﻿362 
  

  

  Mr. 
  C. 
  S. 
  Tomes 
  on 
  the 
  

  

  [Apr. 
  IS, 
  

  

  I. 
  " 
  On 
  the 
  Development 
  of 
  the 
  Teeth 
  of 
  Fishes 
  (Elasmobranchii 
  

   and 
  Teleostei) 
  P 
  By 
  Charles 
  S. 
  Tovies,, 
  M.A. 
  Communicated 
  

   by 
  John 
  Tomes, 
  F.R.S. 
  Received 
  March 
  1, 
  1875. 
  

  

  (Abstract.) 
  

  

  It 
  has 
  usually 
  been 
  supposed 
  that 
  the 
  whole 
  process 
  of 
  the 
  develop- 
  

   ment 
  of 
  the 
  teeth 
  in 
  many 
  fish 
  might 
  be 
  taken 
  to 
  represent 
  the 
  earlier 
  

   stages 
  alone 
  of 
  the 
  process 
  as 
  it 
  is 
  seen 
  in 
  man 
  ; 
  this 
  opinion 
  is 
  forcibly 
  

   expressed 
  by 
  Professor 
  Owen, 
  who, 
  for 
  example, 
  says 
  of 
  the 
  sharks, 
  

   "Here 
  is 
  represented 
  the 
  first 
  and 
  transitory 
  papillary 
  stage 
  of 
  dental 
  

   development 
  in 
  mammals 
  ; 
  and 
  the 
  simple 
  cartilaginous 
  maxillary 
  plate, 
  

   with 
  the 
  open 
  groove 
  behind 
  containing 
  the 
  germinal 
  papillae 
  of 
  the 
  teeth, 
  

   offers, 
  in 
  the 
  shark, 
  a 
  magnified 
  representation 
  of 
  the 
  earliest 
  condition 
  of 
  

   the 
  jaws 
  and 
  teeth 
  of 
  the 
  human 
  embryo." 
  

  

  With 
  this 
  opinion, 
  already 
  objected 
  to 
  by 
  Professor 
  Huxley, 
  I 
  cannot 
  

   concur 
  ; 
  still 
  less 
  can 
  I 
  concur 
  with 
  the 
  statement 
  that 
  " 
  in 
  all 
  fish 
  the 
  

   first 
  step 
  is 
  the 
  simple 
  production 
  of 
  a 
  soft 
  vascular 
  papilla 
  from 
  the 
  free 
  

   surface 
  of 
  the 
  buccal 
  membrane." 
  

  

  The 
  supposed 
  open 
  groove 
  behind 
  the 
  jaws 
  of 
  cartilaginous 
  fish 
  is 
  in 
  

   reality 
  closed 
  ; 
  that 
  is 
  to 
  say, 
  the 
  epithelium 
  of 
  the 
  jaw 
  passes 
  continu- 
  

   ously 
  across 
  on 
  to 
  the 
  thecal 
  fold 
  of 
  mucous 
  membrane 
  which 
  lies 
  be- 
  

   hind 
  the 
  jaw 
  and 
  protects 
  the 
  developing 
  teeth 
  ; 
  and, 
  if 
  the 
  groove 
  be 
  

   opened, 
  it 
  is 
  by 
  the 
  tearing 
  through 
  of 
  this 
  epithelium. 
  

  

  ]N~ear 
  to 
  the 
  base 
  of 
  the 
  jaw, 
  the 
  mucous 
  membrane 
  is 
  cellular 
  and 
  

   dentine-organs 
  are 
  formed 
  by 
  its 
  elevation 
  into 
  conical 
  papillae, 
  without 
  

   apparent 
  structural 
  change 
  ; 
  but, 
  higher 
  up, 
  the 
  dentine-papillae 
  assume 
  

   their 
  characteristic 
  forms 
  and 
  structure, 
  and 
  the 
  residuum 
  of 
  the 
  mucous 
  

   membrane 
  at 
  their 
  bases 
  becomes 
  transformed 
  into 
  a 
  fibrillated 
  tissue. 
  

  

  As 
  the 
  teeth 
  become 
  yet 
  more 
  advanced, 
  the 
  fibrillated 
  tissue 
  at 
  their 
  

   bases 
  becomes 
  specially 
  arranged 
  with 
  reference 
  to 
  the 
  base 
  of 
  each 
  tooth, 
  

   so 
  as 
  to 
  form, 
  in 
  some 
  sense, 
  ligaments 
  to 
  bind 
  it 
  firmly 
  in 
  its 
  place. 
  

  

  Just 
  as 
  the 
  mucous 
  membrane 
  of 
  the 
  exposed 
  surface 
  of 
  the 
  jaw 
  is 
  

   covered 
  by 
  its 
  epithelium, 
  so 
  the 
  dentine-papillae 
  are 
  covered 
  by 
  theirs 
  ; 
  

   in 
  the 
  latter 
  place, 
  however, 
  it 
  has 
  undergone 
  a 
  special 
  development, 
  which 
  

   entitles 
  it 
  to 
  the 
  name 
  of 
  an 
  " 
  enamel-organ." 
  As 
  was 
  originally 
  pointed 
  

   out 
  by 
  Professor 
  Huxley, 
  enamel-organs 
  are 
  but 
  modified 
  epithelium. 
  

  

  The 
  dentine-papillae 
  are 
  processes 
  arising 
  from 
  a 
  continuous 
  sheet 
  of 
  

   mucous 
  membrane 
  ; 
  the 
  enamel-organs 
  also 
  are 
  continuous 
  with 
  one 
  

   another, 
  attaining 
  to 
  a 
  special 
  development 
  where 
  they 
  serve 
  as 
  caps 
  to 
  the 
  

   several 
  dentine-papillae 
  ; 
  the 
  arrangement 
  of 
  these 
  enamel-organs 
  suggests 
  

   a 
  resemblance 
  to 
  the 
  corresponding 
  structures 
  described 
  by 
  me 
  as 
  existing 
  

   in 
  the 
  newt 
  and 
  in 
  certain 
  reptiles. 
  

  

  Enamel 
  is 
  present 
  in 
  noteworthy 
  thickness 
  in 
  some 
  Elasmobranchiate 
  

   fish 
  ; 
  it 
  is 
  absent, 
  or 
  almost 
  so, 
  in 
  others 
  ; 
  but 
  enamel-organs 
  are 
  present 
  

   in 
  all. 
  The 
  enamel-organs 
  consist, 
  on 
  the 
  surfaces 
  directed 
  towards 
  the 
  

  

  