﻿16 
  

  

  GEOFFBEY 
  SMITH. 
  

  

  tympani 
  in 
  Gallus 
  and 
  in 
  Columba 
  may 
  bo 
  seen 
  in 
  the 
  follow- 
  

   ing 
  diagram. 
  

  

  11 
  

  

  I. 
  Columella 
  of 
  Columba 
  ; 
  II, 
  of 
  Gallas, 
  from 
  wilhout. 
  fp. 
  Toot 
  plu?. 
  

   stap. 
  Stapes. 
  Pit. 
  Platner's 
  li.cjameiit. 
  vii. 
  Seventh 
  nerve, 
  ch. 
  Chorda 
  

   tympani. 
  

  

  supra, 
  extra, 
  and 
  infra. 
  Stapedial 
  cartilages. 
  

  

  In 
  these 
  two 
  relations 
  of 
  the 
  chorda 
  tympani 
  to 
  the 
  columella 
  

   Ave 
  see 
  a 
  striking 
  convergence 
  towards 
  the 
  two 
  conditions 
  in 
  

   Lacertilia 
  described 
  by 
  Versluys 
  (10). 
  In 
  Lacertilia 
  the 
  

   chorda 
  tympani 
  may 
  come 
  off 
  the 
  seventh 
  nerve 
  behind 
  the 
  

   columella, 
  and 
  then 
  run 
  forwards, 
  across, 
  and 
  external 
  or 
  

   dorsal 
  to 
  the 
  extra-columella, 
  or 
  else 
  it 
  may 
  come 
  off 
  anteriorly 
  

   to 
  the 
  columella 
  altogether 
  (e. 
  g. 
  Gecko 
  and 
  those 
  forms 
  

   which 
  have 
  no 
  processus 
  internus 
  to 
  the 
  extra-columella). 
  

   There 
  can 
  be 
  little 
  doubt 
  that 
  the 
  backward 
  origin 
  is 
  primi- 
  

   tive, 
  since 
  Sphenodon 
  shows 
  it, 
  and 
  that 
  tlie 
  forward 
  origin 
  

   in 
  the 
  fowl 
  is 
  secondary, 
  as 
  first 
  suggested 
  by 
  Hasse 
  (2), 
  who 
  

   supposed 
  that 
  its 
  forward 
  origin 
  had 
  to 
  do 
  with 
  the 
  peculiar 
  

   development 
  of 
  the 
  quadrate 
  articulation 
  in 
  that 
  bird. 
  

  

  2. 
  Embryology. 
  

  

  The 
  middle 
  ear 
  cavity 
  is 
  formed 
  from 
  the 
  first 
  gill 
  slit 
  (5). 
  

   The 
  earliest 
  stage 
  which 
  is 
  instructive 
  for 
  the 
  purpose 
  in 
  

   hand 
  is 
  the 
  five-day-old 
  chick. 
  As 
  yet 
  no 
  chondrification 
  has 
  

   taken 
  place, 
  but 
  the 
  hyoid 
  arch 
  and 
  the 
  auditory 
  capsule 
  are 
  

   recognisably 
  shown 
  by 
  the 
  thicker 
  aggregation 
  of 
  connective- 
  

  

  