SEA-FISHERIES LABORATORY. 397 



Intrinsic muscles. 



Cardio-pyloric Muscles (c.py.) These consist of one 

 median and two lateral muscles. The median muscle 

 extends from the thickened posterior border of the meso- 

 cardiac ossicle to the upper edge of the propyloric ossicle. 

 The lateral muscles extend from the mesocardiac ossicle 

 to the exopyloric ossicle. These muscles are used in 

 connection with the gastric mill and are concerned in 

 bringing the ossicles of the mill back to their original 

 position after each series of complicated movements 

 effected by means of the gastric muscles. 



Lateral Cardiac Muscles (c.lat.) — three pairs. The 

 three muscles at each side may be distinguished as the 

 upper, middle and lower muscles respectively. The 

 upper muscle arises from the upper edge of the infero- 

 lateral cardiac ossicle and passes upwards and forwards 

 as a broad sheet of muscle to the dorsal border of the 

 zygocardiac ossicle. The middle muscle also arises from 

 the upper edge of the infero-lateral cardiac ossicle below 

 the origin of the upper muscle and passes upwards and 

 forward parallel to this muscle. It is inserted on the 

 prepectineal ossicle, and also on the anterior part of the 

 dorsal border of the zygocardiac ossicle. This muscle is 

 much narrower than the previous one. Both sheets of 

 muscle are broader at their insertion than at their origin. 

 The lower muscle is a short broad sheet arising from the 

 side of the infero-lateral cardiac ossicle, and passing 

 across the upper portion of the postero-lateral cardiac 

 plate. Its insertion is on the antero-superior border of 

 this plate. According to Mocquard, these muscles raise 

 the cardio-pyloric valve. 



The Postero-inferior Cardiac Muscle (Fig. 48, c.i.). 

 This is a median broad sheet of muscle covering' the 



