SEA-FISHERIES LABORATORY. 371 



plane. The flexor muscle, which lias very little power, 

 moves the protopodite forward, and the extensor acts in 

 the opposite direction. 



The extensor (ex. prot.) arises from the posterior 

 region of the tergum of the somite to which the uropod 

 belongs. It passes forward and downward, and is inserted 

 on a small tendon on the anterior wall of the protopodite, 

 some distance below the proximal border of the latter. 



The flexor (/. prot.) arises from the anterior region of 

 the tergum. It passes downward and inward, and its 

 insertion is on a tendon arising from the outer border of ' 

 the protopodite. 



The protopodite also has a slight movement from side 

 to side. The flexor muscle draws the appendage toward 

 the middle line and the extensor pulls it outward. 



The lateral extensor (I. ex. prot.} arises from the outer 

 region of the tergum, and passes downward and inward. 

 Its insertion is on a tendon arising from the outer border 

 of the protopodite. 



The lateral flexor (I. f. prot.} arises from the inner 

 part of the tergum. It passes downward and outward, and 

 is inserted on a tendon arising from the inner border of 

 the protopodite. 



Exopodite. The movement of the exopodite is lateral. 

 There is one extensor and two flexors. 



The extensor (ext. ex.) arises from the outer edge of the 

 protopodite. It passes downward, and is inserted on the 

 inner wall of the exopodite some distance below the 

 arthrodial membrane. 



The flexors (d. f. ex., v. f. ex.) arise from the inner wall 

 of the protopodite. They pass outward, and converge to 

 a single insertion on the inner edge of the exopodite. 



The endopodite is fused to the protopodite, and has no 

 muscles. 





AA 



