PLATE 3 



EXPLANATION OF FIGURES 



4 Graphic reconstruction of two spinal nerves in the region of the posterior 

 extremity of the M. cordis caudalis from a series of a small adult Polistotrema. 

 Observe that the motor and sensory components of both the dorsal and ventral 

 spinal rami are distributed as separate nerves; that no conspicuous branch from 

 the first ventral motor ramus behind the M. cordis caudalis is given off to sup- 

 ply the inner surface of this muscle as is shown in figures 1 and 3; that there is a 

 cluster of peripheral ganglion cells about both dorsal sensory rami in the neigh- 

 borhood of the median dorsal cartilaginous bar, but no peripheral nerve cells 

 were found in either of the ventral sensory rami ; and that there is a marked thin- 

 ning out of the nerve cells in the dorsal pole of the ganglia, indicating a tendency 

 for the cells to migrate peripherally. X 50. 



ABBREVIATIONS 



C.A., caudal artery 



C.V., caudal vein 



D.Myo., dorsal border of myotomes 



D.R., dorsal root (radix posterior) 



D.S., dorsal spine 



M.C.C., M. cordis caudalis 



M.D.B., median dorsal cartilaginous 



bar 

 Nc, notochord 

 N.C., nerve cell 

 R.D.M., ramus 



(motor) 

 R.D.S., ramus 



(sensory) 



dorsalis or posterior 

 dorsalis or posterior 



R.M.C.C., motor rjmi for M. cordis 



caudalis 

 R.V.M., ramus vent rails or anterior 



(motor) 

 R.V.S., ramus ventralis or anterior 



(sensory) 

 Sp.Cd., spinal cord 

 Sp.G., spinal ganglion 

 V.Myo., ventral border of myotomes 

 V.R. (1), cephalic ventral or anterior 



root 

 V.R. {2), caudal ventral or anterior 



root 



200 



