﻿Cranial 
  Region 
  of 
  a 
  Permian 
  Reptile. 
  325 
  

  

  these 
  foramina 
  are 
  very 
  similar 
  in 
  position 
  to 
  the 
  same 
  ones 
  in 
  

   Sphcenodon. 
  

  

  The 
  cast 
  of 
  the 
  brain 
  cavity 
  shows 
  fairly 
  well 
  all 
  parts 
  pos- 
  

   terior 
  to 
  the 
  fifth 
  pair 
  of 
  nerves, 
  and 
  the 
  hypophysis 
  anterior 
  to 
  

   them. 
  As 
  is 
  well 
  known, 
  the 
  brain 
  in 
  the 
  reptilia 
  does 
  not 
  fill 
  

   the 
  brain 
  cavity 
  but 
  is 
  supported 
  by 
  a 
  mass 
  of 
  connective 
  tissue 
  

   carrying 
  lymph 
  and 
  fat 
  masses, 
  so 
  a 
  cast 
  of 
  the 
  brain 
  cavity 
  

   does 
  not 
  give 
  an 
  exact 
  copy 
  of 
  the 
  brain 
  ; 
  however 
  many 
  points 
  

   can 
  be 
  brought 
  out 
  by 
  such 
  a 
  cast. 
  

  

  If 
  the 
  cast 
  be 
  held 
  with 
  the 
  short 
  terminal 
  portion 
  of 
  the 
  

   medulla 
  horizontal, 
  the 
  lower 
  surface 
  pitches 
  downward 
  at 
  a 
  

   sharp 
  angle 
  to 
  a 
  point 
  anterior 
  to 
  the 
  tympanic 
  region 
  and 
  

   then 
  ascends 
  as 
  sharply 
  to 
  the 
  point 
  of 
  origin 
  of 
  the 
  hypo- 
  

   physis. 
  The 
  superior 
  surface 
  is 
  horizontal 
  and 
  arched 
  from 
  side 
  

   to 
  side 
  to 
  a 
  point 
  over 
  the 
  tympanic 
  cavity 
  and 
  there 
  turns 
  

   upward 
  at 
  an 
  angle 
  of 
  4:5°. 
  The 
  angle 
  thus 
  produced 
  is 
  

   marked 
  by 
  a 
  low, 
  narrow 
  ridge 
  running 
  across 
  the 
  cast 
  and 
  

   marking 
  the 
  position 
  on 
  the 
  brain 
  of 
  a 
  narrow 
  and 
  elevated 
  

   cerebellum, 
  figs. 
  1 
  and 
  4 
  Cb., 
  such 
  as 
  occurs 
  in 
  Sphcenodon. 
  

   This 
  region 
  was 
  probably 
  the 
  seat 
  of 
  a 
  large 
  amount 
  of 
  con- 
  

   nective 
  tissue 
  and 
  it 
  is 
  probable 
  that 
  the 
  upper 
  surface 
  of 
  the 
  

   medulla 
  descended 
  at 
  as 
  sharp 
  an 
  angle 
  as 
  the 
  lower. 
  This 
  

   would 
  make 
  still 
  more 
  marked 
  the 
  resemblance 
  to 
  Sphcenodon 
  

   and 
  to 
  the 
  cast 
  figured 
  by 
  Cope.* 
  This 
  sharp 
  bend 
  of 
  the 
  

   medulla 
  downward 
  is 
  not 
  found 
  in 
  other 
  forms, 
  though 
  in 
  the 
  

   brain 
  of 
  Chelonia 
  and 
  some 
  lacertilia 
  a 
  bend 
  is 
  apparent. 
  

  

  The 
  sides 
  of 
  the 
  medulla 
  show 
  most 
  posteriorly 
  the 
  begin- 
  

   ning 
  of 
  the 
  twelfth 
  nerves, 
  tigs. 
  1 
  and 
  4 
  (12), 
  anterior 
  to 
  these 
  

   the 
  cast 
  of 
  the 
  jugular 
  foramen, 
  figs. 
  1 
  and 
  4, 
  Ju., 
  and 
  finally 
  

   the 
  large 
  casts 
  of 
  the 
  tympanic 
  cavity, 
  figs. 
  1 
  and 
  4, 
  Ty. 
  The 
  

   nature 
  of 
  the 
  matrix 
  and 
  the 
  cavities 
  prevented 
  the 
  tympanic 
  

   cavities 
  being 
  cleaned 
  so 
  that 
  the 
  semicircular 
  canals 
  could 
  be 
  

   determined, 
  but 
  it 
  is 
  probable 
  that 
  they 
  were 
  very 
  similar 
  to 
  

   those 
  described 
  by 
  Cope. 
  

  

  Anterior 
  to 
  the 
  tympanic 
  casts 
  a 
  sharp 
  constriction 
  marks 
  

   the 
  ridge 
  defining 
  the 
  limits 
  of 
  the 
  tympanic 
  cavity 
  and 
  then 
  a 
  

   sharp 
  outswelling 
  the 
  point 
  of 
  exit 
  of 
  the 
  trigeminus 
  nerve, 
  

   figs. 
  1 
  and 
  4 
  (5). 
  Near 
  where 
  these 
  leave 
  the 
  body 
  of 
  the 
  cast 
  

   a 
  small 
  stub 
  on 
  each 
  side 
  marks 
  the 
  origin 
  of 
  the 
  seventh 
  pair, 
  

   figs. 
  1 
  and 
  4 
  (7). 
  

  

  The 
  hypophysis 
  is 
  the 
  most 
  interesting 
  feature 
  of 
  the 
  brain. 
  

   Descending 
  between 
  the 
  anterior 
  inferior 
  process 
  of 
  the 
  

   petrosal 
  and 
  turning 
  posteriorly, 
  it 
  occupies 
  a 
  small 
  notch 
  in 
  

   the 
  posterior 
  edge 
  of 
  the 
  upper 
  surface 
  of 
  the 
  basisphenoid 
  and 
  

   then 
  passes 
  directly 
  into 
  the 
  body 
  of 
  the 
  basioccipital 
  through 
  

   the 
  foramen 
  mentioned. 
  In 
  the 
  Crocodilia 
  a 
  somewhat 
  similar 
  

   condition 
  exists. 
  The 
  basisphenoid 
  is 
  excavated 
  for 
  a 
  con- 
  

  

  * 
  Baur 
  and 
  Case, 
  loc. 
  cit. 
  

  

  