PLATE 4 



EXPLANATION OF FIGURES 



5 Graphic reconstruction of a spinal nerve and the vagus trunk from an adult 

 Polistotrema series in the neighborhood of the caudal extremity of the retractor 

 mandibulae muscles. It is clear from this figure: 1) That the dorsal motor and 

 sensory nerves are separate. 2) The ventral motor nerve joins the ventral 

 sensory nerve opposite the notochord to form a mixed ramus ventralis. 3) An 

 isolated peripheral ganglion cell appears in the ramus ventralis about on a level 

 with the ventral border of the myotomes. 4) The vagus nerve is here divided 

 into three or four large bundles, and since all cf those bundles possess nerve cells 

 they all probal)ly contain sensory or receptive fibers. 5) These cells are suffi- 

 ciently numerous in the ventral Inindle to form an elongated ganglion about a 

 segment long, and any section through it would reveal from one or two to four- 

 teen cells. 6) All of the fibers to the oesophagus, both sensory and motor, come 

 from this ventral bundle. X 11. 



ABBREVIATIONS 



D.Mjjo., dorsal border of myotomes 



D.R., dorsal root (radix posterior) 



M.C.P. (1), posterior division of the 

 M. constrictor pharyngis 



A^'c, notochord 



N.C., nerve cell 



Oes., oesophagus or pharynx 



R.D.M., ramus dorsalis or posterior 

 (motor) 



R.D.S., ramus dorsalis or posterior 

 (sensory) 



R. M.C.P. (1), vagus branches to pos- 

 terior division of the M. constrictor 

 pharyngis 



R.Oes., vagus branches to oesophagus 



or pharynx 

 R.V., ramus ventralis or anterior 

 R.V.M., ramus ventralis or anterior 



(motor) 

 R.V.S., ramus ventralis or anterior 



(sensory) 

 Sp.Cd., spinal cord 

 Sp.G., spinal ganglion 

 V.AIyo., ventral border of myotomes 

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



root 

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



root 

 X., vagus nerve 



PLATE 5 ■ 



EXPLANATION OF FIGURES 



6 Graphic reconstruction of a portion of two of the most cephalic spinal 

 nerves from an adult Polistotrema series. This region is in the same segment 

 as the second branchial arch and immediately behind the auditory capsule. 

 The cephalic end of the specimen is at the left. As in the previous reconstruc- 

 tion, the dorsal sensory rami are separate from the motor rami, while the ventral 



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