﻿American 
  Fin-foot. 
  

  

  37 
  

  

  IV. 
  Skull. 
  

  

  The 
  skull 
  of 
  Heliornis 
  (fig. 
  3) 
  differs 
  but 
  slightly, 
  as 
  I 
  have 
  

   already 
  pointed 
  out, 
  from 
  that 
  of 
  Podica. 
  It 
  is 
  smaller, 
  

   and 
  the 
  remaining 
  differences 
  may 
  perhaps 
  be 
  accounted 
  for 
  

   by 
  this 
  : 
  that 
  is 
  to 
  saj^, 
  the 
  processes 
  and 
  fossae 
  from 
  which 
  

   muscles 
  arise, 
  or 
  to 
  -which 
  they 
  are 
  attached, 
  are 
  less 
  strongly 
  

   marked 
  in 
  the 
  more 
  slightly 
  built 
  Heliornis. 
  

  

  Fin-. 
  3. 
  

  

  Skull 
  of 
  Heliornis 
  snrijianiensis, 
  nat. 
  size. 
  

  

  Particularly 
  is 
  this 
  the 
  case 
  with 
  the 
  temporal 
  fossae. 
  In 
  

   Podica 
  {cf. 
  fig. 
  4, 
  p. 
  38) 
  these 
  fossae, 
  although 
  not 
  nearly 
  so 
  

   marked 
  as 
  in 
  the 
  Grebes, 
  are 
  fairly 
  deep 
  and 
  extend 
  back 
  to 
  

   the 
  posterior 
  face 
  of 
  the 
  skull. 
  In 
  Heliornis, 
  on 
  the 
  contrary 
  

   (see 
  fig. 
  3), 
  the 
  fossae 
  are 
  slight 
  ; 
  they 
  only 
  extend 
  over 
  half 
  

   the 
  lateral 
  surface 
  of 
  the 
  brain-case 
  ; 
  furthermore, 
  the 
  two 
  

   processes 
  of 
  the 
  skull-wall 
  (postfrontal 
  and 
  zygomatic) 
  which 
  

   limit, 
  above 
  and 
  below, 
  the 
  commencement 
  of 
  the 
  temporal 
  

   fossae 
  are 
  directly 
  above 
  and 
  below 
  each 
  other 
  respectively 
  

   in 
  Heliornis 
  ; 
  in 
  Podica 
  the 
  lower 
  process, 
  which 
  corresponds 
  

   to 
  the 
  zygomatic 
  process 
  of 
  the 
  squamosal 
  in 
  mammals, 
  does 
  

   not 
  jut 
  out 
  so 
  far 
  forward 
  as 
  to 
  lie 
  beneath 
  the 
  superior 
  process. 
  

  

  In 
  my 
  paper 
  upon 
  Podica 
  senegalensis 
  I 
  drew 
  attention 
  to 
  

   a 
  point 
  of 
  difference 
  between 
  the 
  Rails 
  and 
  the 
  Grebes 
  in 
  the 
  

   large 
  size 
  of 
  the 
  maxillo-palatines 
  of 
  the 
  former. 
  In 
  such 
  a 
  

   Rail 
  as 
  Ocydromus 
  australis 
  the 
  maxillo-palatines 
  are 
  com- 
  

   paratively 
  large 
  inflated 
  bones, 
  Avliich, 
  although 
  covered, 
  are 
  

  

  