122        MR.  R.  OWEN  ON  THE  ANATOMY  OF  THE  CONCAVE  HORNBILL. 
the  beak,  both  from  its  form  and  size,  and  from  the  disposition  of  the  articular  liga- 
ments, to  be  more  especially  destined  to  overcome  the  resistance  offered  to  its  progress 
in  the  last-mentioned  action,  which  the  Hornbills  must  often  be  stimulated  to  practise, 
both  to  reach  fruit,  and,  like  the  Toucans  of  South  America,  to  get  at  the  eggs  and 
callow  young  of  other  birds  :  and  it  is  highly  probable  that  these  singular  genera  per- 
form in  the  continents  which  they  inhabit  the  same  office  of  restraining  the  increase 
of  the  smaller  frugivorous  birds,  which  the  Jays  and  Pies  do  in  more  temperate  climes, 
but  in  a  manner  more  effectual,  inasmuch  as  they  are  better  provided  with  the  means  of 
penetrating  to  the  retreats  and  hiding-places  selected  for  the  purposes  of  nidification. 
PLATE  XVIII. 
Fig.  1.  Posterior  view  of  the  biliary  and  pancreatic  organs  of  the  concave  Hornbill. 
a.  oesophagus ;  b.  proventriculus ;  c.  gizzard ;  d.  d.  duodenal  fold ;  e.  left,  e.  right,  lobe 
of  the  liver ;  /.  gall-bladder ;  g.  right  hepatic  duct ;  h.  termination  of  the  cystic  duct  ; 
i.  cyst-hepatic  duct ;  h.  left  hepatic  duct ;  I.  I.  pancreas ;  m.  m.  m.  pancreatic  ducts ; 
n.  spleen,  drawn  aside. 
Fig.  2.  Gastric  glands,    a.  a  section  of  one,  magnified. 
Fig.  3.  a.  fold  at  the  termination  of  the  rectum ;  b.  rudimentary  urinary  bladder ; 
c.  vestibule ;  d.  orifice  of  the  bursa  Fabricii. 
Fig.  4.  Posterior  view  of  the  cloaca  ;  a.  bursa  Fabricii. 
Fig.  5.  Outline  of  the  cranium  (young),  two  thirds  of  the  natural  size.  a.  the  tem- 
poral muscle  which  closes  the  bill ;  b.  the  analogue  of  the  digastricus  of  Mammalia 
"which  opens  the  bill ;  c.  a  ligament  which  assists  in  supporting  the  lower  mandible  ; 
d.  a  ligament  which  prevents  dislocation  backwards. 
