﻿440 
  REPORT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  [14J 
  

  

  down 
  in 
  the 
  center 
  of 
  each 
  additional 
  segment 
  so 
  formed, 
  we 
  would 
  

   have 
  phalanges 
  produced 
  in 
  excess 
  of 
  the 
  number 
  found 
  in 
  the 
  digits 
  

   of 
  normal 
  forms. 
  Upon 
  comparing 
  this 
  hypothetical 
  method 
  of 
  the 
  

   evolution 
  of 
  the 
  supernumerary 
  phalanges 
  in 
  the 
  digits 
  of 
  the 
  manus 
  

   of 
  cetaceans 
  with 
  what 
  actually 
  happens 
  during 
  development 
  in 
  the 
  

   latter, 
  it 
  is 
  found 
  that 
  the 
  actual 
  development 
  favorably 
  countenances 
  

   the 
  hypothesis. 
  

  

  The 
  terminal 
  or 
  distal 
  phalanges 
  in 
  Cetaceans 
  while 
  they 
  are 
  indi- 
  

   cated 
  by 
  segments 
  of 
  cartilage 
  very 
  early, 
  as 
  will 
  be 
  seen 
  by 
  the 
  foetal 
  

   manus 
  represented 
  on 
  Plate 
  II, 
  by 
  tig. 
  17, 
  ossify 
  from 
  centers 
  which 
  

   actually 
  appear 
  enchondrally 
  much 
  later 
  than 
  those 
  of 
  the 
  proximal 
  

   phalangeal 
  joints, 
  as 
  minute 
  round 
  ossific 
  nodules 
  in 
  the 
  middle 
  of 
  the 
  

   cartilaginous 
  segment. 
  These 
  nodules 
  or 
  nuclei 
  of 
  the 
  osseous 
  terminal 
  

   phalanges 
  also 
  diminish 
  in 
  size 
  from 
  within 
  outwards. 
  It 
  would 
  there 
  

   fore 
  seem 
  that 
  the 
  supernumerary 
  terminal 
  phalanges 
  of 
  the 
  cetacean 
  

   manus 
  develop 
  last, 
  which 
  is 
  in 
  conformity 
  with 
  the 
  hypothesis. 
  

  

  (8.) 
  The 
  muscles 
  of 
  the 
  limbs 
  of 
  seals 
  and 
  the 
  vessels 
  of 
  the 
  flukes 
  of 
  Ceta- 
  

   ceans. 
  — 
  The 
  hind 
  limbs 
  of 
  the 
  pinnipeds 
  and 
  Ichthyosauri, 
  however, 
  re- 
  

   tained 
  their 
  capabilities 
  of 
  movement 
  through 
  a 
  special 
  arrangement 
  of 
  

   muscles 
  arising 
  from 
  the 
  axial 
  skeleton 
  and 
  iuserted 
  mainly 
  into 
  the 
  mid- 
  

   dle 
  third 
  of 
  the 
  skeleton 
  of 
  the 
  limbs. 
  While 
  there 
  has 
  been 
  a 
  consider- 
  

   ble 
  shifting 
  peripherad 
  of 
  the 
  insertions 
  of 
  the 
  muscles 
  in 
  the 
  former 
  there 
  

   has 
  been 
  a 
  tendency 
  for 
  the 
  whole 
  hind 
  limb 
  to 
  diminish 
  in 
  size 
  in 
  the 
  

   latter 
  type 
  and 
  no 
  tendency 
  towards 
  the 
  complete 
  atrophy 
  of 
  the 
  distal 
  

   part 
  of 
  the 
  appendicular 
  skeleton 
  and 
  musculature 
  of 
  the 
  hind 
  limb 
  as 
  in 
  

   Cetacea, 
  in 
  consequence 
  of 
  which 
  in 
  the 
  latter 
  the 
  llukc 
  or 
  distal 
  part 
  of 
  

   the 
  hind 
  limb 
  has 
  become 
  a 
  mere 
  rigid 
  hollow 
  lateral 
  diverticulum 
  of 
  the 
  

   integument, 
  filled 
  with 
  fibrous 
  tissue 
  and 
  possessing 
  no 
  mobility 
  distinct 
  

   from 
  that 
  possessedby 
  the 
  tail 
  as 
  a 
  whole. 
  In 
  short, 
  thedegeneracy 
  of 
  the 
  

   hind 
  limbs 
  of 
  Cetaceans 
  is 
  complete 
  and 
  presents 
  the 
  unexampled 
  con- 
  

   dition 
  of 
  part 
  of 
  a 
  limb 
  permanently 
  developed 
  in 
  the 
  adult 
  to 
  a 
  stage 
  

   which 
  is 
  practically 
  comparable 
  to 
  a 
  transient 
  condition 
  in 
  tne 
  embryo 
  

   when 
  the 
  limb 
  fold 
  is 
  filled 
  with 
  undifferentiated 
  mesoblastic 
  cells. 
  These 
  

   folds, 
  as 
  the 
  flukes, 
  however, 
  approximate 
  the 
  form 
  of 
  the 
  distal 
  half 
  or 
  

   two-thirds 
  of 
  the 
  fore 
  limbs, 
  from 
  which 
  the 
  skeleton 
  has 
  vanished 
  to- 
  

   gether 
  with 
  the 
  muscles, 
  tendons, 
  and 
  nerves 
  appertaining 
  to 
  them, 
  the 
  

   normal 
  mammalian 
  arrangement 
  of 
  the 
  vessels 
  and 
  nerves 
  being 
  ap- 
  

   proximated 
  by 
  a 
  superficial 
  dorsal 
  and 
  ventral 
  system 
  which 
  is 
  not 
  at 
  

   first 
  sight 
  so 
  obviously 
  homologous 
  with 
  the 
  vessels 
  and 
  nerves 
  of 
  the 
  

   typical 
  mammalian 
  hind 
  limb. 
  The 
  vessels 
  are 
  arranged 
  in 
  about 
  ten 
  

   dorsal 
  and 
  eleven 
  ventral 
  pairs 
  just 
  below 
  the 
  integument 
  of 
  the 
  fluke. 
  

   The 
  fourth 
  pair 
  reckoning 
  from 
  the 
  front 
  is 
  most 
  strongly 
  developed 
  and 
  

   extends 
  to 
  the 
  tip 
  of 
  the 
  fluke, 
  giving 
  off 
  smaller 
  branches 
  on 
  either 
  side 
  

   from 
  its 
  distal 
  two-thirds. 
  These 
  secondary 
  branches 
  carry 
  the 
  blood 
  

   supply 
  to 
  the 
  tips 
  of 
  the 
  flukes. 
  The 
  other 
  ten 
  pairs 
  of 
  vessels 
  sent 
  into 
  

   the 
  base 
  of 
  the 
  fluke, 
  three 
  in 
  front 
  of 
  the 
  main 
  vessel 
  and 
  seven 
  behind 
  

  

  