274 
PEOrESSOE  OWE2^  OiS"  THE  MEGATHEEITM. 
the  core  presents  a rough  edge  radiad  and  a vertical  rough  surface  ulnad,  and  is  smooth 
and  convex  transversely  at  its  base,  both  above  and  below. 
The  proximal  and  middle  phalanges  of  the  digitus  medius  {ih.  iii,  1...2)  are  confluent, 
the  line  of  anchylosis  being  indicated  by  a vertical  ridge  along  both  the  inner  and  the 
outer  sides,  and  by  a curved  ridge  convex  backwards  on  the  upper  or  dorsal  side.  The 
proximal  articular  surface  presents  a deep  vertical  channel,  with  a naiTow  elongated 
subconcave  surface  continued  from  its  radial  side,  and  a still  narrower  flat  suiflace  from 
the  opposite  side.  The  distal  articular  surface  of  the  composite  hone  has  a deep  median 
vertical  groove  dividing  two  convexities.  The  compound  phalanx  presents  two  rough 
tuberosities  below,  one  terminating  each  bank  of  the  vertical  articular  proximal  channel ; 
there  is  a smooth  depression  above,  and  another  below,  close  to  the  distal  trochlea.  The 
enormous  distal  phalanx  (ib.  ill,  3),  of  twice  the  vertical  breadth  of  the  adjoining  claw 
phalanges,  is  very  little  longer  than  that  of  the  second  digit ; it  is  flattest  on  the  ulnar 
side,  to  which  the  upper  convexity  slightly  inclines.  The  base  or  palmar  part  of  the 
phalanx  is  the  broadest,  is  convex  both  lengthwise  and  transversely,  and  is  perforated 
by  two  canals,  for  the  large  vessels  and  nerves  supplying  the  claw-core.  The  surface, 
in  which  was  implanted  the  flexor  tendon,  shows  many  linear  impressions  radiating  from 
the  median  tuberosity,  forward  and  laterally.  The  articular  surface  excavates  obliquely 
the  base  of  this  phalanx  which  overhangs  the  joint ; the  concave  border  of  the  median 
angular  prominence  describes  a semicircle  from  above  forward  and  downward ; the  ulnar 
excavation  is  longer  in  that  direction  than  the  radial  one.  The  well-marked  ti’ochlear 
joint  restricts  the  movements  of  the  great  claw  to  flexion  and  extension  on  a vertical 
plane,  whilst  its  position  effectually  prevents  retraction  of  the  claw,  the  preservation  of 
the  effective  condition  of  which  is  due  to  an  opposite  bend  to  that  in  the  Cat-tribe,  as 
Avas  well  explained  by  Cuauer  in  his  description  of  the  Megalon}^*.  The  major  part 
of  this  enormous  phalanx  goes  to  form  the  sheath  of  bone  protecting  the  base  of  the 
claw.  The  bony  core  or  peg  on  which  the  claAV  Avas  fixed  and  moulded  is  compressed, 
Avith  a sharp  edge  above  and  flat  beloAv,  Avhere  it  projects  beyond  the  sheath. 
The  finger  of  the  fourth  digit  has  three  phalanges  and  is  unguiculate,  AAith  a claw 
resembling  in  shape  and  size  that  of  the  second  digit.  The  proximal  phalanx  {ih.  rv,  i) 
is  so  compressed  in  the  direction  of  its  axis,  that  the  proximal  and  distal  articular  surfaces 
almost  meet  above,  only  about  line’s  breadth  of  rough  surface  there  inteiTening : the 
proximal  articular  surface  is  a wide  and  moderately  deep  vertically-elongated  channel. 
AAuth  a semielliptic  flat  surface  continued  from  the  loAver  half  of  the  radial  border ; the 
outer  and  inner  sides  of  the  phalanx  are  narroAv,  elliptic  rough  convexities ; the  distal 
articular  surface  is  gently  convex  vertically,  sinuous  laterally.  The  second  phalanx 
{ih.  IV,  2)  is  deeper  than  long ; its  upper  surface  is  produced  backward  OA  er  the  proximal 
phalanx  into  a rough  obtuse  process ; the  under  surface  is  much  shorter,  but  is  broader 
than  the  upper  surface ; the  convexity  of  the  distal  articular  surface  describes  a semi- 
circle from  above  downAvard,  and  is  dhided  by  a vertical  trochlear  groove  into  two  paifs, 
* Ossemeus  Eossiles,  ed.  cit.  t.  viii.  p.  510. 
