﻿170 
  Mr. 
  A. 
  Sanders 
  on 
  the 
  

  

  These 
  measurements 
  are 
  approximative 
  only 
  and 
  vary 
  

   somewhat 
  in 
  different 
  parts 
  of 
  the 
  cerebrum. 
  

  

  The 
  cells 
  of 
  the 
  inner 
  layer 
  are 
  generally 
  spherical 
  in 
  shape, 
  

   but 
  some 
  oval 
  and 
  pyriform 
  ones 
  are 
  also 
  met 
  with 
  and 
  even 
  

   occasionally 
  fusiform 
  ones 
  are 
  seen. 
  They 
  range 
  in 
  size 
  from 
  

   0*0084 
  millim. 
  to 
  13 
  /j, 
  in 
  diameter 
  ; 
  they 
  show 
  a 
  peculiar 
  

   tendency 
  to 
  become 
  vacuolated, 
  in 
  which 
  state 
  they 
  resemble 
  

   the 
  appearance 
  presented 
  by 
  Infusoria 
  when 
  too 
  much 
  com- 
  

   pressed 
  ; 
  this 
  vacuolation 
  is 
  caused 
  probably 
  by 
  the 
  preserva- 
  

   tive 
  fluid 
  not 
  penetrating 
  with 
  sufficient 
  quickness 
  through 
  

   the 
  parenchyma, 
  as 
  it 
  is 
  only 
  found 
  in 
  those 
  cells 
  which 
  

   occupy 
  the 
  internal 
  surface. 
  When 
  the 
  cells 
  are 
  in 
  this 
  state 
  

   the 
  nucleus 
  and 
  the 
  nucleolus 
  are 
  obscured 
  ; 
  but 
  in 
  the 
  normal 
  

   cells 
  they 
  are 
  quite 
  distinct. 
  These 
  cells 
  are 
  closely 
  crowded 
  

   together 
  and 
  give 
  off 
  processes 
  which 
  join 
  the 
  fibrillar 
  network 
  

   of 
  the 
  neuroglia 
  with 
  which 
  they 
  are 
  surrounded. 
  

  

  In 
  the 
  second 
  layer 
  the 
  fibrils 
  permeating 
  the 
  neuroglia 
  of 
  

   which 
  it 
  is 
  composed 
  have 
  a 
  decidedly 
  longitudinal 
  direction 
  

   and 
  are 
  probably 
  continuations 
  of 
  the 
  fibres 
  of 
  the 
  crura 
  

   cerebri 
  . 
  

  

  The 
  cells 
  of 
  the 
  third 
  layer 
  are 
  on 
  an 
  average 
  of 
  a 
  larger 
  

   size 
  than 
  those 
  of 
  the 
  first 
  or 
  internal 
  layer 
  ; 
  they 
  range 
  from 
  

   17 
  /a 
  long 
  and 
  14 
  yu, 
  wide 
  to 
  30 
  p 
  long 
  and 
  12 
  //, 
  wide; 
  they 
  

   are 
  not 
  so 
  closely 
  packed 
  together, 
  but 
  are 
  rather 
  sparsely 
  

   scattered 
  along 
  the 
  zone 
  which 
  they 
  occupy 
  ; 
  they 
  usually 
  

   give 
  off 
  two 
  or 
  three 
  thick 
  processes 
  instead 
  of 
  numerous 
  fine 
  

   ones 
  ; 
  they 
  resemble 
  the 
  larger 
  cells 
  in 
  the 
  cerebrum 
  of 
  the 
  

   Teleostei. 
  

  

  In 
  some 
  places 
  the 
  first 
  or 
  internal 
  layer 
  extends 
  through 
  

   the 
  parenchyma 
  of 
  the 
  second 
  layer 
  and 
  becomes 
  continuous 
  

   with 
  the 
  third, 
  so 
  that 
  the 
  intervening 
  neuroglia 
  loses 
  its 
  

   distinct 
  individuality 
  and 
  the 
  three 
  layers 
  merge 
  into 
  one. 
  

  

  The 
  fourth 
  or 
  external 
  layer 
  is 
  entirely 
  or 
  very 
  nearly 
  

   devoid 
  of 
  cells, 
  and 
  consists 
  of 
  a 
  fine 
  fibrillar 
  network 
  imbed- 
  

   ded 
  in 
  a 
  finely 
  granular 
  neuroglia, 
  having 
  the 
  usual 
  characters 
  

   and 
  showing 
  a 
  slight 
  tendency 
  to 
  radial 
  striation. 
  

  

  The 
  palissade 
  cells 
  of 
  the 
  external 
  surface 
  are 
  very 
  slightly 
  

   developed 
  and 
  are 
  scarcely 
  perceptible 
  ; 
  yet 
  when 
  they 
  do 
  

   occur 
  they 
  send 
  processes 
  into 
  the 
  interior, 
  as 
  in 
  Plagiosto- 
  

   mata 
  and 
  Teleostei. 
  

  

  The 
  above-described 
  arrangement 
  occurs 
  in 
  the 
  dorsal 
  wall 
  

   of 
  the 
  cerebrum. 
  The 
  ventral 
  parietes 
  forming 
  the 
  bullee 
  

   offer 
  a 
  slightly 
  varying 
  disposition 
  of 
  the 
  elements 
  of 
  the 
  ner- 
  

   vous 
  substance. 
  Here 
  the 
  central 
  layer 
  of 
  cells 
  is 
  absent, 
  

   and 
  only 
  two 
  layers 
  are 
  observable 
  — 
  one 
  internal, 
  composed 
  of 
  

   cells 
  altogether 
  resembling 
  those 
  which 
  form 
  the 
  internal 
  

  

  