﻿AND 
  AVES 
  OF 
  NORTH 
  AMERICA. 
  109 
  

  

  External 
  Form 
  and 
  Posture 
  of 
  Laelaps. 
  — 
  The 
  short 
  fore 
  limbs 
  of 
  this 
  genus 
  suggest 
  

   at 
  once 
  the 
  habit 
  of 
  using 
  the 
  hind 
  limbs 
  chiefly, 
  yet 
  this 
  disproportion 
  is 
  no 
  sufficient 
  

   reason 
  therefor, 
  and 
  is 
  seen 
  to 
  exist 
  in 
  the 
  tailless 
  Batrachia, 
  where 
  no 
  such 
  position 
  is 
  

   assumed. 
  It 
  exists 
  to 
  a 
  less 
  degree 
  among 
  the 
  modern 
  lizards, 
  whose 
  position 
  we 
  well 
  

   know 
  to 
  be 
  always 
  horizontal. 
  

  

  Laelaps 
  had, 
  however, 
  no 
  doubt 
  an 
  erect 
  position 
  for 
  the 
  following 
  reason 
  : 
  The 
  head 
  

   and 
  neck 
  of 
  the 
  femur 
  are 
  at 
  right 
  angles 
  to 
  the 
  direction 
  of 
  motion 
  on 
  the 
  condyles, 
  or 
  in 
  

   the 
  same 
  plane 
  as 
  the 
  transverse 
  direction 
  of 
  the 
  condyles. 
  This 
  indicates 
  that 
  the 
  femur 
  

   has 
  been 
  flexed, 
  and 
  extended 
  in 
  a 
  plane 
  parallel 
  with 
  that 
  of 
  the 
  vertebral 
  column. 
  The 
  

   relations 
  of 
  articulation 
  are 
  those 
  of 
  birds 
  and 
  different 
  from 
  those 
  of 
  reptiles, 
  where 
  the 
  

   directions 
  of 
  the 
  proximal 
  and 
  distal 
  condyles 
  of 
  the 
  femur 
  are 
  oblique 
  to 
  each 
  other, 
  and 
  

   the 
  proximal, 
  of 
  vertically 
  elongate 
  form, 
  thus 
  allowing 
  the 
  femur 
  to 
  be 
  obliquely 
  directed 
  

   as 
  regards 
  the 
  axis 
  of 
  the 
  body, 
  so 
  that 
  in 
  a 
  prone 
  position 
  it 
  rested 
  on 
  the 
  ground 
  

   equally 
  clear 
  of 
  the 
  body 
  and 
  the 
  flexed 
  tibia. 
  

  

  The 
  resemblance 
  of 
  the 
  tibia 
  with 
  its 
  high 
  crest 
  and 
  embracing 
  astragalus, 
  as 
  well 
  as 
  

   the 
  slender 
  fibula, 
  to 
  those 
  of 
  the 
  birds, 
  confirms 
  this 
  position 
  ; 
  so 
  do 
  types 
  of 
  the 
  iliac 
  

   and 
  sacral 
  structures. 
  The 
  same 
  is 
  suggested 
  by 
  the 
  great 
  bird-like 
  reptile 
  tracks 
  found 
  

   in 
  many 
  places. 
  

  

  How 
  must 
  a 
  reptilian 
  form 
  with 
  elongate 
  vertebral 
  column 
  and 
  heavy 
  tooth-bearing 
  

   cranium 
  have 
  stood 
  erect 
  % 
  The 
  elongate 
  form 
  of 
  the 
  femur, 
  as 
  compared 
  with 
  the 
  tibia, 
  

   is 
  only 
  seen 
  in 
  man, 
  who 
  walks 
  erect 
  ; 
  in 
  the 
  birds 
  and 
  kangaroos 
  the 
  femur 
  is 
  very 
  much 
  

   shorter 
  than 
  the 
  tibia 
  ; 
  besides 
  these, 
  no 
  other 
  vertebrates 
  walk 
  on 
  the 
  hind 
  limbs, 
  

   entirely 
  or 
  in 
  part. 
  The 
  lizards, 
  which 
  are 
  prone, 
  present 
  the 
  long 
  femur 
  exceeding 
  or 
  

   equalling 
  the 
  tibia. 
  

  

  The 
  bird-like 
  reptile 
  did 
  not, 
  however, 
  exhibit 
  the 
  slight 
  flexure 
  between 
  femur 
  and 
  

   tibia 
  presented 
  by 
  man. 
  The 
  acetabulum 
  in 
  the 
  known 
  Dinosauria 
  is 
  not 
  or 
  but 
  weakly 
  

   completed 
  below, 
  or 
  what 
  would 
  be 
  in 
  man 
  anteriorly, 
  indicating 
  that 
  the 
  weight 
  of 
  the 
  

   body 
  was 
  supported 
  by 
  a 
  femur 
  placed 
  at 
  a 
  strong 
  angle 
  with 
  the 
  longitudinal 
  axis 
  of 
  the 
  

   ilium 
  ; 
  otherwise 
  the 
  head 
  of 
  the 
  femur 
  would 
  be 
  most 
  readily 
  displaced. 
  If, 
  therefore, 
  

   the 
  ilium 
  were 
  more 
  or 
  less 
  erect, 
  the 
  femur 
  Avas 
  directed 
  forwards 
  ; 
  if 
  horizontal, 
  the 
  

   femur 
  must 
  have 
  projected 
  downwards. 
  I 
  have 
  shown, 
  however, 
  that 
  the 
  position 
  and 
  

   therefore 
  the 
  ilium 
  was 
  oblique 
  or 
  erect 
  ; 
  therefore 
  the 
  femur 
  was 
  directed 
  very 
  much 
  

   forwards.* 
  

  

  * 
  The 
  remarks 
  of 
  Prof. 
  Owen 
  on 
  this 
  relation 
  in 
  Megalosaurns 
  are 
  so 
  pertinent, 
  that 
  they 
  are 
  introduced 
  here 
  : 
  

   " 
  The 
  backward 
  position 
  and 
  production 
  of 
  the 
  corresponding 
  articular 
  prominences 
  or 
  condyles 
  in 
  both 
  femur 
  

   arid 
  tibia 
  indicate 
  that 
  these 
  bones 
  were 
  joined 
  together 
  at 
  an 
  angle, 
  probably 
  a 
  right 
  one 
  when 
  in 
  their 
  intermediate 
  

   state, 
  between 
  flexion 
  and 
  extension 
  ; 
  and 
  that 
  the 
  motion 
  of 
  the 
  tibia 
  could 
  not 
  have 
  taken 
  place 
  to 
  the 
  extent 
  

   required 
  to 
  bring 
  the 
  two 
  bones 
  to 
  the 
  same 
  line." 
  

   AMERI. 
  PHILOSO. 
  SOC. 
  — 
  VOL. 
  XIV. 
  28 
  

  

  