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supplies the pancreas, stomach, and caecum; one branch (d) enters the pancreas; 

 one (a) crosses the lower surface of the lower caecal lobe, passing close to 

 the splanchnic ganglion, and then ramifies over the outer side of the 

 stomach ; another (b) supplies the adherent inner walls of the stomach and 

 caecum; and the last (c) passes to the outer side of the caecum and supplies 

 the caecal folds. A pair of important arteries arises from the aorta as it emerges 

 on the anterior surface of the liver. Each of these immediately divides into 

 several branches; two or three enter the liver (5'): two or more supply the 

 nuchal and siphonal retractors (4'J; one branch (3') passes through the supporting 

 membrane of the gill to the branchial gland and the gill : anothei- branch (2') , 

 passes through a canal in the mantle with the nerves of the fin, to an arterial 

 plexus (9^) on the upper surface neai- the dorsal end of the mantle. The latter 

 artery has a remarkable length compared to its size and has a theoretical 

 interest which will be discussed later. One of its branches anastomoses 

 with the arteries of the ventral end of the fin , and other branches go to the 

 mantle. The arteries of the siphonal retractors enter these muscles near the 

 middle of their length and each divides into a dorsal and a ventral branch. 

 These two branches form a longitudinal trunk from which small arteries radiate 

 to the fibres of the muscle. Near the dorsal end of the nuchal cartilage a 

 median artery (6') arises from the aorta. It immediately bifurcates and each 

 branch , after giving off small branches to the nuchal retractor , passes through 

 that muscle at the edge of the cartilage and enters the mantle under the 

 stellate ganglion to supply the upper ventral portion of the mantle. Several 

 small and inconstant arteries arise from the aorta along its course and supply 

 such adjacent structures as muscles , oesophagus , or liver. 



The aorta forks near the skull and the branches passing around the 

 oesophagus unite behind it , forming an oesophageal arterial ring. Ten vessels 

 arise from this ring : four pairs ; muscular , optic , pharyngeal , and siphonal ; a 

 median , the pedal ; and an azygos artery , the salivary. The upper part of the 

 ring lies in the liver case and the lower part in the skull. .Just before each 

 terminal branch of the aorta enters the skull it bears a „ peripheral heart" , 

 which will be discussed later. The origin of the first pair of arteries of the 

 ring the muscular (7') is quite variable, sometimes the arteries arise at the 

 bifurcation of the aorta and sometimes just distal to the peripheral heart. The 

 arteries suppliy parts of the liver and the cephalic retractoi's. The savilary 

 artery (8') arises from the left vessel at the distal end of the peripheral heart 

 and passes back to the salivary gland. Just beyond the peripheral heart each 

 terminal branch of the aorta enters the skull bj' passing through the fascia -which 



