VENTRAL SPINAL NERVES IN AMPHIOXUS 161 
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PRN SA pennies 
fibrils indicated. A four-branched end-plate. is shown on one fibril. B shows 
approach and terminal branching of motor nerves on ends of muscle fibers, also 
one end-plate of nerve with lateral approach. C, muscle fibers more highly magni- 
fied, showing motor end-plate formed by one branch of motor nerve which broke 
up into six terminal fibers. D, nerve net formed by terminal fibrils of motor 
nerve on surface of muscle plate. 
Fig. 6 Dorsal view of dissection of spinal cord of Amphioxus, showing two 
dorsal and one ventral root. Of special interest’ is the dorsal root which issues 
from the cord, dorsal to the ventral root and on the same side of the cord. The 
bulbous swelling of the cord at the place of issue of the ventral root is shown. 
Fig. 7 Dissection of three myotomes, two dorsal nerves and one ventral, to 
show relation of the latter.to spinal cord and to the muscle segments. The 
group of branches from the dorsal nerve given off near the place of issue between 
the myotomes is largely submyotomic, only the distal parts arriving at the 
surface of the myotomes. The branches from the nerve given off where the 
nerve trunk crosses over the interseptal spaces are indicated; some of these go 
to the body of the myotome. 
