II.] THE CRAYFISH AND LOBSTER. 213 



d. Note incidentally 



a. The metastoma ; its lateral lobes are seen to be 



outwardly directed. 



/?. The basal joints of the first maxillae; two blade- 

 like structures, curving round the bases of a to 

 reach the gullet (cf. Sect. B. 4. i). 

 y. The relations of the gastrolith, if present. 



7. The Gastric muscles. All are paired, those of one 

 side are alone described. Dissect the cephalo-thoracic 

 region from the side, removing the exoskeleton and 

 body-wall to the level of the pro-cephalic process 

 (p. 202). Examine, in the order given, the extrinsic mus- 

 cles. A spirit specimen may be used with advantage. 



a. The anterior and posterior gastric muscles (divari- 

 cators of the gastric skeleton). Those of the ex- 

 posed side will be seen the anterior ; arising from 

 the roof of the cardiac chamber (cardiac ossicle) 

 and inserted into the pro-cephalic process : the 

 posterior ; arising similarly from the roof of the 

 pyloric chamber (pyloric ossicle) and inserted into 

 the carapace, immediately in front of the cervical 

 groove. 



b. The kvator muscles. 



a. A conical mass, arising from the roof of the py- 

 loric chamber, immediately in front of the ccecum. 

 It is attached to the cervical groove (endotergite, 

 Sect. B. 2. d. ft). 



ft. Two thin strips, arising from the side wall of the 

 cardiac sac, and inserted above into the mid- 

 cephalic region of the carapace. They cross 

 each other on nearing their insertions. 



