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Fig. 4 Dissection of motor root of Amphioxus to show the motor fibers leav- 
ing the spinal cord, C, to pass out to their endings. M, group of muscle plates; 
M’, muscle elements inserting among the nerve fibers; 1/’’, muscle elements in- 
serting on and near the dura. 
Fig. 5 Four illustrations of the motor nerve terminals in Amphioxus. A . 
shows a group of fine terminal fibers crossing a muscle plate; striation of muscle 
