THE HEART AND ARTERIES OF POLYODON 429 



is true, but the statement fails to make clear the important 

 fact that the coronary does not come from the hypobranchial 

 end of the efferent artery as in other fishes. AUis does not dis- 

 cuss the hypobranchial arteries. 



THE CORONARY ARTERY 



The coronary arteries as usually described for fishes are desig- 

 nated as anterior and posterior. The former arise from hypo- 

 branchial derivatives of the efferent branchial vessels and reach 

 the heart by passing along the conus arteriosus. The latter, 

 found in skates, arise from the coracoid branch of the subclavian 

 artery and reach the heart from behind. Depending on their 

 relation to the conus, anterior coronary arteries are recognized 

 as dorsal or ventral. In Polyodon anterior coronary arteries 

 are all entirely lacking and, further, the arteries of supply which 

 reach the heart by way of the septum transversum do not cor- 

 respond in other respects to posterior coronaries. 



The vessel which for convenience may be called the coronary 

 artery (figs. 11 and 12 a. cor.), although it represents much more 

 than is usually covered by that term, arises as above described 

 from the fourth efferent branchial artery which it leaves in the 

 epibranchial region. It is somewhat variable in its point of 

 origin (figs. 9, 10 and 11, a. cor) and is not symmetrical with 

 the corresponding vessel of the opposite side, one or the other 

 always being much the larger. Usually it is the right vessel 

 that is best developed. In the region of the oesophagus it gives 

 off a few small branches and then descends in a somewhat spiral 

 course to the base of the pericardium. Its relation in this region 

 to the anterior cardinal and ductus Cuvierii (fig. 11, y. dc.) is 

 variable. It lies for the most part anterior and somewhat medial 

 to. the subclavian artery (fig. 12, a.sc). Dorsal to the pericar- 

 dium there arises a long branch {a.co.-ca) that runs forward 

 between the fifth ceratobranchial and median. hypopharyngeal 

 cartilages to supply the dorsal parts of the mm. pharyngoclavi- 

 culares (fig. 12). This vessel occupies the position of a part 

 of the a. coraco-cardiaca of ScylHum (Hyrtl '58, Carazzi '04), 



JOURNAL OF MOHPHOLOGT, VOL. 23, NO. 3 



