THE  ORNITHORHYNCHUS  PARADOXUS. 
231 
great  expansion.  The  claws  on  the  fore  feet  are  strong,  blunt,  and  well  calculated  for 
burrowing ;  and  the  two  lateral  are  shorter  than  the  three  middle  ones.  The  hind  feet 
are  short,  narrow,  turned  backwards,  and  when  the  animal  is  at  rest  have,  like  those 
of  the  Seal,  some  resemblance  to  a  fin  ;  their  action  is  backwards  and  outwards.  The 
first  toe  is  very  short,  and  the  nails  of  all  are  curved  backwards,  and  are  longer  and 
sharper  than  those  of  the  fore  feet ;  the  web  does  not  extend  further  than  the  roots  of 
the  claws.  The  spur  of  the  male  is  moveable,  and  is  turned  backwards  and  inwards  :  it 
is  situated  some  distance  above  the  claws,  and  rather  towards  the  internal  part  of  the  leg. 
The  head  is  rather  flat ;  and  from  the  mouth  project  two  flat  lips  or  mandibles,  re- 
sembling the  beak  of  a  Shoveller  Duck,  the  lower  of  which  is  shorter  and  narrower 
than  the  upper,  and  has  its  internal  edges  channelled  with  numerous  strits,  resembling 
in  some  degree  those  seen  in  the  bill  of  a  Duck.  The  central  portion  of  the  mandibles 
is  a  bony  continuation  from  the  skull,  and  anteriorly  and  laterally  a  cartilaginous 
substance,  perfectly  moveable,  extends  from  the  bony  portion  to  the  distance  of  ^ths 
of  an  inch.  The  colour  of  the  superior  mandible  above,  when  seen  in  an  animal 
recently  taken  out  of  the  water,  is  of  a  dull  dirty  greyish  black,  covered  with  innu- 
merable minute  dots  ;  while  the  cartilaginous  expansion  around  the  mandible  is  uni- 
formly smooth  and  soft.  The  under  part  of  the  upper  mandible  is  of  a  pale  pink  or 
flesh  colour,  as  well  as  the  internal  or  upper  surface  of  the  lower  mandible,  the  under 
surface  of  which  is  either  perfectly  white  or  mottled  :  in  younger  specimens  it  is  usually 
white,  while  in  the  older  it  assumes  a  mottled  appearance. 
At  the  base  of  both  the  lower  and  upper  mandibles  is  a  transverse  loose  fold  or  flap 
of  the  integument,  always  similar  in  colour  to  the  skin  covering  the  mandibles,  that 
is  to  say,  of  a  dull  dirty  greyish  black  in  the  upper,  and  white  or  mottled  in  the  lower. 
In  the  upper  mandible  this  is  continued  very  nearly  to  the  eyes,  and  may  perhaps  afford 
some  protection  to  those  organs  when  the  animal  is  engaged  in  burrowing  or  seeking 
its  food  in  the  mud.  The  upper  fold  or  flap  is  continuous  with  another  portion  arising 
from  the  lower  mandible  also  at  its  base.  Sir  Everard  Home^  considers  the  apparent 
use  of  these  folds  to  be  to  prevent  the  beak  from  being  pushed  into  the  soft  mud  beyond 
this  part,  which  is  so  broad  as  completely  to  stop  its  further  progress.  From  careful 
observation  of  the  actions  of  living  specimens  I  can,  however,  assign  no  other  use  to 
this  part  than  that  which  I  have  just  mentioned.  In  dried  specimens  the  colour  and 
form  of  the  beak  are  almost  entirely  lost. 
The  eyes  are  very  small,  but  brilliant,  and  of  a  light  brown  colour  :  they  are  situated 
rather  high  up  the  head.  The  external  orifice  of  the  ears  is  situated  near  the  upper 
part  of  the  external  angle  of  the  eye.  When  a  hving  specimen  is  examined  the 
orifice  2  is  easily  discoverable,  as  the  animal  has  the  faculty  of  closing  or  opening  it  at 
•  Observations  on  the  Head  of  the  Ornithorhynchus  paradoxus,  in  the  '  Philosophical  Transactions'  for  1800. 
*  I  could  not  perceive  any  valve  corresponding  to  that  -which  is  usually  possessed  by  animals  that  frequent 
the  water,  but  believe  that  the  muscular  contraction  of  the  orifice  answers  the  same  purpose. 
