﻿JAN. 
  4, 
  1922 
  KENDALL 
  AND 
  CRAWFORD: 
  ARGENTINA 
  SILUS 
  13 
  

  

  to 
  the 
  sphenotic 
  bones 
  on 
  each 
  side 
  and 
  a 
  narrower 
  ridge 
  extends 
  

   upward 
  on 
  the 
  inner 
  side 
  of 
  the 
  alisphenoid. 
  There 
  is 
  a 
  cartilage 
  

   extending 
  downward 
  between 
  parts 
  of 
  the 
  opisthotic^- 
  and 
  epiotic 
  

   bones. 
  

  

  The 
  parietals 
  extend 
  laterally 
  and 
  cover 
  the 
  large 
  pit 
  on 
  either 
  side 
  

   which 
  is 
  bounded 
  by 
  the 
  opisthotics, 
  pterotics, 
  and 
  epiotics. 
  This 
  

   pit 
  is 
  filled 
  ordinarily 
  by 
  the 
  foreward 
  extension 
  of 
  the 
  large 
  lateral 
  

   muscles 
  of 
  the 
  body. 
  In 
  Salmo, 
  this 
  pit 
  is 
  bounded 
  by 
  the 
  same 
  bones 
  

   as 
  in 
  Argentina, 
  but 
  it 
  is 
  not 
  covered 
  over 
  by 
  the 
  parietals. 
  In 
  Os- 
  

   merus, 
  the 
  pit 
  is 
  bounded 
  by 
  the 
  pterotic 
  and 
  epiotic, 
  the 
  parietals 
  

   not 
  covering 
  it. 
  Neither 
  do 
  the 
  parietals 
  in 
  Osmerus 
  meet 
  in 
  front 
  

   of 
  the 
  supraoccipital. 
  

  

  The 
  preoperculum 
  falls 
  almost 
  perpendicularly 
  from 
  its 
  fascet. 
  

   Its 
  two 
  limbs 
  form 
  nearly 
  a 
  right 
  angle, 
  the 
  lower 
  limb 
  which 
  extends 
  

   forw^ard 
  being 
  as 
  long 
  as 
  the 
  upper, 
  and 
  both 
  are 
  connected 
  at 
  the 
  

   angle 
  by 
  a 
  heavy 
  flange 
  which 
  is 
  roughly 
  quadrate 
  in 
  outline. 
  The 
  

   metapterygoids 
  are 
  much 
  reduced. 
  The 
  large 
  mesopterygoids 
  extend 
  

   downward 
  between 
  the 
  metapterygoids 
  and 
  quadrate 
  bones. 
  

  

  The 
  symplectic 
  extends 
  from 
  the 
  hyomandibular 
  diagonall}^ 
  down- 
  

   ward 
  to 
  the 
  top 
  of 
  the 
  lower 
  limb 
  of 
  the 
  preopercle 
  and 
  thence 
  for- 
  

   ward. 
  A 
  part 
  of 
  the 
  quadrate 
  bone 
  extends 
  backward 
  on 
  top 
  of 
  

   the 
  lower 
  limb 
  of 
  the 
  preopercle 
  and 
  overlaps 
  the 
  forward 
  extension 
  

   of 
  the 
  symplectic. 
  The 
  whole 
  apparatus 
  has 
  the 
  appearance 
  of 
  being 
  

   drawn 
  dow^nward 
  and 
  forward. 
  There 
  are 
  no 
  teeth 
  on 
  the 
  mesop- 
  

   terygoids,^^ 
  maxillaries, 
  or 
  premaxillaries, 
  but 
  there 
  are 
  small, 
  sharp 
  

   teeth 
  in 
  single 
  rows 
  on 
  the 
  anterior 
  margin 
  of 
  the 
  vomer 
  and 
  palatines, 
  

   and 
  a 
  few 
  on 
  the 
  tongue. 
  The 
  preorbital 
  and 
  three 
  suborbital 
  bones 
  

   extend 
  from 
  the 
  premaxillary 
  backward 
  across 
  the 
  cheek. 
  There 
  is 
  

   no 
  supplementary 
  maxillary. 
  The 
  premaxillaries 
  are 
  securely 
  fastened 
  

   to 
  the 
  vomer 
  by 
  connective 
  tissue 
  which 
  makes 
  these 
  bones 
  immov- 
  

   able. 
  

  

  The 
  upper 
  margin 
  of 
  the 
  bones 
  of 
  the 
  lower 
  jaw 
  is 
  strongly 
  arched, 
  

   the 
  apex 
  of 
  the 
  arch 
  being 
  at 
  the 
  overlapping 
  of 
  the 
  dentary 
  and 
  artic- 
  

   ular 
  bones. 
  The 
  anterior 
  margin 
  of 
  the 
  dentary 
  is 
  concave 
  and 
  tooth- 
  

   less, 
  but 
  it 
  is 
  hard 
  and 
  chisel-edged. 
  Between 
  the 
  dentary 
  and 
  artic- 
  

   ular 
  bones 
  is 
  a 
  splenial 
  bone, 
  which 
  lies 
  on 
  top 
  of 
  the 
  Meckel's 
  car- 
  

  

  ^2 
  Regan 
  did 
  not 
  recognize 
  the 
  existence 
  of 
  the 
  opisthotic 
  bone 
  in 
  the 
  skull 
  of 
  Argentina. 
  

   It 
  may 
  be 
  seen 
  to 
  best 
  advantage 
  after 
  the 
  f 
  rentals 
  and 
  parietals 
  are 
  removed. 
  

   ^^ 
  There 
  are 
  teeth 
  on 
  the 
  mesopterygoids 
  of 
  Osmerus. 
  

  

  