398 



C. H. DANFORTH 



approximates the teleosteaii type and presents no new points of 

 special interest. The other, represented by Scaphirhynchus and 

 Polyodon, appears to be a modification of the more primitive con- 

 dition found in skates. Functionally, the latter arrangement 

 would seem to be superior to the former, particularly in Polyo- 

 don where the whole supply to the heart and a large part of that 

 to the liver is carried by a special vessel directly from the gills 

 to these organs. 



br.3 br.4 



cor, abd. add. thv. thd. 



Fig. 4 The coronary and hepatic arteries of Aniia. Lotterinji :is in the pre- 

 ceding figures. 



Morphologically, how much significance can be attached to 

 these blood vessels is an open question. In different individuals 

 of the same species of shark, Carazzi ('04) found the various ar- 

 rangements of cardiac and oesophageal vessels that had been 

 supposed to characterize several different species. The dis- 

 section of a few specimens of almost any fish will serve to show 

 how greatly the vessels vary. On the processes involved in the 

 production of such variations considerable work has been done. 

 In other groups of animals blood pressure has been thought to 

 play an important role in determining the interrelations of ar- 

 teries (Thoma, '01). It seems probable to the writer that the 

 distribution of blood vessels in the fish is primarily a functional 



