2 2 MOLLUSC A. 



and supplies this region and the stomach with blood by 

 means of smaller branches. When in the neighborhood 

 of the mouth it sends off a large branch, which passes just 

 posterior to the mouth (^paf) , and supplies the palpi with 

 blood through four secondary branches springing from this 

 arch. A little farther on and a smaller branch {inaf) passes 

 anterior to the mouth, supplying this region with blood. 

 Just beyond this, in the angle of the mantle, it gives off a 

 branch posteriorly, the mantle-border artery on the dorsal 

 side (Fig. 5, dma), and then, turning sharply at right 

 angles {ma), passes along the hinge area, and in its course 

 gives off numerous small arteries on either side, which pass 

 posteriorly, and with their numerous ramifications supply 

 the whole anterior portion of the two leaves of the mantle. 

 These last are often quite conspicuous externally, on ac- 

 count of the opacity of the coagulated blood which they 

 contain. (Fig. 5.) 



At the ventral angle of the mantle (Fig. 5, vmd), it 

 separates into two terminal branches, which traverse the 

 whole ventral side, with numerous branches springing out 

 on the ventral side to supply the borders of the mantle. 



These are the main channels through which blood is 

 conveyed to the various parts of the body, and most of 

 them may be followed out with the knife. 



After passing through the arteries, which divide into 

 smaller and smaller branches as they recede from the 

 heart, the blood is collected in a system of intermediate 

 vessels or spongy cavities (Figs. 12, 7, v), and from 

 thence returned either through the gills or directly 

 collected into small branches and returned to the larger 

 veins. In these it flows on its way back to the auricles, 

 from whence it again enters the ventricle, and begins 

 over the course we have described. 



The principal vessels of the venous system are not 



