MORPHOLOGY OF EYE MUSCLE NERVES 55 



An exclusively medullary origin of the sympathetic elements 

 has been inferred as a possibility by Harrison ('04) on experi- 

 mental grounds, and Froriep ('07) draws the same inference. 

 Kuntz ('10, p. 250) who had stated in an earher paper that 

 Froriep 's conclusion "is probably correct with regard to the neu- 

 rones in the sympathetic trunks and the prevertebral plexuses," 

 in a later paper ('11) supports the view of the double source of 

 the sympathetic elements. 



Held ('09) draws the conclusion that the cells of the motor 

 roots have nothing to do with the formation of the sympathetic 

 system, on the following grounds: First, the anlage of the sym- 

 pathetic ganglion in Selachii lies entirely in the axis of the sen- 

 sory nerve root and not in that of the motor root. Second, the 

 motor root has fewer cells,' is nowhere thickened, and is nowhere 

 united with the sensory nerve by means of cell-strands. More- 

 over, the ventral nerve extends along the myotome parallel with 

 the sensory nerve, but its cellular material is not mixed with 

 that of the latter. Also, the motor root lies lateral to the sen- 

 sory root, nearer the myotome and farther from the sympathetic. 

 The two are not united by cell-strands. Finally, the two unite 

 ventral to the sympathetic anlage. 



With Kohn and Froriep, Held admits the principle of a free 

 cell migration of purely nervous cell clusters, in the formation 

 of the sympathetic, but thinks that the sympathetic ganglia 

 arise by the budding of chain-like connected cell masses and 

 strands containing both ganglion cells and sheath cells. 



Kuntz ('11) is the most recent student of the histogenesis of 

 the sympathetic in Selachii, and his is the latest presentation of 

 the case in favor of the medullary origin of some of the elements 

 of the sympathetic. Kuntz 's argument that the cells of the 

 ventral roots as well as those of the dorsal participate in the 

 formation of the sympathetic appears to consist of the follow- 

 ing considerations: In sections of earlier stages (11 mm. Squalus 

 embryos) scattered cells of large size and deeply staining nuclei 

 appear in the mesenchyma between the myotome and the dorsal 

 aorta. Because of their staining properties and evidence of cel- 

 lular migration along the nerve anlagen, Kuntz assumes these 



