﻿OF 
  THE 
  PLESI0SAUKIAN 
  PECTORAL 
  ARCH. 
  439 
  

  

  bute 
  the 
  better 
  ossification 
  of 
  the 
  pectoral 
  girdle 
  in 
  Plesiosaurs, 
  as 
  

   contrasted 
  with 
  Chelonians, 
  to 
  the 
  larger 
  amount 
  of 
  organic 
  energy 
  

   brought 
  to 
  bear 
  upon 
  the 
  bones 
  in 
  consequence 
  of 
  their 
  external 
  

   position, 
  and 
  the 
  absence 
  of 
  an 
  epipleural 
  skeleton. 
  The 
  structural 
  

   differences 
  of 
  the 
  limbs 
  from 
  those 
  of 
  Chelonians, 
  in 
  view 
  of 
  their 
  

   capacity 
  for 
  work, 
  are 
  only 
  a 
  matter 
  of 
  detail. 
  

  

  The 
  other 
  important 
  constituent 
  element 
  of 
  the 
  articular 
  surface' 
  

   for 
  the 
  humerus 
  is 
  the 
  scapula. 
  In 
  Chelonians 
  this 
  bone 
  is 
  a 
  slender 
  

   rod 
  directed 
  upward 
  to 
  the 
  side 
  of 
  the 
  vertebral 
  column, 
  being 
  thus 
  

   unlike 
  that 
  of 
  a 
  Plesiosaur 
  in 
  disposition 
  even 
  more 
  than 
  in 
  form 
  — 
  

   since 
  in 
  Plesiosaurs 
  the 
  bones 
  are 
  invariably 
  directed 
  forward 
  in 
  

   approximately 
  the 
  same 
  plane 
  with 
  the 
  coracoids, 
  converging 
  ante- 
  

   riorly. 
  This 
  consideration 
  led 
  Cuvier 
  to 
  doubt 
  the 
  determination 
  

   which 
  named 
  them 
  scapula?. 
  Put 
  considering 
  the 
  enormous 
  number 
  

   of 
  vertebrae 
  in 
  the 
  cervical 
  region 
  of 
  Plesiosaurs, 
  as 
  compared 
  with 
  

   Chelonians, 
  I 
  would 
  suggest 
  that 
  potential 
  growth, 
  carrying 
  the 
  

   vertebrae 
  further 
  and 
  further 
  forward, 
  would 
  probably 
  take 
  the 
  free 
  

   ends 
  of 
  the 
  scapulae 
  onward 
  too, 
  till 
  those 
  bones 
  came 
  to 
  occupy 
  

   their 
  singular 
  position 
  anterior 
  to 
  the 
  coracoids. 
  This 
  supposition 
  

   perhaps 
  receives 
  some 
  support 
  from 
  scapula 
  and 
  coracoid 
  being 
  

   approximately 
  in 
  the 
  same 
  plane 
  (though 
  a 
  different 
  one) 
  in 
  Lizards, 
  

   and 
  by 
  the 
  slightly 
  anterior 
  direction 
  that 
  the 
  scapula 
  occasionally 
  

   takes. 
  

  

  These 
  two 
  bones 
  are 
  the 
  essential 
  parts 
  of 
  the 
  Plesiosaurian 
  pec- 
  

   toral 
  arch 
  ; 
  and 
  if 
  clavicles 
  or 
  interclavicle 
  exist, 
  their 
  presence 
  is 
  

   exceptional, 
  and 
  only 
  a 
  generic 
  difference. 
  

  

  In 
  1865 
  I 
  figured 
  and 
  described, 
  under 
  the 
  name 
  of 
  Plesiosaurus 
  

   cliduchus, 
  an 
  animal 
  in 
  which 
  the 
  scapula 
  appeared 
  to 
  carry, 
  on 
  its 
  

   outer 
  and 
  anterior 
  margin, 
  a 
  bone 
  holding 
  the 
  same 
  position 
  as 
  the 
  

   clavicle 
  in 
  Ichthyosaurus. 
  A 
  clavicle 
  being 
  needed 
  to 
  complete 
  the 
  

   resemblance 
  between 
  the 
  two 
  types, 
  I 
  at 
  the 
  time 
  identified 
  the 
  

   process 
  as 
  the 
  clavicular 
  bone. 
  Owing 
  to 
  conditions 
  of 
  fossilization, 
  

   I 
  believe 
  the 
  Woodwardian 
  specimen 
  was 
  delusive, 
  and 
  that 
  what 
  

   appeared 
  to 
  be 
  a 
  separate 
  clavicle 
  was 
  only 
  a 
  thin 
  process 
  of 
  the 
  

   scapula, 
  broken 
  and 
  partly 
  displaced 
  so 
  as 
  to 
  show 
  a 
  sharp 
  line 
  of 
  

   division 
  from 
  the 
  thicker 
  part 
  of 
  the 
  scapula, 
  against 
  which 
  it 
  abuts 
  

   nearly 
  at 
  right 
  angles. 
  Prof. 
  Owen 
  in 
  1839 
  (Brit. 
  Assoc. 
  Ileport, 
  

   L840, 
  p. 
  56), 
  and 
  later, 
  in 
  the 
  'Anatomy 
  of 
  the 
  Vertebrates' 
  (1866, 
  

   vol. 
  i. 
  p. 
  171), 
  stated 
  that 
  the 
  Plesiosaurian 
  "scapula 
  develops 
  an 
  

   acromial 
  process 
  representing 
  the 
  clavicle;" 
  but 
  I 
  do 
  not 
  think 
  

   Prof. 
  Owen 
  and 
  I 
  intended 
  the 
  same 
  interpretation; 
  for 
  in 
  the 
  

   same 
  author's 
  ' 
  Palaeontology 
  ' 
  (1861, 
  2nd 
  edit., 
  p. 
  247) 
  a 
  figure 
  is 
  

   given 
  of 
  the 
  scapula, 
  which 
  does 
  not 
  seem 
  to 
  be 
  in 
  accord 
  with 
  

   any 
  figure 
  or 
  published 
  description 
  of 
  the 
  genus. 
  This 
  figure 
  is 
  

   reproduced 
  in 
  the 
  ' 
  Anatomy 
  of 
  the 
  Vertebrates 
  ' 
  (vol. 
  ii. 
  p. 
  52). 
  

   I 
  have 
  seen 
  no 
  skeleton 
  of 
  Plesiosaurus 
  which 
  will 
  justify 
  such 
  a 
  

   scapula 
  as 
  Prof. 
  Owen 
  figures 
  (fig. 
  4, 
  p. 
  440); 
  and 
  probably 
  the 
  

   broad 
  portion 
  of 
  the 
  bone, 
  which 
  is 
  represented 
  as 
  extending 
  dor- 
  

   sally 
  and 
  backward 
  over 
  the 
  ribs, 
  bearing 
  upon 
  it 
  the 
  number 
  51, 
  

   should 
  have 
  been 
  directed 
  anteriorly 
  along 
  the 
  interclavicle 
  ; 
  so 
  that 
  

  

  