﻿182 
  MR. 
  C. 
  W. 
  ANDREWS 
  ON 
  THE 
  STRUCTURE 
  [May 
  1 
  897, 
  

  

  arrangement 
  differs 
  in 
  any 
  way 
  from 
  that 
  described 
  in 
  the 
  skull 
  of 
  

   Peloneustes, 
  in 
  which 
  this 
  portion 
  of 
  the 
  palate 
  is 
  well 
  preserved, 
  

   and 
  its 
  structure 
  perfectly 
  clear. 
  

  

  The 
  premaxillae 
  (PI. 
  XII, 
  p.moc.) 
  are 
  very 
  large 
  bones, 
  each 
  

   consisting 
  of 
  a 
  dentigerous 
  body, 
  which 
  is 
  produced 
  backward 
  

   on 
  the 
  palate 
  into 
  a 
  short 
  palatine 
  process, 
  and 
  an 
  enormously 
  

   elongated 
  facial 
  process 
  which 
  extends 
  far 
  behind 
  the 
  external 
  nares 
  

   and 
  terminates 
  in 
  a 
  suture 
  with 
  the 
  frontals. 
  

  

  The 
  teeth 
  borne 
  by 
  each 
  premaxilla 
  are 
  five 
  in 
  number. 
  The 
  

   first 
  pair 
  are 
  comparatively 
  small, 
  directed 
  forwards, 
  and 
  almost 
  in 
  

   contact 
  in 
  the 
  middle 
  line. 
  The 
  second, 
  third, 
  and 
  fourth 
  increase 
  

   in 
  size 
  in 
  the 
  order 
  named, 
  while 
  the 
  fifth 
  is 
  considerably 
  smaller 
  

   than 
  the 
  fourth. 
  Between 
  the 
  last 
  premaxillary 
  tooth 
  and 
  the 
  

   first 
  in 
  the 
  maxilla 
  there 
  is 
  a 
  diastema 
  about 
  6 
  cm. 
  long, 
  which 
  is 
  

   crossed 
  near 
  its 
  middle 
  point 
  by 
  the 
  premaxillo-maxillary 
  suture. 
  

   Immediately 
  internal 
  to 
  the 
  alveoli 
  there 
  is 
  a 
  deep 
  groove, 
  at 
  the 
  

   bottom 
  of 
  which 
  the 
  tips 
  of 
  the 
  successional 
  teeth 
  may 
  be 
  seen. 
  

   The 
  inner 
  wall 
  of 
  this 
  groove 
  is 
  formed 
  by 
  a 
  prominent 
  ridge, 
  which, 
  

   joining 
  that 
  of 
  the 
  opposite 
  side, 
  forms 
  an 
  elongated 
  triangular 
  

   raised 
  area 
  in 
  the 
  middle 
  of 
  the 
  anterior 
  end 
  of 
  the 
  palate. 
  By 
  the 
  

   divergence 
  of 
  the 
  ridges 
  posteriorly 
  a 
  short 
  groove 
  is 
  formed, 
  which 
  

   is 
  closed 
  behind 
  by 
  the 
  prominent 
  anterior 
  end 
  of 
  the 
  vomers. 
  The 
  

   upper 
  surface 
  of 
  the 
  body 
  of 
  the 
  premaxillae 
  is 
  rough 
  and 
  pitted 
  

   with 
  numerous 
  foramina. 
  The 
  immense 
  facial 
  processes 
  together 
  

   form 
  a 
  broad 
  convex 
  ridge 
  along 
  the 
  upper 
  surface 
  of 
  the 
  snout 
  ; 
  

   behind 
  they 
  form 
  a 
  complicated 
  zigzag 
  suture 
  with 
  the 
  frontals. 
  

   The 
  suture 
  between 
  the 
  premaxillae 
  'is 
  persistent. 
  

  

  The 
  maxilla 
  (PL 
  XII, 
  mat.) 
  in 
  its 
  general 
  form 
  closely 
  resembles 
  

   that 
  of 
  Peloneustes, 
  but 
  instead 
  of 
  bearing 
  from 
  twenty-eight 
  to 
  thirty 
  

   teeth 
  as 
  in 
  that 
  genus, 
  there 
  are 
  only 
  about 
  twenty. 
  Of 
  these 
  the 
  

   first 
  two 
  were 
  small, 
  the 
  next 
  two 
  very 
  large. 
  Behind 
  these 
  there 
  is 
  a 
  

   gradual 
  decrease 
  in 
  size 
  as 
  far 
  as 
  the 
  ninth. 
  The 
  tenth 
  and 
  eleventh 
  

   are 
  again 
  larger, 
  and 
  behind 
  these 
  the 
  series 
  decreases 
  gradually, 
  

   the 
  hindermost 
  teeth 
  being 
  very 
  small. 
  The 
  whole 
  alveolar 
  margin 
  

   of 
  the 
  jaw, 
  seen 
  from 
  the 
  side, 
  is 
  sinuous 
  in 
  outline 
  : 
  the 
  first 
  con- 
  

   vexity 
  occurring 
  in 
  the 
  premaxilla, 
  the 
  next 
  opposite 
  the 
  second 
  

   and 
  third 
  maxillary 
  teeth, 
  the 
  last 
  and 
  least 
  marked 
  opposite 
  the 
  

   tenth 
  and 
  eleventh. 
  

  

  As 
  already 
  mentioned 
  the 
  anterior 
  palatal 
  portion 
  of 
  the 
  maxilla 
  

   forms 
  an 
  extensive 
  overlap 
  upon 
  the 
  vomer. 
  Opposite 
  the 
  internal 
  

   nares 
  its 
  inner 
  border 
  is 
  raised 
  into 
  a 
  high, 
  thin 
  ridge, 
  which 
  forms 
  a 
  

   kind 
  of 
  outer 
  wall 
  to 
  the 
  opening. 
  Behind 
  the 
  nares 
  the 
  maxilla 
  

   first 
  joins 
  the 
  palatine, 
  then 
  forms 
  the 
  outer 
  boundary 
  of 
  the 
  sub- 
  

   orbital 
  vacuity, 
  behind 
  which, 
  again, 
  it 
  is 
  joined 
  by 
  the 
  trans- 
  

   palatine. 
  It 
  terminates 
  posteriorly 
  in 
  a 
  slender 
  prolongation 
  which 
  

   underlies 
  the 
  lower 
  border 
  of 
  the 
  jugal, 
  and 
  nearly 
  reaches 
  the 
  

   anterior 
  end 
  of 
  the 
  squamosal. 
  Immediately 
  within 
  the 
  alveolar 
  

   region, 
  throughout 
  its 
  wholo 
  extent, 
  there 
  is 
  a 
  deep 
  groove 
  similar 
  

   to 
  that 
  seen 
  in 
  the 
  premaxillae. 
  

  

  The 
  faeial 
  surface 
  of 
  the 
  maxilla, 
  like 
  that 
  of 
  the 
  premaxilla, 
  is 
  

  

  