ME.  HANCOCK  ON  THE  OEOANIZATION  OE  THE  BEACHIOPODA. 
795 
On  removing  the  dorsal  parietes  in  Lingula\  the  alimentary  tube  is  found  to  occupy 
a central  position  as  in  the  articulated  tribes,  the  anterior  portion  being  buried,  as  in 
them,  beneath  the  lobulated  liver,  which  is  rather  bulky.  On  displacing  the  latter,  the 
heart  is  seen  attached  to  the  upper  surface  of  the  stomach,  and  the  two  dorsal  genital 
organs  are  enth'ely  exposed,  extending  nearly  the  whole  length  of  the  perivisceral  cham- 
ber. At  the  sides  and  in  front  of  these  are  the  extremities  of  the  muscles,  and  behind 
are  the  convolutions  of  the  intestine.  The  pseudo-  or  Cuvierian  hearts  are  hidden  below 
the  genitalia  and  muscles. 
Ha-ving  taken  this  general  survey  of  the  external  and  internal  parts,  we  shall  now 
examine,  in  detail,  the  various  systems  of  organs,  beginning  with  that  of  the  muscles. 
Muscular  System. 
In  the  Brachiopods  the  muscular  system  is  very  complicated  and  peculiar  in  its  arrange- 
ment. Five  or  six  pairs  of  muscles  have  been  described  in  the  Terehratulidcv,  all  of 
which  hav^e  relation  to  the  movements  of  the  valves  upon  each  other,  or  to  their  attach- 
ment to,  or  movements  upon  the  peduncle.  Thus  the  muscles  naturally  divide  them- 
selves into  two  groups, — the  valvular,  and  those  for  adjusting  the  shell  to  the  peduncle. 
Of  the  former  there  are  three  pairs,  which  have  been  denominated  respectively  adduc- 
tors, cardinals  and  accessory  cardinals ; of  the  latter  there  are  likemse  three  pairs,  which 
have  deen  designated  the  dorsal  pedicle  muscles,  the  ventral  pedicle  muscles,  and  the 
capsular  muscles.  The  capsulars,  however,  are  generally  blended  into  one,  and  in  this 
state  they  have  been  named  “capsularis”  by  Professor  Owen®. 
Before  entering  upon  the  description  of  these  several  pairs  of  muscles,  it  is  necessary 
to  say  a word  or  two  on  the  names  they  have  received,  which  do  not  appear  satisfactory. 
The  epithets  cardinal  and  accessory  cardinal  given  to  two  of  the  pairs  of  valvular  muscles 
are  objectionable,  for  they  would  seem  to  imply  that  these  muscles  presided  exclusively 
over  the  movements  of  the  hinge,  or  that  they  are  exclusively  the  muscles  of  the  hinge. 
They  open  the  valves,  the  adductors  close  them.  In  this  sense  these,  as  well  as  the 
others,  might  be  called  cardinal  muscles,  all  being  equally  related  to  the  hinge ; but 
surely  it  is  improper  so  to  name  the  first-mentioned  muscles,  and  not  the  last.  And  as 
to  the  attachment  of  the  first-mentioned  to  the  cardinal  process,  this  should  not  entitle 
them  to  be  called  cardinals  any  more  than  the  dorsal  pedicle  muscles,  which,  being  in- 
serted into  the  hinge-plate,  in  most  instances,  would  seem  thereby  to  have  equal  claim  to 
the  title.  These  epithets  will  therefore  be  discarded,  and  those  of  divaricator  and  acces- 
sory divaricator  substituted.  The  adductor  muscles  will  be  named  the  occlusors,  the 
present  denomination  not  being  sufficiently  precise. 
With  regard  to  the  pedicle  muscles,  these,  as  will  be  afterwards  shown,  having  the 
office  of  adjusting  the  shell  to  the  peduncle,  will  receive  the  name  of  adjustor  muscles. 
This  alteration  is  also  rendered  necessary  because  the  capsular  is  really  the  peduncular 
muscle,  and  will  be  so  denominated. 
' Plates  LXIV.  fig.  4 ; LXV.  fig.  3 ; LXVI.  fig.  1. 
’ Introduction  to  Davidson’s  ‘ Britisli  Eossil  Brachiopoda,’  p.  8. 
