54 



Leading into small caeca. Hence the wall of the branchial 



heart is penetrated in every direction by a system of short 

 vessels, which lead ultimately into the lumen of the 

 heart. Therefore venous blood, on entering the organ, 

 penetrates into this system of vessels before it passes on 

 into the afferent vessel which is given off at the antero- 

 external angle of the heart. Cuenot considers that the 

 purplish colour of the branchial heart is due to the 

 purplish concretions found in the cells of which it is 

 composed. By experiment he has proved that these cells 

 are excretory, and therefore that the branchial heart is a 

 glandular organ. The venae cavae, branchial hearts and 

 vessels, and main aortae, as well as the heart, are all 

 rhythmically contractile. 



The Venous Sinus extends from behind the mouth to 

 the posterior edge of the stomach, and is divided into three 

 cavities — anterior, central and posterior, the first two of 

 which communicate by important vessels with the large 

 veins. The wall of the sinus is a tough transparent 

 membrane. 



1. The anterior division is small and is joined to the 

 middle division by a narrow region, which runs with the 

 oesophagus through the cavity of the ring-like central 

 nervous system (fig. 53). The thin wall becomes adherent 

 to the buccal mass about half-way down its length 

 (tig. 53, B.M.), thus forming the anterior boundary of 

 the sinus. Hence the posterior portion of the buccal 

 mass, the anterior salivary glands, and the anterior 

 portion of the oesophagus, are bathed in the blood 

 contained in this division of the venous sinus. 



2. The central division is much larger, and 

 narrower in the middle region than at its two extremities, 

 and contains the oesophagus, crop, posterior salivary 

 glands and stomach. However, the liver and ink sac, 



