SEA-FISHERIES LABORATORY. 393 



The Postero-inferior Pyloric Ossicle is a median 

 curved rod-like ossicle. It is concave anteriorly, and is 

 situated behind the pyloric ampullae. 



In the lateral ivalls of the pyloric fore-gut there are 

 the following principal ossicles : — 



On the supra-ampullary walls there are three pairs of 

 ossicles, viz., the Anterior (a.s.a.), Middle (m.s.a), and 

 Posterior (p.s.a.) Supra-ampullary Ossicles. 



There are also three pairs of ossicles in the pleuro- 

 pyloric walls, viz., the Anterior, Middle and Posterior 

 Pleuropyloric Ossicles. 



The positions of these six pairs of ossicles are 

 indicated by the names. 



Muscles of the Fore-gut. (PL VII.) 



Mocquard* has divided the muscles of the fore-gut into 

 two kinds. The extrinsic muscles are those muscles which 

 have points of origin on some part of the skeletal system 

 outside the fore-gut, and which are inserted on to ossicles 

 lying in the walls of the fore-gut. The intrinsic muscles 

 are attached at both ends to ossicles lying in the walls of 

 the fore-gut. 



Extrinsic Muscles. 



Anterior Gastric Muscles (g.a.)— one pair. Each 

 muscle has its origin on the procephalic process. Both 

 pass directly backwards near the median line, being only 

 slightly separated from one another, and are inserted on 

 the front of the pterocardiac ossicles near the middle line. 



Inner Posterior Gastric Muscles {g.p.i.) — one pair. 

 They arise from two small calcareous projections, almost 

 median in position, situated on the under side of the 

 mesogastric region of the carapace. Each muscle passes 



* Mocquard, Annates Sciences Nattirelles, 6 ser., t. 16, 1883, 

 p. 238. 



