﻿12 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol. 
  G7 
  

  

  It 
  was 
  stated 
  in 
  the 
  preceding 
  paper 
  that 
  the 
  outer 
  plate 
  of 
  the 
  

   pterygoid 
  represented 
  the 
  external 
  pterygoid 
  and 
  the 
  internal 
  plate 
  

   was 
  referred 
  to 
  as 
  the 
  internal 
  pterygoid. 
  This 
  interpretation 
  does 
  

   not 
  appear 
  to 
  be 
  correct, 
  since 
  both 
  plates 
  are 
  continuous 
  on 
  the 
  right 
  

   side 
  of 
  the 
  second 
  skull 
  and 
  overspread 
  the 
  inferior 
  face 
  of 
  the 
  basal 
  

   portion 
  of 
  the 
  alisphenoid; 
  these 
  combined 
  plates 
  and 
  the 
  thin 
  isthmus 
  

   which 
  unites 
  them 
  form 
  the 
  walls 
  of 
  the 
  longitudinal 
  sinus 
  external 
  to 
  

   the 
  basisphenoid. 
  In 
  view 
  of 
  the 
  above, 
  it 
  is 
  apparent 
  that 
  the 
  outer 
  

   plate 
  represents 
  the 
  external 
  reduplication 
  of 
  the 
  pterygoid. 
  The 
  

   loss 
  of 
  the 
  anterior 
  end 
  of 
  the 
  thin 
  platelike 
  external 
  reduplication 
  of 
  

   the 
  pterygoid 
  on 
  the 
  right 
  side 
  exposes 
  the 
  pyramidal 
  cavity 
  on 
  the 
  

   corresponding 
  side 
  of 
  the 
  axial 
  ridge 
  of 
  the 
  vomer 
  for 
  its 
  entire 
  length. 
  

   On 
  the 
  left 
  side, 
  this 
  thin 
  platelike 
  external 
  reduplication 
  of 
  the 
  ptery- 
  

   goid 
  extends 
  forward 
  128 
  mm. 
  in 
  advance 
  of 
  the 
  posterior 
  wall 
  of 
  the 
  

   nasal 
  passage 
  and 
  contributes 
  the 
  external 
  wall 
  of 
  the 
  pyramidal 
  

   cavity 
  on 
  the 
  left 
  side 
  of 
  the 
  vomer. 
  Posteriorly, 
  the 
  external 
  re- 
  

   duplication 
  of 
  the 
  left 
  pterygoid 
  extends 
  backward 
  beyond 
  the 
  nasal 
  

   passages 
  and 
  is 
  bounded 
  by 
  the 
  maxilla 
  anteriorly, 
  by 
  the 
  frontal 
  

   and 
  alisphenoid 
  superiorly, 
  and 
  by 
  the 
  squamosal 
  posteriorly. 
  The 
  

   mandibular 
  branch 
  of 
  the 
  trigeminal 
  nerve 
  passes 
  outward 
  through 
  

   the 
  foramen 
  ovale 
  in 
  the 
  suture 
  between 
  the 
  squamosal 
  and 
  the 
  ex- 
  

   ternal 
  reduplication 
  of 
  the 
  pterygoid 
  and 
  follows 
  the 
  trowellike 
  gutter 
  

   on 
  the 
  external 
  face 
  of 
  the 
  latter. 
  This 
  foramen 
  is 
  situated 
  in 
  ap- 
  

   proximately 
  the 
  same 
  position 
  as 
  in 
  Platanista. 
  There 
  is 
  a 
  remark- 
  

   able 
  resemblance 
  between 
  the 
  size 
  and 
  relations 
  of 
  these 
  pterygoids 
  

   and 
  the 
  corresponding 
  bones 
  in 
  Platanista. 
  The 
  internal 
  plates 
  of 
  the 
  

   pterygoids 
  are 
  not 
  as 
  well 
  preserved 
  on 
  this 
  specimen 
  as 
  on 
  the 
  first 
  

   skull. 
  On 
  the 
  latter 
  the 
  thin 
  internal 
  plate 
  of 
  the 
  pterygoid 
  curves 
  

   around 
  the 
  lower 
  border 
  of 
  the 
  lateral 
  and 
  anterior 
  walls 
  of 
  the 
  cor- 
  

   responding 
  nasal 
  passage 
  and 
  meets 
  the 
  vomer 
  mesially; 
  it 
  then 
  

   turns 
  almost 
  at 
  right 
  angles 
  to 
  the 
  latter 
  and 
  is 
  closely 
  appressed 
  to 
  

   the 
  external 
  surface 
  of 
  the 
  trough 
  of 
  the 
  vomer. 
  On 
  skulls 
  of 
  Inia, 
  

   Lipotes, 
  and 
  Platanista 
  thin 
  plates 
  of 
  the 
  maxillae 
  have 
  overspread 
  

   the 
  external 
  surface 
  of 
  the 
  trough 
  of 
  the 
  vomer 
  and 
  conceal 
  all 
  but 
  

   the 
  axial 
  ridge 
  of 
  the 
  latter. 
  On 
  the 
  Zarhachis 
  skull 
  the 
  external 
  

   surface 
  of 
  the 
  trough 
  of 
  the 
  vomer 
  is 
  not 
  overspread 
  by 
  the 
  maxillae 
  

   below 
  the 
  level 
  of 
  the 
  palatines. 
  Further 
  comparison 
  with 
  the 
  first 
  

   skull 
  is 
  scarcely 
  necessary, 
  as 
  it 
  is 
  now 
  apparent 
  that 
  the 
  thin 
  an- 
  

   teriorly 
  directed 
  internal 
  plate 
  of 
  the 
  pterygoid 
  did 
  not 
  by 
  itself 
  

   form 
  the 
  internal 
  and 
  superior 
  walls 
  of 
  the 
  pyramidal 
  cavity 
  or 
  at 
  

   least 
  a 
  cavity 
  was 
  not 
  formed 
  which 
  was 
  bounded 
  solely 
  by 
  the 
  in- 
  

   ternal 
  plate 
  of 
  the 
  pterygoid 
  and 
  its 
  external 
  reduplication 
  as 
  in 
  

   Platanista. 
  

  

  The 
  palatines 
  are 
  not 
  visible 
  from 
  a 
  ventral 
  view 
  when 
  the 
  ptery- 
  

   goids 
  are 
  complete. 
  The 
  sutures 
  defining 
  the 
  limits 
  of 
  the 
  right 
  

  

  