﻿26 
  J. 
  W. 
  HULKE 
  ON- 
  THE 
  ASTKAGALUS 
  OF 
  IGUANODON. 
  

  

  continuous 
  with 
  the 
  end 
  of 
  the 
  ridge 
  that 
  divides 
  the 
  upper 
  surface 
  ; 
  

   but 
  when 
  undistorted, 
  the 
  ridge 
  ended, 
  not 
  at 
  the 
  outer 
  edge, 
  but 
  on 
  

   the 
  posterior 
  surface 
  of 
  the 
  lip. 
  This 
  lip 
  clearly 
  represents 
  the 
  

   ascending 
  process 
  of 
  the 
  avian 
  astragalus. 
  

  

  To 
  those 
  who 
  were 
  present 
  in 
  June 
  1870, 
  when 
  Professor 
  Huxley 
  

   made 
  his 
  valuable 
  communication 
  " 
  On 
  the 
  Affinities 
  between 
  the 
  

   Dinosaurian 
  Reptiles 
  and 
  Birds," 
  any 
  comments 
  upon 
  the 
  bone 
  will 
  

   be 
  superfluous 
  ; 
  but 
  for 
  others 
  who 
  are 
  not 
  acquainted 
  with 
  that 
  

   paper, 
  I 
  may 
  state 
  that, 
  besides 
  its 
  value 
  as 
  a 
  distinct 
  addition 
  to 
  

   the 
  anatomy 
  of 
  Iguanodon, 
  it 
  has 
  an 
  additional 
  interest 
  as 
  constitu- 
  

   ting 
  another 
  link 
  in 
  the 
  chain 
  which 
  joins 
  these 
  two 
  classes. 
  In 
  all 
  

   extant 
  reptiles, 
  and, 
  excepting 
  the 
  Dinosauria, 
  in 
  all 
  fossil 
  ones 
  which 
  

   have 
  a 
  foot 
  capable 
  of 
  being 
  flexed 
  and 
  extended 
  on 
  the 
  leg, 
  this 
  

   hinge-movement 
  occurs 
  between 
  the 
  leg-bones 
  and 
  the 
  astragalus 
  ; 
  but 
  

   in 
  the 
  Dinosauria 
  the 
  tibia 
  and 
  the 
  astragalus 
  were 
  tightly 
  inter- 
  

   locked, 
  and 
  the 
  movable 
  ankle-joint 
  was 
  between 
  the 
  astragalus 
  

   and 
  the 
  next 
  distal 
  segment 
  of 
  the 
  tarsus, 
  which 
  is 
  its 
  position 
  in 
  

   birds. 
  In 
  most 
  of 
  these, 
  however, 
  the 
  separateness 
  of 
  the 
  astragalus 
  

   and 
  the 
  tibia 
  disappears 
  at 
  an 
  early 
  age 
  ; 
  only 
  in 
  the 
  Ratitse 
  does 
  it 
  

   continue 
  to 
  maturity. 
  In 
  the 
  New-Zealand 
  Dinornithidse 
  and 
  their 
  

   living 
  successors, 
  the 
  Apterygidse, 
  I 
  have 
  seen 
  it 
  present 
  in 
  fully 
  

   grown 
  skeletons. 
  In 
  the 
  Dinosauria 
  the 
  distinctness 
  of 
  these 
  bones, 
  

   transient 
  in 
  birds, 
  persisted 
  throughout 
  the 
  whole 
  life 
  of 
  the 
  indi- 
  

   vidual. 
  

  

  