THE HEART AND ARTERIES OF POLYODON 



417 



a. hb. y 



a. br. a 



a. hb. 4 



a. Ihb. 



a. br. a. 4 



m bmd. 



a. Ihb.' 



m. obv. 4 



cer. 5 



Fig. 4 The principal structures of the hypobranchial region seen from below. 

 The anterior cartilage elements are displaced somewhat laterally and portions of 

 the copulae omitted. 



