﻿American 
  Fin-foot. 
  31 
  

  

  chiefly 
  concern 
  the 
  muscular 
  anatomy. 
  I 
  have 
  not 
  attempted 
  

   any 
  further 
  discussion 
  upon 
  the 
  affinities 
  of 
  the 
  Heliornithidae 
  

   to 
  other 
  families 
  of 
  birds. 
  The 
  facts 
  which 
  I 
  have 
  been 
  able 
  

   to 
  make 
  out 
  with 
  regard 
  to 
  Heliornis 
  do 
  not 
  render 
  neces- 
  

   sary 
  any 
  modification 
  of 
  the 
  opinions 
  which 
  I 
  expressed 
  in 
  

   my 
  paper 
  upon 
  Podica 
  stnegalensis. 
  Such 
  diflerences 
  as 
  

   exist 
  in 
  the 
  anatomy 
  of 
  tlie 
  two 
  genera 
  appear 
  to 
  me 
  to 
  be 
  

   correlated 
  with 
  the 
  smaller 
  size 
  of 
  Heliornis. 
  In 
  many 
  

   groups 
  of 
  the 
  animal 
  kingdom 
  we 
  find 
  that 
  the 
  smaller 
  

   members 
  show 
  a 
  simplification 
  of 
  structure 
  as 
  compared 
  with 
  

   the 
  larger 
  forms. 
  

  

  I. 
  Pterylosis. 
  

  

  The 
  pterylosis 
  of 
  this 
  bird 
  has 
  been 
  already 
  described 
  by 
  

   Nitzsch 
  {op. 
  cit. 
  p. 
  127, 
  pi. 
  viii. 
  fig. 
  9). 
  When 
  the 
  bird 
  is 
  

   plucked 
  the 
  feather- 
  tracts 
  are 
  rendered 
  rather 
  inconspicuous 
  

   by 
  the 
  presence 
  of 
  down 
  feathers, 
  which 
  are 
  scattered 
  more 
  

   or 
  less 
  uniformly 
  all 
  over 
  the 
  back, 
  and 
  which 
  occur 
  on 
  the 
  

   ventral 
  surface 
  of 
  the 
  body, 
  particularly 
  along 
  the 
  line 
  of 
  the 
  

   scernai 
  keel. 
  I 
  find 
  that, 
  as 
  Nitzsch 
  has 
  stated, 
  the 
  neck 
  is 
  

   nearly 
  continuously 
  feathered, 
  there 
  being 
  no 
  lateral, 
  and 
  

   only 
  a 
  short 
  ventral, 
  bare 
  tract. 
  The 
  dorsal 
  tract 
  is 
  strong 
  

   between 
  the 
  shoulder-blades 
  and 
  is 
  distinctly 
  forked; 
  each 
  

   branch 
  of 
  the 
  fork 
  is 
  only 
  two 
  or 
  three 
  feathers 
  wide 
  ; 
  the 
  

   hinder 
  portion 
  of 
  the 
  tracts 
  is 
  weak, 
  but 
  the 
  feathering 
  

   becomes 
  strong 
  soon 
  after 
  they 
  have 
  joined 
  posteriorly 
  ; 
  the 
  

   junction 
  of 
  the 
  two 
  tracts 
  occurs 
  at 
  the 
  anterior 
  end 
  of 
  the 
  

   pelvis. 
  

  

  Nitzsch 
  says 
  nothing 
  of 
  the 
  ventral 
  tracts 
  in 
  his 
  special 
  

   description 
  of 
  Heliornis, 
  but 
  distinguishes 
  the 
  genera 
  Fulica, 
  

   Heliornis, 
  and 
  others 
  by 
  the 
  undivided 
  ventral 
  tracts. 
  This 
  

   was 
  certainly 
  the 
  arrangement 
  in 
  the 
  specimens 
  which 
  I 
  

   examined. 
  The 
  median 
  ventral 
  apterion 
  extends 
  about 
  an 
  

   inch 
  up 
  the 
  neck. 
  

  

  II. 
  Muscular 
  Anatomy. 
  

  

  The 
  patagial 
  muscle 
  is, 
  as 
  in 
  Podica 
  senegalensis, 
  single 
  ; 
  

   just 
  before 
  the 
  origin 
  of 
  the 
  two 
  tendons 
  into 
  which 
  it 
  divides 
  

  

  