﻿AND 
  AVES 
  OF 
  NORTH 
  AMERICA. 
  213 
  

  

  The 
  exoccipital 
  is 
  distinct, 
  and 
  bears 
  a 
  very 
  small 
  segment 
  of 
  the 
  occipital 
  condyle. 
  

  

  The 
  opisthotic 
  stands 
  obliquely 
  upwards 
  and 
  forwards, 
  and 
  furnishes 
  a 
  glenoid 
  cavity 
  

   for 
  the 
  articulation 
  of 
  the 
  quadratum. 
  It 
  has 
  a 
  process 
  directed 
  upwards 
  and 
  forwards, 
  

   which 
  occupies 
  a 
  concavity 
  on 
  the 
  inner 
  face 
  of 
  the 
  squamosal, 
  which 
  has 
  the 
  same 
  

   direction. 
  

  

  The 
  squamosal 
  is 
  flat 
  below, 
  and 
  proximally 
  presents 
  a 
  longitudinal 
  external 
  angle; 
  

   medially 
  it 
  is 
  more 
  cylindric, 
  and 
  receives 
  the 
  posterior 
  process 
  of 
  the 
  post-frontal. 
  

  

  The 
  basioccipital 
  presents 
  a 
  strong 
  transverse 
  condyle. 
  It 
  is 
  a 
  massive 
  bone, 
  and 
  pre- 
  

   sents 
  infero-laterally 
  two 
  powerful 
  processes 
  which 
  diverge 
  posteriorly, 
  and 
  present 
  broad, 
  

   rugose, 
  ovate 
  faces 
  of 
  insertion. 
  There 
  is 
  an 
  obtuse 
  keel 
  on 
  the 
  middle 
  line 
  below, 
  which 
  

   bifurcates 
  posteriorly 
  to 
  each 
  of 
  the 
  lateral 
  processes. 
  The 
  distal 
  portions 
  of 
  these 
  processes 
  

   are 
  overlapped 
  by 
  corresponding 
  cup-like 
  processes 
  of 
  the 
  basi-sphenoid. 
  

  

  The 
  basi-sphenoid 
  is 
  distinct 
  from 
  the 
  basioccipital, 
  and 
  underlaps 
  the 
  latter 
  almost 
  to 
  

   its 
  middle. 
  It 
  is 
  longer 
  than 
  broad, 
  and 
  sends 
  two 
  processes 
  latero-anteriorly 
  to 
  support 
  

   the 
  pterygoids. 
  These 
  are 
  not 
  so 
  long 
  as 
  in 
  most 
  Lacertilians. 
  Latero-superiorly 
  it 
  pre- 
  

   sents 
  a 
  broad 
  surface, 
  on 
  each 
  side 
  of 
  the 
  brain 
  case, 
  for 
  support 
  of 
  the 
  upper 
  side 
  walls. 
  

   Postero-externally, 
  the 
  prootic 
  rests. 
  It 
  thins 
  out 
  anteriorly, 
  and 
  has 
  overlapped 
  the 
  ali- 
  

   sphenoid. 
  The 
  suture 
  for 
  this 
  bone 
  widens 
  anteriorly 
  ; 
  inwardly 
  it 
  is 
  elevated 
  into 
  a 
  low 
  

   crest 
  of 
  the 
  sphenoid. 
  

  

  The 
  presphenoid 
  appears 
  to 
  have 
  been 
  distinct 
  ; 
  its 
  base 
  was 
  small; 
  it 
  is 
  lost. 
  

  

  The 
  floor 
  of 
  the 
  cranial 
  cavity 
  indicates 
  that 
  the 
  medulla 
  oblongata 
  possessed 
  the 
  

   downward 
  flexure 
  characteristic 
  of 
  Reptiles, 
  but 
  it 
  does 
  not 
  take 
  place 
  till 
  the 
  middle 
  

   of 
  the 
  length 
  of 
  the 
  basioccipital 
  is 
  reached. 
  The 
  posterior 
  margin 
  of 
  the 
  sphenoid 
  is 
  

   marked 
  by 
  a 
  deep 
  pit 
  ; 
  its 
  median 
  floor 
  is 
  a 
  transverse 
  elevation 
  ; 
  it 
  there 
  descends 
  again 
  

   and 
  terminates 
  in 
  a 
  deep 
  longitudinal 
  groove. 
  

  

  The 
  roof 
  of 
  the 
  brain-case 
  is 
  marked 
  on 
  the 
  parietal 
  bone 
  by 
  two 
  obtuse 
  divergent 
  

   ridges, 
  which 
  leave 
  its 
  posterior 
  margin, 
  and 
  embrace 
  the 
  fontanelle. 
  The 
  grooves 
  for 
  the 
  

   olfactory 
  pedicels 
  are 
  narrow 
  and 
  well 
  separated, 
  but 
  they 
  unite 
  and 
  are 
  entirely 
  enclosed 
  

   by 
  inferior 
  processes 
  of 
  the 
  frontal 
  bone, 
  as 
  in 
  serpents 
  and 
  Varani. 
  These 
  ridges 
  separ- 
  

   ate, 
  and 
  leave 
  the 
  bulbi 
  exposed 
  below. 
  Behind 
  and 
  between 
  the 
  nares 
  the 
  median 
  ridge 
  

   again 
  appears 
  separating 
  two 
  strong 
  grooves. 
  

  

  The 
  vomer 
  is 
  divided, 
  and 
  is 
  composed 
  of 
  two 
  slender 
  compressed 
  bones 
  in 
  contact 
  ; 
  

   they 
  are 
  broken 
  off 
  posteriorly. 
  

  

  The 
  o. 
  o. 
  palatina 
  terminate 
  anteriorly 
  opposite 
  the 
  posterior 
  margin 
  of 
  the 
  bony 
  nos- 
  

   trils; 
  they 
  are 
  widely 
  separated 
  on 
  the 
  middle 
  line, 
  and 
  closely 
  united 
  posteriorly 
  witli 
  

   the 
  pterygoids. 
  The 
  suture 
  connecting 
  the 
  two 
  runs 
  outwards 
  and 
  backwards. 
  

  

  AMfcfOOA. 
  PHILO. 
  SOC. 
  VOL 
  XIV. 
  54 
  

  

  