﻿art. 
  28 
  SKULL 
  OF 
  ZARHACHIS 
  FLAGELLATOR 
  KELLOGG 
  15 
  

  

  but 
  follows 
  the 
  groove 
  on 
  the 
  ventral 
  face 
  of 
  the 
  attenuate 
  process 
  

   of 
  the 
  orbitosphenoid 
  in 
  company 
  with 
  the 
  trochlearis 
  and 
  the 
  

   ophthalmic 
  division 
  of 
  the 
  trigeminal. 
  This 
  groove 
  is 
  much 
  wider 
  

   than 
  in 
  Inia, 
  and 
  that 
  portion 
  of 
  the 
  orbitosphenoid 
  which 
  separated 
  

   the 
  optic 
  canal 
  from 
  the 
  above-mentioned 
  groove 
  has 
  disappeared 
  

   on 
  the 
  skull 
  of 
  Lipotes. 
  

  

  The 
  observations 
  of 
  Anderson 
  on 
  the 
  peculiarities 
  of 
  the 
  orbito- 
  

   sphenoid 
  in 
  the 
  skull 
  of 
  Platanista 
  have 
  been 
  found 
  to 
  agree 
  with 
  

   specimens 
  in 
  the 
  United 
  States 
  National 
  Museum. 
  This 
  descrip- 
  

   tion 
  7 
  can 
  be 
  consulted 
  for 
  a 
  more 
  detailed 
  discussion. 
  In 
  Platanista, 
  

   the 
  sphenoidal 
  fissure 
  is 
  almost 
  closed 
  and 
  the 
  orbitosphenoid 
  is 
  

   pierced 
  by 
  an 
  extremely 
  small 
  foramen 
  for 
  the 
  optic 
  nerve. 
  The 
  

   orbitosphenoid 
  has 
  been 
  depressed 
  and 
  thrust 
  backward 
  so 
  that 
  its 
  

   posterior 
  border 
  slides 
  backward 
  above 
  the 
  anterior 
  margin 
  of 
  the 
  

   alisphenoid. 
  The 
  ventral 
  surface 
  of 
  the 
  orbitosphenoid 
  is 
  broadly 
  

   and 
  deeply 
  grooved 
  for 
  the 
  trochlearis 
  and 
  the 
  ophthalmic 
  division 
  

   of 
  the 
  trigeminal 
  nerve 
  which 
  pass 
  out 
  through 
  the 
  sphenoidal 
  

   fissure 
  and 
  continue 
  forward 
  along 
  this 
  canallike 
  continuation 
  of 
  the 
  

   fissure. 
  As 
  viewed 
  through 
  the 
  foramen 
  magnum 
  the 
  cranial 
  orifice 
  of 
  

   each 
  optic 
  canal 
  is 
  overhung 
  by 
  a 
  thin 
  platelike 
  process 
  of 
  the 
  orbito- 
  

   sphenoid. 
  The 
  minute 
  ectal 
  orifice 
  of 
  the 
  orbitosphenoid 
  portion 
  

   of 
  the 
  optic 
  canal 
  appears 
  on 
  the 
  inner 
  wall 
  of 
  the 
  canallike 
  continua- 
  

   tion 
  of 
  the 
  sphenoidal 
  fissure 
  near 
  the 
  level 
  of 
  the 
  anterior 
  border 
  

   of 
  the 
  alisphenoid. 
  The 
  upper 
  border 
  of 
  the 
  external 
  reduplication 
  

   of 
  the 
  pterygoid 
  and 
  a 
  thin 
  platelike 
  process 
  of 
  the 
  frontal 
  which 
  

   slides 
  forward 
  under 
  the 
  maxilla, 
  as 
  viewed 
  from 
  in 
  front, 
  enclose 
  the 
  

   passage 
  for 
  the 
  optic 
  nerve 
  from 
  below 
  as 
  it 
  curves 
  forward 
  and 
  

   outward; 
  the 
  ectal 
  orifice 
  of 
  the 
  optic 
  canal 
  appears 
  near 
  the 
  internal 
  

   extremity 
  of 
  the 
  lachrymal. 
  The 
  optic 
  canal, 
  as 
  it 
  passes 
  outward 
  

   along 
  the 
  supraorbital 
  process, 
  is 
  bounded 
  on 
  three 
  sides 
  by 
  the 
  thin 
  

   plates 
  of 
  the 
  frontal 
  and 
  roofed 
  over 
  by 
  the 
  maxilla. 
  This 
  thin 
  plate 
  

   like 
  anteriorly 
  directed 
  process 
  of 
  the 
  frontal 
  also 
  conceals 
  the 
  basal 
  

   half 
  of 
  the 
  supraorbital 
  process 
  from 
  a 
  ventral 
  view. 
  The 
  canallike 
  

   continuation 
  of 
  the 
  sphenoidal 
  fissure 
  for 
  the 
  passage 
  of 
  nerves 
  is 
  

   concealed 
  by 
  the 
  pterygoid. 
  Imperfections 
  in 
  the 
  ossification 
  of 
  the 
  

   walls 
  of 
  the 
  optic 
  canal 
  occur 
  in 
  most 
  skulls 
  of 
  Platanista. 
  

  

  In 
  Zarhachis, 
  the 
  course 
  of 
  the 
  optic 
  nerve 
  from 
  the 
  point 
  where 
  it 
  

   issues 
  from 
  the 
  cranial 
  cavity 
  to 
  the 
  base 
  of 
  the 
  supraorbital 
  process 
  

   is 
  concealed 
  by 
  the 
  external 
  reduplication 
  of 
  the 
  pterygoid. 
  The 
  

   edges 
  of 
  the 
  bones 
  surrounding 
  the 
  ectal 
  orifice 
  of 
  the 
  optic 
  canal 
  are 
  

   broken 
  and 
  jagged 
  on 
  the 
  second 
  skull 
  and 
  no 
  attempt 
  has 
  been 
  made 
  

   to 
  remove 
  the 
  matrix 
  from 
  this 
  region 
  on 
  the 
  first 
  skull 
  because 
  of 
  its 
  

  

  » 
  Anderson, 
  J., 
  Anatomical 
  and 
  Zoological 
  Researches: 
  Comprising 
  an 
  account 
  of 
  the 
  Zoological 
  Results 
  

   of 
  the 
  Two 
  Expeditions 
  to 
  Western 
  Yunnan 
  in 
  1868 
  and 
  1875. 
  London 
  (1878), 
  pp. 
  511-512. 
  1879. 
  

  

  