CIRCULATORY SYSTEM OF THE GRASS-SNAKE. 



617 



heart, which, however, in the course of the further development 

 moves caudally, and ultimately comes to lie a long way from its 

 primitive position. 



Text-fig. 87. 



PV.C. 



Dorsal view of the heart and adjoining vessels. 



C.V. Coronarj' vein. L.P.C. Left pre-caval vein (left common jugular). 

 R.P.C. Right pre-caval vein (right common jugular). S.V. Major part of sinus 

 venosus. S.V.I. Minor part of sinus venosus. Other letters as in text-fig. 86. 



(B) Aclidt Form. 



Tropidonotus in common with all the reptiles, except the 

 Crocodilia, possesses a three-chambered heart. This is situated a 

 considerable distance behind the head and slightly towards the 

 right. It is eiiclosed in a pericardium in which it lies freely, 

 not being attached to it by a gubernaculum cordis as is the case 

 in the heart of the Lacertilia and Crocodilia, Beddard (2) has 

 pointed out that althovigh a gubernaculum cordis is generally 

 absent in snakes, it is not completely so, as a homologous structure 

 occvirs in some species*. The pericardium on the right side lies 



* E. g. Coronella getida, Coelopeltis monspesstdana, and Ophiopliagns lungarus, 

 Beddard {loc. cit.). 



Proc. Zool. See— 1912, No. XLI. 



41 



