THE  ORNITHORHYNCHUS  PARADOXUS. 
223 
Smaller  Orni- 
thorhynchus. 
Breadth  of  the  lower  mandible  at  the  base 
Length  of  the  tail  from  the  vent  . 
Breadth  of  the  tail  at  the  root  .... 
Larger  Orni- 
thorhynchus. 
Lines. 
Lines. 
3 
5 
4i 
10 
4 
8 
3 
5 
3i 
5 
4 
3 
5 
6 
u 
U 
2 
1 
■i 
Length  of  the  fore  foot  
Breadth  of  the  fore  foot  
Length  of  the  hind  foot  
Breadth  of  the  hind  foot  
Distance  between  the  eyes  
Distance  between  the  nostrils  
From  the  exterior  nostrils  to  the  end  of  the  mandible 
From  the  tip  of  the  tongue  to  the  end  of  the  lower  mandible 
The  circumstances  which  first  attract  attention  in  these  singular  objects  are,  the 
total  absence  of  hair',  the  soft  flexible  condition  of  the  mandibles,  and  the  shortness  of 
these  parts  in  proportion  to  their  breadth  as  compared  with  those  of  the  adult. 
The  integument  with  which  the  mandibles  are  covered  is  thinner  than  that  which 
covers  the  rest  of  the  body,  and  smoother,  presenting  under  the  lens  a  minutely  granu- 
lated surface  when  the  cuticle  is  removed,  which  however  is  extremely  thin,  and  has 
none  of  the  horny  character  which  the  claws  at  tbis  period  present.  The  margins  of  the 
upper  beak  are  rounded,  smooth,  thick,  and  fleshy  :  the  whole  of  the  under  mandible  is 
flexible,  and  bends  down  upon  the  neck  when  the  mouth  is  attempted  to  be  opened. 
The  tongue,  which  in  the  adult  is  lodged  far  back  in  the  mouth,  advances  in  the  young 
animal  close  to  the  end  of  the  lower  mandible  ;  all  the  increase  of  the  jaws  beyond  the 
tip  of  the  tongue,  which  in  the  adult  gives  rise  to  a  form  of  the  mouth  so  ill  calculated 
for  suction  or  application  to  a  flattened  surface,  is  peculiar  to  that  period,  and  conse- 
quently forms  no  argument  against  the  fitness  of  the  animal  to  receive  the  mammary 
secretion  at  an  earlier  stage  of  existence.  The  breadth  of  the  tongue  in  the  larger  of 
the  young  specimens  was  34-  lines ;  in  the  adult  it  is  only  one  line  broader ;  and  this 
disproportionate  development  is  plainly  indicative  of  the  importance  of  the  organ  to  the 
young  animal,  both  in  receiving  and  sw^allowing  its  food.  The  mandibles  are  surrounded 
at  their  base  by  a  thin  fold  of  integument,  which  extends  the  angle  of  the  mouth  from 
the  base  of  the  lower  jaw  to  equal  the  breadth  of  the  base  of  the  upper  one,  and  must 
increase  the  facility  for  receiving  the  milk  ejected  from  the  mammary  areola  of  the 
mother.  The  oblique  lines  which  characterize  the  sides  of  the  lower  mandible  in  the 
adult,  running  from  within  outwards  and  forwards,  were  faintl}^  visible  on  the  corre- 
sponding parts  of  the  same  jaw  of  the  young  animal :  a  minute  ridge  at  the  inner  sides 
of  these  lines  indicates  the  situations  of  the  anterior  horny  teeth  of  the  adult. 
'  This  is  not  accidental,  as  in  many  of  the  adult  specimens  sent  over  in  spirit,  for  the  cuticle  is  entire.  In 
the  specimens  which  Mr.  G.  Bennett  discovered,  the  skin  had  a  slight  downy  appearance. 
