﻿110 
  THE 
  EXTINCT 
  BATRACHIA, 
  EEPTILIA 
  

  

  There 
  are, 
  however, 
  other 
  reasons 
  for 
  believing 
  that 
  the 
  femur 
  was 
  directed 
  forwards, 
  

   and 
  somewhat 
  upwards 
  from 
  the 
  ilium. 
  One 
  is, 
  that 
  the 
  centre 
  of 
  gravity 
  of 
  an 
  elongate 
  

   reptilian 
  dorsal 
  and 
  sternal 
  region 
  must 
  have 
  been 
  further 
  forwards 
  than 
  in 
  the 
  short- 
  

   bodied 
  bird, 
  and 
  therefore 
  the 
  knee 
  must 
  have 
  been 
  further 
  forward, 
  in 
  order 
  to 
  bring 
  the 
  

   support, 
  i. 
  e., 
  the 
  tibia, 
  etc., 
  beneath 
  it. 
  Another 
  is, 
  that 
  the 
  articulation 
  of 
  the 
  tarso- 
  

   metatarsal 
  bones 
  with 
  the 
  tibia 
  is 
  excessively 
  oblique, 
  requiring 
  that 
  one 
  or 
  both 
  sections 
  

   of 
  the 
  limb 
  should 
  be 
  very 
  oblique 
  to 
  the 
  vertical 
  line. 
  As 
  the 
  tarso-metatarsal 
  elements 
  

   support 
  the 
  weight 
  immediately 
  on 
  the 
  ground, 
  and 
  as 
  it 
  is 
  obvious 
  that 
  the 
  leverage 
  

   moving 
  the 
  great 
  weight 
  of 
  the 
  body 
  on 
  its 
  support 
  must 
  have 
  been 
  the 
  gastrocnemius 
  

   and 
  soleus 
  muscles 
  extending 
  the 
  tibia 
  on 
  the 
  metatarsal 
  segment 
  as 
  the 
  fixed 
  point 
  ; 
  and 
  

   as 
  there 
  is 
  no 
  indication 
  of 
  correspondingly 
  powerful 
  muscles 
  to 
  flex 
  the 
  metatarsals 
  on 
  

   the 
  phalanges 
  ; 
  it 
  is 
  obvious 
  that 
  the 
  latter 
  has 
  been 
  the 
  more 
  vertical, 
  and 
  the 
  former 
  the 
  

   more 
  oblique 
  segment. 
  And 
  if 
  the 
  tibial 
  segment 
  has 
  been 
  oblique, 
  for 
  reasons 
  just 
  

   given, 
  the 
  femur 
  must 
  have 
  been 
  oblique 
  also.* 
  

  

  The 
  length 
  of 
  the 
  femur 
  has 
  had 
  relation 
  to 
  another 
  peculiarity 
  as 
  well, 
  as 
  follows 
  : 
  

  

  In 
  an 
  animal 
  designed 
  to 
  walk 
  erect, 
  it 
  is 
  necessary 
  that 
  the 
  centre 
  of 
  gravity 
  should 
  

   be 
  transferred 
  as 
  far 
  posteriorly 
  as 
  is 
  consistent 
  with 
  the 
  type. 
  In 
  Laelaps 
  and 
  other 
  Di- 
  

   nosauria 
  we 
  have 
  very 
  elongate 
  pubic 
  and 
  iliac 
  bones, 
  and 
  as 
  I 
  have 
  before 
  described, 
  these 
  

   appear 
  to 
  have 
  been 
  designed 
  to 
  enclose 
  and 
  support 
  an 
  abdominal 
  mass, 
  in 
  a 
  position 
  

   beneath 
  the 
  sacrum, 
  and 
  posterior 
  to 
  the 
  position 
  observed 
  in 
  quadrupedal 
  mammals 
  and 
  

   reptiles. 
  We 
  would 
  thus 
  have 
  a 
  prominent 
  keeled 
  belly 
  between 
  the 
  femora, 
  supported 
  

   by 
  elongate 
  curved 
  ischia 
  behind, 
  and 
  slender 
  pubes 
  directed 
  downwards 
  in 
  front. 
  In 
  

   Poecilopleurum 
  the 
  space 
  between 
  the 
  latter 
  and 
  the 
  sternum 
  was 
  occupied 
  by 
  abdominal 
  

   ribs. 
  The 
  length 
  of 
  femur 
  places 
  the 
  arc 
  through 
  which 
  the 
  knee 
  moves 
  beyond 
  this 
  pro- 
  

   jection. 
  

  

  The 
  confluence 
  of 
  a 
  greater 
  number 
  of 
  vertebra? 
  to 
  form 
  a 
  sacrum 
  seen 
  in 
  this 
  order 
  

   and 
  in 
  the 
  birds, 
  would 
  seem 
  to 
  have 
  a 
  direct 
  relation 
  to 
  the 
  support 
  of 
  the 
  above 
  men- 
  

   tioned 
  greater 
  Aveight 
  by 
  it, 
  than 
  in 
  horizontal 
  vertebrata, 
  where 
  the 
  weight 
  is 
  distributed 
  

   throughout 
  the 
  length 
  of 
  the 
  vertebral 
  column. 
  

  

  The 
  shifting 
  of 
  the 
  neural 
  arches 
  backwards, 
  seen 
  in 
  the 
  same 
  orders, 
  pointed 
  out 
  by 
  

   Owen, 
  would 
  have 
  a 
  mechanical 
  relation 
  to 
  the 
  same 
  necessity; 
  i. 
  e., 
  their 
  partial 
  transfer 
  

   over 
  the 
  intervertebral 
  spaces 
  naturally 
  tending 
  to 
  strengthen 
  the 
  union 
  of 
  the 
  sacral 
  ele- 
  

   ments. 
  

  

  The 
  foot 
  need 
  not 
  however 
  have 
  been 
  placed 
  precisely 
  beneath 
  the 
  centre 
  of 
  gravity 
  of 
  

  

  * 
  Probably 
  in 
  a 
  squatting 
  posture 
  the 
  animal 
  rested 
  on 
  the 
  entire 
  sole 
  as 
  far 
  as 
  the 
  heel, 
  though 
  not 
  under 
  

   ordinary 
  circumstances 
  ; 
  as 
  I 
  have 
  suggested 
  in 
  Amer. 
  Naturalist, 
  I., 
  28, 
  Mycteria 
  and 
  other 
  wading 
  birds 
  assume 
  a 
  

   similar 
  position 
  at 
  times. 
  

  

  