﻿96 
  

  

  On 
  the 
  Development 
  of 
  the 
  Teeth 
  of 
  Ophidia. 
  [Dec. 
  10, 
  

  

  The 
  whole 
  row 
  of 
  tooth-sacs 
  is 
  contained 
  within 
  a 
  single 
  general 
  con- 
  

   nective-tissue 
  investment, 
  which 
  is 
  entered 
  at 
  the 
  top 
  by 
  the 
  descending 
  

   process 
  of 
  oral 
  epithelium, 
  whence 
  the 
  enamel-germs 
  are 
  derived. 
  

  

  As 
  they 
  attain 
  considerable 
  length, 
  the 
  forming 
  teeth, 
  which 
  were 
  at 
  

   first 
  vertical, 
  become 
  nearly 
  horizontal, 
  resuming, 
  of 
  course, 
  their 
  upright 
  

   position 
  once 
  more 
  when 
  they 
  come 
  into 
  place. 
  

  

  The 
  clue 
  to 
  the 
  whole 
  peculiarity 
  of 
  this 
  arrangement 
  is 
  to 
  be 
  found 
  in 
  

   the 
  extreme 
  dilatation 
  which 
  the 
  mouth 
  of 
  the 
  snake 
  undergoes. 
  The 
  

   general 
  capsular 
  investment 
  probably 
  serves 
  to 
  preserve 
  the 
  tooth-sacs 
  

   from 
  displacement 
  ; 
  while, 
  if 
  the 
  forming 
  teeth 
  remained 
  vertical 
  after 
  

   they 
  had 
  attained 
  to 
  any 
  considerable 
  length, 
  their 
  points 
  would 
  be 
  pro- 
  

   truded 
  through 
  the 
  mucous 
  membrane 
  when 
  this 
  was 
  put 
  upon 
  the 
  stretch 
  

   in 
  the 
  swallowing 
  of 
  prey. 
  

  

  Just 
  as 
  the 
  author 
  has 
  shown 
  in 
  a 
  previous 
  communication 
  to 
  be 
  the 
  

   case 
  in 
  the 
  Batrachia 
  and 
  Sauria, 
  the 
  hypothetical 
  " 
  papillary 
  stage 
  " 
  is 
  at 
  

   no 
  time 
  present. 
  

  

  From 
  the 
  oral 
  epithelium 
  there 
  extends 
  downwards 
  a 
  process 
  which, 
  

   passing 
  between 
  and 
  winding 
  around 
  the 
  older 
  tooth-sacs, 
  after 
  pursuing 
  

   a 
  tortuous 
  course, 
  reaches 
  the 
  furthest 
  and 
  lowest 
  extremity 
  of 
  the 
  area 
  

   of 
  tooth-development. 
  Here 
  its 
  csecal 
  end 
  gives 
  origin 
  to 
  an 
  enamel- 
  

   organ, 
  and, 
  while 
  it 
  does 
  so, 
  buds 
  forth 
  again 
  beyond 
  it 
  in 
  the 
  form 
  of 
  a 
  

   cascal 
  extremity. 
  Thus 
  at 
  the 
  bottom 
  of 
  this 
  area 
  of 
  tooth-development 
  

   there 
  is 
  a 
  perpetual 
  formation 
  of 
  fresh 
  enamel-organs, 
  beneath 
  which 
  

   arise 
  corresponding 
  dentine-organs, 
  or 
  papillae, 
  if 
  such 
  they 
  can 
  be 
  called 
  

   when 
  arising 
  thus 
  far 
  away 
  from 
  the 
  surface. 
  

  

  In 
  essential 
  principle, 
  therefore, 
  the 
  formation 
  of 
  a 
  tooth-germ 
  is 
  

   similar 
  to 
  that 
  already 
  described 
  in 
  mammals 
  aud 
  other 
  reptiles, 
  the 
  

   difference 
  lying 
  principally 
  in 
  the 
  enormous 
  relative 
  length 
  of, 
  and 
  the 
  

   tortuous 
  course 
  pursued 
  by, 
  that 
  inflection 
  of 
  the 
  oral 
  epithelium 
  which 
  

   serves 
  to 
  form 
  the 
  enamel-organs. 
  The 
  attachment 
  of 
  the 
  tooth 
  to 
  the 
  

   jaw 
  is 
  effected 
  by 
  the 
  rapid 
  development 
  of 
  a 
  coarse 
  bone, 
  which 
  is 
  not 
  

   derived 
  from 
  the 
  ossification 
  of 
  the 
  feebly 
  expressed 
  tooth-capsule, 
  but 
  

   from 
  tissues 
  altogether 
  external 
  to 
  it. 
  Nevertheless 
  this 
  coarse 
  bone 
  of 
  

   attachment 
  adheres 
  more 
  closely 
  to 
  the 
  tooth 
  than 
  to 
  the 
  rest 
  of 
  the 
  jaw, 
  

   from 
  which, 
  in 
  making 
  sections, 
  it 
  often 
  breaks 
  away. 
  

  

  The 
  base 
  of 
  the 
  dentinal 
  pulp 
  assists 
  in 
  firmly 
  binding 
  the 
  tooth 
  to 
  

   this 
  new 
  bone, 
  being 
  converted 
  into 
  a 
  layer 
  of 
  irregular 
  dentine. 
  

  

  This 
  " 
  bone 
  of 
  attachment 
  " 
  is 
  almost 
  wholly 
  removed 
  and 
  renewed 
  

   with 
  the 
  change 
  of 
  each 
  tooth. 
  

  

  