﻿22 
  J. 
  W. 
  HT7LKE 
  ON 
  THE 
  ANATOMY 
  OF 
  HYPSILOPHODON 
  FOXII. 
  

  

  of 
  a 
  second 
  individual, 
  and 
  so 
  probable 
  that 
  it 
  might 
  be 
  the 
  posterior 
  

   moiety 
  of 
  the 
  near-lying 
  larger 
  sacrum 
  with 
  part 
  of 
  the 
  tail, 
  that 
  at 
  

   first 
  I 
  rather 
  hastily 
  imagined 
  it 
  to 
  be 
  such 
  ; 
  but 
  unwilling 
  to 
  leave 
  

   it 
  doubtful, 
  I 
  laid 
  bare 
  the 
  articular 
  and 
  transverse 
  processes 
  of 
  the 
  

   two 
  vertebras 
  next 
  the 
  sacrum, 
  which 
  proved 
  them 
  to 
  be 
  lumbar. 
  

   After 
  this 
  I 
  could 
  not 
  resist 
  the 
  conviction 
  that 
  I 
  had 
  investigated 
  

   in 
  the 
  same 
  block 
  of 
  stone 
  the 
  remains 
  of 
  two 
  distinct 
  individuals 
  ; 
  

   the 
  smaller 
  sacrum 
  repeats 
  all 
  the 
  essential 
  features 
  of 
  the 
  larger 
  one. 
  

   The 
  third 
  centrum 
  (3 
  s.), 
  missing 
  in 
  that, 
  is 
  here 
  well 
  preserved, 
  as 
  

   is 
  also 
  the 
  second 
  ; 
  but 
  the 
  first 
  and 
  the 
  last 
  lumbar 
  centra 
  are 
  badly 
  

   mutilated. 
  The 
  third 
  lumbar 
  centrum 
  is 
  better 
  preserved 
  than 
  any 
  

   other 
  ; 
  its 
  lateral 
  surface 
  is 
  less 
  convex 
  and 
  more 
  plane 
  vertically 
  

   than 
  the 
  corresponding 
  part 
  of 
  the 
  first 
  lumbar 
  centrum 
  of 
  the 
  larger 
  

   individual. 
  

  

  From 
  beneath 
  the 
  right 
  side 
  of 
  the 
  sacrum, 
  partly 
  hidden 
  by 
  a 
  

   fragment 
  of 
  a 
  pelvic 
  bone, 
  the 
  proximal 
  half 
  of 
  the 
  right 
  femur 
  

   projects 
  (Fe.). 
  Its 
  inner 
  trochanter 
  is 
  well 
  preserved, 
  wanting 
  only 
  

   the 
  thin 
  triangular 
  lower 
  angle. 
  At 
  its 
  inner 
  side 
  is 
  a 
  very 
  distinct 
  

   shallow 
  pit. 
  Near 
  the 
  skull 
  and 
  beneath 
  the 
  larger 
  chain 
  of 
  ver- 
  

   tebrae, 
  I 
  found 
  several 
  very 
  thin 
  bony 
  plates 
  having 
  one 
  surface 
  

   granular, 
  the 
  other 
  smooth 
  and 
  furrowed 
  by 
  a 
  vascular 
  net. 
  Their 
  

   shape 
  was 
  irregularly 
  polygonal 
  ; 
  and 
  their 
  size 
  varied 
  much, 
  some 
  

   attaining 
  an 
  area 
  of 
  about 
  1 
  square 
  inch. 
  I 
  regard 
  them 
  as 
  thin 
  

   scutes 
  (fig. 
  1, 
  sc). 
  

  

  Prof. 
  Owen 
  has 
  taken 
  exception 
  (Quart. 
  Journ. 
  Geol. 
  Soe. 
  vol. 
  xxix. 
  

   p. 
  531) 
  to 
  the 
  generic 
  distinctness 
  of 
  Hypsilophodon, 
  and 
  maintained 
  

   its 
  identity 
  with 
  the 
  genus 
  Iguanodon, 
  basing 
  his 
  argument 
  mainly 
  

   on 
  the 
  similarity 
  of 
  their 
  compressed, 
  ridged 
  teeth, 
  on 
  the 
  peculiar 
  

   mode 
  in 
  which 
  these 
  wear 
  down, 
  and 
  on 
  the 
  spout-like 
  form 
  of 
  the 
  

   edentulous 
  anterior 
  extremity 
  of 
  the 
  mandible 
  in 
  both. 
  Fully 
  re- 
  

   cognizing 
  these 
  points 
  of 
  structural 
  agreement 
  as 
  evidence 
  of 
  a 
  very 
  

   close 
  affinity, 
  it 
  appears 
  to 
  me 
  that 
  there 
  remain 
  so 
  many 
  and 
  so 
  

   great 
  differences 
  as 
  to 
  fully 
  justify 
  the 
  adoption 
  of 
  the 
  separate 
  genus 
  

   Hypsilophodon. 
  As 
  I 
  stated 
  fully 
  in 
  my 
  first 
  note 
  what 
  appeared 
  

   to 
  me 
  the 
  chief 
  structural 
  differences, 
  it 
  is 
  unnecessary 
  to 
  recapitulate 
  

   them 
  here 
  ; 
  they 
  were 
  chiefly 
  those 
  presented 
  by 
  the 
  limbs, 
  and 
  had 
  

   respect 
  to 
  their 
  form 
  and 
  proportions, 
  and 
  to 
  the 
  number 
  of 
  toes. 
  

   In 
  his 
  paper 
  of 
  November 
  10, 
  1869, 
  Prof. 
  Huxley 
  noticed 
  certain 
  

   vertebral 
  differences 
  ; 
  but; 
  his 
  comparison 
  did 
  not 
  extend 
  to 
  the 
  

   sacra, 
  this 
  segment 
  of 
  the 
  spinal 
  column 
  being 
  hidden 
  in 
  the 
  Mantell- 
  

   Bowerbank 
  fossil, 
  the 
  subject 
  of 
  the 
  paper. 
  I 
  have 
  therefore 
  taken 
  

   the 
  opportunity 
  which 
  my 
  recent 
  acquisitions, 
  afford, 
  to 
  compare 
  

   my 
  Hypsilophodon 
  sacra 
  with 
  the 
  type 
  specimen 
  of 
  the 
  Iguanodon- 
  

   Mantelli 
  sacrum 
  figured 
  in 
  the 
  ' 
  Fossil 
  Peptilia 
  of 
  the 
  Wealden 
  

   Formation'*. 
  The 
  result 
  is 
  that 
  I 
  find 
  the 
  form 
  of 
  the 
  vertebral 
  

   centrum 
  quite 
  different, 
  being 
  cylindroid, 
  rounded 
  below 
  in 
  Hypsi- 
  

   lophodon, 
  laterally 
  compressed, 
  so 
  much 
  as 
  to 
  be 
  angulated 
  or 
  almost 
  

   keeled 
  below, 
  in 
  Iguanodon 
  ; 
  this 
  difference 
  seems 
  to 
  me 
  of 
  higher 
  

   than 
  specific 
  value. 
  

  

  * 
  Fossil 
  Keptilia 
  of 
  the 
  Wealden 
  Formation, 
  order 
  " 
  Dinosauria," 
  p. 
  11. 
  

  

  