;i96 



C. H. DANFOKTtI 



patic and coronary vessels and become their main trimk. The 

 original hepatico-coronary trunk (ch) is now reduced to a small 

 branch connecting the coronary artery with the subclavian. It 

 was originally interpreted as merely a secondary anastomosis. 



As in Scaphirhynchus no anterior coronary arteries are present. 

 What might be interpreted as a rudimentary dorsal coronary is 

 lost on the ventral aorta before reaching the heart. Polyodon 

 differs from Scaphirhynchus chiefly in that the origin of the he- 



md. coca. va. cp. ha. ch.abd.cor thv add. Iiv hp 



Fifr. 2 Tlie coi'oiiai'y and licpalic arti'i'ics of Polyodon. Letters as in Hgurc ] 



patico-coronary trunk is transferred from the coracoid branch 

 of the subclavian to the dorsal part of the fom'th efferent bran- 

 chial artery. 



j.i':i'ii)()S'i'EiTs 



In Lepidosteus, posterioi- hepatic and anterior coronary ar- 

 teries alone are present. The latter arise from a vessel which 

 comes off on the right from the large oesopliageal trunk, which 

 arises in turn from the subclavian artery. The anterior coi'o- 

 nary arteries arise from a short median hypobranchial which de- 

 rives its supply partly from the A. niaiidibularis {md) and partly 

 fi'om a commissural artery at the level of the second gill. These 

 two vessels unite laterally and the resulting common trunk reaches 



