SEA-FISHERIES LABORATORY. 389 



of the ossicle points inwards, and the other faces 

 outwards. The inner face is concave and the outer face is 

 convex. The inner edge of the ossicle folds outwards so 

 as to produce a deep groove on the outer side below the 

 convexity. The ossicle has four borders. The anterior 

 border is concave and terminates at its posterior extremity 

 in the large anterior tooth. The dorsal border, which can 

 be seen through the dorsal w r all of the stomach, is also 

 concave. It passes backwards and inwards and ends at 

 the posterior border. The posterior border has a large 

 indentation into which the anterior border of the 

 exopyloric ossicle fits. The inner border lies obliquely, 

 being nearer the middle line at its anterior end. The 

 ossicle appears to be much thicker at its inner border than 

 in any other region. This thickness is not real, but is 

 merely due to the ossicle folding outwards at its inner 

 border. This inner border bears the denticles. Anteriorly 

 there is a large single denticle, which is followed by about 

 seven smaller denticles, which point inwards and decrease 

 in size from before backwards. The folded edge of the 

 inner border is crossed by about twenty-four transverse 

 ridges. This system of denticles and ridges on the 

 zygocardiac ossicle is known as the lateral tooth (lat. t.). 



The Exopyloric Ossicles (ex. py.) are a pair of small 

 triangular plates, each of which lies between the posterior 

 border of the zygocardiac ossicle and the pyloric ossicle. 

 The superior border gives support to the posterior end of 

 the outer part of the cardio-pyloric muscle, and on its 

 external face it provides insertion for the external part 

 of the posterior gastric muscle. 



The Urocardiac Ossicle (u.c.) is a median plate more 

 or less fused with the mesocardiac ossicle in front. It 

 passes backwards and downwards as a broad, thin 

 rectangular plate. At its posterior end, which articulates 



