IN  THE  PERENNIBRANCHIATE  BATRACHIA. 
215 
distinct  auricular  chamber,  which  communicates  with  the  ventricle  by  an  oblong  orifice, 
situated  close  to,  but  separated  from,  the  corresponding  orifice  of  the  great  auricle  of 
the  veins  of  the  body. 
In  the  present  communication  the  heart  of  the  Sir.  lacertina  is  selected  for  more 
immediate  consideration,  as  this  species,  in  presenting  a  combination  of  but  one  pair 
of  extremities  with  persistent  external  branchice,  recedes  furthest  from  the  BatracMan 
type  of  structure,  and  might  be  supposed  to  approximate  Fishes  most  closely  in  the  con- 
struction of  the  central  organ  of  circulation. 
The  heart  of  the  Sir.  lacertina  is  of  an  oblong  figure,  situated  immediately  behind  the 
branchicB  in  the  middle  line  of  the  body  between  the  two  fore  legs  and  surrounded  by 
a  strong  fibrous  pericardium.,  which  is  smooth  and  glistening  on  the  inner  surface,  as  in 
Fishes,  adheres  by  the  whole  of  its  exterior  surface  to  the  surrounding  parts,  and  is 
defended  on  the  ventral  aspect  by  the  expanded  cartilaginous  coracoid  bones.  The 
length  of  the  pericardium  in  a  specimen  two  feet  in  length  was  two  inches,  its  breadtli 
three  fourths  of  an  inch. 
The  heart  when  viewed  externally  seems  composed  of  a  membranous  sinus,  a  large 
muscular  fimbriated  auricle,  a  ventricle,  and  an  elongated  bulbus  arteriosus. 
The  venous  sinus  is  situated  at  the  posterior  part  of  the  pericardium.  The  great 
inferior  cava  terminates  in  this  sinus  by  two  orifices,  separated  from  each  other  by  a 
membranous  septum^,  which  extends  a  little  way  into  the  sinus,  and  terminates  in  a 
concave  edge  anteriorly ;  on  either  side  of  this  free  margin  of  the  septum  there  is  an 
orifice,  one  of  the  right,  the  other  of  the  left,  superior  cava^,  between  which  the  com- 
mon trunk  of  the  pulmonary  veins  ^  is  seen  adhering  by  a  small  part  of  its  posterior  sur- 
face to  the  parietes  of  the  sinus,  but  not  terminating  there. 
If  the  lower  part  of  the  auricle  be  carefully  laid  open  in  the  transverse  direction,  a 
small  cavity  will  be  exposed  distinct  from  the  rest  of  the  auricle,  and  above  the  sinus, 
into  which  the  trunk  of  the  pulmonary  veins  opens.  This  distinct  compartment^,  which 
is  analogous  to  the  left  auricle,  and  is  here  situated  to  the  left  side  of  the  ventricle, 
communicates  with  the  ventricle  by  an  oblong  aperture  close  to  that  by  which  the  right 
auricle  opens  into  the  ventricle,  the  two  apertures  being  separated  by  a  transverse  band 
which  forms  the  point  of  attachment  to  the  simple  membranous  auriculo-ventricular 
valves.  This  division  of  the  auricle  into  two  cavities,  one  for  the  systemic  the  other 
for  the  pulmonic  blood,  would  scarcely  be  suspected  to  exist  upon  an  external  view  of 
the  heart,  on  account  of  the  remarkable  fimbriated  structure  of  the  auricles,  arising 
from  numerous  indentations  of  varying  extent:  the  deepest  of  these  clefts  is,  however, 
that  which  separates  the  appendix  of  the  left  from  that  of  the  right  auricle.  The  inter- 
nal surface  of  both  auricles  presents  numerous  dehcate  muscular  ridges,  which  decus- 
sate in  various  directions  :  the  subdivided  elongated  cylindrical  pouches  continued  from 
the  margin  of  the  auricle  present  a  manifest  analogy  with  the  remarkable  structure  of 
'  c.  Fig.  2.  PI.  xxxi.  -  b,  b.  Fig.  3.  '  m.  Figg.  2.  &  3.  *  e.  Fig.  2. 
