﻿THE 
  MIDDLE 
  EAR 
  AND 
  COLUMELLA 
  OF 
  BIKDS. 
  21 
  

  

  the 
  foot-plug 
  are 
  derived 
  from 
  the 
  hyoid 
  arch 
  and 
  certain 
  

   cells 
  from 
  the 
  auditory 
  capsule. 
  The 
  important 
  fact, 
  how- 
  

   ever, 
  clearly 
  expressed 
  in 
  Figs. 
  4 
  and 
  5 
  is 
  that 
  the 
  dorsal 
  part 
  

   of 
  the 
  hyoid 
  arch, 
  i. 
  e. 
  the 
  part 
  lying 
  between 
  the 
  seventh 
  nerve 
  

   and 
  the 
  auditory 
  capsule 
  {staj^. 
  in 
  Figs. 
  4, 
  5, 
  and 
  6), 
  gives 
  

   rise 
  to 
  part, 
  at 
  least, 
  of 
  the 
  stapes. 
  The 
  meaning 
  of 
  the 
  

   constriction 
  in 
  the 
  five- 
  and 
  six-day 
  chicks 
  must 
  remain 
  

   doubtful 
  ; 
  it 
  corresponds 
  in 
  position 
  to 
  a 
  division 
  between 
  

   hyomandibular 
  and 
  keratohyal, 
  and 
  to 
  the 
  later 
  division 
  

   between 
  stapes 
  and 
  extra-columella. 
  

  

  The 
  following 
  diagrammatic 
  reconstructions 
  will 
  make 
  the 
  

   foregoing 
  observations 
  clear. 
  

  

  3. 
  Conclusion. 
  

  

  The 
  value 
  of 
  the 
  embryological 
  evidence 
  here 
  presented 
  is 
  

   partly 
  positive, 
  partly 
  negative. 
  

  

  Positively, 
  it 
  may 
  be 
  stated 
  that 
  in 
  the 
  chick 
  the 
  contribu- 
  

   tion 
  of 
  the 
  auditory 
  capsule 
  to 
  the 
  columella 
  is 
  exceedingly 
  

   small, 
  probably 
  confined 
  to 
  the 
  foot-plug 
  of 
  the 
  stapes 
  ; 
  at 
  

   any 
  rate 
  the 
  main 
  part 
  of 
  the 
  stapes 
  and 
  the 
  whole 
  of 
  the 
  

   columella 
  is 
  formed 
  from 
  the 
  hyoid 
  arch. 
  Negatively, 
  it 
  

   proves 
  the 
  futility 
  of 
  basing 
  arguments 
  upon 
  this 
  question 
  on 
  

   isolated 
  stages, 
  or 
  on 
  cartilaginous 
  stages 
  which 
  have 
  not 
  

   been 
  traced 
  back 
  to 
  their 
  earliest 
  procartilagiuous 
  forerunners. 
  

   Taking 
  this 
  into 
  consideration 
  the 
  supposed 
  derivation 
  of 
  the 
  

   stapes 
  of 
  Sauropsida 
  from 
  the 
  auditory 
  capsule 
  (9), 
  and 
  the 
  

   possible 
  interpretation 
  of 
  Sphenodon 
  in 
  this 
  manner 
  (12 
  and 
  

   14) 
  becomes 
  exceeding 
  doubtful; 
  in 
  birds, 
  at 
  any 
  rate, 
  as 
  we 
  

   have 
  seen, 
  the 
  condition 
  confirms 
  the 
  opinion 
  arrived 
  at 
  on 
  

   theoretical 
  grounds 
  by 
  Gaupp 
  (11), 
  that 
  the 
  stapes 
  of 
  Saurop- 
  

   sida 
  corresponds 
  to 
  the 
  stapes 
  of 
  Mammalia, 
  and 
  to 
  the 
  hyo- 
  

   mandibular 
  of 
  fishes. 
  Mammalia 
  and 
  Sauropsida 
  have 
  this 
  

   much 
  in 
  common, 
  tliat 
  they 
  have 
  both 
  converted 
  the 
  hyomandi- 
  

   bular 
  or 
  dorsal 
  portion 
  of 
  the 
  hyoid 
  arch 
  into 
  the 
  stapes 
  ; 
  

   but 
  subsequently 
  they 
  have 
  gone 
  on 
  different 
  lines 
  in 
  evolu- 
  

   tion, 
  the 
  Sauropsida 
  making 
  use 
  of 
  the 
  more 
  ventral 
  part 
  of 
  

  

  