THE  CHIMPANZEE  AND  ORANG  UTAN. 
361 
of  the  Hare,  viz.  one  behind  the  other,  with  the  chance  of  being  dislodged,  together 
with  the  contiguous  bicuspis,  by  the  great  laniary  tooth,  which  threatens  to  undermine 
and  sap  their  attachment  to  the  jaw.  But  such  is  the  orderly  action  impressed  upon 
the  agents  of  growth,  that  all  obstacles  are  removed,  and  the  necessary  expansion  of 
the  jaws  takes  place  in  due  succession  in  all  the  requisite  directions,  and  perfect  regu- 
larity in  the  ultimate  position  of  the  adult  teeth  is  the  result.  It  may,  then,  be  reason- 
ably asked,  How  does  it  happen  that  in  Man,  in  whom  the  difference  in  the  size  of  the 
deciduous  and  adult  teeth  is  comparatively  so  inconsiderable,  and  where,  therefore,  the 
chances  of  disarrangement  are  so  much  fewer,  malposition  of  the  permanent  teeth  should 
be  so  frequent  an  occurrence,  and  an  object  of  such  common  solicitude  among  parents? 
The  answer  obviously  is,  that  in  most  cases  it  arises  from  a  mischievous  interference 
with  the  agents  to  which  the  necessary  changes  have  been  entrusted.  The  means  by 
which  the  growth  of  the  permanent  teeth  is  kept  in  due  restraint  are  too  often  prema- 
turely removed  by  anticipating  the  natural  period  of  shedding  the  temporary  teeth. 
The  act  of  extraction  accelerates  the  growth  of  the  concealed  teeth,  both  by  the  removal 
of  the  check  which  nature  had  imposed  upon  it,  and  by  the  irritation  induced  in  the 
surrounding  parts  ;  and  their  full  development  being  consequently  acquired  before  the 
jaws  have  been  sufficiently  enlarged,  they  occupy  more  or  less  of  the  relative  position 
which  they  had  when  half  formed  within  their  bony  cavities. 
In  the  drawings  of  the  Pongo's  skull  (Plates  LIII.  and  LIV.),  figures  of  the  rudiments 
of  the  permanent  teeth  taken  from  the  jaws  of  a  young  Simia  Satyrus  are  added,  so  that 
a  detailed  account  of  their  points  of  correspondence  is  here  unnecessary.  It  will  be  ob- 
vious that  the  difference  that  exists  depends  on  the  proportions  of  the  teeth  which  have 
been  worn  away  in  the  adult  skull. 
The  only  instance  which  I  have  found  recorded  of  a  Simia  Satyrus  having  been  ob- 
served of  that  age  when  part  of  the  anterior  permanent  teeth  had  been  acquired,  is  in  the 
account  given  by  Dr.  Jeffries  of  the  dissection  of  an  Orang,  which  measured  3  feet  and 
6  inches  in  height  ^  The  permanent  incisors  had  advanced  to  their  proper  place,  and 
the  middle  ones  of  the  upper  jaw  are  stated  to  have  measured  Iths  of  an  inch  in  length 
and  4 ths  in  breadth  ;  now  the  same  teeth  in  the  Pongo  precisely  correspond  in  the  latter 
dimensions,  and  their  excess  in  regard  to  length  obviously  results  from  the  completion 
of  the  fang.  , 
The  OS  hyoides  has  a  broader  body  and  shorter  cornua  than  in  the  human  subject, 
but  the  body  is  not  hollowed  out  as  in  the  Chimpanzee. 
I  have  already  alluded  to  the  simple  form  and  great  length  of  the  spines  of  the  cer- 
vical vertebr(B  in  the  Orang.  The  conditions  of  their  superior  development  are  obvi- 
ously the  backward  position  of  the  occipital /oramen,  the  disproportionate  development 
of  the  face,  and  the  general  anterior  inclination  of  the  vertehrcB  themselves.    The  atlas 
'  See  Webster  and  Treadwell's  Boston  Journal  of  Philosophy,  vol.  ii.  p.  570 ;  and  Philosophical  Magazine, 
vol.  Ixvii.  p.  186,  1826. 
