214 
MR.  R.  OWEN  ON  THE  STRUCTURE  OF  THE  HEART 
observes  with  respect  to  its  external  form,  that  in  Salamandra,  Triton,  Siren  pisct- 
formis,  and  Sir.  lacertina  ' '  the  auricle  is  divided  by  a  strong  contraction  into  an  anterior 
larger,  and  a  posterior  lesser  moiety  ;"  '  and  then  proceeds  to  state  that  in  the  genus 
Pipa  he  finds  "  a  very  interesting  transition-structure  in  a  membranous  velum,  which 
extends  from  the  floor  of  the  ventricle  to  the  upper  and  posterior  wall  of  the  auricle, 
where  a  manifest  opening  is  left."^ 
My  own  dissections  have,  however,  satisfied  me  of  the  correctness  of  Dr.  Davy's 
ascription  of  a  distinct  auricle  for  the  pulmonic  blood  to  the  common  Frog  and  Toad'-''; 
and  the  more  recent  researches  of  Dr.  Martin  St.  Ange^  have  shown,  that  not  only  do 
the  Anourous  Caducibranchiata  recede  from  the  character  assigned  by  Cuvier  to  the 
Batrachian  order,  but  that  in  the  Salamanders  also  there  exists  a  small  but  distinct 
pulmonic  auricle. 
In  justice  to  Mr.  Hunter  it  must  be  observed  that  he  had  accurately  ascertained  the 
true  structure  of  the  heart  of  the  higher  Batrackia,  and  included  the  Frogs,  Toads,  and 
Salamanders,  with  Serpents  and  the  higher  Reptiles,  in  the  class  which  he  denominates 
Tricoilia^,  from  the  heart  being  composed  of  three  cavities.  The  Siren,  the  Amphiuma, 
the  Kattewagoe  or  Menopoma  of  Harlan,  in  short,  all  the  Reptiles  douteux  of  Cuvier  that 
Mr.  Hunter  was  acquainted  with,  he  considered  as  a  distinct  class,  which  he  denomi- 
nates Pneumobranchia  in  the  manuscript  which  is  quoted  by  Rusconi  in  the  work  entitled 
'  Amours  des  Salamandres  Aquatiques'^,  and  which  is  now  published  in  the  '  Physio- 
logical Catalogue  of  the  Hunterian  Collection'''.  Neither  Rusconi,  Cuvier,  Meckel,  nor 
Hunter,  who  have  severally  made  one  or  more  of  the  doubtful  Reptiles  the  subjects  of 
particular  investigation,  has  suspected  that  these  remarkable  animals  resemble  the 
higher  Reptiles  in  the  number  of  cavities  of  which  the  heart  is  composed;  but  they 
appear  to  have  been  uniformly  regarded  as  approximating  Fishes,  as  well  in  the  sim- 
plicity of  the  circulating  organ  as  in  the  permanence  of  a  greater  or  less  proportion  of 
the  branchial  apparatus. 
In  the  progress  of  the  arrangement  and  description  of  the  preparations  of  the  circu- 
lating organs  which  are  preserved  in  the  Gallery  of  the  Museum  of  the  Royal  College 
of  Surgeons,  I  have  had  occasion  to  dissect  an  Amphiuma  means,  a  Proteus  anguinus,  and 
a  Siren  lacertina,  in  order  to  reconcile  the  appearances  presented  by  the  Hunterian  pre- 
parations with  published  descriptions,  and  more  especially  with  that  of  the  Siren  lacer- 
tina, given  by  Mr.  Hunter  himself  in  the  56th  volume  of  the  '  Philosophical  Transac- 
tions'8.    In  all  these  animals  I  find  the  pulmonary  veins  terminating  in  a  small  but 
'  "  Der  Vorhof — durch  eine  starke  einschniirung  in  eine  vordere,  grossere  und  eine  hintere,  kleinere  Halfte 
getheilt  ist." — Loc.  cit.,  p.  216. 
*  "  So  eben  finde  ich.  indessen  bei  einem  frischern  Exemplar  eine  interessante  Uebergangsbildung  in  einem 
lifiutigen,  senkrechten  Segel,  das  sich  von  der  Grundflache  der  Herzkammem  bis  zum  obern  und  hintern  Rande 
der  Vorhofe  erstreckt,  bier  aber  eine  deutliche  Liicke  lasst." — Loc.  cit.,  p.  217. 
»  See  the  Zool.  Journal,  vol.  ii.  p.  586.  *  Table  of  the  Circulating  System. 
»  On  the  Blood,  p.  135.  «  p.  12.  '  vol.  ii.  p.  145.  81766.  p.  308. 
