OUTGROWTH OF THE NERVE FIBER 837 
grows out from the trigeminal ganglion across the optic stalk to- 
ward the skin of the front part of the head, spreading out in the 
region above and in front of the eye and above the nose. The 
r. lateralis vagi connects almost immediately with the rudiment 
of the lateral line organs and is drawn out as the latter extends 
towards the tail. The outgrowth of the nerve fibers from the 
dorsal cells has just been described, and as pointed out, the defin- 
itive arrangement can be accounted for by power of growth in a 
straight line modified by deflection as a result of minor obstacles 
in the path. The ventral branches of the spinal nerves reach 
the grooves between successive myotomes and pass ventrally 
in them to the ventral border of the muscles. As the latter are 
carried in mass to near the ventral median line the nerves are 
elongated. These nerves, like the others referred to, have no 
great distance to grow, and one of the guiding factors, the myo- 
septa, is obvious. The formation of the limb plexuses, comes 
about by slight deflections from the main path of growth. The 
nerves to the limbs reach the base of the limb buds in the same 
manner as the ventral nerves reach the abdominal musculature, 
i.e., along the grooves on the inner surface of the muscle plates. 
The nerves are accordingly present in the limbs practically from 
the time when the latter begin their development, and as the limbs 
grow the nerves lengthen with them.^^ Thus the principal 
paths are all at first relatively short and subsequently become 
lengthened by the shifting of parts which takes place during the 
development and growth of the organism. 
It is obvious that the primitive peripheral nerves, which are 
laid down in early embryonic life, consist of but very few fibers — 
in the frog often of not more than two or three at first. These 
first fibers may be called the path-finders; the remaining ones fol- 
" Regarding the period of development at which the nerves reach the limb buds, 
my own observations ('07 a) differ from those of Braus ('05). In referring to this 
discrepancy I failed to consider that it might be due to specific differences between 
Rana and Bufo on the one hand and Bombinator on the other, instead of to errors 
of observation, as implied in my criticism. Braus has since called my attention to 
these specific differences, and I am glad to have this opportunity to express my 
regret at having overlooked this reasonable explanation of the difference in our 
observations. 
