﻿Auditory 
  Apparatus 
  in 
  Sphenodon 
  punctatus. 
  227 
  

  

  Simultaneously 
  with 
  this 
  process 
  there 
  occurs 
  a 
  differentiation 
  of 
  the 
  pars 
  

   superior 
  into 
  a 
  system 
  of 
  communicating 
  canals 
  and 
  sinuses. 
  These 
  are 
  

   formed 
  hy 
  the 
  outgrowth 
  of 
  a 
  number 
  of 
  pockets 
  and 
  the 
  ingrowth 
  of 
  the 
  

   walls 
  of 
  a 
  number 
  of 
  deepening 
  grooves. 
  The 
  septa 
  formed 
  by 
  these 
  double- 
  

   walled 
  epiblastic 
  folds 
  and 
  by 
  the 
  mesoblast 
  included 
  between 
  them 
  result 
  in 
  

   the 
  formation 
  of 
  a 
  central 
  tri-radiate 
  utriculus, 
  the 
  extremities 
  of 
  which 
  are 
  

   united 
  by 
  an 
  anterior 
  vertical, 
  a 
  posterior 
  vertical, 
  and 
  a 
  horizontal 
  semi- 
  

   circular 
  canal, 
  each 
  of 
  which 
  possesses 
  a 
  dilated 
  " 
  ampulla," 
  on 
  the 
  floor 
  of 
  

   which 
  arises 
  a 
  sensory 
  crest 
  or 
  crista 
  acustica. 
  To 
  each 
  of 
  these 
  is 
  distributed 
  

   a 
  ramus 
  of 
  the 
  auditory 
  nerve. 
  On 
  the 
  medial 
  wall 
  of 
  the 
  utriculus 
  occur 
  a 
  

   number 
  of 
  sensory 
  epithelial 
  patches, 
  derived, 
  like 
  the 
  epithelium 
  of 
  the 
  

   cristas 
  acusticse, 
  from 
  the 
  neuroepithelium 
  of 
  the 
  pars 
  superior. 
  These 
  

   macular 
  areas 
  are 
  at 
  first 
  united 
  with 
  one 
  another 
  and 
  with 
  the 
  neuro- 
  

   epithelium 
  of 
  the 
  pars 
  inferior 
  by 
  tracts 
  of 
  neuroepithelium, 
  but 
  in 
  the 
  adult 
  

   organ 
  they 
  are 
  entirely 
  separated. 
  

  

  The 
  appearance 
  of 
  the 
  grooves 
  and 
  pockets 
  of 
  the 
  pars 
  superior 
  suggests 
  

   that 
  the 
  anterior 
  vertical 
  and 
  horizontal 
  semicircular 
  canals 
  are 
  formed 
  some- 
  

   what 
  earlier 
  than 
  the 
  posterior 
  vertical 
  canal, 
  but, 
  on 
  the 
  other 
  hand, 
  the 
  

   crista 
  acustica 
  of 
  the 
  horizontal 
  semicircular 
  canal 
  appears 
  to 
  develop 
  

   somewhat 
  later 
  than 
  do 
  those 
  of 
  the 
  other 
  canals. 
  The 
  development 
  of 
  the 
  

   canals, 
  the 
  macular 
  areas, 
  and 
  the 
  branches 
  of 
  the 
  auditory 
  nerve 
  has 
  been 
  

   fully 
  investigated. 
  A 
  well-developed 
  macula 
  neglecta 
  and 
  a 
  nerve 
  ramulus 
  

   supplied 
  to 
  it 
  were 
  found 
  and 
  the 
  presence 
  of 
  a 
  similar 
  nerve-branch 
  passing 
  

   to 
  the 
  ductus 
  endolymphaticus 
  was 
  noted. 
  No 
  sensory 
  epithelium 
  was, 
  

   however, 
  discovered 
  in 
  the 
  saccus 
  endolymphaticus. 
  The 
  pars 
  inferior 
  

   meanwhile 
  undergoes 
  differentiation 
  into 
  sacculus 
  and 
  cochlea, 
  the 
  latter 
  

   exhibiting 
  a 
  curved 
  distal 
  pars 
  lagenae 
  and 
  a 
  proximal 
  pars 
  basilaris, 
  each 
  

   with 
  its 
  own 
  macular 
  area 
  and 
  nerve 
  supply. 
  

  

  A 
  complete 
  account 
  of 
  the 
  histology 
  of 
  the 
  inner 
  ear 
  was 
  not 
  attempted, 
  

   but 
  sufficient 
  data 
  have 
  been 
  obtained 
  to 
  confirm 
  and 
  supplement 
  the 
  

   histological 
  details 
  recorded 
  by 
  Osawa 
  (1898). 
  The 
  maculae 
  and 
  cristse 
  

   acusticse 
  contain 
  hair-cells 
  (auditory 
  sense 
  epithelium 
  cells) 
  and 
  interstitial 
  

   (supporting) 
  cells, 
  while 
  the 
  non-sensory 
  areas 
  of 
  the 
  inner 
  ear 
  consist 
  of 
  

   flattened 
  or 
  cubical 
  epithelium, 
  supported 
  by 
  an 
  external 
  investment 
  of 
  

   spindle 
  connective 
  tissue. 
  

  

  A 
  detailed 
  investigation 
  of 
  the 
  development 
  of 
  the 
  auditory 
  capsule, 
  

   columella 
  auris, 
  and 
  associated 
  bones 
  was 
  undertaken, 
  special 
  care 
  being 
  

   taken 
  to 
  examine 
  a 
  number 
  of 
  embryos 
  in 
  which 
  chondrification 
  of 
  the 
  

   rudiments 
  of 
  these 
  structures 
  had 
  not 
  yet 
  occurred. 
  The 
  conditions 
  

   obtaining 
  in 
  such 
  early 
  embryos 
  have 
  now 
  been 
  recorded 
  for 
  — 
  it 
  is 
  

  

  