THE HEART AND ARTERIES OF POLYODON 



415 



valve of two cusps. If it were desirable to show a still closer 

 series of gradations, the variable conus of Polyodon might be 

 placed before that of Amia in a series leading back through such 

 forms as Lepidosteus and Polypterus to the complicated struc- 

 ture found among the Dipnoi. Such a finely graded series, 

 however suggestive it might be, would probably not correspond 

 to any line of descent. The morphological value of the exact 

 number and arrangement of these valves cannot be very great, 

 especially where there is a tendency to multiplicity. 



'\ _a. mht. 



a. en. 



Fig. 3 Dorsal aspect of the ventral aorta 



VENTRAL AORTA AND AFFERENT BRANCHIAL ARTERIES 



The ventral aorta (fig. '3) is greatly elongated. In a fish of 

 10 decimeters it is fully one-tenth of the entire length of the 

 specimen. All of its branches arise near together at the anterior 



