THE HEART AND ARTERIES OF POLYODON 



423 



gives off a large posteriorly directed branch (figs. 9, 11 a.cor.), 

 which for the present may be termed the coronary artery. It 

 has a wider range of origin (cf. figs. 10 and 11) than is implied 

 by Allis's account, but always leaves the gill in the epibranchial 

 region, and this, in connection with the fact that there is already 

 a full complement of recurrent arteries below, precluded the 



hb. a. 



hb. p 



m. lev. 4. 



a. br. e. 4 



a hb. 4 



a. br. a. 4 



10 



Fig. 9 Posterior view of dorsal part of fourth gill 

 Fig. 10 The arteries of the fourth gill 



possibility of its belonging to the hypobranchial system. Passing 

 over the dorsal end of the fifth gill cleft it comes into a position 

 lateral to the oesophagus from which point its course will be 

 traced in a subsequent paragraph. 



Near the origin of the 'coronary artery' and in the region 

 where the posterior hemibranch is lacking (fig. 9) , the efferent ves- 

 sel separates into two parts. The main division (a.hr.e. 4), which 



