MORPHOLOGY OF EYE MUSCLE NERVES 67 



results of this method Carpenter ('06, p. 195) says that "a heavy 

 black precipitate along the neuraxons differentiates these clearly 

 against the less darkly colored stroma in which they appear to 

 be imbedded." The appearances presented in sections prepared 

 by this method resemble those in Cajal and Bielchowsky-Paton 

 preparations in demonstrating, in the very earliest stages of 

 histogenesis, deeply staining fibers within the nerve anlagen. 

 And, while the results are not as specific and differential in 

 vom Rath preparations, the staining is more complete than in 

 either of the other two, so that the connection of the fibers with 

 medullary neuroblasts is more clearly demonstrated. Now, since 

 in vom Rath preparations there is no stage in the development 

 of the oculomotor when such deeply stained fibers are absent 

 from the nerve, and since the connection of these fibers with 

 processes of medullary neuroblasts can be readily traced in many 

 sections, and since there is not the slightest evidence that the 

 cells associated with the fibrillar bundle of the nerve have any 

 genetic relations with the fibers, it appears legitimate to con- 

 clude that the neurofibrils are differentiated within the processes 

 of the midbrain neuroblasts, which, by their peripheral exten- 

 sion, form the protoplasmic connection between brain and somite. 



Vignal ('83), Bardeen ('03), Carpenter ('06) and Paton ('09) 

 have called attention to the coarseness of the primary fibers of 

 embryonic nerves as compared with those seen in later stages of 

 histogenesis and have inferred a process of splitting of the prim- 

 itive fibers into true fibrils, an inference that seems to have been 

 convincingly demonstrated by Miss Dunn ('02). The present 

 paper makes no contribution to the discussion of this important 

 histogenetic problem. 



In the neuroblastic origin of its fibrils the- oculomotor resem- 

 bles histogenetically a spinal somatic motor nerve. 



d. Are the neuraxoyis of the oculomotor multicellular in origin 

 or are they the processes of medullary neuroblasts? The evidence 

 that the neuraxons of the oculomotor are formed as the result 

 of protoplasmic movement of neuroblasts in the somatic motor 

 column of the midbrain consists, first, of the fact that the growth 

 of the nerve is centrifugal as stated for various vertebrates by 



