﻿AND 
  AYES 
  OF 
  NORTH 
  AMERICA. 
  89 
  

  

  posterior 
  to 
  its 
  position 
  in 
  ordinary 
  reptilia, 
  This, 
  taken 
  in 
  connection 
  with 
  the 
  anterior 
  

   position 
  of 
  the 
  support 
  of 
  the 
  body 
  — 
  the 
  femur, 
  rendered 
  the 
  erect 
  progress 
  of 
  the 
  Dino- 
  

   sauria 
  possible. 
  

  

  Another 
  approximation 
  to 
  the 
  birds 
  will 
  probably 
  be 
  found 
  in 
  the 
  sternum 
  and 
  

   coracoids. 
  These 
  elements 
  are 
  but 
  little 
  known, 
  and 
  that 
  imperfectly 
  ; 
  the 
  best 
  example 
  

   has 
  been 
  furnished 
  by 
  the 
  great 
  Teratosaurus 
  suevicus 
  Mey. 
  Here, 
  according 
  to 
  Plionin- 
  

   ger, 
  the 
  elements 
  corresponding 
  to 
  the 
  xiphisternum 
  of 
  Lacertilia 
  is 
  a 
  large 
  thin 
  shield- 
  

   like 
  bone, 
  of 
  elongate 
  form. 
  The 
  coracoids 
  are 
  narrow, 
  prismatic 
  bones, 
  and 
  abut 
  against 
  

   the 
  anterior 
  angles 
  of 
  the 
  xiphisternum 
  ; 
  being 
  entirely 
  different 
  from 
  the 
  broad 
  flat 
  

   element 
  of 
  the 
  Lacertilia 
  and 
  other 
  orders, 
  which 
  are 
  usually 
  extensively 
  in 
  contact 
  with 
  

   each 
  other 
  or 
  with 
  the 
  xiphisternum. 
  

  

  \Ye 
  have, 
  however, 
  among 
  Dinosauria, 
  as 
  among 
  Quadrumanous 
  Mammalia, 
  a 
  series 
  of 
  

   forms, 
  from 
  those 
  constantly 
  assuming 
  the 
  prone 
  Lacertian 
  position, 
  to 
  those 
  that 
  walked 
  

   exclusively 
  erect 
  like 
  birds. 
  Perhaps 
  the 
  most 
  Lacertilian 
  form 
  known 
  is 
  the 
  genus 
  

   Sceliclosaurus 
  of 
  Owen 
  : 
  the 
  greater 
  equality 
  in 
  length 
  of 
  the 
  limbs, 
  and 
  the 
  numerous 
  

   toes, 
  as 
  well 
  as 
  lacertilian 
  dentition 
  assign 
  it 
  to 
  this 
  place. 
  Then 
  we 
  find 
  forms 
  like 
  

   Iguanodon 
  and 
  Hadrosaurus, 
  the 
  most 
  gigantic 
  of 
  land 
  animals, 
  where 
  a 
  semi-erect 
  atti- 
  

   tude 
  was 
  the 
  natural 
  one, 
  as 
  they 
  like 
  the 
  Megatherium 
  and 
  Megalonyx, 
  lived 
  on 
  vegeta- 
  

   ble 
  food, 
  and 
  were 
  necessitated 
  to 
  raise 
  themselves 
  on 
  their 
  hinder 
  limbs 
  to 
  reach 
  it. 
  Here 
  

   the 
  bird-like 
  type 
  is 
  approached, 
  in 
  the 
  reduction 
  of 
  the 
  metatarsi 
  to 
  three, 
  and 
  the 
  great 
  

   antero-posterior 
  extent 
  of 
  the 
  ilium. 
  In 
  the 
  genus 
  Laelaps 
  the 
  position 
  was 
  probably 
  

   quite 
  erect, 
  and 
  additional 
  resemblances 
  to 
  the 
  ornithic 
  type 
  are 
  adapted 
  to 
  large 
  animals 
  

   no 
  longer 
  requiring 
  a 
  vegetable 
  diet, 
  but 
  procuring 
  their 
  living 
  food 
  by 
  activity 
  and 
  

   strength. 
  They 
  are 
  accordingly 
  organized 
  so 
  as 
  to 
  be 
  entirely 
  independent 
  of 
  extraneous 
  

   support, 
  and 
  furnished 
  with 
  great 
  powers 
  either 
  of 
  running 
  or 
  leaping. 
  

  

  Intermediate 
  between 
  this 
  extreme, 
  and 
  the 
  type 
  of 
  Ignanodon, 
  comes 
  a 
  large 
  carniv- 
  

   orous 
  genus, 
  the 
  Megalosaurus 
  of 
  Buckland, 
  the 
  representative 
  of 
  types 
  like 
  Laelaps, 
  in 
  

   the 
  old 
  world. 
  In 
  its 
  longer 
  fore 
  limbs 
  it 
  differs 
  Jfrom 
  the 
  most 
  bird-like 
  forms. 
  A 
  car- 
  

   nivorous 
  type 
  only 
  known 
  from 
  teeth, 
  is 
  Aublysodon 
  Leidy 
  ; 
  it 
  is 
  American. 
  

  

  The 
  other 
  herbivorous 
  species, 
  of 
  less 
  size 
  than 
  Iguanodon, 
  which 
  was 
  furnished 
  with 
  a 
  

   dorsal 
  series 
  of 
  dermal 
  bones, 
  is 
  the 
  Hylaeosaurus 
  armatus 
  Mantell, 
  found 
  in 
  the 
  Wealden 
  

   of 
  England 
  ; 
  while 
  an 
  allied 
  form 
  which 
  was 
  covered 
  with 
  long 
  massive 
  dermal 
  spines, 
  

   has 
  recently 
  been 
  discovered 
  in 
  the 
  same 
  formation 
  in 
  the 
  Isle 
  of 
  Wight, 
  and 
  referred 
  to 
  

   the 
  genus 
  Polyacanthus 
  Owen. 
  

  

  The 
  sizes 
  of 
  the 
  best 
  known 
  species 
  of 
  these 
  genera 
  are 
  as 
  follows 
  : 
  

  

  AMERI. 
  PHILOSO. 
  SOC. 
  — 
  VOL. 
  XIV. 
  23 
  

  

  