162 THE MORPHOLOGY OF THE COMMON CRAYFISH. 
gether with the sudden widening of the same parts in 
the posterior cephalic somites, gives rise to the lateral 
depression (fig. 89, ¢f) in which the scaphognathite lies. 
The limit thus indicated corresponds with that marked 
by the cervical groove upon the surface of the carapace, 
and separates the head from the thorax. The three pair 
of maxillipedes (7, 8, 9), the forceps (10), the ambulatory 
™m. 
Fig. 43.—Astacus fluviatilis.—Longitudinal section of the anterior part 
of the cephalothorax (x 3). J—1X, sterna of first nine cephalo- 
thoracic somites; 1, eyestalk ; 2, basal joint of antennule ; 3, basal 
joint of antenna ; 4, mandible; a, inner division of the masticatory 
surface of the mandible ; a’, apophysis of the mandible for muscular 
attachment ; cp, free edge of carapace ; e, endosternite ; enpl, endo- 
pleurite ; epm, epimeral plate; 7, labrum ; ™, muscular fibres con- 
necting epimera with interior of carapace ; mt, metastoma ; pep. 
procephalic process. 
