[    117  ] 
XIII.  On  the  Anatomy  of  the  concave  Hornbill,  Buceros  cavatus,  Lath.  By  Richard 
Owen,  Esq.,  F.Z.S.,  Assistant  Conservator  of  the  Museum  of  the  Royal  College  of 
Surgeons  in  London. 
Communicated  August  27,  1833. 
The  bird  on  which  the  following  observations  were  made  had  been  exhibited  at  the 
Society's  Gardens  for  about  eight  weeks,  and  died  on  the  15th  of  August  last.  It  had 
attained  nearly  its  full  size,  but  had  neither  the  plumage  nor  the  configuration  of  the 
bill  which  characterize  the  adult ;  the  large  quill-feathers  of  the  wing  and  tail  were  in 
progress  of  development,  while  the  warm  and  downy  covering  which  defends  the  young 
bird  had  been  in  great  measure  lost  by  moulting  :  its  death  may  therefore  be  attributed 
to  the  exhaustion  consequent  on  the  unfavourable  circumstances,  as  to  climate  and 
captivity,  in  which  it  was  placed,  while  undergoing  a  process  so  extensive  and  im- 
portant in  its  economy  as  the  acquisition  of  the  adult  plumage. 
It  measured  from  the  end  of  the  bill  to  the  vent  2  feet  2  inches ;  the  length  of  the 
bill  was  7  inches. 
On  the  mandibles  being  separated  the  tongue  is  seen  at  the  back  part  of  the  mouth  ; 
its  tip  being  6  inches  distant  from  the  extremity  of  the  jaws.  It  is  of  a  triangular 
form,  with  the  posterior  angles  produced  backwards  on  either  side  of  the  laryngeal 
aperture ;  measuring  in  length  1  inch,  and  in  breadth  at  the  base  8  lines.  Its  apex 
and  surface  are  smooth.  In  texture,  in  configuration  and  in  size,  it  consequently 
differs  considerably  from  that  of  the  Toucan,  in  which  bird  the  tongue  can  be  pro- 
truded from  the  mouth,  and  from  its  peculiar  structure  is  evidently  adapted  for  more 
extensive  and  varied  actions  than  in  the  Hornbill. 
The  air-cells  are  remarkably  developed  in  the  Hornbill.  They  may  be  observed  ex- 
tending along  the  under  side  to  the  extreme  point  of  the  bones  of  the  wings.  Tlie  en- 
tire neck  is  occupied  by  a  large  cell,  in  which  the  wsophagus  and  trachea  are  contained. 
The  air-tube  is  connected  throughout  its  whole  length  with  the  cesophagus  by  a  dupli- 
cature  of  the  membrane  of  the  air-cell,  resembling  a  mesentery.  This  duplicature 
varies  in  breadth  from  1  to  2  inches,  allowing  a  free  motion  of  the  trachea  from  side  to 
side.  The  nervi  vagi,  the  cervical  arteries  and  veins,  and  the  cesophagus,  are  as  clearly 
exposed  by  the  simple  opening  of  this  air-cell,  as  if  they  had  been  displayed  by  an  ela- 
borate dissection.  At  the  upper  part  of  the  neck  the  cervical  air-cell  communicates 
with  others,  partly  surrounding  the  joint  of  the  lower  jaw  and  continued  into  the  in- 
terior of  that  bone,  and  extending  also  to  the  back  of  the  occiput  to  communicate 
with  the  cranium  and  cellular  structure  of  the  superior  mandible. 
R  2 
