MR.  R.  OWEN  ON  THE  ANATOMY  OF  THE  CONCAVE  HORNBILL.  119 
close  together  at  the  end  of  the  fold  between  the  insertions  of  the  hepatic  ducts.  On 
referring  to  the  table  of  the  insertions  of  these  ducts  in  Cuvier's  '  Anatomic  Com- 
paree'^  the  arrangement  in  the  Hornhill  will  be  found  to  correspond  with  that  in  the 
Heron  there  given,  and  may  be  expressed  thus :  1  st  p.  —  H.  —  2nd  and  3rd  p.  —  C.  H. 
The  spleen  is  situated  at  the  right  side  of  the  upper  end  of  the  gizzard. 
The  trachea  has  a  single  pair  of  muscles. 
The  heart  and  kidneys  present  the  usual  peculiarities  of  the  class. 
The  ureters  emerge  from  the  inner  side  of  the  lower  end  of  the  third  lobe.  Where 
they  emerge,  a  large  vein  from  the  tail  enters  a  deep  groove,  which  continues  along  the 
inner  sides  of  each  lobe,  receiving  the  renal  veins  by  large  orifices.  A  vein  from  the 
posterior  extremity  enters  the  third  lobe  on  its  outer  aspect,  and  ramifies  in  the  gland. 
This  I  conclude  to  be  the  vein  from  which,  as  Jacobson  has  shown,  the  urine  is  in  part 
secreted. 
The  supra-renal  glands,  of  the  usual  bright  yellow  colour,  are  closely  attached  to  the 
coats  of  the  inferior  vena  cava.  The  testes  are  situated  anterior  to  the  above  glands, 
and  were  of  minute  size,  not  exceeding  that  of  a  grain  of  rice. 
On  laying  open  the  cloaca  anteriorly,  the  division  into  which  the  ureters  open,  or 
rudimentary  bladder,  is  seen  to  be  formed  by  two  transverse  semilunar  folds  about  a 
line  in  breadth,  and  gradually  lost  on  the  anterior  part  of  the  rectum.  The  space 
between  these  ridges  is  little  more  than  a  line.  The  bursa  Fahricii  (which  I  regard  as 
analogous  to  the  anal  glandular  scent  organs  of  the  Mammalia,)  opens  into  the  back  part 
of  the  outer  vestibule.  It  is  of  a  triangular  form,  two  thirds  of  an  inch  in  length,  and 
is  surrounded  by  a  capsule  of  muscular  fibres.  The  common  vestibule  is  half  an  inch 
in  length  ;  and  closed  as  usual  by  a  strong  sphincter. 
The  mechanism  by  which  the  movements  of  the  immense  mandibles  of  this  singular 
bird  are  effected,  was  next  examined.  The  os  quadratum  and  the  other  bones  forming 
the  articulation  of  the  jaws,  are  accvirately  described  by  Cuvier^.  The  digastricus,  or 
its  analogue,  which  in  Birds  has  no  middle  tendon,  arises  from  the  whole  occipital  de- 
pression, and  descends  vertically  to  be  inserted  into  the  angle  of  the  lower  jaw,  which 
projects  posteriorly  to  the  articulation.  We  occasionally  find  a  similar  simple  dispo- 
sition in  the  Mammalia,  even  in  the  Orang  Utan. 
The  temporal  muscle  does  not  exceed  half  an  inch  in  breadth ;  it  arises  from  the 
temporal  fossa,  passes  within  the  zygoma,  and  is  inserted  into  the  slightly  developed 
coronoid  process  immediately  anterior  to  the  articulation.  The  pterygoidei  externi  and 
interni  are  proportionately  more  developed  than  the  temporalis :  they  assist  that  muscle 
in  closing  the  bill,  whilst  they  draw  the  inferior  mandible  forwards,  and  perform  the 
lateral  motions  :  these  and  the  muscles  of  the  os  quadratum  have  the  usual  attach- 
ments. A  strong  ligament  occupies  the  place  of  the  masseter ;  it  passes  from  the 
zygoma  to  the  outer  side  of  the  condyle  of  the  lower  jaw,  immediately  in  front  of  the 
*  Tom.  iv.  p.  55.  -  Anat.  Comp.,  torn.  iii.  pp.  63,  64. 
