﻿abt. 
  28 
  SKULL 
  OF 
  ZAK 
  1 
  1 
  AC 
  HIS 
  FLAGELLATOR— 
  KKLI-Odii 
  ( 
  

  

  In 
  most 
  mammals 
  the 
  ethmoid 
  plate 
  ossifies 
  into 
  a 
  median 
  meseth- 
  

   moid 
  bone 
  bounded 
  below 
  on 
  either 
  side 
  by 
  an 
  ectethmoid. 
  These 
  

   ectethmoids 
  develop 
  as 
  the 
  cribriform 
  plate. 
  On 
  each 
  side 
  of 
  the 
  per- 
  

   pendicular 
  mesethmoid 
  in 
  skulls 
  of 
  the 
  Miocene 
  porpoises 
  Diochoti- 
  

   chus, 
  Ceterhinops, 
  and 
  Squalodon 
  there 
  is 
  a 
  relatively 
  large 
  aperture 
  

   through 
  which 
  the 
  nasal 
  branch 
  of 
  the 
  ophthalmic 
  division 
  of 
  the 
  

   fifth 
  cranial 
  nerve 
  passes. 
  In 
  skulls 
  of 
  living 
  porpoises, 
  like 
  Delphinus 
  

   and 
  Pseudorca, 
  there 
  is 
  a 
  continuous 
  sheet 
  of 
  bone 
  extending 
  upward 
  

   to 
  the 
  base 
  of 
  the 
  nasals 
  and 
  from 
  which 
  arises 
  the 
  mesial 
  longitudinal 
  

   perpendicular 
  strip 
  of 
  bone 
  that 
  constitutes 
  the 
  most 
  dorsal 
  portion 
  

   of 
  the 
  wall 
  between 
  the 
  nasal 
  passages. 
  In 
  each 
  nasal 
  passage 
  in 
  the 
  

   skull 
  of 
  Lipotes 
  a 
  fissure 
  appears 
  to 
  separate 
  the 
  longitudinal 
  perpen- 
  

   dicular 
  plate 
  or 
  mesethmoid 
  superiorly 
  from 
  the 
  laterally 
  placed 
  

   ectethmoid. 
  Inferiorly, 
  the 
  fissure 
  extends 
  obliquely 
  downward 
  

   across 
  the 
  posterior 
  wall 
  of 
  each 
  nasal 
  passage. 
  These 
  fissures 
  may 
  

   represent 
  one 
  of 
  the 
  later 
  stages 
  in 
  the 
  closure 
  of 
  foramina 
  similar 
  to 
  

   those 
  in 
  the 
  Zarhachis 
  skull. 
  The 
  thin 
  longitudinal 
  bony 
  partition 
  

   may 
  represent 
  either 
  a 
  dorsal 
  continuation 
  of 
  the 
  combined 
  ecteth- 
  

   moids 
  or 
  the 
  mesethmoid. 
  Most 
  writers 
  in 
  recent 
  years 
  have 
  held 
  

   that 
  the 
  pluglike 
  porous 
  bone, 
  which 
  rests 
  in 
  the 
  trough 
  of 
  the 
  vomer 
  

   and 
  terminates 
  the 
  mesorostral 
  gutter, 
  consists 
  of 
  the 
  presphenoid 
  

   below 
  and 
  the 
  mesethmoid 
  above, 
  the 
  bones 
  being 
  so 
  intimately 
  fused 
  

   with 
  each 
  other 
  that 
  their 
  limits 
  can 
  not 
  be 
  defined 
  with 
  any 
  degree 
  

   of 
  accuracy. 
  Such 
  an 
  interpretation 
  of 
  the 
  mesorostral 
  plug 
  would 
  

   place 
  the 
  mesethmoid 
  below 
  the 
  cribiform 
  plate 
  in 
  most 
  porpoises 
  

   and 
  in 
  others 
  a 
  portion 
  would 
  actually 
  lie 
  behind 
  it. 
  The 
  flat 
  plate- 
  

   like 
  bone 
  which 
  sheathes 
  the 
  anterior 
  surface 
  of 
  the 
  internal 
  borders 
  

   of 
  the 
  frontals, 
  conceals 
  the 
  frontal 
  fontanelle, 
  and 
  extends 
  upward 
  

   to 
  meet 
  the 
  anterior 
  margins 
  of 
  the 
  nasals 
  from 
  below, 
  unquestionably 
  

   represents 
  the 
  combined 
  ectethmoids 
  in 
  the 
  living 
  porpoises 
  or 
  the 
  

   cribiform 
  plate 
  of 
  other 
  mammals. 
  The 
  telescoping 
  of 
  the 
  rostral 
  and 
  

   facial 
  portions 
  of 
  the 
  skull 
  was 
  accompanied 
  by 
  a 
  forward 
  thrust 
  of 
  

   the 
  presphenoid 
  and 
  a 
  backward 
  thrust 
  of 
  the 
  trough 
  of 
  the 
  vomer, 
  

   and 
  as 
  a 
  result 
  of 
  one 
  or 
  the 
  other, 
  or 
  possibly 
  both, 
  of 
  the 
  above 
  

   movements, 
  the 
  lower 
  portions 
  of 
  the 
  ectethmoids 
  were 
  separated 
  on 
  

   the 
  mid 
  line 
  and 
  overspread 
  the 
  presphenoid 
  laterally. 
  Other 
  bones 
  

   may 
  be 
  included 
  in 
  these 
  lateral 
  plates 
  and, 
  in 
  the 
  case 
  of 
  Ziphius 
  

   cavirostris 
  Kernan 
  G 
  refers 
  to 
  them 
  as 
  including 
  the 
  sphenoidal 
  

   turbinals. 
  

  

  A 
  skull 
  of 
  a 
  young 
  Grampus 
  griseus 
  (Cat. 
  No. 
  15, 
  773, 
  division 
  of 
  

   mammals, 
  U.S.N. 
  M.) 
  from 
  Cape 
  Cod, 
  Mass., 
  shows 
  how 
  the 
  

   Zarhachis 
  type 
  of 
  orifice 
  may 
  have 
  developed. 
  On 
  this 
  young 
  

  

  • 
  Kernan, 
  John 
  D., 
  The 
  skull 
  of 
  Ziphius 
  cavirostris. 
  Bull. 
  Amer. 
  Mus. 
  Nat. 
  Hist., 
  vol. 
  38, 
  art. 
  11, 
  p. 
  390. 
  

   August 
  1, 
  1918. 
  

  

  