16 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



ocular attractor muscles which originate on the 

 carapace. Their phylogenetic relation to the 

 protocephalon attractor muscles in Penaeus is 

 unlikely. 



OCULAR PLATE MUSCLES 



Arising in the ocular plate or postocular region 

 dorsal to the brain are several pairs of muscles 

 and a muscle group. Some of these muscles in- 

 sert inside and some outside of the ocular plate. 



OCULAR PLATE COMPRESSOR MUSCLES 



Figures 6, 7 



Attached about the shallow anterodorsal groove 

 of the ocular plate is a group of muscles which 

 runs to the lateral wall of the ocular lobe (tigs. 

 6, 7), the ocular plate compressor muscles. They 

 function to draw the sides of the head lobe and 

 ocular plate mesad, and to depress slightly the 

 center of the ocular plate. 



ANTERIOR BASAL SEGMENT ADDUCTOR MUSCLE 



Figure 6 



The anterior basal segment adductor muscle 

 originates on the ocular plate dorsal to the brain 

 and attaches to connective tissue and apodemal 

 material in the ventral part of the basal seg- 

 ment (tig. 6). Contractions of the muscle turn 

 the basal segment toward the ocular plate in a 

 horizontal plane. 



POSTERIOR BASAL SEGMENT ADDUCTOR 

 MUSCLE 



Figure 6 



The posterior basal segment adductor muscle in- 

 serts in the basal segment at the same point as the 

 anterior basal segment adductors, but originates 

 on the anterior side of the vertical transverse plate 

 posterior to the postocular region (fig. 6). It, too, 

 draws the anterior edge of the basal segment to- 

 ward the ocular plate. The origins of these 

 muscles are so widely separated that we may con- 

 clude that they have never been the same muscle. 

 How the basal segment adductors may be homolo- 

 gized with muscles in Pandalus and CaUinectes, in 

 which forms no knowledge of muscle innervations 

 exists, will be speculation. The ocular adductor 

 muscles of Astacus and Pandalus may well be the 

 homologs of the anterior adductor muscles of 

 Penaeus, but hardly with the ocular adductors of 

 CalUnectes. in which animal the muscles are 



located in the distal end of the long stalk seg- 

 ment. Phylogenetic relationships of the posterior 

 basal segment adductor muscle are even more un- 

 certain, although possibly it is the same muscle 

 as the ocular attractor muscle in Pandalus and 

 Astacus. The basal segment adductor muscles do 

 not appear in Callmectes. 



BASAL SEGMENT LEVATOR MUSCLE 



Figure 0! 



The basal segment levator muscle originates at 

 the anterodorsal corner of the ocular plate and 

 runs ventrally to the connective tissue and apod- 

 emal cuticle on the ventral surface of the basal 

 segment (tig. 6). In the normal spread condition 

 of the eyestalk, contraction of the muscle tends to 

 raise the basal segment and with it the extended 

 eyestalk. 



BASAL SEGMENT MUSCLES 



In the functional descriptions of the muscles 

 which follow, the eyestalks will be considered as 

 in their lifelike, lateral positions. 



BASAL SEGMENT ROTATOR MUSCLE 



Figure 6 



The basal segment rotator muscle is a short, 

 broad structure originating on the anterodorsal 

 edge of the basal segment and inserting on the 

 anteroventral edge of the same segment. Upon 

 contraction, the muscle pulls the dorsal surface of 

 the basal segment anteriorly, thus rotating the 

 entire eyestalk forward. 



EYESTALK DEPRESSOR MUSCLES 



Figure 6 



Two very small muscles, the eyestalk depressor 

 muscles, one slightly lateral to the other (tig. 6), 

 function to draw the eyestalk ventrally. 



EYESTALK MUSCLES 



EYESTALK ABDUCTOR MUSCLE 



Figure 6 



All of the muscles of the eyestalk and optic 

 calathus are associated with retraction and rota- 

 tion of the optic calathus on the eyestalk, except 

 the long eyestalk abductor muscle (fig. 6). The 

 proximal end of the eyestalk abductor muscle is 

 attached in connective tissue in the ventral region 



