GENERAL ANATOMY OF A CRAB. 203 



the stomach- wall, and notice that it is lined by a tough, 

 thin, transparent, chitinous coat, which is thickened and 

 calcified at certain points to form the ossicles of the gastric 

 mill. Open the cardiac pouch in front, to expose the 

 opening into the pyloric pouch and the ossicles which sur- 

 round it, and spreading it out notice again : 



(i.) The pterocardiac ossicles (Fig. 102, a). 



(ii.) The urocardiac ossicle (Fig. 102, cT), projecting 

 downwards and backwards, in front of the opening (f) 

 into the pyloric pouch, and ending below in a dense uro- 

 cardiac tooth. 



(iii.) On each side of and a little anterior to this tooth, 

 notice the zygocardiac teeth (Fig. 102, A), two dense, 

 thick, dark-colored prominences, which are carried upon 

 the inner sides of the zygocardiac ossicles (6), and which 

 have their inner surfaces marked by ridges and furrows, 

 something like the molar teeth cf a rodent. 



(5v.) On the floor of the stomach notice the opening (g) 

 of the oesophagus, guarded by valvular folds of the wall 

 of the stomach, and posterior to the mouth, a groove or 

 channel (i) which runs backwards to the pyloric orifice (/), 

 where it ends in an inferior cardiac tooth, which lies a 

 little behind and below the tip of the urocardiac tooth. 



(v.) On each side of this gutter notice a large, triangular 

 plate (j), the inferior accessory cardiac ossicle, the inner 

 edge of which forms the wall of the gutter, and is marked 

 by a number of parallel ridges. 



(vi.) Above this on each side a long slender superior 

 accessory cardiac ossicle (?), which runs downwards and 

 imvards from the anterior end of the zygocardiac ossicle, 

 to terminate in a soft, hand-like tooth (A 1 ), with a number 

 of slender, finger-like processes. This is the accessory 

 cardiac tooth. 



