262 
PEOFESSOE  OWEX  ON  THE  J^IEGATHEEIl:NI. 
surface,  the  lower  spine  itself  appearing,  at  e,  to  form  the  inferior  costa  for  the  rest  of 
its  course  to  the  glenoid  cavity  [g). 
The  normal  spine  of  the  scapula,  notwithstanding  its  being  the  superior  of  the  two, 
commences  at  only  one-fourth  of  the  entire  base  of  the  bone  from  the  inferior  angle ; it 
is  thence  continued  forwards,  gradually  rising  or  gaining  depth,  parallel  with  the  inferior 
costa,  and  thus  marks  out  a very  large  proportional  extent  of  the  outer  surface  of  the  bone 
for  the  supraspinal  fossa  (Plate  XVIII.  51).  As  the  spine  advances,  it  increases  in  breadth 
as  well  as  depth,  until  it  springs  clear  of  the  main  body  of  the  bone  as  the  acromial 
process,  k.  This  large,  thick  and  rough  process  (Plate  XIX.  fig.  2,  k)  arches  forward 
and  upward  over  the  glenoid  articular  cavity  (^),  and  meets  and  coalesces  with  the 
coracoid  (c),  spanning  the  anterior  outlet  [f)  of  the  supraspinal  fossa  by  a strong  and 
broad  bridge  of  bone.  Through  the  reciprocal  modification  of  the  coracoid,  the  passage 
for  certain  vessels  and  nerves,  which  is  usually  in  Mammals  a mere  notch  of  the  upper 
border  of  the  scapula,  is  converted  into  a complete  foramen  (Plate  XIX.  fig.  I,  h).  The 
second  spine,  which  answers  to  the  ridge  defining  the  upper  part  of  the  fossa  for  the 
‘ teres  major  ’ muscle  in  Man,  runs  parallel  with  the  upper  spine,  and  then  bends  down  to 
terminate  in  the  low  angle  {ih.  fig.  1,  e),  projecting  from  the  inferior  costa  of  the  scapula, 
about  one-third  of  the  length  of  that  border  from  the  glenoid  cavity  (g).  The  shape  of 
that  cavity  is  almost  an  ellipse  (Plate  XIX.  fig.  2,  g),  the  lower  end  being  scarcely  more 
contracted  than  the  upper  one : both  these  parts  of  the  periphery  are  rather  more  pro- 
duced than  the  lateral  borders.  The  entire  margin  of  this  moderately  deep  and  well- 
defined  articular  cavity  is  thin,  but  convex.  The  inner  surface  of  the  scapula  (Plate  XIX. 
fig.  I)  is  divided  into  many  shallow  depressions  by  intermuscular  ridges  (/,?),  ha^ing  a 
general  tendency  to  converge  from  the  basal  border,  where  most  begm,  towai'ds  the 
centre  of  the  bone,  though  none  extend  so  far.  The  inferior  costa  (d)  is  continued 
more  directly  towards  the  inner  side  of  the  glenoid  ca\ity  by  a smooth,  convex  rising  of 
the  inner  surface,  which  grows  broader  as  it  gradually  subsides : the  fore-pail  of  the 
lower  costa  (fig.  I,  e)  is  rather  a continuation  of  the  inferior  spine;  between  which  and 
the  portion  of  the  lower  costa  (d),  is  the  wide  channel,  attestmg  the  size  and  force  of  the 
homologue  of  the  teres  major.  The  vigour  of  the  enormous  subscapiilaris  muscle  is 
manifested  by  the  intermuscular  ridges  (^,  ^). 
Compared  with  the  scapula  of  the  Mylodon,  that  of  the  Megatherium  differs  in  the 
lower  position  of  the  spine,  and  the  consequent  greater  expanse  of  the  supraspinal  fossa : 
the  base  is  straighter  and  relatively  longer,  the  inferior  costa  relatively  shorter.  The 
ridge  extending  from  the  inferior  and  posterior  angle  forwards  upon  the  under  siu-face 
of  the  scapula,  is  relatively  stronger  in  the  Megatherium,  and  gives  to  the  homologue 
of  the  inferior  costa  in  the  Sloth’s  blade-bone  the  character  of  a second  spine.  As  such 
‘ second  spine,’  with  a prolongation  of  the  scapula  below,  characterizes  that  bone  in  the 
Anteaters,  this  indication  of  affinity  to  Mgrmeco^haga,  or  rather  manifestation  of  the 
more  general  characters  of  the  order  ^ruta,  by  the  Megatherium,  is  not  nuthout  interest. 
