﻿[21] 
  DEVELOPMENT 
  OF 
  THE 
  CETACEA. 
  447 
  

  

  constructed 
  so 
  as 
  to 
  admit 
  of 
  full 
  anteroposterior 
  movement 
  ; 
  whereas 
  

   the 
  iliac 
  bones 
  are 
  short 
  and 
  directed 
  outward, 
  presenting 
  flat 
  surfaces 
  

   anteriorly, 
  and 
  the 
  ischiatic 
  bones, 
  though 
  long, 
  are 
  slender, 
  showing 
  

   that 
  the 
  muscles 
  which 
  pass 
  from 
  the 
  pelvis 
  to 
  the 
  short 
  thighs 
  are 
  

   small. 
  These 
  features 
  have, 
  of 
  course, 
  relation 
  to 
  the 
  fact 
  that 
  the 
  

   propulsion 
  of 
  the 
  animal 
  is 
  effected 
  not, 
  as 
  in 
  ordinary 
  mammals, 
  by 
  the 
  

   movements 
  of 
  the 
  limbs 
  upon 
  the 
  pelvis, 
  but 
  rather, 
  as 
  in 
  the 
  fish, 
  by 
  

   the 
  movements 
  of 
  the 
  hinder 
  part 
  of 
  the 
  vertebral 
  column 
  upon 
  the 
  rest 
  

   of 
  the 
  trunk, 
  the 
  limbs 
  of 
  the 
  seal 
  serving 
  chiefly 
  like 
  the 
  tail 
  rays 
  of 
  

   the 
  fish 
  to 
  give 
  width 
  to 
  that 
  part 
  of 
  the 
  column." 
  

  

  (12) 
  Degeneracy 
  of 
  the 
  pelvis 
  in 
  pinnipeds. 
  — 
  The 
  relatively 
  small 
  pelvis, 
  

   with 
  its 
  thin 
  and 
  sleuder 
  pubes 
  and 
  ischia 
  in 
  the 
  PhoddcB, 
  is 
  remarkable, 
  

   though 
  a 
  similar 
  pelvic 
  degeneracj' 
  is 
  even 
  more 
  obvious 
  in 
  the 
  skele- 
  

   ton 
  of 
  the 
  fur-seal 
  Callorhinits. 
  I 
  regard 
  this 
  degeneracy 
  of 
  the 
  pelvis 
  

   and 
  proximal 
  musculature, 
  and 
  the 
  evident 
  translocation 
  of 
  some 
  of 
  the 
  

   muscular 
  insertions 
  backward, 
  the 
  inclusion 
  of 
  the 
  knees 
  by 
  the 
  hinder 
  

   part 
  of 
  abdominal 
  musculature, 
  as 
  very 
  clearly 
  indicative 
  of 
  the 
  mode 
  

   in 
  which 
  the 
  pes 
  of 
  Cetacea 
  were 
  shifted 
  backward, 
  the 
  skeleton 
  finally 
  

   aborting 
  utterly, 
  so 
  as 
  to 
  leave 
  only 
  a 
  pair 
  of 
  pedal 
  folds 
  projecting 
  from 
  

   the 
  sides 
  of 
  the 
  tail, 
  stiffened 
  by 
  a 
  peculiar 
  arrangement 
  of 
  fibers, 
  fully 
  

   described 
  by 
  Eoux,* 
  who 
  develops 
  an 
  elaborate 
  hypothesis 
  to 
  account 
  

   for 
  the 
  arrangement 
  of 
  these 
  connective 
  tissue 
  fibers 
  in 
  the 
  flukes, 
  but 
  

   he 
  continually 
  speaks 
  of 
  the 
  flukes 
  as 
  Flossen 
  (fins), 
  and 
  seems 
  to 
  have 
  

   no 
  suspicion 
  in 
  regard 
  to 
  their 
  true 
  nature, 
  viz, 
  that 
  they 
  are 
  the 
  de- 
  

   generate 
  translocated 
  distal 
  portions 
  of 
  the 
  hind 
  limb. 
  

  

  Dr. 
  Gill,t 
  who 
  seems 
  to 
  have 
  been 
  the 
  first 
  author 
  to 
  appreciate 
  the 
  im- 
  

   portance 
  of 
  the 
  inclusion 
  of 
  the 
  proximal 
  parts 
  of 
  the 
  hind 
  limbs 
  of 
  pin- 
  

   nipeds, 
  and 
  to 
  avail 
  himself 
  of 
  it 
  in 
  taxonomy, 
  uses 
  the 
  important 
  char- 
  

   acter 
  discussed 
  above 
  as 
  diagnostic 
  of 
  the 
  Pinnipedia, 
  contrasting 
  the 
  

   latter 
  with 
  Fissipcdia 
  as 
  follows 
  : 
  Body 
  prone, 
  with 
  the 
  legs 
  confined 
  in 
  

   the 
  common 
  integument 
  beyond 
  the 
  elbows 
  and 
  knees 
  (with 
  the 
  feet 
  ro- 
  

   tated 
  backwards, 
  and 
  with 
  toes 
  connected 
  together), 
  and 
  especially 
  

   adapted 
  for 
  swimming. 
  Manns 
  and 
  pes 
  with 
  first 
  phalanges 
  and 
  digits 
  

   enlarged 
  and 
  produced 
  beyond 
  the 
  others." 
  

  

  Allen 
  \ 
  contrasts 
  the 
  Phocidce 
  and 
  Otariadce 
  as 
  follows: 
  

  

  [1] 
  " 
  In 
  the 
  Phocidcv 
  the 
  hind 
  limbs 
  are 
  extended 
  backwards 
  in 
  a 
  line 
  

   parallel 
  with 
  the 
  body; 
  the 
  legs 
  are 
  so 
  inclosed 
  within 
  the 
  integuments 
  

   of 
  the 
  body 
  that 
  they 
  have 
  little 
  or 
  no 
  motion, 
  and 
  the 
  feet 
  are 
  movable 
  

   only 
  in 
  a 
  relatively 
  small 
  degree, 
  in 
  an 
  obliquely 
  lateral 
  direction. 
  

  

  * 
  Beitrage 
  zur 
  Morphologic 
  tier 
  functionellen 
  Aupassung. 
  1. 
  Structur 
  cines 
  liocli 
  

   differenzirten 
  bindegewebigen 
  Organes 
  (der 
  Sch-wanzilossc 
  des 
  Dolphin). 
  Arch. 
  f. 
  

   Anat.u. 
  Physiol., 
  1883, 
  pp. 
  76-1G1, 
  1 
  pi. 
  

  

  t 
  Synoptical 
  tables 
  of 
  characters 
  of 
  the 
  subdivisions 
  of 
  mammals, 
  with 
  catalogue 
  of 
  

   the 
  genera. 
  Smihsoniau 
  Miscel. 
  Coil. 
  230, 
  Nov., 
  1872. 
  In 
  arraugement 
  of 
  the 
  fami- 
  

   lies 
  of 
  mammals. 
  

  

  $ 
  On 
  the 
  eared 
  seals 
  (Olariadw) 
  with 
  detailed 
  descriptions 
  of 
  the 
  North 
  Pacific 
  spe- 
  

   cies. 
  Bull. 
  Mus. 
  Comp. 
  Zool.^II, 
  No. 
  1, 
  pp. 
  108, 
  pis. 
  3. 
  

  

  