﻿418 
  L. 
  C. 
  MIALL 
  ON 
  THE 
  REMAINS 
  OF 
  LAB 
  VEIN 
  THODONTA 
  

  

  have 
  been 
  spared 
  by 
  the 
  Honorary 
  Curators 
  of 
  the 
  Geological 
  Col- 
  

   lection 
  at 
  Warwick 
  to 
  render 
  every 
  feature 
  apparent. 
  

  

  1. 
  Mastodonsaurtjs 
  pachygnathus, 
  Owen 
  — 
  interorbital 
  tract. 
  Coton 
  

   End, 
  1867. 
  PI. 
  XXVI. 
  fig. 
  1 
  A. 
  

  

  This 
  fragment 
  comprises 
  the 
  frontal, 
  with 
  parts 
  of 
  the 
  prefrontal, 
  

   postfrontal, 
  and 
  parietal 
  ossifications 
  of 
  each 
  side. 
  The 
  anterior 
  

   margin 
  of 
  the 
  right 
  orbit 
  and 
  the 
  internal 
  margins 
  of 
  both 
  orbits 
  are 
  

   shown. 
  The 
  surface 
  displays 
  the 
  characteristic 
  sculpture 
  of 
  Masto- 
  

   clonsaurus, 
  besides 
  the 
  posterior 
  or 
  interorbital 
  portion 
  of 
  the 
  sym- 
  

   metrical 
  mucous 
  canals 
  (m.g.) 
  which 
  form 
  the 
  lyra. 
  A 
  narrow, 
  sharp- 
  

   cut 
  furrow, 
  occasionally 
  interrupted, 
  occupies 
  the 
  middle 
  line. 
  The 
  

   parietal 
  foramen 
  is 
  visible 
  on 
  the 
  broken 
  posterior 
  end 
  (p.f.) 
  ; 
  the 
  

   section, 
  accidentally 
  made 
  by 
  fracture, 
  shows 
  that 
  the 
  foramen 
  is 
  

   much 
  more 
  contracted 
  on 
  the 
  subcutaneous 
  surface 
  than 
  below. 
  

  

  The 
  sutures 
  are 
  nearly 
  obliterated 
  ; 
  but 
  enough 
  of 
  them 
  may 
  be 
  

   distinguished 
  to 
  prove 
  that 
  the 
  frontal 
  bounds 
  a 
  considerable 
  part 
  

   of 
  the 
  inner 
  orbital 
  margin. 
  Such 
  an 
  arrangement 
  is 
  uncommon 
  in 
  

   the 
  Labyrinthodonta 
  ; 
  it 
  occurs, 
  however, 
  in 
  Mastoclonsaurus 
  and 
  

   Capitosaurus. 
  It 
  will 
  be 
  seen 
  in 
  a 
  subsequent 
  part 
  of 
  this 
  paper 
  

   that 
  something 
  turns 
  upon 
  the 
  character 
  of 
  the 
  prefrontal. 
  This 
  is 
  

   clearly 
  seen 
  to 
  have 
  a 
  sharply 
  concave 
  orbital 
  border, 
  bevelled 
  to 
  an 
  

   edge 
  on 
  both 
  sides. 
  The 
  lower 
  surface 
  is 
  quite 
  smooth, 
  and 
  exhibits 
  

   no 
  foramen 
  or 
  other 
  marked 
  feature. 
  The 
  greatest 
  thickness 
  does 
  

   not 
  exceed 
  | 
  inch. 
  

  

  The 
  inferior 
  surface 
  of 
  the 
  coronal 
  bones 
  is 
  rarely 
  seen 
  ; 
  indeed 
  

   I 
  am 
  not 
  aware 
  that 
  it 
  has 
  been 
  exposed 
  in 
  any 
  of 
  the 
  German 
  ex- 
  

   amples 
  of 
  Mastoclonsaurus. 
  It 
  is 
  therefore 
  interesting 
  to 
  find 
  the 
  

   underside 
  of 
  the 
  present 
  fossil 
  clear 
  of 
  matrix, 
  and 
  detached 
  from 
  

   the 
  bones 
  of 
  the 
  palatal 
  tract. 
  The 
  inferior 
  surface 
  is 
  nearly 
  even, 
  

   and 
  quite 
  smooth 
  over 
  the 
  greater 
  part 
  of 
  its 
  extent. 
  It 
  has 
  already 
  

   been 
  stated 
  that 
  part 
  of 
  the 
  orbital 
  margin 
  is 
  bevelled 
  on 
  the 
  lower 
  

   as 
  on 
  the 
  upper 
  surface. 
  The 
  angulation 
  is 
  most 
  apparent 
  upon 
  the 
  

   prefrontal 
  bone, 
  and 
  disappears 
  on 
  the 
  underside 
  of 
  the 
  postfrontal. 
  

   A 
  pair 
  of 
  longitudinal 
  ridges, 
  £ 
  inch 
  apart, 
  and 
  \ 
  inch 
  high, 
  is 
  seen 
  

   upon 
  the 
  underside 
  of 
  the 
  parietals. 
  They 
  subside 
  and 
  diverge 
  for- 
  

   wards, 
  not 
  reaching 
  a 
  line 
  drawn 
  to 
  join 
  the 
  centres 
  of 
  the 
  orbits. 
  

   These 
  ridges 
  are 
  longitudinally 
  striated, 
  especially 
  in 
  their 
  posterior 
  ex- 
  

   tent. 
  Similar 
  ridges 
  exist 
  in 
  other 
  Labyrinthodonts, 
  such 
  as 
  the 
  Car- 
  

   boniferous 
  Loxomma. 
  They 
  have 
  probably 
  served 
  for 
  the 
  attachment 
  

   of 
  vertically 
  placed 
  cartilages, 
  which 
  may 
  represent 
  orbito-sphenoids. 
  

  

  This 
  fragment 
  does 
  not 
  perfectly 
  agree 
  with 
  Mastoclonsaurus 
  

   giganteus, 
  Jager 
  *. 
  There 
  is 
  a 
  row 
  of 
  pits 
  between 
  the 
  internal 
  

   orbital 
  margin 
  and 
  the 
  frontal 
  mucous 
  canal. 
  The 
  interorbital 
  

   space 
  is 
  much 
  narrower 
  than 
  in 
  the 
  large 
  skull 
  of 
  M. 
  giganteus 
  from 
  

   Gaildorf. 
  Difference 
  of 
  size 
  proves 
  nothing 
  in 
  the 
  case 
  of 
  a 
  single 
  

   example 
  ; 
  but 
  if 
  I 
  have 
  restored 
  the 
  orbit 
  correctly, 
  its 
  length 
  in 
  

   proportion 
  to 
  the 
  width 
  of 
  the 
  interorbital 
  space 
  is 
  considerably 
  less 
  

   in 
  the 
  Warwick 
  Mastoclonsaurus 
  than 
  in 
  M. 
  giganteus. 
  In 
  other 
  

   * 
  = 
  M. 
  Jcegeri, 
  Alberti. 
  

  

  