﻿AND 
  AYES 
  OF 
  NORTH 
  AMERICA. 
  179 
  

  

  the 
  other 
  Reptilian 
  types. 
  An 
  important 
  section 
  of 
  the 
  order 
  possesses 
  the 
  zygosphen 
  

   articulation. 
  This 
  is 
  universal 
  in 
  the 
  Ophidia, 
  and 
  exists 
  in 
  one 
  family 
  of 
  the 
  Lacertilia, 
  

   the 
  Iguanidae. 
  In 
  the 
  former 
  order 
  it 
  is 
  placed 
  at 
  a 
  considerable 
  elevation 
  above 
  the 
  

   zygapophyses, 
  while 
  in 
  the 
  latter 
  family 
  it 
  is 
  nearly 
  in 
  the 
  plane 
  of 
  the 
  zygapophyses, 
  thus 
  

   occupying 
  a 
  lower 
  position. 
  The 
  structure 
  in 
  the 
  Pythonomorpha 
  is 
  of 
  the 
  latter 
  charac- 
  

   ter. 
  In 
  species 
  intermediate 
  between 
  this 
  form 
  and 
  the 
  more 
  simple 
  one 
  in 
  the 
  orders, 
  

   the 
  zygosphen 
  is 
  found 
  in 
  a 
  rudimental 
  condition. 
  

  

  The 
  diapophyses 
  present 
  the 
  vertical 
  costal 
  articular 
  face 
  of 
  Ophidians 
  and 
  Lacer- 
  

   tilians. 
  The 
  immensely 
  long 
  tail, 
  used 
  as 
  a 
  powerful 
  swimming 
  organ, 
  is 
  in 
  truly 
  serpen- 
  

   tine 
  proportion, 
  while 
  its 
  chevron 
  bones 
  are 
  a 
  lacertian 
  rather 
  than 
  ophidian 
  character. 
  

  

  The 
  prootic 
  extends 
  from 
  the 
  basioccipital 
  to 
  the 
  parietal, 
  and 
  overlaps 
  the 
  latter 
  by 
  

   its 
  superior 
  anterior 
  margin. 
  This 
  does 
  not 
  occur 
  among 
  Lacertilia 
  except 
  in 
  aberrant 
  

   forms, 
  but 
  is 
  common 
  to 
  all 
  serpents. 
  There 
  is 
  a 
  strong 
  superior 
  and 
  anterior 
  ala 
  on 
  the 
  

   sphenoid, 
  which 
  furnishes 
  part 
  of 
  the 
  suture. 
  

  

  The 
  ribs 
  are 
  cylindrical 
  throughout 
  much 
  of 
  their 
  length, 
  and 
  resemble 
  those 
  of 
  the 
  

   Boas 
  in 
  their 
  articulation 
  by 
  a 
  compressed 
  vertical 
  head 
  to 
  a 
  vertically 
  compressed 
  diapo- 
  

   physis. 
  There 
  is 
  no 
  attached 
  parapophysis 
  as 
  in 
  the 
  serpents. 
  

  

  With 
  respect 
  to 
  the 
  characters 
  in 
  which 
  this 
  order 
  is 
  identical 
  with 
  the 
  Lacertilia, 
  the 
  

   following 
  observations 
  may 
  be 
  made. 
  

  

  The 
  brain 
  case 
  appears 
  to 
  be 
  unossified 
  anteriorly, 
  as 
  in 
  Tortoises, 
  Crocodiles, 
  and 
  La- 
  

   certilians; 
  and 
  the 
  parietal, 
  both 
  descends 
  as 
  in 
  Testudinata, 
  and 
  the 
  ali-spenoid*ascends, 
  

   as 
  in 
  Crocodilia. 
  

  

  The 
  extensive 
  union 
  of 
  the 
  o. 
  o. 
  palatina 
  and 
  maxillaria 
  is 
  a 
  character 
  of 
  Laeertians 
  and 
  

   other 
  Saurian 
  orders, 
  and 
  the 
  existence 
  of 
  separated 
  hypapophyses 
  is 
  a 
  feature 
  seen 
  in 
  a 
  

   few 
  existing 
  Lacertilians. 
  These 
  separate 
  elements 
  are 
  articulated 
  to 
  heavy 
  cylindric 
  

   fixed 
  hypapophyses, 
  which 
  are 
  characteristic 
  of 
  the 
  cervical 
  vertebrae 
  of 
  this 
  whole 
  group 
  

   with 
  the 
  exception 
  of 
  one 
  genus. 
  Though 
  the 
  separation 
  of 
  the 
  extremital 
  pieces 
  is 
  La- 
  

   certilian, 
  they 
  are 
  in 
  the 
  latter 
  sessile, 
  and 
  the 
  great 
  length 
  of 
  the 
  whole 
  hypapophysis 
  

   paralleled 
  by 
  those 
  of 
  the 
  serpents. 
  

  

  The 
  scapula 
  and 
  coracoid 
  are 
  not 
  very 
  different 
  from 
  those 
  of 
  Laeertians, 
  and 
  are 
  not 
  

   coalescent. 
  The 
  scapula 
  appears 
  to 
  have 
  had 
  an 
  angle 
  or 
  process 
  similar 
  to 
  the 
  procora- 
  

   coid, 
  while 
  the 
  coracoid 
  is 
  entirely 
  without 
  the 
  emarginations 
  common 
  to 
  Lacertilia. 
  No 
  

   trace 
  of 
  claviculus, 
  mesosternum 
  or 
  xiphisternum 
  has 
  been 
  found. 
  On 
  the 
  whole, 
  the 
  sca- 
  

   pular 
  arch 
  is 
  quite 
  as 
  similar 
  to 
  that 
  of 
  the 
  Sauropterygia 
  as 
  that 
  of 
  the 
  Lacertilia. 
  

  

  The 
  os 
  quadrature, 
  is 
  like 
  that 
  of 
  the 
  Lacertilia 
  in 
  its 
  form, 
  and 
  in 
  its 
  support 
  by 
  two 
  

   suspensoria. 
  It 
  is 
  as 
  mobile, 
  but 
  much 
  shorter 
  than, 
  in 
  the 
  serpents, 
  and 
  differs 
  from 
  that 
  

   of 
  both 
  these 
  orders 
  in 
  nearlv 
  enclosing 
  the 
  meatus 
  auditorius 
  behind 
  by 
  a 
  large 
  decurved 
  

  

  