DIGESTIVE SYSTEM 143 



principal sclerites will alorie be described here, 

 viz. five median dorsal pieces and two pairs of 

 lateral pieces, the others being small and of less 

 importance. 



Remove the enidre stomach from the body, avoiding injwry 

 to the structures around the asophagus ; place it in a dish 

 under water, and carefully clean away the muscles. 



i. The cardiac ossicle is a broad transverse sclerite 

 in the roof of the cardiac chamber of the 

 stomach. 



ii. The urocardiac ossicle is a median dorsal sclerite 

 in the hinder wall of the cardiac chamber. 

 Its anterior end is broad, and hinged to the 

 hinder edge of the cardiac ossicle ; its posterior 

 end is narrow, and directed downwards and 

 backwards. 



iii. The pyloric ossicle is a narrow transverse 

 sclerite in the anterior part of the dorsal wall 

 of the pyloric chamber. 



iv. The prepyloric ossicle lies in the anterior wall 

 of the pyloric chamber, and is hinged above 

 to the anterior border of the pyloric ossicle. 



v. The median tooth is a strong calcified sclerite, 



. placed at the junction of the cardiac and 



pyloric chambers. With its upper surface 



are articulated the urocardiac ossicle in front 



and the prepyloric behind. 



vi. The pterocardiac ossicles are attached one to 

 each end of the cardiac ossicle by oblique 

 hinges. Their lower ends are curved back- 

 wards. 



vii. The zygocardiac ossicles are a pair of stout 

 sclerites, running from the outer ends of the 

 pyloric ossicle forwards, downwards, and out- 

 wards, to the ventral extremities of the ptero- 

 cardiacs. Their ventral margins are curved 

 inwards to form a pair of stout plates, calcified 



