178 ELEMENTARY BIOLOGY. [CHAP. 



The wide gullet leads almost vertically into the spacious 

 stomach, and both are lined by a chitinous continuation of 

 the exoskeleton. The stomach is divided by a transverse 

 constriction into a spacious cardiac^ and a much smaller 

 pyloric division, from which latter the intestine passes. The 

 walls of the anterior half of the cardiac sac are thin and 

 membranous, but, in the posterior half, they become calci- 

 fied so as to give rise to a gastric skeletoji of considerable 

 complexity. The chief part of this skeleton consists of a 

 median dorsal T-shaped 'cardiac' ossicle, the cross-piece 

 of which forms a transverse arch, while its long median 

 process extends backwards in the middle line. The ends of 

 the transverse arch are articirlated obliquely with two small 

 * antero-lateral' pieces, the extremities of which again are 

 articulated with postero-lateral pieces, and these with a 

 cross-piece, the 'pyloric' ossicle, which arches over the 

 roof of the pyloric division of the stomach. In this manner 

 a sort of hexagonal frame with moveable joints is formed, 

 and the median process projects backwards so far, as to end 

 below the pyloric piece. It is connected with this, however, 

 by a short * pre-pyloric ' ossicle which ascends obliquely 

 forwards and is articulated with the anterior edge of the 

 pyloric piece. The lower extremity of this is produced into 

 the strong median ' uro-cardiac ' tooth ; while the postero- 

 lateral pieces are flanged inwards, and, becoming greatly 

 thickened and ridged, form the large ' lateral cardiac ' teeth. 

 Two powerful muscles are attached to the cardiac ossicle, 

 and ascend obliquely forwards to be inserted into the 

 under face of the carapace. Two other similar muscular 

 bundles arise from the pyloric ossicle, and, passing obliquely 

 upwards and backwards, are also inserted into the under 

 face of the carapace, in the region of the cervical groove. 

 The disposition of all these parts is such that when these 



