﻿A 
  PLESIOSAURIAN 
  FROM 
  THE 
  OXFORD 
  CLAY. 
  201 
  

  

  1| 
  inch 
  long, 
  with 
  the 
  articular 
  surface 
  in 
  front 
  1| 
  inch 
  wide 
  and 
  

   rather 
  less 
  than 
  l|inch 
  deep; 
  on 
  the 
  posterior 
  surface 
  these 
  dimensions 
  

   are 
  somewhat 
  exceeded. 
  The 
  articular 
  surface 
  of 
  the 
  centrum 
  is 
  con- 
  

   cave, 
  more 
  so 
  in 
  front 
  than 
  behind 
  ; 
  both 
  surfaces 
  are 
  margined 
  by 
  a 
  

   groove, 
  which 
  indicates 
  the 
  union 
  of 
  the 
  epiphysis 
  with 
  the 
  centrum. 
  

   The 
  centrum 
  is 
  greatly 
  compressed 
  in 
  its 
  upper 
  half 
  from 
  side 
  to 
  side, 
  

   and 
  is 
  therefore 
  concave 
  from 
  front 
  to 
  back 
  laterally 
  ; 
  below 
  the 
  middle 
  

   on 
  each 
  side 
  there 
  is 
  a 
  sharp 
  slightly 
  elevated 
  ridge, 
  which 
  dies 
  away 
  

   at 
  the 
  articular 
  margins. 
  At 
  the 
  junction 
  of 
  the 
  side 
  of 
  the 
  cen- 
  

   trum 
  with 
  its 
  base 
  the 
  cervical 
  ribs 
  are 
  given 
  off 
  : 
  each 
  is 
  attached 
  

   by 
  a 
  narrow 
  ovate 
  surface 
  about 
  an 
  inch 
  long, 
  is 
  compressed 
  from 
  

   side 
  to 
  side, 
  directed 
  downward 
  and 
  a 
  little 
  outward 
  and 
  backward 
  

   in 
  a 
  curve. 
  The 
  anterior 
  margin 
  of 
  the 
  rib 
  is 
  convex 
  in 
  length 
  and 
  

   sharp 
  in 
  edge 
  ; 
  the 
  posterior 
  margin 
  is 
  concave 
  from 
  above 
  down- 
  

   ward, 
  and 
  rounded 
  from 
  side 
  to 
  side 
  ; 
  the 
  inner 
  surface 
  of 
  the 
  bone 
  

   is 
  flattened 
  ; 
  but 
  the 
  outside 
  is 
  more 
  convex 
  : 
  the 
  free 
  end 
  of 
  the 
  bone 
  

   terminates 
  in 
  a 
  concavity 
  indicating 
  a 
  cartilage. 
  The 
  suture 
  between 
  

   the 
  neural 
  arch 
  and 
  the 
  centrum 
  is 
  obliterated. 
  The 
  total 
  height 
  

   from 
  the 
  base 
  of 
  the 
  centrum 
  to 
  the 
  top 
  of 
  the 
  neural 
  spine 
  is 
  3^ 
  

   inches. 
  The 
  length 
  from 
  the 
  front 
  of 
  the 
  anterior 
  zygapophyses 
  to 
  

   the 
  back 
  of 
  the 
  posterior 
  zygapophyses 
  is 
  2| 
  inches. 
  The 
  anterior 
  

   zygapophyses 
  project 
  about 
  j 
  of 
  an 
  inch 
  in 
  front 
  of 
  the 
  centrum 
  ; 
  

   the 
  posterior 
  zygapophyses 
  project 
  about 
  \ 
  an 
  inch 
  behind 
  it. 
  The 
  

   anterior 
  zygapophyses 
  are 
  large 
  oval 
  facets 
  looking 
  upward 
  and 
  in- 
  

   ward 
  ; 
  the 
  part 
  of 
  the 
  neural 
  arch 
  behind 
  them 
  is 
  constricted 
  ; 
  and 
  

   from 
  their 
  base 
  on 
  each 
  side 
  a 
  ridge 
  arises 
  which 
  is 
  prolonged 
  

   backward, 
  upward, 
  and 
  outward 
  to 
  form 
  the 
  upper 
  margin 
  of 
  the 
  

   posterior 
  zygapophysis 
  (which 
  measures 
  | 
  of 
  an 
  inch 
  from 
  side 
  to 
  

   side) 
  and 
  form 
  the 
  limits 
  of 
  a 
  small 
  table 
  from 
  which 
  the 
  neural 
  

   spine 
  arises 
  ; 
  below 
  this 
  oblique 
  ridge 
  the 
  posterior 
  portion 
  of 
  the 
  

   neural 
  arch 
  is 
  compressed 
  from 
  side 
  to 
  side 
  ; 
  above 
  it 
  the 
  neural 
  arch 
  

   rises 
  1 
  inch. 
  The 
  neural 
  spine 
  terminates 
  in 
  a 
  sharp 
  short 
  pos- 
  

   terior 
  border, 
  a 
  little 
  concave 
  and 
  nearly 
  vertical, 
  and 
  has 
  a 
  sharp 
  

   long 
  anterior 
  border 
  inclined 
  obliquely 
  backward. 
  

  

  In 
  passing 
  down 
  the 
  vertebral 
  column 
  the 
  vertebrae 
  get 
  steadily 
  

   longer 
  from 
  back 
  to 
  front, 
  and 
  steadily 
  larger 
  ; 
  the 
  neural 
  spines 
  

   become 
  a 
  little 
  wider, 
  from 
  back 
  to 
  front, 
  and 
  stronger 
  ; 
  and 
  at 
  the 
  

   eighth 
  vertebra 
  the 
  cervical 
  rib 
  has 
  the 
  usual 
  hatchet-shaped 
  pattern. 
  

   Lower 
  down 
  the 
  vertebral 
  column 
  the 
  antero-posterior 
  ridge 
  on 
  the 
  

   side 
  of 
  the 
  centrum 
  becomes 
  shorter 
  and 
  less 
  elevated, 
  and 
  finally 
  

   disappears 
  about 
  the 
  thirty-second 
  vertebra 
  ; 
  the 
  oblique 
  ridge 
  be- 
  

   tween 
  the 
  anterior 
  and 
  posterior 
  zygapophyses 
  gradually 
  becomes 
  

   more 
  horizontal 
  and 
  less 
  elevated, 
  so 
  that 
  in 
  the 
  lower 
  part 
  of 
  the 
  

   neck 
  there 
  is 
  no 
  trace 
  whatever 
  of 
  a 
  platform 
  from 
  which 
  the 
  

   neural 
  spine 
  arises. 
  From 
  about 
  the 
  fifteenth 
  vertebra 
  to 
  about 
  the 
  

   thirtieth 
  the 
  neural 
  spine, 
  which 
  has 
  become 
  much 
  widened, 
  is 
  com- 
  

   pressed 
  from 
  side 
  to 
  side, 
  and 
  terminates 
  upward 
  in 
  a 
  long 
  flat 
  car- 
  

   tilaginous 
  surface, 
  and 
  has 
  its 
  anterior 
  border 
  nearly 
  vertical, 
  and 
  its 
  

   posterior 
  border 
  inclined 
  obliquely 
  forward. 
  In 
  the 
  seventeenth 
  

   vertebra, 
  which 
  has 
  the 
  centrum 
  1 
  T 
  7 
  ^ 
  inch 
  long, 
  the 
  neural 
  spine 
  

  

  