﻿Ornithosaurian 
  Genus 
  Oruithoclielrus. 
  549 
  

  

  Distal 
  end. 
  

  

  1. 
  Dorsal 
  aud 
  ventral 
  surface 
  slightly 
  convex. 
  

  

  2. 
  Articular 
  surface 
  a 
  convex 
  roll, 
  compressed 
  more 
  or 
  less 
  

  

  dorso-ventralljj 
  in 
  the 
  median 
  area. 
  

  

  3. 
  Preaxial 
  border 
  flat. 
  

  

  In 
  regard 
  to 
  the 
  proximal 
  extremities 
  affixed 
  to 
  tablet 
  

   J. 
  a. 
  13 
  *j 
  specimens 
  5 
  and 
  6 
  belong 
  to 
  the 
  same 
  species 
  as 
  

   far 
  as 
  can 
  be 
  ascertained. 
  No. 
  6 
  is 
  not 
  well 
  preserved. 
  An 
  

   unnum.bered 
  specimen 
  is 
  near 
  to 
  5 
  and 
  6, 
  with 
  the 
  articular 
  

   features 
  less 
  prominent. 
  The 
  main 
  difference 
  between 
  these 
  

   bones 
  and 
  those 
  of 
  Oi'nithodesmus 
  latidens 
  lies 
  in 
  the 
  latter 
  

   being 
  flatter 
  and 
  rapidly 
  lessening 
  in 
  size 
  down 
  the 
  shaft. 
  

   The 
  former 
  are 
  stouter 
  and 
  reveal 
  little 
  or 
  no 
  decrease 
  

   distally. 
  Between 
  the 
  two 
  surfaces 
  of 
  the 
  articular 
  end 
  of 
  

   (Jrnithodesmus 
  latidens 
  there 
  is 
  a 
  transverse 
  ridge 
  across 
  the 
  

   short 
  diameter 
  of 
  the 
  bone, 
  which 
  fits 
  into 
  the 
  valley 
  between 
  

   the 
  two 
  condyles 
  of 
  the 
  trochlea 
  of 
  the 
  humerus. 
  Tliis 
  is 
  

   not 
  seen 
  in 
  the 
  Cambridge 
  specimens 
  ; 
  therefore 
  they 
  

   probably 
  do 
  not 
  belong 
  to 
  distal 
  ends 
  of 
  the 
  humeri 
  

   J. 
  a. 
  6, 
  21 
  and 
  S2, 
  Group 
  A, 
  where 
  a 
  feeble 
  incipient 
  trochlea 
  

   is 
  to 
  be 
  observed, 
  but 
  to 
  Group 
  B. 
  

  

  Of 
  the 
  four 
  specimens 
  of 
  the 
  distal 
  ends 
  of 
  the 
  radius, 
  

   J. 
  a. 
  12, 
  1-4, 
  not 
  one 
  belongs 
  to 
  the 
  same 
  genus 
  as 
  Ornitho- 
  

   desnius 
  latidens, 
  for, 
  although 
  there 
  is 
  a 
  general 
  similarity 
  

   in 
  form^ 
  they 
  difl'er 
  in 
  details. 
  The 
  dorsal 
  and 
  ventral 
  

   surfaces 
  of 
  Ornithodesmus 
  latidens 
  are 
  flatter 
  and 
  more 
  com- 
  

   pressed 
  than 
  any 
  of 
  the 
  Cambridge 
  specimens. 
  The 
  ventral 
  

   surfaces 
  of 
  nos. 
  1 
  and 
  3 
  are 
  more 
  concave. 
  In 
  all 
  four 
  

   specimens, 
  including 
  0. 
  latidens, 
  the 
  articular 
  surface 
  is 
  a 
  

   complete 
  convexity 
  from 
  the 
  pre- 
  to 
  the 
  postaxial 
  border^ 
  

   and 
  all 
  exhibit 
  more 
  or 
  less 
  constriction 
  of 
  this 
  convexity 
  

   on 
  both 
  dorsal 
  and 
  ventral 
  borders 
  in 
  the 
  median 
  region. 
  

   Nos. 
  1 
  and 
  3 
  belong 
  to 
  the 
  same 
  species. 
  The 
  preaxial 
  

   border 
  is 
  not 
  flattened 
  in 
  O. 
  latidens 
  as 
  in 
  the 
  Cambridge 
  

   specimens, 
  but 
  is 
  robust 
  and 
  convex. 
  The 
  bone 
  is 
  much 
  

   more 
  concave 
  near 
  the 
  articulation 
  on 
  the 
  ventral 
  surface, 
  

   preaxial 
  side. 
  There 
  is 
  a 
  longitudinal 
  groove 
  for 
  muscle- 
  

   attachment, 
  contiguous 
  with 
  the 
  postaxial 
  border 
  on 
  the 
  

   ventral 
  surface, 
  which 
  is 
  not 
  seen 
  in 
  the 
  Cambridge 
  

   specimens. 
  In 
  0. 
  latidens 
  on 
  the 
  postaxial 
  side 
  of 
  the 
  

   dorsal 
  surface 
  there 
  is 
  a 
  well-developed 
  ridge 
  aud 
  strise, 
  

   caused 
  by 
  the 
  fibres 
  of 
  the 
  muscles 
  traversing 
  the 
  bone 
  

  

  * 
  There 
  is 
  an 
  unnumbered 
  specimen 
  on 
  tliis 
  tablet. 
  

  

  