﻿H. 
  G. 
  SEELEY 
  ON 
  NETTSTICOSAURTTS 
  PUSILLTJS. 
  

  

  863 
  

  

  is 
  everywhere 
  developed 
  by 
  intermittent 
  pressure 
  and 
  tension, 
  it 
  

   seems 
  to 
  me 
  that 
  the 
  difference 
  between 
  these 
  two 
  is 
  precisely 
  such 
  

   as 
  might 
  be 
  expected 
  to 
  result 
  from 
  conditions 
  of 
  existence 
  such 
  as 
  

   would 
  result 
  from 
  increased 
  leverage 
  of 
  the 
  body 
  being 
  thrown 
  

   upon 
  the 
  anterior 
  distal 
  end 
  of 
  the 
  humerus, 
  in 
  consequence 
  of 
  the 
  

   bone 
  being 
  used 
  as 
  a 
  chief 
  organ 
  in 
  progression, 
  in 
  an 
  animal 
  which 
  

   was 
  adapting 
  itself 
  to 
  aquatic 
  conditions. 
  Further, 
  on 
  the 
  pos- 
  

   terior 
  margin 
  of 
  the 
  humerus 
  of 
  Nothosaurus, 
  in 
  the 
  upper 
  third, 
  is 
  

   a 
  process 
  like 
  a 
  trochanter, 
  which 
  is 
  often 
  seen 
  in 
  certain 
  species 
  of 
  

   Plesiosaurus, 
  in 
  the 
  same 
  position 
  though 
  less 
  developed 
  ; 
  and 
  this 
  

   process 
  I 
  regard 
  as 
  a 
  representative 
  of 
  the 
  radial 
  crest, 
  less 
  developed 
  

   than 
  in 
  the 
  Crocodile, 
  and 
  rotated 
  further 
  backward. 
  "We 
  shall 
  seek 
  

   in 
  vain 
  among 
  existing 
  reptiles 
  for 
  any 
  near 
  analogue 
  of 
  the 
  Notho- 
  

   saurian 
  humerus; 
  and 
  if 
  the 
  character 
  were 
  isolated 
  in 
  the 
  skeleton, 
  

   it 
  would 
  be 
  impossible 
  to 
  say 
  whether 
  the 
  slight 
  crocodilian 
  character 
  

   were 
  an 
  analogy 
  or 
  an 
  affinity. 
  

  

  In 
  Crocodiles 
  and 
  Chelonians, 
  even 
  more 
  than 
  in 
  Lizards, 
  the 
  

   humerus 
  is 
  more 
  elongated 
  than 
  the 
  forearm 
  ; 
  but 
  in 
  Neusticosaurus 
  

   the 
  forearm 
  is 
  relatively 
  shorter 
  even 
  than 
  in 
  the 
  Crocodiles 
  ; 
  for 
  

   while 
  in 
  the 
  Alligator 
  these 
  regions 
  are 
  in 
  the 
  proportion 
  of 
  about 
  

   7 
  to 
  5, 
  in 
  the 
  fossil 
  the 
  proportion 
  is 
  10 
  to 
  6. 
  But 
  while 
  the 
  

   segment 
  of 
  the 
  limb 
  is 
  shortened, 
  the 
  bones 
  have 
  the 
  aspect 
  of 
  those 
  

   of 
  a 
  land 
  animal 
  : 
  the 
  radius 
  is 
  broad 
  at 
  the 
  proximal 
  end, 
  like 
  the 
  

   radius 
  of 
  Plesiosaurus 
  ; 
  and 
  the 
  ulna 
  is 
  broad 
  and 
  curved 
  a 
  little, 
  so 
  

   as 
  to 
  foreshadow 
  the 
  way 
  these 
  bones 
  in 
  Plesiosaurus 
  became 
  short- 
  

   ened 
  as 
  they 
  ceased 
  to 
  support 
  the 
  weight 
  of 
  the 
  body, 
  and 
  at 
  the 
  

   same 
  time 
  increased 
  in 
  width 
  with 
  the 
  increased 
  tension 
  under 
  new 
  

   conditions 
  of 
  use. 
  

  

  The 
  proportions 
  of 
  the 
  bones 
  of 
  the 
  hand 
  and 
  their 
  number 
  show 
  

   no 
  striking 
  departure 
  from 
  the 
  terrestrial 
  type, 
  except 
  in 
  the 
  form 
  

   of 
  the 
  terminal 
  phalanges, 
  which, 
  as 
  being 
  conical, 
  seem 
  to 
  preclude 
  

   the 
  idea 
  of 
  functional 
  terminal 
  claws, 
  and 
  approximate 
  towards 
  the 
  

   condition 
  seen 
  in 
  Plesiosaurus, 
  though 
  the 
  phalanges 
  were 
  few, 
  and 
  

   did 
  not 
  give 
  the 
  limb 
  a 
  Plesiosaurian 
  elongation. 
  (See 
  Fig. 
  2.) 
  

  

  Unfortunately, 
  the 
  limb-bones 
  of 
  Nothosaurus 
  have 
  not 
  yet 
  been 
  

   found 
  in 
  natural 
  association. 
  

  

  The 
  Hind 
  Limb. 
  

  

  The 
  hind 
  limb 
  is 
  no 
  longer 
  than 
  the 
  fore 
  limb, 
  but 
  of 
  an 
  alto- 
  

   gether 
  different 
  character 
  ; 
  for 
  while 
  the 
  latter 
  suggests 
  a 
  swimming 
  

   type, 
  the 
  former 
  is 
  the 
  hind 
  limb 
  of 
  a 
  land 
  animal. 
  

  

  In 
  the 
  type 
  specimen, 
  only 
  the 
  middle 
  of 
  the 
  shaft 
  of 
  the 
  femur 
  

   is 
  preserved 
  ; 
  but 
  the 
  impressions 
  of 
  its 
  extremities 
  in 
  the 
  matrix 
  

   show 
  it 
  to 
  have 
  been 
  21 
  mm. 
  long 
  (PI. 
  XIII. 
  fig. 
  1). 
  In 
  the 
  smaller 
  

   specimen 
  the 
  length 
  is 
  a 
  little 
  less 
  than 
  20 
  mm., 
  and 
  the 
  bone 
  appears 
  

   to 
  be 
  of 
  slightly 
  different 
  form 
  ; 
  for 
  in 
  the 
  larger 
  example 
  the 
  impression 
  

   of 
  the 
  distal 
  end 
  indicates 
  an 
  appreciable 
  widening 
  of 
  the 
  bone, 
  of 
  

   which 
  there 
  is 
  no 
  trace 
  in 
  the 
  small 
  specimen, 
  which 
  has 
  the 
  distal 
  

   end 
  more 
  slender 
  than 
  the 
  difference 
  in 
  length 
  would 
  have 
  suggested. 
  

   But 
  this 
  difference 
  may 
  result 
  from 
  the 
  bone 
  being 
  exposed 
  laterally 
  

   in 
  the 
  case 
  of 
  the 
  small 
  animal, 
  since 
  in 
  section 
  the 
  shaft 
  of 
  the 
  

  

  