II.] THE CRAYFISH AND LOBSTER. 213 



d. Note incidentally — 



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



outwardly directed. 

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

 like structures, curving round the bases of a to 

 reach the gullet (cf. SectB. 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 levator 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. $). 



/?. 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. 



