66 H. V. NEAL 



extend toward the nerve anlage and may in some cases be traced 

 to a point outside the external limiting membrane of the brain 

 wall. 



In later stages (fig. 59) a larger number of processes of med- 

 ullary cells may be traced toward the nerve anlage and a larger 

 number of deeply stained fibers may be seen within the roots of 

 the anlage. In this, as in all subsequent stages, mesenchyma- 

 tous cells may be seen in close proximity to the nerve fibers. 

 Some earlier stages, such as are represented in my ('98) figures 

 G and i/, pages 222-223, show no cells whatever in relation to 

 the oculomotor anlage; the majority of sections of these early 

 stages show cells more or less closely associated with the nerve 

 anlage. That these cells are mesenchymatous seems indicated 

 by the fact that there is in these stages no evidence of medullary 

 migration and that the possibility of a derivation from the meso- 

 cephalic ganglion is excluded, since the nerve has as yet no 

 connection with that ganglion. No evidence of a genetic rela- 

 tion of these cells to the nerve is discoverable. In all respects 

 they resemble the branched granular cells of the surrounding 

 mesenchyma. Comparison of these with later stages in the de- 

 velopment of the oculomotor (figs. 61, 64, 70) favors the infer- 

 ence that the fibers of the oculomotor are of neuroblastic origin 

 and that they have their nidulus of origin in the base of the 

 midbrain. 



The oculomotor therefore attains connection with its terminal 

 organ secondarily, in precisely the same manner as a spinal so- 

 matic motor nerve. 



c. Have these protoplasmic connections genetic relations to the 

 neurofibrils of the oculomotor? Most embryological investigators 

 of the oculomotorius have paid no attention to the genesis of 

 the neurofibrils. This is true of the latest research upon the 

 histogenesis of the oculomotor — that of Gast ('09) — as of the 

 earlier ones. In fact, no investigation of the histogenesis of the 

 nerve by the use of a specifically neurofibrillar stain has been 

 made. The vom Rath method, as apphed by Neal ('98) and 

 Carpenter ('06), comes the nearest to a truly neurofibrillar stain 

 of any which have been used upon the nerve. Of the histological 



