﻿SEMIONOTID^. 
  79 
  

  

  ascending 
  process 
  which 
  fits 
  into 
  a 
  groove 
  on 
  the 
  inferior 
  aspect 
  of 
  

   the 
  frontal 
  bones. 
  The 
  base 
  of 
  the 
  cranium 
  is 
  sheathed 
  by 
  a 
  great 
  

   parasphenoid 
  bone 
  and 
  by 
  the 
  coalesced 
  dentigerous 
  vomers. 
  The 
  

   parasphenoid 
  is 
  narrowest 
  at 
  the 
  origin 
  of 
  the 
  large 
  fan-shaped 
  

   basipterygoid 
  processes, 
  expanding 
  much 
  behind 
  and 
  exhibiting 
  a 
  

   deep 
  cleft 
  in 
  its 
  hinder 
  margin. 
  It 
  bears 
  no 
  teeth 
  and 
  is 
  pierced 
  

   mesially 
  by 
  a 
  foramen 
  for 
  the 
  passage 
  of 
  the 
  internal 
  carotids, 
  

   which 
  appears 
  single 
  on 
  the 
  lower 
  face, 
  but 
  double 
  on 
  emerging 
  

   above 
  ; 
  the 
  superior 
  or 
  attached 
  face 
  also 
  shows 
  the 
  deep 
  excavation 
  

   forming 
  the 
  floor 
  of 
  the 
  basicranial 
  canal. 
  The 
  vomer 
  is 
  a 
  stout 
  

   thickened 
  bone 
  with 
  crushing 
  teeth, 
  showing 
  cavities 
  in 
  which 
  the 
  

   germ-teeth 
  are 
  formed 
  ; 
  and 
  the 
  dentigerous 
  bones 
  of 
  the 
  palato- 
  

   pterygoid 
  arcade, 
  closely 
  connected 
  with 
  the 
  vomer 
  in 
  front, 
  exhibit 
  

   a 
  similar 
  thickening. 
  The 
  hyomandibular 
  is 
  an 
  elongated, 
  laterally 
  

   compressed 
  bone, 
  with 
  its 
  long 
  axis 
  slightly 
  bent 
  at 
  the 
  origin 
  

   of 
  the 
  process 
  of 
  support 
  for 
  the 
  operculum. 
  It 
  is 
  somewhat 
  

   strengthened 
  by 
  longitudinal 
  ridges 
  on 
  the 
  outer 
  face, 
  and 
  the 
  

   surface 
  for 
  attachment 
  with 
  the 
  cranium 
  is 
  much 
  extended. 
  The 
  

   bone 
  is 
  not 
  pierced 
  by 
  any 
  foramen. 
  The 
  symplectic 
  element 
  

   remains 
  unknown, 
  but 
  the 
  hinder 
  border 
  of 
  the 
  quadrate 
  exhibits 
  

   an 
  inner 
  surface 
  evidently 
  for 
  union 
  with 
  it. 
  The 
  quadrate 
  is 
  

   slender 
  for 
  a 
  fish 
  with 
  so 
  powerful 
  a 
  dentition, 
  and 
  in 
  the 
  fine 
  

   example 
  of 
  Lepidotus 
  latifrons 
  from 
  the 
  Oxford 
  Clay 
  (no. 
  P. 
  6841) 
  

   this 
  element 
  is 
  of 
  much 
  interest 
  as 
  exhibiting 
  a 
  very 
  different 
  degree 
  

   of 
  ossification 
  on 
  the 
  two 
  sides. 
  The 
  metapterygoid 
  bone 
  is 
  also 
  

   comparatively 
  delicate, 
  but 
  it 
  shows 
  a 
  broad 
  facette 
  on 
  its 
  upward 
  

   and 
  anteriorly 
  directed 
  process, 
  which 
  may 
  have 
  articulated 
  with 
  

   some 
  lateral 
  element 
  of 
  the 
  cranium. 
  The 
  hinder 
  portion 
  of 
  

   Meckel's 
  cartilage 
  is 
  ossified 
  as 
  a 
  robust 
  articular 
  bone, 
  and 
  to 
  its 
  

   outer 
  face 
  there 
  is 
  apposed 
  a 
  large 
  plate, 
  probably 
  to 
  be 
  interpreted 
  

   as 
  angular. 
  The 
  coronoid 
  region 
  of 
  the 
  mandible 
  is 
  very 
  deep, 
  and 
  

   the 
  summit 
  of 
  the 
  elevation 
  is 
  completed 
  by 
  a 
  very 
  small 
  coronoid 
  

   bone, 
  shown 
  in 
  a 
  Wealden 
  specimen 
  of 
  L. 
  manleUi 
  (no. 
  P. 
  6342). 
  

   The 
  dentary 
  bone, 
  very 
  deep 
  in 
  the 
  coronoid 
  region, 
  becomes 
  much 
  

   narrower 
  in 
  its 
  tooth-bearing 
  portion 
  ; 
  and 
  its 
  anterior 
  half 
  curves 
  

   rapidly 
  inwards 
  to 
  meet 
  its 
  fellow 
  of 
  the 
  opposite 
  side 
  in 
  a 
  somewhat 
  

   deepened 
  symphysis. 
  To 
  the 
  inner 
  side 
  of 
  the 
  dentary 
  bone 
  the 
  

   robust 
  splenial 
  is 
  articulated 
  by 
  a 
  roughened 
  face, 
  and 
  it 
  also 
  enters 
  

   the 
  mandibular 
  symphysis 
  ; 
  whereas 
  the 
  dentary 
  exhibits 
  only 
  one 
  

   regular 
  series 
  of 
  teeth, 
  this 
  element 
  has 
  several 
  irregular 
  series 
  of 
  

   a 
  more 
  tritoral 
  character. 
  The 
  ceratohyal 
  exhibits 
  its 
  ordinary 
  

   hour-glass-shaped 
  form, 
  and 
  is 
  deepest 
  behind. 
  The 
  hypohyals 
  are 
  

   a 
  pair 
  of 
  very 
  small 
  triangular 
  bones 
  ; 
  and 
  no 
  evidence 
  of 
  an 
  ossified 
  

   glossohyal 
  has 
  hitherto 
  been 
  observed. 
  

  

  