﻿PROF. 
  H. 
  G. 
  SEELET 
  ON 
  THE 
  PELVIS 
  OP 
  ORNTTHOPSTS. 
  303 
  

  

  Mr. 
  Hulke 
  does 
  not 
  expressly 
  determine 
  these 
  pelvic 
  bones 
  as 
  

   right 
  or 
  left, 
  and 
  he 
  is 
  equally 
  indefinite 
  with 
  regard 
  to 
  the 
  remains 
  

   of 
  the 
  Wealden 
  Omitliopsis. 
  Still 
  the 
  fact 
  that 
  Professor 
  Marsh 
  

   figured 
  the 
  external 
  surface 
  of 
  the 
  pelvis 
  of 
  Atlantosaurus, 
  and 
  that 
  

   Mr. 
  Hulke 
  has 
  copied 
  that 
  figure 
  reversed 
  in 
  pi. 
  xiv. 
  Quart. 
  Journ. 
  

   Geol. 
  Soc. 
  vol. 
  xxxviii. 
  in 
  illustration 
  of 
  what 
  I 
  regard 
  as 
  Omitliopsis 
  

   MulJcei, 
  is 
  some 
  evidence 
  that 
  the 
  figured 
  surface 
  was 
  regarded 
  as 
  

   external, 
  and 
  the 
  bones 
  as 
  belonging 
  to 
  the 
  right 
  side 
  of 
  the 
  

   skeleton 
  *. 
  However 
  this 
  may 
  be, 
  I 
  had 
  no 
  doubt 
  that 
  the 
  figured 
  

   surface 
  in 
  Omitliopsis 
  Leedsii 
  is 
  the 
  internal 
  or 
  visceral 
  surface, 
  and 
  

   therefore 
  the 
  bones 
  are 
  of 
  the 
  left 
  side 
  ; 
  and 
  the 
  "Wealden 
  specimen 
  

   shows 
  substantially 
  the 
  same 
  characters. 
  This 
  difference 
  in 
  inter- 
  

   pretation 
  involves 
  a 
  totally 
  different 
  conception 
  of 
  the 
  nature 
  of 
  

   the 
  pelvis, 
  and 
  supposing 
  the 
  ilium 
  to 
  have 
  been 
  correctly 
  determined, 
  

   its 
  chief 
  extension 
  may 
  be 
  varied, 
  as 
  I 
  traced 
  the 
  sutural 
  surface 
  

   on 
  the 
  pubic 
  bone 
  which 
  extends 
  in 
  the 
  median 
  line 
  of 
  the 
  body 
  of 
  

   the 
  animal. 
  Mr. 
  Alfred 
  N. 
  Leeds 
  had 
  the 
  kindness 
  to 
  remove 
  these 
  

   massive 
  specimens 
  from 
  their 
  positions 
  in 
  his 
  museum, 
  so 
  that 
  the 
  

   bones 
  from 
  the 
  right 
  and 
  left 
  sides 
  of 
  the 
  body 
  might 
  be 
  adapted 
  to 
  

   each 
  other 
  in 
  the 
  inclined 
  positions 
  which 
  I 
  regarded 
  them 
  as 
  having 
  

   occupied 
  during 
  the 
  life 
  of 
  the 
  animal. 
  It 
  then 
  became 
  manifest 
  

   that 
  the 
  bones 
  were 
  united 
  in 
  the 
  median 
  line 
  almost 
  throughout 
  

   their 
  length 
  by 
  a 
  median 
  suture, 
  and 
  that 
  they 
  formed 
  a 
  saddle- 
  

   shaped 
  surface 
  from 
  front 
  to 
  back, 
  as 
  do 
  the 
  larger 
  Plesiosaurs 
  from 
  

   the 
  Oxford 
  Clay. 
  

  

  The 
  left 
  pubis 
  becomes 
  thickened 
  at 
  its 
  anterior 
  extremity, 
  

   which 
  shows 
  a 
  cartilaginous 
  surface 
  ; 
  but 
  internally 
  there 
  is 
  a 
  well- 
  

   marked 
  suture 
  in 
  the 
  median 
  line, 
  which 
  is 
  bevelled 
  at 
  an 
  angle 
  of 
  

   45°. 
  This 
  articulation 
  is 
  six 
  centimetres 
  deep 
  and 
  about 
  24 
  centim. 
  

   long, 
  terminating 
  posteriorly 
  in 
  a 
  sharp 
  point, 
  where 
  there 
  is 
  a 
  

   small 
  median 
  foramen 
  between 
  the 
  bones, 
  with 
  a 
  well-ossified 
  border. 
  

   This 
  suture 
  ascends 
  in 
  level 
  as 
  it 
  extends 
  backwards. 
  The 
  internal 
  

   surface 
  of 
  the 
  pubis 
  is 
  flattened, 
  and 
  the 
  external 
  surface 
  is 
  convex 
  

   transversely 
  over 
  this 
  anterior 
  portion 
  of 
  the 
  bone. 
  Behind 
  this 
  

   suture 
  the 
  bone 
  is 
  bent 
  in 
  an 
  arch, 
  so 
  that 
  its 
  external 
  surface 
  is 
  con- 
  

   cave 
  from 
  front 
  to 
  back 
  along 
  the 
  median 
  line. 
  On 
  the 
  inner 
  margin 
  

   the 
  median 
  sutural 
  surface 
  is 
  prolonged 
  for 
  25 
  centim., 
  behind 
  which 
  

   the 
  continuity 
  of 
  the 
  bones 
  is 
  interrupted 
  by 
  a 
  smooth 
  border 
  to 
  a 
  

   notch 
  which 
  may 
  have 
  separated 
  the 
  bones 
  by 
  14 
  or 
  15 
  centim. 
  

   In 
  the 
  middle, 
  where 
  it 
  is 
  strongest, 
  this 
  posterior 
  part 
  of 
  the 
  sym- 
  

   physis 
  is 
  4 
  centim. 
  in 
  vertical 
  depth. 
  It 
  is 
  inclined 
  to 
  the 
  internal 
  

   surface, 
  but 
  to 
  a 
  less 
  degree 
  than 
  the 
  anterior 
  part 
  of 
  the 
  symphysis, 
  

   consequent 
  on 
  the 
  arched 
  form 
  bringing 
  the 
  hinder 
  part 
  of 
  the 
  pubic 
  

   symphysis 
  into 
  a 
  superior 
  position, 
  so 
  that 
  the 
  bones 
  of 
  the 
  two 
  

   sides 
  meet 
  at 
  a 
  less 
  acute 
  angle. 
  The 
  two 
  pubic 
  bones 
  are 
  thus 
  so 
  

   inclined 
  to 
  each 
  other 
  as 
  to 
  enclose 
  an 
  anterior 
  basin 
  and 
  a 
  posterior 
  

   basin, 
  which 
  are 
  separated 
  by 
  the 
  intervening 
  saddle-shaped 
  arch. 
  

  

  * 
  Mr. 
  Lydekker 
  adopts 
  this 
  determination 
  in 
  the 
  British 
  Museum 
  Catalogue, 
  

   vol. 
  i. 
  p. 
  150, 
  describing 
  the 
  bones 
  as 
  associated 
  right 
  ischium 
  and 
  pubis. 
  

  

  