88 H. V. NEAL 



superficialis, and on the other with the fibers of the trochlear 

 anlage. 



Thus, in the derivation of its cellular elements, the trochlear 

 resembles the oculomotor and spinal somatic motor nerves. 

 There is no reason to doubt the medullary derivation of some 

 of its cells; mesenchymatous participation is somewhat doubt- 

 ful; and, finally, the migration of cells from a ganglionic nerve 

 in relation with its anlage appears unquestionable. 



g. What is the fate of these cells? Dohrn ('07) makes the inter- 

 esting suggestion that the manner of development of the fibers 

 of the trochlearis in Pristiurus is a natural experiment, confirm- 

 ing Harrison's ('04) experimental demonstration of the origin 

 of the neurilemma in amphibian somatic motor nerves from the 

 neural crest. That is, he concludes that the cells which migrate 

 from the superficialis into the trochlear anlage form the cells of 

 the neurilemma. The possibility that they may be compared 

 with the cells of sympathetic anlagen does not seem to have 

 occurred to Dohrn. Miss Piatt ('91) speaks of these cells as 

 ganglion cells although she has made no attempt to follow their 

 fate in later stages. 



However, the similarity of the cell-cluster, associated with the 

 trochlearis anlage and derived from the superficialis, with the 

 ciliary anlage in its relations to the oculomotor and the pro- 

 fundus is so striking that the suggestion that in this mass we 

 have a sympathetic ganglion seems permissible. The main ob- 

 jection to such a view, and one that may appear insuperable, is 

 that the trochlear appears in the adult to be associated with no 

 sympathetic ganglion. The ganglion of the trochlear anlage — 

 not to be confused with the fragments of the neural crest asso- 

 ciated w^th the trochlear anlage in the Torpedinidae and reptiles 

 — is conspicuous in Squalus embryos of 25 mm. but has disap- 

 peared as a mass of cells in 45 mm. embryos. Since, however, 

 many of the sympathetic anlagen of spinal somatic motor nerves 

 similarly disappear in these stages and do not appear hi the adult, 

 the disappearance as a distinct cell-mass of the hypothetical 

 sympathetic ganglion of the trochlear is not to be regarded as a 

 serious objection to the hypothesis. Moreover, the possibility 



