﻿10 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol 
  .67 
  

  

  The 
  posterior 
  face 
  of 
  the 
  Zarhachis 
  skull 
  resembles 
  Lipotes 
  more 
  

   closely 
  than 
  Inia. 
  The 
  supraoccipital 
  is 
  wider 
  than 
  high, 
  bounded 
  

   on 
  the 
  sides 
  and 
  at 
  the 
  top 
  by 
  a 
  flaring 
  lambdoid 
  crest. 
  In 
  Lipotes, 
  the 
  

   supraoccipital 
  is 
  traversed 
  by 
  a 
  distinct 
  median 
  ridge, 
  extending 
  from 
  

   the 
  lambdoid 
  crest 
  almost 
  to 
  the 
  foramen 
  magnum. 
  A 
  low 
  median 
  

   crest 
  is 
  present 
  on 
  the 
  upper 
  half 
  of 
  the 
  supraoccipital 
  in 
  Zarhachis. 
  

  

  The 
  unusual 
  depth 
  of 
  the 
  thin 
  lambdoid 
  crest 
  is 
  the 
  characteristic 
  

   peculiarity 
  of 
  the 
  back 
  of 
  the 
  skull. 
  On 
  the 
  inner 
  and 
  lower 
  sides 
  of 
  

   the 
  temporal 
  fossa 
  the 
  crest 
  curves 
  ventrally 
  and 
  laterally, 
  following 
  

   the 
  contour 
  of 
  the 
  posterior 
  border 
  of 
  the 
  fossa. 
  At 
  the 
  level 
  of 
  the 
  

   lower 
  border 
  of 
  the 
  temporal 
  fossa, 
  the 
  crest 
  on 
  the 
  right 
  side 
  is 
  fully 
  

   32 
  mm. 
  deep. 
  The 
  thin 
  lambdoid 
  crest 
  overhangs 
  the 
  exoccipital 
  on 
  

   each 
  side. 
  The 
  exoccipitals 
  project 
  downward 
  and 
  backward, 
  and 
  

   are 
  of 
  a 
  different 
  shape 
  than 
  those 
  of 
  Lipotes 
  and 
  Inia, 
  the 
  most 
  no- 
  

   ticeable 
  modification 
  in 
  the 
  latter 
  genera 
  being 
  associated 
  with 
  the 
  

   development 
  of 
  a 
  paroccipital 
  process. 
  In 
  these 
  living 
  river 
  dolphins, 
  

   the 
  exoccipital 
  is 
  distinctly 
  constricted 
  above 
  the 
  paroccipital 
  process. 
  

   This 
  process 
  projects 
  outward 
  and 
  backward. 
  In 
  Zarhachis, 
  the 
  ex- 
  

   occipitals 
  are 
  larger, 
  although 
  they 
  are 
  not 
  produced 
  outward 
  far 
  

   enough 
  to 
  conceal 
  the 
  zygomatic 
  processes 
  from 
  behind. 
  The 
  more 
  

   detailed 
  features 
  of 
  the 
  exoccipitals 
  are 
  shown 
  on 
  the 
  photograph 
  re- 
  

   produced 
  on 
  Plate 
  3. 
  Laterally 
  and 
  anteriorly, 
  the 
  exoccipital 
  is 
  in 
  

   contact 
  with 
  the 
  squamosal, 
  superiorly 
  it 
  is 
  coalesced 
  with 
  the 
  supra- 
  

   occipital, 
  while 
  below 
  and 
  internally 
  it 
  fuses 
  with 
  the 
  basioccipital. 
  

   The 
  deep 
  jugular 
  incisure 
  may 
  mark 
  the 
  junction 
  of 
  the 
  exoccipital 
  

   with 
  the 
  falcate 
  process 
  of 
  the 
  basioccipital. 
  

  

  The 
  foramen 
  magnum 
  originally 
  was 
  probably 
  slightly 
  wider 
  than 
  

   high. 
  The 
  condyles 
  are 
  semielliptical 
  in 
  outline. 
  They 
  are 
  strongly 
  

   convex 
  from 
  side 
  to 
  side 
  and 
  are 
  borne 
  on 
  distinct 
  necks. 
  The 
  

   internal 
  borders 
  of 
  the 
  condyles 
  are 
  sharp 
  edged 
  and 
  concave; 
  the 
  

   external 
  borders 
  are 
  rounded 
  off. 
  

  

  Lateral 
  view. 
  — 
  Aside 
  from 
  the 
  relatively 
  large 
  size 
  of 
  the 
  " 
  upended 
  " 
  

   extremity 
  of 
  the 
  supraorbital 
  process 
  and 
  the 
  massive 
  zygomatic 
  

   process, 
  the 
  skull 
  (pi. 
  4) 
  is 
  characterized 
  by 
  a 
  short 
  temporal 
  fossa 
  

   and 
  a 
  protuberance 
  on 
  the 
  vertex. 
  The 
  protuberance 
  behind 
  the 
  

   nasal 
  passages 
  is 
  the 
  highest 
  point 
  on 
  the 
  dorsal 
  profile. 
  The 
  trans- 
  

   verse 
  crest 
  of 
  the 
  supraoccipital 
  is 
  the 
  next 
  highest 
  point 
  and 
  from 
  

   this 
  crest 
  the 
  maxilla 
  slopes 
  forward 
  to 
  the 
  base 
  of 
  the 
  rostrum. 
  

  

  Above 
  the 
  orbit 
  the 
  extremity 
  of 
  the 
  supraorbital 
  process 
  bends 
  

   abruptly 
  upward 
  and 
  forms 
  a 
  broad 
  crest. 
  Portions 
  of 
  the 
  outer 
  

   margin 
  of 
  the 
  maxilla 
  are 
  visible 
  on 
  the 
  upper 
  margin 
  of 
  this 
  crest 
  

   from 
  a 
  side 
  view 
  and 
  it 
  also 
  sheathes 
  the 
  entire 
  internal 
  surface. 
  

   The 
  greatest 
  vertical 
  depth 
  of 
  the 
  right 
  supraorbital 
  process 
  is 
  64 
  

   mm. 
  and 
  the, 
  greatest 
  anteroposterior 
  diameter 
  is 
  96 
  mm. 
  The 
  

   external 
  face 
  of 
  the 
  extremity 
  of 
  the 
  supraorbital 
  process 
  is 
  more 
  or 
  

  

  