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Ossicles of the Gastric Mill. 



The Mesocardiac Ossicle (r/i.c.) is a small median 

 ossicle in the dorsal wall of the cardiac region. It is 

 triangular in shape, with the apex pointing forwards. It 

 is not clearly separated from the urocardiac ossicle which 

 passes posteriorly, and it is only partially separated from 

 the pterocardiac ossicle which extends laterally. The 

 ossicle is thicker dorso-ventrally at its posterior end, and 

 to the thickened posterior edge the anterior ends of the 

 cardio-pyloric muscles are attached. In the Macrura and 

 the Anomura the mesocardiac ossicle is much larger than 

 in the Brachyura, and the pterocardiac pieces are much 

 smaller. 



One pair of Pterocardiac Ossicles (pt.c). They are 

 situated to the right and left of the mesocardiac piece and 

 in contact with it. The posterior border is almost 

 straight, and the anterior border is curved. Each ossicle 

 is broadest on its inner side, and tapers towards its outer 

 extremity. Near the inner border of each ossicle is a 

 smooth area where the anterior gastric muscle is inserted. 

 Each ossicle extends outwards, and its outer extremity 

 articulates with the zygocardiac ossicle by means of the 

 antero -lateral ligament (lig.). 



One pair of Zygocardiac Ossicles (z.c.) lying in the 

 supero-lateral wall of the cardiac region of the 

 fore-gut. Each passes backwards and inwards, and 

 comes into contact at its posterior end with the exopyloric 

 ossicle, thus forming a connecting link between the 

 ossicle of the cardiac and the pyloric regions. The 

 zygocardiac ossicle is irregular in shape. The anterior 

 part is rod-like, but the ossicle becomes gradually broader 

 as it passes backwards, and the posterior portion is a broad 

 rectangular plate which bears the lateral tooth. One side 



