MANTLE-CAVITY 111 



an inch or more in length. It lies in the roof of 

 the mantle-cavity at its posterior end and left side 

 and is in close contact with the left side of the 

 kidney about the middle of its length. 



Open the pericardial cavity to expose the heart. 



b. The heart has two chambers, of about equal size. 

 i. The auricle is proximal, i.e. nearer the collar, 

 and has thin walls. It receives in front the 

 pulmonary vein, which returns to it aerated 

 blood from the lung, 

 ii. The ventricle is the pear-shaped distal division 

 of the heart, with thick muscular walls. It 

 receives aerated blood from the auricle, and 

 drives it through the aorta to all parts of the 

 body. 



The blood-vessels will be described later on. 



2. The kidney and ureter. 



a. The kidney is a large, pale yellow, triangular body 

 in the posterior part of the roof of the mantle- 

 cavity. Its left side is notched to receive the 

 pericardium, which lies close against it. 

 i. The reno-pericardial canal is a narrow ciliated 

 passage leading from the pericardial cavity to 

 the kidney. Its pericardial opening is about 

 the middle of the length of the cavity, oppo- 

 site the ventricle, and close to the inner or 

 ventral border of the septum between the 

 pericardial cavity and the kidney. 



To see the reno-pericardial passage make a small hole 

 into the pericardial cavity, and inject it with carmine or other 

 colouring matter in suspension. This will pass into the kidney 

 along the passage, which can then be readily followed. 



ii. The structure of the kidney. The kidney is a 

 sac lined by a glandular epithelium, and with 

 its walls thrown into a large number of 

 lamellar folds projecting into its cavity. 



