﻿41-i 
  Wieland 
  — 
  Evolution 
  of 
  the 
  Testudtnate 
  Humerus. 
  

  

  quite 
  constantly 
  when 
  dealing 
  with 
  well 
  marked 
  intervals 
  in 
  

   form 
  there 
  are 
  accompanying 
  generic 
  or 
  family 
  variations. 
  

   This 
  is 
  indeed 
  so 
  persistently 
  the 
  fact 
  th&t 
  presence 
  of 
  humeral 
  

   differences 
  must 
  generally 
  be 
  regarded 
  as 
  of 
  distinct 
  diagnostic 
  

   value, 
  though 
  absence 
  of 
  such 
  may 
  be 
  simply 
  non-determinative. 
  

  

  In 
  the 
  descriptions 
  and 
  notes 
  which 
  follow 
  I 
  shall 
  term 
  the 
  

   most 
  specialized 
  land 
  humerus 
  as 
  parachelic, 
  and 
  the 
  general- 
  

   ized 
  land 
  and 
  freshwater 
  type 
  as 
  chelic. 
  It 
  will 
  be 
  seen 
  that 
  

   there 
  is 
  in 
  general 
  a 
  corresponding 
  humeral 
  distinction 
  between 
  

   the 
  more 
  specialized 
  and 
  the 
  more 
  generalized 
  land 
  turtles. 
  

  

  Certain 
  Mesozoic 
  turtles 
  regarded 
  as 
  transitional 
  brackish 
  or 
  

   salt-water 
  forms 
  have 
  intermediate 
  humeri 
  which 
  may 
  be 
  

   described 
  as 
  chelicoid 
  and 
  thalassoid, 
  the 
  former 
  resembling 
  

   more 
  nearly 
  land, 
  the 
  latter 
  oceanic 
  outlines. 
  Finally, 
  the 
  

   strictly 
  oceanic 
  and 
  the 
  ultra 
  or 
  specialized 
  oceanic 
  humeri 
  will 
  

   be 
  respectively 
  spoken 
  of 
  as 
  thalassic 
  and 
  parathalassic* 
  Here 
  

   also 
  there 
  is 
  a 
  certain 
  corresponding 
  general 
  development. 
  

  

  The 
  land 
  forms 
  [Parachelic 
  and 
  Chelic). 
  

  

  The 
  parachelic 
  humerus 
  is 
  in 
  general 
  that 
  of 
  short-clawed 
  

   dry 
  land 
  tortoises, 
  most 
  of 
  the 
  genera 
  of 
  which 
  are 
  rather 
  

   recent 
  in 
  geological 
  time, 
  and 
  have 
  probably 
  been 
  derived 
  from 
  

   longer 
  clawed 
  ancestors 
  of 
  more 
  aquatic 
  habit. 
  This 
  humerus 
  

   is 
  seen 
  in 
  such 
  genera 
  as 
  Testudo 
  and 
  Cinyxis. 
  Its 
  strongly 
  

   sigmoidal 
  outline 
  in 
  the 
  dorso-ventral 
  plane 
  with 
  the 
  proximal 
  

   end 
  upturned 
  and 
  the 
  distal 
  depressed, 
  the 
  reverse 
  of 
  the 
  

   condition 
  seen 
  in 
  the 
  humerus 
  of 
  running 
  mammals, 
  at 
  once 
  

   strikes 
  the 
  eye. 
  But 
  with 
  reference 
  to 
  other 
  reptilia 
  a 
  most 
  

   important 
  feature 
  is 
  the 
  closely 
  proximal 
  position 
  of 
  the 
  radial 
  

   crest 
  or 
  analogue 
  of 
  the 
  deltoid 
  crest. 
  The 
  ectepicondylar 
  

   foramen 
  or 
  groove 
  is 
  distinctly 
  ectal, 
  diminutive, 
  and 
  situated 
  

   well 
  back 
  from 
  the 
  distal 
  end. 
  There 
  is 
  never 
  a 
  very 
  promi- 
  

   nent 
  ulnar 
  crest 
  or 
  broad 
  and 
  rounded 
  distal 
  extremity 
  as 
  in 
  

   Ghelydra. 
  Instead 
  the 
  distal 
  articular 
  surface 
  forms 
  a 
  roller 
  as 
  

   in 
  the 
  Lacertilia, 
  this 
  being 
  the 
  most 
  important 
  distinguishing 
  

   feature. 
  (See 
  fig. 
  12, 
  introduced 
  to 
  show 
  this 
  point 
  as 
  well 
  as 
  

   the 
  general 
  correspondence 
  of 
  parts 
  in 
  the 
  Lacertilia 
  and 
  the 
  

   Testudi?iata, 
  the 
  same 
  notation 
  having 
  been 
  used 
  for 
  this 
  pur- 
  

   pose.) 
  

  

  It 
  may 
  be 
  noted 
  that 
  there 
  is 
  correlated 
  with 
  this 
  form 
  of 
  

   turtle 
  humerus 
  a 
  tendency 
  to 
  form 
  broad 
  short 
  heavy 
  claws, 
  

  

  * 
  As 
  will 
  be 
  noted, 
  the 
  first 
  three 
  of 
  these 
  adjectives 
  has 
  been 
  derived 
  from 
  the 
  

   Greek 
  XV^V, 
  chele, 
  hoof, 
  claw, 
  — 
  that 
  is 
  humeri 
  bearing: 
  clawed 
  feet. 
  It 
  has 
  been 
  

   thought 
  preferable 
  to 
  derive 
  the 
  second 
  three 
  from 
  Thalassa, 
  the 
  sea, 
  — 
  a 
  habitat 
  

   in 
  which 
  claws 
  are 
  lost, 
  rather 
  than 
  from 
  Trrspv^, 
  pteryx, 
  wing, 
  used 
  once 
  by 
  

   Nicander 
  for 
  the 
  flipper 
  of 
  a 
  turtle. 
  Some 
  might 
  hold 
  it 
  better 
  to 
  derive 
  the 
  

   entire 
  series 
  from 
  habitat. 
  

  

  