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MR.  R.  OWEN  ON  THE  OSTEOLOGY  OF 
and  Chimpanzee.  In  the  latter  animal  this  obliteration  takes  place  at  a  very  early  pe- 
riod, some  time  at  least  before  the  temporary  teeth  are  shed ;  whilst  in  the  Orang  the 
sutures  remain  until  the  permanent  teeth  are  almost  fully  developed.  In  the  human 
subject  the  inter-maxillary  bones  can  be  traced  as  distinct  elements  of  the  jaw  only  at 
the  early  periods  of  foetal  existence. 
The  OS  nasi  of  the  Orang  is  a  flattened  elongated  triangular  bone,  no  part  of  which 
projects,  as  in  the  Chimpanzee,  beyond  the  plane  of  the  nasal  processes  of  the  superior 
maxillary  bones ;  there  are  no  traces  of  its  being  originally  separated  at  the  me- 
sial line,  while  such  are  usually  observable  in  the  Chimpanzee.  Dr.  Traill,  indeed, 
found  two  distinct  nasal  bones  in  the  young  animal  of  that  species  dissected  by  him ' . 
In  the  Orang  a  strong  spine  or  ridge  extends  from  the  posterior  aspect  of  the  os  nasi 
down  the  middle  Une. 
The  whole  outer  boundary  of  the  orbit  has  a  more  anterior  aspect  than  in  the  Chim- 
panzee :  it  is  relatively  broader  and  stronger,  but  has  the  oblique  posterior  ridge  less 
developed.  The  interorbital  space  is  relatively  narrower ;  and  this  difference  between 
the  Orang  and  Chimpanzee  is  naturally  greater  in  the  young  state,  before  the  upper 
maxillary  bones  have  acquired  their  full  development^.  In  this  particular,  again,  the 
Orang  recedes  further  from  the  human  form. 
The  lachrymal  bones  are  proportionally  larger  in  the  Orang  than  in  Man ;  but,  as 
'  Weraerian  Transactions,  vol.  iii.  p.  12. 
-  With  respect  to  the  difference  in  the  proportions  of  the  orbits  in  the  young  Orang  and  the  Pongo,  the  same 
argument  to  prove  a  difference  of  species  might  be  drawn  from  a  comparison  of  the  orbits  of  a  child's  skuU  of  four 
years,  and  those  of  an  adult  human  subject,  which  do  not  differ  more  than  2  lines,  and  in  some  instances  not 
more  than  1,  in  either  the  transverse  or  vertical  diameter;  and  a  similar  proportional  magnitude  of  the  orbits 
prevails  in  the  young  of  most  Mammalia.  The  ingenious  observation,  however,  made  by  Dr.  Harwood  (Lin- 
nean  Transactions,  vol.  xv.  p.  478.)  on  the  difference  in  the  breadth  of  the  interorbital  space,  would  be  appa- 
rently borne  out  by  contrasting  some  skulls  of  the  young  and  adult  Orangs,  since  it  is  not  always  the  same  in 
animals  of  the  same  age  :  but  I  apprehend  that  the  difference  between  the  young  and  adults  in  this  respect  may 
be  accounted  for  by  the  increase  of  size  which  the  nasal  processes  and  every  other  part  of  the  superior  maxil- 
lary bones  undergo  after  the  development  of  the  great  laniarii,  it  being  remembered  that  the  cavities  of  the 
orbits  do  not  increase  in  the  same  ratio.  Having  had  the  opportunity  of  comparing  six  crania  of  the  young 
Orang  with  two  of  the  Pongo,  I  find  the  interorbital  space  of  2^-  lines  to  be  the  minimum  in  the  former,  and 
that  of  half  the  breadth  of  the  orbit  to  be  the  maximum  in  the  latter,  among  the  individual  varieties. 
Young  Orang.  Pongo. 
in.  lines.  in.  lines. 
Breadth  of  the  face  taken  at  the  fronto -malar  sutures    ...    2    10  46 
Breadth  of  the  orbit  11  16 
Interorbital  space  taken  across  the  fronto-maxillary  suture     .  3  74- 
To  determine  the  degree  of  difference  which  existed  in  the  planes  of  the  orbits  of  the  young  Orang  and  Pongo, 
I  drew  a  line  from  the  anterior  part  of  the  auditory  foramen  through  the  part  where  the  sagittal  joins  the  co- 
ronal suture,  and  intersected  it  by  another  drawn  from  the  lower  part  of  the  orbit  across  its  plane.  In  this 
way  a  difference  in  the  plane  of  the  orbit  is  found  to  manifest  itself  in  the  skulls  of  specimens  of  the  immature 
Simia  Satyrus  of  different  ages  and  of  acknowledged  identity  of  species,  the  angle  becoming  more  open  in  the 
older  specimens ;  whilst  in  the  great  Pongo  the  difference  in  the  angle  is  not  more  than  four  degrees. 
