1916-17.] Experiments and Observations on Crustacea. 291 
separate adductor calcification, into which is inserted the powerful adductor 
muscle. These parts are shown in fig. 20. 
The line joining the two articulatory pivots does not correspond with 
the main axis of the semi-cylindrical body. The latter axis lies medial 
and ventral to that of the mandibular hinge, so that in adduction of the 
two mandibles not only are the biting processes brought together, but each 
mandibular body as a whole is carried nearer the middle line and also 
a. 
Fig. 20. — Right mandible of Glyptonotus from dorsal aspect. 
x 6. 
a, incisor process ; b, molar process ; c, anterior 
articulatory pivot ; d, abductor process ; e, posterior 
articulatory pivot ; /, styloid polished surface ; g, ad- 
ductor calcification ; h, membranous band between ad- 
ductor calcification and free edge of mandibular body ; 
i, maxillary polished surface ; k, polished groove, for 
contact with lateral border of paragnath. 
nearer the plane of the buccal frame, thus restricting the space available 
for movement of the first maxillse. The axis of the mandibular hinge, 
while mainly antero-posterior, also runs from behind forwards and medial- 
wards, so that in adduction the mandible is carried to some extent back- 
wards as well as medially. Especially during adduction do the maxillary 
polished surface and the polished groove come in contact with their 
appropriate neighbours, so that when molar compression is applied to the 
food no adjacent crevices are left into which portions might be squeezed. 
The connective tissue band between the adductor calcification and the 
mandible is broad and flexible and allows of a considerable range of simple 
