amphiarthrodial 
  union 
  as 
  in 
  most 
  Mam- 
  

   malia. 
  A 
  well-developed 
  symphysis 
  pubis 
  is 
  absent 
  in 
  all 
  of 
  the 
  species 
  

   of 
  the 
  first-named 
  group, 
  with 
  the 
  exception, 
  perhaps, 
  of 
  the 
  walrus, 
  

   which 
  seems 
  to 
  be 
  less 
  modified 
  generally 
  in 
  the 
  structure 
  of 
  the 
  pelvis 
  

   and 
  hind 
  limbs. 
  The 
  other 
  types 
  in 
  which 
  there 
  is 
  a 
  loose 
  or 
  distant 
  

   connection 
  of 
  the 
  pubes 
  by 
  means 
  of 
  a 
  transverse 
  interpubic 
  ligament 
  

   are 
  the 
  Sloths 
  amongst 
  the 
  Edentata. 
  The 
  separation 
  of 
  the 
  pelvic 
  ele- 
  

   ments 
  in 
  the 
  median 
  line 
  is 
  carried 
  to 
  an 
  extreme 
  decree 
  in 
  the 
  existing 
  

   Cetacea, 
  and 
  in 
  consequence 
  of 
  the 
  fact 
  that 
  the 
  pubic 
  bones 
  are 
  prob- 
  

   ably 
  absent 
  in 
  these 
  forms, 
  Struthers 
  has 
  named 
  the 
  ligamentous 
  bond 
  

   which 
  joins 
  the 
  pelvic 
  rudiments 
  together 
  across 
  the 
  median 
  line 
  the 
  

   interpelvic 
  ligament. 
  To 
  this 
  are 
  attached 
  the 
  crura 
  of 
  the 
  penis 
  in 
  the 
  

   Cetacea. 
  

  

  Struthers 
  regards 
  the 
  pelvic 
  bones 
  of 
  the 
  latter 
  as 
  consisting 
  of 
  the 
  

   ischium 
  alone, 
  since 
  it 
  developes 
  from 
  a 
  single 
  center 
  of 
  ossification, 
  

   which 
  I 
  can 
  fully 
  confirm 
  on 
  the 
  basis 
  of 
  the 
  evidence 
  presented 
  by 
  the 
  

   structure 
  of 
  its 
  cartilaginous 
  rudiment 
  in 
  sections 
  of 
  an 
  embryo 
  of 
  Olobio- 
  

   cepliahis 
  melas, 
  2 
  inches 
  long. 
  In 
  this 
  embryo 
  it 
  seems 
  to 
  be 
  propor 
  

   tionally 
  of 
  greater 
  dimensions, 
  however, 
  than 
  in 
  the 
  adult, 
  which 
  is 
  

   .simply 
  evidence 
  in 
  favor 
  of 
  the 
  view 
  that 
  it 
  is 
  really 
  degenerate 
  in 
  the 
  

   adult 
  and 
  has 
  been 
  reduced 
  from 
  a 
  pelvis 
  which 
  in 
  some 
  ancestral 
  form 
  

   was 
  still 
  more 
  developed. 
  

  

  The 
  ilium 
  has 
  been 
  atrophied, 
  and 
  in 
  this 
  way 
  it 
  happens 
  that 
  the 
  

   pelvis 
  of 
  Cetacea 
  and 
  Sircnia 
  has 
  been 
  separated 
  from 
  the 
  vertebral 
  

   column 
  by 
  a 
  very 
  considerable 
  interval, 
  and 
  has 
  been 
  brought 
  to 
  assume 
  

   only 
  a 
  subsidiary 
  function, 
  as 
  shown 
  by 
  the 
  researches 
  of 
  Struthers, 
  

   viz, 
  that 
  of 
  giving 
  support 
  and 
  attachment 
  to 
  the 
  organs 
  of 
  generation, 
  

   and 
  not 
  that 
  of 
  giving 
  attachment 
  to 
  functionally 
  or 
  strongly 
  developed 
  

   limb 
  muscles 
  as 
  in 
  normal 
  mammals. 
  

  

  The 
  atrophy 
  of 
  the 
  pubes 
  has 
  left 
  only 
  an 
  imperfectly 
  developed 
  is- 
  

   chium, 
  and, 
  perhaps, 
  if 
  anything 
  of 
  ilium, 
  only 
  the 
  abaxial 
  or 
  distal 
  

   part. 
  The 
  nodules 
  of 
  cartilage 
  observed 
  at 
  the 
  ends 
  of 
  the 
  pelvic 
  ele- 
  

  

  