SANGUIFEROUS SYSTEM. 469 



the free margin of the gills to form the wide trunk of the 

 great branchial vein of each organ ; there are thus two bran- 

 chial veins on each side of the body in nautilus, and one in 

 the naked cephalopods. The branchial veins are directed 

 inwards to the median plain, to enter the great systemic 

 muscular ventricle, and generally dilate to form a perceptible 

 sinus on each side, immediately before entering its cavity. 

 The systemic ventricle is larger, and more muscular in its 

 parietes than the branchial auricles, and is extended, sometimes 

 transversely, sometimes longitudinally in the middle of the 

 visceral cavity, enclosed in its pericardium, and situated be- 

 hind the venae cavee and between the auricles. In sepia, 

 loliffo, octopus, and nautilus, the systemic ventricle is ex- 

 tended transversely, and the branchial veins enter its lateral 

 extremities. In sepiola it is pyriform and subtransverse, and 

 in loligopsis it is of a lengthened fusiform shape, extended 

 longitudinally, and receives the branchial veins on each side 

 of its widest middle part. The branchial vein, like the 

 branchial artery, is wide as a sinus in its course along the 

 margin of the gill, and contracts its calibre at the base of 

 that organ. Two semilunar valves at the entrance of each 

 branchial vein into the systemic ventricle, prevent the return 

 of the blood into these veins during the contraction of the 

 heart ; two semilunar valves are also placed at the orifice of 

 the great anterior aorta. The systemic ventricle is more 

 capacious than both the branchial auricles ; it is provided 

 with thick and firm muscular parietes, and the prominent 

 fleshy columns give a cellular appearance to its inner surface. 

 The muscular enlargement of the bulbus arteriosus is ob- 

 vious at the origin of the great anterior or cephalic aorta, 

 as in most of the lower molluscous classes and the cold- 

 blooded vertebrata. Two other arteries are given off from 

 the same systemic heart, one of which, directed backwards, 

 is distributed on the genital organs which occupy the bottom 

 of the abdominal sac, and the other forming a posterior aorta 

 or palleal artery, is ramified chiefly on the intestine and the 

 muscular parietes of the mantle. The anterior or cephalic 

 aorta arises from the posterior part of the heart, and at its 

 origin is directed backwards and to the right between the 

 peritoneal folds which separate the intestinal from the gastric 

 sacs. It passes to the right of the cardiac orifice of the giz- 



