WHITE SHRIMP FROM THE GULF OF MEXICO 



93 



Schmidt describes them as reductors. A single 

 meropodite reductor is shown in the study of 

 Callinectes. The muscle is unopposed by an ex- 

 tensor or productor in Penaeus and the other 

 forms considered here. 



CARPOPODITE EXTENSOR MUSCLE OF FIRST 

 PEREIOPOD 



Figure 49 



The fibers of the carpopodite extensor muscle 

 take origin over very nearly the whole of the lat- 

 eral side of the meropodite. The apodeme upon 

 which they insert extends proximally from the 

 lateral edge of the carpopodite and runs almost 

 the length of the meropodite. The carpopodite 

 extensor straightens the carpopodite on the mero- 

 podite in a horizontal plane. The muscle is rep- 

 resented in Astacus and Callinectes as the carpo- 

 podite abductor muscle. 



CARPOPODITE FLEXOR MUSCLE OF FIRST 

 PEREIOPOD 



Figure 49 



Somewhat like the carpopodite extensor, the 

 carpopodite flexor muscle is a long muscle in- 

 serting on a long apodeme. The muscle origins 

 occur about the medial and ventral surfaces of the 

 meropodite. The carpopodite flexor apodeme 

 arises from the proximal margin of the carpo- 

 podite, mesad of the dicondylic axis. A pull on 

 this apodeme turns the carpopodite and chela 

 deeply on the meropodite, for this joint is a free 

 one. The same muscle is found in the first perei- 

 opod of Astacus and Callinectes. but named the 

 carpopodite adductor muscle. 



CHELA PRODUCTOR MUSCLE OF FIRST 

 PEREIOPOD 



Figure 49 



The fibers of the chela productor muscle arise 

 from lateral, proximal, and medial regions of the 

 dorsal part of the carpopodite and insert on the 

 long productor apodeme of the propodite. Since 

 the joint between the carpopodite and propodite 

 is a free one, tension on the productor apodeme 

 tends to straighten the chela with respect to the 

 carpopodite and even to levate the chela. The 

 propodite productor muscle of Penaeus is found in 

 much the same form in Astacus and Callmectes, 

 under the name of propodite productor muscle. 



468059 O — 58 7 



CHELA REDUCTOR MUSCLE OF FIRST 

 PEREIOPOD 



Figure 49 



Directly ventrad of the chela productor muscle 

 lies the chela reductor muscle, a structure also 

 attaching by several slips to a long apodeme. The 

 reductor apodeme arises from the ventral rim of 

 the propodite. The chela reductor muscle turns 

 the chela ventrad. The same muscle appears in 

 the first pereiopod of Astacus and Callinectes, and 

 in the second pereiopod of Pandalus, as the pro- 

 podite reductor muscle. 



CHELA EXTENSOR MUSCLE OF FIRST PEREIOPOD 

 Figure 49 



As mentioned above, the joint between the car- 

 popodite and propodite a fiords free movements 

 of the latter on the former. The chela extensor 

 muscle straightens the chela with respect to the 

 carpopodite in the horizontal plane. The muscle 

 originates in the distolateral part of the carpopo- 

 dite and inserts on an apodeme projecting prox- 

 imally from the lateral margin of the propodite. 

 Exact counterparts of the chela extensor are miss- 

 ing in the first pereiopod of Astacus and Cal- 

 linectes. Berkeley describes, however, 2 extensors 

 and 2 flexors of the propodite in the second pereio- 

 pod of Pandalus. Homologies of these muscles 

 without information about their innervations is 

 not feasible. 



DACTTLOPODITE ADDUCTOR MUSCLE OF FIRST 

 PEREIOPOD 



Figure 49 



The dactylopodite adductor muscle originates 

 throughout the medial part of the pod-shaped pro- 

 podite and inserts on a heavy apodeme of the dac- 

 tylopodite. Contractions of this large muscle close 

 the dactylopodite on the distal gnathal process of 

 the propodite. The dactylopodite adductor mus- 

 cle is found in the first pereiopod of Astacus and 

 Callinectes. 



DACTYLOPODITE ABDUCTOR MUSCLE OF FIRST 

 PEREIOPOD 



Figure 49 



Functioning in opposition to the dactylopodite 

 adductor muscle, the fibers of the dactylopodite 

 abductor muscle originate about the lateral sur- 

 faces of the propodite and insert on the abductor 



