274 MOLLUSCA. 
We have already referred to the adductor muscles for 
closing the shells and the protractors and retractors of the 
foot. The main substance of the foot is mus- 
cular and it is thrust out ventrally at the will of 
the animal, acting as a burrowing organ. 
The heart is situated dorsally and is three-chambered. 
The median ventricle envelops the intestine and passes for- 
= wards and backwards into main arteries. It is 
ood- é : : A : 
wacesie fed by paired lateral auricles which open into it 
by valves. They receive blood from the ctenidia. 
The heart and this part of the intestine lie in a spacious 
cavity, the pericardium, which is coelomic in origin. The 
Motor. 
Fig. 193.—DorsaL VIEW oF HEART AND PERICARDIUM 
OF ANODONTA. (dd zat.) 
Aperture of Kidney. 
Anterior Artery. 
Intestine. 
Ventricle. 
Auricle. 
Posterior Artery under Intestine. 
venous system, as in the snail, is lacunar, and formed of 
sinuses and cavities in the body. A large median sinus 
below the pericardium feeds the ctenidia. Hence the blood- 
vascular system closely resembles that of the snail; the chief 
difference is the paired condition of the auricles (like that of 
the shells). 
The brain, situated laterally to the mouth, consists of a pair 
of cerebral gangla joined forwards by a connec- 
tive. From the brain there run paired connec- 
tives to the peda/ ganglia in the anterior part of the foot, and 
Nervous. 
