motor rami join the corresponding sensory rami from in front, forming mixed 

 rami ventrales. The dorsal and ventral roots have apparently been carried 

 cephalad instead of caudad in this region, through a more continuous growth 

 of the myotomes than of the skeletal elements. No peripheral nerve cells were 

 found in either of the spinal nerves, but scattered ganglion cells are present in 

 the vagus-glossopharyngeal trunk and in the glossopharyngeal at the point of 

 its separation from the vagus. X 16.5. 



7 . Transverse section through the cephalic end of the same vagus nerve as 

 was reconstructed in figure 5. Observe that the nerve is divided into four bun- 

 dles, three of which possess ganglion cells. X 50. 



8 Similar transverse section to figure 7, but taken from about the central 

 portion of the vagus nerve in figure 5. It consequently passes through the center 

 of the elongated ganglion of the ventral bundle, which shows thirteen ganglion 

 cells in this section. There is also one nerve cell in the median dorsal bundle. 

 X 50. 



9 Cephalic transverse section through the vagus and glossopharnygeal 

 nerves at the point of separation of the glossopharnygeal, taken from one of the 

 caudal sections used in preparing reconstruction 6. Observe the presence of a 

 ganglion cell in the glossopharnygeal and the absence of large bundles of nerve 

 fibers characteristic of the more caudal sections. X 50. 



10 Portion of a transverse section through the caudal heart region of an adult 

 Polistotrema. Introduced to show a cluster of peripheral ganglion cells found 

 along the course of the dorsal sensory ramus at the point of branching a little 

 above the myotomes. X 25. 



11 Enlargement of the peripheral nerve cell shown in figure 5. X 50. 



ABBREVIATIONS 



Ao., aorta Per., perineurium 



Br. A. (2), second branchial arch R.D.M., ramus dorsalis or posterior 



D.Myo., dorsal border of myotomes (motor) 



D.R., dorsal root (radix posterior) R.D.S., ramus dorsalis or posterior 



D.S., dorsal spine (sensory) 



End., endoneurium j^ y ^ ramus ventralis or anterior 



Epi., epineurium R.V.M., ramus ventralis or anterior 



M.& S.F., motor and sensory fibers (motor) 



M.C.P., anterior division of the M. „ ^^ „ , ,. , . 



' . , . R.V.S., ramus ventralis or anterior 



constrictor pharyngis , ^ 



(sensorv) 

 M.C.Q.S., M. copulo-quadratus super- „ ^ , . , , 

 rj • ,• , bp.Cd., spinal cord 



M.D.B., median dorsal cartilaginous '^P-^- ^Pi^al ganglion 



^^j. V.N.B., ventral nerve bundle of X 



M.V.Q., M. velo-quadratus V-R-, ventral root (radix anterior) 



Myo., myotomes or M. parietalis V.R. (1), cephalic ventral or anterior 

 N.B., nerve bundle root 



Nc, notochord IX., glossopharyngeal nerve 



N.C., nerve cell X., vagus nerve 



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