MR.  E.  T.  BENNETT  ON  THE  CHINCHILLID^. 
53 
to  the  intestines  of  the  latter  than  either  Mr.  Yarrell  or  myself :  it  is  probable  that  he 
took  more  pains  in  loosening  them  from  the  loops  of  peritoneum,  for  his  accuracy  of 
observation  is  beyond  question.  He  describes  the  small  intestines  as  measuring  four 
feet  six  inches,  and  the  large  seven  feet  six  inches,  in  length.  On  each  side  of  the 
ileo-caecal  valve,  internally,  he  notices  an  oval  patch  of  glandula  aggregate,  about  two- 
thirds  of  an  inch  in  the  long  diameter.  The  cacum,  he  observes,  is  drawn  up  into 
sacculi  by  two  longitudinal  bands :  these  sacculi  being  directed  alternately  from  right 
to  left,  and  vice  versa,  give  it  at  first  the  appearance  of  being  spirally  twisted,  but  on 
cutting  across  the  longitudinal  bands  the  sacculi  fall  down  and  the  spiral  character  is 
lost.  Connected  with  the  extreme  portion  of  the  colon,  he  states  that  there  is  a  lacteal 
gland  of  large  size,  with  numerous  lacteals  evidently  converging  towards  it ;  a  circum- 
stance which^  if  further  evidence  were  wanting,  proves,  he  remarks,  the  share  taken  by 
the  large  intestines  in  the  process  of  chylification.  The  trachea  was  composed  of 
twenty-three  imperfect  rings  ;  the  larynx  formed  two  shallow  sacculi ;  and  the  epiglottis 
was  small,  with  a  truncated  apex.  Mr.  Owen  adds,  that  Meckel's  muscle  was  furnished, 
in  its  tendinous  part,  with  a  sesamoid  cartilage. 
In  the  general  character  of  the  skeletons  of  the  two  animals  there  exists  a  remark- 
able conformity ;  which  admits,  however,  of  very  striking  modifications,  and  particu- 
larly in  the  form  of  the  cranium.  The  occipital  ridge  is  scarcely  at  all  visible  in  Chin- 
chilla, but  is  strongly  marked  and  prominent  in  Lagotis ;  the  posterior  boundary  of  the 
skull  is  consequently  transversely  truncate,  or  even  retusely  concave  in  the  former, 
while  in  the  latter  it  forms  the  convex  segment  of  a  circle.  In  Chinchilla  the  upper 
surface  of  the  whole  skull  is  remarkably  flattened,  and  may  be  subdivided  into  three 
regularly  graduated  regions,  the  posterior  of  which,  bounded  anteriorly  by  the  coronal 
suture,  is  nearly  square  in  its  outline  ;  the  middle  or  inter-orbital,  formed  wholly  by 
the  frontal  bones,  is  a  much  narrower  parallelogram,  with  the  sides  somewhat  exca- 
vated ;  and  the  anterior,  curved  a  little  downw^ards  and  forwards,  and  formed  by  the 
intermaxillary  and  nasal  bones,  is  still  narrower  and  more  linear.  In  Lagotis  the 
posterior  part  of  the  frontal  and  parietal  bones  is  strongly  arched,  and  the  narrowing 
of  the  skull  forwards  is  more  gradual,  the  inter-orbital  region  being  much  broader  in 
proportion  :  there  is  a  deep  depression  between  the  fore  part  of  the  orbits,  contrasting 
strongly  with  the  posterior  arching  of  the  cranium  ;  and  the  narrow  and  perfectly  linear 
projection,  formed  by  the  nasal  and  intermaxillary  bones,  is  nearly  horizontal,  having 
only  a  slight  elevation  near  its  middle  and  no  downward  curvature.  The  greater 
breadth  of  the  inter-orbital  portion  is  principally  owing  to  the  spreading  out  of  the 
margins  of  the  orbit,  which  also  adds  to  the  expanse  of  the  zygomatic  arch.  In  both 
animals  the  infra- orbital /oramen  on  each  side  is  of  great  magnitude,  its  vertical  diameter 
equalling  two  thirds  of  that  of  the  orbit. 
But  perhaps  the  most  striking  feature  in  the  skull  of  the  Chinchilla  is  the  extra- 
ordinary development  of  the  tympanic  cells,  which  occupy  more  than  half  of  the 
