i6 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 92 



In this appendage a division of the extrinsic muscles into those with 

 dorsal origin and those with ventral origin is first clearly apparent. 

 There is as a matter of fact only one ventral muscle, the greater 

 abductor {41, fig. 5 A, C), and this might be referred to as vmsculus 

 ventralis mesalis, the mesal ventral muscle of the mandible, if posi- 

 tional names were adopted. There are three dorsal muscles of the 



Fig. s.^The mandible. 



A, dorsal view of the mandible in place. 



B, analysis of the mandible as an appendage. 



C, mesal view of the mandible. 



41, musculus abductor maior mandibulae; 42, musculus abductor minor 

 niandibulae ; 43, musculus adductor posterior mandibulae ; 44, musculus adductor 

 lateralis mandibulae; 45, musculus extensor palpi mandibulae; 46, musculus 

 flexor a palpi mandibulae ; 47, musculus flexor b palpi mandibulae. 



x-xx, hinges of the mandible ; T42, tendon of musculus abductor minor 

 mandibulae ; T44, tendon of musculus adductor lateralis mandibulae ; S, cut 

 ends of two stomach muscles ; /, the dorsal promotor ; J, the dorsal remotor ; 

 KL, the ventral promotor and ventral remotor combined; Ant, anterior border 

 of the mandible ; Post, posterior border of the mandible. 



mandible, a posterior outer (4^), a posterior inner {43), and a third 

 one (44), in function a lateral adductor, which is very puzzling to 

 name as to position, since it attaches itself to the now outer posterior 

 angle of the mandible, which has reversed itself in the blue crab from 

 its primitive anterior position. 



It has been repeatedly stated that the blue crab is a highly specialized 

 creature, which departs in certain noticeable ways from the more gen- 

 eralized morphological aspects of many other crustacean types. Hence 



