116 H. V. NEAL 



Then too we have the view that the trochlear was primi- 

 tively a dorsal nerve, innervating visceral musculature, advanced 

 by Schwalbe (79, '81), Dohrn ('85) and von Kupffer ('95); 

 innervating somitic musculature, by Miss Piatt ('91) and Hoff- 

 mann ('97, '99, '00); and finally that it was primarily purely 

 sensor}^ and possibly secondarily mixed but eventually losing 

 its sensory components, by Rabl ('89, possibly), Martin ('90), 

 Oppel ('90), Froriep ('91), Piatt ('91), Mitrophanow ('92, '93), 

 von Kupffer ('95), Hoffmann ('89, '97, '99, '00), and Sewertzoff 

 ('98). 



This brief summary of the views held regarding the morphol- 

 ogy of the trochlearis wiil possibly suffice to show that opinion 

 is about equally divided for and against the view that the troch- 

 lear is a somatic motor nerve. Since a detailed statement of 

 the arguments, for and against, has been given by both Fiir- 

 bringer ('02) and Dohrn ('07) it appears to be unnecessary to 

 discuss slightly divergent individual opinions. 



The chief argument in favor of the comparability of the troch- 

 lear with dorsal ganglionic nerves appears to be, not the evi- 

 dence of its dorsal origin, since the point of emergence of its 

 fibers is ultra-dorsal rather than dorsal and in this respect it 

 differs as much from a dorsal nerve as from a ventral one, but 

 the evidence of its relations with neural crest cells, either aggre- 

 gated as the ramus superficialis V, or as scattered clumps of 

 neural crest cells called ganglia by several investigators. Dohrn 

 ('07) is right in asserting in contradiction to Neal ('98) that the 

 relations of the trochlearis with the ramus superficialis or with 

 transient clumps of neural crest cells have a phylogenetic sig- 

 nificance. But the fallacy of regarding the trochlear as a dorsal 

 nerve on the basis of such evidence has ah-eady been pointed 

 out above. By a similar argument every somatic motor nerve 

 of the body which becomes associated with a ganglionic nerve 

 must be regarded as a dorsal nerve. 



Dohrn is also correct in asserting that the evidence of the 

 formation of the trochlear as a bundle of neuraxon processes of 

 medullary neuroblasts proves that the nerve is a somatic motor 

 nerve no more and no less than it proves the trochlear to be a 



