IX CIRCULATORY ORGANS 437 



aeration, the blood from each hemibranch passes into an efferent 

 branchial artery (ef. br), which, except in the case of the last (ef. br^), 

 joins with its fellow of the same cleft and thus forms a loop surround- 

 ing the cleft, the two halves of adjacent loops being connected in the 

 middle by a commissural vessel. From the upper ends of each of the 

 four loopi arises an epibranchial artery {ep. br) which is connected with 



d.ao 



c^br' ucu) aj 



Fig. iiz. — The heart and branchial arteries oi Scyltiuiii, from the side. 

 a/, br. 1 — 5, afferent branchial arteries ; au. auricle ; c. a. conus arteriosus ; ct.^ — ^, 

 branchial clefts ; cor. coronary artery ; d. ao, dorsal aorta ; d. c. dorsal carotid 

 artery ; ef' br}- — 1*, eflferent branchial arteries ; ep. br} — 4^ epibranchial arteries ; 

 mn. mandibular artery : sp. spiracle ; s. ci. subclavian artery ; s. v. sinus venosus ; 

 V. ventricle ; v. ao. ventral aorta ; v. c. ventral carotid artery. 



the dorsal aorta (d. ao), the blood from the last hemibranch passing 

 into the fourth loop. 



From the dorsal end of the first efferent branchial, a dorsal carotid 

 artery {d. c) is given off: this passes forwards and inwards, gives off a 

 cranch to the upper jaw and snout, and then runs inwards in a groove on 

 the skull-floor, which it penetrates in the middle line so as to reach the 

 tranial cavity. A vessel arises from the middle of the first efferent 

 branchial, and supplies the pseudobranch, from which the blood is col- 

 lected by a ventral carotid artery (v.c) which passes through the orbit 

 into the cranium, giving off branches to the brain and anastomosing 

 with the dorsal carotid. From the "ventral end of 'the first efferent 

 branchial a small mandibiilar artery (mn) passes to the lower jaw. The 



