﻿78 
  ACTINOPTEKYGII. 
  

  

  The 
  chondrocranium 
  in 
  Lepidotus 
  is 
  well 
  ossified, 
  and 
  the 
  basi 
  

   cranial 
  axis 
  is 
  straight. 
  The 
  basioccipital 
  exhibits 
  on 
  its 
  posterior 
  

   face 
  a 
  very 
  deep 
  conical 
  fossa 
  for 
  the 
  notochord 
  ; 
  and 
  the 
  inferior 
  

   aspect 
  of 
  the 
  bone 
  is 
  marked 
  by 
  a 
  broad 
  longitudinal 
  groove, 
  with 
  a 
  

   flattened 
  rim 
  on 
  each 
  margin, 
  probably 
  indicating 
  the 
  backward 
  

   extension 
  of 
  the 
  basicranial 
  canal 
  (for 
  the 
  recti 
  muscles 
  of 
  the 
  eye) 
  

   as 
  far 
  as 
  the 
  occiput. 
  In 
  one 
  example 
  of 
  L. 
  latifrons 
  (no. 
  P. 
  6841) 
  

   there 
  is 
  also 
  some 
  appearance 
  of 
  one 
  vertebral 
  ring 
  being 
  fused 
  

   with 
  the 
  basioccipital 
  on 
  its 
  hinder 
  face. 
  The 
  exoccipital 
  forms 
  a 
  

   considerable 
  part 
  of 
  the 
  lateral 
  wall 
  of 
  the 
  brain-case, 
  and 
  is 
  per- 
  

   forated 
  as 
  usual 
  by 
  a 
  large 
  transversely-oval 
  foramen 
  for 
  the 
  exit 
  

   of 
  the 
  vagus 
  nerve. 
  The 
  pro-otic 
  has 
  a 
  still 
  larger 
  extent 
  than 
  the 
  

   exoccipital, 
  and 
  exhibits 
  a 
  deep 
  oblique 
  notch 
  at 
  its 
  anterior 
  margin 
  

   for 
  the 
  passage 
  of 
  the 
  fifth 
  nerve. 
  The 
  characters 
  of 
  the 
  inter- 
  

   orbital 
  septum, 
  pterotic 
  and 
  opisthotic 
  bones 
  are 
  still 
  unknown 
  : 
  

   and 
  of 
  the 
  ethmoids 
  it 
  can 
  only 
  be 
  said 
  that 
  they 
  surround 
  a 
  pair 
  

   of 
  long 
  closed 
  canals 
  for 
  the 
  passage 
  of 
  the 
  olfactory 
  nerves. 
  The 
  

   membrane 
  bones 
  of 
  the 
  cranial 
  roof 
  form 
  a 
  continuous 
  shield, 
  but 
  

   do 
  not 
  extend 
  backwards 
  quite 
  so 
  far 
  as 
  the 
  occipital 
  border. 
  

   There 
  are 
  two 
  principal 
  pairs 
  of 
  bones, 
  the 
  short 
  parietals 
  behind 
  

   and 
  the 
  longer 
  frontals 
  forwards, 
  not 
  bilaterally 
  symmetrical, 
  but 
  

   uniting 
  in 
  all 
  directions 
  by 
  irregularly 
  angulated 
  sutures, 
  which 
  

   vary 
  in 
  different 
  species. 
  More 
  anteriorly 
  there 
  would 
  be 
  nasals, 
  

   but 
  these 
  are 
  not 
  satisfactorily 
  known. 
  The 
  long 
  and 
  narrow 
  

   squamosal 
  element 
  on 
  each 
  side 
  reaches 
  as 
  far 
  forwards 
  as 
  the 
  

   anterior 
  extremity 
  of 
  the 
  parietals, 
  but 
  not 
  so 
  far 
  backwards 
  as 
  the 
  

   hinder 
  margin 
  of 
  these 
  bones. 
  It 
  is 
  considerably 
  overlapped 
  by 
  

   the 
  supratemporal 
  series 
  of 
  plates, 
  and 
  on 
  the 
  inner 
  aspect 
  there 
  is 
  

   an 
  undetermined 
  amount 
  of 
  connection 
  with 
  some 
  of 
  the 
  ossified 
  

   otic 
  elements. 
  Its 
  surface 
  for 
  articulation 
  with 
  the 
  upper 
  end 
  of 
  

   the 
  hyomandibular 
  is 
  clear, 
  and 
  a 
  triangular 
  walled 
  area 
  at 
  the 
  

   hinder 
  end 
  of 
  its 
  inner 
  surface 
  denotes 
  the 
  boundaries 
  of 
  the 
  small 
  

   temporal 
  fossa. 
  Postfrontal 
  and 
  prefrontal 
  membrane 
  bones 
  are 
  

   not 
  differentiated 
  from 
  the 
  circumorbital 
  ring, 
  and 
  the 
  cheek-plates 
  

   are 
  irregularly 
  subdivided, 
  being 
  often 
  different 
  even 
  on 
  the 
  two 
  

   sides 
  of 
  the 
  same 
  head. 
  The 
  general 
  plan 
  of 
  the 
  cheek-plates, 
  

   however, 
  is 
  distinct, 
  there 
  being 
  a 
  complete 
  circumorbital 
  ring, 
  a 
  

   semicircle 
  of 
  suborbitals, 
  and 
  a 
  short 
  deep 
  series 
  of 
  preorbitals 
  

   flanking 
  the 
  ethmoid 
  region. 
  The 
  maxilla 
  is 
  a 
  very 
  delicate 
  bone, 
  

   deepest 
  behind, 
  tapering 
  forwards, 
  and 
  terminating 
  in 
  front 
  in 
  an 
  

   inwardly-directed 
  process 
  for 
  articulation 
  with 
  the 
  palatine; 
  its 
  

   oral 
  margin 
  is 
  provided 
  with 
  a 
  series 
  of 
  styliform 
  teeth. 
  The 
  

   premaxilla 
  is 
  a 
  smaller, 
  stouter 
  bone, 
  also 
  with 
  a 
  single 
  series 
  of 
  

   styliform 
  teeth, 
  and 
  bearing 
  at 
  its 
  inner 
  extremity 
  a 
  very 
  large 
  

  

  