WHITE SHRIMP FROM THE GULF OF MEXICO 



71 



BASIPODITE ADDUCTOR MUSCLE OF SECOND 

 MAXILLA 



Figure 41 



This small muscle originates on the medial 

 margin of the coxopodite and runs to the proxi- 

 mal region of the gnathal lobe of the basipodite. 

 The second maxilla basipodite adductor muscle 

 turns the basipodite lobes toward the midline. 

 The only muscle in Astacus in a similar position 

 is part of the musculus depressor II maxillae. 



BASIPODITE ABDUCTOR MUSCLE OF SECOND 

 MAXILLA 



Figure 41 



The basipodite abductor muscle runs from the 

 posterior rim of the coxopodite to the proximal 

 region of the basipodite gnathal lobes, laterad of 

 the insertion of the basipodite adductor. Con- 

 tractions of the basipodite abductor open the 

 gnathal lobes. Like the basipodite adductor, the 

 basipodite abductor may be the same muscle as 

 part of Schmidt's musculus depressor II maxillae 

 in Astacus. 



ENDITE ADDUCTOR MUSCLE OF SECOND 

 MAXILLA 



Figure 41 



The endite adductor muscles (fig. 41) arises in 

 the proximal region of the basipodite gnathal 

 lobes and passes laterad to insert on the lateral 

 margin of the basipodite endite. Its contractions 

 turn the endite mesad. The endite adductor of 

 Penaeus is fully homologous with the endopodite 

 adductor muscle of Astacus, Pandalus, and Cal- 

 linectes. 



POSTEROVENTRAL SCAPHOGNATHITE ROTATOR 

 MUSCLE OF SECOND MAXILLA 



Figure 41 



The posteroventral scaphognathite rotator 

 muscle, in company with several of the so-called 

 respiratory muscles, originates on a large, sternal 

 apodeme arising from the sternal brachia between 

 the second maxilla and the first maxilliped. The 

 dorsal, or distal, portion of this apodeme lies close 

 to the dorsal end of the large sternal apodeme upon 

 which muscles of the first maxilla are attached, 

 but the second maxillary apodeme is not deeply 



embedded in the substance of the endosternite as 

 is the first maxillary apodeme. The postero- 

 ventral scaphognathite rotator runs posterolater- 

 ally to a point of insertion on the ventral surface 

 of the scaphognathite. This muscle brings the 

 posterior tip of the gill pump ventrad and re- 

 motes the whole structure. The muscle is evi- 

 dently the homolog of the musculus respiratorius 

 e II maxillae in Astacus and the other forms 

 referred to. 



DORSAL SCAPHOGNATHITE ADDUCTOR MUSCLE 

 OF SECOND MAXILLA 



Figure 41 



This muscle originates on the apodeme of the 

 second maxilla and runs ventrolateral^ to insert 

 on the dorsal surface of the scaphognathite. The 

 dorsal scaphognathite adductor muscle turns the 

 posterolateral margin of the gill pump dorsad. 

 Although far from clear, the muscle may be the 

 same muscle as Schmidt's musculus respiratorius 

 b II maxillae in Astacus. 



POSTERODORSAL SCAPHOGNATHITE ROTATOR 

 MUSCLE OF SECOND MAXILLA 



Figure 41 



The posterodorsal scaphognathite rotator muscle 

 originates on the dorsal part of the sternal 

 apodeme of the second maxilla and passes later- 

 ally to the. dorsal surface of the scaphognathite. 

 In action, the muscle aids the posteroventral ro- 

 tator muscle in remoting the whole scaphogna- 

 thite, but opposes the posteroventral rotator 

 by lifting the posterior tip of the gill pump. 

 The posterodorsal rotator in Penaeus is almost 

 certainly the homolog of the musculus respira- 

 torius d II maxillae of Pandalus, Astacus, and 

 Callinectes. 



VENTRAL SCAPHOGNATHITE ADDUCTOR 

 MUSCLE OF SECOND MAXILLA 



Figure 41 



The ventral scaphognathite adductor muscle 

 originates in the ventral region of the coxopodite 

 and inserts on the scaphognathite ventrad of the 

 insertion of the posteroventral rotator muscle. 

 The muscle turns the lateral margin of the gill 

 pump ventrad, in opposition to the action of the 

 dorsal adductor. 



