OF  THE  THREE-TOED  SLOTH. 
115 
est  oblique,  se  baissant  un  peu  en  avant,  et  y  rentrant  un  peu  en  dedans.  La  huitieme 
a  la  sienne  un  peu  fourchue.  La  neuvieme  I'a  prolongee  en  une  petite  pointe  qui  se 
porte  en  avant  et  en  dehors,  Dans  le  jeune  individu  cette  partie  n'est  pas  soudee  a  la 
vertebre  ;  seroit-ce  un  petit  vestige  de  cote?"^ 
In  the  second  edition  of  the  '  Regne  Animal'  occurs  the  following  observation, 
showing  what  were  the  latest  views  of  Cuvier  on  this  subject.  "  C'est  le  seul  mam- 
mif^re  connu  jusqu'a  ce  jour  qui  ait  neuf  vertebres  cervicales."^ 
The  nearest  approach  which  has  hitherto  been  made  to  the  true  bearing  of  the  fact, 
is  contained  in  the  following  passage  from  Meckel.  Speaking  of  the  points  of  ossifi- 
cation or  nuclei  in  the  cervical  vertebra,  he  says,  "  In  the  last  are  found  a  fourth  and  a 
fifth  [nucleus],  constituting,  as  it  were,  rudiments  of  ribs,  projecting  from  the  sides.  In 
Man  this  elongated  bone  forms  the  anterior  root  of  the  transverse  process,  and  extends 
from  the  body  to  the  posterior  root  of  that  process.  In  the  A'i  a  very  considerable  bony 
nucleus  is  articulated  by  means  of  a  broad  cartilage  to  the  end  of  the  transverse  process 
of  the  ninth  cervical  vertebra  ;  by  means  of  which  .this  vertebra  becomes  suddenly  much 
broader  than  the  rest.  In  the  other  Mammalia  which  I  have  examined,  this  bony  nu- 
cleus is  wanting.  It  is  remarkable  that  in  the  Ai  an  analogous  but  much  smaller  bony 
nucleus  is  found  attached  to  the  same  situation  in  the  eighth  cervical  vertebra ;  so  far  as 
this  goes,  these  two  vertebra  become  similar  to  dorsal,  and  thereby  the  exception  which 
the  Ai  makes  in  this  particular  to  other  Mammalia  is  lessened."^ 
From  this  passage  it  is  evident  that  Meckel  still  considered  the  two  vertebra  in 
question  to  be  truly  cervical,  though  approaching  to  the  character  *of  dorsal  vertebra. 
The  fact,  however,  that  the  rudimentary  ribs  remain  permanently  moveable,  of  which  it 
would  appear  that  both  Cuvier  and  Meckel  were  ignorant,  at  once  proves  that  these 
vertebra  are  not  only  approaching  to  the  dorsal  form,  but  are  essentially  dorsal,  if  it  be 
a  true  character  of  a  rib,  as  distinguished  from  a  transverse  process,  that  it  is  perma- 
nently moveable.  This  is  a  question  certainly  of  considerable  interest,  but  one  into 
which  it  is  not  necessary  on  the  present  occasion  to  enter,  as  the  fact  of  the  permanent 
mobility  of  the  rudimentary  ribs  in  the  A'i,  the  perfect  construction  of  the  capsular 
ligament,  and  the  cartilaginous  surfaces  of  the  joint  are  sufficient,  joined  with  the  ex- 
istence of  a  foramen  for  the  passage  of  vessels  and  other  circumstances  in  their  struc- 
ture and  situation,  to  establish  their  character  beyond  all  doubt.  The  rule  therefore 
which  assigns  seven  cervical  vertebra  to  the  whole  of  the  Mammalia,  is  thus  left  with- 
out a  single  exception. 
The  interesting  paper  of  Professor  Buckland  on  the  habits  of  the  Sloth,  lately  read  at 
the  Linnean  Society,  precludes  the  necessity  of  my  entering  into  any  lengthened  specu- 
lations on  the  utility  of  this  singular  structure  ;  I  may,  however,  remark,  that  the  fact 
'  Ossemens  Foss.,  torn.  v.  p.  83. 
3  Syst.  der  Vergleich.  Anat.,  B.  ii.  pi.  2.  p.  294. 
VOL.  I.  R 
e  RhgUQ  Anim.,  (ed.  2.)  torn.  i.  p.  252. 
