412 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
The other large vessel arising from the posterior aorta 
is the Adductor Artery (fig. 14, A. add.). This leaves the 
aorta at a right angle, and plunges into the adductor 
muscle immediately in front of the deep cleft dividing the 
striped muscle from the unstriped. On entering the 
muscle, small vessels are given off from its posterior side, 
which pass out of the main bundle of striped muscle and, 
crossing the cleft, enter and supply the unstriped portion. 
The main artery, however, passes down towards the middle 
of the adductor, where it divides, sending branches in all 
directions. The figure shows the course taken in one of 
the specimens where the injection mass went very 
successfully, but probably here, as in other places, there 
is great variation in the smaller branches. 
The YrENous System (fig. 18) consists largely of 
sinuses, and contrasts thereby with the fine arterial 
vessels. ‘There are three main sinuses situated between 
the adductor muscle and its connective tissue sheath, 
which account for the large outflow of blood when the 
muscle is cut from a valve. 
A large Dorsal Sinus (fig. 18, S. D.) is situated under 
the pericardium and digestive gland; anteriorly, this 
communicates on both sides with the renal organs. On 
ithe ventral side of the adductor, there are two sinuses, 
which extend from the cleft dividing the striped and 
unstriped portions of the muscle up to the renal organs. 
They are continued under these and the visceral mass, and 
communicate with one another. ‘The main opening of 
these sinuses to the renal organ is at the dorsal end, and 
by slitting up the outer surface, the renal veins may be 
seen branching and becoming much smaller as they pass 
from the pericardial end towards the reno-genital opening 
(fig. 12, Ko.'r.). 
A large Hepatic vein (fig. 18, V.A.) on each side of 
