PEOFESSOE  OWEN  ON  THE  MEOATHEEIUM. 
269 
ligament,  but  also  by  a small  elliptical  flat  sm’face  which  seems  to  have  been  covered 
with  articular  cartilage.  Between  the  two  facets  for  the  os  magnum  the  bone  is  deeply 
excavated  and  has  been  perforated  by  blood-vessels. 
Lunare. — The  ‘ os  hmare  ’ (Plate  XXII,  1)  ofiers,  as  in  Man,  some  rude  resemblance 
to  a crescent ; its  proximal  surface,  very  convex  from  before  backward  and  rather  convex 
from  side  to  side,  is  wholly  covered  by  the  smooth  articular  surface  which  plays  upon 
the  ulnar  half  of  the  terminal  cavity  of  the  radius ; and  this  surface  is  continued  upon 
the  radial  side  of  the  bone  to  form  there  the  crescentic  tract,  adapted  to  the  similarly- 
shaped  tract  on  the  scaphoid.  The  inner  horn  of  this  tract  is  continuous  with  the  surface, 
convex  at  the  fore-part,  then  deeply  concave  from  before  backwards,  for  the  os  magnum 
(ib.  g) : this  articular  surface  is  continuous  with  a similarly  deeply  excavated  and  irre- 
gular one  on  the  ulnar  half  of  the  fore-part  of  the  bone,  which  is  subdivided  into  three 
facets,  the  middle  one  for  the  os  cuneiforme,  the  two  smaller  ones  for  two  parts  of  the 
os  unciforme. 
Cuneiforme. — The  ‘ os  cuneiforme  ’ (ib.  c),  which  is  the  smallest  of  the  three  proximal 
carpals,  presents  at  its  radial  side  a triangular  convex  surface  for  articulation  with  the 
lunare;  and  at  its  fore-part  an  iiTegular  concavo-convex  oblong  surface  for  the  unci- 
fonne  (ib.  Its  proximal  surface  is  tuberous  and  rough  for  ligamentous  attachment 
to  the  ulna,  except  where  the  smooth  articular  surface  for  the  os  pisiforme  is  situated : 
this  surface  is  in  great  part  convex. 
In  the  Mylodon  the  os  cuneiforme  is  the  largest  of  the  carpal  bones. 
Pisiforme. — The  os  pisiforme  (Plate  XXII.  y?)  is  conical  with  an  obtuse  apex,  having 
on  its  base  the  articular  surface  for  the  os  cuneiforme,  and  with  the  rest  of  its  exterior 
surface  more  or  less  irregular,  for  implantation  of  a tendon  and  ligaments. 
Trapezmdes. — The  homologue  of  the  trapezium  being  connate  with  the  scaphoid,  and 
noticed  in  the  description  of  that  compound  bone,  the  trapezoides  (ib.  z)  is  the  first 
independent  cai’pal  bone  of  the  distal  row.  It  is  the  least  of  the  carpal  series,  and  is  a 
relatively  smaller  and  flatter  bone  than  in  the  Mylodon:  the  proximal  or  scaphoidal 
surface  is  convex  transversely,  concave  from  behind  forward,  and  plays  in  a correspond- 
ing concavo-convex  surface  in  the  scaphoid.  The  distal  surface  is  almost  wholly  convex: 
both  surfaces  are  joined  by  a small  articular  facet  on  the  radial  side  of  the  bone,  which 
is  adapted  to  a con-esponding  facet  in  the  small  metacarpal  bone  of  the  thumb ; and  by 
a more  extended  articular  surface  on  the  ulnar  side  of  the  bone  for  junction  with  the  os 
magnum. 
Magnum. — This  bone,  arbitrarily  so  termed,  comes  next  after  the  trapezoides  and 
pisiforme,  in  the  order  of  size,  being  much  inferior  to  the  other  carpals.  It  is  almost 
wholly  covered  by  smooth  articular  siu’faces.  The  small  non-articular  rough  surface  (ib.  g) 
exposed  upon  the  back  of  the  wrist  is  of  a transversely  extended  hexagonal  figure,  with 
the  outer  and  inner  sides  the  shortest.  The  surface  for  the  lunare  is  concave  anteriorly, 
but  very  convex  in  the  greater  part  of  its  extent.  It  is  continuous  at  its  radial  border, 
with  the  two  surfaces,  one  concave,  the  other  flat,  for  the  scaphoides ; and  at  its  ulnar 
MDCCCLVIII.  2 o 
