MORPHOLOGY OF EYE MUSCLE NERVES 61 



the growing tips of the nerve fibers the amoeboid terminations 

 have no intimate relations with plasmodesms extending toward 

 the muscle anlage, although they indisputably have more or 

 less indirect connections with the processes of adjacent mesen- 

 chyma cells. Evidence that these connections are utilized in 

 the extension of the nerve anlage has not been discovered, and 

 the burden of proof rests upon those who assert the absorption 

 of these plasmodesms into the nerve path. 



The relations of the nerve fibers with bipolar neuroblasts in 

 the somatic motor column of the brain are as easily demonstra- 

 ble in Squalus embryos as in the adults and are especially clear 

 in Cajal preparations. Even in Vom Rath preparations it is 

 possible to follow with certainty the deeply stained processes of 

 the neuroblasts into the roots of the nerve anlagen. There 

 appears no good reason to doubt the genetic relation of the 

 neuroblasts to the nerve fibers. The fact that the anlagen of 

 the eye-muscle nerves are primarily fibrillar and not cellular, and 

 that the cells are secondarily added to the anlagen and remain 

 for some time distinctly peripheral in relation to the bundle of 

 fibers, and that none of these cells assume the appearance of 

 neuroblastic cells, constitutes evidence quite irreconcilable with 

 the cell-chain hypothesis. 



The cells which make their appearance in relation with the 

 anlagen of the eye-muscle nerves are partly of mesenchymatous 

 and partly of medullary derivation, like those associated with 

 spinal somatic motor nerves. Cells are also added to the distal 

 portion of the trochlear and oculomotor anlagen from the super- 

 ficial and profundus branches of the trigeminal nerve, forming 

 the anlage of the ciliary ganglion in the case of the former, and 

 of a transient (?) ganglion in the case of the latter. Thus the rela- 

 tions to sympathetic ganglia of these two nerves seem to be the 

 same as those of spinal somatic nerve anlagen. The abducens 

 assumes no connections with ganglionated nerves and (there- 

 fore?) is associated with no sympathetic ganglion. "V\Tiether any 

 of the medullary cells associated with the oculomotor and troch- 

 lear anlagen participate in the formation of the sympathetic 

 ganglia is uncertain, as no criterion of distinction between the 



