﻿524 
  J. 
  W. 
  HULKE 
  ON 
  A 
  MODIFIED 
  FORM 
  OF 
  DIXOSAURIAN 
  ILIUM. 
  

  

  men 
  it 
  is 
  mutilated 
  • 
  but 
  in 
  the 
  larger 
  bone 
  it 
  is 
  a 
  thin 
  compressed 
  

   lip, 
  which 
  projects 
  strongly 
  downwards 
  and 
  forwards), 
  while 
  the 
  

   posterior 
  is 
  stout 
  and 
  bhmt. 
  This 
  latter 
  process 
  (i) 
  forms 
  the 
  poste- 
  

   rior 
  inferior 
  angle 
  of 
  the 
  bone, 
  and 
  it 
  is 
  its 
  stoutest 
  part. 
  Its 
  trun- 
  

   cated 
  terminal 
  aspect 
  looks 
  downwards 
  and 
  backwards, 
  and 
  has 
  the 
  

   characteristic 
  rugosity 
  of 
  a 
  synchondrosis. 
  

  

  The 
  long 
  slender 
  upper 
  process- 
  (typ) 
  given 
  off 
  from 
  the 
  anterior 
  

   margin 
  of 
  the 
  body 
  measures 
  along 
  its 
  upper 
  surface 
  7 
  inches, 
  and 
  about 
  

   1 
  inch 
  less 
  along 
  its 
  under 
  surface 
  ; 
  the 
  free 
  end 
  is 
  missing. 
  Prom 
  

   its 
  base 
  to 
  the 
  free 
  end 
  it 
  makes 
  a 
  gentle 
  double 
  curve, 
  its 
  upper 
  

   outline 
  being 
  first 
  convex, 
  then 
  concave. 
  The 
  cross 
  section 
  of 
  this 
  

   process 
  is 
  roughly 
  trihedral 
  ; 
  its 
  under 
  surface 
  is 
  marked 
  with 
  coarse 
  

   longitudinal 
  grooves. 
  At 
  4-3 
  inches 
  from 
  its 
  free 
  end 
  it 
  bears 
  a 
  

   small 
  process, 
  now 
  mutilated, 
  separated 
  by 
  a 
  wide 
  subcircular 
  notch 
  

   from 
  that 
  which 
  limits 
  anteriorly 
  the 
  large 
  articular 
  arc. 
  This 
  little 
  

   process 
  is 
  clearly 
  the 
  anterior 
  of 
  the 
  two 
  small 
  projections 
  at 
  the 
  

   under 
  surface 
  of 
  the 
  long 
  slender 
  process 
  which 
  tend 
  to 
  convert 
  the 
  

   notch 
  between 
  them 
  into 
  a 
  closed 
  ring 
  in 
  Mantell's 
  specimen. 
  The 
  

   two 
  remaining 
  surfaces 
  of 
  the 
  long 
  slender 
  process 
  (one 
  upper, 
  the 
  

   other 
  lateral) 
  are 
  smooth. 
  From 
  their 
  union, 
  near 
  the 
  base 
  of 
  the 
  

   process, 
  a 
  ridge 
  (r) 
  passes 
  backwards 
  at 
  the 
  distance 
  of 
  1 
  inch 
  above 
  

   the 
  articular 
  arc, 
  concentrically 
  with 
  it, 
  which, 
  gradually 
  widening 
  

   and 
  becoming 
  less 
  conspicuous, 
  is 
  lost 
  near 
  the 
  posterior 
  inferior 
  

   angle 
  of 
  the 
  bone. 
  

  

  Dr. 
  Wilkins's 
  second 
  specimen 
  is 
  from 
  a 
  much 
  larger 
  individual 
  ; 
  

   a 
  much 
  greater 
  portion 
  of 
  the 
  body 
  and 
  smaller 
  piece 
  of 
  the 
  long- 
  

   anterior 
  process 
  are 
  preserved 
  (PI. 
  XXXII. 
  figs. 
  3 
  & 
  4). 
  The 
  smooth 
  

   (enarthrodial) 
  arch 
  (a) 
  at 
  the 
  lower 
  end 
  of 
  the 
  body 
  is 
  flattened 
  and 
  

   distorted 
  by 
  pressure 
  ; 
  its 
  chord 
  now 
  measures 
  7*5 
  inches. 
  In 
  front 
  

   it 
  ends 
  in 
  a 
  sharp 
  compressed 
  lip, 
  which 
  projects 
  strongly 
  downwards 
  

   and 
  forwards 
  ; 
  and 
  behind 
  it 
  terminates 
  in 
  a 
  low 
  massive 
  hummock, 
  

   which, 
  unprotected 
  by 
  matrix, 
  is 
  worn 
  smooth. 
  A 
  splintered, 
  muti- 
  

   lated 
  projection, 
  which, 
  as 
  in 
  the 
  smaller 
  specimen, 
  the 
  long 
  slender 
  

   process 
  detaches, 
  near 
  its 
  base, 
  from 
  its 
  under 
  surface, 
  inclines 
  down- 
  

   wards, 
  and 
  tends 
  to 
  close 
  the 
  notch 
  which 
  separates 
  it 
  from 
  the 
  ar- 
  

   ticular 
  arc, 
  and 
  to 
  convert 
  it 
  into 
  a 
  foramen 
  (<p). 
  

  

  Of 
  the 
  long 
  slender 
  process 
  (Sj?p) 
  only 
  about 
  6 
  inches 
  remain. 
  Its 
  

   cross 
  esction 
  is 
  an 
  oblong, 
  the 
  long 
  axis 
  of 
  which 
  is 
  nearly 
  vertical 
  to 
  

   that 
  of 
  the 
  same 
  section 
  of 
  the 
  body 
  of 
  the 
  bone. 
  The 
  upper 
  surface 
  is 
  

   gently 
  convex 
  transversely, 
  and 
  it 
  is 
  smooth 
  ; 
  the 
  under 
  surface 
  is 
  

   longitudinally 
  grooved 
  and 
  rough. 
  The 
  greater 
  relative 
  breadth 
  of 
  

   the 
  body 
  near 
  the 
  lower 
  articular 
  end, 
  and 
  the 
  obtuse 
  angle 
  which 
  

   the 
  long 
  slender 
  process 
  makes 
  with 
  the 
  body, 
  are 
  matters 
  in 
  which 
  

   this 
  differs 
  conspicuously 
  from 
  the 
  smaller 
  specimen. 
  Perhaps, 
  if 
  

   both 
  bones 
  were 
  complete, 
  these 
  dissimilarities 
  might 
  appear 
  less. 
  

  

  If 
  now 
  we 
  test 
  these 
  four 
  specimens 
  — 
  Mantell's 
  type 
  in 
  the 
  

   British 
  Museum, 
  Mr. 
  G. 
  B. 
  Holmes's, 
  figured 
  by 
  Prof. 
  Owen 
  in 
  the 
  

   Fossil 
  Peptilia 
  of 
  the 
  Wealden 
  Formation, 
  and 
  Dr. 
  Wilkins's 
  two, 
  

   exhibited 
  this 
  evening. 
  — 
  by 
  the 
  scapular 
  hypothesis 
  originally 
  pro- 
  

   pounded 
  by 
  Dr. 
  Mantel], 
  and 
  adopted 
  by 
  Prof. 
  Owen 
  and 
  the 
  Rev, 
  

  

  