﻿424 
  L. 
  C. 
  MIAiL 
  ON 
  THE 
  KEMAINS 
  OF 
  LABYRINTHODONTA 
  

  

  the 
  middle 
  line 
  of 
  the 
  ramus 
  ; 
  when 
  perfect, 
  it 
  extended 
  upwards 
  of 
  

   an 
  inch 
  further 
  inwards. 
  Below 
  the 
  articular 
  cavity 
  the 
  sides 
  of 
  the 
  

   buttress 
  retreat 
  gradually, 
  so 
  that 
  it 
  is 
  broadest 
  above. 
  The 
  postar- 
  

   ticular 
  process 
  (Pt. 
  Art.) 
  is 
  very 
  Crocodilian 
  in 
  character, 
  and 
  agrees 
  

   with 
  no 
  Labyrinthodont 
  genus 
  except 
  Mastodonsaurus. 
  It 
  is 
  an 
  inch 
  

   and 
  three 
  quarters 
  long, 
  and 
  when 
  perfect 
  may 
  have 
  been 
  a 
  quarter 
  

   of 
  an 
  inch 
  longer. 
  On 
  the 
  outer 
  side 
  it 
  rises 
  to 
  a 
  sharp 
  and 
  irregular 
  

   edge, 
  which 
  falls 
  rapidly 
  backwards. 
  The 
  inner 
  surface 
  is 
  smooth 
  ; 
  

   it 
  is 
  concave 
  from 
  before 
  backwards, 
  variable, 
  but 
  on 
  the 
  whole 
  

   convex 
  from 
  above 
  downwards. 
  In 
  front 
  it 
  passes 
  gradually 
  into 
  

   the 
  under 
  surface 
  of 
  the 
  articular 
  buttress. 
  The 
  junction 
  of 
  the 
  

   articular 
  and 
  angular 
  elements 
  may 
  be 
  traced, 
  though 
  not 
  without 
  

   difficulty, 
  for 
  a 
  short 
  distance 
  upon 
  this 
  the 
  inner 
  surface 
  of 
  the 
  

   fossil. 
  A 
  fracture 
  enables 
  us 
  to 
  see 
  that 
  the 
  plane 
  of 
  the 
  suture 
  

   passed 
  nearly 
  vertically 
  through 
  the 
  internal 
  articular 
  buttress, 
  and 
  

   that 
  the 
  surface 
  of 
  junction 
  was 
  very 
  extensive. 
  In 
  this 
  part 
  of 
  the 
  

   ramus 
  the 
  articular 
  bone 
  is 
  securely 
  wedged 
  between 
  the 
  V-shaped 
  

   plates 
  of 
  the 
  angular. 
  The 
  whole 
  of 
  the 
  articular 
  cavity 
  and 
  the 
  

   superior 
  surface 
  of 
  the 
  postarticular 
  process 
  lie 
  above 
  the 
  suture, 
  and 
  

   were 
  therefore 
  furnished 
  by 
  the 
  articular 
  bone. 
  

  

  The 
  internal 
  cavity, 
  or 
  alveolar 
  canal, 
  of 
  the 
  mandible 
  was 
  of 
  large 
  

   size 
  ; 
  but 
  its 
  extent 
  cannot 
  be 
  accurately 
  determined, 
  owing 
  to 
  the 
  

   removal 
  by 
  fracture 
  of 
  its 
  inner 
  wall. 
  A 
  small 
  portion 
  of 
  this 
  inner 
  

   wall, 
  contributed 
  by 
  the 
  articular 
  bone, 
  remains 
  attached 
  to 
  the 
  

   upper 
  border 
  of 
  the 
  fossil 
  in 
  front, 
  forming 
  the 
  inner 
  boundary 
  of 
  

   the 
  previously 
  mentioned 
  groove 
  for 
  the 
  dentary 
  bone. 
  Here 
  it 
  

   seems 
  to 
  be 
  united 
  by 
  suture 
  to 
  the 
  outer 
  plate 
  of 
  the 
  articular 
  bone. 
  

   To 
  complete 
  this 
  part 
  of 
  the 
  ramus, 
  the 
  fragment 
  of 
  the 
  inner 
  wall 
  

   must 
  be 
  produced 
  downwards 
  and 
  backwards 
  into 
  a 
  vertical 
  plate, 
  

   the 
  upper 
  half 
  or 
  more 
  being 
  contributed 
  by 
  the 
  articular, 
  the 
  

   remainder 
  by 
  the 
  angular 
  bone. 
  The 
  restored 
  vertical 
  plate 
  would 
  

   converge 
  behind 
  towards 
  the 
  outer 
  wall 
  of 
  the 
  alveolar 
  canal, 
  leaving 
  

   a 
  long, 
  narrow 
  gap 
  along 
  the 
  upper 
  edge 
  of 
  the 
  ramus. 
  I 
  suppose 
  

   that 
  this 
  gap 
  was 
  occupied 
  by 
  a 
  slip 
  from 
  the 
  dentary 
  bone 
  ; 
  but 
  there 
  

   is 
  no 
  direct 
  evidence 
  that 
  such 
  was 
  the 
  case. 
  The 
  internal 
  wall 
  of 
  

   the 
  ramus 
  would 
  be 
  continued 
  to 
  join 
  a 
  broken 
  edge 
  now 
  visible 
  on 
  

   the 
  inner 
  and 
  upper 
  surface 
  of 
  the 
  angulari-articular 
  suture 
  beneath 
  

   the 
  articular 
  cavity. 
  Were 
  the 
  ramus 
  entire, 
  a 
  large 
  internal 
  man- 
  

   dibular 
  foramen 
  would 
  appear 
  in 
  the 
  inner 
  plate, 
  about 
  6 
  inches 
  from 
  

   the 
  posterior 
  extremity. 
  

  

  This 
  mandible 
  is 
  considerably 
  smaller 
  than 
  that 
  of 
  Mastodon- 
  

   saurus 
  giganteus. 
  Its 
  dimensions 
  agree, 
  so 
  far 
  as 
  can 
  be 
  seen, 
  with 
  

   those 
  of 
  the 
  four 
  fragments 
  of 
  M, 
  pacliygnaihus 
  already 
  described 
  in 
  

   this 
  paper. 
  

  

  Measurements 
  : 
  — 
  in. 
  

  

  Length 
  of 
  fragment 
  of 
  ramus 
  8f 
  

  

  Greatest 
  depth 
  2| 
  

  

  Length 
  of 
  coronoid 
  ridge 
  4 
  

  

  Length 
  of 
  articular 
  cavity 
  f 
  

  

  Length 
  of 
  postarticular 
  process 
  (broken) 
  If 
  

  

  J 
  

  

  