﻿162 
  Mr. 
  A. 
  Sanders 
  on 
  the 
  

  

  pical 
  sections 
  ; 
  on 
  the 
  posterior 
  end 
  of 
  the 
  walls, 
  immediately 
  

   in 
  front 
  of 
  the 
  point 
  where 
  they 
  merge 
  into 
  the 
  optic 
  lobe, 
  

   there 
  is 
  a 
  tuberosity 
  which 
  transverse 
  sections 
  demonstrate 
  

   to 
  be 
  double 
  (PL 
  IX. 
  fig. 
  5) 
  ; 
  these 
  tuberosities 
  form 
  the 
  

   ganglion 
  habenula 
  1 
  , 
  which 
  corresponds 
  to 
  the 
  tuberculum 
  inter- 
  

   medium 
  of 
  Teleostei 
  and 
  Plagiostomata. 
  

  

  Fulliquet 
  in 
  his 
  detailed 
  description 
  of 
  the 
  brain 
  of 
  Proto- 
  

   pterus 
  annectens 
  mentions 
  two 
  tuberosities 
  in 
  a 
  corresponding 
  

   position 
  which 
  much 
  resemble 
  these. 
  He 
  considers 
  that 
  

   they 
  form 
  part 
  of 
  the 
  epiphysis. 
  This 
  surely 
  must 
  be 
  a 
  

   misapprehension 
  ; 
  they 
  might 
  be, 
  and 
  probably 
  are, 
  remains 
  

   of 
  the 
  ganglion 
  which 
  supplied 
  that 
  sense-organ, 
  but 
  they 
  

   could 
  not 
  be 
  part 
  of 
  that 
  sense-organ 
  itself. 
  

  

  On 
  the 
  floor 
  of 
  the 
  thalamencephalon 
  there 
  is 
  visible 
  ante- 
  

   riorly 
  the 
  projecting 
  cord 
  of 
  the 
  commissure 
  of 
  the 
  two 
  hemi- 
  

   spheres, 
  which 
  corresponds 
  to 
  the 
  anterior 
  commissure 
  ; 
  be- 
  

   hind 
  this 
  is 
  an 
  opening 
  leading 
  into 
  the 
  infundibulum. 
  

  

  The 
  pituitary 
  body 
  or 
  hypophysis 
  is 
  a 
  large 
  and 
  extensive 
  

   structure 
  formed 
  apparently 
  of 
  glandular 
  tissue 
  composed 
  of 
  

   interlacing 
  tubules 
  ; 
  it 
  seems 
  to 
  be 
  much 
  larger 
  here 
  than 
  in 
  

   Protopterus. 
  

  

  No 
  part 
  of 
  the 
  chiasma 
  nervorum 
  opticorum 
  is 
  visible 
  ex- 
  

   ternally, 
  but 
  on 
  removal 
  of 
  the 
  pia 
  mater 
  the 
  optic 
  tract 
  is 
  

   distinctly 
  seen 
  passing 
  upward 
  and 
  backward 
  to 
  the 
  summit 
  

   of 
  the 
  optic 
  lobe 
  ; 
  this 
  is 
  much 
  more 
  visible 
  in 
  brains 
  pre- 
  

   served 
  in 
  potassium 
  bichromate 
  than 
  in 
  spirit 
  preparations. 
  

  

  The 
  mesencephalon 
  is 
  a 
  paired 
  tuberosity, 
  small 
  and 
  nar- 
  

   row, 
  and 
  does 
  not 
  present 
  that 
  external 
  transverse 
  striation, 
  

   visible 
  presumably 
  to 
  the 
  naked 
  eye, 
  given 
  in 
  fig. 
  20, 
  

   taf. 
  iii. 
  of 
  Wicdersheim's 
  paper. 
  Fulliquet* 
  lays 
  great 
  stress 
  

   on 
  the 
  fact 
  that 
  in 
  Protopterus 
  annectens 
  the 
  mesencephalon 
  

   is 
  single 
  ; 
  he 
  considers 
  that 
  this 
  indicates 
  a 
  low 
  degree 
  of 
  

   development, 
  the 
  original 
  single 
  state 
  of 
  this 
  segment 
  of 
  the 
  

   encephalon 
  being 
  preserved. 
  

  

  Although 
  the 
  cerebellum 
  is 
  not 
  well 
  developed, 
  being 
  

   merely 
  a 
  bridge 
  crossing 
  the 
  anterior 
  end 
  of 
  the 
  sinus 
  rhom- 
  

   boidalis, 
  yet 
  it 
  appears 
  to 
  exceed 
  that 
  of 
  Protopterus 
  in 
  size 
  ; 
  

   internally 
  it 
  presents 
  a 
  longitudinal 
  ridge, 
  which 
  dwindles 
  

   away 
  posteriorly 
  ; 
  externally 
  the 
  position 
  of 
  this 
  ridge 
  is 
  indi- 
  

   cated 
  by 
  a 
  median 
  longitudinal 
  furrow 
  ; 
  posteriorly 
  it 
  termi- 
  

   nates 
  in 
  a 
  free 
  edge. 
  

  

  The 
  sinus 
  rhomboidalis 
  is 
  a 
  broad 
  shallow 
  trough 
  which 
  

   diminishes 
  posteriorly 
  rather 
  suddenly 
  ; 
  its 
  widest 
  part 
  is 
  just 
  

   behind 
  the 
  crura 
  cerebelli. 
  The 
  floor 
  is 
  flat, 
  and 
  in 
  the 
  central 
  

  

  * 
  L.c. 
  p. 
  20. 
  

  

  