]ME.  HAXCOCK  ON  THE  OEGANIZATION  OE  THE  BEACHIOPODA. 
831 
lacunes,  and  at  the  other  with  the  posterior  portion  of  the  outer  pallial  system  of  the 
dorsal  lobe.  The  lacunes  in  the  ilio-parietal  bands  connect  the  lower  portion  of  the 
visceral  lacunes  with  the  posterior  portion  of  the  outer  pallial  system  of  the  ventral  lobe. 
The  mesenteric  lacunes  ‘ have  the  same  character  as  those  in  the  other  bands,  and  run 
principally  in  a longitudinal  direction,  and  maintain  a communication  between  the 
’visceral  lacunes  and  those  of  the  walls  of  the  body. 
The  liver  has  no  doubt  its  proper  system  of  blood-channels  communicating  with  those 
of  the  other  \iscera ; and  though  they  have  not  been  demonstrated,  it  appears  pretty  cer- 
tain that  they  lie  between  the  walls  of  the  numerous  ramifications  of  this  viscus  and 
a membranous  envelope,  an  expansion  of  the  sheath  of  the  alimentary  tube,  which  has 
the  appearance  of  being  reflected  from  the  stomach  upon  the  hepatic  ducts,  and  is,  there 
can  be  little  doubt,  continued  throughout  its  various  subdivisions. 
The  muscles  seem  likewise  to  be  sheathed  in  a membrane  which  apparently  penetrates 
the  interstices  between  the  bundles  of  fibres,  so  strikingly  displayed  at  their  enlarged 
extremities.  The  blood,  which  goes  to  nourish  these  organs^  will,  for  the  most  part, 
pass  from  the  lacunes  of  the  parietes  to  within  the  sheaths,  and  has  its  course  defined  in 
lacunary  channels,  which  can  be  easily  observed  on  making  a transverse  section  of  the 
occlusor  muscles.  The  occlusors  being  in  connexion  with  the  mesenteric  membrane  and 
the  anterior  parietes  its  blood-channels,  will  be  also  in  direct  communication  with  the 
risceral  system.  It  would  then  appear  that  the  risceral  system  of  lacunes  is  connected 
with  the  parietal  and  pallial  systems  through  the  instrumentality  of  the  several  parietal 
bands ; and  what  may  be  denominated  the  muscular  lacunary  systems  are  probably  in 
communication  with  all  three. 
The  blood-system  of  the  brachial  apparatus  next  claims  attention.  This  is  beautifully 
developed,  and  presents  considerable  variety  in  the  character  of  the  several  plexuses  of 
which  it  is  composed.  The  walls  of  the  great  canal,  the  ridge  supporting  the  cirri,  the 
membranes  that  unite  the  upper  and  lower  members  of  the  loop,  that  which  connects 
the  spirals,  and  those  which  form  the  small  canal  or  channel  at  the  base  of  the  cirri,  as 
well  as  that  forming  the  sheath  of  the  apophysary  support, — all  have  their  system  of 
lacunes  which  intercommunicate  and  compose  the  brachial  system. 
The  processes  of  the  inner  lamina  of  the  mantle  which  pass  along  the  lateral 
brachial  folds,  and  within  the  margins  of  which  the  calcareous  support  is  developed,  are 
fonned  of  two  layers ; and  the  network  of  lacunes  of  the  inner  pallial  system  is  con- 
tinued between  them.  This  continuation  of  these  lacunes  is  in  connexion  with  the 
brachial  system.  The  lacunes  in  the  walls  of  the  great  brachial  canal  also  communicate 
with  those  of  the  same  inner  pallial  system.  There  is  likewise  a small  canal  which  runs 
along  the  arm  from  base  to  point  immediately  below  the  brachial  fold:  The  blood- 
channels  of  the  anterior  wall  of  the  body  communicate  with  the  extremity  of  this  con- 
duit, and  as  it  passes  along  it  pours  its  contents  into  the  plexus  of  the  great  brachial 
canal.  This,  which  may  be  denominated  the  afferent  brachial  canal,  was  not  very 
* Plate  LIV.  fig.  8. 
5q 
MDCCCLVIII. 
