﻿130 
  ACTINOPTERYGIl. 
  

  

  prefrontal 
  and 
  ethmoid, 
  there 
  being 
  no 
  elongation 
  of 
  this 
  foramen 
  

   into 
  a 
  canal 
  ; 
  and 
  Dajpedius 
  thus 
  differs 
  from 
  Amia 
  while 
  agreeing 
  

   with 
  Lepidosteus 
  in 
  the 
  course 
  of 
  the 
  olfactory 
  nerves 
  across 
  the 
  

   orbital 
  cavity. 
  The 
  membrane-bones 
  of 
  the 
  cranial 
  roof 
  form 
  a 
  

   continuous 
  shield, 
  without 
  vacuities 
  ; 
  but 
  a 
  narrow 
  rim 
  of 
  the 
  

   cranium 
  projects 
  behind 
  the 
  covering 
  thus 
  formed. 
  In 
  young 
  

   individuals 
  the 
  paired 
  parietals, 
  frontals, 
  and 
  squamosals 
  are 
  dis- 
  

   tinct, 
  and 
  this 
  condition 
  sometimes 
  persists 
  in 
  the 
  adult 
  ; 
  but 
  more 
  

   usually 
  these 
  principal 
  roof-bones 
  soon 
  become 
  fused 
  into 
  a 
  con- 
  

   tinuous 
  plate. 
  Immediately 
  in 
  advance 
  a 
  pair 
  of 
  short 
  and 
  broad 
  

   nasals 
  meets 
  in 
  the 
  middle 
  line 
  ; 
  and 
  there 
  is 
  a 
  small 
  median 
  plate 
  

   enveloping 
  the 
  ethmoid 
  in 
  front. 
  The 
  premaxillae 
  are 
  separate, 
  

   small 
  and 
  short, 
  apparently 
  without 
  any 
  ascending 
  process 
  ; 
  the 
  

   maxilla 
  is 
  a 
  long 
  stout 
  bone, 
  with 
  a 
  slight 
  spatulate 
  expansion 
  

   posteriorly, 
  and 
  bounded 
  above 
  in 
  its 
  hinder 
  two-thirds 
  by 
  a 
  small, 
  

   narrow 
  supramaxilla. 
  A 
  complete 
  ring 
  of 
  circum 
  orbital 
  plates 
  

   surrounds 
  the 
  eye 
  ; 
  and 
  there 
  is 
  also 
  an 
  incomplete 
  suborbital 
  series, 
  

   reaching 
  from 
  the 
  squamosal 
  to 
  the 
  hinder 
  end 
  of 
  the 
  maxilla, 
  while 
  

   one 
  isolated 
  plate 
  occurs 
  immediately 
  below 
  the 
  nasal 
  opening, 
  above 
  

   the 
  suture 
  between 
  the 
  maxilla 
  and 
  premaxilla. 
  The 
  parasphenoid 
  

   is 
  imperfectly 
  known, 
  but 
  does 
  not 
  appear 
  to 
  have 
  been 
  dentigerous 
  ; 
  

   the 
  vomer, 
  which 
  is 
  probably 
  single, 
  is 
  furnished 
  with 
  a 
  dense 
  

   cluster 
  of 
  comparatively 
  large 
  teeth. 
  The 
  hyomandibular 
  is 
  elon- 
  

   gated 
  and 
  much 
  laterally 
  compressed, 
  with 
  a 
  considerable 
  expansion 
  

   above, 
  but 
  contracted 
  in 
  its 
  lower 
  half 
  into 
  a 
  narrow 
  bar 
  with 
  nearly 
  

   parallel 
  anterior 
  and 
  posterior 
  edges. 
  The 
  symplectic 
  and 
  quadrate 
  

   are 
  unknown, 
  and 
  the 
  palato-pterygoid 
  arcade 
  can 
  only 
  be 
  described 
  

   as 
  delicate, 
  with 
  large 
  teeth 
  on 
  its 
  inferior 
  margin, 
  smaller 
  tuber- 
  

   cular 
  teeth 
  on 
  its 
  inner 
  face. 
  The 
  mandible 
  is 
  remarkably 
  short 
  

   and 
  deep, 
  with 
  a 
  coronoid 
  elevation, 
  comprising 
  distinct 
  dentary, 
  

   splenial, 
  articular, 
  and 
  probably 
  coronoid 
  elements. 
  The 
  dentary 
  

   bears 
  only 
  the 
  marginal 
  series 
  of 
  teeth, 
  and 
  its 
  postero-superior 
  

   portion 
  is 
  smooth 
  and 
  toothless 
  where 
  overlapped 
  by 
  the 
  maxilla 
  ; 
  

   the 
  splenial 
  is 
  less 
  deep, 
  but 
  more 
  robust 
  anteriorly, 
  entering 
  the 
  

   mandibular 
  symphysis 
  and 
  bearing 
  a 
  cluster 
  of 
  teeth, 
  which 
  become 
  

   minute 
  granules 
  behind 
  as 
  the 
  bone 
  rises 
  into 
  the 
  coronoid. 
  The 
  

   angular 
  bone 
  is 
  deep, 
  fixed 
  to 
  the 
  outer 
  face 
  of 
  the 
  articular, 
  and 
  

   uniting 
  with 
  the 
  dentary 
  in 
  a 
  conspicuously 
  zig-zag 
  suture. 
  Not- 
  

   withstanding 
  the 
  prominence 
  of 
  the 
  superficial 
  ornament, 
  the 
  course 
  

   of 
  the 
  sensory 
  canals 
  can 
  scarcely 
  be 
  traced 
  ; 
  but 
  a 
  groove 
  for 
  the 
  

   transverse 
  commissure 
  on 
  the 
  parietals 
  and 
  squamosals 
  is 
  seen, 
  and 
  

   & 
  nearly 
  vertical 
  groove 
  occurs 
  on 
  the 
  angular 
  bone. 
  

  

  The 
  opercular 
  apparatus 
  is 
  complete, 
  but 
  the 
  preoperculum 
  is 
  

  

  